Task
Component B1 – Site investigation design problem (1000 words)
A geotechnical investigation report for a proposed building is on blackboard under the coursework material folder. Produce a detailed critique of the geotechnical investigation report following the recommendation of the code of practice for ground investigations as outlined in BS 5930:2015+A1:2020 and other relevant materials.
Component B2 – Embankment design problem (1000 words)
A slope can be a natural slope or one created by excavation or an embankment created by engineering fill. Slope stability is the potential of a naturally occurring or engineered soil slope such as embankment slopes, cuttings, excavations to withstand ground movement. Geotechnical engineers have to pay particular attention to geology, surface drainage, groundwater, and the shear strength of soils in assessing slope stability however, a previously stable slope may become unstable, leading to a mass movement due to increase in shear stress or decrease in shear strength.
(a) Write a review on ten (10) case histories of recent slope failures and summarise your findings using table, stating the case and the cause of failure.
(b) An embankment slope consisting of a granular fill is underlain by a deep deposit of clay of specific gravity of 2.65. The granular fill has a bulk unit weight of 19.3 kN/m3, effective cohesion, c′ = 7.2 kPa and internal friction angle, φ′ = 30°.
If the clay soil has varying moisture content and undrained shear strength at different times of the year as presented in Table 1, investigate the stability of the embankment slope using the slip circle shown in Figure 1. How does the varying soil properties influence the stability of the slope? Draw the slope to scale on a graph paper or using CAD and split the sliding section up into a suitable number of slices.
Table 1. Properties of clay
Property Values
Moisture content (%) 27 30 35 40
Void ratio 0.71 0.55 0.5 0.48
Undrained shear strength
(kPa)
32.5 28 20 18
(c) Assume that the ground water level is located at the top of the clay layer in Figure 1, and the clay layer has c’ = 75kPa, ø’=7o, γ = 19kN/m3, calculate the factor of safety, and compare with the values calculated in (b) above.
