Precipitation system and precipitation method for sand, gravel and mudstone composite stratum

Abstract

The invention discloses a sand, gravel and mudstone composite stratum dewatering system and method.The system comprises a water collecting well, a dewatering well and a working well, and the water collecting well, the dewatering well and the working well are arranged on the periphery of a foundation pit; the water-collecting well, the water-collecting pipe and the dewatering well form a combined drainage structure; a water collecting pipe is arranged between the water collecting well and the working well; the well depth of the water collecting well is deeper than that of the working well, and the water collecting well is also used as a pumping well; one end of the water collecting pipe is connected with the working well, the other end of the water collecting pipe is connected with the water collecting well, and the end of the water collecting pipe connected with the working well is higher than the end of the water collecting well. According to the drainage system, the water collecting well, the water collecting pipe and the dewatering well are jointly used, the dewatering efficiency is remarkably improved, and the underground water level around the foundation pit is effectively lowered. The dewatering well is located between the water collecting well and the working well, the water filter pipe is used for dewatering, impurities in underground water are effectively filtered, and system blockage is avoided. And the wall protecting pipe is introduced, so that the water filtering pipe is protected, and the service life of the whole dewatering system is prolonged.

Description

Technical Field

[0001] The invention relates to dewatering construction of a subway station, and in particular to a dewatering system and a dewatering method for a sand-pebble-mudstone composite stratum. Background Art

[0002] The construction of deep foundation pits for subway stations is a complex engineering task, especially in the composite strata of gravel and mudstone, where the construction difficulty and risk are significantly increased. Excavation, support and dewatering are the key links, and dewatering is particularly critical because it is directly related to the safety of foundation pit excavation and the quality of construction. In gravel strata, due to its good skeleton effect, the dewatering construction method outside the foundation pit is usually adopted. This method forms a dewatering funnel by laying a dewatering well every 15 to 20 meters around the foundation pit to achieve water-free conditions during foundation pit excavation. However, this dewatering method has obvious disadvantages, including large area occupation, long construction time, and a large amount of sand will be taken away during the pumping process, resulting in settlement of the surface and nearby buildings.

[0003] In addition, when the bottom of a deep foundation pit is in a mudstone formation, it is difficult for the groundwater at the interface between the gravel and mudstone formations to be completely pumped away by the precipitation well, which can lead to water seepage problems during the excavation of the foundation pit and the construction of the main body of the station. In severe cases, this water seepage may even cause sand flow, posing a major safety risk. At the same time, water seepage problems will also have an adverse effect on the construction quality of the main body of the station, and may lead to problems such as insufficient structural strength and reduced durability. Therefore, how to effectively control the flow of groundwater at the interface and prevent water seepage is the key to ensuring construction safety and improving project quality.

[0004] The patent with publication number CN209179037U discloses a foundation pit dewatering construction structure with upper pebbles and lower red sandstone composite strata. The structure adopts a combined method of dewatering structures inside and outside the foundation pit to achieve synchronous dewatering, ensure the continuous dryness of the excavation area in the foundation pit, prevent the infiltration of groundwater from the external red sandstone layer, avoid ground subsidence, and ensure the safe operation of the foundation pit. In addition, a vacuum pump and a connecting main pipe are built into one side of the foundation pit, and multiple branch pipes are set up below for local dewatering to achieve a uniform drop in the water level, improve construction efficiency, reduce costs, and do not damage the foundation pit structure. At the same time, intercepting ditches and dewatering wells are set on the outside of both sides of the foundation pit to intercept the water from the external pebble layer to flow to the red sandstone layer to prevent the softening and collapse of the sandstone. In summary, this construction structure has a certain effect in foundation pit dewatering, but the structure only uses independent dewatering wells and fails to form a comprehensive dewatering with linkage between wells.

[0005] In order to solve these problems, it is urgent to develop a more effective precipitation technology. This technology must ensure that the free water at the interface between the gravel layer and the mudstone layer is smoothly introduced into the precipitation well, effectively curbing the infiltration problem at the interface. At the same time, the technology must also be committed to reducing the probability of sand extraction to reduce interference and impact on the surrounding environment and achieve environmentally friendly precipitation. In addition, we should also consider the economy and sustainability of the technology to ensure its feasibility and wide applicability in practical applications. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a dewatering system and dewatering method for a sand, gravel and mudstone composite stratum, which effectively lowers the groundwater level around the foundation pit through a combined drainage structure of a water collection well, a water collection pipe and a dewatering well; the water collection well also serves as a pumping well, reducing the cost of setting up a separate pumping well.

[0007] The objective of the present invention is achieved through the following technical solutions:

[0008] The first aspect of the present invention provides a dewatering system for a sand-pebble-mudstone composite formation, comprising a water collection well, a dewatering well and a working well, wherein the water collection well, the dewatering well and the working well are arranged at the periphery of a foundation pit; the water collection well, the water collection pipe and the dewatering well form a combined drainage structure, and a water collection pipe is arranged between the water collection well and the working well;

[0009] The depth of the water collection well is deeper than that of the working well, and the water collection well also serves as a pumping well; one end of the water collection pipe is connected to the working well, and the other end of the water collection pipe is connected to the water collection well, and the end of the water collection pipe connected to the working well is higher than the end of the water collection pipe connected to the water collection well;

[0010] The precipitation well is arranged between the water collecting well and the working well and is located above the water collecting pipe; the end of the precipitation well is directly inserted into the water collecting pipe; the precipitation well comprises a wall protection pipe and a water filter pipe, and the wall protection pipe is arranged above the water filter pipe with water filter holes.

[0011] As a preferred embodiment, functional plates are provided at both ends of the water collecting pipe, and the functional plates are sealing plates or water filtering plates.

[0012] As a preferred embodiment, the sand-pebble-mudstone composite stratum includes a sand-pebble stratum disposed on top and a mudstone stratum disposed on the bottom.

[0013] As a preferred method, a station foundation pit is set up on the sand, gravel and mudstone composite stratum. The station foundation pit is rectangular, and a fence is installed directly outside the station foundation pit; the precipitation system is arranged outside the fence.

[0014] As a preferred method, the road is occupied during the construction of the precipitation system. Both the collection well and the working well are closed with manhole covers, and the top of the precipitation well is closed with a cover plate. Traffic is resumed after the precipitation system construction is completed.

[0015] As a preferred embodiment, the precipitation system includes 2 water collection wells, 2 working wells, and 4 water collection pipes. The precipitation wells are arranged between the water collection wells and the working wells, and the ends of the precipitation wells are directly inserted into the water collection pipes.

[0016] The water collection wells and working wells are arranged crosswise, and two water collection pipes are arranged corresponding to one working well. The two water collection pipes are respectively connected to the two water collection wells adjacent to the working well.

[0017] As a preferred embodiment, the inner diameter of the precipitation well is 150mm to 200mm.

[0018] As a preferred embodiment, a plurality of long strip-shaped water filtering holes are arranged on the water filtering pipe.

[0019] The second aspect of the present invention provides a method for dewatering a sandy gravel mudstone composite formation, which comprises constructing a water collection well and a working well. The water collection well should be deeper and also serve as a pumping well. The well wall and the well bottom should be waterproofed.

[0020] When constructing a water collection pipe tunnel in the mudstone formation within the water collection well and the working well, the tunnel should have a certain slope, and the working well should be downhill toward the water collection well to facilitate drainage;

[0021] After the tunnel is formed, the water collecting pipe is installed, and the outer diameter of the water collecting pipe is close to the excavated tunnel;

[0022] The water collecting pipe is fully filled with the second filter material. To achieve good drainage function, the particle size of the second filter material should be of the same grade (for example, 20mm). The particle size of the second filter material should be appropriately larger than the particle size of the first filter material. The inner diameter of the water collecting pipe filled with the second filter material should meet the drainage requirements.

[0023] The two ends of the water collecting pipe (inside the water collecting well and the working well) are first blocked with plugging plates, and then the seamless steel pipe is drilled downward from the top of the water collecting pipe. The diameter of the hole should be 300-400mm, and the drilling depth should be enough to break the top of the water collecting pipe.

[0024] A water filter pipe is installed inside the seamless steel pipe, and a wall protection pipe is installed above the initial water level. The first filter material is filled between the seamless steel pipe, the wall protection pipe and the water filter pipe. The first filter material can be graded gravel with a diameter of 2 to 8 mm. Then the seamless steel pipe is pulled out, and the top of the wall protection pipe and the first filter material is closed with a cover plate to form a precipitation well.

[0025] A water pump is installed at the bottom of the water collection well, and a drainage pipe is installed at the outlet of the water pump. The drainage pipe is used to discharge the water in the water collection well.

[0026] As a preferred method, after the pumping system (pump and drainage pipe) is installed, the sealing plate at the end of the water collecting pipe on the water collecting well side is replaced with a water filter plate, and the water in the water collecting pipe enters the water collecting well and is discharged by the pump. Turn on the pump to discharge water. In order to occupy less ground area, both the working well and the water collecting well are closed with a manhole cover, and traffic can be opened on top.

[0027] As a preferred method, the free water in the sand and gravel stratum below the initial water level line flows into the filter pipe through the numerous filter holes on the filter pipe of the precipitation well through the first filter material, falls downward into the second filter material in the water collecting pipe, is filtered by the second filter material, passes through the filter plate and enters the water collecting well, is discharged through a pump and a drain pipe, and can be pumped into a sedimentation tank on the ground.

[0028] As the pump is started to continuously reduce water, the water level near the foundation pit continues to drop, and finally the water level in the gravel stratum basically drops to the interface of gravel and mudstone, and free water enters the precipitation well through the interface, and then enters the water collection well and is pumped away by the pump. The present invention arranges precipitation wells along the outer side of the foundation pit, and the free water in the stratum penetrates into the filter pipe through the filter material and the filter holes of the filter pipe under the action of gravity, and then enters the water collection pipe, and the free water flows into the water collection well through the water collection pipe filled with filter material, and finally is discharged by a large-displacement pump.

[0029] As a preferred embodiment, the precipitation system also includes a vacuum pump system, which includes a vacuum pressure gauge, a one-way valve, a vacuum filter, a vacuum pump, a motor and related pipelines; the vacuum pressure gauge and the air inlet are connected to the space in the water collection well.

[0030] Start the motor and the vacuum pump will start working. The air in the water collection well will be sucked to the external space through the air inlet, one-way valve, vacuum filter, vacuum pump and air outlet. The air in the water collection well will become less and vacuum will be gradually formed. The vacuum state in the water collection well can be observed by the vacuum pressure gauge. A vacuum is formed in the space inside the water collection well, and the free water in the water collection pipe will be more conducive to entering the water collection well due to the pressure difference, which is more conducive to the drainage of the interface between the sand, gravel and mudstone composite strata.

[0031] The main principle of a vacuum pump (or air pump) is to form a low-pressure area inside the pump through physical or mechanical means, so that the gas moves from the water collection well to the inside of the pump and is discharged through the exhaust port, thereby reducing the pressure in the water collection well and achieving the purpose of vacuuming. The vacuum pump has many advantages such as high efficiency, energy saving, no pollution, simple operation, strong reliability, etc., and is more suitable for use in bustling cities.

[0032] The present invention has at least the following beneficial effects: The present invention significantly improves the drainage efficiency and effectively reduces the groundwater level around the foundation pit by combining the drainage system of the water collection well, the water collection pipe and the precipitation well. The multifunctional design of the water collection well also serves as a pumping well, saving the cost of adding an independent pumping well. The design of the working well being higher than the water collection well ensures the stability of the water flow direction, and the use of the vacuum pump enhances the drainage efficiency. The precipitation well is located between the water collection well and the working well, and the water is discharged by the filter pipe, which effectively filters the impurities in the groundwater and avoids system blockage. The introduction of the wall protection pipe protects the filter pipe, thereby extending the service life of the entire precipitation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only illustrate embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 This is the plan layout of the precipitation system for the sand-pebble-mudstone composite stratum;

[0035] Figure 2 This is a cross-section of the precipitation system in the sand-pebble-mudstone composite stratum;

[0036] Figure 3 This is a schematic diagram of the cross section of a precipitation well;

[0037] Figure 4 This is the schematic diagram of the vacuum pump system;

[0038] In the figure, 1-water collection well, 2-enclosure, 3-working well, 4-foundation pit, 5-dewatering well, 6-well cover, 7-initial water level line, 8-sand and gravel formation, 9-sealing plate, 10-mudstone formation, 11-water pump, 12-drainage pipe, 13-water filter plate, 14-water collection pipe, 15-cover plate, 16-wall protection pipe, 17-first filter material, 18-water filter hole, 19-water filter pipe, 20-second filter material, 21-vacuum pressure gauge, 22-air inlet, 23-check valve, 24-vacuum filter, 25-vacuum pump, 26-air outlet, 27-motor. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0040] Hereinafter, different embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that the present disclosure is not limited to the specific form disclosed herein, but rather, the present disclosure should be interpreted as covering different changes, equivalents and / or replacements of the embodiments of the present disclosure. When describing the accompanying drawings, similar reference numerals may be used to indicate similar components.

[0041] In the present disclosure, if there is a statement "A or B", "at least one of A and / or B", or "one or more of A and / or B", it can include all possible combinations of the listed items. For example, the statement "A or B", "at least one of A and B", or "at least one of A or B" refers to all of the following situations: (1) including at least one A, (2) including at least one B, or (3) including both at least one A and at least one B.

[0042] The expressions used in different embodiments of the present disclosure, if there is "first", "second", "the first" or "the second" can modify different elements, regardless of order and / or importance, without limiting the corresponding elements. For example, a first user device and a second user device refer to different user devices, although both of them are user devices. For example, a first element can be referred to as a second element, and similarly, a second element can be referred to as a first element without departing from the scope of the present disclosure.

[0043] It will be understood that when an element (e.g., a first element) is referred to as being (operably or communicatively) "connected to" or "coupled to" another element (e.g., a second element), the element may be directly connected or coupled to the other element, or any other element (e.g., a third element) may be interposed therebetween. Conversely, when an element (e.g., a first element) is referred to as being "directly connected" or "directly coupled to" another element (the second element), no element (e.g., a third element) is interposed therebetween.

[0044] In the present disclosure, the terms are used to describe specific embodiments and do not limit the present disclosure. As used herein, the singular form is intended to also include the plural form, unless the content clearly indicates otherwise. In the specification, it should be understood that the term "including" or "having" represents the presence of a feature, number, step, operation, structural element, component or combination thereof, without excluding in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, structural elements, components or combinations thereof.

[0045] It should be understood that certain details are provided in the following description to facilitate a complete understanding of the example embodiments. However, one of ordinary skill in the art should understand that the example embodiments can be implemented without these specific details. For example, the system can be shown in a block diagram to avoid obscuring the example with unnecessary details. In other examples, well-known processes, structures, and techniques may not be shown in unnecessary details to avoid obscuring the example.

[0046] like Figure 1 As shown, a dewatering system for sandstone-cobblestone composite formation includes a water collection well 1, a dewatering well 5 and a working well 3. The water collection well 1, the dewatering well 5 and the working well 3 are arranged on the periphery of a foundation pit 4; the water collection well 1, the water collection pipe 14 and the dewatering well 5 form a combined drainage structure, such as Figure 2 As shown, a water collecting pipe 14 is provided between the water collecting well 1 and the working well 3;

[0047] The depth of the water collecting well 1 is deeper than that of the working well 3, and the water collecting well 1 also serves as a pumping well; one end of the water collecting pipe 14 is connected to the working well 3, and the other end of the water collecting pipe 14 is connected to the water collecting well 1, and the end of the water collecting pipe 14 connected to the working well 3 is higher than the end of the water collecting pipe 14 connected to the water collecting well 1;

[0048] The precipitation well 5 is arranged between the water collecting well 1 and the working well 3 and is located above the water collecting pipe 14; the end of the precipitation well 5 is directly inserted into the water collecting pipe 14; the precipitation well 5 includes a wall protection pipe 16 and a water filter pipe 19, and the wall protection pipe 16 is arranged above the water filter pipe 19 with water filter holes 18.

[0049] The sand-pebble-mudstone composite stratum dewatering system realizes the effective control and discharge of groundwater outside the foundation pit 4 through the reasonable layout of the water collection well 1, the dewatering well 5 and the working well 3. The water collection well 1 and the dewatering well 5 form a joint drainage structure, which is connected by the water collection pipe 14, and can efficiently guide the groundwater from the dewatering well 5 to the water collection well 1, thereby lowering the water level of the original stratum and ensuring the smooth progress of the excavation of the foundation pit 4. The depth of the water collection well 1 is designed to be deeper than the working well 3 [such as 5 to 8 meters deeper than the working well], so that it can also serve as a pumping well, which can more effectively extract deep groundwater, expand the dewatering range, and improve the dewatering efficiency. The water collection pipe 14 is connected to the working well 3 at one end and the water collection well 1 at the other end, and the end connected to the working well 3 is higher than the end connected to the water collection well 1. This design helps to utilize the principle of gravity flow to promote the smooth flow of water from the side of the working well 3 to the water collection well 1, and reduce the energy consumption of the pumping equipment. The precipitation well 5 is arranged between the water collection well 1 and the working well 3, and can achieve the effect of multi-head collection and centralized drainage by cooperating with the water collection pipe 14. The end of the precipitation well 5 is directly inserted into the water collection pipe 14, ensuring the close connection between the precipitation well 5 and the water collection pipe 14, improving the precipitation efficiency, while reducing the loss path of groundwater and avoiding hydraulic loss. The precipitation well 5 includes a wall protection pipe 16 and a water filter pipe 19, wherein the wall protection pipe 16 is arranged on the water filter pipe 19 with a water filter hole 18. This structure can effectively prevent particles such as sand and pebbles from entering the precipitation well 5, protect the water filter pipe 19, extend its service life, and ensure smooth filtering and discharge of groundwater.

[0050] In summary, the dewatering system achieves effective control of groundwater in the composite strata through scientific structural design and reasonable layout, ensures the safety and efficiency of foundation pit 4 construction, and reduces construction costs and maintenance difficulties.

[0051] In a preferred embodiment, functional plates are provided at both ends of the water collecting pipe 14, and the functional plates are sealing plates 9 or water filter plates 13. The water collecting pipe 14 connected to the working well 3 is closed by the sealing plates 9, and the construction of the water collecting pipe 14 requires the working well 3.

[0052] In a preferred embodiment, the sand-pebble-mudstone composite stratum includes a sand-pebble stratum 8 disposed on top and a mudstone stratum 10 disposed on the bottom.

[0053] In a preferred embodiment, a subway station foundation pit 4 is set on the sand, gravel and mudstone composite stratum. The subway station foundation pit 4 is rectangular, and a fence 2 is directly installed outside the station foundation pit 4; the precipitation system is arranged outside the fence 2.

[0054] In a preferred embodiment, the road is occupied during the construction of the precipitation system. Both the water collection well 1 and the working well 3 are closed with a manhole cover 6, and the upper part of the precipitation well 5 is closed with a cover plate 15. Traffic is restored after the construction of the precipitation system is completed.

[0055] In a preferred embodiment, the precipitation system includes two water collection wells 1, two working wells 3, and four water collection pipes 14. A precipitation well 5 is arranged between the water collection well 1 and the working well 3, and the end of the precipitation well 5 is directly inserted into the water collection pipe 14;

[0056] The water collecting wells 1 and the working wells 3 are arranged crosswise, and two water collecting pipes 14 are arranged corresponding to one working well 3 . The two water collecting pipes 14 are respectively connected to two adjacent water collecting wells 1 of the working well 3 .

[0057] In a preferred embodiment, the inner diameter of the precipitation well 5 is 150 mm to 200 mm. The precipitation well 5 is composed of multiple sections of wall protection pipes 16 and multiple sections of water filter pipes 19, which are easy to assemble.

[0058] In a preferred embodiment, a plurality of long strip-shaped water filter holes 18 are arranged on the water filter pipe 19 to facilitate drainage. A method for dewatering sandstone-pebble mudstone composite stratum, the construction process of the dewatering system, first, a conventional method (such as rotary drilling, impact drilling, etc.) is used to construct a water collection well 1 and a working well 3. The water collection well 1 should be deeper and also serve as a pumping well. The depth of the working well 3 can meet the construction of the water collection pipe 14. The well wall and the well bottom should be waterproofed;

[0059] Then, a tunnel of a water collection pipe 14 is constructed in the mudstone stratum 10 by using trenchless technical equipment in the water collection well 1 and the working well 3. The tunnel should be formed into a certain slope, and the working well 3 should be formed into a downslope form toward the water collection well 1, which is conducive to drainage;

[0060] After the tunnel is formed, the water collecting pipe 14 is installed, and the outer diameter of the water collecting pipe 14 is closely connected with the excavated tunnel;

[0061] The water collecting pipe 14 is filled with the second filter material 20 (see Figure 3 ), in order to achieve good drainage function, the particle size of the second filter material 20 should be of the same grade (such as 20mm gravel), and the particle size of the second filter material 20 should be appropriately larger than the particle size of the first filter material 17, and the inner diameter of the water collecting pipe 14 filled with the second filter material 20 should meet the drainage requirements;

[0062] The two ends of the water collecting pipe 14 (in the water collecting well 1 and the working well 3) are first blocked with the blocking plate 9, and then the seamless steel pipe is drilled downward with the pipe drilling rig just above the water collecting pipe 14. The diameter of the borehole is preferably 300-400mm, and the drilling depth is preferably enough to break the top of the water collecting pipe 14;

[0063] A water filter pipe 19 is installed in the seamless steel pipe, and a wall protection pipe 16 is installed above the initial water level line 7. The first filter material 17 is filled between the seamless steel pipe, the wall protection pipe 16 and the water filter pipe 19. The first filter material 17 can be graded gravel with a diameter of 2 to 8 mm. Then the seamless steel pipe is pulled out, and the surface of the wall protection pipe 16 and the first filter material 17 is closed with a cover plate 15 to form a precipitation well 5. The spacing of the precipitation wells 5 is preferably 5 to 10 meters to meet the precipitation requirements. If the precipitation at the interface of sand, gravel and mudstone is not ideal in the later stage, the number of precipitation wells 5 can be increased.

[0064] A large-flow pump 11 is installed at the bottom of the water collection well 1, and a drainage pipe 12 is installed at the outlet of the pump 11 until it reaches a sedimentation tank on the ground. After sedimentation, the water is discharged into the municipal pipe network.

[0065] In a preferred embodiment, after the pumping system (pump 11 and drain pipe 12) is installed, the blocking plate 9 at the end of the water collecting pipe 14 on the side of the water collecting well 1 is replaced with a water filter plate 13, and the water in the water collecting pipe 14 enters the water collecting well 1 and is discharged by the pump 11. The pump 11 is turned on to discharge water. In order to occupy less ground area, both the working well 3 and the water collecting well 1 are closed with a manhole cover 6, and traffic can be opened on the top.

[0066] In a preferred embodiment, free water in the gravel stratum 8 below the initial water level line 7 flows into the filter pipe 19 through the numerous filter holes 18 on the filter pipe 19 of the precipitation well 5 through the first filter material 17 under the action of gravity, falls downward into the second filter material 20 in the water collecting pipe 14, and then flows downhill through the second filter material 20 to be filtered through the filter plate 13 into the water collecting well 1, and is discharged through the water pump 11 and the drain pipe 12 and pumped into the sedimentation tank on the ground.

[0067] As the pump 11 starts to continuously lower the water level, the water level near the foundation pit 4 continues to drop, and eventually the water level line in the gravel stratum 8 basically drops to the interface between the gravel and mudstone. Free water enters the precipitation well 5 through the interface, and then enters the collection well 1 and is pumped away by the pump 11.

[0068] In one embodiment, a method for dewatering a sand-pebble-mudstone composite stratum is provided. To facilitate dewatering of the foundation pit 4 , the best method is to form a vacuum in the water collection well 1 .

[0069] The precipitation system also includes a vacuum pump 25 system (such as Figure 4As shown), the vacuum pump 25 system includes a vacuum pressure gauge 21, a one-way valve 23, a vacuum filter 24, a vacuum pump 25, a motor 27 and related pipelines; the vacuum pressure gauge 21 and the air inlet 22 are connected to the space inside the water collection well 1, and the air outlet 26 leads to the external space.

[0070] Start the motor 27 and the vacuum pump 25 starts working. The air in the water collecting well 1 is sucked to the external space through the air inlet 22, the one-way valve 23, the vacuum filter 24, the vacuum pump 25 and the air outlet 26. The air in the water collecting well 1 becomes less and a vacuum is gradually formed. The vacuum state in the water collecting well 1 can be observed through the vacuum pressure gauge 21. A vacuum is formed in the space inside the water collecting well 1, and the free water in the water collecting pipe 14 is more conducive to entering the water collecting well 14 due to the pressure difference, which is more conducive to the drainage of the interface between the sand, gravel and mudstone composite strata.

[0071] The main principle of the vacuum pump 25 is to form a low-pressure area inside the pump through physical or mechanical means, so that the gas moves from the water collection well 1 through the air inlet 22 to the inside of the pump and is discharged through the air outlet 26, thereby reducing the pressure in the water collection well 1 and achieving the purpose of vacuuming. The vacuum pump 25 has many advantages such as high efficiency, energy saving, no pollution, simple operation, strong reliability, etc., and is more suitable for use in prosperous cities.

[0072] The present invention provides a dewatering system and a dewatering method for a sand-pebble-mudstone composite stratum. A plurality of dewatering wells 5 filter free water at the interface of a sand-pebble stratum 8 and a composite stratum through filter material over a long distance and enter a water collection well 1 to be pumped away by a large-flow pump 11. The water collection well 1 is in a vacuum state during the pumping process, which improves the water seepage capacity of the water collection pipe 14, effectively reduces water seepage at the interface of a foundation pit 4, reduces the sand pumping rate, saves electricity consumption, reduces surface settlement, improves the construction safety and quality of the foundation pit 4, and can be promoted and applied in similar strata.

[0073] In some embodiments, advantages and considerations of the sand-pebble-mudstone composite formation dewatering system:

[0074] (1) The dewatering well 5 adopts the following pipe drilling method, and does not need to use mud wall protection. The permeability coefficient of the sand and gravel formation 8 near the borehole is not reduced, which can improve the dewatering effect; and there is no need to wash the well.

[0075] (2) The drainage wells 5 are numerous as water flow channels, which can discharge the free water at the interface of sand, gravel and mudstone through the water collecting pipe 14 to the greatest extent, thereby reducing the probability of water seepage from the interface of sand, gravel and mudstone to the foundation pit 4.

[0076] (3) The free water in the sand and gravel stratum 8 is discharged by gravity and filtered through the first filter material 17 and the second filter material 20, which greatly reduces the sand content during the precipitation process, reduces the loss rate of the sand and gravel stratum 8, and can effectively reduce the surface settlement caused by pumping water.

[0077] (4) To dewater a subway station foundation pit 4, only two large-flow pumps 11 are required, thereby improving equipment efficiency and reducing pumping costs.

[0078] (5) The precipitation system equipment and pipelines are hidden underground and do not occupy the surface area, effectively reducing the construction area.

[0079] (6) If it is found that the dewatering effect at the interface of sand, gravel and mudstone is not good during the excavation of the foundation pit 4, the number of dewatering wells 5 can be increased at any time to improve the dewatering effect.

[0080] (7) No matter how deep the bottom of the foundation pit 4 is, the depth of the designed water collection pipe 14 only needs to be below the interface between the gravel stratum 8 and the mudstone stratum 10. Since the mudstone stratum 10 has an extremely low permeability, it can be ensured that no groundwater will infiltrate the water collection well 1 and the working well 3 during the construction of the water collection pipe 14, thereby ensuring construction safety.

[0081] (8) To ensure that a vacuum state is formed in the water collection well 1, the water collection well 1 and the precipitation well 5 must be in a sealed state.

[0082] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A dewatering system for sand, pebble and mudstone composite strata, characterized by: It includes a water collection well, a drainage well and a working well, which are arranged at the periphery of the foundation pit; the water collection well, the water collection pipe and the drainage well form a joint drainage structure, and a water collection pipe is arranged between the water collection well and the working well; The depth of the water collection well is deeper than that of the working well, and the water collection well also serves as a pumping well; one end of the water collection pipe is connected to the working well, and the other end of the water collection pipe is connected to the water collection well, and the end of the water collection pipe connected to the working well is higher than the end of the water collection pipe connected to the water collection well; The precipitation well is arranged between the water collecting well and the working well and is located above the water collecting pipe; the end of the precipitation well is directly inserted into the water collecting pipe; the precipitation well comprises a wall protection pipe and a water filter pipe, and the wall protection pipe is arranged above the water filter pipe with water filter holes.

2. A dewatering system for sand, pebble and mudstone composite formation according to claim 1, characterized in that: Functional plates are arranged at both ends of the water collecting pipe, and the functional plates are sealing plates or water filtering plates.

3. The dewatering system for sand, pebble and mudstone composite strata according to claim 1, characterized in that: The sand-pebble-mudstone composite stratum includes a sand-pebble stratum disposed on top and a mudstone stratum disposed on the bottom.

4. A dewatering system for sand, pebble and mudstone composite formation according to claim 3, characterized in that: A station foundation pit is set up on the sand, gravel and mudstone composite stratum. The station foundation pit is rectangular, and enclosures are installed directly outside the station foundation pit; the precipitation system is arranged outside the enclosures.

5. A dewatering system for sand, pebble and mudstone composite strata according to claim 1 or 4, characterized in that: The road will be occupied during the construction of the precipitation system. Both the water collection well and the working well will be closed with manhole covers, and the top of the precipitation well will be closed with a cover plate. Traffic will be resumed after the construction of the precipitation system is completed.

6. The dewatering system for sand-pebble-mudstone composite stratum according to claim 3, characterized in that: The precipitation system includes 2 water collection wells, 2 working wells, and 4 water collection pipes. The precipitation well is arranged between the water collection well and the working well, and the end of the precipitation well is directly inserted into the water collection pipe; The water collection wells and working wells are arranged crosswise, and two water collection pipes are arranged corresponding to one working well. The two water collection pipes are respectively connected to the two water collection wells adjacent to the working well.

7. A method for dewatering a sand-pebble-mudstone composite stratum, characterized in that: Construct water collection wells and working wells. The water collection wells should be deeper and also serve as pumping wells. The well walls and bottoms should be waterproofed. When constructing a water collection pipe tunnel in the mudstone formation within the water collection well and the working well, the tunnel should have a certain slope, and the working well should be downhill toward the water collection well to facilitate drainage; After the tunnel is formed, the water collecting pipe is installed, and the outer diameter of the water collecting pipe is close to the excavated tunnel; The water collecting pipe is fully filled with the second filter material, the particle size of the second filter material should be of the same grade, and the particle size of the second filter material should be appropriately larger than the particle size of the first filter material; The two ends of the water collecting pipe are first blocked with plugging plates, and then the seamless steel pipe is drilled downward from the top of the water collecting pipe. The diameter of the hole should be 300-400mm, and the drilling depth should be enough to break the top of the water collecting pipe. A water filter pipe is installed inside the seamless steel pipe, and a wall protection pipe is installed above the initial water level line; the first filter material is filled between the seamless steel pipe, the wall protection pipe and the water filter pipe, and then the seamless steel pipe is pulled out, and the top of the wall protection pipe and the first filter material is closed with a cover plate to form a precipitation well; A water pump is installed at the bottom of the water collection well, and a drainage pipe is installed at the outlet of the water pump. The drainage pipe is used to discharge the water in the water collection well.

8. A dewatering method for sand-pebble-mudstone composite stratum according to claim 7, characterized in that: After the pumping system is installed, the sealing plate at the end of the water collecting pipe on the side of the water collecting well is replaced with a water filter plate. The water in the water collecting pipe enters the water collecting well and is precipitated by the pump.

9. A method for dewatering a sand-pebble-mudstone composite stratum, characterized in that: The free water in the sand and gravel stratum below the initial water level line flows into the filter pipe through the numerous filter holes on the filter pipe of the precipitation well through the first filter material, falls downward into the second filter material in the water collecting pipe, is filtered by the second filter material, passes through the filter plate and enters the water collecting well, and is discharged through the water pump and the drainage pipe.

10. A dewatering method for sand-pebble-mudstone composite stratum according to claim 9, characterized in that: The precipitation system also includes a vacuum pump system, which includes a vacuum pressure gauge, a one-way valve, a vacuum filter, a vacuum pump, a motor and related pipelines; the vacuum pressure gauge and the air inlet are connected to the space in the water collection well; Start the motor and the vacuum pump will start working. The air in the water collection well will be sucked to the external space through the air inlet, one-way valve, vacuum filter, vacuum pump and air outlet. The air in the water collection well will become less and vacuum will be gradually formed. The vacuum state in the water collection well can be observed by the vacuum pressure gauge. A vacuum is formed in the space inside the water collection well, and the free water in the water collection pipe will be more conducive to entering the water collection well due to the pressure difference, which is more conducive to the drainage of the interface between the sand, gravel and mudstone composite strata.

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