10.0000@www unix.ecs.umass.edu@generic af3f57cb224f

2007 NORTHEAST GEOTECHNICAL GRADUATE RESEARCH SYMPOSIUM

PROCEEDINGS

H. Q. Nguyen and A.G. Boscardin, Editors

Amherst, MA - 26 October 2007

Northeast Geotechnical Graduate Research Symposium University of Massachusetts Amherst

Kellogg Room - ELAB II Friday, 26 October 2007 Symposium Program 9:00 Registration and Check-In at the Kellogg Room, Engineering Elab-II Building 9:30 Session IWelcome and Introductory Remarks Student Presentations: Site Characterization and Instrumentation Moderator: Hoang Q. Nguyen (BA) 10:45 Refreshment break 11:00 Session IIStudent Presentations: Case Studies Moderator: Michael Tupper 12:30 Lunch Break 1:30 Session IIIStudent Presentations: Soil Behavior Moderator: Adriane G. Boscardin 3:00 Session IVGuest Lecture Landfill Development over Difficult Site

Conditions- Crossroads Landfill. Scott Luettich, P.E., Geosyntec Consultants. Moderator: Don J. DeGroot 4:00 Session V Presentation of Abstract Awards and Symposium Closing Moderator: Steven E. Poirier, Geosyntec Consultants

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2007 Northeast Geotechnical Graduate Research Symposium

Table of Contents

Presentation Session I: Site Characterization and Instrumentation

1

I.1. Vertical Variability of Hydraulic Conductivity of an Unconfined Aquifer Measured Using a Pneumatic Multilevel Slug Testing Packer System

A. Judge University of Massachusetts Amherst

2

I.2. A New Approach to Liquefaction Potential Mapping Using Satellite Remote Sensing and Machine Learning

T. Oommen Tufts University

4

I.3. Dynamics of Wind Turbine Soil-Structure Interaction M.J. Whelan Clarkson University

6

I.4. Evaluation of Miniature Full Flow Penetrometers and Push Cone for Laboratory Measurement of Remolded Undrained Shear Strength of Soft Clays

A.G. Boscardin University of Massachusetts Amherst

8

I.5. Static and Dynamic Analysis of Annulus Plugging of Large Diameter Pipe Piles M.P. Smith University of Massachusetts Lowell

10

I.6. Effects of Fines on Cone Penetration Resistance and Liquefaction Resistance of Sands

L. Oka University of Vermont

12

I.7. The Hydrogeologic Characterization of a Public Drinking Water Aquifer Site in Dedham, Massachusetts

D.F. LaMesa University of Massachusetts Amherst

14

Session Presentation II: Case Studies

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II.1. Evaluation of an Automated Early Warning System for Unstable Soil Slopes J. Lloyd University of Massachusetts Amherst

17

II.2. Development of a Resistance Factor for the Minnesota Department of Transportation Pile Driving Formula

C. OHearn University of Massachusetts Lowell

19

II.3. Expanding the College Classroom: Developing Engineering Skills through International Service-Learning Projects

M. McCormick Tufts University

20

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II.4. Uncertainty Evaluation of Displacement and Capacity of Shallow Foundations on Rocks

R. Muganga University of Massachusetts Lowell

21

II.5. A Study on Stream Bank Erosion and Instability J. L. Borg University of Vermont

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II.6. Investigating Gas-generated Excess Pore Pressure as a Failure Mechanism for the 1996 Finneidfjord Slide

E. Morgan Tufts University

26

II.7. Full-Scale Pilot Study to Reduce Lateral Stresses in Retaining Structures Using GeoFoam

M.W. Ciuffetti University of Massachusetts Amherst

28

II.8. Kinematics of Tsunamigenic Submarine Failures O. Taylor University of Rhode Island

30

Session Presentation III: Soil Behavior

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III.1. Bender Element Test Setup for Large Soil Specimens R.O. Deniz Northeastern University

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III.2. High Quality Deep Water Geotechnical Sampling and Shear Wave Velocity C.D. Jones University of Massachusetts Amherst

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III.3. Lattice Discrete Particle Model (LDPM) for Quasi Brittle Materials A. Mencarelli Renssellaer Polytechnic Institute

37

III.4. Characterizing Local Heterogeneities in Unsaturated Soils Using Acoustic Techniques

L.A. George University of Vermont

39

III.5. Laboratory Investigation of Disturbance Effects at Preconsolidation Pressure N. Kontopoulos Massachusetts Institute of Technology

41

III.6. Liquefaction Mitigation Using Entrapped Air E.E. Bayat Northeastern University

43

III.7. Experimental Measurements of Geophysical and Mechanical Properties of Weakly Cemented Fine Sand

R. Sharma University of Rhode Island

45

III.8. The Nano-Mechanical Morphology of Shale C.P. Bobko Massachusetts Institute of Technology

47

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III.9. Mobilized Undrained Shear Strength of Cohesive Soils by Constant Volume Direct Simple Shear and Ring Shear Testing

H.Q. Nguyen University of Massachusetts Amherst

49

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Session I: Site Characterization and Instrumentation


1

Vertical Variability of Hydraulic Conductivity of an Unconfined Aquifer Measured Using a Pneumatic Multilevel Slug Testing Packer System

Aaron Judge

UMass Amherst, [email protected]

Abstract

A pneumatic multilevel slug testing packer system (PMSTPS) was designed, fabricated, and proof tested in this research to determine how the hydraulic conductivity of the unconfined sandy aquifer in Plymouth MA varies with depth by performing slug tests with this system from near the surface to the bottom of a fully screened well (25 m). The multilevel slug tester was based on a previously developed slug testing system to use compressed air to displace the water level during a slug test in highly permeable soils. The results of the recovery were used with the model by Ostendorf et al. (2005) to determine K in the unconfined sandy aquifer in Plymouth MA.

Figure 1: Pneumatic slug tester setup (Judge 2007)

Figure 1 presents the setup for conducting a multilevel slug test with the PMSTPS which was lowered into a fully screened well. The packers above and below the screened portion of the PMSTPS were inflated to the appropriate pressure (275-425 kPa) to isolate a vertical interval of the well. The column of water in the riser tubes was then pressurized to (9.7 kPa), lowering the water level by 1 m out of a vertical interval of the well screen of 0.5 m isolated by the packers. The air pressure in the manifold and the pressure of the water


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column at a known elevation were measured by pressure transducers. The air pressure was then released allowing water to instantaneously re-enter the riser tubes through the screen while the entire recovery of the water level was recorded at 1 kHz for 10 to 40 seconds.

Results of Multile

nding result of this

References: 07). Vertical Variability of Hydraulic Conductivity of an Unconfined Aquifer

, Jakubowski, J. (2005). A Closed Form Slug

vel and Regular Slug Tests in wells with a 1.5 m screen were within 15% of each other. Multilevel slug tests were then performed at multiple elevations in fully screened wells (8090 feet long). Most results at a specific depth were within 20% of the average value of K at that depth.

The estudy is a detailed

vertical profile of hydraulic conductivity of the Plymouth Site based on all tests performed in Well CM as shown in Figure 2. The four sharp increases of hydraulic conductivity are believed to be present due to geologic sequences, possibly due to retreats and advances of the glacial front.

Permeability (m2)

0 1e-10 2e-10 3e-10 4e-10 5e-10 6e-10

Elev

atio

n (f

t)

-60

-40

-20

0

20

Hydraulic Conductivity (m/s)

0.000 0.001 0.002 0.003 0.004 0.005

Elev

atio

n (m

Judge, A. (20Measured Using a Pneumatic Multilevel Slug Testing Packer System. Masters Thesis, University of Massachusetts, Amherst, MA. Ostendorf, D.W., DeGroot, D.J., Dunaj, P.J.Test Theory for High Permeability Aquifers. Ground Water, Vol. 43, No.1, pp. 87-101.

)

-20

-15

-10

-5

0

5

10

Figure 2: Hydraulic Conductivity of the Soilin the Basin at the Plymouth Site.


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A NEW APPROACH TO LIQUEFACTION POTENTIAL MAPPING USING SATELLITE REMOTE SENSING AND MACHINE LEARNING

Thomas Oommen

Department of Civil and Environmental Engineering, Tufts University, 113 Anderson Hall, Medford, MA 02155, USA. [email protected]

Abstract

In order to help communities better plan and mitigate the effects of seismic hazards, it is important to use innovations in science and technology to improve our techniques for mapping the spatial extents of seismic hazards. Earthquake induced ground shaking in areas with saturated sandy soils pose a major threat to communities as a result of the soil liquefaction. Liquefaction is the process of changing a saturated cohesionless soil from a solid to liquid state due to increased pore pressure. Many major earthquakes, especially those in coastal regions, result in liquefaction related ground failures that can lead to infrastructure damage or slope stability issues. Currently liquefaction potential is assessed on two scales: regionally based on surficial geologic unit or locally based on geotechnical sample data. Regional liquefaction potential maps fail to capture the variability of liquefaction potential on the local scale. On the other hand, collection of geotechnical data on the local scale is costly and only done for specific engineering projects and therefore not generally available for regional mapping.

Today, the advent of advanced remote sensing products from air and space borne sensors allow us to explore the land surface parameters (geology, moisture content, temperature) at different spatial scales (remote sensor footprint). In this study, we explore the use of satellite based remote sensing data (Landsat 7 ETM+), together with digital elevation model, ground water table, land cover classification, geology, water index and normalized difference vegetation index (NDVI) to characterize the liquefaction potential of northern Monterey and southern Santa Cruz counties in California. A supervised classification of the data into seven classes based on the liquefaction potential map developed by Dupre and Tinsley 1980 was done using Support Vector Machine (SVM). SVM is a machine learning/artificial intelligence algorithm that has the ability to simulate the learning capabilities of a human brain and make appropriate predictions that involve intuitive judgments and a high degree of nonlinearity. Figure 1 shows a comparison of the developed liquefaction potential map using SVM to the map of Dupre and Tinsley 1980. It is observed that the spatial variability in liquefaction potential is well captured by the developed map. The accuracy of the developed liquefaction potential map was tested using independent testing data that was not used for the model development. The results show that the developed liquefaction potential map has an overall classification accuracy of 84%, indicating that the combination of remote sensing data and other relevant spatial data together with machine learning can be a promising approach for liquefaction potential mapping. Further, Machine learning will be used to help understand the relative importance of the various parameters in identifying liquefaction hazard and to optimize future data collection efforts.


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Research Contribution to Geotechnical and Geoenvironmental Engineering Industry: The liquefaction potential of a region is a major design consideration for a geotechnical engineer. The lack of spatial variability captured by the regional liquefaction potential maps based on surficial geologic units and the higher cost of collecting geotechnical data on the local scale, has led the recent research to include geotechnical boring data along with the surficial geology in characterizing the liquefaction potential. However, the challenge in this is deciding how to combine surficial geology information, which is on a regional scale and geotechnical boring information, which is on a site specific scale for the characterization.

Currently, the advancement in air and space borne remote sensing products allow us to explore the land surface parameters (geology, moisture content, temperature, other soil properties) at different spatial scales (0.6cm to 1km spatial resolution). This enables us to capture the variability in surficial soil properties in a much finer scale compared to the earlier regional surficial geology maps. This finer scale information can be further combined with the liquefaction potential obtained from sample data by supervised classification using machine learning/artificial intelligence algorithms. Thus this research provides a viable tool to geotechnical engineers in mapping liquefaction potential of a region combining surficial soil properties to sample data. This project also demonstrates the application of machine learning algorithms in geotechnical engineering. Moreover, machine learning is well suited to many problems in geotechnical engineering involving sparse data conditions and high degree of nonlinearity. Reference: Dupre, W.R., and Tinsley III, J.C., 1980, Maps showing geology and liquefaction potential of northern Monterey and southern Santa Cruz counties, California, U.S. Geological Survey, Map MF-1199.

Figure 1: Comparison of the liquefaction potential map developed using remote sensing and machinelearning to the map of Dupre and Tinsley (1980). It is observed that the spatial variability in liquefaction potential is well captured by the developed map.


5

Dynamics of Wind Turbine Soil-Structure Interaction

Matthew J. Whelan Doctoral Student

Department of Civil and Environmental Engineering Clarkson University

8 Clarkson Ave Box 5712 Potsdam, NY 13699

Email: [email protected] Advisor: Kerop D. Janoyan

Abstract Wind energy has been the fastest growing energy source in recent years and thus the number of wind turbines has rapidly increased. However, wind turbines have been historically prone to component failures; on average two or three incidents occur per year for a wind turbine with half of the failures relating to mechanical components (Hahn, 1999). The predominant focus of existing experimental research has been specific to the turbine mechanics, in particular to the improvement of the rotor aerodynamics, blade efficiency, and optimum blade concentration. Understanding the behavior of the entire system, including the response of the structure and substructure, is needed to fully optimize the design of the wind turbine. Energy losses due to reactionary dissipation of kinetic energy to the structure and sub-structure supporting the generator should be investigated to address power generation efficiency as well as system robustness. In this study, a large-scale distributed wireless sensor network is proposed for measurement of the dynamic response of the entire wind turbine system, including the geo-structural system. Extraction of modal properties of the coupled geo-structural system serve as a means of examining the energy lost due to translation and rotation of the foundation as a result of dynamic soil-structure interaction. The effect of soil-foundation interaction on the dynamic response of the structure can be calculated using accelerometers to measure vibrations at the foundation and across the structure (Luco et al., 1988). Fixed-base structures exhibit inherently different motion response from structures with soil-structure interaction. Vibrations induced along the height of the structure are coupled with the foundation motion when soil-structure interaction is present. This coupling results in a first natural frequency of motion that is less than either the fundamental frequency of the structure on a fixed-base or of the foundation without the structure. Safak (1995) presented the theoretical correlation between ratio of the coupled natural frequency to the fixed-base structural natural frequency and the ratio of the fixed-base structural natural frequency to the foundation natural frequency based on a two-degree of freedom spring and damper model. The presence of soil-structure interaction effects on the structural response was shown to be detected using the impulse response obtained from the acceleration at the foundation and at the apex of the structure as the input and output, respectively. Furthermore, a method to estimate the natural frequency of the structure for the case of a fixed-base was presented utilizing the same measurement data. Stewart and Fenves (1998) presented a single-degree of freedom model of the soil-structure interaction for analysis relevant to the primary modal frequency to develop a method of estimating natural frequency and damping ratio for the fixed and flexible base foundations. In summary, using a simplified system model and estimated natural frequency of the structure under fixed-base conditions, it is possible to obtain an estimate of the modal


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properties of the foundation, such as natural frequency and damping ratio, which are a function of the soil-structure interaction. A distributed wireless sensor network is proposed in this study to measure the dynamic response of the coupled geo-structural system to examine the soil-foundation interaction and its consequence to the overall structure. The wireless network enables sensors to be placed across the sizable wind turbine structure, including the rotating blades, without the burdens associated with cabling. Furthermore, free-field ground vibrations nearby the turbine foundation can also be incorporated into the wireless system to enable measurement of ambient, environmental vibration inputs for open-loop system identification. A high-rate wireless sensor network for large-scale dynamic monitoring using low-cost micro-electro-mechanical systems (MEMS) accelerometers has been developed and validated through laboratory and field deployments (Whelan et al., 2007a; Whelan et al., 2007b). The system has been demonstrated to accommodate up to forty channels of measurement data from twenty distributed nodes at a sampling rate of 128Hz with virtually no packet loss. A large array of multi-axis accelerometers will be utilized to evaluate the modal properties of the geo-structural system and could be installed permanently to enable long-term structural condition monitoring of the wind turbine as well. Additionally, sensors for measurement of ambient parameters, including wind speed, temperature, and humidity, will be interfaced with companion wireless nodes for correlation and investigation of the effect of environmental loads. Deployment of this system on in-service wind turbines will provide a method of investigating the behavior of the structural and geo-structural response to aid in the design of next generation and retrofit of existing wind turbines with reduced mechanical failures and maintenance costs. References Hahn, B. (editor) (1999) Reliability Assessment of Wind Turbine in Germany. Results of the National 250 MW Wind Programme Institut fur Solare Energieversorgungstechnk. Luco, J.E., Trifunac, M.D., and Wong, H.L. Isolation of soil-structure interaction effects by full-scale forced vibration tests. Earthquake Engineering & Structural Dynamics 16(1) 1-21. Safak, E. (1995) Detection and Identification of Soil-Structure Interaction in Buildings from Vibration Recordings. Journal of Structural Engineering 121(5), 899-906. Stewart, J.P. and Fenves, G.L. (1998) System Identification for Evaluating Soil-Structure Interaction Effects in Buildings from Strong Motion Recordings. Earthquake Engineering and Structural Dynamics 27(8), 869-885. Whelan, M.J., Fuchs, M.P., Gangone, M.V., and Janoyan, K.D. (2007a) Development of a Wireless Bridge Monitoring System for Condition Assessment using Hybrid Techniques. SPIE International Symposium on Sensor Systems and Networks: Phenomena, Technology and Applications for NDE and Health Monitoring Ed. Kara J. Peters, 6530H. Whelan, M.J., Gangone, M.V., Janoyan, K.D., Cross, K., and Jha, R. (2007b) Reliable High-Rate Bridge Monitoring using Dense Wireless Sensor Arrays Structural Health Monitoring 2007 Ed. Fu-Kuo Chang. 1207-1214.


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Evaluation of Miniature Full Flow Penetrometers and Push Cone for Labora-tory Measurement of Remolded Undrained Shear Strength of Soft Clays

Adriane G. Boscardin

University of Massachusetts Amherst, [email protected]

Abstract Remolded undrained shear strength, sur, is an important parameter for design of offshore struc-tures, pipelines, and slope stability and debris flow modeling (both on and offshore). In general, many offshore soils are soft, sensitive, structured clays and lose strength upon disturbance. Yet there are no internationally recognized standards for measurement of sur. This research focused on developing a method to measure sur that has a sound theoretical basis, repeatable procedures, and reliable results for design applications. Three types of miniature full flow penetrometers (Ball, T-bar, and Shaft) and Push Cone (a cone with a 60o apex), shown in Figure 1, were developed to investigate their use as tools to evaluate the remolded shear strength, sur, of soft clays. The evaluation of sur using the miniature penetro-meters were compared with sur values obtained using the Fall Cone, Torvane, and Miniature Laboratory Vane on seven soft clays collected from both onshore and offshore test sites.

(d) (d)

(a) (b) (c)

Figure 1. Smooth (left) and rough (right) Miniature (a) Ball, (b) T-bar, and (c) Shaft Penetrome-

ters, and (d) Push Cone with smooth surface finish. The remolded undrained shear strength was measured with the miniature penetrometers by cy-cling a penetrometer over a 50 mm interval at a rate of 1 mm/s until the resistance stabilized to a minimum value, which typically occurred within 10 cycles. Figure 2 presents a typical cyclic Miniature Ball curve. A resistance factor of N = 13 was used to evaluate sur from Miniature Ball and T-bar test results based on theoretical and empirical recommendations presented in the litera-ture (Randolph & Andresen, 2006; Yafrate & DeJong, 2006). N-values were also back calcu-lated using sur values measured from the Fall Cone, Torvane, and Lab Vane. The range of NBall was between 5.4 and 23.4 and NT-bar ranged between 4.5 and 20.6. Since the location of the load cell was located outside the specimen, the Miniature Shaft Pene-trometer was developed to assess the resistance due to the shaft during Miniature Ball and T-bar testing and if the contribution of this resistance to the was significant enough (> 10%) to warrant

A. Boscardin 1 of 2


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corrections on Miniature Ball and T-bar results. Shaft resistance accounted for 11 % to 26% of the total measured Miniature Ball and T-bar resistances. These percentages reduced to 8-17% when accounting for an open cavity of 2 cm depth at the top of the test specimen resulting from probe insertion. Cyclic Miniature Shaft test results were also used to evaluate sur using pile de-sign theory from both Shaft Penetration and extraction measurements, assuming = 1 and Nc = 9. The values of sur calculated from penetration and extraction strokes generally differed by 11% and produced the lowest measure of sur for a given soil. Force (N)

-6.0 -4.0 -2.0 0.0 2.0 4.0 6.0

Figure 2. Typical Smooth Ball Penetrometer (a) cyclic force-depth curve, and (b) force-cycle

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

Onsy Smooth Ball(a)

Cycle

0 1 2 3 4 5 6 7 8 9 10 11Fo

rce

(N)

0

1

2

3

4

5

Onsy Smooth Ball

(b)

m)

h (c

Dep

t

data for z = 7.5 cm. The Push Cone was manufactured with a 60o apex and a height of 50.8 mm and pushed into test specimens at a constant rate of 1 mm/s to a depth of approximately 5 cm. Based on theoretical conical footing analysis (Houlsby & Martin's, 2003), sur was calculated from the test geometry and resistance curves. The Miniature Ball, T-bar and Push Cone tests were relatively easy to perform and produced re-peatable results. The Fall Cone (NGI), Torvane, and Push Cone measured the highest sur values and the Miniature Shaft Penetrometer the lowest values. Lab Vane sur results are similar to Miniature Ball and T-bar results using N = 13. Table 1 summarizes these sur results. Based on results from this investigation, the Miniature Ball and T-bar is recommended for measuring the sur of soft clays, but the Push Cone can potentially be used to measure sur of stiffer soils as well.

Table 1. Summary of sur results.

1) N = 13

Remolded Undrained Shear Strength, sur (kPa) FC FC LV Miniature Penetrometers Shaft (pen) Push Push

Soil NGI SGI TV HR HR-VR Ball1 T-bar1 Shaft (pen) Shaft (ext) Shaft (ext) Cone Cone (3 cm)

EPK Kaolin 3.5 2.2 4.7 2.0 1.4 2.0 2.2 0.51 0.47 1.1 4.7 4.0 BBC 2.4 1.5 3.6 1.9 1.8 1.5 1.7 0.48 0.43 1.1 3.5 3.0

BBC (0.8wL) 15.1 20.1 14.3 2.9 2.9 2.5 8.6 2.4 1.5 1.6 11.52 -- Burswood 9.6 6.0 10.0 3.3 2.4 3.6 3.3 1.0 1.1 0.9 7.0 6.7

Dalia 4.8 3.0 6.1 2.7 2.2 2.0 2.5 1.2 1.1 1.1 4.9 4.6 Gulf of Mexico 7.8 4.9 8.9 3.1 2.4 3.0 3.5 1.8 1.7 1.1 7.1 6.8

Onsy 5.4 3.4 5.3 2.3 2.3 2.0 2.0 0.64 0.44 1.5 3.5 2.7

2) Test stopped before 3 cm depth

A. Boscardin 2 of 2


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Static and Dynamic Analysis of Annulus Plugging of

Large Diameter Pipe Piles

Michael P. Smith University of Massachusetts Lowell, [email protected]

Advisor: Samuel Paikowsky, Research supported by GTR Abstract

A supplemental test program in new england was carried out as part of a design of a foundation system for a bridge replacement. The program was commissioned because the site consist of problematic sensitive soil with high variability (fine sands and silts with densitys ranging from loose to very-dense with bedrock deeper than 300 ft) and the foundation is to be designed using the newly implemented AASHTO LRFD specifications for deep foundations. A Phase I testing program conducted in 2006 with a HP14x117 ft pile, a 42 inch diameter x 69 ft open pipe pile, a 72 inch diameter drilled shaft, and a 72 inch diameter x 114 ft open pipe pile (denoted as pile 72-I). The test yielded undesirable results, requiring alternative options to be explored. Of the piles tested in Phase I, the 72 inch pipe pile had the best performance; therefore options for the pile were explored. Such options were to continue to drive the pile to refusal or bedrock, increase the number of piles at the piers, or try to artificially plug the pile. Thus, a Phase II test program was performed to examine alternative economical solutions.

Large diameter steel pipe piles have been typically used for offshore applications such as oil rigs. Recent extreme events loading (mostly brought about by earthquakes) demands the need of using such piles for bridges where smaller piles are not a feasible solution for the high lateral loads demand. Large pipe piles are ideal for difficult sites such as poor soil, inclement weather, and tidal waters; unlike drilled shafts which are sensitive to the later during drilling and concreting. These piles have high strength to weight ratios; hence can carry large vertical and lateral loads. Pipe piles however are expensive due to material and installation cost; and therefore it is worth while investigating innovative designs that will make them more economical.

Plugging on open-ended pipe piles is a phenomena the occurs when the soil entering the inner section of pile builds up resistance and prevents soil ahead of the pile from entering making the pile behave as a closed-ended pile. The affect of plugging significantly increases static capacity as well as the energy required to drive the pile. Plugging typically occurs in smaller pipe piles and partially occurs in medium sized pipe piles. Plugging of large diameter open-ended piles rarely happens due to the low displacement nature of the pile and soil deformations ahead of the pile. In this research an original design is examined, in an attempt to artificially plug the pile at a relatively shallow depth below 150 ft.


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For the Phase II test program two piles were tested in two stages. The first pile was an experimental 72 inch diameter pipe pile fitted with a reinforced annulus 40 ft from the pile tip (denoted as pile 72-II), as shown in Figure 1. The second pile is a 72 inch diameter open pipe pile (denoted as pile 72-III). In the first stage piles 72-II and 72-III were driven to a depth of 133 ft using an IHC S-600 hydraulic hammer. Dynamic measurements were taken on both piles during driving by: using a PDA, the S-600 hammer to record the energy per blow, and manually recording blows per foot and plugging. In addition electric strain gages were used on 72-II and pore pressure was monitored directly under the annulus to determine the effect of the pore pressure build up on the driving. Once driven; one day, seven day, and fourteen day restrikes were performed on the piles. The piles were then statically load tested via the quick load test to 6,000 kips or failure. After completing the load test on both piles the test program proceeded to stage two. The purpose of stage two was to continue to drive the piles to refusal (400 kip-ft at 12-14 blows/in for 6 inches consecutively) or bedrock, and perform load tests to determine gain in capacity. Dynamic measurements were taken and restrikes performed, as outline.

From the data obtained during the test program a dynamic and static analyses were performed comparing piles 72-II to 72-I and 72-III. The dynamic analysis consist of analyzing the energy per blow, energy per foot, blows per foot, total energy, energy approach capacity, energy measured by the PDA versus the hammer, electric strain gage data, CAPWAP capacity, the effect of pore pressure build up, and plugging. The static analysis consisted of analyzing the load displacement, load distribution, modeling the pile as linearly elastic pile, and modeling the pile in finite element software.

The above analysis showed the dynamic behavior of the annulus pile during driving is similar to a closed-end pile requiring more than three times the total energy than the open pile to drive to a specific depth, as shown in Figure 2. The static capacity for 72-II is almost double compared 72-III at 133 ft due to the increase of end bearing capacity, depicted in Figure 3. The success of the design is already proven, but fine tuning for future applications may be required.


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Effects of Fines on Cone Penetration Resistance and Liquefaction Resistance of Sands

Lalita Oka and Mandar Dewoolkar School of Engineering, University of Vermont

For many years, liquefaction related phenomena were

thought to be limited to clean sands. Finer-grained soils were considered incapable of generating high pore pressures, which are commonly associated with soil liquefaction. Numerous field performance data during earthquakes indicate that liquefaction-related failures have also occurred at numerous sites with sands containing fines and fine-grained soils. Fig (1) shows CPT-based liquefaction curves (Stark and Olson, 1995) for granular soils used in the recent form of the Simplified Procedure for liquefaction potential evaluation (Youd, et al., 2001). These curves reflect the effects of fines in such a way that at constant penetration resistance, soils have increased cyclic strength with increased fines (Ishihara, 1993). Whether this increase is caused by an increase of liquefaction resistance or decrease of penetration resistance is not clear (Youd, et al., 2001). Some recent studies supported the present form of fines

correction shown in Fig (1), whereas some showed different trends. For example, Cetin, et al. (2004) using probabilistic approaches and data from over 450 SPT-based case histories seem to indicate that only incremental change may be required in the fines correction factors recommended by Youd, et al. (2001). Carraro, et al. (2003) developed liquefaction curves using cyclic triaxial tests and stress-normalized cone penetration using cavity expansion theory. Unlike Cetin, et al. (2004), they found an opposite trend contradicting the curves currently used in practice. Sakai, et al. (2002) evaluated SPT data from a total of 846 borings from liquefied and non-liquefied sites during 11 earthquakes in Japan and observed an evidence of limiting silt content to which liquefaction resistance stays constant and increases for silt contents greater than this threshold value. Green, et al. (2006) reanalyzed 98 SPT case histories from 14 earthquakes to examine if any evidence of the limiting silt content can be observed in the field data. They indeed showed significant reduction in the cyclic resistance of silty sands with fines content greater than about 35%, indicating that current fines correction factors may overestimate the liquefaction resistance of silty sands with fines greater than 35%. As evident, there is still no consensus on what effects fines content have on liquefaction resistance in the context of the Simplified Procedure, which is used in virtually every seismic evaluation worldwide.

Fig (1) Liquefaction curves based on CPT data (Stark and Olson 1995)

The focus of the study is to investigate effects of nonplastic fines on the penetration resistance, shear wave velocity, and liquefaction resistance of sands, and the manner in which they affect the Simplified Method and fines correction factors currently used in practice. The specific objectives of the study are to: (1) investigate effects of increasing nonplastic fines content on cone penetration resistance and shear wave velocity in sands; (2) develop the liquefaction curves of cyclic resistance ratio versus normalized cone penetration resistance and shear wave velocity for different fines contents; (3) based on these curves, validate or suggest revisions for the fines correction factors currently used in practice; and (4) attempt developing a set of fines correction factors that incorporate both cone penetration resistance and Vs.

The research employs four devices: (i) a miniature cone penetrometer (piezocone), (ii) a calibration chamber, (iii) an automated cyclic triaxial apparatus, and (iv) two sets of bender elements to measure initial Vs in both calibration chamber and cyclic triaxial specimens. The cone penetration resistance and liquefaction resistance will be measured on sets of two separate, but nearly identical soil samples, one in the calibration chamber and the other in cyclic triaxial apparatus. The initial Vs


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measurements have two purposes: (1) to ensure that the calibration chamber and cyclic triaxial specimens have very similar fabric thus ensuring that the cone penetration resistance, Vs, and liquefaction resistance were determined on essentially identical specimens, and (2) to develop Vs based liquefaction curves.

Fig (2) shows the photograph of the calibration chamber and piezocone setup. The soil specimens in the flexible wall calibration chamber are 50 cm in diameter and about 50 cm high. The diameter of miniature piezocone is 1.1 cm. Fig (3) shows a photograph of cyclic triaxial testing setup. We have refurbished an older CKC cyclic triaxial apparatus with a new data acquisition and control system. Fig (4) shows the bender elements incorporated in the triaxial device.

Fig(2)Calibration chamber Fig(3)Cyclic Triaxial test setup Fig(4) Bender elements

As a pilot experimental study we have conducted cone penetration test on clean sand sample in fixed walled setup. We have also been successful in incorporating the bender elements in cyclic triaxial tests. Shear wave velocity data using bender elements is being obtained with the help of AutoLab acoustic data acquisition system modified for the use of bender elements. The charts in Fig (5) shows typical onset of liquefaction in the cyclic triaxial test and Fig (6) shows the shear wave velocity (Vs) arrival signal processing for different frequencies.

corrresiwor


Fig (5) Cyclic triaxial test

It is expected that the analysis of the reelations or will help enhance the understandstance leading to modifications in liquefaldwide.

Fig (6) Bender element: shear wave velocity arrival

sults obtained will either support the existing liquefaction ing of effects of fines on liquefaction resistance and CPT ction curves in the simplified procedure that are used

13

The hydrogeologic characterization of a public drinking water aquifer site in Dedham, Massachusetts

Daniel F. LaMesa

University of Massachusetts, Amherst, MA Abstract This research project is part of a large multidisciplinary research project that is aimed at determining if the Dedham Westwood Drinking Water Aquifer is being contaminated by road deicing salt from the adjacent Route 128. A hydrogeologic characterization of the site is required in order to determine the current and future transport of road salt runoff in the vicinity of the aquifer. The Dedham Westwood Drinking Water Aquifer resides under the former lake bed of Glacial Lake Neponset. The aquifer has two distinct layers that overlay it. Directly above the aquifer are lake bottom sediments and above that are delta deposits. The aquifer itself is one of 15 stratified-drift aquifers in the 117 square mile Neponset River Basin. The aquifer is thought to sit on a thin layer of glacial till and granite bedrock. The site has two major hydraulic forces that oppose one another. On the eastern part of the site is the Neponset River, which has a mean average discharge of 400 gallons per second. Opposing the Neponset River is a large public drinking water supply well. The well is screened in the aquifer from 80 to 97 feet below the ground surface and pumps out approximately 12.5 gallons per second. The public supply well runs almost continually during the summer months and less during the fall, winter, and spring months. It is speculated that either the river or the public supply well is controlling the direction of the ground water flow at the site. An extensive subsurface investigation is being conducted at the site to determine the soil profile, soil properties (such as hydraulic conductivity), water levels and spatial hydraulic gradients. Five locations at the site were chosen to perform continuous split spoon sampling to a depth of 15 feet into the aquifer. The depth to the top of the aquifer ranged from 78 to142 feet. Fixed Piston Osterberg samples were collected at one of the locations for future laboratory hydraulic conductivity testing. At each location a cluster of 5 to 11 monitoring wells was installed. The wells varied in depth from 5 feet to 153 feet. Grain size and water content analyses are currently being conducted on the SPT samples. Atterberg Limits and specific gravity tests are being performed on select samples to fully classify the different soil units at the site. The fixed piston samples will be used in constant head flexible wall tests with vertically and horizontally oriented specimens to determine the vertical and horizontal hydraulic conductivities. The piston samples may also be used for various strength tests in the future. In situ slug testing is presently being done in all of the wells at the site to get an in situ value for the horizontal hydraulic conductivity. Empirical grain size equations for determining the hydraulic conductivity will also be used. Monthly ground water levels are being taken at each well along with precipitation data using a rain gage. Using the collective data from the monthly ground water levels and the rain gage data; ground water plots at various depths in the formation will be constructed. The


14

ground water plots will used in conjunction with the hydraulic conductivity data to determine what direction the ground water is flowing and how fast it is flowing.


Figure 1. Site Map

Figure 4. Typical Slug Test Equipment

Well 15

Figure 2. Split Spoon Sampling

Computer and Transducer

Slug

Figure 3. Split Spoon Sample

B Cluster

Session II: Case Studies


16

Evaluation of an Automated Early Warning System for Unstable Soil Slopes

Jeffrey Lloyd

University of Massachusetts, Amherst, MA [email protected]

Abstract The movement of unstable slopes can create unsafe and costly damage to property and infrastructure. Traditional monitoring of slope movement to provide early warning of failure using inclinometers and site visits is personnel and time intensive and may still not give sufficient warning. Use of automated monitoring via instrumentation data acquisition, cellular technology and server based data reporting can provide an economical solution. Instrumentation was installed within an unstable slope at a research site in Waterbury Center, VT. A CR10X datalogger with a cell phone monitors data from in-place inclinometers, piezometers, a barometer, and a rain gauge (Figure 1). Continuous monitoring of slope movement and ground water elevation has been ongoing since January 2006. A dedicated server at UMass Amherst running Multilogger DB from Canary Systems automatically collects the stored data every two days, adding it to a database and publishes the calculated results to a website (Figure 2), which can be viewed by any registered user from any internet connected PC.

Figure 1. CR10X installation


17

Figure 2. Multilogger web interface Direct shear and constant rate of strain tests were conducted on tube samples collected during the inclinometer casing installation. Using the results of the lab testing and the boring logs, a model of the slope was created using slope stability software, Slide 5.0 from Rocscience (Figure 3). Current research includes refining the model to accurately reflect actual slope behavior since 2006 and determining a critical water table elevation at which the factor of safety of the slope drops below an acceptable value.

Figure 3. Waterbury Slide model A secondary function of Multilogger DB is the ability to create alarms when specific data elements reach predefined levels. Future research will focus on determining set points for the ground water monitoring data to trigger an alarm if the water elevation reaches the critical level as determined by the slope stability model. Such alarms can send email or page key personal alerting them to potential slope movement.


18

Development of a Resistance Factor for the Minnesota Department of Trans-

portation Pile Driving Formula

Colin OHearn University of Massachusetts Lowell

[email protected]

Abstract A dynamic equation is an equation used to determine the capacity of a pile based on observing the pile driving in the field. The equation traditionally uses such parameters as the pile penetra-tion under a slow (set), the height of the ram fall, weight of the ram, weight of pile, and effi-ciency of the hammer. There have been many different formulations of these equations over the years. Many of these formulas work well for one type of pile, soil strata, or hammer but fall short when they come to different conditions other than those they were developed for. Some other equations are plainly based on wrong mechanics. In order to develop a resistance factor for the Minnesota DOT, different types of soil strata, pile types, and hammers used in the State of Minnesota will be reviewed. In order to review all these different parameters a database has been established. This database contains only H-Piles and Pipe Piles due to the fact that the MnDOT does not use precast prestressed concrete piles. A specific pile driving equation will be examined, its uncertainty determined, and the resistance factors associated with its use will be determined.


19

Expanding the College Classroom: Developing Engineering Skills through International Service-Learning Projects

Suggested authors: Mary McCormick, Chris Swan, Doug Matson, David M. Gute,

John Durant

Abstract Project-based service-learning is a valuable pedagogical tool which confers educational benefits that extend far beyond the charter of traditional classrooms. This unique form of experiential education is based on a synergistic model in which community service is compatible and integrated with the academic learning objectives. In the context of pro-viding engineering services to poor communities in developing countries, students are able to participate in all aspects of the engineering design process including problem formulation, consideration of alternative technologies, and design, construction, and evaluation of selected technologies. The reciprocal relationship that forms between the students and community nurtures personal growth and a deeper sense of social responsi-bility among students while empowering communities as they become more self-sufficient. As a prominent advocate of this pedagogy, Tufts University has provided op-portunities for students to work on water infrastructure projects in Ecuador, El Salvador, Ghana, and Tibet over the past four years. Although the challenges students face are unique to each project, overcoming them allows students to develop problem solving skills that they would not otherwise get in their college education. A prospective evaluation, comprised of a series of surveys, questionnaires, and personal reflections, is currently being performed. The goal of this research is to quantify the bene-fits to participants of an international service-learning experience. This paper focuses on the rigorous examination of two distinct types of skills: social and critical thinking. The social skills include leadership and teamwork qualities, competency in communication, and students abilities to perceive the societal, economic, and environmental impacts of a solution. Critical thinking skills, which describe the ability of a student to solve real world problems, will be assessed by examining when and how the student balances crea-tive, practical and analytical approaches to problem solving. The methodology employed in evaluating social and critical thinking skills will be reality based open-ended questions. As a comparison population, students who have not participated in international service-learning projects will be given the same open-ended questions and the results will be compared. This study aims to demonstrate that students who become engaged in service-learning projects enrich their education by developing new skills and strengthening oth-ers, receiving an education that cannot be gained in a classroom. The results are expected to bolster the argument for implementation of service-learning projects into college-level engineering curricula.


20

Uncertainty Evaluation of Displacement and Capacity of Shallow Foundations on Rocks

Robert Muganga

University of Massachusetts, Lowell Advisor: Prof. Samuel Paikowsky

Research supported by NCHRP Project 24-31 through GTR Abstract

NCHRP Project 24-31 LRFD Design Specifications for Shallow Foundations is aimed at improving LRFD (Load and Resistance Factor Design) over the traditional Working Stress Design (WSD). Compared to WSD, LRFD has the ability to provide a more consistent level of reliability between different designs and the possibility of accounting for load and resistance uncertainties separately. In the development of LRFD, a framework for the objective, logical assessment of resistance factors is needed. Additionally, in order for LRFD to fulfill its promise for designs with more consistent reliability, the methods used to execute a design must be consistent with the methods assumed in the development of the LRFD factors. The research addresses the need of resistance factors for the Ultimate Limit State (ULS) and the Serviceability Limit State (SLS) of shallow foundations on rock. Figure 1 presents a flow chart outlining the research process leading to the establishment of resistance factors to be used in the AASHTO specifications. The research emphasizes the loading conditions applicable for bridge foundations. The topic of shallow foundations on rock is quite complex therefore significant effort has been put into addressing different Bearing Capacity (BC) models, establishing uncertainty of parameters extracted for material and load testing and correlations between rock index properties and strength parameters.

A database of 122 case histories that includes cases by Zhang and Einstein (1998) and Prakoso and Kulhawy (2002) was assembled. The data were analyzed with the goals being: (a) establishing uncertainty of methods and parameters, (b) development of resistance factors (c) development of final resistance factors and the conditions for their implementation. Figure 2 presents some preliminary results of the relationship between the Uniaxial Compressive Strength (qu) and the Interpreted Foundation Capacity (qL2) obtained from load-displacement curves using Hirany and Kulhawy (1988) method.

1


21

Laboratory Indentation Tests

Inherent & Variability of Intact Rock & Rock

Mass

Failure Modes of BC on Rock Sowers (1979)

3.8 mm < B < 30.5 mm Database

Utilization of Rock Test Data to Establish the

Uncertainty of Strength and Modulus

Parameters of Intact Rock & Rock Mass, Their Inter-relations, and Correlations to

Index Properties

Open Open Open Discontinuities Discontinuities Discontinuities

Sj < B Sj < B Sj < B (Uniaxial (Uniaxial (Shear Zone) Uncertainty in BC (Nc) and

Shape Factors Compression) Compression)

AASHTO (2006) Specification 10.6.3.2.1

BC on rock (not specific), Sect. 10.6.2.1

Identify Models for BC, Settlement and Associated

Factors for each of the Failure modes, e.g.:

Load Ranges &

Distributions

used in NCHRP 24-17 & other Codes

Worldwide Presumptive Bearing

Values, and Sect. 10.6.2.4.4 Settlement; FHWA GEC 6 section

5.3.6 Kimmerling (2002). FHWA

Reference Manual Munfakh et al. (2001)

Bell (1915) Bishnoi (1968) Establish the

Range of Reliability

Index Implicit in Existing

Design Using RBD format

Due to Limitation of Data Use the Typical Values and Conduct

MC Simulations Assessing the BC and

Displacement Parameters of Shallow Foundations on Rock

Kulhawy et al. (1983) Resistance

Factors for BC and

Settlement

Goodman (1980)

FE (PLAXIS) Investigation of BC and

Shape Factors as a Function of Discontinuity

Spacing & Orientation

Examine Typical

Structures/Case

Histories

SLS Methodology from NCHRP

12-66

Final Resistance Factors and

Conditions for Implementation

Established BC & Settlement Models

Notes: B Foundation Width Sj Discontinuity Spacing AASHTO Modified Specification Target Reliability RBD Reliability Based Design SLS Serviceability Limit State ULS Ultimate Limit State

Figure 1 Flow Chart Outlining the Research Plan to Develop LRFD Parameters for the ULS and SLS Design of Shallow Foundations on Rock (GTR proposal NCHRP 24-31,

2006)

2


22

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Figure 2 Interpreted Foundation Capacity (qL2) versus Uniaxial Compressive Strength (qu) for 122 case histories; Comparison of Zhang and Einstein (1998) with the Hoek-Brown

Analytical Relation

References

Carter, J. P., and F. H. Kulhawy (1988). "Analysis and Design of Foundations Socketed into Rock. " Report No. EL-5918, Empire State Electric Engineering Research Corporation and Electric Power Research Institute, New York, NY, p. 158.

Einstein, H. and Zhang, L. (1998). "End Bearing Capacity of Drilled Shafts in Rock." Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 124(7), July, pp. 574-584.

Geosciences Testing and Research, Inc. "NCHRP 24-31 LRFD Design Specifications for Shallow Foundations." TRANSPORTATION RESEARCH BOARD, COOPERATIVE RESEARCH PROGRAMS, October 18th, 2006.

Goodman, R.E. "Introduction to Rock Mechanics." Second Edition, John Wiley & Sons, 1989.

Hirany, A. and Kulhawy, F.H., "Conduct and Interpretation of Load Tests on Drilled Shaft Foundation: Detailed Guidelines", Report EL-5915 (1), Electric Power Research Institute, Palo Alto, Jul. 1988, 374 p.

Prakoso, W.A. (2002). "Reliability-Based Design of Foundations on Rock Masses for Transmission Line and Similar Structures." PhD. Dissertation, Cornell University.

3


23

A STUDY ON STREAM BANK EROSIN AND INSTABILITY By

Jaron L. Borg, Paul Bierman, & Mandar Dewoolkar University of Vermont

Burlington, VT

Today as we learn more about the nature of our streams and rivers and their vital role to the ecosystem and our surface water quality, we have become less likely to straiten or mechanically stabilize our often failing stream banks. The eroding banks are a non-point source

for phosphorous and nitrogen deposition in the waterway. This is especially true in Vermont where the large amount of agriculture and use of fertilizer has increased these levels in the soil significantly. The agriculture use has also degraded the stability of the stream banks allow them to erode at an increased rate. This decrease in stability is illustrated in figures 1 and 2. With the difficulty of obtain a permit to alter streams directly, more property owners and the State are in a need to be able predict how the streams will change in the future.

The objective of this research is to gain a fundamental understanding of the soil mechanics governing stream bank erosion in Vermonts rivers. Our quantitative evaluation is based on comprehensive geotechnical analysis of bank stability in order to understand and thus be able to predict what makes some banks stable and other banks fail over time, changing river, and groundwater conditions. An attempt will be made to incorporate the soils strengths and their erosion potential, bank geometries, and ground and stream water levels into slope stability models. The semi-quantitative evaluation will be similar; however, soil strength parameters will be empirically correlated to index properties (such as grain size), which are cheaper and less time consuming to determine than soil cohesion and friction angle.

So far we have been working on the banks of Lewis Creek and Winooski River, in northern Vermont. We have selected about 8 sites along the banks of these streams, approximately half that are on the verge of failure and the rest that are marginally stable. All site investigations are performed using hand operated drilling and sampling equipment because of restrictive access to the sites. In-situ shear strengths have been measured using a borehole shear tester (BST). At the same locations, relatively undisturbed Shelby tube samples were obtained.

Figure 2. Selected site locations along

Winooski River and analysis of aerial photos

Figure 1. Example of a riverbank failure


24

Shear strength of these soil samples were determined through direct shear testing. From the testing conducted thus far there is a trend indicating that shear strengths based on direct shear tests are generally slightly larger but close to those measured using BST. The soil suction was also measured however the coarse soils found along the reaches studied have provided values too small to be read by our tensiometers.

Thus far, at one site along Winooski River with the lowest perceived stability, piezometers and tilt switches equipped with data logging have been installed. Piezometers were placed to monitor changes in the groundwater levels in the bank; an example readout can be seen in figure 3. A pressure transducer was also placed in the channel to monitor the stream level. The goal is to capture the bank failure event using the readout from the tilt switches and then

observing the water levels in the stream and the bank at the same instant.

During the summer of 2007 investigations were made into the shear strength contributions from the grass root systems present at the investigated reaches. It is hoped that an empirical equation may be derived to relate the root density to the increase of shear strength in the soil. The ability to measure the erosion coefficients of the soils will be made possible by the construction of a Jet Erosion Test apparatus. The read out from this device allows for reasonable estimation of both the critical shear stress for the soil; the shear stress at which the soil particles begin to disassociate, as

well as the erosion coefficient that allows the speed of the incision to be determined.

This work will have an impact on our understanding of bank stability and sediment input to streams in Vermont and elsewhere. Once we understand these processes quantitatively at specific sites, the future work will include looking for ways for making more broad-ranging predictions of stream and riverbank behavior hopefully under a variety of different conditions. In particular, we hope to be able to use our models to predict bank stability response to channel evolution over time and space as well as draw conclusions about erosion hazards.

Depth to Water Table Below Top of Casing

-8.5

-8

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th to

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able

(ft)

well_1Well_2Well_3

Note: Numbers increasing with

increasing distance from

river edge

Figure 3. ground water in bank during a 16hr storm event


25


Investigating Gas-generated Excess Pore Pressure as a Failure Mechanism for the 1996 Finneidfjord Slide

Eugene Morgan

Dept. of Civil and Environmental Engineering, Tufts University, 200 College Ave., Medford, MA, 02155, USA; [email protected]

Abstract On the 20th of June, 1996 approximately 1 million m3 of sediment failed near the Finneidfjord village on the western coast of Norway. This slide involved quick clays, and occurred in stages, starting under water and retrogressing on to land. Initial surveying of the slide site deduced the sequence and timing of failure from all available evidence, including eye-witness accounts. Silty clay comprised the bulk of the slide material, and seismic reflection surveying, sediment coring, and piezometer logging indicate that initial failure of a 2-meter-thick slab occurred on a thin, weak, coarser-grained layer. It has also been suggested that trapped gas in this weak layer may have generated excess pore pressures, leading to failure.

The natural production of gas within submarine sediments can reduce the shear strength of sediments enough to cause failure. The volumetric expansion of gas bubbles trapped in the pore space of sediment will reduce the effective stress of the soil matrix by pushing against the soil particles and by increasing pore water pressure. Gas pressure must exceed static pore water pressure in order for bubble expansion to occur, and so this expansion can be quantified by evaluating excess pore pressure.


26

This study determines the gas pressure necessary to initiate the 1996 Finneidfjord slide by performing a transient slope stability analysis with variable excess pore pressure. The slope and sub-seafloor conditions prior to failure are modeled in the slope stability analysis program SLOPE/W. The Morgenstern and Price method calculated factors of safety for a fully-defined failure mass whose geometry was determined from seismic profiling. Applying a piezometric surface exclusively to the thin coarse-grained layer simulates excess pore pressures in that layer, and incrementally increasing the elevation of this piezometric surface generates the pressures for the transient analysis. The excess pressure on this layer is adjusted until afactor of safety of unity is achieved. I corequired to initiate failure. Theoretical equations from previous studies calculate the corresponding gas fraction of pore volume at failure to be 0.48. This fraction is homogenousalong the coarse-grained layer that lies in the failure plane; however the absolute gas pressurevaries directly with water depth. This indicates that shallower slopes are much more susceptible to failure via excess gas pressure, given a constant rate of gas production within a layer at adepths.

nclude that an excess gas pressure of 8.80 kPa is

ll


27

Full-Scale Pilot Study to Reduce Lateral Stresses in Retaining Structures Using GeoFoam

Matt Ciuffetti [email protected]

University of Massachusetts Amherst Amherst, MA 01002

The use of alternative lightweight materials in the construction of earth retention structures has several benefits, resulting in an increasing interest to identify potential new materials and expansion of the range of applications for existing materials. One material that is gaining popularity in construction applications is Expanded Polystyrene (EPS) in block form, now referred to as GeoFoam. Originally used in highway construction for insulation and frost damage mitigation, GeoFoam now has a wide range of applications including lightweight fill in bridge approach embankments and as a backfill in conventional earth retention structures. The very low unit weight (1-2 lb/ft3) and constitutive stress-strain relationship of GeoFoam reduces settlement and pressures normally attributed to heavier fill materials. The ease of installation also greatly reduces construction time. A full-scale pilot study was conducted on the use of EPS GeoFoam for the construction of the approach embankments for a bridge abutment in Leicester, Vermont. This was a joint venture by the University of Massachusetts Amherst and the Vermont Agency of Transportation. The design of the Leicester Junction bridge to be constructed over deep compressible deposits utilized EPS GeoFoam to reduce lateral earth pressures on the abutment wall face and minimize differential settlements between the approach and abutment.

Figure 1. Placement of EPS Geofoam Blocks


28

In-situ tests prior to construction and laboratory tests were performed on tube samples in order characterize the soft clay deposits found at the site. Laboratory testing included soil classification, consolidation, and undrained shear strength using a lab vane apparatus.

Instrumentation was installed during the construction of the abutments which included earth pressure cells embedded vertically at the abutment/GeoFoam interface and horizontally installed pressure cells at various depths within the GeoFoam fill. Vertical and lateral pressures were monitored during the construction period and after completion of the bridge. Temperatures were also recorded in order to determine the thermal effects on fill performance.

Figure 2. Earth Pressure Cell (2A1 2A6) Locations


29

Kinematics of Tsunamigenic Submarine Failures

Oliver-Denzil S. Taylor University of Rhode Island, Kingston, RI, [email protected]

Abstract

The kinematics of tsunamigenic landslides is, in particular, poorly understood. Unlike subaerial landslides, submarine landslides tend to propagate for very large distances, sometimes as debris flows, suggesting that there must be a significant reduction in the shear strength of the sediment. However current modeling, especially for the occurrence of tsunamigenic submarine slides, does not accurately reflect realistic soil behavior. Most submarine failures occur at gentle slopes (less than 5-degrees), once failure occurs soil mechanics are often simplified or ignored, by assuming that the soils shear strength instantly attains either remolded or residual state upon failure, when modeling kinematics and runout distances of these events. This research combines theoretical, laboratory, and numerical investigation to examine and model the role of soil behavior on the kinematics and probability of submarine mass failures and the impact the behavior has on tsunami generation.

According to current landslide tsunami generation models, the initial acceleration time history of a submarine mass failure is an important factor influencing the source characteristics of tsunami waves. Translational models developed thus far typically simulate rigid or deforming bodies sliding down an inclined plane, assuming either negligible basal resistance or an idealized basal resistance, with or without the inclusion of hydrodynamic forces. However no known models incorporate realistic basal resistance, hydrodynamic forces, and hydroplaning together to quantify their effects on the initial kinematics of submarine failures. In all current models it is assumed that the maximum initial acceleration occurs nearly instantaneously after the moment of failure.

A new rigid body model is proposed that incorporates hydrodynamic drag, with realistic basal resistance and hydroplaning effects (Bradshaw et al. 2007; Taylor et al. 2008). Utilizing the post failure shear strength of the sediment, this new model investigates the initial kinematics and time histories of the slide event in relation to tsunami generation over varying slope angles and idealized hydroplaning conditions. Current results (Fig. 1) indicate an increased importance for the inclusion of more realistic soil behavior on the initial kinematics of tsunamigenic failures, as seen in the refined acceleration and velocity time histories.

Validation and refinement the proposed model will be accomplished via a

laboratory-testing program. The experimental program will consist of a series of model slope failure tests in a wave tank at 1-g conditions. These tests are designed to capture the most significant aspects of tsunamigenic landslides, namely progressive failure of intact blocks of cohesive soil along a weak layer. The tests will be performed at 1-g conditions in existing wave tanks at the University of Rhode Island. The effective stress conditions will be very low in these tests and the cohesion of the clays will dominate both


30

the shear strength and the mode of failure. However, it is important to perform tests at this scale (as opposed to centrifuge testing), in order to effectively model the physics of the problem and gather detailed measurements of the slide and wave kinematics.

The expected benefits of this experimental program will be the first measurements of the kinematics of a submarine landslide in cohesive soils complete with the resulting waves that are generated. This data coupled with the will both help further our physical understanding of this complex phenomenon and be invaluable to the tsunami modeling community for validating models and assessing tsunami hazards for coastal communities.

Figure 1: Influence of hydroplaning effects for the proposed basal resistance model, at various degrees of hydroplaning Hy, on slide velocity and acceleration time histories as a function of slope (2 and 5 deg). The solid line is the zero basal resistance solution neglecting soil behavior (from Taylor et al. 2008). References Bradshaw, A.S., Baxter, C.D.P., Taylor, O-D.S. and Grilli, S.T. (2007). Role of Soil Behavior on the Initial Kinematics of Tsunamigenic Slides. Proc. 3rd Intl. Symp. on Submarine Mass Movements and their Consequences (Santorini, Greece, October 2007) (in press). Taylor,O-D.S., Bradshaw, A.S., Baxter, C.D.P., Grilli, S.T., (2008) The effects of basal resistance and hydroplaning on the initial kinematics of seismically induced tsunamigenic landslides. ASCE 2008 GeoCongress Symposium (accepted).


31

Session III: Soil Behavior


32

Bender Element Test Setup for Large Soil Specimens

Remzi O. Deniz1, Mishac K. Yegian2, Ece Eseller-Bayat3, Akram Alshawabkeh21 Masters Student, 2 Professor of Civil Engineering, 3 Ph.D. Candidate, Northeastern University, Boston, MA

e-mail: [email protected]

One of the most important soil parameters used in geotechnical earthquake engineering analysis is shear wave velocity, Vs. Bender elements have been used successfully in triaxial test setups to measure Vs. The use of bender elements in large soil specimens, typically tested in shaking table tests, poses significant challenges. The wave form generated by a bender element source is three dimensional and attenuates quickly as the distance between the source and receiver bender elements get larger. The focus of this research is to develop a bender element test setup which enables accurate measurement of shear wave velocity in soil specimens much larger in size than the typical specimens tested in triaxial cells.

Bender elements are very sensitive tiny plates made of piezoelectric ceramics. They are designed to bend when electric energy is applied and to create a voltage difference when mechanically stressed. Figure 1 shows typical bender elements that are used in this research. Figure 2 shows a Plexiglas box, filled with sand, which is used for measurement of shear waves as a function of distance between source and receiver bender elements. Figure 3 shows the brass fitting that was designed and manufactured for the installation of benders, through holes on the sides of the Plexiglas box, in a soil specimen. Oscilloscope

Power Amplifier Sand Specimen in

Plexiglas Box Oscilloscope Data Acquisition

Function Generator

Fig.2 Bender element test setup for large soil specimens.

Fig.1 Unmounted bender elements.

Fig.3 Bender element mounted

in a brass fitting.


33

Because of complex wave forms, wave travel paths, and boundary effects, it was determined that high voltage was needed to excite the source bender in order to measure the much smaller amplitudes of vibration arriving at the receiver bender. To achieve this goal, a bender element test setup was developed that included a digital signal generator, power amplifier that can transmit up to 200 DC volts, and a multi-channel digital oscilloscope that can record accurately the zero time of the generated signal and the wave arrival times of multiple receiver benders. The oscilloscope specific software provides digital access to the data for analysis and presentation. Figure 2 shows the different components of the developed bender element test setup.

Typical test results are shown in Figures 4 and 5. Figure 4 shows the test results where the distance between the source bender and the receiver bender was 17.4 cm. The figure shows the transmitted signal which has a frequency of 400 Hz and amplitude of 140 V. The received signal has amplitude of 7 mV. Based on the travel time and the distance between the source and receiver benders, the shear wave velocity of the sand was calculated to be Vs = 17.4 cm/3.8 ms = 45.8 meter/sec. Figure 5 shows the test results on another sand specimen where the distance between the source bender and the receiver bender was 43 cm. The amplitudes of the source and receiver benders are 130 V and 2.5 mV, respectively. Based on a signal arrival time of 10.4 ms, the shear wave velocity of the specimen, which was of the same sand and relative density as that of the test shown in Figure 4, was Vs = 43 cm/10.4 ms = 41.4 meter/s

Transmitted Signal Received Signal Transmitted Signal Received Signal

Fig.4 Transmitted and received signals for wave travel distance of 17.4 cm.

Fig.5 Transmitted and received signals for wave travel distance of 43 cm.

The bender element test setup developed in this research enables performance of tests

on large soil specimens, typically used in shaking table tests. This setup is now being used to develop a relationship between required voltage for source benders as a function of distance between source and receiver benders, soil density, overburden stress, and frequency of excitation.


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High Quality Deep Water Geotechnical Sampling and Shear Wave Velocity

Cody D. Jones University of Massachusetts Amherst, Amherst, MA, [email protected]

Abstract Accurate determination of offshore engineering soil parameters is of growing importance in many modern engineering projects and of particular interest to the oil and gas industry. Undisturbed soil sampling is just as imperative to meeting this goal on large scale marine projects as it is to their terrestrial counterparts. Unfortunately, current industry practice for deep water sampling often uses poor sampling equipment and techniques, leaving vital parameters such as undrained shear strength and preconsolidation stress in question. The Norwegian Geotechnical Institute (NGI) developed a Deep Water Sampler (DWS, Lunne and Long 2006) with the intention of collecting high quality geotechnical samples from the ocean floor for engineering projects and research use. This new sampler uses a seabed push frame, modified tube geometry and special sample liners to enhance sample recovery and quality (Figure 1). The DWS was used for the first time in 2006 by NGI to collect samples from the North Sea Troll A site. The Troll A Clay is a slightly overconsolidated, highly plastic, very soft to firm, homogeneous clay (Huslid, 2001). Subsequent onshore laboratory tests conducted on the samples confirm that high quality samples were successfully collected. Follow-on research is now being conducted by UMass Amherst in collaboration with NGI to develop a method for nondestructively accessing sample quality of DWS samples offshore during drilling operations.

Figure 1. a) Deep Water Sampler frame ready for deployment to the seabed, and b) Deep Water Sampler cutting tube (pictures courtesy of Statoil, Norway).


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Figure 2. New bender element jig formeasuring shear wave velocity of soil samplescollected using the Deep Water Sampler.

Shear wave velocity measurements are being used as a basis for nondestructively evaluating the quality of DWS samples. Measurements are being made using a new portable test jig designed and built by UMass Amherst to support soil samples from the DWS sampler (Figure 2). The jig uses oriented bender elements to measure shear wave velocity and its construction is based on a jig developed by UMass Amherst for evaluation of terrestrial tube samples and Sherbrooke Block samples. A new electronic system is being developed using a compact set of National Instrument components and LabView data acquisition and control software running on a laptop. This will enhance the portability of the test equipment which is essential for successful implementation in an offshore geotechnical testing laboratory.

Shear wave velocity tests are currently being performed on the Troll DWS samples to check repeatability of results on the same sample as material is removed for additional laboratory testing. Once the prototype is evaluated in the laboratory, it will be deployed for offshore use. The objective is to create an accurate and reliable system to take shear wave velocity measurements shipboard as the samples are recovered and ideally to assess sample quality in near real time. In parallel to this work, DWS samples of the Troll A clay are being tested in the laboratory at UMass Amherst to measure its fundamental stress-strain-strength behavior in Constant Rate of Strain consolidation and Triaxial and Direct Simple Shear testing. Results from this testing will provide a valuable framework for behavior of low OCR offshore sediments which can be used as a guide for future site investigations. Development of an effective affordable system of high quality sample recovery and testing will have a significant demand from developers of future ocean infrastructure and continental slope stability researchers where zones of highly unstable underconsolidated clays are theorized to play a role.

References Huslid, C. (2001) Full-Scale Monitoring of Troll A Concrete Platform: A Huge Gravity-Based Structure on Soft Clay, Proceedings of the Eleventh International Offshore and Polar Engineering Conference, June 17-22, Stavanger, Norway 2001, pp. 647-653 Lunne, T. and Long, M. (2006). Review of long seabed samplers and criteria for new sampler design. Marine Geology. Vol. 226, Issues 1-2, pp. 145-165.


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Lattice Discrete Particle Model (LDPM) for quasi brittle materials.

Andrea Mencarelli Rensselaer Polytechnic Institute, Troy, NY, [email protected]

Abstract

In this paper a numerical model called Lattice Particle Discrete Model (LDPM) is presented. This model comes from the family of the microplane and lattice model and can describe the behavior of quasi brittle materials like rock and concrete. Until now only simulations about concrete were performed, but the plan for the future is to try to simulate, like for the Microplane, also experimental test involving rocks.

The model can reproduce the composition of the material, considering, in the case of the concrete the cement content c, the water cement ratio w/c, the aggregate cement ratio a/c and the diameter distribution of the aggregates. These ones are disposed in the specimen with a randomly procedure, starting from the biggest ones until the smallest ones. The type of connection between the particles is defined by a three dimension Delaunay triangulation and by a dual domain tessellation. In this way we have facets starting from the middle of every edge of the tetrahedron. Considering these facets, the deformations can be defined in term of displacements and rotation vectors referred to the center of the facets, respect to the centre of the nodes. The hypotheses to define these deformations are: 1) the axial velocity is linearly distributed between the aggregates centers; 2) the two transversal velocities, perpendicular between them, and on a plane perpendicular to the axial velocity, are the effect of a rigid motion of the center of the aggregates. After the deformations are described it is possible to define the constitutive relations, based on the behavior at the facets in their center of gravity, from which normal and shear forces are transmitted, representing friction and cohesion. The elastic behavior is expressed by the Hook Law with a different Young Modulus for the normal direction and the transversal one. The evolution of the stress and the strain follows the previous law until the stress does not reach a certain limit, after the behavior becomes inelastic and follows an incremental law, where the slope depends from the total strain and from a parameter , which says if the material is in a softening, plastic or hardening phase.

After defining the model some numerical simulations are performed trying to simulate experimental test in compression and in tension. In particular a uniaxial unconfined compression from VanMier, 1996 in Fig. 1 and a three point bending test from Horvath and Persson, 1984 in Fig. 2 are simulated. The numerical results fit very well the experimental ones, considering the elastic part, the value of the peak and the slope of the post peak. The next step is to try to simulate rocks.


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Fig. 1: Unconfined Compression from VanMier with High Friction plates.

Fig. 2: Three Point Bending Test from Horvath and Persson, 1984.


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Characterizing local heterogeneities in unsaturated soils using acoustic techniques L. A. George & M. M. Dewoolkar

School of Engineering, University of Vermont, Burlington, Vermont, USA

Accurately predicting and modeling flow through unsaturated soils is difficult due to the complexities that stem from the heterogeneities inherent in soil deposits. In simulating subsurface non-equilibrium flow, it is possible to take into account the heterogeneous nature of the material by using a rate dependent, dynamic capillary pressure saturation relationship. Generally unsaturated soil properties, e. g. the capil-lary pressure function and the hydraulic conductivity function, are measured at static or steady state con-ditions. These static properties are then used to analyze both steady-state and transient flow, which has been shown to be an incorrect assumption [1, 2]. A new dynamic capillary pressure function has been de-veloped [3] which includes the rate dependence, describes the hereditary effect of capillarity, and is based on the characterization of local flow caused by heterogeneities. This dynamic capillary pressure function is formulated with commonly known and relatively commonly measured soil properties, along with one additional parameter, the capillary relaxation time, which can be determined using acoustic techniques [4]. A device has been developed at the University of Vermont which will allow for simultaneous meas-urement of the acoustic velocity and attenuation as well as the hydraulic properties, including the static capillary pressure and hydraulic conductivity functions (see Figs. 1 and 2).

Acoustic techniques provide powerful means to characterize the mesoscale heterogeneity in porous media in a non-destructive manner. A procedure has been proposed which would explicitly evaluate the dynamic capillary effects, and has been successfully used to infer the capillary relaxation times and the sizes of local structures in porous media [4]. When a locally heterogeneous porous medium is subjected to an external disturbance, fluids in different regions respond with different pressures, resulting in local fluid flow [5]. The local flow induced by a stress wave dissipates wave energy, resulting in intrinsic wave at-tenuation and velocity dispersion (velocity depending upon frequency). Given the measured acoustical data, specifically the velocity and attenuation of the compressional wave, the characteristic time of local flow can be determined based on a viscoporoelastic model [6]. Since local flow is governed by the details of local heterogeneities, the obtained characteristic times can in turn be used to infer the information on local heterogeneities, and their effects on macroscopic fluid flow through the dynamic capillary pressure function.

Figure 1. Schematic of the device Figure 2. Photograph of entire set up

THE EXPERIMENTAL DEVICE The laboratory device is capable of housing a cylindrical soil sample 100 mm in diameter and up to

125 mm in height. The sample is confined by cell pressure in a semi-flexible Viton rubber jacket equipped with an acoustic transmitter and receiver (see Figs 1 and 2). The acoustic equipment developed by New England Research, Inc. (NER) of White River Junction, Vermont, includes flat piezo-ceramic transducers, a waveform function generator, an oscilloscope and the data acquisition system. The unsatu-rated hydraulic properties are found using the axis translation technique and a constant flow method.


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Conically shaped water reservoirs are located on either end of the sample, separated from the sample by the high air entry discs. The water reservoirs are conically shaped to aid in removal of diffused air bub-bles which may pass through the high air entry disc and are modeled after the work of Lu et. al. [7].

Figure 3. Preliminary compressional wave speed ver-sus Saturation of a sand sample collected at 7500 Hz.

Figure4

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