ENG 464 Assignment 2 1 ENG464 Geotechnical Engineering Assignment 2 Analysis of group-pile foundations A pile group consisting of 8 x 8 cylindrical bored and cast in situ piles at 2.4 m centres, each with a diameter of 600 mm and extending from 3 m depth to 18 m depth is constructed in a 28 m deep stratum of stiff clay overlying bedrock. The undrained shear strength of the clay at a depth of 18 m is 120 kPa and an average value over the length of the piles is 60 kPa. The undrained elastic modulus Eu of the clay is approximately 25 MPa. (a) If the pile group supports a fully-factored load of 30 MN, determine the global factor of safety. (19) (b) Estimate the immediate pile head settlement and comment upon the practical effects of its magnitude and likely accuracy. (6) Coefficients for vertical displacement are given below in Figure 1. Christian J.T. & Carrier W.D. (1978) Janbu, Bjerrum and Kjærnsli's chart reinterpreted. Canadian Geotech. J. 15(1) 123-128. Janbu N., Bjerrum L. & Kjærnsli B. (1956) Veiledning ved løsning av fundamenteringsoppgaver. (Soil mechanics applied to some engineering problems), Norwegian Geotech. Inst. Publ. 16, Oslo, Norway. Figure 1 Coefficients for vertical displacement (Total marks 25)ENG 464 Assignment 2 2 The small print This is not a task which can be completed simply by looking at the InterNet. Original thinking is required, demonstrating sound reasoning and rational argument (including diagrams, calculations, and spreadsheets developed as appropriate) to support your conclusions. Students' attention is drawn to the University's policy on plagiarism. The report must be set out as a formal technical submission/calculation sheet. This report is worth 10 % of the marks for this unit. Submissions are due by 1630 (ACST) on the Thursday of Week 7 (see Learnline for details).