Characteristics of Geology in Khulna City Corporation (KCC) Area, Bangladesh

Abstract

This study represents the general characteristics of foundation soil in Khulna City Corporation (KCC) area. The KCC is situated in southwestern part in Bangladesh. Lithologically the area is composed of coarse to very fine silty sand, silt, silty clay, clayey silt and clay in various proportion. The SPT (Standard Penetration Test) value of the investigated area range between 0 and 7 from surface to 8 m deep. Here, the liquid limit and the natural moisture content (NMC) range from 32 to 64%, 27 to 65% respectively. The shear strength of the upper subsoil horizons in the investigated area is low. Low shearing strength in the upper soil horizon is indicative of soil vulnerability to excessive settlement under high load. The cohesive nature of upper soil in the KCC area with high colloidal content, high liquid and plastic limit indicate medium to high sensitivity of the soil to moisture that could not support heavily loaded buildings and structures. The problems can be avoided by considering special type of foundation, increasing the width of basements of structures and granular backfilling. Based on geomorphology, stratigraphic litho-succession, soil types, percentage of sand, silt and clay in the soil, liquid limit, plasticity index, NMC, liquefaction, settlement and SPT zonation, the study area have been classified as lowest for urbanization. Considering the factors of geotechnical parameters for design of structural foundations this zone is rated as severe for shallow foundations without replaced the existing soil by well graded sandy material. It is understood from the investigation that the deep foundation is necessary with sufficient pile length (>35 m) is required to resist heavy structural load.

Keywords: Urban Geology, Khulna City Corporation, Bangladesh