CN112081118A - A kind of pile-anchor support foundation pit deepening reinforcement support structure and construction method thereof - Google Patents

Abstract

The invention relates to a pile-anchor supporting foundation pit deepening reinforcing and supporting structure and a construction method thereof, wherein the reinforcing and supporting structure comprises an original supporting pile (1), a waist beam (3) and an original prestressed anchor cable in an original pile-anchor supporting system, a newly-increased supporting pile (2), a newly-increased prestressed anchor cable (4) and a newly-arranged crown beam (5); the newly-increased supporting piles (2) are arranged among the original supporting piles (1), the newly-increased supporting piles (2) penetrate through the new excavation depth of the whole foundation pit, the top parts of the newly-increased supporting piles are flush with the top parts of the original supporting piles (1), and the newly-increased supporting piles are connected into a whole through newly-arranged crown beams (5) in a pouring mode; the newly added prestressed anchor cables (4) are distributed between the new pile and the old pile, and the outer ends of the newly added prestressed anchor cables are fixed on the wale (3). The invention adopts a reinforcing mode of inserting long supporting piles and prestressed anchor cables between the original supporting piles, and forms a unified whole with the original supporting structure through the connection of the waist beam, the anchor cable and the newly-arranged crown beam, thereby effectively increasing the integral rigidity and the cooperative deformation capability of the enclosure structure and enhancing the bearing capacity of the enclosure structure.

Description

A kind of pile-anchor support foundation pit deepening reinforcement support structure and construction method thereof

technical field

The invention relates to the technical field of foundation pit engineering support and reinforcement, in particular to a pile-anchor support foundation pit deepening reinforcement support structure and a construction method thereof.

Background technique

With the rapid development of economy and urbanization, there is less and less land available for construction. In order to meet the various needs of people's living and working space, the utilization and development of urban underground space has become a hot spot that more and more people pay attention to. The excavation scale and depth of the foundation pit are getting larger and larger, and the difficulty of supporting the foundation pit and the complexity of the surrounding environment have also increased. When the foundation pit supporting structure has been or will be completed, but due to the modification of the design plan, such as the basement addition layer design, etc., the foundation pit needs to be further excavated on the basis of the original design.

However, the internal force value of the foundation pit caused by the deepening and excavation of the foundation pit will exceed the design value of the internal force value of the original foundation pit support plan, which will inevitably lead to the original foundation pit support design cannot meet the support strength requirements. The stability impact is huge. This makes the existing foundation pit face two choices: one is to give up the existing foundation pit and re-design the support, or to design and strengthen on the basis of the original support. For the construction unit, the safety and economic benefits of the foundation pit are the main considerations. Obviously, if the existing foundation pit supporting structure is abandoned, it will cause a lot of waste of resources and increase the project cost, but if the existing foundation pit supporting structure can be used for design and strengthening, at the same time, reasonable design and transformation can reduce the cost. The cost is bound to achieve good benefits for the project. Therefore, it is of great value to strengthen the design of the support structure on the original support structure and ensure the safety and stability of the foundation pit during the construction process.

In the prior art, the reinforcement method of the supporting structure after the excavation of all the foundation pits where the original supporting method is the pile-anchor support is mainly the reinforcement method of adding layers of anchor cables, that is, when the supporting piles are in the original design After the construction of the prestressed anchor cable is completed, a reinforcement method of adding a layer of prestressed anchor cable in a suitable position. Among them, the traditional pile-anchor support system mainly includes: support piles, anchor cables, waist beams, crown beams, etc. The supporting pile is vertically driven into the soil layer on the side wall of the foundation pit; the crown beam and the supporting pile are poured together at the top of the pile; the prestressed anchor cable is driven into the soil layer through the waist beam, and the waist beam is set along the side wall of the foundation pit to make The anchor cable, the supporting pile and the crown beam form a whole that can be deformed cooperatively.

Although the above anchor cable reinforcement method can make up for the insufficient bearing capacity of the original support system caused by the insufficient depth of the original support pile due to the deepening and excavation of the foundation pit to a certain extent, it has the following aspects: Disadvantages:

(1) The function of adding anchor cables is to strengthen the connection strength between the supporting pile body and the soil on the pit wall, and indirectly limit the displacement of the soil on the pit wall through the supporting pile, which can reduce the excessive displacement of the embedded end of the supporting pile. , to make up for the weakening of its bearing capacity, but it has not fundamentally solved the problem of insufficient embedding depth of the original support piles. When the pressure is high, this reinforcement method is easy to fail, causing great safety hazards to the construction.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a pile-anchor support foundation pit deepening reinforcement support structure and a construction method thereof with better reinforcement effect, so as to solve the problem of the pile-anchor support system caused by the deepening and excavation of the foundation pit. The problem of insufficient protective strength.

In order to solve the above problems, the pile-anchor support foundation pit deepening and strengthening support structure according to the present invention includes the original support pile in the original pile-anchor support system, and the waistband arranged on the original support pile. The beam and the original prestressed anchor cables whose outer ends are fixed on the waist beam, as well as the new growth support piles, the newly added prestressed anchor cables and the new crown beams; the new growth support piles are in the original support The piles are arranged between the piles and the two are kept on the same plane. The newly increased support piles run through the new excavation depth of the entire foundation pit, and the tops of the new growth piles are flush with the tops of the original support piles and pass through the new crown beams. The pouring and connection are integrated; the newly added prestressed anchor cables are distributed between the original support piles and the newly increased support piles, and their outer ends are fixed on the waist beam.

Preferably, the diameter of the newly grown support pile is equal to or greater than the diameter of the original support pile.

Preferably, the newly grown support piles are arranged at intervals of one or two or more of the original support piles.

The present invention also correspondingly provides a construction method for the pile-anchor support foundation pit to deepen and strengthen the support structure, and the construction method includes:

Break the original crown beam in the original pile anchor support system, and try to avoid breaking the main reinforcement of the original support pile during the breaking process;

Interpolate and implement new growth support piles as required;

After all the new growth support piles are implemented, the construction of the newly added prestressed anchor cables and the pouring of the new crown beams are completed. in the new crown beam.

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

1. The present invention adopts the reinforcement method of "inserting long support piles + prestressed anchor cables between the original support piles", and the newly increased support piles run through the entire excavation depth of the foundation pit, and are connected by the waist beam and the newly installed crown beam. , forming a unified whole with the original supporting structure, which can effectively increase the overall stiffness and cooperative deformation capacity of the enclosure structure, and strengthen the bearing capacity of the enclosure structure. And the reinforcement form of the present invention proves that the deformation control effect of the foundation pit is better through numerical simulation, field test and monitoring. 2. The present invention utilizes the existing foundation pit supporting structure to carry out design enhancement, carries out reasonable design transformation and construction, reduces the cost of construction, and obtains good benefits for the project.

Description of drawings

The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a reinforced support structure provided by an embodiment of the present invention.

FIG. 2 is a top view of distribution among piles according to an embodiment of the present invention.

FIG. 3 is a sectional view of the construction of the prestressed anchor cable according to the embodiment of the present invention.

In the picture: 1—the original supporting pile, 2—the newly increased supporting pile, 3—the waist beam, 4—the newly added prestressed anchor cable, 5—the new crown beam.

Detailed ways

First of all, it should be noted that although the long and short pile support system is well known in the prior art, this is a foundation pit support method, and the present invention proposes a pile anchor support foundation pit depth reinforcement The support structure is a reinforcement method for foundation pit support. The difference lies in the premise of deepening the excavation, strengthening the structure, and inserting long supporting piles between the original supporting piles. Different premise involves different fields.

Referring to FIGS. 1 and 2 , an embodiment of the present invention provides a pile-anchor support foundation pit deepening reinforcement support structure, which mainly includes the original support pile 1 in the original pile anchor support system, and the original support pile 1 provided in the original pile anchor support system. The upper waist beam 3 and the original prestressed anchor cable whose outer end is fixed on the waist beam 3, as well as the newly increased support pile 2, the newly added prestressed anchor cable 4 and the new crown beam 5.

The new growth support pile 2 is arranged between the original support pile 1, and the inner sides of the two are flush and kept in the same plane. The new growth support pile 2 runs through the new excavation depth of the entire foundation pit, and its top is the same as the original support pile 1. The top is flush and connected as a whole by the new crown beam 5 pouring. Among them, the new growth support pile 2 and the original support pile 1 are kept on the same plane, and will not affect the excavation face of the foundation pit.

The newly added prestressed anchor cables 4 are distributed between the original support piles 1 and the newly increased support piles 2 and their outer ends are fixed on the waist beam 3 . In practical applications, the specific arrangement form, spacing and quantity of prestressed anchor cables and anchor cables, as well as applied loads, depend on the specific requirements of the project.

The diameter of the newly grown supporting pile 2 is equal to or greater than that of the original supporting pile 1 . In practical applications, the newly increased support pile 2 can increase the section size according to the design while meeting the sufficient embedding depth to strengthen the rigidity of the pile body.

The new growth support piles 2 are arranged at intervals of one or two or more original support piles 1 . In practical applications, according to the actual situation of the foundation pit, and comprehensively considering the safety and economic benefits of the foundation pit, different layout spacings can be selected. The weaker places can be appropriately increased in density depending on the situation. Figure 1 shows the situation of "adding a long support pile every two original support piles".

Based on the reinforced support structure disclosed in the above embodiments, the embodiments of the present invention provide a construction method correspondingly, and the construction method mainly includes the following steps:

1. Remove the original crown beam in the original pile anchor support system, and try to avoid breaking the main reinforcement of the original support pile 1 during the removal process.

2. Interpolate and implement new growth support piles 2 as required.

3. After the implementation of all the new growth supporting piles 2, complete the construction of the newly added prestressed anchor cables 4 and the pouring of the new crown beams 5. During the pouring process, try to straighten the main reinforcement of the original supporting piles 1 and be close to the principle. Anchorage is placed in the newly installed crown beam 5.

Among them, in addition to the content pointed out and emphasized above, the construction technology of the newly increased support pile 2 in step 2, the newly added prestressed anchor cable 4 in step 3 and the new crown beam 5 can refer to the existing technology itself. . However, in order to facilitate those skilled in the art to understand the content of the solution, the detailed implementation content is still given below.

In the above step 2, the implementation of the new growth support pile 2 can refer to the following:

①Hole forming process and technical requirements

(1) The hole can be formed by mechanical mud retaining wall;

(2) The preparation work should be fully prepared before drilling, the hole forming construction should be completed at one time without interruption, and the drilling should not be stopped for no reason; the interval between hole forming and pouring should not exceed 24 hours;

(3) The drilling speed should be controlled when opening the hole to prevent collapse in the hole and inclination of the hole;

(4) The pile position deviation is less than or equal to 50mm, the verticality deviation is less than 1%, and the thickness of the sediment at the bottom of the pile is less than or equal to 200mm;

②Rebar cage production

(1) The dimensions of the steel cage should meet the design requirements, and the allowable deviations are as follows:

Spacing between main bars: ±10mm Spacing between stirrups: ±20mm

Steel cage diameter: ±10mm Total length of steel cage: ±100mm

Reinforcing cage protection layer: ±20mm

(2) The main reinforcement of the reinforcement cage can be connected by lap welding. When using lap welding, the length of the lap joint shall be welded on one side, the length of the weld shall not be less than 10 times the diameter of the steel bar, and the length of the double-sided welding shall not be less than 5 times the diameter of the steel bar. The reinforcing bars in the cage and the main bars are connected by welding, and the stirrups and the main bars are connected by binding or spot welding;

(3) The steel cage should be made in a whole section. Measures should be taken to prevent deformation during lifting, transportation and installation. The outer hoop or inner hoop reinforcement should be set at the lifting point. Pay special attention to the welding quality. The number of joints on the same section shall not be greater than 50%, and the distance between adjacent joints shall be 35d and not less than 500mm; the placement direction of the reinforcement cage is consistent with the design direction.

③Pile body concrete pouring

(1) When the bored pile reaches the design elevation of the bottom of the hole, it shall be checked and accepted in time, and the pile body shall be poured in time after the acceptance is passed;

(2) The concrete mix ratio should be determined by calculation or trial mix;

(3) The materials used shall have quality certificates and have passed the inspection before they can be used;

(4) When mixing concrete, it should be strictly measured according to the mixing ratio;

(5) The concrete of the pile body should be poured by the conduit method. The concrete must have good workability and fluidity. The slump is generally 180~220mm.

(6) The pouring conduit should be buried in the concrete surface. It is strictly forbidden for the conduit to lift the concrete surface. The dismantling time of the conduit should be strictly controlled. Concrete pouring should be carried out continuously. When pouring concrete, special personnel should record the buried depth of the conduit and the height difference between the inner and outer concrete surfaces of the conduit, so that the conduit can be lifted and removed in time.

(7) Before the construction of the crown beam, the floating slurry on the top of the pile should be chiseled and cleaned up, and the length of the exposed steel bars above the top of the pile should meet the anchoring requirements.

In the above step 3, the implementation of the newly added prestressed anchor cable 4 can refer to the following:

①Prestressed anchor cable into hole

The prestressed anchor cable is made of mechanical holes, and the inclination angle of the anchor hole is 12-20° horizontally. The anchor hole should be drilled with a pipe to prevent the collapse in the hole; considering the influence of sediment, in order to ensure the depth of the anchor cable, The actual drilling depth should be greater than the design depth by 0.50m. After the anchor hole is formed, the sediment in the anchor hole must be cleaned, and strive to clean it up.

②Prestressed anchor cable setting

The rod body of the prestressed anchor cable should be straight, rust-removed, and oil-removed before use, and the material should be cut strictly according to the design size; When the stress anchor cable and grouting pipe are put into the anchor hole, they should be placed along the center line of the anchor hole to avoid the disturbance and collapse of the hole wall soil. If the hole wall soil collapses, the anchor cable should be pulled out to remove the collapsed soil; After entering the anchor hole, it should be blocked and grouted in time.

③ Prestressed anchor cable grouting

The grouting body should be prepared in strict accordance with the design requirements and must not be changed at will. When grouting, the grouting pipe should be inserted to 50-100mm from the bottom of the hole, the grouting pressure should reach 0.60MPa, and the pressure should be stabilized for 2 minutes, until the slurry overflows from the orifice, otherwise the grouting should be carried out. After grouting, the anchor cable shall not be disturbed until the strength of the grout does not meet the design requirements.

④Prestressed anchor cable tensioning and locking

When the strength of the slurry reaches 85% of the design strength, tensioning and locking are performed. After the tensioning and locking are normal, the exposed prestressed tendons shall not be removed, so as to facilitate the supplementary tensioning in the later stage.

actual case

In a deep excavation foundation pit project in Lanzhou, the project adopts the pile-anchor support system. Due to the later design change (basement addition), after discussion, the original support structure should be reinforced and designed, so the commonly used in the existing technology is adopted. However, the deformation control of the foundation pit is an important indicator to test whether the supporting structure is effective, and this reinforcement method has not achieved the desired effect: after using this reinforcement method, the horizontal displacement of the foundation pit soil , vertical displacement, deep soil displacement of supporting piles and other foundation pit deformation indicators do not meet the requirements, it can be seen that this reinforcement scheme is not suitable for some foundation pits where the excavation is deep and the lateral soil pressure of the foundation pit is large. Be applicable.

Therefore, based on the actual situation of the foundation pit (the excavation of the foundation pit is deep and the lateral earth pressure of the foundation pit is large), it is found that the essence of the problem is that the depth of the original support pile is insufficient. The reinforcement scheme of bearing capacity, that is, the reinforcement scheme of "inserting long supporting piles + prestressed anchor cables between the original supporting piles" of the present invention: after a rigorous numerical simulation analysis in the early stage, the results show that the deformation indicators of the foundation pit are consistent with the foundation pit. The requirements of relevant specifications, and the indicators are within the safe range. In the later stage, on-site testing was carried out, which is on-site construction, and in conjunction with on-site monitoring of foundation pit deformation, the reinforcement effect of this reinforcement method was further verified through monitoring data, and compared with the previous simulation results. The reinforcement structure of inserting long supporting piles + prestressed anchor cables between the piles can well control the deformation of the foundation pit, and can provide a strong guarantee for the deepening and reinforcement of the pile-anchor support foundation pit.

The technical solutions provided by the present invention have been introduced in detail above. The principles and implementations of the present invention are described herein by using specific examples, and the descriptions of the above embodiments are only used to help understand the method and the core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can also be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (4)

1. A pile-anchor support foundation pit deepening reinforcement support structure is characterized in that, the reinforcement support structure comprises the original support pile (1) in the original pile anchor support system, and the original support pile (1) provided in the original support The waist beam (3) on the pile (1) and the original prestressed anchor cable whose outer end is fixed on the waist beam (3), as well as the newly increased supporting pile (2) and the newly added prestressed anchor cable (4) and the new crown beam (5); the new growth support piles (2) are arranged between the original support piles (1) and the two are kept in the same plane, and the new growth support piles (2) Through the new excavation depth of the entire foundation pit, the top of the top is flush with the top of the original support pile (1) and is connected by pouring the new crown beam (5) into one; the newly added prestressed anchor cable (4) Distributed between the two piles of the original support pile (1) and the new growth support pile (2) and the outer ends thereof are fixed on the waist beam (3). 2 . The reinforced support structure according to claim 1 , wherein the diameter of the newly increased support pile ( 2 ) is equal to or greater than that of the original support pile ( 1 ). 3 . 3. The reinforced support structure according to claim 1, characterized in that, the newly increased support piles (2) are arranged at intervals of one or two or more of the original support piles (1). 4. a construction method of pile-anchor support foundation pit deepening reinforcement support structure according to claim 1, is characterized in that, this construction method comprises: Break the original crown beam in the original pile anchor support system, and try to avoid breaking the main reinforcement of the original support pile (1) during the breaking process; Interpolate and implement new growth support piles (2) as required; After all the new growth support piles (2) are implemented, the construction of the newly added prestressed anchor cables (4) and the pouring of the new crown beams (5) are completed, and the original support should be as straight as possible during the pouring process. The main reinforcement of the guard pile (1) is anchored and poured in the new crown beam (5) according to the principle of proximity.

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