A slope has been excavated in clay, with a stormwater pipe located near the cres
ID: 1712298 • Letter: A
Question
A slope has been excavated in clay, with a stormwater pipe located near the crest of the slope as shown in Figure 1. Also shown in Figure 1 is the position of the critical failure surface for the slope when the pipe is full of water, and the groundwater level when the slope was first excavated. The factor of safety (FoS) for the critical failure surface is 1.0 Stormwater pipe (full of water) Clay soil Critical failure surface FoS-1 Initial groundwater level Figure 1 What will be the effect on stability of the following changes to the slope? Provide an explanation for your answers (no calculation is required), describing the change in the forces acting on the slope, the strength of the soil, and the FoS Water leaks from the pipe (Figure 2a) ii. A fill bund is placed at the toe of the slope as shown in Figure 2b. iii. Fill is stockpiled at the crest of the slope as shown in Figure 2c. iv. The pipe is removed by excavating a trench, with the trench then backfilled with gravel (Figure 2d). (15 marks) Leaking water Fill bund Figure 2a Figure 2b Pipe removed and excavated trench backfilled with gravel ck Figure 2c Figure 2dExplanation / Answer
1. If the water leaks from the pipe then definitely the strength of the clay is going to be lower down, causing lowering of FOS, which further causes reduction in the stability of slope.
2. If a fill bund is placed at toe position then there will be increase in resisting force whuch will help to hold tge soil at slope more firmly. FOS will increase. Hence increase in the slope stability will be there.
3. If fill is stokepiled then it will increase the force which triggers the slope failure. FOS will lower down and slope stability will decrease.
4. If the pipe is removed and gravel is filled in the trench then the shear strength of soil will increase, FOS will increase and the slope stability will increase consequently.