阅读说明：本技术 一种现浇预应力地下连续墙的布筋型式及其张拉方法 (Rib distribution type of cast-in-place prestressed underground diaphragm wall and tensioning method thereof ) 是由 张德锋 侯建青 胡祖光 于 2019-11-19 设计创作，主要内容包括：本发明的一种现浇预应力地下连续墙的布筋型式及其张拉方法,针对现有预应力地下连续墙墙体变形控制效果差,预应力筋线形布置缺乏针对性及需在墙体顶部进行张拉,施工周期长且难以保证施工质量等问题,现浇预应力地下连续墙内的预应力筋呈两段反向抛物线光滑连接的线形布置型式,它包括呈抛物线形状的第一段预应力筋和第二段预应力筋,第一段预应力筋底部的固定端位于基坑开挖面以下并锚固于墙体内,第一段预应力筋的开口朝向地下连续墙迎土面；第二段预应力筋位于第一段预应力筋顶部且与其开口方向相反,第二段预应力筋顶部的张拉端设置在地下连续墙内侧并采取从墙体内侧进行张拉的方法,第一段预应力筋和第二段预应力筋在反弯点处光滑连接。(The invention relates to a bar distribution type of a cast-in-place prestressed underground continuous wall and a tensioning method thereof, aiming at the problems that the existing prestressed underground continuous wall has poor deformation control effect, the linear arrangement of prestressed bars is lack of pertinence, tensioning needs to be carried out at the top of the wall, the construction period is long, the construction quality is difficult to ensure and the like, the prestressed bars in the cast-in-place prestressed underground continuous wall are in a linear arrangement type of two sections of reverse parabolic line smooth connection, the cast-in-place prestressed underground continuous wall comprises a first section of prestressed bars and a second section of prestressed bars in a parabolic shape, the fixed end of the bottom of the first section of prestressed bars is positioned below the excavation surface of a foundation pit and anchored in the wall, and the opening of the first section of prestressed bars faces the soil facing surface of the; the second section of prestressed tendon is positioned at the top of the first section of prestressed tendon and is opposite to the opening direction of the first section of prestressed tendon, the tensioning end at the top of the second section of prestressed tendon is arranged at the inner side of the underground continuous wall and adopts a method of tensioning from the inner side of the wall body, and the first section of prestressed tendon and the second section of prestressed tendon are smoothly connected at a reverse bending point.)

1. The utility model provides a cloth muscle pattern of cast-in-place prestressing force underground continuous wall which characterized in that: the prestressed tendons in the cast-in-place prestressed underground continuous wall are in a linear arrangement mode of two sections of reverse parabolic smooth connection, each prestressed tendon comprises a first section of prestressed tendon and a second section of prestressed tendon which are in parabolic shapes, the fixed end of the bottom of each first section of prestressed tendon is located below the excavation surface of a foundation pit and anchored in the wall body, and the opening of each first section of prestressed tendon faces the soil facing surface of the cast-in-place prestressed underground continuous wall; the second section of prestressed tendon is positioned at the top of the first section of prestressed tendon, the opening direction of the second section of prestressed tendon is opposite to that of the first section of prestressed tendon, the tensioning end at the top of the second section of prestressed tendon is arranged at the inner side of the cast-in-place prestressed underground continuous wall and positioned above the horizontal support of the underground layer, and the first section of prestressed tendon and the second section of prestressed tendon are smoothly connected at a reverse bending point.

2. The rib arrangement type of the cast-in-place prestressed underground continuous wall according to claim 1, wherein: the span L of the prestressed tendons in the underground continuous wall is equal to the vertical distance between the fixed end and the underground layer horizontal support, the parabola vertex of the first section of prestressed tendons is positioned at the bottom of the foundation pit, and the vertical distance between the fixed end and the parabola vertex of the first section of prestressed tendons is 0.4L; the span of the second section of prestressed tendons is 0.25L, and the parabola vertex of the second section of prestressed tendons is the same as the central elevation of the horizontal support axis of the underground layer.

3. The rib arrangement type of the cast-in-place prestressed underground continuous wall according to claim 1, wherein: the cast-in-place prestressed underground continuous wall is characterized in that the tension end on the inner side is built in, a wedge-shaped cavity mold is reserved at the position of the tension end in the concrete pouring stage of the wall body and is filled with foam, and after the prestressed tendons are tensioned, the wedge-shaped cavity mold is closed by fine stone concrete which is higher than the cast-in-place prestressed underground continuous wall by one mark.

4. The rib arrangement type of the cast-in-place prestressed underground continuous wall according to claim 1, wherein: the prestressed tendons adopt unbonded steel strands.

5. A method for tensioning a cast-in-place prestressed underground continuous wall as claimed in any one of claims 1 to 4, wherein the steps are as follows:

s1: in the concrete pouring stage, prestressed tendons are arranged in the cast-in-situ prestressed underground continuous wall to be poured, the prestressed tendon is in a linear arrangement form of two sections of reverse parabolic smooth connection, and comprises a first section of prestressed tendon and a second section of prestressed tendon which are in parabolic shapes, the fixed end of the bottom of the first section of prestressed tendon is positioned below the excavation surface of the foundation pit and anchored in the wall body, the opening of the first section of prestressed tendon faces the soil-facing surface of the cast-in-place prestressed underground continuous wall, the second section of prestressed tendon is positioned at the top of the first section of prestressed tendon, and the opening direction of the second section of prestressed tendon is opposite to that of the first section of prestressed tendon, the tensioning end of the top portion of the second section of prestressed tendon is arranged on the inner side of the cast-in-situ prestressed underground continuous wall, the first section of prestressed tendon and the second section of prestressed tendon are smoothly connected at a reverse bend point;

and S2, after the foundation pit is excavated to the elevation of the underground floor and the underground horizontal support is installed, tensioning the tensioning end of the prestressed tendon, and sealing the tensioning end of the prestressed tendon after tensioning is completed.

6. A tensioning method according to claim 5, characterized in that: in the step S1, reserving a wedge-shaped cavity mold at the position of the prestressed tendon tensioning end on the inner side of the cast-in-situ prestressed underground continuous wall and filling foam; in the step S2, after the installation of the underground layer of horizontal supports is completed, the foam in the wedge-shaped cavity mold is taken out and the prestressed tendons are tensioned, and after the tensioning is completed, the wedge-shaped cavity mold is closed by fine aggregate concrete which is higher than the cast-in-place prestressed underground continuous wall by one mark.

7. A tensioning method according to claim 5, characterized in that: in step S2, when the underground horizontal support is constructed, the horizontal rigidity is enhanced by increasing the number of reinforcing bars and/or increasing the cross-sectional area.

Technical Field

The invention relates to the technical field of civil engineering, in particular to a rib arrangement type of a cast-in-place prestressed underground continuous wall and a tensioning method thereof.

Background

The underground continuous wall is one of the common forms of deep foundation pit supporting retaining walls, is widely applied to underground foundation pit retaining structures of high-rise buildings, municipal works and the like, and particularly becomes a preferred retaining and retaining mode for soft soil foundations, city central areas and foundation pits which need to protect adjacent buildings and underground pipelines. However, as the foundation pit is excavated deeper and deeper, the soil and water pressure on the enclosure structure is higher and higher, and in order to effectively control the lateral deformation of the underground continuous wall, the thickness of the underground continuous wall needs to be increased or the distance between the supports of the foundation pit needs to be reduced, the former can increase the construction cost of the enclosure structure of the underground continuous wall, and the latter can improve the difficulty of the excavation construction of the foundation pit.

The prestress technology can effectively increase the rigidity of the structural member, actively control the deformation of the structural member under the action of load, has the advantages of saving materials, improving the structural performance and the like, and is widely applied and developed in the ground structure of the building engineering. The prestress technology is applied to the underground continuous wall structure, so that the strength, the rigidity and the crack resistance of the underground continuous wall structure can be improved, the steel bar consumption of the wall body and the deformation under water and soil pressure are reduced, the aims of reducing the construction cost, accelerating the construction progress and the like are fulfilled, and the obvious economic benefit and social benefit are achieved. However, most of the existing prestressed underground continuous walls are prefabricated, prestressed tendons are mostly arranged in a straight line, and compared with the structure stress of the underground continuous wall, the prestressed tendons arranged in a straight line lack pertinence, even some of the prestressed tendons are unreasonably arranged in a line shape, so that the consumption of the prestressed tendons is excessive, the economic benefit is low, and the control effect of the applied prestressed on the deformation of the underground continuous wall is poor; in addition, because the tensioning end of the prestressed tendon is arranged at the top of the underground continuous wall, and concrete at the top of the underground continuous wall is difficult to pour densely, the concrete at the tensioning end of the prestressed tendon needs to be chiseled off and poured again before tensioning, and the prestressed tensioning end needs to be specially protected in the pouring stage of the underground continuous wall, so that the construction method of the prestressed underground continuous wall is complicated in steps, long in construction period and difficult to ensure construction quality.

Disclosure of Invention

The method aims at the problems that the existing prestressed underground continuous wall is poor in wall deformation control effect, the linear arrangement of prestressed tendons is lack of pertinence, the prestressed tendons need to be tensioned at the top of the wall, the construction period is long, the construction quality is difficult to guarantee, and the like. The invention aims to provide a novel bar distribution type of a cast-in-place prestressed underground continuous wall and a tensioning method thereof, wherein a prestressed bar adopts a two-section reverse parabola linear arrangement type, not only can the length and the span of the prestressed bar be reduced, the vector-span ratio of the prestressed bar be increased, the using amount of the prestressed bar be reduced, the equivalent load value generated by tensioning prestress can be effectively increased, but also the effect of the prestress effect can be fully exerted, the optimal deformation control effect of the underground continuous wall can be realized, in addition, the prestressed bar is tensioned from the inner side of the underground continuous wall body, the tensioning end is not required to be specially protected in the concrete pouring stage, concrete chiseling and re-pouring in the area of the tensioning end are avoided, the construction process is reduced, the construction period is shortened, and the construction quality is favorably ensured.

The technical scheme adopted by the invention for solving the technical problems is as follows: a tendon distribution type of a cast-in-place prestressed underground continuous wall is characterized in that prestressed tendons in the cast-in-place prestressed underground continuous wall are in a linear arrangement type of two sections of reverse parabolic smooth connection, each prestressed tendon comprises a first section of prestressed tendon and a second section of prestressed tendon which are in parabolic shapes, the fixed end of the bottom of the first section of prestressed tendon is located below a foundation pit excavation surface and anchored in the wall body, and the opening of the first section of prestressed tendon faces the soil facing surface of the cast-in-place prestressed underground continuous wall; the second section of prestressed tendon is positioned at the top of the first section of prestressed tendon, the opening direction of the second section of prestressed tendon is opposite to that of the first section of prestressed tendon, the tensioning end at the top of the second section of prestressed tendon is arranged at the inner side of the cast-in-place prestressed underground continuous wall and positioned above the horizontal support of the underground layer, and the first section of prestressed tendon and the second section of prestressed tendon are smoothly connected at a reverse bending point.

The prestressed tendon in the cast-in-place prestressed underground continuous wall is in a linear arrangement form of two sections of reverse parabolic smooth connection, and comprises a first section of prestressed tendon and a second section of prestressed tendon which are arranged from bottom to top, wherein the fixed end of the bottom of the first section of prestressed tendon is positioned below the excavation surface of a foundation pit and anchored in the wall body, the opening of the fixed end faces the soil-facing surface of the cast-in-place prestressed underground continuous wall, and the equivalent load generated after the first section of prestressed tendon is tensioned is used for resisting the water and soil pressure outside the cast-in-place prestressed underground continuous wall; the opening direction of the second section of prestressed tendon is opposite to that of the first section of prestressed tendon, the tensioning end at the top of the second section of prestressed tendon is arranged at the inner side of the cast-in-place prestressed underground continuous wall close to the foundation pit and above the horizontal support of the underground layer, the first section of prestressed tendon and the second section of prestressed tendon are smoothly connected at the inflection point, the second section of prestressed tendon realizes the steering of the first section of prestressed tendon and performs tensioning at the inner side of the cast-in-place prestressed underground continuous wall, and the construction is more convenient; and the equivalent load generated after the second section of prestressed tendon is tensioned transfers the water and soil pressure borne by the outer side of the cast-in-place prestressed underground continuous wall to the underground layer of horizontal support, so that the stress transfer of the cast-in-place prestressed underground continuous wall is realized.

Preferably, the span L of the prestressed tendons in the underground continuous wall is equal to the vertical distance between the fixed end and the underground layer horizontal support, the vertex of the first section of the prestressed tendon parabola is positioned at the bottom of the foundation pit, and the vertical distance between the fixed end of the prestressed tendon parabola and the vertex of the first section of the prestressed tendon parabola is 0.4L; the span of the second section of prestressed tendons is 0.25L, and the parabola vertex of the second section of prestressed tendons is the same as the central elevation of the horizontal support axis of the underground layer.

Preferably, the tensioning end at the inner side of the cast-in-place prestressed underground continuous wall is built in, a wedge-shaped cavity mold is reserved at the position of the tensioning end in the concrete pouring stage of the wall body and is filled with foam, and after the prestressed tendons are tensioned, the wedge-shaped cavity mold is closed by fine aggregate concrete which is higher than the cast-in-place prestressed underground continuous wall by one mark.

Preferably, the prestressed tendons are unbonded steel strands.

In addition, the invention also provides a tensioning method of the cast-in-place prestressed underground continuous wall, which comprises the following steps:

s1: in the concrete pouring stage, prestressed tendons are arranged in the cast-in-situ prestressed underground continuous wall to be poured, the prestressed tendon is in a linear arrangement form of two sections of reverse parabolic smooth connection, and comprises a first section of prestressed tendon and a second section of prestressed tendon which are in parabolic shapes, the fixed end of the bottom of the first section of prestressed tendon is positioned below the excavation surface of the foundation pit and anchored in the wall body, the opening of the first section of prestressed tendon faces the soil-facing surface of the cast-in-place prestressed underground continuous wall, the second section of prestressed tendon is positioned at the top of the first section of prestressed tendon, and the opening direction of the second section of prestressed tendon is opposite to that of the first section of prestressed tendon, the tensioning end of the top portion of the second section of prestressed tendon is arranged on the inner side of the cast-in-situ prestressed underground continuous wall, the first section of prestressed tendon and the second section of prestressed tendon are smoothly connected at a reverse bend point;

and S2, after the foundation pit is excavated to the elevation of the underground floor and the underground horizontal support is installed, tensioning the tensioning end of the prestressed tendon, and sealing the tensioning end of the prestressed tendon after tensioning is completed.

The invention relates to a tensioning method of a cast-in-situ prestressed underground continuous wall, which comprises the steps of firstly, pre-arranging prestressed tendons at the concrete pouring stage of the cast-in-situ prestressed underground continuous wall, wherein the prestressed tendons are in a linear arrangement form of two sections of reverse parabolic smooth connection, the opening of a first section of prestressed tendons faces the soil facing surface of the cast-in-situ prestressed underground continuous wall, the opening of a second section of prestressed tendons at the top of the prestressed tendons faces the pit facing surface of the cast-in-situ prestressed underground continuous wall, the first section of prestressed tendons and the second section of prestressed tendons are smoothly connected into a whole at the reverse bending point, wherein the fixed end at the bottom of the first section of prestressed tendons is positioned below the excavation surface of a foundation pit and anchored in a wall body, the tensioning end at the top of the second section of prestressed tendons is arranged at the inner side of the cast-in-situ prestressed underground continuous wall and above an underground layer of horizontal support, when the foundation pit is excavated to, tensioning the tensioning end of the prestressed tendon, and sealing the tensioning end after tensioning is finished; the tensioning method is simple and convenient to operate, simple in construction steps, and capable of reducing the length and span of the prestressed tendons, increasing the rise-to-span ratio of the prestressed tendons, reducing the using amount of the prestressed tendons, effectively increasing the equivalent load value generated by tensioning the prestressed tendons, fully playing the effect of the action of the prestressed force, realizing the optimal deformation control effect of the underground continuous wall and being beneficial to ensuring the construction quality; and moreover, by adopting a mode of tensioning the prestressed ribs from one end of the inner side of the cast-in-place prestressed underground continuous wall, the applied prestress can transfer the water and soil pressure borne by the wall body to the underground layer of horizontal support, so that the stress transfer of the cast-in-place prestressed underground continuous wall is realized, the tensioning end does not need to be specially protected in the concrete pouring stage, the concrete chiseling and the re-pouring in the area of the tensioning end are avoided, the construction process is reduced, the construction period is shortened, the prestressed tensioning construction and the sealing construction of the tensioning end are more convenient, the construction efficiency is improved, the construction quality of the prestressed underground continuous wall is ensured, and the prestressed underground continuous wall has remarkable economic and social benefits.

Preferably, in the step S1, a wedge-shaped cavity mold is reserved at the position of the prestressed tendon tensioning end inside the cast-in-place prestressed underground continuous wall, and foam is filled in the cavity mold; in the step S2, after the installation of the underground layer of horizontal supports is completed, the foam in the wedge-shaped cavity mold is taken out and the prestressed tendons are tensioned, and after the tensioning is completed, the wedge-shaped cavity mold is closed by fine aggregate concrete which is higher than the cast-in-place prestressed underground continuous wall by one mark.

Preferably, in step S2, when constructing the horizontal support of the underground layer, the horizontal stiffness of the horizontal support is reinforced by increasing the number of reinforcing bars and/or increasing the cross-sectional area of the horizontal support.

Drawings

FIG. 1 is a schematic view showing the linear arrangement of prestressed tendons according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of the prestress equivalent load of an embodiment of the rib arrangement type of the cast-in-place prestressed underground continuous wall according to the present invention;

FIG. 3 is a schematic view showing the structure of the prestressed tendon tensioning end in the installation stage in one embodiment of the tendon distribution type of the cast-in-place prestressed underground diaphragm wall according to the present invention;

FIG. 4 is a schematic view showing the structure of the tensioned end of the prestressed tendon after the completion of tensioning in one embodiment of the tendon arrangement type of the cast-in-place prestressed underground diaphragm wall according to the present invention;

FIG. 5 is a schematic view of a computational analysis model of a cast-in-place prestressed underground continuous wall according to an embodiment of the present invention;

FIG. 6 is a wall deformation envelope diagram of an embodiment of the cast-in-place prestressed underground diaphragm wall of the present invention;

FIG. 7 is a wall bending moment envelope diagram in an embodiment of the cast-in-place prestressed underground diaphragm wall of the present invention.

The numbers in the figures are as follows:

a cast-in-place prestressed underground continuous wall 1; a wedge-shaped cavity die 1 a; a prestressed tendon 8; a first section of tendon 8 a; a second section of prestressed tendons 8 b; a tensioning end 9; a fixed end 10; a subterranean horizontal support 11; the equivalent load 14 is generated after the first section of the prestressed tendon is tensioned; the equivalent load generated after the second section of prestressed tendon is tensioned 15; a parabola vertex A of the first section of prestressed tendon; a second section of prestressed tendon parabola vertex B; a foam 16; an elastic support 2; a horizontal spring support 3; a vertical spring support 4; soil pressure 5; water pressure 6; and 7, ground load.

Detailed Description

The invention is described in further detail below with reference to the figures and specific examples. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention. For convenience of description, the directions of "up" and "down" described below are the same as the directions of "up" and "down" in the drawings, but this is not a limitation of the technical solution of the present invention.

The cast-in-place prestressed underground continuous wall 1 of the invention is described by combining the drawings of fig. 1 and fig. 2, the prestressed tendons 8 in the cast-in-place prestressed underground continuous wall 1 are in a linear arrangement mode of two sections of reverse parabolic smooth connection, the prestressed tendons 8 comprise a first section of prestressed tendons 8a and a second section of prestressed tendons 8b which are in parabolic shapes, a fixed end 10 at the bottom of the first section of prestressed tendons 8a is positioned below a foundation pit excavation surface and anchored in the wall body, and an opening of the first section of prestressed tendons 8a faces the soil facing surface of the cast-in-place prestressed underground continuous wall 1; the second section of prestressed tendon 8b is located first section of prestressed tendon 8a top, and second section of prestressed tendon 8b is opposite with first section of prestressed tendon 8 a's opening direction, and the tensioning end 9 at second section of prestressed tendon 8b top sets up at cast-in-place prestressed underground continuous wall 1 near the inboard of foundation ditch, and is located one deck horizontal brace 11 top underground, near one deck floor elevation promptly, and first section of prestressed tendon 8a and second section of prestressed tendon 8b are in the smooth connection of inflection point department.

The prestressed tendon 8 in the cast-in-place prestressed underground continuous wall 1 is in a linear arrangement form of two sections of reverse parabolic smooth connection, and comprises a first section of prestressed tendon 8a and a second section of prestressed tendon 8b which are arranged from bottom to top, wherein the fixed end 10 at the bottom of the first section of prestressed tendon 8a is positioned below the excavation surface of a foundation pit and anchored in the wall body, the opening of the fixed end faces the soil facing surface of the cast-in-place prestressed underground continuous wall 1, and the equivalent load generated after the first section of prestressed tendon 8a is tensioned is used for resisting the soil pressure 5 and the water pressure 6 outside the cast-in-place prestressed underground continuous wall 1; the opening direction of the second section of prestressed tendon 8b is opposite to that of the first section of prestressed tendon 8a, the tensioning end 9 at the top of the second section of prestressed tendon 8b is arranged at the inner side, close to the foundation pit, of the cast-in-place prestressed underground continuous wall 1 and is positioned above the horizontal support 11 of the underground layer, the first section of prestressed tendon 8a and the second section of prestressed tendon 8b are smoothly connected at a reverse bending point, and the second section of prestressed tendon 8b realizes the steering of the first section of prestressed tendon 8a and performs tensioning on the inner side of the cast-in-place prestressed underground continuous wall 1, so that the construction is more convenient; and the equivalent load generated after the second section of prestressed tendon 8b is tensioned transmits the soil pressure 5 and the water pressure 6 borne by the outer side of the cast-in-place prestressed underground continuous wall to the underground layer of horizontal support 11, so that the stress transfer of the cast-in-place prestressed underground continuous wall 1 is realized.

As shown in fig. 1, the span L of the tendon 8 is equal to the vertical distance between the fixed end 10 and the horizontal support 11 of the underground layer, the vertex a of the parabola of the first section of the tendon is located at the bottom of the foundation pit, wherein the vertical distance between the fixed end 10 and the vertex a of the parabola of the first section of the tendon is 0.4L, the span of the second section of the tendon 8B is 0.25L, the vertex B of the parabola of the second section of the tendon is the same as the central elevation of the horizontal support axis of the underground layer, and the tendon 8 in the linear arrangement can achieve the best effect of controlling the deformation of the cast-in-situ prestressed underground continuous wall 1 by the prestress generated after the tendon is tensioned.

As shown in fig. 3, a wedge-shaped cavity mold 1a is reserved on the inner side of the cast-in-place prestressed underground continuous wall 1, namely the position of the tensioning end 9 of the prestressed tendon 8, and foam 16 is pre-buried in the wedge-shaped cavity mold 1a, as shown in fig. 4, after the horizontal support 11 of the underground layer is installed, the foam 16 is taken out and the prestressed tensioning is carried out on the prestressed tendon 8, the wedge-shaped cavity mold 1a is closed by fine stone concrete which is higher than the cast-in-place prestressed underground continuous wall 1 by one grade, and as the concrete pouring stage does not need to specially protect the tensioning end 9, nor does the concrete chiseling and re-pouring of the tensioning end 9, the construction period is saved, and the construction quality of the prestressed underground continuous wall 1 can be effectively ensured.

Above-mentioned prestressing tendons 8 adopt the unbonded steel strand wires, and the unbonded steel strand wires outside is equipped with grease and sheath for steel strand wires and concrete are effectively kept apart, allow prestressing tendons 8 and concrete around to take place vertical relative slip, and prestressing force leans on the ground tackle to transmit to the concrete completely, and its advantage is that the construction speed is fast, convenient operation, easily recycle. In addition, the unbonded steel strand has small diameter, and can increase the acting force arm and the prestressing effect of the parabolic prestressed tendon.

The method for tensioning the cast-in-situ prestressed underground continuous wall 1 of the invention is described below with reference to fig. 1 to 7, and comprises the following specific steps:

s1: as shown in fig. 1, in the concrete pouring stage, a prestressed tendon 8 is arranged in a cast-in-situ prestressed underground continuous wall 1 to be poured, the prestressed tendon 8 is in a linear arrangement form of two sections of reverse parabolic smooth connection, and comprises a first section of prestressed tendon 8a and a second section of prestressed tendon 8b which are in parabolic shapes, a fixed end 10 of the bottom of the first section of prestressed tendon 8a is positioned below a foundation pit excavation surface and anchored in the wall body, an opening of the first section of prestressed tendon 8a faces the soil facing surface of the cast-in-situ prestressed underground continuous wall 1, the second section of prestressed tendon 8b is positioned at the top of the first section of prestressed tendon 8a, and the opening direction of the second section of prestressed tendon 8b is opposite to that of the first section of prestressed tendon 8a, the tensioning end 9 of the top portion of the second section of prestressed tendon 8b is placed in the inner side of cast-in-situ prestressed underground continuous wall 1, the first section of prestressed tendon 8a and the second section of prestressed tendon 8b are smoothly connected at the reverse bending point;

and S2, after the foundation pit is excavated to the elevation of the underground floor and the underground horizontal support 11 is installed, tensioning the tensioning end 9 of the prestressed tendon 8, and sealing the tensioning end 9 of the prestressed tendon 8 after tensioning is finished.

The invention relates to a tensioning method of a cast-in-situ prestressed underground continuous wall, which comprises the following steps of firstly, arranging prestressed tendons 8 in advance at the concrete pouring stage of a cast-in-situ prestressed underground continuous wall 1, wherein the prestressed tendons 8 are in a linear arrangement mode of two sections of reverse parabolic smooth connection, the opening of a first section of prestressed tendons 8a faces the soil facing surface of the cast-in-situ prestressed underground continuous wall 1, the opening of a second section of prestressed tendons 8b positioned at the top of the prestressed tendons 8b faces the pit facing surface of the cast-in-situ prestressed underground continuous wall 1, the first section of prestressed tendons 8a and the second section of prestressed tendons 8b are smoothly connected into a whole at the reverse bending point, wherein the fixed end 10 at the bottom of the first section of prestressed tendons 8a is positioned below the excavation surface of a foundation pit and anchored in the wall body, the tensioning end 9 at the top of the second section of prestressed tendons 8b is arranged at the inner side of the cast-in-, when the foundation pit is excavated to the elevation of the underground floor and an underground horizontal support 11 is installed, tensioning the tensioning end 9 of the prestressed tendon 8, and sealing the tensioning end 9 after tensioning is finished; the tensioning method is simple and convenient to operate, simple in construction steps, and capable of reducing the length and span of the prestressed tendon 8, increasing the rise-to-span ratio of the prestressed tendon 8, reducing the using amount of the prestressed tendon 8, effectively increasing the equivalent load value generated by tensioning prestress, fully playing the effect of prestress action, realizing the optimal deformation control effect of the underground diaphragm wall and being beneficial to ensuring the construction quality; moreover, by adopting the mode of stretching the prestressed tendons 8 from one end of the inner side of the cast-in-place prestressed underground continuous wall 1, the applied prestress can transfer the soil pressure 5 and the water pressure 6 borne by the wall body to the underground layer of horizontal supports 11, so that the stress transfer of the cast-in-place prestressed underground continuous wall 1 is realized, the prestressed tensioning construction and the sealing construction of the tensioning end 9 are more convenient, the construction efficiency is improved, the construction quality of the prestressed underground continuous wall is ensured, and the construction method has remarkable economic and social benefits.

As shown in fig. 3, in step S1, a wedge-shaped cavity mold 1a is reserved at the position of the tension end 9 of the prestressed tendon 8 in the cast-in-place prestressed underground continuous wall 1, and foam 16 is embedded in advance; as shown in fig. 4, in step S2, after the horizontal supports 11 on the underground layer are installed, the foam 16 is taken out and the prestressed tendons 8 are tensioned, and after tensioning, the wedge-shaped cavity mold 1a is closed by fine stone concrete which is higher by one grade than the cast-in-place prestressed underground diaphragm wall 1, and since the concrete pouring stage does not need to specially protect the tensioning ends 9, nor does the concrete of the tensioning ends 9 need to be chiseled off and poured again, the construction steps are simple, the construction period is shortened, and the construction quality of the prestressed underground diaphragm wall can be effectively ensured.

In the step S1, the optimal linear arrangement pattern of the prestressed tendons 8 is determined based on the bending moment envelope diagram and the deformation envelope diagram of the cast-in-place prestressed underground continuous wall 1, and the specific steps are as follows:

s11: as shown in figure 5, according to the actual engineering condition and the excavation and supporting scheme of the foundation pit, a calculation analysis model of the cast-in-situ prestressed underground continuous wall 1 is established, the internal force and the deformation of the cast-in-situ prestressed underground continuous wall 1 are calculated and analyzed by adopting a vertical elastic ground beam method, the rigidity of a horizontal support in the foundation pit, the rigidity of a soil body below an excavation surface in the foundation pit, the construction working condition and the influences of soil pressure 5, water pressure 6 and ground load 7 outside the foundation pit are considered during calculation, the calculation analysis model comprises the cast-in-situ prestressed underground continuous wall 1 arranged at the edge of the foundation pit, the horizontal support in the foundation pit is simulated by an elastic support 2, the resistance of the soil body below the excavation surface in the foundation pit to the wall body of the cast-in-situ prestressed underground continuous wall 1 is simulated by a horizontal spring support 3, the resistance of the soil body at the, the acting load on the outer side of the wall body of the cast-in-place prestressed underground continuous wall 1 comprises soil pressure 5 and water pressure 6, and the acting load on the outer part of the foundation pit is a ground load 7;

s12: as shown in fig. 6 and 7, according to the calculation and analysis results of the internal force and deformation at each stage of the construction of the cast-in-place prestressed underground continuous wall 1, drawing a deformation graph and a bending moment graph, a deformation envelope graph and a bending moment envelope graph of each stage of the construction of the cast-in-place prestressed underground continuous wall 1;

s13: determining the optimal linear arrangement mode of the prestressed ribs 8 in the cast-in-place prestressed underground continuous wall 1 based on the deformation envelope diagram and the bending moment envelope diagram obtained in the step S12;

s14: calculating to obtain equivalent load generated by the prestress action and the internal force and deformation of the cast-in-place prestressed underground continuous wall 1 under the prestress action, combining the prestress action with the internal force of the cast-in-place prestressed underground continuous wall 1 under the load action, and calculating and determining the reinforcement amount of prestressed ribs 8 in the cast-in-place prestressed underground continuous wall 1 based on the foundation pit lateral deformation control index determined by the foundation pit environmental protection grade; combining a bending moment envelope value at the control section of the cast-in-situ prestressed underground continuous wall 1 with a secondary bending moment generated by the action of prestress to serve as a design value to calculate the bearing capacity, and determining the reinforcement allocation amount of non-prestressed reinforcements in the cast-in-situ prestressed underground continuous wall 1;

s15: checking the bearing capacity and the crack width of the cast-in-place prestressed underground continuous wall 1, and performing subsequent construction if the requirements of the specification limit are met; if the requirements of the specification limit value are not met, adjusting the reinforcement allocation amount of the prestressed reinforcement 8, and recalculating or checking the bearing capacity and the crack width of the cast-in-situ prestressed underground continuous wall 1 until the relevant requirements of the specification are met.

In the step S13, the tendon 8 is in a linear arrangement form of two sections of reverse parabolic smooth connections, and includes a first section of tendon 8a and a second section of tendon 8b in a parabolic shape, the opening of the first section of tendon 8a faces the soil-facing surface of the cast-in-place prestressed underground continuous wall 1, the fixed end 10 of the bottom of the first section of tendon 8a is located below the excavation surface of the foundation pit and anchored in the wall body, the top end of the first section of tendon 8a is flush with the horizontal support 11 of the underground layer of the foundation pit, and the equivalent load generated after the first section of tendon 8a is tensioned can resist the soil pressure 5 and the water pressure 6 outside the cast-in-place prestressed underground continuous wall 1; the second section of prestressed tendon 8b is positioned at the top of the first section of prestressed tendon 8a, the opening direction of the second section of prestressed tendon 8b is opposite to that of the first section of prestressed tendon 8a, the tensioning end 9 at the top of the second section of prestressed tendon 8b is arranged at the inner side of the cast-in-situ prestressed underground continuous wall 1 and is positioned above the underground layer horizontal support 11, namely near the elevation of the underground floor, the first section of prestressed tendon 8a and the second section of prestressed tendon 8b are smoothly connected at the reverse bend point, the second section of prestressed tendon 8b realizes the steering of the first section of prestressed tendon 8a and carries out tensioning on the inner side of the cast-in-situ prestressed underground continuous wall 1, and the second section of prestressed tendon 8b generates equivalent load after being tensioned to transmit the soil pressure 5 and the water pressure 6 borne by the wall body to the underground layer of horizontal support 11, so that the stress transfer of the wall body is realized, and the water-soil pressure 5 and the water pressure 6 outside the cast-in-place prestressed underground continuous wall 1 are balanced. Therefore, the prestressed tendons 8 are arranged in a parabolic shape, so that the effect of the prestress can be fully exerted, the soil pressure 5 and the water pressure 6 borne by the cast-in-situ prestressed underground continuous wall 1 are effectively balanced, the external load borne by the cast-in-situ prestressed underground continuous wall 1 is balanced to the maximum extent, the lateral deformation of the cast-in-situ prestressed underground continuous wall 1 is effectively controlled, the optimal deformation control effect is obtained, the using amount of the prestressed tendons 8 can be reduced, and the economic benefit and the social benefit are remarkable.

In the step S1, in order to increase the acting force arm of the prestressed tendon 8 and simplify the construction process, the prestressed tendon 8 is made of an unbonded steel strand, and the outer side of the unbonded steel strand is provided with grease and a sheath, so that the steel strand is effectively isolated from the concrete, the prestressed tendon 8 and the surrounding concrete are allowed to longitudinally slide relatively, and the prestress is completely transferred to the concrete by the anchorage device.

In the step S2, since the wall of the cast-in-place prestressed underground continuous wall 1 transmits the received soil pressure 5 and water pressure 6 to the horizontal supports 11 of the underground floor, the horizontal rigidity of the horizontal supports 11 of the underground floor needs to be enhanced during the design of the foundation pit support, for example, the number of reinforcing bars and/or the cross-sectional area of the horizontal supports are increased for the horizontal supports 11 of the underground floor, which is not described herein again.

The above description is only for the purpose of describing the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention, and any variations and modifications made by those skilled in the art based on the above disclosure are within the scope of the appended claims.