Inverted construction method prefabricated shaft and its construction method

Abstract

The present invention discloses an inverse construction method for an assembled shaft and its construction method. The wellhead is a collar beam, the well wall is composed of several layers of annular structures, and the bottom of the well is a floor slab. The collar beam and all annular structures are vertically reinforced and connected by ring beams between adjacent layers; each layer of annular structure is spliced by several segments of precast well walls and one segment of cast-in-situ well wall. The precast well wall is in the shape of an arc sheet, with the upper part narrower and the lower part wider on the outside, notches at the upper and lower corners on the inside, reserved steel bars, prestressed ducts distributed in the left-right direction, and small conduit reserved holes distributed in the inside-outside direction. The precast well walls of the same layer are pre-tightened and connected by steel strands. The precast well wall and the soil body are grouted and reinforced by small conduits. The collar beam, all precast well walls and the floor slab are connected by reserved steel bars between adjacent layers. The ring beam steel bars are respectively connected to the reserved steel bars of the upper and lower layers and cast together with the cast-in-situ well wall of the lower layer. The structure of the present invention is simple, the construction period is short, the ring and vertical connections are reliable, the connection with the soil body is tight, and the settlement is small.

Description

Technical Field

[0001] The present invention belongs to the field of civil engineering construction, and particularly relates to a reverse construction method assembled shaft and a construction method thereof. Background Art

[0002] Underground shafts are widely used in pipe jacking and mined tunnels. When constructing new pipe jacking pipelines in cities, conventional cast-in-situ concrete shafts are used, which not only have uneven pouring quality but also long construction periods, inevitably occupying urban roads for a long time and affecting traffic. Although the construction period can be shortened by using prefabricated assembled shafts, the prefabricated assembled shafts have the following problems: 1) The circumferential and vertical connections of sheet-like prefabricated structures are unreliable and the integrity is poor; 2) When the sheet-like prefabricated structures are buried in the soil, voids will be generated between them and the soil, and the side wall friction resistance is insufficient, which is not conducive to the overall force; 3) The prefabricated structures are prone to vertical settlement during the excavation process, resulting in deviation. Summary of the Invention

[0003] The purpose of the present invention is to provide a reverse construction method assembled shaft and a construction method thereof. The structure of the present invention is simple, the construction period is short, the circumferential and vertical connections are reliable, the connection with the soil is tight, and the settlement is small.

[0004] The technical solution adopted by the present invention is as follows:

[0005] A reverse construction method assembled shaft, the wellhead is a cast-in-situ collar beam for vertical force, the shaft wall is several layers of annular structures vertically arranged in sequence, and the bottom of the well is a cast-in-situ bottom plate. The collar beam and all annular structures are vertically and reinforcedly connected at the inner corner positions between adjacent layers through a ring beam; each layer of annular structure is spliced by several sections of precast shaft walls and a section of cast-in-situ shaft wall. The precast shaft wall is in an arc-shaped sheet shape, with a narrow upper part and a wide lower part on the outside, notches at the upper and lower corners on the inside and reserved steel bars are provided, prestressed pipes are distributed in the left-right direction, and small conduit reserved holes are distributed in the inside-outside direction. The precast shaft walls of the same layer are pre-tightened and connected by steel strands passing through the prestressed pipes in the circumferential direction. The precast shaft wall and the soil are grouted and reinforcedly connected by small conduits passing through the small conduit reserved holes. The collar beam, all precast shaft walls and the bottom plate are connected by reserved steel bars between adjacent layers. The ring beam steel bars are respectively connected with the reserved steel bars of the upper and lower layers and are poured together with the cast-in-situ shaft wall of the lower layer.

[0006] Further, the cross-sectional dimension of the collar beam is 0.9 - 1.5 m in width and 0.7 - 1 m in height; the height H of the precast shaft wall is 1 - 1.5 m, the width B is 1.5 - 2 m, the thickness S1 of the upper end including the notch is 0.35 - 0.5 m, the thickness S2 of the lower end including the notch is 0.7 - 1.2 m, and S2 / S1 = 1.3 - 2. The thickness of the reserved steel bar area is S3, and S3 / S1 = 0.5 - 0.8.

[0007] Furthermore, the prestressed ducts are evenly distributed on the cross-section of the precast shaft wall. The tail of the prestressed duct is a protruding inner socket and spigot. After the adjacent precast shaft walls of the same layer are installed, the tails of the prestressed ducts can be butt-jointed into the corresponding heads of the prestressed ducts.

[0008] Furthermore, the diameter of the small conduit reserved holes is 45 - 55 mm, which inclines from the upper inner side to the lower outer side with an inclination of 30° - 45°. There are no less than 3 small conduits vertically for each section of the precast shaft wall. When the width of the precast shaft wall is greater than 1.5 m, two rows are arranged along the width direction.

[0009] Furthermore, the precast shaft wall is made of C30 concrete, and the concrete strength of the ring beam and the cast-in-place shaft wall is not less than C30.

[0010] The construction method of the above top-down assembled shaft includes the following steps:

[0011] S1. Construct the collar beam: Take points and set out the outline of the shaft, measure the center line and side lines of the collar beam. After the earthwork is excavated to the bottom elevation of the collar beam, compact the surface soil and construct the cushion layer, bind the steel bars of the collar beam, set the reserved steel bars at the inner lower corner, install the formwork of the ring beam, and pour concrete after the formwork of the collar beam is supported.

[0012] S2. Excavate the earthwork and install the shaft wall and small conduits: The soil in the shaft is excavated in layers by small equipment, and the soil of the shaft wall is excavated manually. Trim the soil according to the outline of the precast shaft wall. After the earthwork excavation is completed, manually cooperate with the machinery to install the precast shaft wall in sections in time. Before installing the precast shaft wall, thread the steel strands into the prestressed ducts, weld and position the reserved steel bars at the upper end of the precast shaft wall with the reserved steel bars at the lower end of the upper structure in time, and insert the small conduits into the reserved holes of the small conduits to enter the soil to prevent the precast shaft wall from shifting.

[0013] S3. Prestress tensioning: After the installation of a single layer of precast shaft wall is completed, use the reserved section of the cast-in-place shaft wall as the tensioning working surface, and tension the steel strands through the tensioning equipment. After the tensioning is completed, ensure that the connections between the precast shaft walls are firm and there is no looseness, and grout the prestressed ducts in time until the pores are filled.

[0014] S4. Pour the ring beam and backfill and grout the small conduits: Thread the main steel bars of the ring beam in the circumferential direction and bind them with the reserved steel bars of the upper and lower layers. Set up the formwork and pour it together with the cast-in-place shaft wall of the lower layer. After the strength of the ring beam reaches a certain level, carry out backfill grouting on the small conduits and backfill the slurry into the pores between the shaft wall and the side wall soil.

[0015] S5. Cast the in-situ bottom seal: Repeat steps S2 to S4 until the bottom of the shaft is constructed. Bind the bottom plate steel bars with the reserved steel bars of the precast shaft wall, and cast the in-situ bottom plate with concrete.

[0016] Furthermore, when manually excavating the soil of the shaft wall, random overexcavation is strictly prohibited. The overexcavation in the height direction shall not exceed 5 cm, and the overexcavation in the thickness direction shall not exceed 5 cm.

[0017] Furthermore, when installing the small conduits, if the soil has good self-stability, the small conduits shall be uniformly inserted after the excavation of the soil of a single-layer shaft wall and the installation of the precast shaft wall of a single layer are completed; if the soil has poor self-stability, the soil of a section of the shaft wall shall be excavated, then a section of the precast shaft wall shall be installed, and then the small conduits shall be promptly inserted and double-fluid grouting reinforcement shall be carried out.

[0018] Furthermore, when uniformly inserting the small conduits, the grouting sequence shall be symmetrically implemented from both ends to the middle.

[0019] Furthermore, the tensioning sequence of the steel strands is to first tension the middle position and then tension the upper and lower positions.

[0020] The beneficial effects of the present invention are as follows:

[0021] The structure of the present invention is simple, the construction period is short, the circumferential and vertical connections are reliable, the connection with the soil is tight, and the settlement is small: the lock beam, the precast shaft wall and the bottom plate are connected by the reserved steel bars between adjacent layers, the lock beam and all the ring structures are vertically reinforced and connected by the ring beams between adjacent layers, the ring beam steel bars are respectively connected with the reserved steel bars of the upper and lower layers and are cast together with the cast-in-place shaft wall of the lower layer, this setting enhances the overall vertical stability and solves the problem of the vertical connection of the shaft wall; the precast shaft walls of the same layer are pre-tensioned and connected by the steel strands, this setting makes the precast shaft walls of the same layer form an integral body, enhances the lateral stiffness, resists lateral deformation, and solves the problem of the circumferential connection of the precast shaft walls; the precast shaft wall and the soil are connected by small conduit grouting reinforcement, this setting not only keeps the precast shaft wall and the soil in close contact and the structure is more stable in force, but also can increase the frictional resistance between the shaft wall and the soil, improve the strength of the soil around the shaft, and solve the problem of the pores existing between the precast shaft wall and the soil; the upper part of the precast shaft wall is narrow and the lower part is wide, this setting transfers a part of the vertical load of the precast shaft wall to the side soil, forming a stable vertical stress body and solving the problem of the vertical settlement of the shaft structure during the excavation process. Description of the Drawings

[0022] Figure 1 is the vertical sectional view of the inverted construction method prefabricated shaft in the embodiment of the present invention.

[0023] Figure 2 is the horizontal sectional view of the inverted construction method prefabricated shaft in the embodiment of the present invention.

[0024] Figure 3 is the sectional view of the precast shaft wall in the embodiment of the present invention.

[0025] Figure 4 is the front view of the precast shaft wall in the embodiment of the present invention.

[0026] In the figure: 1 - ground surface; 2 - collar beam; 3 - precast shaft wall; 4 - ring beam; 5 - prestressed duct; 6 - small duct; 7 - bottom slab; 8 - cast-in-place shaft wall; 9 - anchorage end of steel strand; 10 - tension end of steel strand; 11 - reserved steel bars; 12 - reserved hole for small duct; 13 - internal socket joint. Detailed implementation manners

[0027] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0028] As Figures 1 to 4 shown, an inverse construction method assembled shaft has a collar beam 1 for vertical force bearing and cast-in-place at the wellhead, the shaft wall is a ring structure composed of several layers arranged vertically downward in sequence, and the bottom of the well is a cast-in-place bottom slab 7. The collar beam 1 and all ring structures are vertically reinforced and connected at the inner corner position between adjacent layers through a ring beam 4; each layer of the ring structure is composed of several segments of precast shaft walls 3 and a segment of cast-in-place shaft wall 8 spliced together. The precast shaft wall 3 is in an arc-shaped sheet with a narrow upper part and a wide lower part on the outside, notches at the upper and lower corners on the inside and provided with reserved steel bars 11, prestressed ducts 5 are distributed in the left-right direction, and reserved holes 12 for small ducts are distributed in the inside-outside direction. The precast shaft walls 3 of the same layer are pre-tightened and connected by steel strands passing through the prestressed ducts 5 in the circumferential direction. The precast shaft wall 3 and the soil body are grouted and reinforced by small ducts 6 passing through the reserved holes 12 for small ducts. The collar beam 1, all precast shaft walls 3 and the bottom slab 7 are connected through reserved steel bars 11 between adjacent layers. The steel bars of the ring beam 4 are respectively connected with the reserved steel bars 11 of the upper and lower layers and are cast together with the cast-in-place shaft wall 8 of the lower layer.

[0029] In this embodiment, the cross-sectional dimension of the collar beam 1 is 0.9 - 1.5 m in width and 0.7 - 1 m in height; the height H of the precast shaft wall 3 is 1 - 1.5 m, the width B is 1.5 - 2 m, the thickness S1 including the notch at the upper end is 0.35 - 0.5 m, the thickness S2 including the notch at the lower end is 0.7 - 1.2 m, and S2 / S1 = 1.3 - 2. The thickness of the area of the reserved steel bars 11 is S3, and S3 / S1 = 0.5 - 0.8. The above dimensions are the preferred dimensions provided by the present invention, considering factors such as fabrication, transportation, installation, and force bearing. Of course, the actual dimension of the collar beam 1 can also be adjusted according to the well depth and the thickness of the shaft wall, and the actual dimension of the precast shaft wall 3 can also be adjusted according to the size of the shaft, geological conditions, and soil self-stability.

[0030] As Figure 3 and Figure 4 shown, in this embodiment, the prestressed ducts 5 are evenly distributed on the cross-section of the precast shaft wall 3. The tail of the prestressed duct 5 is an extended internal socket joint 13. After the precast shaft walls 3 of the same layer are installed adjacent to each other, the tails of the prestressed ducts 5 can be butted and inserted into the corresponding heads of the prestressed ducts 5, ensuring that there will be no large gaps between the shaft walls due to the interfaces and also avoiding grout leakage.

[0031] In this embodiment, the diameter of the small duct reserved hole 12 is 45 - 55 mm, which slopes from the inner upper direction to the outer lower direction with an inclination of 30° - 45°. There are no less than 3 small ducts in each vertical section of the precast shaft wall 3. When the width of the precast shaft wall 3 is greater than 1.5 m, two rows are arranged along the width direction to ensure firm connection.

[0032] In this embodiment, the precast shaft wall 3 is made of C30 concrete, and the concrete strength of the ring beam 4 and the cast-in-place shaft wall 8 is not less than C30.

[0033] The construction method of the above inverse construction method assembled shaft includes the steps:

[0034] S1. Construct the collar beam 1

[0035] Take points and set out the profile of the shaft, measure the center line and side lines of the collar beam 1. After the earthwork is excavated to the bottom elevation of the collar beam 1, tamp the surface soil layer and construct the cushion layer, bind the steel bars of the collar beam 1, set the reserved steel bars 11 at the inner lower corner, install the formwork of the ring beam 4, and pour concrete after the formwork of the collar beam 1 is supported.

[0036] S2. Excavate the earthwork and install the shaft wall and small ducts 6

[0037] The soil in the shaft is excavated in layers by small equipment, and the soil of the shaft wall is excavated manually. The soil is trimmed according to the profile of the precast shaft wall 3. After the earthwork excavation is completed, the precast shaft wall 3 is installed in sections in time with the cooperation of manual and mechanical work. Before the installation of the precast shaft wall 3, steel strands are inserted into the prestressed pipeline 5. The reserved steel bars 11 at the upper end of the precast shaft wall 3 are welded and positioned in time with the reserved steel bars 11 at the lower end of the upper structure. The small ducts 6 are inserted into the small duct reserved holes 12 and enter the soil to prevent the displacement of the precast shaft wall 3;

[0038] When manually excavating the soil of the shaft wall, random over-excavation is strictly prohibited. The over-excavation in the height direction does not exceed 5 cm, and the over-excavation in the thickness direction does not exceed 5 cm;

[0039] When installing the small ducts 6, if the soil has good self-stability, after the excavation and installation of the single-layer shaft wall soil and the single-layer precast shaft wall 3 are completed, the small ducts 6 are inserted uniformly. When inserting the small ducts 6 uniformly, the grouting sequence is implemented symmetrically from both ends to the middle; if the soil has poor self-stability, excavate a section of the shaft wall soil, install a section of the precast shaft wall 3, and then insert the small ducts 6 in time and carry out double-fluid grouting reinforcement.

[0040] S3. Prestress tensioning

[0041] After the installation of the single-layer precast shaft wall 3 is completed, using the reserved cast-in-place shaft wall 8 as the tensioning working surface, the steel strands are tensioned by tensioning equipment (such as jacks). After the tensioning is completed, ensure that the connection between the precast shaft walls 3 is firm and there is no looseness, and grout the prestressed pipeline 5 in time until the pores are filled;

[0042] The tensioning sequence of the steel strand is to first tension the middle position and then the upper and lower positions.

[0043] S4. Pour the ring beam 4 and backfill and grout the small conduit 6

[0044] Insert the main reinforcement of the ring beam 4 axially and bind it to the reserved reinforcement 11 of the upper and lower layers. Set up the formwork and pour it together with the cast-in-place shaft wall 8 of the lower layer. After the strength of the ring beam 4 reaches a certain level (e.g., 75% of the design strength), backfill and grout the small conduit 6 to backfill the slurry into the pores between the shaft wall and the side wall soil.

[0045] S5. Cast the in-situ bottom seal

[0046] Repeat steps S2 to S4 until the bottom of the well is reached. Bind the reinforcement of the bottom slab 7 to the reserved reinforcement 11 of the precast shaft wall 3 and cast the in-situ concrete bottom slab 7.

[0047] The structure of the present invention is simple, with a short construction period, reliable circumferential and vertical connections, close connection with the soil, and no settlement. The collar beam 1, precast shaft wall 3, and bottom slab 7 are connected by reserved reinforcement 11 between adjacent layers. The collar beam 1 and all circular structures are vertically reinforced and connected by the ring beam 4 between adjacent layers. The reinforcement of the ring beam 4 is respectively connected to the reserved reinforcement 11 of the upper and lower layers and poured together with the cast-in-place shaft wall 8 of the lower layer. This setting enhances the overall vertical stability and solves the problem of vertical connection of the shaft wall. The precast shaft walls 3 of the same layer are pre-tensioned and connected by steel strands. This setting makes the precast shaft walls 3 of the same layer form a whole, enhances the lateral stiffness, resists lateral deformation, and solves the problem of circumferential connection of the precast shaft walls 3. The precast shaft wall 3 and the soil are connected by grouting and reinforcement through the small conduit 6. This setting not only keeps the precast shaft wall 3 and the soil in close contact, making the structure more stable under force, but also increases the frictional resistance between the shaft wall and the soil, improves the strength of the soil around the well, and solves the problem of the existence of pores between the precast shaft wall 3 and the soil. The upper part of the outer side of the precast shaft wall 3 is narrow and the lower part is wide. This setting transfers part of the vertical load of the precast shaft wall 3 to the side soil, forming a stable vertical force-bearing body, and solves the problem of vertical settlement of the shaft structure during the excavation process.

[0048] It should be understood that those of ordinary skill in the art can make improvements or changes according to the above description, and all such improvements and changes should fall within the protection scope of the appended claims of the present invention.

Claims

1. An inverse construction method prefabricated shaft, characterized in that: The wellhead is a cast-in-place collar beam for vertical load-bearing, the well wall is composed of several layers of sequentially vertical annular structures, the bottom of the well is a cast-in-place floor slab, and the collar beam and all annular structures are vertically reinforced and connected at the inner corner positions between adjacent layers by ring beams; each layer of annular structure is spliced by several precast well walls and a cast-in-place well wall. The precast well walls are arc-shaped sheets with a narrow upper part and a wide lower part on the outside, notches at the upper and lower corners on the inside and are provided with reserved steel bars, prestressed ducts are distributed in the left-right direction, and small conduit reserved holes are distributed in the inside-outside direction. The precast well walls of the same layer are pre-tightened and connected by steel strands passing through the prestressed ducts in the circumferential direction. The tail of the prestressed duct is an extended inner socket. After the installation of adjacent precast well walls of the same layer, the tail of the prestressed duct can be butted into the head of the corresponding prestressed duct. The precast well wall and the soil body are grouted and reinforced by small conduits passing through the small conduit reserved holes. The collar beam, all precast well walls and the floor slab are connected by reserved steel bars between adjacent layers. The ring beam steel bars are respectively connected to the reserved steel bars of the upper and lower layers and are cast together with the cast-in-place well wall of the lower layer.

2. The top-down assembled shaft according to claim 1, wherein: The cross-sectional dimensions of the collar beam are 0.9 - 1.5 m in width and 0.7 - 1 m in height; the height H of the precast well wall is 1 - 1.5 m, the width B is 1.5 - 2 m, the thickness S1 of the upper end including the notch is 0.35 - 0.5 m, the thickness S2 of the lower end including the notch is 0.7 - 1.2 m, and S2 / S1 = 1.3 - 2. The thickness of the reserved steel bar area is S3, and S3 / S1 = 0.5 - 0.

8.

3. The top-down assembled shaft according to claim 1, characterized in that: The diameter of the small conduit reserved holes is 45 - 55 mm, inclined from the upper inner direction to the lower outer direction, with an inclination of 30° - 45°. There are no less than 3 small conduits vertically for each precast well wall segment. When the width of the precast well wall is greater than 1.5 m, two rows are arranged along the width direction.

4. The top-down assembled shaft according to claim 1, wherein: The precast well wall is made of C30 concrete, and the concrete strength of the ring beam and the cast-in-place well wall is not less than C30.

5. The construction method of the top-down assembled shaft according to any one of claims 1 to 4, characterized in that: Including steps, S1. Construct the collar beam: Take points and set out the vertical shaft contour line, measure the center line and side lines of the collar beam. After the earthwork is excavated to the bottom elevation of the collar beam, compact the surface soil layer and construct the cushion layer, bind the collar beam steel bars, set the reserved steel bars at the inner lower corner, install the ring beam formwork, and pour concrete after the collar beam formwork is set up; S2. Excavate the earthwork and install the well wall and small conduits: The soil in the well is excavated in layers by small equipment, and the soil of the well wall is excavated manually. The soil is trimmed according to the contour of the precast well wall. After the earthwork excavation is completed, the precast well walls are installed in segments in time with the cooperation of manual labor and machinery. Before the installation of the precast well wall, steel strands are inserted into the prestressed ducts. The reserved steel bars at the upper end of the precast well wall are welded and positioned in time with the reserved steel bars at the lower end of the upper structure. Insert the small conduits into the small conduit reserved holes and into the soil body to prevent the displacement of the precast well wall; S3. Prestress tensioning: After the installation of a single layer of precast well walls is completed, taking the reserved cast-in-place well wall segment as the tensioning working surface, tension the steel strands by the tensioning equipment. After the tensioning is completed, ensure that the connection between the precast well walls is firm and there is no looseness, and grout the prestressed ducts in time until the pores are filled; S4. Pour the ring beam and backfill the grouting small pipes: Insert the small pipes along the circumferential direction through the main reinforcement bars of the ring beam, and tie them with the reserved reinforcement bars of the upper and lower layers. Set up the formwork and pour it together with the cast-in-place shaft wall of the lower layer. After the strength of the ring beam reaches a certain level, carry out backfill grouting on the small pipes to backfill the slurry into the pores between the shaft wall and the side wall soil. S5. Cast the in-situ bottom seal: Repeat steps S2 to S4 until the bottom of the well is constructed. Tie the bottom plate reinforcement bars with the reserved reinforcement bars of the precast shaft wall, and cast the in-situ concrete bottom plate.

6. The construction method of the inverted construction method prefabricated shaft according to claim 5, characterized in that: When manually excavating the shaft wall soil, random over-excavation is strictly prohibited. The over-excavation in the height direction shall not exceed 5 cm, and the over-excavation in the thickness direction shall not exceed 5 cm.

7. The construction method of the top-down assembled shaft according to claim 5, characterized in that: When installing the small pipes, if the soil has good self-stability, then after the excavation of the single-layer shaft wall soil is completed and the installation of the single-layer precast shaft wall is completed, insert the small pipes uniformly; if the soil has poor self-stability, then excavate a section of the shaft wall soil, install a section of the precast shaft wall, and then insert the small pipes in time and carry out double-fluid grouting reinforcement.

8. The construction method of the top-down assembled shaft according to claim 7, characterized in that: When inserting the small pipes uniformly, the grouting sequence is implemented symmetrically from both ends to the middle.

9. The construction method of the top-down assembled shaft according to claim 5, characterized in that: The tensioning sequence of the steel strands is to first tension the middle position and then the upper and lower positions.

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