A variable diameter screw pile and construction method thereof

Abstract

The present invention discloses a variable diameter screw pile and a construction method thereof, wherein the variable diameter screw pile comprises a lower pile body and an upper pile body, wherein the lower pile body is a threaded section pile body, wherein the threaded section pile body comprises a first thread structure and a second thread structure, wherein the outer diameter of the second thread structure is greater than the outer diameter of the first thread structure; the construction method comprises the following steps: 1. determining the length of the lower pile body; 2. determining the number of the second thread structures; 3. placing the pile driver drill rod in place; 4. drilling holes; 5. construction of the first pile section; 6. construction of the second pile section; 7. construction of the third pile section; 8. construction of the fourth pile section; 9. construction of the straight section pile body. The present invention is novel and reasonable in design, wherein the bearing capacity of the pile body is improved by setting the second thread structure in some soil layers that can well exert the bearing capacity of the thread; at the same time, the construction steps are simple, the drilling process is carried out simultaneously with the concrete pouring process, and the amount of excavation during the drilling process is small or no excavation is required, which is convenient for promotion and use.

Description

Technical Field

[0001] The invention belongs to the technical field of foundation construction, and particularly relates to a variable diameter screw pile and a construction method thereof. Background Art

[0002] A cast-in-place pile refers to a pile that is directly bored at the designed pile position, and then a steel cage is placed in the hole after the hole is formed, and concrete is poured in. At present, in infrastructure projects such as construction, water conservancy, and highways, cast-in-place piles with long spiral holes are widely used for their advantages of fast speed, low noise, no need for mud wall protection, and low construction cost. An existing reverse screw pile, with the authorization announcement number CN204753577U, has a uniform external spiral structure of the pile body, and the inner and outer diameters of the threads are the same. The external spiral structure of the pile body increases the bearing capacity of a single pile, and the effect is good in actual use. However, the thread structure of the same diameter can produce different bearing capacities in different soil layers due to different soil properties; in some soil layers that can well exert the bearing capacity of the thread, such as in clay, silt, fill, etc., if the thread section diameter of the screw pile in the soil layer can be appropriately increased, the bearing capacity of the pile body can be greatly improved with only a small amount of concrete added. Therefore, there is a need for a variable diameter screw pile and a construction method thereof, which can form screw piles with different outer diameters to improve the bearing capacity of a single pile. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a variable diameter screw pile in view of the deficiencies in the above-mentioned prior art. The design of the variable diameter screw pile is novel and reasonable. By arranging a second thread structure and a second pile core in some soil layers that can well exert the bearing capacity of the thread, the lateral resistance between the pile and the soil layer is increased, and the bearing capacity of the pile body can be greatly improved with only a small amount of concrete added. At the same time, the construction steps are simple, the drilling process and the concrete pouring process are carried out simultaneously, and the amount of excavation during the drilling process is small or no excavation is required, which simplifies the construction steps, is economical and practical, and is easy to promote and use.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a variable diameter screw pile, characterized in that it comprises a lower pile body and an upper pile body located directly above the lower pile body, the lower pile body is a threaded section pile body, the upper pile body is a straight rod section pile body, and the straight rod section pile body and the threaded section pile body are coaxially arranged;

[0005] The threaded pile body includes a pile core, and the pile core includes a first pile core and a second pile core arranged alternately from top to bottom, a first thread structure is arranged on the outer wall of the first pile core, and a second thread structure is arranged on the outer wall of the second pile core; the outer diameter of the second pile core is greater than the outer diameter of the first pile core, and the outer diameter of the second thread structure is greater than the outer diameter of the first thread structure;

[0006] The straight rod segment pile body, the first pile core, the second pile core, the first threaded structure and the second threaded structure are cast as one body.

[0007] The above-mentioned variable diameter screw pile is characterized in that: the outer diameter D of the straight rod section pile body is equal to the outer diameter d2 of the first thread structure; the inner diameter B1 of the second thread structure is larger than the inner diameter d1 of the first thread structure, the outer diameter B2 of the second thread structure is larger than the outer diameter d2 of the first thread structure, the outer diameter B2 of the second thread structure is not larger than 800 mm, and the inner diameter d1 of the first thread structure is not less than 200 mm.

[0008] The above-mentioned variable diameter screw pile is characterized in that the thread structure is an equal pitch thread and is a single-thread or multi-thread thread.

[0009] The above-mentioned variable diameter screw pile is characterized in that the thread structure is a trapezoidal thread.

[0010] The above-mentioned variable diameter screw pile is characterized in that a pile cap is arranged on the upper part of the straight rod segment pile body, and the pile cap is a concrete structure and is cast as a whole with the straight rod segment pile body.

[0011] The above-mentioned variable diameter screw pile is characterized in that: the number of the first thread structure and the second thread structure are both multiple, the M second thread structures include the second thread structure at the pile bottom and M-1 second thread structures in the pile, M is a positive integer and 2≤M≤6.

[0012] The above-mentioned variable diameter screw pile is characterized in that: the length L1 of the straight rod pile body is L-L2, wherein L2 is the length of the threaded pile body, L is the sum of the length of the straight rod pile body and the length of the threaded pile body, the sum of the length of the straight rod pile body and the length of the threaded pile body L is not greater than 60m, and the length L2 of the threaded pile body has a value range of

[0013] At the same time, the present invention also discloses a method for constructing variable diameter screw piles with simple construction steps and reasonable design, which is characterized in that the method comprises the following steps:

[0014] Step 1: Determine the length of the lower pile body: According to the geological report of the construction area and the required single pile bearing capacity, the length L2 of the lower pile body is determined to have a value range of

[0015] The length of the straight-rod pile body L1=L-L2, wherein L2 is the length of the lower pile body, and L is the sum of the length of the straight-rod pile body and the length of the lower pile body, which is not greater than 60m;

[0016] Step 2, determine the number of second thread structures: according to the formula M=X+Z+1, determine the number M of second thread structures, M second thread structures include X+Z second thread structures in the pile and one second thread structure at the bottom of the pile, wherein X is the number of soil layers in the geological report that can well exert the bearing capacity of the thread, and Z is the number of second thread structures that make up the position. When the distance between two adjacent thread structures is greater than Δ, the second thread structure that makes up the position is arranged between the two adjacent thread structures, so that the distance between the two adjacent thread structures is less than or equal to Δ; when the distance between the thread structure and the straight rod pile body is greater than Δ, the second thread structure that makes up the position is arranged between the thread structure and the straight rod pile body, so that the distance between the thread structure and the straight rod pile body is less than or equal to Δ; wherein Δ=8m;

[0017] Step 3: Put the pile driver drill rod in place: Move the spiral pile driver to the side of the construction pile position and align the drill rod with the pile position;

[0018] The spiral pile driver comprises a frame and a drilling device, wherein the drilling device comprises a drill rod and an electric rotary drive mechanism for driving the drilling device to rotate continuously, and the electric rotary drive mechanism is in transmission connection with the upper end of the drill rod;

[0019] The drill rod comprises an inner tube and an outer tube sleeved outside the inner tube, and threaded drill teeth are arranged on the outer side of the outer tube, and the threaded drill teeth comprise fixed-diameter threaded drill teeth and variable-diameter threaded drill teeth, and a first guide hole is opened on the variable-diameter threaded drill teeth, and a first drill block cooperates with the first guide hole through a first jacking device; a second guide hole is opened on the outer tube section corresponding to the variable-diameter threaded drill teeth, and a second drill block cooperates with the second guide hole through a second jacking device; there are multiple first drill blocks and first jacking devices, and multiple first drill blocks are evenly arranged along the direction of the variable-diameter threaded drill teeth; there are multiple second drill blocks and second jacking devices, and the second drill block comprises a vertical drill block and a circumferential drill block, the vertical drill block is arranged along the length direction of the outer tube, and the circumferential drill block is arranged along the circumferential direction of the outer tube; the threaded drill teeth are single-line threaded drill teeth and are trapezoidal threaded drill teeth;

[0020] Step 4, drilling: the spiral pile driver drives the drill rod to drill downward counterclockwise until the hole reaches the designed hole depth; during this process, the first drill block, the vertical drill block and the circumferential drill block are all retracted;

[0021] Step 5, construction of the first pile section: the second threaded structure at the bottom of the pile and the second pile core matched therewith constitute the first pile section. When the bottom of the drill rod is at the designed hole depth, the first drill block, the vertical drill block and the circumferential drill block are all extended, and the spiral pile driver drives the drill rod to rotate clockwise to lift the length Lb1 of the second threaded structure at the bottom of the pile; Lb1 is 1m to 2m; during the upward lifting of the drill rod, the grouting equipment is connected through the inner tube to synchronously perform concrete pouring construction to form the first pile section;

[0022] Step 6, construction of the second pile section: the pile section between the second thread structure at the pile bottom in the threaded section pile body and the second thread structure in the pile adjacent to the second thread structure at the pile bottom is the second pile section, the first drill block, the vertical drill block and the circumferential drill block are all retracted, and the drill rod continues to be lifted upward; during the upward lifting of the drill rod, the grouting equipment is connected through the inner tube to synchronously perform concrete pouring construction to form the second pile section;

[0023] Step 7, construction of the third pile section: the second threaded structure in the pile and the second pile core matched therewith constitute the third pile section. When the bottom of the drill rod is lifted to the bottom elevation of the second threaded structure in the pile, the first drill block, the vertical drill block and the circumferential drill block are all extended, and the spiral pile driver drives the drill rod to rotate clockwise to lift the length Lb2 of the second threaded structure in the pile. During the upward lifting of the drill rod, the grouting equipment is connected through the inner tube to synchronously perform concrete pouring construction to form the third pile section. Among them, Lb2 is 1m to 2m.

[0024] Step 8, construction of the fourth pile section: the pile section in the threaded section pile body that is located on the upper side of the second threaded structure in the pile and cooperates with the first threaded structure is the fourth pile section, the first drill block, the vertical drill block and the circumferential drill block are all retracted, and the drill rod continues to be lifted up; during the upward lifting of the drill rod, the grouting equipment is connected through the inner tube to synchronously perform concrete pouring construction to form the fourth pile section; when the bottom of the drill rod is not lifted to a distance of L2 from the bottom of the borehole, step 7 is executed; when the bottom of the drill rod is lifted to a distance of L2 from the bottom of the borehole, step 9 is executed;

[0025] Step nine, construction of the straight-rod pile body: the spiral pile driver drives the drill rod to rotate counterclockwise and lift it up until the drill rod is lifted out of the formed borehole; during the upward lifting of the drill rod, the grouting equipment is connected through the inner tube to simultaneously perform concrete pouring construction to form the straight-rod pile body; and then the variable-diameter screw pile is constructed.

[0026] The above method is characterized in that: the reducing thread drill teeth are located below the fixed-size thread drill teeth, the reducing thread drill teeth, the first drill block, the first jacking device, the second drill block, the second jacking device, the outer tube section cooperating with the reducing thread drill teeth and the inner tube section cooperating with the first jacking device constitute a reducing drill rod, the fixed-size thread drill teeth, and the outer tube and inner tube sections cooperating with the fixed-size thread drill teeth constitute a fixed-size drill rod, and the reducing drill rod and the fixed-size drill rod are connected by threads.

[0027] The above method is characterized in that a drill bit is provided at the lower end of the variable diameter drill rod, the drill bit is coaxially installed at the bottom of the outer tube, the drill bit is conical and its diameter gradually decreases from top to bottom, the upper end diameter of the drill bit is not larger than the outer diameter of the outer tube, and the drill bit is provided with a slurry outlet communicating with the interior of the inner tube.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. The variable diameter screw pile adopted by the present invention increases the lateral resistance between the pile and the soil layer by arranging a second thread structure and a second pile core in some soil layers that can well exert the bearing capacity of the thread, thereby greatly improving the bearing capacity of the pile body with only a small amount of concrete added. The invention is economical, practical and easy to promote and use.

[0030] 2. The variable diameter screw pile adopted by the present invention is applicable to many types of strata and has strong adaptability to soil layers. It can be widely used in complex soil layers such as sand layers, pebble layers, silt, miscellaneous stone backfill, and strongly weathered soil layers that cannot be effectively overcome by traditional pile construction.

[0031] 3. The variable diameter screw pile adopted by the present invention has a straight rod section pile body, which is a cylindrical pile body and is arranged above the threaded section pile body. Based on the structural characteristics of the pile hole in which the straight rod section pile body and the threaded section pile body are located, the straight rod section pile body is almost impossible to move downward regardless of looseness or shaking, thereby effectively improving the vertical bearing capacity of the single pile.

[0032] 4. The construction method adopted by the present invention has simple steps. The drilling process and the concrete pouring process are carried out simultaneously. In addition, the amount of excavated concrete is small or no excavation is required during the drilling process, which simplifies the construction steps, saves construction time, makes single pile construction more efficient, saves construction costs, and is easy to promote and use.

[0033] To sum up, the design of the present invention is novel and reasonable. By arranging a second thread structure and a second pile core in some soil layers that can well exert the bearing capacity of the thread, the lateral resistance between the pile and the soil layer is increased, and the bearing capacity of the pile body can be greatly improved with only a small amount of concrete added. At the same time, the construction steps are simple, the drilling process and the concrete pouring process are carried out simultaneously, and the amount of excavation during the drilling process is small or no excavation is required, which simplifies the construction steps, is economical and practical, and is easy to promote and use.

[0034] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic structural diagram of the variable diameter screw pile of the present invention.

[0036] Figure 2 This is a schematic diagram of the construction state when the drill block is extended after the drill rod reaches the designed hole depth in the method adopted by the present invention.

[0037] Figure 3 This is a schematic diagram of the structure of the drill rod used in the present invention.

[0038] Figure 4 It is a schematic structural diagram of the pushing device used in the present invention when it is retracted.

[0039] Figure 5 for Figure 4 Top view of the .

[0040] Figure 6 This is a schematic diagram of the structure of the pushing device used in the present invention when the extended distance is the longest.

[0041] Figure 7 for Figure 6 Top view of the .

[0042] Figure 8 This is a schematic diagram of the construction state when the drill rod is lifted up to the bottom elevation of the straight rod section pile body and the drill block is retracted in the method adopted by the present invention.

[0043] Fig. 9 This is a schematic diagram of the construction state when the drill rod is pulled out from the formed drill hole in the method adopted by the present invention.

[0044] Fig.10 The figure is a flowchart of the method of the present invention.

[0045] Description of reference numerals:

[0046] 1-Fixed diameter drill rod; 2-Fixed diameter threaded drill teeth; 3-Variable diameter drill rod;

[0047] 4-outer tube; 5-reducing threaded drill teeth; 6-first drill block;

[0048] 7-inner tube; 8-drill bit; 9-first jacking device;

[0049] 10-vertical drill block; 11-second jacking device; 12-circumferential drill block;

[0050] 13-upper pile body; 14-lower pile body; 15-first pile core;

[0051] 16-first thread structure; 17-second thread structure; 18-second pile core. DETAILED DESCRIPTION

[0052] like Figure 1 As shown, a variable diameter screw pile according to the present invention comprises a lower pile body 14 and an upper pile body 13 located directly above the lower pile body 14, wherein the lower pile body 14 is a threaded section pile body, and the upper pile body 13 is a straight section pile body, and the straight section pile body and the threaded section pile body are coaxially arranged;

[0053] The threaded pile body includes a pile core, which includes a first pile core 15 and a second pile core 18 arranged alternately from top to bottom, a first thread structure 16 is arranged on the outer wall of the first pile core 15, and a second thread structure 17 is arranged on the outer wall of the second pile core 18; the outer diameter of the second pile core 18 is greater than the outer diameter of the first pile core 15, and the outer diameter of the second thread structure 17 is greater than the outer diameter of the first thread structure 16;

[0054] The straight-rod pile body, the first pile core 15 , the second pile core 18 , the first threaded structure 16 and the second threaded structure 17 are cast as one body.

[0055] In this embodiment, the pile core is a cylindrical pile core, the straight rod section pile body is a cylindrical pile body, and the pile body is arranged vertically.

[0056] It should be noted that, by providing the threaded pile body, since the pile hole in which the threaded pile body is located is an internal threaded hole with a spiral groove, based on the thread shear stress, the vertical bearing capacity of the threaded pile body itself is high.

[0057] By setting a thread structure with a larger outer diameter and a pile core with a larger outer diameter in a soil layer that can well exert the bearing capacity of the thread, the bearing capacity of a single pile can be greatly improved with only a small increase in the amount of concrete.

[0058] By setting the straight rod segment pile body, the straight rod segment pile body is a cylindrical pile body and is set above the threaded segment pile body. Based on the structural characteristics of the pile hole in which the straight rod segment pile body and the threaded segment pile body are located, the straight rod segment pile body is almost impossible to move downward regardless of looseness or shaking, thereby effectively improving the vertical bearing capacity of the single pile.

[0059] In this embodiment, the outer diameter D of the straight rod pile body is equal to the outer diameter d2 of the first threaded structure 16; the inner diameter B1 of the second threaded structure 17 is greater than the inner diameter d1 of the first threaded structure 16, the outer diameter B2 of the second threaded structure 17 is greater than the outer diameter d2 of the first threaded structure 16, the outer diameter B2 of the second threaded structure 17 is not greater than 800 mm, and the inner diameter d1 of the first threaded structure 16 is not less than 200 mm.

[0060] It should be noted that the inner diameter B1 of the second thread structure 17 is the outer diameter of the pile section where the pile core cooperates with the second thread structure 17 , and the inner diameter d1 of the first thread structure 16 is the outer diameter of the pile section where the pile core cooperates with the first thread structure 16 .

[0061] In this embodiment, the thread structure is an equal pitch thread and is a single-thread or a multi-thread.

[0062] In this embodiment, the thread structure is a single-thread; in actual use, the thread structure may also be a multi-thread; and when the thread structure is a multi-thread, the number of spiral threads is not greater than 4.

[0063] In this embodiment, the thread structure is a trapezoidal thread.

[0064] In this embodiment, the thread structure may also be a rectangular thread or a cylindrical thread.

[0065] It should be noted that threads are divided into two types according to the direction of the helix: left-handed threads and right-handed threads. Left-handed threads, also known as reverse threads, are threads that are screwed in counterclockwise. Threads are divided into two types according to the number of helical threads: single-thread threads and multi-thread threads. Single-thread threads are threads formed along one helical thread, and multi-thread threads are threads formed along two or more equidistant helical threads.

[0066] In this embodiment, the thread structure is a reverse thread; in actual use, the thread structure may also be a forward thread.

[0067] In this embodiment, a pile cap is provided on the upper part of the straight rod segment pile body, and the pile cap is a concrete structure and is cast as one body with the straight rod segment pile body.

[0068] In this embodiment, the number of the first thread structure 16 and the second thread structure 17 are both multiple, and the M second thread structures 17 include a second thread structure at the bottom of the pile and M-1 second thread structures in the middle of the pile, where M is a positive integer and 2≤M≤6.

[0069] In this embodiment, the length L1 of the straight rod pile body is L-L2, wherein L2 is the length of the threaded pile body, L is the sum of the length of the straight rod pile body and the length of the threaded pile body, the sum of the length of the straight rod pile body and the length of the threaded pile body is not greater than 60m, and the length L2 of the threaded pile body has a value range of

[0070] During actual construction, the length L1 of the straight-rod pile body and the length L2 of the threaded-rod pile body can be adjusted accordingly according to specific needs.

[0071] like Figures 2 to 10 A construction method shown comprises the following steps:

[0072] Step 1: Determine the length of the lower pile body: According to the geological report of the construction area and the required single pile bearing capacity, the length L2 of the lower pile body 14 is determined to have a value range of

[0073] The length of the straight-rod pile body L1=L-L2, wherein L2 is the length of the lower pile body 14, and L is the sum of the length of the straight-rod pile body and the length of the lower pile body 14, which is not greater than 60m;

[0074] In actual construction, the length L1 of the straight section pile body and the length L2 of the threaded section pile body can be adjusted accordingly according to specific needs; wherein, when the side resistance required by a single pile is large, since the side resistance of the straight section pile body is higher, The straight rod pile body accounts for a higher proportion of the entire variable diameter screw pile; when the shear strength required for the single pile is large, The longer the thread structure, the greater the shear strength;

[0075] Step 2, determine the number of second thread structures: according to the formula M=X+Z+1, determine the number M of second thread structures, M second thread structures include X+Z second thread structures in the pile and one second thread structure at the bottom of the pile, wherein X is the number of soil layers in the geological report that can well exert the bearing capacity of the thread, and Z is the number of second thread structures that make up the position. When the distance between two adjacent thread structures is greater than Δ, the second thread structure that makes up the position is arranged between the two adjacent thread structures, so that the distance between the two adjacent thread structures is less than or equal to Δ; when the distance between the thread structure and the straight rod pile body is greater than Δ, the second thread structure that makes up the position is arranged between the thread structure and the straight rod pile body, so that the distance between the thread structure and the straight rod pile body is less than or equal to Δ; wherein Δ=8m;

[0076] Step 3: Put the pile driver drill rod in place: Move the spiral pile driver to the side of the construction pile position and align the drill rod with the pile position;

[0077] The spiral pile driver comprises a frame and a drilling device, wherein the drilling device comprises a drill rod and an electric rotary drive mechanism for driving the drilling device to rotate continuously, and the electric rotary drive mechanism is in transmission connection with the upper end of the drill rod;

[0078] The drill rod includes an inner tube 7 and an outer tube 4 sleeved outside the inner tube 7, and a threaded drill tooth is arranged on the outer side of the outer tube 4, and the threaded drill tooth includes a fixed-diameter threaded drill tooth 2 and a variable-diameter threaded drill tooth 5. A first guide hole is opened on the variable-diameter threaded drill tooth 5, and a first drill block 6 cooperates with the first guide hole through a first jacking device 9; a second guide hole is opened on the outer tube 4 section corresponding to the variable-diameter threaded drill tooth 5, and a second drill block cooperates with the second guide hole through a second jacking device 11; the first drill block 6 and the first jacking device 9 are both multiple, and the multiple first drill blocks 6 are evenly arranged along the direction of the variable-diameter threaded drill tooth 5; the second drill block and the second jacking device 11 are both multiple, and the second drill block includes a vertical drill block 10 and a circumferential drill block 12, the vertical drill block 10 is arranged along the length direction of the outer tube 4, and the circumferential drill block 12 is arranged along the circumferential direction of the outer tube 4; the threaded drill tooth is a single-line threaded drill tooth and a trapezoidal threaded drill tooth;

[0079] Step 4, drilling: the spiral pile driver drives the drill rod to drill downward counterclockwise until the hole reaches the designed hole depth; during this process, the first drill block 6, the vertical drill block 10 and the circumferential drill block 12 are all retracted;

[0080] Step 5, construction of the first pile section: the second threaded structure at the bottom of the pile and the second pile core 18 matched therewith constitute the first pile section. When the bottom of the drill rod is at the designed hole depth, the first drill block 6, the vertical drill block 10 and the circumferential drill block 12 are all extended, and the spiral pile driver drives the drill rod to rotate clockwise to lift the length Lb1 of the second threaded structure at the bottom of the pile; Lb1 is 1m to 2m; during the upward lifting of the drill rod, the grouting equipment is connected through the inner tube 7 to synchronously perform concrete pouring construction, and the first pile section is constructed;

[0081] Step 6, construction of the second pile section: the pile section between the second thread structure at the pile bottom in the threaded section pile body and the second thread structure in the pile adjacent to the second thread structure at the pile bottom is the second pile section, the first drill block 6, the vertical drill block 10 and the circumferential drill block 12 are all retracted, and the drill rod continues to be lifted up; during the upward lifting of the drill rod, the grouting equipment is connected through the inner tube 7 to synchronously perform concrete pouring construction, so as to form the second pile section;

[0082] Step 7, construction of the third pile section: the second threaded structure in the pile and the second pile core 18 matched therewith constitute the third pile section. When the bottom of the drill rod is lifted to the bottom elevation of the second threaded structure in the pile, the first drill block 6, the vertical drill block 10 and the circumferential drill block 12 are all extended, and the spiral pile driver drives the drill rod to rotate clockwise to lift the length Lb2 of the second threaded structure in the pile. During the upward lifting of the drill rod, the grouting equipment is connected through the inner tube 7 to synchronously perform concrete pouring construction to form the third pile section; wherein, Lb2 is 1m to 2m;

[0083] Step 8, construction of the fourth pile section: the pile section in the threaded section pile body located on the upper side of the second threaded structure in the pile and matched with the first threaded structure 16 is the fourth pile section, the first drill block 6, the vertical drill block 10 and the circumferential drill block 12 are all retracted, and the drill rod continues to be lifted up; during the upward lifting of the drill rod, the grouting equipment is connected through the inner tube 7 to synchronously perform concrete pouring construction to form the fourth pile section; when the bottom of the drill rod is not lifted to a distance of L2 from the bottom of the borehole, step 7 is executed; when the bottom of the drill rod is lifted to a distance of L2 from the bottom of the borehole, step 9 is executed;

[0084] In actual construction, when L = 60m, When Lb1=1m, Lb2=1m, X=1 and the soil layer is 30m away from the designed hole depth, three second thread structures are evenly arranged between the soil layer and the second thread structure at the bottom of the pile to make the distance between the thread structures less than 8m, and one second thread structure is arranged between the soil layer and the straight-rod pile body to make the distance between the thread structure and the straight-rod pile body less than 8m, so that the single pile has a stronger bearing capacity;

[0085] Step 9, construction of the straight-rod pile body: the spiral pile driver drives the drill rod to rotate counterclockwise and lift it up until the drill rod is lifted out of the formed borehole; during the upward lifting of the drill rod, the grouting equipment is connected through the inner tube 7 to simultaneously perform concrete pouring construction to form the straight-rod pile body; and then the variable-diameter screw pile is constructed.

[0086] In this embodiment, the variable diameter screw pile is a partially threaded pile consisting of the straight rod pile body and the threaded pile body. In actual construction, the variable diameter screw pile can also be a fully threaded pile according to specific needs, and the pile length of the fully threaded pile body is not more than 60m; the construction steps of the fully threaded pile are the same as steps 1 to 8;

[0087] In this embodiment, the drilling speed of the drill rod is set so that the drill rod rotates one circle and the drill rod is increased by one drill rod pitch.

[0088] In this embodiment, the pitch of the first thread structure 16 is the same as the pitch of the second thread structure 17 , and the pitch of the second thread structure 17 is the same as the pitch of the drill rod.

[0089] In this embodiment, the reducing threaded drill teeth 5 are located below the fixed-size threaded drill teeth 2. The reducing threaded drill teeth 5, the first drill block 6, the first jacking device 9, the second drill block, the second jacking device 11, the pipe section of the outer tube 4 cooperating with the reducing threaded drill teeth 5, and the pipe section of the inner tube 7 cooperating with the first jacking device 9 constitute a reducing drill rod 3. The fixed-size threaded drill teeth 2, and the outer tube 4 and the inner tube 7 pipe sections cooperating with the fixed-size threaded drill teeth 2 constitute a fixed-size drill rod 1. The reducing drill rod 3 and the fixed-size drill rod 1 are connected by threads.

[0090] In this embodiment, a drill bit 8 is provided at the lower end of the variable diameter drill rod 3, and the drill bit 8 is coaxially installed at the bottom of the outer tube 4. The drill bit 8 is conical and its diameter gradually decreases from top to bottom. The upper end diameter of the drill bit 8 is not larger than the outer diameter of the outer tube 4, and the drill bit 8 is provided with a slurry outlet connected to the inside of the inner tube 7.

[0091] In this embodiment, the threaded drill teeth are reverse threaded drill teeth; in actual use, the threaded drill teeth may also be forward threaded drill teeth.

[0092] In this embodiment, the first jacking device 9 and the second jacking device 11 constitute a jacking device, which is an oil cylinder and is arranged on the outer wall of the inner tube 7. When the first jacking device 9 extends to the maximum distance, the first drill block 6 does not completely extend out of the variable diameter threaded drill teeth 5. When the second jacking device 11 extends to the maximum distance, the second drill block does not completely extend out of the outer tube 4, so as to prevent impurities outside the drill rod from entering the drill rod and affecting the normal operation of the drill rod. In actual use, the jacking device can also be a cylinder; by selecting different diameters of the inner tube 7 and the outer tube 4, gaps of different sizes are formed between the inner tube 7 and the outer tube 4, so that jacking devices with different extension amounts can be set.

[0093] In this embodiment, the plurality of vertical drill blocks 10 are symmetrically arranged in two rows along the axis of the outer tube 4. The length of the line segment connecting the head and tail of each row of vertical drill blocks 10 is greater than the pitch of the variable diameter threaded drill teeth 5. The purpose is to form a cylindrical drill hole instead of a threaded drill hole during the rotation and lifting of the drill rod after the second drill block is extended.

[0094] In actual use, the thread drill teeth may also be multi-threaded thread drill teeth. Moreover, when the thread drill teeth are multi-threaded thread drill teeth, the number of spiral lines is not greater than 4; the thread drill teeth may also be rectangular thread drill teeth or cylindrical thread drill teeth.

[0095] The outer diameter of the thread of the variable diameter drill rod 3 at the variable diameter position is not greater than 800 mm.

[0096] In this embodiment, the sizing threaded drill teeth 2 are arranged on the outer wall of the outer tube 4 of the sizing drill rod 1 from bottom to top, and the length of the threaded section of the outer tube 4 of the sizing drill rod 1 accounts for 1 / 10 of the length of the outer tube 4 of the entire sizing drill rod 1. In actual use, the outer side wall of the outer tube 4 of the sizing drill rod 1 can also be completely provided with sizing threaded drill teeth 2 .

[0097] In this embodiment, the pitch of the variable diameter threaded drill teeth 5 is equal to the pitch of the fixed diameter threaded drill teeth 2, and the pitch of the variable diameter threaded drill teeth 5 is 100 mm to 1000 mm.

[0098] In this embodiment, the variable diameter threaded drill teeth 5 are arranged in one circle along the length direction of the outer tube 4; in actual use, the variable diameter threaded drill teeth 5 can also be arranged in multiple circles. In this case, the variable diameter drill rod 3 has a higher stress strength after the diameter is reduced, and the use effect is better.

[0099] In this embodiment, the number of the first drill blocks 6 is N, where N is a positive integer and ranges from 5 to 8.

[0100] In this embodiment, N is 6, which can meet the design requirements while reducing consumables and saving costs;

[0101] It should be noted that, when the variable diameter thread drill teeth 5 are multiple circles, the number of the first drill blocks 6 on one circle of variable diameter thread drill teeth 5 is N.

[0102] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A construction method for variable diameter screw piles, characterized in that: The variable diameter screw pile comprises a lower pile body (14) and an upper pile body (13) located directly above the lower pile body (14), the lower pile body (14) is a threaded section pile body, the upper pile body (13) is a straight section pile body, and the straight section pile body and the threaded section pile body are coaxially arranged; The threaded pile body comprises a pile core, and the pile core comprises a first pile core (15) and a second pile core (18) arranged alternately from top to bottom, a first thread structure (16) is arranged on the outer wall of the first pile core (15), and a second thread structure (17) is arranged on the outer wall of the second pile core (18); the outer diameter of the second pile core (18) is greater than the outer diameter of the first pile core (15), and the outer diameter of the second thread structure (17) is greater than the outer diameter of the first thread structure (16); The straight-rod pile body, the first pile core (15), the second pile core (18), the first threaded structure (16) and the second threaded structure (17) are cast as one body; The construction method comprises the following steps: Step 1: Determine the length of the lower pile body: According to the geological report of the construction area and the required single pile bearing capacity, the length L2 of the lower pile body (14) is determined within the range of The length of the straight-rod pile body L1=L-L2, wherein L2 is the length of the lower pile body (14), and L is the sum of the length of the straight-rod pile body and the length of the lower pile body (14), which is not greater than 60 m; Step 2, determining the number of second thread structures: according to the formula M=X+Z+1, determining the number M of second thread structures (17), the M second thread structures (17) include X+Z second thread structures in the pile and one second thread structure at the bottom of the pile, wherein X is the number of soil layers in the geological report that can well exert the bearing capacity of the thread, and Z is the number of second thread structures that make up the position. When the distance between two adjacent thread structures is greater than Δ, the second thread structure that makes up the position is arranged between the two adjacent thread structures, so that the distance between the two adjacent thread structures is less than or equal to Δ; when the distance between the thread structure and the straight rod pile body is greater than Δ, the second thread structure that makes up the position is arranged between the thread structure and the straight rod pile body, so that the distance between the thread structure and the straight rod pile body is less than or equal to Δ; wherein Δ=8m; Step 3: Put the pile driver drill rod in place: Move the spiral pile driver to the side of the construction pile position and align the drill rod with the pile position; The spiral pile driver comprises a frame and a drilling device, wherein the drilling device comprises a drill rod and an electric rotary drive mechanism for driving the drilling device to rotate continuously, and the electric rotary drive mechanism is in transmission connection with the upper end of the drill rod; The drill rod comprises an inner tube (7) and an outer tube (4) sleeved outside the inner tube (7); a threaded drill tooth is arranged on the outer side of the outer tube (4); the threaded drill tooth comprises a fixed-diameter threaded drill tooth (2) and a variable-diameter threaded drill tooth (5); a first guide hole is provided on the variable-diameter threaded drill tooth (5); a first drill block (6) cooperates with the first guide hole through a first jacking device (9); a second guide hole is provided on the outer tube (4) section corresponding to the variable-diameter threaded drill tooth (5); a second drill block cooperates with the second guide hole through a second jacking device (11); The first drill block (6) and the first jacking device (9) are both multiple, and the multiple first drill blocks (6) are evenly arranged along the direction of the variable diameter thread drill teeth (5); the second drill block and the second jacking device (11) are both multiple, and the second drill block includes a vertical drill block (10) and a circumferential drill block (12), the vertical drill block (10) is arranged along the length direction of the outer tube (4), and the circumferential drill block (12) is arranged along the circumferential direction of the outer tube (4); the thread drill teeth are single-line thread drill teeth and trapezoidal thread drill teeth; Step 4: Drilling: The screw pile driver drives the drill rod to drill downward counterclockwise until the hole reaches the designed hole depth; during this process, the first drill block (6), the vertical drill block (10) and the circumferential drill block (12) are all retracted; Step 5, construction of the first pile section: the second threaded structure at the bottom of the pile and the second pile core (18) matched therewith constitute the first pile section. When the bottom of the drill rod is at the designed hole depth, the first drill block (6), the vertical drill block (10) and the circumferential drill block (12) are all extended, and the spiral pile driver drives the drill rod to rotate clockwise to lift the length Lb1 of the second threaded structure at the bottom of the pile; Lb1 is 1m to 2m; during the upward lifting of the drill rod, the grouting equipment is connected through the inner tube (7) to synchronously perform concrete pouring construction, so as to form the first pile section; Step 6, construction of the second pile section: the pile section between the second thread structure at the pile bottom in the threaded section pile body and the second thread structure in the pile adjacent to the second thread structure at the pile bottom is the second pile section, the first drill block (6), the vertical drill block (10) and the circumferential drill block (12) are all retracted, and the drill rod continues to be lifted upward; during the upward lifting of the drill rod, the grouting equipment is connected through the inner tube (7) to synchronously perform concrete pouring construction, so as to form the second pile section; Step 7, construction of the third pile section: the second threaded structure in the pile and the second pile core (18) matched therewith constitute the third pile section. When the bottom of the drill rod is lifted to the elevation of the bottom of the second threaded structure in the pile, the first drill block (6), the vertical drill block (10) and the circumferential drill block (12) are all extended, and the spiral pile driver drives the drill rod to rotate clockwise to lift the length Lb2 of the second threaded structure in the pile. During the upward lifting of the drill rod, the grouting equipment is connected through the inner tube (7) to synchronously perform concrete pouring construction, so as to form the third pile section. Among them, Lb2 is 1m to 2m. Step 8, construction of the fourth pile section: the pile section in the threaded section pile body which is located on the upper side of the second threaded structure in the pile and cooperates with the first threaded structure (16) is the fourth pile section, the first drill block (6), the vertical drill block (10) and the circumferential drill block (12) are all retracted, and the drill rod continues to be lifted upward; during the upward lifting of the drill rod, the grouting equipment is connected through the inner tube (7) to synchronously perform concrete pouring construction, and the fourth pile section is constructed; when the bottom of the drill rod is not lifted to a distance of L2 from the bottom of the borehole, step 7 is executed; when the bottom of the drill rod is lifted to a distance of L2 from the bottom of the borehole, step 9 is executed; Step 9, construction of the straight-rod pile body: the spiral pile driver drives the drill rod to rotate counterclockwise and lift it up until the drill rod is lifted out of the formed drill hole; during the upward lifting of the drill rod, the grouting equipment is connected through the inner tube (7) to synchronously perform concrete pouring construction to form the straight-rod pile body; and then the variable-diameter screw pile is constructed; The variable diameter threaded drill teeth (5) are located below the fixed diameter threaded drill teeth (2); the variable diameter threaded drill teeth (5), the first drill block (6), the first jacking device (9), the second drill block, the second jacking device (11), the pipe section of the outer tube (4) matched with the variable diameter threaded drill teeth (5), and the pipe section of the inner tube (7) matched with the first jacking device (9) constitute a variable diameter drill rod (3); the fixed diameter threaded drill teeth (2), and the pipe sections of the outer tube (4) and the inner tube (7) matched with the fixed diameter threaded drill teeth (2) constitute a fixed diameter drill rod (1); the variable diameter drill rod (3) and the fixed diameter drill rod (1) are connected via threads.

2. The construction method of a variable diameter screw pile according to claim 1, characterized in that: The outer diameter D of the straight rod pile body is equal to the outer diameter d2 of the first threaded structure (16); the inner diameter B1 of the second threaded structure (17) is greater than the inner diameter d1 of the first threaded structure (16); the outer diameter B2 of the second threaded structure (17) is greater than the outer diameter d2 of the first threaded structure (16); the outer diameter B2 of the second threaded structure (17) is not greater than 800 mm, and the inner diameter d1 of the first threaded structure (16) is not less than 200 mm.

3. The construction method of a variable diameter screw pile according to claim 1, characterized in that: The thread structure is an equal pitch thread and is a single-line thread or a multi-line thread.

4. The construction method of a variable diameter screw pile according to claim 1, characterized in that: The thread structure is a trapezoidal thread.

5. The construction method of a variable diameter screw pile according to claim 1, characterized in that: A pile cap is arranged on the upper part of the straight rod segment pile body. The pile cap is a concrete structure and is cast as a whole with the straight rod segment pile body.

6. The construction method of a variable diameter screw pile according to claim 1, characterized in that: The number of the first thread structure (16) and the second thread structure (17) are both multiple, and the M second thread structures (17) include a second thread structure at the bottom of the pile and M-1 second thread structures in the pile, where M is a positive integer and 2≤M≤6.

7. The construction method of a variable diameter screw pile according to claim 1, characterized in that: A drill bit (8) is provided at the lower end of the variable diameter drill rod (3), and the drill bit (8) is coaxially mounted on the bottom of the outer tube (4). The drill bit (8) is conical and its diameter gradually decreases from top to bottom. The diameter of the upper end of the drill bit (8) is not greater than the outer diameter of the outer tube (4). The drill bit (8) is provided with a slurry outlet that communicates with the interior of the inner tube (7).

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