Warta Geologi, Vol. 46, No. 3, December 2020, pp. 186–190

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

Najmiah Rosli, Rosli Saad, Nazrin Rahman, Nur Azwin Ismail*

Geophysics Program, School of Physics, Universiti Sains
Malaysia, 11800 Pulau Pinang, Malaysia

* Corresponding author email address: nurazwin@usm.my

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.

Keywords:
Soft soil, porosity, shear strength, excessive settlement, Nibong Tebal,
SPT

DOI :
https://doi.org/10.7186/wg463202002

ISSN
0126–5539; e-ISSN 2682-7549