bestämningar av odränerad skjuvhållfasthet med specialiserade...

Bestämningar av odränerad skjuvhållfasthet

med specialiserade metoder i praktiska

tillämpningar

Delrapport 1a

Resultat från en internationell

enkätundersökning

(på svenska)

Göteborg 2016

2

Trafikverket

Postadress: 781 89 Borlänge

E-post: [email protected]

Telefon: 0771-921 921

Dokumenttitel: Bestämningar av den odränerade skjuvhållfastheten med specialiserade

metoder i praktiska tillämpningar. Delrapport 1a - Resultat från en internationell

enkätundersökning

Författare: Göran Sällfors

Dokumentdatum: 2016-09-30

Ärendenummer: TRV 2014/86131

Version: 1.0

Kontaktperson: Anders Hansson Trafikverket

Publikationsnummer: 2016:167

ISBN 978-91-7725-038-8

3

Förord

Trafikverket har beviljat medel för ett utvecklingsprojekt rörande bestämning och

val av odränerad hållfasthet för lös lera.

Projektet omfattar följande delar:

- Enkät avseende vilka metoder som används för bestämning av

den odränerade skjuvhållfastheten, cu, i olika länder där lös lera

förekommer.

- Rapport med detaljerade anvisningar för genomförande,

redovisning och tolkning av specialiserade laboratorieförsök

(Direkta skjuvförsök, triaxialförsök och CRS-försök).

- Sammanställning av ett stort antal ’case records’ där såväl

traditionella metoder (vingförsök, konförsök och CPT) som

specialiserade metoder (direkta skjuvförsök, triaxialförsök samt

CRS-försök och empiri) använts för bestämning av cu.

- Ett systerprojekt där en ny vinge tillverkas och testas där

rotation och mätning av torsion sker nere vid vingen.

- Rekommendation för val av cu.

För att genomföra projektet tillsatte Trafikverket en arbetsgrupp bestående av

- Anders Kullingsjö, Skanska

- Torbjörn Edstam, Skanska

- Tara Wood, NCC

- Per-Evert Bengtsson, SGI

- Rolf Larsson, SGI

- Urban Högsta, Golder Associates

- Göran Sällfors, Chalmers och GeoForce

- Jan Ekström, Trafikverket

- Anders Hansson, Trafikverket

I denna rapport redovisas resultatet av den internationella enkätundersökningen

som genomförts.

Göteborg 2016-09-30

Göran Sällfors

5

Innehållsförteckning

Beteckningar och definitioner 6

1. Bakgrund 7

2. Sammanfattning av enkäter 9

2.1 Australien 9

2.2 Baltiska staterna 10

2.3 Finland 11

2.4 England och Irland 13

2.5 Frankrike 14

2.6 Holland 15

2.7 Kanada 17

2.8 Norge 19

2.9 Singapore 21

2.10 Sverige 22

2.11 Tyskland och Schweiz 23

2.12 Vietnam 24

3. Sammanfattande slutsatser 25

4. Bilagor – samtliga inkomna enkäter 26

6

Beteckningar och Definitioner

ADP Analys som omfattar skjuvhållfasthet bestämd i tre olika riktningar

CAU Ko- konsoliderat, odränerat triaxialförsök

CIU Isotropt konsoliderat, odränerat triaxialförsök

CU Konsoliderat, odränerat triaxialförsök

cu Odränerad skjuvhållfasthet

cua Aktiv, odränerad skjuvhållfasthet

cuDS Odränerad skjuvhållfasthet bestämd med direkt skjuvförsök

cup Passiv, odränerad skjuvhållfasthet

CPT Spetstrycksondering

CPTU Spetstrycksondering med samtidig portrycksmätning

DS Direkt skjuvförsök

OCR Överkonsolideringsgrad

PMT Pressometerförsök

σ’c Förkonsolideringstryck

7

1. Bakgrund

En leras odränerade skjuvhållfasthet, cu, är en geoteknisk parameter som används i

en rad olika dimensioneringssituationer som släntstabilitet, jordtryck och

stödkonstruktioner samt kohesionspålars bärförmåga.

Genom åren har traditionen för hur cu bestäms i Sverige utvecklats, men varierar en

hel del mellan olika konsultbolag och landsändar. Det finns i och för sig standarder

för varje enskild metods genomförande, men det finns inte samma strikta regler

eller riktlinjer för hur en sammanvägning av olika resultat skall göras. Inte minst på

senare tid har denna fråga diskuterats beroende på kanske främst två orsaker:

1. Vingförsök på större djup visar ofta inte den ökningen av skjuvhållfastheten

med djupet som man kan förvänta sig, ökningen är många gånger orimligt låg.

Detta får stora konsekvenser, dels vid dimensionering av långa kohesionspålar,

dels vid dimensionering av djupa schakter.

2. Användandet av avancerade försök som direkta skjuvförsök och triaxialförsök,

aktiva såväl som passiva, har ökat dramatiskt det senaste decenniet. Eftersom

dessa försök används för att bestämma graden av hållfasthetsanisotropi och

ofta ger högre värden på hållfasthetens medelvärden än resultat som erhålls

med traditionella metoder som vingförsök och konförsök, uppstår frågan hur

man ska väga samman resultaten och vilket värde på hållfastheten man ska

välja.

Trafikverket har därför tagit ett initiativ för att så allsidigt som möjligt belysa denna

fråga. Det var då naturligt att inte bara gå igenom standarder och

forskningsrapporter i ämnet utan även genom en enkät skaffa en bild av hur man i

realiteten/verkligheten går tillväga i olika länder när man bestämmer en lös leras

skjuvhållfasthet.

Det är naturligtvis så att det i ett och samma land finns många olika tillvägagångssätt

beroende, dels på det aktuella jobbets komplexitet, dels beroende på vilken

landsände det rör sig om och vilken geologi som dominerar.

Ett stort antal enkäter har därför skickats ut till geotekniker i länder där det

förekommer lösa leror, med huvudsyftet att dokumentera:

1. a. Vilka fältmetoder som dominerar

b. Vilken typ av provtagare som används

2. a. Vilka laboratoriemetoder som normalt används

b. Finns det kriterier för att bedöma provernas störningsgrad

3. Vilka empiriska samband som används

8

4. Dessutom gavs möjligheter till att kommentera landets praxis

Totalt skickades drygt sextio enkäter ut, medan 27 fullständiga svar erhölls.

Svarprocenten varierade för de olika länderna, men de länder som kan anses vara av

störst intresse för undersökningen hade en mycket god svarprocent, det gäller

speciellt Norge och Finland, men i viss mån även Holland och Kanada. En kortfattad

sammanställning av enkätsvaren redovisas i kapitel 2 och sammanfattande

slutsatser presenteras i kapitel 3. I bilagorna återfinns de fullständiga svaren samt

en tabellformad sammanställning för varje land och dessutom en beskrivande

sammanfattning i löpande text.

9

2. Sammanfattning av enkäter, land för land

2.1 Australien

Bestämning av odränerad skjuvhållfasthet

Fältundersökningar

CPT och vingförsök, där Nkt kalibreras mot vingförsök i enstaka punkter.

Provtagning sker med tubprovtagare i förborrat hål.

Laboratorieundersökningar

Triaxialförsök, UU (okonsoliderade, odränerade enligt Brittisk tradition) samt CU.

Provkvalitet bedöms nästan enbart genom ’engineering judgement’. Ibland studerar

man ödometerförsök och använder Schmertmanns korrektion.

Korrelationer

cu = a * σ’c

där a = 0,23 +- 0,04

Övriga kommentarer

-

Tabell 1 – Sammanställning, Australien

1.a. In situ test for determination of cu

1.b Sampler

2.a Laboratory test for determination of cu

2.b Assessment of sample quality

3. Empirical correlations

4. Other comments

CPT och vingförsök. Nkt i ekv cu=(qt – σv)/Nkt Kalibreras mot vingförsök

Tube sampler i ett förborrat hål

UU eller CU1 triaxialförsök

Ingenjörs-kunnande

cu = 0,23 (+-0,04) * σ’c

-

1 UU – okonsoliderat, odränerat triaxialförsök , CU – konsoliderat, odränerat triaxialförsök

10

2.2 Baltiska staterna



Vingförsök och ibland CPT

Provtagning görs inte särskilt ofta. Vacuum provtagare angiven.


Triaxialförsök, nämns men det verkar som om UU är vanligast (om de alls har tagit

några prover).

Provkvalitet verkar inte ägnas något intresse.

Korrelationer

cu = 0,22 * σ’c (om σ’c har bestämts)

Tabeller för cu beroende av vattenkvot och konflytgräns

cu = (qt – σvo)/Nkt, där Nkt = 15 à 20

Övriga kommentarer

-

Tabell 2 – Sammanställning, Baltiska staterna


1.b Sampler




4. Other comments

Vingförsök och CPT (CPT,CPTU, SCPT,SCPTU)

Inga ostörda prover tas i lera

Triaxialförsök och direkta skjuvförsök

Inga speciella metoder, mer än vad som eventuellt finns i ISO

cu = 0,22 * σ’c cu = (qt - σv0)/Nkt där Nkt = 15 à 20

-

Vingförsök Vacuum provtagare

UU och enaxliga tryckförsök

- Samband mellan vattenkvot, konflytgräns och cu i tabeller

-

11

2.3 Finland


1. Fältundersökningar

Vingförsök, typ Nilcon, är absolut vanligast. I speciella fall används vinge med

skyddsrör. Hållfastheten korrigeras med hänsyn till wL.

Man har noterat att hållfasthetstillväxten på större djup underskattas med Nilcon-

vingen.

CPTU-utrustning finns och används en hel del, men ännu inte för bestämning av cu.

Provtagning sker nästan uteslutande med ST II. Det finns några provtagare med

större diameter, 54 mm och 56 mm, men dessa används sällan.

2. Laboratorieundersökningar

Konförsök används, men egentligen bara som en indextest. Utvärderade värden

används inte i design.

Triaxialförsök, CAU används ibland. Det finns inga riktlinjer för hur cua skall

användas och ADP-analys används inte.

Direkta skjuvförsök används inte alls för lera, däremot ibland för torv och grövre

jordar.

Provkvalitet bedöms som regel överslagsmässigt från ödometerförsöken (om man

får ett σ’c kan man vara nöjd). Om man genomfört triaxialförsök studerar man

konsolideringstöjningarna. I övrigt bedöms provkvaliteten visuellt i fält och i

laboratorium.

3. Korrelationer

cu = a * σ’c

där a = 0,22 +- 0,02 för odränerad skjuvhållfasthet

a = 0,25 – 0,30 för cua

4. Övriga kommentarer

Man uppfattar bestämningen av den odränerade hållfastheten som ett problem, men

har nu startat forskning rörande vingförsök med mätning nere vid vingen. Man har

även börjat titta på CPTU och hoppas kunna utvärdera cu från dessa

sonderingsresultat.

12

Tabell 3 – Sammanställning, Finland


1.b Sampler




4. Other comments

Vingförsök (underskattar cu )

St II (54 mm, ibland) 86 mm for forskning

KoCUA och KoCUP DSS och konförsök används inte

ΔV/Vo för triax Inga riktlinjer

a = 0,22 som medelvärde 0,25 – 0,30 för cua

Detta är problematiskt. FoU pågår om CPTU och vinge där man mäter nere vid vingen

Vingförsök (90% Nilcon, 10% med skyddskåpa) (CPTU finns men används ännu inte för bestämning av cu)

St II (det finns bara två större prov-tagare i Finland)

Triaxförsök, ibland. (ADP används inte i Finland) DSS används för torv och grövre material.

Om de kan bestämma σ’c är de ’nöjda’

cu = (0,20 à 0,27)* σ’c

Nilcons vinge fungerar dåligt på stora djup

Vingförsök (ibland CPTU) Korr μ = f(wL)

St II Konförsök, ibland triaxialförsök

‘Bedöms’ i fält, samt i lab och ödometerförsök

Finns men används inte i design

-

13

2.4 England och Irland



Vingförsök, och CPT och CPTU, i sämsta fall SPT.

Provtagning varierar. Här har angetts 100 mm kolvprovtagare och ’hydraulic push

in sampler’.


Triaxialförsök, CIU eller CAU. Fortfarande används en del UU.

Provkvalitet bedöms inte efter något speciellt mönster men det norska kriteriet

Δe/eo börjar så smått tillämpas.

Korrelationer

cu = 0,22 * σ’c

Övriga kommentarer

Prispress på geotekniska undersökningar medför dålig kvalitet och att det görs

överlag för lite undersökningar.

Tabell 4 – Sammanställning, England och Irland


1.b Sampler




4. Other comments

CPTU och Vingförsök

100 mm ELE kolvprovtagare

CAUC eller CIU (UU används sällan)

Egentligen ingen, men norska Δe/eo lite

cu = 0,22 * σ’c

Problem med prov-kvalitet, samt vattenmättnad av CPTU-filter

Vingförsök och CPT och SPT

Hydraulic push in sampler

CIU eller ibland UU

Medveten om frågeställningen, men inga konkreta regler

Strouds korrelation för SPT

Prispress på geotekniska undersökningar medför dålig kvalitet och att det görs för lite undersökningar

14

2.5 Frankrike



Vingförsök på grunda djup och PMT på större djup (> 50 m)

Provtagning görs med kolvprovtagare 70 mm. På större djup (>20m) används

’double envelope sampler’


Triaxialförsök, Ko-konsoliderade, odränerade aktiva försök används mestadels.

Provkvalitet bedöms genom ingenjörskunnande.

Korrelationer

cu = a * σ’c

där a = 0,22 +- 0,04

Övriga kommentarer

Tabell 5 – Sammanställning, Frankrike


1.b Sampler




4. Other comments

Vingförsök för grunda djup. PMT för djup 20 till 50 m

Kolvprovtagare 70 mm. På större djup

(>20m) ’double envelope sampler’

CAU, svårt att välja Ko.

Ingenjörskunnande - -

15

2.6 Holland



CPTU, Nk = 20, eller Lunne, Nk = 15 – 17

Ibland vingförsök utan korrigering

Provtagning sker nästan uteslutande med Ackermann 50 – 60 mm.

Ibland används Begemannprovtagaren, som tar kontinuerliga prover.


Triaxialförsök, CAU, ibland CIU. Ibland används även ’pocket penetrometer’,

konförsök eller UU.

Provkvalitet

Inga kriterier, bara inspektion, då laboratoriebestämda värden sällan/aldrig

används i design.

Design är normalt väldigt konservativ.

Korrelationer

Konservativa värden, se tabell, baserade på CPT. Annars inget.

qc / 20

Övriga kommentarer

Man uppfattar bestämningen av den odränerade hållfastheten som ett problem, men

har nu startat forskning rörande vingsondering med mätning nere vid vingen. Man

har även börjat titta på CPTU och hoppas kunna utvärdera cu från dessa

sonderingsresultat.

Verkar som om man är oroad över bristen på intresse för cu men det verkar som om

det är viss förbättring på gång.

16

Tabell 6 – Sammanställning, Holland


1.b Sampler




4. Other comments

In situ försök för best. av cu används sällan. CPTU används ibland, då med tolkning enligt Lunne. DSS används bara för torv.

Begemann 66 mm Ackermann 50 – 60 mm

Triax CUA

Inga laboratorie-bestämda värden används i design

Försiktiga värden används, se tabell som kräver CPT. Annars inga

cu bestäms sällan

CPT, ibland vingförsök, utan korrektion.

‘Push in sampler’

(ibland används fick penetrometer, vinge, UU eller konförsök)

Ingen tradition, bara inspektion

Inga

CPTU . Nk = 20, eller enl. Lunne med Nk = 15 – 17

Ackermann (80 %)

Triax CIUA Bara för torv. Design är väldigt konservativ. Alla ’förbättringar’ verkar ge ännu konservativare design.

qc / 20 Inte särskilt stolt över holländsk praxis, men förbättringar är på gång

17

2.7 Kanada



Kanada är ju ett stort land där lösa leror förekommer främst i östra delen, primärt

Quebec. Tillämpning av fältundersökningar varierar och det verkar inte vara helt

ovanligt, på vissa håll, att man bara ’gissar’ värdet på cu.

Vingförsök, typ Nilcon, är absolut vanligast, främst i Quebec. I speciella fall används

vinge med skyddsrör. Hållfastheten korrigeras med hänsyn till wL. På större projekt

används CPTU, men då kalibrerad mot vingförsök.

Det förekommer även att CPT, kalibrerad mot triax, förekommer.

Provtagning sker rutinmässig med Shelby 73 mm provtagare.

I viss omfattning används 70 mm piston sampler, framförallt när det handlar om

sättningar. I exceptionella fall används större provtagare. Några anser att ’piston

sampler is unheard of’.


Triaxialförsök, CIU eller CAU används ibland. (ASTM). Många använder UU

Provkvalitet

Används sällan, möjligen Lunne, 2006.

Bedömning baserat på ödometerresultat.

Korrelationer

SHANSEP. Ibland Bjerrum f(IP)

Lerouiel, 1983, cu /σ’c = 0,20 + 0,0024 IP

Vissa använder cu = 0,22 * σ’c

Övriga kommentarer

18

Tabell 7 – Sammanställning, Kanada


1.b Sampler




4. Other comments

CPT, Nkt kalibrerat mot triax. (vingförsök används sällan)

Shelby 73 mm CIU (ASTM), CAU ibland Stora project – SHANSEP

Egentligen inte, möjligen enligt Lunne, 2006

SHANSEP Occationally Bjerrum IP

-

Vingförsök, ibland CPTU men då är den kalibrerad mot vingförsök.

70 mm kolvprovtagare

Fallkon Bedömning från ödometer

Lerouiel, 1983, f(σ’c)

-

Vingförsök för små projekt CPTU, Nkt kalibrerad mot vingförsök.

Shelby Kolvprovtagare när sättningar är viktigt

Triax i exeptionella projekt. Konförsök för att verifiera, när det krävs.

Nej, eftersom labvärden på cu sällan används

Lerouiel, 1983, f(σ’c) cu / σ’c = 0,20 + 0,0024 IP

-

Förutom att “Gissa” används vingen, helst Nilcon CPTU, korrelerad mot, (see Mayne, 2007) Vingförsök underskattar hållfastheten på större djup

Shelby tubes. 100 mm används sällan Kolvprovtagare är ‘unheard of’.

Triax UU och ibland CIU.

Försummas oftast. Ibland index från ödometer eller ibland används triax

0,22 * σ’c Önskar mer Nilconvinge, men problem med utbildning av

fältpersonal.

19

2.8 Norge



CPTU korrelerat med triax på block prover. CPTU-utrustning, Karlsrud, 2010

Kanske vingförsök, då med mätning nere vid vingen, är på väg tillbaka.

Provtagning sker vanligen med 72 – 76 mm kolvprovtagare. Ibland, för indextester

används 54 mm. Blockprover för att verifiera CPTU och triax från kolvprovtagare.


Triaxialförsök aktiva o passiva, samt ibland DS.

Konförsök används, men endast för definiera skiktning och bestämning av St.

Provkvalitet bedöms som regel med, ΔV/V (Lunne), MOC/Mmin (ödometer). Även

failure strain är av intresse som underlag.

Korrelationer

Shansep, samt cuDS/cua och cup/cua f(Ip), samt även Janbu f(σ’c)

Övriga kommentarer

Det påtalas att anisotropieffekterna är större i de norska magra lerorna än i våra

svenska fetare leror. Vid värden bestämda på blockprover måste man beakta

deformationsmjuknande och hastighetseffekter.

20

Tabell 8 – Sammanställning, Norge


1.b Sampler




4. Other comments

CPTU (NGI-KK) 73 - 76 mm kolvprovtagare (förr 54 mm) Block- provtagare

Triax, CAU (Booker Davis) Ibland DSS

ΔV/V för triax Shansep cuDS/cua och cup/cua f(Ip)

Norska leror lågplastiska och uppvisar mer ani-sotropi än Svenska

2 CPTU korrelerat till cua från triax på block prover

72 – 76 mm kolvprovtagare Ibland 54 mm

Triax aktiva o passiva Ibland DSS (cukon)

ΔV/V för triax Brottöjning samt initialmodul i ödometer och triax

Shansep CPTU (NGI-KK) Janbu f(σ’c)

-

CPTU 76 mm (triax + DSS) 54 mm (indextester) Blockprover för att kolla CPTU o 76 mm

Triax och DSS ΔV/V (Lunne) MOC/Mmin (ödometer)

K Karlsrud o H Martinez

Vid resultat från blockprover, beakta strain softening

CPTU (NGF Standard)

72 mm cua, cup, DSS (cukon, cuUC för koll av lager och St)

Töjning vid brott eller yield

cu = 0,3 σ’o för NC CPTU korr block prover (OCR, St, IP)

Vi gör ofta för lite lab- och fältundersökningar

CPTU (Vingförsök på väg tillbaks om mätning sker nere vid vingen)

75 mm (54 mm) Block prover

Triax (konförsök, enaxligt tryckförsök)

ΔV/Vo (Δe/eo) –kriterium

Shansep CPTU (NGI-KK)

-

CPTU (KK, Norsk Std) (vinge)

70 mm Triax , DSS (för design av pålar)

Δe/eo

ΔV/Vo cu/po = f(Ip, OCR) Korr för ’rate effect’ i

vissa fall Använd cua cuDS cua

CPTU (KK, NGF Std) Korr. cua block prover

72 – 76 mm kolvprovtagare 54 mm för indextester Blockprover för att bekräfta CPTU och triax (76 mm provtagare)

Triax cua (cup – ADP) Ibland DSS Kon o vingförsök för skiktning och St

ΔV/Vo

MOC/Mmin cuDS/cua och cup/cua = f(Ip) Shansep

21

2.9 Singapore



Vingförsök och CPT,

Provtagning görs med tunnväggig kolvprovtagare.


Triaxialförsök, UU alternativt CIU

Provkvalitet – ingen bedömningsgrund finns

Korrelationer

cu = a * σ’v

där a = 0,25 – 0,35

cu = 5 à 6 * NSPT

Övriga kommentarer

-

Tabell 9 – Sammanställning, Singapore


1.b Sampler




4. Other comments

CPT och vingförsök

Tunnväggig kolvprovtagare

Triax UU och CIU Ingen cu = 0,25 à 0,35 * σ’v cu = 5 à 6 * NSPT

-

22

2.10 Sverige

En separat undersökning gällande svenska förhållanden håller på att

genomföras och kommer att redovisas i en egen rapport i december 2015.

23

2.11 Tyskland och Schweiz



Vingförsök och CPT, CPTU

Provtagning i Schweiz inte särskilt sofistikerad. I Tyskland används tunnväggig

kolvprovtagare.


Triaxialförsök, UU och CIU. Skepsisism visavi labförsök p.g.a. av störning och

apparatfel.

Provkvalitet bedöms genom ingenjörskunnande.

Korrelationer

cu= 0,20 à 0,30 * σ’o

cu= 0,5 à 0,10 * qc

cu= (qc – σv0)/ Nk; Nk = 19

Övriga kommentarer

Stor skillnad mellan tyska och schweizisk praxis. Tyskland har en lång lista med

möjliga normer och litteratur

Tabell 10 – Sammanställning, Tyskland och Schweiz


1.b Sampler




4. Other comments

CPTU Stor variation, men som regel ganska störda prover

Triax CU och direkta skjuvförsök

Egentligen inte cu= a * σ’o * OCRb, men egentligen bara för NC leror. Uppgift om OCR saknas ofta.

Stor skillnad mellan tyska o franska delen av Schweiz

Vingförsök och CPT (Lunne et al)


Triax UU och CU, ibland direkt skjuvbox Skeptisk till labförsök pga störning och fel i försöksutrustning. Belastningshastighet uppmärksammas

ingenjörskunnande Olika möjligheter Kuhalaway & Mayne, 1990 Gebreselassie 2003 cu= 0,20 `0,30 * σ’o

cu= 0,05 à 0,10 * qc cu= (qc – σv0)/ Nk; Nk = 19

Lång lista med normer och litteratur

24

2.12 Vietnam



Vingförsök och CPT samt CPTU

Provtagning görs med tunnväggig kolvprovtagare


Direkta skjuvförsök, triaxialförsök och enkla tryckförsök.

Korrelationer

Saknas, då flertalet geotekniker utbildades under sovjettiden och de vet inte vad

förkonsolideringstryck är

Övriga kommentarer

Tabell 11 – Sammanställning, Vietnam


1.b Sampler




4. Other comments

CPT cu = (qc –σv0)/Nk

CPTU cu = Δu/NΔu = (u2 - u0)/NΔu

Vingförsök


Skjuvförsök, triaxialförsök och enkla tryckförsök

Problem med förståelse för detta

Inga, saknar kunskap om förkonsolideringstryck

-

25

3. Sammanfattande slutsatser

Det är ganska uppenbart att praxis varierar en hel del runtom i världen, även inom

ett och samma land. Det finns säkert skillnader i svaren, som är avhängiga av i vilken

omfattning geoteknikern ifråga varit engagerad i komplicerade projekt eller ej där

lös lera förekommer. Sammanställningen är därför troligen inte representativ i alla

avseenden.

Det är emellertid slående hur stort gap det kan vara i vissa länder, mellan den

kunskap som finns inom forskarvärlden i landet och vad som sedan används i

praktiken.

Det är vidare ganska uppenbart att länder som Sverige och Norge, och i viss mån

Finland, ligger väl framme när det gäller att tillämpa fördjupad kunskap om lösa

lerors hållfasthet. Det skall dock betonas att tolkning och utvärdering av parametrar

rörande lösa lerors hållfasthets- och deformationsegenskaper för användande i

FEM-analyser inte berörts i denna undersökning. Troligen är skillnaden hos olika

konsulter i olika länder ännu större i detta avseende.

26

4. Bilagor – Samtliga inkomna enkäter

Först redovisas det följebrev och den enkät som skickades ut. Därefter återfinns de

kompletta svaren på enkäten, land för land, dock har namn och arbetsgivare på de

som svarat tagits bort.

sid

Följebrev 27

Enkät, så som den sändes ut 28

Svar

Australien 29

Baltiska staterna 31

Finland 35

Frankrike 41

Holland 44

Kanada 52

Norge 61

Singapore 74

Tyskland och Schweiz 76

England och Irland 82

Vietnam 86

27

Följebrev

Dear N.N.

Geotechnical engineering here in Sweden is becoming more and more challenging as

excavations go deeper and deeper in our soft clays. For example, a new railroad

tunnel under the city of Göteborg is being planned and the excavations depths will

probably be as deep as 25 to 30 meters.

Traditionally the undrained strength of the clay in Sweden was determined using

the vane and the fall-cone test and most designs regarding support structures,

friction piles and stability of slopes, were based on these values. During the last

decades triaxial tests and direct shear tests and also CPTs have been more

frequently used, at least compared to before. As most experience and empirical

relations generally are based on the undrained strength determined by means of the

vane and fall-cone tests there is now an uncertainty, as the so determined cu-value,

especially for larger depths, deviate from the well winnowed experience and what

can be anticipated based on results obtained by direct shear tests and triaxial tests.

In a project for the Swedish Department of Transportation dealing with the

mentioned issues, we have a subtask where we intend to map and investigate how

the undrained shear strength of soft clays are generally determined and used in

other countries. I therefore would very much appreciate if you, or a colleague of

yours, had time to briefly answer the attached questionnaire. In return I will

eventually send you the final report, which is due at the end of next year and next

time we meet, I will treat you to a nice dinner.

To facilitate our planning, we would very much appreciate if you could acknowledge

the receipt of this e-mail and then also let us know if you will be able to answer the

questionnaire and if so, within what time frame.

On behalf of the project committee

Göran Sällfors

28

Enkät

Questionnaire regarding determination and use of the undrained shear

strength of soft clays1.

(Exclude specially designed tests for rendering parameters for advanced FEM

analysis)

Please type your answers directly in this document (will appear in red)

1. a. Which in-situ tests are most widely used for the determination of the

undrained shear strength in geotechnical design in your experience?

(Please, if possible also briefly refer to or describe any document or procedure

for interpretation of the test results)

Answer:

b. What type of sampler do you most commonly use for the extraction of

samples for laboratory test determination of undrained shear strengths?

Answer:

2. a. Which laboratory tests do you most commonly use for the determination of

the undrained strength for geotechnical design?


used for interpretation of the test results)

Answer:

b. Is there any tradition or consensus regarding assessment of sample quality

and how these are incorporated into the geotechnical design?

Answer:

3. Are there any empirical correlations for the undrained shear strength that are

commonly used in your country (e.g. with reference to in situ stresses,

preconsolidation pressure, OCR or any other geotechnical property, such as

index properties or well winnowed experience)?

Answer:

4. Other comments which might be important?

1 Here we primarily refer to the undrained shear strength used in design of retaining walls, friction piles and stability of slopes and excavations

29

Australia




analysis)






Answer: CPT and shear vane, with shear vane often used to calibrate the

strength profile inferred from the CPT – i.e. to assess Nkt in the equation

Su=(qt-σv)/Nkt.

The SPT and DCP are also used on occasion (begrudgingly) for a crude

assessment of shear strength in stiffer clays.



Answer: Tube sample (U63) in a rotary drilled borehole





Answer: UU or CU triaxial test, or vane shear test.

Pocket penetrometers are regularly used to assess (crudely) the undrained

shear strength of stiffer clays in the field.



Not really, engineering judgment is typically used where results are variable or

disturbance is inferred but there is little consensus on how/where this should

be applied.


30

I have only seen the effects of sampling disturbance accounted for regularly in

assessments of oedometer tests – i.e. by applying the Schmertmann correction

or similar.





Answer: “0.23±0.04 x effective stress” for normally consolidated clays is

popular. The same is also adopted for slightly over-consolidated clays by

replacing effective stress with pre-consolidation pressure.


Answer: -

31

The Baltic States 1




analysis)






Answer: Field value test (FVT), Cone Penetration Tests

(CPT/CPTU/SCPT/SCPTU).

Documents referred to this respectively are: ISO 22476-1:2012, E DIN EN ISO

19901-8:2013-04.



Answer: For clayey soils, samples extraction is not preferable application,

because from this point of view, data reliability will damage. But in most cases

soil samples are taken with soil extractor, and with drilling aggregate. To keep

samples with natural moisture, it is conserved in special dishes.





Answer: Triaxial text (TX), Direct simple shear test (DSS):

Documents referred to this: ISO/TS 17892-8:2004, ISO/TS 17892-10:2004,



Answer: There isn’t any traditions at all. Everything is strictly stated by ISO

standards .


http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=38521

http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=38523

32





Answer: cu=0,22σ*OCR, - via OCR, via CPT - , Nkt – 20 – 25,

via effective shear test , when clayey soils are undrained, then


Answer: -

33

The Baltic States 2




analysis)






Answer: Vane test. We use Floote coefficients and the recommendation from

EC7.



Answer: Vacuum sampler. This is used if Ip is larger than 8-10 %. It is

impossible to get good samples from silt! – the only help there is either the Vane

test, or CPTu.





Answer: We generally use the UU test, but similar results can be gained from

the one axel strength test. The differential remains within +/- 5 %.



Answer: No




34



Answer: We have fairly good correlations between undrained shear strength,

water content and the liquid limit. We are happy to elaborate, and send these to

you, if need be. In Estonian geotechnics, these correlations are used frequently.


Answer: In practice, the values of undrained strength determined by the vane

test and the UU test correlate fairly well with the results of load plate tests and

can be calculated with the formulae of Skempton and Jurgenson.

35

Finland 1




analysis)






Answer: Field vane test. 90% of them are made with Nilcon type vane equipped

with slip coupling. Rest with the vane with casing. The use of casing vane is

increasing as problems related to Nilcon are becoming clearer for us. CPTU is

coming and there is quite many modern equipment in Finland but in practice

it’s not yet so much used for Su determination.



Answer: All consults use St-type sampler, mainly StII. All the samples are d50

mm. There are only 1-2 samplers in Finland which diameter is 70-90 mm. Poor

quality of d50mm samples is known issue though.





Answer: Fall cone test but it’s used more like indicative test beside the FVT’s.

Triaxial is used every now and then but we don’t have good enough guidelines

how to use compression strength in Su stability analysis (we don’t use ADP

analysis like Norwegians). Direct shear test is used for peat and coarser

materials. Also consolidation pressure from oedometer is used as indicative

value assuming Su=0,20…0,27simga_c


36



Answer: Unfortunately no. Evaluation of sample quality is not much discussed

even if it’s major problem. Quite often if one can find the consolidation pressure

from oedometer test, it’s good enough! Method proposed by Lunne et.al. is well

suitable for our clays though, but due d50mm samples category “fair to good” is

best we can get.

There has been some studies concerning the sample quality. One example is a

master thesis study that has been made in Helsinki University of Technology

1995 (now Aalto University) by Esa Rauhala – “Sampling of undisturbed

samples” (Häiriintymättömien maanäytteiden otto).





Answer: For clays Su=0,20…0,27simga_c based on the oedometers is used quite

often. Same relation is used also for sigma_v’ if the clay is NC.


Answer: The Nilcon vane is very poor in deep soundings. It often shows that

strength is not much increasing in depth. That is mainly caused by over

prediction of the rod friction, but there are other issues too.

Undrained shear strength have been studied in TUT several years now and

there is quite some knowledge about the Nilcon related issues already.

Deep excavations in soft clay are very demanding to model. Hardening Soil

model is perhaps not the best model for that (eg. Västlänken). But we don’t have

the answer either which would be the right one. Probably the HSsmall and ADP

are worth studying.

37

Finland 2




analysis)






Answer: The field vane has by far been the most dominant method for the

determination of undrained shear strength. For the procedure, the guidelines by

the Finnish Geotechnical society has been used. However, lately there has been

clear evidence that the results by field vane tests may underpredict the actual

strength even considerably. This has then mostly been related to the use of

Nilcon type of vane without any casing. This has also been studied in a master’s

thesis at TUT (still in progress).



Answer: Consulting companies are mostly using STII type of sampler (to minor

degree also 54 mm piston sampler). For research also 86 mm piston sampler is

used by TUT and Aalto university





Answer: Fall cone is used as a standard test, but the undrained shear strength

from it is usually not used in design. In laboratory active triaxial tests are

mostly done, but also extension tests have been done (mostly for research).

Consolidation is done to in situ stress (anisotropic) or close to it if isotropic. DSS

is not in use in Finland (no equipment so far).


38



Answer: No guidelines for this, so depends on laboratory. TUT uses axial

deformation at preconsolidation pressure in oedometer as standard criteria.

For triaxial test volumetric compression to in situ might be used.





Answer: Mostly relationships between preconsolidation pressure and

undrained shear strength is used, the alfa value commonly in the order of 0,22

for average undrained strength and 0,25-,3 for active strength.


Answer: Determination of undrained shear strength is commonly seen as a

problem in Finland. Regarding this, TUT has started a project that mainly aims

in rising the use of CPTU for undrained shear strength determination, by doing

research , verifications and training. In this connection we have in addition to a

new CPTU device also a new field vane, which measures the rotation and torque

right above the vane. The intention is not to replace the field vane (totally), but

improve on the reliability of su determination.

39

Finland 3




analysis)






Answer: Most widely used is the field vane test (in some cases CPTU). The

interpretation is done according to the attached pdf p. 5-7 (sorry, it is in

Finnish). The strength is reduced using the value of liquid limit.



Answer: In my experience, Swedish type of piston sampler (St2), 50 mm or 60

mm in diameter.





Answer: For all the undisturbed samples, the undrained shear strength is

measured using the fall cone test. In selected cases, triaxial shear tests are used.



Answer: The sample quality is assessed firstly right after sampling in the field. If

the sampling tube is not full, the sample is not regarded as undisturbed. In the

laboratory the sample is checked for visible signs of disturbance. Sometimes the

test results (e.g. oedometer test) show the disturbance. So, the sample quality is

assessed in all stages starting from the field.


40





Answer: There are empirical correlations, most popular is probably the

correlation between the undrained shear strength and the in situ stress. They

should be used for preliminary assessments only, not for geotechnical design.


Answer:

41

France




analysis)






Answer: At shallow depth under embankment for high speed train lines mainly

shear vane tests are used but for tunneling for depths between 20 to 50 m and

deeper, French practice is to use Menard pressuremeter. Correlation used to

derive undrained shear strength are not standardized and papers or books as

Baguelin Jezequel and Shields the pressuremeter Transtec are the main

references.



Answer: For shallow depth, piston sampler with a minimum internal diameter

of 70 mm (it was one of our points of disagreement with Ulf Bergdahl during

drafting of 22475-1) and deeper, practice is to use double envelope sampler and

triple envelope sampler for undisturbed samples.





Answer: Mostly triaxial, cone or vane tests are not privileged. The French

standard for triaxial is written more like a textbook than a standard so it is self-

suffisant. Other recommendations are sometime briefly proposed in the

different guides send with this questionnaire.

The main problems arise with:

- definition of tests confining pressures according to in situ vertical effective

stresses

- disturbance of samples or specimens leading to more detailed

interpretation and therefore analysis by a experimented engineer




42

Answer: No, as French geotechnical community (mostly private design firms)

has defined role of each parties in a standard on geotechnical services (NF P94-

500), it is the responsibility and knowhow of each company to check sample

quality by cross checking quality of triaxial tests, water content, void ratio, over-

consolidation pressure etc. By experience there is no real official of implicit

consensus on this point.





Answer: Mainly if it is not clearly indicated in the document written for the new

metro line given in annex, it is the limit pressure of pressuremeter tests that are

correlated and used as a benchmark to judge finally of the values obtained with

triaxial. At these depths between 20 to 50 m parameters obtained with

pressuremeter are reliable, tests are not technically hard and a lot of companies

are equipped for this range and operator are trained.


Answer: As pointed out in the different documents send with this questionnaire,

the main control of the global quality is based on the progressivity of the design

(including more steps compared to international anglo-saxon practice).

The project start with: AVP avant projet/Preliminary design

APS Avant projet sommaire/summary pre-design

APD Avant projet définitif/final pre-design

Followed by: PRO Projet/ design

EXE Etude d’execution/ construction design

VISA visa etude d’execution/External control

And the role of the owner (contracting authority) help by an assistant and a

technical controller (which has a specific role in French law), the prime

contractor and all the sub-contractor

However the quality of the design relying on the quality of the samples and

therefor the reliability of the geotechnical model is not precisely defined. It’s

probably why sometime the system fails when complex or unexpected

geological context is encountered.

All the significant ground collapses which occurred over the last 20 years in

Paris, have been associated with the construction of new suburb lines: Eole

(now RER E) in 1995 and Meteor (now Metro Line 14) in 2003. For these

projects, the amount of ground investigations carried out during the project

study reflects an effort to ensure a safe and economical underground

construction process and allow decreased geotechnical risks but do not

necessarily remain sufficient to avoid ground collapses. In Toulon, the digging

of the second, 3,300 m tube, which is designed to ease traffic between Marseille

and Nice and run parallel to the first tunnel subject of a major collapse in 1996,

at approximately 50 m distance, has also faced difficulties. Despite the

43

knowledge gained from the first tube construction, tunnelling had to be

suspended after damages occurred to a light manufacturing building. Below the

water table, this 120 m2 section tunnel construction has been very complex

with just 15 m of overburden and the presence of very irregular geological

horizons caused by Tertiary tectonic movements. Finally, in Rennes in a more

simple geotechnical context, several less spectacular collapses have appeared

along the road during the construction of the first metro line across the city.

44

Holland 1








Answer:

First of all it should be noted that in the Dutch tradition it is common to work

with the drained strength parameters c’ and ’. In daily engineering the

undrained shear strength is not often used in The Netherlands. Therefore, in

comparison to other countries, the experience with assessment of su in is

probably poor. For daily engineering the strength parameters, including su= if

used, is either obtained from guidelines or handbooks providing conservative

values or lab testing. In-situ tests are rarely used, which is probably explained

by the tradition of using drained parameters which do not correlate easily to in-

situ tests. If in-situ tests are used for parameter assessment it is the CPTu. In my

experience the correlation is made per project relating CPTu measurements to

lab test results. I am not aware of specific documentation except from the well-

known international literature in this field (like Lunne 1999 or Eurocode for

CPTu testing etc.). However we do have some documentation on lab. Testing

that is used for making the correlation with su. One of the specifications is doing

Direct Simple Shear tests for peat. The tests should be consolidated at field tress

level. If needed I can send this documentation, however it is written in Dutch.



Answer:

For most of the projects I was involved in the Begemann sampler was used. This

is a continuous sampler, 66 mm diameter, which uses bentonite to support the

sample during sampling. This type of sampler is however rarely used. Most

common in The Netherlands (90% of the samples) is the Ackermann sampler.

This is a tube sampler, height 30 cm, diameter 66 mm or 50 mm, which is

hammered during sampling.





Answer: For clays (including organic clays) single stage CU triaxial tests,

preferably consolidated anisotropically. For peats Direct Simple Shear tests,


45

sheared at constant volume. There is documentation, however in Dutch. If you

want to I can sent it to you. However it is basically not different from

internationally used.

In daily engineering, the multi stage CU triaxial tests, isotroppically

consolidated are often used in which failure is defined at 2% vertical strain. For

peat also 5% vertical strain is used.



Answer:

There is no tradition of assessing the sample quality or using it in geotechnical

design in The Netherlands.





Answer:

It is common in daily engineering of small projects to determine the soil

parameters from guidelines providing “save” values. The most well-known

example is the table provided in the Dutch annex of the Eurocode. This table is

added to this questionnaire. Another option is using databases of parameters

used in nearby projects.


Answer:

As stated above in Dutch practice either parameters are obtained from

guidelines or from laboratory testing. The middle way, correlations is not often

used. Since I am involved in water retaining structures which require a high

safety level, my experience is mainly in using lab. test data.

As an example I added Table 2b from the Dutch annex of the Eurocode

providing conservative parameters. It should be noted that the table gives

characteristic values and a partial safety factor should be applied before used in

design. The table entry is the combination of soil type (grind = gravel, zand =

sand, klei = clay, leem = silt, veen = peat) in combination to cone resistance. So,

some information, a cpt reading, is required. For some soil types, some

parameters should be corrected or stress level. If needed I can explain how that

works.

47

Holland 2




analysis)






Answer: CPT dominates, occasional VST, BPT, TBT (ISO 22476-1; ISO 19901-8;

Table 4 of Peuchen 2012; FEBV/CDE/APP/012), vane shear test with no

Bjerrum correction



Answer: Push samplers and selfweight samplers (ISO 22475-1; ISO 19901-8)





Answer: pocket penetrometer, torvane, lab vane, hand vane, fall cone, mini T-

bar/ball, UU triaxial compression, CU triaxial extension, DSS (ASTM, BS, ISO

19901-8)



Answer: No tradition, evaluation done according to visual inspection, checks on

intact/remoulded strengths, X-ray, multi-sensor core logging, Lunne et al. and

Terzaghi on void ratio change. Qualitatively incorporated in design.




48



Answer: not that I am aware of.


49

Holland 3




analysis)


1 a. Which in-situ tests are most widely used for the determination of the




Answer:

This question may be answered in two ways: A) how it is conventionally done in

the Netherlands; B) how we try to do it on all our projects if we can prescribe

and control the sampling, storage en laboratory testing.

This procedure is followed hereafter.

A) A piezocone with application class 2-3 is conventionally used in the

Netherlands with flow area of 100 cm2 and apex angle of 60 degrees. Typical

manufactures are A.P. van den Berg, GeoMill, GeoPoint and Fugro. Testing

and calibration should be done according to NEN-EN-ISO-22476-1 (2005),

although rarely calibration files are requested prior to testing. The

“undrained shear strength” is determined by using a Nk factor of 20 or Nkt

factors of 15-17 according to Lunne et al. (1997). However, there is to my

knowledge no national scientific ground/ database which justifies the use of

these factors for Dutch highly organic Holocene deposits. Recently the

applicability of full flow penetrometers is investigated for in-situ tests.

When laboratory tests are used (which is not compulsory for the design of a

project) either Isotropic Consolidated Undrained Triaxial compression tests

are used, where the peak value is chosen at a limiting strain (arbitrary

chosen at 2-5%). The mobilized shear resistance undrained boundary

conditions is unfortunately regarded as undrained shear strength.

References:

NEN-EN-ISO-22476-1 (2005) Geotechnical investigation and testing - Field

testing - Part 1: Electrical cone and piezocone penetration tests. Delft, NEN.

Lunne, T., Robertson, P.K., & Powell, J.J.M. (1997) Cone Penetration Testing in

Geotechnical Practice, Blackie Academic and Professional, London.


50



Answer:

In the Netherlands the hammered Ackermann (tube sampler) is in 80% of

the cases used for soil investigation. These samples are also used for

laboratory testing.

We have relative good experience with the 120mm hollow auger for

testing organic soils and peat in particular.

Which laboratory tests do you most commonly use for the determination of the

undrained strength for geotechnical design?



Answer:

Most commonly isotropic single stage consolidated undrained triaxial

compression tests are used according to the following standard:

NEN-5117 (1991) Geotechnics. Determination of shear resistance

and deformation parameters of soil. Triaxial test. (in Dutch).

Nederlands Normalisatie Instituut, Delft, the Netherlands.

NEN 5117:1991/A1:1997 nl (addendum)



Answer:

No. In 2011 an investigation started to investigate if sampling induced

disturbance was an issue for organic soils and peat in particular. Block

samples were for economic reasons not included in the investigation.

Trends within this research are indicating that sampling induced

disturbance plays a role, but the investigation is not of academic nature.

Previously Dr. Evert den Haan has investigated sampling induced

disturbance of OVP-clay with an organic content up to 40%. Piston types

samplers were used with the Laval sampler (operated by LCPC) as

benchmark. No significant difference was found between the Ackermann

and the Laval.

den Haan, E. J., & de Feijter, J. W. (2001) Sample disturbance effects on

a soft organic Dutch clay. Delft Cluster.

51

den Haan, E. J. (2003) Sample disturbance of soft organic

Oostvaardersplassen clay. Proc. 3rd Int. Symp. on Deformation

Characteristics of Geomaterials. Lyon. Swets & Zeitlinger, Lisse, 1:

49-55.

There is extreme conservatism in Dutch geotechnical design allowing for

much optimization possibilities. Each new innovative approach aimed at

more economic designs is up to now more conservative than the previous

method.





Answer:

qc/20


Answer:

I have answered your questions without any restriction and in complete

openness. I am not proud of our present state of practice but fortunately

recently some people are eager to make a difference and improve our

practice.

52

Canada 1




analysis)






Answer:

Unfortunately, many of our competitors use the in situ testing method called

“guessing.” I do not recommend this. Others, still, correlate undrained shear

strength to “pocket penetrometer” testing carried out on Shelby tube or split

spoon samples done in situ (before the samples are put into their bags or jars),

or split spoon SPT ‘N’ values. I even recommend these in situ tests less because

of the false sense of security these tests proved. This is what a cost-competitive

environment does to the geotechnical field in North America.

Common practice in Ontario and many places in eastern Canada and the US is to

use field vane shear tests (FVT). Unfortunately, many FVT devices are

rudimentary vanes where torque wrenches are used and the rate of strain is not

well controlled. Sometimes, these tests can be as much as 30% unconservative.

In good practice, on critical jobs in very soft soil in Ontario and Quebec, we try

and use the Nilcon vane where the rate of strain is better controlled and a

record of torque and degrees of rotation is obtained showing rod friction, peak,

post-peak, and residual friction.

If we have sufficient data for site or locality-specific correlations to high-quality

FVT or laboratory triaxial testing, we use the peizocone penetration test to

provide a consistent rate of penetration and a well-known testing system. When

using the CPTu, we often compare multiple correlations using Nk, Nt, and

various uses of pore-water pressure correlations to find the best and most

representative correlation for the particular mineralogy and geologic conditions

of the site. Mayne’s synthesis is often used as a base reference to develop or use

existing correlations (NCHRP SYNTHESIS 368, Cone Penetration Testing, A

Synthesis of Highway Practice, P. Mayne, 2007).

One problem I have observed is that when carrying out FVT in deep boreholes,

there can be significant disturbance of the ground from squeezing toward the


53

hole, particularly if augers are used for drilling. Drilling activities such as the

level of water or mud in the hole, the size of the hole, the rate at which the bit is

removed prior to testing, etc. can all have a negative influence on FVTs if they

are not carried out some adequate distance below the bottom of the hole. FVTs

in this case underestimate the in situ strength and this is when the piezocone or

pushed-in Nilcon FVT methods are far superior.



Answer: Unfortunately, conventional “Shelby” tubes are used. Larger (100 mm

or more) samplers are rarely used. Piston samplers are unheard of except for

research work (and even then are rare).





Answer: The most common test is the unconsolidated undrained isotropic

compression test with pore water pressure measurements (UICU) followed by

the consolidated version (CIUC). Typically, practitioners in this region use the in

situ vertical effective stress as the means to choose the consolidation stress.

However, it is my belief that in soft soils this can destroy the fabric of the

structure. Therefore, I always specify the consolidation phase to be no more

than about ½ of the vertical effective stress. The undrained shear strength

obtained in this manner is typically consistent with conventional comparisons

between high-quality triaxial test and high-quality FVT testing and other

correlations with ’p, OCR, etc. However, these are completed on samples

obtained with conventional “Shelby” tubes and, depending on the conditions

and the driller, the samples may not b of the best quality.

See my comments above with respect to the adverse influence of drilling control

on FVT since similar issues affect the quality of tube samples.



Answer: I think most people ignore sample quality unless it is really pointed out

to them. On high-complexity jobs, several of us in Golder and a few of our good

competitors might apply the conventional quality index determined from

oedometer tests or the consolidation phase of CIUC tests. When I worked in NY,

the NYSDOT had a great lab where they x-rayed the samples to see the

condition of the varves and quality of the samples before extracting them from

the tubes. I bet this equipment is now gathering dust.

54





Answer: The most common correlations that are applied are those suggested by

Mesri (1975 and 1989) where 0.22’vo =Su for NC soils and 0.22’p =Su for OC

soils. Liquidity index might give some insight – if you are particularly fortunate.


Answer: I would very much like Golder to promote use of high-quality FVT

devices (Nilcon) etc. We have one or two in circulation in eastern Canada. The

challenge is training and maintaining field personnel to use these devices. I

hope that the practice in Europe is a little more enlightened.

55

Canada 2




analysis)






Answer: CPT, often calibrated to triaxial tests to obtain Nkt. Less frequently

using in situ vane tests for determination of Nkt.



Answer: Shelby tubes (push samplers, 73 mm ID approx.)





Answer: Triaxial compression tests, CIU (ASTM procedure). ON high level

projects, which are technically difficult and where budget permits, we would

move toward a SHANSEP type approach for interpretation, therefore needing

also consolidation tests. Occasionally might use CKoU triaxial compression

tests.



Answer: Not really – seems to be practice nowadays to refer back to Lunne et al

(2006) as a method to assess disturbance.




56



Answer: SHANSEP is common – but I am not sure this counts. It is more of a

framework than a correlation.

Occasionally people might invoke Bjerrum’s plasticity correction if appropriate.


Answer:

57

Canada 3




analysis)






Answer:

The most widely used are vane shear tests (using the Nilcon apparatus). Some

engineers also use tip resistance (qt) from CPTU test, but only after the CPTU

profile has been calibrated with a vane shear test performed closely.



Answer:

The Fixed piston sampler with Thin-walled tubes of 768 mm (length) x 70 mm

(inner diameter)

Recovery approx. : 610 mm.

Wall Thickness : 1,59 mm.

Tip edge angle : 6 degrees.

Tip edge wall : 25,4 mm.

Inside Clearance ratio : 0


the undrained shear strength for geotechnical design?



Answer:

The Fall cone penetrometer test is systematically done. Sometimes engineers

use the correlations (Leroueil et al., 1983) with the preconsolidation pressure

measured with the odeometer test to estimate the undrained strength.

(The procedure is attached to the email)


58



Answer:

The shape of the consolidation curve obtained with the oedometer test on

samples containing a high clay fraction (many clays are silty clays or clayey silts

in Quebec) can tell us if the sample is more or less disturbed. However, each

engineer will decide to use the laboratory results or not (i.e. to use the

correlations instead).





Answer: We usually use the correlations established by Leroueil et al. 1983 on Champlain sea clay and the values of cone factor Nkt (once the CPTU profile has been calibrated with vane shear tests performed closely).


Answer:

59

Canada 4




analysis)






Answer: For small projects, we generally use vane shear tests to define the

undrained shear strength to be used in the design. For larger projects, a

combination of CPTu soundings aand vane shear tests (in order to define NkT)

is performed (in most cases).

The vane tests are performed according to the Canadian standard (NQ 2501

200) while the CPT test procedure follows the international standard.



Answer: By default, a simple sampler with Shelby tubes is used. For sensitive

projects or when settlements prediction is of major importance, piston sampler

is used (for consolidation tests). Larger samplers are used in exceptional cases.





Answer: We seldom use laboratory measured values of the undrained shear

strength for design. We rather use in situ measured values. When required or

for verification purposes, the fall cone apparatus is commonly used (Canadian

standard NQ 2501-110). Triaxial (CIU) tests could also be used in exceptional

cases.




60

Answer: No. This is among the reasons, if not the main one, for the non

utilization of the laboratory measured cu in the design.





Answer: We often used the relation developed for Eastern Canada sensitive

clays by Leroueil et al.2 in 1983 (cu/’p = 0,2+0,0024.Ip). But this relation is

generally used to estimate ’p from vane tests values and not to define the cu

values.


Answer:

2 Leroueil S., Tavenas, F., Le Bihan J.P. Propriétés caractéristiques des argiles de l’est du Canada. Revue canadienne de Géotechnique, vol 20 (4), pp.681-705.

61

Norway 1




analysis)






Answer: CPTU (NGF standardprosedyre for CPTU)



Answer: 72 mm piston sampler





Answer: direct simple shear, active and passive triaxial tests.

Fall cone tests and unconfined compression tests are also performed standard

tests on all samples, but these are give less emphasis in determining the

characteristic strength, as we know they are often lower that the in-situ

strength. They are used to determine layering and the sensitivity of the soil.



Answer: The results from the CRS and triaxial tests are usually compared with

what should have been expected from “high quality” samples, with respect to

strain levels at failure/yield. This gives and indication of the sample disturbance

and the quality of the test results.




62



Answer:

1. Correlations with in-situ stress: sua=0.3p’0 for NC-clay

2. Correlations with CPTU-test results and triaxial test on hgh quality block

samples, correlations with OCR, St and Ip


Answer: We do too little testing to determine the properties of the soil! It is

difficult to convince clients that testing will lead to a cost reduction for the

overall project.

63

Norway 2




analysis)






Answer: CPTU tests



Answer: 76 mm piston samples for triaxial and DSS testing. 54 mm piston

samples if only classification tests are needed. Block sampling giving very high

quality sampling is increasingly used to check strength and compressibility

from 76 mm samples, and to check strength derived from CPTU correlations.





Answer: Triaxial tests and DSS tests.



Answer: The quality is normally checked against normalized volume change

(Δe/e0) during re-consolidation to in-situ effective stresses using the Lunne et al

(1998, 2006) criteria.

If oedometer tests are available a check is also made against the ratio between

Moc/Mmin as suggested by Karlsrud & Hernandez-Martinez (2013).


64





Answer: Yes, the correlations against tests on high quality block samples

presented by Karlsrud & Hernandez-Martinez (2013) are now in common use.


Answer: If strengths are derived from high quality block samples it is becoming

common to consider possible impact of strain softening on stability, especially

for highly sensitive clays.

65

Norway 3




analysis)






Answer: CPTU – interpreted according to NGI – Kjell Karlsrud’s

recommendations.



Answer: This used to be the 54mm Geonor piston tube sampler, but I think

today it is just as common to use a 73 – 76 mm piston samplers to obtain

sufficiently good samples. Block sampling is also used for a few special, and

large projects.





Answer: Triaxial undrained compression test, consolidated to in situ effective

stresses, is recommended and most commonly used, - and used for active

undrained strength. For consolidation vertical in situ effective stresses are

evaluated based on measured unit weight and preferably measured

porepressures. Lateral in situ stresses are preferably estimated using Booker

and Davies or similar curves based on effective vertical preconsolidation stress

from an oedometer test.

Directy simple shear or passive triaxial tests may be used to get a full set of ADP

strengths, but most often the direct and passive strengths are selected as

fractions of the active strength. The factors used are empirically related to Ip.


66



Answer: The triaxial test must be of high quality. This is evaluated based on

expelled water during consolidation.





Answer: Shansep is widely used.


Answer: Norwegian clays are often very low plastic clays and show more

anisotropy than most Swedish clays.

67

Norway 4




analysis)






Answer: Since the end of the 1990s, CPTU is the dominating in situ method for

determination of undrained shear strength in Norway. Before that, the

mechanical field vane test was the dominating method. Today, the undrained

shear strength is mostly interpreted by use of correlations to results obtained

by anisotropically consolidated triaxial tests on high-quality block samples,

yielding an active (compression) shear strength.



Answer: Nowadays, the 54 mm piston sampler with steel tubes is the most

important sampler in Norway. A 54 mm sampler with inner composite and

outer steel cylinder is also used, but in a lesser extent. In recent years, we have

also seen an increasing use of 72-76 mm piston samplers, and in some projects

also block samplers (diameters 160 mm and 250 mm).





Answer: Undrained triaxial tests (CUa and Cup) are by far the most used

methods for design values of the undrained shear strength. Direct shear tests

(DSS) are used in some projects. Some occasionally also use index methods such

as fall cone tests and unconfined compression tests if results from more

sophisticated methods are not available.

No general standards or nationally recommended guidelines are available for

interpretation of the test results. This is generally taken care of through internal

procedures in each company/institution performing design work.


68

For design of friction piles, some procedures for assessment of soil strength is

given in the Norwegian guidelines for pile design (NGF Peleveiledningen).



Answer: Sample quality is now based on criteria related to laboratory tests.

Objective criteria exist for unconfined compression test (related to failure

strain), oedometer and triaxial tests (based on changes in void ratio and/or

volumetric strain during consolidation). Besides, criteria related to visual

evaluation of soil behavior are used, e.g. stiffness in preconsolidated stress

range in oedometer tests, initial stiffness of stress-strain curve in triaxial tests

etc.





Answer: Comprehensive correlations are developed and in use correlating

CPTU recordings (net cone resistance and excess pore pressure) to active

undrained shear strength (Karlsrud et al (1996, 2005)). These correlations are

based on consistent use of reference undrained shear strength from high-

quality block samples. In addition, the Shansep-concept and relations given by

e.g. Janbu is used to relate undrained shear strength to the preconsolidation

stress or stress history (OCR). To a lesser extent, statistical relations between

undrained shear strength and various index properties are used in some project

where quality soil parameters are deficient or lacking.


Answer: Work is ongoing in the joint venture project NIFS (Naturfare .

infrastruktur, flom og skred) as how to obtain a recommended design profile

for the active undrained shear strength for various applications. The work will

be completed in 2014, with recommendations how to assess the strength

profile, also introducing relative weight of the used method with considerations

of testing concept, sample or test quality. This work is carried out by a working

group comprising members of the NIFS project (Statens vegvesen,

Jernbaneverket, NVE, NGI, Multiconsult/SINTEF and NTNU). Similar work was

carried out by the same team in how to assess the anisotropy factors between

active, direct and passive shear strength for use in stability calculations (ADP-

analysis).

69

Norway 5




analysis)






Answer:

DNVGL is primarily involved in offshore geotechnical engineering. Therefore, the

following apply for offshore soil investigations.

Piezocone (CPTU) tests, calibrated with triaxial test results, are most widely

used for the determination of the undrained shear strength in DNV GL.

Reference is made to T. Lunne, P.K. Robertson and J.J.M. Powell, “Cone

Penetration Testing in Geotechnical Practice”, first published in 1997.

In addition some other in-situ devices are used for offshore soil investigations

as plane strain T-bare and ball penetrometers (see 16th International

Conference of Soil Mechanics and Geotechnical Engineering, Osaka 2005,

“Challenges of offshore geotechnical engineering”, M Randolph et al.)



Answer:

For offshore purposes, the most commonly used sampler is the piston sampler,

using a 70mm inner diameter.





Answer:

We prefer to base our design on anisotropic undrained shear strength,

emphasizing results from triaxial compression and extension tests (CAUC,

CAUE) and Direct Simple Shear Test (DSS). However, since offshore pile design


70

often is based on empirical methods that are calibrated towards UU triaxial

tests, such tests are also commonly used.

For immediate results provided in the field, simplified tests are performed

including pocket penetrometer, torvane, motorized miniature vane and

unconsolidated undrained triaxial tests (UU). Results from such tests are also

used to complement the results of more advanced tests mentioned above.

For offshore structures exposed to wave loading the effect of cyclic loading on

the undrained shear strength is accounted for by defining cyclic strengths.

These are normally defined accounting for anisotropy and are defined as a

function of the average shear stress level. The background is triaxial extension

and compression tests and direct shear tests, all performed with cyclic loading.

The cyclic load level is varied between the tests, and the development of strains

(cyclic and average) and of pore pressure is monitored as a function of number

of cycles until failure or for a defined maximum number of cycles.



Answer:

The disturbance of the sample can be related to volumetric change during

consolidation phase of triaxial or oedometer tests by evaluating the change in

void ratio normalized to initial void ratio: e/ei (ref. Lunne et al., 2006).

Alternatively sample quality can be qualitatively (visually) assessed by

examination of sample X-rays.

Typically results from poor quality tests would be excluded when establishing

the design profile and more weight would be given to shear strength derived

from in-situ tests (CPTU) and correlated against good quality samples.





Answer:

We use correlations between su/po =f(Ip, OCR) and other correlations presented

in the 23rd Bjerrum’s lecture, see Norwegian Geotechnical Society, 2010.


Answer:

As already mentioned, DNV GL’s main experience of site investigations in soft

clay is related to offshore projects, which is also reflected in the replies given in

this questionnaire. However, most sampling, in-situ test methods and

71

laboratory tests used for soft clays offshore are also applicable for on-shore

projects.

When appropriate, design values are corrected for rate effects. This is amongst

others, to account for differences in loading rate during testing and real loading.

The anisotropy is also important. Therefore, we prefer to use anisotropic

undrained shear strength (suC, suD and suE), whenever possible.

For some analyses we use remoulded undrained shear strength (su/St) or set-up

shear strength (re-consolidated su), where the set-up factor is determined by

thixotropy laboratory tests or through consolidation analyses.

72

Norway 6




analysis)






Answer: CPTU. Seen some field vane tests. Seems to be making a comeback with

availability of modern vanes where torque is applied at the vane location thus

eliminating rod friction.



Answer: Big debate in Norway of course. Geonor 54 mm composite sampler still

widely used. Geonor / NGI 75 mm steel sampler now accepted as best but not

always used. The NTNU mini-block sampler (which is essentially a reduced

version of the Sherbrooke sampler) has become popular.





Answer: CUAC, CIUC, fallcone, Enaks



Answer: Yes a strong tradition of using either the V/V0 or e/e0 criteria




73



Answer: The Ladd (Ladd, 1991) type correlations are sometimes used. However

correlation between CPTU and su is very common (Karlsrud et al., 2005)


Answer:

Karlsrud, K., Lunne, T., Kort, D.A. and Strandvik, S., 2005. CPTU correlations for clays, 16th International Conference on Soil Mechanics and Geotechnical Engineering, Osaka, pp. 693-702. Ladd, C.C., 1991. Stability evaluation during staged construction. Journal of Geotechnical Engineering Division ASCE, 117(4): 540-615.

74

Singapore




analysis)






Answer: CPT, field vane shear test. BS 5930: Code of practice for site

investigation



Answer: thin-walled sampler





Answer: un-consolidated undrained triaxial test and consolidated undrained

triaxial test. BS 1377: Methods of test for soils for civil engineering



Answer: not at this moment. Coming 1 Apr 2015, Eurocode will be

implemented. The quality class of soil samples and sampling category will need

to be complied with in accordance with EN1997-2 and EN ISO 22475-1


75





Answer: cu = 0.25 ~ 0.35 v’, v’=effective vertical stress; cu=5~6N, N = SPT

blow count


Answer:

76

Germany and Switzerland 1




analysis)






Answer: This nowadays more common using CPTU (there are only 3-4

companies available in Switzerland offering this tests. About ten years ago in

most cases standard values provided by guidelines (depending on location and

glacier thicknesses were used). I attach a document from an actual site

investigation report. Please do not refer to it as such.



Answer: This highly depends on who is requesting it. The awareness of sample

disturbance is increasing also because of increasing awareness in teaching at

Uni and “Technical Highschool” level





Answer: Its basically Triaxial (CU) or Simple shear box tests usually referring to

German or ASCE Standards



Answer: ….. not really …. See 1b


77





Answer: su/sv=a*OCR^b. This approach is used but rather rarely on almost

normal consolidated clays. For Swiss OCR clays the necessary investigations are

missing


Answer: There are big differences between the French and German speaking

regions. This answers are more related to the German speaking part of

Switzerland (East an Middle).

78

Germany and Switzerland 2




analysis)






Answer:

- Field shear vane test according to DIN EN ISO 22476-9 (old DIN 4096); see

also EAB 2014 (english version).

- Indirect determination from CPT field test according to DIN EN ISO 22476-1

(old DIN 4094); interpretation of the results according to Lunne et al.

(1997), Gebreselassie et al. (2003); Jörß (1998); Geotechnical Engineering

Handbook (1997)

- Indirect determination using interpretations according to Kulhawy and

Mayne (1990)



Answer:

- General sampling methods are described in DIN 4021 (EN ISO 22475-1)

- Thin wall piston sampling device is recommended in soft and sensitive soils

- Quality class 1 type of sample is required for determination of the strength

and deformation properties in laboratory. Quality class 1 is equivalent to

sample category A according to EN ISO 22475-1

- A special type of sampler for soft soils can also be referred to Scherzinger

1991 (more or less for research purposes)





Answer:

- Triaxial test: unconsolidated undrained (UU) and consolidated undrained

(CU) Tests according to DIN 18137-2 and occasionally direct shear test

according to DIN 18137-3


79

- Generally, there is a reservation in Germany on determination of the

undrained strength in the laboratory for the following reasons (see also

EAB 2014, R 94):

o Sampling errors and errors installing the sample in the shear box or

triaxial cell may lead to strength reduction,

o Increase in apparent strength due to frictional resistance of the

direct shear box

o The resistance of the rubber membrane in triaxial tests may lead to

an apparent increase in strength

- There is a general consensus that the undrained shear strength is best

determined by field tests (see point 1) with due consideration of the

influence of the shearing rate in field test.



Answer:

- There is no as such a general consensus regarding assessment of sample

quality, except that the sample quality requirements as described in DIN

4021 (see Point 1b above) and the caution to be done during the

preparation of the samples for laboratory tests according to the respective

code of standard (for e.g., DIN 18137-1 and 2 for triaxial test and DIN

18137-3 for direct shear box test).

- The geotechnical expert is free to decide on the characteristic soil

parameters taking into account the sample disturbance and other effects as

well as the local experiences.

- As pointed out in Point 2a above, EAB 2014 recommends to determine the

undrained shear strength from field vane shear test or eventual from CPT

test rather than from laboratory tests.

- EAB also recommends to carefully assess the effective cohesion and the

undrained shear strength determined in the laboratory in selecting the

characteristic values.





Answer:

- There is no a particular correlation for undrained shear strength, which is

specified or recommended in code of practice or similar documents.

- As necessary, correlations from international literature (see for e.g.

Kulhawy and Mayne (1990); Gebreselassie 2003; Kempfert/Gebreselassie

2006) are adopted for preliminary design.

- The normalized undrained shear strength (cu = cu/´vo) for lacustrine soils

in south Germany ranges between 0.20 and 0.30 (Gebreselassie 2003;

Kempfert/Gebreselassie 2006).

80

- cu = (0.05 to 0.10)qc according to EAB 2014 R94.

- cu = (qc - vo)/Nk, Nk 19 for lacustrine soil in southern Germany

(Gebreselassie et al. 2003).

- The following are correlation given in Geotechnical Engineering Hand Book

(2002), which are adopted from international literature


Answer:

The behavior of soils is primary governed by the effective stresses independent

of the drainage conditions (see Kempfert/Gebreselassie (2006), pp 35 – 40). In

other words, there exists a relationship between the undrained shear strength

and the effective strength parameters. Hence, the feasibility of the undrained

and drained soil parameters should be checked against each other. Sometimes a

higher value of effective strength parameters (’ and c’) and a very low value of

cu are assigned for the same type of soil, which is not correct.

References:

[1] EAB (2014): Recommendations on Excavations. German Working Groups on

Excavation, German Society of Geotechnical Engineering (DGGT), 3rd ed., Ernst &

Sohn, Berlin.

[2] DIN 18137-1 to 3: Soil Testing Procedure and Testing Equipment (Triaxial,

direct shear box).

[3] DIN 4021-1990: Soil exploration using Test pits and Borings, sampling.

[4] DIN EN ISO 22476-1 (2012): Ground investigation and testing –Field testing-

Part 1: Electrical cone and piezocone penetration test

81

[5] DIN EN ISO 22476-9 (2014): Ground investigation and testing –Field testing –

Part 9: Field vane test

[6] EN ISO 22475-1 (2006): Geotechnical investigation and testing – Sampling

methods and groundwater measurements – Part 1: Technical principles for

execution.

[7] Geotechnical Engineering Handbook (2002), vol. 1, 1st ed. (English version),

edited by Smoltczyk, U., Ernst & Sohn, Berlin.

[8] Gebreselassie, B. / Kempfert, H.-G. / Raithel, M. (2003): Correlation between

cone penetration test results and undrained shear strength. 6th Intl. Symposium

on Field Measurements in GeoMechanics, Oslo, pp 45-52.

[9] Gebreselassie B. (2003): Experimental, analytical and numerical investigations

of excavations in normally consolidated soft soils. Schriftreihe Geotechnik,

University of Kassel, Heft 14.

[10] Kempfert, H.-G. / Gebreselassie, B. (2006): Excavations and Foundations in Soft

Soils. 1st ed., Springer Verlag, Berlin, Heidelberg, New York.

[11] Kulhawy, F.H. / Mayne, P.W. (1990): Manual on estimating Soil Properties for

Foundation Design, Cornell University Ithaca, New York, Prepared for Electric

Power Research Institute, Palo Alto, California.

[12] Scherzinger, T. (1991): Materialverhalten von Seetonen - Ergebnisse von

Laboruntersuchungen und Ihre Bedeutung für das Bauen in weichem

Baugrund; Institut für Bodenmechanik und Felsmechanik der Universität

Fridericiana in Karlsruhe, Heft 122.

82

England and Ireland 1




analysis)






Answer: CPTU, Field vane



Answer: 100 mm diameter ELE type piston sampler, 1 m long, 1.7 mm wall

thickness, 30 deg cutting edge – though efforts have been made in recent times

to use new tubes with a sharp 5 deg. Cutting edge.





Answer: CAUC or CIU. UU tests used to be done but no longer used as they are

recognized to be flawed. No use made of fall cone or Enaks test etc.



Answer: Very little. Recently the NGI e/e0 approach or the SGI approach

(which is essentially an extension of the NGI approach to higher water contents)

has been used.




83



Answer: The correlations published by Hight et. al (1987) between su and

v0'and su and pc' are often used. Sometimes the su = 0.22 v0' of Mesri (1988) is

used as an “operational” value.


Answer: sample quality and tests on poor samples is a big issue, saturation of

CPTU is often not done properly, proper correction of CPTU for temperature

effects, pore water pressure effects etc. also important

References:

Hight, D.W., Jardine, R.J. and Gens, A., 1987. The behaviour of soft clays, Embankments on Soft Clays. Special Publication Bulletin of the Public Works Research Centre, Ministry of the Environment, Physical Planning and Public Works, Athens, Greece.

Mesri, G., 1988. A re-evaluation of su(mob) = 0.22`p using laboratory shear tests

Canadian Geotechnical Journal,, 26: 162-164.

84

England and Ireland 2




analysis)






Answer: in soft clays there would be an in-situ shear vane test. This is more

common using a hand held vane on a sample from a trial pit and not seen so

frequently in a borehole. Where the soft clay is mixed with alluvial silt and fine

sand, the SPT test is still the most commonly attempted insitu test. Next to

these static cone penetration testing with dissipation tests would be the next

most common.



Answer: For soft clays this should be a hydraulic push in sampler such as

‘Mosstap’ or recently I have seen some direct push equipment in the UK. For

stronger clays the percussive hammered U100 is still the most common method

of extraction of a clay sample for lab testing.





Answer: The most common test is a quick undrained triaxial lab test, however,

multi stage triaxial tests and effective stress triaxial testing are also quite

common in the UK.



Answer: The general consensus would be that triaxial testing and consolidation

testing on a sample recovered by traditional U100 percussive sampling


85

methods can only be treated as a guide and a more representative result would

be obtained from a thin wall hydraulic push sample. Sample disturbance by

percussive sampling is clearly illustrated in the UK by the difference in

undrained shear strength recorded in 3 x U38 samples compared to U100

samples in the same ground at the same site.





Answer: Stroud correlation between SPT ‘N’ value and undrained shear

strength as well as correlation to the coefficient of consolidation is the most

common. The clay stiffness is also estimated as a multiple of the undrained

shear strength using Terzaghi range figures.


Answer: Site investigation Procurement for private and public enterprise in the

capital market in the UK does not work as the model is based on competitive

tender and the cheapest SI contractor wins. The model means that each

contractor bidding reduces the scope of the investigation. There needs to be a

government led initiative to define a minimum quantity of site investigation for

a range of developments. The range could be based on project value or based

on the complexity of the proposed structure.

86

Vietnam




analysis)






Answer:

a.1. Cone penetration test

su = (qc –σv0)/Nk where

su is the undrained shear strength, Nk is the empirical cone factor,

σv0 is the total overburden stress. a.2. Piezocone + dissipation test

su = Δu/NΔu = (u2 - u0)/NΔu where

NΔu is the empirical cone factor (for the expression using Δu), u0 is the in-situ pore water pressure.

a.3. VST (vane shear test)

b. What type of sampler do you most commonly use for the extraction of samples for laboratory test determination of undrained shear strengths? Answer: - Thin walled sampler (mostly).

- Piston sampler (required for foreign consultants)





Answer:

- Unconfined compression test.

- Direct shear test.

- Triaxial test.


87



Answer:

Due to the education system in Vietnam, there are problems in the soil

parameters interpretation. The designers, who are mainly educated in Civil

Engineering Schools, only know how to use the soil parameter, taken from the

soil investigation report, and have a limited knowledge about soil investigation.

The engineers, who carry out the soil investigation, both the field and lab tests,

are graduated from Geological Engineering Schools, and are not interested in

what soil parameters are useful for the design, i.e. they have a limited

knowledge about foundation design. There are therefore no differences

between soil investigation programs for different type of project.





Answer:

The conception of preconsolidation pressure, OCR or in situ stress is not

common in Vietnam, due to most of experienced engineers have been educated

during 1960 to 2000, following the Soviet/Russian school. Within this time the

education system, as well as the construction standards, are based on the Soviet

school.


Answer: