A method for forming a hole for a cast-in-place pile in an ultra-thick block stone backfill layer

Abstract

The application discloses a kind of super-thick block stone backfill layer bored pile hole-forming methods, comprising: prefabricated outer sleeve bottom section, outer sleeve standard section, inner sleeve bottom section and inner sleeve standard section, at least one pad steel plate is prepared;After excavating foundation pit in preset position, outer sleeve bottom section is buried in foundation pit, and backfill is carried out in the periphery of outer sleeve bottom section;Pile foundation percussion drill is used to drill, the process of using drill bit to probe into the hole drilled in outer sleeve bottom section, repeatedly use measuring rope to measure hole depth;When hole depth exceeds 1-2m at the bottom of outer sleeve bottom section, pause drilling, outer sleeve standard section is welded on the upper end of outer sleeve bottom section, pad steel plate is placed on the top of outer sleeve standard section, pad steel plate is hammered using the impact force of drill bit drop, pad steel plate is removed, and outer sleeve standard section is repeatedly welded in the process of following up, until the situation that outer sleeve bottom section cannot follow up appears.

Description

Technical Field

[0001] This invention relates to the field of bored pile technology, and in particular to a method for bored piles in ultra-thick riprap backfill layers. Background Technology

[0002] In the construction of foundation engineering projects in ports, docks, bridges, and coastal soft soil areas, bored piles are widely used due to their high bearing capacity and strong adaptability. However, in some coastal areas and artificial reclamation areas, there are often thick layers of rubble backfill (usually more than 10m thick) in the foundation. These strata are composed of rubble and gravel of varying sizes and high strength, with a loose structure, high porosity, and poor cementation, which brings great difficulties to the drilling and construction of bored piles.

[0003] Currently, the construction of bored piles in riprap backfill layers typically employs an impact drilling rig combined with a single steel casing. However, in practical engineering applications, this traditional method has revealed the following significant problems when constructing in ultra-thick riprap backfill layers: Firstly, the resistance to the entire casing is high, which can easily cause jamming or even seizing. The stones in the backfill layer are large in size and have sharp edges. During the sinking process, the casing is subjected to strong compression and friction with the stones. Especially when the bottom of the casing encounters large-diameter stones, the resistance increases sharply, often causing the casing to be unable to continue to advance and forcing the hammer to stop, which seriously affects the construction progress. Secondly, there are relatively few devices capable of drilling in geological conditions with ultra-thick rock backfill layers. Conventional rotary drilling rigs cannot cut hard rocks, rotary drilling rigs have extremely low drilling efficiency in rock layers and the borehole walls are prone to collapse. Although impact drilling rigs can break rocks, the depth of single-layer casing is limited (usually only 5-8m before getting stuck). Specialized equipment such as full casing drilling rigs and large vibratory hammers are scarce, difficult to deploy, and costly. Third, the large gaps in the rock layer make it prone to grout leakage due to moisture, which can lead to borehole collapse. The large pore structure of the rock backfill layer causes a large amount of mud to seep into the formation during drilling, which not only increases the cost of mud consumption, but also makes it impossible to effectively establish mud column pressure, further exacerbating the risk of borehole instability. Therefore, there is an urgent need for a drilling and grouting method for ultra-thick rock backfill layers that is suitable for the special geological conditions of coral fine sand, resistant to strong marine corrosion, resistant to tidal erosion, and prevents fine sand leakage. Summary of the Invention

[0004] The purpose of this invention is to provide a method for drilling and grouting piles in ultra-thick boulders backfill layers to solve the above-mentioned problems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for drilling and grouting piles in ultra-thick riprap backfill layers, characterized by comprising: S1. Prefabricate the outer casing bottom section, outer casing standard section, inner casing bottom section and inner casing standard section in batches according to the design dimensions, and prepare at least one pad steel plate at the same time. S2. After excavating the foundation pit at the preset location using an excavator, the bottom section of the outer casing is buried in the foundation pit, and backfilling is carried out around the bottom section of the outer casing. S3. Use a pile foundation impact drilling rig to drill holes. During the drilling process, repeatedly use a measuring rope to measure the hole depth while the drill bit is inserted into the bottom section of the outer casing. S4. When the hole depth exceeds the bottom of the outer casing bottom section by 1-2m, stop drilling, weld the outer casing standard section to the upper end of the outer casing bottom section, place a pad steel plate on the top of the outer casing standard section, and use the impact force of the drill bit to hammer the pad steel plate until the distance between the pad steel plate and the working surface is less than 30cm, then remove the pad steel plate. S5. Repeat step S3 and repeatedly weld the outer casing standard section during the casing follow-up process until the outer casing bottom section cannot be followed up. Measure the overall depth of the outer casing structure formed by the outer casing bottom section and multiple outer casing standard sections, and compare it with the length of the inner casing bottom section. Adjust the length of the inner casing structure of the inner casing bottom section and the inner casing standard section in advance according to the comparison results. S6. After replacing the drill bit of the pile foundation impact drilling rig, put the inner cylinder structure consisting of the inner casing bottom section and the inner casing standard section into the outer cylinder structure consisting of the outer casing bottom section and multiple outer casing standard sections. Place a pad steel plate on top of the inner casing structure consisting of the inner casing bottom section and the inner casing standard section, and use the impact force below the drill bit to hammer the pad steel plate until the inner casing bottom section can no longer follow. S7. Use a drill bit to drill into the bottom section of the inner casing and repeatedly use a measuring rope to measure the hole depth. S8. When the hole depth exceeds the bottom of the inner casing bottom section by 1-2m, stop drilling, weld the inner casing standard section to the upper end of the inner casing bottom section, place a pad steel plate on the top of the inner casing standard section, and use the impact force of the drill bit to hammer the pad steel plate until the distance between the pad steel plate and the working surface is less than 30cm, then remove the pad steel plate. S9. Repeat step S8, and repeatedly weld the standard section of the inner casing during the casing follow-up process until the bottom section of the inner casing passes through the rubble backfill layer.

[0006] Preferably, the length of the bottom section of the outer casing is 4-6m, the length of the bottom section of the inner casing is not less than 10m, and the lengths of the standard sections of the outer and inner casings are 2m.

[0007] Preferably, the bottom section of the outer casing, the standard section of the outer casing, the bottom section of the inner casing, and the top of the standard section of the inner casing are welded with annular steel plates that match their diameters. The length of the annular steel plates is not less than 30cm and the thickness is not less than 10mm.

[0008] Preferably, in step S2, during the backfilling of the bottom section of the outer casing, fine-grained soil is first filled in, followed by the original soil, and then compaction is performed after the backfilling is completed.

[0009] Preferably, in any of steps S3 to S9, mud concentration adjustment is required.

[0010] Preferably, if a mud leak occurs in any of steps S3-S9, the sealing material is stirred into a lump, and an excavator is used to put the sealing material into the borehole. The backfill thickness is not less than 1m, and the material is compacted with a drill bit. The borehole is left to stand for 4-6 hours, and drilling is resumed only after it is confirmed that there is no mud leak.

[0011] Preferably, the sealing material is made of clay, silt, cement and water, wherein the ratio of clay:silt:cement:water is 1:1:2:0.8~1.

[0012] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses a double-layer casing structure with an outer casing and an inner casing. The outer casing advances first to form an outer protective channel. Then, the inner casing continues to advance downwards under the protection of the outer casing to pass through the boulders backfill layer. During the advance, the outer casing pre-crushes and compacts the surrounding boulders, creating favorable conditions for the sinking of the inner casing. This effectively solves the problem that a single-layer casing has too much resistance in an ultra-thick boulders layer and cannot continue to advance, enabling the casing to reliably pass through boulders backfill layers with a thickness of more than 10m. 2. In this invention, the casing is constructed by combining the bottom section of the casing with multiple standard sections of the casing. On-site, the casing is lengthened section by section according to the actual hole depth, avoiding transportation and hoisting difficulties caused by excessively long casings. It is also convenient to flexibly adjust the total length when the follow-up is obstructed, thereby reducing the equipment requirements for drilling and grouting piles. It has strong construction adaptability and is easy to operate. At the same time, this invention makes full use of the advantages of impact drilling rigs, which can not only meet the work requirements of breaking up rocks, but also meet the work requirements of drilling by using the impact force of the drill bit being lowered. 3. This invention addresses the problem of large pores in the rubble backfill layer, which is prone to mud leakage due to tidal water. It uses a block-shaped sealing material made of clay, silt, cement, and water in a ratio of 1:1:2:0.8~1. After being applied to the leakage area and compacted by the drill bit, it can quickly fill the gaps between the rubble and solidify to form a water-proof sealing layer, effectively blocking the path of mud loss, restoring the liquid column pressure in the hole, ensuring the stability of the hole wall, and preventing hole collapse accidents caused by slurry leakage. The use of silt as one of the sealing materials, which is locally sourced, indirectly reduces the cost of sealing. Attached Figure Description

[0013] Figure 1 This is a construction schematic diagram of the installation of the bottom section of the outer casing in this invention.

[0014] Figure 2This is a schematic diagram of the construction process of percussion drilling in this invention.

[0015] Figure 3 This is a construction schematic diagram of the standard section of the welded outer casing in this invention.

[0016] Figure 4 This is a construction diagram illustrating the follow-up installation of the outer casing in this invention.

[0017] Figure 5 This is a schematic diagram of the installation of the bottom section of the inner casing in this invention.

[0018] Figure 6 This is a construction schematic diagram of the standard section of the welded inner casing in this invention.

[0019] Figure 7 This is a construction diagram illustrating the follow-up installation of the inner casing in this invention.

[0020] Figure 8 This is a construction diagram of the inner casing penetrating the riprap backfill layer in this invention.

[0021] 1. Outer casing bottom section; 2. Outer casing standard section; 3. Inner casing bottom section; 4. Inner casing standard section; 5. Pad steel plate; 6. Annular steel plate. Detailed Implementation

[0022] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. In the following detailed description, many specific details are set forth for ease of explanation to provide a full understanding of the embodiments of the present invention. However, it is obvious that one or more embodiments may be implemented without these specific details. Furthermore, in the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concept of the present invention.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising”, “including”, etc., as used herein indicate the presence of features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0024] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted in a manner consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0025] Please see the appendix Figure 1 -Appendix Figure 8 A method for drilling and grouting piles in ultra-thick riprap backfill layers includes: S1. Prefabricate the outer casing bottom section 1, outer casing standard section 2, inner casing bottom section 3, and inner casing standard section 4 in batches according to the design dimensions, and prepare at least one pad steel plate 5. The length of the outer casing bottom section 1 is 4-6m, the length of the inner casing bottom section 3 is not less than 10m, and the lengths of the outer casing standard section 2 and the inner casing standard section 4 are 2m. The top of the outer casing bottom section 1, outer casing standard section 2, inner casing bottom section 3, and inner casing standard section 4 is welded with an annular steel plate 6 that matches its diameter. The length of the annular steel plate 6 is not less than 30cm and the thickness is not less than 10mm. Considering that drilling is carried out by the impact force of the drill bit of the impact drilling rig, although the steel plate 5 is equipped as the impact medium during the impact process, the cylinder deformation still occurs. In order to avoid the above situation, annular steel plates 6 with matching diameters are welded to the top of the outer casing bottom section 1, the outer casing standard section 2, the inner casing bottom section 3 and the inner casing standard section 4 to improve the overall ring stiffness of the casing and prevent deformation during the casing advance.

[0026] S2. After excavating the foundation pit at the preset location using an excavator, the bottom section 1 of the outer casing is buried in the foundation pit. Backfilling is carried out around the bottom section 1 of the outer casing. During the backfilling of the bottom section 1 of the outer casing, fine-grained soil is first filled in, and then the original soil is backfilled in. After the backfilling is completed, compaction is carried out. After the bottom section 1 of the outer casing is buried in the foundation pit, it is necessary to backfill the foundation pit to fix the position of the bottom section 1 of the outer casing. In this invention, the foundation pit backfilling first involves backfilling fine-grained soil around the bottom section 1 of the outer casing. The fine-grained soil can reduce the friction of the casing wall during the outer casing's installation and play a certain lubricating role. After the fine-grained soil is backfilled, the original soil is backfilled to reinforce the position of the bottom section 1 of the outer casing.

[0027] S3. Drilling is carried out using a pile foundation impact drilling rig. During the drilling process, the drilling depth is repeatedly measured using a measuring rope while the drill bit is inserted into the bottom section 1 of the outer casing. During the drilling process, the hole depth needs to be measured repeatedly using a measuring rope, usually once every 0.5m of drilling, and the hole depth data is recorded. S4. When the hole depth exceeds the bottom of the outer casing bottom section 1 by 1-2m, stop drilling, weld the outer casing standard section 2 to the upper end of the outer casing bottom section 1, place the pad steel plate 5 on the top of the outer casing standard section 2, and use the impact force of the drill bit to hammer the pad steel plate 5 until the distance between the pad steel plate 5 and the working surface is less than 30cm, then remove the pad steel plate 5. When the hole depth exceeds the bottom of the outer casing section 1 by 1-2m, stop drilling, hoist a standard outer casing part 2 to the hole opening, align it with the upper end of the outer casing section 1, and then perform full welding connection. The weld height should not be less than 8mm. Then, place a shim steel plate 5 on top of the standard outer casing section 2, restart drilling, and use the impact force generated by the drill bit to hammer the shim steel plate 5 to achieve the purpose of the outer casing following the overall progress. Continue until the distance between the shim steel plate 5 and the working surface is less than 30cm, and then remove the shim steel plate 5. It should be noted that the drill bit diameter is slightly smaller than the inner diameter of the casing. Usually, the difference between the drill bit diameter and the inner diameter of the casing is 150mm-300mm.

[0028] S5. Repeat step S3 and repeatedly weld the outer casing standard section 2 during the casing follow-up process until the outer casing bottom section 1 cannot follow up. Measure the overall depth of the outer casing structure formed by the outer casing bottom section 1 and multiple outer casing standard sections 2, and compare it with the length of the inner casing bottom section 3. Adjust the length of the inner casing structure of the inner casing bottom section 3 and the inner casing standard section 4 in advance according to the comparison result. Repeat the steps of drilling, measuring, and welding the outer casing standard section 2 until the outer casing bottom section 1 can no longer follow, which means that the entire outer casing structure is completed. Then measure the length of the entire outer casing structure and pre-adjust the inner casing mechanism. Taking the inner casing bottom section as 10m and the outer casing structure as 13m as an example, the inner casing structure needs to be longer than the outer casing structure. Therefore, it is necessary to pre-weld two inner casing standard sections 4 on the inner casing bottom section 3 so that the length of the inner casing structure reaches 14.6m, in preparation for the subsequent follow-up of the inner casing structure.

[0029] S6. After replacing the drill bit of the pile foundation impact drilling rig, place the inner cylinder structure consisting of the inner casing bottom section 3 and the inner casing standard section 4 into the outer cylinder structure consisting of the outer casing bottom section 1 and multiple outer casing standard sections 2. Place the pad steel plate 5 on top of the inner casing structure consisting of the inner casing bottom section 3 and the inner casing standard section 4, and use the impact force below the drill bit to hammer the pad steel plate 5 until the inner casing bottom section 3 can no longer follow. S7. Use a drill bit to drill a hole inside the bottom section 3 of the inner casing, and repeatedly use a measuring rope to measure the hole depth. S8. When the hole depth exceeds the bottom of the inner casing bottom section 3 by 1-2m, stop drilling, weld the inner casing standard section 4 to the upper end of the inner casing bottom section 3, place the pad steel plate 5 on the top of the inner casing standard section 4, and use the impact force of the drill bit to hammer the pad steel plate 5 until the distance between the pad steel plate 5 and the working surface is less than 30cm, then remove the pad steel plate 5. S9. Repeat step S8, and repeatedly weld the inner casing standard section 4 during the casing follow-up process until the inner casing bottom section 3 passes through the rubble backfill layer. After replacing the drill bit with one that is compatible with the inner casing bottom section 3, the drilling, measurement and welding of the inner casing standard section 4 are repeated, based on the inner casing bottom section 3 and the inner casing standard section 4, until the inner casing bottom section 3 passes through the rubble backfill layer, which means the grouting pile hole is completed. The method to determine that the inner casing bottom section 3 has passed through the rubble backfill layer is that the drill bit impact sound becomes dull and the returned rock cuttings contain a large number of cohesive soil particles.

[0030] Specifically, in any of steps S3 to S9, mud concentration adjustment is required. Throughout the entire drilling process, mud concentration needs to be continuously adjusted to keep the mud level above the groundwater level or the highest tide level. Typically, the mud specific gravity is controlled at 1.25-1.40, and the viscosity is controlled at 22-25s.

[0031] Specifically, if mud leakage occurs in any of steps S3 to S9, the sealing material is stirred into lumps, and an excavator is used to put the sealing material into the borehole. The backfill thickness is not less than 1m, and the material is compacted with a drill bit. After standing for 4-6 hours, drilling can resume only after confirming that there is no mud leakage. There is a risk of mud leakage in any of the steps S3 to S9. If mud leakage occurs, it is necessary to immediately seal it with a plugging material. The specific plugging operation method is to add lumpy plugging material according to the ratio, about 1m³ each time, with a thickness of about 1 to 1.2m. If there is no mud leakage after standing for 4 to 6 hours, the plugging is complete. If there is still leakage, repeat the above plugging steps until the plugging is complete.

[0032] Specifically, the sealing material is made of clay, silt, cement, and water, with the ratio of clay:silt:cement:water being 1:1:2:0.8~1. Existing leak-sealing materials typically use a mixture of clay, cement, and water, and all of these materials need to be purchased in advance. In order to reduce the cost of use, this invention uses locally sourced materials and replaces part of the clay with silt. After multiple experiments, the leak-sealing effect is best when the ratio of clay:silt:cement:water is 1:1:2:0.8~1.

[0033] Considering the high resistance during the advancement of the entire casing in the existing technology, which can easily lead to jamming or even seizing, this invention adopts a double casing advancement process for the formation of cast-in-place piles.

[0034] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for drilling and grouting piles in ultra-thick riprap backfill layers, characterized in that, include: S1. Prefabricate the outer casing bottom section (1), outer casing standard section (2), inner casing bottom section (3) and inner casing standard section (4) in batches according to the design dimensions, and prepare at least one pad steel plate (5). S2. After excavating the foundation pit at the preset location using an excavator, the bottom section (1) of the outer casing is buried in the foundation pit, and backfilling is carried out around the bottom section (1) of the outer casing. S3. Drilling is carried out using a pile foundation impact drilling machine. During the drilling process, the drilling bit is used to probe into the bottom section (1) of the outer casing. The hole depth is measured repeatedly using a measuring rope. S4. When the hole depth exceeds the bottom of the outer casing bottom section (1) by 1-2m, stop drilling, weld the outer casing standard section (2) to the upper end of the outer casing bottom section (1), place the pad steel plate (5) on the top of the outer casing standard section (2), and use the impact force of the drill bit to hammer the pad steel plate (5) until the distance between the pad steel plate (5) and the working surface is less than 30cm, and remove the pad steel plate (5). S5. Repeat step S3 and repeatedly weld the outer casing standard section (2) during the casing follow-up process until the outer casing bottom section (1) cannot follow up. Measure the overall depth of the outer casing structure formed by the outer casing bottom section (1) and multiple outer casing standard sections (2) and compare it with the length of the inner casing bottom section (3). Adjust the length of the inner casing structure of the inner casing bottom section (3) and the inner casing standard section (4) in advance according to the comparison result. S6. After replacing the drill bit of the pile foundation impact drilling rig, place the inner cylinder structure consisting of the inner casing bottom section (3) and the inner casing standard section (4) into the outer cylinder structure consisting of the outer casing bottom section (1) and multiple outer casing standard sections (2). Place the pad steel plate (5) on top of the inner casing structure consisting of the inner casing bottom section (3) and the inner casing standard section (4), and use the impact force below the drill bit to hammer the pad steel plate (5) until the inner casing bottom section (3) can no longer follow. S7. Use a drill bit to drill into the bottom section (3) of the inner casing and repeatedly use a measuring rope to measure the hole depth. S8. When the hole depth exceeds the bottom of the inner casing bottom section (3) by 1-2m, stop drilling, weld the inner casing standard section (4) to the upper end of the inner casing bottom section (3), place the pad steel plate (5) on the top of the inner casing standard section (4), and use the impact force of the drill bit to hammer the pad steel plate (5) until the distance between the pad steel plate (5) and the working surface is less than 30cm, and remove the pad steel plate (5). S9. Repeat step S8 and repeatedly weld the inner casing standard section (4) during the casing follow-up process until the inner casing bottom section (3) passes through the rubble backfill layer.

2. The method for drilling and grouting piles in ultra-thick riprap backfill layers according to claim 1, characterized in that: The outer casing bottom section (1) is 4-6m long, the inner casing bottom section (3) is not less than 10m long, and the outer casing standard section (2) and the inner casing standard section (4) are 2m long.

3. The method for drilling and grouting piles in ultra-thick riprap backfill layers according to claim 1, characterized in that: The outer casing bottom section (1), the outer casing standard section (2), the inner casing bottom section (3) and the inner casing standard section (4) are welded with annular steel plates (6) that match their diameters. The annular steel plates (6) are not less than 30cm in length and not less than 10mm in thickness.

4. The method for drilling and grouting piles in ultra-thick riprap backfill layers according to claim 1, characterized in that: In step S2, during the backfilling of the bottom section (1) of the outer casing, fine soil is first filled in, followed by the original soil, and then compaction is carried out after the backfilling is completed.

5. The method for drilling and grouting piles in ultra-thick riprap backfill layers according to claim 1, characterized in that: In any of steps S3 to S9, mud concentration adjustment is required.

6. The method for drilling and grouting piles in ultra-thick riprap backfill layers according to claim 5, characterized in that: If mud leakage occurs in any of steps S3 to S9, stir the sealing material into clumps, use an excavator to put the sealing material into the borehole, backfill to a thickness of not less than 1m, compact it with a drill bit, let it stand for 4-6 hours, and resume drilling only after confirming that there is no mud leakage.

7. The method for drilling and grouting piles in ultra-thick riprap backfill layers according to claim 6, characterized in that: The sealing material is made of clay, silt, cement and water, with the ratio of clay:silt:cement:water being 1:1:2:0.8~1.

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