CN101408023A - Method for supporting and protecting row pile pit - Google Patents

Abstract

The invention discloses a pile row foundation pit support method. The pile row is a single row of pile piles inclined to the outside of the foundation pit. The method comprises the following steps: (a) determining the pile row inclination according to site conditions and calculation and analysis Angle, determination of pile length and pile body strength, determination of foundation pit support structure, determination of excavation levels of foundation pit; (b) construction of piles; (c) construction of foundation pit support structure; (d) excavation of foundation pit (e) Cleaning and leveling the bottom of the foundation pit, and carrying out the next step of construction work. The invention can largely reduce pile top displacement, reduce pile body bending moment, reduce engineering cost, increase excavation depth and reduce the possibility of overturning damage.

Description

Method of row pile foundation pit support

technical field

The invention relates to the field of foundation foundations, in particular to a method for supporting foundation pits by using row piles.

Background technique

The pile row support structure has many advantages such as simple construction technology, low cost, and flexible layout. It is one of the most widely used forms of foundation pit support at home and abroad. The support structure of row piles can be divided into three types: cantilever type, pull-anchor type and internal support type. When the excavation of the foundation pit is shallow, the geological conditions are good, and the deformation of the support structure and the control of ground settlement outside the pit are not high, the cantilever pile row support form can be used. Pile row support can also be combined with pit support or bolt anchorage to improve support capacity. In the soft soil area, when the excavation area of the foundation pit is large, the deformation of the support structure and the ground settlement outside the pit are high, the support form of the inner support row pile can be adopted. When the soil conditions of the foundation pit can be set with anchor rods and the surrounding environment is not greatly affected, the anchor-type row pile support form can also be used.

The current row of pile support structures all use vertical piles. The common problem when using vertical row of piles for foundation pit support is that the top of the pile is prone to large displacement, resulting in large deformation of the ground outside the foundation pit behind the pile. It endangers the surrounding environment; when the strength of the pile is not enough, it is easy to cause the slope protection pile to break and make the foundation pit unstable; the excavable depth of the foundation pit is small, and it is easy to overturn when the excavation depth increases.

A small number of inclined piles such as one or two are widely used in pile foundations of docks, bridges, power transmission towers, etc., and can be used for hanging prefabricated piles, bored piles, casing auger drilled piles, and artificially dug piles, etc. A variety of construction methods, is a relatively mature construction technology.

Contents of the invention

In order to solve the technical problems existing in the known technology, the present invention provides a method that can greatly reduce the pile top displacement, reduce the pile body bending moment, reduce the engineering cost, increase the excavation depth and make the possibility of overturning damage occur. Reduced row pile foundation pit support method.

The technical solution adopted by the present invention for solving the technical problems existing in the known technology is: a pile row foundation pit support method, the pile row is a single row of pile piles inclined to the outside of the foundation pit, and the method includes the following steps:

(a) According to site conditions and calculation and analysis, determine the inclination angle of the pile row, determine the length of the pile and the strength of the pile body, determine the support structure of the foundation pit, and determine the excavation stages of the foundation pit;

(b) Construction pile arrangement;

(c) construction of foundation pit support structure;

(d) excavation of foundation pits;

(e) Clean up and level the bottom of the foundation pit, and proceed to the next step of construction.

The inclination angle of the row of piles is 1-15°.

The row piles are bored cast-in-place piles, prefabricated piles or casing bored cast-in-place piles.

The support structure of the foundation pit is a cantilever pile type support, an inner support type support or an anchor type support.

The advantages and positive effects of the present invention are as follows: the present invention is an improvement to the support of ordinary vertical pile rows, replacing vertical piles with inclined piles with appropriate angles, and according to site conditions and safety and stability checking results, the foundation pit The supporting row of piles is inclined at a certain angle to the outside of the foundation pit as a whole. This method overcomes many deficiencies of vertical pile support, can greatly reduce pile top displacement, reduce pile body bending moment, reduce engineering cost, increase excavation depth and reduce the possibility of overturning damage decrease. Compared with the prior art, the present invention has the following advantages: in the case of the same excavation depth, the method can greatly reduce the pile top displacement, greatly reduce the deformation of the ground behind the pile, and avoid damage to the surrounding environment. At the same time, it can reduce the bending moment of the pile body, so that the reinforcement amount of the pile body can be significantly reduced, thereby reducing the project cost and having great economic benefits; when the pile length and pile design strength are the same as ordinary piles, the excavation depth can be increased , has good technical value; due to the slope of the excavation surface, the possibility of overturning damage to the foundation pit is reduced, which is beneficial to the safety of the foundation pit project. Due to the advantages of the above inclined pile support, the foundation pit project that may originally need to use internal support or pull anchor support can meet the design requirements only by using cantilever pile support, thus making the design and construction easier. And save material, reduce engineering cost. It is applicable to the foundation pit engineering supported by rows of piles. Compared with the vertical pile foundation pit support method, the application of the present invention can increase the excavation depth of the foundation pit, reduce the displacement of the pile tops of the supporting piles, and increase the anti-overturning resistance of the rows of piles. Sex, reduce the design strength of row piles, can further reduce the project cost.

Description of drawings

Fig. 1 is the schematic diagram of cantilever support of the present invention;

Fig. 2 is the schematic diagram of anchor type support of the present invention;

Fig. 3 is a schematic diagram of the inner support of the present invention.

In the figure: 1. Row of piles, 2. Crown beam, 3. Foundation pit bottom, 4. Anchor rod, 5. Internal support.

Detailed ways

In order to further understand the invention content, characteristics and effects of the present invention, the following examples are given, and detailed descriptions are as follows in conjunction with the accompanying drawings:

Please refer to Fig. 1～Fig. 3, the present invention utilizes inclined row pile to carry out foundation pit support and comprises the following steps:

(a) According to the site conditions and the calculation and analysis of safety and stability, determine the optimal angle of inclination of the single row of piles 1 to the outside of the foundation pit. The inclination angle of the row of piles can be: 1-15°; According to different site conditions and engineering conditions, cantilever pile support, internal support or pull-anchor support can be used respectively. If the cantilever pile support does not meet the design requirements, internal support or anchor support can be used according to the actual situation, and the support or anchor rod can be designed to determine the excavation level of the foundation pit;

(b) Construction row pile 1. As the row of piles is an inclined support, when the soil condition is relatively good, bored piles can be used; when the soil condition is relatively poor and hole collapse is prone to occur, prefabricated piles or casing auger drilling machines can be used to drill and pour into piles . Various methods can be used for the construction of inclined piles, such as hanging prefabricated piles, bored piles, casing auger drilled piles and artificially dug piles. Among them, the construction method of casing auger drilling and pouring into piles has been widely used because of its advantages such as fast drilling speed, high pile quality, casing wall protection is not easy to collapse holes, and the inclination of pile body can be accurately controlled.

(c) Construction of foundation pit support structure. For the support structure of single-row piles, according to the characteristics of the soil layer where the foundation pit is located and the surrounding environment, it can be divided into the following three forms:

① Cantilever pile support. Please refer to Figure 1. When the excavation of the foundation pit is relatively shallow, the geological conditions are good, and the requirements for deformation control are not high, the support form of cantilever piles with a crown beam 2 on the row of piles 1 can be used. After the strength of the cantilever pile meets the specified requirements, the excavation of the soil layer can be carried out.

② Internal support. Please refer to Fig. 3, when the excavation area of the foundation pit is large, the foundation is weak, and the deformation control requirements are high, the internal support of the internal support 5 arranged inside the row of piles 1 can be used. First, excavate the earthwork of the foundation pit to the bottom of the cushion at the bottom of the first reinforced concrete support beam, then cut out the connection surface between the retaining structure and the purlin, and carry out the construction of the reinforced concrete support cushion, and then tie the support steel bars to support the side After the formwork is completed, the concrete is poured and maintained. When the concrete strength reaches the specified level, the formwork removal and cleaning work will be carried out.

③Anchor support. Please refer to Fig. 2, when the condition of the soil layer of the foundation pit is good enough to meet the conditions for pulling the anchor, and the surrounding environment requirements are not high, the anchoring type support with the anchor rod 4 arranged outside the row of piles 1 can be used. When the foundation pit is firstly excavated to a certain depth below the center line of the first anchor rod, mechanical drilling is used to make anchor rods and insert rods according to regulations, and then grouting is carried out to form the anchor section. Finally, when the anchor body reaches After a certain strength, it is stretched and locked.

(d) Excavation of foundation pit. For foundation pits excavated in stages, for different pile row support forms, repeat step (c) until the bottom of the foundation pit is excavated.

(e) Clean up and level the bottom 3 of the foundation pit, and carry out the next construction work.

The invention adopts row piles with a certain slope to support the foundation pit, which increases the stability and overturning resistance of the foundation pit; the soil body with slope on the outside of the pile row reduces the soil pressure on the pile row, and reduces the displacement and displacement of the top of the pile row. Bending moment of the pile body, thereby relatively improving the support stiffness of the row of piles and increasing the excavation depth of the foundation pit.

Example 1

The foundation pit project of a dormitory building is 65.0m long, 15.0m wide, and the excavation depth is 5.120m. The geotechnical engineering investigation report shows that the range from the ground to the buried depth of 2m is miscellaneous fill, and the range from the buried depth of 2m to 12m is powder earth. There are no important buildings around the construction site of the foundation pit project. The support structure adopts cantilever support of inclined piles with an inclination of 10°. The support piles are 11m long, 800mm in pile diameter, and 100mm in pile distance. Drainage wells are used for dewatering in the pit, and the open cut method is used for construction. The four right angles of the foundation pit are sloped at a slope angle of 45°.

Example 2

The foundation pit project of a subway station is 190.0m long, 20.7m wide, and 14.070m deep. The two sides of the long side adopt inclined row piles and bolt support structure, and the two ends are blocked in advance by underground diaphragm walls.

The vertical distribution of strata within the excavation depth range of the foundation pit from top to bottom is: fill soil, thickness 2.70-4.50m; ②silt, thickness 8.10-13.00m; ③coarse gravel sand, thickness 1.0-8.0m; ④silty Clay, thickness 0.18-2.80m; ⑤ residual sandy cohesive soil, thickness 1.40-13.10m; ⑥ fully weathered granite, thickness 0.85-7.85m; ⑦-1 sandy strongly weathered granite, thickness 0.40-14.50m; ⑦-2 Fragmented strongly weathered granite, with a thickness of 1.0-3.9m; ⑧medium weathered granite, with a thickness of 1.10-12.20m; ⑨slightly weathered granite.

The support structure adopts inclined row of piles and bolt support. The inclination of the row of piles is 10°. The length of the supporting piles is 29m, the diameter of the piles is 800mm, and the distance between piles is 100mm.

The length of the anchorage section of the anchor bolt is 19m. The anchor bolts are located in three rows at 3.20m, 7.35m and 9.95m below the pile top. The diameter of the anchor hole is 150mm. The inclination angle of the anchor bolts is α=15°. Grade III (HRB400) steel bars.

Example 3

A circular foundation pit with a diameter of 126 meters and a depth of 12.650 meters is supported by inclined row piles and back pressure soil. The ground elevation of the foundation pit site is 2.143 meters above sea level, the range from the ground to the elevation -18 meters is miscellaneous fill and silt, the elevation -18 meters to the elevation -27 meters is silty clay, and the soil quality is good. Tube wells are arranged in the foundation pit for dewatering and dewatering.

The support structure of the foundation pit adopts cantilever support of inclined row of piles. The inclination angle of the row of piles is 1°. The length of the supporting piles is 26m, the diameter of the piles is 800mm, and the distance between the centers of the pile bottoms is 850mm.

Back pressure soil is reserved at the bottom of the pit. The height of the back pressure soil is 3.5 meters. Sprayed concrete facing.

The basic principle of the invention is: the side slope with small slope is more stable than that with large slope, and is less prone to overturning damage and overall stability damage. Similarly, slopes with a certain slope are more stable than vertical slopes, so the requirements for supporting structures are lower. The method of the present invention is just based on this idea, and the foundation pit is supported by rows of piles with a certain slope when the site permits. When inclined piles are used for foundation pit support, the wedge-shaped body with sliding tendency behind the pile is smaller than the wedge-shaped body when the pile is vertical, because the wedge-shaped body behind the pile is partly less due to the slope. Therefore, the force of the soil on the pile will be greatly reduced, so that the displacement of the pile top and the force of the pile body will be greatly reduced. Theoretically speaking, the larger the slope of the pile, the smaller the force of the pile and the displacement of the pile top, which is more economical, but the slope of the pile cannot be increased without limit, because due to the limitation of the construction site, there may not be enough space Make the inclination of pile too large, on the other hand, when the inclination of pile is big, the pile below its foundation pit depth may affect the construction of pile foundation owing to stretching below foundation pit internal space. In addition, the inclination of the pile will increase the length of the pile, offset part of the economy caused by the reduction of the strength of the pile body, and make the construction of the supporting pile more difficult. Therefore, in the actual application process of inclined pile support, the determination of its inclination should fully consider various factors.

Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are only illustrative and not restrictive. Those of ordinary skill in the art Under the enlightenment of the present invention, people can also make many forms without departing from the purpose of the present invention and the scope of protection of the claims, and these all belong to the protection scope of the present invention.

Claims (4)

1. a row of pile foundation pit support method is characterized in that, described pile row is the single row of pile row that inclines to the outside of foundation pit, and the method may further comprise the steps: (a) According to site conditions and calculation and analysis, determine the inclination angle of the pile row, determine the length of the pile and the strength of the pile body, determine the support structure of the foundation pit, and determine the excavation stages of the foundation pit; (b) Construction pile arrangement; (c) construction of foundation pit support structure; (d) excavation of foundation pits; (e) Clean up and level the bottom of the foundation pit, and proceed to the next step of construction. 2. The foundation pit support method according to claim 1, characterized in that: the inclination angle of the pile row is 1-15°. 3. The foundation pit supporting method according to claim 2, characterized in that: said piles are bored piles, prefabricated piles or casing bored piles. 4. The foundation pit support method according to claim 2, characterized in that: the foundation pit support structure is a cantilever pile type support or an inner support type support or an anchor type support.

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