Lec4_Piled Raft

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20-Oct-15 Realistic estimation of subgrade modulus: ‣ Estimate settlements considering all soil layers upto 1.5 times the actual raft width. ‣ Calculate the k value as ratio of actual bearing on the raft to the calculated settlement. ‣ Structural designer to use this value for structural design of the raft. Prof. V.S.Raju Consultants 15 Structural analysis of the <strong>Piled</strong> <strong>Raft</strong>: Pile Spring (Ps) upto 4 to 6 cm settlement, Ps = (P u / 4 to 6) in kg/cm. If the settlements exceeds 4 to 6 cm, replace springs with Pu. Prof. V.S.Raju Consultants 16 V.S.Raju Consultants 8
20-Oct-15 Drawbacks of Current Practice: ‣ In a plate load test, dimensions of the plate are much smaller than actual raft size. ‣ Hence k value obtained from plate load test does not take into account settlement contribution of all the soil layers upto 1.5 times width of the raft. ‣ This may lead to over estimation of subgrade modulus leading to under-design of the raft (unsafe). ‣ For eg. for a raft size 30 x 60 m, thickness = 2.5 m, analysis was done for 2 cases with k = 1 kg/cm 3 and k = 0.5 kg/cm 3 . In the 2 nd case, moments were higher by 20%, resulting in 20% higher reinforcement steel or 10% thicker raft. Prof. V.S.Raju Consultants 17 Predicting the Settlements on cohesionless soils S = Settlement S = H ∆σ z Es H = Thickness of the layer ∆σ z = Pressure increase @ middle of the layer (obtained Es = Soil Modulus from stress distribution curves) Es is determined by correlating (a) (b) (c) With SPT N value Static cone penetration value Footing / Plate load test (at shallow depth only) Prof. V.S.Raju Consultants 18 V.S.Raju Consultants 9
Page 1 and 2: 20-Oct-15 PILED RAFT by Prof. V.S.R
Page 3 and 4: Load (t) 20-Oct-15 Raft Piles Settl
Page 5 and 6: 20-Oct-15 Steps involved in Piled R
Page 7: 20-Oct-15 Zone of Influence Prof. V
Page 11 and 12: 20-Oct-15 Predicting the settlement
Page 13 and 14: Settlement (mm) 20-Oct-15 Results f
Page 15 and 16: 20-Oct-15 Structure Forum(Kastor Ta
Page 17 and 18: 20-Oct-15 We need number of settlem
Page 19 and 20: 20-Oct-15 PROJECTS NEAR DELHI: Sect
Page 21: 20-Oct-15 Katzenbach R, Arslan V a

Lec4_Piled Raft

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