Construction method of short-distance entry section of bar-pulling pipe in sandbar

Abstract

The application discloses a sandbank short-distance entry section pipe-pulling construction method, which comprises the following steps: S1, preparation before construction; S2, measurement and lofting; S3, well chamber foundation pit construction; S4, equipment positioning and guide drilling; S5, hole expansion and mud hole blocking; S6, secondary hole expansion and hole cleaning; S7, pipe welding, pipe pulling back, and high-pressure grouting; S8, mud cleaning, pipe cutting at the well access, and equipment transfer; and S9, well chamber construction, foundation pit backfilling and cleaning. The application makes full use of the sandbank short-distance entry section pipe-pulling construction method, reasonably uses the trenchless technology to solve the problems of one-end construction site obstruction, pipe-pulling pipe hole forming failure, pipe-pulling construction resistance being too large, pipe deformation being affected by flowing sand and water level, sand surface appearing grouting and settlement, and the like, solves the problems of high cost and inability to carry out pipe jacking construction under the condition of shallow covering, and realizes the pipe-pulling construction of the entry section.

Description

Technical Field

[0001] This invention relates to the field of drainage engineering pipe laying technology, specifically to a method for laying pipes in short-distance access sections in sandbars, and to measures and methods for successful construction of access sections in sandbars using pipe laying, suitable for the sandbar environment. Background Technology

[0002] With rapid urban development and continuous construction of infrastructure, the area of ​​urban water bodies is decreasing, leading to an increase in urban drainage projects. However, as buildings become increasingly dense in cities, open-cut excavation can significantly impact existing underground pipelines, traffic, and the environment. Therefore, trenchless pipe laying technology is being widely adopted.

[0003] During the construction of the access well section across obstacles in the sandbar geological and hydrological environment of the Yuliangzhou and Dengcheng Avenue projects in Xiangyang City, it was found that the well spacing was 15-45m, the design elevation of the well chamber bottom was 1.5-3.8m lower than the original ground surface, the normal groundwater level was 0.2m below the pipeline bottom elevation, and the 1.8m below the surface consisted of silty clay and fine sand, followed by a gravel layer. HDPE pipes were used, with diameters ranging from 400mm to 800mm. The following difficulties were encountered during construction: 1) The access well chamber was close to the structure, and there was no effective working surface at the pipe entry end. 2) The soil was gravelly, making borehole formation impossible. 3) The borehole expansion was affected by pebbles and gravel, resulting in reduced pullback speed, excessive grouting volume, and grout seepage at the ground surface. 4) The HDPE pipes were flexible, and bending deformation was likely to occur under stress and disturbance. 5) Drilling fluid is composed of water, bentonite, and polymers. It is not advisable to add cement or other hardeners, as this can easily cause drill pipe blockage. Etc.

[0004] Therefore, there is an urgent need to find a method for successful construction of the pipe-drawing process in sandy environments and access well sections, in order to control grout leakage, reinforce the pipes, reduce the number of grouting sections, and reduce drag friction, so as to successfully implement the pipe-drawing process. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for constructing short-distance access sections of pipes in sandy areas. This method solves problems such as obstructed construction sites at one end, excessive resistance during pipe laying due to the inability to drill holes, pipe deformation caused by quicksand and water levels, and grout leakage and settlement on sandy surfaces. This method enables the use of pipe laying for access sections.

[0006] The main construction process adopted in this invention is as follows: construction preparation → surveying and setting out → well chamber foundation pit construction → equipment positioning and directional drilling → hole enlargement and mud filling → secondary hole enlargement and hole cleaning → pipe welding, pipe pullback and high-pressure grouting → mud cleaning, pipe cutting at the well connection point, and equipment transfer → well chamber construction and foundation pit backfilling.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The construction method for short-distance pipe laying in sandbars includes the following steps:

[0009] S1, Pre-construction preparation: planning and design and material preparation;

[0010] S2, Measurement and Layout: Based on the design plan, measure and lay out the on-site machine location, well location, support structure line position, drill pipe line position, and pipeline center and edge line.

[0011] S3, Well chamber foundation pit construction: Steel sheet pile structure and jet grouting pile construction are carried out for the well chamber foundation pit at the pipe inlet end and the well access pit according to the layout line and point. Then, while excavating, the jet grouting piles at the support port of the dragging pipeline are reinforced until the bottom of the pipe. Grouting reinforcement is carried out in the area below the bottom of the foundation pit. After solidification, the surface laitance is cleaned and the well chamber bottom plate is constructed. The area around the bottom plate is used as a mud and water storage area.

[0012] S4, Equipment positioning and guide drilling: The dragging pipe equipment is precisely positioned at the well pit end according to the required drilling rod entry angle. Align it with the predetermined hole position and use a small arrow-shaped drill bit that is slightly larger than the outer diameter of the drill rod to drill a guide hole. The drill rod is drilled from the ground. Control the direction and depth of the drill bit to drill an accurate positioning guide hole until the drill rod is precisely drilled into the well pit at the pipe end.

[0013] S5, Enlargement and Mud Filling: Install a fishtail or three-pronged enlargement head in the well chamber at the inlet pipe end. Use a staged pullback enlargement method to pull it into the inlet well chamber. The water injection machine continuously injects drilling fluid to form a borehole, squeezing unbroken pebbles and gravel onto the outer wall of the borehole, so that the drilling fluid and the mud mixture formed with fine mud and sand fill the borehole.

[0014] S6, Secondary reaming and cleaning: Start the drill pipe to rotate in place and drill from the access well foundation pit to the well chamber foundation pit of the pipe entry section. Install a fishtail or three-pronged reaming head in the well chamber at the pipe entry end and pull it back in stages for secondary reaming.

[0015] S7, pipe welding, pipe pulling back, and high-pressure grouting: Clean the mud in the pits of both ends of the well chambers, reset the drill rod and drill bit to the pit of the well chamber at the pipe inlet, install the anti-spiral bullet-shaped reamer, rotary joint, grouting plug, and grouting pipe, weld the pipe section and hook out the grouting pipe head from the middle to connect with the grouting machine; then, pull back the pipe section and continuously inject cement grout under high pressure, then weld the pipe, pull back the pipe, and perform high-pressure grouting in sequence until the pipeline between the two well chambers is pulled into place;

[0016] S8, mud cleaning, wellhead pipe cutting, and equipment transfer;

[0017] S9, well chamber construction, foundation pit backfilling and cleaning.

[0018] Furthermore, in step S1, the pre-construction preparation steps are as follows:

[0019] Prepare for trajectory design, drilling fluid preparation, and testing of pipes and welded joints;

[0020] The horizontal section of the towing pipe is positioned between the two well chambers. The foundation pit support meets the construction requirements of the towing pipe. The drilling fluid ratio meets the requirements of the towing speed and the solidification of the sand. The ring stiffness of the pipe and the pull-out resistance of the welded joints meet the requirements of the pipeline's resistance to deformation and damage.

[0021] Furthermore, in step S3, while excavating, the jet grouting piles at the support port of the dragging pipeline are reinforced until 20cm below the bottom of the pipe, and the bottom of the foundation pit is reinforced with grouting to a depth of ≥1.5m. After solidification, the surface laitance is cleaned up to ≥5cm.

[0022] Furthermore, in step S4, the pipe-pulling device is precisely positioned at the wellhead pit end according to the requirement that the drill pipe entry angle be ≤15°.

[0023] Furthermore, in step S5, the method of graded back-pulling for borehole enlargement is as follows: different sizes of enlargement heads (such as enlargement heads of 25%, 50%, 75%, and 100% of the final borehole diameter) are used sequentially to pull the borehole head from the inlet end well chamber pit into the inlet well foundation pit. The enlargement head is removed, and the drill rod is drilled into the inlet end well chamber pit in the opposite direction to replace it with a higher-level enlargement head. The process is repeated back and forth to enlarge the borehole step by step, squeezing the pebbles and gravels in the sand into the borehole wall soil layer. The fine sand, silt and slurry are mixed to form a mud slurry that fills the cylinder of the borehole (the borehole filling soil).

[0024] Form a borehole with a diameter ≥ 1.6 times the pipe diameter and ≥ pipe diameter + 50 cm.

[0025] Furthermore, in step S6, the method of graded back-pulling reaming is as follows: start the drill pipe to idle in place, drill the drill pipe from the access well foundation pit to the well chamber foundation pit of the pipe section, and use different reaming heads of different sizes (such as reaming heads of 25%, 50%, 75%, and 100% of the final hole diameter) to pull the drill pipe from the well chamber foundation pit of the pipe section into the access well foundation pit in sequence, remove the reaming head and drill the drill pipe into the well chamber foundation pit of the pipe section in the opposite direction to replace it with a higher-level reaming head, and pull back and forth repeatedly to gradually enlarge the hole, reduce the back-pulling resistance of the reaming hole, and ensure the hole diameter.

[0026] The secondary reaming stage results in a borehole diameter of 1.0 to 1.2 times the pipe diameter.

[0027] Furthermore, in step S6, during the secondary reaming, a zipper is installed at the tail of the drill bit. When the drill hole is re-reamed and reaches the working pit, the reaming drill bit is removed, and a mud-pulling disc is installed at one end of the zipper to pull it back and forth to the access well to perform mud-pulling and hole-forming work, forming a smooth and round pipe-laying channel.

[0028] Furthermore, in step S7, the diameter of the anti-spiral bullet-shaped reamer is 1.0 to 1.2 times.

[0029] Further, in step S7, the high-pressure grouting uses a cement-water glass (sodium silicate)-fly ash grout, with a cement grout:water glass solution:fly ash grout ratio of 6:2:1 (volume ratio). It requires the addition of 2-3% retarder, 1-2% micro-expansion agent, and 1-2% anti-permeability agent by weight of cement. The water-cement ratio of the cement grout is preferably 0.75-1.2, the water glass content is 35-40 Be′, and the grouting pressure is 3-5 MPa. Preferably, the cement grout:water glass solution:fly ash grout ratio is 6:2:1 (volume ratio).

[0030] Furthermore, step S8 is as follows:

[0031] Clean the mud piled up in the foundation pits of both ends of the well chamber to the vicinity of the foundation pit of the inlet well chamber, cut off the grouting plug pulled to the foundation pit of the access well, remove the enlarged hole head, pull the drill rod back to the drilling rig and transfer the equipment.

[0032] Furthermore, step S9 is as follows:

[0033] The well chamber floor slab was thoroughly cleaned and the structure was constructed. Next, the foundation pit was backfilled in layers while the support structure was dismantled. The pipe section backfilled in the foundation pit at the pipe inlet end was wrapped with mud piled nearby. Subsequently, the site was cleaned and restored.

[0034] The beneficial effects of this invention are:

[0035] This invention fully utilizes the short-distance pipe-dragging construction method for access sections in a sandbar, and rationally uses trenchless technology to solve problems such as obstruction at one end of the construction site, inability to drill holes in the pipe leading to excessive resistance during dragging construction, pipe deformation due to quicksand and water level, and grout leakage and settlement on sandy soil surfaces. It also solves the problem of not being able to carry out pipe jacking construction in cases of shallow soil cover and the high cost, and realizes the use of pipe-dragging construction for access sections.

[0036] The method provided by this invention employs a two-stage borehole enlargement process. The first enlargement stabilizes the loose sand into a cylindrical soil mass, while the second enlargement utilizes the soil mass created in the first enlargement to remove the more moist core soil, thus creating a stable borehole. The first enlargement can also push larger pebbles and gravels to the outer layer, avoiding disturbance to the soil mass caused by the second enlargement and cleaning process, and preventing scraping of the pipeline, thereby greatly ensuring the construction quality of the pipeline.

[0037] The method provided by this invention forms two layers of protection and reinforcement around the pipeline, effectively solving the problems of buoyancy and flexural deformation caused by temporary water rise. Simultaneously, it reduces resistance during dragging construction and mitigates the risks associated with using small pipe sections with multiple welded joints due to space constraints.

[0038] The method provided by this invention is simple and easy to implement, can meet the actual site conditions, and has significant effects in controlling ground grouting, reinforcing pipelines, reducing grouting sections, and reducing drag friction. It also reduces the impact of construction on the surrounding environment, and is low in cost and safe and reliable. Attached Figure Description

[0039] Figure 1 This is a top-down view of the towing process.

[0040] Figure 2 This is a schematic diagram of secondary hole enlargement;

[0041] Figure 3 This is a schematic diagram of the pull-back pipe (top view);

[0042] Figure 4 This is a schematic diagram (side view) of the pull-back pipe;

[0043] Figure 5 This is a schematic diagram of secondary hole enlargement;

[0044] Figure 6 This is a schematic diagram of a grouting plug;

[0045] In the picture:

[0046] 1-Sheet pile, 2-Jet grouting pile, 3-Well chamber bottom plate, 4-Warden, 5-Curve stone, 6-Wall, 7-Drill rod, 8-Grouting soil layer, 9-Enlarging head, 10-Secondary enlarging hole wall, 11-Welding device, 12-Pipe section, 13-Grouting pipe, 14-Rotary joint, 15-Reverse jet elbow, 16-Screw, 17-HDPE pipe, 18-Pebble, gravel, 19-Cylinder (hole-supporting soil), 20-Secondary enlarging, 21-Grouting coating layer. Detailed Implementation

[0047] The invention will be further illustrated below with specific examples, but the scope of the invention is not limited thereto.

[0048] Figures 1-3 In the middle, the left side is the inlet manhole, and the right side is the access manhole.

[0049] Example

[0050] The construction method for short-distance pipe laying in sandbars includes the following steps:

[0051] S1. Pre-construction preparation: Before construction, complete relevant preparations such as trajectory design, drilling fluid ratio, and pipe and welded joint testing to ensure that the horizontal section of the towing pipe is located between the two well chamber pits, the pit support meets the needs of towing pipe construction, the drilling fluid ratio meets the needs of towing speed and solidified sand, and the pipe ring stiffness and welded joint pull-out resistance meet the needs of pipeline deformation and damage.

[0052] S2, Measurement and Layout: According to the optimized implementation plan, conduct on-site measurement and layout of machine positions, well positions, support structure lines, drill pipe lines, and pipeline center and edge lines.

[0053] S3, well chamber foundation pit construction, such as Figure 1 As shown: Steel sheet piles 1 and jet grouting piles 2 are constructed according to the layout lines and points of the inlet well pit and the access well pit. Then, while excavating, the jet grouting piles 2 at the support port of the drag pipeline are reinforced until 20cm below the bottom of the pipe. The bottom of the pit is reinforced with grouting to a depth of ≥1.5m. After solidification, the surface laitance of ≥5cm is cleaned. A diversion ditch can be made around the perimeter for easy cleaning later. The bottom slab of the well is constructed, and the perimeter of the bottom slab is used as a mud and water storage area.

[0054] S4. Equipment Positioning and Guide Drilling: After the tow pipe equipment is in place, align it with the designated hole position. Use a small arrow-shaped drill bit, slightly larger than the outer diameter of drill rod 7, to drill a guide hole. Drill rod 7 is then drilled from the ground. The drilling position is determined based on the required angle of the drill rod's inclined section and the available space. Water injection drilling may be used as needed. The surface instruments receive signals from the transmitter inside the underground drill bit, controlling the direction and depth of the drill bit to create an accurate positioning guide hole until the drill rod precisely enters the well chamber pit at the pipe end. During drilling, use light pressure and slow rotation, carefully controlling the drill bit temperature to prevent overheating of the probe.

[0055] S5, Enlargement and Mud Filling: Install a fishtail or three-pronged enlarger head 9 in the well chamber at the inlet pipe end. Use a staged pullback enlargement method. The water injection machine continuously injects drilling fluid. The enlargement should be carried out at a uniform and slow speed to form a borehole with a diameter ≥ 1.6 times the pipe diameter and ≥ pipe diameter + 50 cm. The unbroken pebbles and gravels are squeezed to the outer wall of the borehole, and the mud mixture formed by the drilling fluid and mud fills the borehole.

[0056] The pipe diameter refers to the diameter of the pull-back pipe, i.e., the diameter of the construction pull-back pipe.

[0057] S6, secondary hole enlargement and cleaning, such as Figure 2 As shown: After standing for 48 hours, clean up the mud flowing out of both well chambers; then, start the drill pipe and idle for 3 minutes in place, drill from the access well foundation pit to the pipe section well chamber foundation pit, install a fishtail or three-pronged reamer 9 in the pipe end well chamber, and pull back the hole in stages to form a borehole diameter of 1.0 to 1.2 times the pipe diameter (such as 400mm, 500mm, 600mm, 800mm, etc.). If the resistance is large, use a water injection machine to inject a small amount of drilling fluid for secondary reaming; then, during the reaming, install a zipper (rod) at the end of the drill bit. When the borehole reaches the working pit, remove the reamer drill bit, replace the mud-pulling disc at one end of the zipper (rod) and pull it back and forth to the access well to perform mud-pulling hole-forming work, forming a smooth and round pipe installation channel.

[0058] S7, Pipe Welding, Pipe Retraction, and High-Pressure Grouting: Clean the mud from the pits at both ends of the well chambers. Reposition the drill rod and drill bit to the pit at the pipe inlet. Install a reverse spiral bullet-shaped reamer with a diameter of 1.0 to 1.2 times the pipe diameter, rotary joint 14, grouting plug, and grouting pipe. Weld the pipe section and hook out the grouting pipe head from the middle to connect it to the grouting machine. Next, pull back the pipe section and continuously inject cement grout under high pressure. Then, weld the pipe, pull back the pipe, and perform high-pressure grouting in sequence until the pipeline between the two well chambers is pulled into place. Figure 3 , Figure 4 A schematic diagram of the pullback pipe is shown.

[0059] S8, Mud Cleaning, Pipe Cutting at Well Access Point, and Equipment Transfer: Clean the mud piled up in the well chamber pits at both ends and move it to the vicinity of the well chamber pit at the pipe access end. Cut off the grouting plug pulled to the well access pit, remove the enlarged hole head, pull the drill rod back to the drilling rig, and transfer the equipment.

[0060] S9, Well Chamber Construction and Foundation Pit Backfilling: Clean the well chamber floor slab and construct the structure; then, backfill the foundation pit in layers while dismantling the support structure. The pipe section backfilled in the foundation pit at the pipe inlet end of the well chamber is backfilled and wrapped with mud piled nearby; subsequently, the site is cleaned and restored.

[0061] As a specific embodiment, in step S4, the pipe-pulling device is precisely positioned at the wellhead pit end according to the requirement that the drill pipe entry angle be ≤15°.

[0062] As a specific embodiment, the step S5 method of graded hole enlargement is as follows: different sizes of enlargement heads (such as enlargement heads of 25%, 50%, 75%, and 100% of the final hole diameter) are used sequentially to drag from the well chamber pit at the inlet end to the well foundation pit. The enlargement head is removed and the drill rod is drilled into the well chamber pit of the inlet section in the opposite direction to replace the enlargement head of a higher grade. The process is repeated back and forth to enlarge the hole step by step, squeezing the pebbles and gravels in the sand into the soil layer of the hole wall. The fine sand, silt and slurry are mixed to form a mud slurry that fills the cylinder of the hole (the soil filling the hole).

[0063] Form a borehole with a diameter ≥ 1.6 times the pipe diameter and ≥ pipe diameter + 50 cm. The pipe diameter refers to the diameter of the pull-back pipe, i.e., the diameter of the construction pull-back pipe.

[0064] As a specific embodiment, the method for staged hole expansion in step S6 is as follows:

[0065] Start the drill pipe to idle in place, and drill the drill pipe from the access well foundation pit to the well chamber foundation pit of the pipe section. Then, use different reaming heads of different sizes (such as reaming heads of 25%, 50%, 75%, and 100% of the final hole diameter) to pull the drill pipe from the well chamber foundation pit of the pipe section into the access well foundation pit. Remove the reaming head and reverse the drill pipe to drill into the well chamber foundation pit of the pipe section. Replace with a reaming head of a higher size. Pull back and forth repeatedly to gradually enlarge the hole, reduce the resistance of the reaming pullback, and ensure the hole diameter.

[0066] The secondary reaming process, which involves staged pullback, results in a borehole diameter of 1.0 to 1.2 times the pipe diameter (e.g., 400mm, 500mm, 600mm, and 800mm pipe diameter models).

[0067] As a specific embodiment, the diameter difference of the hole wall formed by the two enlargements, as shown in Figure "10 - Secondary Enlargement Hole Wall", is ≥15cm. Figure 5 As shown.

[0068] As a specific embodiment, the water loss of the drilling fluid and mud should be controlled below 5 ml. During the reaming and mud filling stages, the drilling fluid mix ratio should be 22-28% bentonite, 1-2% fluid transfer agent, 65-72% water, and 2% caustic soda by weight of bentonite. During the secondary reaming stage, the drilling fluid mix ratio should be 30-35% bentonite, 2-3% fluid transfer agent, 56-68% water, and 2% caustic soda by weight of bentonite. All the above ratios are by weight.

[0069] As a specific embodiment, the well chamber pit is arranged with the pipeline as the axis. The distance between the pit wall and the outer wall of the well chamber is ≥0.5m. The excavation depth is 20cm below the bottom of the pipe. The bottom of the pit is reinforced with grout to a depth ≥1.5m. After solidification, the surface laitance is cleaned to a depth of ≥5cm. The strength of the grouting soil layer should be ≥15MPa. It can only be used for bearing load after the strength reaches 75%. The length of the well chamber pit at the pipe inlet end is ≥ pipe section + 2m. The length of the pipe section is 2-5m, preferably 3m.

[0070] As a specific embodiment, in step S5, the hole enlargement and mud filling should be carried out at a uniform and slow speed. A staged hole enlargement head is used to squeeze pebbles and gravel to the outer wall one after another, so that the sand and soil can be fully integrated with the drilling fluid to fill the entire channel. The channel diameter is ≥1.6 times the pipe diameter and ≥ pipe diameter + 50cm, forming a cylinder that can be enlarged a second time.

[0071] In one specific embodiment, in step S6, the secondary reaming and cleaning need to be allowed to stand for 48 hours to allow the cylinder formed by the primary reaming to solidify and stabilize due to water loss. Drilling fluid should not be used for the secondary reaming. If the resistance is too high, 60% to 70% of the grouting volume per unit time can be used. The diameter of the secondary reaming is 1.0 to 1.2 times the pipe diameter.

[0072] As a specific embodiment, in step S7, the anti-spiral bullet-shaped reaming head is bullet-shaped with threads on its outer surface. During the pull-back process, the drill rod should be rotated in the opposite direction so that the reaming head can generate a forward thrust while squeezing the potentially deformable channel, reducing the pulling resistance and pushing the soil out of the hole again, leaving a gap and good bonding for subsequent high-pressure grouting.

[0073] As a specific embodiment, in step S7, the high-pressure grouting uses cement-water glass (sodium silicate)-fly ash grout, with a cement grout:water glass solution:fly ash grout ratio of 6:2:1 (volume ratio). It requires the addition of 2-3% retarder, 1-2% micro-expansion agent and 1-2% anti-permeability agent by weight of cement. The water-cement ratio of cement grout should be 0.75-1.2, the water glass should be 35-40Be′, and the grouting pressure should be 3-5MPa.

[0074] As a specific embodiment, in step S8, the grouting plug is as follows: Figure 6 As shown, it is bullet-shaped, including a straight section and an arc-shaped head section. The straight section has a multi-connector and a reverse-bend nozzle at its tail end. The multi-connector connects to the pressure drop pipe 13, and the other end connects to the reverse-bend nozzle. The reverse-bend nozzle extends from the inside out and connects to the outer wall of the straight section, with 3-6 evenly distributed reverse-bend nozzles. The reverse-bend nozzles are connected by embedded welding. The connection between the grouting plug and the grouting pipe should be fixed to a section of HDPE pipe ≥30cm long using screws, with a fixing width ≥12cm.

[0075] As a specific embodiment, in step S8, the final cleaning of the mud is preferably done manually, and pumping is not recommended. The mud contains cement components and can be used as backfill soil to wrap the backfill section in the well chamber foundation pit at the pipe inlet.

[0076] This invention rationally utilizes the pipe-dragging process to solve the problems of not being able to perform open excavation and pipe jacking construction when crossing obstacles and with shallow overburden. It also solves the problems of large-diameter gravity flow HPDE flexible drainage pipes in terms of elevation control, large construction site area, and inability to drill holes in sandy soil. It has the characteristics of rationally utilizing sandy soil, can reduce pressure relief wells, and lower costs.

[0077] The present invention employs the following technical means to achieve the corresponding technical effects, as detailed below:

[0078] (1) Grouting at the bottom of the foundation pit not only increases the bearing capacity of the foundation, but also creates a good environment for mud cleaning, which facilitates construction in the foundation pit and effectively avoids mud and sand erosion of the foundation.

[0079] (2) Two-stage borehole enlargement is adopted. The first enlargement stabilizes the loose sand into a cylindrical soil body. The second enlargement utilizes the soil body formed by the first enlargement to remove the relatively moist core soil and create a stable borehole. The first enlargement can squeeze larger pebbles and gravels to the outer layer, avoiding disturbance to the soil body caused by the second enlargement and cleaning, and also avoiding scraping of the pipeline, which greatly ensures the construction quality of the pipeline.

[0080] (3) The anti-spiral bullet-shaped reaming head has threads on its surface. The direction of the threads is opposite to that of the rotating drill rod during the pull-back process. This allows the reaming head to restore the deformable hole while generating a forward thrust in the opposite direction, reducing the dragging resistance and pushing the soil out of the hole again, leaving a gap and good bonding for subsequent high-pressure grouting.

[0081] (4) The grouting plug with a reverse-bend nozzle can evenly inject grout into the voids around the pipe. The pore walls formed by the two-stage borehole expansion hinder the grout from seeping into the sand, creating high pressure within the voids and ensuring the grout effectively fills them. The grout creates suspension pressure during pipe dragging and generates forward thrust through the reverse-bend nozzle, reducing frictional resistance during pipe dragging. Subsequent grout solidification reinforces the pipe body and enhances its resistance to deformation.

[0082] (5) This method forms two layers of protection and reinforcement around the pipeline, effectively addressing the impact of temporary water rise on the pipeline's resistance to buoyancy and flexural deformation. The two layers of protection include: the first layer, the secondary borehole wall formed by the primary and secondary borehole expansion; and the second layer, the grout coating layer formed by high-pressure grouting around the pipeline during the pullback process. Simultaneously, by reducing resistance during the pullback construction, the risk of using small pipe sections with multiple welded joints due to space constraints is reduced.

[0083] (6) The effective construction section of the dragging is located between the two well chambers, reducing the ineffective construction sections of the grouting section and the skewing section, reducing construction costs and environmental impact.

[0084] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the invention.

Claims

1. A method for constructing short-distance pipe-drawing sections for household access in sandbars, characterized in that: Includes the following steps: S1, Pre-construction preparation: planning and design and material preparation; S2, Measurement and Layout: Based on the design plan, measure and lay out the on-site machine location, well location, support structure line position, drill pipe line position, and pipeline center and edge line. S3, Well chamber foundation pit construction: Steel sheet pile structure and jet grouting pile construction are carried out for the well chamber foundation pit at the pipe inlet end and the well access pit according to the layout line and point. Then, while excavating, the jet grouting piles at the support port of the dragging pipeline are reinforced until the bottom of the pipe. Grouting reinforcement is carried out in the area below the bottom of the foundation pit. After solidification, the surface laitance is cleaned and the well chamber bottom plate is constructed. The area around the bottom plate is used as a mud and water storage area. S4, Equipment positioning and guide drilling: The dragging pipe equipment is precisely positioned at the well pit end according to the required drilling rod entry angle. Align it with the predetermined hole position and use a small arrow-shaped drill bit that is slightly larger than the outer diameter of the drill rod to drill a guide hole. The drill rod is drilled from the ground. Control the direction and depth of the drill bit to drill an accurate positioning guide hole until the drill rod is precisely drilled into the well pit at the pipe end. S5, Enlargement and Mud Filling: Install a fishtail or three-pronged enlarger head in the well chamber at the inlet pipe end. Use a staged pullback enlargement method to pull it into the inlet chamber. The water injection machine continuously injects drilling fluid and slowly pulls back the rotating drill rod to squeeze the unbroken pebbles and gravel to the outer wall of the borehole in stages, so that the drilling fluid and the mud mixture formed with fine mud and sand fill the borehole. S6, Secondary reaming and cleaning: Start the drill pipe to rotate in place and drill from the access well foundation pit to the well chamber foundation pit of the pipe entry section. Install a fishtail or three-pronged reaming head in the well chamber at the pipe entry end and pull it back in stages for secondary reaming. S7, pipe welding, pipe pulling back, and high-pressure grouting: Clean the mud in the pits of both ends of the well chambers, reset the drill rod and drill bit to the pit of the well chamber at the pipe inlet, install the anti-spiral bullet-shaped reamer, rotary joint, grouting plug, and grouting pipe, weld the pipe section and hook out the grouting pipe head from the middle to connect with the grouting machine; then, pull back the pipe section and continuously inject cement grout under high pressure, then weld the pipe, pull back the pipe, and perform high-pressure grouting in sequence until the pipeline between the two well chambers is pulled into place; S8, mud cleaning, wellhead pipe cutting, and equipment transfer; S9, well chamber construction, foundation pit backfilling and cleaning.

2. The method for constructing short-distance access pipe sections in sandbars according to claim 1, characterized in that: In step S1, the pre-construction preparation steps are as follows: Prepare for trajectory design, drilling fluid preparation, and testing of pipes and welded joints; The horizontal section of the towing pipe is positioned between the two well chambers. The foundation pit support meets the construction requirements of the towing pipe. The drilling fluid ratio meets the requirements of the towing speed and the solidification of the sand. The ring stiffness of the pipe and the pull-out resistance of the welded joints meet the requirements of the pipeline's resistance to deformation and damage.

3. The method for constructing short-distance access pipe sections in sandbars according to claim 1, characterized in that: In step S3, while excavating, the jet grouting piles at the support port of the drag pipeline are reinforced until 20cm below the bottom of the pipe, and the bottom of the foundation pit is reinforced with grouting to a depth of ≥1.5m. After solidification, the surface laitance is cleaned up to ≥5cm.

4. The method for constructing short-distance access pipe sections in sandbars according to claim 1, characterized in that: In step S5, the method of graded back-pulling and hole enlargement is as follows: different hole enlargement heads are used in sequence to pull the drill rod from the well chamber pit at the inlet end of the pipe into the well foundation pit. The enlargement head is removed and the drill rod is drilled into the well chamber pit at the inlet end of the pipe in the opposite direction to replace the enlargement head of the next larger size. The hole is enlarged step by step by pulling back and forth. The pebbles and gravels in the sand are squeezed into the soil layer of the hole wall. The fine sand, silt and slurry are mixed to form mud and soil to fill the cylinder of the hole. After the hole is enlarged, a hole with a diameter ≥ 1.6 times the pipe diameter and ≥ pipe diameter + 50 cm is formed.

5. The method for constructing short-distance access pipe sections in sandbars according to claim 1, characterized in that: In step S6, the method of graded back-pulling and hole enlargement is as follows: start the drill rod to rotate in place, drill the drill rod from the access well foundation pit to the well chamber foundation pit of the pipe section, and use different diameter hole enlargement heads to pull the drill rod from the well chamber foundation pit of the pipe section into the access well foundation pit in sequence. Remove the hole enlargement head and drill the drill rod in the opposite direction into the well chamber foundation pit of the pipe section to replace the hole enlargement head of the next larger size. Pull back and forth repeatedly to enlarge the hole step by step. The secondary reaming stage results in a borehole diameter of 1.0 to 1.2 times the pipe diameter.

6. The method for constructing short-distance access pipe sections in sandbars according to claim 1, characterized in that: In step S6, during the secondary reaming, a zipper is installed at the tail of the drill bit. When the drill hole is re-reamed and reaches the working pit, the reaming drill bit is removed, and a mud-pulling disc is installed at one end of the zipper to pull it back and forth to the access well to perform mud-pulling and hole-forming work, forming a smooth and round pipe-laying channel.

7. The method for constructing short-distance access pipe sections in sandbars according to claim 1, characterized in that: In step S7, the diameter of the anti-spiral bullet-shaped reamer is 1.0 to 1.2 times.

8. The method for constructing short-distance access pipes in sandbars according to claim 1, characterized in that: In step S7, the high-pressure grouting uses cement-water glass-fly ash grout, with the volume ratio of cement grout, water glass solution, and fly ash grout being (4.5-7.5):(1.5-3):

1. It requires the addition of 2-3% retarder, 1-2% micro-expansion agent, and 1-2% anti-permeability agent by weight of cement. The water-cement ratio of the cement grout should be 0.75-1.2, the water glass should be 35-40Be′, and the grouting pressure should be 3-5 MPa.

9. The method for constructing short-distance access pipe sections in sandbars according to claim 1, characterized in that: The steps of step S8 are as follows: Clean the mud piled up in the foundation pits of both ends of the well chamber to the vicinity of the foundation pit of the inlet well chamber, cut off the grouting plug pulled to the foundation pit of the access well, remove the enlarged hole head, pull the drill rod back to the drilling rig and transfer the equipment.

10. The method for constructing short-distance access pipe sections in sandbars according to claim 1, characterized in that: The steps of step S9 are as follows: The well chamber floor slab was thoroughly cleaned and the structure was constructed. Next, the foundation pit was backfilled in layers while the support structure was dismantled. The pipe section backfilled in the foundation pit at the pipe inlet end was wrapped with mud piled nearby. Subsequently, the site was cleaned and restored.

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