Inner and outer core variable cross-section composite pile and construction method thereof

Abstract

This invention discloses a composite pile with variable cross-section and inner and outer cores, and its construction method. The composite pile includes an outer core and an inner core. The inner core is a precast concrete pile, comprising an upper variable cross-section segment and at least one lower constant cross-section segment. The cross-sectional area of ​​the variable cross-section segment decreases from top to bottom. The variable cross-section segment and the constant cross-section segment, as well as adjacent constant cross-section segments, are connected by connecting components. The outer core is a cement-soil mixing pile formed in situ on-site, with some cross-section segments using an enlarged diameter design. The central axes of the inner core and the outer core coincide. This invention comprehensively improves the bearing capacity, economic efficiency, environmental friendliness, and construction quality and efficiency of the pile foundation.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering pile foundation construction technology, and in particular to a composite pile with variable cross-section of inner and outer core that can significantly improve bearing capacity and its construction method. Background Technology

[0002] In building construction, bridge engineering, and road engineering, pile foundations are widely used to bear the loads of the superstructure and transfer them to deep, stable strata. However, traditional pile foundation types, such as bored piles and prestressed concrete pipe piles, have certain limitations: in soft soil layers, the pile side friction is low, and the pile end resistance is insufficient, resulting in limited single pile bearing capacity. Furthermore, pile verticality control often relies on manual experience or simple devices, which are bulky, inconvenient to transport, and difficult to guarantee, easily causing pile tilting, affecting the bearing capacity of the pile foundation, and even leading to engineering safety accidents.

[0003] Existing technologies include composite piles or combined piles, such as precast concrete piles inserted into cement-soil mixing piles. However, these traditional uniform cross-section composite piles suffer from poor bonding between the inner and outer cores, resulting in a mismatch between the axial force distribution and structural dimensions, failing to fully utilize the performance of the composite materials, and leading to material waste. This is particularly problematic in deep soft soil areas, where composite piles exhibit significant drawbacks such as low interfacial resistance and low end resistance. Furthermore, existing composite piles primarily use cement grout, which is costly, has low strength, high shrinkage, and poor corrosion resistance, negatively impacting the long-term durability and bearing capacity of the pile foundation. Current construction equipment suffers from low automation, large size, and transportation difficulties, lacking precise verticality control methods, which can easily cause pile deviation, affecting pile quality and bearing capacity, and making it difficult to adapt to complex and variable on-site construction environments.

[0004] Therefore, in order to achieve the goals of green economy and sustainable development, and to alleviate the environmental pressure caused by the large accumulation of industrial solid waste such as red mud and desulfurization gypsum, it is of great engineering value and practical significance to develop a new type of composite pile system that can effectively improve the bearing capacity, construction quality and efficiency of pile foundations and also has environmental benefits. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a composite pile with inner and outer core variable cross-section that is structurally reasonable, has superior performance, is precise in construction, and is green and economical, as well as its construction method, thereby solving the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a composite pile with variable cross-section and inner core, comprising an outer core and an inner core. The inner core is a precast concrete pile, comprising a variable cross-section segment at the top and at least one equal cross-section segment at the bottom. The cross-sectional area of ​​the variable cross-section segment decreases from top to bottom. The variable cross-section segment and the equal cross-section segment, as well as two adjacent equal cross-section segments, are connected by connecting components. The outer core is a cement-soil mixing pile formed in situ on site, with some cross-section segments adopting an enlarged diameter form. The central axis of the inner core coincides with that of the outer core.

[0008] As a specific technical solution of the present invention, the connecting assembly includes two symmetrically distributed steel clamps, a main bolt group connected between the middle parts of the two steel clamps, and two auxiliary bolt groups respectively connected between the same side ends of the two steel clamps.

[0009] As a specific technical solution of the present invention, the lower surface of the variable cross-section segment, the upper surface of the uppermost equal cross-section segment, and the splicing surface of two adjacent equal cross-section segments are all reserved with positioning grooves for positioning and installing the main bolt group.

[0010] As a specific technical solution of the present invention, the taper of the variable cross-section segment is less than or equal to 1%.

[0011] Secondly, the present invention also provides a construction method for a composite pile with variable cross-section of inner and outer core, comprising the following steps:

[0012] S1. Prefabrication of inner core: Prefabricate variable cross-section segments and constant cross-section segments respectively, and pre-embed or process positioning grooves at the connection ends of variable cross-section segments and constant cross-section segments respectively;

[0013] S2. Pile location measurement and setting out: Determine the construction location and the placement of the base of the fully automatic telescopic precast pile verticality control device;

[0014] S3. External core construction: In-situ mixing is carried out at the designed pile location using mixing equipment. Cement-soil pile holes with variable cross-sections are formed by adopting a segmented construction method. At the same time, grouting material is injected to form the external core.

[0015] S4. Control device entry: Move the fully automatic telescopic precast pile verticality control device to the designed pile position and ensure that the center axis of the locator coincides with the center axis of the outer core.

[0016] S5. Core implantation: Before the cement and soil in the cement-soil pile hole formed in step S3 initially set, the fully automatic telescopic precast pile verticality control device is activated to sequentially hoist and implant each equal cross-section segment and variable cross-section segment until the core reaches the design elevation. The upper and lower adjacent equal cross-section segments and the variable cross-section segment are firmly connected by the installation connection components.

[0017] S6. Curing and Shaping: After construction is completed, allow it to cure statically until the cement soil of the outer core has finally hardened, thus forming a composite pile with variable cross-section of inner and outer core.

[0018] As a specific technical solution of the present invention, in step S3, the grouting material is prepared from the following raw materials by weight percentage: 30%~35% cement, 20%~30% red mud, 15%~20% calcium sulfate waste powder, 0.7%~1% flocculant, 0.6%~1% retarder, 0.8%~1.5% polycarboxylate superplasticizer, 0.1%~0.3% air-entraining agent, and the balance being water.

[0019] As a specific technical solution of the present invention, the flocculant is a mixture of polyaluminum chloride and sodium hydroxypropyl cellulose, wherein the mass ratio of polyaluminum chloride to sodium hydroxypropyl cellulose is 1:1, and the weight-average molecular weight of sodium hydroxypropyl cellulose is 16 million.

[0020] As a specific technical solution of the present invention, the retarder is a mixture of sodium gluconate and polyacrylamide, wherein the mass ratio of sodium gluconate to polyacrylamide is 27:53, and the weight-average molecular weight of polyacrylamide is 14 million.

[0021] As a specific technical solution of the present invention, the air-entraining agent is sodium rosinate.

[0022] As a specific technical solution of the present invention, the preparation method of the grouting material includes the following steps: first, the polycarboxylate superplasticizer, retarder, flocculant, air-entraining agent and water are mixed to form an aqueous solution, and then cement, red mud and calcium sulfate waste powder are mixed evenly and added to the aqueous solution, and stirred thoroughly until a uniform slurry is formed.

[0023] As a specific technical solution of the present invention, in step S4, the fully automatic telescopic precast pile verticality control device includes a support base, a locator, and a pile driving assembly located above the locator. The support base includes an integrated control console and a vertically distributed first telescopic hydraulic cylinder. The locator has a vertically through guide channel. The pile driving assembly includes a vertically distributed second telescopic hydraulic cylinder and a pile lifting device for applying a vertical load downward to the inner core. The pile lifting device is connected to the telescopic end of the second telescopic hydraulic cylinder. Horizontally distributed third telescopic hydraulic cylinders are connected between the locator and the fixed end of the first telescopic hydraulic cylinder, and between the fixed end of the second telescopic hydraulic cylinder and the telescopic end of the first telescopic hydraulic cylinder.

[0024] As a specific technical solution of the present invention, there are multiple first telescopic hydraulic cylinders and multiple third telescopic hydraulic cylinders, which are arranged in a circular array around the positioner; a fourth telescopic hydraulic cylinder for leveling is arranged vertically at the lower part of the fixed end of the first telescopic hydraulic cylinder, and a laser level is arranged at the upper part of the fixed end of the first telescopic hydraulic cylinder.

[0025] Compared with the prior art, the present invention provides a composite pile with variable cross-section of inner and outer core and its construction method, which has the following beneficial effects:

[0026] (1) Structural stability: The variable cross-section design of the upper part of the inner core forms a mechanical interlock with the cement-soil, which can effectively reduce the damage of the inner and outer core interface and greatly improve the vertical bearing capacity. The cross-sectional area of ​​the inner core is larger at the top and smaller at the bottom, which can fully match the characteristics of the inner core axial force being larger at the top and smaller at the bottom during bearing, making the axial force transmission and frictional resistance distribution of the pile more reasonable and avoiding material waste. At the same time, the upper section of the inner core adopts a variable cross-section design. When under pressure, the pile body generates radial compression on the surrounding cement-soil outer core, which significantly increases the normal stress between the various structures, thereby greatly improving the pile side frictional resistance.

[0027] (2) The outer core adopts an enlarged diameter form. By increasing the side surface area, the defects of the side friction resistance and end resistance caused by the poor properties of some soil layers can be reduced. At the same time, the load can be effectively diffused to the deep soil, providing reliable end bearing capacity for the pile foundation and jointly suppressing the penetration deformation of the pile body.

[0028] (3) Material innovation: This invention develops and uses grouting material based on industrial solid waste to form the outer core. It has excellent performance and is environmentally friendly, realizing "waste treatment" and achieving green economy and sustainable development.

[0029] (4) Equipment innovation: The present invention combines a laser level with a telescopic hydraulic cylinder to achieve full automation and high-precision leveling of the device during construction, eliminating the influence of uneven settlement of the foundation and uneven force on the pile lifting caused by the tilting of the device; at the same time, the positioner can ensure that the prefabricated inner core has high verticality during the pressing process, thus improving the construction quality.

[0030] (5) Wide applicability and convenient transportation. The fully automatic telescopic precast pile verticality control device designed in this invention adopts telescopic hydraulic cylinders, which can reasonably adjust the position of the device base according to the size of the site. By combining the vertically distributed first telescopic hydraulic cylinder and the horizontally distributed third telescopic hydraulic cylinder, the size of the device can be scaled up or down, which is convenient for transportation.

[0031] (6) Mechanical connection is achieved by using prefabricated connection components in the factory, eliminating the need for on-site concrete pouring or welding. This avoids the problems of unstable quality and low efficiency of on-site welding, resulting in high connection strength and fast construction speed.

[0032] (7) Systematic solution: This invention provides a complete solution from pile structure and core materials to construction equipment and technology, which work together to comprehensively improve the performance, quality and economic and environmental benefits of pile foundation engineering. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the overall structure of a composite pile with variable cross-section of inner and outer cores in one embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the inner core structure in one embodiment of the present invention;

[0036] Figure 3 This is a top view of the connection component in one embodiment of the present invention;

[0037] Figure 4 This is a three-dimensional structural diagram of the connection component in one embodiment of the present invention;

[0038] Figure 5 This is a schematic diagram of the steel locking hoop in one embodiment of the present invention;

[0039] Figure 6 This is a flowchart illustrating the core docking process in one embodiment of the present invention;

[0040] Figure 7 This is a schematic diagram of the fully automatic telescopic precast pile verticality control device in the retracted state in one embodiment of the present invention.

[0041] Figure 8 This is a schematic diagram of the fully automatic telescopic precast pile verticality control device in the deployed state according to one embodiment of the present invention.

[0042] Figure 9 This is a schematic diagram of the fully automatic telescopic precast pile verticality control device in one embodiment of the present invention when the pile lifting device is raised.

[0043] Figure 10 This is a schematic diagram of the fully automatic telescopic precast pile verticality control device in the pile driving state according to one embodiment of the present invention.

[0044] Figure 11This is a perspective view of the support base in one embodiment of the present invention;

[0045] Figure 12 This is a side view of the support base in one embodiment of the present invention;

[0046] Figure 13 This is a schematic diagram of the structure of the pile driving assembly in one embodiment of the present invention;

[0047] Figure 14 This is a three-dimensional structural diagram of the pile lifting device in one embodiment of the present invention;

[0048] Figure 15 This is a schematic diagram of the overall structure of the composite pile with variable cross-section of inner and outer core according to the second structure of the present invention;

[0049] Figure 16 This is a schematic diagram of the overall structure of the composite pile with variable cross-section of inner and outer cores according to the third structure of the present invention.

[0050] Reference numerals: 1. Outer core; 11. Expanded diameter section; 2. Inner core; 21. Variable cross-section section; 22. Constant cross-section section; 23. Positioning groove; 3. Connecting assembly; 31. Steel locking clamp; 32. Main bolt group; 33. Secondary bolt group; 4. Support base; 41. First telescopic hydraulic cylinder; 42. Fourth telescopic hydraulic cylinder; 43. Laser level; 44. Integrated control console; 45. Support base plate; 5. Third telescopic hydraulic cylinder; 6. Pile driving assembly; 61. Second telescopic hydraulic cylinder; 62. Pile lifting device; 63. Pulley block; 64. Hook; 7. Positioner; 71. Guide channel. Detailed Implementation

[0051] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] refer to Figures 1-6 , Figure 15 and Figure 16A composite pile with variable cross-section and inner core includes an outer core 1 and an inner core 2. The inner core 2 is a precast concrete pile, comprising a variable cross-section segment 21 at the top and at least one constant cross-section segment 22 at the bottom. The cross-sectional area of ​​the variable cross-section segment 21 decreases uniformly from top to bottom, forming an inverted square frustum structure. The cross-sectional dimensions of the constant cross-section segment 22 remain unchanged. The variable cross-section segment 21 and the constant cross-section segment 22, as well as adjacent constant cross-section segments 22, are connected by connecting components 3. The outer core 1 is a cement-soil mixing pile formed in situ with some cross-section segments using an expanded diameter, which can form a stepped variable cross-section structure. The central axis of the inner core 2 coincides with that of the outer core 1.

[0053] refer to Figures 3-6 In some specific embodiments, the connecting assembly 3 includes two symmetrically distributed steel clamps 31, a main bolt group 32 connected between the middle of the two steel clamps 31, and two auxiliary bolt groups 33 respectively connected between the same end of the two steel clamps 31. Thus, the main bolt group 32 and the auxiliary bolt group 33 can work together with the two steel clamps 31 to enhance the mechanical engagement and connection reliability between the upper and lower sections of the inner core 2. Specifically, the outer wall of the steel clamp 31 can be smooth, or it can have a rough surface or stiffening ribs to enhance the bonding with the cement and soil of the outer core 1.

[0054] refer to Figure 2 In some specific embodiments, the lower surface of the variable cross-section segment 21, the upper surface of the uppermost constant cross-section segment 22, and the splicing surface of two adjacent constant cross-section segments 22 are all provided with positioning grooves 23 for positioning and installing the main bolt assembly 32. Specifically, the positioning groove 23 is a semi-circular groove with a radius 2-3 mm larger than the radius of the main bolt assembly 32. The positioning groove 23 is filled with adhesive between the main bolt assembly 32 and the inner core 2. As an example, the adhesive is conventional grouting mortar or glue. By using grouting to connect the gap between the main bolt assembly 32 and the inner core 2, the mechanical engagement and connection reliability of the upper and lower sections of the inner core 2 are enhanced.

[0055] In some improved embodiments, the top of the variable cross-section section 21 may be reserved with a pile top connection structure, such as a pre-embedded steel plate or exposed reinforcing bars, for connection with the upper foundation or for extension of the pile body when necessary.

[0056] In some specific implementations, the taper of the variable cross-section segment 21 is less than or equal to 1%. This ensures smooth axial force transmission and reduces stress concentration. Specifically, the formula for calculating the taper n of the variable cross-section segment 21 is: n = / 2h, where, is the difference in side length or diameter between the top and bottom surfaces of the variable cross-section segment 21, and h is the height of the variable cross-section segment 21.

[0057] In some specific embodiments, the cross-section of the inner core 2 is square. The side length of the constant cross-section segment 22 is equal to the bottom side length of the variable cross-section segment 21. The area ratio of the top cross-section of the inner core 2 to the top cross-section of the outer core 1 is 0.2~0.3, and the area ratio of the cross-section of the inner core 2 at the constant cross-section segment 22 to the cross-section of the outer core 1 at the non-expanded diameter segment is 0.1~0.15. The diameter ratio of the expanded diameter segment 11 of the outer core 1 to the non-expanded diameter segment is 1.2~1.8, and the diameter of the expanded diameter segment 11 of the outer core 1 should not be greater than the spacing between two adjacent inner and outer core variable cross-section composite piles. Specifically, the expanded diameter segments 11 on the outer core 1 are distributed and positioned to correspond to the soft strata areas; therefore, as Figure 16 As shown, the expanded diameter segments 11 on the outer core 1 can be correspondingly distributed on the upper part of the outer core 1; or, as... Figure 1 As shown, the expanded diameter segments 11 on the outer core 1 can be correspondingly distributed in the middle of the outer core 1; or, as... Figure 15 As shown, the expanded diameter section 11 on the outer core 1 can be correspondingly distributed in the lower part of the outer core 1.

[0058] In some specific implementations, it is preferred that when the length of the inner core 2 is less than the length of the outer core 1, the core length ratio of the inner core 2 to the outer core 1 is 0.7 to 0.8; when the length of the inner core 2 is greater than the length of the outer core 1, it is optimal for the inner core 2 to penetrate deep into the bearing layer.

[0059] refer to Figure 1 , Figures 6-10 A construction method for a composite pile with variable cross-section of inner and outer core includes the following steps:

[0060] S1, Inner core 2 prefabrication: Prefabricate variable cross section 21 and constant cross section 22 respectively, and pre-embed or process positioning grooves 23 at the connection end of variable cross section 21 and constant cross section 22 respectively;

[0061] S2. Pile location measurement and setting out: Determine the construction location and the placement of the base of the fully automatic telescopic precast pile verticality control device;

[0062] S3, Outer Core 1 Construction: In-situ mixing is carried out at the designed pile location using mixing equipment. Cement-soil pile holes with variable cross-sections are formed by adopting a segmented construction method. At the same time, grouting material is injected to form outer core 1.

[0063] S4. Control device entry: Move the fully automatic telescopic precast pile verticality control device to the designed pile position to ensure that the central axis of the locator 7 coincides with the central axis of the outer core 1.

[0064] S5. Core 2 implantation: Before the cement and soil in the cement-soil pile hole formed in step S3 initially set, the fully automatic telescopic precast pile verticality control device is activated to sequentially hoist and implant each equal cross-section segment 22 and variable cross-section segment 21 until the core 2 reaches the design elevation. The two adjacent equal cross-section segments 22 and the variable cross-section segment 21 are firmly connected by the installation connection component 3.

[0065] S6. Curing and Shaping: After construction is completed, allow it to cure statically. Once the cement and soil of the outer core 1 have fully hardened, a composite pile with variable cross-section of inner and outer cores will be formed.

[0066] In some specific embodiments, in step S3, the grouting material used is prepared from the following raw materials by weight percentage: 30%~35% cement, 20%~30% red mud, 15%~20% calcium sulfate waste powder, 0.7%~1% flocculant, 0.6%~1% retarder, 0.8%~1.5% polycarboxylate superplasticizer, 0.1%~0.3% air-entraining agent, and the balance being water.

[0067] The flocculant is a mixture of polyaluminum chloride and sodium hydroxypropyl cellulose, with a mass ratio of 1:1 and a weight-average molecular weight of 16 million for sodium hydroxypropyl cellulose. The retarder is a mixture of sodium gluconate and polyacrylamide, with a mass ratio of 27:53 and a weight-average molecular weight of 14 million for polyacrylamide. Sodium rosinate is used as the air-entraining agent.

[0068] The preparation method of this grouting material includes the following steps: First, polycarboxylate superplasticizer, retarder, flocculant, and air-entraining agent are mixed with water to form an aqueous solution. Then, dry powder materials such as cement, red mud, and calcium sulfate waste powder are mixed evenly and added to the aqueous solution. The mixture is stirred thoroughly until a uniform, highly fluid slurry is formed. It can be used after stirring evenly for ≥3 minutes.

[0069] refer to Figures 7-14In some specific embodiments, in step S4, the fully automatic telescopic precast pile verticality control device includes a support base 4, a positioner 7, and a pile driving assembly 6 located above the positioner 7. The support base 4 includes an integrated control console 44 and vertically distributed first telescopic hydraulic cylinders 41. The positioner 7 has a vertically through guide channel 71. The pile driving assembly 6 includes a vertically distributed second telescopic hydraulic cylinder 61 and a pile lifting device 62 for applying a vertical load downward to the inner core 2, the pile lifting device 62 being connected to the telescopic end of the second telescopic hydraulic cylinder 61. Horizontally distributed third telescopic hydraulic cylinders 5 are respectively connected between the positioner 7 and the fixed end of the first telescopic hydraulic cylinder 41, and between the fixed end of the second telescopic hydraulic cylinder 61 and the telescopic end of the first telescopic hydraulic cylinder 41. The first telescopic hydraulic cylinder 41 is used to drive the pile driving assembly 6 to a suitable height so as to suspend the equal cross-section segment 22 and the variable cross-section segment 21 used for splicing and forming the inner core 2; the pile lifting device 62 is used to suspend the equal cross-section segment 22 or the variable cross-section segment 21 and apply a vertical load downward; the second telescopic hydraulic cylinder 61 is used to extend downward synchronously during the implantation of the equal cross-section segment 22 or the variable cross-section segment 21, and uses the guide channel 71 on the locator 7 to form guidance and constraint to ensure vertical downward pressure; the third telescopic hydraulic cylinder 5 can be used to drive the support base 4 to unfold to provide more stable support.

[0070] refer to Figures 7-11 In some preferred embodiments, multiple first telescopic hydraulic cylinders 41 and third telescopic hydraulic cylinders 5 are arranged in a circular array around the locator 7, thus providing more stable support for the pile driving assembly 6 to complete the implantation of the inner core 2. A vertically distributed fourth telescopic hydraulic cylinder 42 for leveling is located at the lower fixed end of the first telescopic hydraulic cylinder 41, and a laser level 43 for emitting a horizontal laser to form a reference horizontal plane is located at the upper fixed end of the first telescopic hydraulic cylinder 41. After the third telescopic hydraulic cylinder 5 extends to support the base 4, the fourth telescopic hydraulic cylinder 42 is operated via the integrated control console 44 to adjust the height of the corresponding first telescopic hydraulic cylinder 41, thereby ensuring that the bottom ends of all the first telescopic hydraulic cylinders 41 are at the same horizontal height. Specifically, as an example, four first telescopic hydraulic cylinders 41 and eight third telescopic hydraulic cylinders 5 are arranged in a cross-shaped pattern in two layers.

[0071] In some improved embodiments, the guide channel 71 of the locator 7 may be provided with a constraint frame with guide rollers, thereby facilitating the smooth pressing through of the constant cross-section segment 22 or the variable cross-section segment 21.

[0072] The present invention will now be described in further detail through detailed embodiments and in conjunction with the accompanying drawings.

[0073] Example 1

[0074] This embodiment provides a grouting material with the following formula (by weight percentage): 35% cement, 20% red mud, 20% calcium sulfate waste powder, 0.7% flocculant, 0.6% retarder, 1.5% polycarboxylate superplasticizer, 0.2% air-entraining agent, and 22% water. The flocculant is a mixture of polyaluminum chloride and sodium hydroxypropyl cellulose, with a mass ratio of 1:1 and a weight-average molecular weight of 16 million for the sodium hydroxypropyl cellulose. The retarder is a mixture of sodium gluconate and polyacrylamide, with a mass ratio of 27:53 and a weight-average molecular weight of 14 million for the polyacrylamide. Sodium rosinate is used as the air-entraining agent.

[0075] The preparation method of this grouting material includes the following steps: First, polycarboxylate superplasticizer, retarder, flocculant, and air-entraining agent are mixed with water to form an aqueous solution. Then, dry powder materials such as cement, red mud, and calcium sulfate waste powder are mixed evenly and added to the aqueous solution. The mixture is stirred thoroughly until a uniform, highly fluid slurry is formed. It can be used after stirring evenly for ≥3 minutes.

[0076] The following technical indicators were measured for the grouting material obtained in Example 1:

[0077] 1. Initial flowability and 4-hour flowability: determined according to standard GB / T 2419-2005 "Test Method for Mortar Flowability";

[0078] 2. 1-day strength, 7-day strength, and 28-day strength: determined according to standard JGJ / T 70-2009 "Standard for Test Methods of Basic Performance of Building Mortar";

[0079] 3. 28-day impermeability pressure: determined according to standard JC / T 985-2017 "Cement-based self-leveling mortar for flooring";

[0080] 4. Expansion rate: Determined according to Appendix C of standard GB / T 50119-2013;

[0081] 5. A separate control group was set up to evaluate the compatibility between the grouting material and the sludge: The control group used sludge with a water content of 55% to replace the water in the formula (keeping the water content in the formula unchanged), and the other conditions remained unchanged. Specifically, the formula settings of the control group are shown in Table 1 below.

[0082] The test results for each indicator are shown in Table 2 below.

[0083] Table 1. Composition of the control group formula

[0084]

[0085] Table 2. Test results of various indicators in Example 1 and the control group.

[0086]

[0087] As shown in Table 2, the initial fluidity, 4-hour fluidity, 1-day strength, 7-day strength, 28-day strength, 28-day impermeability pressure, and expansion rate of the control group all meet the requirements of the standards on which each index is measured, proving that the material provided by this invention has good compatibility with silt through formula adjustment.

[0088] Example 2

[0089] refer to Figures 7-14 This embodiment provides a fully automatic telescopic precast pile verticality control device for implanting the inner core 2 and controlling its verticality during the construction of composite piles with variable cross-sections of inner and outer cores. Specifically, the fully automatic telescopic precast pile verticality control device includes a support base 4, a locator 7, and a pile driving assembly 6 located above the locator 7. The support base 4 includes four vertically distributed first telescopic hydraulic cylinders 41 and an integrated control console 44 correspondingly installed on the fixed ends of the first telescopic hydraulic cylinders 41. The first telescopic hydraulic cylinders 41 are arranged in a circumferential array around the locator 7, which can more stably support the pile driving assembly 6 to complete the implantation of the inner core 2. The locator 7 is a square metal frame with vertically distributed guide channels 71, which can guide the inner core 2 to ensure verticality control. The pile driving assembly 6 includes vertically distributed second telescopic hydraulic cylinders 61 and a pile lifting device 62 for applying a vertical load downward to the inner core 2. The pile lifting device 62 is connected to the telescopic end of the second telescopic hydraulic cylinders 61. Eight horizontally distributed third telescopic hydraulic cylinders 5 are connected between the fixed end of the locator 7 and the first telescopic hydraulic cylinder 41, and between the fixed end of the second telescopic hydraulic cylinder 61 and the telescopic end of the first telescopic hydraulic cylinder 41. These third telescopic hydraulic cylinders are arranged in two layers in a cross shape. Four of the first telescopic hydraulic cylinders 41 work together to stably drive the pile-driving assembly 6 to a suitable height for suspending the equal-section segment 22 and the variable-section segment 21 used to assemble the inner core 2. The pile lifter 62 suspends the equal-section segment 22 or the variable-section segment 21 and applies a vertical load downwards to complete the implantation of the inner core 2. The second telescopic hydraulic cylinder 61 extends downwards synchronously during the implantation of the equal-section segment 22 or the variable-section segment 21, using the guide channel 71 on the locator 7 to provide guidance and constraint, ensuring vertical downward pressure. The third telescopic hydraulic cylinders 5 can drive the support base 4 to unfold, providing relatively stable support.

[0090] Furthermore, such as Figures 7-11As shown, each first telescopic hydraulic cylinder 41 has a vertically distributed fourth telescopic hydraulic cylinder 42 for leveling at its fixed end. The end of the fourth telescopic hydraulic cylinder 42 away from the first telescopic hydraulic cylinder 41 has a supporting base plate 45. The upper part of the fixed end of the first telescopic hydraulic cylinder 41 has a laser level 43 for emitting horizontal laser light to form a reference horizontal plane. The fourth telescopic hydraulic cylinder 42 and the laser level 43 can form an automatic leveling system. After the third telescopic hydraulic cylinder 5 unfolds its supporting base 4, the integrated control console 44 drives the fourth telescopic hydraulic cylinder 42 to extend and retract, adjusting the height of the corresponding first telescopic hydraulic cylinder 41, thereby ensuring that the bottom ends of each first telescopic hydraulic cylinder 41 are at the same horizontal height. Preferably, the laser level 43 is designed as a curved surface, and the emitted laser surface is fan-shaped. By using the multiple laser emitters of two symmetrically distributed laser levels 43 to form a reference horizontal plane through mutual laser beam exchange, interference from the second telescopic hydraulic cylinder 61 can be avoided.

[0091] In addition, refer to Figure 9 , Figure 13 and Figure 14 To facilitate the secure hoisting of the precast constant cross-section section 22 and variable cross-section section 21, the bottom of the pile lifting device 62 has a square groove for applying vertical static load and restricting lateral slippage of the pile body. Hooks 64 for hoisting the constant cross-section section 22 or variable cross-section section 21 are connected to both sides of the pile lifting device 62 via pulley blocks 63. The hooks 64 maintain connection with the precast inner core 2 pile body for lifting. Since the area of ​​the square groove is larger than the top surface area of ​​the inner core 2, the precast constant cross-section section 22 or variable cross-section section 21 can be smoothly embedded into the square groove as the pulley blocks 63 on both sides are lifted.

[0092] It should be noted that the first telescopic hydraulic cylinder 41, the second telescopic hydraulic cylinder 61, the third telescopic hydraulic cylinder 5, and the fourth telescopic hydraulic cylinder 42 are all commonly used telescopic hydraulic cylinders in this field. Each telescopic hydraulic cylinder is connected to a hydraulic control system. The telescopic hydraulic cylinders and their hydraulic control are conventional technologies, and therefore will not be described in detail. The integrated control console 44 integrates an operation panel with buttons and a control circuit board. By connecting the hydraulic control system used to control the operation of each telescopic hydraulic cylinder to the integrated control console 44, fully automatic operation can be achieved on the integrated control console 44.

[0093] Example 3

[0094] This embodiment provides a composite pile with variable cross-section inside and outside the core and its construction method.

[0095] refer to Figures 1-6 Specifically, the inner and outer core variable cross-section composite pile includes an outer core 1 and an inner core 2 with their central axes coinciding.

[0096] The outer core 1 is a cement-soil mixing pile formed in situ on site. The outer core 1 is 8m long and includes an enlarged diameter section 11 with a height of 2m and a non-enlarged diameter section with a height of 6m. According to the distribution of the soft strata area, the enlarged diameter section 11 is located in the middle of the outer core 1. The diameter of the enlarged diameter section 11 of the outer core 1 is 800mm, and the diameter of the non-enlarged diameter section of the outer core 1 is 500mm, so that the outer core 1 can form a stepped variable cross-section structure.

[0097] The inner core 2 is a precast concrete pile with a square cross-section (precast using C30 concrete). The inner core 2 includes an upper variable cross-section segment 21 and two lower equal cross-section segments 22. The cross-sectional area of ​​the variable cross-section segment 21 decreases uniformly from top to bottom (the upper cross-section has a side length of 200mm, and the lower cross-section has a side length of 150mm), a height of 6m, and a taper of approximately 0.83%, forming an inverted square frustum structure. The cross-sectional dimensions of the equal cross-section segments 22 remain constant (side length 150mm), and both equal cross-section segments 22 have a height of 4m.

[0098] The variable cross-section segment 21 and the constant cross-section segment 22, as well as two adjacent constant cross-section segments 22, are connected by prefabricated connecting components 3. The connecting components 3 include two symmetrically distributed steel clamps 31, a main bolt group 32 connected between the middle of the two steel clamps 31, and two auxiliary bolt groups 33 connected between the same end of the two steel clamps 31. Positioning grooves 23 for positioning and installing the main bolt groups 32 are pre-drilled on the lower surface of the variable cross-section segment 21, the upper surface of the uppermost constant cross-section segment 22, and the splicing surfaces of two adjacent constant cross-section segments 22. The positioning grooves 23 are semi-circular grooves with a radius 2-3 mm larger than the radius of the main bolt groups 32. After splicing, the gap between the main bolt groups 32 and the inner core 2 is filled with grout to enhance the mechanical engagement and connection reliability of the upper and lower sections of the inner core 2.

[0099] refer to Figures 7-14 The construction method for this composite pile with variable cross-section of inner and outer cores is carried out in the order of "inner core prefabrication - outer core construction - inner core implantation", specifically including the following steps:

[0100] S1, Inner core 2 prefabrication: Variable cross section 21 and constant cross section 22 are prefabricated in the factory in advance. After curing, the concrete strength and dimensional accuracy are guaranteed. Positioning grooves 23 for connecting with connecting component 3 are pre-embedded or processed at the connection ends of variable cross section 21 and constant cross section 22 respectively.

[0101] S2. Pile location measurement and setting out: Determine the construction location, level the site, and determine the placement position of the base of the fully automatic telescopic precast pile verticality control device.

[0102] S3, Outer Core 1 Construction: In-situ mixing is carried out at the designed pile location using a mixing equipment. A variable cross-section cement-soil pile hole is formed by adopting a segmented construction method. At the same time, the grouting material prepared in Example 1 is injected to form the outer core 1.

[0103] S4. Control device entry: Move the fully automatic telescopic precast pile verticality control device of Example 2 to the designed pile position to ensure that the central axis of the locator 7 coincides with the central axis of the outer core 1.

[0104] S5. Deployment control device: Sequentially activate each of the third telescopic hydraulic cylinders 5 to ensure that each of the first telescopic hydraulic cylinders 41 of the support base 4 is in the planned position.

[0105] S6. Base leveling: Activate the fourth telescopic hydraulic cylinder 42 below each of the first telescopic hydraulic cylinders 41, and with the laser reference of the laser level 43, ensure that the four first telescopic hydraulic cylinders 41 are at the same horizontal height.

[0106] S7. Lifting the pile driving assembly 6: Simultaneously activate the four first telescopic hydraulic cylinders 41 until the pile driving assembly 6 rises to the appropriate height and is then connected to the prefabricated equal cross-section section 22 by the pile lifting device 62.

[0107] S8. Restart the automatic leveling system to prevent the whole structure from shifting or tilting during the pile lifting process, and at the same time ensure that the equal section segment 22 coincides with the central axis of the locator 7.

[0108] S9. Core 2 implantation: Before the cement soil in the cement soil pile hole formed in step S3 initially sets, the second telescopic hydraulic cylinder 61 is activated to implant the lower end of the equal cross section 22 into the bottom of the cement soil pile hole through the guide channel 71 of the locator 7. After reaching the predetermined elevation, the connecting component 3 is installed on its top. First, the main bolt group 32 is placed in the preset positioning groove 23, and one of the steel locking clamps 31 is fixed to the side wall of the equal cross section 22 through the main bolt group 32.

[0109] S10. Restart the second telescopic hydraulic cylinder 61 to drive the pile lifting device 62 to rise to the appropriate height and connect the second equal section segment 22. Repeat steps S8 and S9 to start implanting the inner core 2 of the next segment. After the positioning groove 23 at its lower end is embedded in the main bolt group 32, install another steel locking clamp 31. Finally, the tight connection between the upper and lower segments of the inner core 2 is achieved through the two auxiliary bolt groups 33.

[0110] S11. After restarting the second telescopic hydraulic cylinder 61 to drive the pile lifting device 62 to rise to the appropriate height, repeat steps S8~S10 to sequentially press down and implant the remaining equal cross-section section 22 and variable cross-section section 21 until the inner core 2 reaches the design elevation. During the pressing process, the two adjacent equal cross-section sections 22 and the variable cross-section section 21 are firmly connected by the installation connection component 3. At the same time, the uncured outer core 1 is squeezed to be dense and fully combined with the surface of the inner core 2.

[0111] S12. Curing and Shaping: After construction is completed, remove the equipment and let it stand for 28 days for curing. After the cement and soil of the outer core 1 has finally hardened, a composite pile with variable cross-section of inner and outer cores is formed, and subsequent construction can be carried out.

[0112] The above embodiments are merely illustrative of the concept and technical solution of the present invention and are not intended to limit the present invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

[0113] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A construction method for a composite pile with variable cross-section of inner and outer core, characterized in that, Includes the following steps: S1. Prefabrication of inner core: Prefabricate variable cross-section segments and constant cross-section segments respectively, and pre-embed or process positioning grooves at the connection ends of variable cross-section segments and constant cross-section segments respectively; S2. Pile location measurement and setting out: Determine the construction location and the placement of the base of the fully automatic telescopic precast pile verticality control device; S3. External core construction: In-situ mixing is carried out at the designed pile location using mixing equipment. Cement-soil pile holes with variable cross-sections are formed by adopting a segmented construction method. At the same time, grouting material is injected to form the external core. S4. Control Device Arrival: Move the fully automatic telescopic precast pile verticality control device to the designed pile position, ensuring that the central axis of the locator coincides with the central axis of the outer core. The fully automatic telescopic precast pile verticality control device includes a support base, a locator, and a pile driving assembly located above the locator. The support base includes an integrated control console and vertically distributed first telescopic hydraulic cylinders. The locator has vertically distributed guide channels. The pile driving assembly includes vertically distributed second telescopic hydraulic cylinders and a pile lifting device for applying a vertical load downwards to the inner core. The pile lifting device... The telescopic end of the second telescopic hydraulic cylinder is connected to the positioner. Horizontally distributed third telescopic hydraulic cylinders are connected between the positioner and the fixed end of the first telescopic hydraulic cylinder, and between the fixed end of the second telescopic hydraulic cylinder and the telescopic end of the first telescopic hydraulic cylinder. Multiple first and third telescopic hydraulic cylinders are provided, arranged in a circular array around the positioner. A vertically distributed fourth telescopic hydraulic cylinder for leveling is provided below the fixed end of the first telescopic hydraulic cylinder, and a laser level is provided above the fixed end of the first telescopic hydraulic cylinder. S5. Core implantation: Before the cement and soil in the cement-soil pile hole formed in step S3 initially set, the fully automatic telescopic precast pile verticality control device is activated to sequentially hoist and implant each equal cross-section segment and variable cross-section segment until the core reaches the design elevation. The upper and lower adjacent equal cross-section segments and the variable cross-section segment are firmly connected by the installation connection components. S6. Curing and Shaping: After construction, allow for static curing. Once the cement-soil of the outer core has fully hardened, a composite pile with variable cross-sections of inner and outer cores is formed. The composite pile with variable cross-sections of inner and outer cores includes an outer core and an inner core. The inner core is a precast concrete pile, which includes a variable cross-section section at the top and at least one equal cross-section section at the bottom. The cross-sectional area of ​​the variable cross-section section decreases from top to bottom. The variable cross-section section and the equal cross-section section, as well as two adjacent equal cross-section sections, are connected by connecting components. The outer core is a cement-soil mixing pile formed in situ on site, with some cross-section sections using an expanded diameter. The central axis of the inner core coincides with that of the outer core.

2. The construction method of the composite pile with variable cross-section of inner and outer core according to claim 1, characterized in that, In step S3, the grouting material is prepared from the following raw materials by weight percentage: 30%~35% cement, 20%~30% red mud, 15%~20% calcium sulfate waste powder, 0.7%~1% flocculant, 0.6%~1% retarder, 0.8%~1.5% polycarboxylate superplasticizer, 0.1%~0.3% air-entraining agent, and the balance being water.

3. The construction method of the composite pile with variable cross-section of inner and outer core according to claim 2, characterized in that, The flocculant is a mixture of polyaluminum chloride and sodium hydroxypropyl cellulose, with a mass ratio of 1:1 and a weight-average molecular weight of 16 million for sodium hydroxypropyl cellulose; the retarder is a mixture of sodium gluconate and polyacrylamide, with a mass ratio of 27:53 and a weight-average molecular weight of 14 million for polyacrylamide; and the air-entraining agent is sodium rosinate.

4. The construction method of the composite pile with variable cross-section of inner and outer core according to claim 2, characterized in that, The preparation method of the grouting material includes the following steps: first, the polycarboxylate superplasticizer, retarder, flocculant, and air-entraining agent are mixed with water to form an aqueous solution; then, cement, red mud, and calcium sulfate waste powder are mixed evenly and added to the aqueous solution, and stirred thoroughly until a uniform slurry is formed.

5. The construction method of the composite pile with variable cross-section of inner and outer core according to claim 1, characterized in that, The connecting assembly includes two symmetrically distributed steel clamps, a main bolt group connected between the middle of the two steel clamps, and two auxiliary bolt groups respectively connected between the same end of the two steel clamps.

6. The construction method of the composite pile with variable cross-section of inner and outer core according to claim 5, characterized in that, The lower surface of the variable cross-section section, the upper surface of the uppermost equal cross-section section, and the splicing surface of two adjacent equal cross-section sections are all reserved with positioning grooves for positioning and installing the main bolt assembly.

7. The construction method of the composite pile with variable cross-section of inner and outer core according to claim 1, characterized in that, The taper of the variable cross-section segment is less than or equal to 1%.

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