According to longtime monitor on residual strain states of two large-diameter rock-socketed cast-in-place piles (dig by hand) before loading

inducing factors and distribution rules of residual strain

and its influence on bearing behaviours of pile are analyzed

some conclusions are obtained as follows: (1) the main factor of inducing residual strain is drying shrinkage of concrete; (2) the residual strain distribution of the two piles are regularly changing with space and curing time

but some construction factors

such as blowing up

groundwater and type of casting pile

will disturb residual strain distribution or soften restricting force which comes from rock beside pile side. (3) local strain of piles can exceed ultimate tensile strain of concrete

which can result in crazing of concrete and losing of capability of protection to reinforcement bar

and the shrinkage of the whole pile will decrease contact force between pile bottom and rock. The foregoing conclusions provide reference to engineering practice.