Apparatus and method for simulating the slump of backfill material in vertical buried pipe boreholes

Abstract

This invention discloses an apparatus and method for simulating the slump of backfill material in a vertical buried borehole. The apparatus includes a lower pipe body, an upper pipe body, a bedding layer, and a pressure platform. The lower and upper pipe bodies are coaxial and have the same inner diameter, simulating a formation borehole through their inner holes. The upper end of the lower pipe body has a first outer flange, and the lower end of the upper pipe body has a second outer flange, which are fixedly connected. The bedding layer is placed between the first and second outer flanges to form a gap between them to simulate formation fractures. The pressure platform has an outer contour matching the inner hole size of the lower pipe body, allowing it to slide up and down within the lower and upper pipe bodies to compress the backfill material below it. Compared to existing technologies, this invention can simulate the situation where underground fractures traverse the borehole, and based on this, test the slump of different backfill materials within the fractures.

Description

Technical Field

[0001] This invention relates to the field of geotechnical material testing technology, and in particular to an apparatus and method for simulating and testing the slump of backfill material in vertical buried pipe boreholes. Background Technology

[0002] Shallow geothermal energy is a highly competitive green and low-carbon renewable energy source, and southwestern my country possesses abundant shallow geothermal energy resources. However, due to the karst topography of southwestern my country, the strata where boreholes are located often exhibit intersecting fracture structures, leading to different collapse patterns of backfill materials under various load pressures. These complex fracture structures often allow for karst water infiltration, thus affecting the heat exchange of buried pipes. Currently, some scholars have noted the significant relationship between heat exchange of buried pipes in boreholes and fracture structures and the collapse of backfill materials, but feasible experimental devices and methods are lacking to guide the slump determination of different backfill materials. Summary of the Invention

[0003] The purpose of this invention is to provide an apparatus and method for simulating and testing the slump of backfill material in vertical buried pipe boreholes. The apparatus simulates the situation where underground fissures cross the borehole, and on this basis, tests the slump of different backfill materials in the fissures.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] This invention discloses an apparatus for simulating the slump of backfill material in a vertical buried pipe borehole, comprising a lower pipe body, an upper pipe body, a cushion layer, and a pressure platform. The lower pipe body and the upper pipe body are coaxial and have the same inner diameter, simulating a formation borehole through their inner holes. The upper end of the lower pipe body has a first outer flange, and the lower end of the upper pipe body has a second outer flange, which are fixedly connected. The cushion layer is disposed between the first and second outer flanges to form a gap between them to simulate formation fractures, and this gap communicates with both the inner holes of the lower and upper pipe bodies. The pressure platform has an outer contour matching the size of the inner hole of the lower pipe body, allowing it to slide up and down within the lower and upper pipe bodies to compress the backfill material below it.

[0006] Preferably, it also includes a base, which is fixed to the lower end of the lower tube.

[0007] Preferably, the padding layer comprises two pads, and the gap is located between the two pads.

[0008] Preferably, the first outer flange and the second outer flange are fixedly connected by bolts and nuts.

[0009] Preferably, the bolt's thread passes through the pad to limit the pad's position.

[0010] Preferably, both the lower tube and the upper tube are made of transparent material.

[0011] Preferably, the padding layers comprise multiple layers that are interchangeable, and the multiple padding layers have different thicknesses.

[0012] This invention also discloses a method for simulating the slump of backfill material in vertical buried pipe boreholes, using the aforementioned apparatus for simulating the slump of backfill material in vertical buried pipe boreholes, comprising the following steps:

[0013] Step 1: Use the ring cutter method to measure multiple sets of backfill sand density data, and take the average value as the approximate value ρ of backfill sand density;

[0014] Step 2: Using backfill sand collected on-site, neglecting the friction between the backfill sand and the borehole wall, the total weight of the overlying backfill sand is used to simulate the vertical load on the backfill sand at a certain location; the experiment simulates the collapse of backfill sand with different gap widths within the fracture at a depth h, and the borehole cross-sectional area S = πr 2 The pressure at the corresponding depth is P = ρgh, and the load to be applied is F = PS = ρghS. Calculate the total weight of the required overlying backfill sand according to the above formula.

[0015] Step 3: Pour the backfill sand to be tested into the upper pipe from the top of the upper pipe until the upper and lower pipes are filled. Observe and measure the spread of the backfill sand under natural falling conditions, record the length and width of the spread, and calculate the collapse area.

[0016] Step 4: Smooth the top of the backfill sand in the simulated borehole, place the lower surface of the pressure platform horizontally at the center of the backfill sand surface; apply a predetermined downward pressure to the pressure platform and maintain the predetermined pressure, observe and measure the spreading of the backfill sand, record the length and width of the spreading, and calculate the collapse area.

[0017] Step 5: Keep the predetermined pressure constant, observe and measure the spreading of the backfill sand at predetermined intervals, record the length and width of the spread, and calculate the collapse area;

[0018] Step 6: Pour out the backfill sand from the upper and lower pipe bodies; keep the thickness of the cushion layer and the backfill sand material unchanged, change the size of h, and repeat steps 2 to 5 to measure the collapse of the same backfill material under the same gap width and different borehole depths.

[0019] Step 7: Pour out the backfill sand from the upper and lower pipe bodies; keeping the size of h and the backfill sand material unchanged, change the thickness of the cushion layer, repeat steps 2 to 5, and measure the collapse of the same backfill material at the same borehole depth and different gap widths.

[0020] Step 8: Pour out the backfill sand from the upper and lower pipe bodies; change the backfill sand material, keep h and the thickness of the cushion layer unchanged, and repeat steps 1 to 5 to measure the collapse of different backfill materials under the same gap width and the same borehole depth.

[0021] Preferably, in step 4, pressure is applied to the pressure table using a uniaxial testing machine.

[0022] Preferably, in step 5, the predetermined time is 15 minutes.

[0023] The present invention achieves the following technical effects compared to the prior art:

[0024] The apparatus and method disclosed in this invention can, on the one hand, simulate the collapse of the same backfill material in the same gap width under different depth loads, and obtain the relationship between slump and load magnitude; on the other hand, they can simulate the collapse of the same backfill material in different gap widths under the same magnitude of overhead load, and obtain the relationship between slump and gap width; they can also simulate the collapse of different particle backfill materials under the same gap width and the same magnitude of overhead load, and obtain the relationship between slump and different particle backfill materials.

[0025] Therefore, this invention solves the problem of the lack of experimental equipment for testing the slump of existing borehole backfill materials. It has a simple structure and is of great significance for guiding the production of new reliable backfill materials and methods for backfilling cracks. Attached Figure Description

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 This is a top-view schematic diagram of the device for simulating and testing the slump of backfill material in a vertical buried pipe borehole according to an embodiment of the present invention.

[0028] Figure 2 for Figure 1 A cross-sectional view along the AA direction;

[0029] Explanation of reference numerals in the attached drawings: 1-Upper pipe body; 2-Second outer flange; 3-Bushing layer; 4-First outer flange; 5-Lower pipe body; 6-Base; 7-Pressure platform; 8-Bolt. Detailed Implementation

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] The purpose of this invention is to provide an apparatus and method for simulating and testing the slump of backfill material in vertical buried pipe boreholes. The apparatus simulates the situation where underground fissures cross the borehole, and on this basis, tests the slump of different backfill materials in the fissures.

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Reference Figures 1-2 This embodiment provides a device for simulating the slump of backfill material in vertical buried pipe boreholes (hereinafter referred to as the simulation test device), which includes a lower pipe body 5, an upper pipe body 1, a cushion layer 3 and a pressure platform 7.

[0034] The lower pipe body 5 and the upper pipe body 1 are coaxial and have the same inner diameter, simulating a formation borehole through their inner holes. In this embodiment, the simulated formation borehole is a vertical hole. The upper end of the lower pipe body 5 has a first outer flange 4, and the lower end of the upper pipe body 1 has a second outer flange 2. The first outer flange 4 and the second outer flange 2 are fixedly connected to ensure that the inner hole of the lower pipe body 5 and the inner hole of the upper pipe body 1 are not misaligned. A pad 3 is provided between the first outer flange 4 and the second outer flange 2 to form a gap between them to simulate formation fractures. This gap is connected to the inner holes of the lower pipe body 5 and the upper pipe body 1.

[0035] The working principle of the simulation testing device in this embodiment is as follows:

[0036] Due to the presence of formation fractures, the formation borehole is divided into upper and lower parts by the formation fractures. In this embodiment, the gap between the first outer flange 4 and the second outer flange 2 is used to simulate formation fractures, the inner hole of the upper pipe body 1 is used to simulate the upper part of the formation borehole, and the inner hole of the lower pipe body 5 is used to simulate the lower part of the formation borehole.

[0037] As a possible example, in this embodiment, the pressure platform 7 has an outer contour that matches the inner diameter of the lower pipe 5, allowing the pressure platform 7 to slide up and down within the lower pipe 5 and the upper pipe 1 to press down the backfill material below the pressure platform 7. In this embodiment, the pressure platform 7 is preferably clearance-fitted with the inner diameter of the upper pipe 1 and with the inner diameter of the lower pipe 5, so as to ensure that the pressure platform 7 can press down the entire surface layer of the backfill material while facilitating the up and down movement of the pressure platform 7.

[0038] As a possible example, in this embodiment, the simulation testing device further includes a base 6, which is fixed to the lower end of the lower tube 5. The base 6 can be placed on the ground or a workbench to improve the stability of the simulation testing device. Specifically, in this embodiment, the base 6 is a square plate, and the axis of the lower tube 5 passes perpendicularly through the geometric center of the base 6. Depending on the actual needs, the base 6 can also be other types, such as a circular plate.

[0039] As a possible example, in this embodiment, the pad 3 includes two pads with a gap between them. Specifically, the two pads are symmetrically arranged about the longitudinal section of the upper tube 1. Each pad includes two radial plates, two outer plates, and a middle plate. The two radial plates are arranged radially along the upper tube 1 and perpendicular to each other. The two ends of the middle plate are respectively connected to the ends of the two radial plates away from the axis of the upper tube 1. The ends of the outer plates away from the axis of the upper tube 1 are connected to the ends of the middle plate. The two outer plates are respectively connected to the two ends of the middle plate. Depending on the actual needs, the pad 3 can also be of other types. For example, the pad 3 can be an integral square plate with a through hole coaxial with the lower tube 5. The diameter of the through hole is larger than the inner diameter of the lower tube 5 so that the gap is annular.

[0040] As one possible example, in this embodiment, the first outer flange 4 and the second outer flange 2 are fixedly connected by bolts 8 and nuts. The thread of the bolt 8 passes through the second outer flange 2 and the first outer flange 4 in sequence and is then threadedly connected to the nut. Depending on the actual needs, those skilled in the art may also choose other methods to fix the first outer flange 4 and the second outer flange 2 together.

[0041] As one possible example, in this embodiment, the bolt 8 passes through the gasket 3 to limit the gasket 3. Depending on the actual needs, those skilled in the art can also limit the movement of the gasket 3 by clamping the gasket 3 between the first outer flange 4 and the second outer flange 2.

[0042] As a possible example, in this embodiment, both the first outer flange 4 and the second outer flange 2 are square flanges, and they are positioned opposite each other. Four bolts 8 are included, installed at the four right angles of the first outer flange 4 and threadedly connected to corresponding nuts. Two bolts 8 pass through both ends of the middle plate of one of the gaskets, and the other two bolts 8 pass through both ends of the middle plate of the other gasket.

[0043] As a possible example, in this embodiment, both the lower tube 5 and the upper tube 1 are made of transparent material to facilitate observation of the internal conditions.

[0044] As one possible example, in this embodiment, the padding layer 3 comprises multiple layers that are interchangeable, and the multiple padding layers 3 have different thicknesses. Depending on the actual needs, padding layers 3 of appropriate thickness can be selected for use.

[0045] As a possible example, in this embodiment, the pad is 600mm long, 250mm wide, and the pad thickness is 0.5mm to 2.5mm. The inner diameter of the upper pipe body 1 cylindrical section is 100mm to 140mm, the wall thickness of the upper pipe body 1 cylindrical section is not less than 5mm, and the depth of the upper pipe body 1 cylindrical section is 200mm. The thickness of the first outer flange 4 and the second outer flange 2 is not less than 3mm, and the length and width of the first outer flange 4 and the second outer flange 2 are both 600mm. The dimensions of the lower pipe body 5 cylindrical section are the same as those of the upper pipe body 1 cylindrical section. The length and width of the base 6 are both not less than 600mm, the outer diameter of the bolt 8 is 5mm to 10mm, and the height of the pressure platform 7 is 150mm. Depending on the actual needs, those skilled in the art can also choose other dimensions.

[0046] This invention also discloses a method for simulating the slump of backfill material in vertical buried pipe boreholes (hereinafter referred to as the simulation test method), which uses the above-mentioned simulation test device and includes the following steps:

[0047] Step 1: Using the ring cutter method, multiple sets of backfill sand density data were measured, and the average value was taken as the approximate backfill sand density ρ. In this embodiment, the ring cutter dimensions were 70mm in diameter (φ) × 52mm in height (H), and ten sets of data were measured. The approximate backfill sand density ρ was rounded to two decimal places. It should be noted that in actual backfilling, the backfill sand density at a certain depth is mainly affected by the pressure from the backfill sand above and the friction between the backfill sand and the borehole wall. The actual density is not a stable value. The approximate value was measured after the backfill sand was compacted in the ring cutter during the experiment, and this density was used to calculate the overburden load on the backfill sand at different depths as the basis for the applied pressure.

[0048] Step 2: Using backfill sand collected on-site, neglecting the friction between the backfill sand and the borehole wall, the total weight of the overlying backfill sand is used to simulate the vertical load on the backfill sand at a certain location. The experiment simulates the collapse of backfill sand with different gap widths within the fracture at depth h, and the borehole cross-sectional area S = πr. 2 The pressure at the corresponding depth is P = ρgh, and the load to be applied is F = PS = ρghS. Calculate the total weight of the backfill sand required based on the above formula, and round the result to the nearest integer.

[0049] Step 3: Inject the backfill sand to be tested from the top of the upper pipe 1 until both the upper pipe 1 and the lower pipe 5 are filled. Observe and measure the spreading of the backfill sand under natural falling conditions (the backfill sand spreads in the gap used to simulate formation fractures), record the length and width of the spread, and calculate the collapse area (the collapse area is the spread area of ​​the backfill sand in the gap). The length, width, and collapse area are all integers, and similar data in subsequent steps are also integers. Specifically, in this embodiment, the simulation testing device is placed at the center of the platform below the uniaxial testing machine for operation, so that the pressure table 7 can be pressed down by the uniaxial testing machine later.

[0050] Step 4: Smooth the top of the backfill sand in the simulated borehole, and place the lower surface of the pressure platform 7 horizontally at the center of the backfill sand surface. Apply a predetermined downward pressure to the pressure platform 7 and maintain the predetermined pressure (the predetermined pressure is the total gravity calculated in Step 1). Observe and measure the spreading of the backfill sand, record the length and width of the spread, and calculate the collapse area. Since this embodiment uses a uniaxial testing machine for downward pressure, the predetermined pressure value and the time to maintain the predetermined pressure can be set through the control panel of the uniaxial testing machine.

[0051] Step 5: Maintaining a constant predetermined pressure, observe and measure the spreading of the backfill sand at predetermined time intervals, record the length and width of the spread sand, and calculate the collapse area. In this embodiment, the predetermined time is 15 minutes.

[0052] Step 6: Pour out the backfill sand from the upper pipe 1 and the lower pipe 5. Keeping the thickness of the cushion layer 3 and the backfill sand material constant, change the size of h and repeat steps 2 to 5 to measure the collapse of the same backfill material under the same gap width and different borehole depths.

[0053] Step 7: Pour out the backfill sand from the upper pipe 1 and the lower pipe 5. Keeping the size of h and the backfill sand material unchanged, change the thickness of the cushion layer 3 and repeat steps 2 to 5 to measure the collapse of the same backfill material at the same borehole depth and different gap widths.

[0054] Step 8: Pour out the backfill sand from the upper pipe 1 and the lower pipe 5. Change the backfill sand material, keep h and the thickness of the cushion layer 3 unchanged, and repeat steps 1 to 5 to measure the collapse of different backfill materials under the same gap width and the same borehole depth.

[0055] The simulation test method in this embodiment uses the simulation test device described above. On the one hand, it can simulate the collapse of the same backfill material in the same gap width under different depth loads to obtain the relationship between slump and load size. On the other hand, it can simulate the collapse of the same backfill material in different gap widths under the same size of overhead load to obtain the relationship between slump and gap width. It can also simulate the collapse of different particle backfill materials under the same gap width and the same size of overhead load to obtain the relationship between slump and different particle backfill materials.

[0056] This specification uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A device for simulating and testing the slump of backfill material in vertical buried pipe boreholes, characterized in that, The system includes a lower pipe body, an upper pipe body, a bedding layer, and a pressure platform. The lower pipe body and the upper pipe body are coaxial and have the same inner diameter, simulating formation drilling through their inner bores. The upper end of the lower pipe body has a first outer flange, and the lower end of the upper pipe body has a second outer flange, which are fixedly connected. The bedding layer is disposed between the first and second outer flanges to form a gap between them to simulate formation fractures. This gap communicates with both the inner bores of the lower and upper pipe bodies. The pressure platform has an outer contour matching the inner bore size of the lower pipe body, allowing it to slide up and down within the lower and upper pipe bodies to compress the backfill material below it. The padding layers comprise multiple layers that are interchangeable, and the multiple padding layers have different thicknesses.

2. The apparatus for simulating and testing the slump of backfill material in vertical buried pipe boreholes according to claim 1, characterized in that, It also includes a base, which is fixed to the lower end of the lower tube body.

3. The apparatus for simulating and testing the slump of backfill material in vertical buried pipe boreholes according to claim 1, characterized in that, The padding layer includes two pads, and the gap is located between the two pads.

4. The apparatus for simulating and testing the slump of backfill material in vertical buried pipe boreholes according to claim 1, characterized in that, The first outer flange and the second outer flange are fixedly connected by bolts and nuts.

5. The apparatus for simulating the slump of backfill material in vertical buried pipe boreholes according to claim 4, characterized in that, The bolt's thread passes through the pad to limit the pad's position.

6. The apparatus for simulating and testing the slump of backfill material in vertical buried pipe boreholes according to claim 1, characterized in that, Both the lower tube and the upper tube are made of transparent material.

7. A method for simulating the slump of backfill material in vertical buried pipe boreholes, characterized in that, The apparatus for simulating the slump of backfill material in a vertical buried pipe borehole, as described in any one of claims 1 to 6, comprises the following steps: Step 1: Use the ring cutter method to measure multiple sets of backfill sand density data, and take the average value as the approximate value ρ of backfill sand density; Step 2: Using backfill sand collected on-site, neglecting the friction between the backfill sand and the borehole wall, the total weight of the overlying backfill sand is used to simulate the vertical load on the backfill sand at a certain location; the experiment simulates the collapse of backfill sand with different gap widths within the fracture at a depth h, and the borehole cross-sectional area S = πr 2 The pressure at the corresponding depth is P = ρgh, and the load to be applied is F = PS = ρghS. Calculate the total weight of the required overlying backfill sand according to the above formula. Step 3: Pour the backfill sand to be tested into the upper pipe from the top of the upper pipe until the upper and lower pipes are filled. Observe and measure the spread of the backfill sand under natural falling conditions, record the length and width of the spread, and calculate the collapse area. Step 4: Smooth the top of the backfill sand in the simulated borehole, place the lower surface of the pressure platform horizontally at the center of the backfill sand surface; apply a predetermined downward pressure to the pressure platform and maintain the predetermined pressure, observe and measure the spreading of the backfill sand, record the length and width of the spreading, and calculate the collapse area. Step 5: Keep the predetermined pressure constant, observe and measure the spreading of the backfill sand at predetermined intervals, record the length and width of the spread, and calculate the collapse area; Step 6: Pour out the backfill sand from the upper and lower pipe bodies; keep the thickness of the cushion layer and the backfill sand material unchanged, change the size of h, and repeat steps 2 to 5 to measure the collapse of the same backfill material under the same gap width and different borehole depths. Step 7: Pour out the backfill sand from the upper and lower pipe bodies; keeping the size of h and the backfill sand material unchanged, change the thickness of the cushion layer, repeat steps 2 to 5, and measure the collapse of the same backfill material at the same borehole depth and different gap widths. Step 8: Pour out the backfill sand from the upper and lower pipe bodies; change the backfill sand material, keep h and the thickness of the cushion layer unchanged, and repeat steps 1 to 5 to measure the collapse of different backfill materials under the same gap width and the same borehole depth.

8. The method for simulating the slump of backfill material in a vertical buried pipe borehole according to claim 7, characterized in that, In step 4, pressure is applied to the pressure table using a uniaxial testing machine.

9. The method for simulating the slump of backfill material in a vertical buried pipe borehole according to claim 7, characterized in that, In step 5, the scheduled time is 15 minutes.

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