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At a site in the Christchurch CBD, the standard penetration test (SPT) was performed for the design of shallow foundations. The SPT blow counts are in Table 1 below. The split spoon samples collected from these investigations suggest a relatively uniform layer of clean sand down to a depth of

`8m`

. The energy efficiency of the SPT hammer was measured to be

`75%`

and the water table was found to be

`1m`

below the ground surface. Using the Hatanaka and Uchida (1996) SPT-to-friction angle correlation, provided in the lecture notes and in Figure 1 below, compute the average friction angle for the sand layer. Use this average friction angle to estimate the ultimate bearing capacity of a square

`2\times 2m`

footing embedded to a depth of

`1m`

. Assume the unit weight of soil above

`8m`

is

`20k(N)/(m^(3))`

. Using a strengt reduction factor of 0.5 , calculate the allowable bearing pressure that can be used for design. ( 50 marks) Table 1: Raw SPT N values from borehole BH-1. \table[[Depth (m),0.5,1.0,2.0,3.0,4.0,5.0,6.0,7.0,8.0],[SPT blow count, N,8,9,12,12,14,13,15,15,16]] Figure 1: SPT to friction angle correlation by Hatanaka and Uchida (1996)