Resistivity tomography as an aid to planning gas‐pipeline construction, Risha area, north‐east Jordan

Two‐dimensional (2D) electrical resistivity tomography measurements were conducted with the Iris Syscal R2 resistivity instrument to map the ground resistivity in advance of gas‐pipeline construction in the Risha area, north‐east Jordan. The cost of pipeline construction is strongly dependent on the ground conditions encountered. Accurate prediction of these conditions can reduce the planning risk considerably. The determination of ground conditions reduced the time and cost associated with gaining land access and permission for trenching. It is also served to detect areas of high ground conductivity due to clays or saline soils, which can create conditions in which pipeline corrosion is accelerated. Resistivity measurements were carried out utilizing a Wenner‐array with 1‐m electrode spacing along approximately 52 km of the proposed gas‐pipeline lane. The survey took six days to complete, providing a map of the resistivity of the surficial deposits and the bedrock. The results obtained, based on 2D inversion of field data and borehole information, were interpreted to determine the extent of shallow bedrock, which would require blasting, and deeper overburden, which could be trenched down to the depth necessary for the pipeline. The thickness of the overburden layer along the gas‐pipeline lane in the north‐eastern Jordanian plateau was found to be relatively thin: in the range 0.5– 8 m. The largest values are observed over topographic lows because of the tectonic uplift of the area which leads to fast erosion. Correlation between the field results obtained shows that the overburden depth is the main factor controlling the electrical resistivity of the near‐surface material.