阅读说明：本技术 一种桩基托换施工中托换桩帽基坑支护结构的施工方法 (Construction method for underpinning pile cap foundation pit supporting structure in pile foundation underpinning construction ) 是由 廖令军 周凯 莫成 黄勇 吴昊 刘利峰 于 2020-10-30 设计创作，主要内容包括：本发明公开了一种桩基托换施工中托换桩帽基坑支护结构的施工方法,该施工方法先开挖用于施作托换桩帽的基坑,清除基坑开挖面的浮石、石渣和堆积物；再在基坑的四周侧壁上锚设锚筋；最后在基坑的四周侧壁上一次施工形成混凝土底层、钢筋网和混凝土表层,最终形成钢筋混凝土结构的支护结构。该施工方法施工方便、流程简单,施工所获得支护结构的支护性能好、稳固性高,并具有较好的防水性。(The invention discloses a construction method of a underpinning pile cap foundation pit supporting structure in pile foundation underpinning construction, which comprises the steps of firstly excavating a foundation pit for constructing an underpinning pile cap, and removing pumice, stone slag and deposits on the excavation surface of the foundation pit; anchoring ribs are anchored on the peripheral side wall of the foundation pit; and finally, constructing on the peripheral side wall of the foundation pit for one time to form a concrete bottom layer, a reinforcing mesh and a concrete surface layer, and finally forming the supporting structure of the reinforced concrete structure. The construction method is convenient to construct, simple in process, good in supporting performance and high in stability of the supporting structure obtained by construction, and has good waterproofness.)

1. A construction method for underpinning a pile cap foundation pit supporting structure in pile foundation underpinning construction is characterized by comprising the following steps:

(A) excavating a foundation pit for constructing a underpinning pile cap, and removing pumice, stone slag and deposits on the excavation surface of the foundation pit;

(B) anchoring a plurality of anchor bars on the side wall of the periphery of the foundation pit;

(C) and spraying and constructing on the peripheral side wall of the foundation pit to form a concrete bottom layer with the thickness not less than 4cm, paving a reinforcing mesh connected with the anchor bars on the concrete bottom layer, and spraying and constructing on the concrete bottom layer to form a concrete surface layer covered with the reinforcing mesh.

2. The construction method according to claim 1, wherein the steel bar pitch of the steel bar net is 140cm to 160 cm; the concrete for forming the concrete bottom layer and the concrete surface layer by the spray construction is prepared by mixing water, P.O42.5 cement, an accelerator, medium coarse sand with the particle size of 0.25-1 mm and broken stone with the diameter of 5-10 mm.

3. The construction method according to claim 1, wherein the reinforcing mesh is formed by overlapping a plurality of reinforcing mesh sheets, and the overlapping length between two overlapping reinforcing mesh sheets is 20cm to 25 cm.

4. The construction method according to claim 1, wherein the bottom concrete layer and the top concrete layer are formed by spraying, the side wall around the foundation pit is divided into a plurality of areas, and concrete is sprayed to the areas one by one.

5. The construction method according to claim 4, wherein the concrete is sprayed in an S-shaped course in a bottom-up direction when the concrete is sprayed to each slab.

6. The construction method according to claim 1, wherein the concrete bottom layer and the concrete top layer are formed by spraying using a wet sprayer, and in the process of spraying the concrete top layer, the spraying direction of the spray head is perpendicular to the reinforcing bar net when spraying the concrete to the positions of the gaps between the reinforcing bars of the reinforcing bar net, and the spraying direction of the spray head forms an inclination angle of not less than 70 ° with the reinforcing bar net when spraying the concrete to the positions of the reinforcing bars of the reinforcing bar net.

7. The construction method according to claim 1, wherein the concrete bottom layer and the concrete surface layer are formed by concrete spraying construction with a strength grade of C25 or more.

8. The construction method according to claim 1, wherein the concrete surface layer has a flatness tolerance of ± 30mm and a chord loss ratio of not more than 1/6.

9. The construction method according to any one of claims 1 to 8, wherein the concrete surface layer is divided into a plurality of layers and the spraying construction is performed sequentially, and the spraying construction of the later layer is performed before the spraying construction of the previous layer is solidified, and the spraying construction of the later layer is performed after the spraying construction of the previous layer is performed with water to wet the surface of the spraying construction layer.

Technical Field

The invention relates to the technical field of civil engineering construction, in particular to a construction method of a underpinning pile cap foundation pit supporting structure in pile foundation underpinning construction.

Background

With the vigorous development of urban construction, urban ground traffic is increasingly busy, and in order to relieve ground traffic pressure, the construction of convenient and rapid underground railways becomes a choice of a plurality of urban traffics. Because underground excavation construction underground railways have small influence on ground traffic, and the underground excavation method becomes the main construction method of urban underground railway construction along with the maturity of the underground excavation construction method, but inevitably can cross ground buildings, the pile foundation underpinning technology is needed to underpin the pile foundation of the ground buildings deeply into the tunnel, and the upper structure load born by the part of the pile foundation is transferred to the pile foundation outside the influence range of tunnel construction through the newly constructed underpinning structure.

In the pile foundation underpinning construction, a foundation pit needs to be excavated in the top area of the underpinning pile, and then a pile cap is constructed in the foundation pit for installing jacking equipment to carry out subsequent jacking of the underpinning beam. In order to prevent the collapse of the peripheral side wall of the foundation pit from influencing the construction of the pile cap, a supporting structure is generally arranged on the peripheral side wall of the foundation pit, the existing supporting structure adopts a form of directly piling and building concrete, and the defects of low structural strength, poor supporting effect and poor waterproof performance exist.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a construction method for a underpinning pile cap foundation pit supporting structure in pile foundation underpinning construction.

In order to solve the technical problems, the invention adopts the following technical scheme:

a construction method for underpinning a pile cap foundation pit supporting structure in pile foundation underpinning construction comprises the following steps:

(A) excavating a foundation pit for constructing a underpinning pile cap, and removing pumice, stone slag and deposits on the excavation surface of the foundation pit;

(B) anchoring a plurality of anchor bars on the side wall of the periphery of the foundation pit;

(C) and spraying and constructing on the peripheral side wall of the foundation pit to form a concrete bottom layer with the thickness not less than 4cm, paving a reinforcing mesh connected with the anchor bars on the concrete bottom layer, and spraying and constructing on the concrete bottom layer to form a concrete surface layer covered with the reinforcing mesh.

In the construction method, preferably, the distance between the steel bars of the steel bar mesh is 140cm to 160 cm; the concrete for forming the concrete bottom layer and the concrete surface layer by the spray construction is prepared by mixing water, P.O42.5 cement, an accelerator, medium coarse sand with the particle size of 0.25-1 mm and broken stone with the diameter of 5-10 mm.

In the construction method, preferably, the reinforcing mesh is formed by overlapping a plurality of reinforcing mesh sheets, and the overlapping length between two mutually overlapped reinforcing mesh sheets is 20 cm-25 cm.

In the construction method, preferably, when the concrete bottom layer and the concrete surface layer are constructed by spraying, the peripheral side wall of the foundation pit is divided into a plurality of sheet areas, and the concrete is sprayed to the plurality of sheet areas one by one.

In the above construction method, preferably, the concrete is sprayed in an S-shaped course in a direction from bottom to top for each slab.

In the construction method, preferably, the concrete bottom layer and the concrete surface layer are formed by spraying construction by a wet sprayer, and in the process of spraying the concrete surface layer, the spraying direction of the spray head is vertical to the reinforcing bar mesh when the concrete is sprayed to the gap position between the reinforcing bars of the reinforcing bar mesh, and the spraying direction of the spray head forms an inclination angle of not less than 70 degrees with the reinforcing bar mesh when the concrete is sprayed to the reinforcing bar position of the reinforcing bar mesh.

In the above construction method, the concrete bottom layer and the concrete surface layer are preferably formed by concrete spraying construction with a strength grade of not less than C25.

In the construction method, the surface flatness tolerance of the concrete surface layer is preferably +/-30 mm, and the chord loss ratio is not more than 1/6.

In the construction method, preferably, the concrete surface layer is divided into a plurality of layers to be successively sprayed, the later spraying construction layer is carried out before the former spraying construction layer is solidified, and the later spraying construction layer is sprayed after the former spraying construction layer is sprayed with water to be wet and then sprayed.

Compared with the prior art, the invention has the advantages that:

the construction method of the underpinning pile cap foundation pit supporting structure in the pile foundation underpinning construction adopts the mode of firstly forming the concrete bottom layer by construction, then laying the reinforcing mesh on the concrete bottom layer, and finally spraying and constructing on the concrete bottom layer to form the concrete surface layer covered by the reinforcing mesh, so that the reinforced concrete supporting structure is formed. Simultaneously, the anchor bars connected with the reinforcing mesh are arranged on the side walls around the foundation pit in an anchoring mode, so that the reinforcing mesh is convenient to install, the accuracy of the installation position is guaranteed, and the strength and the stability of the supporting structure can be further enhanced.

Drawings

Fig. 1 is a flow chart of a construction method of an underpinning pile cap foundation pit supporting structure in pile foundation underpinning construction.

Detailed Description

The invention is described in further detail below with reference to the figures and specific examples.

As shown in fig. 1, the construction method of the underpinning pile cap foundation pit supporting structure in pile foundation underpinning construction of the embodiment includes the following steps:

(A) excavating a foundation pit for constructing a underpinning pile cap, and removing pumice, stone slag and deposits on the excavation surface of the foundation pit;

(B) anchoring a plurality of anchor bars on the side wall of the periphery of the foundation pit;

(C) and spraying and constructing on the peripheral side wall of the foundation pit to form a concrete bottom layer with the thickness not less than 4cm, paving a reinforcing mesh connected with the anchor bars on the concrete bottom layer, and spraying and constructing on the concrete bottom layer to form a concrete surface layer covered by the reinforcing mesh. Preferably, the anchor bars and the reinforcing mesh are connected and fixed in a steel wire binding mode.

The construction method of the underpinning pile cap foundation pit supporting structure in pile foundation underpinning construction adopts a mode of firstly forming a concrete bottom layer by construction, then laying a reinforcing mesh on the concrete bottom layer, and finally spraying and constructing on the concrete bottom layer to form a concrete surface layer covered by the reinforcing mesh, so that the reinforced concrete supporting structure is formed. Simultaneously, the anchor bars connected with the reinforcing mesh are arranged on the side walls around the foundation pit in an anchoring mode, so that the reinforcing mesh is convenient to install, the accuracy of the installation position is guaranteed, and the strength and the stability of the supporting structure can be further enhanced.

In the embodiment, the distance between the steel bars of the steel bar mesh is 140 cm-160 cm; the concrete for forming the concrete bottom layer and the concrete surface layer by the spray construction is prepared by mixing water, P.O42.5 cement, an accelerator, medium coarse sand with the particle size of 0.25-1 mm and broken stone with the diameter of 5-10 mm. This kind of steel bar interval and concrete cooperation, the concrete easily sees through the steel bar interval, makes concrete top layer and concrete bottom form good combination, improves supporting construction's structural strength and stability, and changes in the injection formation concrete top layer, reduces the construction degree of difficulty, improves the efficiency of construction.

In this embodiment, the reinforcing mesh is formed by overlapping a plurality of reinforcing mesh sheets, and the overlapping length between two mutually overlapped reinforcing mesh sheets is 20cm to 25 cm. The lap joint length range reduces the using amount of the reinforcing mesh while ensuring the overall structural strength, the stability and the supporting performance of the supporting structure, and reduces the area of a lap joint area with high difficulty in spraying concrete.

In this embodiment, when spraying construction concrete bottom and concrete top layer, divide into a plurality of districts with foundation ditch lateral wall all around, spray concrete one by one to a plurality of districts, this kind of mode can improve the efficiency of construction.

In the embodiment, when the concrete is sprayed to each section, the concrete is sprayed along the S-shaped route from bottom to top, so that the concrete is combined and the spraying uniformity is improved.

In this embodiment, the wet sprayer is used for spraying to form the concrete bottom layer and the concrete surface layer, and in the process of spraying the concrete surface layer, the spraying direction of the sprayer is perpendicular to the reinforcing mesh when the concrete is sprayed to the gap position between the reinforcing bars of the reinforcing mesh, so that the smoothness of the spraying surface is ensured, and the spraying direction of the sprayer and the reinforcing mesh form an inclination angle of not less than 70 degrees when the concrete is sprayed to the reinforcing bar position of the reinforcing mesh, so that the gap can be avoided.

In this embodiment, the concrete bottom layer and the concrete surface layer are formed by concrete spraying construction with a strength grade of not less than C25.

In the embodiment, the flatness allowable deviation of the surface of the concrete surface is +/-30 mm, the chord loss ratio is not more than 1/6, the surface of the concrete after being sprayed is guaranteed to be compact, flat and free of cracks, and the phenomena of falling, spraying leakage, rib leakage, hollowing, water leakage and the like are avoided.

In this embodiment, the concrete surface layer is divided into a plurality of layers and is successively sprayed and constructed, the later spraying construction layer is sprayed and constructed before the former spraying construction layer is solidified, and the later spraying construction layer is sprayed and constructed after the surface of the former spraying construction layer is sprayed with water and is wetted, so that the compactness and the flatness of the sprayed concrete surface can be improved, the concrete can be better combined with a reinforcing mesh, and hollowing cannot occur.

The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-described embodiments. Modifications and variations that may occur to those skilled in the art without departing from the spirit and scope of the invention are to be considered as within the scope of the invention.