A dewatering structure and construction method for aquifer and aquiclude interlayer with slow slope

Abstract

The present invention provides a dewatering structure for the gently inclined interlayer of an aquifer and a water-blocking layer, comprising a water-stopping curtain, water-blocking piles and a dewatering well. The water-stopping curtain is arranged at the periphery of a foundation pit, and the water-blocking piles are closely connected to each other to form multiple rows of water-blocking walls and are vertically driven into the water-blocking layer, so that multiple independent areas are formed between the water-blocking piles, the water-stopping curtain and the water-blocking layer. The present invention also provides a construction method for the above-mentioned dewatering structure, by calculating the insertion depth of the water-blocking piles and the row spacing of each area, and calculating the number of dewatering wells to be set in each area, using the water-blocking inclined rock layer, the water-blocking piles and the outer water-stopping curtain to form an independent area with the foundation pit excavation area as the boundary, realizing the combination of block excavation and block dewatering, reducing the number of pumping wells and the impact range of local dewatering; the embedded section of the water-blocking pile can increase the weight of the pit bottom soil, and enhance the safety of the pit bottom soil against sudden surge.

Description

Technical Field

[0001] The invention belongs to the field of engineering dewatering, and in particular relates to a dewatering structure and a construction method for a gentle-sloping interlayer of an aquifer and an aquiclude. Background Art

[0002] Groundwater is the main cause of underground engineering safety accidents, especially near rivers. As the excavation depth of the foundation pit continues to increase, the difficulty of supporting it is also increasing. The continuous replenishment of river water makes precipitation more difficult. To ensure the safety of construction in the foundation pit, both support and precipitation must be taken into account.

[0003] For general deep foundation pit dewatering, a water-stop curtain is used to combine the water-stop structure with the support structure to increase the water seepage path and isolate the inside of the foundation pit from the outside. At this time, the foundation pit only needs to extract groundwater above a certain depth below the bottom of the pit, thereby ensuring the safety of the foundation pit project. However, for special strata with strong water replenishment and gentle inclination of the aquifer and the aquiclude, the vertical water-stop curtain cannot block the water flow, and the water flow can still be continuously replenished through the aquifer. In this case, the commonly used treatment method is to use multiple precipitation wells inside and outside the pit to concentrate precipitation to achieve the requirement that the groundwater level is lower than the bottom of the foundation pit. Because the river in this area has a super strong water replenishment capacity, it will cost a lot of financial resources to arrange precipitation wells and conduct uninterrupted pumping to control the water level. If the groundwater level cannot be controlled in time during the excavation process and the on-site construction environment cannot be guaranteed, the excavation will also suffer great inconvenience; if the water level connection inside and outside the foundation pit cannot be cut off, the precipitation in the foundation pit will not only cause uneven settlement of the soil outside the pit and surrounding buildings, but also cause lateral deformation of the retaining structure, making it difficult to ensure the safety of the entire foundation pit. Large-scale extraction of groundwater will also greatly destroy the seepage balance of groundwater, thereby causing sudden surges. Summary of the invention

[0004] The purpose of the present invention is to provide a precipitation structure for the gently inclined interlayer of aquifer and aquiclude, so as to solve the problem that the special strata of the gently inclined aquifer and aquiclude in deep foundation pit near the river have strong water replenishment capacity and great precipitation difficulty.

[0005] The technical solution of the present invention is as follows:

[0006] A dewatering structure for the gently sloping interlayers of an aquifer and an impermeable layer comprises a water-stop curtain, impermeable piles and a dewatering well. The water-stop curtain is arranged at the periphery of a foundation pit. The impermeable piles are closely connected to each other to form multiple rows of impermeable walls and are vertically driven into the impermeable layer. Multiple independent areas are formed between the impermeable piles, the water-stop curtain and the impermeable layer.

[0007] Preferably, the water-blocking piles are made of plain concrete cast-in-place piles, and the water-stop curtains are made of bored cast-in-place piles.

[0008] Preferably, there are multiple precipitation wells in each independent area and they are evenly distributed on the same side of the retaining wall.

[0009] Preferably, the precipitation wells are arranged in a row parallel to the water-blocking wall with a distance of 1-2 m, and a water collection channel is provided beside each row of precipitation wells.

[0010] Another object of the present invention is to provide a construction method of the above-mentioned precipitation structure, comprising the following steps:

[0011] 1) Carry out water-stop curtain construction around the foundation pit;

[0012] 2) Excavate the foundation pit until the surface pebble layer ends;

[0013] 3) Calculate the insertion depth of water-blocking piles and the spacing between rows in each area, and set water-blocking piles according to the obtained values;

[0014] 4) Calculate the number of precipitation wells to be set up in each independent area and carry out the construction of precipitation wells;

[0015] 5) Each area separated by the watertight wall shall be subjected to separate precipitation;

[0016] 6) Excavate in sections and blocks, carry out prestressed anchor cable construction at the same time, and remove the water-blocking piles exposed at the bottom of the pit;

[0017] 7) The overall construction is completed, and the waterproof piles deep underground are retained at the bottom of the pit.

[0018] Preferably, in step 3), the insertion depth and spacing of the water-blocking piles are calculated according to the following formula:

[0019]

[0020] H=(L1+L2+L3+……+L n-1 )×tanα

[0021] S=H+d

[0022] Among them, D is the distance between the waterproof walls of each independent area; B is the depth of the foundation pit; α is the angle between the gentle interlayer of the aquifer and the waterproof layer and the horizontal; H is the calculated depth of the waterproof pile in the independent area; L1, L2, L3...L n-1 , L n is the length of different aquifers and impermeable layers on the horizontal line; S is the actual depth of the impermeable pile; d is the depth of the end of the impermeable pile inserted into the lowest impermeable layer.

[0023] Preferably, in step 4), the number of precipitation wells in each area is calculated according to the total water inflow of foundation pits in each area and the water output capacity of a single precipitation well, and is calculated according to the following formula:

[0024] Q=μA m

[0025]

[0026] A=P1+P2+P3+……+P i

[0027] P1=L n-1 ×(L1+L2+L3+……+L n-1 )×tanα

[0028] P i =L n- ( 2i-1) ×(L1+L2+L3+……+L n- ( 2i-1) )×tanα

[0029] Where: Q is the total water inflow of the foundation pit; A is the area of ​​multiple aquifers in each independent area; μ is the water supply degree of the drained aquifer; m is the longitudinal distance of the foundation pit; M is the thickness of the aquifer; e is the porosity of the aquifer; S s is the aquifer water storage rate, P1, P i is the area of ​​the first and i-th inclined closed aquifers, L1, L2, L3, ... L n-1 , L n is the length of different aquifers and aquicludes on the horizontal line;

[0030]

[0031] Where: q0 is the water output capacity of a single well; r s is the radius of the filter; l is the length of the water inlet part of the filter; k is the permeability coefficient of the aquifer;

[0032]

[0033] Where: n is the number of dewatering wells; t is the pre-dewatering time before foundation pit excavation.

[0034] The dewatering structure of the gently inclined interlayer of the aquifer and the aquiclude provided by the present invention and the construction method thereof utilize the water-isolating inclined rock layer, the water-isolating piles and the outer waterproof curtain to form an independent area separated by the foundation pit excavation area. A row of dewatering wells are distributed at intervals in each independent area to carry out dewatering, thereby greatly reducing the number of pumping wells and the impact range of local dewatering. The multiple rows of water-isolating piles also play the role of block excavation, thereby realizing the combination of block excavation and block dewatering. The weight of the soil at the bottom of the foundation pit can be increased under the action of the embedded section of the water-isolating piles, thereby enhancing the safety of the soil at the bottom of the pit against sudden surges. Cutting off the water supply ensures that the water flow balance at the bottom of the foundation pit is not destroyed, thereby forming a new water circulation balance.

[0035] Instruction Manual

[0036] Figure 1 It is a schematic diagram of the stratum structure of the present invention;

[0037] Figure 2 It is a partial schematic diagram of the stratum structure of the present invention;

[0038] Figure 3 It is a schematic diagram of the overall structure of the foundation pit of the present invention;

[0039] As shown in the figure: 1- water-stop curtain; 2- water-proof piles; 3- precipitation well; 4- water-proof layer; 5- aquifer. DETAILED DESCRIPTION

[0040] The present invention will be further described in detail below in conjunction with specific embodiments and accompanying drawings.

[0041] It should be noted that the structures, proportions, sizes, etc. drawn in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the invention, so they have no substantial technical significance. Any modification of the structure, change in the proportional relationship or adjustment of the size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical content disclosed by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and so on quoted in this specification are only for the convenience of description, and are not used to limit the scope of the implementation of the present invention. The change or adjustment of their relative relationship should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0042] like Figures 1 to 3 As shown, a dewatering structure for the gently sloping interlayer of an aquifer and an impermeable layer comprises a water-stop curtain 1, impermeable piles 2 and a dewatering well 3. The water-stop curtain 1 is arranged at the periphery of the foundation pit, and the impermeable piles 2 are vertically driven into the impermeable layer 4 in the excavation area of ​​the foundation pit, and are closely connected to each other to form multiple rows of impermeable walls. The impermeable piles 2, the water-stop curtain 1 and the impermeable layer 4 are used to cut off the entire water replenishment system and form multiple independent areas, thereby making full use of the naturally formed impermeable layer 4 to achieve the effect of blocking groundwater.

[0043] Furthermore, since the water-blocking piles 2 only play a water-blocking role and do not bear loads, the water-blocking piles 2 are made of plain concrete cast-in-place piles, and the water-stop curtain 1 is made of bored cast-in-place piles, using a plain concrete and reinforced concrete interlocking structure, with adjacent concrete piles partially embedded in the circumference, and steel cages are inserted into the piles constructed in sequence to form an overall continuous protective curtain with good anti-seepage effect. The specific construction process is carried out in accordance with the requirements of the "Technical Code for Construction Foundation Pit Support" (JGJ 120-2012).

[0044] Furthermore, a plurality of precipitation wells 3 are arranged in each independent area and are evenly distributed on the same side of the water-blocking wall formed by the water-blocking piles 2, so as to facilitate the centralized treatment of the extracted groundwater in the later stage.

[0045] Furthermore, a row of multiple precipitation wells 3 in each independent area is parallel to the water-isolating piles 2 with a distance of 1-2m, which can effectively control the groundwater inside the foundation pit. A water collection channel is provided next to each row of precipitation wells 3 to collect the extracted groundwater.

[0046] A construction method of the above-mentioned precipitation structure comprises the following steps:

[0047] 1) Carry out the construction of water-stop curtain 1 around the foundation pit;

[0048] 2) Excavate the foundation pit until the surface pebble layer ends;

[0049] 3) Calculate the insertion depth of the water-blocking pile 2 and the spacing between rows in each area, and set the water-blocking pile 2 according to the obtained values;

[0050] 4) Calculate the number of precipitation wells 3 to be set in each area and construct the precipitation wells 3;

[0051] 5) Each area separated by the watertight wall shall be subjected to separate precipitation;

[0052] 6) Excavate in sections and blocks, carry out prestressed anchor cable construction at the same time, and remove the water-blocking piles 2 exposed at the bottom of the pit;

[0053] 7) The overall construction is completed, and the water-blocking piles 2 deep underground at the bottom of the pit are retained.

[0054] The depth of the dewatering well is the same as the calculated depth of the water-blocking piles. The depth of the dewatering well can also be determined according to the water area to be controlled, but it must not be less than the excavation depth of the foundation pit. Since the pipe well dewatering method is generally adopted in the dewatering process of deep foundation pits, the permeability coefficient of the aquifer needs to be applicable in the range of 0.1-200m / d. After the dewatering well 3 starts working, the dewatering is completed according to the predetermined dewatering time. The foundation pit is excavated in sections and blocks according to the water-blocking wall connected by the water-blocking piles 2. The water-blocking piles 2 protruding from the ground are removed while excavating, and prestressed anchor cables are supported around the foundation pit. After the overall excavation of the foundation pit is completed, the water-blocking piles 2 located deep underground at the bottom of the foundation pit are not removed. This structure can both reinforce the soil at the bottom of the pit and prevent sudden surges at the bottom of the pit.

[0055] The precautions for the construction of dewatering well 3 are as follows: According to the requirements of the Technical Code for Construction Foundation Pit Support (JGJ 120-2012), the control range of a single well should be calculated, and the wellhead diameter, pump power, and number of wellheads should be determined. When using a deep well pump or a deep well submersible pump to pump water, the water output of the pump should be determined based on the water output capacity of the single well, and the water output of the pump should be greater than 1.2 times the water output capacity of the single well; the filter pipe of the pipe well can be a sandless concrete filter pipe, a steel cage, a steel pipe, or a cast iron pipe; the inner diameter of the filter pipe should be determined according to the pump specifications configured to meet the design flow requirements of the single well, and should be greater than the outer diameter of the pump by 50mm. The outer diameter of the filter pipe should not be less than 200mm. The diameter of the tube well hole should meet the requirements of filling filter material; the construction technology of the tube well hole should be suitable for the characteristics of the formation, and clean water drilling should be used for the formation that is not easy to collapse and shrink; the drilling depth should be 0.3m~0.5m greater than the design depth of the precipitation well; when using mud wall protection, the sediment at the bottom of the hole should be removed after drilling to the bottom of the hole, and the well pipe should be placed immediately and clean water should be injected. The filter material can only be added when the mud specific gravity is not greater than 1.05; the well pipe shall not be placed in the event of hole collapse, and the filter material filling volume should not be less than 95% of the calculated amount; after filling the filter material, the well should be washed in time until the filter and filter material filter water smoothly, and water should be pumped to test the water filtering effect of the well.

[0056] Furthermore, in the above step 3), the insertion depth and spacing of the water-blocking piles 2 are calculated according to the following formula:

[0057]

[0058] H=(L1+L2+L3+……+L n-1 )×tanα

[0059] S=H+d

[0060] Among them, D is the distance between the waterproof walls of each independent area; B is the depth of the foundation pit; α is the angle between the gently inclined interlayer of the aquifer 5 and the waterproof layer 4 and the horizontal; H is the calculated depth of the waterproof pile 2 in the independent area; L1, L2, L3...L n-1 , L n is the length of different aquifers 5 and impermeable layers 4 on the horizontal line; S is the actual depth of the impermeable pile 2; d is the depth of the end of the impermeable pile 2 inserted into the lowest impermeable layer 4.

[0061] Furthermore, in step 4), the number of precipitation wells 3 in each area is calculated according to the total water inflow of the foundation pit in each area and the water discharge capacity of the single well of the precipitation well 3, and is calculated according to the following formula:

[0062] Q=μA m

[0063]

[0064] A=P1+P2+P3+……+P i

[0065] P1=L n-1 ×(L1+L2+L3+……+L n-1 )×tanα

[0066] P i =L n-(2i-1) ×(L1+L2+L3+……+L n-(2i-1) )×tanα

[0067] Where: Q is the total water inflow of the foundation pit; A is the area of ​​multiple aquifers in each independent area; μ is the water supply degree of the drained aquifer; m is the longitudinal distance of the foundation pit; M is the thickness of the aquifer 5; e is the porosity of the aquifer 5; S s is the water storage rate of aquifer 5, P1, P i is the area of ​​the first and i-th inclined closed aquifers 5, L1, L2, L3, ... L n-1 , L n are the lengths of different aquifers 5 and aquicludes 4 on the horizontal line;

[0068]

[0069] Where: q0 is the water output capacity of a single well; r s is the radius of the filter; l is the length of the water inlet part of the filter; k is the permeability coefficient of the aquifer 5;

[0070]

[0071] Wherein: n is the number of dewatering wells 3; t is the pre-dewatering time before foundation pit excavation.

[0072] In the above formula, μ refers to the volume of water released by a unit area of ​​rock column extending from the groundwater level to the ground surface under the action of gravity when the groundwater level drops by one unit depth. It is usually expressed as a decimal and is dimensionless. It can be obtained by looking up a table or calculated using the following formula. S s It indicates the elastic water volume released (or stored) from the unit volume of the aquifer due to the expansion (or compression) of the water volume and the compression (or extension) of the medium skeleton when the water head of the aquifer changes by one unit. The formula can be used to calculate Ss = ρg (α + nβ), where ρgα is the water squeezed out of the pores due to the compression of the aquifer skeleton; ρgnβ is the water released due to the elastic expansion of water. It can also be obtained by looking up the table, such as: water storage rate of sandy aquifer: 10-7 ~ 10-6cm-1. K uses the indoor permeability coefficient provided by the project geological survey report. When conditions permit, a pumping test can also be carried out on site to calculate the permeability coefficient of the soil layer based on the pumping test data.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for constructing a dewatering structure for a gentle interlayer of an aquifer and an impermeable layer, comprising a water-stop curtain (1), impermeable piles (2) and a dewatering well (3), wherein the water-stop curtain (1) is arranged at the periphery of a foundation pit, the impermeable piles (2) are closely connected to each other to form a plurality of rows of impermeable walls and are vertically driven into the impermeable layer (4), and a plurality of independent areas are formed between the impermeable piles (2), the water-stop curtain (1) and the impermeable layer (4); The construction method of the precipitation structure comprises the following steps: 1) Carry out the construction of water-stop curtain (1) outside the foundation pit; 2) Excavate the foundation pit until the surface pebble layer ends; 3) Calculate the insertion depth of the water-blocking piles (2) and the spacing between rows in each area, and set the water-blocking piles (2) according to the obtained values; The insertion depth and spacing of water-blocking piles (2) are calculated according to the following formula: <h2 style=";text-align:left;direction:ltr">H=(L1+L2+L3+……+L<h2 style=";text-align:left;direction:ltr"> n-1 <h2 style=";text-align:left;direction:ltr"> )×tanα S=H+d Where D is the distance between the waterproof walls of each independent area; B is the depth of the foundation pit; α is the angle between the gently inclined interlayer of the aquifer (5) and the waterproof layer (4) and the horizontal; H is the calculated depth of the waterproof pile (2) in the independent area; L1, L2, L3...L n-1 , L n is the length of different aquifers (5) and aquicludes (4) on the horizontal line; S is the actual depth of the aquiclude (2); d is the depth of the end of the aquiclude (2) inserted into the bottom aquiclude (4); 4) Calculate the number of precipitation wells (3) to be set in each independent area and construct the precipitation wells (3); The number of dewatering wells (3) in each independent area is calculated based on the total water inflow of the foundation pit in each independent area and the water discharge capacity of each dewatering well (3), and is calculated according to the following formula: Q=μAm A=P1+P2+P3+……+P i <h2 style=";text-align:left;direction:ltr">P1=L<h2 style=";text-align:left;direction:ltr"> n-1 <h2 style=";text-align:left;direction:ltr"> ×(L1+L2+L3+……+L<h2 style=";text-align:left;direction:ltr"> n-1 <h2 style=";text-align:left;direction:ltr"> )×tanα <h2 style=";text-align:left;direction:ltr">P<h2 style=";text-align:left;direction:ltr"> i <h2 style=";text-align:left;direction:ltr"> =L<h2 style=";text-align:left;direction:ltr"> n- <h2 style=";text-align:left;direction:ltr"> (<h2 style=";text-align:left;direction:ltr"> 2i-1) <h2 style=";text-align:left;direction:ltr"> ×(L1+L2+L3+……+L<h2 style=";text-align:left;direction:ltr"> n- <h2 style=";text-align:left;direction:ltr"> (<h2 style=";text-align:left;direction:ltr"> 2i-1) <h2 style=";text-align:left;direction:ltr"> )×tanα Where: Q is the total water inflow of the foundation pit; A is the area of ​​multiple aquifers (5) in each independent area; μ is the water supply degree of the drained aquifer (5); m is the longitudinal distance of the foundation pit; M is the thickness of the aquifer (5); e is the porosity of the aquifer (5); S s is the water storage rate of the aquifer (5), P1, P i is the area of ​​the first and i-th inclined confined aquifers (5), L1, L2, L3, ... L n-1 , L n are the lengths of different aquifers (5) and aquicludes (4) on the horizontal line; Where: q0 is the water output capacity of a single well; r s is the radius of the filter; l is the length of the water inlet portion of the filter; k is the permeability coefficient of the aquifer (5); Where: n is the number of dewatering wells (3); t is the pre-dewatering time before excavation of the foundation pit; 5) Each area separated by the watertight wall shall be subjected to separate precipitation; 6) Excavate in sections and blocks, and simultaneously carry out prestressed anchor cable construction and remove the water-blocking piles (2) exposed at the bottom of the pit; 7) The overall construction is completed, and the water-blocking piles (2) deep into the ground are retained at the bottom of the pit.

2. The method for constructing a precipitation structure for aquifer and aquiclude gently inclined interlayer according to claim 1, characterized in that: The water-blocking piles (2) are made of plain concrete cast-in-place piles, and the water-stop curtain (1) is made of bored cast-in-place piles.

3. The method for constructing a precipitation structure for aquifer and aquiclude gently inclined interlayer according to claim 2, characterized in that: There are multiple precipitation wells (3) in each independent area and they are evenly distributed on the same side of the water-blocking wall.

4. The method for constructing a precipitation structure for aquifer and aquiclude gently inclined interlayer according to claim 3, characterized in that: The precipitation wells (3) are arranged in a row and parallel to the water-blocking wall, with a distance of 1-2 m. A water collection channel is arranged beside the precipitation wells (3).

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