System and method for flexibly loading controllable boundary based on true triaxial test

The invention discloses a system and a method for flexibly loading a controllable boundary based on a true triaxial test. The system comprises a test piece, a loading device, a hydraulic control device and a liquid-filled bladder; the loading device is disposed at the outer side of the test piece, and the liquid-filled bladder is disposed between the loading device and the test piece; the liquid-filled bladder comprises a plate-shaped bladder and a plurality of divided bladders successively arranged at two sides of the plate-shaped bladder, all of the divided bladders are communicated with the plate-shaped bladder; and the hydraulic control device injects a liquid into the divided bladders and discharges the liquid; and the loading device loads the test piece with stress through the liquid-filled capsule. Through arrangement of the plate-shaped bladder and the divided bladders, flexible loading on the test piece is realized, also when the stress of the lateral side of the divided bladder exceeds a specified stress value, the divided bladders moves inwards by discharging the liquid, and thus the corner extrusion effect of loading plates at two adjacent sides in an true triaxial test is effectively solved, and finally relatively accurate mechanical behaviors and penetration characteristics of rock under three-dimension loading effect are obtained.