Calculation of pile bearing capacity:

Loads:-

(1) Dead load:

Slab weight = (0.25)(25) = 6.25 kN/m2.

Tails weight = (0.08)(25) = 2 kN/m2.

Partition weight = 2 kN/m2.

Total dead load = 10.25 kN/m2.

(2) Live load:

Assume live load (300 kg / m2) = 3 kN/m2.

Imposed load (75 kg / m2) = 0.75 kN/m2.

Total live load = 3.75 kN/m2.

═► Total service load W = 10.25 + 3.75 = 14 kN/m2.

═► Total ultimate load Wu = (1.2)(10.25) + (1.6)(3.75) = 18.3 kN/m2.

Area of basement roof = 4935 m2. No. = 1

Area of ground roof = 4935 m2. No. = 1

Area of typical roof = 2430 m2. No. = 13

═► Total service load of building = (14)(4935 x 2 + 2430 x 13) = 580,440 kN.

= 58,044 Ton

═► Total weight of columns = (1.5)(0.4)(3.2)(25)(16)(8) = 6,144 kN.

= 614.4 Ton

═►Total weight pile cap = (4935)(1.2)(25) = 148,050 kN

= 14,805 Ton

═► Total Service Load of Building Resist by Piles = 734,634 kN

= 73,463.4 Ton

Single Pile Capacity According to Standard Penetration Test:

Length of pile = 23 m

Diameter of pile = 0.6 m

Piles are embedded in layers (2), (3), and (4) according to soil reports

Properties of layers

Layer (2) N = 22, Lb = 10 m (proportion for pile location)

Layer (3) N = 33, Lb = 2 m

Layer (4) N = 49, Lb = 11 m

qu = qb + qs

qu: ultimate bearing capacity of pile.

qb: base bearing capacity of pile.

qs: skin bearing capacity of pile.

qb = 1.4N(Lb/B)Ab (in Ton)

Ab = (0.6)(0.6)(3.14)(0.25)

= 0.2626

Lb = 11 m

B = 0.6 m

qb = 1.4(49)(11/0.6)(0.2826)

= 355.4 Ton

qs = (0.067N)(As) (in Ton) …… (bored pile in sand or silty sand soil)

qs = (0.5N)(As) (in Ton) …… (bored pile in clay or silty clay soil)

Layer (2) N = 22, As = (0.6)(3.14)(10)

= 18.84 m2

═►qs2 = (0.067)(22)(18.84)

= 27.7 Ton

═►qs3 = 62 Ton

═►qs4 = 68 Ton

═►qs = 27.7 + 62 + 68 = 157.7 Ton

═►qu = 355.4 + 157.7 = 513.1 Ton ultimate bearing capacity

According to ASHTO specification minimum S.F = 2.5 for skin resistance

S.F = 4 for base resistance

Use S.F = 3 for skin resistance, and S.F = 4 for base resistance

═► Allowable bearing capacity of single pile becomes

qall = (157.7/3) +(355.4/4) = 141.4 Ton.

Use allowable bearing capacity of pile = 135 Ton

Total allowable bearing capacity of group piles (piled raft foundation) is

qtotal = (E)(qall)(n)

E: is efficiency of group piles

qall: is allowable bearing capacity of single pile

n: is number of piles

According to ASHTO specification E = 0.8

═► 73,463.4 Ton = (0.8)(135 Ton)(n)

═► n = (73463.4/90.45) = 680.22

═► Minimum number of piles required to resist the total load of building is

681 piles

═► Use 688 piles satisfy the uniformly distributed of load under cap of piles.