Water-rich fine sand stratum dewatering construction method

Abstract

The application discloses a water-rich fine sand stratum precipitation construction method, which comprises the following steps: determining the position of a surface precipitation well, installing a drilling device, surface precipitation treatment, and hole precipitation treatment, wherein the surface precipitation treatment comprises drilling a hole, enlarging the hole, and removing sundries in the surface precipitation hole; water injection is performed for slurry mixing and slurry replacement, a water filter pipe is installed and filled with gravel, and the water filter pipe is fixed; a water pump is connected to the port of the water filter pipe to pump water; the hole precipitation treatment comprises advanced deep hole precipitation, vertical precipitation, light well point precipitation, and vacuum precipitation pumping; and then curtain grouting is performed to excavate a tunnel. The water-rich fine sand stratum is first subjected to the surface precipitation treatment outside the hole, and then subjected to the hole precipitation treatment in the tunnel, so that the phenomenon of sand gushing and collapse of the tunnel in the construction process is effectively reduced, the safety of the construction is improved, the operation is convenient, the water content of the water-rich fine sand stratum is effectively reduced, and the stability of the water-rich fine sand stratum is improved.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, and in particular to a method for dewatering construction in water-rich silty fine sand strata. Background Technology

[0002] With the rapid development of underground space development, more and more projects will encounter water-rich silty fine sand strata. These strata are rich in water and have a certain degree of pressure resistance. The large volume of sand and water inflow may cause accidents such as water inrush, collapse, and landslide. At best, they may cause deformation of the initial support of the tunnel, endangering construction safety. At worst, they may lead to tunnel collapse, causing safety accidents and seriously affecting the tunnel's construction period, project quality, production safety, and production costs.

[0003] Currently, in tunnel construction in my country, when encountering water-rich geological conditions, the following two methods are generally adopted: First, the lightweight wellpoint method is used. Although this method can dewater within the tunnel, if the permeability coefficient of the water-rich silty fine sand fluid plastic strata inside the tunnel is low, the dewatering cannot penetrate the tunnel in time, and sand inrush and collapse are likely to occur inside the tunnel. Therefore, this method has limitations on the amount of dewatering inside the tunnel, and the effective dewatering range cannot meet the construction requirements. Second, gravity deep wells are used. Although this method is not limited by the amount of dewatering inside the tunnel, in water-rich silty fine sand fluid plastic strata with low permeability coefficients, the time cycle for dewatering is long, which seriously affects the tunnel construction progress.

[0004] In summary, during construction in water-rich silty fine sand fluid plastic strata within the tunnel, existing dewatering methods are ineffective and cannot promptly and effectively reduce the water content of the water-rich silty fine sand strata inside and around the tunnel. Consequently, sand inrush and collapse are likely to occur within the tunnel, making it impossible to adequately guarantee the safety of construction. Summary of the Invention

[0005] The main objective of this invention is to provide a dewatering construction method for water-rich silty fine sand strata, which solves the problem that existing dewatering methods used in water-rich silty fine sand strata in tunnels cannot effectively reduce the water content in the tunnel, and that sand inrush and collapse are prone to occur in the tunnel.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for dewatering water-rich silty fine sand formations, characterized by the following steps:

[0008] S100: Determine the location of surface dewatering wells and install drilling equipment;

[0009] S200: Surface precipitation treatment;

[0010] S210: Wellbore: A wellbore with mud slurry wall is formed by drilling a hole at the determined location of the surface dewatering well using drilling equipment.

[0011] S220: Enlarge the surface precipitation well hole;

[0012] S230: Inject water into the enlarged surface dewatering well hole to adjust the slurry. After the slurry adjustment is completed, continue to inject water to replace the slurry until the mud flowing out of the surface dewatering well hole does not contain mud lumps, and then stop injecting water.

[0013] S240: Measure the actual depth of the surface precipitation well hole, install a filter pipe in the surface precipitation well hole according to the actual depth of the surface precipitation well hole, fill it with gravel, and fix the filter pipe.

[0014] S250: Seal the surface dewatering well holes and connect a water pump to the port of the filter pipe to pump water, so that the groundwater level is lower than the construction working face inside the tunnel;

[0015] S300: Dewatering treatment inside the tunnel;

[0016] S310: Divide the tunnel excavation face into three parts from top to bottom and excavate them to form an upper step, a middle step and a lower step, and level the steps of the upper step, the middle step and the lower step;

[0017] S320: Install a drilling rig near the tunnel excavation face and on the steps of the upper and middle steps, drill advanced deep hole dewatering holes through the drilling rig, install advanced deep hole dewatering pipes, and fill the gap between the advanced deep hole dewatering pipes and the advanced deep hole dewatering holes with coarse sand.

[0018] A vertical dewatering well operation platform is constructed on the surface of the lower step. Drilling equipment is installed on the vertical dewatering well operation platform to drill vertical dewatering well holes. Vertical dewatering well pipes are installed in the vertical dewatering well holes and backfilled with coarse sand.

[0019] Lightweight wellpoint dewatering holes are inclinedly opened on the step surfaces of the upper step, the middle step, and the lower step at positions located near the sidewall, and lightweight wellpoint dewatering pipes are installed in the lightweight wellpoint dewatering holes;

[0020] S330. Vacuum dewatering pumps are connected to the outer ends of the advanced deep hole dewatering pipe, the vertical dewatering well pipe, and the lightweight wellpoint dewatering pipe to continuously pump water and detect the water content in the water-rich silty fine sand formation.

[0021] S400: Curtain grouting; Several grouting holes are opened on the tunnel excavation surface, and grout is injected into the grouting holes. After the grouting is completed, the tunnel is excavated. The excavation stops when the tunnel is close to the end of the grouting hole. Then the construction starts again from S100 until the water-rich fine sand strata or the deep-buried tunnel is excavated.

[0022] Furthermore, in step S230, the density of the prepared mud is 1.0 g / cm³. 3 ~1.1g / cm 3 The viscosity is 18–20 s;

[0023] After the slurry was replaced, the sediment at the bottom of the surface dewatering well was less than 30cm.

[0024] Furthermore, in S240, the height of the water filter pipe exposed above the ground is greater than 20cm.

[0025] Furthermore, the gravel has a particle size of 2-4 mm and a mud content of ≤3%.

[0026] When filling with gravel, the height of the gravel is 10-13 cm lower than the opening of the filter pipe.

[0027] Furthermore, in S320, the length of the upper step, the middle step, and the lower step is 4-5m, and the height is 3-5m.

[0028] Furthermore, the vertical dewatering well pipe is wrapped with a first filter screen and geotextile, with the geotextile located on the inner layer and the first filter screen on the outer layer; the outer wall of the lightweight wellpoint dewatering pipe is wrapped with a double-layer second filter screen.

[0029] Furthermore, the first filter screen and the second filter screen are made of carbon fiber, and the first filter screen has a filtration diameter of 200 mesh and the second filter screen has a filtration diameter of 100 mesh.

[0030] Furthermore, there are 83 grouting holes, of which 82 are arranged in a circle around one grouting hole.

[0031] Furthermore, the grouting material is a cement-water glass two-component grout.

[0032] Furthermore, in the cement-water glass two-component slurry, the volume ratio of cement slurry to water glass is 1:1, and the mass ratio of water to lime in the cement slurry is 1:1.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] This invention discloses a dewatering construction method for water-rich silty fine sand strata. First, surface dewatering is performed outside the tunnel in the water-rich silty fine sand strata. Then, in-tunnel dewatering is carried out, specifically by installing lightweight wellpoint dewatering at the bottom of the sidewalls of the upper, middle, and lower steps on the tunnel excavation face. Vertical dewatering wells are installed at the bottom of the lower step, and deep-hole dewatering holes are pre-drilled outside the tunnel excavation face outline to reduce the water content in the water-rich silty fine sand strata within the tunnel. This is further supplemented by curtain grouting to improve the water-rich silty fine sand strata, forming a continuous water-blocking curtain to cut off water flow. This construction method effectively reduces the occurrence of sand inrush and collapse during construction, improves construction safety, is easy to operate, and effectively reduces the water content and stability of the water-rich silty fine sand strata. Attached Figure Description

[0035] Figure 1 A construction flowchart of the dewatering construction method for water-rich silty fine sand strata provided by the present invention;

[0036] Figure 2 A schematic diagram of the structure of precipitation in water-rich silty fine sand formations provided by the present invention;

[0037] Figure 3 A front view of the borehole for grouting in the tunnel in the dewatering construction method for water-rich fine sand strata provided by the present invention;

[0038] Figure 4 A borehole surface diagram of grouting in the tunnel in the dewatering construction method for water-rich fine sand strata provided by the present invention.

[0039] In the diagram: 1. Surface dewatering well; 2. Advanced deep-hole dewatering well; 3. Lightweight wellpoint dewatering well; 4. Vertical dewatering well; 5. Upper step; 6. Middle step; 7. Lower step; 8. Tunnel excavation face outline; 9. Grouting hole. Detailed Implementation

[0040] 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.

[0041] See Figure 1This invention discloses a dewatering construction method for water-rich silty fine sand strata. The method first involves deep well dewatering outside the tunnel to lower the groundwater level below the working face inside the tunnel. Then, dewatering is performed inside the tunnel, followed by further dewatering of the water-rich silty fine sand strata. Finally, curtain grouting is carried out. This method effectively reduces the occurrence of sand inrush and collapse during construction, improves construction safety, is easy to operate, and effectively reduces the water content and stability of the water-rich silty fine sand strata. The specific steps of this construction method are as follows:

[0042] S100: Determine the location of surface dewatering wells and install drilling equipment;

[0043] Construction workers determine the outline of the tunnel above the tunnel to be built, and use existing equipment (such as excavators, bulldozers, etc.) to level the initial position where the tunnel needs to be built and build a construction platform;

[0044] Construction workers used surveying tools to locate the positions of multiple surface dewatering wells along the tunnel excavation direction, and then marked them.

[0045] Install drilling equipment on the construction platform, that is, build and install the rig at the marked point on the construction platform, keep the rig level, and install the turret, overhead crane and drilling rig on the rig.

[0046] S200: Surface precipitation treatment;

[0047] S210: Drilling surface dewatering wells:

[0048] The drilling rig installed in S100 is started, causing the drill rod inside to rotate in a positive cycle. The well is vertically driven at the marked point. When the well reaches the set depth, the drill rod is kept at that depth and continues to rotate, so that the drill rod produces mud in the drilled well, thereby forming a surface dewatering well with mud slurry wall protection.

[0049] S220: Continue to rotate the drill rod in the drilling rig, raise the drill rod a certain distance, fix the position of the drill rod, and continue to rotate the drill rod to enlarge the well hole in S210, thereby increasing the diameter of the well hole at the bottom position.

[0050] During the borehole enlargement process, the rotation of the drill rod removes debris from the inner wall of the drilled borehole and clears this debris to the outside of the drilled borehole, forming a surface dewatering well.

[0051] S230: Water is injected into the surface dewatering wellbore in S220 to adjust the mud density so that the mud density in the wellbore is 1.0 g / cm³. 3 ~1.1g / cm 3With a viscosity of 18-20s, the drill rod in the drilling rig stops rotating, and then the drill rod is pulled out of the surface dewatering well hole to complete the slurry preparation.

[0052] After the slurry preparation is completed, continue to inject water to replace the slurry in the surface dewatering wells until the slurry flowing out of the surface dewatering wells does not contain mud lumps and the sediment at the bottom of the surface dewatering wells is less than 30cm. Stop injecting water to ensure that a thick mud cake does not form on the inner wall of the surface dewatering wells when they enter the aquifer.

[0053] S240: Construction personnel measure the actual depth of the surface dewatering well hole and check whether the surface dewatering well hole meets the requirements. If it does not meet the requirements, repeat S220 and S230. If it meets the requirements, install a filter pipe in the corresponding surface dewatering well hole according to the measured depth. After installation, the height of the filter pipe exposed above the ground should be greater than 20cm. Then fill it with gravel. The gravel should be continuously and evenly filled along the outer wall of the filter pipe, and the height of the gravel should be 10-13cm lower than the opening of the filter pipe. Fix the filter pipe stably in the surface dewatering well hole. In this example, the particle size of the gravel is 2-4mm and the mud content of the gravel is ≤3%.

[0054] Ideally, when the filter pipe is installed inside the surface dewatering well hole, a layer of nylon mesh is wrapped around the outer wall of the filter pipe, and the end of the filter pipe at the bottom of the surface dewatering well hole is also wrapped with nylon mesh to prevent mud and sand from entering the surface dewatering pipe and causing blockage.

[0055] S250: Collect cohesive soil, break up the cohesive soil, slowly fill the broken cohesive soil into the surface water purification well, seal the surface dewatering well, then connect a water pump to the port of the filter pipe located outside the surface to pump water, so that the groundwater level is lower than the working face inside the tunnel, and then disassemble the water pump.

[0056] S300: Dewatering treatment inside the tunnel;

[0057] S310: The tunnel excavation face is divided into three parts from top to bottom: the upper part, the middle part, and the lower part. These parts are excavated to form an upper step, a middle step, and a lower step. The length of the upper step, the middle step, and the lower step are 4 to 5 meters, and the height is 3 to 5 meters. The surfaces of the upper step, the middle step, and the lower step are then leveled to provide a working platform for subsequent construction.

[0058] S320: Drilling rigs are installed near the outer edge of the tunnel excavation face outline. Multiple advanced deep-hole dewatering holes are drilled at an angle along the tunnel excavation direction. The depth of these holes is 21–25 m. Specifically, the closer each advanced deep-hole dewatering hole is to the tunnel excavation face outline, the smaller the distance between the hole opening and the center point of the outline (inclination angle is 10°). These advanced deep-hole dewatering holes are arranged in a semi-circular shape around the tunnel excavation face outline, with the center-to-center distance between adjacent holes being 0.5–1 m. Simultaneously, drilling rigs are also installed on the upper and middle bench surfaces. The drill bits are horizontally positioned, and multiple advanced deep-hole dewatering holes are drilled below the upper and middle bench surfaces on the tunnel excavation face. These advanced deep-hole dewatering holes are drilled along the tunnel excavation direction. The excavation direction is horizontal, and the holes are arranged in a row along the length of the upper and middle steps. The distance between two adjacent deep-hole dewatering holes is 0.5m, and the length is 21-25m. The diameter of the deep-hole dewatering holes is 6-7cm. Before removing the drilling casing after the drilling of the deep-hole dewatering holes is completed, the deep-hole dewatering pipe is first inserted into the borehole. After the deep-hole dewatering pipe is installed, the casing is pulled out, and coarse sand is slowly filled into the deep-hole dewatering hole. The gap between the deep-hole dewatering pipe and the deep-hole dewatering hole is filled with coarse sand, and the deep-hole dewatering pipe is fixed in the deep-hole dewatering hole. The deep-hole dewatering pipe is used to carry out deep-hole dewatering treatment in the tunnel, which can form a stable funnel-shaped dewatering surface in front of the tunnel excavation face and improve the self-stabilization ability of the water-rich fine sand strata on the tunnel excavation face after excavation.

[0059] A vertical dewatering well operation platform is also constructed on the lower step surface. Drilling equipment is installed on the platform, and vertical dewatering well holes are drilled on the lower step surface using the drilling equipment. The diameter of the vertical dewatering well holes is 18-22 cm, and the depth is 6-10 m. The distance between two adjacent vertical dewatering well holes is 6-10 m. After drilling, vertical dewatering well pipes are installed in the vertical dewatering well holes, and coarse sand is filled into the vertical dewatering well holes along the outer wall of the vertical dewatering well pipes. The vertical dewatering well pipes are used for vertical dewatering in the tunnel, which can lower the groundwater level in the construction area of ​​the tunnel and drain the groundwater at the bottom of the tunnel out of the tunnel. This prevents water seepage or water accumulation at the bottom of the tunnel during tunnel construction, which would soften the water-rich fine sand strata at the bottom of the tunnel and prevent sand inrush in the tunnel, thus avoiding affecting the tunnel construction.

[0060] Lightweight wellpoint dewatering holes are installed at the sidewall locations on the upper, middle, and lower steps using high-pressure blowers / high-pressure water pumps, inclined along the tunnel excavation direction. These holes are 3–5 m deep, 4–5 cm in diameter, and inclined at 28°–32°. Simultaneously, lightweight wellpoint dewatering pipes are installed within the holes. These pipes are used for lightweight wellpoint dewatering within the tunnel, ensuring the stability of the water-rich silty sand strata, facilitating subsequent tunnel excavation, preventing collapses or sand inrushes during excavation, and improving construction safety.

[0061] Preferably, the vertical dewatering well pipe is wrapped with a first filter screen and geotextile, with the geotextile on the inner layer and the first filter screen on the outer layer; the outer wall of the lightweight wellpoint dewatering pipe is wrapped with a double-layer second filter screen, the first and second filter screens are made of carbon fiber, the first filter screen has a filtration diameter of 200 mesh and the second filter screen has a filtration diameter of 100 mesh; the first and second filter screens can filter groundwater in water-rich silty sand strata, preventing sand and gravel from entering the vertical dewatering well pipe and the lightweight wellpoint dewatering pipe and causing blockage.

[0062] After all pipelines in S320 are laid out, vacuum dewatering pumps are connected to the outer ends of all deep-hole dewatering pipes, all vertical dewatering well pipes, and all lightweight wellpoint dewatering pipes. The vacuum dewatering pumps continuously pump water from the water-rich silty sand strata through the deep-hole dewatering pipes, vertical dewatering well pipes, and lightweight wellpoint dewatering pipes. The water content in the water-rich silty sand strata is then measured. Changes in water content are used to confirm whether the water-rich silty sand strata are self-stable. If the water content is below 12%, the strata are considered self-stable. If the water content is above 12%, pumping must continue to prevent excessive water content, which could lead to collapse or sand inrush during later tunnel construction, causing serious accidents.

[0063] Preferably, valves are installed on the connecting pipelines between the vacuum dewatering pump and the advanced deep-hole dewatering pipe, the vertical dewatering well pipe, and the lightweight wellpoint dewatering pipe to control the dewatering rate.

[0064] S400: Curtain grouting; Several grouting holes are opened on the tunnel excavation face, with a depth of 25-28m and a diameter of 7.5-8cm. Grout is then injected into the grouting holes, with each cycle lasting 24-26m. After grouting, a water-proof curtain is formed around the excavation face, effectively limiting the drainage of water-rich fine sand strata during tunnel excavation and preventing sand inrush or collapse in the water-rich fine sand strata during tunnel excavation.

[0065] After grouting is completed, tunnel excavation begins. Excavation stops at 19-21m, leaving a certain thickness as a stop rock mass for the next grouting. This completes this stage of construction, and the next stage begins, starting construction again from S100, until the water-rich fine sand strata are excavated or the deep-buried tunnel is completed.

[0066] Preferably, there are 83 grouting holes, of which 82 grouting holes are arranged in a circle around one grouting hole, and these 82 grouting holes form multiple annular layers, arranged in 6 layers from the inside out, so that the grout can be evenly distributed in all water-rich fine sand strata within the grouting range, so as to achieve the best water blocking effect with the least amount of grout.

[0067] Furthermore, the grouting material is a cement-water glass two-component grout; wherein, in the cement-water glass two-component grout, the volume ratio of cement grout to water glass is 1:1, the water glass concentration is 40 Baume (Be'=40), and the water glass modulus is 2.410; the mass ratio of water to lime in the cement grout is 1:1. During construction, if the seepage in the grouting hole is large, phosphoric acid chemical grout can be added to increase the viscosity of the cement-water glass two-component grout, making the grouting hole more tightly sealed and reducing the seepage in the grouting hole.

[0068] Example 1

[0069] S100: Determine the location of surface dewatering wells and install drilling equipment;

[0070] Construction workers determine the outline of the tunnel above the tunnel to be built, and use existing equipment (such as excavators, bulldozers, etc.) to level the initial position where the tunnel needs to be built and build a construction platform;

[0071] Construction workers used surveying tools to locate the positions of multiple surface dewatering wells along the tunnel excavation direction, and then marked them. Each marked point was 4m away from the nearest tunnel outline, and the distance between two marked points was 20m.

[0072] Install drilling equipment on the construction platform, that is, build and install the rig at the marked point on the construction platform, keep the rig level, and install the turret, overhead crane and drilling rig on the rig.

[0073] S200: Surface precipitation treatment;

[0074] S210: Drilling well 1 for surface dewatering:

[0075] Start the drilling rig installed in S100, so that the drill rod inside it rotates in a positive cycle and opens a well hole vertically at the marked point. When the opened well hole reaches the set depth, keep the drill rod at that depth and continue to rotate, so that the drill rod makes mud in the drilled well hole, thereby forming a surface dewatering well hole 1 with mud wall protection.

[0076] S220: Continue to rotate the drill rod in the drilling rig, raise the drill rod a certain distance, fix the position of the drill rod, and continue to rotate the drill rod to enlarge the well hole drilled in S210 and remove the debris on the inner wall of the well hole to form surface dewatering well hole 1.

[0077] S230: Water is injected into surface dewatering well 1 in S220 to adjust the mud density, so that the mud density in surface dewatering well 1 is 1.05 g / cm³. 3 With a viscosity of 19s, the drill rod in the drilling rig stopped rotating, and then the drill rod was pulled out of the surface dewatering well hole 1 to complete the slurry preparation.

[0078] After the slurry preparation is completed, continue to inject water to replace the slurry in surface dewatering well 1 until the slurry flowing out of surface dewatering well 1 does not contain mud lumps and the sediment at the bottom of surface dewatering well 1 is less than 30cm, then stop injecting water.

[0079] S240: Construction personnel measure the actual depth of surface dewatering well hole 1 and check whether surface dewatering well hole 1 meets the requirements. If it does not meet the requirements, repeat S220 and S230. If it meets the requirements, install a filter pipe in the corresponding surface dewatering well hole 1 according to the measured depth. During the installation of the filter pipe, when the pipe opening of the surface dewatering well pipe inserted into the surface dewatering well hole 1 is 20cm away from the well opening, connect the next section of surface dewatering well pipe.

[0080] After installation, the height of the filter pipe exposed above the ground is 22cm. Then, gravel is filled in. The gravel is continuously and evenly filled along the outer wall of the filter pipe, and the height of the gravel is 10cm lower than the opening of the filter pipe. The filter pipe is then stably fixed to the surface dewatering well hole. The gravel has a particle size of 3mm and a mud content of 3%.

[0081] Ideally, when the filter pipe is installed inside the surface dewatering well hole 1, a layer of nylon mesh will be wrapped around the outer wall of the filter pipe, and the nylon mesh has a filtration diameter of 100 mesh.

[0082] S250: Collect cohesive soil, break it up, and after breaking it up, the particle size of the cohesive soil is less than 3cm. Slowly fill the broken cohesive soil into the surface water purification well, seal the surface dewatering well, and then connect a water pump to the port of the filter pipe located outside the surface to pump water, so that the groundwater level is lower than the working face inside the tunnel, and then disassemble the water pump.

[0083] S300: Dewatering treatment inside the tunnel;

[0084] S310: As Figure 3 As shown, the tunnel excavation face is divided into three parts from top to bottom: the upper part, the middle part, and the lower part. These parts are excavated to form an upper step, a middle step, and a lower step. The length of each step is 4.5m and the height is 4m. The surfaces of the upper step, the middle step, and the lower step are then leveled to provide a working platform for subsequent construction.

[0085] S320: A drilling rig is installed on the outer side of the tunnel excavation face outline 8. Multiple advanced deep-hole dewatering holes 2 are drilled at an angle along the tunnel excavation direction. The depth of the advanced deep-hole dewatering holes 2 is 24m. The closer each advanced deep-hole dewatering hole 2 is to the tunnel excavation face outline 8, the smaller the distance between the hole opening and the center point of the tunnel excavation face outline 8 (inclination angle is 10°). These advanced deep-hole dewatering holes 2 are arranged in a semi-circular shape around the tunnel excavation face outline 8, with a center-to-center distance of 0.75m between adjacent advanced deep-hole dewatering holes 2. Simultaneously, drilling rigs are also installed on the steps of the upper step 5 and the middle step 6. The drill bits of the drilling rigs are horizontally positioned. The drilling rigs drill into the tunnel excavation face at the steps of the upper step 5 and the middle step 6. Multiple advanced deep-hole dewatering holes 2 are also drilled below the surface of step 6. These advanced deep-hole dewatering holes 2 are horizontally arranged along the tunnel excavation direction and are arranged in a row along the length of the surface of the upper step 5 and the middle step. The distance between two adjacent advanced deep-hole dewatering holes 2 is 0.5m, and the length is 24m. The diameter of the aforementioned advanced deep-hole dewatering holes 2 is 6.5cm. After the drilling of the advanced deep-hole dewatering holes 2 is completed and before the drilling casing is removed, the advanced deep-hole dewatering pipe is first inserted into the borehole. After the dewatering pipe is installed, the casing is pulled out, and coarse sand is slowly filled into the advanced deep-hole dewatering holes 2. The gap between the advanced deep-hole dewatering pipe and the advanced deep-hole dewatering holes 2 is filled by the coarse sand, and the advanced deep-hole dewatering pipe is fixed in the advanced deep-hole dewatering holes 2.

[0086] A vertical dewatering well operation platform is also constructed on the surface of the lower step 7. Drilling equipment is installed on the vertical dewatering well operation platform, and vertical dewatering well holes 4 are drilled on the surface of the lower step 7 using the drilling equipment. The diameter of the vertical dewatering well hole 4 is 20cm and the depth is 8m. The distance between two adjacent vertical dewatering well holes is 8m. After drilling is completed, a vertical dewatering well pipe is installed in the vertical dewatering well hole 4, and coarse sand is filled into the vertical dewatering well hole 4 along the outer wall of the vertical dewatering well pipe to fix the vertical dewatering well pipe in the vertical dewatering well hole 4.

[0087] Lightweight wellpoint dewatering holes 3 are installed at the sidewall locations on the upper step 5, middle step 6, and lower step 7, inclined along the tunnel excavation direction using high-pressure blowers / high-pressure water pumps. The depth of the lightweight wellpoint dewatering holes 3 is 4m, the diameter of the holes is 4.5cm, the distance between two adjacent lightweight wellpoint dewatering holes 3 is 8m, and the inclination is 30°. During the installation process, lightweight wellpoint dewatering pipes are installed inside the lightweight wellpoint dewatering holes 3.

[0088] Preferably, the vertical dewatering well pipe is wrapped with a first filter screen and geotextile, with the geotextile located on the inner layer and the first filter screen on the outer layer; the outer wall of the lightweight well point dewatering pipe is wrapped with a double-layer second filter screen, the material of the first and second filter screens is carbon fiber, the filtration diameter of the first filter screen is 200 mesh, and the filtration diameter of the second filter screen is 100 mesh.

[0089] After all the pipelines in S320 are laid out, vacuum dewatering pumps are connected to the outer ends of all advanced deep hole dewatering pipes, all vertical dewatering well pipes, and all lightweight wellpoint dewatering pipes to carry out continuous pumping.

[0090] The water content in the water-rich silty sand strata was measured; if the sandstone water content was below 12%, it was considered that the sandstone had reached self-stability. If the water content of the surrounding rock was above 12%, pumping was required to continue.

[0091] Preferably, valves are installed on the connecting pipelines between the vacuum dewatering pump and the lightweight wellpoint dewatering pipe, the advanced deep hole dewatering pipe, the vertical dewatering well pipe, and the lightweight wellpoint dewatering pipe to control the dewatering rate.

[0092] S400: Curtain grouting; such as Figure 4 As shown in Figure 5, 83 grouting holes 9 are opened on the tunnel excavation face. Among them, 82 grouting holes 9 are arranged in a circle around 1 grouting hole 9, and these 82 grouting holes 9 form multiple annular layers, arranged in 6 layers from the inside to the outside. The depth of the grouting hole 9 is 26m and the diameter of the grouting hole 9 is 7.6cm. Then, cement-water glass double liquid grout is injected into the grouting hole 9, and the grouting length of each cycle is 25m.

[0093] After grouting is completed, if there is a large amount of water seepage in grouting hole 9, phosphoric acid chemical grout can be added;

[0094] Then, tunnel excavation begins. Excavation stops after 20m, leaving a 5m thick grouting bed for the next grouting. This completes this stage of construction, and the next stage begins, starting construction again from S100, until the water-rich fine sand strata are excavated or the deep-buried tunnel is completed.

[0095] 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 process, method, article, or apparatus.

[0096] 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 method for dewatering construction in water-rich silty fine sand formations, characterized in that, Includes the following steps: S100: Determine the location of surface dewatering wells and install drilling equipment; S200: Surface precipitation treatment; S210: Wellbore: A wellbore with mud slurry wall is formed by drilling a hole at the determined location of the surface dewatering well using drilling equipment. S220: Enlarge the surface precipitation well hole; S230: Inject water into the enlarged surface dewatering well hole to adjust the slurry. After the slurry adjustment is completed, continue to inject water to replace the slurry until the mud flowing out of the surface dewatering well hole does not contain mud lumps, and then stop injecting water. S240: Measure the actual depth of the surface precipitation well hole, install a filter pipe in the surface precipitation well hole according to the actual depth of the surface precipitation well hole, fill it with gravel, and fix the filter pipe. S250: Seal the surface dewatering well holes and connect a water pump to the port of the filter pipe to pump water, so that the groundwater level is lower than the construction working face inside the tunnel; S300: Dewatering treatment inside the tunnel; S310: Divide the tunnel excavation face into three parts from top to bottom and excavate them to form an upper step, a middle step and a lower step, and level the steps of the upper step, the middle step and the lower step; S320: Install a drilling rig near the tunnel excavation face and on the steps of the upper and middle steps, drill advanced deep hole dewatering holes through the drilling rig, install advanced deep hole dewatering pipes, and fill the gap between the advanced deep hole dewatering pipes and the advanced deep hole dewatering holes with coarse sand. That is, a drilling rig is installed on the outer side of the tunnel excavation face outline. Multiple advanced deep-hole dewatering holes are drilled at an angle along the tunnel excavation direction. The closer the advanced deep-hole dewatering hole is to the tunnel excavation face outline, the smaller the distance between the hole opening and the center point of the tunnel excavation face outline. The inclination angle is 10°. The advanced deep-hole dewatering holes in the tunnel excavation direction are arranged in a semi-arc around the tunnel excavation face outline. Meanwhile, drilling rigs are also installed on the surfaces of the upper and middle steps. The drill bits of the drilling rigs are set horizontally. Multiple advanced deep-hole dewatering holes are also drilled on the tunnel excavation surface below the surfaces of the upper and middle steps. The advanced deep-hole dewatering holes on the upper and middle steps are set horizontally along the tunnel excavation direction and are arranged in a row along the length of the surfaces of the upper and middle steps. The depth of the advanced deep-hole dewatering holes is the same. A vertical dewatering well operation platform is constructed on the surface of the lower step. Drilling equipment is installed on the vertical dewatering well operation platform to drill vertical dewatering well holes. Vertical dewatering well pipes are installed in the vertical dewatering well holes and backfilled with coarse sand. Lightweight wellpoint dewatering holes are inclinedly opened on the step surfaces of the upper, middle, and lower steps at positions near the sidewalls, and lightweight wellpoint dewatering pipes are installed in the lightweight wellpoint dewatering holes; S330, vacuum dewatering pumps are connected to the outer ends of the advanced deep-hole dewatering pipes, the vertical dewatering well pipes, and the lightweight wellpoint dewatering pipes to continuously pump water and detect the water content in the water-rich silty fine sand stratum; the change in water content is used to confirm whether the water-rich silty fine sand stratum is self-stable, that is, if the water content of the water-rich silty fine sand stratum is lower than 12%, it is considered that the water-rich silty fine sand stratum has reached self-stable; if the water content of the water-rich silty fine sand stratum is higher than 12%, pumping needs to continue to prevent the water content in the water-rich silty fine sand stratum from exceeding the limit, which could lead to collapse or sand inrush during the later stages of tunnel construction and cause serious accidents. S400: Curtain grouting; Several grouting holes are opened on the tunnel excavation surface, and grout is injected into the grouting holes. After the grouting is completed, the tunnel is excavated. The excavation stops when the tunnel is close to the end of the grouting hole. Then the construction starts again from S100 until the water-rich fine sand strata or the deep-buried tunnel is excavated.

2. The dewatering construction method for water-rich silty fine sand formations according to claim 1, characterized in that, In S230, the density of the prepared mud is 1.0 g / cm3 to 1.1 g / cm3, and the viscosity is 18 to 20 s; after the mud is replaced, the sediment at the bottom of the surface dewatering well is less than 30 cm.

3. The dewatering construction method for water-rich silty fine sand formations according to claim 1, characterized in that, In S240, the height of the water filter pipe exposed above the ground is greater than 20cm.

4. The dewatering construction method for water-rich silty fine sand formations according to claim 1, characterized in that, The gravel has a particle size of 2-4 mm and a mud content of ≤3%; when filling the gravel, the height of the gravel is 10-13 cm lower than the opening of the filter pipe.

5. The dewatering construction method for water-rich silty fine sand formations according to claim 1, characterized in that, In S320, the length of the upper step, the middle step, and the lower step is 4-5m, and the height is 3-5m.

6. The dewatering construction method for water-rich silty fine sand formations according to claim 1, characterized in that, The vertical dewatering well pipe is wrapped with a first filter screen and geotextile, with the geotextile located on the inner layer and the first filter screen on the outer layer; the lightweight wellpoint dewatering pipe is wrapped with a double-layer second filter screen on its outer wall.

7. The dewatering construction method for water-rich silty fine sand formations according to claim 6, characterized in that, The first filter and the second filter are made of carbon fiber, and the first filter has a filtration diameter of 200 mesh and the second filter has a filtration diameter of 100 mesh.

8. The dewatering construction method for water-rich silty fine sand formations according to claim 1, characterized in that, There are 83 grouting holes, of which 82 are arranged in a circle around one grouting hole.

9. The dewatering construction method for water-rich silty fine sand formations according to claim 1, characterized in that, The grouting material is a cement-water glass two-component grout.

10. The dewatering construction method for water-rich silty fine sand formations according to claim 9, characterized in that, In the cement-water glass two-component slurry, the volume ratio of cement slurry to water glass is 1:1, and the mass ratio of water to lime in the cement slurry is 1:1.

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