What measures are there for the back cover of foundation pit?

The bottom sealing measure of independent foundation pit is to use the specified concrete cushion and pour it in the original groove to avoid long-term exposure of the bearing layer to air and mud pollution before foundation pouring, which is convenient for cleaning. The bottom sealing measure of the cast-in-place pile hole is to fill the "pot bottom" with the same concrete as the pile body to a thickness of about 300, so as to avoid the bearing layer being exposed to the atmosphere for a long time before the pile foundation is poured, and the rock layer is weathered, which is easy to eliminate flooding.