Device and method for testing compression amount of pile body of rock-socketed cast-in-place pile

A device for testing the compression of a rock-socketed cast-in-place pile, including open flexible pipes 5 correspondingly bound with two reinforcements 2 in the pile body. The lengths of the open flexible pipes and main reinforcements are equal; where the length of one of the reinforcements is the height of the pile and the length of the other is the height of the pile minus the height of the rock stratum. One end of each of the two open flexible pipes is connected with a first sealing sheet 6, and the other ends of the two open flexible pipes are located at the pile block of the pile and connected with second sealing sheets 10. A closed rigid pipe 7 is located inside of (but not in contact with) the open flexible pipe, the bottom ends of which are connected together through the first sealing sheet. Displacement sensors 9 measure the relative displacement of the first and second sealing sheets, i.e., compression of the pile body. One end of each displacement sensor is fixed to the second sealing sheet. The other ends of the displacement sensors are connected with the top ends of the closed rigid pipes, and the top ends of all the closed rigid pipes are kept at the same height.