Apply cross-borehole resistivity tomography and 2D resistivity technique with Geomative (GD-10) resistivity instrument for:
1. to determine the existing of abandon tunnel under express way foundation.
2. to locate the position and depth of tunnel for design of Saraburi-Nakorn Ratch asima express way foundation.
Location of line survey for 2D and borehole for cross-borehole measurement
It may follows previous study cases of cavity in Limestone with similar resistivity measurement. Cavities can be grouped into three conditions as following types.
1. Empty Cavity (filled with air) : very high resistivity >1000 Ωm)
2. Cavity filled with water : low resistivity (≈30-100 Ωm)
3. Cavity filled with clay/soil very low resistivity (<20 Ωm)
2D Resistivity Imaging
Multi-electrode (60) with electrode spacing of 2.5 m for target depth > 20 m;
Interpretation of2D resistivity imaging：
Tunnel found at depth of 10-15mb