For excavation case: ~ULD{Ov'F
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1) Clay: low permeability, undrained condition. In this type of soil, l%$~X0%DM
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for example, in PLAXIS, you can have three options: {FIr|R&
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A) analysis in terms of effective stresses (undrained material with E', v', DEdJH4
c', phi' and psi') J}$St|1y
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B) analysis in terms of effective stresses with undrained strength [8-. T4
parameters (undrained material with E', v', but with c_u, phi=0) 15o<'4|=Lm
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C) analysis in terms of total stresses (material is drained and dry, or non \!+sL JP
porous, E_u, v_u, c_u and phi = 0) xWZ87
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If you want to know the detail, please see the PLAXIS MANUAL. /|
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2) Sand: drained condition because it has high permeability. The effective poisson's ratio should be input. Cu=0, and phi=some value. Undrained strength for sand should be zero. Dz<"eyB\
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Currently: Hardening soil model can not model the undrained condition for clay(total stress analysis). L7\rx w
Duncan-Chang model is best model due to the modulus depending on the stress level that is more suitable for excavation and backfill. 'U9l
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Mohr-Coulomb model is quick for trial. The parameters are easy to get and the result can give you overview. I used this model, the results are good compared to the measure data. Yy,i,c`r
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To geofem: K
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"对于强透水性土", if the soil is clay, whatever the permeability is high, please use undrained condition, because it is the most unsafe status. If it is sand, use drained condition. 2X:OS/
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To:daniellb1023: 4pYscB
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"固结不排水": 1)固结, of course it is under drainage. Can you imagine soil can consolidate without water drainage. z5V~m_RO
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2)不排水, that means the after using confining stress, adding more deviator stress causing failure is under undrained(without pore pressure dissipate)