CN116446385A - Karst filling-free filling pile structure and construction method thereof - Google Patents

Abstract

The invention discloses a karst unfilled cast-in-situ pile structure and a construction method thereof. The karst unfilled cast-in-place pile includes a designed steel reinforcement cage placed in the pile hole, and an additional steel reinforcement cage penetrating through the karst distribution section is added to the designed steel reinforcement cage , the outside of the additional reinforcement cage is fully covered with galvanized steel wire mesh and dense mesh nylon mesh, and there is an annular filling gap between the additional reinforcement cage and the design reinforcement cage; The pile body is composed of spiral stirrups and pile body stiffening rings; the additional reinforcement cage is composed of multiple additional longitudinal reinforcements, additional spiral stirrups, and additional stiffening rings. The pile-forming technology of this application is simple, with remarkable features such as safety and reliability, quality controllability, economic rationality and on-site implementability, etc., which can ensure production safety on the construction site, improve quality control of cast-in-place piles, and reduce engineering costs And increase engineering benefits, etc.

Description

A karst non-filled cast-in-place pile structure and its construction method

technical field

The invention belongs to the field of cast-in-place piles, in particular to a karst unfilled cast-in-place pile structure and a construction method thereof.

Background technique

Karst, also known as karst, refers to the geological action of water on soluble rocks (carbonate rock, gypsum, rock salt, etc.), mainly by chemical dissolution, supplemented by mechanical actions such as erosion, latent erosion and collapse of flowing water. , the landforms formed by karstification are most widely distributed in Guangxi, Guizhou and eastern Yunnan, and are also widely distributed in western Hunan, western Hubei, eastern Sichuan, Shandong, and Jin. Most of the development and formation of karst have a great impact on the foundation or site of buildings. Therefore, the difficulty of engineering construction in karst areas lies in construction and stability evaluation. Therefore, it is necessary to study karst landforms, predict and solve the problems caused by karst landforms. Various engineering geological problems.

The geological conditions in the karst development area are complex and changeable, and the common karst landforms mainly include: karst ditch, stone bud; karst funnel; sinkhole; dry valley; ,underground river. Geological problems faced by various engineering constructions in karst areas: karst foundation instability; karst surface subsidence; karst ground deformation; karst ground cracking; karst seepage water inrush;

At present, pile foundation construction in karst areas usually uses pile foundation hole-forming equipment to form holes, such as rotary drilling rigs and impact drilling rigs. In the process of pile foundation construction, when inclined rock is encountered, problems such as drilling deviation, drill sticking, slurry leakage and hole collapse often occur. In order to ensure the quality of the pile, we mainly start from two aspects: on the one hand, by adjusting the design plan, optimizing or trying to Avoid karst bad geology and reduce construction risks to a certain extent, such as optimization methods such as foundation structure form and structure form; Add mud retaining wall, pre-grouting, throwing rubble or backfilling with low-strength concrete, etc., and then mechanically form holes and piles.

However, the above methods have shortcomings such as slow progress of the project, serious consumption and waste of grouting materials or concrete, and difficulty in controlling the initial setting time of backfill concrete, which affects the efficiency of mechanical pore formation and wear equipment, and there is also the possibility of karst caused by the seepage of mud retaining wall The rock and soil mass in the upper part of the pile hole that has been completed diffuses and loses to form a collapse hole, which leads to the overall collapse of the soil around the pile hole, affecting the production safety of the working face, and the quality problems of the surrounding piles.

Contents of the invention

The main purpose of the present invention is to provide a karst non-filled cast-in-place pile structure and its construction method, aiming to effectively solve the problem of poor geological conditions such as karst affecting the quality of cast-in-place piles in the prior art, as well as high cost and low construction efficiency. And other issues. .

For this reason, the karst non-filled cast-in-situ pile structure provided by the embodiment of the present invention includes a designed reinforcement cage arranged in the pile hole and an additional reinforcement cage installed outside the designed reinforcement cage and running through the karst distribution section of the pile hole;

The design reinforcement cage is composed of multiple pile body main reinforcements, pile body spiral stirrups, and pile body stiffening rings;

The additional reinforcement cage is composed of multiple additional longitudinal reinforcements, additional spiral stirrups, and additional stiffening rings.

There is an annular filling gap between the additional reinforcement cage and the design reinforcement cage;

The outside of the additional reinforcement cage is fully covered with galvanized steel wire mesh and dense mesh nylon mesh; or,

A galvanized steel casing is arranged outside the additional reinforcement cage.

Specifically, the two ends of multiple additional longitudinal reinforcements in the additional reinforcement cage are bent and anchored in the design reinforcement cage, and the additional longitudinal reinforcements are welded and fixed to the ends at the bends with additional stiffening rings.

Specifically, the galvanized steel wire mesh is overlapped and overlapped in a manner similar to spiral stirrups, and is fixed on the additional reinforcement cage in a quincunx-shaped manner with iron wires, and the dense mesh nylon mesh is completely covered on the galvanized steel wire mesh. The outer side is firmly fixed with iron wire at a certain distance.

Specifically, the galvanized steel casing is welded on-site by galvanized steel sheets, first wrapped in an additional reinforcement cage in a fully covered manner, and then welded into a round steel pipe. The reliability and corrosion resistance of galvanized steel sheets are as good as those of the coating Strong toughness, can be used as the material of the pile body.

Specifically, the diameter of the additional longitudinal steel bar is increased by 100 mm on the basis of the designed pile diameter (5) of the cast-in-place pile in a water environment, and by 70 mm in an anhydrous environment.

Specifically, the diameter of the pile hole is larger than the designed pile diameter of the cast-in-situ pile, and the diameter of the pile hole in the karst distribution section and above is the inner diameter of the long steel casing, and is not less than the design pile diameter + 2 times [design reinforced cage protection Layer thickness (35mm (without water environment)/50mm (with water environment) + additional steel cage protective layer thickness (35mm (without water environment)/50mm (with water environment)]; the pile hole diameter below the karst distribution section, Based on whether the long steel casing is followed up or not, if the long steel casing is not followed up, the diameter of the pile hole is generally the designed pile diameter, otherwise it is the same as the diameter of the pile hole at the karst distribution section and above. Specifically, the plating The spiral reinforcement stirrup added outside the zinc-steel casing is fixed by spiral welding.

Specifically, the design reinforcement cage and the additional reinforcement cage are welded and fixed by supporting reinforcement to form a combined reinforcement cage.

Another aspect of the embodiment of the present invention provides a construction method for a karst unfilled cast-in-situ pile structure, including:

Site leveling, positioning, mud preparation, long steel casing production, material preparation, etc.;

The pile foundation hole-forming equipment is matched with the long steel casing, and the cast-in-situ piles are excavated to the depth of the rock-socketed. During the excavation, the geological survey report is used to record the starting position of the karst, the final hole acceptance and slag removal. Pile holes are formed, and the elevation of the bottom of the long steel casing is lower than a certain depth at the lowest position of the karst distribution section;

According to the starting position of unfavorable formations such as karst without filling, determine the position and length of the additional reinforcement cage on the design reinforcement cage;

Design reinforcement cage fabrication, additional reinforcement cage fabrication;

Additional reinforcement cage installation, the outside is covered with galvanized steel wire mesh and dense mesh nylon mesh or set with galvanized steel casing to form a combined reinforcement cage structure of cast-in-situ piles;

Hanging and placement of cast-in-place pile composite reinforcement cage in the pile hole, measurement of sediment thickness and secondary hole cleaning;

Conduit installation, pouring pile body concrete into the pile hole to form a pouring pile;

Mechanical equipment (hoisting machinery, vibratory hammer) pulls out long steel casings.

Specifically, the net distance between the additional reinforcement cage and the original design reinforcement cage should be ≥35mm (without water environment)/50mm (with water environment). Generally lower than the concrete pouring surface elevation ≮10m.

Specifically, the inner diameter of the long steel casing is 140 mm larger than the designed pile diameter of the cast-in-situ pile (in an environment without water)/200 mm (in an environment with water), and the wall thickness is generally 20 mm.

The above construction methods specifically include:

Step 1: site preparation, pile stake out, material preparation, etc.

Step 2: Embedding of long steel sheathing and mud preparation

The third step: Drilling, final hole acceptance and one-time cleaning

Step 4: Combined reinforcement cage installation

Step 5: Sediment index inspection and secondary hole cleaning

After installing the accessory reinforcement cage on the design reinforcement cage, hoist the combined reinforcement cage into the pile hole as a whole, and control the position of the reinforcement cage according to the design elevation and other requirements, and at the same time take corresponding measures to fix it on the top of the reinforcement cage to prevent concrete pouring process The middle reinforcement cage rises;

Set up the concrete cover block in advance to control the net distance between the reinforcement cage and the hole wall.

Step 6: Pouring Concrete Underwater

During the pouring process, the position of the concrete surface in the pile hole should be detected frequently, the buried depth of the conduit should be adjusted in time, the pile foundation concrete should be poured continuously, and the long steel casing should be mechanically pulled out in time after completion;

Step Seven: Pile

Compared with the prior art, at least one embodiment of the present invention has the following beneficial effects:

Applying the technical scheme of the present invention can effectively solve the problems of karst non-filled cast-in-situ piles in the prior art such as hole formation, pile formation quality, and low construction efficiency. At the same time, the construction technology is simple, safe, reliable, quality controllable, and technically feasible. , economical and reasonable, on-site implementability and other remarkable features can ensure production safety, improve quality control, reduce construction costs, and increase project benefits.

Safe and reliable: the karst non-filled cast-in-place pile structure adopted is constructed with long steel casings, and the additional reinforcement cage can effectively prevent the concrete of the pile body from entering the nearby pile positions (holes), without increasing the construction of surrounding unconstructed pile positions At the same time as the difficulty, the mud retaining wall is less permeable to a certain extent, and the karst causes the soil loss of the completed pile hole and the overall collapse of the soil around the pile hole, which does not affect the production safety and the quality of the surrounding piles.

Quality controllability: Compared with the current cast-in-place pile treatment measures in karst areas, the use of karst unfilled cast-in-situ pile structure overcomes the shortcomings of the current treatment measures. When the pile body runs through the karst distribution section, an additional reinforcement cage is added outside the design reinforcement cage to ensure that the protective layer of the design reinforcement cage meets the design requirements and effectively prevent the diffusion and loss of pile concrete and the entry of mud or rock and soil around the pile into the pile body At the same time, the quality of cast-in-situ piles can be easily guaranteed;

Technically feasible: the karst non-filled cast-in-place pile structure adopted is suitable for karst and other adverse geological conditions, and has a leading edge in technology. At the same time, the maturity and practicability of the technology have been tested through rich engineering practice;

Economical and reasonable: Compared with the current construction measures in karst areas, the use of karst unfilled cast-in-situ pile structure can ensure production safety and quality control requirements, and has significant advantages in terms of construction period and cost: ① In terms of cost. There is no need to consider filling and other treatment measures, such as backfilling with low-grade concrete, without considering material consumption and waste, ensuring the overfilling of concrete in the pile body, and effectively controlling the cost of investment; ② In terms of construction period. There is no backfilling and other measures, and the karst non-filling cast-in-place pile structure does not need to consider optimization in design, which shortens the design time. There is no backfilling and other measures in the construction, no need to consider the karst treatment period, no need to consider the impact of backfilling treatment on mechanical pore forming benefits and equipment wear, the efficiency of pile foundation construction is high, and the construction period is easy to be guaranteed. Comprehensive analysis shows that the karst non-filled cast-in-situ pile structure has certain advantages in terms of safety, construction period, quality and construction cost, especially in terms of safety and cost.

On-site implementability: The karst non-filled cast-in-place pile structure adopted is not much different from the usual construction process. Only additional reinforcement cages are added in the karst distribution section, and the additional reinforcement cages are fully covered with galvanized steel wire mesh and dense mesh nylon mesh. process or set galvanized steel casing. The pile forming technology and method are simple, the construction site is easy to organize construction, and the quality of the pile concrete is easy to control, which is conducive to production safety and at the same time reduces the cost of manpower, materials, and machinery for pile foundation construction in karst areas, and meets the requirements of low-carbon environmental protection.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings that need to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained based on these drawings without creative effort.

Fig. 1 is the structural representation of the karst non-filling cast-in-place pile of the embodiment of the present invention;

Fig. 2 is a schematic diagram of the cross-sectional structure of the cast-in-place pile above the karst distribution section of the embodiment of the present invention;

Fig. 3 is a schematic diagram of the cross-sectional structure of the cast-in-place pile at the karst distribution section of the embodiment of the present invention;

Fig. 4 is a schematic diagram of the cross-sectional structure of the cast-in-place pile below the karst distribution section of the embodiment of the present invention;

In the figure: 1. Karst distribution section; 2. Main reinforcement of pile body; 3. Spiral stirrup of pile body; 4. Stiffening ring of pile body; 5. Design pile diameter; 6. Pile hole; 7. Additional longitudinal reinforcement; 8. Additional Spiral stirrup; 9. Additional stiffening ring; 10. Supporting steel bar; 11. Galvanized steel wire mesh and dense mesh nylon mesh; 12. Ring filling gap; 13. Long steel casing; 14. Construction pile diameter.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

In describing the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", " Back", "Left", "Right", "Vertical", "Horizontal", "Top", "Bottom", "Inner", "Outer", "Clockwise", "Counterclockwise", "Axial", The orientation or positional relationship indicated by "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying the referred device or element Must be in a particular orientation, be constructed in a particular orientation, and operate in a particular orientation, and therefore should not be construed as limiting the invention.

Referring to Fig. 1-Fig. 4, the karst non-filled cast-in-situ pile structure provided by the embodiment of the present invention includes a designed reinforcement cage inserted in the pile hole 6 and a steel cage fixedly sleeved outside the designed reinforcement cage and covering the karst distribution section 1 of the pile hole 6. Additional reinforcement cage, the design reinforcement cage is composed of multiple pile body main reinforcement 2, pile body spiral stirrup 3, and pile body stiffening ring 4, and the additional reinforcement cage is composed of multiple additional longitudinal reinforcement 7, additional spiral stirrup 8, and additional stiffening ring 9 Composition, there is an annular filling gap 12 between the additional reinforcement cage and the design reinforcement cage, the diameter of the pile hole 6 located in the karst distribution section 1 and above is larger than the design pile diameter 5 of the cast-in-place pile, and the additional reinforcement cage is fully covered with galvanized steel wire Mesh and dense mesh nylon mesh11.

During the construction, the pile foundation hole-forming equipment is matched with the long steel casing, and the cast-in-situ piles are constructed to the depth of the rock-socketed. During the excavation, the geological survey report is used to record the initial elevation of the karst, the final hole acceptance and slag removal, and then according to the karst Filling and other unfavorable geological starting positions, determine the elevation position and length of additional reinforcement cages that need to be added to the design reinforcement cages, hoist the combined reinforcement cages of cast-in-place piles as a whole into the pile hole 6, and conduct sediment thickness measurement and secondary hole cleaning again , and control the position of the combined reinforcement cage according to the design elevation and other requirements, and at the same time take corresponding measures to fix it on the top of the reinforcement cage to prevent the reinforcement cage from rising during the concrete pouring process. The net distance between the cage and the hole wall; use the conduit to pour the pile body concrete into the pile hole 6 to form a cast-in-situ pile, and use mechanical equipment (hoisting machinery, vibrating hammer) to pull out the long steel casing 13.

In this embodiment, during the pouring process, the pile body concrete in the karst distribution section is restricted by the galvanized steel wire mesh and the dense mesh nylon mesh 11, effectively blocking the diffusion and loss of the pile body concrete in the karst distribution section to the surroundings, and the mud Or the rock and soil around the pile enter the pile body, replacing the conventional method of pre-treating the foundation for the construction of cast-in-situ piles in lava areas, reducing costs, shortening the construction period, and ensuring the construction quality of pile foundations. In addition, even if all the concrete outside the additional reinforcement cage in the karst distribution section diffuses and loses to the surroundings, the concrete between the additional reinforcement cage and the design reinforcement cage can be used as the protective layer of the design reinforcement cage to prevent the design reinforcement cage from directly contacting the rock and soil around the pile. Accelerated corrosion of design reinforcement cages caused by contact.

The cast-in-situ pile structure has a wide range of applications, and there is no need to consider too much the influence of bad geology on the pile foundation in terms of design. There is no mechanical drilling equipment and other restrictions on construction, and it is equipped with long steel casing 13 for construction. The construction of the distribution section can ensure smooth hole formation and high work efficiency. The lateral pressure of the concrete of the poured pile body on the composite structure is small, and the construction of the poured pile without filling in the karst distribution section 1 can be realized.

What needs to be explained is that in the actual design, the diameter of the pile hole 6 in the karst distribution section 1 and above is the inner diameter of the long steel casing 13, and is not less than the design pile diameter + 2 times [the design reinforcement cage protective layer (35mm( No water environment)/50mm (with water environment) + additional reinforcement cage protection layer (35mm (without water environment)/50mm (with water environment)]; the diameter of the additional reinforcement cage in karst distribution section 1 is generally larger than the diameter of the design reinforcement cage 2 times larger [35mm (without water environment)/50mm (with water environment)]; 6 diameters of pile holes below the karst distribution section 1, based on whether the long steel casing is followed up or not, if the diameter of pile holes 6 is not followed up In order to design the pile diameter, otherwise it is the same as the diameter of the pile hole 6 in the karst distribution section 1 and above. The galvanized steel wire mesh is overlapped and overlapped in a manner similar to spiral stirrups, and is fixed on the additional steel cage in a plum blossom shape with iron wires. The mesh nylon mesh is fully covered on the outside of the galvanized steel mesh, and is firmly fixed with iron wires at a certain distance.

Referring to Fig. 1-Fig. 4, a kind of construction method of the cast-in-place pile structure without filling in karst comprises the following steps:

Step 1: Site Preparation

The construction site should meet the following requirements to prevent the pile foundation hole-forming equipment from tilting, toppling or sinking during the construction process, causing production safety accidents:

1) It is a dry land construction site, surface sundries should be removed, soft soil should be replaced, compacted and leveled, etc.;

2) For construction sites with slopes or thick silt layers, a working platform should be erected;

3) It is a construction site in a shallow water area, and the island construction method should be adopted for construction, and cofferdams are generally used;

4) It is a construction site in a deep water area, and a Bailey beam working platform can be erected.

Step 2: Embedding of long steel sheathing and mud preparation

The functions of the long steel casing 13 are: fixing the pile position, protecting the hole, drilling the wall, guiding the direction of the drill bit, verticality of the hole, treating inclined rock, maintaining the height of the mud level, clearing the hole, and avoiding mud leakage caused by karst non-filling Diffusion and loss of concrete, collapse and shrinkage cavities.

1) The long steel casing 13 is generally made of a steel plate with a thickness of about 20mm, which is processed and manufactured in a factory. The inner diameter of the casing is generally related to the long steel casing, geological conditions, quota, and pile-forming technology.

2) The elevation of the top of the long steel casing 13 should be 1.5m to 2.0m higher than the groundwater level or the water level outside the hole, and should be 0.3m higher than the working surface.

3) Embedding depth of the bottom end of the long steel casing 13: it should run through the karst distribution section 1 and be 1m lower than the lowest level. The bottom end is generally lower than the concrete surface elevation ≮10m, so as to avoid pulling out the casing prematurely, this is because in the karst distribution section 1, the lateral pressure of the pile body concrete on the composite reinforcement cage is too large, which will damage the galvanized steel wire on the composite reinforcement cage Net and dense mesh nylon mesh 11, resulting in two effects: on the one hand, the necking of the cast-in-place pile and the lack of the protective layer of the steel cage; body concrete mixing, affecting the quality of cast-in-place piles, etc.

4) The deviation of the plane position of the long steel casing 13 shall not be greater than 50mm, and the deviation of the verticality of the long steel casing 13 shall not be greater than 1%.

5) The mud consists of water, clay (or bentonite) and additives. The effect of the mud is to infiltrate and fill the gaps in different soil layers in the borehole, so that the leakage of water in the hole reaches the minimum, and maintain a certain pressure in the pile hole 6 to stabilize the hole wall without the long steel casing section. Therefore, the mixing ratio of the mud should be strictly controlled during the hole forming process.

Step Three: Drilling

1) After the pile foundation hole-forming equipment is installed in place, the base and top should be stable, and there should be no inclination, dumping or subsidence during the construction process. At the same time, the top center of the hole-forming equipment or the drill rod, drill bit (hammer) and pile hole 6 centers should be on the same plumb line.

2) The hole-forming operation should be carried out continuously, pay attention to geological changes and take slag samples to determine the geological state and elevation position, especially the unfavorable geology such as karst, and record it in time for checking with the geological profile to determine the parameters of the combined reinforcement cage.

3) When drilling without long steel casing 13, it is necessary to ensure the amount of mud and the specified height of the liquid level before continuing the drilling construction.

4) When the drilling operation is suspended midway, the water level in the pile hole 6 and the relative density and viscosity of the mud should be maintained to prevent the collapse or shrinkage of the long steel casing.

Step Four: Assemble the Reinforcement Cage

1) The composite reinforcement cage is composed of a design reinforcement cage and an additional reinforcement cage.

2) The additional reinforcement cage is composed of additional longitudinal reinforcement 7, additional spiral stirrup 8, additional stiffening ring 9 and so on.

3) The additional reinforcement cage is welded on the design reinforcement cage with support reinforcement 10.

4) The additional longitudinal reinforcement 7 is anchored in the design reinforcement cage by bending, and the anchorage length is not less than LaE.

5) When the design pile diameter is ≯1200mm, the location of the support reinforcement 10 should avoid affecting the conduit and the poured pile foundation concrete; when the design pile diameter is ≥1200mm, add triangular support reinforcement to ensure that the combined reinforcement cage is not easy to lift during lifting and installation. Deformation, increase the overall stability of the reinforcement cage, etc.

6) When the design reinforcement cage and the additional reinforcement cage are installed in combination, the support reinforcement is first welded, and then the additional longitudinal reinforcement 7 and the additional spiral stirrup 8 of the additional reinforcement cage are welded to ensure that the clear distance between the design reinforcement cage and the additional reinforcement cage is consistent .

7) After the additional longitudinal steel bar 7 is bent, the bending part and the end are welded into a whole with a stiffening ring, and the bending angle should not be too large, so as not to affect the installation of the conduit and the pouring of concrete.

Step 5: Combined reinforcement cage design and processing

1) The appearance of the additional reinforcement cage is fully covered with galvanized steel wire mesh and dense mesh nylon mesh in the order from inside to outside.

2) Galvanized steel wire mesh should have good flexibility and plasticity. Even if it is partially subjected to excessive concrete lateral pressure and no desoldering occurs, it can still block the collapse of concrete and the entry of mud into the pile; secondly, the steel wire mesh is galvanized Finally, it has good corrosion resistance and durability. It can be used as the material of the pile body. At the same time, the galvanized steel wire mesh is covered outside the additional reinforcement cage. Design requirements for the protective layer of longitudinal reinforcement, which is why the diameter of the additional reinforcement cage is required to be the diameter of the designed pile diameter 5 and the expansion diameter of the karst unfilled section and above. Therefore, hot-dip galvanized steel wire mesh is generally used, the mesh is diamond-shaped, and the wire diameter is ≮1.0mm.

3) The galvanized steel wire mesh is wound and fixed on the additional reinforcement cage in a manner similar to spiral stirrups. The wire mesh overlaps ≮ 200mm in an overlapping manner, and then is fixed on the additional reinforcement cage with iron wire plum blossoms.

4) The galvanized steel wire mesh is generally arranged in a double-layer dislocation, the dislocation distance is 1/2 the width of the steel wire mesh, and the fixing method is also fixed on the additional steel cage by iron wire plum blossom.

5) The material of dense-mesh nylon mesh is generally HDPE high-density polyethylene with a mesh density of 2000 mesh/100cm2, and it should have the characteristics of high toughness, good elasticity, and corrosion resistance.

6) The full coverage of the dense-mesh nylon mesh is installed on the surface of the galvanized steel mesh. Generally, iron wire @1500mm is used for binding installation. The installation length of the nylon mesh is the length of the additional steel cage.

7) Install the additional reinforcement cage after installing galvanized steel wire mesh and dense mesh nylon mesh, and the net distance between the long steel casing 13 and the long steel casing 13 is generally not less than 35mm (without water environment)/50mm (with water environment), so as to ensure that the long steel casing 13 runs smoothly. plugging etc.

Step 6: Clear the hole

After the hole reaches the depth requirement of the drawing, the hole should be cleaned immediately. The method of hole cleaning is related to the pile foundation hole-forming equipment, pile-forming technology, and geological conditions. For example, a rotary drilling rig should choose a slag-removing drill bit. Clearing holes should meet the requirements of JGJ94 and design drawing requirements of "Technical Specifications for Building Pile Foundations".

When cleaning the hole, the water level inside the long steel casing should be maintained and 1.5-2.0m higher than the groundwater level or the water level outside the hole to prevent the hole wall without the long steel casing section from collapsing.

1) Positive mud circulation hole cleaning method: After the final hole, lift the drill bit or drill cone to 10cm to 20cm from the bottom of the hole. There should be a certain gap between the diameter of the drill bit (hammer) and the long steel casing to avoid direct contact with the casing. Contact, press in the mud with a low relative density (1.1-1.2) at a medium speed, and replace the mud with more suspended drilling slag in the borehole.

2) Mud reverse circulation hole cleaning method: generally suitable for various pile foundation hole forming equipment, divided into two types: pump suction reverse circulation and gas lift reverse circulation: ① pump suction reverse circulation. According to the installation position of the pump, it can be divided into direct suction by submersible mud pump at the bottom of the hole or negative pressure suction on the ground. It is generally suitable for large-diameter piles and deep piles. Pump suction reverse circulation hole cleaning has the advantages of strong suction capacity, short hole cleaning time, and clean hole bottom. However, the amount of mud used by pump suction reverse circulation is relatively large. It is necessary to control the performance and parameters of the mud and at the same time do a good job of waste slurry and residue processing. ②The gas lift reverse circulation process has large pressure difference, fast flow rate and strong slag removal ability, but the gas lift reverse cycle equipment is more complicated, and the slag removal efficiency is easily affected by the selection of the air compressor, the length of the intake pipe and the pipe joint. At the same time, gas lift reverse circulation will cause suction negative pressure at the bottom of the pile hole 6, and maintain the head height of the mud, so as to control the amount of mud that is difficult to flow back into the hole and the suction balance to avoid hole collapse.

3) Slag removal without mud circulation for hole cleaning, which is generally used for rotary drilling rigs. After the hole is completed, use a special slag removal drill bucket to remove the sediment at the bottom of the hole. After the thickness of the drilling slag at the bottom of the hole meets the requirements, special mud preparation measures are adopted Making the bottom of the pile hole 6 form high-viscosity mud, which can protect the hole wall from collapsing and stabilizing and suspend the sediment above the bottom of the hole, and keep the sediment at the bottom of the hole to meet the design and specification requirements.

4) Sediment partial suspension method: suitable for rotary drilling equipment, about 2m away from the final hole (two secondary final holes), the prepared CMC (Shuttle methyl cellulose) solution is transported to the The bottom of the hole is stirred by the rotary drilling machine in the two rounds before the final hole, and mixed with the mud in the lower part of the hole to improve the degree of density and the ability to suspend the sediment, so as to achieve the effect that the local sediment is in suspension.

5) The sedimentation fishing method is suitable for rotary drilling machines. It has one more process than the partial suspension method of sediment. Generally, the sedimentation bucket is used to realize the removal of slag. According to the sedimentation speed of drilling slag in different strata in the mud and the sedimentation thickness within a certain period of time The correlation with the time period determines the slag removal time, and the rainbow sediment detection equipment conducts detection at the same time.

6) The method of deepening the depth of the pile bottom shall not be used as a substitute for clearing the hole.

Step 7: Pouring Concrete Underwater

1) Before pouring underwater concrete, the combined reinforcement cage of the cast-in-situ pile should be hoisted into the pile hole 6 as a whole, and the position of the reinforcement cage should be controlled according to the design elevation and other requirements, and corresponding measures should be taken to fix it on the top of the reinforcement cage to prevent concrete The reinforcement cage rises during the filling process.

2) The concrete protective layer pads are set in advance for the combined reinforcement cage to control the net distance between the reinforcement cage and the hole wall. The protective layer pads should be firmly and reliably set (bundled) on the steel cage, generally arranged in a plum blossom shape, and the distance between them should not exceed 4m.

3) pouring of underwater concrete.

a. Before pouring concrete, the slag thickness index at the bottom of the hole should comply with the "Technical Specifications for Pile Foundations" JGJ94 and the requirements of the design drawings. If it does not meet the requirements, the hole should be cleaned a second time according to the hole cleaning method in the sixth step.

b. Concrete is prepared strictly according to the mix ratio, and the amount and particle size of fine stone and coarse aggregate are well controlled. Every truck of concrete must be inspected on site to reduce construction risks such as segregation of underwater poured concrete and ensure the quality of pile formation.

c. Concrete can be added with an appropriate amount of quick-setting agent to reduce the lateral pressure of the flow of concrete on galvanized steel wire mesh and dense mesh nylon mesh.

d. When pouring concrete, the temperature of the concrete should not be lower than 5°C. When the temperature is lower than 0°C, insulation measures should be taken after pouring concrete.

e. Conduits with a diameter of 200-250mm are used for pouring underwater concrete. The distance from the lower opening of the conduit to the bottom of the hole should be 300-500mm. The depth of the conduit buried in the concrete should be 2-6m. When the pouring speed is fast, there is enough to lift the conduit When the capacity is limited, the buried depth of the conduit can be appropriately increased. Matters needing attention, the reserve amount of primary poured concrete in each pile hole 1 should be calculated according to the requirements of hole diameter and conduit embedding depth, so as to ensure that the conduit is buried below the concrete surface at a depth of ≮0.8m. The formula for calculating the amount of concrete poured at the beginning of pouring:

H _C ＝H _D +H _E

In the formula: H _C — the required pouring depth of the first batch of concrete (m);

H _D — the height from the bottom of the pipe to the bottom of the pile hole (m);

H _E — the buried depth of the conduit (m);

D—diameter of cast-in-place pile (m);

h ₁ — When the concrete in the pile hole reaches HC, the required height of the concrete in the conduit and the hydraulic pressure outside the conduit (m);

_Hw — the height of the concrete in the pile hole from the mud surface of the hole after the initial pouring of concrete, that is, the depth of the mud in the pile hole (m);

γ _w — specific gravity of mud in the pile hole;

γ _C - concrete weight;

d—the inner diameter of the catheter (m);

f. During the pouring process, the position of the concrete surface in the pile hole 6 should be detected from time to time, the buried depth of the conduit should be adjusted in time, and the pile foundation concrete should be poured continuously. After completion, the long steel casing 13 should be pulled out in time by a lifting machine or a vibrating hammer.

g. The elevation of the formed pile top should be 0.5m~1.0m higher than the design elevation to ensure the quality. At the same time, after removing the laitance and roughening, ensure that the strength level and elevation of the pile top concrete meet the specifications and design requirements.

Step Eight: Pile

As shown in Figure 3, the karst non-filled cast-in-situ pile structure is to add additional steel cages, galvanized steel wire mesh and dense nylon mesh covering the surface in the unfavorable geological distribution section such as karst, so as not to need to deal with unfavorable geology such as karst To ensure the thickness of the protective layer of the design reinforcement cage and control the cost requirements of cast-in-place piles.

Referring to Figure 2-4, above the unfavorable geological distribution section (karst distribution section 1) such as karst, adopt the method of Figure 2 to set the reinforcement cage; Below the unfavorable geological distribution section, adopt the method shown in Figure 4 to set the reinforcement cage, and at the same time, the embedding depth of the long steel casing 13 should be lower than a certain depth below the level of the lowest karst distribution section 1, which together constitute the cast-in-place pile structure with unfavorable geological conditions such as karst . The length of the additional reinforcement cage in the karst distribution section 1 of the cast-in-situ pile structure should not be less than the thickness of multi-layer unfavorable geology, and the top and bottom positions of the additional reinforcement cage should exceed the total thickness of the karst and other unfavorable geological distribution sections by a certain distance, so that There is no need to take filling and other treatment measures for the unfavorable geological distribution section, so as to realize the construction of cast-in-situ piles and achieve the purpose of improving quality, reducing cost and increasing efficiency.

Precautions:

1) The net distance between the additional reinforcement cage and the original design reinforcement cage should be ≥ 35mm (without water environment) / 50mm (with water environment), to ensure that the thickness of the protective layer of the design reinforcement cage meets the design requirements. Therefore, in the karst distribution section 1 and the upper part, the diameter of the hole is related to the long steel casing, and should be enlarged by at least 2 times [35mm (without water environment)/50mm (with water environment)], the diameter of the pile hole below the karst distribution section 1 is based on the long steel casing Whether to follow up or not to confirm, if not followed up, the diameter of the pile hole is the design pile diameter, otherwise, it is the same as the diameter of the pile hole in the karst distribution section 1 and above. When constructing parts below the karst distribution section 1 and no long steel casing section is installed, the drill bit (hammer) matching the designed pile diameter needs to be replaced.

2) The parameters of the additional reinforcement cage should be designed and calculated according to the pile diameter, pile length, and the location of the karst distribution section. On the premise of ensuring the pile quality and production safety, the cost input can be controlled and the economic benefit can be improved.

3) After the pile is formed, the mud liquid level is maintained until the initial setting of the concrete, so as to prevent the mud water pressure and the lateral pressure of the concrete on the galvanized steel wire mesh and the dense mesh nylon mesh from being unbalanced, resulting in the destruction of the combined steel cage support structure, and the concrete is not The subsidence of blocking and entry into the karst without filling will cause two effects: on the one hand, the necking of the cast-in-situ pile or the cavity of the pile body, and the lack of the protective layer of the steel cage; Layer and pile body concrete mixing, further affect the quality of cast-in-place piles and so on.

In addition, the construction method of karst non-filled cast-in-situ piles of the present invention can also be applied to geological structures such as soil caves, goafs, and collapsible loess. In terms of mechanical hole-forming equipment in its construction method, it can be common pile foundation hole-forming equipment such as rotary drilling rig, full-casing full-rotary drilling rig, positive and negative circulation drilling rig, impact drilling rig, down-the-hole drilling rig, etc., but it needs to comprehensively consider environmental protection, construction speed, Impact indicators such as usability and automation.

It can be understood that the galvanized steel wire mesh and dense-mesh nylon mesh 11 outside the additional reinforcement cage can also be replaced with a galvanized steel casing, and set and fixed outside the additional reinforcement cage, between the additional reinforcement cage and the designed reinforcement cage There is an annular fill gap. In order to prevent the galvanized steel casing from being deformed or damaged under the lateral pressure during concrete construction, a spiral reinforcement stirrup can be added outside the galvanized steel casing and fixed by spiral welding.

The above-mentioned embodiments are only examples for clearly illustrating the present invention, rather than limiting the implementation. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the embodiments here. However, the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims (10)

1. A kind of karst cast-in-place pile structure without filling, is characterized in that: comprise the design reinforcement cage that is placed in pile hole (6) and set up outside described design reinforcement cage and run through pile hole (6) karst distribution section (1) Additional reinforcement cage; The design reinforcement cage is composed of a plurality of pile body main reinforcements (2), pile body spiral stirrups (3), and pile body stiffening rings (4); The additional reinforcement cage is composed of multiple additional longitudinal reinforcements (7), additional spiral stirrups (8) and additional stiffening rings (9). There is an annular filling gap (12) between the additional reinforcement cage and the design reinforcement cage; The outside of the additional reinforcement cage is fully covered with galvanized steel wire mesh and dense mesh nylon mesh (11); or, A galvanized steel casing is arranged outside the additional reinforcement cage. 2. The karst unfilled cast-in-place pile structure according to claim 1, characterized in that: the two ends of the multiple additional longitudinal reinforcements (7) in the additional reinforcement cage are bent and anchored in the design reinforcement cage, and the The above-mentioned additional longitudinal reinforcement (7) adopts additional stiffening ring (9) to weld and fix at the bend and the end. 3. The karst non-filled cast-in-situ pile structure according to claim 1, characterized in that: the galvanized steel wire mesh is overlapped and overlapped in a manner similar to spiral stirrups, and is fixed on the additional steel bar in a quincunx-shaped manner with iron wires On the cage, the dense-mesh nylon mesh is completely covered on the outside of the galvanized steel wire mesh, and is firmly fixed with iron wires at a certain distance. 4. The karst cast-in-place pile structure without filling according to claim 1, characterized in that: the diameter of the additional longitudinal reinforcement cage is generally increased by 100mm on the basis of the designed pile diameter (5) of the cast-in-place pile in a water environment, Anhydrous environment will increase by 70mm. 5. The karst unfilled cast-in-situ pile structure according to claim 1, characterized in that: the diameter of the pile hole (6) is larger than the designed pile diameter (5) of the cast-in-place pile, and the karst distribution section (1) and above parts The diameter of the pile hole (6) is the inner diameter of the long steel casing (13), and is not less than the design pile diameter (5) + 2 times the thickness of the design reinforcement cage protective layer + 2 times the thickness of the additional reinforcement cage protection layer; in the karst distribution section (1 ) diameter of the pile hole (6) is based on whether the long steel casing (13) is followed up or not. If the long steel casing (13) is not followed up, the diameter of the pile hole (6) is generally the design pile diameter ( 5), otherwise it is the same as the pile hole (6) diameter of the karst distribution section (1) and the above position. 6. The karst non-filled cast-in-situ pile structure according to claim 1, characterized in that: spiral reinforcement stirrups are added outside the galvanized steel casing. 7. The karst unfilled cast-in-place pile structure according to claim 1, characterized in that: the design reinforcement cage and the additional reinforcement cage are welded and fixed by supporting reinforcement bars (10) to form a combined reinforcement cage. 8. A karst non-filled cast-in-situ pile construction method structure, characterized in that it includes: Site leveling, stake setting, mud preparation, long steel casing (13) production, material preparation, etc.; The pile foundation hole-forming equipment is matched with the long steel casing (13), and the cast-in-situ piles are excavated to the depth of the rock-socketed. A pile hole (6) is formed in the steel casing (13), and the bottom elevation of the long steel casing (13) is lower than a certain depth at the lowest position of the karst distribution section (1); According to the starting position of unfavorable formations such as karst without filling, determine the position and length of the additional reinforcement cage on the design reinforcement cage; Design reinforcement cage fabrication, additional reinforcement cage fabrication; Additional reinforcement cage installation, the outer side is covered with galvanized steel wire mesh and dense mesh nylon mesh (11) or set with galvanized steel casing to form a composite reinforcement cage structure for cast-in-situ piles; The cast-in-place pile combination reinforcement cage in the pile hole (6) is hoisted, the thickness of the sediment is measured and the hole is cleaned for the second time; The conduit is installed, pouring pile body concrete into the pile hole (6) to form a cast-in-situ pile; Mechanical equipment pulls out the long steel casing. 9. The construction method of karst unfilled cast-in-situ pile structure according to claim 8, characterized in that: the net distance between the additional longitudinal reinforcement cage and the originally designed reinforcement cage should be ≥ D mm; Among them, for an anhydrous environment, the value of D is 35, and for a water environment, the value of D is 50; When pouring concrete, the bottom end of the long steel casing is generally ≮10m below the level of the concrete pouring surface. 10. karst no-fill cast-in-place pile structure construction method according to claim 8, is characterized in that: the diameter of described long steel casing is at least larger than the design pile diameter (5) of cast-in-place pile by 8 mm; Wherein, for an anhydrous environment, the value of S is 140, and for a water environment, the value of S is 200.