A method for treating karst diseases by using soft soil grouting during foundation pit excavation

Abstract

The invention discloses a method for treating karst diseases by grouting soft soil excavated from a foundation pit, comprising the steps of S1. determining a cement-soil mix ratio; S2. preparing cement-soil and performing grouting, and using an analytical method to judge whether the grouting of the cave is completed during the grouting process; the method rationally utilizes the soft soil generated by the foundation pit excavation to prepare cement-soil to treat the karst diseases, thereby greatly reducing the amount of cement used, lowering the project cost, and avoiding the "emptying" phenomenon at the top of the cave, and having the characteristics of good prevention and control effect, low cost, and simple and convenient operation; at the same time, a grouting pipe is designed, comprising a positioning pipe sleeve, an anti-backflow connector, and a grouting inner pipe. When in use, the grouting inner pipe moves in the positioning pipe sleeve to fix the positioning pipe sleeve in the surrounding rock, thereby fixing the grouting pipe; and the provision of the anti-backflow connector can effectively prevent the slurry from backflowing during use, and has the advantages of simple structure, good fixation and anti-backflow effect.

Description

Technical Field

[0001] The invention relates to the technical field of foundation treatment, and in particular to a method for treating karst diseases by utilizing soft soil grouting during foundation pit excavation. Background Art

[0002] my country has a vast territory and a complex geological and geomorphological environment, with karst landforms posing numerous threats to human production and life. Furthermore, with the increasing number of subway construction projects in recent years, encountering karst caves, a unique geological phenomenon, has become commonplace during subway construction in southern Chinese cities. During subway line construction, underground karst caves pose the risk of sudden water (mud) inrush and karst collapse, endangering the safety of surface roadbeds, buildings, and underground engineering structures, seriously impacting the effectiveness and safety of project construction.

[0003] Therefore, eliminating karst hazards on the line before construction is necessary to prevent major geological hazards and ensure the safety of subway tunnel construction. Commonly used karst treatment methods have the following problems:

[0004] (1) Drilling and blasting will cause strong disturbance to the surrounding rock mass, and the risk of landslide in the broken rock mass is high;

[0005] (2) Bridge spanning methods require large amounts of steel and cement, are costly, and require long construction periods. Grouting methods for treating karst caves are mainly based on the full-fill grouting method.

[0006] (3) Grouting has the advantages of being easy to operate in small spaces such as urban subway construction, and being able to effectively prevent surface water from seriously eroding the upper soil during its return to the groundwater. However, the grouting method requires a large amount of cement, which is expensive, and there is also uncertainty about the amount of cement used, which can sometimes lead to significant waste.

[0007] (4) The large amount of soft soil generated during foundation pit excavation is usually transported to one place for centralized storage, but this leads to the problem of increased use of ground materials and transportation costs;

[0008] Therefore, it is urgent to design a method for treating karst diseases by grouting soft soil during foundation pit excavation to solve the problems existing in the above-mentioned prior art. Summary of the Invention

[0009] In response to the above-mentioned problems, the present invention aims to provide a method for treating karst diseases by grouting soft soil produced by foundation pit excavation. This method rationally utilizes the soft soil produced by foundation pit excavation to prepare cement soil to treat karst diseases, greatly reducing the amount of cement used, lowering the project cost, and avoiding the "hollowing out" phenomenon at the top of the cave. It has the characteristics of good prevention and control effect, low cost and simple and convenient operation.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0011] A method for treating karst diseases by grouting soft soil during foundation pit excavation, comprising the following steps:

[0012] S1. During the excavation process, soil samples were taken and the cement-soil mix ratio of the excavated soil was determined;

[0013] S101. During the excavation process, a certain amount of excavated soil is removed and the natural moisture content and air-dried soil moisture content of the excavated soil are measured;

[0014] S102. Select the amount of excavated soil and cement;

[0015] S103. Conduct cement-soil trial mixes and perform unconfined compression tests, compression tests, and shear tests on the cement-soil trial mix specimens.

[0016] S2. After determining the cement-soil mix ratio, prepare the cement-soil and perform grouting;

[0017] S201. Stirring is performed in a high-speed and low-speed mixing manner;

[0018] S202. The grouting process adopts the pressure grouting method.

[0019] Preferably, the specific process of selecting the amount of excavated soil and cement in step S102 includes:

[0020] (1) When selecting the amount of excavated soil and cement, the excavated soil and cement are taken with a cement-soil mix ratio of 0.65-2.0;

[0021] (2) During the mixing process, the cement mixing ratio is 25%-30%, and the slump of the obtained cement soil is 25~75mm; and an accelerator is added to the cement soil.

[0022] Preferably, the grouting process described in step S202 includes

[0023] S2021. Install a grouting hose at the slurry outlet of the mixing equipment, and install a grouting pipe at the end of the grouting hose. At the same time, open a hole on the upper side of the cave and install the grouting pipe in the cave;

[0024] Wherein, an air outlet hole is drilled near the drill hole, and an exhaust pipe is installed in the air outlet hole;

[0025] S2022. Then, carry out sequential drilling and grouting according to the design requirements. The construction order is to drill holes in sequence from the outside to the inside, and grout every other hole.

[0026] S2023. Use analytical methods to determine whether cave grouting is complete

[0027] (1) When using the analytical method, it is necessary to draw the PQt curve based on the grouting hole parameter information, observe the changes in the PQt curve during the grouting process, and control the grouting speed within the range of 30-45L / min when starting grouting;

[0028] (2) With the extension of grouting time, the grouting pressure shows a significant increasing trend, and the grouting speed shows a significant decreasing trend; when the designed grouting volume is reached, the grouting final pressure reaches a stable value, and the grouting speed becomes 10-15 L / min;

[0029] (3) When the final grouting pressure is reached, the stratum basically no longer absorbs grout, so the grouting speed begins to drop sharply, and the grouting pressure instantly rises to the final grouting pressure, which means that the grouting operation of the grouting hole is completed.

[0030] Preferably, during the grouting process described in step S2022, attention should be paid to

[0031] (1) Lay the slats at the location where grouting is to be done, and place the slats between the grouting machine and the ground;

[0032] (2) Use the one-time drilling and grouting method within the range of the slab. The grouting stopping standard is: grouting pressure 0.5MPa, grouting volume less than 1L / min, steady pressure for 3 minutes, and grouting stops normally; otherwise, make a record and handle it specially;

[0033] (3) Two drilling and grouting methods are used in addition to the slab. The first hole depth is 2-3 m, the grouting pressure is controlled at 0.1-0.2 MPa, the grouting volume is less than 1 L / min, the pressure is maintained for 3 minutes, and the grouting is stopped normally;

[0034] (4) When the hole depth is less than 5 m and the slurry leakage can be effectively controlled, the one-time drilling and grouting method is also used in addition to the slab;

[0035] (5) During pressure grouting, the hole mouth is sealed with a slurry stopper, the slurry is stirred evenly and used immediately after mixing, and stones and debris are strictly prevented from mixing into the slurry. Continuous grouting is ensured and the slurry is screened before grouting to prevent pipe blockage.

[0036] Preferably, the grouting pipe includes a positioning pipe sleeve, an anti-backflow connector and a grouting inner pipe;

[0037] The grouting inner tube includes several standard sections and grouting sections. The grouting section is arranged at the lower end of the lowest standard section and is provided with several grouting holes. The grouting holes are circular holes with larger outer sides and smaller inner sides. A weight block is also provided on the inner side of the front end cone of the grouting section.

[0038] The positioning sleeve is an arc-shaped sleeve with an opening, and the movable sleeve is arranged outside the standard section and is used in conjunction with the surrounding rock on the upper side of the cave;

[0039] The anti-backflow connector is arranged at the top of the uppermost standard section and is connected to the grouting hose.

[0040] Preferably, the standard sections and the standard sections, and the standard sections and the grouting sections are staggeredly connected through threaded connecting tubes, and a sealing ring is provided on the inner cross-section of the connecting end faces of the standard sections and the grouting sections, and an "S"-shaped sealing corrugation is provided on the upper surface of the sealing ring for use with each other.

[0041] Preferably, a plurality of extrusion pads are provided on the outside of the standard section, and the extrusion pads are used in conjunction with the clearance pads provided on the inside of the positioning sleeve, and the extrusion pads and the clearance pads are both arc-shaped limit plates, wherein the lower inclined surface of the clearance pad is used in conjunction with the upper inclined surface of the extrusion pad, and the upper inclined surface of the clearance pad is used in conjunction with the lower inclined surface of the extrusion pad; and the clearance pads and the extrusion pads are symmetrically arranged in the positioning sleeve and the standard section, and the curvature of the clearance pads and the extrusion pads does not exceed π / 2.

[0042] Preferably, the anti-backflow connector includes an outer shell, and a guide pipe and a cow-horn bend pipe arranged in the outer shell, wherein the guide pipe is arranged at the liquid inlet end of the outer shell, and the liquid inlet end of the guide pipe is connected to the grouting hose, and the liquid outlet end is connected to the liquid inlet end of the cow-horn bend pipe, the cow-horn bend pipes are symmetrically arranged on both sides of the liquid outlet end of the guide pipe, and the liquid outlet end of the cow-horn bend pipe is connected to the manifold, and a connecting thread is provided in the manifold for use with the threaded connecting section provided on the standard section, and an anti-backflow mechanism is also installed in the anti-backflow cavity on the lower side of the guide pipe.

[0043] Preferably, the anti-backflow mechanism includes a sealing member, a rubber sealing head and a telescopic member, the telescopic member is movably arranged in the anti-backflow cavity through a guide column, and a first return spring is sleeved on the guide column on the lower side of the telescopic member, the sealing member is movably mounted on the upper mounting platform of the telescopic member through a connecting column and a dust baffle, the dust baffle is located below the mounting platform, the dust baffle is connected to the bottom of the connecting column, and a second return spring is sleeved on the connecting column on the lower side of the seal, the second return spring is located between the connecting member and the mounting platform, the rubber sealing head is installed at the upper end of the sealing member, and is used in conjunction with the guide pipe, and a slurry sealing sleeve is also provided on the lower side of the telescopic member, the slurry sealing sleeve is used in conjunction with the inner wall of the anti-backflow cavity, and moves along the anti-backflow cavity.

[0044] The beneficial effects of the present invention are as follows: the present invention discloses a method for treating karst diseases by grouting soft soil during foundation pit excavation. Compared with the prior art, the present invention has the following improvements:

[0045] 1. To address the drawbacks of existing grouting methods, such as high cement slurry consumption and the inability to properly utilize excavated soil generated during subway line excavation, the present invention provides a method for treating karst damage by grouting soft soil excavated from foundation pits.

[0046] (1) This method makes rational use of the soft soil produced by foundation pit excavation, eliminating the need to transport the excavated soil to a storage site, thus saving transportation costs;

[0047] (2) The traditional grouting method requires a large amount of cement, mud and other building materials. This method uses soft soil mixed with cement to make cement soil, which greatly reduces the amount of cement used and reduces the project cost;

[0048] (3) The traditional grouting method often consumes more cement slurry than expected during the grouting process. The use of soft soil mixed cement can make up for the shortage of cement budget to a certain extent and avoid the "empty" phenomenon at the top of the cave. It has the advantages of good prevention and control effect, low cost and simple and convenient operation.

[0049] 2. The present invention designs a grouting pipe, which includes a positioning pipe sleeve, an anti-backflow connector and a grouting inner pipe. When in use, the grouting inner pipe moves in the positioning pipe sleeve to fix the positioning pipe sleeve in the surrounding rock, thereby fixing the grouting pipe and facilitating the positioning and removal of the grouting pipe during the grouting process. At the same time, the provision of the anti-backflow connector can effectively prevent the slurry from backflowing during use, thereby affecting use. The grouting pipe has the advantages of simple structure, good fixing and anti-backflow effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The present invention is a flow chart of a method for treating karst hazards by using soft soil grouting during foundation pit excavation.

[0051] Figure 2 This is a schematic diagram of the principle of treating karst hazards by grouting soft soil during foundation pit excavation according to the present invention.

[0052] Figure 3 This is a diagram showing the use status of the grouting pipe of the present invention.

[0053] Figure 4 It is a structural schematic diagram of the positioning sleeve of the present invention.

[0054] Figure 5 It is a cross-sectional view of the positioning sleeve of the present invention.

[0055] Figure 6 It is a cross-sectional view of the grouting pipe of the present invention.

[0056] Figure 7 It is a partial enlarged view of the grouting pipe A of the present invention.

[0057] Figure 8 It is a structural schematic diagram of the positioning member of the present invention.

[0058] Figure 9 It is a cross-sectional view of the grouting pipe of the present invention from a top view angle.

[0059] Figure 10 It is a cross-sectional view of the grouting section of the present invention.

[0060] Figure 11 It is a partial enlarged view of the grouting section B of the present invention.

[0061] Figure 12 It is a cross-sectional view of the anti-backflow connector of the present invention.

[0062] Figure 13 This is a partial enlarged view of the anti-backflow connector C of the present invention.

[0063] Among them: 1. Cave, 2. Exhaust pipe, 3. Grouting hose, 4. Grouting pipe, 5. Positioning pipe sleeve, 51. Opening, 52. Positioning convex ring, 53. Prismatic slot, 54. Displacement pad, 6. Anti-backflow connector, 61. Outer shell, 611. Anti-backflow cavity, 62. Diversion pipe, 63. Ox-horn elbow, 64. Seal, 641. Dust baffle, 65. Rubber sealing head, 66. Telescopic member, 661. Grouting sleeve, 67. Guide column, 68. First return spring, 69. Second return spring, 7. Grouting inner pipe, 71. Standard section, 711. Extrusion pad, 712. Threaded connection section, 72. Grouting section, 73. Grouting hole, 74. Threaded connection tube, 75. Sealing ring, 76. Weight block, 8. Positioning piece, 81. Column. DETAILED DESCRIPTION

[0064] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0065] Example 1: Refer to the attached Figure 1-2 The method for treating karst damage by grouting soft soil during foundation pit excavation is shown, comprising the following steps:

[0066] S1. Determine the cement-soil mix ratio for treating karst landforms

[0067] S101. During the excavation process, a certain amount of excavated soil is removed and the natural moisture content and air-dried soil moisture content of the excavated soil are measured;

[0068] S102. The water-cement ratio of the cement slurry is selected within the range of 0.65-2.0 for the amount of excavated soil and cement;

[0069] In the mixing process, the cement mixing ratio is 25%-30%, and the prepared cement mortar is a low-slump cement mortar with a slump of 25-75 mm and a grouting pressure of 1-7 MPa; at the same time, in order to shorten the setting time of the cement slurry, an accelerating agent is added to the cement slurry;

[0070] S103. Conduct trial mixes of cement and soil, and perform unconfined compression tests, compression tests, and shear tests on the cement and soil trial mix specimens to ensure that the cement and soil mix ratio meets the strength requirements.

[0071] S2. After determining the cement-soil mix ratio, prepare the cement-soil and perform grouting

[0072] S201. Mix the cement soil. To ensure uniform mixing, use a mixer with adjustable speed, mixing at both high and low speeds. The slurry should be thoroughly stirred and continuously stirred before grouting, ensuring immediate use. However, the mixing time should not exceed the initial setting time. The slurry for grouting should be thoroughly mixed in the mixer before grouting. The slurry should be screened before pumping. To prevent splashing of the cement soil during high-speed mixing, use a closed mixing pot.

[0073] S202. The grouting process adopts the pressure grouting method, and the grouting process includes:

[0074] S2021. Install the grouting hose 3 at the outlet of the mixing equipment, and install the grouting pipe 4 at the end of the grouting hose 3, while opening a hole on the upper side of the cave and installing the grouting pipe 4 in the cave;

[0075] Among them, in order to reduce the impact of the original water and air in the cave 1 on the grouting quality, two more holes should be drilled near the drill hole as air outlet holes, which is conducive to the full filling of the cave;

[0076] S2022. Then, carry out sequential drilling and grouting according to the design requirements. The construction order is to drill holes in sequence from the outside to the inside, and grout every other hole. Generally, there are 2-3 sequences, but if conditions permit, a single sequence can be used.

[0077] S2023. Use analytical methods to determine whether cave grouting is complete;

[0078] During construction, the complete rock layer on site should be taken and the average uniaxial compressive strength should be measured; the solidification strength of the cement slurry should reach more than 80% of the average uniaxial compressive strength of the complete rock layer.

[0079] Preferably, the quick-setting agent in step S102 is water glass, and the concentration of the water glass is 35Be, and the setting time is 2 minutes.

[0080] Preferably, during the grouting process described in step S2022:

[0081] (1) Lay a slab at the location where grouting is to be done. The slab is placed between the grouting machine and the ground to reduce the adverse settlement of the ground during grouting and prevent the grouting machine from jumping over the platform. The slab can be made of reinforced concrete slab with a thickness of not less than 0.25m. The length and width can be selected according to the size of the grouting machine.

[0082] (2) Use the one-time drilling and grouting method within the range of the slab. The grouting stopping standard is: grouting pressure 0.5MPa, grouting volume less than 1L / min, steady pressure for 3 minutes, and grouting stops normally; otherwise, make a record and handle it specially;

[0083] (3) In addition to the slab, the drilling and grouting method is used twice. The first hole depth is 2-3 m, the grouting pressure is controlled at 0.1-0.2 MPa, the grouting volume is less than 1 L / min, and the pressure is maintained for 3 minutes, and the grouting can be stopped normally;

[0084] (4) When the hole depth is less than 5 m and the slurry leakage can be effectively controlled, the one-time drilling and grouting method is also used in addition to the slab;

[0085] (5) During pressure grouting, the hole mouth is sealed with a slurry stopper, the slurry is stirred evenly and used immediately after mixing, and stones and debris are strictly prevented from mixing into the slurry. Continuous grouting is ensured and the slurry is screened before grouting to prevent pipe blockage.

[0086] Preferably, in the process of using the analytical method to determine whether the cave grouting is completed as described in step S2023: (1) when using the analytical method, it is necessary to complete the drawing of the PQt curve based on the grouting hole parameter information. By observing the changes in the grouting process, it can be found that the grouting pressure is relatively small at the beginning of grouting, and the grouting speed is controlled within the range of 30-45L / min; (2) with the extension of grouting time, the grouting pressure shows a significant increasing trend, and the grouting speed shows a significant decreasing trend; when the designed grouting volume is reached, it can be observed that the grouting final pressure value reaches a stable value, and the grouting speed becomes 10-15L / min; (3) when the grouting final pressure value is reached, the formation basically no longer absorbs grout, so the grouting speed begins to drop sharply, and the grouting pressure instantly climbs to the grouting final pressure value, that is, the grouting operation of the grouting hole is completed; in the actual construction process, the grouting termination pressure should also be adjusted according to the groundwater level and pressure.

[0087] Example 2: As shown in the attached instructions Figure 3-13 As shown, the difference from the above embodiment 1 is that, during the grouting process, in order to prevent the grouting pipe 4 from being pressed out during the grouting process and to prevent backflow during the grouting process, the grouting pipe 4 is designed to include a positioning pipe sleeve 5, an anti-backflow connector 6 and a grouting inner pipe 7;

[0088] The grouting inner tube 7 includes several standard sections 71 and a grouting section 72. The grouting section 72 is arranged at the lower end of the lowest standard section 71 and extends into the cave for grouting in the cave.

[0089] The positioning sleeve 5 is an arc-shaped sleeve with an opening 51, which is installed in the rock formation borehole when in use, and is used to fix the standard section 71 during the grouting process to prevent the grouting inner tube 7 from being squeezed out by the pressure in the cave due to excessive slurry pressure;

[0090] The anti-backflow connector 6 is arranged at the top of the uppermost standard section 71 and is connected to the grouting hose 3 to prevent backflow during connection and grouting.

[0091] Preferably, the standard sections 71 and the standard sections 71, and the standard sections 71 and the grouting sections 72 are staggeredly connected by threaded connecting tubes 74, and a sealing ring 75 is provided on the inner cross-section of the connecting end faces of the standard sections 71 and the grouting sections 72, and an "S"-shaped sealing corrugation is provided on the upper surface of the sealing ring 75, thereby relying on the clamping sealing effect of the crests and troughs of the two sealing rings 75 in contact with each other to enhance the sealing effect of the sealing ring 75 during use, and is used to prevent external moisture from entering the standard sections 71 and the grouting sections 72 during the grouting process, thereby ensuring the grouting effect of the standard sections 71 and the grouting sections 72, and preventing the grouting pipes of the standard sections 71 and the grouting sections 72 from rusting.

[0092] Preferably, in order to facilitate use, the positioning sleeve 5 can be stretched by the grouting squeezing effect of the lower standard section 71 moving upward under the action of grouting pressure, and an squeezing pad 711 is provided on the outside of the standard section 71. The squeezing pad 711 is used in conjunction with the giving pad 54 provided on the inner side of the positioning sleeve 5, and the squeezing pad 711 and the giving pad 54 are both arc-shaped limit plates. During grouting, the lower side slope of the giving pad 54 is used in conjunction with the upper side slope of the squeezing pad 711, that is, when the standard section 71 moves upward under the reaction force below the hand during grouting, the force on the lower side slope of the giving pad 54 and the upper side slope of the squeezing pad 711 The positioning sleeve 5 is stretched open and the opening 51 becomes larger, so that the positioning convex ring 52 arranged on the outside of the positioning sleeve 5 is pressed into the outer rock mass, fixing the position of the positioning sleeve 5 in the rock formation, and preventing the grouting inner tube 7 from being squeezed out as a whole by the pressure in the cave due to the grouting reaction force; at the same time, when the grouting is completed and the entire grouting pipe 4 needs to be taken out, a press can be used to act on the upper part of the standard section 71 at the very end to make the grouting inner tube 7 move downward. At this time, the upper side inclined surface of the positioning pad 54 contacts the lower side inclined surface of the extrusion pad 711. Under the action of pressure, the opening 51 of the positioning sleeve 5 becomes smaller, the positioning convex ring 52 breaks away from contact with the outer rock mass, and the entire grouting pipe 4 is taken out.

[0093] Preferably, in order to facilitate the installation of the lower standard section 71 in the positioning sleeve 5 during use, the said clearance pad 54 and the extrusion pad 711 are symmetrically arranged in the positioning sleeve 5 and the standard section 71, and the said clearance pad 54 and the extrusion pad 711 are both arc-shaped pads, and the curvature thereof does not exceed π / 2, that is, during installation, the said clearance pad 54 and the extrusion pad 711 are adjusted to be offset from each other, and after the standard section 71 is installed in the positioning sleeve 5, the clearance pad 54 and the extrusion pad 711 are placed on the same side through the standard section 71 or the positioning sleeve 5, and the installation of the standard section 71 in the positioning sleeve 5 is completed.

[0094] Preferably, in order to facilitate the installation of the standard section 71 in the positioning sleeve 5, the standard section 71 or the positioning sleeve 5 rotates, causing the displacement pad 54 and the extrusion pad 711 to be misaligned with each other, affecting the use effect, a prismatic groove 53 is provided at the tail of the positioning sleeve 5, and the prismatic groove 53 is used in conjunction with the clamping column 81 on the positioning member 8. The clamping column 81 is also provided with a prismatic groove for use in conjunction with the prism 77 provided on the standard section 71, that is, when in use, the standard section 71 and the positioning sleeve 5 are relatively limitedly connected by installing the positioning member 8.

[0095] Preferably, in order to facilitate grouting, a plurality of grouting holes 73 are provided on the grouting section 72. The grouting holes 73 are evenly arranged on the grouting section 72, and the grouting holes 73 are a circular hole structure with a larger outside and a smaller inside. At the same time, in order to ensure the verticality and weight of the grouting section 72 when in use, a weight block 76 is also provided on the inner side of the front end cone of the grouting section 72.

[0096] Preferably, in order to prevent backflow during the grouting process and affect the grouting and grouting effect, the anti-backflow connector 6 includes an outer shell 61, and a guide tube 62 and a cow-horn bend 63 arranged in the outer shell 61, wherein the guide tube 62 is arranged at the liquid inlet end of the outer shell 61, and the liquid inlet end of the guide tube 62 is connected to the grouting hose 3, and the liquid outlet end is connected to the liquid inlet end of the cow-horn bend 63, and the cow-horn bend 63 is symmetrically arranged on both sides of the liquid outlet end of the guide tube 62, and the liquid outlet end of the cow-horn bend 63 is connected to the manifold, and a connecting thread is provided in the manifold for use with the threaded connection section 712 provided on the standard section 71, that is, when in use, the anti-backflow connector 6 is installed on the upper end of the standard section 71 by utilizing the mutual use of the manifold and the threaded connection section 712, and in order to prevent backflow in the guide tube 62, an anti-backflow mechanism is also installed in the anti-backflow cavity 611 on the lower side of the guide tube 62.

[0097] The anti-backflow mechanism includes a seal 64, a rubber sealing head 65 and a telescopic member 66. The telescopic member 66 is movably arranged in the anti-backflow cavity 611 by a guide column 67, and a first return spring 68 is sleeved on the guide column 67 on the lower side of the telescopic member 66, for resetting the telescopic member 66 when in use. The seal 64 is movably mounted on the upper mounting platform of the telescopic member 66 through a connecting column and an ash baffle 641. The ash baffle 641 is located below the mounting platform, the ash baffle 641 is connected to the bottom of the connecting column, and a second return spring 69 is sleeved on the connecting column on the lower side of the seal 64. The second return spring 69 is located between the seal 64 and the mounting platform. When in use, the seal 64 is reset by the second return spring 69. The rubber sealing head 65 is mounted on the upper end of the seal 64 and is used in conjunction with the guide tube 62. When in use, the guide tube 62 is sealed to prevent backflow in the guide tube 62. In the natural state, The first return spring 68 and the second return spring 69 are both in an extended state, that is, at this time the rubber sealing head 65 is stuck in the guide tube 62 to prevent external stones and soil from entering the lower horn bend tube 63. During grouting, the rubber sealing head 65 is subjected to the grouting pressure, causing the rubber sealing head 65 to move downward, and the second return spring 69 is compressed first. When the clearance distance of the rubber sealing head 65 is not enough to meet the slurry pressure, the telescopic member 66 moves downward along the guide column 67, causing the first return spring 68 to be compressed. At this time, the grouting passage of the guide tube 62 is completely opened, facilitating grouting; when the grouting pressure is less than the grouting back pressure, the ash baffle 641 first moves upward under the action of the back pressure, causing the rubber sealing head 65 to move upward. When the ash baffle 641 contacts the bottom plate of the mounting platform of the telescopic member 66, the telescopic member 66 is lifted up, thereby causing the rubber sealing head 65 to move upward and be re-stuck in the guide tube 62, sealing the guide tube 62 to prevent backflow.

[0098] Preferably, in order to prevent the slurry on the lower side of the telescopic member 66 mounting platform from entering the position of the guide columns 67 on both sides and affecting the movement of the telescopic member 66, a slurry sealing sleeve 661 is also provided on the lower side of the telescopic member 66. The slurry sealing sleeve 661 is tightly attached to the inner wall of the anti-backflow cavity 611 and moves along the anti-backflow cavity 611.

[0099] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for treating karst damage by grouting soft soil during foundation pit excavation, characterized in that: Including steps: S1. During the excavation process, soil samples were taken and the cement-soil mix ratio of the excavated soil was determined; S101. During the excavation process, a certain amount of excavated soil is removed and the natural moisture content and air-dried soil moisture content of the excavated soil are measured; S102. Select the amount of excavated soil and cement; S103. Conduct cement-soil trial mixes and perform unconfined compression tests, compression tests, and shear tests on the cement-soil trial mix specimens. S2. After determining the cement-soil mix ratio, prepare the cement-soil and perform grouting S201. Stirring is performed in a high-speed and low-speed mixing manner; S202. Grouting is performed using a pressure grouting method; S202 includes: installing a grouting hose at the slurry outlet of the mixing equipment, installing a grouting pipe at the end of the grouting hose, and simultaneously drilling a hole on the upper side of the cave and installing the grouting pipe in the cave; drilling an air outlet hole near the drill hole and installing an exhaust pipe in the air outlet hole; The grouting pipe comprises a positioning pipe sleeve, an anti-backflow connector and a grouting inner pipe; The grouting inner tube includes several standard sections and grouting sections. The grouting section is arranged at the lower end of the lowest standard section and is provided with several grouting holes. The grouting holes are circular holes with larger outer sides and smaller inner sides. A weight block is also provided on the inner side of the front end cone of the grouting section. The positioning sleeve is an arc-shaped sleeve with an opening, and the movable sleeve is arranged outside the standard section and is used in conjunction with the surrounding rock on the upper side of the cave; The anti-backflow connector is arranged at the top of the uppermost standard section and is connected to the grouting hose; The anti-backflow connector includes an outer shell, and a guide pipe and a bulldog pipe arranged in the outer shell, wherein the guide pipe is arranged at the liquid inlet end of the outer shell, and the liquid inlet end of the guide pipe is connected to the grouting hose, and the liquid outlet end is connected to the liquid inlet end of the bulldog pipe, the bulldog pipes are symmetrically arranged on both sides of the liquid outlet end of the guide pipe, and the liquid outlet end of the bulldog pipe is connected to the manifold, the manifold is provided with a connecting thread for use with the threaded connection section provided on the standard section, and an anti-backflow mechanism is also installed in the anti-backflow cavity on the lower side of the guide pipe; The anti-backflow mechanism includes a seal, a rubber sealing head and a telescopic member. The telescopic member is movably arranged in the anti-backflow cavity through a guide column, and a first return spring is sleeved on the guide column on the lower side of the telescopic member. The seal is movably installed on the upper mounting platform of the telescopic member through a connecting column and a dust baffle. The dust baffle is located below the mounting platform. The dust baffle is connected to the bottom of the connecting column, and a second return spring is sleeved on the connecting column on the lower side of the seal. The second return spring is located between the seal and the mounting platform. The rubber sealing head is installed at the upper end of the seal and is used in conjunction with the guide pipe. A slurry sealing sleeve is also provided on the lower side of the telescopic member. The slurry sealing sleeve is used in conjunction with the inner wall of the anti-backflow cavity and moves along the anti-backflow cavity.

2. The method for treating karst damage by using soft soil grouting during foundation pit excavation according to claim 1, characterized in that: The specific process of selecting the amount of excavated soil and cement in step S102 includes: (1) When selecting the amount of excavated soil and cement, the excavated soil and cement are taken with a cement-soil mix ratio of 0.65-2.0; (2) During the mixing process, the cement mixing ratio is 25%-30%, and the slump of the obtained cement soil is 25~75mm; and an accelerator is added to the cement soil.

3. The method for treating karst damage by using soft soil grouting during foundation pit excavation according to claim 1, characterized in that: The grouting process described in step S202 further includes: Carry out sequential hole-drilling and jump-grouting construction according to design requirements. The construction order is to drill holes sequentially from the outside to the inside and grout every other hole. Use analytical methods to judge whether the cave grouting is completed. (1) When using the analytical method, it is necessary to draw the PQt curve based on the grouting hole parameter information, observe the changes in the PQt curve during the grouting process, and control the grouting speed within the range of 30-45L / min when starting grouting; (2) With the extension of grouting time, the grouting pressure shows a significant increasing trend, and the grouting speed shows a significant decreasing trend; when the designed grouting volume is reached, the grouting final pressure reaches a stable value, and the grouting speed becomes 10-15 L / min; (3) When the final grouting pressure is reached, the stratum basically no longer absorbs grout, so the grouting speed begins to drop sharply, and the grouting pressure instantly rises to the final grouting pressure, which means that the grouting operation of the grouting hole is completed.

4. The method for treating karst damage by using soft soil grouting during foundation pit excavation according to claim 3, characterized in that: During the grouting process described in step S202, it should be noted that (1) Lay the slats at the location where grouting is to be done, and place the slats between the grouting machine and the ground; (2) Use the one-time drilling and grouting method within the range of the slab. The grouting stopping standard is: grouting pressure 0.5MPa, grouting volume less than 1L / min, steady pressure for 3 minutes, and grouting stops normally; otherwise, make a record and handle it specially; (3) Two drilling and grouting methods are used in addition to the slab. The first hole depth is 2-3 m, the grouting pressure is controlled at 0.1-0.2 MPa, the grouting volume is less than 1 L / min, the pressure is maintained for 3 minutes, and the grouting is stopped normally; (4) When the hole depth is less than 5 m and the slurry leakage can be effectively controlled, the one-time drilling and grouting method is also used in addition to the slab; (5) During pressure grouting, the hole mouth is sealed with a slurry stopper, the slurry is stirred evenly and used immediately after mixing, and stones and debris are strictly prevented from mixing into the slurry. Continuous grouting is ensured and the slurry is screened before grouting to prevent pipe blockage.

5. The method for treating karst damage by using soft soil grouting during foundation pit excavation according to claim 1, characterized in that: The standard sections and the standard sections, as well as the standard sections and the grouting sections are staggeredly connected through threaded connection tubes, and a sealing ring is provided on the inner cross-section of the connecting end surface of the standard section and the grouting section, and an "S"-shaped sealing corrugation is provided on the upper surface of the sealing ring for use with each other.

6. The method for treating karst damage by using soft soil grouting during foundation pit excavation according to claim 1, characterized in that: A plurality of extrusion pads are arranged on the outside of the standard section, and the extrusion pads are used in conjunction with the clearance pads arranged on the inside of the positioning sleeve, and the extrusion pads and the clearance pads are both arc-shaped limit plates, wherein the lower side inclined surface of the clearance pad is used in conjunction with the upper side inclined surface of the extrusion pad, and the upper side inclined surface of the clearance pad is used in conjunction with the lower side inclined surface of the extrusion pad; and the clearance pads and the extrusion pads are symmetrically arranged in the positioning sleeve and the standard section, and the curvature of the clearance pads and the extrusion pads does not exceed π / 2.

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