Finite Element Analysis and Constitutive Modelling in Geomechanics

A: Option A feels harmless because lab data is 'real' data. The miss is scale and strain level. At 300 m depth, initial effective stress is several MPa; early tunnel convergence sits at shear strains well below those mobilised at 50% deviator stress in CU tests. Dropping small‑strain G by an order of magnitude gives you centimetres instead of millimetres. Option B sounds dangerous, but plane stress would actually under‑predict confinement and often reduce settlement at depth, not inflate it. Option C breaks in-situ stress, yet removing self‑weight usually reduces deformation unless combined with other errors. Option D causes numerical grief and odd stress paths, but it doesn't by itself create 50 mm of settlement unless the stiffness is already wrong.

A: A global FoS from Mohr–Coulomb looks comforting, and Option B is exactly what it checks: peak shear resistance against a kinematic mechanism. Option C tempts anyone with excavation scars, but base heave is still captured if undrained strength is modelled correctly. Option D sounds advanced, yet unless you couple consolidation, excess pore pressure isn't even generated, so it's a modelling scope issue rather than a 'not protected' failure mode. Option A is the trap: Mohr–Coulomb has no memory. Once peak strength is mobilised, it doesn't degrade, so progressive failure and time‑dependent collapse slip straight past that safeguard.

A: Option B is seductive under programme pressure: match the inclinometer and move on. The break is traceability; you’ve lost the physical link to stress path and drainage. Option C gets the numerics right but assumes the starting stress is fine, which is rarely true on brownfield sites. Option D leans on 'conservatism', a word auditors love to dismantle when behaviour doesn't match. Option A is dull but defensible: stress path first, in‑situ state next, then parameters, then check the numerics didn’t bend the physics.

A: Option A looks academic, but it's the lever arm. Oedometer E reflects 1D compression at small strains; plugging that into an undrained 3D problem collapses stiffness and lets the base lift unrealistically. Option B shifts stress state, yet K0 errors usually tweak heave by tens of percent, not a factor. Option C matters for effective stress, but buoyancy errors of a few kN/m³ don't buy you 120 mm alone. Option D affects load transfer to the wall, not the undrained bearing response of the base.