Hi there,

I’m trying to model an excavation in clay using FLAC2D. The stratigraphy goes as follow, 27m of clay, purple zones, laying on the bedrock, green zone. Here is my mesh:

Gravity is taken to be 9.81m/s2, units are m, Mg, kPa and s and boundary conditions are:

fix x (sides)

fix x y (bottom)

The strategy is to use the Mohr-Coulomb Model to evaluate displacement resulting from the unloading of the clay (excavation). The rock is modelled as an elastic medium. Material properties are :

model mohr group ‘Clay’

prop density=1.3 bulk=8300 shear=3800 group ‘Clay’

prop cohesion=13.5 friction=31.0 group ‘Clay’

model elastic group ‘Rock’

prop density=2.3 bulk=6.7E4 shear=4E4 group ‘Rock’

I established effective stresses and pore pressures using a FISH function called Ininv.fis and solved mechanical only.

set flow off

water density 1

;

; Call Fish functions

call ‘Ininv.fis’

set cd back

set wth=17 k0x=1 k0z=1

ininv

;

; Solve

history 999 unbalanced

solve

The equilibrium is reached with minimal displacements. Vertical displacement reached 0.4 m total which seems normal for a 272m high model. I then initialize velocities and displacement and proceed to excavate the clay using model null on zones to be excavated.

initial xdisp 0 ydisp 0

initial xvel 0 yvel 0

set flow off

water bulk 0

model null i=215,250 j=133,148

history 999 unbal

solve

The solution converges but the zones atop of the slope start to strain very weirdly. Anybody can help?