A construction method of artificial hole digging pile for force-bearing layer containing soft interlayer

Abstract

This invention discloses a method for constructing manually excavated bored piles in bearing strata containing weak interlayers, comprising the following steps: S1: excavating and supporting the pile hole to the design elevation; S2: investigating the geological conditions of the bearing stratum at the pile tip, clarifying the size and distribution of the weak interlayer; S3: based on the investigation results, selecting an area without weak interlayers, horizontally excavating along the sidewall of the pile hole, and forming an expanded excavation space using a method of excavation and support as needed; S4: setting up a reinforcing cage in the supported expanded excavation space, and connecting the reinforcing cages in each expanded excavation space with steel plates to form an integral load-bearing structure; S5: lowering the pile body reinforcing cage and pouring and curing concrete. By selecting an area without weak interlayers for horizontal excavation, combined with the excavation and support of the spring-loaded self-locking support unit, the construction is safe and reliable; it increases the effective contact area between the pile tip and the bearing stratum, compensating for the insufficient bearing capacity caused by the weak interlayer, and is suitable for manually excavated bored pile construction under complex geological conditions such as karst mountainous areas.

Description

Technical Field

[0001] This invention relates to the field of civil engineering pile foundation construction technology, and in particular to a method for constructing manually excavated bored piles in bearing strata containing weak interlayers. Background Technology

[0002] Manually excavated bored piles have been widely used in the mountainous areas of southwest my country and karst regions due to their advantages such as simple construction equipment, low cost, high single pile bearing capacity, and strong environmental adaptability. However, due to limitations of traditional exploration techniques, it is often difficult to accurately identify the presence of weak interlayers such as mudstone layers, fracture zones, and karst cave filling materials in the bearing stratum at the pile tip before construction. If these weak interlayers are not detected and treated in time, they will significantly reduce the bearing capacity of the pile tip, leading to excessive or uneven settlement of the pile foundation, and in severe cases, even endangering the safety of the entire project.

[0003] Existing technologies primarily employ several methods to address the issue of weak interlayers in the bearing stratum at the pile tip. One method involves high-pressure grouting into the weak interlayer to fill the pores and solidify the interlayer, thereby increasing its bearing capacity. However, this method suffers from drawbacks, as the grouting effect is highly dependent on geological conditions, making it difficult to ensure uniform grout diffusion. Another method involves setting up longitudinal reinforcement structures at the pile bottom, such as driving micropiles or steel reinforcement bundles, to transfer the load to a deeper, more stable bearing stratum. However, this method requires additional drilling, causing significant disturbance to the bottom of the pile hole. Yet another method utilizes high-pressure water to cut through the weak rock layer followed by grout replacement. This method requires complex equipment and is unsuitable for the confined working environment of manually excavated piles. Additionally, another approach involves forming an enlarged head at the pile bottom to increase the contact area between the pile tip and the bearing stratum. However, traditional enlarged-head piles typically enlarge uniformly throughout the entire circumference, failing to consider the specific distribution of the weak interlayer; furthermore, the lack of effective on-site support during excavation increases the risk of borehole wall collapse. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for constructing bored piles in bearing strata containing weak interlayers. This method can effectively compensate for bearing capacity loss, simplify construction, and ensure safety.

[0005] Technical solution: This invention provides a method for constructing manually excavated bored piles in bearing strata containing weak interlayers, comprising the following steps:

[0006] S1: Excavate and support the pile holes to the design elevation;

[0007] S2: Investigate the geological conditions of the bearing stratum at the pile tip and determine the size and distribution of the weak interlayer;

[0008] S3: Based on the survey results, select an area without weak interlayers, and carry out horizontal excavation along the sidewall of the pile hole, and use the method of excavating and supporting at the same time to form the excavation space;

[0009] S4: Install steel cages in the supported excavation space, and connect the steel cages in each excavation space with steel plates to form an integral load-bearing structure.

[0010] S5: Lower the pile reinforcement cage and pour and cure the concrete.

[0011] Furthermore, the "excavate and support simultaneously" method in S3 is as follows: at the selected location, the first section of horizontal excavation is carried out, and after clearing the excavated soil, the first support unit is inserted to support the already excavated section; the next section of horizontal excavation is continued, and the subsequent support units are connected to the previous support units through a spring-loaded self-locking mechanism, and the connected support units are pushed forward to support the newly excavated section; this process is repeated until the excavation reaches the predetermined depth, forming an excavated space composed of multiple support units connected end to end.

[0012] Furthermore, the support unit is a cylindrical or frame structure adapted to the cross-sectional shape of the excavated space, with protruding teeth at the front end and a groove matching the teeth at the rear end; the first support unit only has a groove.

[0013] Furthermore, the locking teeth are equipped with a compression spring and a spring-loaded fastener connected to the compression spring and capable of extending and retracting laterally along the locking teeth.

[0014] Furthermore, the spring-loaded self-locking connection is as follows: when the locking teeth at the front end of the subsequent support unit are inserted into the locking slot at the rear end of the preceding support unit, the compression spring is first compressed and drives the spring-loaded fastener to retract; after the locking teeth are fully inserted into the predetermined position of the slot, the compression spring rebounds and drives the spring-loaded fastener to pop out, limiting the locking teeth to the slot and achieving self-locking.

[0015] Furthermore, in S4, the lap length between the reinforcing cage and the steel plate shall not be less than 15d, where d is the diameter of the main reinforcing bar of the reinforcing cage, and the lap joint shall be welded.

[0016] Furthermore, in S2, at least one geophysical exploration method, either ground-penetrating radar or sonic CT, is used to investigate the bearing stratum at the pile tip, clarifying the size, depth, and spatial distribution of the weak interlayer.

[0017] Furthermore, the cross-sectional dimensions and depth of the excavated space are determined after calculation based on the size, burial depth, distribution range of the weak interlayer, and the design bearing capacity requirements of the pile foundation.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0019] (1) Instead of directly treating the weak interlayer, the horizontal excavation is selectively carried out in areas without weak interlayer, which increases the effective contact area between the pile end and the bearing layer. During the horizontal excavation, the spring-locked self-locking support unit is used to support the newly excavated section in time to avoid the risk of hole wall collapse.

[0020] (2) No complex equipment is required. The location and size of the excavation can be flexibly adjusted according to the size and distribution of the weak interlayer. The construction cost is lower than that of increasing the pile length or the full expansion scheme. Compared with post-grouting, deepening the pile length and other methods, the material consumption and time are significantly reduced, which has good economic benefits.

[0021] (3) The protruding structure formed by the excavation increases the friction and embedment between the pile body and the surrounding soil and rock, significantly improving the pull-out bearing capacity of the pile body. At the same time, the steel cage in the excavation space forms an integral load-bearing structure by welding steel plates, so that the excavation part works in coordination with the pile body, effectively compensating for the bearing capacity loss caused by the weak interlayer. Attached Figure Description

[0022] Figure 1 This is a schematic diagram showing the excavation of the pile hole to the bottom of the pit for the manually excavated bored pile of the present invention;

[0023] Figure 2 This is a schematic diagram of the horizontal enlargement of the pile hole in the manually excavated bored pile of the present invention;

[0024] Figure 3 This is a schematic diagram of the support unit of the present invention;

[0025] Figure 4 This is a schematic diagram of the tooth structure of the support unit of the present invention;

[0026] Figure 5 This is a schematic diagram showing the connection between the support units of the present invention;

[0027] Figure 6 This is a schematic diagram of the connection plan of the steel cage within the excavated space of the present invention;

[0028] Figure 7 This is a schematic diagram showing the connection between the reinforcing cage and the connecting steel plate within the excavated space of the present invention.

[0029] Figure 8 This is a schematic diagram of a manually excavated bored pile cast using the method of the present invention. Detailed Implementation

[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0031] A method for constructing bored piles in bearing strata containing weak interlayers is presented. This method is commonly used in mountainous karst formations. After excavating to the design elevation using conventional techniques, it is discovered that the bearing stratum contains strip-shaped weak interlayers distributed in multiple directions around the pile, while the remaining rock mass is relatively intact. The specific method is as follows:

[0032] S1: Excavate and support the pile holes to the design elevation, such as Figure 1As shown, the pile hole is excavated in layers in the soil and rock mass 2 according to the conventional process of manually excavated pile, and the hole wall is supported at the same time until the design elevation of the pile bottom is reached. The bottom of the pile hole is then preliminarily cleaned and leveled.

[0033] S2: Investigate the geological conditions of the bearing layer at the pile tip; using geophysical exploration methods, ground-penetrating radar and sonic CT, conduct a comprehensive investigation of the bearing layer 3 within 3m below the pile tip to determine the distribution of weak interlayers.

[0034] S3: As Figure 2 As shown, based on the results of the bearing stratum investigation, an area without weak interlayers was selected, and horizontal excavation was carried out along the sidewall of the pile hole towards the interior. The specific operation is as follows:

[0035] First, at the selected location, the first section of the excavation is horizontally expanded. After the excavation is cleaned up, the first support unit 5 is inserted to support the expanded section.

[0036] Then, continue to excavate horizontally to the next distance, connect the subsequent support unit with the previous support unit through a spring-loaded self-locking device, and push the connected support unit forward to support the new excavation section;

[0037] This process of excavation and support is repeated until the predetermined depth is reached, forming an expanded excavation space 4 composed of multiple support units connected end to end. The cross-sectional dimensions and depth of the expanded excavation space 4 are not fixed but determined by calculations based on the size, depth, and distribution of the weak interlayer 1, as well as the design bearing capacity requirements of the pile foundation. For example, for a 1.2m diameter pile hole, if the weak interlayer is found to be located within the 0°~90° range of the sidewall, then the expansion is carried out in the 180°~270° direction on the opposite side.

[0038] like Figure 3 , Figure 4 As shown, the support unit 5 is shaped to match the cross-sectional shape of the excavated space 4. The figure shows a rectangular frame structure, but a cylindrical structure can also be used. Each support unit 5 has a protruding locking tooth 6 at its front end and a locking groove 9 at its rear end that matches the locking tooth 6. The first support unit only has the locking groove 9 and no locking tooth at its front end. The locking tooth 6 is equipped with a compression spring 7 and a spring-loaded fastener 8. The locking tooth 6 has a receiving cavity inside or on its side. The compression spring 7 is installed in the receiving cavity, and the spring-loaded fastener 8 is connected to the compression spring 7 and can extend or retract radially or laterally along the locking tooth 6. The end of the spring-loaded fastener 8 has a guide slope, which facilitates smooth push-back by the inner wall of the locking groove 9 during insertion, avoiding jamming.

[0039] like Figure 5As shown, when the protruding locking tooth 6 at the front end of the subsequent support unit is inserted into the locking groove 9 at the rear end of the preceding support unit, the inner wall of the locking groove 9 presses against the spring-loaded fastener 8, compressing the compression spring 7 and causing the spring-loaded fastener 8 to retract into the locking tooth 6. After the spring-loaded fastener 8 aligns with the limiting recess on the inner wall of the locking groove 9 or passes through the outlet of the locking groove 9, the compression spring 7 rebounds, causing the spring-loaded fastener 8 to pop out, limiting the locking tooth 6 within the locking groove 9. Once the locking tooth 6 is fully inserted into the predetermined position of the locking groove 9, a self-locking connection is achieved. This connection method requires no additional tools; it automatically locks upon insertion, making operation simple and reliable.

[0040] S4: Reinforcing cages are installed within the supported excavated space and overlapped with each other, such as... Figure 6 , Figure 7 As shown, prefabricated steel cages 10, matching the dimensions of each excavation space 4, are hoisted and placed within the excavation space 4. Subsequently, steel plates 11 are welded between the corresponding steel cages 10, with the steel plates 11 positioned close to the bottom of the steel cage 10, i.e., near the center of the pile hole, thus connecting the steel cages within each excavation space to form an integral load-bearing structure. The lap length between the steel cage and the steel plate is not less than 15 times the diameter of the main reinforcement bars of the steel cage, and the lap joint is fully welded on both sides to ensure a firm connection and form an integral load-bearing structure.

[0041] S5: Lower the pile reinforcement cage and pour and cure the concrete. For example... Figure 8 As shown, the prefabricated pile reinforcement cage is slowly lowered to the design elevation at the bottom of the pit, and then concrete is poured into the pile hole. During the process, a vibrating device is used to compact the concrete in layers to ensure that the pile hole and the enlarged excavation space 4 are filled densely. After the pouring is completed, it is cured according to the specifications until the concrete reaches the design strength, and finally a manually excavated pile is formed by the enlarged excavation section 12 and the original pile body 13.

[0042] The above-described implementation methods can be flexibly applied under different engineering conditions. Depending on the actual distribution of the weak interlayer, excavation can be carried out in one or more directions, and the number, size, and depth of the excavated space can be adjusted as needed.

Claims

1. A method for constructing manually excavated bored piles in bearing strata containing weak interlayers, characterized in that, Includes the following steps: S1: Excavate and support the pile holes to the design elevation; S2: Investigate the geological conditions of the bearing stratum at the pile tip and determine the size and distribution of the weak interlayer; S3: Based on the survey results, select an area without weak interlayers, and carry out horizontal excavation along the sidewall of the pile hole, and use the method of excavating and supporting at the same time to form the excavation space; S4: Install steel cages in the supported excavation space, and connect the steel cages in each excavation space with steel plates to form an integral load-bearing structure. S5: Lower the pile reinforcement cage and pour and cure the concrete.

2. The method according to claim 1, characterized in that, The method of excavating and supporting simultaneously includes: horizontally excavating a first section at a selected location, clearing away the excavated soil, and inserting the first support unit to support the already excavated section; continuing to horizontally excavate the next section, connecting the subsequent support unit to the preceding support unit with a spring-loaded self-locking mechanism, and advancing the connected support unit forward to support the newly excavated section; repeating this process until the excavation reaches a predetermined depth, forming an excavated space composed of multiple support units connected end to end.

3. The method according to claim 2, characterized in that, The support unit is a cylindrical or frame structure adapted to the cross-sectional shape of the excavated space, with protruding teeth at the front end and a groove matching the teeth at the rear end; the first support unit only has a groove.

4. The method according to claim 3, characterized in that, The locking teeth are equipped with a compression spring and a spring-loaded fastener connected to the compression spring and capable of extending and retracting laterally along the locking teeth.

5. The method according to claim 4, characterized in that, The spring-loaded self-locking connection is as follows: when the locking teeth at the front end of the subsequent support unit are inserted into the locking slot at the rear end of the preceding support unit, the compression spring is first compressed and drives the spring-loaded fastener to retract; after the locking teeth are fully inserted into the predetermined position of the slot, the compression spring rebounds and drives the spring-loaded fastener to pop out, limiting the locking teeth to the slot and achieving self-locking.

6. The method according to claim 1, characterized in that, In S4, the lap length between the reinforcing cage and the steel plate is not less than 15d, where d is the diameter of the main reinforcing bar of the reinforcing cage, and the lap joint is welded.

7. The method according to claim 1, characterized in that, In S2, at least one geophysical exploration method, either ground-penetrating radar or acoustic CT, is used to investigate the bearing stratum at the pile tip, clarifying the size, depth, and spatial distribution of the weak interlayer.

8. The method according to claim 1, characterized in that, The cross-sectional dimensions and depth of the excavated space are determined after calculation based on the size, burial depth, distribution range of the weak interlayer, and the bearing capacity requirements of the pile foundation design.

Images