Construction method of cast-in-situ bored pile in desert area

Abstract

The invention relates to a construction method of a cast-in-situ bored pile in a desert area. The construction method sequentially comprises the steps of site treatment, steel pile casing burying, drilling slurry configuration, drilling, hole cleaning, necking-proof pile casing mounting, secondary hole cleaning, reinforcement cage hoisting and pile forming through concrete pouring. The anti-necking pile casing comprises a first steel pile casing and n second steel pile casings, and n is an integer greater than or equal to 2; the wall thickness of the second steel casing and the inner diameter of the first steel casing are the same, the wall thickness of the second steel casing is w, the inner diameter of the first steel casing is also the same, the inner diameter of the second steel casing is also the same, the inner diameter of the second steel casing is D, w ranges from 16 mm to 25 mm, D is larger than or equal to 1.2 m, and the first steel casing and the second steel casing can be arranged in the steel casings in an embedded mode. The problems of necking, hole collapse, corrosion prevention and construction efficiency of the cast-in-situ bored pile in the desert area are solved through the segmented necking-proof pile casing, mathematical construction parameter control and the synchronous corrosion prevention spraying technology.

Description

Technical Field

[0001] This application relates to the field of building construction technology, specifically to a construction method for bored piles in desert areas. Background Technology

[0002] Due to the unique geological conditions of desert regions, the application of bored piles is relatively complex, requiring the adoption of appropriate drilling techniques, construction methods, and precautions tailored to the characteristics of desert areas. Key issues to address include borehole collapse and necking. The sandy layers in desert regions easily lead to borehole collapse or necking, resulting in poor borehole wall stability. Furthermore, existing casing structures are often simple and insufficient in length, making it difficult to effectively isolate loose sand layers. In addition, corrosion prevention needs to be addressed. On one hand, the high salt and alkaline content of soils in many desert regions allows these salts to be adsorbed into the concrete through capillary action, leading to electrochemical corrosion of the reinforcing steel. On the other hand, water resources are scarce in desert regions, limiting the feasibility of concrete curing. Without proper curing, the strength and durability of concrete decrease, making it more susceptible to corrosion. Current corrosion prevention measures generally employ steel casings with built-in corrosion protection to protect the concrete piles. While this provides some protection, it is costly and involves complex construction processes. Therefore, a comprehensive construction method that adapts to the desert environment and integrates necking prevention, corrosion protection, and efficient casing operation is urgently needed. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this application proposes a construction method for bored piles in desert areas that is convenient to construct and can effectively prevent borehole collapse and necking.

[0004] This application discloses a construction method for bored piles in desert areas. The construction method includes, in sequence, site preparation, installation of steel casing, preparation of drilling mud, drilling, hole cleaning, installation of anti-necking casing, secondary hole cleaning, placement of reinforcing cage, and concrete pouring to form the pile. The anti-necking casing includes one first steel casing and n second steel casings, where n is an integer ≥ 2. The second steel casing and the first steel casing have the same wall thickness and the same inner diameter, which are w and D, respectively, where w = 16mm ~ 25mm and D ≥ 1.2m. The first steel casing and the second steel casing can be nested inside the steel casing. The process of installing the anti-neck casing includes: firstly, detachably installing the end of the first second steel casing to the tail of the first steel casing, and then pushing the first second steel casing downwards; then detachably installing the end of the second second steel casing to the tail of the first second steel casing, and then pushing the second second steel casing downwards; until the nth second steel casing is installed, after the process of installing the anti-neck casing is completed, the end of the first steel casing reaches the bottom of the hole; The concrete pouring pile formation process includes: inserting a guide pipe to continuously pour concrete, wherein the water-cement ratio of the concrete is W / C≤0.4; after the pouring is completed and a suitable time is waited, the first steel casing and the second steel casing are pulled out at a uniform speed. Each time the second steel casing is completely pulled out, the pulling process is paused, the completely pulled-out second steel casing is removed, and then the pulling is continued at a uniform speed until the first steel casing and the second steel casing are completely pulled out.

[0005] Furthermore, in the concrete pouring pile formation process of the construction method described in this invention, the concrete pouring speed is υ1, H is the drilling depth, and the time for the concrete to be poured is Δt1. Then, Δt1 satisfies the following condition: Δt1 = (π·D) 2 ·H) / 4·υ1, and 3m³ / h≤υ1≤8m³ / h, H≤60m; If the start time of injection is recorded as t0, then the start time for pulling out the first and second steel casings is t2, satisfying t2 = t0 + Δt1 + Δt2, where Δt2 = k 2 ·W / C·T, where T is the temperature at the end of the first steel casing, Δt2 is the time required to ensure that the compressive strength σ of the cast-in-place pile is greater than or equal to 5 MPa; satisfying 5℃≤T≤30℃, and k is a coefficient satisfying 0.5≤k≤1.5; The extraction speed is υ2, and it satisfies: 0.5m / min≤υ2≤1m / min.

[0006] Furthermore, the concrete pouring and pile formation process of the construction method of the present invention also includes an anti-corrosion liquid spraying process, which includes spraying an anti-corrosion layer onto the outer surface of the concrete pile through nozzle A during the process of pulling out the first steel casing and the second steel casing. The end of the first steel casing includes an annular fixing part fixedly connected to the body of the first steel casing and a movable part movably connected to the body of the first steel casing. A miniature electric cylinder is provided between the movable part and the body. A nozzle A is also provided on the side of the movable part near the fixing part. The nozzle A is connected to the anti-corrosion liquid storage tank through a pipe A. The pipe A is embedded in the cylinder wall of the first steel casing and the second steel casing. The number of the movable part and the miniature electric cylinder is N, and N = D / 3, where N is an integer ≥ 3; The anti-corrosion liquid storage tank is also equipped with a switch, which is electrically connected to both the spray head A and the miniature electric cylinder.

[0007] Furthermore, the anti-corrosion liquid spraying process of the construction method of the present invention specifically includes: before starting to pull out the first steel casing and the second steel casing, firstly, the micro electric cylinder is started by switching on the switch, so that the moving part is away from the annular fixed part; then, the steel casing is slowly pulled out, and at the same time, the nozzle A is opened so that the nozzle A sprays the anti-corrosion layer onto the outer surface of the concrete pile.

[0008] Furthermore, in the construction method of the present invention, the cross-section of the annular fixed part is triangular, the cross-section of the movable part is trapezoidal, and the cross-sections of the annular fixed part and the movable part form a large triangle; The trapezoid includes an upper base, a lower base, a short side, and a long side adjacent to the annular fixing part, and the short side is movably connected to the body. The upper bottom is provided with a recess, and the nozzle A is disposed in the recess.

[0009] Furthermore, the process of burying the steel casing in the construction method of the present invention includes placing the steel casing at a designated location, and then filling and compacting clay in the gap between the outer wall of the steel casing and the hole wall to prevent quicksand from flowing in.

[0010] Furthermore, the drilling process of the construction method described in this invention employs rotary drilling and mud wall protection; the hole cleaning process employs mud circulation for slag removal to ensure that the slag thickness is ≤30cm.

[0011] Furthermore, the site treatment of the construction method of the present invention includes site leveling and pile foundation construction platform treatment; the drilling mud preparation includes preparing a mixed mud with sodium bentonite, caustic soda and carboxymethyl cellulose; the secondary hole cleaning adopts the air lift reverse circulation method to remove the sediment at the bottom of the hole, ensuring that the sediment thickness is ≤15cm; the main reinforcement of the steel cage is connected by a straight threaded sleeve during the process of hoisting and placing the steel cage.

[0012] Furthermore, in the construction method of the present invention, the tail end of the first steel casing and the tail end of the second steel casing are both provided with annular grooves, and the head end of the second steel casing is provided with annular protrusions that can cooperate with the annular grooves. Fixing bolts are provided through the annular grooves and the annular protrusions.

[0013] Furthermore, the construction method of the present invention includes a process of spraying anti-corrosion liquid at the bottom of the hole between the process of installing the anti-neck casing and the process of hoisting the steel cage. The process of spraying anti-corrosion liquid at the bottom of the hole includes spraying anti-corrosion liquid onto the bottom of the hole through a nozzle B. The nozzle B is connected to the anti-corrosion liquid storage tank through a pipe B.

[0014] The beneficial effects of this application are: The construction method for bored piles in desert areas described in this application firstly employs a segmented nested anti-neck casing. Specifically, a first steel casing is combined with multiple second steel casings, reinforced by annular groove-protrusion connections and fixing bolts, nested within the first steel casing to form a continuous rigid support, thereby effectively suppressing borehole necking caused by desert shifting sand layers. The design of the first and second steel casings with a wall thickness ≥16mm and an inner diameter >1.2m enhances their resistance to deformation. Combined with the segmented, step-by-step pressing installation process, the risk of borehole collapse is significantly reduced, and the stability of the formed hole is greatly improved, making it suitable for desert pile foundation construction up to 60m deep.

[0015] Secondly, the construction method described in this invention adopts coordinated control of casing extraction and concrete pouring. By controlling the pouring speed (υ1=3~8m³ / h), time (Δt1=π·D²·H / 4υ1), and temperature correction coefficient (Δt2=k·W / C·T), the starting time of casing extraction (t2=t0+Δt1+Δt2) is accurately calculated to avoid hole collapse or casing jamming caused by the concrete not having set properly.

[0016] Furthermore, the construction method described in this invention also involves simultaneously spraying an anti-corrosion coating onto the entire outer surface of the concrete pile through a nozzle A located at the end of the first steel casing after the concrete pile is poured, while pulling the steel casing upwards. This method is not only simple to construct and highly adaptable, but also cost-effective. On the other hand, after the secondary hole cleaning is completed, the precast reinforcing cage is vertically lowered into the hole. At this time, an anti-corrosion layer is first sprayed onto the bottom of the hole through nozzle B, thereby achieving a comprehensive anti-corrosion process for the entire concrete pile with excellent anti-corrosion effect.

[0017] This application can also achieve the opening or closing of the movable part relative to the annular fixed part by extending and retracting the miniature electric cylinder. When the movable part is open relative to the annular fixed part, it not only facilitates the spraying of anti-corrosion liquid from nozzle A onto the concrete pile, but also provides a certain amount of drying space and time for the anti-corrosion coating that has just been sprayed onto the concrete pile, so as to ensure a good anti-corrosion effect. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the anti-neck sleeve described in Embodiment 1 of this application; Figure 2 This is a cross-sectional structural diagram of state A of end 30 as described in Embodiment 1 of this application; Figure 3 This is a cross-sectional structural diagram of state B of end 30 as described in Embodiment 1 of this application; Figure 4 This is a schematic diagram of the structure of the first steel casing 10 and the second steel casing 20 in Embodiment 1 of this application; Wherein: 10, first steel casing; 20, second steel casing; 30, end; 40, body; 50, tail. 101. Annular fixed part; 102. Movable part; 103. Miniature electric cylinder; 104. Nozzle A; 105. Pipe A; 106. Anti-corrosion liquid storage tank; 107. Switch; 108. Annular groove; 109. Annular protrusion; 110. Fixing bolt; 111. Pipe B; 112. Nozzle B. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the specific embodiments of this application clearer, the technical solutions in the specific embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the specific embodiments, they shall be performed according to conventional conditions or conditions recommended by the manufacturer.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in the specification herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] A construction method for bored piles in desert areas, comprising the following steps in sequence: site preparation, installation of steel casing, preparation of drilling mud, drilling, hole cleaning, installation of anti-necking casing, secondary hole cleaning, placement of reinforcing cage, and concrete pouring to form the pile; the anti-necking casing comprises one first steel casing and n second steel casings, where n is an integer ≥ 2; the second steel casings and the first steel casings have the same wall thickness and the same inner diameter, w and D respectively, where w = 16mm ~ 25mm and D ≥ 1.2m, and the first and second steel casings can be nested within the steel casing; The process of installing the anti-neck casing includes: firstly, detachably installing the end of the first second steel casing to the tail of the first steel casing, and then pushing the first second steel casing downwards; then detachably installing the end of the second second steel casing to the tail of the first second steel casing, and then pushing the second second steel casing downwards; until the nth second steel casing is installed, after the process of installing the anti-neck casing is completed, the end of the first steel casing reaches the bottom of the hole; The concrete pouring pile formation process includes: inserting a guide pipe to continuously pour concrete, wherein the water-cement ratio of the concrete is W / C≤0.4; after the pouring is completed and a suitable time is waited, the first steel casing and the second steel casing are pulled out at a uniform speed. Each time the second steel casing is completely pulled out, the pulling process is paused, the completely pulled-out second steel casing is removed, and then the pulling is continued at a uniform speed until the first steel casing and the second steel casing are completely pulled out.

[0022] In other embodiments, during the concrete pouring pile formation process, the concrete pouring speed is υ1, H is the drilling depth, and the time for the concrete to be poured is Δt1. Then, Δt1 = (π·D) / (2π·H) = 1 / (2π·H ... 2 ·H) / 4·υ1, and 3m³ / h≤υ1≤8m³ / h, H≤60m; If the start time of injection is recorded as t0, then the start time for pulling out the first and second steel casings is t2, satisfying t2 = t0 + Δt1 + Δt2, where Δt2 = k 2·W / C·T, where T is the temperature at the end of the first steel casing, Δt2 is the time required to ensure that the compressive strength σ of the cast-in-place pile is greater than or equal to 5 MPa; satisfying 5℃≤T≤30℃, and k is a coefficient satisfying 0.5≤k≤1.5; The extraction speed is υ2, and it satisfies: 0.5m / min≤υ2≤1m / min.

[0023] In other embodiments, the concrete pouring and pile formation process also includes an anti-corrosion liquid spraying process, which includes spraying an anti-corrosion layer onto the outer surface of the concrete pile through nozzle A during the process of pulling out the first steel casing and the second steel casing. The end of the first steel casing includes an annular fixing part fixedly connected to the body of the first steel casing and a movable part movably connected to the body of the first steel casing. A miniature electric cylinder is provided between the movable part and the body. A nozzle A is also provided on the side of the movable part near the fixing part. The nozzle A is connected to the anti-corrosion liquid storage tank through a pipe A. The pipe A is embedded in the cylinder wall of the first steel casing and the second steel casing. The number of the movable part and the miniature electric cylinder is N, and N = D / 3, where N is an integer ≥ 3; The anti-corrosion liquid storage tank is also equipped with a switch, which is electrically connected to both the spray head A and the miniature electric cylinder.

[0024] In other embodiments, the anti-corrosion liquid spraying process specifically includes: before starting to pull out the first steel casing and the second steel casing, firstly, the micro electric cylinder is started by switching on the switch, so that the moving part is away from the annular fixed part; then, the steel casing is slowly pulled out, and at the same time, the nozzle A is opened so that the nozzle A sprays the anti-corrosion layer onto the outer surface of the concrete pile.

[0025] In other embodiments, the cross-section of the annular fixed part is triangular, the cross-section of the movable part is trapezoidal, and the cross-sections of the annular fixed part and the movable part form a large triangle; The trapezoid includes an upper base, a lower base, a short side, and a long side adjacent to the annular fixing part, and the short side is movably connected to the body. The upper bottom is provided with a recess, and the nozzle A is disposed in the recess.

[0026] In other embodiments, the process of burying the steel casing includes placing the steel casing at a designated location, and then filling and compacting clay in the gap between the outer wall of the steel casing and the hole wall to prevent quicksand from flowing in.

[0027] In other embodiments, the drilling process employs rotary drilling and mud wall protection; the hole cleaning process employs mud circulation for slag removal to ensure that the slag thickness is ≤30cm.

[0028] In other embodiments, the site treatment includes site leveling and pile foundation construction platform treatment; the drilling mud preparation includes a mixed mud made of sodium bentonite, caustic soda, and carboxymethyl cellulose; the secondary hole cleaning adopts the air lift reverse circulation method to remove sediment at the bottom of the hole, ensuring that the sediment thickness is ≤15cm; the main reinforcement bars of the steel cage are connected by straight threaded sleeves during the process of hoisting and placing the steel cage.

[0029] In other embodiments, the tail of the first steel casing and the tail of the second steel casing are provided with annular grooves, and the head of the second steel casing is provided with annular protrusions that can cooperate with the annular grooves. Fixing bolts are provided through the annular grooves and the annular protrusions.

[0030] In other embodiments, between the process of installing the anti-neck casing and the process of hoisting the reinforcing cage, there is also a process of spraying anti-corrosion liquid at the bottom of the hole. The process of spraying anti-corrosion liquid at the bottom of the hole includes spraying anti-corrosion liquid onto the bottom of the hole through a nozzle B, and the nozzle B is connected to the anti-corrosion liquid storage tank through a pipe B. Example 1

[0031] This application discloses a construction method for bored piles in desert areas. The construction method includes, in sequence, site preparation, installation of steel casing, preparation of drilling mud, drilling, hole cleaning, installation of anti-neck casing, secondary hole cleaning, placement of reinforcing cage, and concrete pouring to form the pile. Figures 1-4 As shown, the anti-neck casing includes a first steel casing 10 and n second steel casings 20, where n is an integer ≥ 2; the second steel casings 20 and the first steel casing 10 have the same wall thickness and the same inner diameter, which are w and D respectively, where w = 16mm ~ 25mm and D ≥ 1.2m, and the first steel casing 10 and the second steel casings 20 can be nested inside the steel casing.

[0032] In this embodiment 1, the site treatment includes site leveling and pile foundation construction platform treatment; the sand dunes around the pile location are leveled using a bulldozer (or loader). Before construction, a 4-5 meter layer of mud-bound gravel should be replaced on top of the pile according to the ground elevation, and compacted in layers with a road roller to form a stable bearing layer, ensuring the safe operation of equipment and the arrival of materials.

[0033] The process of burying the steel casing includes placing the steel casing at a designated location, then filling the gap between the outer wall of the steel casing and the hole wall with clay and compacting it to prevent quicksand from flowing in.

[0034] The drilling mud preparation includes a mixed mud made from sodium bentonite, caustic soda, and carboxymethyl cellulose. In Example 1, before adding bentonite powder, caustic soda (NaOH) is dissolved in a small container and then poured into the mud pool and stirred. The pH of the water in the mud pool is adjusted to 10-11 using pH test paper. Then, bentonite is added at a ratio of water:bentonite = 10:1 (by weight). Cellulose is then added at a dosage of 0.1% of the bentonite. The mud prepared according to the above requirements has a specific gravity of approximately 1.05, a viscosity of 20-26 Pa·s, a colloid content of 98%, and a mud cake thickness ≤ 2 mm / 30 min. When there is a quicksand layer, the mud specific gravity and the amount of bentonite used need to be increased, with a ratio of water:bentonite = 9:1, and a mud specific gravity of 1.05-1.06. The drilling mud prepared according to the above proportions has strong suspension capacity, good sand-carrying effect, and high stability. After drilling, fine sand does not easily settle. At this time, the relative specific gravity of the mud reaches 1.10 to 1.25. The equipment for preparing drilling mud includes mud flushing machines and mud mixers. Depending on the application, mud mixers can fully dissolve bentonite particles and mix the mud evenly, with better results than mud flushing machines.

[0035] The drilling process employs rotary drilling rigs and mud wall protection; the hole cleaning process uses mud circulation to remove slag, ensuring that the slag thickness is ≤30cm.

[0036] The process of installing the anti-neck protection sleeve includes: firstly, detachably installing the end of the first second steel sleeve 20 to the tail 50 of the first steel sleeve 10, and then pushing the first second steel sleeve 20 downward; then detachably installing the end of the second second steel sleeve 20 to the tail of the first second steel sleeve 20, and then pushing the second second steel sleeve 20 downward; until the nth second steel sleeve 20 is installed, after the process of installing the anti-neck protection sleeve is completed, the end 30 of the first steel sleeve 10 reaches the bottom of the hole; in this embodiment 1, the tail of the first steel sleeve 10 and the tail of the second steel sleeve 20 are both provided with annular grooves 108, and the head of the second steel sleeve 20 is provided with annular protrusions 109 that can cooperate with the annular grooves, and fixing bolts 110 are provided through the annular grooves 108 and the annular protrusions 109.

[0037] The secondary hole cleaning uses an air-lift reverse circulation method to remove sediment from the bottom of the hole, ensuring that the sediment thickness is ≤15cm; the main reinforcing bars of the reinforcing cage are connected by straight threaded sleeves during the process of hoisting and placing the reinforcing cage.

[0038] The concrete pouring pile formation process includes: inserting a guide pipe to continuously pour concrete, wherein the water-cement ratio of the concrete is W / C≤0.4; after the pouring is completed and a suitable time is waited, the first steel casing 10 and the second steel casing 20 are pulled out at a uniform speed. Each time a second steel casing 20 is completely pulled out, the pulling process is paused, the completely pulled-out second steel casing 20 is removed, and then the pulling is continued at a uniform speed until the first steel casing 10 and the second steel casing 20 are completely pulled out.

[0039] During the concrete pouring and pile formation process, the concrete pouring speed is υ1, H is the drilling depth, and the time for the concrete to be poured is Δt1. Then, Δt1 = (π·D) / (2π·H) = 1 / (2π·H ... 2 ·H) / 4·υ1, and 3m³ / h≤υ1≤8m³ / h, H≤60m; If the start time of injection is recorded as t0, then the start time for pulling out the first steel casing 10 and the second steel casing 20 is t2, satisfying t2 = t0 + Δt1 + Δt2, where Δt2 = k 2 ·W / C·T, where T is the temperature at the end 30 of the first steel casing 10, Δt2 is the time required to ensure that the compressive strength σ of the cast-in-place pile is greater than or equal to 5 MPa; satisfying 5℃≤T≤30℃, and k is a coefficient satisfying 0.5≤k≤1.5; The extraction speed is υ2, and it satisfies: 0.5m / min≤υ2≤1m / min.

[0040] The concrete pouring and pile formation process also includes an anti-corrosion liquid spraying process, which includes spraying an anti-corrosion layer onto the outer surface of the concrete pile through a nozzle A104 during the process of pulling out the first steel casing 10 and the second steel casing 20. The end 30 of the first steel casing 10 includes an annular fixing part 101 fixedly connected to the body 40 of the first steel casing 10 and a movable part 102 movably connected to the body 40 of the first steel casing 10. A miniature electric cylinder 103 is provided between the movable part 102 and the body 40. A nozzle A104 is also provided on the side of the movable part 102 near the fixing part 101. The nozzle A104 is connected to the anti-corrosion liquid storage tank 106 through a pipe A105. The pipe A105 is embedded in the cylinder wall of the first steel casing 10 and the second steel casing 20. The number of the movable part 102 and the miniature electric cylinder 103 is N, and satisfies N=D / 3, where N is an integer ≥3; The anti-corrosion liquid storage tank 106 is also equipped with a switch 107, which is electrically connected to the nozzle A104 and the miniature electric cylinder 103.

[0041] The anti-corrosion liquid spraying process specifically includes: before starting to pull out the first steel casing 10 and the second steel casing 20, firstly, the micro electric cylinder 103 is activated by a switch, so that the moving part 102 is moved away from the annular fixed part 101, and the end 30 is ensured as... Figure 3 State B is shown; then slowly pull out the steel casing while opening nozzle A 104 to spray the anti-corrosion layer onto the outer surface of the concrete pile.

[0042] The cross-section of the annular fixed part 101 is triangular, and the cross-section of the movable part 102 is trapezoidal. The cross-sections of the annular fixed part 101 and the movable part 102 together form a large triangle. The trapezoid includes an upper base, a lower base, a short side, and a long side adjacent to the annular fixing part 101, and the short side is movably connected to the body 40; The upper bottom is provided with a recess, and the nozzle A104 is disposed in the recess.

[0043] Between the process of installing the anti-neck casing and the process of hoisting the steel cage, there is also a process of spraying anti-corrosion liquid at the bottom of the hole. The process of spraying anti-corrosion liquid at the bottom of the hole includes spraying anti-corrosion liquid onto the bottom of the hole through nozzle B112. The nozzle B112 is connected to the anti-corrosion liquid storage tank 106 through pipe B111. Example 2

[0044] The only difference between Example 2 and Example 1 is that the parameter settings are as follows: Concrete pouring speed υ1 = 8 m 3 / h; Drilling depth H=60 m; Casing inner diameter D=1.2 m; Water-cement ratio W / C=0.35; Temperature T=17.5℃; Coefficient k=1.

[0045] Calculate Δt1≈8.5h, Δt2≈6h; assuming t0=0, then t2=t0+Δt1+Δt2=14.5h. Example 3

[0046] The only difference between this embodiment 3 and embodiment 1 is that the parameter settings are as follows: Concrete pouring speed υ1 = 8 m 3 / h; Drilling depth H=40m; Casing inner diameter D=1.2 m; Water-cement ratio W / C=0.4; Temperature T=20℃; Coefficient k=0.625.

[0047] Calculate Δt1≈5.6, Δt2≈5h; assuming t0=0, then t2=t0+Δt1+Δt2=15.6h.

[0048] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A construction method for bored piles in desert areas, characterized in that, The construction method includes site preparation, installation of steel casing, drilling mud preparation, drilling, hole cleaning, installation of anti-neck casing, secondary hole cleaning, hoisting and placing of steel cage, and concrete pouring to form piles; the anti-neck casing includes one first steel casing (10) and n second steel casings (20), and n is an integer ≥2; the second steel casing (20) and the first steel casing (10) have the same wall thickness and the same inner diameter, which are w and D respectively, and w=16mm ~ 25mm, D≥1.2m, and the first steel casing (10) and the second steel casing (20) can be nested inside the steel casing; The process of installing the anti-neck protection sleeve includes: firstly, the end of the first second steel sleeve (20) is detachably installed at the tail (50) of the first steel sleeve (10), and then the first second steel sleeve (20) is pushed down; then the end of the second second steel sleeve (20) is detachably installed at the tail of the first second steel sleeve (20), and then the second second steel sleeve (20) is pushed down; until the nth second steel sleeve (20) is installed, after the process of installing the anti-neck protection sleeve is completed, the end (30) of the first steel sleeve (10) reaches the bottom of the hole; The concrete pouring pile process includes: inserting a guide pipe to continuously pour concrete, wherein the water-cement ratio of the concrete is W / C≤0.4; after the pouring is completed and a suitable time is waited, the first steel casing (10) and the second steel casing (20) are pulled out at a uniform speed. The pulling process is paused after each second steel casing (20) is completely pulled out, the completely pulled-out second steel casing (20) is removed, and then the pulling is continued at a uniform speed until the first steel casing (10) and the second steel casing (20) are completely pulled out.

2. The construction method for bored piles in desert areas according to claim 1, characterized in that, During the concrete pouring and pile formation process, the concrete pouring speed is υ1, H is the drilling depth, and the time for the concrete to be poured is Δt1. Then, Δt1 = (π·D) / (2π·H) = 1 / (2π·H ... 2 ·H) / 4·υ1, and 3m³ / h≤υ1≤8m³ / h, H≤60m; Record the start time of injection as t0, then the start time of pulling out the first steel casing (10) and the second steel casing (20) is t2, and t2 = t0 + Δt1 + Δt2, Δt2 = k 2 ·W / C·T, where T is the temperature at the end (30) of the first steel casing (10), Δt2 is the time required to ensure that the compressive strength σ of the cast-in-place pile is greater than or equal to 5 MPa; satisfying 5℃≤T≤30℃, k is a coefficient, satisfying 0.5≤k≤1.5; The extraction speed is υ2, and it satisfies: 0.5m / min≤υ2≤1m / min.

3. The construction method for bored piles in desert areas according to claim 1, characterized in that, The concrete pouring and pile formation process also includes an anti-corrosion liquid spraying process, which includes spraying an anti-corrosion layer onto the outer surface of the concrete pile through a nozzle A (104) during the process of pulling out the first steel casing (10) and the second steel casing (20). The end (30) of the first steel casing (10) includes an annular fixing part (101) fixedly connected to the body (40) of the first steel casing (10) and a movable part (102) movably connected to the body (40) of the first steel casing (10). A miniature electric cylinder (103) is provided between the movable part (102) and the body (40). A nozzle A (104) is also provided on the side of the movable part (102) near the fixing part (101). The nozzle A (104) is connected to the anti-corrosion liquid storage tank (106) through a pipe A (105). The pipe A (105) is embedded in the cylinder wall of the first steel casing (10) and the second steel casing (20). The number of the movable part (102) and the miniature electric cylinder (103) is N, and satisfies N=D / 3, where N is an integer ≥3; The anti-corrosion liquid storage tank (106) is also equipped with a switch (107), which is electrically connected to the nozzle A (104) and the miniature electric cylinder (103).

4. The construction method according to claim 3, characterized in that: The anti-corrosion liquid spraying process specifically includes: before starting to pull out the first steel casing (10) and the second steel casing (20), firstly, start the micro electric cylinder (103) by switching on the switch so that the moving part (102) moves away from the annular fixed part (101); then start to slowly pull out the steel casing, and at the same time open the nozzle A (104) so ​​that the nozzle A (104) sprays the anti-corrosion layer onto the outer surface of the concrete pile.

5. The construction method according to claim 4, characterized in that: The cross-section of the annular fixed part (101) is triangular, and the cross-section of the movable part (102) is trapezoidal. The cross-sections of the annular fixed part (101) and the movable part (102) together form a large triangle. The trapezoid includes an upper base, a lower base, a short side, and a long side adjacent to the annular fixing part (101), and the short side is movably connected to the body (40); The upper bottom is provided with a recess, and the nozzle A (104) is located in the recess.

6. The construction method according to claim 1, characterized in that: The process of burying the steel casing includes placing the steel casing at a designated location, then filling the gap between the outer wall of the steel casing and the hole wall with clay and compacting it to prevent quicksand from flowing in.

7. The construction method according to claim 1, characterized in that: The drilling process employs rotary drilling rigs and mud wall protection; the hole cleaning process uses mud circulation to remove slag, ensuring that the slag thickness is ≤30cm.

8. The construction method according to claim 1, characterized in that: The site treatment includes site leveling and pile foundation construction platform treatment; the drilling mud preparation includes a mixed mud made of sodium bentonite, caustic soda and carboxymethyl cellulose; the secondary hole cleaning adopts the air lift reverse circulation method to remove sediment at the bottom of the hole, ensuring that the sediment thickness is ≤15cm; the main reinforcement bars of the steel cage are connected by straight threaded sleeves during the process of hoisting and placing the steel cage.

9. The construction method according to claim 1, characterized in that: The tail of the first steel casing (10) and the tail of the second steel casing (20) are provided with an annular groove (108). The head of the second steel casing (20) is provided with an annular protrusion (109) that can cooperate with the annular groove. Fixing bolts (110) are provided through the annular groove (108) and the annular protrusion (109).

10. The protective device for bored piles in desert areas according to claim 1, characterized in that: Between the process of installing the anti-neck casing and the process of hoisting the steel cage, there is also a process of spraying anti-corrosion liquid at the bottom of the hole. The process of spraying anti-corrosion liquid at the bottom of the hole includes spraying anti-corrosion liquid onto the bottom of the hole through nozzle B (112). The nozzle B (112) is connected to the anti-corrosion liquid storage tank (106) through pipe B (111).

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