Figure P9.30 shows a 20 m thick layer of normally consolidated clay ( t = 18.6

Figure P9.30 shows a 20 m thick layer of normally consolidated clay ( γ_t = 18.6 kN/m3) that is one-dimensionally loaded by Δσ_v = 60 kPa. The clay layer is below a 3 m thick layer of granular fill ( γ_t  = 19.6 kN/m3), and a dense, compacted glacial till underlies the clay. The water table is located at the top of the clay layer. A 1-D consolidation test is performed on a 2.20 cm thick, doubly drained specimen from the middle of the clay layer. When the stress conditions from the field (including  Δσ_v = 60 kPa) are applied to this specimen, it takes 4 min for 90% average consolidation to occur.

(a) From the lab test data, determine cv for the soil.

(b) Compute the pore pressure at depth 18 m before and immediately after the 60 kPa stress is applied.

(c) Compute the total vertical (σ_v) stress at depth 18 m after the 60 kPa stress is applied in the field.

(d) At depth 18 m, compute the effective vertical stress (σ_v) 5 years after the 60 kPa is applied.

Transcribed Image Text:

Lab (double drainage) Field 60 kPa v Granular fill, Y = 19.6 kN/m³ 3 m 2.20 cm Clay, y = 18.6 kN/m³ 20 m Dense glacial till