Water-rich composite stratum deep foundation pit dewatering system and method

Abstract

The invention relates to a water-rich composite stratum deep foundation pit dewatering system and method. The water-rich composite stratum deep foundation pit dewatering system comprises a composite dewatering well pipe device and a well wall plugging detection device. The pipe has the beneficial effects that the pipe has multiple purposes, synchronous rapid precipitation of water-rich composite stratums such as an aquitard and a double confined aquifer in the excavation range of the foundation pit is achieved, operation is convenient and fast, and the cost is reduced; whether the well wall of the water-resisting layer is tightly blocked or not can be judged by detecting the content of the edible coloring agent in the water sample in the submersible pump, and the precipitation effect is prevented from being affected by double-layer confined water communication. Cement paste is refilled through the second grouting pipe, the sealing performance of the clay material of the water-resisting layer is further improved, and remedy is timely and effective; by means of the annular pipeline, edible coloring agents or cement paste can be evenly injected into the periphery of the well wall, and the accuracy of well wall plugging detection and the compactness of paste supplementing are effectively improved.

Description

Technical Field

[0001] The invention belongs to the field of foundation pit dewatering, and in particular relates to a deep foundation pit dewatering system and method in a water-rich composite stratum. Background Art

[0002] As urban construction continues to accelerate, a large number of high-rise and super-high-rise buildings are rising from the ground, the scale of underground space development continues to expand, and deep foundation pit projects are increasing. Among them, deep foundation pit construction in water-rich composite strata faces many severe challenges.

[0003] Water-rich composite strata refer to special geological conditions that are composed of a variety of rock and soil bodies of different properties, with a high groundwater level and rich water content. This type of stratum has a complex structure, the mechanical properties of the rock and soil bodies vary greatly, and the permeability coefficients of different strata vary widely, which may range from high permeability of sand to low permeability of clay. For example, in some coastal cities or river alluvial plains, there is often a situation where the upper part is a highly permeable sand layer, the lower part is a relatively weakly permeable clay layer, and gravel layers of different particle sizes are interspersed in the middle.

[0004] For deep foundation pit projects, effective dewatering construction is a key link to ensure project safety and quality. Dewatering construction can lower the groundwater level, keep the foundation pit excavation surface in a drained state, avoid the occurrence of adverse phenomena such as water gushing, sand flow, and pipe gushing, enhance the stability of the pit wall soil, and ensure the smooth progress of foundation pit excavation and foundation construction.

[0005] However, the existing deep foundation pit dewatering construction methods have many limitations in water-rich composite formations. Traditional dewatering methods, such as light well point dewatering, have poor adaptability to formations with different permeability coefficients in composite formations, and are difficult to meet the requirements of effectively lowering groundwater levels over a large range, and are prone to insufficient or excessive local dewatering. Although pipe well dewatering can be applied to formations of a certain depth, in water-rich composite formations, due to the heterogeneity of the formations, the layout and parameter determination of pipe wells are relatively difficult, which may lead to poor dewatering effects and may also cause environmental problems such as excessive ground subsidence in the surrounding areas. In addition, the existing dewatering methods often cause large disturbances to the formations during construction, which can easily destroy the original structural stability of the formations and increase construction risks. Therefore, there is an urgent need for a deep foundation pit dewatering construction method tailored to the characteristics of water-rich composite formations to address the deficiencies of the existing technology and ensure the safe, efficient, and environmentally friendly construction of deep foundation pit projects. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide a system and method for dewatering a deep foundation pit in a water-rich composite stratum.

[0007] This water-rich composite stratum deep foundation pit dewatering system includes a composite dewatering well pipe device and a well wall plugging and detection device; a retaining structure is provided on the inner wall of the foundation pit, there is a composite stratum outside the retaining structure, and drill holes are drilled in the composite stratum; the composite dewatering well pipe device is arranged in the drill holes, and the composite dewatering well pipe device includes an upper vacuum well pipe ring, a middle impervious pipe and a lower permeable pipe; a vacuum pipe is connected to the top of the upper vacuum well pipe ring, and a vacuum pump is connected to the connection of the vacuum pipes; an upper impervious pipe is sleeved in the center of the upper vacuum well pipe ring; the upper impervious pipe, the middle impervious pipe and the lower permeable pipe are of an integral hollow structure; a submersible pump is arranged inside the lower permeable pipe, and a drain pipe is connected to the top of the submersible pump; the well wall plugging and detection device includes a first grouting pipe, a second grouting pipe and a fixing rod; the first grouting pipe is anchored on one side of the middle impervious pipe through the fixing rod, and a food coloring grouting machine is connected to the top; the second grouting pipe is anchored on the other side of the middle impervious pipe through the fixing rod, and a cement slurry grouting machine is connected to the top.

[0008] Preferably, the composite stratum includes a weakly permeable layer, a first confined aquifer, an aquitard and a second confined aquifer from top to bottom; the bottom of the foundation pit is within the range of the second confined aquifer; the length of the upper vacuum well pipe ring is the same as the depth of the weakly permeable layer, the length of the middle impervious pipe is the same as the sum of the depths of the first confined aquifer and the aquitard, and the length of the lower permeable pipe is the same as the depth of the second confined aquifer; the bottom of the first grouting pipe is located at the interface between the first confined aquifer and the aquitard; the bottom of the second grouting pipe is located within the aquitard.

[0009] Preferably, an outer filter screen, an outer sleeve ring, an inner filter screen, an inner core ring and an upper impervious pipe are sequentially sleeved inside the upper vacuum well pipe ring from outside to inside; a sealing cover is provided at the top of the upper vacuum well pipe ring, and a sealing bottom is provided at the bottom; the space formed by the sealing cover, the sealing bottom, the inner core ring and the upper impervious pipe is a vacuum ring; a vacuum pipe is connected to the top of the vacuum ring, and a vacuum pump is connected to the connection of the vacuum pipes.

[0010] Preferably, the lower permeable pipe includes a coarse filter screen, a permeable filter pipe and iron wires; the coarse filter screen is fixedly sleeved outside the permeable filter pipe through the iron wires; a submersible pump is arranged inside the permeable filter pipe, and a drain pipe is connected to the top of the submersible pump and extends to the ground surface.

[0011] Preferably, the well wall plugging and detection device further includes a three-way pipe, a first annular pipe and a second annular pipe; the bottom of the first grouting pipe is connected to the first annular pipe through the three-way pipe; the bottom of the second grouting pipe is connected to the second annular pipe through the three-way pipe; a food coloring liquid outlet is provided below the first annular pipe, and the first annular pipe surrounds the middle impervious pipe; cement slurry outlets are provided around the second annular pipe, and the second annular pipe surrounds the middle impervious pipe.

[0012] This water-rich composite stratum deep foundation pit dewatering method includes the following steps:

[0013] Step 1: Determine the thickness of each soil layer in the composite stratum and design the structural dimensions of the composite dewatering well pipe device and the wellbore plugging detection device.

[0014] Step 2: Drill a borehole, simultaneously lower the composite dewatering well pipe device and the wellbore plugging detection device, and backfill and plug the voids around the wellbore.

[0015] Step 3: Install a submersible pump and a drain pipe, connect the vacuum pipe and the vacuum pump, and then use an edible coloring agent grouting machine to inject edible coloring agent into the first grouting pipe. Conduct a trial pumping for dewatering. By detecting the content of edible coloring agent in the water sample in the submersible pump, determine whether the plugging of the aquitard wellbore is dense.

[0016] Step 4: After passing the trial pumping test, start the submersible pump and the vacuum pump to start the dewatering operation.

[0017] Preferably, in Step 2, the voids around the aquitard wellbore are backfilled with clay material, and the voids around the wellbores of the weakly permeable layer, the first confined aquifer, and the second confined aquifer are backfilled with gravel filter material.

[0018] Preferably, in Step 4, if the plugging of the aquitard wellbore is not dense, use a cement slurry grouting machine to inject supplementary cement slurry into the second grouting pipe, and repeat the detection until the plugging of the aquitard wellbore is dense.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1) The present invention proposes a composite dewatering well pipe device for strata with a relatively large coefficient of permeability, which combines the well pipe dewatering method. For strata with a relatively small coefficient of permeability, a light well point dewatering method is proposed. Through the multi-purpose use of one pipe, synchronous and rapid dewatering of water-rich composite strata such as weakly permeable layers and double confined aquifers existing in the foundation pit excavation range is achieved. There is no need for two sets of devices and operations, the operation is convenient, and the cost is reduced.

[0021] 2) The wellbore plugging detection device in the present invention combines the functions of plugging effect detection and remedial treatment. By detecting the content of edible coloring agent in the water sample in the submersible pump, determine whether the edible coloring agent penetrates and seeps down through the clay material of the aquitard, and then it can be judged whether the plugging of the aquitard wellbore is dense, avoiding the influence of the penetration of the double confined aquifers on the dewatering effect; by injecting supplementary cement slurry through the second grouting pipe, the sealing performance of the clay material of the aquitard is further improved, and the remedial treatment is timely and effective.

[0022] 3) The wellbore plugging detection device in the present invention is provided with an annular pipeline, which can evenly inject edible coloring agent or cement slurry around the wellbore, effectively improving the accuracy of wellbore plugging detection and the density of supplementary grouting.

[0023] 4) The wellbore plugging detection device in the present invention can be lowered into place synchronously with the composite dewatering well pipe, avoiding secondary drilling and installation, and effectively improving the construction efficiency. Brief Description of the Drawings

[0024] Figure 1 It is a schematic diagram of the dewatering construction for a deep foundation pit in a water-rich composite stratum;

[0025] Figure 2 It is an overall diagram of the dewatering system for a deep foundation pit in a water-rich composite stratum;

[0026] Figure 3 It is a sectional view of the dewatering system for a deep foundation pit in a water-rich composite stratum;

[0027] Figure 4 It is a sectional view of the upper vacuum well pipe ring of the composite dewatering well pipe device;

[0028] Figure 5 It is a sectional view of the lower water-permeable pipe of the composite dewatering well pipe device;

[0029] Figure 6 It is a schematic diagram of the well wall plugging detection device.

[0030] Description of the reference numerals: 1 upper vacuum well pipe ring; 1-1 outer filter screen; 1-2 outer sleeve ring; 1-3 inner filter screen; 1-4 inner core ring; 1-5 sealing cover; 1-6 vacuum ring; 1-7 upper water-impermeable pipe; 1-8 sealing bottom; 2 middle water-impermeable pipe; 3 lower water-permeable pipe; 3-1 coarse filter screen; 3-2 water-permeable filter pipe; 3-3 iron wire; 4 first grouting pipe; 5 second grouting pipe; 6 first annular pipe; 7 second annular pipe; 8 three-way pipe; 9 edible coloring agent liquid outlet; 10 cement slurry outlet; 11 fixing rod; 12 drain pipe; 13 vacuum pipe; 14 edible coloring agent grouting machine; 15 cement slurry grouting machine; 16 vacuum pump; 17 submersible pump; 18 foundation pit; 19 retaining structure; 20 composite stratum; 20-1 weakly permeable layer; 20-2 first confined aquifer; 20-3 aquitard; 20-4 second confined aquifer; 21 borehole; 22 gravel filter; 23 clay material. Detailed Description of the Preferred Embodiments

[0031] The present invention will be further described below in conjunction with the embodiments. The description of the following embodiments is only for helping to understand the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several modifications can still be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0032] Embodiment 1

[0033] As an embodiment, a dewatering system for deep foundation pits in water-rich composite strata is proposed, including a composite dewatering well pipe device and a well wall plugging and detection device; a retaining structure 19 is provided on the inner wall of the foundation pit 18, and there is a composite stratum 20 outside the retaining structure 19, and a borehole 21 is drilled in the composite stratum 20; the composite dewatering well pipe device is arranged in the borehole 21, and the composite dewatering well pipe device includes an upper vacuum well pipe ring 1, a middle impervious pipe 2 and a lower permeable pipe 3; a vacuum pipe 13 is connected to the top of the upper vacuum well pipe ring 1, and a vacuum pump 16 is connected to the connection of the vacuum pipes 13; an upper impervious pipe 1-7 is sleeved in the center of the upper vacuum well pipe ring 1; the upper impervious pipe 1-7, the middle impervious pipe 2 and the lower permeable pipe 3 are of an integral hollow structure; a submersible pump 17 is arranged inside the lower permeable pipe 3, and a drain pipe 12 is connected to the top of the submersible pump 17; the well wall plugging and detection device includes a first grouting pipe 4, a second grouting pipe 5 and a fixing rod 11; the first grouting pipe 4 is anchored on one side of the middle impervious pipe 2 through the fixing rod 11, and a food coloring grouting machine 14 is connected to the top; the second grouting pipe 5 is anchored on the other side of the middle impervious pipe 2 through the fixing rod 11, and a cement slurry grouting machine 15 is connected to the top.

[0034] As Figure 1 shown, the composite stratum 20 includes a weakly permeable layer 20-1, a first confined aquifer 20-2, an aquitard 20-3 and a second confined aquifer 20-4 from top to bottom; the bottom of the foundation pit 18 is within the range of the second confined aquifer 20-4; the length of the upper vacuum well pipe ring 1 is the same as the depth of the weakly permeable layer 20-1, the length of the middle impervious pipe 2 is the same as the sum of the depths of the first confined aquifer 20-2 and the aquitard 20-3, and the length of the lower permeable pipe 3 is the same as the depth of the second confined aquifer 20-4; the bottom of the first grouting pipe 4 is at the interface between the first confined aquifer 20-2 and the aquitard 20-3; the bottom of the second grouting pipe 5 is within the aquitard 20-3.

[0035] The well wall sealing detection device includes a first grouting pipe 4, a second grouting pipe 5, a first annular pipe 6 and a second annular pipe 7. The first grouting pipe 4 is fixed on one side of the middle impervious pipe 2 through a fixing rod 11, and its bottom is connected to the first annular pipe 6 through a tee 8, and a food coloring grouting machine 14 is connected to the top.

[0036] As Figure 2 and Figure 1 shown, the second grouting pipe 5 is fixed on the other side of the middle impervious pipe 2 through a fixing rod 11, and its bottom is connected to the second annular pipe 7 through a tee 8, and a cement slurry grouting machine 15 is connected to the top. Both the first annular pipe 6 and the second annular pipe 7 are made of high-strength PVC material to ensure that they do not rupture during high-pressure grouting.

[0037] As Figure 4As shown in the figure, the upper vacuum well pipe ring 1 sequentially includes an outer filter screen 1-1, an outer sleeve ring 1-2, an inner filter screen 1-3, an inner core ring 1-4, and an upper impervious water pipe 1-7 from outside to inside. The lower water permeable pipe 3 is composed of a coarse filter screen 3-1 and a water permeable filter pipe 3-2, the coarse filter screen 3-1, the water permeable filter pipe 3-2. The upper impervious water pipe 1-7, the middle impervious water pipe 2, and the lower water permeable pipe 3 together form an integral hollow structure to ensure the stability and sealing performance of the well pipe.

[0038] The upper vacuum well pipe ring 1 further includes a sealing cover 1-5 and a sealing bottom 1-8, which together with the inner core ring 1-4 and the upper impervious water pipe 1-7 form a vacuum ring 1-6. The sealing cover 1-5 and the sealing bottom 1-8 are made of rubber material and have good sealing performance. The vacuum ring 1-6 is connected to a vacuum pump 16 through a vacuum pipe 13. The vacuum pump 16 is an energy-efficient type device, which can form a stable negative pressure environment in a short time and improve the precipitation efficiency.

[0039] As Figure 5 shown in the figure, a submersible pump 17 is provided inside the lower water permeable pipe 3 and extends to the ground surface through a drain pipe 12. The submersible pump 17 is made of corrosion-resistant stainless steel material and can operate stably for a long time. The coarse filter screen 3-1 is wrapped and fixed around the water permeable filter pipe 3-2 with iron wires 3-3 to ensure that it will not fall off due to excessive water pressure during the pumping process.

[0040] As Figure 6 and Figure 1 shown in the figure, an edible coloring agent outlet 9 is provided below the first annular pipe 6. The first annular pipe 6 surrounds the middle impervious water pipe 2 and is located at the interface between the first confined aquifer 20-2 and the aquitard 20-3. The edible coloring agent outlet 9 adopts an adjustable valve design, which can control the injection amount of the edible coloring agent according to actual needs.

[0041] A slurry outlet 10 is provided around the second annular pipe 7. The second annular pipe 7 surrounds the middle impervious water pipe 2 and is located inside the aquitard 20-3. The slurry outlet 10 adopts a porous design to ensure that the slurry can be evenly distributed around the well wall to form an effective sealing layer.

[0042] Embodiment 2

[0043] As another embodiment, this Embodiment 2 is proposed on the basis of Embodiment 1, a deep foundation pit dewatering method for a water-rich composite stratum.

[0044] Step 1. Geological exploration: Through drilling and geological radar detection, determine the thickness and distribution of each soil layer in the composite stratum 20, and design the structural dimensions of the composite dewatering well pipe and the well wall sealing detection device.

[0045] Step 2. Installation of the precipitation system: Use a drill rig to drill boreholes 21 with a diameter slightly larger than the outer diameter of the well pipe to ensure that the well pipe can be smoothly lowered. Simultaneously lower the composite precipitation well pipe and the well wall sealing detection device, and use the layered backfilling method to seal the gaps around the well wall.

[0046] The gaps around the well wall of the aquitard 20-3 are backfilled with clay material 23. The clay material 23 is screened and compacted to ensure its density and water impermeability. The gaps around the well wall of the slightly permeable layer 20-1, the first confined aquifer 20-2, and the second confined aquifer 20-4 are backfilled with gravel filter material 22. The gravel filter material 22 is cleaned and graded to ensure its water permeability and stability.

[0047] Step 3. Connection of pipeline equipment: Install the submersible pump 17 and the drain pipe 12. The drain pipe 12 is made of high-strength PVC material to ensure that it does not rupture during long-term pumping. Connect the vacuum pipe 13 and the vacuum pump 16. The vacuum pipe 13 is made of high-pressure resistant rubber hose to ensure that it does not leak air in a negative pressure environment.

[0048] Step 4. Detection of well wall sealing: Use an edible coloring agent grouting machine 14 to inject an edible coloring agent into the first grouting pipe 4. The edible coloring agent uses sodium fluorescein, which can quickly dissolve and color in the water sample. Conduct a precipitation test pumping, and judge whether the well wall sealing of the aquitard is tight by detecting the content of the edible coloring agent in the water sample of the submersible pump.

[0049] If the well wall sealing of the aquitard is not tight, use a cement slurry grouting machine 15 to supplement and inject cement slurry into the second grouting pipe 5. The cement slurry uses high-strength quick-setting cement, which can form a solid sealing layer in a short time. Repeat the detection until the well wall sealing of the aquitard is tight. During the supplementary injection process, monitor the grouting pressure and grouting volume in real time to ensure that the cement slurry is evenly distributed and achieves the expected effect.

[0050] Step 5. Normal pumping: After the test pumping detection is qualified, start the submersible pump 17 and the vacuum pump 16 to start the precipitation operation. Regularly monitor the water level change and the pumping volume to ensure the stable operation of the precipitation system.

[0051] It should be noted that the parts that are the same or similar to those in Embodiment 1 in this embodiment can be referred to each other and will not be elaborated in this application.

[0052] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts between each embodiment can be referred to each other.

Claims

1. A water-rich composite stratum deep foundation pit dewatering system, characterized in that: It comprises a composite dewatering well pipe device and a well wall plugging detection device; a retaining structure is arranged on the inner wall of the foundation pit, a composite stratum is arranged outside the retaining structure, and a borehole is drilled in the composite stratum; the composite dewatering well pipe device is arranged in the borehole, and the composite dewatering well pipe device comprises an upper vacuum well pipe ring, a middle impermeable pipe and a lower permeable pipe; a vacuum pipe is connected to the top of the upper vacuum well pipe ring, and a vacuum pump is connected to the connection part of the vacuum pipes; an upper impermeable pipe is arranged on the center sleeve of the upper vacuum well pipe ring; the upper impermeable pipe, the middle impermeable pipe and the lower permeable pipe are an integrated hollow structure; a submersible pump is arranged inside the lower permeable pipe, and a drainage pipe is connected to the top of the submersible pump; the well wall plugging detection device comprises a first grouting pipe, a second grouting pipe and a fixing rod; the first grouting pipe is anchored on one side of the middle impermeable pipe by the fixing rod, and an edible colorant grouting machine is connected to the top; the second grouting pipe is anchored on the other side of the middle impermeable pipe by the fixing rod, and a cement slurry grouting machine is connected to the top.

2. The water-rich composite stratum deep foundation pit dewatering system according to claim 1 is characterized in that: The composite formation includes a weakly permeable layer, a first pressure water layer, a water-proof layer and a second pressure water layer from top to bottom; the bottom of the foundation pit is located within the second pressure water layer; the length of the upper vacuum well pipe ring is consistent with the depth of the weakly permeable layer, the length of the middle impermeable pipe is consistent with the sum of the depths of the first pressure water layer and the water-proof layer, and the length of the lower permeable pipe is consistent with the depth of the second pressure water layer; the bottom of the first grouting pipe is located at the interface between the first pressure water layer and the water-proof layer; the bottom of the second grouting pipe is located in the water-proof layer.

3. The water-rich composite stratum deep foundation pit dewatering system according to claim 1 is characterized in that: The upper vacuum well pipe ring is sequentially sleeved with an outer filter screen, an outer ring, an inner filter screen, an inner core ring and an upper watertight pipe from the outside to the inside; a sealing cover is provided at the top of the upper vacuum well pipe ring, and a sealing bottom is provided at the bottom; the space formed by the sealing cover, the sealing bottom, the inner core ring and the upper watertight pipe is a vacuum ring; a vacuum pipe is connected to the top of the vacuum ring, and a vacuum pump is connected to the connection between the vacuum pipes.

4. The water-rich composite stratum deep foundation pit dewatering system according to claim 1 is characterized in that: The lower permeable pipe comprises a coarse filter screen, a permeable filter pipe and iron wire; the coarse filter screen is fixedly sleeved outside the permeable filter pipe by an iron wire clamp; a submersible pump is arranged inside the permeable filter pipe, and a drainage pipe is connected to the top of the submersible pump and extends to the ground surface.

5. The water-rich composite stratum deep foundation pit dewatering system according to claim 1 is characterized in that: The well wall plugging detection device also includes a tee, a first annular pipe and a second annular pipe; the bottom of the first grouting pipe is connected to the first annular pipe through a tee; the bottom of the second grouting pipe is connected to the second annular pipe through a tee; an edible colorant outlet is provided below the first annular pipe, and the first annular pipe surrounds the middle watertight pipe; cement slurry outlets are provided around the second annular pipe, and the second annular pipe surrounds the middle watertight pipe.

6. The method for dewatering a deep foundation pit in a water-rich composite stratum according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: determine the thickness of each soil layer in the composite stratum, and design the structural dimensions of the composite dewatering well pipe device and the well wall plugging detection device; Step 2: Drill a hole, lower the composite well pipe device and the well wall plugging detection device simultaneously, and backfill and plug the gap around the well wall; Step 3: After installing the submersible pump and the drainage pipe and connecting the vacuum pipe and the vacuum pump, use the edible colorant grouting machine to inject edible colorant into the first grouting pipe, conduct a trial pumping of precipitation, and determine whether the aquiclude well wall is densely sealed by detecting the edible colorant content of the water sample in the submersible pump; Step 4: After the trial sampling is qualified, start the submersible pump and vacuum pump to start the precipitation operation.

7. The method for dewatering a deep foundation pit in a water-rich composite stratum according to claim 6, characterized in that: In the step 2, the gaps around the aquitard well wall are backfilled with clay material, and the gaps around the aquitard, the first pressure water layer and the second pressure water layer are backfilled with gravel filter material.

8. The method for dewatering a deep foundation pit in a water-rich composite stratum according to claim 6, characterized in that: In the step 4, if the waterproof layer of the well wall is not tightly sealed, a cement slurry grouting machine is used to inject cement slurry into the second grouting pipe, and the test is repeated until the waterproof layer of the well wall is tightly sealed.

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