294 Pile groups under compressive loading
Layer Depth to centre z (m) z/B (^) z mv(MN/m^2 ) oed (mm)
of layer (m)
1 11.3 2 0.19 0.80174 0.09 50.1
2 15.3 6 0.57 0.51174 0.07 24.8
3 19.3 10 0.95 0.33174 0.05 11.5
4 23.3 14 0.33 0.22174 0.04 6.1
5 27.3 18 0.71 0.15174 0.04 4.2
Total oedometer settlement 96.7
Dividing equivalent raft into four rectangles, each 6.95.25 m. From Figure 5.20 for
L/B 6.9/5.25 1.3, H/B 20/5.25 3.8 and k 1.1, Ipis 0.13. From equation in Figure 5.19:
Settlement at corner of rectangle
Settlement at centre of equivalent raft 4 3.7 14.8 mm
Oedometer settlement for Layer 1
Depth to centre of layer 9.32.0 11.3 mm
From Figure 5.13 with L/B 13.8/10.5 1.3 and z/B 2/10.5 0.19, stress at the centre
of layer 0.8174 kN/m^2. From Figure 5.43 average mvat centre of layer 0.09 MN/m^2.
Therefore
oedometer settlement from equation 5.23 oed
50.1 mm
The oedometer settlements for all five layers are calculated in a similar manner and are
tabulated thus.
0.090.80^174 ^4 ^1000
1000
174 5.250.13^1000
32 1000
3.7 mmFrom Figure 5.23 the depth factor dfor , is 0.78
and for London Clay the geological factor gis about 0.5. Therefore
corrected consolidation settlement c 0.50.7896.7 37.7 mm.
Total settlement of pile group ic 8.837.7 46.5 mm.In practice a settlement between 30 and 60 mm would be expected.Example 5.2
Part of the jetty structure referred to in Example 4.4 carries bulk handling equipment with
a total dead and imposed load of 6 MN. Design a suitable pile group to carry this equipment
and calculate the settlement under the dead and imposed loading.
It has been calculated in Example 4.4 that a 450450 mm precast concrete pile driven
to 7 m below the sea bed could carry a working load of 250 kN in compression with a safety