Study on the Bearing Capacity of Pile Foundation in Khulna Soil

Abstract

Khulna is situated at the southwest region of Bangladesh. Due to the variation of soil profile in different areas, the city area is divided into two zones. Zone-I is situated at the west side of Khulna city which includes the area of Daulatpur, Natun Rastar Mor, Bastuhara, west part of Rayer Mahal, Chak Mathurabad, Khulna University area. While Zone-Il is situated at the east side of Khulna city which includes the area of Khalishpur, east part of Rayer Mahal, Khulna Medical College area, Sonadanga, New Market, Dakbangla, Borobazar, KCC office area, Baniakhamar, Gollamari, Tutpara, Labanchura. In zone-I the sub-soil consists of predominantly silt which is at greater depth than 125 ft. In most areas of this zone the sub-soil is of very soft to soft consistency ranging Nvalue from about 1 to 5 up to about 50 to 70 ft depth. From sub-soil investigation it was not possible to find out the depth of sandy layer because boring was not performed up to this depth. There exists an organic layer which is mainly at depth 15fl to 25 ft in most of the areas. In some places this organic layer exists from top of the existing ground level. Most probably this area was filled up with dumping garbage and organic sold wastes. In zone-I1 the sub-soil consists of predominantly silt up to about 50 ft depth in most areas. The soil is of very soft to soft consistency ranging Nvalue from 1 to 5. Below silt deposit, the soil contains mainly sandy soil. In this zone there exists an organic layer from 10 ft to 20 ft depth in most of the areas of this zone. To find out the suitability of any existing equation with the pile capacity from static load test, ten pile load tests were performed in two zones of the city in which seven load test in zone-I and three in zone-TI. From load tests 9 piles did not show failure point and their maximum settlements were about 16.87 mm. In this case allowable pile capacities were determined from permissible settlement. Among all the equations, only Mayerhof's equation gave the pile capacity at maximum places which is near the value of load test. Other equations gave much higher values than load test values. So no suitable common equation was selected to compare with the pile capacity in both the zones. However, in the south end of zone-I Meyerhof's equation gave close value to pile load test for the four sites in Khulna University area and Mayur Bridge.