Construction method for breaking underwater boulder obstacles through lake-penetrating pipe jacking

Abstract

The invention discloses a lake-penetrating pipe-jacking underwater boulder obstacle breaking construction method, and belongs to the technical field of pipe-jacking engineering. Comprising the following core steps that after pipe jacking construction is paused, the range, hardness and burial depth of boulders are determined through combination of sound wave detection and drilling sampling, and a three-dimensional geologic model is constructed through the BIM technology according to exploration data so as to determine the spatial relation between the boulders and a pipe jacking machine; an impact crushing scheme is designed according to boulder parameters, then the pipe jacking machine and jacked pipelines are subjected to graded rollback, and synchronous grouting is conducted to maintain soil pressure balance; the modularized buoyancy tank barges are assembled to build an overwater operation platform; and the boulders are broken through the grading impact technology, micro-expansive cement mortar is poured to seal the holes after hole finishing, the pile casing is pulled out, and finally, a pipe jacking machine conducts re-jacking and monitors jacking force fluctuation. According to the method, the problems of long period, large disturbance and high safety risk in traditional lake-penetrating pipe-jacking boulder treatment are effectively solved, the boulder breaking efficiency and construction safety are remarkably improved, and disturbance to water and lake bed ecology is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of pipe jacking engineering technology, and in particular to a construction method for removing underwater boulder obstacles during pipe jacking across a lake. Background Technology

[0002] In urban pipeline construction, pipe jacking is widely used in pipeline laying projects that cross rivers, lakes, bridges, and buildings because it does not require large-scale surface excavation. However, when pipe jacking passes under lakes, rivers, or other bodies of water, it often encounters isolated boulders or groups of boulders due to the complex geology of the lakebed, causing the pipe jacking machine's cutterhead to jam and preventing further jacking, which becomes a core obstacle to the progress of the project.

[0003] Traditional methods for handling isolated boulders have significant drawbacks: First, surface excavation requires partial drainage of the lake or excavation of the lakebed, which not only takes 30 to 60 days to complete but also severely disturbs the lakebed soil structure, damages the aquatic ecosystem, and is poorly applicable to lakes with a depth exceeding 5 meters. Second, artificial underwater fracturing relies on divers operating underwater, resulting in low efficiency (less than 1 m³ per day). Furthermore, it is ineffective for siliceous rocks with a uniaxial compressive strength >70 MPa, and divers face safety risks such as underwater hypoxia and accidental injury from impact drills. Third, existing fracturing methods lack precise positioning techniques, easily leading to incomplete fracturing or over-fracture, causing subsequent jacking to encounter obstacles or lakebed soil collapse. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a construction method for removing underwater boulder obstacles during pipe jacking across lakes. Through an integrated process of "detection-modeling-protection-fragmentation-repair-verification," the problem of boulder obstacles during pipe jacking across lakes can be solved.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for removing underwater boulder obstacles during pipe jacking across a lake, the specific steps of which are as follows: Suspend pipe jacking construction to locate isolated boulders: Suspend pipe jacking construction, arrange exploration holes in front of the pipe jacking machine, and use sonic detection (such as side-scan sonar) to initially locate the range of isolated boulders. Then, obtain the hardness (uniaxial compressive strength R), burial depth and volume parameters of the isolated boulders by drilling and sampling. The layout of exploration holes should cover the area where isolated boulders may be distributed to ensure that no location is missed. Constructing a 3D geological model: Based on the geological data obtained from the exploration boreholes, draw geological cross-section maps and use BIM technology (such as Revit software) to construct a 3D geological model. The model intuitively presents the shape, volume, and spatial relationship of the boulder with the pipe jacking machine, and clarifies the extent of the boulder intrusion into the pipe jacking tunnel, providing a precise basis for the subsequent impact scheme design.

[0006] Impact scheme design: Based on the volume V of the boulder and the uniaxial compressive strength R, select the impact drill type (e.g., a high-torque impact drill is suitable for high-hardness boulders) and the casing specifications; the diameter of the impact drill hole must be larger than the outer diameter of the pipe jacking machine to ensure that the crushing range covers the boulder and avoid residual boulders from hindering subsequent jacking.

[0007] Protective retraction of the pipe jacking system: Connect the pipe jacking machine to the already jacked pipeline to form a whole to avoid pipeline disassembly during retraction; retract in stages at distances of 1.5 to 2 times the outer diameter of the pipeline. During the retraction process, inject a clay-bentonite-cement-water mixture into the soil chamber in front of the pipe jacking machine to maintain earth pressure balance, prevent lakebed soil collapse, and protect the pipe jacking machine cutterhead and cutters from subsequent impact damage.

[0008] Constructing a floating rock-breaking platform: Standard modular floating barges are assembled to form a floating operation platform; the barge needs to be divided into a steel sheet pile driving and extraction machinery operation area and an impact drilling operation area to ensure that the equipment layout is reasonable and does not interfere with each other; the platform's load-bearing capacity must match the weight of the impact drilling, steel sheet pile machinery and other equipment to avoid the platform tilting during operation. Platform positioning and fixation: Steel sheet piles are driven into the barge to achieve platform positioning. The length of the steel sheet piles must be more than 3 times the water depth, and the ratio of the penetration depth to the cantilever length is controlled at 2:1 to ensure that the platform does not shift during impact operations. The top of the piles is fixed to the barge by welding with chamfered steel plates to further improve the stability of the platform.

[0009] Casing guidance and positioning: A double-layer casing structure is used for guidance. The diameter of the outer casing is more than 0.2m larger than that of the inner casing to form a protective gap. The bottom of the casing is embedded more than 2m into the lake bottom, and the top surface is 1m above the lake water level. This not only prevents lake water and debris from entering the hole, but also ensures the accuracy of the impact direction. Clay balls are backfilled around the casing to enhance the stability of the connection between the casing and the lakebed.

[0010] Staged impact crushing: A three-stage impact process is adopted: The first stage uses a short stroke (<1m) to drill into the periphery of the casing to form a solid mud cake to prevent the borehole wall from collapsing; the second stage uses a normal stroke (2-3m) to crush the main body of the boulder, breaking the hard rock boulder through high-frequency impact; the third stage controls the final borehole depth to ensure that the final borehole depth is at least 0.5m below the bottom elevation of the jacking tunnel to avoid residual boulders; mud slurry is used to protect the wall during the crushing process to maintain stable pressure inside the borehole.

[0011] Sealing and casing removal: After the final hole is accepted, underwater M10 micro-expansion cement mortar is injected to fill the broken pores; the mortar needs to be poured to the bottom of the lake bottom silt layer, and clay balls are backfilled in the silt layer to optimize the soil stability; after the initial setting strength of the mortar reaches the design value, the casing is removed, and all hole construction is completed in sequence.

[0012] Re-jacking acceptance: After all holes are sealed and the mortar reaches its final setting strength, start the pipe jacking machine for re-jacking; during the re-jacking process, monitor the fluctuation of the jacking thrust to ensure that the fluctuation does not exceed 10% of the design value; after the pipe jacking machine successfully passes through the boulder treatment section, dismantle the equipment and leave the site.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) Precise positioning: The combined positioning method of acoustic wave + drilling + BIM modeling has a positioning error of ≤0.5m for isolated boulders, which is far lower than the 2-3m error of traditional methods, greatly reducing ineffective construction.

[0014] (2) High efficiency: The graded impact crusher is suitable for high-hardness boulders and can process 5 to 8 m³ of boulders per day. Compared with the crushing efficiency of <1 m³ per day by artificial diving, it is 5 to 8 times more efficient and the construction cycle is shortened to 10 to 15 days.

[0015] (3) High safety: The entire process is mechanized, eliminating the need for underwater manual operation and eliminating the safety risks to divers; the combination of pipe jacking retreat and grouting reduces the equipment damage rate by more than 90%.

[0016] (4) Environmentally friendly: The floating platform does not require drainage or excavation of the lakebed, and the impact on the turbidity of the lake water is controlled within 5 NTU. The disturbance range of the lakebed soil is ≤1m, which meets the requirements of ecological and environmental protection.

[0017] (5) Low cost: Modular floating boxes can be reused with a turnover rate of ≥5 times. The cost of sealing materials is 30% lower than that of traditional concrete, and the overall construction cost is 20% to 30% lower than that of surface excavation. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a flowchart illustrating the construction method in the embodiments of this application; Figure 2 A schematic diagram of the drilling and hole filling process in front of the tunnel face in this application embodiment; Figure 3 This is a schematic diagram of the plan view of the impact drilling operation on water in the embodiments of this application; Figure 4 This is a schematic cross-sectional view of the impact drilling operation on water in an embodiment of this application; Figure 5 This is a schematic diagram of the pipe jacking machine retraction in an embodiment of this application; Figure 6 This is a schematic diagram of the contour line of the isolated rock range and the impact hole pattern in the embodiment of this application; Figure 7 This is a detailed drawing of the sealing hole in an embodiment of this application.

[0019] Among them, 1 is the pipe jacking machine, 2 is the already jacked pipe, 3 is the boulder, 4 is the exploration hole, 5 is the modular floating barge, 6 is the impact drill, 7 is the steel sheet pile, 8 is the double-layer casing, 9 is the micro-expansion cement mortar, 10 is the clay ball, 11 is the lakebed, and 12 is the water surface. Detailed Implementation

[0020] To make the technical solution of this invention clearer and more operable, a pipe jacking project across a lake in Wuhan is used as an example to further illustrate the implementation process of this invention. This project uses DN1600mm steel pipes with an outer diameter D=1.6m and a total length of 720m. After jacking 141m, it encountered an underwater boulder. The overall construction process follows... Figure 1 The steps shown are as follows, and the specific implementation steps are as follows.

[0021] 1. Suspend pipe jacking construction and locate the boulder. The operation of pipe jacking machine 1 was suspended, and the area around boulder 3 was initially probed using an EdgeTech 4200MP side-scan sonar; then... Figure 2 The exploration borehole 4 is arranged in the following manner in front of the tunnel face: In front of the tunnel face of the pipe jacking machine 1, exploration borehole 4 is arranged at 1m intervals (borehole positions: 1m, 2m, 2.4m, 3m, 5m from the tunnel face). The depth of exploration borehole 4 extends to the bedrock and is 1m lower than the bottom elevation of the pipe jacking machine. For the unconstructed section ahead, exploration borehole 4 is arranged in a zigzag pattern at 10m intervals. The net distance between the borehole and the outer edge of the pipe jacking tunnel is 3m, and the depth is the same as before. The core drilling test showed that the uniaxial compressive strength of the boulder 3 is R=70~116MPa, and the volume is about 25m³.

[0022] 2. Construct a three-dimensional geological model in accordance with Figure 2 Geological cross-section diagrams were drawn using data from borehole 4, and a three-dimensional geological model was constructed using Revit software. The model shows that boulder 3 is an irregular block that intrudes into the working face of pipe jacking machine 1, with the most protruding part penetrating 0.8m into the tunnel, thus clarifying the spatial relationship between boulder 3 and pipe jacking machine 1.

[0023] 3. Impact Scheme Design Based on the parameters of boulder 3 (volume 25 m³, uniaxial compressive strength R = 70–116 MPa), combined with... Figure 6 The outline of the boulder area and the schematic diagram of the impact hole layout are shown. A CK2000 impact drill 6 is selected, with a punching diameter of 1.8m (1.125 times the outer diameter of the pipe of 1.6m, which meets the requirement of 1.05 to 1.2 times). At the same time, a Q235 steel plate rolled into a protective casing 8 with an inner diameter of 1.8m is selected to ensure that the impact and breaking range completely covers the boulder 3 and avoids residual boulder from hindering subsequent jacking. 4. Protective retraction of the pipe jacking system Reference Figure 5The diagram showing the pipe jacking machine's retraction is as follows: First, the pipe jacking machine 1 is connected to the already jacked DN1600mm steel pipe 2 via flanges to prevent the pipe from becoming disconnected during retraction. Then, it is retracted in three steps, with a total retraction distance of 2.5m (1.56 times the outer diameter of the 1.6m pipe, meeting the 1.5 to 2 times requirement). During the retraction process, a clay-bentonite-cement-water mixture is injected into the soil chamber ahead through the grouting port of the pipe jacking machine 1. The grouting pressure is controlled at 0.2 to 0.5MPa to maintain soil pressure balance, prevent the lakebed 11 from collapsing, and protect the cutterhead and cutting tools of the pipe jacking machine 1 from subsequent impact and vibration damage.

[0024] 5. Construct a water-based rock-breaking platform according to Figure 3 The schematic diagram of the impact drilling operation plan shows that barge 5 is assembled using standard modular floating boxes (each floating box measures 3m×4m×1.5m). Every three floating boxes form one barge. Each barge 5 has a plan area of ​​120m² and a load-bearing capacity of 65 tons. One barge is designated as the steel sheet pile driving and extraction machinery operation area, and the other is designated as the impact drilling operation area. The CK2000 impact drill 6 (7000mm×2000mm×7000mm, total weight approximately 6.7t) is installed in the center of the impact drilling operation area to ensure a reasonable equipment layout and sufficient working space.

[0025] 6. Platform Positioning and Fixing Combination Figure 4 The cross-sectional view of the impact drilling operation on water shows that interlocking type IV steel sheet piles 7 are driven into the barge 5. The steel sheet piles 7 are 9m long (the water depth at the construction site is 3m, and the pile length is 3 times the water depth), with a soil penetration depth of 6m and a cantilever length of 3m. The ratio of soil penetration depth to cantilever length is strictly controlled at 2:1. The top of the pile is welded to the barge 5 through a 20mm thick, 150mm×150mm chamfered steel plate with a weld height of 8mm, forming a stable connection structure to ensure that the barge 5 does not shift or tilt during the impact operation.

[0026] 7. Casing guiding and positioning Reference Figure 4 The cross-sectional structure features a double-layered casing (8 layers). The outer casing has a diameter of 2.0m, and the inner casing has a diameter of 1.8m. A 0.2m gap is reserved between the two casings to buffer impact vibration. The casing (8 layers) is lowered into place using sheet pile driving and extraction machinery. Figure 6 The holes K1 to K5 shown (hole position deviation ≤ 100mm) have the bottom of the casing 8 embedded 112.2m into the lake bottom and the top surface 121m above the water surface. Clay balls 10 are symmetrically backfilled around the casing 8 to fill the gap between the casing and the lakebed soil, further enhancing the stability of the casing 8 and preventing lake water and debris from entering the hole.

[0027] 8. Staged impact crushing Start the impact drill 6 and break the isolated rock 3 according to the three-stage process (combined with...) Figure 4 , Figure 6 The drilling process is as follows: In the first stage, a short-stroke (0.8m) drill is used to drill around the 8th perimeter of the casing, forming a solid mud cake on the borehole wall to prevent collapse. In the second stage, a normal stroke (2.5m) is used to break up the main body of the boulder at an impact frequency of 12 times / min. During the breaking process, the mud viscosity is maintained for 18-22 seconds, and the broken rock fragments are carried out through mud circulation. In the third stage, the final borehole depth is controlled to ensure that it is 0.6m below the bottom elevation of the jacking tunnel. After the borehole is completed, a plumb bob is used to... Figure 6 The hole depths at 8 points (uniformly distributed around the holes) of the casing 8 shown were checked to confirm that the depths at all points met the requirement of "≥0.5m below the tunnel bottom".

[0028] 9. Removal of sealing holes and casing Reference Figure 7 The detailed diagram of the borehole sealing process shows that underwater M10 micro-expansion cement mortar 9 is injected into the borehole after the borehole is completed. The mortar mix ratio is cement:sand:water = 1:3:0.4, with the addition of an expansion agent (expansion coefficient 1.1) and a quick-setting agent (initial setting time 10h). The mortar expansion rate is controlled at 0.03%. The pouring surface extends to the bottom of the silt layer 11 at the lake bottom. Clay balls 10 are backfilled in the silt layer section, replacing traditional concrete sealing, which reduces costs and water pollution. After the initial setting strength of mortar 9 reaches the design value (C10 strength), the casing 8 is removed using sheet pile driving and extraction machinery, completing the process sequentially. Figure 6 Construction of five boreholes from K1 to K5. 10. Roofing Inspection After the mortar 9 has set, start the pipe jacking machine 1 for re-jacking. Monitor the jacking thrust using pressure sensors and record that the maximum fluctuation of the jacking force is 8% (≤10%) of the design value. When the pipe jacking machine 1 successfully passes through... Figure 5 After the isolated rock section 3 is treated, the barge 5, impact drill 6 and other equipment are dismantled and removed from the site, and the project resumes normal jacking.

[0029] This embodiment demonstrates that the method of the present invention can complete the treatment of isolated boulders within 12 days without damage to the equipment, and the turbidity change of the lake water is ≤3 NTU. The construction cost is reduced by 25% compared with the traditional surface excavation method, which verifies the efficiency, safety and environmental friendliness of the method.

[0030] Working principle This method achieves efficient handling of isolated boulders through the synergy of multiple technologies: Precise positioning mechanism: Sonic detection enables large-scale boulder search, drilling and sampling obtain precise geological parameters, and BIM 3D modeling transforms abstract geological data into a visual model. The combination of these three elements avoids ineffective construction caused by the ambiguity of traditional positioning and ensures the "targeting" of the impact plan.

[0031] Dual protection mechanism for equipment and environment: staged pipe jacking and retreat avoids impact and vibration damage to equipment, synchronous grouting maintains earth pressure balance and prevents lakebed 11 from collapsing; the floating platform does not require excavation of lakebed 11, and the sealing materials, micro-expansion mortar and clay balls 10, have no environmental pollution, achieving the dual goals of "equipment protection and ecological protection".

[0032] High-efficiency crushing mechanism: The double-layer casing with 8 guides ensures that the impact energy is concentrated on the boulder 3. The graded impact process is adapted to the hardness characteristics of the boulder 3. Short-stroke wall protection, normal-stroke rock crushing, and ultra-deep final hole root cleaning improve efficiency by 3 to 5 times compared with manual crushing, and is especially suitable for high-hardness boulder 3.

[0033] Quality verification mechanism: final hole depth detection at no less than 8 points to ensure complete crushing of boulder 3; monitoring of jacking force to verify construction quality, forming a closed-loop control of "construction-detection-verification" to avoid subsequent jacking risks.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for removing underwater boulders as part of a pipe jacking project across a lake, characterized in that, Includes the following steps: Step (1) Pause pipe jacking construction and locate the boulder: Pause pipe jacking construction, arrange exploration holes in front of the tunnel boring machine, and use sonic detection combined with drilling sampling to determine the range, hardness and burial depth of the boulder; Step (2) Construct a three-dimensional geological model: Fit the shape of the boulder based on the exploration data in step (1) and simulate the spatial relationship between the boulder and the pipe jacking machine; Step (3) Impact scheme design: Select the impact drilling rig type and casing specifications based on the volume V of the boulder and the uniaxial compressive strength R; Step (4) Protective retraction of the pipe jacking system: The pipe jacking machine and the jacked pipe are retracted in stages by a distance L=1.5~2D, where D is the outer diameter of the pipe. Simultaneously, a clay-bentonite-cement-water mixture is injected into the soil chamber to maintain soil pressure balance. Step (5) Construct a floating rock-breaking platform: Assemble a modular floating barge, hoist it onto the top of the boulder to form a floating working platform, and install an impact drill in the center of the barge; Step (6) Platform positioning and fixing: Steel sheet piles are driven into the barge for positioning. The length of the piles is more than 3 times the water depth. The top of the piles is welded to the barge through chamfered steel plates. Step (7) Guiding and positioning of the protective casing: A double-layer protective casing structure is used for guiding and positioning. The diameter of the outer protective casing is more than 0.2m larger than that of the inner casing. The bottom of the protective casing is embedded more than 2m into the lake bottom, and the top surface is 1m above the lake water level. Step (8) Graded impact crushing: Implement three-stage crushing, namely, drilling around the casing with a short stroke of <1m → crushing the main body with a normal stroke of 2~3m → controlling the final hole depth to ≥0.5m below the bottom of the tunnel; Step (9) Sealing and Casing Removal: After the final hole is accepted, underwater M10 micro-expansion cement mortar is injected. After the initial setting strength reaches the design value, the casing is removed and the construction of the next hole is carried out. Step (10) Re-jacking acceptance: After the pipe jacking machine passes through the treatment section, the jacking thrust fluctuation is monitored to be no more than 10% of the design value. After passing through the rock treatment section, the equipment is removed from the site.

2. The method for removing underwater boulder obstacles during pipe jacking across a lake as described in claim 1, characterized in that, In step (1), exploratory holes with a spacing of 1m are arranged in front of the tunnel boring machine. The depth of the exploratory holes extends into the bedrock and is 1m lower than the bottom elevation of the jacking pipe. For the unconstructed section in front of the tunnel boring machine, exploratory holes with a spacing of 10-20m are arranged in a zigzag pattern. The net distance between the exploratory holes and the outer edge of the tunnel is 3m. The depth extends into the bedrock and is 1m lower than the bottom elevation of the jacking pipe.

3. The method for removing underwater boulder obstacles during pipe jacking across a lake as described in claim 2, characterized in that, In step (2), a geological cross-section map is drawn based on the exploration borehole location, and a three-dimensional geological model is constructed using BIM technology. The shape of the boulder and the spatial relationship between the boulder and the pipe jacking machine are analyzed through the model.

4. The method for removing underwater boulder obstacles during pipe jacking across a lake as described in claim 1, characterized in that, In step (3), the selected impact drill has a punching diameter of 1.05 to 1.2 times the outer diameter of the pipe jacking machine.

5. The method for removing underwater boulders during pipe jacking across a lake as described in claim 1, characterized in that, In step (4), when the pipe jacking machine and the jacked pipe are retracted as a whole, the pipe jacking machine is first connected to all the pipes to form a whole, and then retracted in stages and steps. During the retraction process, clay-bentonite-cement-water mixed colloid is injected into the soil chamber in front of the pipe jacking machine, and the grouting pressure is controlled at 0.2 to 0.5 MPa.

6. The method for removing underwater boulders during pipe jacking across a lake as described in claim 1, characterized in that, In step (5), the modular pontoon is assembled from standard units to form a barge. The barge is equipped with a sheet pile driving and extraction machinery operation area and an impact drilling operation area. The plan area of ​​a single barge is not less than 120m² and the load-bearing capacity is not less than 65 tons.

7. The method for removing underwater boulder obstacles during pipe jacking across a lake as described in claim 1, characterized in that, In step (6), lock-type type IV steel sheet piles are used for positioning. The ratio of the depth of the steel sheet pile into the soil to the length of the cantilever is 2:

1. The top of the pile is welded to the barge through a 20mm thick, 150mm×150mm chamfered steel plate with a weld height of 8mm.

8. The method for removing underwater boulders during pipe jacking across a lake as described in claim 1, characterized in that, In step (8), the graded impact crushing process uses mud slurry for wall protection, the mud viscosity is maintained at 18-22s, and the impact frequency is controlled at 10-15 times / min; the inner casing is made of Q235 steel plate, and the hole deviation of the casing is no more than 100mm.

9. The method for removing underwater boulders during pipe jacking across a lake as described in claim 1, characterized in that, In step (9), the underwater M10 micro-expansion cement mortar is mixed with cement:sand:water = 1:3:0.4, the expansion agent is controlled with an expansion coefficient of 1.1, the quick-setting agent is controlled with an initial setting time of no more than 12 hours, the pouring surface reaches the bottom of the lake bottom silt layer, and clay balls are backfilled in the silt layer.

10. The method for removing underwater boulder obstacles during pipe jacking across a lake as described in claim 1, characterized in that, In step (8), after the hole is closed, a plumb bob is used to check the hole depth at different points on the casing. There are no fewer than 8 check points to ensure that the hole depth is at least 0.5m below the bottom elevation of the jacking tunnel.

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