The Contractor shall carry out an earth resistivity survey on each site and report in writing to the Engineer in accordance with the approved program. The report shall detail the methods and instruments used and the results of the surveys. Based on the results the Contractor shall include in the report his proposals for the resistivity to be used in the design of the earthing system.
The value of resistivity to be used in the design of the earthing system shall be subject to the Engineer's approval.
The surveys shall show the variation of resistivity across the site and with the depth below the site. The Contractor shall consider if there is a need to model the resistivity in two layers and if there is any advantage in the use of long rods. The surveys shall also determine the depth and nature of any underlying rock, which may limit the depth for driving earth rods or if boring will be necessary for installing earth rods.
The weather conditions prior to and at the time of the surveys shall be recorded in the report and an assessment made of the seasonal variations in resistivity based on meteorological data for the area. The program for the project should, as far as possible, time the resistivity surveys to take place during a dry season.
The report should also state if there are any indications that the ground is corrosive to copper or if there is any risk of galvanic corrosion on other metal structures in the neighborhood.
The report shall be approved by the Engineer before proceeding with the design of the earthing system.
The calculations shall be submitted for approval prior to commencing the design of the earthing systems.