Integrated Study of Geotechnical and Geophysical Methods to Assess the Soil Corrosion Potential for Construction Site

Abstract

Corrosion of subsurface steel structures is very critical issue especially in moisture subsoil. The use of physiochemical properties such as pH, salts concentration, electrical resistivity is very common to quantify corrosive nature of subsoil. However, the laboratory measurements of these parameters are quite difficult due to time and budget constraints. In this work soil corrosion potential of a power plant site was evaluated using geophysical and geotechnical investigations. Soil samples were collected from 15 boreholes drilled up-to 50 m depth for laboratory testing whereas 3 probes of four electrodes vertical electrical sounding (VES) using Wenner configuration were also performed to measure the electrical resistivity of the subsurface soil up to 50 m depth. According to the USCS soil system silty clay (CL-ML) was interpreted as dominant material in all boreholes as shallow depth. Poorly graded sand (SP) including silt (SM) was found of variable depth in almost each borehole. The true resistivity values at the depth of 30 meters lies between the 19.9 ohm- meters to 59.8-ohm meters. All observation points of electrical resistivity survey VES-I, VES-II and VES-III near-surface material show moderate soil corrosion potential which is favorable for design of earthing. Up to depth of 4 m, the values of resistivity 52.6 to 59.8 ohm-meters shows adequate estimation of corrosion. According to the International standard these curves belong to bell type or K type curve of resistivity model. Their resistivity values with respect to depth show low to moderate corrosion potential which is satisfactory for construction at this depth after applying the nominal cathodic protections. Thus, electric pipe lines may be installed at this depth.