Direct shear test device and method based on unloading effect

Abstract

The invention belongs to the technical field of deformation body mechanical testing, and particularly relates to a direct shear test device and method based on an unloading effect. The device comprises a shearing box, a top plate, an air bag, a pressure transmission pad, a fixing device, a water absorption mechanism, an air inlet pipe and a moving mechanism; the shearing box is composed of an upper box and a lower box, the upper box is of a rectangular frame structure with neither a cover nor a bottom, the lower box is of a rectangular box-shaped structure without a cover, and the upper box is connected onto the lower box; the top plate is connected to the upper box; the air bag, the pressure transmission pad and the water absorption mechanism are sequentially arranged under the top plate from top to bottom; the fixing device is fixedly connected to the outer side wall of the upper box; the air bag is communicated with an air inlet pipe penetrating through the side wall of the upper box; and the shearing box is placed on the moving mechanism. Normal force is provided by the air bag, and pressure application is more uniform. According to the device, direct shearing under the unloading condition is considered, unloading is also achieved through the air bag, unloading can be smoother instead of instantaneous unloading, and the device better conforms to engineering practice.

Description

technical field [0001] The invention belongs to the technical field of mechanical testing of deformable bodies, and in particular relates to a direct shear test device and a test method based on unloading consideration. Background technique [0002] The foundation pit engineering involves soil excavation and unloading, the stress level in the soil near the foundation pit decreases, the strength of the soil is greatly affected by the unloading effect, and the engineering properties of the soil are significantly different from the loading state. The current design of foundation pit support seldom considers this essential problem, and the strength parameters required for the design are mostly determined by ordinary direct shear tests that only consider the loading effect. Calculation, resulting in large errors, making it difficult for designers to grasp the safety of the project. The key to the excavation of foundation pit engineering is unloading, so it is necessary to find ...

AI Technical Summary

Problems solved by technology

The conventional direct shear test uses the method of taking weights to complete the unloading. Although this method is easy to operate, it cannot accurately control the unloading process.

The stress path triaxial instrument can obtain the soil strength parameters under unloading conditions, but the instrument is precise and difficult to operate, and the test takes a long time

Existing soil mechanics test methods cannot meet the requirements of fast and convenient acquisition of shear strength parameters of soil samples under unloading action

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