A method for stopping water precipitation in a foundation pit in a coastal dynamic water area

Abstract

The application discloses a method for stopping water lowering in a foundation pit in a coastal dynamic water area, and belongs to the technical field of foundation pit water lowering stopping.The method comprises the following steps: collecting the topography and geomorphology of an engineering area, the distribution of rock-soil layers, the calculation parameters of each rock-soil layer and the distribution of underground water; obtaining the final drawdown in the foundation pit under different recharge distances and the influence of different recharge distances on the seepage field near the foundation pit; dividing the dynamic water recharge area into a recharge blocking area, a recharge transition area and a recharge low-influence area; obtaining the distance between the dynamic water recharge source and the foundation pit of the current construction project, and judging the area where the dynamic water recharge source is located; when the dynamic water recharge source is located in the recharge blocking area, the water lowering in the foundation pit is stopped by adopting the measure of blocking the recharge water source; when the dynamic water recharge source is located in the recharge transition area, the water lowering in the foundation pit is stopped by adjusting the design parameters; and when the dynamic water recharge source is located in the recharge low-influence area, the water lowering in the foundation pit is stopped by adopting a conventional method.The method selects a reasonable water lowering stopping method according to different dynamic water recharge areas, ensures the safety of a deep and large foundation pit, and reduces the design and construction cost of the foundation pit.

Description

Technical Field

[0001] This invention relates to the field of foundation pit engineering technology in civil engineering, specifically to a method for preventing water from flowing into foundation pits in coastal watersheds. Background Technology

[0002] With the continuous development and utilization of urban underground space, the size, scale, and excavation depth of foundation pits are increasing year by year. Deep foundation pits in water-rich strata often contain confined aquifers, making them prone to problems such as sudden surges of confined water at the pit bottom, structural uplift, and subsidence of the surrounding surface during construction. These problems are even more prominent in deep and large foundation pit projects in coastal areas with flowing water. Compared with foundation pit projects under conventional groundwater levels, deep and large foundation pits in coastal areas with flowing water often employ combined dewatering measures such as interception (water-stopping curtain) and drainage. Due to the specific hydraulic conditions of groundwater recharge from seawater and river water, the groundwater around these foundation pits may exhibit different unstable flow states. In actual projects, the presence of water-stopping curtains and nearby water sources will have a significant impact on foundation pit dewatering. If conventional water-stopping and dewatering methods are still used in the design of water-stopping and dewatering for deep and large foundation pits in coastal areas with flowing water, certain safety hazards may exist.

[0003] Deep foundation pits in coastal dynamic water areas employing cutoff (water-stop curtain) drainage generate extremely complex seepage fields during dewatering. On one hand, deep foundation pit projects in coastal dynamic water areas typically have a stable water supply source nearby, causing changes in groundwater seepage within the aquifer. On the other hand, groundwater outside the pit bypassing the bottom of the cutoff curtain and entering the pit prolongs the groundwater seepage path, reducing the hydraulic gradient inside and outside the pit; the cutoff curtain's insertion into the aquifer reduces the seepage cross-sectional area, thus impacting the seepage field. Furthermore, deep foundation pit projects in coastal dynamic water areas have high requirements for groundwater control. Therefore, calculating and analyzing the seepage field during dewatering of such deep foundation pits, developing reasonable dewatering designs, and implementing appropriate dewatering measures are crucial design aspects of deep foundation pit projects in coastal dynamic water areas. Summary of the Invention

[0004] This invention provides a method for preventing dewatering in foundation pits in coastal dynamic water areas. It overcomes the problem that existing dewatering methods do not consider the impact of the foundation pit's water-stopping curtain and the replenishment of the coastal dynamic water area. It simplifies the extremely complex seepage field generated during the dewatering process, calculates and analyzes the seepage field during the dewatering process of deep and large foundation pits in coastal dynamic water areas, carries out reasonable dewatering design, and takes appropriate dewatering measures.

[0005] A method for preventing dewatering in a foundation pit in a coastal dynamic water area includes:

[0006] Collect information on the topography and geomorphology of the project area, the distribution of soil and rock layers, the calculation parameters of each soil and rock layer, and the distribution of groundwater in the site.

[0007] Obtain the final drawdown depth within the foundation pit at different resupply distances;

[0008] Based on the final drawdown within the foundation pit under different recharge distances, the influence of different recharge distances on the seepage field near the foundation pit was obtained;

[0009] Based on the influence of recharge distance on the seepage field near the foundation pit, the area is divided according to the length of the recharge distance, and the dynamic water recharge area is divided into a recharge blocking zone, a recharge transition zone, and a recharge low-impact zone; the recharge distance refers to the distance between the recharge source in the coastal dynamic water area and the foundation pit;

[0010] Obtain the distance between the current water supply source and the foundation pit, and determine the area where the water supply source is located;

[0011] When the dynamic water supply source is located in the supply blockage area, measures to cut off the water supply source are adopted to stop the dewatering of the foundation pit;

[0012] When the dynamic water supply source is located in the supply transition zone, the pit can be dewatered by adjusting the design parameters.

[0013] When the dynamic water supply source is located in the low-impact zone, conventional methods are used for dewatering of the foundation pit.

[0014] Preferably, the final drawdown within the foundation pit at different resupply distances is obtained as follows:

[0015] ;

[0016] ;

[0017] ;

[0018] ;

[0019] ;

[0020] ;

[0021] Where s represents the final drawdown within the foundation pit under different recharge distances; x is the horizontal distance from the central axis of the foundation pit; z is the vertical distance from the bottom plate of the confined aquifer; t is time; M is the thickness of the confined aquifer; d is the depth to which the stop curtain is inserted into the confined aquifer; Q is the pumping rate of the pumping well; K x and K z These are the radial and vertical permeability coefficients of a confined aquifer, respectively; S s The water storage rate of the confined aquifer represents the amount of water released from a unit area of ​​the aquifer when the water head changes by 1m; x1 is the horizontal distance from the stop curtain to the center axis of the foundation pit; x2 is the horizontal distance from the fixed dynamic water supply source to the center axis of the foundation pit, i.e., the supply distance; N is an even number, ranging from 8 to 14. Let π be 3.14; n is taken as 1 to 1. The positive integer; i is a positive integer from 1 to N.

[0022] Preferably, the step of obtaining the influence of different recharge distances on the seepage field near the foundation pit based on the final drawdown within the foundation pit at different recharge distances specifically includes:

[0023] Obtain the final drawdown depth within the foundation pit without considering the impact of dynamic water supply;

[0024] Based on the final drawdown of the foundation pit under different recharge distances and the final drawdown of the foundation pit without considering the influence of dynamic water recharge, the relative drawdown ratio is calculated.

[0025] Based on the relative drawdown ratio, the influence of different recharge distances on the seepage field near the foundation pit was obtained.

[0026] Preferably, the measures for adopting isolation water supply include adopting cofferdams and / or adding isolation measures.

[0027] Preferably, the design parameters include the pumping rate of the pumping well and / or the depth of the waterstop curtain inserted into the confined aquifer.

[0028] Preferably, the adjustment coefficient for the pumping volume of the pumping well is 1.2 to 1.9.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention discloses a method for preventing dewatering in deep and large foundation pits in coastal dynamic water areas. By establishing three dynamic water supply zones, the extremely complex seepage field generated in deep and large foundation pits during dewatering is simplified. Furthermore, by selecting reasonable dewatering prevention design measures, the design and construction costs of the foundation pits are reduced while ensuring their safety, resulting in certain economic benefits. Attached Figure Description

[0031] Figure 1 This is a flowchart of the method for preventing water from flowing into a foundation pit in a coastal dynamic water area according to Embodiment 1 of the present invention;

[0032] Figure 2 This is the rainwater control design method for the transition zone of the present invention, as described in Embodiment 2.

[0033] Figure 3 This is the design method for preventing precipitation in the supply blockage zone according to Embodiment 3 of the present invention. Detailed Implementation

[0034] This aspect will be further described below with reference to the accompanying drawings and embodiments.

[0035] Example 1

[0036] See Figure 1As shown, the present invention provides a method for preventing dewatering in a foundation pit in a coastal dynamic water area, comprising:

[0037] S101, collect the topography and geomorphology of the project area, the distribution of soil and rock layers, the calculation parameters of each soil and rock layer, and the distribution of groundwater in the site;

[0038] S102, Obtain the final drawdown depth within the foundation pit under different resupply distances;

[0039] S103, based on the final drawdown in the foundation pit under different recharge distances, the influence of different recharge distances on the seepage field near the foundation pit is obtained;

[0040] S104, Based on the influence of recharge distance on the seepage field near the foundation pit, the area is divided according to the length of the recharge distance, and the dynamic water recharge area is divided into a recharge blocking zone, a recharge transition zone, and a recharge low-impact zone; the recharge distance refers to the distance between the recharge source of the coastal dynamic water area and the foundation pit;

[0041] S105, obtain the distance between the current water supply source and the foundation pit, and determine the area where the water supply source is located;

[0042] S106, When the dynamic water supply source is located in the supply blockage area, measures to cut off the water supply source shall be adopted to stop the dewatering of the foundation pit;

[0043] S107, When the dynamic water supply source is located in the supply transition zone, the pit is dewatered by adjusting the design parameters;

[0044] S108. When the dynamic water supply source is located in the low-impact zone, conventional methods shall be used for dewatering of the foundation pit.

[0045] It should be noted that the water supply source can be a river, sea, lake, pond, ditch, etc., near the project site.

[0046] Specifically, in S102, the final drawdown within the foundation pit at different resupply distances is obtained as follows:

[0047] (1);

[0048] (2);

[0049] (3);

[0050] (4);

[0051] (5);

[0052] (6);

[0053] In this embodiment, the foundation pit is a strip-shaped foundation pit, with the origin of the coordinate system located at the pumping well at the bottom of the confined aquifer, and the z-axis pointing upwards as positive; x is the horizontal distance from the central axis of the foundation pit, in meters; z is the vertical distance from the bottom of the confined aquifer, in meters; t is time, in seconds; M is the thickness of the confined aquifer, in meters; d is the depth to which the stop curtain is inserted into the confined aquifer, in meters; and Q is the pumping rate of the pumping well, in cubic meters per second. 3 / s; s is the drawdown depth, in meters; K x K z These are the radial and vertical permeability coefficients of the confined aquifer, respectively, in m / s; S s The water storage capacity of a confined aquifer is m. -1 , represents the amount of water released from the aquifer per unit area when the water head changes by 1m; x1 is the horizontal distance from the stop curtain to the center axis of the foundation pit, in meters; x2 is the horizontal distance from the fixed dynamic water supply source to the center axis of the foundation pit, in meters; N is an even number, ranging from 8 to 14. Let π be 3.14; n is taken as 1 to 1. The positive integer; i is a positive integer from 1 to N.

[0054] Furthermore, considering the impact of the distance between the coastal dynamic water supply area and the foundation pit on the seepage field near the foundation pit, the impact of dynamic water supply on the seepage field is divided into zones according to the distance, and each zone is discussed separately, thereby simplifying the complex seepage field.

[0055] Since the distribution of soil and rock layers in coastal areas is mostly similar, consisting of confined aquifers composed of sand, clay and silt, in this embodiment, the final drawdown and recharge zones within the foundation pit under different fixed recharge distances are shown in Table 1, taking into account the geological conditions and soil layer distribution.

[0056] In Table 1, s0 represents the final drawdown within the foundation pit when the influence of fixed recharge is completely disregarded. s0 is calculated based on the drawdown formula in formula (1), specifically x2. The result calculated by inputting the final drawdown formula (1) is s0, which is the final drawdown in the foundation pit when the influence of fixed supply is not considered at all.

[0057] Table 1;

[0058]

[0059] As shown in the table, the relative drawdown ratio represents the difference between considering fixed recharge and not considering fixed recharge. A smaller ratio indicates that fixed recharge can be disregarded, while a larger ratio indicates that fixed recharge needs to be considered. To some extent, this ratio reflects the impact of fixed recharge on pit dewatering within the region. Specifically, if the fixed recharge distance is within 150m and the relative drawdown ratio exceeds 50%, this has a significant impact on pit dewatering, requiring recharge interruption measures. If the fixed recharge distance is greater than 1000m and the relative drawdown ratio is less than 10%, this area is classified as a low-impact recharge zone, where the impact of fixed recharge on pit dewatering is minimal and negligible.

[0060] The dynamic water supply area is divided into a supply interruption zone, a supply transition zone, and a supply low impact zone. When the coastal dynamic water supply is located in different zones, different precipitation control design measures can be adopted.

[0061] Specifically, when the dynamic water supply source is located in the supply interruption zone, i.e., the distance between the dynamic water supply source and the center of the foundation pit is 0~150m, it has a significant impact on the dewatering of the foundation pit, and it is difficult to guarantee the dewatering effect in the foundation pit by using only general dewatering measures. In actual engineering, certain measures to isolate the water supply source can be adopted, such as using cofferdams or adding barriers.

[0062] When the dynamic water supply source is located in the supply transition zone, that is, when the distance between the dynamic water supply source and the center of the foundation pit is 150m to 1000m, its impact on the foundation pit pumping is relatively small. The dewatering effect of the foundation pit can be ensured by adjusting the design parameters, such as the design pumping volume of the foundation pit pumping well and the insertion depth of the water-stop curtain.

[0063] The designed pumping capacity of the foundation pit pumping well is determined based on the distance between the dynamic water supply source and the center of the foundation pit, and a certain adjustment coefficient can be taken, with the coefficient ranging from 1.2 to 1.9.

[0064] When the dynamic water supply source is located in the low-impact zone, that is, when the distance between the dynamic water supply source and the center of the foundation pit is greater than 1000m, its impact on the pumping of the foundation pit is almost negligible, and conventional methods (existing specifications and design methods, such as interception (water-stop curtain) drainage) can be used.

[0065] The above describes the regional division of confined aquifers composed of sand, clay, and silt. For highly permeable strata, such as coarse stone and gravel layers with significant thickness, the impact of dynamic water recharge on the seepage field increases. Therefore, the zoning distance should be adjusted using a coefficient of approximately 1.1 to 1.4. For low-permeability strata, such as silty clay layers with relatively short thickness, the impact of dynamic water recharge on the seepage field decreases. Therefore, the zoning distance should be adjusted using a coefficient of approximately 0.85 to 0.95.

[0066] Example 2

[0067] This embodiment provides a more detailed description of the invention in conjunction with a coastal deep foundation pit project.

[0068] The site of a coastal foundation pit project mainly contains unconfined and confined water. Unconfined water is found in miscellaneous fill and silty clay; silty clay and silty clay form impermeable layers. Confined water is mainly found in sandy silt and silty sand. The thickness of the confined aquifer is about 26.7m. The diaphragm wall is inserted into the confined aquifer to a depth of 11.0m, forming a suspended water-stop curtain. The closest distance from the center of the foundation pit to the dynamic water recharge is 197.0m.

[0069] Based on the impact of the distance between the recharge area and the foundation pit on the seepage field near the foundation pit in different coastal dynamic water zones, the fixed recharge in this project is located in the recharge transition zone, which has a relatively small impact on the dewatering of the foundation pit. The dewatering effect of the foundation pit can be ensured by adjusting the design parameters. See details below. Figure 2 As shown.

[0070] This project adjusted the design pumping capacity of the foundation pit dewatering well; the original design pumping capacity was 17.9 m³. 3 / h, adjusted design pumping capacity 27.8m 3 The actual and calculated depths of the foundation pit after adjustment are shown in Table 2.

[0071] Table 2;

[0072]

[0073] The calculation results show that the adjusted design pumping volume can basically meet the dewatering requirements in the foundation pit, indicating that the dewatering control adjustment method in this embodiment is applicable to the dewatering control design of deep foundation pits in coastal dynamic water areas.

[0074] Example 3

[0075] This embodiment provides a more detailed description of the invention in conjunction with the foundation pit project of a subway station on the southern extension section.

[0076] The foundation pit for this project has a depth of 22.85m. The strata surrounding the pit consist of miscellaneous fill, silty clay, medium-coarse sand, completely weathered granite, and loose, strongly weathered granite. The silty clay layer is particularly thick. The subway station passes under a sheltered dock connecting to the open sea, with a water width of 60.0–100.0m and a riverbed elevation ranging from -1.18 to 0.0m. During the survey, the water surface was affected by tides, with a high-low tide difference of 1.5–3.0m. The dock is shaped like a "T" embedded in the island. This section of the dock has a sluice gate, and the water volume and level are mainly affected by the seasons, tides, and also by irregular annual river dredging.

[0077] Based on the impact of the distance between the recharge area and the foundation pit in different coastal dynamic water zones on the seepage field near the foundation pit, the dynamic water recharge source for this project is located in the recharge blockage zone. Because the station partially passes under a typhoon shelter, with the station roof approximately 1.5m below the bottom of the shelter, this has a significant impact on the foundation pit dewatering. General dewatering measures alone are insufficient to guarantee effective dewatering within the foundation pit. (See [reference needed]). Figure 3 As shown, the cofferdam construction for the typhoon shelter will be carried out first during the final construction period.

[0078] The above embodiments are merely illustrative of the present invention and are not intended to limit the technical solutions described herein. Although this specification has described the present invention in detail with reference to the above embodiments, the present invention is not limited to the specific embodiments described above. Therefore, any modifications or equivalent substitutions to the present invention, without departing from the spirit and scope of the invention, and all improvements thereof, should be covered within the scope of the claims of the present invention.

[0079] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preventing water seepage in a foundation pit in a coastal dynamic water area, characterized in that, include: Collect information on the topography and geomorphology of the project area, the distribution of soil and rock layers, the calculation parameters of each soil and rock layer, and the distribution of groundwater in the site. Obtain the final drawdown depth within the foundation pit at different resupply distances; Based on the final drawdown within the foundation pit under different recharge distances, the influence of different recharge distances on the seepage field near the foundation pit was obtained; Based on the influence of recharge distance on the seepage field near the foundation pit, the area is divided according to the length of the recharge distance, and the dynamic water recharge area is divided into a recharge blocking zone, a recharge transition zone, and a recharge low-impact zone; the recharge distance refers to the distance between the recharge source in the coastal dynamic water area and the foundation pit; Obtain the distance between the current water supply source and the foundation pit, and determine the area where the water supply source is located; When the dynamic water supply source is located in the supply blockage area, measures to cut off the water supply source are adopted to stop the dewatering of the foundation pit; When the dynamic water supply source is located in the supply transition zone, the pit can be dewatered by adjusting the design parameters. When the dynamic water supply source is located in the low-impact zone, conventional methods are used for dewatering of the foundation pit. The method for obtaining the impact of different recharge distances on the seepage field near the foundation pit based on the final drawdown within the foundation pit at different recharge distances specifically includes: Obtain the final drawdown depth within the foundation pit without considering the impact of dynamic water supply; Based on the final drawdown of the foundation pit under different recharge distances and the final drawdown of the foundation pit without considering the influence of dynamic water recharge, the relative drawdown ratio is calculated. Based on the relative drawdown ratio, the impact of different recharge distances on the seepage field near the foundation pit was obtained. Among them, when the relative drawdown ratio is greater than 50%, the impact on foundation pit pumping is extremely large, and the area where the corresponding recharge distance is located is identified as the recharge blockage zone; when the relative drawdown ratio is between 10% and 50%, the impact on foundation pit pumping is relatively small, and the area where the corresponding recharge distance is located is identified as the recharge transition zone; when the relative drawdown ratio is less than 10%, the impact on foundation pit pumping is minimal, and the area where the corresponding recharge distance is located is identified as the low-impact recharge zone.

2. The method for preventing water seepage in a foundation pit in a coastal dynamic water area according to claim 1, characterized in that, The proposed water supply isolation measure employs a cofferdam.

3. The method for preventing dewatering in a foundation pit in a coastal dynamic water area according to claim 1, characterized in that, The design parameters include the pumping rate of the pumping well and / or the depth of the cutoff wall inserted into the confined aquifer.

4. The method for preventing dewatering in a foundation pit in a coastal dynamic water area according to claim 3, characterized in that, The adjustment coefficient for the pumping volume of the pumping well is 1.2 to 1.9.

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