Tunnel erosion, also known as “Piping”, is the subsurface erosion of soil by percolating waters to produce pipe-like conduits below ground especially in non-lithified earth materials. This is a type of mechanical soil movement where by fine subsurface sediment moves in underground channel ways through permeable materials.
Geophysical investigation: GD-10 Series was utilized in the site for ERT Study. Our team has used total of ‘60’ electrodes at ‘3m’ & ‘1m’ spacing , so, total survey line went up to 180mts & 60mts respectively. GPS co-ordinates are marked on 1, 11,21,31,41,51,60 electrodes to label the electrode position & corresponding elevation. The instrument is placed at the center of the target (above the cavity) to arrive greater depth of penetration. Rg (Grounding Resistance) or ‘earth contact resistance’ was found to be falling between 4 to 9K Ohms, so, it was reduced to 2K Ohms by pouring ‘Salt Water’ Solution into the grounding pits for better penetration. The Survey line is treated with Wenner, Schlumberger & Dipole-Dipole array to study the earth resistivity responses,w.r.t to changing electrode array configuration. The best resultant cross-sectional image is plotted in this report. The data retrieved is stored in GD-10 Series’s mainframe & it was transferred using USB cable to Laptop or PC. The Geomative data format convert software can transform data into ‘RES2DINV ‘and ‘Surfer’ format. Besides, for 1D data, surfer format is available; while for 2D data, not only surfer format but also RES2D is available. Here; measured data is processed using RES2DINV Software.
Conclusion: The 2D Electrical Resistivity Imaging technique gives the ‘pseudo section’ of subsurface resistivity changes in sand pipe , groundwater zone & associated base rock in the study area. The 2D ERI study is useful in estimating the structural features and water flow direction confined to area of study in the best possible way. It acts a best tool for preliminary investigation for understanding the Sub-Soil classification & buried structure. These conclusions are based on resistivity images initially, geological or drilling & further studies were conducted by our clients.