Geophysical investigations were carried out for evaluation of damage
and to assess the possible causes for repeated occurrence of damage at one
of the buildings constructed for oil pumping in the northern part of India.
Electrical Resistivity Tomography (ERT) and Seismic Refraction Tomography
(SRT) techniques were adopted for studying the subsurface of the area around
the building with an objective of ascertaining the cause of damage. High
resolution imaging was done using both the techniques in this investigation.
ERT delineated the presence of low resistivity (2 ohm-m) water filled voids
below the structures and mapped different subsurface layers such as sandy
soil, clay and sandstone in the study area. SRT revealed P-wave velocity ( V
P ) of the subsurface medium in the range of
400–3,400 m/s. Corresponding densities and S-wave velocities ( V
S ) were determined based on Gardner's and
Castagna's relationships. Subsequently, the V P , V
S and the modulus values were used in estimating
compressibility of soil and rock strata. Results showed near surface layers
were characterized by high compressibility (26.673 × 10
−5 Pa −1 ), decreases with
depth. This paper presents the details of the site, techniques used in the
investigation and correlation of geophysical results with lithological
information, and the subsequent analysis for understanding the distress in
the subsurface of the study area.
INSIGHT INTO SEISMIC REFRACTION AND ELECTRICAL RESISTIVITY TOMOGRAPHY TECHNIQUES IN SUBSURFACE INVESTIGATIONS