Question 1. The soil profile of a site consists of 18m of sand (γ=18kN/m3, E'0=70MPa) underlain by incompressible bedrock. Figure 1a shows the plan view of a proposed new building (solid line) with an adjacent car park (dashed line). The new building and car park will be founded at a depth of 2m, following excavation of the sand. The building will exert 150kPa on the remainder of the soil profile, but the car park will exert no load.
a) Use the Newmark chart of Figure 1b to estimate the change in vertical stress in the sand below points A and B of the building and car park. As this will vary with depth, consider that the sand is split in three different layers as shown in Figure 1a, and estimate the change in vertical stress at the middle of the layers you need to consider.
b) Estimate the final settlement below points A and B of the building and car park. In your calculations you should account for the decrease in vertical stress that excavation will cause. Also, you should consider the loads to apply on the surface of the FINAL soil profile, after excavation has taken place. You should use as many copies of Figure 1b as you need and hand them in as part of your answer.
Figure 1a: Plan view of proposed new building and car park (left) and proposed subdivision of the site's soil profile (right).
Figure 1b: Newmark chart with 200 elements.
Question 2. Figure 2 shows a cross-section of a dam founded on clay (k = 10-8 m/sec) underlain by impermeable bedrock. The depth of the reservoir behind the dam is 35m, while the depth of the river in front of the dam is 7m. As shown in Figure 2, a vertical, impermeable grout curtain has been constructed under the toe of the dam.
Assuming that the water level in the reservoir and the river is constant, use a carefully sketchedflownet to estimate the amount of water lost from the reservoir due to seepage, permetre length of the dam. Sketch your flownet on Figure 2 and hand it in as part of your answer. Assume γw = 10kN/m3.
Question 3 A rectangular footing 2m x 5m is to be founded at 3m depth, in a very thick layer of soil. Calculate the maximum vertical force that the footing can carry in each of the following cases.
a) The soil is sand with friction angle 280 and unit weight 18kN/m3. Groundwater level is well below the foundation level and the sand can be considered dry.
b) The soil is clay with uniform undrained shear strength of 70kPa and unit weight 20kN/m3.
Figure 2: Cross-section through a dam.