A preliminary study of continuous discharge flow from horizontal drains using 3-dimensional resistivity model

A massive slope failure occurred on the 22^nd March 2007 after 3 days of continuous rainfall at Precinct 9, Putrajaya, Malaysia. Back analysis carried out identified that the main cause of failure is due to the existing high groundwater level within the cut slope. It is also observed that the continuous discharge from the horizontal drains yield approximately 100 ml/s even during dry season. Thus, it is suspected that the main contribution to the high groundwater level is due to the leakage from the large water tank constructed on the crest of the slope. Electrical resistivity survey was adopted to facilitate the investigation for the source of high groundwater level within the slope. A 3-dimensional resistivity model was developed using the Inverse Distance Weighting (IDW) interpolation method. The 3D resistivity model shows that the high water content zone is not caused by the leakage of water tank but is originated from an unknown source at the south-east side of the slope.