a closed end into a deep deposit of normally consolidated marine clay. The undrained shearing
strength–depth profile of the clay is shown in Figure 4.42. Determine the depth to which the
pile must be driven to carry the working load with a safety factor of 2.0.
In dealing with problems of this kind it is a good practice to plot the calculated values of
ultimate shaft friction, end bearing and total resistance for various depths of penetration. The
required pile length can then be read off from the graph. This is a convenient procedure for
a marine structure where the piles may have to carry quite a wide range of loading.
Outside perimeter of pile =
Overall base area of pile =From Figure 4.42, at 160 m,
From Figure 4.6a, the adhesion factor, is 1.0 over the full depth.
At 50 m below the sea bed:
Average shearing strength along shaft =
From Figure 4.6b, adhesion factor for L/Bvalue of 50/1.22 = 41 is 1.0.
From equation 4.8, total shaft friction on outside of shaft=From equation 4.4, end-bearing resistance =.Thus total pile resistance = 8.50 MN
At 75 m below the sea bed:
Average shearing strength along shaft =Length factor for L/Bvalue of 61 is 0.9.
Thus total skin friction on outside of shaft =End-bearing resistance =
Thus total pile resistance = 16.77 MN.Similarly the total pile resistances at depths of 100, 125, and 150 m below the sea bed are
26.19, 38.01, and 50.78 MN respectively.
The calculated values of pile resistance are plotted in Figure 4.42, from which it may be
seen that a penetration depth of 113 m is required to develop an ultimate resistance of
32 MN, which is the value required to support a compressive load of 16 MN with a safety
9 120 1.169
1000
1.26 MN
1 0.9 60 3.83 75
1000
15.51 MN
120 60 kN/m^2.
1
29 80 1.169
1000
0.84 MN
1.01.0 40 3.83 50
1000
7.66 MN.
80 40 kN/m^2.
1
2(^) p
cu
vo
260
0.659.81 160
0.25.
1.220^2 1.169 m^2.
1
41.220 3.83 m.Resistance of piles to compressive loads 225