Relatively undisturbed soil samples have been retrieved from the clay layers at a proposed project site. The samples were retrieved from a new boring, C-1, drilled as part of the project’s subsurface exploration program.
engineering
Description
Relatively undisturbed soil samples have been retrieved from the clay layers at a proposed project site. The samples were retrieved from a new boring, C-1, drilled as part of the project’s subsurface exploration program. Samples from the clay layers were retrieved from depths of 2.0, 4.4, 9.2, and 14 meters, as shown in Figure 1. The water content of each sample is also shown in Figure 1, along with the depth to groundwater, which is 2 m. Corrected “field” consolidation curves from incremental consolidation tests performed on the three specimens in the grey clay layer are shown in Figure 2 (no consolidation tests were run on the shallower specimen, which was identified in the field as stiff and hence likely highly overconsolidated). Time-settlement plots from various increments of the consolidation tests (not included with this assignment package) indicate that the effective coefficient of consolidation for the gray clay layer is cv = 0.42 m2 /yr. Your job: Evaluate the height of the levee embankment (to the nearest 0.3 m) that will be necessary to satisfy the client’s objective, which is a top-of-embankment elevation of at least +6 m (MSL) after 50 years. Design the levee with a crest width of 4 m, and side slopes of 2:1 (H:V). You will recommend that prior to the construction of the levee, the tan weathered silty clay layer will be excavated to a depth of 0.5 m (i.e., to elevation 1.5 m MSL) to remove organics and surficial disturbed materials so as to provide a firm foundation for the levee. For now, you may assume that the borrow fill will have a total as-compacted unit weight of 18.8 kN/m3 (the basis for this number will be made clear in a subsequent homework).
Hints:
a) Start by computing the saturated density (in kN/m3 ) of the clay at the four sample depths.
b) Compute and plot the initial (prior to embankment construction) distribution with depth of total stress, pore water pressure, and effective stress for the clay layer. Assume that the tan weathered silty clay layer has the same total unit weight above and below the ground water table.
c) Sub-layer the clay layer for consolidation analysis, use the lab data to evaluate representative
values of Cc, Cr, p, 0, and e0 for each sub-layer. For this assignment, 3 sub-layers are
sufficient for the computations.
