Graded pressure drop type detection system and detection method of borehole cracks

Abstract

Within the technical field of detecting a mining-induced failure range of rock mass, and particularly relating to a graded-pressure drop type detection system and detection method of borehole cracks, a detection system is provided including a test probe, a drilling rig, a drill pipe and a control operation platform. The test probe includes a plugging device and a pressure conversion assembly. The pressure conversion assembly is connected with the plugging device at the rear end through a connected pipe and includes a first stage pressure converting device and a second stage pressure converting device. The detection system simplifies the existing operating system, avoids the problem of drill pipes winding in drill hole, realizes plugging process and detection process with the same external water source, and ensures that the plugging process and the observation process operate under respective predetermined pressures.

1 . A graded pressure drop type detection system of borehole cracks, comprising a test probe, a drilling rig, a drill pipe and a control operation platform, wherein
 the test probe comprises a plugging device and a pressure conversion assembly; the plugging device comprises a plugging device at the front and a plugging device at the rear end; the pressure conversion assembly is connected with the plugging device at the rear end through a connected pipe and comprises a first stage pressure converting device and a second stage pressure converting device; the second stage pressure converting device is sheathed on the outer end of the first stage pressure converting device and is in threaded connection with the first stage pressure converting device;   the plugging device comprises a water leakage pipe, a joint and a rubber bag; the rubber bag is wrapped around the outer end of the water leakage pipe, and forms a blocked cavity with the water leakage pipe; both ends of the rubber bag are fixed by a fastening iron ring; a water leakage hole is formed in the water leakage pipe; an outside water source enters the blocked cavity through the water leakage hole in the water leakage pipe; a water injection cavity is formed between the swelling rubber bags and drill hole;   the drilling rig is connected with the test probe through the drill pipe for extending and pushing the test probe to a designated region; the drill pipe is a hollow pipe in which the outside high pressure water source can be delivered; the drill pipe and the test probe are in threaded connection and are detachable;   the control operation platform is connected with the drill pipe through a high pressure resistant hose and is responsible for providing the outside water source with designated pressure for the test probe and displaying pressure and flow values;   the outside water source enters the blocked cavity through the water leakage hole in the plugging device at the front and the plugging device at the rear end; the water injection cavity is formed between the corresponding swelling rubber bags and drill hole;   the left end and the right end of the pressure conversion assembly are respectively in threaded connection with the connected pipe and a type II joint; the high pressure water source in the connected pipe is graded and converted by the first stage pressure converting device and the second stage pressure converting device successively into a low pressure water source and delivered into the water injection cavity;   a central through hole and four peripheral through holes are formed in the first stage pressure converting device; the four peripheral through holes are symmetrically distributed around the central through hole; the central through hole is a ladder port, where the left aperture is less than the right aperture; side drain holes are formed in the side walls of the peripheral through holes;   a conversion body, an inner spring and a regulating screw are successively installed in the peripheral through holes; threads are arranged on the left inner walls of the peripheral through holes and are matched with the regulating screw so that the regulating screw rotates and compresses the inner spring within a certain range of the peripheral through holes to control the opening pressure of the conversion body;   a hexagonal through hole is formed in the side wall of the regulating screw so that rotation of the regulating screw is facilitated and feedback water pressure acts on the left end surface of the conversion body;   the conversion body is a cylinder of unequal diameters, and the diameter of the left end surface of the conversion body is larger than the diameter of the right end surface; a sealed conical surface is at the transition of the cylinder of unequal diameters, and coincides with the sealed conical surface of the inner wall of the peripheral through holes; the sealed conical surface has an angle of 30°;   an “L ”-shaped limber of No. 1 is formed in the conversion body; an annular flume is formed in a cylindrical external surface near the left end surface of the conversion body; the limber of No. 1 is communicated with the annular flume; when the conversion body moves to the left driven by the outside water source, the annular flume is communicated with the side drain holes;   the second stage pressure converting device comprises an external annular component, an internal annular component, an annular conversion body, an external spring and a cross filiform ring; a thread is arranged on the right inner wall of the external annular component, is sheathed on the right outer wall of the first stage pressure converting device, and a central transitional cavity is formed with the first stage pressure converting device; the side drain holes and the hexagonal through hole are communicated with the central transitional cavity;   the internal annular component is in the shape of a cylindrical ring, and a thread is arranged on the inner wall of the internal annular component and is wrapped around the outer wall of the connected pipe; four protruding parts are arranged on the outer wall of the internal annular component to limit the maximum leftward movement range of the annular conversion body; water collecting slots and water diversion holes are disposed in the pipe wall of the internal annular component; four water diversion holes are disposed and are respectively vertically communicated with the water collecting slots to diverse and drain water in the water collecting slots;   the annular conversion body is positioned between the external annular component and the internal annular component and slides left and right along the surface of the internal annular component;   four “L”-shaped limbers of No. 2 are correspondingly formed in the annular conversion body; when the annular conversion body moves to the left, the limbers of No. 2 are communicated with the water collecting slots to deliver the high pressure water source in the central transitional cavity into the water collecting slots; at this moment, the left end surface of the annular conversion body just comes into contact with the protruding part; the diameter of the left end surface of the annular conversion body is larger than that of the right end surface, and the sealed conical surface is arranged in the middle connected position;   the external spring is positioned between the annular conversion body and the cross filiform ring, and has the same diameter as the left end surface of the annular conversion body;   the cross filiform ring is in the shape of “cross”, and the middle position thereof is circular; a thread is arranged on the inner wall of the cross filiform ring and is matched with the internal annular component; the cross filiform ring rotates on the thread by means of an external tool to change the compression extent of the external spring so as to control the opening pressure of the annular conversion body;   the working principle of the first stage pressure converting device is:   (1) when the conversion body satisfies P mid S left +k inner ≤P right S right , the conversion body moves to the left, and then the annular flume is communicated with the side drain holes to supply water into the central transitional cavity to realize first stage pressure drop;   (2) when the conversion body satisfies P mid S left +k inner ≥P right S right , the conversion body moves to the right, and then the annular flume is closed by the inner walls of the peripheral through holes to stop supplying water into the central transitional cavity;   (3) if P right  is too large, in order to prevent extreme water pressure of P right  from damaging the inner wall of the drill hole in the water injection cavity through the pressure conversion assembly, the conversion body moves to the left under the action of the outside water source until the annular flume moves to the left end of the side drain hole and forms another closing role on the inner walls of the peripheral through holes;   wherein P mid  is the water source pressure of the central transitional cavity, ranging from 0.8 to 1 MPa. P right  is the pressure of the supplied water source in the connected pipe, which is 1.5 MPa; S left  is the area of the left end surface of the conversion body; S right  is the area of the right end surface of the conversion body; k inner  is an elastic coefficient of the inner spring; and x is compression length;   the working principle of the second stage pressure converting device is:   (1) the annular conversion body satisfies P left S left +k outer ≤P mid S right , the annular conversion body moves to the left, and then the limbers of No. 2 are communicated with the water collecting slots to inject low pressure water into the water injection cavity through the water diversion holes to realize second stage pressure drop;   (2) when the annular conversion body satisfies P left S left +k outer ≥P mid S right , the annular conversion body moves to the right, and then the limbers of No. 2 are closed by the outer wall of the internal annular component to stop supplying water into the water injection cavity;   wherein P left  is the observed water source pressure of the water injection cavity, ranging from 0.2 to 0.5 MPa; P mid  is the pressure of the water source in the central transitional cavity, ranging from 0.8 to 1 MPa; S left  is the contact area between water and the left end surface of the annular conversion body; S right  is the contact area between water and the right end surface of the annular conversion body; k outer  is an elastic coefficient of the external spring; and x is compression length;   the control operation platform comprises a water release switch, a flow meter, a mechanical pressure gauge, a total control switch and an electronic pressure gauge the water release switch is responsible for releasing pressure water in the test probe after pressurized pressure testing completed so that the rubber bag is out of contact with the drill hole to facilitate the drilling rig in pushing the test probe, the total control switch is responsible for interruption of the outside water source supply; the flow meter is responsible for displaying the real-time water input from the external water source to the test probe; the mechanical pressure gauge is compared with the reading of the electronic pressure gauge for inspection; if the mechanical pressure gauge is roughly equal to the reading, then the pressure is effective.   
     
     
         2 . The graded pressure drop type detection system of borehole cracks according to  claim 1 , wherein the plugging device at the front consists of a type I joint, a water leakage pipe, a type II joint and a rubber bag; the type I joint, the type II joint and the water leakage pipe are in threaded connection; the rubber bag is wrapped outside the water leakage pipe, is fixed outside the type I joint and the type II joint through a fastening iron ring, and forms a blocked cavity with the water leakage pipe; the external end of the type I joint is in threaded connection with a guide head; and the guide head has a guide effect and is used to guide the test probe to smoothly slide in the drill hole. 
     
     
         3 . The graded pressure drop type detection system of borehole cracks according to  claim 1 , wherein the plugging device at the rear end comprises two type III joints, a water leakage pipe and a rubber bag; and the rubber bag is fixed between the two type III joints through a fastening iron ring. 
     
     
         4 . The graded pressure drop type detection system of borehole cracks according to  claim 3 , wherein a circular baffle is installed outside the type III joints the diameter of the circular baffle is larger than that of the rubber bag to prevent the rubber bag from falling; and the circular baffle and the type III joints are in threaded connection and are detachable to convenient replacement of the rubber bag. 
     
     
         5 . A graded pressure drop type detection method of borehole cracks, comprising the following steps:
 (1) constructing drill holes: constructing three to five drill holes with different directions and inclined angles in the region of rock mass to be detected through the drilling rig in accordance with predesigned construction requirements; the drill holes having a diameter of 89 mm and a length of about 70 m; and cleaning scraps in the drill holes;   (2) installing equipment: installing all components of the test probe; successively connecting the drilling rig, the drill pipe, the high pressure resistant hose and the control operation platform; and then pushing the test probe to the initial positions of the drill holes through the drilling rig;   (3) seal inspection: firstly, turning off a water release switch of the control operation platform; turning on the total control switch to provide detection water pressure for the test probe; conducting a plugging seal inspection on the rubber bag; conducting next operation if there is no obvious water leakage phenomenon, otherwise, returning to operation of step to inspect the connection and installation among all components until qualified,   (4) detecting water leakage rate: conducting pressurized-water test after passing the seal inspection; allowing the test probe to be in the initial position; turning off the water release switch and turning on the total control switch to provide a high pressure water source for the test probe, allowing the water source to enter the blocked cavity through the connected pipe and the water leakage pipe; inflating the rubber bags of the plugging device at the front and the plugging device at the rear end to form a water injection cavity with the drill holes; adjusting the pressure of the outside water source to gradually rise to 1.5 MPa; converting the high pressure water source into a low pressure detection water source through the first stage pressure converting device and the second stage pressure converting device into the water injection cavity; and recording the steady reading Q i  of the flow meter and a detection length L i  after the reading of the flow meter is steady;   (5) pressure relief propulsion: turning off the total control switch; turning on the water release switch to release the pressure of the blocked cavity; turning off the water release switch after the rubber bag is out of contact with the drill holes; taking another drill pipe to connect to the test probe, pushing the test probe to a next detection region through the drilling rig; and repeating the operation of step until all lengths of the drill holes is detected;   (6) calculation and analysis: respectively drawing flow distribution maps in different drill holes according to the length of the drill holes and corresponding injected water leakage of drilling hole; analyzing fracture development and permeability characteristics at different positions within the length range of the drill holes; and further calculating failure range of the rock mass within different spatial ranges by combining the inclined angles of the drill holes in different directions with accumulated successive water leakage length L n  (n=1+2+ . . . +k).