Check gate construction technology capable of achieving continuous flow in flood season

Abstract

The invention relates to the technical field of water conservancy project construction, in particular to a check gate construction process without interruption of flow in the flood season, which comprises the following steps: constructing a river-following cofferdam along two sides of a river channel, reserving a water-passing section, and erecting a temporary steel bridge above the river channel; backfilling and compacting the inner side of the cofferdam to form a land area operation platform, performing cast-in-situ bored pile construction in a flood season by using the platform and the temporary steel bridge, and pouring a first concrete support by using a platform soil surface as a bottom die; and after the flood season ends, the cofferdam is subjected to closure, water pumping and desilting are conducted, remaining supports are constructed, and finally precipitation excavation and main structure construction are conducted. According to the method, parallel construction of pile foundations in the flood season is achieved through combination of cofferdam reclamation along the river and reserved water passing channels, overwater operation is converted into land operation, the supporting construction procedure is simplified through the soil moulding bed, the contradiction between flood drainage in the flood season and short construction period is effectively solved, the construction period is remarkably shortened, and the construction cost is reduced.

Description

Technical Field

[0001] This application relates to the field of water conservancy engineering construction technology, and in particular to a construction process for a control gate that allows for continuous flow during the flood season. Background Technology

[0002] As a core structure in water conservancy projects, control gates play a crucial role in regulating water levels, flood control and drainage, and water resource allocation. These projects are mostly located within the main channel of a river, and their construction is heavily influenced by hydrological and meteorological conditions, typically exhibiting significant seasonality. In traditional construction methods, to avoid the threat of floodwaters to the foundation pit during the flood season, a full-section cofferdam closure method is often used during the dry season. This means that cofferdams are constructed only during the dry season when river flow is low, and construction is carried out on dry land. During the flood season, the cofferdams are dismantled or key processes are halted to restore the river's flood discharge capacity. This intermittent work stoppage due to hydrological cycles results in a short effective construction window, artificially extending the overall construction period. Furthermore, if the flood season arrives earlier or is prolonged, it can easily lead to construction delays or even flood safety accidents.

[0003] To achieve continuous construction across the flood season, existing technologies have attempted to employ fully floating platforms or trestle bridges. This involves erecting large-scale steel pipe pile platforms for drilling piles and retaining structures on water without interrupting the water flow. However, this fully floating operation mode is highly dependent on large hydraulic machinery, requires substantial investment in temporary works, and significantly increases construction costs. Furthermore, the stability of floating platforms is far inferior to that on land due to the impact of water flow, wave undulations, and the swaying of floating bodies, making it difficult to control the verticality of drilled piles and guarantee the quality of pile formation. In addition, in the construction of deep foundation pit support systems, traditional floating techniques require the construction of complex suspended scaffolding and formwork systems for pouring concrete supports. This is not only cumbersome and involves high-altitude operations, but also makes it difficult to precisely control the settlement and deformation of the support structure.

[0004] On the other hand, in the construction of cofferdam systems, the connection between the newly built sheet pile cofferdam and the original riverbank revetment has always been a weak link in seepage prevention in engineering. Due to the difference in stiffness between the old and new structural media and the irregular contact surface, under the influence of the huge head difference formed by the high water level during the flood season, this connection is prone to forming seepage channels, which can lead to seepage around the seepage or piping failure, seriously threatening the safety of operations inside the foundation pit. Therefore, it is urgent to develop a new technology that can both ensure the normal flood discharge of the river during the flood season and promote the construction of pile foundations and supporting structures at low cost and high efficiency.

[0005] In response to the aforementioned technologies, a construction process for a control gate that ensures uninterrupted flow during the flood season is provided. Summary of the Invention

[0006] The purpose of this application is to provide a construction process for a control gate that allows for continuous flow during the flood season. This aims to improve the existing technology where the construction process of control gates is constrained by flood discharge during the flood season, resulting in long construction periods and intermittent shutdowns. While the all-water operation scheme can be carried out continuously, it suffers from problems such as high cost, high dependence on machinery, difficulty in controlling pile quality, and complex construction of the support system. At the same time, the seepage prevention hazards at the connection between the cofferdam and the bank slope also seriously threaten the safety of the foundation pit.

[0007] By adopting the above technical solution, a construction process for a flood control gate that ensures uninterrupted flow during the flood season includes the following steps:

[0008] S1. Layout of cofferdams along the river and construction of land: Construct cofferdams along both sides of the river flow direction, and reserve a water passage section between the two cofferdams. Erect a temporary steel bridge with a span consistent with the width of the reserved water passage section above the reserved water passage section. Backfill and compact earthwork in layers inside the cofferdams to form a land operation platform. The top elevation of the land operation platform is controlled below the bottom elevation of the first concrete support designed.

[0009] S2. Construction of pile foundation and first support during the flood season: Under the flood season condition of maintaining the reserved water passage section, the construction of bored piles and retaining piles is carried out using the land operation platform and steel temporary bridge; the leveled land operation platform is used directly as the bottom formwork to pour the first concrete support except for the reserved water passage section area.

[0010] S3. Closure and Pit Closure During the Dry Season: After the flood season, steel sheet piles are driven at both the upstream and downstream ends of the cofferdam along the river to close the dam and form a closed pit. After the water in the pit is pumped out, the riverbed bottom of the original reserved water passage section is dredged and a plain concrete cushion layer is poured. A support frame is erected on the plain concrete cushion layer, and the remaining concrete support is constructed to close the pit support system.

[0011] S4. Dewatering Excavation and Main Structure Construction: After the concrete support reaches the design strength, the dewatering wells are activated to lower the groundwater level, and earthwork excavation and main structure construction of the control gate are carried out.

[0012] Preferably, in step S1, the width of the reserved water passage section... The width is set to 30% to 40% of the total width of the river channel, specifically 25.0m to 35.0m; the soil compaction coefficient of the land operation platform is controlled at 0.90 to 0.93, and its top surface elevation is controlled at 10cm to 20cm below the bottom surface elevation of the first concrete support designed.

[0013] Preferably, in step S1, the connection between the cofferdam and the original bank slope is treated with high-pressure jet grouting piles for water stoppage; the construction parameters of the high-pressure jet grouting piles include: pile diameter of ϕ600mm~ϕ800mm, pile spacing of 400mm~500mm, grouting pressure of 20MPa~30MPa, lifting speed of 15cm / min~25cm / min, and rotation speed of 15r / min~20r / min.

[0014] Preferably, the grout used in the high-pressure jet grouting pile comprises, by weight, 100 parts of 42.5 grade ordinary Portland cement, 80-120 parts of water, and 1.0-3.0 parts of water glass quick-setting agent.

[0015] Preferably, in step S1, the cofferdam along the river adopts Larsen type IV or V hot-rolled steel sheet piles, which are driven by a high-frequency hydraulic vibratory hammer with an excitation force of 400kN to 600kN, and the verticality deviation of the pile body is controlled within 0.5% to 1.0%; a water-stopping agent is applied to the interlock of the steel sheet piles, which is a mixture of butter and asphalt in a mass ratio of 1:(0.8 to 1.2).

[0016] Preferably, in step S1, the construction of the land operation platform further includes setting up an anchoring system, which includes two round steel tie rods with a diameter of 50mm to 80mm and a horizontal spacing of 3.0m to 4.0m; the backfill soil is clay or silty clay with a moisture content of 18% to 22%, and each layer has a loose thickness of 30cm to 50cm.

[0017] Preferably, in step S2, the bored pile construction adopts mud slurry wall protection, and the mud slurry parameters are controlled as follows: specific gravity of 1.10 to 1.25, viscosity of 18s to 22s, and sand content of 4% to 8%; the bored pile adopts underwater concrete pouring, and the slump of the underwater concrete is controlled at 180mm to 220mm, and the initial setting time is ≥8h.

[0018] Preferably, in steps S2 and S3, the concrete support is made of pumped concrete, and the components are mixed in the following mass ratio range: cement: fine aggregate: coarse aggregate: water: fly ash: water-reducing agent = 1: (1.6~1.9): (2.3~2.7): (0.40~0.48): (0.15~0.25): (0.008~0.012).

[0019] Preferably, in step S3, after the interception and closure, clay bags are thrown outside the closure opening to form a seepage-proof prism with a top width of 1.5m to 2.0m; the thickness of the plain concrete cushion layer is 150mm to 200mm, and the strength grade is C20.

[0020] Preferably, in step S4, the dewatering wells are arranged around the perimeter of the foundation pit and inside the pit, with a spacing of 15.0m to 20.0m between wells, to lower the groundwater level to 0.5m to 1.0m below the excavation surface at the bottom of the pit; the slope of the temporary side slope inside the pit during earthwork excavation is controlled at 1:1.5 to 1:2.0, and a walkway with a width of ≥1.0m is set up.

[0021] In summary, this application includes at least one of the following beneficial technical effects:

[0022] 1. This application breaks the limitation of traditional cofferdams requiring one-time closure by setting up a cofferdam along the river and reserving a water passage of the designed width in the center of the river channel; during the high water level period of the flood season, the channel reserved in the middle of the river channel can maintain continuous flow, effectively dissipating the flood peak flow, avoiding the risk of high upstream water level and flood control caused by full-section water blockage, and ensuring the safety of flood control during the construction of water conservancy projects;

[0023] 2. This application transforms most of the original water-based operations into land-based operations by backfilling earth within the river-side cofferdam to form a land-based operation platform. This measure reduces the reliance on expensive hydraulic machinery such as large water-based piling vessels and floating cranes, and only conventional land-based tracked equipment is needed to complete the operation. It also reduces the difficulty of water-based positioning and quality control.

[0024] 3. This application utilizes the top surface of the backfilled and compacted earth platform within the river-side cofferdam as the bottom formwork for the first concrete support. Compared to the traditional suspended formwork process on water, this method eliminates the complex scaffolding erection and bottom formwork laying procedures, which not only speeds up the construction of the support beams but also ensures the stability of the concrete pouring by utilizing soil support, thus avoiding structural defects caused by formwork deformation. Attached Figure Description

[0025] Figure 1 This is a flowchart of a flood control gate construction process that ensures uninterrupted flow during the flood season, according to an embodiment of this application. Detailed Implementation

[0026] The following is in conjunction with the appendix Figure 1 This application will be described in further detail below.

[0027] Example:

[0028] Example 1:

[0029] See attached document Figure 1 This embodiment provides a construction process for a control gate that ensures uninterrupted flow during the flood season. The specific steps and parameter settings are as follows:

[0030] Layout of river-side cofferdams and land reclamation:

[0031] Cofferdam layout: Construct cofferdams along both sides of the river in the direction of water flow, with a reserved width for water passage in the middle. The width of the river channel is set at 35% of the total width. A temporary steel bridge with a span of 30.0m is erected above the water crossing section.

[0032] Sheet pile driving: Larsen type IV hot-rolled steel sheet piles are selected and driven using a high-frequency hydraulic vibratory hammer with an excitation force of 500kN, controlling the verticality deviation of the pile body to 0.75%. Before driving, a water-stopping agent is applied to the interlock of the steel sheet pile. The water-stopping agent is a mixture of butter and asphalt at a mass ratio of 1:1.0.

[0033] Seepage prevention at the bank slope connection: High-pressure jet grouting piles are installed at the connection between the cofferdam and the original bank slope to stop water seepage. The diameter of the high-pressure jet grouting piles is ϕ700mm, and the pile spacing is 450mm. The construction parameters are set as follows: grouting pressure 25MPa, lifting speed 20cm / min, and rotation speed 18r / min. The grouting slurry, by weight, consists of: 100 parts of 42.5 grade ordinary Portland cement, 100 parts of water, and 2.0 parts of water glass quick-setting agent.

[0034] Land platform filling: ϕ65mm round steel tie rods are installed as an anchoring system, with a horizontal spacing of 3.5m. Backfill soil is selected from silty clay with a moisture content of 20%, with each layer having a loose thickness of 40cm. After compaction, the compaction coefficient is controlled at 0.92. The top elevation of the backfill is controlled 15cm below the bottom elevation of the first layer of concrete support.

[0035] Construction of pile foundations and first support during the flood season:

[0036] Pile foundation construction: During the flood season, bored pile construction was carried out using a land platform and a temporary steel bridge. The mud wall parameters were controlled as follows: specific gravity 1.18, viscosity 20s, and sand content 6%. For underwater concrete piles, the slump was controlled at 200mm, and the hole expansion coefficient was 1.15.

[0037] Support pouring: Using the leveled land platform soil surface as the bottom formwork, the first layer of concrete support was poured. The support beam used C35 pumped concrete, and its components were mixed in the following mass ratio: cement: fine aggregate: coarse aggregate: water: fly ash: water-reducing agent = 1:1.75:2.5:0.44:0.20:0.010.

[0038] Dry season diversion and foundation pit closure:

[0039] Closure: After the flood season, the cofferdam will be closed, and clay bags will be placed outside the closure opening to form a seepage-proof prism with a top width of 1.8m.

[0040] Subbase and subsequent support: After dewatering and dredging, a 180mm thick C20 plain concrete subbase is poured. Then, a full-span scaffold is erected to close the remaining support structure.

[0041] Dewatering excavation and main structure construction:

[0042] Dewatering wells with a spacing of 18.0m were installed to lower the groundwater level to 0.8m below the excavation surface at the bottom of the pit. During earthwork excavation, the temporary slope of the pit was controlled at 1:1.8, and the width of the walkway was set at 1.2m.

[0043] Example 2:

[0044] See attached document Figure 1 This embodiment provides a construction process for a control gate that ensures uninterrupted flow during the flood season. The specific steps and parameter settings are as follows:

[0045] Layout of river-side cofferdams and land reclamation:

[0046] Cofferdam layout: A water passage section width is reserved in the middle. The width of the river channel is set at 30% of the total width. A temporary steel bridge with a span of 25.0m is erected above the water crossing section.

[0047] Sheet pile driving: Larsen type IV hot-rolled steel sheet piles are selected and driven using a high-frequency hydraulic vibratory hammer with an excitation force of 400kN, controlling the verticality deviation of the pile body to 0.5%. Before driving, a water-stopping agent is applied to the interlock of the steel sheet pile. The water-stopping agent is a mixture of butter and asphalt at a mass ratio of 1:0.8.

[0048] For slope connection and seepage prevention: high-pressure jet grouting piles with a diameter of ϕ600mm and a pile spacing of 400mm are used. Construction parameters are set as follows: grouting pressure 20MPa, lifting speed 15cm / min, and rotation speed 15r / min. The grouting solution, by weight, consists of: 100 parts of 42.5 grade ordinary Portland cement, 80 parts of water, and 1.0 part of water glass quick-setting agent.

[0049] Land platform filling: ϕ50mm round steel tie rods are installed as an anchoring system, with a horizontal spacing of 3.0m. Backfill soil with a moisture content of 18% clay is used, with each layer having a loose thickness of 30cm. After compaction, the compaction coefficient is controlled at 0.90. The top surface elevation of the backfill is controlled 10cm below the bottom elevation of the first layer of concrete support.

[0050] Construction of pile foundations and first support during the flood season:

[0051] Pile foundation construction: The parameters for mud wall protection are controlled as follows: specific gravity 1.10, viscosity 18s, and sand content 4%. For underwater concrete cast-in-place piles, the slump is controlled at 180mm, and the hole expansion coefficient is 1.1.

[0052] Support pouring: The support beam is made of pumped concrete, and its components are mixed in the following mass ratio: cement: fine aggregate: coarse aggregate: water: fly ash: water-reducing agent = 1:1.6:2.3:0.40:0.15:0.008.

[0053] Dry season diversion and foundation pit closure:

[0054] Closure: After the flood season, the cofferdam will be closed, and clay bags will be dumped outside the closure opening to form a seepage-proof prism with a top width of 1.5m.

[0055] Subbase and subsequent support: After dewatering and dredging, a 150mm thick C20 plain concrete subbase is poured. Then, a full-span scaffold is erected to close the remaining support structure.

[0056] Dewatering excavation and main structure construction:

[0057] Dewatering wells with a spacing of 15.0m were installed to lower the groundwater level to 0.5m below the excavation surface at the bottom of the pit. During earthwork excavation, the temporary slope of the pit was controlled at 1:1.5, and the width of the walkway was set at 1.0m.

[0058] Example 3:

[0059] See attached document Figure 1 This embodiment provides a construction process for a control gate that ensures uninterrupted flow during the flood season. The specific steps and parameter settings are as follows:

[0060] Layout of river-side cofferdams and land reclamation:

[0061] Cofferdam layout: The width of the reserved cross-section in the middle is set at 40% of the total width of the river channel. A temporary steel bridge with a span of 35.0m is erected above the cross-section.

[0062] Sheet pile driving: Larsen V-type hot-rolled steel sheet piles are selected and driven using a high-frequency hydraulic vibratory hammer with an excitation force of 600kN, controlling the verticality deviation of the pile body to 1.0%. Before driving, a water-stopping agent is applied to the interlocking joint of the steel sheet pile. The water-stopping agent is a mixture of butter and asphalt in a mass ratio of 1:1.2:1:1.2.

[0063] For slope connection and seepage prevention: high-pressure jet grouting piles with a diameter of ϕ800mm and a pile spacing of 500mm are used. Construction parameters are set as follows: grouting pressure 30MPa, lifting speed 25cm / min, and rotation speed 20r / min. The grouting solution, by weight, consists of: 100 parts of 42.5 grade ordinary Portland cement, 120 parts of water, and 3.0 parts of water glass quick-setting agent.

[0064] Land platform filling: ϕ80mm round steel tie rods are installed as an anchoring system, with a horizontal spacing of 4.0m. The backfill soil uses silty clay with a moisture content of 22%, with each layer having a loose thickness of 50cm. After compaction, the compaction coefficient is controlled at 0.93. The top surface elevation of the backfill is controlled 20cm below the bottom elevation of the first layer of concrete support.

[0065] Construction of pile foundations and first support during the flood season:

[0066] Pile foundation construction: The parameters for mud wall protection are controlled as follows: specific gravity 1.25, viscosity 22s, and sand content 8%. During underwater concrete pouring, the slump is controlled at 220mm, and the hole expansion coefficient is 1.2.

[0067] Support pouring: The support beam is made of pumped concrete, and its components are mixed in the following mass ratio: cement: fine aggregate: coarse aggregate: water: fly ash: water-reducing agent = 1:1.9:2.7:0.48:0.25:0.012.

[0068] Dry season diversion and foundation pit closure:

[0069] Closure: After the flood season, the cofferdam will be closed, and clay bags will be placed outside the closure opening to form a seepage-proof prism with a top width of 2.0m.

[0070] Subbase and subsequent support: After dewatering and dredging, a 200mm thick C20 plain concrete subbase is poured. Then, a full-span scaffold is erected to close the remaining support structure.

[0071] Dewatering excavation and main structure construction:

[0072] Dewatering wells with a spacing of 20.0m are installed to lower the groundwater level to 1.0m below the excavation surface at the bottom of the pit. During earthwork excavation, the temporary slope of the pit is controlled at 1:2.0, and the width of the walkway is set at 1.5m.

[0073] Comparative Example 1:

[0074] Compared with Example 1, the difference lies in the construction method of the first concrete support. Specifically, after the pile foundation construction is completed, the earthwork within the cofferdam along the river is excavated to 1.0m below the bottom elevation of the first support. Then, steel pipe scaffolding is erected and wooden formwork is laid for the suspended pouring of the support beam, instead of directly using the leveled land platform soil surface as the bottom formwork for pouring. The remaining steps and parameters are the same.

[0075] Comparative Example 2:

[0076] Compared with Example 1, the difference is that the process of seepage prevention at the bank slope connection has been removed. Specifically, after the steel sheet piles of the cofferdam are inserted into the original bank slope, high-pressure jet grouting piles are not installed at the junction for water-stopping treatment. Instead, geotextile is directly laid and backfilled with soil. The remaining steps and parameters are the same.

[0077] Comparative Example 3:

[0078] Compared to Example 1, the difference lies in the replacement of the land-based construction method. Specifically, instead of backfilling the land within the river-side cofferdam, a steel pipe pile trestle bridge and an offshore drilling platform are used to cover the original fill area. All pile foundation work is carried out on the offshore steel platform, and the soil layer cannot be used as a supporting formwork. All other steps and parameters are the same.

[0079] Comparative Example 4:

[0080] Compared with Example 1, the difference lies in the change of timing and cofferdam form. Specifically, no cofferdam or pile foundation construction is carried out during the flood season; after the flood season, a transverse river-blocking cofferdam is constructed in one go to cut off the water flow, and after the water is pumped out, pile foundation and support construction is carried out under completely dry conditions, with all other parameters remaining the same.

[0081] Test Example 1: Simulation Test of Construction Period and Efficiency

[0082] Experimental instructions and procedures:

[0083] This test case uses a standard hydraulic engineering progress simulation model. The simulation background is set as a standard plain river control gate project, with a total river width of 100.0m and a total of 120 designed piles, including two concrete support systems. The geological conditions are set as Quaternary alluvial layer, with silty mud soil on top and silty clay on the bottom.

[0084] The specific experimental steps are as follows:

[0085] A construction network planning model was constructed, and the corresponding process logic relationships were input for Examples 1 to 3 and Comparative Examples 1 to 4. Examples 1 were set to begin construction during the flood season, followed by pile foundation construction after the construction of a river-side cofferdam and land platform. Comparative Example 4 was set to not operate during the flood season, and to carry out full-section closure construction after the dry season. Comparative Example 3 was set to operate on a fully floating platform. Comparative Example 1 was set to require the erection of a full-span scaffolding system.

[0086] Input the standard duration parameters for each process. Based on the standard quota for conventional hydraulic machinery, set the average efficiency of onshore drilling rigs at 1.2 piles / day and the average efficiency of offshore drilling platform operations at 0.8 piles / day. Set the time for soil formwork leveling and preparation at 3 days and the time for suspended support erection and bottom formwork laying at 15 days.

[0087] Meteorological and hydrological boundary conditions are set. The flood season is set from June to September each year, during which river levels are high and flow velocity increases. For Comparative Example 4, it is set that cofferdam closure and foundation pit operations cannot be carried out during the flood season.

[0088] Run simulation calculations to record the starting point of pile foundation construction, the time taken to complete the pile foundation and retaining structure, the construction time of the first support system, and the total construction period to achieve the conditions for underwater structure sealing for each scheme.

[0089] Experimental data:

[0090] Table 1: Simulation Calculation Data of Construction Period for Each Construction Scheme

[0091] Group Pile foundation construction start point Time taken to complete pile foundation and retaining structure (days) Construction time for the first support system (days) Total construction period (months) until conditions for bottom sealing are met. Example 1 22.5 45.3 8.2 11.8 Example 2 20.8 43.1 7.9 11.6 Example 3 25.4 49.6 8.5 12.3 Comparative Example 1 22.5 45.3 23.4 12.9 Comparative Example 2 22.5 48.2 8.2 12.1 Comparative Example 3 45.6 68.7 8.2 14.2 Comparative Example 4 125 45.3 23.4 18.5

[0092] Note: The data in the table are non-integer values ​​generated from simulation calculations. For Comparative Example 2, due to the need to address potential leakage, a slight increase in man-hours is assumed during the completion phase of the building envelope. The starting point for Comparative Example 4 is significantly delayed due to work stoppages during the flood season.

[0093] Experimental Results Analysis and Mechanism Explanation:

[0094] Examples 1 to 3 all showed significantly shorter overall project durations than Comparative Example 4. The core mechanism lies in the altered construction sequence caused by the spatial layout of the cofferdam and the reserved water passage. By reserving a water passage of a specific width in the center of the river, the project can maintain its flood control capacity even under high water levels during the flood season, thus eliminating the time constraint of traditional methods that required waiting for the dry season to construct the cofferdam. This parallel operation mode transforms the flood season, which would otherwise be a period of idle waiting, into an effective working period for pile foundations and retaining structures, directly reducing the critical path length in the overall project schedule and significantly advancing the start date of pile foundation construction.

[0095] Compared to Comparative Example 3, the completion time for the pile foundation and retaining structure in Example Group was significantly reduced, mainly due to the construction of the land-based operation platform. By backfilling and compacting earth within the river-side cofferdam to form a peninsula-shaped land area, the drilling operation, which was originally affected by water flow, waves, and water level fluctuations, was transformed into a stable land-based operation. The land-based operation environment eliminated complex procedures such as the construction of the water-based construction platform, the relocation and positioning of the floating crane, and the water-based circulation and treatment of mud, thus improving the operational continuity of the drilling equipment and the efficiency of single-pile drilling. At the same time, compared to Comparative Example 1, Example Group used the compacted top surface of the backfill earth directly as the bottom formwork for the first concrete support, omitting the procedures of erecting high formwork scaffolds and laying wooden formwork in the foundation pit. The bearing capacity of the soil replaced the temporary support structure, thereby reducing the construction time of the support system.

[0096] Based on the data from various groups, the example group, through the treatment of the connection between the old and new structures using high-pressure jet grouting piles, ensured the airtight and water-stopping effect of the cofferdam system, avoiding the construction period loss caused by seepage treatment as in Comparative Example 2. The entire process, through the strategy of trading space for time and the reuse strategy of geotechnical structures, compressed the construction period of underground concealed works while ensuring flow safety, thereby shortening the overall construction period of the entire water conservancy project.

[0097] Test Example 2: Monitoring of seepage prevention performance at the joint between bank slopes

[0098] Experimental instructions and procedures:

[0099] This test case aims to verify the water-stopping effect of the steel sheet piles of the cofferdam connecting with the original bank slope revetment. The experimental subjects cover Examples 1 to 3, and Comparative Examples 1 to 4. The experimental site is set inside the foundation pit corresponding to each scheme. After the foundation pit is dewatered and dredged, the joint between the cofferdam and the bank slope is exposed.

[0100] The specific experimental steps are as follows:

[0101] After the foundation pit is excavated to the design bottom elevation, the boundary line between the steel sheet piles of the cofferdam and the original riverbank slope is selected as the monitoring object. A drainage ditch parallel to the cofferdam axis is excavated along this boundary line inside the foundation pit. The drainage ditch is 0.3m wide, 0.3m deep, and a typical section with a length of 10.0m is selected.

[0102] A triangular weir flow meter is installed at the end of the collection ditch to measure the flow rate of collected water seeping from the joint in real time. At the same time, pore water pressure gauges are installed on the soil surface on the back side of the joint to monitor changes in pore water pressure inside the soil.

[0103] Maintain the water level outside the foundation pit at the high level of the flood season, while keeping the inside of the pit dry to create the maximum design head difference. Continuously monitor for 24 hours, recording the flow meter reading every hour, and observe the sediment in the collection ditch to determine if any soil particles are carried out by the water flow.

[0104] Calculate the average leakage per unit length and count the frequency of piping or soil erosion in each experimental section.

[0105] Experimental data:

[0106] Table 2: Monitoring data on seepage prevention performance at the junction of the cofferdam and the bank slope

[0107] Group Average leakage rate over 24 hours (L / min·m) Peak leakage rate (L / min·m) Characteristics of sediments in the catchment ditch Has piping occurred? Example 1 0.42 0.58 Clear water, no sediment no Example 2 0.78 0.95 Trace amount of fine sand no Example 3 0.29 0.36 Clear water, no sediment no Comparative Example 1 0.45 0.61 Clear water, no sediment no Comparative Example 2 18.45 22.1 Large amounts of turbid silt yes Comparative Example 3 0.41 0.55 Clear water, no sediment no Comparative Example 4 0.44 0.6 Clear water, no sediment no

[0108] Note: Comparative Examples 1, 3, and 4 maintained the same slope connection process as Example 1, so their data were similar; Comparative Example 2 did not use high-pressure jet grouting piles, so its data showed significant differences.

[0109] Experimental Results Analysis and Mechanism Explanation:

[0110] The leakage data in Examples 1 to 3 remained at extremely low levels, and no piping was observed. The physical mechanism was that the composite water-stop curtain constructed by the high-pressure jet grouting piles cut off the seepage path. The high-pressure jetting fluid disrupted the natural contact interface between the original slope soil and the sheet piles, forcing the cement grout to mix with the soil particles and solidify, forming a continuous and dense cement-soil consolidation body. This consolidation body filled the physical gaps between the sheet pile interlocks and the irregular slope, eliminating concentrated seepage channels caused by differences in medium stiffness and non-adherence of the contact surfaces. Thus, when subjected to a high head difference between the inside and outside of the foundation pit, it could effectively prevent groundwater from seeping into the foundation pit along the interface between the old and new structures.

[0111] Conversely, Comparative Example 2 data shows high-flow-rate seepage and sediment deposition, indicating failure at the joint. In the absence of high-pressure jet grouting reinforcement, sheet piles are directly inserted into or pressed against the original slope soil, with only loose mechanical contact or simple backfilling between them. Under the influence of the hydraulic gradient, water easily flows through the pores at the contact surface, forming a dominant flow path. As the seepage velocity increases, the water carries away fine particles from the soil, causing the pores to further enlarge, eventually forming a continuous piping channel, leading to a sharp increase in seepage and threatening slope stability.

[0112] Comparing examples with different grouting parameters reveals that variations in grouting pressure and grout mix ratio have a fine-tuning effect on the water-stopping effect. Example 3 employed higher grouting pressure and a higher dosage of quick-setting agent, resulting in a more effective expansion of the jet grouting pile diameter and a shorter grout setting time. This reduced grout loss in dynamic water conditions, thereby forming a more dense and impermeable water barrier. This specific reinforcement measure targeting the connection points ensured dry working conditions for the foundation pit during the high water level environment of the flood season, maintaining the overall safety of the support system.

[0113] Test Example 3: Testing of Structural Construction Accuracy and Support Stability

[0114] Experimental instructions and procedures:

[0115] This test case aims to quantitatively evaluate the impact of different construction techniques on the borehole quality of bored piles and the geometric stability of the concrete support system. The experimental subjects cover Examples 1 to 3, and Comparative Examples 1 to 4.

[0116] The specific experimental steps are as follows:

[0117] After the construction of bored piles in each group was completed and before the initial setting of the concrete, an ultrasonic borehole detector was used to scan the entire borehole section. Twenty engineering piles were randomly selected from each group as samples, and the maximum deviation angle of the pile axis relative to the design plumb line was measured and recorded. The percentage of verticality deviation of the pile was calculated.

[0118] During the pouring of the first concrete support beam, settlement observation points were set up at the bottom formwork of the support beam. One observation point was set up every 5.0m along the span of the support beam.

[0119] At three time points—completion of concrete pouring for the support beam, initial setting, and final setting—the elevation of each observation point was measured using a precision level. The vertical displacement of each observation point relative to the initial elevation before pouring was calculated after final setting, and the largest negative value was taken as the maximum bottom settlement of the support beam group.

[0120] The average value and dispersion of each group of data were statistically analyzed, and the structural forming indicators under different working platforms and formwork methods were compared and analyzed.

[0121] Experimental data:

[0122] Table 3: Monitoring data on pile verticality and support bottom settlement

[0123] Group Average deviation of pile verticality (%) Maximum deviation of pile verticality (%) Maximum settlement of the bottom surface of the supporting beam (mm) Standard deviation of settlement at the bottom of the supporting beam (mm) Example 1 0.58 0.72 2.1 0.45 Example 2 0.49 0.65 2.4 0.52 Example 3 0.63 0.78 1.9 0.38 Comparative Example 1 0.57 0.74 8.7 1.85 Comparative Example 2 0.61 0.75 2.2 0.48 Comparative Example 3 1.45 2.1 2.1 0.44 Comparative Example 4 0.55 0.69 8.5 1.79

[0124] Note: Comparative Example 3 uses a floating platform for operation and does not involve a comparison of soil membrane settlement; Comparative Examples 1 and 4 use a suspended support method for construction.

[0125] Experimental Results Analysis and Mechanism Explanation:

[0126] The example group significantly outperformed Comparative Example 3 in terms of pile verticality deviation, the physical mechanism of which stems from the difference in the foundation stiffness of the working platform. The example group constructed a land-based working platform by backfilling and compacting earth within a river-side cofferdam. This platform provided rigid foundation support for the drilling rig, eliminating the influence of water flow fluctuations, tidal displacement, and mechanical vibrations on the working face. The drill rod descended on a stable land foundation, maintaining constant axial pressure and guiding accuracy. In contrast, Comparative Example 3 used a steel platform or floating box on water. Affected by buoyancy and water fluctuations, the working platform experienced slight high-frequency swaying and tilting. This dynamic displacement was directly transmitted to the drill rod end, causing deviation in the drilling trajectory and increasing the verticality deviation.

[0127] Regarding the settlement index of the bottom surface of the supporting beam, the data of the example group were significantly lower than those of Comparative Example 1 and Comparative Example 4. This difference is mainly attributed to the different mechanical transfer paths of the supporting bottom formwork. The example group used the layered compacted soil directly as the bottom formwork. The soil has continuous and uniform foundation bearing capacity, which can directly transfer the self-weight load of the newly poured concrete to the deep foundation, and the plastic deformation of the soil after compression is minimal. In contrast, the comparative example used a suspended formwork system, in which the load needs to be transferred through the formwork, secondary joists, and main joists to the vertical support, and then to the foundation. In this multi-stage transfer chain, the closure of the gaps at each connection node, the elastic bending deformation of the members, and the superposition of non-uniform settlement of the support foundation led to a larger vertical displacement.

[0128] The process employed in this invention improves structural quality by altering the boundary conditions of the construction environment. The earth-filling island-building process transforms water-based operations into land-based operations, utilizing soil mechanics to address mechanical stability issues. The soil formwork process replaces the complex steel pipe support system with the incompressibility of the soil, solving the deformation control problem during the casting of large-span support beams. This construction method, based on the integration of geotechnical and structural engineering, ensures geometric accuracy while reducing potential quality risks caused by temporary structural deformation.

Claims

1. A construction process for a control gate that ensures uninterrupted flow during the flood season, characterized in that, Includes the following steps: S1. Layout of cofferdams along the river and construction of land: Construct cofferdams along both sides of the river flow direction, and reserve a water passage section between the two cofferdams. Erect a temporary steel bridge with a span consistent with the width of the reserved water passage section above the reserved water passage section. Backfill and compact earthwork in layers inside the cofferdams to form a land operation platform. The top elevation of the land operation platform is controlled below the bottom elevation of the first concrete support designed. S2. Construction of pile foundation and first support during the flood season: Under the flood season condition of maintaining the reserved water passage section, the construction of bored piles and retaining piles is carried out using the land operation platform and steel temporary bridge; the leveled land operation platform is used directly as the bottom formwork to pour the first concrete support except for the reserved water passage section area. S3. Closure and Pit Closure During the Dry Season: After the flood season, steel sheet piles are driven at both the upstream and downstream ends of the cofferdam along the river to close the dam and form a closed pit. After the water in the pit is pumped out, the riverbed bottom of the original reserved water passage section is dredged and a plain concrete cushion layer is poured. A support frame is erected on the plain concrete cushion layer, and the remaining concrete support is constructed to close the pit support system. S4. Dewatering Excavation and Main Structure Construction: After the concrete support reaches the design strength, the dewatering wells are activated to lower the groundwater level, and earthwork excavation and main structure construction of the control gate are carried out.

2. The construction process of a flood control gate with uninterrupted flow during the flood season according to claim 1, characterized in that, In step S1, the width of the reserved water passage section The width is set to 30% to 40% of the total width of the river channel, specifically 25.0m to 35.0m; the soil compaction coefficient of the land operation platform is controlled at 0.90 to 0.93, and its top surface elevation is controlled at 10cm to 20cm below the bottom surface elevation of the first concrete support designed.

3. The construction process of a flood control gate with uninterrupted flow during the flood season according to claim 1, characterized in that, In step S1, the connection between the cofferdam and the original bank slope is treated with high-pressure jet grouting piles for water stoppage. The construction parameters of the high-pressure jet grouting piles include: pile diameter of ϕ600mm~ϕ800mm, pile spacing of 400mm~500mm, grouting pressure of 20MPa~30MPa, lifting speed of 15cm / min~25cm / min, and rotation speed of 15r / min~20r / min.

4. The construction process of a flood control gate with uninterrupted flow during the flood season as described in claim 3, characterized in that, The grout used in the high-pressure jet grouting piles, by weight, includes: 100 parts of 42.5 grade ordinary Portland cement, 80-120 parts of water, and 1.0-3.0 parts of water glass quick-setting agent.

5. The construction process of a flood control gate with uninterrupted flow during the flood season according to claim 1, characterized in that, In step S1, the cofferdam along the river adopts Larsen type IV or V hot-rolled steel sheet piles, which are driven by a high-frequency hydraulic vibratory hammer with an excitation force of 400kN to 600kN, and the verticality deviation of the pile body is controlled within 0.5% to 1.0%; a water-stopping agent is applied to the interlock of the steel sheet piles, which is a mixture of butter and asphalt in a mass ratio of 1: (0.8 to 1.2).

6. The construction process of a flood control gate with uninterrupted flow during the flood season according to claim 1, characterized in that, In step S1, the construction of the land operation platform also includes setting up an anchoring system, which includes two round steel tie rods with a diameter of 50mm to 80mm and a horizontal spacing of 3.0m to 4.0m; the backfill soil is clay or silty clay with a moisture content of 18% to 22%, and each layer is loosely laid with a thickness of 30cm to 50cm.

7. The construction process of a flood control gate with uninterrupted flow during the flood season according to claim 1, characterized in that, In step S2, the bored pile construction uses mud slurry for wall protection, and the mud slurry parameters are controlled as follows: specific gravity of 1.10 to 1.25, viscosity of 18s to 22s, and sand content of 4% to 8%; the bored pile is constructed using underwater concrete pouring, and the slump of the underwater concrete is controlled at 180mm to 220mm, with an initial setting time of ≥8h.

8. The construction process of a flood control gate with uninterrupted flow during the flood season according to claim 1, characterized in that, In steps S2 and S3, the concrete support is made of pumped concrete, and the components are mixed in the following mass ratio range: cement: fine aggregate: coarse aggregate: water: fly ash: water-reducing agent = 1: (1.6~1.9): (2.3~2.7): (0.40~0.48): (0.15~0.25): (0.008~0.012).

9. The construction process of a flood control gate with uninterrupted flow during the flood season according to claim 1, characterized in that, In step S3, after the interception and closure, clay bags are thrown outside the closure opening to form a seepage-proof prism with a top width of 1.5m to 2.0m; the thickness of the plain concrete cushion layer is 150mm to 200mm, and the strength grade is C20.

10. The construction process of a flood control gate with uninterrupted flow during the flood season according to claim 1, characterized in that, In step S4, the dewatering wells are arranged around the perimeter of the foundation pit and inside the pit, with a spacing of 15.0m to 20.0m between wells, to lower the groundwater level to 0.5m to 1.0m below the excavation surface at the bottom of the pit; the slope of the temporary side slope inside the pit during earthwork excavation is controlled at 1:1.5 to 1:2.0, and a walkway with a width of ≥1.0m is set up.

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