Abaqus - Sorption saturation and initial conditions

[Barbalera]

Hi everyone,

I'm a new user of Abaqus and a new user of eng-tips. I'm just trying to simulate a very simple geotechnical analysis (in Abaqus 6.3) of a sheet pile wall, in which the soil is only partially saturated. In doing so, i have to create an absorption curve defining the saturation values in elements upon the phreatic level, and i have to define some initial conditions, consistent with the chosen curve.
That seems to be easy, but my input file doesn't work: elements are distorting so much that they turn inside out.
What may be the problem? The file seems correct to me..
i beg your help.
This is the file:
*HEADING
SCAVO SOSTENUTO
MOHR-COULOMB
12 SCAVI
c=1
s=0
*NODE
1,,
201,100,
50001,,50
50201,100,50
*NGEN, NSET=BOT
1,201,1
*NGEN, NSET=TOP
50001,50201,1
*NFILL, NSET=ALLN
BOT, TOP, 100, 500
*NSET, NSET=LEFT, GENERATE
1,50001,500
*NSET, NSET=RIGHT, GENERATE
201,50201,500
**
**
*ELEMENT,TYPE=CPE8RP,ELSET=sand
1,1,3,1003,1001,2,503,1002,501
*ELGEN,ELSET=sand
1,100,2,1,50,1000,1000
*nset, nset=sand, elset=sand
**
*ELEMENT,TYPE=CPE8R,ELSET=wall
25016,25031,25033,26033,26031,25032,25533,26032,25531
*ELGEN,ELSET=wall
25016,1,2,1,25,1000,1000
**
*ELSET, ELSET=SCAVO1, GENERATE
49001, 49015,1
*ELSET, ELSET=SCAVO2, GENERATE
48001, 48015,1
*ELSET, ELSET=SCAVO3, GENERATE
47001, 47015,1
*ELSET, ELSET=SCAVO4, GENERATE
46001, 46015,1
*ELSET, ELSET=SCAVO5, GENERATE
45001, 45015,1
*ELSET, ELSET=SCAVO6, GENERATE
44001, 44015,1
*ELSET, ELSET=SCAVO7, GENERATE
43001, 43015,1
*ELSET, ELSET=SCAVO8, GENERATE
42001, 42015,1
*ELSET, ELSET=SCAVO9, GENERATE
41001, 41015,1
*ELSET, ELSET=SCAVO10, GENERATE
40001, 40015,1
*ELSET, ELSET=SCAVO11, GENERATE
39001, 39015,1
*ELSET, ELSET=SCAVO12, GENERATE
38001, 38015,1
*ELSET, ELSET=SCAVO13, GENERATE
37001, 37015,1
*ELSET, ELSET=SCAVO14, GENERATE
36001, 36015,1
**
*SOLID SECTION,ELSET=sand,MATERIAL=sand
*MATERIAL, NAME=sand
*DENSITY
1.73469
*ELASTIC
30000,0.3
*permeability, specific=10
5.787e-06, 0
*sorption
-100.,.04
-10.,.05
-4.5,.1
-3.5,.18
-2,.45
-1,.91
0.,1.
**
**
*SOLID SECTION, ELSET=wall, MATERIAL=wall
*MATERIAL, NAME=wall
*DENSITY
2.5
*ELASTIC
30000000,
**
*BOUNDARY
LEFT,1,1
RIGHT,1,1
BOT,1,1
BOT,2,2
**
*INITIAL CONDITIONS,TYPE=PORE PRESSURE
sand, -10
*INITIAL CONDITIONS,TYPE=RATIO
sand,.43
*INITIAL CONDITIONS,TYPE=saturation
sand,.05
*INITIAL CONDITIONS,TYPE=stress, geostatic
sand, 0,-850,50,0,.421
wall, 16, -625, 50, 0, 0.0
**
**
*STEP, NAME=GRAV, nlgeom, unsymm=yes
*GEOSTATIC
*DLOAD
sand, grav, 10, 0, -1, 0
wall, GRAV, 10, 0, -1, 0
*CONTROLS,ANALYSIS=DISCONTINUOUS
*OUTPUT, FIELD
*NODE OUTPUT
POR, U
*ELEMENT OUTPUT
E, S
*END STEP
**
*STEP, NAME=SCAVO1, nlgeom, unsymm=yes
*soils, cetol=0.0001, utol=1
10.,50.
*MODEL CHANGE, TYPE=ELEMENT, REMOVE
SCAVO1
*CONTROLS,ANALYSIS=DISCONTINUOUS
*OUTPUT, FIELD
*NODE OUTPUT
POR, U
*ELEMENT OUTPUT
E, S,por, flvel
*END STEP
**