PENETRATION TEST PARAMETERS AND THEIR CORRELATIONS FOR SOILS FROM SELECTED LOCATIONS OF BANGLADESH

Abstract

Local geological information plays an important role in determining the soil parameters required for designing of foundations. Cone penetration test (CPT) and standard penetration test (SPT) are the most widely used penetration test methods in investigating subsoil condition of a site. Though both the methods, in principles, determines the similar soil parameters and their extent, yet there are marked difference in acquiring the subsoil information. The CPT is a continuous method of penetration using static loading, while SPT is a dynamic and intermittent method of investigation. There are many relations reported by various investigators and they are, however, based on broad qualitative categories of soil. With these concerns, the present study was mainly aimed at finding the relations of the soil parameters obtained from both the investigation methods and engineering soil classes. In total 24 CPT tests were conducted at a site within the proximity SPT borehole’s locations of radial distances of 6 m. Soil profiles were prepared using both CPT and SPT data, and similar types of soil were isolated from all the soil profiles for statistical analysis. If case where no consensus soil profiles were obtained SPT profile was given preference. Five classes of soil were considered for investigation like sand and silty sand (SM), silt of low plasticity (ML), silt of high plasticity (MH), clay of low plasticity (CL) and clay of high plasticity (CH). The analyses indicated that strong linear correlations existed between field SPT N-value, and both CPT cone resistance and sleeve friction for non-plastic silty sand (SM). For nonplastic silt (ML), silt of high plasticity (MH) and clay of low plasticity (CL), moderate linear correlations were obtained. For clay of high plasticity (CH), a moderate linear correlation was observed between field SPT N-value and CPT cone resistance, however, a very weak correlation was found between SPT N-value and CPT sleeve friction. For sandy soil CPT and SPT were found to assess reasonably identical soil profiles. Some deviations were noticed in identifying finer soil layer like silt and clay.