Earth pressures and stability of retaining walls - The Mechanics of Soils and Foundations - page 380

Figure 24.4 Mechanisms of failure of retaining walls.

Figure 24.6(a) shows a retaining wall loaded by excavation. For convenience the
excavation if kept full of water so the long term pore pressures after construction are
the same as those before construction. If the excavation is kept dry by pumping, which
would be the usual case, the long term pore pressures are governed by a steady state
seepage flownet and will usually be less than those before construction. For both the
elements shown on the critical slip surfaces, one on the active side and one on the
passive side, the shear stresses increase while the mean normal total stresses decrease.
The total and effective stress paths are shown in Fig. 24.6(b); these are like those for a
slope, shown in Fig. 21.4. The effective stress path A →

B corresponds to undrained
loading: the exact path will depend on the characteristics of the soil and on its initial
overconsolidation ratio, as discussed in Chapter 11.
As shown in Fig. 24.6(b), the pore pressure immediately after construction u i is
less than the final steady state pore pressure u ∞ and so there is an initial excess pore