A method and device for predicting the pull-out force of compaction grouting soil nails and an application method of the device

Abstract

The present invention discloses a method and device for predicting the pull-out force of compaction grouting soil nails and a method for applying the device. The method uses a CPT test to replace a pull-out model test to infer the pull-out force of the grouting sphere of the compaction grouting soil nails. When conducting the test, multiple soil pressure gauges are set in the soil sample in the model box, and a loading device pressurizes the soil sample. The soil pressure gauges are used to obtain accurate soil compressive stress values. The CPT test is conducted under different soil compressive stresses, and the resistance generated by the soil sample under different compressive stresses to the probing device can be obtained in the laboratory. The resistance data of the grouting sphere under the soil sample state with known pressure are compared and fitted to infer the pull-out force of the compaction grouting soil nail under the boundary conditions of other soils. The method is very suitable for engineering sites of slopes or foundation pits that need to be reinforced with compaction grouting soil nails. The standard CPT probe is uniformly inserted into the slope, and the density of the compaction grouting soil nails and the diameter of the grouting sphere required for the soil layer can be accurately calculated according to the cone tip resistance value obtained from the test.

Description

Technical Field

[0001] The invention belongs to the field of geotechnical testing, and in particular relates to a method and a device for predicting the pull-out resistance of compaction grouting soil nails, and an application method of the device. Background Art

[0002] Compacted grouting soil nails are a new type of slope and foundation pit reinforcement technology. The grouting sphere formed by it is the main part of its pull-out resistance. The size of the surface area of ​​the grouting sphere and the boundary conditions of the soil in which it is located affect the pull-out resistance of the compacted grouting soil nails. The pull-out model test using the traditional soil nail pull-out test box is complicated, costly, and difficult to conduct on-site tests.

[0003] The cone tip resistance between the cone probe and the soil obtained in the CPT test is also proportional to the cross-sectional area of ​​the probe, which is similar to the force mode of the grouting sphere in the soil. Therefore, the CPT test can be used to establish its relationship with the pull-out resistance of the compaction grouting soil nails under different soil density, stress field and other boundary conditions, so as to predict the pull-out resistance of the compaction grouting soil nails when they are used on site. In this way, only the CPT test needs to be carried out on the corresponding slope at the engineering site, and the cone tip resistance value obtained from the CPT test can be used to predict the pull-out resistance of the compaction grouting soil nails in the soil layer. This test is simpler than the pull-out test of the compaction grouting soil nails. Summary of the invention

[0004] One of the purposes of the present invention is to provide a method to calculate the pull-out resistance of a grouting sphere of a compaction grouting soil nail, which can use a simpler and lower-cost CPT test to replace the compaction grouting soil nail tensile test with a complex and higher-cost test process; a second purpose is to provide a test device for implementing the aforementioned method; a third purpose is to provide a method for performing a CPT test using the aforementioned device.

[0005] The method for predicting the pull-out force of compaction grouting soil nails provided by the present invention comprises the following steps: setting a model box, filling the model box with soil samples, and setting a micro soil pressure gauge in the soil samples; applying horizontal static pressure to the soil samples by means of a loading device outside the model box; and then pressing a static probe into the soil sample by means of a probing device arranged on the top of the model box to perform a CPT test, so as to obtain a cone tip resistance value received by the probe in the soil sample; and then comparing and fitting the cone tip resistance with the pull-out force of a grouting sphere under a known pressure soil sample state, so as to find a correlation between the two and infer the pull-out force of the grouting sphere under other states.

[0006] The device for performing CPT test according to the above method provided by the present invention comprises a model box, a reaction frame, a loading device and a probing device. The model box comprises a square box body with a top surface and a side opening, and a movable plate installed at the side opening of the square box body. One end of the reaction frame is connected to the side plates on both sides of the side opening of the square box body. The loading device is installed and fixed between the reaction frame and the movable plate. The probing device is fixed at the center position of the top surface of the square box body through a mounting beam.

[0007] In one embodiment of the technical solution of the above device, the side panels on both sides of the side opening of the square box are symmetrically provided with vertical inward folded edges, and the outer walls of each side panel of the square box are connected with a criss-cross ribbed frame.

[0008] In one embodiment of the technical solution of the above-mentioned device, the height of the movable plate is smaller than the height of the square box, grooved baffles are symmetrically arranged on both sides of the height direction of the movable plate, pulleys are symmetrically connected on both sides of the bottom surface, and a M-shaped ribbed bar frame is arranged on the outer side of the movable plate.

[0009] In one embodiment of the technical solution of the above device, a groove with a size larger than the pulley is provided on the inner surface of the bottom plate of the square box body corresponding to the position of the pulley. When the movable plate is installed, the grooved baffle is limited by the bent edge, and the pulley is rotatably embedded in the groove.

[0010] In one implementation of the technical solution of the above device, a circle of threaded holes are provided on the three side panels of the square box at heights corresponding to the movable panels, and screws or bolts are connected to each threaded hole.

[0011] In one embodiment of the technical solution of the above-mentioned device, the reaction frame is an A-type frame, which is horizontally arranged with its sharp corners facing outward, and its horizontal height corresponds to the center plane of the height direction of the movable plate, and its two long side rods are respectively connected and fixed to the side panels on both sides of the side opening of the square box.

[0012] In one embodiment of the technical solution of the above-mentioned device, the static probing device adopts a static probing machine with a matching double-bridge probe; the loading device adopts a hydraulic jack, which is arranged in the horizontal direction, one end of which is fixed at the center position of the M-shaped ribbed frame on the outer side of the movable plate, and the other end is fixed to the short side rod of the reaction frame.

[0013] In one implementation of the technical solution of the above device, a plurality of groups of mounting holes for mounting the loading device are provided on the reaction frame.

[0014] The method for performing a CPT test using the above device provided by the present invention comprises the following steps:

[0015] (1) A plurality of micro earth pressure gauges are arranged on the inner side of the side plate opposite to the side opening of the square box as earth pressure data acquisition instruments, and then the soil sample is loaded into the model box until it is close to the position of the upper limit rod of the side plate of the square box and then leveled, and a pressure plate is placed on the top surface of the soil sample and pressed by the limit rod;

[0016] (2) Connect the data lines of the double-bridge probe and the micro-earth pressure gauge installed in the soil sample to their respective data acquisition instruments, and ensure that the double-bridge probe and each micro-earth pressure gauge are in normal condition;

[0017] (3) Applying pressure to the movable plate through a hydraulic jack to horizontally pressurize the soil sample in the model box;

[0018] (4) When the soil pressure reaches the design value, the hydraulic jack stops applying pressure;

[0019] (5) The double-bridge probe is driven into the soil sample at a uniform speed by a static penetration machine on the top of the model box. At the same time, the double-bridge probe records the cone tip resistance values ​​at different penetration depths through its data acquisition instrument;

[0020] (6) Remove the loading device, unload the soil sample, reload the soil sample into the model box, level it, cover it with the pressure plate and fix it, adjust the pressure value of the hydraulic jack to apply different horizontal pressures to the soil sample, and repeat steps (2) to (5) using a probe with the same diameter.

[0021] (7) Remove the loading device, unload the soil sample, refill the soil sample and level it, then cover and fix the pressure plate, replace the double-bridge probe with a different diameter, and repeat steps (2) to (5) while maintaining the loading pressure of step (6).

[0022] (8) The data acquisition instrument connected to the double-bridge probe records the cone tip resistance value that changes with the penetration depth, and draws a curve chart showing the relationship between the cone tip resistance and the penetration depth; the data obtained from the static penetration test are compared and fitted with the pull-out resistance data of the grouting sphere under a known pressure soil sample state to find the correlation between the two, establish a connection, and infer the pull-out resistance of compacted grouting soil nails with different sphere diameters under other conditions.

[0023] The present invention first proposes a prediction method for calculating the pull-out resistance of the grouting sphere of the compaction grouting soil nail by using the CPT test instead of the pull-out model test, and under the guidance of the method, a corresponding test device is proposed, and a method for using the device to perform a simulation test is also given. Specifically, a plurality of soil pressure gauges are arranged on the inner side of the side plate opposite to the movable plate of the model box, the soil sample is loaded into the model box, the soil sample is flattened and covered with a pressure plate and fixed, the soil sample is pressurized by a static load application device, and the soil pressure in the soil sample is monitored by the soil pressure gauge to obtain an accurate value of the compressive stress in the soil, and the CPT test is performed under different soil compressive stresses, so that the resistance generated by the soil sample under different compressive stresses to the probing device can be obtained more conveniently in the laboratory, and then compared and fitted with known data (the pull-out resistance data of the grouting sphere under the soil sample state with known pressure), so that the pull-out resistance of the compaction grouting soil nail under the boundary conditions of other soils can be calculated according to the cone tip resistance value obtained by the CPT test. The present invention is very suitable for engineering sites where compaction grouting soil nails are required to reinforce slopes or foundation pits. It is only necessary to uniformly penetrate the slope with a standard CPT probe that meets the requirements of the specification, and then the density of the compaction grouting soil nails required for the soil layer and the diameter of the grouting sphere can be conveniently and accurately calculated based on the cone tip resistance value obtained from the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the main structure of an embodiment of the present invention.

[0025] Figure 2 for Figure 1 Schematic diagram of the structure after removing the movable plate from the middle square box (soil samples have been loaded in the square box).

[0026] Figure 3 for Figure 1 Schematic diagram of top view (static penetration machine not shown).

[0027] Figure 4 for Figure 3 A magnified schematic diagram of part A in FIG. DETAILED DESCRIPTION

[0028] The present invention firstly proposes a prediction method for using CPT test to replace the current pull-out model test to infer the pull-out resistance of the grouting sphere of the compaction grouting soil nail: a model box is set, a soil sample is filled in the model box, and a soil pressure gauge is set in the soil sample, a horizontal static pressure is applied to the soil sample by a static loading device outside the model box, and then a static probe is pressed into the soil sample by a probing device set on the top of the model box to perform a CPT test, and the cone tip resistance value of the probe in the soil sample is obtained, and then the cone tip resistance is compared and fitted with the pull-out resistance of the grouting sphere under a known pressure soil sample state, and the correlation between the two is found and the pull-out resistance of the grouting sphere under other states is inferred.

[0029] Under the guidance of the above method, a corresponding test device was designed, and a method for conducting simulation tests using the device was also given.

[0030] like Figure 1 As shown, the CPT test device disclosed in this embodiment includes a model box 1, a reaction frame 2, a loading device 3, a probing device 4, and a static probe 5.

[0031] Combination Figures 1 to 3 It can be seen that the model box 1 includes a square box body surrounded by three side panels 11 and a bottom panel 12, and a movable panel 13 installed at the side opening of the square box body.

[0032] In order to enhance the overall rigidity of the square box, a crisscross-shaped rib frame 111 is connected to the outer sides of the three side panels 11 thereof.

[0033] The two opposite side panels have inward vertical bending edges at the corresponding opening sides, and the bending edges are used to install the movable panel 13.

[0034] Combination Figure 1 , Figure 3 and Figure 4 It can be seen that the height of the movable plate 13 is less than the height of the square box, and grooved baffles 131 with openings facing outward are symmetrically arranged on both sides of the height direction of the movable plate, and the opening width of the grooved baffles is much larger than the thickness of the bent edge of the side panels of the square box. Pulleys are symmetrically connected to both sides of the lower end of the movable plate 13. In order to increase the rigidity of the movable plate 13, a cross-shaped rib frame 132 is connected to the outer side of the movable plate. There is a groove on the inner surface of the bottom plate 12 of the square box corresponding to the position of the pulley, and the size of the groove is larger than the size of the pulley. When the movable plate 13 is installed, the bent edges of the side panels on both sides of the side opening of the square box are inserted into the two grooved baffles of the movable plate, and the pulley at the lower end of the movable plate is embedded in the groove on the bottom plate of the direction box.

[0035] Therefore, after the movable plate is installed on the square box, it can move horizontally within a certain range. And the friction between the movable plate and the bottom plate can be reduced by the pulley, so that the force loss of the jack can be minimized. In addition, if the friction between the movable plate and the bottom plate is too large, it may cause excessive torque and uneven force on the soil sample, and the pulley can effectively reduce this effect.

[0036] A circle of round holes is arranged on the three side plates of the square box body 11 at the height position corresponding to the movable plate 13, and nuts are welded at the round holes, and screw rods 14 are connected in the nuts. After the soil sample is loaded into the model box, the pressing plate 6 on the top surface of the soil sample is pressed and fixed by bolts.

[0037] The reaction frame 2 is an A-shaped frame made of rectangular steel pipe, and the ends of the long side rods on both sides have straight folded edges. When installed on the square box 11, it is arranged horizontally, and the installation height corresponds to the middle position in the height direction of the movable plate 12. The straight folded edges of the ends of the long side rods on both sides are welded to the side plates on both sides of the side opening of the square box. In this way, the model box structure itself can offset the force, and no reaction facilities outside the structure are required.

[0038] After the reaction frame 2 is installed on the square box 11, the loading device 3 is installed.

[0039] The loading device 3 of this embodiment adopts a hydraulic jack. When installed, the fixed end of the hydraulic jack is fixed to the short side rod of the reaction frame 2 through a fastener, and the telescopic movable end is fixed to the center position of the cross-shaped rib frame outside the movable plate 12. The probing device 4 adopts a CLD-2 static penetration machine. The loading device is used to simulate the pressure of the overlying soil layer of the test soil sample.

[0040] Two cross beams are welded between the top ends of two opposite side plates of the square box, and the two cross beams are symmetrically arranged about the transverse center plane of the square box. The lower end of the feeler device 4 is fixed to the two cross beams 15 by fasteners.

[0041] The static probe 5 adopts a double-bridge probe that can measure the cone tip resistance. The double-bridge probe is installed at the lower end of the probe rod. The CLD-2 static penetration machine clamps the probe rod and can uniformly press the double-bridge probe at the lower end of the probe rod into the soil sample in the model box.

[0042] The following is an example of a model box with a size of 100cm×100cm×120cm to explain in detail the specific steps of using the above device to conduct a CPT test:

[0043] 1. Model box test

[0044] (1) Make a model box that meets the test requirements and prepare the soil samples required for the test. This test uses loose sand as the soil sample.

[0045] (2) Install the movable panel door at the side opening of the square box, and assemble it using the grooved baffles on both sides of the movable panel and the bent edge of the square side panel. At the same time, make sure that the pulley at the bottom of the movable panel is embedded in the groove under the box. Since the width of the grooved baffle is much larger than the thickness of the bent edge, and the size of the groove is larger than the size of the pulley, when a horizontal force is applied to the movable panel, the movable panel can move horizontally within a certain range.

[0046] (3) A YT-200G strain gauge micro soil pressure gauge is installed in the middle of the inner side of the side plate corresponding to the side opening of the square box: five rows in the upper and lower parts, three in each row, and five in each row with a spacing of 15 cm. It is used to monitor the magnitude of the compressive stress in the soil sample when the loading device applies pressure. The data line of the pressure gauge passes through the side plate and extends from the upper end of the square box to connect with the data acquisition instrument.

[0047] (4) Fill the model box with soil samples and level it. When the soil samples are filled to 0.5 cm above the movable door, cover the top of the soil samples with a pressure plate and press the pressure plate with bolts. A circular hole is set at the center of the pressure plate to allow the double bridge probe to pass through.

[0048] (5) The bottom surface of the fixed end of the hydraulic jack is fixed to the short side rod of the reaction frame by bolts. The fixing position is based on the center position of the movable plate corresponding to the telescopic end of the hydraulic jack, so that the soil sample in the model box is subjected to more uniform force during loading. After the hydraulic jack is installed, static force (about 12KN) is applied to the movable plate. At the same time, the compressive stress in the soil is monitored by the YT-200G strain-type micro soil pressure gauge installed in the model box and recorded by the data acquisition instrument.

[0049] (6) Fix the CLD-2 static penetration tester to the crossbeam on the top surface of the model box with bolts, install the double-bridge probe on the probe rod, and install the probe rod on the static penetration tester, keeping the probe rod vertical.

[0050] (7) The data lines of the double-bridge probe with a diameter of 35.7 mm and the YT-200G strain-type micro earth pressure gauge installed in the soil sample are connected to their respective data acquisition instruments, and the double-bridge probe and each YT-200G strain-type micro earth pressure gauge are debugged to ensure that they are in normal condition.

[0051] (8) Rotate the shaft of the CLD-2 static penetration machine and penetrate the double-bridge probe into the soil sample at a uniform speed. Control the penetration rate at 1.2 m / min. Stop penetration when the double-bridge probe penetrates about 50 cm into the soil sample. Record the cone tip resistance values ​​at different penetration depths using the data acquisition instrument connected to the double-bridge probe.

[0052] (9) Unload the loading device, unload the soil sample, refill the soil sample and level it, replace the double-bridge probe with a diameter of 43.7 mm, and repeat steps (5) to (8) at the same pressure as step (5).

[0053] (10) Unload the loading device, unload the soil sample, refill the soil sample and level it, change the pressure applied by the hydraulic jack, and repeat steps (5) to (8) using the two diameters of the double bridge probe in steps (7) and (9) respectively.

[0054] 2. Analysis

[0055] The data acquisition instrument connected to the double-bridge probe records the cone tip resistance value that changes with the penetration depth, and draws a curve chart of the relationship between the cone tip resistance and the penetration depth. Then the data obtained by static penetration is compared and fitted with the pull-out resistance data of the grouting sphere under a known pressure soil sample state to find the correlation between the two, establish a connection, and deduce the pull-out resistance of the compaction grouting soil nails with different sphere diameters under other conditions.

[0056] The present invention first proposes a test method for calculating the pull-out resistance of the grouting sphere of the compaction grouting soil nail by using the CPT test instead of the pull-out model test, and under the guidance of the method, a corresponding test device is proposed, and a method for using the device to perform a simulation test is also provided. A plurality of soil pressure gauges are arranged on the inner side of the side plate opposite to the movable plate of the model box, the soil sample is loaded into the model box, the soil body is leveled, and the pressure plate is covered and fixed, the soil sample is pressurized by the static load application device, and the soil pressure in the soil body is monitored to obtain an accurate soil compressive stress value, and the CPT test is performed under different soil compressive stresses, so that the resistance generated by the soil sample under different compressive stresses to the probing device can be obtained more conveniently in the laboratory, and then compared and fitted with known data (the pull-out resistance data of the grouting sphere under known pressure and soil sample state), so that the pull-out resistance of the compaction grouting soil nail under the boundary conditions of other soils can be calculated according to the cone tip resistance value obtained by the CPT test.

[0057] This method is very suitable for engineering sites where slopes or foundation pits need to be reinforced with compaction grouting soil nails. It only requires a standard CPT probe that meets the requirements of the specification to be uniformly penetrated into the slope. The density of the compaction grouting soil nails and the diameter of the grouting sphere required for the soil layer can be conveniently and accurately calculated based on the cone tip resistance value obtained from the test.

Claims

1. A method for predicting the pull-out force of compaction grouting soil nails, characterized in that: The test device used in the method includes a model box, a reaction frame, a loading device and a static penetration device. The model box includes a square box body with a top surface and a side opening, and a movable plate installed at the side opening of the square box body. One end of the reaction frame is connected to the side plates on both sides of the side opening of the square box body. The loading device is installed and fixed between the reaction frame and the movable plate. The static penetration device is fixed to the center position of the top surface of the square box body through a mounting beam. The model box is filled with soil samples, and a miniature soil pressure gauge is set in the soil sample. Horizontal static pressure is applied to the soil sample by a loading device outside the model box. Then, the static probe is pressed into the soil sample by a probing device set on the top of the model box to carry out a CPT test. The cone tip resistance value of the probe in the soil sample is obtained, and then the cone tip resistance is compared and fitted with the pull-out force of the grouting sphere under the known pressure soil sample state, so as to find the correlation between the two and deduce the pull-out force of the grouting sphere under other states.

2. The method according to claim 1, characterized in that: The side panels on both sides of the side opening of the square box body are symmetrically provided with vertical inwardly folded edges, and the outer walls of the side panels of the square box body are connected with a well-shaped corrugated bar frame.

3. The method according to claim 2, characterized in that: The height of the movable plate is smaller than that of the square box, grooved baffles are symmetrically arranged on both sides of the height direction of the movable plate, pulleys are symmetrically connected on both sides of the bottom surface, and a M-shaped ribbed bar frame is arranged on the outer side of the movable plate.

4. The method according to claim 3, characterized in that: A groove whose size is larger than the size of the pulley is arranged on the inner surface of the bottom plate of the square box body at the position corresponding to the pulley. When the movable plate is installed, the groove-shaped baffle is limited by the bent edge, and the pulley is rotatably embedded in the groove.

5. The method according to claim 3, characterized in that: A circle of threaded holes are arranged on the three side plates of the square box body at the height positions corresponding to the movable plates, and screws or bolts are connected to each threaded hole as a limiting rod.

6. The method according to claim 5, characterized in that: The reaction frame is an A-shaped frame, which is arranged horizontally with its sharp corners facing outwards. The horizontal height corresponds to the center plane of the height direction of the movable plate. Its two long side rods are respectively connected and fixed to the side plates on both sides of the side opening of the square box.

7. The method according to claim 6, characterized in that: The static penetration device adopts a static penetration machine with a double-bridge probe; the loading device adopts a hydraulic jack, which is arranged in the horizontal direction, one end of which is fixed to the center position of the M-shaped rib frame outside the movable plate, and the other end is fixed to the short side rod of the reaction frame.

8. The method according to claim 7, characterized in that: The reaction frame is provided with a plurality of mounting holes for mounting the loading device.

9. The method of claim 7, comprising the steps of: (1) Multiple micro earth pressure gauges are set on the inner side of the side plate opposite to the side opening of the square box, and then the soil sample is loaded into the model box until it is close to the position of the upper limit rod on the side plate of the square box and leveled. A pressure plate is placed on the top surface of the soil sample and pressed down by the limit rod; (2) Connect the data cables of the double-bridge probe and the micro earth pressure gauge installed in the soil sample to their respective data acquisition instruments, and ensure that the double-bridge probe and each micro earth pressure gauge are in normal condition; (3) Applying pressure to the movable plate through the hydraulic jack to achieve horizontal pressure on the soil sample in the model box; (4) When the data acquisition instrument connected to the micro soil pressure gauge reflects that the soil pressure reaches the design value, the hydraulic jack stops applying pressure; (5) The double-bridge probe is driven into the soil sample at a uniform speed through the static penetration device on the top of the model box. At the same time, the double-bridge probe records the cone tip resistance value that changes with the penetration depth through its data acquisition instrument; (6) Remove the loading device, unload the soil sample, reload the soil sample into the model box, level it, cover it with the pressure plate and fix it, adjust the pressure value of the hydraulic jack to apply different horizontal pressures to the soil sample, and repeat steps (2) to (5) using the probe of the same diameter; (7) Remove the loading device, unload the soil sample, refill the soil sample and level it, then cover and fix the pressure plate, replace the double-bridge probe with a different diameter, and repeat steps (2) to (5) while maintaining the loading pressure of step (6); (8) Based on the cone tip resistance measured by the double-bridge probe, record the relationship between the cone tip resistance and penetration depth of the double-bridge probe in each test and draw a curve graph; compare and fit the data obtained from the static penetration test with the pull-out resistance data of the grouting sphere under a known pressure soil sample state to find the correlation between the two, establish a connection and deduce the pull-out resistance of the compacted grouting soil nails with different sphere diameters under other conditions.

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