Factors Influencing Subsurface Resistivity Variation in Gradually Expanding Subsurface Cavity Areas(Thai)

Abstract

A two-dimensional resistivity survey for mapping and monitoring subsurface cavity expansion was conducted to determine physical and geological factors that could cause lateral and vertical resistivity variations. Seven repeated measurements of 2D apparent resistivity data were acquired at different times from 2002-2006. The length of the 2D resistivity survey line was 380 meters and was located nearly across the sinkhole surface location at Ban Bo Dang, Amphoe Ban Muang, Changwat Sakon Nakorn. Results from the four-year measurements of subsurface cavity expansion revealed that (1) the means of seven repeated data could be divided into two groups by using the Krustal-Wallis test (∝ = 0.05). Group I has four repeated data and they were measured while the sinkhole was filled with water whereas Group II has three repeated data and they were measured while the sinkhole was filled with air. Thus water in the cavity is a major significant factor causing vertical and lateral apparent resistivity variations. Gradual increase of cavity diameter together with nearsurface soil collapsing into the cavity appear to be insignificant factors causing vertical and lateral apparent resistivity variations. (2) Dissolution of rock salt from a bowl shape located underneath the sinkhole location appears to correspond to the expansion of sinkhole diameter and the sinkhole will continue to collapse.