A method for repairing defects in the pile-soil interface of cast-in-place piles in permafrost areas

Abstract

The present invention discloses a method for repairing pile-soil interface defects in permafrost areas. The method pre-buries a repair pipe on the wall of a drilled hole and covers the prefabricated hole of the repair pipe with a pressure-sensitive membrane. After the concrete bored pile is poured and fully hydrated, the frozen soil refreezes to form a pile-soil interface defect. Low-temperature mud / mortar is then injected into the repair pipe in stages. When the injection pressure is greater than the rupture pressure of the pressure-sensitive membrane, the pressure-sensitive membrane at the pile-soil interface defect ruptures, thereby effectively filling the pile-soil interface defect, improving the construction quality of the bored pile, significantly enhancing the bearing capacity of the bored pile, and strengthening the stability of the structure.

Description

Technical Field

[0001] The invention relates to the technical field of foundation engineering in permafrost areas, in particular to a method for repairing defects in the pile-soil interface of cast-in-place piles in permafrost areas. Background Art

[0002] Permafrost is a rock mass with ice and a temperature below 0°C. In permafrost areas, there are significant differences in the ice content of the underground soil layer, especially near the upper limit of permafrost, where there is often a thick layer of underground ice. According to the load transfer characteristics of friction pile foundations, theoretically, this part of the permafrost layer is the key area that mainly bears the upper load, that is, the freezing force of the pile-soil interface in this area mainly bears the upper load in the form of lateral friction resistance. However, Figure 1 As shown, during cast-in-place pile construction in permafrost regions, the transfer of concrete hydration heat significantly alters the hydrothermal state of the soil surrounding the pile. This manifests itself in the melting of frozen soil adjacent to the pile and the redistribution of moisture in the thawed area under the action of gravity. When the thawed soil surrounding the pile refreezes under the influence of the infinite cold source of permafrost, the ice content distribution in the soil adjacent to the pile changes significantly compared to its original state, often leading to poor contact or voids at the pile-soil interface. These issues not only lead to significant deviations between the actual bearing capacity of cast-in-place piles in permafrost regions and drilling estimates, but also severely weaken the bearing capacity and structural stability of cast-in-place piles, posing potential safety hazards to construction projects. Currently, solutions to these problems are relatively limited and present certain technical challenges. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for repairing pile-soil interface defects in permafrost areas, targeting the redistribution of moisture in the pile-side melting zone caused by the thermal disturbance of the frozen soil on the pile side by the heat of concrete hydration and the pile-soil interface defects formed during the refreezing process.

[0004] The technical solution adopted to achieve the purpose of the present invention is:

[0005] A method for repairing defects in the pile-soil interface of a cast-in-place pile in a permafrost region comprises the following steps:

[0006] Step 1: pre-embedding of repair pipes: one or more repair pipes are vertically installed along the circumference of a borehole in a permafrost region, each of which has an open top, a top surface flush with the ground surface, and a bottom surface close to the bottom of the borehole. The repair pipe has multiple prefabricated holes spaced apart in sequence along the depth direction of the borehole, with the openings of the prefabricated holes facing the borehole wall and close to the borehole wall, and each prefabricated hole is covered with a single or multiple layers of pressure-sensitive film;

[0007] Step 2, pouring concrete: After the repair pipe is pre-buried, concrete is poured into the drilled hole to form a bored pile. During the pouring process, the soil around the concrete bored pile melts. When the melted soil refreezes, a pile-soil interface defect is formed between the bored pile and the surrounding soil;

[0008] Step 3, injecting low-temperature mud / mortar: injecting low-temperature mud / mortar from the surface into the repair pipe until the injection pressure exceeds the rupture pressure of the pressure-sensitive membrane. The pressure-sensitive membrane at the pile-soil interface defect ruptures, and the low-temperature mud / mortar enters the pile-soil interface defect through the prefabricated hole to fill it.

[0009] Step 4, forming a filling layer: After the injection is completed, the low-temperature mud / mortar freezes and forms a filling layer at the defects in the pile-soil interface, and the defects in the pile-soil interface are repaired.

[0010] In the above technical solution, in step 1, the repair pipe is divided into three sections, namely a top section located at the top of the borehole, a middle section located in the middle of the borehole, and a bottom section located at the bottom of the borehole;

[0011] The rupture pressure of the pressure-sensitive membrane covered by the prefabricated holes located in the top section of the repair tube is a first rupture pressure, the rupture pressure of the pressure-sensitive membrane covered by the prefabricated holes located in the middle section is a second rupture pressure, and the rupture pressure of the pressure-sensitive membrane covered by the prefabricated holes located in the bottom section is a third rupture pressure. The first rupture pressure is greater than the second rupture pressure, and the second rupture pressure is greater than the third rupture pressure.

[0012] In the above technical solution, in step 3, a strain gauge is pasted on the center of the surface of the pressure-sensitive membrane. The strain gauge is connected to a data acquisition system. During the process of injecting low-temperature mud / mortar into the repair pipe, the output signal of the strain gauge is recorded in real time by the data acquisition system. Based on the output signal of the strain gauge, combined with the elastic modulus and Poisson's ratio of the pressure-sensitive membrane material, the pressure change borne by the pressure-sensitive membrane is calculated.

[0013] Another aspect of the present invention further includes a method for evaluating the pouring quality of a concrete cast-in-place pile, comprising the following steps:

[0014] Step 1: Drill holes in the permafrost area and detect the ice content in each area at different depths;

[0015] Step 2: pre-embedding of repair pipes: one or more repair pipes are vertically installed along the circumference of the borehole wall in the permafrost region, each of which has an open top, with the top surface of the repair pipe flush with the ground surface and the bottom surface close to the bottom of the borehole. The repair pipe has multiple prefabricated holes spaced apart in sequence along the depth direction of the borehole, with the openings of the prefabricated holes facing the borehole wall and close to the borehole wall. Each prefabricated hole is covered with a single-layer or multi-layer pressure-sensitive film, and a strain gauge is attached to the center of the surface of the pressure-sensitive film. The strain gauge is connected to a data acquisition system.

[0016] Step 3, pouring concrete: After the repair pipe is pre-buried, concrete is poured into the drilled hole to form a bored pile. During the pouring process, the soil around the concrete bored pile melts due to the effect of hydration heat. When the melted soil refreezes, a pile-soil interface defect is formed between the bored pile and the surrounding soil;

[0017] Step 4: Injecting low-temperature mud / mortar to form a filling layer: injecting low-temperature mud / mortar from the ground surface into the repair pipe until the injection pressure exceeds the rupture pressure of the pressure-sensitive membrane, causing the pressure-sensitive membrane to rupture and the low-temperature mud / mortar to fill the pile-soil interface defects, including the first defects formed between the bored pile and the surrounding frozen soil and the second defects formed by uneven concrete pouring during the formation of the bored pile;

[0018] Step 5, pouring quality assessment: The data acquisition system collects signals from the strain gauges to determine whether each pressure-sensitive membrane is ruptured. If the location of the ruptured pressure-sensitive membrane corresponds to an area with high ice content, the rupture is caused by the first defect. If the location of the ruptured pressure-sensitive membrane corresponds to an area with low ice content, the rupture is caused by the second defect. If the pressure-sensitive membrane corresponding to the area with high ice content is ruptured, the first defect has been repaired. If the pressure-sensitive membrane corresponding to the area with low ice content is ruptured, the second defect has been repaired.

[0019] In the above technical solution, low-temperature mud / mortar is injected in stages. When the bottom section is injected, if the difference between the pressure on the pressure-sensitive membrane in the middle section and its rupture pressure reaches a predetermined value and / or the difference between the pressure on the pressure-sensitive membrane in the top section and its rupture pressure reaches a predetermined value, the system will issue an early warning signal to remind the construction personnel to adjust the pressure of the low-temperature mud / mortar injection to avoid premature rupture of the pressure-sensitive membrane and inaccurate injection position of the low-temperature mud / mortar.

[0020] When injecting the middle section, when the difference between the pressure on the pressure-sensitive membrane of the top section and its rupture pressure reaches a predetermined value, the system will issue an early warning signal to remind the construction personnel to adjust the pressure of injecting low-temperature mud / mortar to avoid premature rupture of the pressure-sensitive membrane and inaccurate injection position of the low-temperature mud / mortar.

[0021] In the above technical solution, first, low-temperature mud / mortar is injected into the bottom section of the repair pipe, and the injection pressure is greater than the rupture pressure of the pressure-sensitive membrane at the prefabricated hole in the bottom section. After the low-temperature mud / mortar enters the pile-soil interface defect and refreezes, the middle section of the repair pipe is injected with low-temperature mud / mortar, and the injection pressure is greater than the rupture pressure of the pressure-sensitive membrane at the prefabricated hole in the middle section. After the low-temperature mud / mortar enters the pile-soil interface defect and refreezes, finally, low-temperature mud / mortar is injected into the top section of the repair pipe, and the injection pressure is greater than the rupture pressure of the pressure-sensitive membrane at the prefabricated hole in the top section. The low-temperature mud / mortar enters the pile-soil interface defect and refreezes, wherein the injection pressure of the bottom section is less than the injection pressure of the middle section, and the injection pressure of the middle section is less than the injection pressure of the top section.

[0022] In the above technical solution, the pressure sensitive film is a polyester film.

[0023] In the above technical solution, a prefabricated hole is set in the repair pipe every 1 to 2 meters along the depth direction of the drilling.

[0024] In the above technical solution, the diameter of the prefabricated hole is 5 mm to 1 cm, and is smaller than half of the diameter of the repair tube.

[0025] In the above technical solution, the diameter of the repair tube does not exceed 5 cm, preferably 2 to 3 cm.

[0026] In the above technical solution, the repair tube is a plastic tube, preferably a PVC tube.

[0027] In the above technical solution, when multiple repair pipes are installed along the circumference of the borehole wall in the permafrost area, the prefabricated holes of the multiple repair pipes are staggered along the depth direction of the borehole to ensure that prefabricated holes are set on any horizontal surface in the borehole.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention can effectively fill the pile-soil interface defects and improve the construction quality of cast-in-place piles by pre-embedding a repair pipe on the borehole wall and covering the prefabricated hole of the repair pipe with a pressure-sensitive membrane;

[0030] 2. The present invention improves the contact condition of the pile-soil interface by injecting low-temperature mud / mortar in stages, significantly increasing the bearing capacity of the bored pile and enhancing the stability of the structure;

[0031] 3. The present invention is simple to operate and easy to implement, does not require complicated equipment and processes, and reduces construction costs;

[0032] 4. The repair method of the present invention is applicable to a variety of frozen soil conditions and engineering environments and has wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the background technology of the present invention, wherein a is pouring concrete in a borehole in permafrost, b is the initial setting of concrete during pouring concrete to form a bored pile, and c is the formation of a pile-soil interface defect on the side of the bored pile.

[0034] Figure 2 It is a schematic diagram of the construction process of the present invention, wherein a is the pre-embedding of the repair pipe, b is the initial setting of concrete, c is the injection of low-temperature mud / mortar into the repair pipe, d is the application of different injection pressures in sections during the injection process, e is the rupture of the pressure-sensitive membrane for filling, and f is the formation of a filling layer on the side of the cast-in-place pile.

[0035] Figure 3 This is a schematic diagram of two repair pipes installed on the wall of a drilled hole according to the present invention.

[0036] Figure 4 Schematic diagram of the repair tube of the present invention.

[0037] Figure 5 Schematic diagram of the repair pipe of the present invention, wherein ① is the top section of the repair pipe, ② is the middle section of the repair pipe, and ③ is the bottom section of the repair pipe.

[0038] Among them, 1: repair pipe, 2: pressure sensitive membrane, 3: cast-in-place pile, 4: pile-soil interface defect, 5: filling layer. DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0040] Example 1

[0041] like Figure 2-Figure 4 As shown, a method for repairing the soil-pile interface defect of a bored pile in a permafrost region comprises the following steps:

[0042] Step 1: pre-buried repair pipes. One or more repair pipes 1 (PVC pipes in this embodiment) with a diameter of 3 cm are vertically installed along the circumference of the borehole wall in the permafrost region. The top of each repair pipe is open, the top surface of the repair pipe is flush with the ground surface, and the bottom surface is close to the bottom of the borehole. The repair pipe 1 has a prefabricated hole with a diameter of 1 cm every 1 m along the depth of the borehole. The opening of the prefabricated hole faces the borehole wall and is close to the borehole wall. Each prefabricated hole is covered with a single-layer or multi-layer pressure-sensitive membrane 2. The bursting pressure of the pressure-sensitive membrane 2 is set to 0.3 MPa. This bursting pressure is greater than the pressure at the location of the pressure-sensitive membrane 2, so that the prefabricated hole is sealed with the pressure-sensitive membrane 2.

[0043] Step 2, pouring concrete: After the repair pipe 1 is pre-buried, concrete is poured into the drilled hole to form a bored pile 3. During the pouring process, the soil around the concrete bored pile 3 melts due to the effect of hydration heat. When the melted soil refreezes, a pile-soil interface defect 4 is formed between the bored pile 3 and the surrounding soil (the pile-soil interface defect is formed by voids, cracks or poor contact between the bored pile body and the re-frozen soil, as well as uneven concrete pouring during the formation of the bored pile). The pressure sensitive membrane 2 effectively prevents moisture or soil from entering the repair pipe 1;

[0044] Step 3, injecting low-temperature mud: inject low-temperature mud / mortar from the surface into the repair pipe 1 until the injection pressure is greater than the rupture pressure of the pressure-sensitive membrane 2, the pressure-sensitive membrane 2 at the pile-soil interface defect 4 is ruptured, and the low-temperature mud / mortar enters the pile-soil interface defect 4 through the prefabricated hole to fill it;

[0045] Step 4, forming a filling layer: After the injection is completed, the low-temperature mud / mortar freezes and forms a filling layer 5 at the pile-soil interface defect 4. The pile-soil interface defect is repaired, thereby improving the contact condition between the bored pile 3 and the soil interface and increasing the bearing capacity of the bored pile 3.

[0046] Furthermore, the diameter of the repair pipe 1 of this embodiment is selected based on actual project requirements and construction conditions, generally ranging from 2 to 3 cm and not exceeding 5 cm. The diameter of the precast holes in the repair pipe 1 does not exceed 1 / 2 of the diameter of the repair pipe 1. The spacing between adjacent precast holes and the number of precast holes are adjusted accordingly based on the thickness and ice content of the permafrost layer. The adjustment principle is to have a higher density of precast holes in sections with high ice content and a lower density in sections with low ice content.

[0047] Furthermore, when multiple repair pipes 1 are vertically installed along the circumference of a borehole in a permafrost region, in this embodiment, two repair pipes 1 are installed, and the prefabricated holes of the two repair pipes 1 are staggered along the depth direction of the borehole.

[0048] Example 2

[0049] like Figure 5 As shown, based on Example 1, the rupture pressure of the pressure sensitive membrane 2 is adjusted according to the drilling depth to ensure that the low-temperature mud / mortar can be accurately injected into the pile-soil interface defect 4.

[0050] In step 1, by changing the thickness and number of layers of the pressure-sensitive membrane 2, its rupture pressure can be flexibly adjusted to meet the construction requirements at different depths and frozen soil conditions. This is specifically achieved by the following steps:

[0051] The repair pipe 1 is divided into three sections, namely the top section located at the top of the borehole, the middle section located in the middle of the borehole, and the bottom section located at the bottom of the borehole. The prefabricated holes in the top section of the repair pipe 1 are covered with three layers of pressure-sensitive membranes 2, the prefabricated holes in the middle section are covered with two layers of pressure-sensitive membranes 2, and the prefabricated holes in the bottom section are covered with one layer of pressure-sensitive membrane 2. The pressure-sensitive membrane 2 is a polyester film, which has good low-temperature resistance and mechanical strength and can adapt to the construction environment in permafrost areas. Furthermore, the bursting pressure of one layer of pressure-sensitive membrane is 0.3 MPa.

[0052] Furthermore, in step 3, in order to minimize the heat input during construction and avoid the difficulty of refreezing around the bored piles, low-temperature mud / mortar is injected into the repair pipe 1 in stages from the ground surface. First, low-temperature mud / mortar is injected into the bottom section of the repair pipe. When the injection pressure is within the range of 0.3~0.6MPa, the pressure-sensitive membrane 2 at the prefabricated hole in the bottom section ruptures, and the low-temperature mud / mortar enters the pile-soil interface defect 4 and refreezes. Then, low-temperature mud / mortar is injected into the middle section of the repair pipe. When the injection pressure is within the range of 0.6~0.9MPa, the pressure-sensitive membrane 2 at the prefabricated hole in the middle section ruptures, and the low-temperature mud / mortar enters the pile-soil interface defect 4 and refreezes. Finally, low-temperature mud / mortar is injected into the top section of the repair pipe. When the injection pressure is greater than 0.9MPa, the pressure-sensitive membrane 2 at the prefabricated hole in the top section ruptures, and the low-temperature mud / mortar enters the pile-soil interface defect 4 and refreezes.

[0053] Example 3

[0054] In order to calculate the pressure change of the pressure sensitive membrane 2, the pressure of the pressure sensitive membrane 2 is monitored in real time to provide real-time data support for the construction process, and to give early warning of possible rupture of the pressure sensitive membrane 2, and further infer the distribution of ice content in the frozen soil around the bored pile and the position and degree of the pile-soil interface defects after heat and mass migration. On the basis of Example 1 and / or Example 2, a strain gauge is evenly attached to the center of the surface of the pressure sensitive membrane 2, and the strain gauge is connected to the data acquisition system. During the process of injecting low-temperature mud / mortar into the repair pipe 1, the output signal of the strain gauge is recorded in real time by the data acquisition system. According to the output signal of the strain gauge, combined with the elastic modulus of the pressure sensitive membrane 2 material, the strain gauge is used to measure the pressure sensitive membrane 2. , Poisson's ratio ,thickness ,radius , center displacement , use the formula to calculate the pressure on the pressure sensitive membrane 2 P At the same time, the position and range of the rupture of the pressure sensitive membrane 2 can be analyzed, and the position and severity of the pile-soil interface defect can be preliminarily determined. P The calculation formula is:

[0055] ;

[0056] Furthermore, during the staged injection of low-temperature mud / mortar, when the bottom section is injected, if the difference between the pressure on the pressure-sensitive membrane 2 in the middle section or the top section and its rupture pressure reaches a predetermined value, the system will issue an early warning signal to remind the construction personnel to adjust the pressure of the low-temperature mud / mortar injection to avoid premature rupture of the pressure-sensitive membrane 2 and inaccurate injection position of the low-temperature mud / mortar.

[0057] When the middle section is injected, when the difference between the pressure borne by the pressure-sensitive membrane 2 of the top section and its rupture pressure reaches a predetermined value, the system issues an early warning signal to remind the construction personnel to adjust the pressure of the injected low-temperature mud / mortar to avoid premature rupture of the pressure-sensitive membrane 2 and inaccurate injection position of the low-temperature mud / mortar.

[0058] Example 4

[0059] The ice content in frozen soil will affect the degree of heat and mass transfer after the bored pile is poured, and thus affect the stress state of the pile-soil interface after the pile-soil around the bored pile is frozen. For example, after melting, the ice layer or frozen soil with high ice content will cause the soil volume to decrease and the voids to increase. After freezing again, the pile-soil interface defects will appear. At the same time, during the process of pouring concrete bored piles, the pouring will be uneven. By analyzing the rupture data of the pressure sensitive membrane (the location, range and pressure of the pressure sensitive membrane rupture), the pressure of the pile will be increased. P By comparing the ice content distribution with the drilling data, we can have a more comprehensive understanding of the defects in the pile-soil interface or the uneven concrete pouring phenomenon, more accurately locate and analyze the causes of defects, and improve the quality of concrete pouring.

[0060] Based on the above, this embodiment provides a method for evaluating the pouring quality of cast-in-place concrete piles, comprising the following steps:

[0061] Step 1: Drill holes in the permafrost area and detect the ice content in each area at different depths;

[0062] Step 2: pre-embedding of repair pipes: one or more repair pipes are vertically installed along the circumference of the borehole wall in the permafrost region, with each repair pipe having an open top, the top surface of the repair pipe being flush with the ground surface, and the bottom surface being in close contact with the bottom of the borehole. The repair pipe is provided with a plurality of prefabricated holes spaced in sequence along the depth direction of the borehole, with the openings of the prefabricated holes facing the borehole wall and in close contact with the borehole wall. Each prefabricated hole is covered with a single-layer or multi-layer pressure-sensitive film, and a strain gauge is evenly attached to the center of the surface of the pressure-sensitive film. The strain gauge is connected to a data acquisition system.

[0063] Step 3, pouring concrete: After the repair pipe is pre-buried, concrete is poured into the drilled hole to form a bored pile. During the pouring process, the soil around the concrete bored pile melts due to the effect of hydration heat. When the melted soil refreezes, a pile-soil interface defect is formed between the bored pile and the surrounding soil;

[0064] Step 4: Injecting low-temperature mud / mortar to form a filling layer: injecting low-temperature mud / mortar from the ground surface into the repair pipe until the injection pressure exceeds the rupture pressure of the pressure-sensitive membrane, causing the pressure-sensitive membrane to rupture and the low-temperature mud / mortar to fill the pile-soil interface defects, including the first defects formed between the bored pile and the surrounding frozen soil and the second defects formed by uneven concrete pouring during the formation of the bored pile;

[0065] Step 5, injection quality assessment: The data acquisition system acquires the signal of the strain gauge to obtain the rupture data of each pressure sensitive membrane (the location, range and pressure of the pressure sensitive membrane rupture) P If the location where the pressure-sensitive membrane is ruptured corresponds to an area with a high ice content, it indicates that the rupture of the pressure-sensitive membrane is caused by the first defect; if the location where the pressure-sensitive membrane is ruptured corresponds to an area with a low ice content, it indicates that the rupture of the pressure-sensitive membrane is caused by the second defect; if the pressure-sensitive membrane corresponding to the area with a high ice content is ruptured, it indicates that the first defect has been repaired; if the pressure-sensitive membrane corresponding to the area with a low ice content is ruptured, it indicates that the second defect has been repaired.

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for repairing defects in the pile-soil interface of cast-in-place piles in permafrost areas, characterized in that: The following steps are involved: Step 1: pre-embedding of repair pipes: one or more repair pipes are vertically installed along the circumference of a borehole in a permafrost region, each of which has an open top, a top surface flush with the ground surface, and a bottom surface close to the bottom of the borehole. The repair pipe has multiple prefabricated holes spaced apart in sequence along the depth direction of the borehole, with the openings of the prefabricated holes facing the borehole wall and close to the borehole wall, and each prefabricated hole is covered with a single or multiple layers of pressure-sensitive film; Step 2, pouring concrete: After the repair pipe is pre-buried, concrete is poured into the drilled hole to form a bored pile. During the pouring process, the soil around the concrete bored pile melts. When the melted soil refreezes, a pile-soil interface defect is formed between the bored pile and the surrounding soil; Step 3, injecting low-temperature mud / mortar: injecting low-temperature mud / mortar from the surface into the repair pipe until the injection pressure is greater than the rupture pressure of the pressure-sensitive membrane, the pressure-sensitive membrane at the pile-soil interface defect ruptures, and the low-temperature mud / mortar enters the pile-soil interface defect through the prefabricated hole to fill it; Step 4, forming a filling layer: After the injection is completed, the low-temperature mud / mortar freezes and forms a filling layer at the pile-soil interface defect, and the pile-soil interface defect is repaired; In step 1, the repair pipe is divided into three sections, namely a top section located at the top of the borehole, a middle section located in the middle of the borehole, and a bottom section located at the bottom of the borehole; The rupture pressure of the pressure-sensitive membrane covered by the prefabricated holes in the top section of the repair tube is a first rupture pressure, the rupture pressure of the pressure-sensitive membrane covered by the prefabricated holes in the middle section is a second rupture pressure, and the rupture pressure of the pressure-sensitive membrane covered by the prefabricated holes in the bottom section is a third rupture pressure. The first rupture pressure is greater than the second rupture pressure, and the second rupture pressure is greater than the third rupture pressure. Low-temperature mud / mortar is injected in stages. When the bottom section is injected, if the difference between the pressure on the pressure-sensitive membrane in the middle section and its bursting pressure reaches a predetermined value, or if the difference between the pressure on the pressure-sensitive membrane in the top section and its bursting pressure reaches a predetermined value, the system will issue an early warning signal to remind construction workers to adjust the pressure of the low-temperature mud / mortar injection; When the middle section is injected, when the difference between the pressure on the pressure-sensitive membrane of the top section and its bursting pressure reaches a predetermined value, the system sends out an early warning signal to remind the construction personnel to adjust the pressure of injecting low-temperature mud / mortar.

2. The repair method according to claim 1, characterized in that: In step 3, a strain gauge is attached to the center of the surface of the pressure-sensitive membrane. The strain gauge is connected to a data acquisition system. During the process of injecting low-temperature mud / mortar into the repair pipe, the output signal of the strain gauge is recorded in real time by the data acquisition system. Based on the output signal of the strain gauge, combined with the elastic modulus and Poisson's ratio of the pressure-sensitive membrane material, the pressure change borne by the pressure-sensitive membrane and the rupture position of the pressure-sensitive membrane are calculated.

3. The repair method according to claim 1, characterized in that: First, low-temperature mud / mortar is injected into the bottom section of the repair pipe, and the injection pressure is greater than the rupture pressure of the pressure-sensitive membrane at the prefabricated hole in the bottom section. After the low-temperature mud / mortar enters the pile-soil interface defect and refreezes, low-temperature mud / mortar is injected into the middle section of the repair pipe, and the injection pressure is greater than the rupture pressure of the pressure-sensitive membrane at the prefabricated hole in the middle section. After the low-temperature mud / mortar enters the pile-soil interface defect and refreezes, finally, low-temperature mud / mortar is injected into the top section of the repair pipe, and the injection pressure is greater than the rupture pressure of the pressure-sensitive membrane at the prefabricated hole in the top section. The low-temperature mud / mortar enters the pile-soil interface defect and refreezes. Among them, the injection pressure of the bottom section is less than the injection pressure of the middle section, and the injection pressure of the middle section is less than the injection pressure of the top section.

4. The repair method according to claim 1, characterized in that: The pressure sensitive film is a polyester film.

5. The repair method according to claim 1, characterized in that: The repair pipe is provided with a prefabricated hole every 1 to 2 meters along the depth direction of the drilling hole. The aperture of the prefabricated hole is 5 mm to 1 cm and is smaller than half of the diameter of the repair pipe.

6. The repair method according to claim 5, characterized in that: The diameter of the repair tube does not exceed 5 cm.

7. The repair method according to claim 1, characterized in that: The repair tube is a plastic tube.

8. The repair method according to claim 1, characterized in that: When a plurality of repair pipes are installed along the circumference of a borehole wall in a permafrost region, the plurality of repair pipes are staggered along the prefabricated holes in the depth direction of the borehole.

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