-
PREDICTION OF ULTIMATE JACKED PILE CAPACITY IN HARD CLAY BY
USING
FINITE ELEMENT METHOD
(Apichit Kumpala)1 (Suksun Horpibulsuk)2
1 [email protected]
2 [email protected] : ( Modified Cam Clay Soft Soil) Modified Cam
Clay ABSTRACT : Soil in Nakhon Ratchasima provinces in Thailand is
mainly residual soil consisting clay, silt and sand. There are few
researches related to engineering properties and design of pile
capacity. An attempt has been made to bring out engineering
characteristics of Korat clay in Suranaree University of Technology
and to predict ultimate jacked pile capacity by finite element
method in the present paper. It has been found that the soil is
uncemented overconsolidation clay. The yield surface of the soil
can be simulated by ellipse function for compression test. Using
the modified cam clay model the prediction of ultimate jacked pile
capacity by finite element method is done. The model is verified as
an appropriate model for predicting load-settlement curve. KEYWORDS
: Modified Cam Clay model, Engineering characteristics, Jacked
pile. 1.
2.5 (Hard clay) [1] (Steel micro-pile)
[1]
-
SHANSEP (Standard penetration test) 0.8/ 0.278u vcS OCR =
/1.1uS N= (Classical method) (Numerical method) (Finite element)
(Element) (Soil model) Cam Clay, (CC) [2] Modified Cam Clay, (MCC)
[3] Soft Soil, (SS) [4] (Yield function) (Failure criteria)
2.
3 50 100 (Isotropically consolidated drained triaxial
compression test, CIDC test) (Isotropically consolidated undrained
triaxial compression test, CIUC test)
(Shear behavior) SIGMA/W CC MCC PLAXIS SS
10.0, 12.5 15.0
3. Cambridge stress path [5] (Deviator stress,q ) (Mean
effective stress, p ) (Shear strain, s ) (Volumetric strain, v
)
1 3q = (1)
1 3(1/ 3)( 2 )p = + (2)
1 3(2 / 3)( )s = (3)
1 32v = + (4)
1 3 1 3
CC, MCC SS Elastic-plastic Strain-hardening CC (Logarithmic
curve) MCC SS (Ellipse curve)
ln 0o
pq Mpp
+ = : Logarithmic curve (5)
2
22 0o
qp p pM
+ = : Ellipse curve (6)
-
op (Yield surface) M Critical State Line (Stress paths) 1
Drained pathCritical state line
Undrained path
Mean effective pressure, p' (kPa)
Dev
iato
r stre
ss, q
(kPa
)
Elliptical curve (MCC and SS Model)Logarithmic curve (CC
Model)
1 Logarithmic curve Ellipse curve
CC MCC Modified von Mises M (Compression failure) (Extension
failure) SS Mohr-Coulomb failure (Effective angle of internal
friction, cs ) 2 (Modified von Mises Mohr-Coulomb failure) ( 1, 2
3)
1 2 3 = =
1
3 2
Failure surface
Mohr-Coulomb failure
Modified von Mises failure
2 3
1 1
2 3
2 Modified von Mises Mohr- Coulomb (Atkinson, 1978) [9]
4. 3
(Isotropic consolidation) (), () Critical State Line ln p = 1
(e) 0.10, 0.015 1.55
10 50 100 500 10000.9
1.0
1.1
1.2
1.3
Initial mean effective stress, P'o (kPa)
Initi
al v
oid
ratio
, e
P'c = 554 kPa
Normally consolidation line : NCL
Overconsolidation line
Silty claye =1.55 = 0.1 = 0.015
Critical stateline :CSL
3
4 (Undrained stress paths) (Elastoplastic behavior) (Critical
state) () (Drained stress paths) 3:1 ( , loge p ) (Elastoplastic
behavior)
-
10 50 100 500 10000.8
0.9
1.0
1.1
1.2
1.3
Normal consolidation line : NCL
CSL
log p' (kPa)
Voi
d ra
tio, e
e= 1.55= 0.10= 0.015
p'o = 200 kPa
p'o = 400 kPa
0 100 200 300 400 500 600 700 8000
100
200
300
400
500
600
700
800
CSL
Mc = 1.13
Normally consolidated clay
Dev
iato
r stre
ss, q
Mean effective pressure, p' (kPa)
p'o = 50 kPa
p'o = 100 kPa
p'o = 50 kPap'o = 100 kPap'o = 200 kPap'o = 400 kPa
CIUC test CIDC test
. 4
( , loge p ) ( ,q p ) (Critical state line, CSL) (Normal
consolidation line, NCL) [6] 1
State boundary surface [6]
Normalization Mean equivalent pressure, ep [6]
exp oe oe e
p p = (7)
oe e
1
Parameters Value
Mc 1.13 0.10 0.015 2.55
5 ( / , /e eq p q p ) ( 4 ) Normalization Roscoe (Roscoe
surface)
0 0.2 0.4 0.6 0.8 1.0 1.20
0.2
0.4
0.6
0.8
1.0
1.2
Nor
mal
ized
dev
iato
r stre
ss, q
/p' e
Normalized mean normal stress, p'/p'e
CSL
Hard clay (CD test) : Po' = 50-400 kPaHard clay (CU test) : Po'
= 50-400 kPaPredicted by CC modelPredicted by MCC and SS
modelKaolin Clay : Balasubramaniam, 1969Bangkok Clay :
Balasubramaniam and Chaudhry, 1978
5 Normalized (stress paths)
-
Roscoe MCC SS Roscoe [7] [8] Roscoe State boundary surface ( MCC
SS)
MCC SS 6
0 5 10 15 20 250
200
400
600
800
1000
Dev
iato
r stre
ss, q
(kPa
)
0 5 10 15 20 25-6
-3
0
3
6
Overconsolidated clay
Shear strain, s (%)
Vol
umet
ric st
rain
, (%
) + Compression
- Dilated
p'o = 50 kPa : OCR = 11.1p'o = 100 kPa : OCR = 5.5p'o = 200 kPa
: OCR = 2.8p'o = 400 kPa : OCR = 1.4Predicted
6
6 ( OCR 1) MCC SS
5.
3 MCC SS 2 7 9 10.0, 12.5 15.0
2 Parameters Steel Pile Sandy clay Silty clay
Model Linear elastic Linear elastic MCC Depth (m) 0.0-10.5 0-2.5
2.5-12.0
Eref (kN/m2) 206 x109 250x103 - 0.33 0.35 0.35
wet (kN/m3) 78.57 18.15 20.06 ' - 37 27.83 - - 0.10 - - 0.015 -
- 2.55
OCR - - 30 Rinter Rigid 0.67 0.75
7 9 SS
-
MCC MCC
0
10
20
30
0 10 20 30 40 50 60
Settl
emen
t (m
m)
Vertical force (ton)
Qu= 35 ton
PLT 1 : 10.0 cm. diameterPrediction by MCCPrediction by SS
7 10.0
0
4
8
12
16
0 10 20 30 40 50 60 70 80
Settl
emen
t (m
m)
Vertical force (ton)
PLT 2 : 12.5 cm. daimeterPrediction by MCCPrediction by SS
Qu= 40 ton
8 12.5
0
5
10
15
0 10 20 30 40 50 60 70 80
PLT 3 : 15.0 cm. daimeterPrediction by MCCPrediction by SS
Qu= 55 ton
Vertical force (ton)
Settl
emen
t (m
m)
9 15.0
6.
State boundary surface ( MCC SS) Modified von Mises ( MCC)
7. SIXMA/W PLAXIS
8. [1] , (2548).
. .
[2] Schofield, A.N. and Wroth, C.P. (1968). Critical State Soil
Mechanics. McGraw-Hill Book Co., London.
[3] Britto, A.M. and Gunn, M.J. (1987). Critical State Soil
Meechanics via Finite Element. John Wiley & Sons, p.79.
[4] Stolle D.F.E., P.G. Bonnier & P.A. Vermeer. (1977). A
Soft Soil model and experiences with two integration schemes.
Numerical Model in Geomechanics. Numog, pp. 123-128.
[5] Roscoe, K. H., Schofield, A. N. and Wroth, C.P. (1958). On
the yielding of soil. Geotechnique, Vol. 8 No.1 pp. 22.
[6] Roscoe, K.H., and Burland, J.B. (1968). On the generalized
stress-strain behaviour of wet clay. Engineering Plastic. Cambridge
University Press, Cambridge: England. pp 535-609.
[7] Balasubramaiam, A. S. (1969). Some Factors Influencing the
Stress-Strain Behaviour of Clay. Thesis presented to Cambridge
University, at Cambridge: England.
[8] Balasubramaiam, A. S. and Chaudhry A.R. (1978). Deformation
and Strength Characteristics of Soft Bangkok Clay. Journal of The
Geotechnical Engineering Division. GT9, pp. 1153-1167.
[9] Atkinson J.H. and Bransby P.L., (1978). The Mechanics of
Soils An Introduction to Critical State Soil Mechanics. McGraw-Hill
Company (UK) Limited. 375p.
