[ppt]soil mechanics - مخزن مركز تحميل صور ملفات العاب فلاش ... · web...

Soil Mechanics

DEEP FOUNDATIONS

PILES

Pile foundation used to support structure when

poor quality soil

bearing capacity failure

excessive settlement

piles

END BEARING PILES

SKIN FRICTION PILES

End-bearing pilepile driven until it comes to rest on a hard impenetrable layer of soil or rock

End Bearing Piles

ROCK

SOFT SOIL

PILES

End bearing pile rests on a relative firm soil . The load of the structure is transmitted through the pile into this firm soil or rock because the base of the pile bears the load of the structure, this type of pile is called end bearing pile

Friction pileload of the structure must come from the skin friction or adhesion between surface of the pile and the soil

SOFT SOIL

Friction Piles

If the firm soil is at a considerable depth, it may be very expensive to use end bearing piles. In such situations, piles are driven through the soil for some distance. Piles transmit the load of structure to the soil by means of skin friction

between the

Soil and the

piles.

14 April 2015

Deep Foundations

8

Pile Applications

Low

Weight

Soft to

Firm Clay

Large Distributed

Weight

Very Large Concentrated

Weight

Dense Sand

Strong Rock

TYPES OF PILE

Concrete Piles

- Cast In Place Concrete Piles

- Precast Concrete Piles

Steel Piles

- H Piles

- Cylindrical

Timber Piles

Composite Piles

Common Driven Pile Types

CAST IN PILES

Combinations of vertical, horizontal and moment loading may be applied at the soil surface from the overlying structure

For the majority of foundations the loads applied to the piles are primarily vertical

For piles in jetties, foundations for bridge piers, tall chimneys, and offshore piled foundations the lateral resistance is an important consideration

The analysis of piles subjected to lateral and moment loading is more complex than simple vertical loading because of the soil-structure interaction.

Loads applied to Piles

V

M

H

Modes of failure

The soil is always failure by punching shear.

The failure mode of pile is always in buckling failure mode.

Drilling Pile

Usuallyused for those tall buildings or massive industrial complexes, which require foundations which can bear the load of thousands of tons, most probably in unstable or difficult soil conditions. The method of drilling bored pile is different from RC Square pile or spun pile which are using driving method, the

Procedure for drilling pile

Introduction

Piles are structural members that are made of steel, concrete, or timber.

They are used to build pile foundations, which are deep and cost more than shallow foundations.

Despite the cost, the use of piles often is necessary to ensure structural safety.

dr. isam jardaneh / foundation engineering 61303 / 2010

When to use Pile Foundations

The following list identifies some of the conditions that require pile foundations (Vesic 1977):







Types of Piles and Their Structural Characteristics











(unreinforced



Installation of Piles

Two methods are mainly exist:

1- Driven Method

2- Bored Cast in-situ Piles Method

Load Transfere Mechanism


The load on the pile is resisted by

Qs = side friction (skin friction), and

Qp = end (point, tip) bearing

Equations for Estimating Single Pile Capacity


Qall = [qu design] Ap / FS

example

305mm

12m

SAND

=16KN/m

=35

Es=30000KN/m

=0.3

Qwp=98KN

Qws=240KN

338KN

Find elastic settlement Se

Solution

Se = Se1 + Se2 + Se3

Se1= -------------------------- = 0.00148 m = 1.48mm

[98+(0.6x240)] 12

[(0.305) (21x10)]

qwp = Qwp/Ap = 98/(0.305) = 1053.5KN/m]

Se2 = ----------------------(1-0.3)(0.85) = 0.0083m = 8.3mm

(1053.5)(0.305)

(30000)

Se3 = (-------------------)(0.305/30000)(1-0.3)(4.2)=0.64mm

240

(4x0.305)(12)

Se = Se1 + Se2 + Se3

Se = 1.48 + 8.3 + 0.64 = 10.42mm

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