NAME_________ ID Number ____________ 7) Bearing capacity Estimate the bearing capacity when the ground conditions are as follows

NAME_________ ID Number ____________

7) Bearing capacity

Estimate the bearing capacity when the ground conditions are as follows. Is the bearing capacity sufficient?

(Estimate the volume of the Brodie tower using the breadth, length, and height obtained from the Field

Survey. Assume that the unit weight of concrete ( ) is 25 , and that 10% of the total volume

of the building is the concrete volume). [10/100 Marks]

Figure 3 Ground condition 2

8) Groundwater conditions

Estimate the bearing capacity for each case when the groundwater level is as follows.

[8/100 Marks]

Figure 4 Ground condition 3

9) How does groundwater level affect bearing capacity? In Case 1, suggest through references what method you can apply to reduce the groundwater level during construction (maximum: 500 words).

Rotational slips in drained soil the method of slices

In this method, the potential failure surface, in section, is again assumed to be a circular arc with centre O and radius r. The soil mass (ABCD) above a trial failure surface (AC) is divided by vertical planes into a series of slices of width b, as shown in Figure 1. The base of each slice is assumed

to be a straight line. For the i- height, measured on the centre-line, is hi. The analysis is based on the use of factor of safety (F ), defi f mob) which must be mobilised to maintain a condition of limiting equilibrium along the slip surface, i.e.

(1)

Figure 1 The method of slices.

The factor of safety is taken to be the same for each slice, implying that there must be mutual

support between slices, i.e. inter-slice forces must act between the slices (E1, X1, E2 and X2 in

Figure 1). The forces (per unit dimension normal to the section) acting on a slice are:

1 the total weight of the slice, Wi i sat where appropriate);

2 the total normal force on the base, Ni ili) in general this force has two

components, the effective normal force N i (equal to ili) and the boundary pore water force Ui (equal to uili), where ui is the pore water pressure at the centre of the base and li

the length of the base;

3 the shear force on the base, Ti = Tmobli;

4 the total normal forces on the sides, E1 and E2;

5 the shear forces on the sides, X1 and X2.

Any external forces (e.g. surcharge, pinning forces from inclusions) must also be included in the analysis.