Construction method of rotary drilling cast-in-place pile crossing subsurface runoff zone

Abstract

The application discloses a construction method of a rotary drilling bored pile crossing an underground runoff zone, and specifically comprises the following steps: firstly, confirming the pile hole position of the bored pile and the corresponding drilling depths of the pile hole in a soft soil layer, a runoff zone layer and a rock-embedded section; secondly, drilling multiple times and sequentially burying the soft soil layer steel casing and the runoff zone protection casing; thirdly, after the support of the runoff zone protection casing is completed, removing the soft soil layer steel casing and carrying out the subsequent pouring of the bored pile; and finally, adopting the method of multilayer step-by-step support and gap filling and compacting during construction, so that the soft soil layer steel casing forms effective protection for the soft soil layer, the collapse of the soft soil layer in the subsequent rotary drilling process is avoided, the influence on the underground water system and the construction progress is avoided, the runoff zone layer protection casing penetrates the runoff zone, forms effective support for the underground water system, and fills the melon stone outside the runoff zone layer protection casing to compact the gap, so that the mud or concrete in the pouring process can be effectively prevented from flowing into the runoff zone.

Description

Technical Field

[0001] This invention belongs to the field of building construction technology and relates to a construction method for rotary drilling and grouting piles that traverse underground runoff zones. Background Technology

[0002] With the high-quality development of the economy and society, people are paying increasing attention to the groundwater environment. Relevant departments have strengthened the protection of groundwater. In water-rich areas with karst topography, underground pile foundation construction often encounters various soft soil layers and underground runoff consisting of aquifers, water-rich rock formations, karst fissure water channels, and underground rivers. Because the hydrogeological environment is not only about the relationship between different soil and rock layers, the geological conditions in aquifers fluctuate with changes in groundwater level and water quality, which also has a certain impact on the relationship between soil and rock layers. This has a crucial impact on the stability and safety of construction projects.

[0003] Rotary drilling piles are a type of foundation pile constructed by creating a pile hole through rotary drilling and then pouring concrete to form the pile. When constructing rotary drilling piles in complex geological environments with soft soil layers and underground runoff, conventional methods often encounter challenges. During the drilling process, the soft soil layer is prone to collapse, leading to pollution or blockage of groundwater systems when the runoff zone is being excavated. Furthermore, during concrete pouring, the concrete can easily seep into the groundwater runoff zone, affecting water quality or blocking groundwater channels, causing springs to dry up or change course. This approach fails to effectively protect groundwater resources, is environmentally unfriendly, and concrete leakage increases construction costs and reduces construction efficiency.

[0004] To solve the above problems, a new construction method is needed, one that can be applied to complex geological environments with soft soil layers and underground runoff, and can effectively protect the underground. Summary of the Invention

[0005] In view of this, the present invention provides a construction method for rotary-drilled cast-in-place piles traversing underground runoff zones. During construction, a multi-layered, progressively supporting method with gap-filling and compaction is employed. A steel casing effectively protects the weak soil layer, preventing its collapse during subsequent rotary drilling and its impact on the groundwater system and construction progress. The runoff zone protection casing penetrates the runoff zone, providing effective support for the groundwater system. Gravel is filled outside the runoff zone protection casing to compact the gaps, effectively preventing mud or concrete from flowing into the runoff zone during pouring. This construction method effectively protects the groundwater system, is more environmentally friendly, and improves construction efficiency while reducing construction costs.

[0006] This invention discloses a construction method for rotary-drilled cast-in-place piles traversing underground runoff zones, the method specifically including the following steps:

[0007] S1. Conduct hydrogeological surveys and tests, and perform simulations to confirm the location of the pile holes and the corresponding drilling depths of the pile holes in the soft soil layer, runoff zone layer and bottom bedrock.

[0008] S2, Harden the hole opening at the location of the pile hole confirmed in step S1, and build a drainage ditch.

[0009] S3. After the borehole has hardened, perform initial rotary drilling at the drilling location and install the initial casing.

[0010] S4. The first rotary drilling operation is carried out in the soft soil layer. When the drill bit penetrates the soft soil layer and enters the runoff zone, the first rotary drilling operation is stopped. The steel casing of the soft soil layer is buried in the rotary drilling hole corresponding to the soft soil layer to form support for the soft soil layer.

[0011] S5; Perform the second rotary drilling operation. Stop the second rotary drilling operation after the drill bit has penetrated the runoff zone to the bottom bedrock.

[0012] S6, insert the runoff zone protection casing into the opening of the soft soil layer steel casing, wait until the bottom of the runoff zone protection casing abuts against the bottom of the pile hole formed by the second rotary drilling operation, and the top of the runoff zone protection casing is completely buried in the soft soil layer steel casing, and the installation of the runoff zone protection casing is completed.

[0013] S7. After the runoff zone protection casing is installed, pull out the soft soil layer steel casing. As the soft soil layer steel casing is pulled out, fill the radial gap between the runoff zone protection casing and the soft soil layer steel casing with gravel to compact the radial gap between the runoff zone protection casing and the corresponding borehole in the soft soil layer.

[0014] S8, the steel casing is pulled out of the weak soil layer, and the third rotary drilling operation is carried out. The drill bit rotates downward from the bottom bedrock to the set depth to form a rock-embedded section.

[0015] S9, After the rotary drilling of the rock-embedded section is completed, the drill bit is pulled out, the pile hole is inspected as a whole and the hole is cleaned;

[0016] S10, after passing the acceptance test, the pile foundation steel cage is hoisted into the pile hole, the guide pipe is installed and concrete is poured.

[0017] S11, After the concrete pouring is completed, remove the guide pipe and the protective casing for the runoff zone.

[0018] Furthermore, in step S3, the initial rotary drilling depth is 1m to 3m.

[0019] Furthermore, the borehole diameter for the first rotary drilling operation is D1, the borehole diameter for the second rotary drilling operation is D2, and the borehole diameter for the third rotary drilling operation is D3, with the order of diameter being D1>D2>D3.

[0020] Furthermore, an impermeable layer is wound around the radial outer surface of the bottom of the runoff zone protective casing.

[0021] Furthermore, in step S7, the filling height of the gravel is no more than 500mm.

[0022] The beneficial effects of this invention are:

[0023] This invention provides a construction method for rotary-drilled cast-in-place piles that traverse underground runoff zones. During construction, a multi-layered, progressively supported, and gap-filled compaction method is employed. A steel casing effectively protects the weak soil layer, preventing its collapse during subsequent rotary drilling and ensuring the smooth operation of the groundwater system and construction progress. The runoff zone protection casing penetrates the runoff zone, providing effective support for the groundwater system. Gravel is filled outside the runoff zone protection casing to compact the gaps, effectively preventing mud or concrete from flowing into the runoff zone during pouring. An anti-seepage layer at the bottom of the runoff zone protection casing effectively prevents upward-flowing mud from entering the outside of the large-diameter steel casing during concrete pouring. The construction method of this invention first supports the weak soil layer and then supports the runoff zone section. This not only solves the problem of borehole collapse during rotary drilling of weak soil layers, but also protects the runoff zone from blockage, ensuring that the water flow, water level, and water quality of the runoff zone remain unchanged. This effectively protects the groundwater system, is more environmentally friendly, and can improve construction efficiency and reduce construction costs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the support structure for the steel casing for weak soil layers and the protective casing for runoff zones according to the present invention;

[0025] Figure 2 This is a schematic diagram of the pile hole structure of the present invention. Detailed Implementation

[0026] It should be noted that in the description of this specification, the terms "upper", "lower", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0027] As shown in the figure, this embodiment discloses a construction method for rotary drilled cast-in-place piles that traverse underground runoff zones. The method specifically includes the following steps:

[0028] S1. Conduct hydrogeological surveys and tests, and perform simulations to confirm the location of the cast-in-place piles and the corresponding drilling depths in the soft soil layer 3, the runoff zone layer 4, and the underlying bedrock 5. Utilize the differences in conductivity between rocks and minerals—high-resistivity media repel current lines, while low-resistivity media attract them—to analyze the vertical distribution of rock strata with different electrical properties, confirm the runoff zone trend, the hydrogeological characteristics of groundwater, and the development of karst. Confirm the location of the cast-in-place piles to be constructed, and conduct pumping and monitoring work at the groundwater source point at the construction location to confirm the water volume, level, and quality. During construction, conduct dynamic monitoring of groundwater to ensure that the underground runoff zone is not affected.

[0029] S2, at the location of the pile hole confirmed in step S1, the hole opening is hardened and a drainage ditch is built; site clearing, excavation and backfilling are carried out in the construction area of ​​the cast-in-place pile, and then a 200mm to 300mm thick C20 concrete cushion layer is poured at the pile hole location to harden the hole opening. At the same time, drainage ditches and sedimentation tanks are built around the cushion layer. A mud pump is installed in the tank to pump mud into the mud tank to prevent mud from seeping into the surrounding water bath during construction.

[0030] S3. After the borehole opening has hardened, initial rotary drilling is performed at the drilling location, and the initial casing is installed. After the concrete strength of the subgrade reaches more than 75%, the pile position is located using a total station. Depending on the soil conditions, initial rotary drilling is performed downwards for 1m to 3m on the subgrade, and the initial casing is installed. The initial casing is tightly attached to the concrete subgrade. If there are gaps between the initial casing and the concrete subgrade, they are backfilled and compacted with gravel (7-grade). The horizontal position and verticality of the casing are checked to prevent deviation, and the borehole opening elevation is measured. A 20mm thick steel plate is laid around the borehole opening to support the weight of the rotary drilling equipment and ensure the stability of the borehole opening. The initial casing is a steel casing, and after its installation, the opening of the casing is higher than the subgrade.

[0031] S4. The first rotary drilling operation is carried out in the soft soil layer 3. Once the drill bit penetrates the soft soil layer 3 and enters the runoff zone layer 4, the first rotary drilling operation is stopped. The steel casing 1 for the soft soil layer is then installed in the corresponding rotary drilling hole in the soft soil layer 3 to provide support for it. The first drill bit is selected according to the design, and after the drilling rig is in place, the first rotary drilling operation is initiated based on the hydrogeological survey. This first rotary drilling operation is conducted on the soft soil layer 3. For the portion of the soft clay layer above the groundwater level, depressurization and deceleration drilling are used, with the drill bit repeatedly moved up and down to sweep the hole and prevent necking. After the hole in the soft soil layer 3 is formed, the pre-fabricated steel casing 1 is hoisted into the hole. If lowering is difficult, a vibratory hammer can be used for assistance, vertically vibrating it downwards along the opening position. The steel casing 1 effectively prevents hole wall collapse, providing stable support and a favorable construction environment for subsequent rotary drilling.

[0032] S5; Conduct the second rotary drilling operation. After the drill bit penetrates the runoff zone 4 to the bottom bedrock 5, stop the second rotary drilling operation; replace with a second drill bit and continue rotary drilling downwards. The second rotary drilling operation is a rotary drilling operation to cross the underground runoff zone. Decompression and deceleration drilling are adopted. The drill bit is suspended and repeatedly swept up and down to avoid the collapse of the hole. After the rotary drilling is completed, the drill bit is pulled out. Because the runoff zone 4 is eroded by flowing water all year round, the lithology is complex and the rock mass is very fragile. When it is disturbed by the rotary drilling machine, the stability of the hole wall itself is very poor. Large-scale collapses can easily occur along the hole wall, making hole formation often difficult. Appropriate support needs to be taken during hole formation. At the same time, during the second rotary drilling operation, after reaching the bottom bedrock 5, it is necessary to over-dig appropriately and continue drilling to ensure complete penetration of the runoff zone. This construction can also provide strong support for the subsequent installation of the runoff zone protection casing 2, preventing the runoff zone protection casing 2 from sinking or tilting due to its own weight.

[0033] S6, insert the runoff zone protection casing 2 into the opening of the steel casing 1 in the weak soil layer. The bottom of the runoff zone protection casing 2 should abut against the bottom of the pile hole formed by the second rotary drilling operation, and the top of the runoff zone protection casing 2 should be completely buried in the steel casing 1 in the weak soil layer, thus completing the installation of the runoff zone protection casing 2. Before hoisting the runoff zone protection casing 2, a seepage-proof layer should be wrapped around the radial outer surface of the bottom of the runoff zone protection casing 2. In this embodiment, geotextile is used as the seepage-proof layer. The verticality of the runoff zone protection casing 2 should be controlled before entering the hole, and the speed should be slowed down during the entry process until hoisting is complete. When installing the runoff zone protection casing 2, the bottom of the runoff zone protection casing 2 should rest on the bottom bedrock 5, which is the starting position of the subsequent third rotary drilling operation, and the opening of the runoff zone protection casing 2 should be below the opening of the steel casing 1 in the weak soil layer, indicating complete burial.

[0034] S7. After the runoff zone protection casing 2 is installed, pull out the soft soil layer steel casing 1. As the soft soil layer steel casing 1 is pulled out, fill the radial gap between the runoff zone protection casing 2 and the soft soil layer steel casing 1 with gravel 7 to compact the radial gap between the corresponding boreholes of the runoff zone protection casing 2 and the soft soil layer 3. When pulling out the soft soil layer steel casing 1, fill the gap with gravel 7 gradually as the soft soil layer steel casing 1 is pulled out. The soft soil layer steel casing 1 is pulled out by vibratory hammer, high-frequency bottom pulling. Every 300mm of vibratory pulling, 300mm of gravel 7 is added. This cycle is repeated until the soft soil layer steel casing is pulled out. While pulling out the pores, the filling process is carried out simultaneously, and vibration is used to evenly fill the pores. However, the filling height needs to be controlled. If the filling height is too high, the pulling process will become more difficult and may even be impossible. Therefore, the filling height of the 7-gravel material should not exceed 500mm. In this embodiment, the filling height is 500mm. After the pore wall is filled, the protective casing of the flow zone layer will be more stable, and it can also prevent mud or concrete from flowing into the runoff zone during the pouring process.

[0035] S8, at the exit of the steel casing 1 in the weak soil layer, the third rotary drilling operation is carried out. The drill bit drills downwards from the bottom bedrock 5 to the set depth to form the rock-embedded section 6. A third drill bit is then used, and with the support of the protective casing 2 in the runoff zone, the rotary drilling in the bottom bedrock 5 is accelerated to promote the formation of the rock-embedded section 6. During the rotary drilling of the bottom bedrock 5, the drilling depth must exceed the design requirements, and over-drilling must not exceed 300mm.

[0036] After the rotary drilling of section S9, the rock-embedded section 6, is completed, the drill bit is pulled out, and the pile hole is inspected and cleaned. For pile holes that meet the inspection conditions, the holes are cleaned by first using a rotary drilling rig to remove the slag, then using a mud pump to pump out the mud and water in the hole until the bottom of the hole is basically reached. The remaining slag is then removed by the rotary drilling rig until the required thickness of the slag is met. If some slag is too thick to be completely removed, it may be necessary to use low-grade quick-setting bagged cement to be put into the hole, mixed with the slag, and then cleaned to form the hole.

[0037] S10, after acceptance, the pile foundation reinforcement cage is hoisted into the pile hole, the guide pipe is installed, and concrete is poured. The mechanical properties, processing methods, and processing dimensions of the main reinforcement, stirrups, and stiffening hoops of the reinforcement cage should all meet the design and specification requirements. The reinforcement connection, lifting ring setting, stirrup welding, sonic logging tube installation, and protective layer spacer setting should all meet the design and specification requirements. The reinforcement cage is installed using a one-time integral hoisting method, and the lifting points are determined according to the length and weight of the reinforcement cage. During installation, the reinforcement cage should be vertical, accurate, and slowly lowered, and friction (impact) between the reinforcement cage and the casing should be avoided or minimized.

[0038] S11, After the concrete pouring is completed, remove the guide pipe and the runoff zone protective casing 2. The guide pipe should be removed after the concrete pouring is completed but before the concrete sets, and the runoff zone protective casing 2 also needs to be removed before the concrete is completely set. Therefore, it is necessary to choose whether to remove the runoff zone protective casing 2 or leave it in the pile hole according to the actual situation to prevent unset concrete from entering the groundwater system. Therefore, when making the runoff zone protective casing 2, its length can be set according to whether it needs to be recycled. If it needs to be recycled, its length should be close to the opening of the pile hole. If it does not need to be recycled, its length can be appropriately shortened to reduce costs. However, it must be ensured that the runoff zone protective casing 2 and the soft soil layer steel casing 1 overlap axially before the soft soil layer steel casing 1 is removed, and the overlap length is not less than the filling depth of the gravel 7.

[0039] In this embodiment, the drilling diameter for the first rotary drilling operation is D1, the drilling diameter for the second rotary drilling operation is D2, and the drilling diameter for the third rotary drilling operation is D3, with the order D1 > D2 > D3. To ensure that the final cast-in-place pile hole meets the design requirements, in accordance with the construction method of this invention, three different drill bits are used for rotary drilling, resulting in different hole diameters for the three rotary drilling operations. This is more conducive to the support of each casing and ensures the quality of the finished cast-in-place pile.

[0040] In this embodiment, both the runoff zone protection casing 2 and the soft soil layer steel casing 1 are steel casings, which can be prefabricated in the factory and then welded on-site according to the required length, realizing factory prefabrication and pre-assembly, and improving construction efficiency.

[0041] 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 construction method for rotary-drilled cast-in-place piles traversing underground runoff zones, characterized in that: The method specifically includes the following steps: S1. Conduct hydrogeological surveys and tests, and perform simulations to confirm the location of the pile holes and the corresponding drilling depths of the pile holes in the soft soil layer, runoff zone layer and bottom bedrock. S2, Harden the hole opening at the location of the pile hole confirmed in step S1, and build a drainage ditch. S3. After the borehole has hardened, perform initial rotary drilling at the drilling location and install the initial casing. S4. The first rotary drilling operation is carried out in the soft soil layer. When the drill bit penetrates the soft soil layer and enters the runoff zone, the first rotary drilling operation is stopped. The steel casing of the soft soil layer is buried in the rotary drilling hole corresponding to the soft soil layer to form support for the soft soil layer. S5; Perform the second rotary drilling operation. Stop the second rotary drilling operation after the drill bit has penetrated the runoff zone to the bottom bedrock. S6, insert the runoff zone protection casing into the opening of the soft soil layer steel casing, wait until the bottom of the runoff zone protection casing abuts against the bottom of the pile hole formed by the second rotary drilling operation, and the top of the runoff zone protection casing is completely buried in the soft soil layer steel casing, and the installation of the runoff zone protection casing is completed. S7. After the runoff zone protection casing is installed, pull out the soft soil layer steel casing. As the soft soil layer steel casing is pulled out, fill the radial gap between the runoff zone protection casing and the soft soil layer steel casing with gravel to compact the radial gap between the runoff zone protection casing and the corresponding borehole in the soft soil layer. S8, the steel casing is pulled out of the weak soil layer, and the third rotary drilling operation is carried out. The drill bit rotates downward from the bottom bedrock to the set depth to form a rock-embedded section. S9, After the rotary drilling of the rock-embedded section is completed, the drill bit is pulled out, the pile hole is inspected as a whole and the hole is cleaned; S10, after passing the acceptance test, the pile foundation steel cage is hoisted into the pile hole, the guide pipe is installed and concrete is poured. S11, After the concrete pouring is completed, remove the guide pipe and the protective casing for the runoff zone.

2. The construction method for rotary drilled cast-in-place piles traversing underground runoff zones according to claim 1, characterized in that: In step S3, the initial rotary drilling depth is 1m to 3m.

3. The construction method for rotary-drilled cast-in-place piles traversing underground runoff zones according to claim 1, characterized in that: The borehole diameter for the first rotary drilling operation is D1, the borehole diameter for the second rotary drilling operation is D2, and the borehole diameter for the third rotary drilling operation is D3. In terms of diameter, D1>D2>D3.

4. The construction method for rotary drilled cast-in-place piles traversing underground runoff zones according to claim 1, characterized in that: An impermeable layer is wound around the radial outer surface of the bottom of the runoff zone protective casing.

5. The construction method for rotary drilled cast-in-place piles traversing underground runoff zones according to claim 1, characterized in that: In step S7, the filling height of the gravel is no more than 500mm.

Images