A method of dewatering under reduced pressure in combination with improving the properties of the formation

Abstract

The application discloses a method for pressure relief and dewatering by improving stratum characteristics, and relates to the technical field of underground engineering dewatering. In view of the problems that the aquifer below the basement is separated by the relative aquifuge, the traditional method needs to separately arrange wells, the waterproof curtain is deep, and the cost is high, the method is characterized in that: the geological and hydrological parameters are found out, the relative aquifuge is improved and constructed, and the hydraulic connection channel of the upper and lower aquifers is constructed; then, the short-depth waterproof curtain is arranged according to the requirement of the shallow flow blocking, the dewatering well is arranged in the upper confined aquifer, the sand and gravel filter material is filled in the lower part of the well, and the waterproof clay ball is backfilled in the upper part; the water head of each layer of aquifer is lowered by extracting the upper confined water and utilizing the hydraulic connection. The method does not need to separately arrange multiple wells, shortens the length of the waterproof curtain, greatly reduces the engineering cost, simplifies the construction process, guarantees the pressure relief effect, effectively avoids the risks of pit water gushing and sudden gushing, and is suitable for the pit engineering under the geological condition of multiple confined aquifers.

Description

Technical Field

[0001] This invention relates to the field of underground engineering dewatering technology, specifically a decompression dewatering method that combines improvement of geological characteristics. Background Technology

[0002] In underground construction scenarios such as foundation pit engineering, when multiple confined aquifers separated by impermeable layers exist below the foundation and all require decompression and dewatering, existing technologies face significant limitations. Because each aquifer is independently separated by relatively impermeable layers, the hydraulic connection is interrupted, necessitating the separate installation of decompression wells for each aquifer to achieve decompression and dewatering. Furthermore, the depth of the cutoff wall needs to be determined based on the decompression wells of the deepest target aquifer to determine the bypass path, typically requiring a deep cutoff wall to block groundwater flow, resulting in high construction costs.

[0003] The aforementioned traditional methods have several shortcomings: Individual depressurization of multiple aquifers requires the installation of numerous depressurization wells, leading to a significant increase in equipment and construction costs and overall project expenses; the construction process for deeper cutoff walls is complex and time-consuming, further increasing construction difficulty and costs; and simultaneous operation of multiple wells can easily result in cumbersome coordination issues, affecting construction efficiency. Therefore, how to optimize formation characteristics to establish hydraulic connections between aquifers, achieve simultaneous depressurization and dewatering of multiple aquifers, thereby shortening the depth of the cutoff wall, reducing the number of dewatering wells, lowering project costs, and simplifying the construction process has become a pressing technical problem to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a decompression precipitation method that combines improved formation characteristics to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a decompression and dewatering method that combines improving the geological characteristics. In the foundation pit area, there are two confined aquifers, A and B, with a relatively impermeable layer between them. A water-stop curtain is used to block the flow path between the confined aquifers and the outside environment within the foundation pit area. Different drilling methods are adopted according to the different depths of the relatively impermeable layer, thereby adopting the optimal drilling method, shortening the water-stop curtain, reducing the number of decompression wells, reducing costs, and facilitating construction. Preferably, when the relative impermeable layer thickness is ≤2m, boreholes are directly drilled to penetrate the relative impermeable layer, forming a pressure relief well for confined aquifer A and a pressure relief well for confined aquifer B, to dewater and reduce pressure on the foundation within the pit area; Preferably, when the relative impermeable layer thickness is >2m, jet grouting is used to penetrate the relative impermeable layer. Simultaneously, high-pressure water and high-pressure air are injected to create cracks in the strata, disrupting the integrity of the relative impermeable layer and increasing its permeability. The relative impermeable layer within the pit area is transformed into a permeable layer, forming a pressure relief well for the confined aquifer AB. By pumping water from the pressure relief well in the confined aquifer AB layer, the water level in confined aquifer A decreases. Through the hydraulic connection between the upper and lower layers, as the water level in confined aquifer A decreases, the water head in confined aquifer B decreases synchronously due to the presence of the permeable layer. This establishes a hydraulic connection between the originally independent multi-layered confined aquifers, achieving synchronous pressure relief and dewatering. This eliminates the need for separate pressure relief wells for each aquifer, significantly reducing the number of dewatering wells; the depth of the cutoff wall does not need to be adapted to the deepest aquifer, significantly shortening the construction length.

[0006] Preferably, after using different drilling methods for relatively waterproof layers of different thicknesses, sand and gravel are backfilled into the borehole through the drill rod while the drill is being lifted to prevent the borehole from collapsing. Preferably, the backfill thickness extends beyond 1 / 2 the thickness of the confined aquifer A. If it is too thin, the conduction channels will not be connected, and an effective hydraulic connection cannot be formed; if it is too thick, the amount of backfilling work will increase, the construction period will be extended, and the original stability of the strata may be damaged. Preferably, the sand and gravel are backfilled with water-stopping clay balls to block the flow of groundwater, form a water-stopping barrier, and prevent the loss of filter material and soil pollution. Preferably, when the relatively impermeable layer is large and relatively hard, blasting, drilling and connecting, and chemical treatment are used to transform the relatively impermeable layer into a permeable layer. Blasting uses the energy of explosives to create cracks and fracture zones in the relatively impermeable layer, improving its permeability. Drilling and connecting involves using multiple boreholes to penetrate the impermeable layer and then connecting them to create water flow channels, enhancing permeability. Chemical treatment uses chemical agents to dissolve and erode the cementing substances in the relatively impermeable layer, expanding pores and cracks, further improving permeability and ensuring the permeability of the permeable layer.

[0007] Compared with the prior art, the beneficial effects of the present invention are: This invention creates a permeable layer by disrupting the relatively impermeable layers. By improving the geological characteristics of these impermeable layers, it hydraulically connects the originally independent multi-layered confined aquifers, achieving synchronous decompression and dewatering. It eliminates the need for separate decompression wells for each aquifer, significantly reducing the number of dewatering wells required; the depth of the cutoff wall does not need to be adapted to the deepest aquifer, significantly shortening the construction length. This not only reduces equipment, material, and construction costs but also simplifies the construction process, improves operational efficiency, and ensures effective decompression of the multi-layered aquifers, effectively avoiding the risks of water inrush and sudden surges in the foundation pit, thus guaranteeing construction safety and the stability of the surrounding environment. Attached Figure Description

[0008] Figure 1This is a construction diagram for a water-resistant layer greater than 2m in this invention; Figure 2 This is a construction diagram for a relative waterproof layer of 2m or less in this invention; Figure 3 This is a schematic diagram of the interior of the decompression well after borehole backfilling in this invention; Figure 4 This is a schematic diagram of the high-pressure destruction construction of the relative water-resistant layer according to the present invention. Detailed Implementation

[0009] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0010] Example 1: Please see Figure 1-4 This invention provides a technical solution: a decompression and dewatering method that combines improving the geological characteristics. In the foundation pit area, there are two confined aquifers, A and B, with a relatively impermeable layer between them. A water-stop curtain is used to block the flow path between the confined aquifers and the outside world within the foundation pit area. Different drilling methods are adopted according to the different depths of the relatively impermeable layer, thereby adopting the optimal drilling method, shortening the water-stop curtain, reducing the layout of decompression wells, reducing costs, and facilitating construction. When the relative impermeable layer thickness is ≤2m, boreholes are directly drilled to penetrate the relative impermeable layer, forming a pressure relief well for confined aquifer A and a pressure relief well for confined aquifer B, to dewater and reduce pressure on the foundation within the pit area. When the relative impermeable layer thickness exceeds 2m, jet grouting is used to penetrate the impermeable layer. Simultaneously, high-pressure water and air are injected to create cracks in the formation, disrupting the integrity of the impermeable layer and increasing its permeability. The impermeable layer within the pit area is transformed into a permeable layer, forming a pressure relief well for the confined aquifer AB. By pumping water from the pressure relief wells in the confined aquifer AB, the water level in confined aquifer A decreases. Through the hydraulic connection between the upper and lower layers, the water head in confined aquifer B decreases synchronously due to the presence of the permeable layer, thus forming a hydraulic connection between the originally independent multi-layered confined aquifers and achieving synchronous pressure relief and dewatering. This eliminates the need for separate pressure relief wells for each aquifer, significantly reducing the number of dewatering wells; the depth of the cutoff wall does not need to be adapted to the deepest aquifer, significantly shortening the construction length.

[0011] After using different drilling methods for relatively waterproof layers of different thicknesses, sand and gravel are backfilled into the borehole through the drill rod while the drill is being pulled up to prevent the borehole from collapsing. The backfill thickness extends beyond half the thickness of the confined aquifer A. If it is too thin, the conduction channels will not be connected, and an effective hydraulic connection cannot be formed. If it is too thick, the amount of backfilling work will increase, the construction period will be extended, and the original stability of the strata may be damaged. Sand and gravel are backfilled with water-stopping clay balls to block groundwater flow, form a water-stopping barrier, and prevent filter material loss and stratum contamination. When the relatively impermeable layer is large and relatively hard, auxiliary methods such as blasting, drilling and connecting, and chemical treatment are used to transform the relatively impermeable layer into a permeable layer. Blasting uses the energy of explosives to create cracks and fracture zones in the relatively impermeable layer, improving its permeability. Drilling and connecting involves using multiple boreholes to penetrate the impermeable layer and then connecting them to create water flow channels, enhancing permeability. Chemical treatment uses chemical agents to dissolve and erode the cementing substances in the relatively impermeable layer, expanding pores and cracks, further improving permeability and ensuring the permeability of the permeable layer.

[0012] Working principle: Before construction, the foundation pit is first excavated as needed, and then the distribution, thickness, initial water head of the confined aquifer below the foundation pit, as well as the position, thickness, permeability coefficient and other parameters of the relative aquitard are investigated to determine the range of the aquitard that needs to be improved.

[0013] Construction for improving the relative impermeable layer: Depending on the thickness of the target relative impermeable layer, if the thickness is ≤2m, direct drilling is used to penetrate the relative impermeable layer, forming pressure relief wells for confined aquifer A and confined aquifer B. This dewaters and reduces pressure on the foundation within the pit area. During back-drilling, permeable materials (such as sand and gravel) are used for backfilling. If the relative impermeable layer thickness is >2m, jet grouting is used to penetrate the relative impermeable layer. High-pressure water and high-pressure air are injected simultaneously during drilling to create cracks in the strata, destroying the integrity of the relative impermeable layer and improving its permeability. The relative impermeable layer within the pit area is then improved into a permeable layer. During back-drilling, permeable materials (such as sand and gravel) are also used for backfilling, allowing the backfill to penetrate half the thickness of confined aquifer A. This creates a hydraulic connection between the originally independent multi-layered confined aquifers, achieving synchronous pressure reduction and dewatering. There is no need to install pressure relief wells for each aquifer, which greatly reduces the number of dewatering wells; the depth of the water-stop curtain does not need to be adapted to the deepest aquifer, which significantly shortens the construction length.

[0014] Water-stop curtain construction: Based on the connected hydraulic system, the depth is determined according to the requirement of blocking shallow groundwater flow, and the water-stop curtain is laid out. It is not necessary to extend to the deepest aquifer, thus shortening the depth of the water-stop curtain.

[0015] Dewatering well layout and backfilling: Dewatering wells are only laid in the upper confined aquifer. The lower part of the well is filled with sand and gravel filter material, and the upper part is backfilled with water-stopping clay balls to seal the gaps and prevent groundwater from flowing through and the filter material from being lost.

[0016] Synchronous decompression and precipitation: Start pumping water from the upper decompression wells and use the hydraulic connection channel to guide the groundwater in the lower aquifer to replenish upwards, simultaneously reducing the water head of each aquifer to a safe threshold.

[0017] Dynamic monitoring and adjustment: Real-time monitoring of water head changes in each aquifer, foundation pit stability, and surrounding ground settlement; adjustment of pumping volume based on data to ensure dewatering effectiveness and construction safety.

[0018] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0019] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A decompression precipitation method combining improved formation characteristics, characterized in that: There are two confined aquifers, A and B, at the bottom of the foundation pit. There is a relatively impermeable layer between the confined aquifers A and B. A water-stop curtain is used to block the flow path between the confined aquifers and the outside world within the foundation pit area. Different drilling methods are used according to the different depths of the relatively impermeable layer. When the relative impermeable layer thickness is ≤2m, boreholes are directly drilled to penetrate the relative impermeable layer, forming a pressure relief well for confined aquifer A and a pressure relief well for confined aquifer B, to dewater and reduce pressure on the foundation within the pit area. When the relative impermeable layer thickness is >2m, a jet grouting borehole is used to penetrate the relative impermeable layer. High-pressure water and high-pressure gas are injected simultaneously during drilling to create cracks in the strata, thereby destroying the integrity of the relative impermeable layer and increasing the permeability of the strata. The relative impermeable layer within the pit area is transformed into a permeable layer, forming a decompression well for the confined aquifer AB. By pumping water from the decompression well in the confined aquifer AB layer, the water level of the confined aquifer A decreases. Through the hydraulic connection between the upper and lower layers, as the water level of the confined aquifer A decreases, the water head of the confined aquifer B decreases synchronously due to the presence of the permeable layer.

2. The decompression and precipitation method according to claim 1, characterized in that: After using different drilling methods for relatively waterproof layers of different thicknesses, sand and gravel are backfilled into the borehole through the drill rod while the drill is being lifted.

3. The decompression and precipitation method according to claim 2, characterized in that: The backfill thickness extends through half the thickness of the confined aquifer A.

4. The decompression and precipitation method according to claim 3, characterized in that: Sand and gravel are backfilled with water-stopping clay balls.

5. The decompression and precipitation method according to claim 1, characterized in that: During jet grouting, the drill rod is located on the upper part of the ground and is connected to a mud pit, an air storage tank, and a clear water tank. High-pressure cement pumps, air compressors, and high-pressure water pumps are used to deliver cement, high-pressure gas, and high-pressure water to the jet grouting pile at the bottom of the drill rod for backfilling and destruction of the relative impermeable layer.

6. The decompression and precipitation method according to claim 1, characterized in that: After jet grouting, drilling was carried out to form an observation well for the confined aquifer B.

7. The decompression and precipitation method according to claim 1, characterized in that: When the relatively impermeable layer is large and relatively hard, methods such as blasting, drilling and connection, and chemical treatment can be used to transform the relatively impermeable layer into a permeable layer.

8. The decompression and precipitation method according to claim 7, characterized in that: Blasting utilizes the energy of explosives to create cracks and fracture zones in relatively impermeable layers, improving permeability; drilling and interconnection utilize multiple boreholes to penetrate the impermeable layer, and then interconnection technology creates water flow channels between different boreholes, enhancing permeability. Chemical treatment uses chemical agents to dissolve and erode the cementing material in the relatively waterproof layer, expanding pores and cracks to improve permeability.

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