NATURE OF PROJECT: GEOPHYSICAL SURVEY
DURATION: 1 MONTH
LOCATION: PETALING JAYA, SELANGOR
INTRODUCTION
Three method of geophysical survey (Ground Penetrating Radar, Electrical Resistivity Tomography and Induced Polarization surveys) on New Pantai Expressway (NPE). The purpose of this survey works is to map-out the subsurface information and identify the possibility of any voids that may had triggered the subsidence on the highway road. Fieldworks were carried out between 27th May to 28th May 2020.
Figure 1: Eight (8) lines of ground penetration radar survey conducted within the study area
Figure 2: Two (2) lines of electrical resistivity tomography and induced polarization survey conducted within the study area
RESULT AND DISCUSSION
Based on the GPR image, all the image shows some underground utility cables near the surface. There are also anomalies detected near the settlement which may interpreted as subsidence. However, the features of the subsidence cannot be seen clearly in the GPR data due to the limitation of the GPR survey which is very sensitive with water and water saturated zone.
The resistivity and IP surveys were conducted in order to proof the GPR result since there are some limitations in GPR survey in which they are very sensitive to water. The resistivity survey can see the water or wet condition in clearer image.
Based on the 2D resistivity and IP results, there is a subsidence which may be filled with clay due to the low resistivity but high chargeability values.
Observations made from the GPR, resistivity and induced polarization tests indicated cavities present at 3.1 m depths below the road surface. The voids measuring 800 mm diameter and 13 m length is probably a broken utilities pipe and settlement very likely is due to migrations of fines into the voids.
Figure 3: 2D image of ground penetration radar result for Line NPE 3
Figure 4: 2D image of electrical resistivity tomography and induced polarization results for Line NPE R1
