Soft soils: A study on their electrical resistivity values and geotechnical properties (porosity, SPT and particle size distribution)

Abstract

Soft soils pose abundant engineering issues due to its low bearing capacity and shear strength. Comprehensive study on soft soil’s physical properties such as shear strength and ability to store water (porosity) could help in devising the optimum ground improvements and foundations techniques. Therefore, physical properties of soft marine clay in Nibong Tebal were thoroughly studied using 2-Dimensional Resistivity Imaging (2-DRI) method in conjunction with porosity measurements, standard penetration test values (SPT-n) and particle size distribution (PSD) analysis. The 2-DRI profile depicts three lithologies, which are unsaturated topsoil, saturated soft clayey soil and saturated sandy soil in the area. The soft soil extends up to 32 m in thickness where it overlies the sandy layer and could be correlated back to lithology profile from borehole record. Additionally, soil samples were collected at three locations along the survey line for porosity measurements via saturation porosimetry method. The samples demonstrate that the clay layer has a very large porosity range and signifies that the soil will compress tremendously under load. On the other hand, SPT-N values of the soft clay is also very low; thus, could be classed as very soft to soft cohesive soil with very low shear strength as compared to a higher range SPT-n values of the sandy layer. The PSD result also compliments the 2-DRI, porosity and SPT results to show distinct differences between topsoil and the soft clay layer in terms of the presence of fine grains. These results further indicate that the thick upper layer is not capable of bearing immense loads such as high-rise infrastructures due to the soil’s high porosity and low shear strength. Hence, the area must undergo ground remediations prior to any infrastructure developments on the land.