week 8 tut solution

# week 8 tut solution - Answers to Tutorial questions(Class 8...

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Answers to Tutorial questions (Class 8) 2.1 As shown in the sketch, a group of seven piles is arranged in a circle. All the piles are floating concrete piles with a diameter of 1.2m and cast in place with 12 meters imbedded into sand. No water exists within the layer. The sand has a total weight of 20 kN/m 3 . Suppose the efficiency of the pile group is 75%, determine the bearing capacity of the pile group. The results of standard penetration tests on the sand are listed below. Using the empirical expression N 2 f s = and kPa 400N D L 0N 4 f b = for the estimation of the bearing capacity of the pile group in sand. D g = 8m Results of standard penetration tests Soil depth z (m) 0.2 3 6 8 11.5 N Standard penetration resist. 8 15 18 20 23 Answer (Step 1) The efficiency of a pile group (e pg ) is given by pile single a of capacity bearing pile per capacity bearing Average e pg = Therefore the bearing capacity of a pile group can be described P u,g =n*e pg *P u (1) (Step 2) The bearing capacity of a single pile can be worked out by P u =P s +P b -W Considering that the effect of pile weight and that of the overburden pressure for the base resistance can be balanced, then P u =f s A s +f b A b (Step 3) The soil is sand and drained analysis is used. Parameter f s and f b are determined from standard penetration resistance. (Step 4) Find out P s The average standard penetration resistance along the pile shaft N ave =(8+15+17+20+23)/5=17 f s,ave =2N ave = 34 kPa P s =f s,ave π DL =34*3*1.2*12 =490 kN (Step 5) Find out f b A b The standard penetration resistance at the base N=23 kPa, L/D=10 f b =400N =400*23=9200 kN/m 2 f b A b =f b π (D/2) 2

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=9200*3*(1.2/2) 2 =9900 kN (Step 6)
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week 8 tut solution - Answers to Tutorial questions(Class 8...

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