Geotechnical Properties of Gopalganj Sub-soil in Bangladesh

Abstract

Gopalganj town is situated on southern region of Bangladesh which is near to the coastal region. The sub-soil in this region is formed by the alluvial deposits from different rivers. For economical and effective selection and design of foundation, it is very important for geotechnical engineers to go for detailed investigations of geotechnical properties of sub-soil. Some soil samples were collected from Gopalganj town area and tested in the Geotechnical laboratory of Khulna University of Engineering and Technology (KUET), Khulna to determine the geotechnical properties of soil and other data were collected from soil investigation reports prepared by CRTS (Civil), KUET, Khulna. The sub-soil is composed of fine grained soils of soft to medium stiff consistency up to 30 ft depth from the existing ground surface and the soil predominantly consists of course grained soils of medium to very dense compactness below 30 ft depth. For the Gopalganj sub-soil the values of unit weight, specific gravity, natural moisture content, liquid limit, plastic limit, unconfined compressive strength, cohesion, angle of internal friction, compression index and natural void ratio varies from 13.23 kN/m³ to 14.21 kN/m³, 2.68 to 2.73, 32% to 65%, 33% to 60%, 26% to 48%, 5kPa to 90kPa, 0.93kPa to 8.20kPa, 27° to 38°, 0.16 to 1.0 and 0.83 to 2.30 respectively. For the construction of low rise building, shallow foundation may be used with or without replacing the soil layer below the foundation with sand having proper compaction. For medium to high rise buildings, pile or piled raft foundations may be used that penetrate through the soils of very soft to stiff consistency to deeper strata of dense compactness located at 30 to 40ft depth from the ground surface. The results obtained in this study will be useful for those owners who are interested to construct building without soil investigation.