CN107642040A - Construction method of super large diameter hollow pile group anchorage - Google Patents

Abstract

The invention discloses a construction method for super large-diameter hollow pile group anchorage, which includes: 1) Excavating a plurality of pile holes from top to bottom to the bottom of the pile; mold, and fill rockfill grouting between the hole wall and the inside; 2) set the inner mold inside the outer mold, then set the steel cage and the grouting pipe between the inner mold and the outer mold, and then pour concrete; 3) Carry out secondary grouting to the bottom of the pile through the grouting pipe until the load-bearing requirements are met; 4) Pre-embed the cap to connect the steel bars at the top of the pile, and install the capping inner mold to cap the pile; wait until the pile body and the capping concrete on the pile top reach After the strength, the cap formwork is installed, and finally the cap and the anchorage system are poured; among them, the calibers of the pile holes, the inner mold, and the outer mold all decrease in steps from top to bottom. The ultra-large-diameter hollow pile group anchorage constructed by this construction method has excellent bearing capacity.

Description

Construction method of super large diameter hollow pile group anchorage

technical field

The invention relates to a suspension bridge anchorage, in particular to a construction method for an ultra-large-diameter hollow pile group anchorage.

Background technique

The load-bearing components of the suspension bridge are mainly composed of three parts: the main cable, the bridge tower and the anchorage. The self-weight and main load of the bridge structure are transmitted to the bridge tower through the main cable, while the two ends of the main cable are only anchored by the anchorage structure, and its internal force is transmitted to the foundation through the anchorage. Therefore, the bearing capacity of the anchorage structure is the decisive factor for the suspension bridge. A key building block for overall stability.

Current status of gravity anchorage foundations of highway suspension bridges in China: The most commonly used anchorage bearing scheme in China is gravity anchorage. The friction between them is used to balance the horizontal tension of the anchor cable. The construction scheme of suspension bridge anchorage includes underground diaphragm wall, caisson and other schemes, and its characteristics include:

(1) Construction scheme of underground diaphragm wall anchorage

This scheme is the most commonly used and is suitable for a variety of geological conditions. In this scheme, the cofferdam of the underground diaphragm wall is firstly constructed. After the construction of the cofferdam is completed, the reinforcement mesh is lowered in the foundation pit, the concrete is poured in layers, and finally the reinforced concrete anchorage structure is formed. Among them, the outsourcing range of the underground diaphragm wall is much larger than the stress range of the anchorage structure. Like other support systems, its function is only to retain soil and water, and does not participate in sharing the load of the main cable, resulting in a great waste of materials. At the same time, the construction of the underground diaphragm wall requires the use of special machines such as slot milling machines. When constructing in strata with rich groundwater, it is also necessary to pay attention to the occlusal water stop between the wall widths, which requires high construction requirements, so the cost is relatively expensive.

(2) Construction scheme of caisson anchorage

The scheme is to take soil in a large-volume shaft, and the shaft structure sinks synchronously under the action of its own weight to form a basic structure. This kind of wellbore structure has huge volume and good integrity, and its bearing capacity can reach tens of thousands of tons. However, restricted by the construction method, the soil around the caisson is inevitably cut during the sinking process, resulting in excessive relative displacement, which destroys the frictional resistance of the soil around the caisson, and results in a serious loss of the vertical bearing capacity of the caisson foundation. Moreover, during the construction process, the self-weight required for caisson sinking often exceeds the structural strength limit, and construction in uneven geological soil layers is prone to inclination, which is extremely difficult to correct. Therefore, the caisson scheme has not been widely used in the anchorage construction of suspension bridges in recent years.

It can be seen from the above two schemes that the general volume of the gravity anchorage is huge, which determines its characteristics of large excavation volume, large amount of concrete, long construction period and high cost. Taking a large-scale suspension bridge under construction in Hunan as an example (Fig. 10), the tension of the main cable is as high as 8.75×10 ⁵ kN, and the anchorage on one side is in the cohesive soil weathered rock stratum, and the traditional underground diaphragm wall gravity anchorage foundation is adopted. The concrete consumption of the gravity anchor is as high as 160,000 cubic meters, accounting for 90% of the total concrete consumption of the whole bridge, and the cost is 137 million. The total cost of the anchorage on both sides is 15% of the total cost of the whole bridge, which shows its importance.

Although the gravity-type anchorage structure load-bearing scheme is the most widely used, its fundamental defects lie in the completely abandoned soil resistance and excessive self-weight. The bearing principle of the gravity anchor is to balance the vertical component force of the main cable by its own huge counterweight, and to balance the force of the main cable through the frictional resistance (f=0.2G) or embedded force generated between the anchorage foundation and the base surface. Horizontal component force, where the horizontal component force is the main part of the main cable load. Another very important horizontal load-bearing factor in the design of the gravity anchorage scheme—the passive resistance of the anchorage tension surface soil is completely ignored, so in order to achieve the purpose of increasing the base friction force, the anchorage volume must be designed It is very large, which not only causes excessive waste of materials, but also requires a very high load-bearing capacity of the base bearing layer soil due to excessive self-weight. This defect is the main reason for the high cost of the gravity anchorage structure. Widespread promotion of suspension bridges.

(3) Group pile anchorage scheme

The pile group foundation is composed of piles and caps. It is suitable for geological conditions with high shear strength and can fully exert the resistance of the pile side soil to resist horizontal loads. It is a commonly used horizontal bearing scheme. The load transfer route is that the upper load is distributed to each pile through the cap, and the foundation pile transfers the load to the deep foundation. In this process, the strength of the pile body and the resistance of the soil around the pile are the key factors determining the horizontal bearing capacity. The diameter of the pile body The larger the value, the stronger the strength of the pile body. At present, the hole diameter limit of domestic large-diameter pile drilling rigs is 3-5m, which is not enough to resist the tens of thousands of tons of main cable horizontal tension on the anchorage. Therefore, the pile group foundation bearing scheme for the anchorage requires a pile diameter of more than 10 meters. pile.

According to the principle of structural mechanics, when the two ends of the foundation pile structure bearing uniform load are fixed at one end and hinged at one end, the maximum bending moment of the pile body is about 1.5 times that of the fixed support at both ends. Both ends must be fixed as much as possible to reduce the internal force of the pile body. Generally, the bottom of the pile can be fixed by embedding it into the bedrock, while the top of the pile can only meet the condition of fixed support by increasing the stiffness of the cap. The height of the cap will reach tens of meters, which will greatly increase the volume of the cap, which is not conducive to structural optimization. If the hollow pile structure is used, the thickness of the cap that meets the fixed support conditions can be greatly reduced. The hollow pile scheme not only reduces the self-weight of the foundation, saves the cost, but also has no greater bending resistance compared with the solid pile. reduce. It can be seen that the hollow structure of the foundation pile is the only way for the super large diameter pile group scheme of the anchorage foundation.

Improvement of super-large-diameter corrugated steel cofferdam excavated hollow foundation pile scheme: The construction scheme of super-large-diameter piles for anchor pile group foundations needs to meet two principles: one is to ensure that the hole does not leak or collapse during the hole forming process, and the other is not to damage the surrounding piles. Excessive soil disturbance will destroy soil resistance. At present, my country's drilling rig technology has developed to the point where large-diameter bored piles with a diameter of 4 to 5 m can be completed, but ultra-large-diameter piles with a diameter of more than 10 m cannot be drilled at present. half of the force) is the main reason for limiting its development. This kind of construction plan is difficult to ensure water stop and no collapse of the hole during the hole forming process of super-large diameter piles, and cannot meet the above principles, so it should not be adopted.

Anhui Provincial Expressway Corporation once proposed a method of implanting root keys on the side wall of traditional caisson foundations to form a root foundation bearing method (as shown in Figure 11, see patent literature: root foundation and construction method, patent number 200610038147.5), this The method is different from the traditional caisson foundation and pile foundation, the structure form is more complicated, the force mechanism when it interacts with the soil is not clear, and the settlement deformation is also difficult to predict. Because this method is still based on the caisson structure, the soil will be cut during the construction process, destroying the side friction of the soil, and the concrete drill inserted into the wall of the cylinder will obviously disturb the soil around the cylinder, destroying the resistance of the soil, so This scheme is also not suitable for the construction of piles with super large diameter piles.

Contents of the invention

The purpose of the present invention is to provide a construction method for super large-diameter hollow pile group anchorage. The super-large-diameter hollow pile group anchorage constructed by this construction method has excellent bearing capacity, and also has the characteristics of saving the volume of bored piles and shortening the construction period. Thereby making it have significant economic benefits.

In order to achieve the above object, the present invention provides a super-large-diameter hollow pile group anchorage, which includes a super-large-diameter hollow pile group, a cap and an anchoring system; the super-large-diameter hollow pile group is composed of a plurality of vertical piles, The bottom end of the body is embedded in the rock-soil body and the upper end is embedded in the bottom end of the cap; the anchor system is set on the top of the cap to connect the main cable; the pile body is a hollow pile body, and the inner diameter of the pile body Both the outer diameter and the outer diameter decrease stepwise from top to bottom.

The invention provides a construction method for super large-diameter hollow pile group anchorage, comprising:

1) Excavating multiple pile holes from top to bottom to the bottom of the pile: while excavating each pile hole, set an outer mold inside the pile hole, and fill the hole wall and the inside with rock-fill grouting;

2) An inner mold is set inside the outer mold, and then a reinforcement cage and a grouting pipe are arranged between the inner mold and the outer mold, and then concrete is poured;

3) Carry out secondary grouting to the bottom of the pile through the grouting pipe until the bearing requirements are met;

) Pre-embed the cap to connect the steel bars at the top of the pile, and install the capping inner mold to cap the pile body; after the pile body and the capping concrete on the pile top reach the strength, install the cap form, and finally pour the cap and the anchoring system;

Among them, the calibers of pile holes, inner molds, and outer molds all decrease stepwise from top to bottom.

In the above technical scheme, the present invention successfully solves the pile-forming problem of super-large-diameter piles by adopting the scheme of internal mold manual digging; upper anchor block, loose cable saddle and front support) three parts. The ultra-large-diameter hollow pile group is the main flexural member of the system. The bottom end is embedded in the bedrock, and the top end is embedded in the cap to a certain depth. The outer diameter of the pile decreases stepwise from top to bottom, and the diameter of the pile does not change when it enters the micro-weathered rock to achieve the condition of not collapsing the hole, and the inside of the pile body is a hollow structure (see Figure 12 for the construction drawing); The inner and outer molds are used inside the pile, and grouting is filled between the outer mold and the hole wall to form a drilled and buried hollow pile; during the construction process, the side wall can be guaranteed not to collapse, and the inner, outer mold and pile structure can be integrally poured. From the perspective of structural optimization, when the bottom of the pile is supported in the bedrock, the pile diameter at the bottom can be appropriately reduced to form a vertically variable cross-section pile with a large top and a small bottom. This type is more economical in terms of the amount of steel and concrete, and the force characteristics are perfectly unified with the manual excavation construction scheme, and the construction technology is more mature.

Compared with solid pile groups, the present invention has the following advantages:

1) Hollow structure that better meets the force characteristics

For the pile group foundation, in order to effectively distribute the upper load and give full play to the bearing capacity of the pile group, it is necessary to ensure that the size of the cap must correspond to the diameter of the foundation pile. The larger the foundation pile, the larger the cap size. At the same time, in order to reduce the maximum bending moment of the pile body, it is also required to form a fixed support connection at the pile end, and the stiffness of the cap is much greater than that of the pile body. The outer diameter of super-large-diameter piles can reach more than 10 meters. Based on the above considerations, the corresponding cap thickness will reach tens of meters. Such a large-volume cap not only increases the self-weight of the anchorage foundation, but also increases the bearing capacity of the lower bearing layer. It puts forward a great test, and wastes the volume of concrete, which increases the cost of the project. In order to solve the problem of excessively large caps, the foundation piles must be set in a hollow structure, thereby greatly reducing the size of the foundation piles and the volume of the caps, and effectively solving the adverse effects of super-large caps.

In addition, the foundation pile is the main part of the bending resistance, and its bending performance is directly related to the moment of inertia I of the bending section. The advantage of the hollow structure of the foundation pile is that although the net area of the circular section is much smaller than that of the solid pile, the loss value of the section moment of inertia I is very weak (for example, the inner diameter of the pile is half of the outer diameter, and the inertia The moment is only lost by 7%). In addition, under the bending condition of the pile section, the maximum bending moment is located on the outside of the pile section. In order to give full play to the tensile performance of the steel bar, the stressed main reinforcement is arranged at the maximum bending moment on the section, so the hollow annular section makes more use of the stressed main reinforcement. layout.

2) Realization of secondary grouting at pile bottom

The pre-buried grouting hole is used to press the concrete slurry into the bottom of the pile under high pressure, which makes the pile body slightly lifted, which is equivalent to applying prestress to the bottom of the pile. This process not only strengthens the soil layer at the bottom of the pile, but also greatly reduces the post-construction settlement of the pile body. Moreover, when the bearing layer is a hard soil layer, the reverse lifting of the pile body after the second grouting is equivalent to a test of the bearing capacity of the hollow pile. According to the corresponding relationship between the grouting pressure σ and the lifting amount Δ of the hollow pile, it can be back-calculated The allowable bearing capacity of the pile is obtained to check the design bearing capacity of the single pile. However, the traditional solid pile structure is limited by the excessive self-weight and the huge pressure of the concrete entity, and the concrete grout cannot be injected through the grouting pipe. The realization of secondary grouting is a unique advantage of the hollow pile structure.

3) Staircase deformation cross-section structure with uniform force characteristics and construction technology

When the lower end of the ultra-large-diameter hollow pile is embedded in the bedrock, and the upper end is embedded in the bottom of the cap to a certain depth, the bending moment distribution of the pile body presents the characteristics that the upper and lower ends are large and the middle is small. Since the lower end is embedded in the bedrock, the bending rigidity is relatively large, so the section of the pile bottom can be optimized, and the diameter of the pile bottom can be appropriately reduced to achieve the purpose of saving materials. However, the diameter of the pile top is relatively large, and a large bending stiffness can also be achieved by embedding the cap. In summary, setting the pile diameter from top to bottom as a step-wise decreasing scheme can give full play to the bending resistance of the pile body. From the construction point of view, the stepped variable section pile diameter is not only conducive to the hoisting of construction equipment, but also ensures the tightness of pouring between the upper and lower adjacent rings to a greater extent, and the construction process is simpler.

4) Manual digging construction of corrugated steel retaining wall

For the excavation construction of super-large diameter piles, the scheme of corrugated steel cofferdam retaining wall and manual digging is adopted. Compared with the traditional caisson foundation, the artificial hole-forming method has the least disturbance to the soil around the pile, and can retain the friction of the soil around the pile to the greatest extent, and the gap between the corrugated steel cofferdam and the surrounding soil wall is poured with concrete. , the frictional resistance around the pile can be increased several times. However, the traditional drilling method is not only limited by the diameter of the pile, but also needs to be supplemented by mud wall protection during the excavation process. The mud will weaken the frictional resistance of the soil wall around the hole. Under the same geological conditions, the side friction resistance of caisson construction is about 0.3 to 0.5 times that of the drilling construction plan, while the side friction resistance of corrugated steel retaining wall manual excavation construction is about 1.3 times that of the drilling construction plan. Therefore, using this scheme to form holes, the frictional resistance around the pile can be fully exerted, and the construction technology is the most convenient.

In the specific application process, on the basis of the successful application of super large-diameter corrugated steel cofferdam hollow piles in Ji'an City, the single pile construction technology is introduced into the anchor pile group foundation, and a suspension bridge oversized structure is proposed according to the bearing characteristics of the anchor structure Diameter hollow pile group anchorage structure scheme and construction method. This structural form can not only fully mobilize the passive resistance of the soil around the pile, the friction of the soil at the bottom of the pile, and the soil resistance of the tension side of the rigid cap, but also reduce the weight of the hollow structure by about 30% without losing the bearing capacity. A safe, reasonable, economical and effective design scheme for the anchorage foundation of a new type of suspension bridge has been formed.

Other features and advantages of the present invention will be described in detail in the following detailed description.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the description, together with the following specific embodiments, are used to explain the present invention, but do not constitute a limitation to the present invention. In the attached picture:

Fig. 1 is the structural representation of the preferred embodiment of super-large-diameter hollow pile group anchorage provided by the present invention;

Fig. 2 is a schematic diagram of the horizontal bearing of the ultra-large-diameter hollow pile group anchorage provided by the present invention;

Fig. 3 is a schematic plan view of the super large-diameter hollow pile group anchorage provided by the present invention;

Fig. 4 is a sectional enlarged view of part A in Fig. 3;

Fig. 5 is a schematic plan view of super large-diameter hollow pile group in Fig. 1;

Fig. 6 is a schematic diagram of the assembled structure of corrugated steel and bolts provided by the present invention;

Fig. 7 is the schematic plan view of the corrugated steel cofferdam provided by the present invention;

Fig. 8 is the three-dimensional structural diagram of the corrugated steel cofferdam provided by the present invention;

Fig. 9 is a schematic diagram of the construction process of the ultra-large-diameter hollow pile group anchorage provided by the present invention;

Fig. 10 is a structural schematic diagram of a gravity anchorage structure of a suspension bridge in the prior art;

Fig. 11 is a structural schematic diagram of a root foundation in the prior art;

Fig. 12 is a construction site diagram of the super large-diameter hollow pile group anchorage provided by the present invention.

Explanation of reference signs

1. Pile body 2. Cap

3. Upper anchor block 4. Scatter saddle

5. Front support block 6. Main cable

7. Rock and soil mass 8. Bolts

10. The first corrugated steel cofferdam 11. The middle corrugated steel cofferdam

12. Bottom corrugated steel cofferdam 13. Rock filling and grouting

14. Pebble sand cushion layer 15. Corrugated steel inner mold in the bottom section

16. Corrugated steel inner mold in the middle section 17. Concrete

18. Capping concrete 19. Grouting pipe

20. Rock bolt

detailed description

Specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

In the present invention, in the absence of a contrary description, the orientation words included in the term "inner, outer, upper, and lower" only represent the orientation of the term in the normal use state, or are commonly known as understood by those skilled in the art. , and should not be construed as a limitation of this term.

The present invention provides a super-large-diameter hollow pile group anchorage, which includes a super-large-diameter hollow group pile, cap 2 and an anchoring system as shown in Figures 1-5 and Figure 9; the super-large-diameter hollow group pile consists of multiple vertically arranged The pile body 1 is organically composed, the bottom end of the pile body 1 is embedded in the rock soil body 7 and the upper end is embedded inside the bottom end of the cap 2; the anchoring system is arranged on the top of the cap 2 to connect the main cable 6; wherein, The pile body 1 is a hollow pile body, and the inner diameter and the outer diameter of the pile body 1 decrease stepwise from top to bottom.

In the super-large-diameter hollow pile group anchorage mentioned above, by setting the pile body 1 in a stepwise decreasing manner from top to bottom, for the pile group foundation, in order to effectively distribute the upper load and fully exert the bearing capacity of the pile group, it is necessary to ensure that the cap The size of the pile must correspond to the diameter of the foundation pile. The larger the foundation pile, the larger the size of the cap. At the same time, in order to reduce the maximum bending moment of the pile body, it is also required to form a fixed support connection at the pile end, and the stiffness of the cap is much greater than that of the pile body. The outer diameter of super-large-diameter piles can reach more than 10 meters. Based on the above considerations, the corresponding cap thickness will reach tens of meters. Such a large-volume cap not only increases the self-weight of the anchorage foundation, but also increases the bearing capacity of the lower bearing layer. It puts forward a great test, and wastes the volume of concrete, which increases the cost of the project. In order to solve the problem of excessively large caps, the foundation piles must be set in a hollow structure, thereby greatly reducing the size of the foundation piles and the volume of the caps, and effectively solving the adverse effects of super-large caps.

In addition, the foundation pile is the main part of the bending resistance, and its bending performance is directly related to the moment of inertia I of the bending section. The advantage of the hollow structure of the foundation pile is that although the net area of the circular section is much smaller than that of the solid pile, the loss value of the section moment of inertia I is very weak (for example, the inner diameter of the pile is half of the outer diameter, and the inertia The moment is only lost by 7%). In addition, under the bending condition of the pile section, the maximum bending moment is located on the outside of the pile section. In order to give full play to the tensile performance of the steel bar, the stressed main reinforcement is arranged at the maximum bending moment on the section, so the hollow annular section makes more use of the stressed main reinforcement. layout.

In the present invention, the internal structure of the pile body 1 can be selected in a wide range, but in order to make the super-large-diameter hollow pile group anchorage have more excellent mechanical properties, preferably, the pile body 1 includes an outer mold and an inner mold; The mold is arranged between the soil around the pile and the inner mold; the rockfill grouting 13 is arranged between the outer mold and the soil around the pile, and a reinforcement cage is arranged between the outer mold and the inner mold and concrete 17 is poured; more preferably, as As shown in 6-8, both the outer mold and the inner mold are composed of corrugated steel cofferdams, and the corrugated steel cofferdams are formed by splicing multiple pieces of corrugated steel through 8 dislocation bolts.

After pouring concrete in the gap between the corrugated steel cofferdam and the surrounding soil wall, the frictional resistance around the pile can increase several times. However, the traditional drilling rig excavation method is not only limited by the pile diameter. Under the same geological conditions, the side friction resistance of caisson construction is about 0.3 to 0.5 times that of the drilling construction plan, while the side friction resistance of manual excavation of corrugated steel retaining walls The resistance is about 1.3 times that of the drilling construction scheme. Therefore, using this scheme to form holes, the frictional resistance around the pile can be fully exerted, and the construction technology is also the most convenient.

In the above-mentioned embodiment, in order to further improve the performance of the super-large-diameter hollow pile group anchorage, preferably, a grouting pipe 19 is preset between the outer mold and the inner mold; one end of the grouting pipe 19 can extend to the pile body 1 The other end extends to the bottom of the pile wall so that the concrete slurry can pass through the grouting pipe 19 to perform secondary grouting on the pile body 1 .

The pre-buried grouting hole is used to press the concrete slurry into the bottom of the pile under high pressure, which makes the pile body slightly lifted, which is equivalent to applying prestress to the bottom of the pile. This process not only strengthens the soil layer at the bottom of the pile, but also greatly reduces the post-construction settlement of the pile body. Moreover, when the bearing layer is a hard soil layer, the reverse lifting of the pile body after the second grouting is equivalent to a test of the bearing capacity of the hollow pile. According to the corresponding relationship between the grouting pressure σ and the lifting amount Δ of the hollow pile, it can be back-calculated The allowable bearing capacity of the pile is obtained to check the design bearing capacity of the single pile. However, the traditional solid pile structure is limited by the excessive self-weight and the huge pressure of the concrete entity, and the concrete grout cannot be injected through the grouting pipe. The realization of secondary grouting is a unique advantage of the hollow pile structure.

In the above embodiment, in order to further improve the anchorage performance of the ultra-large-diameter hollow pile group, preferably, the grouting pipe 19 extends to the inside of the cap 2 . When the lower end of the ultra-large-diameter hollow pile is embedded in the bedrock, and the upper end is embedded in the bottom of the cap to a certain depth, the bending moment distribution of the pile body presents the characteristics that the upper and lower ends are large and the middle is small. Since the lower end is embedded in the bedrock, the bending rigidity is relatively large, so the section of the pile bottom can be optimized, and the diameter of the pile bottom can be appropriately reduced to achieve the purpose of saving materials. However, the diameter of the pile top is relatively large, and a large bending stiffness can also be achieved by embedding the cap. It can be seen that setting the pile diameter from top to bottom as a stepwise decreasing scheme can give full play to the bending resistance of the pile body. From the construction point of view, the stepped variable section pile diameter is not only conducive to the hoisting of construction equipment, but also ensures the tightness of pouring between the upper and lower adjacent rings to a greater extent, and the construction process is simpler.

In the present invention, in order to further improve the performance of the super-large-diameter hollow pile group anchorage, preferably, the bottom of the concrete at the bottom of the pile body 1 is backfilled with a pebble sandstone cushion 14 . The setting of pebble sandstone cushion layer 14 can be more convenient for the pouring of the concrete at the bottom of pile body 1; When pile bottom encounters rock stratum and can't continue to excavate, can adopt blasting excavation.

At the same time, in the present invention, in order to further improve the pull-out effect of the super-large-diameter hollow pile group anchorage, preferably, a rock bolt 20 is arranged in the concrete at the bottom of the pile body 1, and the rock bolt 20 extends to the lower bedrock middle. When the foundation is on deeply buried bedrock, the bottom of the pile cannot be embedded in the bedrock to form a consolidated end. In order to stabilize the stress on the bottom of the pile, a hole can be opened at the bottom of the foundation pile that bears the uplifting force, and rock anchors 20 are drilled to penetrate into the lower bedrock, and then piles are poured in layers, and the anchors provide tension to resist the tension of the main cable. caused by excessive bending moments. The hollow pile structure is convenient for bolt construction, and can form an effective pullout system to a certain extent.

In addition, in order to further improve the bearing capacity of the foundation pile, preferably, a borehole is drilled on the side wall of the pile body 1, and a tendon type steel pipe brazing is arranged in the borehole, and the root tendon type steel pipe brazing extends out of the pile body 1 to Form a tendon-like foundation. When the bearing capacity of the foundation pile is insufficient, holes can be drilled in the inner wall of the hollow pile, and the tendon-type steel pipe brazing can be pushed out of the hole with a jack to form a root-key type pile group foundation to remedy the defect of insufficient bearing capacity of the foundation pile.

Further, in order to further improve the bending moment resistance of the ultra-large-diameter hollow pile group anchorage, preferably, the inner cavity of the pile body 1 away from the main cable 6 is filled with sand and gravel. When the tensile force of the main cable is too large, and the anchorage pile group foundation relies on its own weight to produce resisting bending moment and cannot resist the bending moment imposed by the main cable, sand and gravel can be filled in the hollow foundation pile on the tension side (away from the main cable end), through Increase the self-weight of this part of the foundation pile to improve the moment resistance of the anchorage foundation. In this scheme, the role of sand and gravel filling is only to increase the counterweight of the pile body, and does not participate in the bending resistance of the foundation pile, so it will not affect the load distribution of the cap, nor will it cause excessive cap size.

In the super-large-diameter hollow pile group anchorage described above, the specific structure of the anchorage system can be selected within a wide range, but in order to further improve the anchorage effect of the super-large-diameter hollow pile group anchorage, preferably, the anchorage system includes an upper anchor block 3, a discrete The cable saddle 4 and the front support block 5, the upper anchor block 3 and the front support block 5 are arranged at intervals on the top of the bearing platform 2, and the loose cable saddle 4 is located on the top of the upper anchor block 3 and the front support block 5 and is located at the upper anchor block 3, Between the front support blocks 5, the top of the scatter saddle 4 is connected with the main cable 6. In this way, the force guiding system formed by the cooperation between the upper anchor block 3, the loose cable saddle 4 and the front support block 5 can effectively transmit the tension of the upper main cable 6 to the cap 2, thereby improving the bearing capacity of the anchorage .

At the same time, in the present invention, the combination form of each pile body 1 in the hollow pile group is changeable, but for the convenience of construction, preferably, as shown in Figure 5, the distribution form of multiple pile bodies 1 is: horizontal and vertical vertically staggered distributed. The ultra-large-diameter hollow piles are arranged in a regular rectangular array, which not only enables the setting of the pile spacing to meet the requirements of the pile group effect, but also achieves the purpose of not affecting the excavation construction of adjacent piles.

In order to further improve the anchorage effect of the ultra-large-diameter hollow pile group in the present invention, preferably, mud is laid on the inner wall of the soil around the pile. In the process of excavation, it is necessary to supplement the mud protection wall, and the mud will weaken the frictional resistance of the soil wall around the hole, so that the frictional resistance around the pile can be fully exerted, and the construction process is also the most convenient.

The present invention also provides a construction method for super large-diameter hollow pile group anchorage, as shown in Figure 9, comprising:

1) Excavating multiple pile holes from top to bottom to the bottom of the pile: while excavating each pile hole, an external mold is set inside the pile hole, and rock filling grouting 13 is filled between the hole wall and the inside; The speed of the hole depends on the soil fetching speed. For efficient soil fetching, a gantry crane grab bucket can be installed on both sides of the pile top instead of an excavator to fetch soil. Excavate the first section of pile holes and assemble the first layer of corrugated steel cofferdam 10 as the lining cofferdam. The excavation depth of the first section is generally not more than 4m without support safety depth. Fill stone grouting 13 between first floor corrugated steel cofferdam 10 and hole wall in time, and excavate the second section necking foundation pit simultaneously. After the corrugated steel of the second section is assembled into the corrugated steel cofferdam of the middle layer, rock filling and grouting 13 are carried out around it, and then the necking foundation pit of the third section is excavated, and the pile hole excavation steps of the first and second sections are repeated until Assemble the bottom corrugated steel cofferdam 12 at the bottom of the hole and fill it with stone grouting 13 . The excavation of earth and the assembly of corrugated steel must be carried out simultaneously, and the construction procedures and speed of the two parts must be reasonably arranged. In areas with abundant groundwater, it is necessary to do a good job of cofferdam water-stop protection, and the bottom of the pit should be drained and dried in time during the construction process.

Multiple piles can be excavated at the same time, and the excavation process should be excavated in a plane dislocation, so as to avoid the small excavation spacing from affecting the stability of the side soil of adjacent piles and causing hole collapse. Excavate the pile holes of the first section and assemble the cofferdam of the first section (part a in Fig. 9). Corrugated steel can be directly used as the cofferdam 10 of the first section in areas without groundwater influence. After the completion of the cofferdam of the first section, the area between the cofferdam and the soil around the pile should be filled with rock and grouted 13 at the same time, and the necking foundation pit of the second section should be excavated at the same time. The diameter of the pile hole necking of the second section is 1m, and the unsupported excavation depth should be about 4m. After completing the assembly of the corrugated steel cofferdam of the second section, rock filling and grouting around it, excavation of the necking foundation pit of the remaining sections, and assembly of the cofferdam 11 of the middle section (part b in Fig. 9 ). Repeat the cofferdam construction of the first and second sections, and stop necking after the necking reaches 10m, until the corrugated steel cofferdam 12 at the bottom section is completed (part c in Figure 9).

2) Set the inner mold inside the outer mold, then set the reinforcement cage and grouting pipe 19 between the inner mold and the outer mold, and then pour concrete 17; after the strength of the concrete at the bottom of the hole reaches the standard, hang the corrugated steel of the corresponding pipe joint Inner mold, grouting pipe 19 and inner mold (comprising bottom section corrugated steel inner mold 15, middle section corrugated steel inner mold 16 from top to bottom) are bundled together, sinking synchronously. The grouting pipe is placed in the center of the pile wall on the plane, that is, between the inner and outer longitudinal steel bars. It can be used as the main bar if it is buried without taking it out. A reinforcement cage is lowered between the inner mold and the hole wall and the concrete 17 is poured through the grouting pipe to form the solid part of the hollow pile. Repeat the steps of installing the hollow inner formwork, lowering the reinforcement cage and pouring concrete until the pouring of the entire hollow pile body is completed.

After excavating to the bottom of the hollow pile, pour plain bottom concrete cushion, and bind steel bars, tie grouting pipes on the steel bars, and pour concrete at the bottom. After the concrete has a certain strength, install the hollow pile inner mold 15 at the bottom, lower the reinforcement cage and pour concrete 17 (part d in Fig. 9). Repeat the steps of installing the corrugated steel hollow inner mold 16 in the middle section, lowering the reinforcement cage and pouring concrete until the pouring of the entire pile body wall is completed (part e in Figure 9).

3) Carry out secondary grouting to the bottom of the pile through the grouting pipe 19 until the load-bearing requirements are met; after 60 days of grouting on the pile side, the rockfill layer at the bottom of the pile can be grouted again through the grouting holes at the bottom of the pile. The grouting process Detect and record the pressure data of the cement slurry and the lifting amount of the hollow pile in order to calculate the bearing capacity of the hollow pile. By controlling the grout pressure and grouting volume, the strength and rigidity of a certain range of pile ends can be fully improved, which not only increases the end bearing capacity, but also increases the pile side friction resistance at the same time.

4) Pre-embed the cap to connect the steel bars at the top of the pile, and install the capping inner mold to cap the pile body; after the pile body and the capping concrete on the pile top reach the strength, install the cap form, and finally pour the cap 2 and the anchoring system; Among them, the calibers of pile holes, inner molds, and outer molds all decrease stepwise from top to bottom. Pre-embed the connecting reinforcement of the cap at the top of the pile, then install the capping inner mold, and cap the pile body to obtain the capping concrete 18. After the construction of the pile group is completed, after the pile body and pile top capping concrete reach a certain strength, the cap formwork is installed and the cap is poured. Pre-embed the connecting reinforcement of the cap at the top of the pile, and then install the capping inner mold to cap the pile body (part f in Figure 9). After the pile body and pile foundation capping concrete reach a certain strength, the cap formwork is installed, and the cap 2, the upper anchor block 3, the loose cable saddle 4 and the front support 5 are poured.

In this construction method, in order to further reduce the disturbance to the soil around the pile, preferably, in step 1), the excavation of the pile hole is done manually. Compared with the traditional caisson foundation, the artificial hole forming method has the least disturbance to the soil around the pile, and can retain the friction of the soil around the pile to the greatest extent.

In the present invention, the internal structure of the pile body 1 can be selected in a wide range, but in order to make the super-large-diameter hollow pile group anchorage have more excellent mechanical properties, preferably, the outer mold and the inner mold are both made of corrugated steel. The corrugated steel cofferdam is composed of multiple pieces of corrugated steel spliced by 8 dislocation bolts.

In the above-mentioned construction method, in order to further facilitate the pouring of concrete at the bottom of the pile body 1, preferably, in step 2), before the reinforcement cage and the grouting pipe 19 are set, the construction method also includes backfilling pebbles at the bottom of the pile hole Sand and gravel cushion 14. After excavating to the bottom of the pit, backfill the pebble sand and gravel cushion to the elevation of the bottom of the hole, bind the steel mesh at the bottom of the pile, and pour the bottom concrete. When the bottom of the pile encounters a rock formation and cannot continue to excavate, blasting can be used for excavation.

At the same time, in the present invention, in order to further improve the pullout effect of the ultra-large-diameter hollow pile group anchorage, preferably, in step 2), before pouring the concrete 17, the bottom of the pile bottom is driven with a rock anchor 20 to the lower part in bedrock. When the foundation is on deeply buried bedrock, the bottom of the pile cannot be embedded in the bedrock to form a consolidated end. In order to stabilize the stress on the bottom of the pile, a hole can be opened at the bottom of the foundation pile that bears the uplifting force, and rock anchors 20 are drilled to penetrate into the lower bedrock, and then piles are poured in layers, and the anchors provide tension to resist the tension of the main cable. caused by excessive bending moments. The hollow pile structure is convenient for bolt construction, and can form an effective pullout system to a certain extent.

In addition, in order to further improve the bearing capacity of the foundation pile, preferably, the construction method further includes: drilling a hole on the side wall of the pile body 1 , and then extending the tendon-type steel pipe brazing into the rock-soil body 7 through the hole. When the bearing capacity of the foundation pile is insufficient, holes can be drilled in the inner wall of the hollow pile, and the tendon-type steel pipe brazing can be pushed out of the hole with a jack to form a root-key type pile group foundation to remedy the defect of insufficient bearing capacity of the foundation pile.

Further, in order to further improve the bending moment resistance of the super-large-diameter hollow pile group anchorage, preferably, the construction method further includes: placing sand and gravel in the inner cavity of the pile body 1, and the sand and gravel are located far away from the main cable 6- side. When the tensile force of the main cable is too large, and the anchorage pile group foundation relies on its own weight to produce resisting bending moment and cannot resist the bending moment imposed by the main cable, sand and gravel can be filled in the hollow foundation pile on the tension side (away from the main cable end), through Increase the self-weight of this part of the foundation pile to improve the moment resistance of the anchorage foundation. In this scheme, the role of sand and gravel filling is only to increase the counterweight of the pile body, and does not participate in the bending resistance of the foundation pile, so it will not affect the load distribution of the cap, nor will it cause excessive cap size.

In the above construction method, in order to further ensure the frictional resistance of the surrounding soil wall, preferably, in step 1), during the excavation of the pile hole, the inner wall of the pile hole is supplemented with a mud wall. In the excavation process, it is necessary to supplement the mud wall, and the mud will weaken the frictional resistance of the soil wall around the hole.

At the same time, for the safety of digging holes in the construction process, preferably, in step 1), among all pile holes, the depth of the top pile hole is no more than 4m, and the depth of other pile holes is 3.9-4.1m; The diameter of the pile hole at the end is 10m.

Finally, in the above-mentioned construction method, in order to further ensure the safety of the pile hole, preferably, in step 1, in the area with abundant groundwater, the construction method also includes the protection of the cofferdam water stop, and at the same time, the bottom of the pit is protected during the construction process. Drain and dry.

The present invention is further set forth below by embodiment, specifically as follows:

Taking a suspension bridge project with a main span of 1480m under construction in Hunan Province as an example, it has the following characteristics:

1) High innovative technology content and good economic benefits. Six features, seven crafts, the world's first

Compared with the gravity anchor (underground diaphragm wall cofferdam) of the original scheme, the concrete volume of the super-large-diameter hollow pile anchorage can be saved by nearly 40,000 cubic meters, the excavation of rock and soil for the anchorage can be reduced by 2/3, and the construction period can be shortened by half. The total estimated cost is about 20% lower, and its economic benefits are very significant. The super-large-diameter hollow pile anchorage foundation has a greater horizontal bearing capacity. During the bearing process, the resistance of the soil around the pile is fully utilized, and the horizontal tension of the anchor cable is resisted through the interaction between the large-diameter pile body and the cap and the soil. In addition, the use of hollow structure not only effectively utilizes the flexural strength of the pile body, reduces the self-weight, but also saves a lot of concrete materials and engineering costs, see Table 1 for details.

Table 1

The present invention selects corrugated steel with high rigidity and thin wall as the inner mold of super large-diameter pile foundation, which reduces the amount of flat steel plate by half compared with that of flat steel plate. At the same time, corrugated steel cofferdam and soil wall are bonded by concrete, and the huge friction force generated is higher than that of ordinary pebble soil layer. The frictional resistance is more than 1.5 times larger.

2) The construction process is simple

Compared with large-volume cofferdam construction schemes such as caissons and underground diaphragm walls, the number of pile foundations for ultra-large-diameter pile group foundations is small, and multiple piles can be started at the same time, and the construction speed is faster. The foundation pit can be directly constructed by an excavator, with simple hole forming, fast construction speed and simple process. Corrugated steel cofferdam construction does not require special construction equipment, and the cost is low. The invention has unique advantages in construction progress, energy saving and environmental protection, quality control, project cost and the like.

3) Flexible post-work remedial solutions

Another great advantage of hollow piles is post-work recovery. If the bearing capacity of the pile fails to meet the design requirements, a hole can be drilled in the inner wall of the hollow pile, and a tendon-type steel pipe brazing can be pushed out of the hole with a jack to form a root-key foundation to remedy the defect of insufficient bearing capacity of the pile body. It is in stark contrast to the fact that there is no cure for the defects of the solid pile after the pile is formed. In addition, in order to balance the bending moment, the pile group can be partially compared with the solid structure, and the reinforcement scheme of the hollow structure is flexible and adaptable to various working conditions.

To sum up, the super-large-diameter hollow pile anchorage foundation has simple hole-forming equipment, strong applicability to different geology, simple process, and good economic benefits. Compared with traditional reinforced concrete caissons and double-wall steel cofferdams, corrugated steel cofferdams are lighter in weight, less in consumable materials, and require simpler hoisting equipment. It has advantages in construction progress, energy saving and environmental protection, quality control, and cost.

The preferred embodiment of the present invention has been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the specific details of the above embodiment, within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, These simple modifications all belong to the protection scope of the present invention.

In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable way if there is no contradiction. The combination method will not be described separately.

In addition, various combinations of different embodiments of the present invention can also be combined arbitrarily, as long as they do not violate the idea of the present invention, they should also be regarded as the disclosed content of the present invention.

Claims (10)

1. A kind of 1. construction method of the hollow clump of piles anchorage of super-large diameter, it is characterised in that including：

   1) multiple stake holes are from top to bottom excavated until stake bottom：In the inside of the stake holes, setting is outer while each stake holes is excavated Mould, and slip casting (13) of being rockfilled between hole wall and inside；

   2) the external mold inside set internal model, then by steel reinforcement cage, Grouting Pipe (19) be arranged at the internal model, external mold it Between, then casting concrete (17)；

   3) secondary grouting is carried out until reaching bearing requirements to stake bottom by Grouting Pipe (19)；

   4) in the pre-buried cushion cap connection reinforcing bar of stake top, and the internal model that binds is installed, pile body is bound；Treat pile body and stake top bind it is mixed After solidifying soil reaches intensity, installation platform mould, cushion cap (2) and anchor system are finally poured；

   Wherein, the stake holes, internal model, the bore of external mold successively decrease in step type from top to bottom.
2. 2. construction method according to claim 1, it is characterised in that in step 1), the excavation of the stake holes is to pass through It is accomplished manually.
3. 3. construction method according to claim 1, it is characterised in that the external mold, internal model are by ripple steel cofferdam group Into the ripple steel cofferdam is to be spliced by polylith corrugated steel by bolt (8) dislocation.
4. 4. construction method according to claim 1, it is characterised in that in step 2), steel reinforcement cage, Grouting Pipe are being set (19) before, the construction method is additionally included in the bottom backfill cobble sand-gravel cushion (14) of the stake holes.
5. 5. according to the construction method described in any one in claim 1-4, it is characterised in that in step 2), pouring Before stating concrete (17), the bottom at the stake bottom has set rock-bolt (20) into bottom basement rock.
6. 6. according to the construction method described in any one in claim 1-4, it is characterised in that the construction method also includes： Drill in the side wall of the pile body (1), then extend to root tendon formula steel pipe pricker in Rock And Soil (7) by hole.
7. 7. according to the construction method described in any one in claim 1-4, it is characterised in that the construction method also includes： Sandstone is arranged in the inner chamber of the pile body (1), and the sandstone is located remotely from the main push-towing rope (6) side.
8. 8. according to the construction method described in any one in claim 1-4, it is characterised in that in step 1), the stake holes Digging process in, be also aided with mud off on the inwall of the stake holes.
9. 9. according to the construction method described in any one in claim 1-4, it is characterised in that in step 1), in all piles Kong Zhong, the stake holes depth of top are no more than 4m, and other stake holes depth are 3.9-4.1m；The stake holes of lowermost end it is a diameter of 10m。
10. 10. according to the construction method described in any one in claim 1-4, it is characterised in that in the step 1), on ground The abundant region of lower water, the construction method also includes carrying out cofferdam sealing protection, while cheats bottom in work progress and arranged Water is dried.