L09-1_d_settlement_calculation

L09-1_d_settlement_calculation - Soil Mechanics CIVL2410 9...

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Soil Mechanics CIVL2410 9. Settlement Calc 1 9. CALCULATION OF SETTLEMENT Contents 1. Settlement of a Single Layer ........................................................................................................ 1 2. Calculation of Stress Changes ..................................................................................................... 5 3. Calculation of Stress Changes ..................................................................................................... 6 a) Stresses due to Circular foundation loads applied at the ground surface. ............................... 7 b) Stresses due to Rectangular foundation loads applied at the ground surface. ........................ 8 9.3.2.1 Calculation of Stress below an interior point of the loaded area. .................................. 9 9.3.2.2 Calculation of stress below a point outside the loaded area. ...................................... 11 c) 9.3.3 Stresses due to foundation loads of arbitrary shape applied at the ground surface. ...13 1. Settlement of a Single Layer The settlement Δ s of a single relatively thin layer, shown in Figure 1, can be calculated once the change in void ratio is known. Figure 1: Settlement of a soil layer For confined compression the horizontal strains are negligible i.e. ε xx = 0, ε yy = 0 and thus: ) 1 ( 1 1 e H e S thus e e H S v zz + - = + - = = = ε The settlement of a thicker layer can be calculated by dividing the layer into a number of sub layers as shown in Figure 2. This is necessary because both the initial and final effective stress vary with depth as do the voids ratio and the OCR. Figure 2: Division of soil layers into sub-layers.
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Soil Mechanics CIVL2410 9. Settlement Calc 2 The settlement of the soil layer is calculated by calculating the settlement of the individual sub- layers and adding them, in doing this it is assumed that the voids ratio and the effective stress are constant throughout the sub-layer and equal to their values at the centre of the sub-layer. ) 2 ( ] 1 [ 1 1 1 + - = = + - = - n i i i n i i i i i e H e S S t Setttlemen Total that so e H e S i layer sub For thus Example - Settlement Calculation A soil deposit, shown in Figure 3 consists of 5 m of gravel overlaying 8 m of clay. Initially the water table is 2 m below the surface of the gravel. Calculate the settlement if the water table rises to the surface of the gravel slowly over a period of time and surface loading induces an increase of total stress of 100 kPa at the point A and 60 kPa at the point B. The preconsolidation pressure at A is 120 kPa, and the deposit is normally consolidated at B. The gravel has a saturated bulk unit weight of 22 kN/m 3 and a dry unit weight of 18 kN/m 3 and is relatively incompressible when compared to the clay. The void ratio of the clay is 0.8 and the skeletal particles have a specific gravity of 2.7. The compression index of the clay is 0.2 and the recompression index is 0.05. In solving this problem it will be assumed that the gravel is far less compressible than the clay
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This note was uploaded on 08/30/2011 for the course CIVL 2410 taught by Professor Dairey during the Three '11 term at University of Sydney.

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L09-1_d_settlement_calculation - Soil Mechanics CIVL2410 9...

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