Mohr-Coulomb

[otask]

Dear all,

I am a new abaqus user and not very familiar with the geotechnical issues.. I have a question which is probably trivial but I would be glad if somebody answer that..

I modeled a 3d soil volume in abaqus using the Mohr-Coulomb material for the soil and element type c3d8r. As far as I know Mohr-Coulomb is a failure criterion based on shear stresses (t=c+s*tanphi). My problem is that I can't apply the self weight of the soil (abaqus makes some iterations and applies 60% of the self weight but finally it cannot converge and aborts the analysis). I realized that it can finish the analysis only if I increase the soil cohesion. But the self weight creates vertical stresses (not shear stress) and I don't understand why it is related with the cohesion... Maybe I am missing something.. Could you please help me?
Please find in the following the material properties that I used (the soil column is 20x20x5m and at the base I expect 2*9.81*20=392kPa).

** MATERIALS
**
*Material, name=soil
*Density
2.,
*Elastic
20000., 0.3
*Mohr Coulomb
20.,5.
*Mohr Coulomb Hardening
100., 0.
250., 0.1
**

Regards,
Oly.

 

[mohamedgk]

i am civil engineer and interesting in geotechnical engineer espisially in soil improvement(stone column technique). i have a minor problem in abaqus i hope u can help me.



i try to solve the following problem with abaqus but there is a nimor problem in the attach file . i hope u can help me and correct the file and give me the guid for the right solution



thanks for your help





the problem

i want to calculate the effect of encase stone column in clay model to incraese the bearing capacity of clay (increasing the bearing capcity of clay, soil improvemet).


calculate the following :

1-consolidation settlement as a function of time and stress.

2-the the variation of stress in soft soil(ration between horizontal/vertical stress) with distance from column

3-radial stress on encased material as function to height of encased column

4-pore pressure





for a clay sample that is 8m in diameter and 8 m high confined by an impermeable, smooth, rigid cylindrical container and encased stone column with diameter 1.0 m and depth 4 m . the composite model subjected to a surcharge applied on footing dimension 2X2X0.5m. beneath the raft, sand blanket is placed with 1m depth. The top surface of the soft clay is permeable. The clay is normally consolidated and has a constant permeability k = 6 × 10-9 m/s, and initial void ratio e0 = 1.125. Assume that the clay is elastoplastic, obeying the extended Cam clay model.





Cam clay model parameters

General
Plasticity





ρ (kg/m3)
1600
λ
0.1173

k (m/s)
6 × 10-9
Stress ratio, M
1

γw (kg/m3)
1000
p0/2 (Pa)


e0
1.125
Wet yield surface size
1

Elasticity
Flow stress rate
1

κ =0.01957

ν =0.28





gesynthetic material (ENCASED MATERIAL)
Linear elastic : E= 600 Mpa v= o.3

Elongation=4%

Weft diameter =5 mm

Hole size=25.4X25.4 mm



tensile strength=140 KN/m


stone material

friction angle = 40
c=1 kpa
dilation angle=0
E= 60 Mpa

v= o.3

UNIT WEIGHT = 19 KN/m3


sand blank material


friction angle = 30

dilation angle=4
E= 20000Mpa

v= o.3

UNIT WEIGHT = 16 KN/m3



the coefficient of sliding friction between the geosynthetic and stone column and between the geosynthetic and the soft soil was assumed to be 0.4 and 0.2 respectively


i place a sand mat with 1 m depth over the clay model but the model is not submit



i hope u can correct the model and tell me the mistakes i made in the model .



i will attach the files of the model



i hope u can help me



if there is any site concern with ABAQUS for soil analysis , please tell me



thanks





best regard

 

[mohamedgk]

i am civil engineer and interesting in geotechnical engineer espisially in soil improvement(stone column technique). i have a minor problem in abaqus i hope u can help me.



i try to solve the following problem with abaqus but there is a nimor problem in the attach file . i hope u can help me and correct the file and give me the guid for the right solution



thanks for your help





the problem

i want to calculate the effect of encase stone column in clay model to incraese the bearing capacity of clay (increasing the bearing capcity of clay, soil improvemet).


calculate the following :

1-consolidation settlement as a function of time and stress.

2-the the variation of stress in soft soil(ration between horizontal/vertical stress) with distance from column

3-radial stress on encased material as function to height of encased column

4-pore pressure





for a clay sample that is 8m in diameter and 8 m high confined by an impermeable, smooth, rigid cylindrical container and encased stone column with diameter 1.0 m and depth 4 m . the composite model subjected to a surcharge applied on footing dimension 2X2X0.5m. beneath the raft, sand blanket is placed with 1m depth. The top surface of the soft clay is permeable. The clay is normally consolidated and has a constant permeability k = 6 × 10-9 m/s, and initial void ratio e0 = 1.125. Assume that the clay is elastoplastic, obeying the extended Cam clay model.





Cam clay model parameters

General
Plasticity





ρ (kg/m3)
1600
λ
0.1173

k (m/s)
6 × 10-9
Stress ratio, M
1

γw (kg/m3)
1000
p0/2 (Pa)


e0
1.125
Wet yield surface size
1

Elasticity
Flow stress rate
1

κ =0.01957

ν =0.28





gesynthetic material (ENCASED MATERIAL)
Linear elastic : E= 600 Mpa v= o.3

Elongation=4%

Weft diameter =5 mm

Hole size=25.4X25.4 mm



tensile strength=140 KN/m


stone material

friction angle = 40
c=1 kpa
dilation angle=0
E= 60 Mpa

v= o.3

UNIT WEIGHT = 19 KN/m3


sand blank material


friction angle = 30

dilation angle=4
E= 20000Mpa

v= o.3

UNIT WEIGHT = 16 KN/m3



the coefficient of sliding friction between the geosynthetic and stone column and between the geosynthetic and the soft soil was assumed to be 0.4 and 0.2 respectively


i place a sand mat with 1 m depth over the clay model but the model is not submit



i hope u can correct the model and tell me the mistakes i made in the model .



i will attach the files of the model



i hope u can help me







thanks





best regard