When using the SRM you apply a factored shear strength based on the shear strength of the soil divided by a strength reduction factor (SRF). For soils defined using cohesion only: cohesionfactored = cohesion/SRF. Now you can see that if you chose a SRF=0.7 the slope may be marginally stable as...
Correct, with the emphasis on "accurate". We may have the ability to calculate PWP to use in an effective stress based model, but not with the accuracy or confidence generally needed throughout the entire range of possible loading. So in your embankment dam example you look at the...
Sorry, misread your question. I think you're assuming a scenario where the clay is heavily over consolidated prior to placing the embankment but the embankment loading is such that the post construction effective stress exceeds the preconsolidation pressure beneath the embankment but doesn't at...
Keep in mind that you don't need to reach failure to develop shear stress, the shear stresses throughout the foundation change as the embankment is constructed. The shear stress in the clay, beyond the pressure bulbs shown in your example, is increasing and as the shear stress increases one...
You probably want to do both drained and undrained analyses but not for the reason you're thinking. Think of pore-water pressure generation in two ways; (1) from volume changes such as loading from the dam trying to consolidate the underlying clay as evidenced by the bulbs of pressue, and (2)...
What BigH is describing is the basis of Critical State Soil Mechanics. For simplicity separate pore-water pressure generation into 2 parts, the first being related to compression/rebound and second related to shear. If you apply an all around pressure to a fine grained soil sample, like in an...
To add to the above, often when short term load conditions control design, such as construction of an embankment on soft foundations, factors of safety can control lateral displacement during and immediately after construction and then with time the foundation consolidates and gains strength so...
1. Too much to say to try to cover here but there are two main concepts you should consider: LEM is based on plasticity and you are solving directly for a SF for a trial slip surface and then you need to check other trial surfaces to find the slip surface with the lowest SF; FEM is indirectly...
If there is no automated SRF routine in Abaqus you can manually factor Mohr-Coulomb strength values, c and tan phi, by a SRF. When the model no longer converges that SRF is the FS. For models that do not have structural element the SRF approach has agreed well with limit equilibrium results...
Abaqus can give you the safety factor but since I am not an Abaqus user I don't know whether Abaqus has a built in routine for finding the safety factor. Stress deformation programs do not solve directly for factor of safety, but can be used to find factor of safety through non-convergence of...
In addition to strength, the wall will respond to soil stiffness variation. When you switched to drained strength properties did you have a corresponding change in soil modulus (it's common to have drained modulus values lower than undrained). Without knowing your model it may be that the...
Right or wrong I typically think of the difference in terms of critical state soil mechanics where heavily OC soils tend to dilate under drained shear and normally to lightly OC soils tend to contract. Then the OC ratio associated with drained shearing at no change in void ratio would define...
Luca,
From your initial post you recognize that there will be rebound associated with unloading but you question why there is upward displacement at the crown. How is the model built? It appears you have a finer mesh around the tunnel opening, do you have a liner installed? If so, is it...
Because you discuss using the M-C and hardening soil models it seems you are running some type of FEM analysis. Based on what you describe you probably don't have sufficient information to say anything about displacements so why not use a limit equilibrium approach? If you care only about...
I fully agree with IODirt that this is a SSI problem. When using structures to improve slope stability it is unconservative to think you can simply assign the shear resistance of the pile as a resisting force in a LE model. As a start you would only be able to use the resistance associated...
