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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 10-25 m: Very/Weak Sandstone 25-30 m: Very/Weak Siltstone 30-40 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.4 4.75 mm No.10 2.0 mm No.40 0.425 mm No.200 0.075 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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050100150 0m 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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