CN111058456A

CN111058456A - Cast-in-place pile construction method in foundation pit supporting process

Info

Publication number: CN111058456A
Application number: CN201911200567.2A
Authority: CN
Inventors: 高飞
Original assignee: China Third Metallurgical Group Co Ltd
Current assignee: China Third Metallurgical Group Co Ltd
Priority date: 2019-11-29
Filing date: 2019-11-29
Publication date: 2020-04-24

Abstract

The invention relates to the technical field of foundation pit supporting construction, and discloses a cast-in-place pile construction method in a foundation pit supporting process, which comprises the following steps: s1, drilling holes in the open cut land section by using a long spiral drilling machine, pouring concrete into the holes after the drilling is finished, and performing construction on the next hole site 48 hours after the pouring of the holes; s2, performing crown beam construction on each hole site after the drilling construction is finished; s3, after the construction of the crown beam is completed, digging a pipe gallery foundation pit at the elevation of the center of the crown beam, and performing steel support construction at the foundation pit; s4, after the construction of the steel support is completed, side slope spray anchor construction is carried out, the construction method of the cast-in-situ bored pile support is adopted, the process difficulty of foundation pit construction in the silty clay sand gravel area is reduced, the construction cost is greatly reduced, the pile forming bearing capacity and the water stop effect formed by adopting the long spiral drilling method are optimized, meanwhile, unstable factors caused by soil body creep property to the foundation pit support can be effectively avoided aiming at the construction of larger and deeper foundation pits, and the stability of the foundation pit support is improved.

Description

Cast-in-place pile construction method in foundation pit supporting process

Technical Field

The invention relates to the technical field of foundation pit supporting construction, in particular to a cast-in-place pile construction method in a foundation pit supporting process.

Background

In some areas where the ground layer is mainly silty clay sand gravel, the influence degree of the soil body creep on the foundation pit supporting deformation is increased when the foundation pit construction depth is increased due to the creep property of the foundation pit construction process, soil flowing phenomenon is easy to generate during excavation, pile forming is not facilitated, and slope releasing treatment construction cannot be adopted in areas with buildings and signal towers around individual places, so that the construction process difficulty is high, the construction period is long, and the cost is high.

Disclosure of Invention

Aiming at the defects of the background technology, the invention provides the cast-in-place pile construction method in the foundation pit supporting process, which has the advantages of effectively performing foundation pit supporting construction aiming at the geological conditions of the silty clay sand gravel, having better foundation pit supporting effect and solving the problems provided by the background technology.

The invention provides the following technical scheme: the cast-in-place pile construction method in the foundation pit supporting process comprises the following steps:

s1, drilling holes in the open cut land section by using a long spiral drilling machine, pouring concrete into the holes after the drilling is finished, and performing construction on the next hole site 48 hours after the pouring of the holes;

s2, performing crown beam construction on each hole site after the drilling construction is finished;

s3, after the construction of the crown beam is completed, digging a pipe gallery foundation pit at the elevation of the center of the crown beam, and performing steel support construction at the foundation pit;

and S4, performing side slope anchor spraying construction after the steel support construction is completed.

Preferably, the S1 drilling construction is carried out by firstly measuring and positioning hole positions in open cut sections, pre-burying pile casings according to pile positions, secondly moving the drilling machine to the hole positions and aligning the drilling machine to a horizontal position, thirdly starting the drilling machine to drill holes at the specified positions to specified depths through the drilling holes, fourthly checking and accepting problems occurring in the drilled holes, fifthly reversing to lift the drilling rod to compact soil layers in the holes, sixthly pumping the poured concrete from the drilling holes at the bottom of the drilling rod, seventh lifting the drilling rod while pouring the concrete, integrally pouring the concrete to a height of 0.5m above the specified height, eighth hoisting a reinforcement cage to a preset height in the poured concrete in the holes, and ninth moving the reinforcement cage to the next hole position to carry out operation.

Preferably, in the S2 crown beam construction, earth covering and inter-pile earthwork are excavated according to a designed elevation in the first step, pile head floating slurry is chiseled and steel bar anchoring treatment is performed in the second step, measurement lofting, installation of steel bars and embedded parts are performed in the third step, installation adjustment and reinforcement of a template are performed in the fourth step, concrete construction is performed in the fifth step, and concrete maintenance is performed in the sixth step.

Preferably, the S3 steel support construction is that a pipe gallery foundation pit with the depth of less than 10m is dug in the first step, a steel pipe support is arranged at the center of a crown beam, a deep foundation pit with the depth of 10m-13m is dug in the second step, 2 steel pipe supports are arranged, the distance between the second horizontal supports is 5m, the vertical distance between the two supports is more than 3m, and the steel pipe with the diameter of phi 609mm and the diameter of delta 16mm is adopted as the steel support.

Preferably, the S4 side slope spray anchor construction is carried out by earth excavation in the first step, trimming side walls in the second step, measuring and paying off in the third step, inserting steel bars to install a steel bar framework in the fourth step, inserting anchor bars and installing steel bar nets in the fifth step, embedding concrete spraying thickness control piles in the sixth step, arranging and installing water drain pipes in the seventh step, carrying out concrete spraying operation in the eighth step, carrying out water spraying maintenance on the sprayed concrete 2 hours after final setting in the ninth step, and enabling the maintenance time to be longer than 7 days.

Preferably, the earth excavation is conducted in a segmented and layered mode from top to bottom, and the length of each segment is controlled to be 25 m.

Preferably, the slope is trimmed manually, the flatness of the slope is within +/-5 cm, and the slope is +/-3 degrees.

Preferably, the water drain pipes are installed by using 75PVC pipes, four rows of side slopes are arranged from the top of the slope to the bottom of the slope, the vertical intervals are uniformly distributed according to the actual situation on site, and the horizontal intervals are 2000 mm.

The invention has the following beneficial effects:

by adopting the construction method of the bored pile support, the process difficulty of foundation pit construction in the powdery clay sand gravel area is effectively reduced, the construction period is effectively shortened, and the construction cost is greatly reduced.

Drawings

FIG. 1 is a schematic view of a foundation pit supporting process according to the present invention;

FIG. 2 is a schematic view of a drilling process according to the present invention;

FIG. 3 is a schematic view of the construction process of the crown beam of the present invention;

fig. 4 is a schematic diagram of the slope spray anchor construction process of the invention.

Detailed Description

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 only a part of the embodiments of the present invention, and not all of the embodiments. 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.

Referring to fig. 1-4, a method for constructing a cast-in-place pile in a supporting process of a foundation pit includes:

In the technical scheme, the S1 drilling construction comprises the steps of firstly measuring and positioning hole positions in an open cut section, embedding a protective cylinder according to the pile position, wherein the inner diameter of the preset protective cylinder is about 100mm larger than that of a designed pile, the height of the preset protective cylinder is 0.8m-1.0m, the embedding error between the center of the protective cylinder and the center of the pile position is less than 50mm, the embedding of the protective cylinder is kept vertical, the hole opening of the embedded protective cylinder is more than 200mm larger than the diameter of the protective cylinder, tamping needs to be filled from bottom to top around the protective cylinder, drilling can be carried out after the position is rechecked by a measuring person by an instrument, secondly, moving a drilling machine to the hole positions and aligning the drilling machine to the horizontal position, so that the center of a crown block, the center of a gyrator and the center of a drill rod are on the same plumb line, ensuring the vertical drilling of the drilling machine, thirdly, starting the drilling machine to drill the drilling machine to the appointed position by drilling, idling without advancing the, gradually increasing the rotating speed and adjusting the bit pressure, observing the footage and slag discharge conditions in the drilling process, controlling the footage speed (drilling by adopting a long spiral drilling method) according to the types and the amount of slag discharge, checking and accepting the problems occurring in the drilling holes, reversely rotating and lifting a drill rod to compact the soil layer in the holes, pumping poured concrete from the inside of the drilling holes at the bottom of the drill rod in the sixth step, lifting the drill rod while pouring the concrete in the seventh step, integrally pouring the concrete to be 0.5m above the designated height, immediately lifting a drilling tool away from the bottom of the holes and keeping the liquid level of the slurry when abnormal conditions such as hole collapse and the like occur in the holes during drilling, if necessary, conveying the slurry with the performance meeting the requirements into the holes, improving the slurry pressure in the holes to inhibit the continuous hole collapse, and in the eighth step, hanging a reinforcement cage into the preset height in the poured concrete in the holes, and slowly placing the reinforcement cage into the holes in a quasi-light manner, when the obstacle is met, the reason needs to be found out, the treatment is carried out, the lower part cannot be forced, and the ninth step is carried out to the next hole position for operation;

the long spiral drilling method is a quick dry drilling method of a long spiral middle drill rod driven by a high-torque power head, wherein the soil in a drill hole is partially extruded, the majority of the soil is conveyed to a blade of the spiral drill rod, the soil is extruded to be compact when rising, the soil and the drill rod form a soil column, the clearance between the soil column and the drill rod is only a few millimeters, the soil column is similar to a long piston, even in a stratum with underground water, the drill hole cannot collapse because the clearance between the soil column and the drill hole is small and the drilling speed is high and little water seeps out and accumulates in the drill hole, a check valve is arranged in the drill hole at the bottom of the drill rod, the drill rod stops rotating after the drill rod reaches the designed depth, the stirred and accumulated concrete is pressed to the bottom of the drill bit through a pump pipe under the pressure of 1-5.5Mpa, the check valve is opened at the moment, the concrete is pressed out and pushes the drill rod to rise while drilling, the concrete can be filled more at the soft soil section to form an expanded diameter pile, which is very beneficial to improving the bearing capacity and water stopping effect.

In the technical scheme, drainage ditches are arranged around a crown beam foundation pit before construction of the crown beam foundation pit, the drainage ditches are led into a designed water collecting pit, a water suction pump is adopted for pumping drainage in the water collecting pit, S2 crown beam construction is carried out by firstly excavating earth covering and inter-pile earthwork according to a designed elevation, after construction of a drilling pile is completed, after strength is achieved, a crown beam earthwork excavating wiring is determined by measuring and paying off, an excavator is adopted for excavating the crown beam foundation pit earthwork to the bottom of the crown beam, the position of the hole pile is cleaned by manually matching with machinery, the earthwork is cleaned to the designed bottom elevation of the crown beam, after surface layer earth covering and inter-pile earthwork are excavated, a central line control point and an elevation are applied to the top surface of the cast-in-situ bored pile according to the designed position and elevation of the crown beam, the central line control point can be led out of the pile, a control point mark and a point position protection device are prepared to prevent the construction from being damaged, determining the bottom elevation of the top beam of each cast-in-situ bored pile at each construction section through two or more points, marking each pile with red paint, performing pile head laitance chiseling and steel bar anchoring treatment in the second step, chiseling redundant pile head concrete of the cast-in-situ bored pile (underground continuous wall) according to the red line mark of each pile head, chiseling the pile head from the horizontal direction only and from the pile head downwards when the pile head is chiseled, so that the pile head is prevented from becoming a conical shape, and meanwhile, the steel bars in the cast-in-situ bored pile can not be moved left, right, front and back freely. After the pile head drills 5cm above the elevation of the bottom of the crown beam, loose concrete blocks are removed, the chiseling surface is blown and sprayed completely by an air pump, reinforcing steel bars can be bound after being checked and accepted by a quality inspector, third step of measurement and lofting, the reinforcing steel bars and embedded parts are installed, after the pile head is cleaned, the control points of the center line of the crown beam are encrypted and led to the pile top, the center point of the crown beam is released, all the points are connected into a line to serve as the construction control center line of the crown beam, the side lines of the crown beam are separated from left and right according to the center line of the crown beam, the steel bars are anchored and overlapped according to the design requirements, the main bars are connected in a lap welding mode, the axes of the main bars are ensured to be on the same straight line, the main bars of the bored pile are placed on the inner sides of the reinforcing steel bars of the crown beam in a segmented construction, the connecting steel bars are reserved at the joint part of each segment, steel plate, and the corner position also needs to be pre-buried constructional column reinforcing steel bars, the pre-buried reinforcing steel bars are arranged on the outer side of the crown beam, cushion blocks are installed, when the reinforcing steel bars are installed, the concrete cushion blocks are firmly bound at the intersection of main reinforcing steel bars and side reinforcing steel bars on the outer side of the side reinforcing steel bars of the crown beam, the fourth step of installation adjustment and reinforcement of the template is carried out, the template adopts a bamboo template, the fifth step of concrete construction is carried out, a layered pouring method is adopted, the thickness of each layer is 300mm, the pouring sequence of each layer needs to be the same, the upper layer of concrete is poured before the initial setting of the lower layer of concrete, the poured concrete is compacted by using an inserted vibrating rod, the surface of the concrete crown beam is trowelle.

In the technical scheme, the S3 steel support construction is characterized in that a pipe gallery foundation pit with the depth smaller than 10m is dug in the first step, a steel pipe support is arranged at the center of a crown beam, a deep foundation pit with the depth of 10m-13m is dug in the second step, 2 steel pipe supports are arranged, the distance between the second horizontal supports is 5m, the vertical distance between the two supports is larger than 3m, and the steel pipes with the diameter phi 609mm and the diameter delta 16mm are adopted as the steel supports.

In the technical scheme, the S4 slope spray anchor construction comprises the steps of firstly excavating earth, secondly trimming side walls, thirdly measuring and setting line, fourthly inserting steel bars to install a steel bar framework, fifthly inserting anchor bars and installing steel bar nets, binding and fixing the steel bar nets according to design requirements, firmly connecting the steel bar net sheets in a surface layer with an anchoring device to meet the thickness requirement of a steel bar protection layer specified by the design, binding the steel bar net sheets on the steel bar net by iron wires at an interval of 1000 multiplied by 1000, preventing the steel bar net sheets from shaking when spraying concrete, binding the steel bar net sheets, controlling grid deviation within a range of +/-10 mm, laying the steel bar net sheets at a lap joint length of each side of not less than 300mm, sixthly embedding a concrete spraying thickness control pile, seventhly arranging and installing a water drainage pipe, and eighthly spraying concrete,

firstly, if the sprayed surface has water drops and drenches, the following method should be done before spraying:

① when there is obvious water outlet point, the conduit can be buried for drainage;

② the soil layer with poor water guiding effect can be provided with blind ditches for drainage;

the mixing proportion of the sprayed concrete is determined by tests, the maximum particle size of the coarse aggregate is not more than 10mm, the water cement ratio is not more than 0.45, the early strength time and the required working schedule are adjusted by adding the accelerator according to requirements, and the mixing amount of the accelerator is determined by tests.

And (III) the raw materials are strictly metered according to the mixing proportion, the weighing deviation of the cement and the accelerator is +/-2%, and the weighing deviation of the sand and the stone is +/-3%.

And (IV) in the transportation and storage processes of the mixture, impurities such as rain, water leakage, large stones and the like are strictly prevented from being mixed, and the mixture is sieved before being filled into a spraying machine.

And fifthly, vertically driving short steel bars into the side wall at intervals of 1500mm multiplied by 1500mm in a two-way distance to ensure that the thickness of the sprayed concrete is uniform, wherein the short steel bars are used as thickness control standard points.

And (VI) the sprayed concrete is sprayed to the thickness of 60mm, and one-time spraying construction is completed.

And (seventhly) spraying concrete between the reinforcing steel bars and the slope surface to prevent gaps from appearing on the back surfaces of the reinforcing steel bars. The spray distance of the sprayed concrete is preferably kept within the range of 0.6-1.0 m, and the jet flow is perpendicular to the wall surface. And spraying by adopting a spiral track in a way of pressing a circle and a half circle.

(eighth) if the concrete dropped off during the spraying is caught by the steel bar net frame, the concrete should be removed in time.

And (ninthly) controlling the water-cement ratio during spraying, and keeping the surface of the concrete smooth, moist and glossy, and free from dry spots and slippage and flowing phenomena.

The rebound resilience of the (ten) injection should not be more than 15%.

(eleventh) the flatness requirement of the slope after molding is as follows: and measuring by using a 1-meter guiding rule and a clearance gauge, wherein the unevenness within the range of measuring a point 1 square meter is not more than 50 mm.

And step nine, performing water spraying maintenance on the sprayed concrete for 2 hours after final setting, wherein the maintenance time is more than 7 days.

The construction method comprises the following steps of carrying out excavation on earth from top to bottom in a segmented and layered mode, controlling the length of each segment to be 25m, shortening the excavation length when meeting a soft soil layer, enabling the length of each horizontal segment of each layer of excavation to depend on the self-stability capability of the soil wall, and mutually connecting the horizontal segment of each layer of excavation with a supporting construction process, wherein the excavation length of each single segment of excavation is not more than 25m, carrying out next procedure construction after each excavation is finished, requiring site supervision and qualified acceptance of owners, when the area of a foundation pit is large, allowing the middle part of the foundation pit at a certain distance from the peripheral slopes of the foundation pit to freely excavate, paying attention to be coordinated with the excavation of a layered operation area, continuously excavating among the horizontal segments when the soil layer condition is good, adopting excavation jumping when the soil quality is poor, and strictly preventing the side wall from being over-excavated or causing the side.

The method is characterized in that the slope is maintained manually, the flatness of the slope is within +/-5 cm, the slope is +/-3 degrees, the soil body which is easy to collapse is made into the following measures according to the field condition, a layer of thin mortar or concrete is sprayed on the trimmed side wall immediately, the steel bar net piece is installed to spray the concrete after the concrete is condensed, the slope is excavated in the horizontal direction at small intervals, and the steel bar reinforced soil body is vertically hit into the slope along the excavation face during excavation.

The water drain pipe is installed by adopting 75PVC pipes, four rows of side slopes are arranged from the top to the bottom of the slope, the vertical intervals are uniformly distributed according to the actual situation on site, the transverse intervals are 2000mm, the water drain pipe is high inside and low outside, geotextile is wrapped on the side close to the soil, a gravel soil reverse filter bag is made, the gravel soil reverse filter bag extends out and is sprayed to the slope surface of the concrete side by 5cm, when the concrete is sprayed, an outer pipe head is blocked by a cement bag, the pipe is prevented from being plugged by the concrete, and the pipe is dredged after the concrete is finished.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

1. The cast-in-place pile construction method in the foundation pit supporting process is characterized by comprising the following steps:

2. The cast-in-place pile construction method in the foundation pit supporting process according to claim 1, characterized in that: s1 drilling construction is carried out, a hole position is measured and fixed in an open cut section in the first step, pile casings are embedded according to pile positions, the drilling machine is moved to the hole position and is aligned to the horizontal position to adjust the drilling machine, the drilling machine is started to drill holes in the specified position to the specified depth in the third step, idling is carried out, the drilling is not carried out, problems occurring in the drilling are checked and accepted in the fourth step, a fifth step is carried out, the drilling rod is reversely rotated to compact a soil layer in the hole, the cast-in-place concrete is pumped from the drilling hole at the bottom of the drilling rod in the sixth step, the drilling rod is lifted while the cast-in-place concrete is poured in the seventh step, the whole cast-in-place concrete is poured to 0.5m above the specified height, a steel reinforcement cage is hung in the cast-in-place concrete in the hole.

3. The cast-in-place pile construction method in the foundation pit supporting process according to claim 1, characterized in that: the method comprises the following steps of S2 crown beam construction, wherein the first step is to excavate covering soil and earthwork between piles according to a designed elevation, the second step is to remove floating slurry of a pile head and anchor reinforcing steel bars, the third step is to measure lofting, install reinforcing steel bars and embedded parts, the fourth step is to install, adjust and reinforce templates, the fifth step is to construct concrete, and the sixth step is to maintain the concrete.

4. The cast-in-place pile construction method in the foundation pit supporting process according to claim 1, characterized in that: the construction method comprises the steps of S3 steel support construction, wherein a pipe gallery foundation pit with the depth smaller than 10m is dug in the first step, a steel pipe support is arranged at the center of a crown beam, a deep foundation pit with the depth of 10m-13m is dug in the second step, 2 steel pipe supports are arranged, the distance between the second horizontal supports is 5m, the vertical distance between the two supports is larger than 3m, and steel pipes with the diameter phi 609mm and the diameter delta 16mm are adopted as the steel supports.

5. The cast-in-place pile construction method in the foundation pit supporting process according to claim 1, characterized in that: the method comprises the following steps of S4 slope spray anchor construction, wherein earthwork excavation is carried out in the first step, the side wall is trimmed in the second step, line measurement and paying-off are carried out in the third step, a steel bar framework is installed in the fourth step, an anchor rod is inserted and a steel bar net is installed in the fifth step, a sprayed concrete thickness control pile is embedded in the sixth step, a water drain pipe is installed in the seventh step, concrete spraying operation is carried out in the eighth step, water spraying maintenance is carried out 2 hours after sprayed concrete is finally set in the ninth step, and the maintenance time is longer than 7 days.

6. The cast-in-place pile construction method in the foundation pit supporting process according to claim 5, characterized in that: and carrying out subsection and layering construction from top to bottom in the earth excavation, wherein the length of each section is controlled to be 25 m.

7. The cast-in-place pile construction method in the foundation pit supporting process according to claim 5, characterized in that: the slope trimming is manual trimming, the flatness of the slope is within +/-5 cm, and the slope is +/-3 degrees.

8. The cast-in-place pile construction method in the foundation pit supporting process according to claim 5, characterized in that: the water drain pipe is installed by adopting 75PVC pipes, four rows of side slopes of each stage are arranged from the top of the slope to the bottom of the slope, the vertical intervals are uniformly distributed according to the actual situation on site, and the transverse intervals are 2000 mm.