2 Capacity of Single Pile Using Theory (c,φ)Using SPT valueUsing SCPT ValueUsing Dynamic FormulaPile Load TestStatic FormulaIn-situ Penetration Tests
3 Dynamic Formula - PRINCIPLE EnergyWorkdoneWhQusW - weight of the driving hammerh height of fall of hammerWh - energy of hammer blowQ - ultimate resistance to penetrationS - pile penetration under one hammer blowQus - resisting energy of the pile
4 Energy used by pile to move down DYNAMIC FORMULAHileys FormulaEngineering NewsEnergy used by pile to move downEnergy lossesEnergy Input
5 Hiley’s FormulaThe energy loss E1 due to the elastic compressions of the pile cap, pile material and the soil surrounding the pileThe energy loss E2 due to the interaction of the pile hammer system
6 Hileys Formula - Energy losses The energy loss E1 due to the elastic compressions of the pile cap, pile material and the soil surrounding the pilec1 = elastic compression of the pile capc2 = elastic compression of the pilec3 = elastic compression of the soil.
7 Hileys Formula - Energy Losses The energy loss E2 due to the interaction of the pile hammer systemWp = weight of pileCr = coefficient of restitution
8 Hileys Formulawhere,ηh – Efficiency of the hammer
9 Hileys Formula Elastic compression c1 of cap and pile head Pile MaterialRange of Driving Stress kg/cm2Range of c1Precast concrete pile with packing inside cap30-150Timber pile without capSteel H-pileElastic compression c2 of pileElastic compression c3 of soilType of soilc3Hard SoilResilient Soil0.2
10 Hileys Formula Efficiency of pile hammer Hammer Type ηh Drop hammer 1.00Single actingDouble acting0.85DieselCoefficient of restitution CrMaterialCrWood pile0.25Compact wood cushion of steel pile0.32Cast iron hammer on concrete pile without cap0.40Cast iron hammer on steel pile without cushion0.55
11 Engineering News Formula W - weight of hammer in kg H - height of fall of hammer in cm s - final penetration in cm per blow (set) C - empirical constantThe set is taken as the average penetration per blow for the last 5 blows of a drop hammer or 20 blows of a steam hammerC = 2.5 cm for a drop hammerC = 0.25 cm for single acting hammer
12 ProblemA 40 x 40 cm reinforced concrete pile 20 m long is driven through loose sand and then into dense gravel to a final set of 3 mm/blow, using a 30 kN single-acting hammer with a stroke of 1.5 m.Determine the ultimate driving resistance of the pile if it is fitted with a helmet, plastic dolly and 50 mm packing on the top of the pile. The weight of the helmet and dolly is 4 kN. The other details are: weight of pile = 74 kN; weight of hammer = 30 kN; pile hammer efficiency ηh = 0.80 and coefficient of restitution Cr =Use the Hiley formula. The sum of the elastic compression C is C = c1 +c2 +c3 = 19.6 mm.
14 Pile Load TestLoad tests may be carried out on a working pile or a test pilePile load tests on a single pile or group of pilesFor the determination ofVertical load bearing capacityUplift load capacityLateral load capacityLoad test may be of two typesContinuous load test.Cyclic load test.
17 Determination of Qu from Load-Settlement Curve Qu, can be determined as the abscissa of the point where the curved part of the load-settlement curve changes to a falling straight lineQu is the abscissa of the point of intersection of the initial and final tangents of the load-settlement curveQa is 50 percent of the ultimate load at which the total settlement amounts to one-tenth of the diameter of the pile for uniform diameter piles.Qa is sometimes taken as equal to two-thirds of the load which causes a total settlement of 12 mmQa is sometimes taken as equal to two-thirds of the load which causes a net (plastic) settlement of 6 mm
18 Recap - Capacity of Single Pile Using Theory (c,φ)Using SPT valueUsing SCPT ValueUsing Dynamic FormulaPile Load TestStatic FormulaIn-situ Penetration Tests
27 Minimum Spacing between Piles Stipulated in building codesFor straight uniform diameter piles - 2 to 6 dFor friction piles – 3dFor end bearing pilespassing through relatively compressible strata, the spacing of piles shall not be less than 2.5dFor end bearing piles passing through compressible strata and resting in stiff clay - 3.5dFor compaction piles - 2d.
29 Efficiency of pile groups in sand (Vesic, 1967) 1. Point efficiency—average of all tests2. 4 pile group—total efficiency3. 9 pile group—total efficiency4. 9 pile group—total efficiency with cap5. 4 pile group—total efficiency with cap6. 4 pile group—skin efficiency7. 9 pile group—skin efficiency
30 CAPACITY OF PILE GROUP Feld’s Rule Converse-Labarre Formula Block failure criteria
31 FELD'S RULEReduces the capacity of each pile by 1/16 for each adjacent pile
32 CONVERSE-LABARRE FORMULA m = number of columns of piles in a group,n = number of rows,θ = tan-1( d/s) in degrees,d = diameter of pile,s = spacing of piles center to center.
33 PILE GROUP Driven piles Bored piles Pile group in sandy soil Pile group in clayey soil
34 Block Failure c = cohesive strength of clay beneath the pile group, L = length of pile,Pg = perimeter of pile group,A g= sectional area of group,Nc = bearing capacity factor which may be assumed as 9 for deep foundations.
35 RecapCapacity of single pileCapacity of pile group