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Foundation Design Building structural system By Dr. Sompote Youwai

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Contents Fundamental of Soil Mechanics Interpretation from Soil Report – Subsurface investigation – Field and laboratory testing Pile Foundation Design – Single Pile – Pile Group Fundamental of retaining structure – Sheet pile – Diaphragm wall

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Additional text book Das M. B., Foundation Engineering. Tomlinson, M. J. Foundation Design & Construction Hunt, Geotechnical Engineering Investigation Handbook. Handout

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Method for Pile Design Hand Calculation Finite Element Analysis

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5 2. Foundations for Signature Towers Dubai 75-F Office 65-F Hotel 55-F Residential Nicknamed “Dancing Towers” Office 351 m, Hotel 305 m, Residential 251 m high Piled raft foundations Bored piles 483 nos., 1.5 m dia, 45 m long Ground conditions: 0-10 m: Sand m: Very/Weak Sandstone m: Very/Weak Siltstone m: Very/Weak Conglomerate >40m: Very/Weak Claystone

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6 Foundation Layout Office (168 nos) Hotel (126 nos) Residenti al (184 nos)

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7 3DF Mesh 505m 590m 150m No of elements = 32,000 Pile rafts 5.5 m thick, located at 10 metre below ground level

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8 3DF Mesh 168 nos. 126 nos. 184 nos. Embedded piles: 1.5 m dia. 45 m long Pile raft Loa d Office Tower Hotel Tower Residential Tower

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9 3DF Outputs Office Tower Hotel Tower Residential Tower Contours of Settlements

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10 3DF Outputs Office Residential Hotel Office Hotel Residential

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11 3DF Outputs Deformations of Office piles Axial forces of Office piles

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Fundamental of Soil Mechanics

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Bangkok Subsoil condition

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Keyword from boring log ST, SS Atterberg’s limits Water content Unit weight Sieve analysis Unconfined shear Standard penetration test

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Soil is generally a three phase material Contains solid particles and voids Voids can contain liquid and gas phases VsVs VwVw VaVa

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Soil is generally a three phase material Contains solid particles and voids Voids can contain liquid and gas phases VsVs VwVw VaVa

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Soil is generally a three phase material Contains solid particles and voids Voids can contain liquid and gas phases VsVs VwVw VaVa

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Units Lengthmetres Masstonnes (1 tonne = 10 3 kg) Densityt/m 3 Weightkilonewtons (kN) Stresskilopascals (kPa) 1 kPa= 1 kN/m 2 Unit weightkN/m 3 AccuracyDensity of water, w = 1 t/m 3 Stress/Strength to 0.1 kPa

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Weight and Unit weight Force due to mass (weight) more important than mass W = M g Unit weight

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Weight and Unit weight Force due to mass (weight) more important than mass W = M g Unit weight = g

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Weight and Unit weight Force due to mass (weight) more important than mass W = M g Unit weight = g vv z v = g z v = z

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Specific Gravity G s 2.65 for most soils G s is useful because it enables the volume of solid particles to be calculated from mass or weight This is defined by

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Moisture Content The moisture content, m, is defined as

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Moisture Content The moisture content, m, is defined as In terms of e, S, G s and w W w = w V w = w e S V s W s = s V s = w G s V s

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Procedure for grain size determination Sieving - used for particles > 75 m Hydrometer test - used for smaller particles –Analysis based on Stoke’s Law, velocity proportional to diameter

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Sieve analysis

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Atterberg Limits Particle size is not that useful for fine grained soils Moisture content versus volume relation during drying

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Liquid Limit – The minimum water content at which the soil can be flow under its own weight Plastic Limit – The minimum water content at which soil can be roller into a thread 3 mm diameter with out breaking up Shrinkage – The maximum water content at which further loss of moisture does not cause a decrease in the volume of soil Atterberg’s Limit

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LL - Liquid limit

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PL – Plastic limit SL – Shrinkage limit

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Atterberg Limits SL - Shrinkage Limit PL - Plastic Limit LL - Liquid limit Plasticity Index = LL - PL = PI or I p Liquidity Index = (m - PL)/I p = LI

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Definition of Grain Size Boulders Cobbles GravelSand Silt and Clay CoarseFineCoarseFineMedium 300 mm 75 mm 19 mm No mm No mm No mm No mm No specific grain size-use Atterberg limits

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Symbols Soil symbols: G: Gravel S: Sand M: Silt C: Clay O: Organic Pt: Peat Liquid limit symbols: H: High LL (LL>50) L: Low LL (LL<50) Gradation symbols: W: Well-graded P: Poorly-graded Example: SW, Well-graded sand SC, Clayey sand SM, Silty sand, MH, Elastic silt

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Plasticity Chart (Holtz and Kovacs, 1981) LL PI HL The A-line generally separates the more claylike materials from silty materials, and the organics from the inorganics. The U-line indicates the upper bound for general soils. Note: If the measured limits of soils are on the left of U-line, they should be rechecked.

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Soil Classification Procedure

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Effective stress theory - Fully Saturated: Sr=100% - = Total stress to boundary - u = pore water pressure -u = Effective stress which is transmitted to the soil structure Bishop (1954): ’ = -u : No change in soil strength if no change in ’. f =c ’ + ’ tan( ’ ) c ’ and ’ are effective cohesion and friction angle of soil. - Fully Saturated: Sr=100% - = Total stress to boundary - u = pore water pressure -u = Effective stress which is transmitted to the soil structure Bishop (1954): ’ = -u : No change in soil strength if no change in ’. f =c ’ + ’ tan( ’ ) c ’ and ’ are effective cohesion and friction angle of soil. - Equilibrium condition - impermeable membrane - Equilibrium condition - impermeable membrane

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m 2m 4m 6m 8m kPa pore water pressure Effective stress Total Stress (5m) Depth

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Stresses acting on a soil element x y z z x

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