A geogrid reinforcement-soil interface cyclic pull-out test device and test method

Abstract

The present invention discloses a geogrid reinforcement-soil interface cyclic pull-out test device and test method, the device comprises a test box in which the geogrid is buried and a pull-out loading mechanism, the pull-out loading mechanism comprises a main loading arm assembly, a secondary loading arm assembly and a guide rail frame assembly arranged outside the test box, the main loading arm assembly and the secondary loading arm assembly are linked by a jacking trolley arranged at the front end of the main loading arm assembly and a force transmission vehicle arranged at the front end of the secondary loading arm assembly, the jacking trolley and the force transmission vehicle are arranged on the cross rail of the guide rail frame assembly, the secondary loading arm assembly is symmetrically arranged along the pulling direction, and a roller-type winding tool is arranged on the inner side. Compared with the cyclic single shear test, the present invention better simulates the situation where the geogrid is completely buried in the soil, directly and symmetrically loads the geogrid and the soil in a cyclic manner, the error generated in the non-pulling direction is small, the accuracy of the pull-out force parameters in the cyclic process is improved, and a new experimental means is provided for studying the cyclic effect of reinforcement and soil.

Description

Technical Field

[0001] The invention relates to a geotechnical test device and method, in particular to a geogrid reinforcement-soil interface cyclic pull-out test device and test method. Background Art

[0002] Geogrid is a geotechnical engineering material made of plastic, chemical fiber, synthetic rubber, etc., which buries the reinforcement material in the soil to diffuse the stress of the soil, increase the modulus of the soil, limit the lateral deformation of the soil, and improve the overall stability of the structure. Therefore, adding tensile materials to the fill can not only enhance the stability of the soil, but also improve the overall strength of the soil. It has been widely used in dams, retaining walls, bank protection projects, road projects and soft foundation treatment.

[0003] Under cyclic loads such as earthquake loads, wave loads or traffic loads, retaining walls generate cyclic reciprocating loads along the slip surface of the slope foot, which is manifested in the form of cyclic shear between the soil and the geogrid at the microscopic level. At present, there are few studies on the interaction between the reinforcement and soil interface under cyclic shear, and there are only cyclic single shear tests based on the mutual displacement between shear boxes. This experiment is considered to have a relatively uniform shear stress distribution, but it cannot fully simulate the actual stress conditions of the geogrid buried in the soil. Summary of the invention

[0004] Purpose of the invention: The present invention aims to provide a geogrid reinforcement-soil interface cyclic pullout test device and test method which can directly cyclically load and improve the accuracy of the pullout test.

[0005] Technical solution: A geogrid-soil interface cyclic pull-out test device described in the present invention comprises a test box in which the geogrid is buried and a pull-out loading mechanism, wherein the pull-out loading mechanism comprises a main loading arm assembly, an auxiliary loading arm assembly and a guide rail frame assembly arranged outside the test box, wherein the main loading arm assembly and the auxiliary loading arm assembly are linked by a jacking trolley arranged at the front end of the main loading arm assembly and a force transmission trolley arranged at the front end of the auxiliary loading arm assembly, wherein the jacking trolley and the force transmission trolley are arranged on the cross rail of the guide rail frame assembly, and the auxiliary loading arm assembly is symmetrically arranged along the pulling direction, and a reel for clamping the geogrid is provided on the inner side.

[0006] Preferably, the test box is provided with drawing openings symmetrically along the drawing direction, and guide rollers for ensuring the drawing direction of the geogrid are provided at four corners of each drawing opening.

[0007] Preferably, the drawing and loading mechanism further comprises a servo motor, the servo motor is connected to the main loading arm assembly, and a displacement sensor is provided on the servo motor.

[0008] Preferably, the guide rail frame assembly includes a column and a cross rail, the column is connected to the test box through an L-shaped bottom plate and separates the four corners of the long side of the test box, and the cross rail is horizontally arranged on the column and flush with the drawing port.

[0009] Preferably, the main loading arm assembly comprises a main arm and a side arm which are detachably connected, and caster brackets for horizontal positioning and supporting installation are provided below the main arm and the side arm.

[0010] Preferably, the auxiliary loading arm assembly includes a main frame and a side frame that are detachably connected, and an inverted T-shaped bracket is provided under the main frame, and the inverted T-shaped bracket cooperates to maintain the main frame parallel to the ground and keeps the height of the roller-type coil aligned with the drawing port; a support rod is provided on the inverted T-shaped bracket, which cooperates with the positioning pin hole reserved part set at the bottom of the test box; a tension sensor is provided on the connecting rod between the main frame and the coil, which is convenient for eliminating the error influence of the front-end force transmission component on the pulling force, and is only subjected to tension for easy calibration.

[0011] Preferably, the reel is a roller reel, which is parallel to the drawing port, has a surface provided with a slot matching the geogrid mesh, and has anti-rotation brakes at both ends of the rotating shaft. The length of the roller reel is not less than the width of the drawing port.

[0012] Preferably, the trolley is a rectangular body with eight rollers arranged at the octagonal parts of the body to reduce the friction of the trolley in the track. The height between the upper and lower rollers is consistent with the height of the cross rail. A bolt hole connected to the side arm of the main loading arm assembly is arranged at the center of the outer side surface. Side ribs are evenly distributed between the outer side surface of the body and the front and rear pushing surfaces to prevent possible deformation of the body during loading. The pushing surface of the body is provided with a guide column adapted to the force transmission vehicle to meet the guidance of the trolley and the force transmission vehicle from separation to fitting during cyclic drawing.

[0013] Preferably, the force transmission vehicle is a flatbed vehicle body connected to the front end of the side frame of the auxiliary loading arm assembly, and is equipped with four rollers at the four corners of the vehicle body. The height between the upper and lower rollers is consistent with the height of the cross rail, and the plate surface is provided with a guide groove that matches the guide column of the jacking vehicle.

[0014] The test method of the geogrid reinforcement-soil interface cyclic pull-out test device of the present invention comprises the following steps:

[0015] (a) Assemble the roller-type reel that matches the mesh size of the geogrid with the main frame of the auxiliary loading arm assembly, align the support rod on the inverted T-shaped bracket with the reserved part of the positioning pin hole of the test box and insert the positioning pin bolt to preliminarily fix the position of the main frame of the auxiliary loading arm assembly;

[0016] (b) After the soil in the test box is filled in layers according to the required compaction coefficient to a height slightly higher than the drawing port, a geogrid of appropriate length is laid on the soil, and pulled out from the drawing ports at both ends and fixed on the roller-type reel. The roller-type reel is tightened to ensure that the geogrid is straight in the box, and the soil is continued to be filled in layers to reach the specified height of the experiment;

[0017] (c) Assemble one end of the side frame of the auxiliary loading arm assembly with the force transmission vehicle and push it into the cross rail. Connect the other end of the side frame to the main frame. Push the jacking vehicle into the cross rail and connect both ends to the force transmission vehicle respectively. Complete the installation of the two auxiliary loading arm assemblies in the same way as above.

[0018] (d) The main arm of the main loading arm assembly is pushed to the initial calibration position by the displacement sensor of the servo motor, the connecting bolts between the side arm and the main arm are installed, and the connecting bolts between the side arm and the trolley are installed;

[0019] (e) Pull out the positioning pin of the inverted T-shaped bracket of the auxiliary loading arm, and enter the required cycle amplitude, pulling rate and various experimental parameters according to the experimental requirements to complete the experiment.

[0020] (f) After completing the experiment, disassemble the components in the reverse order of the installation steps.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. Compared with the cyclic single shear test, it better simulates the situation where the geogrid is completely buried in the soil, and the geogrid and the soil are directly cyclically loaded instead of being cyclically loaded through a shear box, so the parameters obtained from the experiment are more reasonable; 2. The clamp is a roller-type winding fixture, so that when the active end generates pulling during the cyclic pulling process, the passive end will not generate resistance to the pulling force, thereby improving the accuracy of the pulling force parameters during the cyclic process; 3. The structure is more reasonably utilized, and only one servo motor is required for the pulling of the grids at both ends, and the loading is symmetrical at the same time, and the error generated in the non-pulling direction is small; 4. The structure is simple, and it is convenient to modify conventional pulling instruments; 5. It provides a new experimental means for studying the cyclic effect of reinforcement and soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the present invention;

[0023] Figure 2 It is a left side view of the structure of the test box of the present invention;

[0024] Figure 3 It is a schematic structural diagram of the push cart of the present invention;

[0025] Figure 4 It is a schematic structural diagram of the power transmission vehicle of the present invention. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0027] like Figure 1-2 As shown, a geogrid-soil interface cyclic pull-out test device described in the present invention comprises a test box 1 in which a geogrid is buried and a pull-out loading mechanism, wherein the pull-out loading mechanism comprises a guide frame assembly, a main loading arm assembly 3, an auxiliary loading arm assembly 4, a roller-type reel 7 and a servo motor, wherein the servo motor is connected to the main loading arm assembly 3, and a displacement sensor is provided on the servo motor.

[0028] The test box 1 has symmetrically arranged narrow slit openings in the drawing direction as the drawing openings 11, and four guide rollers 8 are arranged at the four corners of each drawing opening 11 to ensure the drawing direction of the geogrid. The guide rail frame assembly includes a column 21 and a cross rail 22, and the column 21 is bolted to the test box 1 through an L-shaped bottom plate, and is separated from the four corners of the long side of the test box 1. Two groups of H-shaped steels are used on each of the left and right sides to form the cross rail 22 and are rigidly fixed on the column 21. The fixed position makes the cross rail 22 horizontal and straight, and the center line of the track is flush with the drawing opening 11. At the same time, the height of the cross rail 22, the jacking trolley 5 and the force transmission trolley 6 are consistent.

[0029] The main loading arm assembly 3 includes a main arm 31 and a side arm 32 that are detachably connected. A caster bracket 33 for horizontal positioning and supporting installation is provided below the main arm and the two side arms. The side arm 32 of the main loading arm assembly is connected to the trolley through the bolt opening 52 of the trolley. The trolley 5 is a rectangular body, and eight rollers 51 are arranged at the octagonal parts of the body to reduce the friction of the trolley in the track. The height between the upper and lower rollers is consistent with the height of the cross rail 22. A bolt opening 52 connected to the side arm of the main loading arm assembly is provided at the center of the outer side surface. Side ribs 53 are evenly distributed between the outer side surface of the body and the front and rear pushing surfaces to prevent possible deformation of the body during loading. The pushing surface of the body is provided with a guide column 54 adapted to the force transmission vehicle to meet the guidance of the loading trolley and the force transmission vehicle from separation to fitting during cyclic drawing. Figure 3 shown.

[0030] The auxiliary loading arm assembly 4 includes a main frame 41 and a side frame 42 that are detachably connected. An inverted T-shaped bracket 43 is provided below the main frame 41 to form a separate support and positioning. A support rod 44 is provided on the inverted T-shaped bracket 43 to cooperate with the positioning pin hole reserved part 12 provided at the bottom of the test box. A tension sensor 10 is provided on the connecting rod between the main frame 41 and the roller-type reel 7 to eliminate the error influence of the front-end force transmission component on the pulling force, and only the tension is subjected to facilitate calibration. A roller-type reel 7 is provided on the inner side of the main frame 41. The roller-type reel 7 is parallel to the pulling port 11, and its length is not less than the width of the pulling port 11. A slot matching the geogrid mesh is provided on the surface, and a stop brake 9 is provided at both ends of the rotating shaft. The built-in rotating shaft of the roller reel 7 can rotate flexibly, and the anti-rotation brakes 9 at both ends fix the reel to generate a pulling force. The guide rollers 8 arranged at the matching pulling port reduce the angle difference generated when the geogrid is wound, and the front and rear ends can be tightened separately when installing the geogrid; when pulling, the anti-rotation brake on the roller reel at the active end fixes the roller reel to generate a pulling force, and the anti-rotation brake on the roller reel at the passive end is relaxed, thereby eliminating the force influence of the reel on the geogrid at the passive end, so that the displacement of the geogrid at the passive end is not restricted.

[0031] The auxiliary loading arm assembly 4, the roller-type reel 7 and the force transmission vehicle 6 constitute an additional load combined vehicle. The force transmission vehicle 6 is a vertical flat-bed vehicle body, which receives the horizontal load transmitted by the push vehicle 5. The vehicle body is equipped with four rollers 51 at the four corners. The height between the upper and lower rollers is consistent with the height of the cross rail 22. The plate surface is provided with a guide groove 61 that matches the guide column 54 of the push vehicle 5. The guide groove is hollow to ensure surface contact to transfer the load. A pad 62 is provided on one side of the force transmission vehicle 6 relative to the push surface, which is connected to the front end of the side frame 42 of the auxiliary loading arm assembly by bolts.

[0032] The geogrid cyclic pull-out test device consists of a closed-loop control system consisting of a servo controller, software program, servo motor, tension sensor, displacement sensor, and anti-rotation brake. The pulling rate, cyclic displacement amplitude, and cyclic amplitude in the cyclic pull-out experiment can be controlled by integrated software.

[0033] The working principle of the present invention is: in the cyclic pulling experiment, the servo motor drives the main loading arm assembly 3 to generate a pulling load and transmit it to the jacking trolley 5. The jacking trolley is subjected to the force to drive the force transmission trolley 6 to generate a horizontal displacement in the pulling direction. The force transmission trolley 6 transmits the load to the auxiliary loading arm assembly 4. The roller-type winder 7 on the loaded active end auxiliary loading arm assembly drives the geogrid to cooperate with the main loading arm assembly to generate the same displacement. At this time, the anti-rotation brake 9 of the roller-type winder 7 on the active end auxiliary loading arm assembly automatically turns on the braking state through the integrated software to generate a pulling force, and the anti-rotation brake 9 of the roller-type winder 7 on the passive end remains in a relaxed state to reduce the error of the pulling force. The active end tension sensor 10 records and uploads the pulling force data. While waiting to reach the displacement amplitude of a single cycle pulling, the servo motor is loaded and changed direction, and the jacking cart 5 contacts the force transmission cart at the other end through the guide column. The original passive end auxiliary loading arm assembly becomes the active end, and the anti-rotation brake and the tension sensor are adjusted accordingly according to the changed active end. When the directional displacement reaches the cycle amplitude, the whole stage is a complete cycle amplitude pulling. Repeat the cycle amplitude required for the experiment to complete the complete experiment.

[0034] The test method of the geogrid reinforcement-soil interface cyclic pull-out test device of the present invention comprises the following steps:

[0035] (a) Assemble the roller-type reel 7 that matches the mesh size of the geogrid with the auxiliary loading arm assembly main frame 41, align the support rod 44 on the inverted T-shaped bracket with the positioning pin hole reserved part 12 of the test box and insert the positioning pin bolt to preliminarily fix the position of the auxiliary loading arm assembly main frame 41;

[0036] (b) After the soil in the test box 1 is filled in layers according to the required compaction coefficient to a height slightly higher than the drawing port, a geogrid of appropriate length is laid on the soil, and is pulled out from the drawing ports 11 at both ends and wound and fixed on the roller-type reel 7. The roller-type reel 7 is tightened to ensure that the geogrid is straight in the box, and the soil is continued to be filled in layers to reach the specified height of the experiment;

[0037] (c) Assemble one end of the side frame 42 of the auxiliary loading arm assembly with the force transmission vehicle 6 and push it into the cross rail 22. The other end of the side frame is connected to the main frame. Push the trolley 5 into the cross rail 22 and connect both ends to the force transmission vehicle 6 respectively. The installation of the two auxiliary loading arm assemblies is completed in the same steps as above.

[0038] (d) The main arm of the main loading arm assembly is pushed to the initial calibration position by the displacement sensor of the servo motor, and the connecting bolts between the side arm and the main arm are installed, and the connecting bolts between the side arm and the trolley are installed;

[0039] (e) Pull out the positioning pin of the inverted T-shaped bracket of the auxiliary loading arm, and enter the required cycle amplitude, pulling rate and various experimental parameters according to the experimental requirements to complete the experiment.

Claims

1. A geogrid-soil interface cyclic pull-out test device, comprising a test box (1) in which a geogrid is embedded and a pull-out loading mechanism, characterized in that: The pulling and loading mechanism comprises a main loading arm assembly (3), a secondary loading arm assembly (4) and a guide rail frame assembly arranged outside the test box (1); the main loading arm assembly (3) and the secondary loading arm assembly (4) are linked by a jacking trolley (5) arranged at the front end of the main loading arm assembly and a force transmission trolley (6) arranged at the front end of the secondary loading arm assembly; the jacking trolley (5) and the force transmission trolley (6) are arranged on a transverse rail (22) of the guide rail frame assembly; the secondary loading arm assembly (4) is symmetrically arranged along the pulling direction, and a coil (7) for clamping the geogrid is arranged inside; The main loading arm assembly (3) comprises a main arm (31) and a side arm (32) which are detachably connected, and a caster bracket (33) for horizontal positioning and supporting installation is provided below the main arm and the side arm; The auxiliary loading arm assembly (4) comprises a main frame (41) and a side frame (42) which are detachably connected. An inverted T-shaped bracket (43) is provided below the main frame. A support rod (44) is provided on the inverted T-shaped bracket (43) and cooperates with a positioning pin hole reserved piece (12) provided at the bottom of the test box. A tension sensor (10) is provided on the connecting rod between the main frame (41) and the coil (7). The reel is a roller-type reel (7), which is parallel to the drawing opening (11), has a surface provided with a slot matching the geogrid mesh, and has anti-rotation brakes (9) at both ends of the rotating shaft; the length of the roller-type reel is not less than the width of the drawing opening (11); The push cart (5) is a rectangular parallelepiped body, and eight rollers (51) are arranged at the octagonal parts of the body. The height between the upper and lower rollers is consistent with the height of the cross rail (22). A bolt hole (52) connected to the side arm of the main loading arm assembly is arranged at the center of the outer side surface. Side ribs (53) are evenly distributed between the outer side surface of the body and the front and rear push surfaces. The push surface of the body is provided with a guide column (54) adapted to the force transmission vehicle. The force transmission vehicle (6) is a flat vehicle body connected to the front end of the side frame (42) of the auxiliary loading arm assembly. Four rollers (51) are provided at the four corners of the vehicle body. The height between the upper and lower rollers is consistent with the height of the cross rail (22). The plate surface is provided with a guide groove (61) matching the guide column (54) of the push vehicle (5).

2. The geogrid reinforcement-soil interface cyclic pull-out test device according to claim 1, characterized in that: The test box (1) is symmetrically provided with drawing openings (11) along the drawing direction, and each of the four corners of the drawing opening (11) is provided with guide rollers (8) for ensuring the drawing direction of the geogrid.

3. The geogrid reinforcement-soil interface cyclic pull-out test device according to claim 1, characterized in that: The drawing and loading mechanism further comprises a servo motor, which is connected to the main loading arm assembly (3) and is provided with a displacement sensor.

4. The geogrid reinforcement-soil interface cyclic pull-out test device according to claim 2, characterized in that: The guide rail frame assembly comprises a column (21) and a cross rail (22); the column (21) is connected to the test box (1) via an L-shaped bottom plate and is separated from the four corners of the long side of the test box (1); the cross rail (22) is horizontally arranged on the column (21) and is flush with the drawing opening (11).

5. A test method for the geogrid reinforcement-soil interface cyclic pull-out test device according to any one of claims 1 to 4, characterized in that: The following steps are involved: (a) Assemble a roller-type reel (7) matching the mesh size of the geogrid with the auxiliary loading arm assembly main frame (41), align the support rod (44) on the inverted T-shaped bracket with the positioning pin hole reserved part (12) of the test box and insert the positioning pin bolt to preliminarily fix the position of the auxiliary loading arm assembly main frame (41); (b) After the soil in the test box (1) is filled in layers according to the required compaction coefficient to a height slightly higher than the drawing port, a geogrid of appropriate length is laid on the soil, and is pulled out from the drawing ports (11) at both ends and wound and fixed on a roller-type reel (7). The roller-type reel (7) is tightened to ensure that the geogrid is straight in the box, and the soil is continued to be filled in layers to reach the specified height of the experiment; (c) Assemble one end of the side frame (42) of the auxiliary loading arm assembly with the force transmission vehicle (6) and push it into the cross rail (22). The other end of the side frame is connected to the main frame. Push the pusher vehicle (5) into the cross rail (22). Connect the two ends to the force transmission vehicle (6) respectively. Complete the installation of the two auxiliary loading arm assemblies in the same way as above. (d) The main arm of the main loading arm assembly is pushed to the initial calibration position by the displacement sensor of the servo motor, and the connecting bolts between the side arm and the main arm are installed, and the connecting bolts between the side arm and the trolley are installed; (e) Pull out the positioning pin of the inverted T-shaped bracket of the auxiliary loading arm, and enter the required cycle amplitude, pulling rate and various experimental parameters according to the experimental requirements to complete the experiment.

Images