Overwater cast-in-situ bored pile construction method for unfavorable geology

Abstract

The invention discloses an overwater cast-in-situ bored pile construction method aiming at unfavorable geology, and belongs to the technical field of overwater foundation engineering construction.According to the overwater cast-in-situ bored pile construction method aiming at unfavorable geology, the geological condition of the pile foundation position can be accurately mastered through pile-by-pile advanced drilling, and a reliable basis is provided for subsequent construction; and the construction risk caused by unknown geological conditions is avoided. A three-dimensional geologic model is established, dynamic adjustment of the mud proportion and drilling parameters can be guided, and the construction efficiency and the hole forming quality are improved. Aiming at different stratum conditions, a layered control drilling machine percussion drill is adopted, and a double-wall steel casing is combined for use, so that hole wall collapse and drill hole deflection can be effectively prevented, and the hole forming stability is ensured. And shrinkage compensation concrete is adopted, shrinkage cracks of the pile body are reduced, and the durability and bearing capacity of the pile foundation are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of water-based foundation engineering construction, and in particular to a construction method for underwater bored cast-in-place piles for poor geological conditions. Background Art

[0002] The bored cast-in-place pile process commonly used in the current industry mainly has three major technical bottlenecks: Firstly, in terms of geological prediction, conventional advanced drilling uses discrete exploration with a spacing of 30 - 50m, and the recognition accuracy of the spatial distribution characteristics of karst caves is insufficient. Especially in the judgment of the connectivity of karst pipelines, the error rate reaches more than 40%. During the construction process, there is a lack of a real-time geological radar monitoring system, and it is impossible to dynamically adjust the drilling parameters. As a result, among the pile foundation accidents in the karst cave area counted in the past three years, 78% are caused by sudden slurry leakage leading to the instability of the hole wall. Secondly, in terms of the hole wall stability technology level, the dynamic plasticity ratio of the traditional sodium-based bentonite mud system in the fluidized silt layer is only 0.3 - 0.5 Pa / mPa·s, and it is difficult to form an effective hole protection structure. When encountering a fractured zone with a permeability coefficient greater than 10⁻³ cm / s, the slurry leakage rate can reach more than 5 m³ / h, resulting in a hole wall collapse accident rate as high as 22%. Especially in waters with significant water level differences, the fluctuation of the water head difference inside and outside the hole leads to the deterioration of the performance of the hole protection slurry. In the past five years, the proportion of pile body diameter reduction defects caused by this has reached 31%. Thirdly, there are obvious defects in the concrete pouring process. The existing conduit method construction has insufficient adaptability to complex strata. When passing through multiple karst caves, the fluidity loss of the concrete accelerates, and the initial setting time is shortened by about 30%, which is extremely easy to form muddy and broken piles. Statistics show that in the karst cave development area, the proportion of Class I piles using the conventional pouring process is less than 65%, a decrease of 27 percentage points compared with ordinary strata. In addition, the bond strength between the pile body concrete and the hole wall in the fluidized layer decays by 40% - 60%, resulting in a vertical bearing capacity reduction coefficient of the pile foundation of 0.7 - 0.8.

[0003] The prior art attempts to improve through methods such as grouting reinforcement and steel casing following, but there are significant limitations: The success rate of plugging beaded karst caves by pre-grouting treatment is less than 50%; The full casing following process increases the construction cost by 2 - 3 times and reduces the work efficiency by 40%; The intelligent mud system mostly adopts a single-parameter feedback mechanism and fails to establish a multi-factor coupling regulation model. These technical defects have led to an average construction period delay of 45 days per project caused by geological problems in the water-related pile foundation projects in the past three years, with a direct economic loss exceeding 1.2 billion yuan. Summary of the Invention

[0004] An object of the present invention is to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a construction method for underwater bored cast-in-place piles for poor geological conditions, which can solve the problems of slurry leakage, hole collapse, and unqualified pile body quality.

[0005] The construction method for underwater bored cast-in-place piles for poor geological conditions according to the embodiments of the present invention includes: Step 1: Conduct advanced drilling exploration for each pile foundation one by one. Through the exploration, master the geological conditions of the pile foundation location, record the positions, sizes of karst caves and the thickness of the silt layer; establish a three-dimensional geological model to guide the adjustment of mud proportioning and drilling parameters; Step 2: Install the drilling rig; Step 3: According to the geological conditions, select clay as the mud material, use adjacent steel casing as the temporary mud pit, and conduct mud circulation through the mud circulation system to ensure that the mud performance meets the construction requirements; Step 4: According to different stratum conditions, adjust the stroke and impact frequency of the impact drilling rig, control the relative density and viscosity of the mud, control the impact drilling of the drilling rig in layers, install double-wall steel casing, isolate the flow plastic layer with the inner cylinder and grout to reinforce the edge of the karst cave with the outer cylinder; Step 5: Use the positive and reverse circulation system to clean the hole, remove the drill cuttings at the bottom of the hole, and ensure that the sediment thickness at the bottom of the hole meets the design and specification requirements; Step 6: Fabricate the steel reinforcement cage in sections, and the section length is determined according to the hoisting method and transportation conditions; when installing the steel reinforcement cage, use a crane and a flatbed truck to transport the steel reinforcement cage to the site and install it by a floating crane; Step 7: After the steel reinforcement cage is installed in place, conduct the second hole cleaning to ensure that all the mud indexes meet the specification requirements; Step 8: Use shrinkage-compensating concrete for concrete pouring, dynamically control the buried depth of the conduit, and monitor the height of the concrete surface in real time through ultrasonic waves.

[0006] The construction method of the waterborne bored cast-in-place pile for adverse geology according to the embodiment of the present invention has at least the following beneficial effects: Through advanced drilling exploration for each pile, the geological conditions of the pile foundation location can be accurately mastered, providing a reliable basis for subsequent construction and avoiding construction risks caused by unknown geological conditions. Establishing a three-dimensional geological model can guide the dynamic adjustment of mud proportioning and drilling parameters, improving construction efficiency and hole-forming quality. For different stratum conditions, using layered control of the impact drilling of the drilling rig and combining with the use of double-wall steel casing can effectively prevent hole wall collapse and drilling deviation, ensuring the stability of the formed hole. Using shrinkage-compensating concrete can reduce shrinkage cracks in the pile body and improve the durability and bearing capacity of the pile foundation.

[0007] According to some embodiments of the present invention, in Step 1, during the advanced drilling exploration of the pile foundation, the drilling depth reaches 5m below the designed pile foundation elevation, and the advanced drilling exploration work for each pile is not less than 1 hole.

[0008] According to some embodiments of the present invention, in Step 2, when installing the drilling rig, lay mobile steel rails and sleepers to ensure the stability of the drilling rig.

[0009] According to some embodiments of the present invention, in Step 2, after the drilling rig is in place, adjust and fix the drilling rig to ensure that the deviation between the verticality of the rotary device and the center of the hole position is not greater than 2cm.

[0010] According to some embodiments of the present invention, in step 3, for the flowing and plastic silt layer, high-density mud is used and bentonite and carboxymethyl cellulose are added.

[0011] According to some embodiments of the present invention, in step 3, for the karst cave area, high-viscosity mud is used, and a mixture of clay and riprap is filled synchronously to block the fissures.

[0012] According to some embodiments of the present invention, in step 4, for the flowing and plastic silt layer, the drilling rig uses a small stroke and high-frequency dense hammering to reduce the disturbance to the hole wall.

[0013] According to some embodiments of the present invention, in step 4, for the karst cave area, the clay and riprap are filled first to level the bottom, and the drilling rig uses a medium stroke impact to ensure the flatness of the hole bottom.

[0014] According to some embodiments of the present invention, in step 6, the main reinforcement joints of the steel reinforcement cage adopt mechanical connection, and the welding length is not less than ten times the diameter of the main reinforcement.

[0015] According to some embodiments of the present invention, in step 8, the overpouring height during final grouting is ≥1.5 m to ensure the density of the pile top.

[0016] The additional aspects and advantages of the present invention will be partly given in the following description, partly will become obvious from the following description, or will be understood through the practice of the present invention. Brief Description of the Drawings

[0017] The present invention will be further described below in conjunction with the drawings and embodiments: Figure 1 is a flow chart of the construction method of the water drilling cast-in-place pile for adverse geology in the embodiment of the present invention; Figure 2 is a structural diagram of the hole formation of the drilling cast-in-place pile in the embodiment of the present invention.

[0018] Reference Signs: Impact drilling rig 100; impact bit 110; temporary extended steel casing 200; U-shaped steel plate mud tank 300; implemented drilling steel pipe pile 400; steel pipe pile for temporarily making mud pit 500. Detailed Embodiments

[0019] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as up, down, front, back, left, right, etc., is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0020] In the description of the present invention, "several" means one or more, "multiple" means more than two, and understandings such as "greater than", "less than", "exceeding", etc. do not include the corresponding number, while understandings such as "above", "below", "within", etc. include the corresponding number. If there is a description of "first" and "second", it is only for the purpose of distinguishing technical features and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features or implicitly specifying the sequence relationship of the indicated technical features.

[0021] In the description of the present invention, unless otherwise clearly defined, terms such as "set", "install", "connect", etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific content of the technical solution.

[0022] Reference Figures 1 to 2 Describe the construction method of cast-in-place pile with underwater drilling in bad geological conditions according to an embodiment of the present invention.

[0023] As Figures 1 to 2 As shown, the construction method of cast-in-place pile with underwater drilling in bad geological conditions according to an embodiment of the present invention includes: Step 1: Conduct advanced drilling exploration for each pile foundation one by one, master the geological conditions of the pile foundation position through exploration, record the positions, sizes and thicknesses of the karst caves and the silt layers; establish a three-dimensional geological model to guide the adjustment of mud proportioning and drilling parameters; Step 2: Install the drilling rig; Step 3: Select clay as the mud material according to the geological conditions, use adjacent steel casings as temporary mud pits, and conduct mud circulation through the mud circulation system to ensure that the mud performance meets the construction requirements; Step 4: Adjust the stroke and impact frequency of the impact drilling rig according to different stratum conditions, control the relative density and viscosity of the mud, control the impact drilling of the drilling rig in layers, install double-wall steel casings, isolate the flow plastic layer with the inner cylinder and grout to reinforce the edge of the karst cave with the outer cylinder; Step 5: Use the positive and negative circulation system to clean the hole, remove the drill cuttings at the bottom of the hole, and ensure that the sediment thickness at the bottom of the hole meets the design and specification requirements; Step 6: Fabricate the steel reinforcement cage in sections, and the section length is determined according to the hoisting method and transportation conditions; when installing the steel reinforcement cage, use a crane in cooperation with a flatbed truck to transport the steel reinforcement cage to the site and install it by a floating crane; Step 7: After the steel reinforcement cage is installed in place, conduct a second hole cleaning to ensure that all the mud indexes meet the specification requirements; Step 8: Conduct concrete pouring with shrinkage-compensating concrete, dynamically control the buried depth of the conduit, and monitor the height of the concrete surface in real time through ultrasonic waves.

[0024] As Figure 1 And Figure 2As shown, by conducting advance drilling for each pile, the geological conditions at the pile foundation location can be accurately grasped, providing a reliable basis for subsequent construction and avoiding construction risks caused by unclear geological conditions. Establishing a three-dimensional geological model can guide the dynamic adjustment of mud proportioning and drilling parameters, improving construction efficiency and hole-forming quality. For different stratum conditions, by using a hierarchical control drilling rig's impact drill and combining with the use of double-wall steel casing, the collapse of the hole wall and drilling deviation can be effectively prevented, ensuring the stability of the hole formed. Using expansive compensating concrete can reduce shrinkage cracks in the pile body, improving the durability and bearing capacity of the pile foundation.

[0025] As Figure 2 As shown, the impact drill 100 controls the impact bit 110 to drill the implementation bored steel pipe pile 400. There is a temporary extension steel casing 200 above the implementation bored steel pipe pile 400. The steel casings adjacent to the implementation bored steel pipe pile 400 are used as steel pipe piles 500 for temporarily making a mud pit. There is a U-shaped steel plate mud trough 300 between the implementation bored steel pipe pile 400 and the steel pipe pile 500 for temporarily making a mud pit.

[0026] In step 1, during the advance drilling exploration of the pile foundation, the drilling depth reaches 5 m below the designed pile foundation elevation, and the advance drilling exploration work for each pile is not less than 1 hole.

[0027] In step 2, when installing the drilling rig, moveable steel rails and sleepers are laid to ensure the stability of the drilling rig. By laying moveable steel rails and sleepers, the stability of the drilling rig installation is ensured, reducing errors and accidents caused by the instability of the drilling rig during the construction process.

[0028] In step 2, after the drilling rig is in place, adjust and fix the drilling rig to ensure that the deviation between the verticality of the rotary table and the center of the hole position is not greater than 2 cm. Improve the accuracy and quality of drilling.

[0029] In step 3, for the fluid plastic silt layer, use high-density mud with bentonite and carboxymethyl cellulose added. Enhance the wall protection and stability of the mud, reducing the collapse of the hole wall and mud leakage.

[0030] In step 3, for the karst cave area, use high-viscosity mud and simultaneously fill and block the fissures with a mixture of clay and crushed stone. Prevent mud loss and ensure the stability of the hole wall.

[0031] In step 4, for the fluid plastic silt layer, the drilling rig uses a small stroke and high-frequency dense hammering to reduce the disturbance to the hole wall. Reduce the risk of hole wall instability and improve the hole-forming quality.

[0032] In step 4, for the karst cave area, first fill and level with a mixture of clay and crushed stone, and the drilling rig uses a medium stroke for impact to ensure the flatness of the hole bottom. Reduce problems such as drilling deviation and uneven hole bottom.

[0033] In step 6, the main reinforcement joints of the steel cage are mechanically connected, and the welding length is not less than ten times the diameter of the main reinforcement. Ensure the connection strength and integrity of the steel cage, and improve the bearing capacity of the pile foundation.

[0034] In step 8, the overpouring height during final grouting ≥ 1.5m to ensure the compactness of the pile top. Ensure the compactness of the pile top concrete, reduce pile top defects, and improve the overall quality of the pile foundation.

[0035] Thus, this construction method for waterborne bored cast-in-place piles in poor geological conditions can accurately grasp the geological conditions of the pile foundation location through advanced drilling exploration, provide a reliable basis for construction, and effectively avoid construction risks caused by unclear geological conditions. For poor geological conditions such as karst caves and flowing plastic silt layers, adopting a suitable mud preparation and circulation system can effectively prevent hole wall collapse and drilling deviation, and improve the hole forming quality. The segmented manufacturing and installation method of the steel cage can ensure the installation quality and construction efficiency of the steel cage, and at the same time avoid deformation and damage caused by the excessive length of the steel cage. Adopting secondary hole cleaning and strict underwater concrete pouring technology can effectively reduce the thickness of bottom sediment in the hole, improve the pouring quality of concrete, and ensure the bearing capacity of the pile foundation. Through ultrasonic transmission method and core drilling method for pile foundation quality inspection, the quality and bearing capacity of the pile foundation can be comprehensively and accurately evaluated, providing a strong guarantee for the safety and reliability of the project.

[0036] The following uses a specific construction example to illustrate this construction method for waterborne bored cast-in-place piles in poor geological conditions.

[0037] A port project is located in the lower reaches of the Yangtze River, with complex geological conditions and poor geological conditions such as karst caves and flowing plastic silt layers. The construction method of the present invention is used for waterborne bored cast-in-place pile construction, and the specific steps are as follows: (1) Construction preparation: According to the engineering geology and hydrological conditions, formulate a detailed construction plan, select an impact drill as the drilling equipment, prepare enough clay for mud preparation, and organize professional construction personnel for construction.

[0038] (2) Advanced drilling exploration: Conduct advanced drilling exploration for each pile foundation one by one, with the drilling depth reaching 5m below the designed pile foundation elevation, and the advanced drilling exploration work for each pile is not less than 1 hole. Through exploration, the geological conditions of the pile foundation location are accurately grasped, including the location and scope of karst caves and flowing plastic silt layers.

[0039] (3) Drill rig installation and positioning: Use an impact drill for drilling construction. When installing the drill rig, lay mobile steel rails and sleepers to ensure the stability of the drill rig. After the drill rig is positioned, adjust and fix the drill rig to ensure that the deviation of the verticality of the rotary device from the hole position center is not greater than 2cm.

[0040] (4) Mud preparation and circulation: According to the geological conditions, clay is selected as the mud material, and adjacent steel casing is used as the temporary mud pit. Mud circulation is carried out through the mud circulation system to ensure that the mud performance meets the construction requirements.

[0041] For the flowing plastic silt layer, high-density mud (density 1.4 - 1.5, viscosity 28 - 32 s) is used, and bentonite and CMC are added to enhance the wall protection performance; for the karst cave area, high-viscosity mud (viscosity ≥ 35 s) is used, and a mixture of clay and crushed stone is filled synchronously to seal the fissures.

[0042] (5) Drilling and hole formation: According to different formation conditions, adjust the stroke and impact frequency of the impact drill, and control the relative density and viscosity of the mud. During the drilling process, pay attention to observing the formation changes, adjust the construction parameters in a timely manner to prevent the collapse of the hole wall and the deviation of the drill hole. After the drill hole reaches the design depth, conduct hole formation inspection to ensure that the hole diameter, hole depth, inclination and other indicators meet the design requirements.

[0043] For the flowing plastic silt layer, use a small stroke (40 - 60 cm) and high frequency (20 - 25 times / min) for dense impact to reduce the disturbance to the hole wall; in the karst cave area, first fill and level with a mixture of clay and crushed stone (ratio 1:1), and then use a medium stroke (60 - 80 cm) for impact to ensure the flatness of the hole bottom; install a double-wall steel casing, with the inner cylinder isolating the flowing plastic layer and the outer cylinder grouting to reinforce the edge of the karst cave.

[0044] (6) Hole cleaning: Use the positive and reverse circulation system to clean the hole, remove the drill cuttings at the bottom of the hole, and ensure that the sediment thickness at the bottom of the hole meets the design and specification requirements.

[0045] (7) Fabrication and installation of steel reinforcement cage: The steel reinforcement cage is fabricated in sections, and the section length is determined to be 10 m according to the hoisting method and transportation conditions. The main reinforcement joints of the steel reinforcement cage adopt mechanical connection, and the welding length is not less than 10d (d is the diameter of the main reinforcement). When installing the steel reinforcement cage, use a crane in cooperation with a flatbed truck to transport the steel reinforcement cage to the site, which is carried out by a hoisting ship.

[0046] (8) After the steel reinforcement cage is installed in place, conduct the second hole cleaning to ensure that all the mud indicators meet the specification requirements, and the sediment thickness shall not be greater than 50 mm.

[0047] (9) Use compensated shrinkage concrete (expansion agent dosage 8% - 10%) to reduce shrinkage cracks; dynamically control the depth of the catheter buried (2 - 6 m), and real-time monitor the height of the concrete surface through ultrasonic waves; when finally grouting, the over-grouting height ≥ 1.5 m to ensure the compactness of the pile top.

[0048] For the karst cave area, advanced drilling revealed a karst cave with a diameter of 2 m at the pile position. Clay and crushed stones were filled to the bottom elevation of the hole. High-viscosity mud (density 1.45, viscosity 38 s) was used, and the impact drilling stroke was 60 cm with a frequency of 18 times / min. A double-wall steel casing was installed, and the outer casing was grouted to reinforce the edge of the karst cave. Compensating shrinkage concrete was poured with an overpour height of 1.8 m, and the pile integrity test showed no defects.

[0049] For the flowing plastic silt layer, the mud density was adjusted to 1.5, and 0.3% CMC was added to enhance the shaft protection. Impact drilling was carried out with a small stroke (50 cm) and a high frequency (22 times / min), and reverse circulation slag cleaning was started synchronously. The inner steel casing was sunk to a stable formation to isolate the flowing plastic layer. The buried depth of the concrete pouring was ≥3 m throughout the process, and the ultrasonic test of the pile body showed no necking.

[0050] The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made without departing from the spirit of the present invention within the knowledge scope of those of ordinary skill in the art.

Claims

1. A construction method for underwater bored cast-in-place piles in poor geological conditions, characterized in that, Including: Step 1: Conduct advanced drilling exploration for each pile foundation one by one. Through the exploration, master the geological conditions of the pile foundation location, record the positions, sizes and the thickness of the silt layer of the karst caves; establish a three-dimensional geological model to guide the adjustment of mud proportioning and drilling parameters; Step 2: Install the drilling rig; Step 3: According to the geological conditions, select clay as the mud material, use adjacent steel casing as the temporary mud pit, and conduct mud circulation through the mud circulation system to ensure that the mud performance meets the construction requirements; Step 4: According to different stratum conditions, adjust the stroke and impact frequency of the impact drilling rig, control the relative density and viscosity of the mud, control the impact drilling of the drilling rig in layers, install double-wall steel casing, isolate the flow plastic layer with the inner cylinder and grout to reinforce the edge of the karst cave with the outer cylinder; Step 5: Use the positive and reverse circulation system to clean the hole, remove the drill cuttings at the bottom of the hole, and ensure that the sediment thickness at the bottom of the hole meets the design and specification requirements; Step 6: Fabricate the steel reinforcement cage in sections, and the section length is determined according to the hoisting method and transportation conditions; when installing the steel reinforcement cage, use a crane and a flatbed truck to transport the steel reinforcement cage to the site, and install it by a floating crane; Step 7: After the steel reinforcement cage is installed in place, conduct the second hole cleaning to ensure that all mud indexes meet the specification requirements; Step 8: Use shrinkage-compensating concrete for concrete pouring, dynamically control the buried depth of the conduit, and real-time monitor the height of the concrete surface by ultrasonic wave.

2. The construction method of the cast-in-place pile in water for adverse geology according to claim 1, characterized in that, In Step 1, in the advanced drilling exploration of the pile foundation, the drilling depth reaches 5m below the designed pile foundation elevation, and the advanced drilling exploration work for each pile is not less than 1 hole.

3. The construction method of the cast-in-place pile in water for bad geology according to claim 1, characterized in that, In Step 2, lay moving steel rails and sleepers during the installation of the drilling rig to ensure the stability of the drilling rig.

4. The construction method of underwater bored cast-in-place pile for bad geological conditions according to claim 3, characterized in that, In Step 2, after the drilling rig is in place, adjust and fix the drilling rig to ensure that the deviation of the verticality of the rotary table from the center of the hole position is not greater than 2cm.

5. The construction method of the cast-in-place pile in water for poor geological conditions according to claim 1, characterized in that, In Step 3, for the flow plastic silt layer, use high-density mud and add bentonite and carboxymethyl cellulose.

6. The construction method of the cast-in-place pile in water for poor geological conditions according to claim 1, characterized in that, In Step 3, for the karst cave area, use high-viscosity mud and simultaneously fill and block the fissures with a mixture of clay and crushed stone.

7. The construction method of underwater bored cast-in-place piles for bad geological conditions according to claim 1, characterized in that, In Step 4, for the flow plastic silt layer, the drilling rig uses a small stroke and high-frequency dense impact to reduce the disturbance to the hole wall.

8. The construction method of the cast-in-place pile in water for poor geological conditions according to claim 1, characterized in that, In Step 4, for the karst cave area, first fill and level with a mixture of clay and crushed stone, and the drilling rig uses a medium stroke for impact to ensure the flatness of the bottom of the hole.

9. The construction method of the cast-in-place pile in water for bad geological conditions according to claim 1, characterized in that, In Step 6, the main reinforcement joints of the steel reinforcement cage adopt mechanical connection, and the welding length is not less than ten times the diameter of the main reinforcement.

10. The construction method of the cast-in-place pile in water for poor geological conditions according to claim 1, characterized in that, In Step 8, the overpouring height during final pouring ≥1.5m to ensure the compactness of the pile top.

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