Question

1. How much load can safely be carried by a 20 m long, 0.3 x 0.3 m square concrete pile driven in very stiff clay. Address the safe load issue but not the settlement issue. Soil properties: su = 100 kPa, q_c = 5 MPa, f_c = 70 kPa, p_L = 500 kPa, E₀ = 7.5 MPa, C_c = 0.3, c_v = 10-4 cm²/s, γ = 18 kN/m³. If you need additional properties assume reasonable values.

Answer 1

Solution –

Pile driven in clay

Given Data –

Length = 20 m

Cross-section = 0.3 m x 0.3 m

Undrained shear strength (S_u) = 100 kPa

Adhesion factor (α) for stiff clay = 0.3

N_c for clay = 9

Now,

Pile load capacity (Q_u) = point bearing capacity (Q_pu) + frictional capacity (Q_f)

Point bearing capacity (Q_pu) = q_p * A_b

Where,

q_p = S_u * N_c

   = 100 * 9

   = 900 kPa

A_b =area of base

   = 0.3 * 0.3

   = 0.09 m²

Q_pu = 900 * 0.09

               = 81 KN

Frictional capacity (Q_f) = f_s * A_s

Where,

f_s = α * S_u

   = 0.3 * 100

   = 30 kPa

A_s = Area of side

   = 4 * 0.3 *20

   = 24 m²

Q_f = 30 * 24

     = 720 KN

So,

Pile load capacity (Q_u) = 81 + 720

                                             = 801 KN

So, the pile load capacity is 801 KN.