Split combined suspension protection cylinder and method of use

Abstract

This invention belongs to the technical field of casing in pile foundation construction, and discloses a split-type combined suspended casing and its usage method. This split-type combined suspended casing converts the lateral frictional force and bottom surface force of conventional buried extrusion casings into the force on a bearing steel plate on the ground surface at the borehole opening, while increasing the vertical bearing area, converting the high pressure borne by the casing into compressive stress on the ground. Specifically, it includes: a bearing steel plate, a casing, and a bearing seat. This invention addresses the construction of ultra-deep, large-diameter pile foundations, especially in situations with high casing bearing capacity and low foundation bearing capacity. It improves the design of the conventional buried extrusion casing installation technology, effectively solving several construction problems associated with buried extrusion casings under high bearing capacity conditions, such as low foundation bearing capacity, easy casing settlement and tilting, numerous and inefficient installation procedures, high lateral frictional resistance making extraction difficult and prone to damage and deformation, and low reusability.

Description

Technical Field

[0001] This invention belongs to the field of casing technology in pile foundation construction, and particularly relates to a split-type combined suspended casing and its usage method. Background Technology

[0002] For conventional borehole casings used in pile foundation construction, the filling and extrusion type casing is used. The process technology for this type of casing is as follows: measurement and positioning, excavation of casing pit, leveling and compaction of the bottom of the pit foundation, laying of the bedding layer, hoisting and positioning of the casing, leveling and fixing, symmetrical layering and compaction of soil around the casing, excavation of grouting trench, cleaning of soil around the casing opening, and borehole construction.

[0003] In the above process flow, there are two main methods for excavating the casing pit: one is using excavation equipment such as excavators, and the other is using rotary drilling rigs to enlarge the hole. Then, granular materials such as gravel and soil are filled around the casing and compacted. In addition, some projects use hydraulic vibratory clamps to install small-diameter casings in soft foundations. This method is suitable for use when the casing has a relatively low load-bearing capacity.

[0004] Conventional buried extrusion casing technology has several shortcomings, especially when the casing needs to withstand high pressure during the construction of large-diameter deep pile foundations. It also has problems such as complex process, low efficiency, difficulty in meeting the bearing capacity of the casing, easy deviation, easy deformation, and low reusability.

[0005] For projects involving large-diameter, deep pile foundations with high vertical accuracy and bearing capacity, the existing buried compression casing technology for orifice protection, guidance, and bearing the weight of objects at the orifice has the following drawbacks and limitations:

[0006] ① The protection of the borehole opening was inadequate, the surface near the borehole opening was muddy and watery, the construction environment was dirty and messy, and the on-site civilized construction did not meet the standards;

[0007] ② The casing is prone to uneven settlement (uneven stress on the casing during filling, low or uneven strength of the bottom contact surface of the casing), which in turn causes the casing to tilt.

[0008] ③ The casing length is generally short (usually around 2m), resulting in poor guiding performance and difficulty in ensuring the vertical accuracy of the pile foundation;

[0009] ④ Conventional casings have low load-bearing capacity and cannot withstand the weight of heavy steel cages and other objects such as guide pipes placed below the borehole, making them prone to tilting.

[0010] ⑤ When installing casings with high bearing capacity, the casing base (especially in soft soil foundations) needs to be compacted or a cushion layer applied to increase the bearing capacity of the foundation and prevent casing settlement and deformation. This addresses the issue of both low foundation bearing capacity and low casing bearing capacity. After installation, the surrounding soil needs to be backfilled and compacted to compress the casing, increasing the friction on its sides and thus increasing the bearing capacity of the top surface. The bottom edge of the casing has a small area and low bearing capacity; the bearing capacity of the top surface mainly relies on the friction of the outer wall. When the top surface bears a large load, it is prone to settlement and tilting.

[0011] ⑥ When pulling out the casing, the casing is prone to deformation, resulting in high wear and tear and low reuse rate. Because conventional casings rely on filling and compaction to increase their bearing capacity, the outer side of the casing is often filled, compacted, and tightly compressed. After the concrete is poured, when pulling out and retrieving the casing, it is difficult to pull out or deforms due to high frictional resistance. In particular, the utilization rate of casings longer than 5m is extremely low.

[0012] ⑦ Conventional buried casing installation is complex, slow, costly, prone to settlement and tilting, and difficult to guarantee project quality and safety. Conventional casing installation process: site compaction and leveling, measurement and positioning, excavation of casing pit, leveling and compaction of the bottom of the pit foundation or laying of a pad layer, hoisting the casing into place, leveling and fixing, symmetrical layering and compaction of soil around the casing, excavation of grouting trench, cleaning of soil around the casing opening, grouting and drilling. Summary of the Invention

[0013] To overcome the problems existing in related technologies, the present invention discloses an embodiment of a split-type combined suspension sleeve and a method of using it.

[0014] The technical solution is as follows: a split-type combined suspended protective sleeve, equipped with:

[0015] The pressure-bearing steel plate is designed separately from the casing and is fixed to the ground by pressure-bearing steel plate fixing pins and bears compressive stress. The interior of the pressure-bearing steel plate is hollow, and the casing passes through the hollow circle.

[0016] The casing has a fully welded pressure-bearing seat at the top;

[0017] The pressure-bearing seat is fixed to the pressure-bearing steel plate by a pressure-bearing seat fixing pin.

[0018] Furthermore, the casing is parallel to the wall of the expanded hole of the pile foundation and at a distance of not less than 30mm, and the casing is at a depth of not less than 50cm from the bottom of the casing pit formed by the expanded hole, so that the casing is suspended in the casing pit.

[0019] Furthermore, the pressure-bearing steel plate is provided with a lifting hole, and the casing is provided with a slurry supply through hole and a casing lifting hole.

[0020] Furthermore, the outer periphery of the pressure-bearing steel plate is a cubic structure, the thickness of the pressure-bearing steel plate is not less than 40mm, and the diameter of the hollow circle is the same as the diameter of the pile hole.

[0021] The casing is made of steel, with a length of 6m-7m and a thickness of not less than 20mm.

[0022] Another objective of this invention is to provide a method for using a split-type combined suspended casing. This method utilizes the split-type combined suspended casing to convert the lateral frictional force and the force on the bottom surface of the casing into the force on the bearing steel plate on the ground at the orifice, while increasing the vertical bearing area, thus converting the high pressure borne by the casing into compressive stress on the ground. Specifically, it includes the following steps:

[0023] S1, Prepare a split-type combined suspension casing;

[0024] S2, Excavation of the casing pit;

[0025] S3, installation of the casing at the bottom;

[0026] S4, the casing is pulled out and retrieved.

[0027] In step S2, the excavation of the casing pit includes: leveling and compacting the pile foundation construction site, measuring and positioning the pile foundation center, using a rotary drilling rig to check the verticality of the hole position and guide rod, and then enlarging the hole for excavation. The excavation depth is to the predetermined depth below the casing and then deepened by 0.5m to form a reserved casing pit. The diameter of the enlarged hole exceeds the outer wall of the casing and is 30mm vertically away.

[0028] In step S3, the installation of the casing includes: leveling and compacting the borehole opening, drilling the hole using a rotary drilling rig and enlarging the hole to a predetermined depth according to the designed diameter, injecting wall grout, connecting the grout supply pipe to the grout supply through hole of the casing, supplying grout to 0.5m below the ground and maintaining the grout surface at this elevation, with the grout surface depth not less than 0.5m from the ground, hoisting the pressure-bearing steel plate, hoisting the casing, drilling construction, and simultaneously supplying grout from the grout supply through hole of the casing and maintaining the top surface of the grout in the hole at the original elevation until the final hole depth is reached.

[0029] The installation of the casing includes the following:

[0030] Step 1: Excavate the casing pit, measure and position the center of the pile foundation, check the verticality of the hole position and the guide rod, and carry out the enlarged hole excavation construction. The excavation depth is to the predetermined depth under the casing and to a depth of more than 0.5m, forming a reserved casing pit. The enlarged hole diameter exceeds the outer wall of the casing and the vertical distance is more than 30mm.

[0031] Step 2: Grouting;

[0032] Step 3: Spray release agent to reduce drag and loss. Spray release agent on the inner and outer sides of the pressure-bearing steel plate and the casing in advance.

[0033] Step 4: Lay leveling sand for leveling. Lay about 30mm of fine sand around the perimeter of the casing pit for leveling the pressure steel plate.

[0034] Step 5: Lift and level the pressure-bearing steel plate. Use two steel wire ropes to symmetrically pass through the lifting holes on both sides of each pressure-bearing steel plate, and hang the four sleeves of the steel wire on the hook of a conventional truck crane. Lift the pressure-bearing steel plate into place and level it. Use fine sand and thin steel shims for leveling. After leveling, fix it.

[0035] Step 6, hoisting and leveling the casing: Use steel wire ropes symmetrically threaded through the lifting holes on both sides of the top of the casing and hooked onto the crane hook. Slowly lift the casing and transport it to the pile hole for alignment and lowering. Once the bearing seats on both sides of the top of the casing are on the bearing steel plates, correct the hole positions. Then, use a long spirit level and thin steel shims to correct the verticality of the casing. For the side where the top surface of the casing is lower, add thin steel shims to the bearing seat until the top surface of the casing is at the same elevation. After leveling, fix the casing.

[0036] Step 7, pile foundation drilling: Start the rotary drilling rig to drill the hole. At the same time, the self-contained casing grout is supplied through the hole to ensure that the top surface of the grout on the wall remains unchanged during the drilling process.

[0037] In step S4, the extraction and recovery of the casing includes: after the pile foundation is completed and the hole is cleaned, the reinforcing cage is installed and the pouring is completed, all the fixing pins of the pressure steel plate and the fixing pins of the pressure seat are removed, the casing is extracted and cleaned, the pressure steel plate is lifted and cleaned and transferred for later use; the fixing pins of the pressure seat are opened, the casing is extracted, cleaned and transferred, the fixing pins of the pressure steel plate are opened, and the pressure steel plate is cleaned and hoisted for transfer.

[0038] Furthermore, this method is applicable to foundations with high, medium, and low bearing capacity, and the weight of the load can reach over 200 tons; it is especially applicable in the construction of pile groups in soft soil foundations with ultra-deep and large-diameter piles; it is used for situations where the casing has high bearing capacity, the foundation bearing capacity is low, and the casing load is high.

[0039] Combining all the above technical solutions, the advantages and positive effects of this invention are as follows:

[0040] (1) This invention addresses the construction of ultra-deep, large-diameter pile foundations, especially in cases of high bearing capacity of casings. It improves the conventional buried extrusion casing installation technology by designing a suspended combined casing, which effectively solves many construction problems of buried extrusion casings under high bearing capacity conditions, such as low foundation bearing capacity, easy settlement and tilting of casings, multiple installation procedures and low efficiency, high friction and difficulty in lifting casings due to high pressure on the sides, easy damage and deformation, and low reusability.

[0041] (2) This invention can effectively solve the problem of uneven settlement and deviation of the casing caused by low foundation bearing capacity; it can better protect the strata at the borehole opening from disturbance, and at the same time prevent the generation of a large amount of mud or mud slurry and other debris at the borehole opening, ensuring that the borehole opening is flat and clean, realizing civilized and environmentally friendly construction; it can effectively prevent uneven settlement and casing deviation caused by small bottom contact area and high compressive strength of the casing, better ensure the stability of the strata near the borehole opening, prevent borehole collapse, and ensure the vertical accuracy of the pile foundation; it has good guiding performance, which can solve the problems of short length (generally about 2m) and poor guiding performance of conventional casings; it greatly improves the bearing capacity of the casing and reduces the compressive stress of the casing on the foundation. It can be used for construction with greater bearing pressure on soft foundations.

[0042] (3) The casing of this invention has low wear, is easy to pull out, and has a high reuse rate during construction. It solves the problems of easy deformation, high wear, and low reuse rate of conventional buried pressurized casings during the pulling out process. The casing of this invention is simple and convenient to hoist and install, with high efficiency and high utilization rate. It can effectively solve the problems of complex installation process, slow speed, messy site, high cost and settlement deviation of conventional casing installation, and realize high quality, high efficiency and energy saving and environmental protection in pile foundation construction.

[0043] (4) The installation process of the present invention is simple and easy to implement: After the pile foundation is measured and positioned, the site is leveled and compacted. After the rotary drilling machine digs the pit, the bearing steel plate is hoisted and leveled. Then the casing is hoisted, leveled and fixed, thus completing the entire process of the casing installation, leveling and fixing. Attached Figure Description

[0044] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure;

[0045] Figure 1 This is a flowchart illustrating the method of using the split-type combined suspension casing provided in this embodiment of the invention;

[0046] Figure 2 This is an isometric schematic diagram of the split-type combined suspension sleeve provided in an embodiment of the present invention;

[0047] Figure 3 This is a side view of the split-type combined suspension casing provided in an embodiment of the present invention;

[0048] Figure 4 This is a top view of the split-type combined suspension casing provided in an embodiment of the present invention;

[0049] In the diagram: 1. Pressure-bearing steel plate; 2. Casing; 3. Pressure-bearing seat; 4. Pressure-bearing steel plate fixing pin; 5. Pressure-bearing seat fixing pin; 6. Grout supply through hole; 7. Pressure-bearing steel plate lifting hole; 8. Casing lifting hole. Detailed Implementation

[0050] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0051] The innovation of the split-type combined suspended casing and its usage method provided in this invention lies in the following: the technology of force conversion and reduction of the large load compressive stress of the casing 2 in this invention; the side friction force and the bottom surface force of the conventional landfill extrusion casing 2 are converted into the force of the bearing steel plate 1 on the ground at the orifice, while increasing the vertical bearing area, and converting the large pressure borne by the casing 2 into compressive stress on the ground and reducing it by tens of times.

[0052] The design of the casing 2 structure: Based on the characteristic parameters such as pile diameter and pile depth, the diameter and wall thickness of the casing 2 are designed. Simultaneously, the ground and lateral forces on the casing 2 are eliminated and converted into ground bearing pressure. This reduces the compressive stress on the casing 2, improves its utilization rate, and significantly reduces the ground pressure stress on the ground under heavy loads. This expands the applicable range of foundation strength for the pile foundation casing 2.

[0053] The method for connecting the components and main parts of the protective sleeve 2 of the present invention;

[0054] (A) Main Components:

[0055] 1. Pressure-bearing steel plate; 2. Casing; 3. Pressure-bearing seat; 4. Pressure-bearing steel plate fixing pin; 5. Pressure-bearing seat fixing pin; 6. Grouting through hole (or through hole); 7. Pressure-bearing steel plate lifting hole; 8. Casing lifting hole (or lifting lug).

[0056] (B) Main Components and Connection Methods:

[0057] The main components are a bearing steel plate 1, a bearing seat 3, and a casing 2 (an extended cylindrical steel casing). The bearing steel plate 1 is a separate component, designed separately from the casing 2 and fixed to the ground via a fixing pin 4. The bearing seat 3 is fully welded to the top of the casing 2. The casing 2 is connected to the bearing steel plate 1 via the bearing seat 3 and fixed to the bearing steel plate 1 via the fixing pin 4. The load pressure on the top surface of the casing 2 is transferred to the bearing steel plate 1 through the bearing seat 3, thereby creating compressive stress on the ground. The casing 2 is parallel to the borehole wall and 30mm away from it. At the same time, the casing 2 is 0.5m away from the bottom of the pile hole, using a suspended design. This protects the borehole wall from construction disturbance and does not compress the casing 2, greatly reducing wear and increasing the utilization rate of the extended cylindrical casing.

[0058] The main installation methods for casing 2 are as follows: leveling and compacting the borehole opening, drilling the hole using a rotary drilling rig and enlarging the hole to the predetermined depth according to the design diameter (generally exceeding the casing by 0.5m, injecting wall grout into the hole, and maintaining the elevation at a position 0.5m away from the borehole opening), hoisting the bearing steel plate 1 (splitting, leveling, and fixing the pins), hoisting the casing (aligning, leveling, fixing the pins and removing the pins), drilling the hole with the rotary drilling rig until the pile is poured, opening the bearing seat and fixing the pin 5, pulling out and flushing the casing 2, opening the bearing steel plate and fixing the pin 4, cleaning and hoisting the bearing steel plate 1.

[0059] Example 1: The method of using the split-type combined suspension casing provided in this embodiment of the invention includes:

[0060] The site was compacted and leveled, measured and positioned, and the rotary drilling rig was used to excavate to 0.5m below the bottom of the casing 2. The pressure-bearing steel plate 1 was hoisted and positioned and leveled, the suspended casing was hoisted and positioned, leveled, fixed, and the grout supply pipe was connected to supply grout and drill holes for construction.

[0061] Specifically, such as Figure 1 As shown, it includes the following steps:

[0062] S1, Prepare a split-type combined suspension casing;

[0063] like Figures 2-4 The main components of the split-type suspended casing include: a pressure-bearing steel plate 1, a casing 2, a pressure-bearing seat 3, a pressure-bearing steel plate fixing pin 4, a pressure-bearing seat fixing pin 5, a grout supply through hole 6 (or through hole), a pressure-bearing steel plate lifting hole 7, and a casing lifting hole 8 (or lifting lug).

[0064] Connection method of main components: The main components are pressure-bearing steel plate 1, pressure-bearing seat 3 and casing 2. The pressure-bearing steel plate 1 is a separate component, designed separately from the casing 2 and fixed to the ground by the pressure-bearing steel plate fixing pin 4 and bearing the compressive stress. The outer periphery of the pressure-bearing steel plate 1 is a cube structure of 4m*4m with a thickness of 40mm. The inside is a hollow circle with the same diameter as the pile hole.

[0065] The bearing seat 3 and the top of the casing 2 are fully welded. The casing 2 is connected to the bearing steel plate 1 through the bearing seat 3 and fixed by the bearing seat fixing pin 5. The load pressure on the top surface of the casing 2 is transferred to the bearing steel plate 1 through the bearing seat 3, thereby forming compressive stress on the ground. The casing 2 is parallel to the wall of the pile foundation borehole and 30mm away. At the same time, the casing 2 is 0.5m away from the bottom of the borehole depth, forming a suspended casing. This protects the borehole wall from construction disturbance and does not compress the casing 2, which can greatly reduce wear and improve the utilization rate of the casing 2.

[0066] S2, Excavation of the casing pit;

[0067] After leveling and compacting the pile foundation construction site, and measuring and positioning the center of the pile foundation, a rotary drilling rig is used to check the verticality of the hole position and the guide rod before enlarging the hole and excavating. The excavation depth is to the predetermined depth under the casing and then deepened by 0.5m to form a reserved casing pit (or well). The diameter of the enlarged hole exceeds the outer wall of the casing and the vertical distance is 30mm.

[0068] S3, installation of the casing at the bottom;

[0069] The process includes: leveling and compacting the borehole opening; drilling the hole using a rotary drilling rig and enlarging it to the predetermined depth (generally 0.5m beyond the casing; injecting wall-protecting grout into the hole; maintaining the elevation at 0.5m from the borehole opening); hoisting the bearing steel plate 1 (assembling, leveling, and fixing the bearing steel plate with fixing pins 4); hoisting the casing (aligning, leveling, and fixing the bearing seat with fixing pins 5); and drilling the hole using a rotary drilling rig until the pile is poured. It is necessary to periodically check the wear and tear of the casing release agent and replenish it promptly. Specifically, this includes:

[0070] Step 1, laying leveling sand for leveling: spread about 30mm of fine sand around the perimeter of the casing pit to level the pressure plate 1;

[0071] Step 2, spraying release agent to reduce drag and loss: spray release agent on the inner and outer sides of the pressure-bearing steel plate 1 and the casing in advance;

[0072] Step 3, hoisting and leveling the pressure-bearing steel plate 1: Use two steel wire ropes to symmetrically pass through the lifting holes on both sides of each pressure-bearing steel plate 1, and hang the four sleeves of the steel wires on the hook of a conventional truck crane. Hoist the pressure-bearing steel plate 1 into position and level it. Use fine sand (not shown, fine sand or soil can be used to level the pressure-bearing steel plate 1) and thin steel shims (not shown) for leveling. After leveling, use the pressure-bearing steel plate fixing pins 4 for fixing.

[0073] Step 4, hoisting and leveling the casing: Wire ropes are symmetrically threaded through the lifting holes on both sides of the top of the casing and hooked onto the crane hook. The casing is slowly lifted and transported to the pile hole for alignment and lowering. Once the bearing seats 3 on both sides of the top of the casing rest on the bearing steel plates 1, the hole positions are corrected. Then, the verticality of the casing is corrected using a long spirit level and thin steel shims. For the side where the top surface of the casing is lower, thin steel shims are added to the ground of the bearing seat 3 until the top surface of the casing is level. After leveling, the casing is fixed.

[0074] Step 5, supply grout into the casing: Connect the grout supply pipe to the grout supply through hole 6 of the casing, supply grout to 0.5m below the ground and maintain the grout level at this elevation;

[0075] Step 6, Drilling holes for pile foundation: Start the rotary drilling rig and excavate to drill holes.

[0076] S4, the casing is pulled out and retrieved;

[0077] After the pile foundation is completed, the hole is cleaned, the reinforcing cage is installed, and the concrete is poured, all the bolt pins are removed, the casing is lifted and rinsed clean, and the pressure plate 1 is lifted, rinsed clean, and transferred for later use; the pressure seat fixing bolt pin 5 is opened, the casing 2 is lifted, rinsed, and transferred, the pressure plate fixing bolt pin 4 is opened, and the pressure plate 1 is cleaned and hoisted for transfer.

[0078] Example 2: The suspended casing of the present invention re-transforms the stress on the casing: the suspended casing prevents the casing from being deformed or tilted due to the pressure of the landfill, and also avoids the uneven settlement of the casing caused by the ground stress on the narrow bottom surface of the casing exceeding the bearing capacity of the foundation.

[0079] This invention designs and uses a large-area high-strength (4cm thick) pressure-bearing steel plate 1: its main function is to bear the pressure on the top surface of the casing, effectively converting (the force from the bottom and sides of the casing to the pressure plate on the top surface of the casing) and reducing the ground pressure stress of the casing.

[0080] Based on the actual project conditions, taking a pile foundation with a pile diameter of 2.5m as an example, the maximum compressive stress of the bearing plate of the suspended casing patent is designed to be 3030 kPa (the existing technology is a buried extrusion casing, and the total bearing capacity of this type of casing, F at the bottom edge and f of the side resistance, is 50t / 2*3.14*1.31*0.02m). 2 =50*10 / 8.23*0.02=3030(KPa), since the maximum F is 300KPa (the bottom edge of the casing can only withstand a maximum of 300*0.1646=49.38≈50KPa), the upward frictional stress f borne by the casing is not less than 3030-50=2980(KPa) and is reduced to (50t / 10.6m) 2=4.72*10*1000=)47.2KPa, which is far less than the ground bearing capacity (200-300KPa). At the same time, the installation and construction of the casing can ensure the stability of the borehole opening and prevent disturbance to the foundation. This method has a significant advantage in bearing capacity for soft soil foundations, and this type of casing can greatly expand the bearing range of the casing.

[0081] This invention designs and employs an extended steel casing: a high-strength steel casing, extended (6-7m) (deep) and 20mm thick; its main function is to protect the stability of the borehole wall, enhance the guiding performance of the casing, and ensure the vertical accuracy of the pile foundation;

[0082] The present invention designs and adopts a protective casing pressure seat 3: the protective casing pressure seat 3 is made of thickened steel plate (4cm thick steel plate) and welded with full seams in both horizontal and vertical directions, which increases the pressure resistance of the pressure seat 3 to withstand the full pressure of the suspended protective casing. After on-site testing, it was put into use.

[0083] Example 3: The method of using the split-type combined suspended casing provided in this embodiment of the invention is applied to the construction of ultra-deep large-diameter pile foundations on medium-soft foundations with low bearing capacity. This application is for cases where the casing has high bearing capacity, the foundation has low bearing capacity, and the casing has high bearing capacity. Grouting is performed to a depth of more than 50cm from the ground.

[0084] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0085] To further illustrate the effects of the embodiments of the present invention, the following experiment was conducted: Based on a certain ultra-high tower pile foundation project, the basic bearing capacity of the foundation of the project is 200-300KPa, the pile foundation depth is 67m, the pile diameter is 2.5m, the concrete grade is C55, and the pile foundation type is reinforced concrete pile foundation.

[0086] Based on the above characteristic parameters of the project, and considering the total weight of the single-pile reinforcement cage is 39.8 tons, including the guide pipe, derrick, and other components, the top surface of the casing needs to withstand a ballast force of approximately 50 tons. The groundwater level is relatively high, about 1 meter below the surface. Given the poor geological conditions and potential for borehole collapse within the shallow ground area of ​​5-6 meters, a 6-meter-long, 2cm-thick, compacted casing was installed below the casing to improve its bearing capacity, prevent collapse, and enhance its guiding performance. Since the top surface of the casing can withstand a pressure of up to 50 tons, and considering the foundation bearing capacity of 200-300 kPa, the maximum compressive stress on the bottom surface of the 2cm-thick casing with an inner diameter of 2.52 meters is approximately 50 kPa. Using a friction coefficient of 0.04 between steel and sand, the frictional resistance on the casing's sides is 2980 kPa, and the normal pressure on the casing's sides is 149 tons per meter. 2 If a 2m long buried compression-type short casing is used to protect the bearing capacity of the orifice, the normal pressure on its side is 447t / m.2 The aforementioned landfill-type casing causes construction problems such as easy deformation, uneven settlement, tilting, difficulty in extraction and recovery, and low efficiency.

[0087] In summary, the use of buried extrusion casings during the early stages of project construction has resulted in several challenges, including casing deformation, uneven settlement, difficulty in controlling borehole inclination, low work efficiency, and difficulties in casing extraction and recovery. These issues have negatively impacted the quality, economic benefits, and environmental impact of the pile foundation project, necessitating timely and effective measures or innovative technological solutions for improvement.

[0088] This invention designs a suspended combined casing and a scientifically sound method for its use. Its main purpose is to solve the problems of casing settlement, deformation, tilting, difficulty in lifting and retrieving the casing, low efficiency, poor construction quality and environmental protection, and difficulty in achieving symmetrical compaction during casing backfilling when constructing large-diameter deep pile foundations on medium-soft foundations with low bearing capacity. These problems are caused by high bearing pressure (pressure generated by the heavy objects such as steel cages and guide pipes ballasting the casing).

[0089] 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 modifications, equivalent substitutions and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention and within the spirit and principles of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for using a split-type combined suspension casing, characterized in that, The split-type combined suspension sleeve is equipped with: The pressure-bearing steel plate (1) is designed separately from the protective cylinder (2) and is fixed to the ground by the pressure-bearing steel plate fixing pin (4) opened on the pressure-bearing steel plate (1) to bear the compressive stress; the interior of the pressure-bearing steel plate (1) is a hollow circular structure, and the protective cylinder (2) runs through the hollow circle. The casing (2) is topped with a fully welded pressure-bearing seat (3); The pressure-bearing seat (3) is fixed to the pressure-bearing steel plate (1) by the pressure-bearing seat fixing pin (5); This method converts the lateral frictional force and the force on the bottom surface of the buried extrusion casing into the force on the bearing steel plate (1) on the ground surface at the orifice, while increasing the vertical bearing area, thus converting the high pressure borne by the casing into compressive stress on the ground; specifically, it includes the following steps: S1, Prepare a split-type combined suspension casing; S2, Excavation of the casing pit; Excavate the casing pit, measure and position the center of the pile foundation, check the verticality of the hole position and the guide rod, and carry out the enlarged hole excavation. The excavation depth is to the predetermined depth under the casing and deepen it by more than 0.5m to form a reserved casing pit. The enlarged hole diameter exceeds the outer wall of the casing and the vertical distance is more than 30mm. S3, installation of the casing at the bottom; S4, the casing is pulled out and retrieved; The installation of the casing includes the following: Step 1, laying leveling sand for leveling: spread 30mm fine sand around the perimeter of the casing pit so that the pressure plate (1) can be leveled; Step 2, spray release agent to reduce drag and loss: spray release agent on the inner and outer sides of the pressure-bearing steel plate (1) and the casing in advance; Step 3: Lift and level the pressure-bearing steel plate (1). Use two steel wire ropes to symmetrically pass through the lifting holes on both sides of each pressure-bearing steel plate (1), and hang the four loops of the steel wire ropes on the hook of a conventional truck crane. Lift the pressure-bearing steel plate (1) into place and level it. Use fine sand and thin steel shims for leveling. After leveling, fix it. Step 4, hoisting and leveling the casing: use wire ropes to symmetrically hang the lifting holes on both sides of the top of the casing and hang them on the hook of the truck crane. Slowly lift the casing and transport it to the pile hole for alignment and lowering. When the bearing seats (3) on both sides of the top of the casing fall on the bearing steel plate (1), the hole position is corrected. Then, the verticality of the casing is corrected by using a long level and thin steel shims. For the side where the top surface of the casing is lower, add thin steel shims to the bottom of the bearing seat (3) until the top surface of the casing is consistent. After leveling, fix the casing. Step 5, pile foundation drilling: Start the rotary drilling rig to drill the hole. At the same time, the self-supporting casing grout supply hole (6) supplies grout to ensure that the top surface of the grout on the wall remains unchanged during the drilling period.

2. The method of using the split-type combined suspension casing according to claim 1, characterized in that, The pressure-bearing steel plate (1) is provided with a pressure-bearing steel plate lifting hole (7), and the protective casing (2) is provided with a grout supply through hole (6) and a protective casing lifting hole (8).

3. The method of using the split-type combined suspension casing according to claim 2, characterized in that, The outer periphery of the pressure-bearing steel plate (1) is a cube structure, the thickness of the pressure-bearing steel plate (1) is not less than 40mm, and the diameter of the hollow circle is the same as the diameter of the pile hole. The casing (2) is made of steel with a length of 6m-7m and a thickness of not less than 20mm.

4. The method of using the split-type combined suspension casing according to claim 1, characterized in that, In step S4, the lifting and retrieval of the casing includes: opening the pressure seat fixing pin (5), lifting and flushing the transferred casing (2), opening the pressure steel plate fixing pin (4), and cleaning and hoisting the transferred pressure steel plate (1).

Images