CN111764380A

CN111764380A - Cast-in-situ bored pile construction method

Info

Publication number: CN111764380A
Application number: CN202010656979.3A
Authority: CN
Inventors: 古力再拉·艾买尔江; 陈云泽; 杨凡; 魏红刚; 杨志刚; 高润宝; 孟淑豪; 杨毕俩; 卞玉宝
Original assignee: Xinjiang Road & Bridge Construction Group Co ltd
Current assignee: Xinjiang Road & Bridge Construction Group Co ltd
Priority date: 2020-07-09
Filing date: 2020-07-09
Publication date: 2020-10-13

Abstract

The invention provides a cast-in-situ bored pile construction method, which belongs to the technical field of cast-in-situ bored pile construction and comprises the following steps: embedding a pile casing in a pile position on the ground, wherein part of the pile casing is exposed out of the ground; drilling to form a hole: drilling a hole in the soil layer in the pile casing to form a pile hole, and injecting slurry into the pile casing during drilling; the slurry comprises water, clay, bentonite and a copolymer filter reducing agent, and the mass ratio of the water to the clay to the bentonite to the copolymer filter reducing agent is (0.9-1): (0.3-0.5): (0.07-0.09): (0.005-0.015); placing a reinforcement cage into the pile hole; and pouring concrete into the pile hole to a preset height to form the cast-in-situ bored pile. The chemical slurry is adopted for carrying out the retaining wall construction of the sand soil, so that the self-supporting strength of the wall of the pile hole can be enhanced, the retaining wall effect is improved, and the hole collapse probability is effectively reduced.

Description

Cast-in-situ bored pile construction method

Technical Field

The invention relates to the technical field of cast-in-situ bored pile construction, in particular to a cast-in-situ bored pile construction method.

Background

The cast-in-situ bored pile is a deep foundation form commonly used in bridge construction. The construction process of the cast-in-situ bored pile mainly comprises the steps of digging pile holes in a ground soil layer in advance, placing a reinforcement cage in the pile holes, and finally pouring concrete into the pile holes, wherein after the concrete reaches a preset strength, the concrete in the pile holes and the reinforcement cage are integrated into a whole to form the cast-in-situ bored pile.

In the construction process of the cast-in-situ bored pile, the hole wall of the pile hole cannot stand by itself, so that hole collapse is caused, and construction is influenced. In recent years, the bridge industry in China is rapidly developed, the span of a newly-built bridge is larger and larger, the structure is more and more complex, the length and the diameter of a cast-in-situ bored pile are longer and larger, and the hole collapse phenomenon becomes a common phenomenon in the construction of the cast-in-situ bored pile. Particularly, in the soil layer construction of the sand soil, the hole collapse phenomenon is serious because the soil quality of the sand soil is loose.

Disclosure of Invention

The invention aims to provide a cast-in-situ bored pile construction method which can effectively reduce the hole collapse probability in the process of constructing a cast-in-situ bored pile made of sand soil.

The embodiment of the invention is realized by the following steps:

the embodiment of the invention provides a cast-in-situ bored pile construction method, which comprises the steps of burying a pile casing in a pile position on the ground, wherein part of the pile casing is exposed out of the ground; drilling to form a hole: drilling a hole in the soil layer in the pile casing to form a pile hole, and injecting slurry into the pile casing during drilling; the slurry comprises water, clay, bentonite and a copolymer filter reducing agent, and the mass ratio of the water to the clay to the bentonite to the copolymer filter reducing agent is (0.9-1): (0.3-0.5): (0.07-0.09): (0.005-0.015); placing a reinforcement cage into the pile hole; and pouring concrete into the pile hole to a preset height to form the cast-in-situ bored pile.

Optionally, injecting the slurry into the casing while drilling includes: the liquid level of the slurry in the protective cylinder is 30-40 cm lower than the port of the protective cylinder exposed out of the ground.

Optionally, the slurry satisfies: the PH value is 8-10, and the specific gravity is less than or equal to 1.15g/cm³The viscosity is 20 s-25 s, the colloid rate is more than or equal to 96%, the water loss rate is 19ml/30 min-21 ml/30min, and the sand content is 2% -4%.

Optionally, the drilling for hole forming adopts stepped drilling, and the stepped drilling comprises: pouring the slurry into the casing to a port of the casing exposed out of the ground; in the first section, a scraper drill bit is adopted to drill a hole in the soil layer in the casing, and the drilling speed is 4-6 m/h; the first section is from a port of the casing exposed out of the ground to a position 1.9-2 m above the port of the casing buried in the ground; in the second section, a flat-bottom drill bit is adopted to drill holes in the soil layer in the pile casing, and the drilling speed is 0.3-0.8 m/h; wherein the second section is from 1.9 m-2 m above the port of the casing buried in the ground to 4.9 m-5 m above the port of the casing buried in the ground; and in a third section, drilling a hole in the soil layer in the pile casing by using a drill bit of a rotary drilling machine, wherein the drilling speed is 0.3-6 m/h, and the third section is from 4.9-5 m below a port of the pile casing buried in the ground to the bottom of the formed pile hole.

Optionally, the vertical degree of the pile hole is less than or equal to 1%.

Optionally, drilling the soil layer in the casing to form a pile hole further comprises: acquiring the vertical degree of a drilled hole formed in the pile casing; and adjusting the drilling angle of the drilled hole according to the vertical degree.

Optionally, the central deviation between the pile casing and the pile position is less than or equal to 5 cm.

Optionally, after the placing of the reinforcement cage into the pile hole and before the pouring of the concrete into the pile hole, the method further includes: inserting a guide pipe into the pile hole, and pouring concrete into the pile hole through the guide pipe; after the concrete is poured into the pile hole, the method further comprises the following steps: withdrawing the catheter; and after the concrete forms a pile column, pulling out the pile casing to form the cast-in-situ bored pile.

Optionally, after the drilling to form the hole and before the placing of the reinforcement cage into the pile hole, the method further comprises: cleaning holes; after the conduit is inserted into the pile hole and before the concrete is poured into the pile hole, the method further comprises the following steps: and (5) secondary hole cleaning.

Optionally, the clearing comprises: continuously flushing sediment at the bottom of the pile hole by using high-pressure water for 5-6 min; and sucking out the sediments.

The embodiment of the invention has the beneficial effects that:

according to the construction method of the cast-in-situ bored pile provided by the embodiment of the invention, slurry is injected into the pile casing during drilling, the slurry comprises water, clay, bentonite and a copolymer filter reducing agent, and the mass ratio of the water, the clay, the bentonite and the copolymer filter reducing agent is (0.9-1): (0.3-0.5): (0.07-0.09): (0.005-0.015), the mud is prepared according to the proportion, compared with the traditional clay or bentonite mud, the copolymer filtration reducing reagent is added, the copolymer filtration reducing reagent belongs to a chemical reagent, is fully dissolved into a semitransparent paste in water, has high viscosity, can improve the viscosity of a mud skin formed by the mud on a hole wall, forms a filter cake with low permeability, flexibility, thinness and compactness, improves the viscosity of the mud, is more effectively suitable for construction of a soil layer with loose soil, such as sand soil, the high viscosity of the mud can increase the binding force of the loose soil, and the mud is adopted in a pile hole, so that a thin film protective layer on the surface of the hole wall is increased, the self-supporting strength of the hole wall of the pile hole is enhanced, the wall protection effect is increased, and the hole collapse probability is effectively.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

Fig. 1 is a flowchart of a cast-in-situ bored pile construction method according to an embodiment of the present invention;

fig. 2 is a second flowchart of a cast-in-situ bored pile construction method according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.

The cast-in-situ bored pile is a pile formed by forming a pile hole in foundation soil through mechanical drilling, steel pipe soil extrusion or manual excavation and the like on an engineering site, placing a reinforcement cage in the pile hole and pouring concrete into the pile hole. The cast-in-situ bored pile is a deep foundation form commonly used in bridge construction.

During the construction process of the cast-in-situ bored pile, hole collapse is a common problem. When the drill hole is deep, the hole wall soil below the underground water level collapses into the hole under the hydrostatic pressure, and even a sand flowing phenomenon occurs, so that the hole collapse is called as hole collapse.

In recent years, the bridge industry in China is rapidly developed, the span of a newly-built bridge is larger and larger, the structure is more and more complex, the length and the diameter of a cast-in-situ bored pile are longer and larger, and the hole collapse phenomenon becomes a common phenomenon in the construction of the cast-in-situ bored pile. Particularly, in the soil layer construction of the sand soil, the hole collapse phenomenon is serious because the soil quality of the sand soil is loose. Meanwhile, in order to improve the construction progress, rotary drilling rigs with high drilling efficiency are selected for many projects, but the possibility of hole collapse is further increased, the problem that how to prevent and reduce the hole collapse phenomenon and how to quickly form holes become the difficult problem of construction of the sand-type soil cast-in-situ bored pile is solved.

In order to solve the above problems, the embodiment provides a bored pile construction method, which is suitable for the construction of a bored pile of a large and medium bridge pile foundation in a geological region which is mainly sandy soil and has poor cohesiveness and easy collapse, and adopts chemical slurry wall protection construction to improve the friction bearing capacity of the pile foundation and reduce the hole collapse probability.

Specifically, the cast-in-situ bored pile construction method comprises the following steps:

referring to fig. 1, S100: and embedding a pile casing in the pile position of the ground, wherein part of the pile casing is exposed out of the ground.

The method comprises the following steps of embedding the pile casing, and before the step, preparing construction and determining a pile position.

Before mechanical equipment enters a field, an organization survey staff uses a total station to perform pile position lofting and retest according to closed wire points, pile position lines are discharged, pile position control piles are additionally arranged and reinforced, and the positions of the control piles are selected in places which are not easy to move and can not be pressed by vehicles.

In order to prevent the inclination accident of the drilling machine in the drilling process, the in-place position of the drilling machine is leveled, and is tamped by a tamping machine such as a road roller and manually leveled.

And drawing a geological profile at the hole position, hanging the geological profile on a drill floor, and using the geological profile as a reference for selecting proper drill bits, bit pressure, drilling speed and mud specific gravity for different soil layers.

The protective cylinder is made of steel plates with the thickness of 8mm in a rolling mode, and the length of each section of the protective cylinder is 200 cm-300 cm. After the pile is dug by manually pressing the diameter of the pile casing at the pile position, the pile casing is hoisted by a crane, and the pile casing slowly slides downwards when no wind or little wind exists, so that the pile casing is ensured to be vertical, and the pile casing can not be unhooked until the mud is stably filled. The embedding depth is not less than 2m, and when the surface soil is soft, the pile casing is preferably embedded in the hard dense soil layer for at least 0.5 m. The embedded protection cylinders are symmetrical around, and the filled clay is tamped layer by layer to ensure firmness, tightness and no leakage.

After the pile casing is buried, the center, perpendicularity and deviation of the pile casing need to be checked, the center of the pile casing needs to coincide with the center of the pile foundation, and the perpendicularity and deviation of the pile casing need to meet the requirements of the pile foundation on perpendicularity and deviation.

Specifically, this embodiment adopts the vibration hammer and portable leading truck to beat and establishes a pile casing, uses the vibration hammer to beat and protects a section of thick bamboo and make and protect a section of thick bamboo and get into the soil layer fast and control the error (adopting the plummet method) of a steel pile casing center and stake center with portable leading truck, makes the central deviation of protecting a section of thick bamboo and stake position be less than or equal to 5cm to guarantee to protect a section of thick bamboo and can bury in the central point of stake position and put.

S110: drilling to form a hole: drilling a hole in a soil layer in the pile casing to form a pile hole, and injecting slurry into the pile casing during drilling; wherein the slurry comprises water, clay, bentonite and a copolymer filter reducing agent, and the mass ratio of the water to the clay to the bentonite to the copolymer filter reducing agent is (0.9-1): (0.3-0.5): (0.07-0.09): (0.005-0.015).

In the drilling hole forming step S110, preparation work is required before drilling, including the positioning of a drilling machine and slurry preparation and circulation treatment.

Before the drilling machine is in place, the center of the casing (namely the center of the pile foundation) is marked, the drilling machine is installed according to the center, the adjustment is stable, and the center of a drill bit of the drilling machine is aligned to the center of the casing.

The experimental operation is carried out after the drilling machine is adjusted and installed, the stability of the drilling machine, the three-in-one of the pile casing center, the pile foundation center and the drill bit center of the drilling machine are tested, and the deviation is controlled within 20 mm so as to meet the requirement that the verticality of a pile hole is less than or equal to 1%. If the center coincidence requirement is not met, adjustment is needed.

The main performance parameters of the drilling rig can be referred to table 1:

TABLE 1 drilling rig main performance parameter table

Drill model	GDY400
		Maximum bore diameter (m)	3.0
Maximum depth of borehole (m)	45
		Output torque (KN m)	≥150
Maximum lift capacity (KN)	1000
		Maximum drilling speed rpm	15
Bore diameter mm of drill rod	≥330
		Counter weight (KN)	Not less than 300KN
Circulation mode	Direct and reverse circulation

Slurry preparation and circulating treatment: the slurry of the embodiment is chemical slurry, the slurry comprises water, clay, bentonite and a copolymer filter reducing agent, and the mass ratio of the water, the clay, the bentonite and the copolymer filter reducing agent is (0.9-1): (0.3-0.5): (0.07-0.09): (0.005-0.015).

The copolymer is white granular in appearance, the purity is more than or equal to 78 percent, the water content is less than or equal to 10 percent, the apparent viscosity of a 1 percent aqueous solution is more than or equal to 15mpa.s, the pH value of the 1 percent aqueous solution is 7-9, the copolymer filtrate reducing reagent is an easily mixed powder granular polymer, the copolymer filtrate reducing reagent is fully dissolved into semitransparent paste in water, the viscosity is high, the speed of depositing impurities in holes is very high, and slurry is always clear and transparent and is non-toxic in the drilling process of a drilling tool in the holes.

There are many types of copolymers, such as butadiene-styrene, sulfonated phenol-formaldehyde resins (SMP), polymerized humol, carboxymethylcellulose (CMC), polyacrylamide (PHP).

The mud proportion has great influence on the pore-forming quality, the mud proportion directly influences the pore-forming time of the pile hole, and the mud with proper proportion can ensure that the mud fully permeates into a soil layer, so that more solid particles are attached to soil body particles to ensure that the mud skin on the wall of the hole has enough development time to form the mud skin with certain thickness; the characteristics of poor permeability, good water stopping performance and low shearing strength of the mud skin promote the mud skin with enough thickness to effectively reduce the pile side frictional resistance of the concrete cast-in-place pile and ensure the construction quality of the concrete cast-in-place pile; the mud skin is thickened, the mud consumption is increased, the hole cleaning difficulty is increased, and the drilling rate and the bearing capacity of the pile after the pile is formed are influenced due to the fact that the specific gravity of the mud is too large.

The water, the clay, the bentonite and the copolymer filtration reducing reagent are mixed according to a certain proportion and are sent into a clay dissolving tank, and the prepared slurry is stored in a slurry pond after being fully stirred by a stirring device. The slurry mixing proportion is determined after a basic mixing proportion is selected according to geological conditions, construction machinery and other conditions and a preparation experiment and correction are carried out.

Compared with the traditional clay or bentonite slurry, the chemical slurry prepared by mixing the clay, the bentonite and the copolymer filter reducing agent adopted by the embodiment is used for carrying out the wall protection construction of sand soil, the slurry dissolution speed is improved, the flocculation and precipitation of drilling cuttings and sand are accelerated, the self-cleaning effect is realized, the sand content is low, the chemical slurry wall protection product belongs to light slurry, and the wall protection effect is ensured, and meanwhile, the dosage is small, the specific gravity is low, the viscosity is high, and the sand content is extremely low; the pouring is smooth, the pipe is not easy to block, the phenomenon that concrete sandwiches is avoided, the friction bearing capacity of the pile foundation can be improved by the chemical slurry wall protection, the quality of the pile foundation is improved, and the bearing capacity of the pile is increased. By adopting the slurry of the embodiment, the wall protection and hole forming speed is high, the hole cleaning time is effectively reduced, and the thickness of formed slag is effectively ensured.

The mud circulation purification is carried out by adopting a mud pit and a sedimentation tank on a construction site, the pool surface of the mud pit and the sedimentation tank is 0.5-1 m lower than that of a protective cylinder so as to facilitate the mud to flow back smoothly, the position layout is reasonable, a crane and a drilling machine cannot walk according to the scheme, the capacity of the mud pit is the slag discharge amount of each pile hole, and the capacity of the sedimentation tank is 1.5-2 times of the slag discharge amount of each pile hole.

And measuring various technical indexes of the slurry when the drilling process advances by 5-10 m, and adjusting in time when the drilling process does not meet the requirements to keep the various indexes meeting the requirements. In the drilling process, the lost and leaked slurry is replenished in time to be 1-1.5 m higher than the water level outside the hole or the underground water level; the slurry concentration in the drilled hole is ensured, and quality accidents such as hole collapse and hole shrinkage are prevented.

The mud performance should meet the mud performance index shown in table 2 at different construction stages to ensure that the drilling machine is not blocked and the construction is normal.

TABLE 2 mud Performance index Table

Drilling: before drilling, the equipment state, whether the water and electricity pipeline is smooth, whether the slurry preparation is sufficient, whether the slurry is discharged and whether the impurity removal is smooth and the like are checked. So as to ensure that drilling equipment and various preparations of drilling holes meet the requirements.

Before formal drilling, the slurry pump is started to idle for a period of time, and after the slurry is filled in the casing, slow drilling is carried out. In the drilling process, deviation of the drilling machine, three-center coincidence, slurry parameters, wall protection conditions, drilling verticality and the like are checked at any time, the drilling speed and the slurry concentration are adjusted according to the conditions, and the slurry liquid level height is kept. Meanwhile, the speed stability of the drilling machine during drilling is strictly controlled, the center position of a drill bit of the drilling machine is checked and verified at any time, and the protective cylinder is used for checking and verifying. The drilling operation is continuously carried out without interruption. For stopping drilling, a protective cover is added on the hole opening, and the drill bit is lifted out of the hole channel to prevent burying drilling, and simultaneously, the height of the mud surface in the hole and the specific gravity and viscosity of the mud are kept to meet the requirements.

Specifically, the present embodiment adopts a staged drilling method:

and (4) pouring slurry into the pile casing to the port of the pile casing exposed out of the ground, namely, filling the pile casing with the slurry.

In the first section, a scraper drill bit is adopted to drill a hole in the soil layer in the casing, and the drilling speed is 4-6 m/h; the first section is from the port of the casing exposed out of the ground to a position 1.9-2 m above the port of the casing buried in the ground.

And in the drilling process in the casing, a scraper bit with matched diameter is adopted for reverse circulation pressurized clear water drilling, the rod feeding is controlled to be 4-6 m/h per hour, clear water is supplemented in the hole, and the mixed slurry is treated by a slurry purifier and then flows back into the casing.

In the second section, a flat-bottom drill bit is adopted to drill holes in the soil layer in the pile casing, and the drilling speed is 0.3-0.8 m/h; wherein the second section is from 1.9 m-2 m above the port of the casing buried in the ground to 4.9 m-5 m above the port of the casing buried in the ground.

After the drilling reaches 1.9-2 m above the bottom opening of the casing, the improved flat-bottom drill bit with the matched diameter is exchanged, the drill bit is reversely circulated and idled during the drilling, a slurry circulation system is started to replace slurry in the hole, and after the index of the slurry in the hole meets the requirement, the high-quality slurry wall protection reverse circulation reduced pressure drilling is carried out, so that the drilling speed of the bottom opening of the casing is consistent with the drilling speed in the casing (0.3-0.8 m/h).

And in the third section, drilling a hole in the soil layer in the pile casing by using a drill bit of a rotary drilling machine at the drilling speed of 0.3-6 m/h, wherein the third section is formed by burying the pile casing below a port of the ground by 4.9-5 m to the bottom of a formed pile hole.

After the drill bit drills into the casing by 5m, the drill bit drills at a normal drilling speed, according to the characteristics of different soil layers, the indexes and the drilling speed of the wall protection slurry are adjusted in time in the drilling process, and high-quality slurry is supplemented in holes. When the distance between the drill hole and the designed elevation is 1m, the drilling speed and the depth are controlled, the drill hole is dug for 30cm, and geological data is verified to judge whether the drill hole enters the designed stratum or not. The liquid level of the slurry in the protective cylinder is strictly controlled in the drilling process, the liquid level is always kept 30-40 cm away from the upper edge of the protective cylinder, namely the liquid level of the slurry in the protective cylinder is 30-40 cm lower than a port of the protective cylinder exposed out of the ground.

The construction process strictly follows the principle of three slow speeds: the rotation speed of lifting, releasing and drilling is slow, the disturbance of mud on the hole wall is reduced by strictly controlling the movement speed of the drilling tool, and sufficient time is left for forming mud skin.

In addition, the following method can be adopted to ensure that the verticality of the drilled hole is less than or equal to 1 percent: acquiring the vertical degree of a formed drill hole in the pile casing; and adjusting the drilling angle of the drilled hole according to the vertical degree.

The construction equipment generally comprises a drilling machine, a controller and a total station, wherein the drilling machine of the embodiment is a rotary drilling machine, the drilling machine comprises a mast and a drill bit, the drill bit is replaceable, the mast is used for monitoring the verticality of a drilled hole, the total station monitors the verticality of the mast, and the drilled hole is connected with the controller.

The verticality of the formed drill hole in the pile casing is consistent with the verticality of the mast, so that the verticality of the formed drill hole in the pile casing is reflected through the verticality of the mast, the whole process of the mast is monitored by adopting a total station, the verticality of the mast is fed back to the controller, the drilling angle of the drill bit is adjusted by the controller according to the verticality of the mast, the verticality of the drill hole is ensured, and the verticality of the pile hole after hole forming is not more than 1%.

After the hole is formed, in order to ensure the quality of the cast-in-place pile, the over-excavation depth of the same row of piles is required to be basically consistent and controlled within +/-5 cm.

The mud index during drilling can be seen in table 3, and the drilling parameters for different formations can be seen in table 4.

TABLE 3 drilling mud index

TABLE 4 drilling parameters table for different strata

Formation of earth	Weight drill (KN)	Number of revolutions (rpm)	Drilling speed (m/h)
				Drilling in casing			≤6.0
Dense fine sand layer	100～150	10～15	1.5～2.0
				Soft plastic loam layer	100～120	10～15	1～2
Dense medium and coarse sand layer	150～300	5～10	2.0～3.0
				Bottom opening stratum of pile casing	＜100	5～10	0.3～0.8

S120: and placing a reinforcement cage into the pile hole.

Referring to fig. 2, after drilling the hole at S110 and before placing the reinforcement cage in the pile hole at S120, the method further includes:

s111: and (6) cleaning the holes.

And when the drilling depth meets the design requirement, checking the hole depth, the hole diameter and the hole shape, and clearing the hole after confirming that the design requirement is met. And lifting the drilling tool away from the slag surface of the drilling tool at the bottom of the hole by about 30-50 cm during hole cleaning, slowly rotating the drilling tool, supplementing high-quality slurry, maintaining reverse circulation for cleaning the hole for more than 4 hours until the sediment at the bottom of the hole is cleaned, the mud skin on the wall of the hole is thinned, and the performance indexes of the slurry meet the requirements, and simultaneously keeping a water head in the hole to prevent hole collapse. After drilling, the hole picker is used for lifting the hole to detect the aperture and the vertical degree, and a steel wire measuring rope is used for detecting the hole depth.

In the hole cleaning of the embodiment, the sediment at the bottom of the pile hole is continuously flushed by high-pressure water for 5-6 min, and the sediment in the pile hole is sucked out to complete the hole cleaning.

Specifically, a high-strength water gun is used for stretching into the bottom of the hole from the guide pipe to pressurize and flush sediments, the operation lasts for 5-6 min, and the back suction function of a drilling machine is utilized to complete one-time hole cleaning of the formed sediments. The hole cleaning is finished before the drill is lifted, so that the open-air sediment meets the specification and design requirements, and meanwhile, the stability of the pile hole before the pouring is ensured.

S120, preparing and placing a reinforcement cage: and (4) blanking the reinforcement cage in a processing workshop, and manufacturing the reinforcement cage in sections. The main ribs are connected by adopting double-sided welding, the number of joints on each section is not more than 50%, and the section distance between adjacent joints is not less than 1.5 m. The sounding pipe is installed in the same groove when the same groove machining of the steel reinforcement cage is carried out, and the joint is welded and is properly staggered with the steel reinforcement joint so as to be convenient to butt joint.

And after the pore-forming inspection is qualified, putting down the lengthened reinforcement cage. In order to accelerate the lowering speed of the reinforcement cage, the reinforcement cage can be pre-lengthened according to construction conditions. After the steel reinforcement cage is installed and transferred, fix the steel reinforcement cage on protecting a section of thick bamboo to bear steel reinforcement cage dead weight and prevent that the concrete from pouring in-process steel reinforcement cage come-up.

After the step S120 of placing the reinforcement cage into the pile hole and before the step S130 of pouring concrete into the pile hole, the method further includes:

s121: and inserting a guide pipe into the pile hole, and pouring concrete into the pile hole through the guide pipe.

The underwater concrete pouring guide pipe is generally a seamless steel pipe with the wall thickness of 12mm and the outer diameter of 325mm, and is connected with a T-shaped threaded quick connector. The conduit diameter watertight test is watertight, and the maximum internal pressure of the conduit diameter watertight test is more than 1.3 times of the depth pressure of mud in the hole.

S121, after inserting the guide tube into the pile hole, and before casting concrete into the pile hole S130, the method further includes:

s122: and (5) secondary hole cleaning.

Before pouring the concrete, need carry out the secondary inspection to the pore-forming quality, when sediment thickness is unsatisfactory when pore-forming quality testing, need carry out the clear hole operation of secondary, clear hole process adopts the clear hole operation of pump suction reverse cycle, constantly will supply the mud of capacity simultaneously.

And the secondary hole cleaning is also carried out in a hole cleaning mode matched with the suck-back function of the high-pressure water gun and the drilling machine in S111, and the hole cleaning is completed at one time.

S130: and pouring concrete into the pile hole to a preset height to form the cast-in-situ bored pile.

The concrete pouring bottom sealing adopts a ball pulling method. And after the bottom sealing is successful, the normal filling stage is immediately carried out. And pumping the concrete, and continuously pouring the concrete into the water through the collecting hopper, the pouring hopper and the guide pipe until the pouring of the whole pile is completed. And (3) controlling the buried depth of the guide pipe to be 2-6 m in a normal pouring stage, measuring the elevation of the concrete surface every 20-30 min, wherein not less than 2 measuring points are arranged, adjusting the buried depth of the guide pipe in time when a large height difference occurs in the measuring points, and simultaneously keeping the slurry surface in the protective cylinder to be higher than the water level by 1.5m when the concrete is below the edge foot of the protective cylinder.

When the concrete pouring is close to the end, checking the pouring quantity of the concrete to determine whether the height of the measured concrete is accurate, stopping pouring after determining that the top surface elevation of the concrete is in place, and removing the pouring guide pipe in time. When the pouring is finished, the concrete surface is not less than the designed pile top elevation by 0.5-0.8 m so as to ensure the pile head concrete quality.

When the concrete is poured, the quality and the slump of the concrete are well controlled, the concrete is prevented from being separated, the pouring speed of the concrete is well controlled, the reinforcement cage is ensured to be stable and not to float upwards, and the change condition of the poured concrete surface is checked at any time.

The cast-in-situ bored pile construction method provided by the embodiment is used for performing cast-in-situ bored pile construction according to the series of steps of S100, S110, S120 and S130, wherein in the step of drilling and forming a hole by drilling S110, slurry is injected into a pile casing during drilling, the slurry comprises water, clay, bentonite and a copolymer filter reducing agent, and the mass ratio of the water to the clay to the bentonite to the copolymer filter reducing agent is (0.9-1): (0.3-0.5): (0.07-0.09): (0.005-0.015), the mud is prepared according to the proportion, compared with the traditional clay or bentonite mud, the copolymer filtration reducing reagent is added, the copolymer filtration reducing reagent belongs to a chemical reagent, is fully dissolved into a semitransparent paste in water, has high viscosity, can improve the viscosity of a mud skin formed by the mud on a hole wall, forms a filter cake with low permeability, flexibility, thinness and compactness, improves the viscosity of the mud, is more effectively suitable for construction of a soil layer with loose soil, such as sand soil, the high viscosity of the mud can increase the binding force of the loose soil, and the mud is adopted in a pile hole, so that a thin film protective layer on the surface of the hole wall is increased, the self-supporting strength of the hole wall of the pile hole is enhanced, the wall protection effect is increased, and the hole collapse probability is effectively.

S130, after pouring concrete into the pile hole, the method further includes:

s131: the catheter is withdrawn.

In this step, the pipe dismantling process is strictly controlled, and the pipe must be buried in the concrete for a minimum of 1.5m, otherwise the pile breakage phenomenon may occur.

S132: and after the concrete forms the pile column, pulling out the pile casing to form the cast-in-situ bored pile.

After the concrete in the pile hole reaches the preset strength to form a reinforced concrete column, pulling out the pile casing; and removing the reinforced concrete column above the ground to form the cast-in-situ bored pile.

And (5) carrying out pile foundation detection 28 days after the pouring of the pile foundation concrete is finished. The ultrasonic pulse is used for detecting in a detection pipeline which is embedded in parallel in the length direction of the pile foundation, the detection pipe is used as a channel of an ultrasonic detection and receiving transducer, the probe moves synchronously in the four pipes respectively, various parameters of the ultrasonic pulse on the cross section when the ultrasonic pulse passes through the concrete are measured point by point along the unknown depth, and the quality of the concrete on each cross section is analyzed according to the ultrasonic defect detection principle.

In summary, the bored pile construction method provided in this embodiment adopts a reverse circulation rotary drilling pore-forming process to mix slurry containing clay, bentonite and a copolymer filtrate-reducing agent, the viscosity of the mud skin formed on the hole wall by the mud is improved by adding the components of the chemical reagent, a filter cake with low permeability, flexibility, thinness and compactness is formed, the viscosity of the mud is improved, thereby increasing the surface film protective layer of the hole wall, increasing the self-supporting force of the hole wall, preventing hole collapse, preventing strange contraction caused by excessive water absorbed by the hole wall due to the loss of water of slurry, effectively carrying sediment at the bottom of the hole, meanwhile, after the hole is drilled to a specified elevation, a high-pressure water gun is selected to cooperate with a drilling machine to successfully clean the hole at one time, after the slurry circularly enters a sedimentation tank, under the static condition, the dispersant copolymer filter-reducing agent in the slurry can promote the regeneration of the polluted slurry and improve the circulation progress of the slurry. The slurry has very high impurity depositing speed in the hole, and the slurry is clear and transparent and non-toxic during drilling.

According to the cast-in-situ bored pile construction method provided by the embodiment, due to the adoption of a chemical reagent treatment mode, the wall protection and hole forming speed is high, the hole cleaning time is effectively shortened, and the slag forming thickness is effectively ensured. Compared with the traditional clay or bentonite slurry, the chemical slurry prepared by mixing the clay, the bentonite and the copolymer filter reducing agent is used for carrying out the wall protection construction of sand soil, the slurry dissolution speed is improved, the flocculation and precipitation of drilling cuttings and sand are accelerated, the self-cleaning effect is realized, the sand content is low, the chemical slurry wall protection product belongs to light slurry, and the wall protection effect is ensured, and meanwhile, the using amount is small, the specific gravity is low, the viscosity is high, and the sand content is extremely low; the pouring is smooth, the pipe is not easy to block, the phenomenon that concrete sandwiches is avoided, the friction bearing capacity of the pile foundation can be improved by the chemical slurry wall protection, the quality of the pile foundation is improved, and the bearing capacity of the pile is increased.

The vertical degree of the formed hole is high, and the stability of the hole wall is strong. According to the method, the steel casing is arranged by adopting the vibration hammer and the movable guide frame, and the verticality of the drilled hole is ensured by using a reciprocal inclination prevention technical measure in the drilling process, so that the verticality of the formed hole is ensured. And a low-permeability, flexible, thin and compact filter cake is formed on the well wall through the chemical mud, so that the filtration water loss of the drilling fluid is reduced as much as possible. The viscosity of the slurry is improved, so that a thin film protective layer on the surface of the hole wall is increased, the self-supporting force of the hole wall is increased, hole collapse is prevented, strangeness caused by excessive water absorbed by the hole wall due to water loss of the slurry is prevented, and the sediment at the bottom of the hole can be effectively carried.

The hole cleaning is efficient, and the problem of repeated hole cleaning of sandy soil is effectively avoided. Compared with the traditional sand soil hole cleaning construction process, the construction method has the advantages that the reverse suction function of the water gun and the drilling machine is adopted, the hole cleaning is completed before the drill is lifted, the open-ground sediment is ensured to meet the specification and design requirements, and meanwhile, the stability of the pile hole before the pouring is also ensured.

The benefits of the present method are discussed below by way of specific examples:

example (c): the Gedalang bridge constructed by Xinjiang road and bridge construction group Limited company consists of 10 cast-in-place bored piles, the length of each pile is 45m, the diameter of each pile is 1.5m, and the Gedalang bridge is the deepest pile foundation constructed by the existing company.

The conventional cast-in-place bored pile adopts a percussion drill to drill, and the rotary drilling machine is arranged in the embodiment, so that the construction period of the pile foundation is greatly shortened, and a large amount of time and labor are saved. The hole cleaning time of the drilling machine is short, and the hole cleaning can meet the standard requirement only once, so that a large amount of energy sources such as electricity and diesel oil can be saved, and the economic benefit is shown in table 5.

TABLE 5 comparative analysis table of economic benefits

Process for the preparation of a coating	Coefficient of hole expansion	Pore-forming days (1.5m ＊ 49.8.8 m)
			Drill hole filling pile of rotary drill	1.01～1.09	1
Impact drill drilling bored concrete pile	1.11～1.16	2

Social benefits are as follows: the project is the main traffic between the Kyowa and the Arthush city, the full-line through of the project shortens the transportation distance of the region, reduces the energy consumption of transportation vehicles, saves the transportation time between the Kyowa and the Arthush city, and reduces the emission of carbon dioxide.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A cast-in-situ bored pile construction method is characterized by comprising the following steps:

embedding a pile casing in a pile position on the ground, wherein part of the pile casing is exposed out of the ground;

drilling to form a hole: drilling a hole in the soil layer in the pile casing to form a pile hole, and injecting slurry into the pile casing during drilling; the slurry comprises water, clay, bentonite and a copolymer filter reducing agent, and the mass ratio of the water to the clay to the bentonite to the copolymer filter reducing agent is (0.9-1): (0.3-0.5): (0.07-0.09): (0.005-0.015);

placing a reinforcement cage into the pile hole;

and pouring concrete into the pile hole to a preset height to form the cast-in-situ bored pile.

2. The cast-in-situ bored pile construction method according to claim 1, wherein the injecting of the slurry into the casing while drilling includes:

the liquid level of the slurry in the protective cylinder is 30-40 cm lower than the port of the protective cylinder exposed out of the ground.

3. The cast-in-situ bored pile construction method according to claim 1, wherein the slurry satisfies: the PH value is 8-10, and the specific gravity is less than or equal to 1.15g/cm³The viscosity is 20 s-25 s, the colloid rate is more than or equal to 96%, the water loss rate is 19ml/30 min-21 ml/30min, and the sand content is 2% -4%.

4. The cast-in-situ bored pile construction method according to claim 1, wherein the drilling for forming the hole is a step drilling, and the step drilling includes:

pouring the slurry into the casing to a port of the casing exposed out of the ground;

in the first section, a scraper drill bit is adopted to drill a hole in the soil layer in the casing, and the drilling speed is 4-6 m/h; the first section is from a port of the casing exposed out of the ground to a position 1.9-2 m above the port of the casing buried in the ground;

in the second section, a flat-bottom drill bit is adopted to drill holes in the soil layer in the pile casing, and the drilling speed is 0.3-0.8 m/h; wherein the second section is from 1.9 m-2 m above the port of the casing buried in the ground to 4.9 m-5 m above the port of the casing buried in the ground;

and in a third section, drilling a hole in the soil layer in the pile casing by using a drill bit of a rotary drilling machine, wherein the drilling speed is 0.3-6 m/h, and the third section is from 4.9-5 m below a port of the pile casing buried in the ground to the bottom of the formed pile hole.

5. The cast-in-situ bored pile construction method according to claim 1, wherein a vertical degree of the pile hole is not more than 1%.

6. The cast-in-situ bored pile construction method according to claim 5, wherein the drilling the soil layer in the casing to form a pile hole further comprises:

acquiring the vertical degree of a drilled hole formed in the pile casing;

and adjusting the drilling angle of the drilled hole according to the vertical degree.

7. The cast-in-situ bored pile construction method according to claim 1, wherein a center deviation between the casing and the pile site is not more than 5 cm.

8. The cast-in-situ bored pile construction method according to claim 1, wherein after the placing of the reinforcement cage into the pile hole and before the pouring of the concrete into the pile hole, the method further comprises:

inserting a guide pipe into the pile hole, and pouring concrete into the pile hole through the guide pipe;

after the concrete is poured into the pile hole, the method further comprises the following steps:

withdrawing the catheter;

and after the concrete forms a pile column, pulling out the pile casing to form the cast-in-situ bored pile.

9. The method of cast-in-situ bored pile construction as recited in claim 8, wherein after said drilling and forming a hole, and prior to said placing a reinforcement cage in said pile bore, said method further comprises:

cleaning holes;

after the conduit is inserted into the pile hole and before the concrete is poured into the pile hole, the method further comprises the following steps:

and (5) secondary hole cleaning.

10. The cast-in-situ bored pile construction method according to claim 9, wherein the hole cleaning includes:

continuously flushing sediment at the bottom of the pile hole by using high-pressure water for 5-6 min;

and sucking out the sediments.