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if the project has already started and you knew exactly where the underground cables will run, i suggest that you measure the actual length of the proposed run. then take the depth of the excavation including the sub-base from the electrical detail plan as well as the width of the trench. normally, when i do this especially for excavation deeper than1 meter (others do this at2 meters deep), i always make sure to include a degree cut allowance from the two vertical sides of the trench for soil erosion if it not made of hard-compact soil. then, getting the total volume by multiplying the total length x height x average width. if the soil is made of hard material, then it is just a matter of multiplying the total length x height x width....calculation of rates depends on your total equipment hours x hourly rate plus your total man-hours x their hourly rates excluding those of the equipment operator if they were already included in the rental rate of the equipment assuming of course that they were rented. if this is for tendering purposes, measure the total length of the trench as shown on the plan x depth as shown on the detail section of the cable trench x average width as explained above. equipment rate will be your calculation of time based on the known capacity of the equipment multiplied by the rental rate per hour, rate of the operator included.
multiply length x tickness x height
