Design and Implementation of an Instrumentation Program to Minimize Risk of Damage to a High-Voltage Electrical Ductbank

In the process of replacing a corroding 2.4-meter diameter corrugated metal culvert, the utility contractor determined that the culvert paralleled a high voltage electrical ductbank for a distance of approximately 91.5 meters. The invert of the culvert was on the order of 9.2 to 10.7 meters below and as close as 4.1 meters away from the ductbank. The goal of the instrumentation program developed and described in this paper was to minimize the risks assumed by the owner, design engineer and contractor in pursuing this project by: 1) enabling all parties involved to know the actual movements along the ductbank as they occurred so that construction could be stopped if excessive displacements were observed, thus ensuring protection of the ductbank; and, 2) providing the design engineer with data that would enable back-analysis resulting in reasonable estimates of material properties that could be used for predicting the displacements that might be expected during the next and successive stages of construction. This process was developed with the intention that additional lateral support and soil improvement strategies would be decided upon during the excavation process.