A backfilling method for old civil air defense tunnels under urban water-rich strata

Abstract

The present invention provides a method for backfilling old civil air defense tunnels beneath water-rich urban strata, characterized by comprising the following steps: S1. Preparing sand for tunnel backfill: Pile the backfill sand near the civil air defense tunnel exit or shaft; S2. Constructing a sand blowing pit: Constructing a sand blowing pit around the backfill sand deposited in step S1; S3. Pumping water out of the tunnel using a submersible pump through the civil air defense tunnel exit or shaft, lowering the water level to 1-2 meters below the tunnel vault to provide space for subsequent operations; S4. Piping layout; S5. Sand blowing with membrane bags; and S6. Grouting. This construction method addresses the significant safety risks associated with pumping out water, high construction costs, long construction periods, and limited urban space when backfilling old civil air defense tunnels with conventional foam concrete.

Description

Technical Field

[0001] The present invention belongs to the technical field of construction engineering, and in particular relates to a backfill construction method for an old civil air defense tunnel under a water-rich stratum in a city. Background Art

[0002] Currently, older civil air defense tunnels are typically backfilled with foamed concrete or poured concrete. Because foamed concrete is diluted by water and its bubbles are destroyed, foamed concrete backfill must be constructed in a water-free state within the tunnel. For civil air defense projects with severe leakage or below the groundwater level, water must be pumped out and sealed. Excessive pumping can disrupt the force balance within the tunnel, leading to safety hazards such as collapse and water inrush. Furthermore, sealing leaks in tunnels with severe leakage requires significant manpower and resources, resulting in high costs and a long construction period. Underwater poured concrete backfill is expensive and requires drilling holes in the road surface. Drilling holes in busy, downtown arterials inevitably leads to traffic paralysis, negatively impacting the city's image and the environment. Furthermore, the high-strength concrete backfill is not conducive to the future development and utilization of urban underground space. Summary of the Invention

[0003] In response to the above problems, the present invention provides a method for backfilling old civil air defense tunnels under urban water-rich strata to solve the problems of great pumping safety hazards, high construction costs, long construction period, and limited urban space when conventional foam concrete is used to backfill old civil air defense tunnels.

[0004] The present invention is achieved through the following technical solutions.

[0005] A method for backfilling an old civil air defense tunnel under a water-rich urban stratum, characterized by comprising the following steps:

[0006] S1. Preparation of sand for tunnel backfill

[0007] Pile the backfill sand near the exit of the civil air defense tunnel or the shaft;

[0008] S2. Construction sand blowing pit

[0009] A sand blowing pit is constructed around the backfill sand piled in step S1;

[0010] S3. Precipitation in the cave

[0011] Use a submersible pump to pump out water from the civil air defense tunnel exit or shaft to lower the water level in the tunnel to 1-2 m below the civil air defense tunnel vault to provide space for subsequent operations.

[0012] S4. Pipeline layout

[0013] After the dewatering in the tunnel is completed in step S3 to ensure that there is an operating space, the sand blowing pipeline is first laid between the sand blowing working pit and the designed location for laying the membrane bag. The sand blowing pipeline outside the civil air defense tunnel and at the exit of the civil air defense tunnel or in the vertical shaft uses a hard pipe. The sand blowing pipeline inside the tunnel uses a high-pressure wear-resistant water hose, and a buoy is fixed on the high-pressure wear-resistant water hose every 3 to 6 meters.

[0014] S5, film bag sand blowing

[0015] The measurement and layout are carried out according to the designed position of the film bag laying. After the measurement and layout are completed, the film bag sand blowing construction is carried out layer by layer from bottom to top with the sand blowing thickness of the film bag as one layer until the backfill height is reached; and the film bag sand blowing construction of each layer is carried out in the following manner, with each film bag as a section, and the film bag laying and sand blowing construction are carried out section by section along the length direction of the tunnel until the required backfill length of the tunnel is reached; wherein, the film bag is water permeable; the sand blowing thickness in each film bag of the same layer is the same; the specific method of sand blowing construction is to flush the stacked backfill sand into the sand blowing working pit by spraying high-pressure water at a sand-water mass ratio of 1:3 to 5, so that the sand and water are evenly mixed and flow into the working pit, and then the sand and water mixture is blown from the working pit along the sand blowing pipeline into the laid film bag by a high-pressure mud pump until the film bag is full;

[0016] S6. Grouting construction

[0017] Before completing the sand blowing of the last layer of membrane bags in step S5, a grouting pipe is reserved in advance on the tunnel vault; after the sand blowing of the membrane bags in step S5 is completed, the sand body is consolidated and settled, and grouting is backfilled and densely packed from the top surface of the last layer of membrane bags to the arc position at the top of the tunnel through the reserved grouting pipe.

[0018] Preferably, the backfill sand is river sand, preferably river sand with a fineness modulus of fine sand; the sand blowing working pit is formed by excavating downward from the ground and laying brick walls and plastering the surface, or by using a mud box prefabricated with iron sheets.

[0019] Preferably, in step S4, the sand blasting pipeline is laid out in a manner that avoids crossing obstacles and forming sharp bends, and at the same time ensures that the pipeline joints are firmly sealed to prevent leakage from causing blockage along the pipeline.

[0020] Preferably, the length of the membrane bag is 30 to 50 m, the width of the membrane bag is determined according to the cross-sectional size of the tunnel, the membrane bag is made of polypropylene woven cloth, and two sand blasting ports are arranged at each end of the membrane bag for connecting to the sand blasting pipeline; the diameter of the sand blasting port is 15 to 25 cm, and the length is 30 to 50 cm.

[0021] Preferably, in step S5, when measuring and staking out, for the shallow water construction area of ​​the tunnel, the membrane bags are laid and positioned by artificial underwater operation; for the deep water construction area of ​​the tunnel, kayaks or wooden boats are used to lay and position the membrane bags.

[0022] Preferably, in step S5, the film bags are laid with the sand blowing ports facing upward, the film bags on the same layer are arranged compactly, the upper and lower film bags are firmly connected by tie rods at the buckles, and the end seams of the upper and lower film bags are staggered by 4 to 6 m to prevent through seams.

[0023] Preferably, in step S5, during the sand blowing construction, the four corner ends of the film bag are first blown to make the film bag sink to the bottom, and then the middle part is blown to fill.

[0024] Preferably, in step S5, during the sand blowing construction, the sand blowing thickness in the membrane bag is controlled to be 0.6 to 1 m. When the thickness of the sand body in the membrane bag is close to the design thickness, the sand blowing speed is reduced, and at the same time, the construction personnel are arranged to step on the top surface of the membrane bag to facilitate the discharge of water in the membrane bag and make the sand body in the membrane bag evenly distributed.

[0025] Preferably, in step S5, during the sand blowing construction, a submersible pump is used to pump out water while blowing sand, so as to control the water level in the tunnel to always be 1 to 2 m below the arch of the civil air defense tunnel.

[0026] Preferably, in step S6, the grouting material is 42.5 grade ordinary Portland cement with a water-cement ratio of 1:1.

[0027] Compared with the prior art, the beneficial effects of the present invention include at least:

[0028] 1. The construction is safe and reliable, and water operations can be carried out. There is no need to pump out all the water in the tunnel and stop water leaks. Sand can be directly blown backfilled in the civil air defense tunnel, which is safer and more convenient.

[0029] 2. Save costs. The sand blowing material uses river sand, which greatly reduces the cost compared with the previous foam concrete backfill and underwater concrete backfill.

[0030] 3. Fast construction speed. The sand blowing backfilling method of the present invention saves the construction period of drilling and road surface restoration. There is no need to wait for the time similar to the increase in concrete strength during the backfilling process. The speed of blowing sand to the film bag is fast, and a lot of construction period can be saved by constructing multiple shafts at the same time.

[0031] 4. It occupies a small area, has a long conveying distance and is easy to construct. Sand blowing operations are carried out to both ends simultaneously through the vertical shaft. The sand blowing and conveying distance at each end can reach 600 m. There is no need for ground drilling and backfilling, which can solve the problem of rapid backfilling of civil air defense tunnels in confined spaces in cities.

[0032] 5. The backfill quality is reliable. Due to the restraint of the membrane bag and the original structure of the tunnel, the overall stability of the sand body is good. After being saturated and compacted, there will be no uneven settlement. Grouting is performed in the gaps on the top of the sand layer, making the backfill more compact.

[0033] 6. Green and environmentally friendly, sand blowing backfill only requires water and sand, and will not cause pollution or damage to the water, atmosphere, soil and other environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention is further described in detail below with reference to the drawings. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0035] Figure 1 is a schematic diagram of the backfilling method of the present invention;

[0036] Figure 2 for Figure 1 Schematic diagram outside the civil air defense tunnel;

[0037] Figure 3 for Figure 1 Schematic diagram of the interior of the civil air defense tunnel;

[0038] Figure 4 This is a schematic diagram of the interior of the civil air defense tunnel after backfilling is completed;

[0039] Figure 5 for Figure 4 Cross-section at AA;

[0040] Figure 6 This is the actual construction drawing of the high-pressure mud pump pumping sand in the sand blowing pit;

[0041] Figure 7 Actual construction drawings for pipeline layout;

[0042] Figure 8 Actual construction drawings for film bag laying and sand blowing;

[0043] Figure 9 Actual construction drawings for grouting construction;

[0044] The meanings of the symbols in the above figure are: 1-backfill sand, 2-sand blowing working pit, 3-high-pressure mud pump, 4-sand blowing pipeline, 401-high-pressure wear-resistant water hose, 402-PE hard pipe, 5-buoy, 6-high-pressure water gun, 7-water pipe, 8-submersible pump, 9-membrane bag, 10-grouting pipe, 11-cement slurry, 12-bracket, 13-sand-water mixture, 14-ground line, 15-water level line in the tunnel, 16-civil defense tunnel exit or shaft. DETAILED DESCRIPTION

[0045] The following is a detailed description of the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described 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 work are within the scope of protection of the present invention. Example 1

[0046] A backfill method for old civil air defense tunnels under urban water-rich strata, please refer to Figures 1 to 5 , which includes the following steps:

[0047] S1. Preparation of sand for tunnel backfill

[0048] See also Figure 1 and Figure 2 , the backfill sand 1 is piled near the exit of the civil air defense tunnel or the shaft 16; wherein, the backfill sand 1 is river sand, and the river sand fineness modulus is selected into three types: medium-coarse sand, fine sand, and extra-fine sand. The medium-coarse sand has a larger particle size, a short pumping distance, and is easy to clog the pipe; the fine sand has a lower cost, good fluidity in the sand blowing operation, and a long pumping distance; the extra-fine sand has a higher mud content and a large loss during the operation; after comprehensive comparison, in this embodiment, river sand with a fineness modulus of fine sand is selected as the backfill sand;

[0049] S2. Construction sand blowing pit

[0050] See also Figure 1 and Figure 2 A sand-blowing pit 2 is constructed around the backfill sand 1 deposited in step S1. A steel mesh is laid on the top of the sand-blowing pit 2 to filter debris. The sand-blowing pit, serving as a sand-water mixing area, can be formed by excavating downward from the ground and laying brick walls or by using a prefabricated slurry box made of sheet metal. In this embodiment, the sand-blowing pit has a length of 3 m, a width of 2 m, and a height of 2 m, with a volume of 12 cubic meters. The pit is excavated downward from the ground and laid brick walls.

[0051] S3. Precipitation in the cave

[0052] See also Figure 1 and Figure 3 Because the civil air defense tunnel has been in disrepair for a long time and its structural performance has deteriorated, it has serious leakage and is filled with water. It is necessary to first reduce the water level appropriately, that is, to use a submersible pump 8 to pump out water through the civil air defense tunnel outlet or vertical shaft to reduce the water level in the tunnel to 1 to 2 meters below the civil air defense tunnel arch to provide construction space for subsequent operations;

[0053] S4. Pipeline layout

[0054] See also Figures 1 to 3After the dewatering in the tunnel is completed in step S3 and there is an operating space, the sand blasting pipeline 4 is first laid between the sand blasting working pit 2 and the designed position for laying the membrane bag. The sand blasting pipeline outside the civil air defense tunnel and at the exit of the civil air defense tunnel or in the vertical shaft adopts a PE hard pipe 402 with a diameter of 150 mm. The sand blasting pipeline inside the tunnel adopts a high-pressure wear-resistant water hose 401 with a diameter of 150 mm, and a buoy 5 is fixed on the high-pressure wear-resistant water hose every 5 m to make the sand blasting pipeline in the tunnel float in the tunnel; when laying the sand blasting pipeline 4, avoid crossing obstacles and avoid forming sharp bends, and ensure that the pipeline joints are firmly sealed to prevent leakage from causing blockage along the line; during sand blasting construction, the pipe end of the sand blasting pipeline is connected to the membrane bag 9 through the sand blasting port;

[0055] S5, film bag sand blowing

[0056] The membrane bag laying design position is measured and laid out. During the measurement and layout, for the shallow water construction area of ​​the tunnel, the membrane bag is laid and positioned by manual underwater operation; for the deep water construction area of ​​the tunnel, the membrane bag is laid and positioned by kayak or wooden boat;

[0057] See also Figure 3 and Figure 4 After the measurement and layout are completed, the film bag sand blowing construction is carried out layer by layer from bottom to top along the height direction of the tunnel, with the sand blowing thickness of the film bag as one layer, until the construction reaches the filling height; and the film bag sand blowing construction of each layer is carried out in the following way, with each film bag as a section, and the film bag laying and sand blowing construction are carried out section by section along the length direction of the tunnel, that is, after the sand blowing construction of each section of the film bag is completed, the sand blowing pipeline is extended above the film bag of that section, and then the next adjacent film bag is laid and sand blowing construction is carried out, and the cycle is repeated until the construction is carried out section by section to the required backfill length of the tunnel, that is, the film bag sand blowing construction of this layer is completed; the extension of the sand blowing pipeline is connected by an inner-lined steel pipe, and the sand blowing pipeline must not be bent to prevent blockage;

[0058] Among them, the length of the membrane bag is 30 to 50 m, and the width of the membrane bag is determined according to the cross-sectional size of the tunnel. In this embodiment, the cross-sectional width of the civil air defense tunnel is 4.2 m, so the membrane bag width is designed to be 6.2 m; the membrane bag is made of polypropylene woven cloth and is water-permeable. Two sand blowing ports are arranged at each end of the membrane bag for connection with the sand blowing pipeline. The diameter of the sand blowing port is 20 cm and the length is 40 cm; when laying the membrane bag, keep the sand blowing port facing upward, and the membrane bags on the same layer are arranged compactly. The upper and lower membrane bags are firmly connected at the buckle with reinforcement, and the end seams of the upper and lower membrane bags are staggered by 5 m control to prevent the occurrence of through-cracks; the specific method of sand blowing construction is to use a high-pressure water gun to spray high-pressure water at a sand-water mass ratio of 1:4 to flush the stacked backfill sand into the sand blowing working pit, so that the sand and water are evenly mixed and flow into the working pit, and then the sand and water mixture is blown from the working pit along the sand blowing pipeline into the membrane bag through a high-pressure mud pump until the membrane bag is full; during sand blowing construction, the thickness of the blown sand in each membrane bag of the same layer is controlled to be the same; during sand blowing construction, the four corners of the membrane bag are first blown to make the membrane bag sink to the bottom, and then the middle part is blown to fill, and the thickness of the blown sand in the membrane bag is controlled to be 0.6~1 m. When the thickness of the sand body in the membrane bag is close to the design thickness, the sand blowing speed is reduced, and the construction personnel are arranged to step on the top surface of the membrane bag to facilitate the discharge of water in the membrane bag, so that the sand body in the membrane bag is evenly distributed. At the same time, while blowing sand, a submersible pump is used to pump water to the ground municipal pipe network to control the water level in the cave to always be 1~2 m below the arch of the civil air defense tunnel m; In addition, during sand blowing construction, the submersible pump installed at the exit of the civil air defense tunnel or in the shaft can be connected to the high-pressure water gun through a water pipe, so that part of the water pumped out of the tunnel can be used for sand blowing construction to save water resources;

[0059] S6. Grouting construction

[0060] See also Figure 4 and Figure 5 Before completing the last layer of film bag sand blowing construction in step S5, a grouting pipe 10 is reserved in advance on the tunnel vault; after the film bag sand blowing construction in step S5 is completed, the sand body is consolidated and settled, and grouting is backfilled and compacted from the top surface of the last layer of film bag to the arc position at the top of the tunnel through the reserved grouting pipe; the grouting material is 42.5 grade ordinary Portland cement with a water-cement ratio of 1:1.

Claims

1. A method for backfilling old civil air defense tunnels under urban water-rich strata, characterized in that The steps include: S1. Preparation of sand for tunnel backfill Pile the backfill sand near the exit of the civil air defense tunnel or the shaft; S2. Construction sand blowing pit A sand blowing pit is constructed around the backfill sand piled in step S1; S3. Precipitation in the cave Use a submersible pump to pump out water from the civil air defense tunnel exit or shaft to lower the water level in the tunnel to 1-2 m below the civil air defense tunnel vault to provide space for subsequent operations. S4. Pipeline layout After the dewatering in the tunnel is completed in step S3 to ensure that there is an operating space, the sand blowing pipeline is first laid between the sand blowing working pit and the designed location for laying the membrane bag. The sand blowing pipeline outside the civil air defense tunnel and at the exit of the civil air defense tunnel or in the vertical shaft uses a hard pipe. The sand blowing pipeline inside the tunnel uses a high-pressure wear-resistant water hose, and a buoy is fixed on the high-pressure wear-resistant water hose every 3 to 6 meters. S5, film bag sand blowing The measurement and layout are carried out according to the designed position of the film bag laying. After the measurement and layout are completed, the film bag sand blowing thickness is taken as one layer, and the film bag sand blowing construction is carried out layer by layer from bottom to top until the backfill height is reached; and the film bag sand blowing construction of each layer is carried out in the following manner, with each film bag as a section, and the film bag is laid and sand blowing construction is carried out section by section along the length direction of the tunnel until the required backfill length of the tunnel is reached; wherein, the film bag is water permeable; the sand blowing thickness in each film bag of the same layer is the same; the specific method of sand blowing construction is to flush the stacked backfill sand into the sand blowing working pit by spraying high-pressure water at a sand-water mass ratio of 1:3 to 5, so that the sand and water mixture flows evenly into the working pit, and then the sand and water mixture is blown from the working pit along the sand blowing pipeline into the laid film bag by a high-pressure mud pump until the film bag is full; wherein, the length of the film bag is 30 to 50 m, the width of the film bag is determined according to the cross-sectional dimensions of the tunnel. The film bag is made of polypropylene woven cloth, and two sand blowing ports are arranged at each end of the film bag to connect to the sand blowing pipeline; the diameter of the sand blowing port is 15 to 25 cm and the length is 30 to 50 cm; when laying the film bag, the sand blowing port should be kept facing upwards, the film bags on the same layer should be laid compactly, the upper and lower film bags should be firmly connected by tie bars at the buckles, and the end seams of the upper and lower film bags should be staggered by 4 to 6 m to prevent the occurrence of through seams; S6. Grouting construction Before completing the sand blowing of the last layer of membrane bags in step S5, a grouting pipe is reserved in advance on the tunnel vault; after the sand blowing of the membrane bags in step S5 is completed, the sand body is consolidated and settled, and grouting is backfilled and densely packed from the top surface of the last layer of membrane bags to the arc position at the top of the tunnel through the reserved grouting pipe.

2. A method for backfilling old civil air defense tunnels under urban water-rich strata according to claim 1, characterized in that: The backfill sand is river sand with a fineness modulus of fine sand; the sand blowing working pit is formed by excavating downward from the ground and building brick walls with plastering, or by using a mud box prefabricated with iron sheets.

3. The backfilling method of an old civil air defense tunnel under a water-rich urban stratum according to claim 1, characterized in that: In step S4, the sand blasting pipeline is laid out in such a way as to avoid crossing obstacles and forming sharp bends, and at the same time ensure that the pipeline joints are firmly sealed to prevent leakage from causing blockage along the pipeline.

4. The backfilling method of an old civil air defense tunnel under a water-rich urban stratum according to claim 1, characterized in that: In step S5, during measurement and layout, for the shallow water construction area of ​​the tunnel, the membrane bags are laid and positioned by manual underwater operation; for the deep water construction area of ​​the tunnel, kayaks or wooden boats are used to lay and position the membrane bags.

5. The backfilling method of an old civil air defense tunnel under a water-rich urban stratum according to claim 1, characterized in that: In step S5, during the sand blowing operation, the four corners of the film bag are first blown to fill the film bag to make it sink to the bottom, and then the middle part is blown to fill the film bag.

6. A method for backfilling old civil air defense tunnels under urban water-rich strata according to claim 1, characterized in that: In step S5, during the sand blowing construction, the sand blowing thickness in the membrane bag is controlled to be 0.6 to 1 m. When the thickness of the sand body in the membrane bag is close to the designed thickness, the sand blowing speed is reduced, and at the same time, construction workers are arranged to step on the top surface of the membrane bag to facilitate the discharge of water in the membrane bag and make the sand body in the membrane bag evenly distributed.

7. The backfilling method of an old civil air defense tunnel under a water-rich urban stratum according to claim 1, characterized in that: In step S5, during the sand blowing construction, a submersible pump is used to pump out water while blowing sand, so as to control the water level in the tunnel to always be 1 to 2 meters below the arch of the civil air defense tunnel.

8. The backfilling method of an old civil air defense tunnel under a water-rich urban stratum according to claim 1, characterized in that: In step S6, the grouting material is 42.5 grade ordinary Portland cement with a water-cement ratio of 1:1.

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