Cast-in-place concrete pile construction method for complex geology of karst cave rock stratum

Abstract

The invention discloses a cast-in-place concrete pile construction method for complex geology of a karst cave rock stratum. The cast-in-place concrete pile construction method comprises the steps that S100, positioning and paying off are conducted; the method comprises the following steps: S101, burying a pile casing; s102, a drilling machine is aligned and starts to drill; s103, carrying out karst cave identification and dynamic treatment; S104, forming a hole; s105, hole cleaning is carried out; s106, a reinforcement cage is hoisted and placed; and S107, pile body concrete is poured. According to the method, a karst cave recognition and dynamic staged treatment mode is adopted, the large karst cave with the height larger than or equal to 5 m is divided into a plurality of layers in the vertical direction by adopting a layered drilling and layered pouring reinforcing method, concrete is poured for reinforcement every time one layer is drilled, construction of the next layer is conducted after the strength is achieved, the hole wall is effectively supported, and the construction efficiency is improved. Sudden slurry pressure drop and hole wall instability caused by one-time uncovering of a large karst cave are avoided, and major safety accidents such as hole collapse and drill burying are completely eradicated.

Description

Technical Field

[0001] This invention relates to the field of building foundation engineering construction technology, and in particular to a method for constructing concrete cast-in-place piles for complex geological conditions such as karst caves. Background Technology

[0002] Concrete cast-in-place piles, as a form of deep foundation, are widely used in construction, bridges, and other engineering fields. However, when constructing pile foundations in karst areas, the complex distribution of underground karst caves and the diverse properties of the filling materials make construction extremely difficult.

[0003] Traditional construction methods suffer from limitations in handling karst caves, leading to a reliance on a single approach and increasing the risk of borehole collapse and drill bit burial. Existing technologies often lack tailored, tiered treatment strategies for karst caves of varying sizes. This is particularly true when encountering large karst caves (height ≥ 5m), where traditional methods frequently fail to provide adequate solutions. Figure 1 One-time drilling or conventional backfilling methods are not feasible. Due to the large space of large karst caves, the sudden drop in mud pressure upon drilling can easily lead to borehole instability and collapse, potentially causing serious safety accidents such as drill bit burial and equipment overturning. Furthermore, in complex karst geological formations, the upper layer is often covered by fill or sedimentary soil layers. Existing construction methods typically only use short casings or thin-walled casings, which cannot effectively isolate the unstable upper soil layers. During drilling, due to drilling rig vibration and mud erosion, the bottom of the casing is prone to leakage and collapse, leading to borehole enlargement or deviation, affecting the quality of the pile. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a method for constructing cast-in-place concrete piles for complex geological conditions such as karst caves.

[0005] To provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not intended as a general commentary, nor is it intended to identify key / important components or to describe the scope of protection of these embodiments. Its sole purpose is to present some concepts in a simple form as a prelude to the detailed description that follows.

[0006] The present invention adopts the following technical solution: This invention provides a method for constructing cast-in-place concrete piles in complex geological conditions such as karst caves, comprising the following steps: S101: Installing the casing: At the pile hole location, use a driving and pulling machine to press the casing in, the inner diameter of the casing being larger than the designed pile diameter; S102: Drilling rig alignment and start drilling: Center and level the rotary drilling rig, use the sand-scooping drill bit to drill, and when drilling to the karst development layer, proceed to S103; S103: Cave Identification and Dynamic Processing: S1031: If the height of the karst cave is ≤3m and the hole does not collapse after drilling, continue drilling; otherwise, pour C20 concrete into the hole. S1032: When the height of the karst cave is 3m-5m, after drilling through, pour C20 concrete into the hole to a predetermined height above the top of the karst cave. After it reaches the set strength, continue drilling downwards. S1033: When the height of the karst cave is ≥5m, layered drilling and layered grouting reinforcement shall be adopted: the karst cave shall be set up in several layers in the vertical direction. After each layer is drilled through, C20 concrete shall be poured into the space of the layer. After the concrete of the layer reaches the predetermined strength, the next layer shall be drilled through until the karst cave is completely penetrated. S104: Hole Formation: After passing through the karst development layer, use a core drill bit to drill to the designed bearing layer and rock penetration depth to complete the hole formation.

[0007] Furthermore, in S1033, the height of each layer is ≤5m.

[0008] Furthermore, in S104, the construction parameters for using the core drill bit are: rotation speed 6-8 r / min, feed rate 3-4 m / h, and torque pressure 25-30 kPa.

[0009] Furthermore, the method for constructing cast-in-place concrete piles in complex geological conditions such as karst caves also includes: S105: Clean the hole; S106: Lowering the steel cage: Vertically lowering the prefabricated steel cage into the hole; S107: Pile body concrete pouring: underwater concrete of the design strength grade is poured through the tremie pipe method to form the pile body.

[0010] Furthermore, in S102, when the sand-dredging bucket drill bit is drilling, the rotation speed is 15-20 r / min, the feed rate is 15-20 m / h, and the torque pressure is 16-18 kPa.

[0011] Furthermore, in S101, the casing is made of steel plate with a thickness of 4-8mm and a height of 4-8m. The inner diameter of the casing is 20cm larger than the designed pile diameter.

[0012] Furthermore, in S1032, the predetermined height is at least 1m.

[0013] The method for constructing cast-in-place concrete piles for complex geological conditions in karst caves is described above. The complex geological conditions in karst caves include, from top to bottom, at least a fill layer, a sedimentary soil layer, a karst development layer, and a base mudstone layer.

[0014] Furthermore, the fill layer includes at least: a miscellaneous fill layer and a plain fill layer; The sedimentary soil layer includes at least: a silty clay layer and a mixed layer of clay and silty clay; The karst development layer includes at least: a strongly weathered limestone layer, a moderately weathered limestone layer, and a karst infill layer; The base mudstone layer includes at least: a mixed layer of strongly weathered mudstone, argillaceous siltstone and silty mudstone, and a mixed layer of moderately weathered mudstone, argillaceous siltstone and silty mudstone.

[0015] The beneficial effects of this invention are as follows: This application adopts a cave identification and dynamic grading method. For large caves with a height of ≥5m, a layered drilling and layered grouting reinforcement method is adopted. The large cave is divided into several layers in the vertical direction. Concrete is poured to reinforce each layer after drilling through it. The next layer is constructed only after the strength is reached. This effectively supports the borehole wall and avoids the sudden drop in mud pressure and borehole wall instability caused by a one-time breakthrough of a large cave. It completely eliminates the occurrence of major safety accidents such as borehole collapse and drill bit burial. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart of a concrete cast-in-place pile construction method for complex geological conditions such as karst caves. Detailed Implementation

[0018] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] like Figure 1 As shown in some illustrative embodiments, a method for constructing cast-in-place concrete piles for complex geological conditions such as karst cave strata is provided, comprising the following steps: S100: Positioning and laying out.

[0020] The layout of the pile points should be accurate, the pile positions should be easy to find and not easily lost. After the pile points are laid out, the supervising engineer should verify the lines and points and make records. Construction can only proceed after the layout is accurate and error-free.

[0021] S101: Install casing.

[0022] At the pile hole location, a casing is pressed in using a driving and pulling machine. The inner diameter of the casing is larger than the designed pile diameter.

[0023] Due to the long pile length, complex geology, and the presence of karst caves, multiple concrete pouring operations are required, resulting in a long drilling time. To ensure the upper soil layer of the borehole does not collapse during drilling, a steel casing will be installed using a drilling machine to ensure construction safety. Specifically, the casing will be made of 4-8mm thick steel plates, 4-8m high, and its inner diameter will be 20cm larger than the designed pile diameter.

[0024] The casing's greater burial depth and wall thickness design can effectively penetrate and isolate the upper fill and sediment layers, providing a stable borehole guarantee for subsequent drilling of the karst cave section and preventing problems such as diameter expansion and borehole deviation caused by the loosening and collapse of the upper soil layer.

[0025] S102: The drilling rig is aligned and drilling begins.

[0026] First, position the drilling rig by centering and leveling it. This involves aligning the drill bit with the pre-determined pile location and adjusting its verticality using a pile rig verticality gauge. During alignment, ensure the drill bit tip is perpendicular to the pile location. If the drill bit tip is found to be off-center, readjust and reposition until the drill bit tip is aligned with the pile location.

[0027] Drilling can only begin after all preparations are complete and the pile locations have been verified to be correct.

[0028] Then, using the weight of the drilling rig, the drill bit is pressed into the soil, and the sand-dredging drill bit is used to drill. When drilling reaches the karst development layer, S103 karst cave identification and dynamic processing are carried out. When encountering karst caves during the hole-forming process, the drilling speed needs to be reduced to prevent serious hole collapse.

[0029] When the sand-dredging bucket drill bit is drilling, the rotation speed is 15-20 r / min, the advance speed is 15-20 m / h, and the torque pressure is 16-18 kPa.

[0030] S103: Cave identification and dynamic processing, that is, cave processing is carried out according to the principle of dynamic adjustment.

[0031] S1031: If the height of the karst cave is ≤3m and the hole does not collapse after drilling, continue drilling; otherwise, pour C20 concrete into the hole.

[0032] S1032: When the karst cave is 3m-5m high, after drilling through it, pour C20 concrete into the hole to a predetermined height above the top of the karst cave, with a predetermined height of at least 1m. After it reaches the set strength, continue drilling downwards. Specifically, when using C20 concrete for filling, the filling volume depends on the extent of the karst cave collapse, but it must be filled to at least 1 meter above the collapsed hole. After filling, wait for the concrete to reach a certain strength, at least 1-2 days, before drilling the next layer of holes to prevent serious collapses during subsequent drilling.

[0033] S1033: When the height of the karst cave is ≥5m, layered drilling and layered grouting reinforcement shall be adopted: the karst cave shall be divided into several layers in the vertical direction. After each layer is drilled through, C20 concrete shall be poured into the space of that layer. After the concrete of that layer reaches the predetermined strength, the next layer shall be drilled until the karst cave is completely penetrated, so as to ensure the stability and bearing capacity of the pile foundation when penetrating the karst cave. The height of each layer shall be ≤5m.

[0034] During construction, large karst caves and small karst cave piles are constructed in an alternating manner to prevent the large karst caves from waiting for layered concrete filling and thus reduce the waste of time and construction delays.

[0035] After drilling into the karst development layer, the drill bit is replaced with a coring drill bit, and the construction parameters are adjusted to a rotation speed of 8-15 r / min, a drilling speed of 5-6 m / h, and a torque pressure of 20-23 kPa.

[0036] S104: Hole formation.

[0037] After penetrating the karst development layer, a core drill bit is used to drill to the designed bearing layer and rock penetration depth to complete the hole formation. The construction parameters for the core drill bit are: rotation speed 6-8 r / min, drilling speed 3-4 m / h, and torque pressure 25-30 kPa.

[0038] This application specifies corresponding drilling parameters for different geological formations: when traversing soil layers, a sand-scooping drill bit is used with a rotation speed of 15-20 r / min and a fast drilling speed (15-20 m / h) to ensure drilling efficiency in soil layers; when entering the bearing layer, a core-taking drill bit is switched on, and the rotation speed is reduced to 6-8 r / min, with the drilling speed controlled at 3-4 m / h. This dynamic adjustment of parameters protects the drilling tools, reduces energy consumption, and effectively prevents rock surface deviation, ensuring the verticality of drilling into the bearing layer and the quality of the borehole.

[0039] S105: Clean the hole.

[0040] When the drilling rig reaches the designed hole depth, the drill bit is replaced to clean the hole. Once the thickness of the sediment is within acceptable limits, this process is completed.

[0041] S106: Lifting and lowering the steel reinforcement cage.

[0042] The prefabricated steel cage is vertically hoisted into the borehole. The steel cage is prepared in advance according to the design drawings. The steel cage is placed using a Zoomlion 25T truck crane. When lowering the steel cage, protective pads for the steel bars must be set up as required, and collisions with the borehole wall should be minimized. The lowering should be done quickly and promptly to reduce waiting time.

[0043] S107: Pour concrete into the pile body.

[0044] The pile body is formed by pouring underwater concrete of the designed strength grade using the tremie pipe method. A crane is used to lift the tremie pipe for concrete pouring. During pouring, the tremie pipe's embedment depth and the height difference between the concrete surfaces inside and outside the pipe are measured. The rise of the concrete surface is measured continuously as the pouring progresses. The tremie pipe's embedment depth is controlled between 2 and 6 meters, and it is strictly forbidden for the tremie pipe to be pulled out of the concrete surface. This process continues until the required design elevation is reached. The final pour volume is controlled, ensuring the pile top is not too low, with an over-pouring volume of approximately 1 meter as per design requirements.

[0045] This application discloses a method for constructing cast-in-place concrete piles in complex geological conditions of karst caves. The complex geological conditions of karst caves include, from top to bottom, at least a fill layer, a sedimentary soil layer, a karst development layer, and a base mudstone layer.

[0046] The fill layer includes at least two layers: miscellaneous fill and plain fill.

[0047] Miscellaneous fill layer: variegated, loose, filled with broken bricks and tiles mixed with a small amount of silty clay, with a crushed stone content of 35%-40%, a particle size of 1-10cm, some larger than 10cm, filled for more than 10 years, and a layer thickness of 0.3~3.8m.

[0048] Plain fill layer: grayish-yellow to yellowish-brown, soft to plastic, composed of silty clay mixed with a small amount of plant roots and stems, locally containing a small amount of silt, filled for more than 5 years, with the top buried at a depth of 0.0~3.2m and the layer thickness of 0.2~4.0m.

[0049] The sedimentary soil layer includes at least: a silty clay layer and a mixed layer of clay and silty clay.

[0050] Silty clay layer: grayish-yellow, plastic, contains iron and manganese oxides, slightly glossy cut surface, medium toughness and dry strength, top buried depth 0.5~4.2m, layer thickness 1.0~5.0m; yellowish-gray to gray, soft to plastic, contains a small amount of organic matter, slightly glossy cut surface, medium toughness and dry strength, top buried depth 4.3~6.8m, layer thickness 0.4~6.9m.

[0051] Mixed clay and silty clay layer: yellowish-brown, containing iron and manganese oxides, with a glossy cut surface, moderate toughness and dry strength, with weathered rock fragments at the bottom, the top of the layer is buried at a depth of 0.2~12.3m, and the layer thickness is 0.3~9.8m.

[0052] The karst development layer includes at least: strongly weathered limestone layer, moderately weathered limestone layer, and karst infill layer.

[0053] Strongly weathered limestone layer: grayish-yellow, strongly weathered, with most of the structure destroyed, the rock core is easily broken by hand, it is an extremely soft rock, which softens very easily when exposed to water, with local interbedded moderately weathered rock blocks, the top of the layer is buried at a depth of 0.2~16.5m, and the layer thickness is 0.1~1.5m.

[0054] Moderately weathered limestone layer: grayish-yellow to grayish-purple, soft rock, with slightly developed open and open fractures, relatively broken rock mass, with developed karst caves and fissures, the basic quality grade of the rock mass is V, the top of the layer is buried at a depth of 22.9~42.0m, and the layer thickness is 0.5~1.4m; grayish-yellow, relatively soft to relatively hard rock, relatively broken rock mass, with developed karst caves and fissures, the basic quality grade of the rock mass is IV, the top of the layer is buried at a depth of 0.3~16.7m, the exposed layer thickness is 0.5~8.7m, and some areas are not drilled through.

[0055] Karst infill layer: grayish-yellow to brownish-red, filled with soft to plastic silty clay mixed with weathered rock fragments and rock fragments, locally filled with weathered rock fragments and rock fragments, with a filling rate of 50% to 90%, a top burial depth of 0.2 to 43.0 m, and a layer thickness of 0.2 to 15.3 m.

[0056] The basement mudstone layer includes at least: a mixed layer of strongly weathered mudstone, argillaceous siltstone and silty mudstone, and a mixed layer of moderately weathered mudstone, argillaceous siltstone and silty mudstone.

[0057] Mixed layer of strongly weathered mudstone, argillaceous siltstone and silty mudstone: brownish-red, strongly weathered, most of the rock structure destroyed, the rock core can be crushed by hand, and is sandy. It is an extremely soft rock that is easily softened when exposed to water. The basic quality grade of the rock mass is V. The top of the layer is buried at a depth of 26.2~51.5m and the layer thickness is 1.3~12.1m.

[0058] Mixed layer of moderately weathered mudstone, argillaceous siltstone and silty mudstone: purplish-red, extremely soft rock, easily softened by water, relatively intact rock mass, basic quality grade of rock mass is classified as Class V, top buried depth 31.0~54.5m.

[0059] Based on the above geological conditions, the geological conditions during construction are extremely uneven, the karst caves are complex, and the rock layer strength varies greatly, resulting in slow drilling speed and a tendency for hole collapse. This makes it impossible to meet the design requirements and achieve the required quality for the engineering piles. Given these geological conditions, the concrete cast-in-place pile construction method proposed in this application for complex karst cave rock layers needs to be adopted.

[0060] The pile foundation design overview is shown in the table below:

[0061] A total of 177 engineering piles were constructed, including 26 piles with a diameter of 1100mm and 151 piles with a diameter of 800mm. The pile lengths ranged from 6 meters to 56.3 meters, and the hole depths are shown in the table below.

[0062] Each pile passes through a karst cave, with the number of caves ranging from 2 to 12. The details of the caves are shown in the table below:

[0063] The testing of pile foundation engineering shall be carried out in accordance with the "Technical Specification for Testing of Building Pile Foundations" (JGJ106-2014) and the "Code for Testing of Building Foundations" (DB32-T-3916), and the construction quality acceptance standards shall be implemented in accordance with the relevant provisions of the "Standard for Acceptance of Construction Quality of Building Foundation Engineering" (GB50202-2018).

[0064] 18 boreholes underwent quality testing (verticality, borehole diameter, and bottom sediment detection); 18 piles underwent ultrasonic testing, and 127 piles underwent low-strain testing; 10 piles underwent static load testing (static pressure and self-balancing), and 4 piles underwent tensile testing. The test data are as follows:

[0065] In summary, all tests met the design and relevant specifications, and economic costs were effectively controlled while the ecological environment was effectively protected.

[0066] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for constructing cast-in-place concrete piles in complex geological conditions such as karst caves, characterized in that, Includes the following steps: S101: Installing the casing: At the pile hole location, use a driving and pulling machine to press the casing in, the inner diameter of the casing being larger than the designed pile diameter; S102: Drilling rig alignment and start drilling: Center and level the rotary drilling rig, use the sand-scooping drill bit to drill, and when drilling to the karst development layer, proceed to S103; S103: Cave Identification and Dynamic Processing: S1031: If the height of the karst cave is ≤3m and the hole does not collapse after drilling, continue drilling; otherwise, pour C20 concrete into the hole. S1032: When the height of the karst cave is 3m-5m, after drilling through, pour C20 concrete into the hole to a predetermined height above the top of the karst cave. After it reaches the set strength, continue drilling downwards. S1033: When the height of the karst cave is ≥5m, layered drilling and layered grouting reinforcement shall be adopted: the karst cave shall be set up in several layers in the vertical direction. After each layer is drilled through, C20 concrete shall be poured into the space of the layer. After the concrete of the layer reaches the predetermined strength, the next layer shall be drilled through until the karst cave is completely penetrated. S104: Hole Formation: After passing through the karst development layer, use a core drill bit to drill to the designed bearing layer and rock penetration depth to complete the hole formation.

2. The method for constructing cast-in-place concrete piles for complex geological formations such as karst caves, as described in claim 1, is characterized in that... In S1033, the height of each layer is ≤5m.

3. The method for constructing cast-in-place concrete piles for complex geological formations such as karst caves, as described in claim 2, is characterized in that... In S104, the construction parameters for using the coring drill bit are: rotation speed 6-8 r / min, feed rate 3-4 m / h, and torque pressure 25-30 kPa.

4. A method for constructing cast-in-place concrete piles for complex geological conditions such as karst caves, as described in claim 3, characterized in that, Also includes: S105: Clean the hole; S106: Lowering the steel cage: Vertically lowering the prefabricated steel cage into the hole; S107: Pile body concrete pouring: underwater concrete of the design strength grade is poured through the tremie pipe method to form the pile body.

5. A method for constructing cast-in-place concrete piles for complex geological formations such as karst caves, as described in claim 4, characterized in that, In S102, when the sand-dredging bucket drill bit is drilling, the rotation speed is 15-20 r / min, the advance speed is 15-20 m / h, and the torque pressure is 16-18 kPa.

6. A method for constructing cast-in-place concrete piles for complex geological formations such as karst caves, as described in claim 5, characterized in that, In S101, the casing is made of steel plate with a thickness of 4-8mm and a height of 4-8m. The inner diameter of the casing is 20cm larger than the designed pile diameter.

7. A method for constructing cast-in-place concrete piles for complex geological formations such as karst caves, as described in claim 6, characterized in that, In S1032, the predetermined height is at least 1m.

8. A method for constructing cast-in-place concrete piles for complex geological conditions such as karst cave strata, according to any one of claims 1-7, characterized in that, It is applied to complex geological formations of karst caves; the complex geological formations of karst caves include, from top to bottom, at least a fill layer, a sedimentary soil layer, a karst development layer, and a base mudstone layer.

9. A method for constructing cast-in-place concrete piles for complex geological conditions such as karst caves, as described in claim 8, characterized in that, The fill layer includes at least: a miscellaneous fill layer and a plain fill layer; The sedimentary soil layer includes at least: a silty clay layer and a mixed layer of clay and silty clay; The karst development layer includes at least: a strongly weathered limestone layer, a moderately weathered limestone layer, and a karst infill layer; The base mudstone layer includes at least: a mixed layer of strongly weathered mudstone, argillaceous siltstone and silty mudstone, and a mixed layer of moderately weathered mudstone, argillaceous siltstone and silty mudstone.

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