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400 500 009 A B X 0 SCALE 500 1 Tyres с 1 Figure 0.5(a) (Should be submitted with your answer booklet if you answer Q.5)
a Q.5 (a) The design and construction of underground structures such as foundations and tunnels require a detailed geological investigation to be carried out. In a structural geology study, the topographic survey map of a natural terrain is prepared as shown in Figure Q.5(a) on p.12. The geology of the ground consists of three layers of sedimentary rock strata, namely, “A”, “B” and “C”. The outcrops of the layers are plotted on the map as shown. (1) Define the terms strike line and dip angle. (2 marks) (ii) Draw strike lines and dip line for layer “B”. (2 marks) (iii) Find the strike direction, dip direction and dip angle. (6 marks) (iv) Estimate the true thickness of layer “B”. (4 marks) (v) A ground investigation will be carried out in this area. If a drill hole is sunk at location “X”, estimate the depth from the ground surface that layer “B” will be encountered. (3 marks) (vi) Determine which layer is the youngest stratum among the three sedimentary rocks. (2 marks) (Note: Submit Figure 0.5(a) on page 12 for answering this question.) (b) Before an engineer can design a foundation professionally, one must have a reasonably accurate conception of the physical properties and arrangement of the underlying materials. State any six objectives for conducting a site investigation (6 marks)