Testing apparatus and method for testing tensile strength of fissured rock

Abstract

The invention discloses a testing apparatus and method for testing tensile strength of fissured rock. The apparatus comprises a fissured platform Brazilian specimen processing device, a stress loadingsystem, an acoustic emission system and a VIC-3D non-contact full-field strain measurement system. The fissured platform Brazilian specimen processing device comprises a base, a specimen mold, a chute, a slide block and a fissure shaping piece; the stress loading system comprises an electronic universal testing machine and a first computer; the acoustic emission system comprises a second computer, a data acquisition case, a pre-amplifier and an acoustic emission sensor; and the VIC-3D non-contact full-field strain measurement system comprises a VIC-3D measuring instrument and a third computer. The method comprises the following steps: 1, preparing a fissured platform Brazilian specimen; 2, building a testing apparatus; and 3, performing axial compression test. The measured data can reallyreflect the tensile strength of the fissured rock, a fissure spreading evolution law and a fracture mode as well as influence laws of fissures on the rock.

Description

technical field [0001] The invention belongs to the technical field of geotechnical engineering, and in particular relates to a test device and method for testing the tensile strength of rocks containing fissures. Background technique [0002] The tensile strength of rock is an important index to measure the mechanical properties of rock mass. It is an indispensable parameter for establishing rock strength criteria, determining the strength envelope and selecting building stones. Studying the tensile properties of rock mass is of great significance to the surrounding rock mass of tunnels, engineering slopes and underground engineering caverns. At present, the methods for determining the tensile strength of rocks include: direct tensile test, Brazilian split method, square plate axial fracturing test, axial compression die tensile test, etc. Because Brazilian splitting is easy to operate and has low requirements for samples, the Brazilian splitting method is usually used to ...

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Problems solved by technology

However, this classic test method has many shortcomings

For example, when carrying out the Brazilian splitting test, the loaded part will be brittle first due to the stress concentration, and the central cracking condition of the Brazilian splitting cannot be guaranteed.

And the loading form of line load will inevitably cause the sample to crack from the loading point, which does not meet the condition of center cracking; and the stiffness and strength of the pad, the size and shape of the pad directly affect the contact degree between the load and the contact surface of the specimen, Thus affecting the test accuracy of the rock tensile strength; the tensile strength formula of the existing platform Brazilian splitting test is based on the elastic mechanics analytical solution of the plane stress problem of the complete Brazilian disc specimen, and the specimen is actually in a three-dimensional stress state and the sample is a platform Brazilian sample, there is a large error in the tensile strength formula; in addition, most of the existing Brazilian split tensile strength test methods are carried out on the complete rock sample, without considering the cracks on the tensile strength. and failure mode, not to mention the influence of crack eccentricity on its tensile strength and failure mode

However, a large number of microcracks and pores contained in the rock have a great influence on the tensile strength of the rock block, which directly weakens the tensile strength of the rock block.

Therefore, the methods in the prior art are not suitable for testing the tensile strength of rock-like brittle materials, especially the tensile strength of crack-containing rock materials.

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