Question

An extensive filling project to form a platform for a subdivision housing development is proposed. Preliminary data based on several site investigation boreholes suggests that the geology of the proposed site is as shown in Figure 1, which implies the fill will be placed over a swampy area of soft saturated normally consolidated clay overlaying a bed of relatively incompressible well-drained dense sand. The water table in the clay layer is at the surface of the clay layer, and it can be assumed that the entire fill layer will remain dry after the platform construction due to a good provision of drainage measures. In order to provide information for analysis, two piezometers have already been installed at different levels in the clay layer (refer to Figure 1). You can assume g equal to 10 m/sec2.

▼ Proposed Final Fill Level Proposed Gravelly Fill (Pay #1 800 kg/m3) 3.5m 1 Original Ground Level 2m 4.5m Saturated Soft Clay (Psat 1900 kg/m3) 2m Dense Sand Figure 1 - Geostratigraphy and additional information of the site

Assume coefficient of consolidation (Cv) = 0.0119 m2/day and coefficient of compressibility mv = 0.00043 m2/kN.

a).What are the pore water pressure measurements that you would expect to record at the upper and lower piezometers (Figure 1) prior to the proposed filling?

b). Based on the information given, estimate the magnitude of the final ground settlement that would result from the filling.

c).Houses on shallow footings will be built after the completion of the platform, and the relevant building code suggests that they should not be built on a ground surface that could be subject to a settlement in excess of 50 mm. In order to meet this requirement, estimate how many months after the completion of filling one has to wait before any houses can be built on the platform.

d). At the above time as estimated in (c), what are the pore water pressure measurements you would expect to observe at the upper and lower piezometers?

Answer 1

Fll clou ina gseund b) final-一ground Settlement --H mo DO

23 cm 230mm 三50m Su 23omm to wcit fox Settement r (S wight eFill CS" 230-50 230 p.26- > 601 0 9332 lop (1-18.2 2

Condition O. O 642.0d exces pox waka p Us 03s or overall la 63-64 x (63-0) = &.ig kN'нґ

0.47 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0. 0.9 1.0 0.87 Consolidation ratio, U

Same fo both Louwe