Cast-in-place pile casing under geological condition of deep riprap layer and mounting method

Abstract

The invention belongs to the field of building construction, and particularly relates to a cast-in-place pile casing under the geological condition of a deep riprap layer and a mounting method. A double-layer structure is adopted and comprises an outer pile casing and an inner pile casing, the inner pile casing is located in the middle of the outer pile casing, and the length of the inner pile casing is larger than that of the outer pile casing. The pile casing structure has the beneficial effects that by designing the inner and outer double-layer pile casing structure, the problems of slurry leakage and hole collapse easily occurring in the construction of the cast-in-place pile of the deep and thick riprap layer are effectively solved, and the stability of hole forming and the construction quality are ensured. The outer pile casing enhances the strength and the pressure resistance of the pile casing, and the inner pile casing ensures effective protection on the hole wall in the hole forming process. And the stability of the hole wall and the hole forming efficiency are improved by adopting a composite slurry retaining wall and a reasonable filling treatment measure. By means of the overall design, the safety and efficiency of cast-in-place pile construction are greatly improved, the construction requirements under the complex geological condition are met, and reliable technical support is provided for construction of the cast-in-place pile of the deep riprap layer.

Description

Technical Field

[0001] The invention belongs to the field of building construction, and in particular relates to a cast-in-place pile casing and an installation method under the geological condition of a deep riprap layer. Background Art

[0002] The piles at the nuclear power plant approach bridge are located in an area of ​​the embankment where blasting and riprap have been used. The riprap layer is as thick as 48 meters at its thickest point, representing a deep riprap layer. This method is unprecedented in domestic water-based cast-in-place pile construction, making punching extremely difficult. During the bored pile drilling process, grout leakage and hole collapse are common. Preventing these leaks and hole collapses is crucial to cast-in-place pile construction. Summary of the Invention

[0003] The purpose of the present invention is to provide a bored pile casing and installation method under deep riprap geological conditions, which can solve the problems of leakage and hole collapse that easily occur during bored pile construction in deep riprap layers in the prior art, and ensure the stability of the hole and the construction quality.

[0004] The technical solution of the present invention is as follows: a cast-in-place pile casing under deep riprap geological conditions adopts a double-layer structure, including an outer casing and an inner casing, the inner casing is located in the middle of the outer casing, and the length of the inner casing is longer than the outer casing.

[0005] The lower part of the outer casing is the original riprap stratum, and the lower parts of the inner casing and the outer casing are inserted into the original riprap stratum.

[0006] The upper part of the original riprap stratum is a gap with an inverted trapezoidal cross section, the middle position of the outer casing is backfilled clay with a trapezoidal cross section, and the upper part of the backfilled clay is backfilled gravel.

[0007] The backfill gravel and the original riprap stratum have a horizontal line.

[0008] The outer casing bears the external pressure and protects the inner casing.

[0009] The inner casing is used for protection and support during the hole forming process.

[0010] A method for installing a cast-in-place pile casing under deep riprap geological conditions comprises the following steps:

[0011] Step 1: casing processing;

[0012] Step 2: Put the pile driver in place and bury the casing.

[0013] In step 1, a plate rolling machine with a power of 75 kW is used to process the inner and outer casings to ensure the dimensional accuracy and roundness of the casings.

[0014] In step 2, a cross-shaped drill bit is used for the outer casing, and an impact drill bit is used for the inner casing. For onshore construction, the pile driver is directly placed on a leveled site with a site elevation of +6m. For offshore construction, a crawler crane is used to disassemble the pile driver and lift it onto a constructed steel platform. After the pile driver is assembled, it is placed in place. Before the pile driver is placed in place, the pile position is measured and determined.

[0015] For onshore steel casing burial, the steel casing is buried with inner and outer double casings. During construction, the first section of the outer casing is buried first, and the outer side is backfilled and compacted with clay. Clay is added to make slurry while punching. When the punching depth is 3-4m, the steel casing is extended. The following process is repeated: punching → extending the steel casing → vibrating and following up the steel casing. When the outer casing can no longer follow up, stop following up the outer casing and continue punching. When the punching depth reaches 26m, prepare to place the inner casing, place the inner casing and continue punching and following up the inner casing. Continue to extend the inner casing and follow up the inner steel casing while punching.

[0016] The beneficial effects of the present invention are as follows: by designing an inner and outer double-layer casing structure, the invention effectively solves the problems of slurry leakage and hole collapse that are prone to occur during the construction of cast-in-place piles in deep riprap layers, thereby ensuring the stability of the hole and the quality of construction. The outer casing enhances the strength and pressure resistance of the casing, while the inner casing ensures effective protection of the hole wall during the drilling process. The use of composite mud wall protection and reasonable filling treatment measures improves the stability of the hole wall and the drilling efficiency. The overall design greatly improves the safety and efficiency of cast-in-place pile construction, adapts to the construction needs under complex geological conditions, and provides reliable technical support for the construction of cast-in-place piles in deep riprap layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of a cast-in-place pile casing under deep riprap geological conditions provided by the present invention.

[0018] In the figure: 1 inner casing, 2 outer casing, 3 backfill gravel, 4 backfill clay, 5 first section casing excavation edge, 6 original riprap formation. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] like Figure 1As shown, a cast-in-place pile casing for deep riprap geological conditions employs a two-layer structure, specifically comprising an outer casing 2 and an inner casing 1. The inner casing 1 is located in the middle of the outer casing and is longer than the outer casing 2. The lower portion of the outer casing 2 is the original riprap layer 6. The lower portions of the inner casing 1 and the outer casing 2 are inserted into the original riprap layer 6. The upper portion of the original riprap layer 6 is a gap with an inverted trapezoidal cross-section. The middle portion of the outer casing 2 is backfill clay 4 with a trapezoidal cross-section. The upper portion of the backfill clay 4 is backfill gravel 3, which is aligned with the original riprap layer 6. The outer casing 2 has a diameter of 2400 mm and a wall thickness of 20 mm, primarily serving to absorb external pressure and protect the inner casing. The inner casing 1 has a diameter of 2000 mm and a wall thickness of 20 mm, primarily providing protection and support during the drilling process.

[0021] A method for installing a cast-in-place pile casing under deep riprap geological conditions comprises the following steps:

[0022] Step 1: Casing processing

[0023] Because the rock layer in the drilling area is approximately 48 meters thick, posing the risk of grout leakage and hole collapse, the casing adopts a double-layer structure to enhance its strength and stability. The outer casing (2) has a diameter of 2400mm and a wall thickness of 20mm, primarily absorbing external pressure and protecting the inner casing. The inner casing (1) has a diameter of 2000mm and a wall thickness of 20mm, primarily providing protection and support during the drilling process. The casing is processed using a 75kW plate rolling machine to ensure dimensional accuracy and roundness.

[0024] Step 2: Put the pile driver in place and bury the casing

[0025] According to the diameter of the cast-in-place pile and the on-site engineering geological conditions, the outer casing 2 drill bit is a cross type with a diameter of 2350mm. The inner casing 1 impact drill bit has a diameter of 1950mm.

[0026] Onshore construction involves directly positioning the pile driver on a leveled site at an elevation of +6m. For offshore construction, the pile driver is disassembled and hoisted onto a pre-assembled steel platform using a crawler crane. Once assembled, the pile driver is positioned. Before positioning the pile driver, the pile position is measured and clearly marked.

[0027] For onshore steel casing burial, the steel casing is buried with inner and outer casings. During construction, the first section of the outer casing (4m long) is buried first, and the outer side is backfilled and compacted with clay. Clay is added while punching to make slurry. When the punching depth reaches 3-4m, the steel casing is extended. The following process is repeated: punching → extending the steel casing → vibrating and following up the steel casing. Due to the large friction between the riprap layer and the outer casing, the outer casing can only be followed up to about 18m. When the outer casing can no longer be followed up, the outer casing is stopped and punching is continued. When the punching depth reaches about 26m, the inner casing is prepared to be placed. The inner casing is placed and punching is continued to follow up the inner casing. The inner casing is continued to be extended while punching. When the inner steel casing reaches about 34m, the friction between the inner casing and the riprap layer is too large to continue to follow up.

[0028] This example describes the bored pile punching process for a nuclear power plant's large-scale wharf in detail. The wharf is connected to the East Intake Dyke via a high-pile beam-slab approach bridge. The approach bridge's pile foundation at the breakwater section utilizes 34 bored piles with a diameter of 2000 mm and a length of 104.6 to 107.1 meters. The East Intake Dyke utilizes explosive silt removal for silt replacement, resulting in a riprap layer up to 48 meters thick at the approach bridge.

[0029] Implementation Effect

[0030] The design of a double-layer casing structure effectively addresses the problems of grout leakage and hole collapse commonly encountered in the construction of cast-in-place piles in deep riprap layers, ensuring hole stability and construction quality. The outer casing enhances its strength and pressure resistance, while the inner casing effectively protects the hole wall during the drilling process. The use of composite slurry wall protection and appropriate filling treatment measures improves hole wall stability and drilling efficiency. The overall design significantly enhances the safety and efficiency of cast-in-place pile construction, adapts to the needs of construction in complex geological conditions, and provides reliable technical support for the construction of cast-in-place piles in deep riprap layers. Ultrasonic testing confirmed the pile body to be intact and classified as a Class I pile.

Claims

1. A cast-in-place pile casing for deep riprap geological conditions, characterized by: It adopts a double-layer structure, including an outer casing and an inner casing. The inner casing is located in the middle of the outer casing and is longer than the outer casing.

2. The cast-in-place pile casing for deep riprap geological conditions according to claim 1, characterized in that: The lower part of the outer casing is the original riprap stratum, and the lower parts of the inner casing and the outer casing are inserted into the original riprap stratum.

3. The cast-in-place pile casing for deep riprap geological conditions according to claim 2, characterized in that: The upper part of the original riprap stratum is a gap with an inverted trapezoidal cross section, the middle position of the outer casing is backfilled clay with a trapezoidal cross section, and the upper part of the backfilled clay is backfilled gravel.

4. The cast-in-place pile casing for deep riprap geological conditions according to claim 3, characterized in that: The backfill gravel and the original riprap stratum have a horizontal line.

5. The cast-in-place pile casing for deep riprap geological conditions according to claim 1, characterized in that: The outer casing bears the external pressure and protects the inner casing.

6. The cast-in-place pile casing for deep riprap geological conditions according to claim 1, characterized in that: The inner casing is used for protection and support during the hole forming process.

7. A method for installing a cast-in-place pile casing under deep riprap geological conditions, characterized in that: The steps include: Step 1: casing processing; Step 2: Put the pile driver in place and bury the casing.

8. The method for installing a cast-in-place pile casing under deep riprap geological conditions according to claim 1, characterized in that: In step 1, a plate rolling machine with a power of 75 kW is used to process the inner and outer casings to ensure the dimensional accuracy and roundness of the casings.

9. The method for installing a cast-in-place pile casing under deep riprap geological conditions according to claim 1, characterized in that: In step 2, a cross-shaped drill bit is used for the outer casing, and an impact drill bit is used for the inner casing. For onshore construction, the pile driver is directly placed on a leveled site with a site elevation of +6m. For offshore construction, a crawler crane is used to disassemble the pile driver and lift it onto a constructed steel platform. After the pile driver is assembled, it is placed in place. Before the pile driver is placed in place, the pile position is measured and determined. For onshore steel casing burial, the steel casing is buried with inner and outer double casings. During construction, the first section of the outer casing is buried first, and the outer side is backfilled and compacted with clay. Clay is added to make slurry while punching. When the punching depth is 3-4m, the steel casing is extended. The following process is repeated: punching → extending the steel casing → vibrating and following up the steel casing. When the outer casing can no longer follow up, stop following up the outer casing and continue punching. When the punching depth reaches 26m, prepare to place the inner casing, place the inner casing and continue punching and following up the inner casing. Continue to extend the inner casing and follow up the inner steel casing while punching.

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