Lest check Bearing Capacity for a rectangular foundation first Assume 2m x 3m

Lest check bearing capacity for a rectangular

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Lest check Bearing Capacity for a rectangular foundation first Assume 2m x 3m rectangular footing B=2m L=3m We are assuming the depth of footing D f =2m inorder to pass soft Organic top soil qu = cNc ( 1 + 0.3 B L ) + γDfNq + 1 2 γBNγ ( 1 0.2 B L ) Eq.134 C: Cohesion from laboratory testing (0,93kg/cm3) : 91,22 kN/m2 ? : unit weight of soil at foundation level from laboratory test : 20.11 kN/m N c , N q and N ɣ are the bearing capacity factors. They are functions of the angle of friction 𝝓. Figure 215 Hawever Before that we need to get Anfle of Shear Resistance 186
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Figure 216 We can get the blow N number from SPT log which is 14 Figure 217 Figure 218 N c (38) , N q (25) and N ɣ (25) qu = cNc ( 1 + 0.3 B L ) + γDfNq + 1 2 γBNγ ( 1 0.2 B L ) qu = 91.22 38 ( 1 + 0.3 2 3 ) + 20.11 2 25 + 1 2 20.11 25 ( 1 0.2 3 2 ) qu = 5382.13 kN m 2 qnu = 5382.13 γDf ( 20.11 2 ) = 5341.91 kN m 2 qna = 5341.91 3 = 1780 kN m 2 q = Fd + Wf A γDf Eq. 135 q = Structural Loading G = 4190.15 Tn = 41750.72 kN (From Static Calculations) Q = 948.86 Tn = 9454.45 kN Fd = 1.4G + 1.6Q = 58451 + 15127 = 73578 kN A = Area under the foundation(2*3) 6 m 2 187
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? D f = 21.11*2 = 42.22 kN/m 2 W f = (B*L*D* ? con ) = 2*3*2*23.6 = 319.2 kN (unit weight of concrete = 23.6 kN/m 3 ) q = (73578 + 319.2)/6 - 42.22 = 12273 kN/m 2 qna ( 1780 kN/m 2 ) < q (12273 kN/m 2 ) NOT ACCEPTABLE !!! 11.11 TRY RAFT FOUNDATION We used modifide equation of Meyerhof (1963) qn ( u ) = cu c Fcs Fcd ¿ { cu Nc | 1 + B L ( Nq Nc ) | | 1 + 0.4 ( Df B ) | } Eq. 136 qn ( a ) = { cu Nc | 1 B L ( Nq Nc ) | | 1 + 0.4 ( Df B ) | } Fs Eq. 137 Where q n(U) = net ultimate bearing capacity q n(a) = net allowable bearing capacity c u = undrained cohesion N c ,N q = bearing capacity factors with respect to cohesion and surcharge respectively 188
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F cs = shape factor with to cohesion F cd = shape factor with respect to depth B,L = breadth and length of foundation respectively D f = depth of foundation FS = factor of safety From Structural Engineers Suggestions we use; Df : 1,5m B : 14m L : 28m Cu : 91,22 kN/m2 Nc (38) , Nq(25) and Nɣ (25) qnu = 91.22 38 [ 1 + 14 28 ( 25 38 ) ] [ 1 + 0.4 ( 1.5 14 ) ] = 4804 kN m 2 qna = 4804 3 = 1600 kN m 2 q = Fd + Wf A γDf q = Structural Loading G = 4190.15 Tn = 41750.72 kN (From Static Calculations) Q = 948.86 Tn = 9454.45 kN Fd = 1.4G + 1.6Q = 58451 + 15127 = 73578 kN A = Area under the foundation(14.71*28) 411 m 2 ? D f = 21.11*2 = 42.22 kN/m 2 189
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W f = (B*L*D* ? con ) = 14*28*1.5*23.6 = 14580 kN (unit weight of concrete = 23.6 kN/m 3 ) q = (73578 + 14580)/411 - 42.22 = 172 kN/m 2 qna ( 1600 kN/m 2 ) > q (172 kN/m 2 ) NOT ACCEPTABLE !!! 11.12 SETTLEMENT 11.12.1 Elastic Settlement (Si) Jambu. Bjerrum and Kjaernslı formulation for unitial settlement Se = qo ( α B ' ) ( 1 μs 2 ) Es IsIf Eq. 138 q o = qn from raft foundation bearing capacity calculation = 172 kN/m 2 α = 4 for the centre of the foundation B’ = B/2 for the centre of foundation = 14/2 = 7m µ s = 0,3 poisons ratio E s : Elastic modulus Butler and Bjerrum relationship for consolidated clays : Es/Cu = 400 E s = 400 x 91,22 = 36488 kN/m 2 For example ; 190
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If = 0.97 Df/B = 1.5/14 = 0.11 L/B = 28/14 = 2 Figure 219 m ' = L B = 28 4 = 2 n ' = H B 2 = 2 14 2 = 0.28 F 1 = 0.022 F2 = 0.060 Is = F 1 + 1 2 μs 1 μs F 2 Eq. 139 Is = 0.022 + 1 2 0.3 1 0.3 0.060 = 0.056 Se = 172 4 14 2 1 0.3 2 36488 0.056 0.97 = 0.006 m = 6 mm 11.12.2 Consolidation Settlement (Sc) Sc = mv Δσ ' H Eq. 140 191
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Mv = 1 1 + e 0 ( e 0 e 1 ) σ 1 σ 0 Eq. 141 Mv = 1 1 + e 0 ( e 0 e 1 ) σ 1 σ 0 = 1 1 + 0.79 0.79 0.59 294 29 = 4.2 10 4 m 2 kN = 0.42 m 2 MN Şekil 220 H= 2m settlement will occur in that layer from log Figure 221 192
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Figure 222 m = 2 m mz = 14/2 = 7 m = 3.5 nz = 7/2 = 3.5 n = 1.75 I r = 0.23 ?? ' 0 = 4*0.23*172 = 158.24 kN/m 2 S c = 0.42*158.24*2 = 132 mm (Eq.140) Total Settlement ST = S e + S c = 132+6 = 138 mm 193
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CHAPTER 12 PILE FOUNDATIONS 12.1 OUTLINE of LECTURES Pile Types Selection Capacity of Single Piles Capacity of Pile Groups Settlement Considerations 12.2 LOAD/SETTLEMENT RESPONSE
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