How to Determine Elevations and Excavation Depths with A Transit Level 3

Determining Foundation Excavation Depths

The transit level can be used to determine the correct excavation depth for a building's foundation. Grade stakes are driven into the ground at 3 to 5 metre intervals around the boundary of the proposed excavation. The elevation at the top of each grade stake is established and elevation at the bottom of the excavation is calculated in relation to the benchmark. The excavation elevation is then subtracted from the elevation at the top of each stake to determine how much to cut or fill. Positive answers mean the excavation has to be dug out or cut and negative answers mean fill has to be added to raise the excavation. For example, if the elevation of a stake is 102.652 M and the elevation of the excavation is 97 M, the amount to be cut will be 102.652 M - 97 M = (+) 5.652 M. If the elevation of another stake is  95.324 M, then the amount to be filled is 95.324M - 97 M = (-) 1.676 M. The stakes are marked CUT or FILL or abbreviated C or F. Sometimes an arrow is added pointing downward for cut and upward for fill. The amount to be cut or filled is also marked on the stakes.

Figure 6                                                               Definitions
 Benchmark:   Starting reference point. Station:          Any location or point where a rod reading or                                   elevation is needed. Backsite:        Known elevation reading. Foresite:         Unknown elevation reading. Turning point: A point used for a backsite after it has been used for                       a foresite.

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1.Elevations and Excavation Depths: Measure Elevation Differences With A Transit.
2.Elevations and Excavation Depths: Establish Benchmark Before Elevations.
3.Elevations and Excavation Depths: Determine Foundation Excavation Depth.

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Written and maintained by
Ronald Hunter

All images and text are copyright Ronald Hunter 2005 to 2011