Calculation of Pile Load Capacity in Weathering or Soft Rock
This method of calculating pile load capacity was suggested by Cole & Stroud. Cole & Stroud used the ‘n’ value, or the results of standard penetration tests, to determine the allowable load capacity of piles in weathered rocks.
The formula suggested by Cole & Stroud is given below. in formula, 1scheduled tribe Term end gives bearing resistance and 2Ra The term gives the socketed bond strength between the rock and the pile.
Whya = Allowable load capacity of the pile, kN. In
CU1 = shear strength of the rock below the base of the pile, kN/m. In2, (This is shown in Figure-1 below)
CU 2 = Average shear strength of the rock over the socketed length of the pile, kN/m. In2, (This is shown in Figure-1 below)
nC = bearing capacity factor 9. taken as
Fs = factor of safety usually 3 . is taken as
α = adhesion factor, (recommended value is 0.9)
B = Minimum width of pile shaft (or diameter in case of circular pile) in metres.
L = socket length of the pile, m . In
notes to remember
- A rock is considered a weathering rock or soft rock when the SPT value or N value is greater than 60. If less then it is considered clay.
- If N values are greater than 200, the pile load capacity should be calculated on the basis of shear strength or rock.