Foundation Design Building structural system By Dr. Sompote Youwai

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

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

Method for Pile Design Hand Calculation Finite Element Analysis

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

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

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

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

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

10 3DF Outputs Office Residential Hotel Office Hotel Residential

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

Fundamental of Soil Mechanics

Bangkok Subsoil condition

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

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

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

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

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

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

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

Weight and Unit weight Force due to mass (weight) more important than mass W = M g Unit weight  =  g vv z  v =  g z  v =  z

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

Moisture Content The moisture content, m, is defined as

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

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

Sieve analysis

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

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

LL - Liquid limit

PL – Plastic limit SL – Shrinkage limit

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

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

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

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.

Soil Classification Procedure

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

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

Stresses acting on a soil element x y z z x