TECHNICAL FIELD

The disclosure relates to the technical field of indoor simulation test of underground engineering, in particular to a variable dip fault slip simulation test method.

BACKGROUND

Fault is one of the important geological factors affecting the production process of coal mine. The existence of fault geological structure not only affects the mine field division, development system layout and roadway excavation of coal mine production, but also poses a major threat to the safety production and economic benefits of coal mine. The coal mining near the fault causes the change of local stress field, makes the fault activate or energy accumulate, and may eventually lead to the occurrence of rockburst. Therefore, the study on the physical and mechanical behavior of fault slip process is of great significance to the mining design near the fault, the stability control of roadway surrounding rock and the mechanism of fault rockburst.

Most of the test devices used to simulate faults are based on similar simulation tests and horizontal shear tests of rock (rock-like) samples. The model of similar simulation test can not be completely similar to the original model in terms of physical and mechanical parameters and stress conditions of materials, and the boundary conditions of the model are simple. In addition, the magnitude of horizontal stress depends on the top load, so it can not realize biaxial and true triaxial experiments with given confining pressure. Although the horizontal shear test of rock samples is not easy to simulate the complex geological conditions of multi strata, it can simulate the determined stress boundary conditions, and can study the mechanical behavior of rock samples and weakness planes under different stress loading conditions.

At present, most of the tests simulating fault slip are horizontal shear tests of rock samples and biaxial or triaxial compression tests with fixed dip angle, which can not simulate fault slip with different dip angles. The impact risk of mining near the fault is related not only to the mining location, but also to the dip angle of the fault.

SUMMARY OF THE INVENTION

The objective of the disclosure is to provide a variable dip fault slip simulation test method, which can prepare rock-like samples with different dip interfaces and simulate the slip failure process of different dip faults, so as to study the sliding conditions of different dip faults and the mechanical behavior in the slip process.

The technical solution of the disclosure is as follows:

A variable dip fault slip simulation test method, which is characterized in that a sample device and a loading device are adopted;

the sample device comprises a bottom plate, a sliding partition plate, a combined pressing plate and a rotating baffle; front and rear edges of the bottom plate are provided with sliding grooves, left and right sides of the bottom plate are provided with the sliding partition plates, front and rear ends of the the sliding partition plates are provided with sliding blocks, and the sliding blocks are slidably connected in the sliding grooves; the front and rear sides of the bottom plate are provided with the combined pressing plates, wherein the combined pressing plates are formed by splicing a plurality of the pressing blocks from head to tail, and two ends of the combined pressing plate are spliced with ends of the sliding partition plate; a rotating baffle is arranged at a middle position of the bottom plate, wherein the rotating baffle comprises a fixed plate and a sliding plate, the fixed plate is rotatably connected with the middle position of the bottom plate and the fixed plate is detachably connected with the bottom plate, and both sides of the fixed plate are slidably connected with a sliding plate; an end of the sliding plate is provided with a positioning member, wherein the positioning member is detachably connected with the combined pressing plate;

the loading device comprises a loading support platform, a top loading indenter, a top pressure bearing unit, a bottom loading indenter, a side loading indenter, a side pressure bearing unit, a bearing seat, a strain gauge, an acoustic emission detector, a computer and a camera; the loading support platform comprises a base, a left loading support frame, a right loading support frame and an upper loading support frame; the left and right sides of the base are respectively provided with the left loading support frame and the right loading support frame, and the upper loading support frame is provided on the left loading support frame and the right loading support frame; a top loading indenter is arranged on the upper loading support frame; the top bearing unit comprises a force transfer column, a roller and an upper pressure bearing plate, an upper end of the force transfer column is connected with the top loading indenter, a lower end of the force transfer column is rotated side by side and is connected with a plurality of rollers, and one side of the upper pressure bearing plate is provided with a baffle bent downward; the bottom loading indenter is set on the base; the bearing seat is arranged on the left loading support frame, and a right end of the bearing seat is rotated side by side from top to bottom to connect a plurality of rollers; a side loading indenter is arranged on the right loading support frame; the side pressure bearing unit comprises a guide shaft, a linear bearing, a side pressure bearing plate and the rollers, the guide shaft is arranged on a right side of the base, the linear bearing is arranged on the guide shaft, the side pressure bearing plate is arranged on the linear bearing, and a left end of the side pressure bearing plate is rotated side by side from top to bottom to connect a plurality of rollers;

the method comprises the following steps:

Step 1. Sample Preparation

rotating the fixed plate to a preset angle to simulate the fault inclination with the preset angle, so as to make the sliding plate stretch out and draw back relative to the fixed plate; connecting the sliding plate with the combined pressing plate for positioning through the positioning member; wherein the bottom plate, the sliding partition plate and the combined pressing plate form a semi-enclosed cavity, and the rotating baffle separates the semi-enclosed cavity into two cavities; applying lubricating oil on an upper surface of the bottom plate, an inner wall of the sliding partition plate, an inner wall of the combined pressing plate, and a surface of the rotating baffle, injecting a first type of rock material into the two cavities, removing the rotating baffle and the bottom plate after the first type of rock material solidifies into a rock-like sample, removing the lubricating oil on the surface of the rock-like sample, and maintaining the rock-like sample;

wherein, the first type of rock material injected into the two cavities is the same material or different materials;

Step 2. Sample Assembly

defining the rock-like sample in the cavity behind the rotating baffle as a footwall sample, and defining the rock-like sample in the cavity in front of the rotating baffle as the hanging wall sample, and the footwall sample and the hanging wall sample together form the rock-like sample; an overlapping interface between the footwall sample and the hanging wall sample is a fault interface, placing the combined pressing plates on upper and lower sides of the rock-like samples, placing the sliding partition plates on left and right sides of rock-like samples, splicing the combined pressing plate with the the sliding partition plate, wherein the combined pressing plate is disconnected at the fault interface;

Step 3. Loading Preparation

in the rock-like samples, placing the footwall sample at the lower left and the hanging wall sample at the upper right, wherein the combined pressing plate on the lower side of the footwall sample is attached to the bottom loading indenter, the sliding partition plate on the left side of the footwall sample is attached to a plurality of the rollers on the bearing seat; placing the top pressure bearing unit on the upper side of the hanging wall sample, wherein the combined pressing plate on the upper side of the hanging wall sample is attached to the upper pressure bearing plate, the top position of the sliding partition plate on the right side of the hanging wall sample is attached to the baffle, and the other positions except the top position of the sliding partition plate on the right side of the hanging wall sample are attached to the plurality of rollers on the side pressure bearing plate;

or, in the rock-like samples, placing the footwall sample at the lower right and the hanging wall sample at the upper left; wherein the combined pressing plate on the lower side of the hanging wall sample is attached to the bottom loading indenter, and the sliding partition plate on the left side of the hanging wall sample is attached to the plurality of the rollers on the bearing seat; placing the top pressure bearing unit on the upper side of the footwall sample, wherein the combined pressing plate on the upper side of the footwall sample is attached to the upper pressure bearing plate, the top position of the sliding partition plate on the right side of the footwall sample is attached to the baffle, and the other positions except the top position of the sliding partition plate on the right side of the footwall sample are attached to the plurality of the rollers on the side pressure bearing plate;

arranging the strain gauges along the fault interface on the surface of rock-like samples, arranging acoustic emission detectors on the left and right sides of the surface of rock-like samples, applying speckle on the surface of rock-like samples, aligning the camera with the surface of rock-like samples, connecting the top loading indenter, the bottom loading indenter, the side loading indenter, the strain gauges, the acoustic emission detectors and the camera with computer via signals, respectively;

Step 4. Sample Loading

when “in the rock-like sample, placing the footwall sample at the lower left and the hanging wall sample at the upper right”,

the computer first drives the side loading indenter to apply a lateral stress of the preset pressure to the rock-like sample, and then the computer drives the top loading indenter to apply an axial stress of the preset pressure to the rock-like sample; during the normal dip slip of the hanging wall sample relative to the footwall sample, the side pressure bearing plate moves horizontally to the right, the plurality of the rollers at the lower end of the force transfer column roll along the surface of the upper pressure bearing plate, and the plurality of the rollers at the left end of the side pressure bearing plate roll along the surface of the sliding partition plate on the right side of the hanging wall sample;

when “in the rock-like sample, placing the footwall sample at the lower right and the hanging wall sample at the upper left”,

the computer first drives the side loading indenter to apply a lateral stress of the preset pressure to the rock-like sample, and then the computer drives the bottom loading indenter to apply an axial stress of the preset pressure to the rock-like sample; during the reverse dip slip of the hanging wall sample relative to the footwall sample, the side pressure bearing plate moves horizontally to the left, the plurality of the rollers at the right end of the bearing seat roll along the surface of the sliding partition plate on the left side of the hanging wall sample; the plurality of the rollers at the lower end of the force transfer column roll along the surface of the upper pressure bearing plate, and the plurality of the rollers at the left end of the side pressure bearing plate roll along the surface of the sliding partition plate on the right side of the footwall sample;

the computer records the real-time axial stress data of the top loading indenter, the real-time support pressure data of the bottom loading indenter, the real-time lateral stress data of the side loading indenter, the real-time strain data monitored by the strain gauge, the real-time acoustic emission data monitored by the acoustic emission detector and the real-time speckle change data monitored by the camera; after loading, removing the rock-like sample, observing and recording the failure of the fault interface on the surface of the rock-like sample.

The advantages of the disclosure are as follows:

The variable dip fault slip simulation test method of the disclosure can prepare rock-like samples with different dip interfaces. The interface types include ordinary fracture interfaces, different roughness interface and low-intensity weak interfaces. It can simulate the slip failure process of faults with different dip angles, as well as the normal dip slip and reverse dip slip of faults. The operation of slip simulation test is convenient, the test data can be collected automatically and accurately to study the slip conditions and mechanical behavior of faults with different dip angles. The sample device applied in the variable dip fault slip simulation test method of the disclosure can not only be used to prepare rock-like samples with different dip interfaces, but also be used as a loading fixture for rock-like samples, which has the dual functions of sample making mold and loading fixture.

