SOIL STRENGTH ESTIMATION USING SCREW DRIVING SOUNDING TECHNIQUE FOR BANGKOK CLAY LAYERS

: The Screw Driving Sounding (SDS) test is an improvised and modified version of the Swedish Weight sounding (SWS) test. It is an emerging technique for in-situ field characterization used to estimate strength parameters from field tests directly, rather than by obtaining samples from the field and performing laboratory tests. For this research, several boreholes with standard penetration tests (SPTs) were conducted in the central region of Bangkok. SDS tests and field vane shear tests were performed in the vicinity of these boreholes. The undrained shear strengths from these tests were correlated separately to the SDS torque for marine and intertidal clay deposits. These equations differed slightly due to the difference in the shearing during failure of soil. These empirical equations are supported by an analytical equation that is derived based on the shearing mechanism of soil when the SDS screw head is penetrated into the soil. The correlation to estimate the SPT N was developed for stiff and hard alluvium clay, and compared with the equation from past research. Plots of SDS penetration energy with the consistency index showed that the clays could be clustered as two distinct groups based on their state and consistency. The SDS penetration resistance parameters were extremely affected by differences in the state of clay, which depended on the soil’s depositional history and depositional environment. The past researches were mainly empirical and dealt with sand or Japanese clay, formed in different depositional environment. Those equations do not give reliable results when applied directly to Bangkok clay. Hence, from this research, the undrained shear strength of soft clay and SPT N of stiff clay of the Bangkok deposit can be estimated directly from the equations.