A method of reverse anchoring pre-construction

Abstract

The present application relates to the field of building construction, and discloses a reverse anchor cable pre-construction method, which comprises the following steps: forming a support pile at a construction red line, determining an anchor cable hole opening position, and excavating a flat anchor cable pre-construction platform with a multilayer ladder structure according to the anchor cable hole opening position within the construction red line; when installing the anchor cable, starting from the anchor cable hole of the Nth layer, and corresponding pre-buried steel sleeves are installed after the installation of the anchor cable is completed; earthwork is backfilled to the N+1th layer of the anchor cable pre-construction platform, and then the anchor cable hole of the Nth layer after the installation is completed is subjected to grouting construction, and the anchor cable and the pre-buried steel sleeve are installed on the N+1th layer of the anchor cable pre-construction platform, and then the construction is circularly performed until all the anchor cables are installed, and finally the earthwork is backfilled to the top of the support pile, and after the cement slurry reaches the strength requirement, anchor cable tensioning and locking construction is started. The present application can avoid occupying the field outside the red line during the construction process, reduce the construction difficulty, improve the construction efficiency, and speed up the construction progress.

Description

Technical Field

[0001] This invention relates to the field of building construction, and in particular to a method for pre-construction of reverse anchor cables. Background Technology

[0002] With the increasing number of urgent, difficult, and dangerous tunnel projects in my country, traditional anchoring methods are no longer sufficient to meet the requirements of surrounding rock support. Therefore, active support methods using anchor cables to reinforce structures are becoming more widely used. Currently, anchor cable support is mainly applied in fields such as foundation pits, bridges, coal mines, and slopes. The structure of an anchor cable includes an anchored section and a free section. After drilling a hole in the rock stratum, the anchored section of the anchor cable is anchored into the borehole, while the free section is exposed outside the rock stratum. Prestress is provided by tensioning the free section of the anchor cable to achieve the anchoring effect.

[0003] There are two main types of existing anchor cable construction methods: single anchor cable construction and bundled anchor cable construction. Single anchor cable construction is suitable for coal mine and tunnel support, while bundled anchor cable construction is suitable for slope, foundation pit, and tunnel (bundled anchor cables are used when the required anchoring force is large) support.

[0004] During the construction of anchor cables, it is often necessary to level and set up a pre-construction platform in advance to facilitate the normal progress of anchor cable construction. However, in the current technology, the setting up of the pre-construction platform often encroaches on the site outside the construction boundary. When the terrain outside the construction boundary is relatively steep, the backfilling and construction of the pre-construction platform becomes more complicated and difficult, increasing the construction difficulty and slowing down the anchor cable construction progress. When the area outside the construction boundary is a protected forest area or a scenic spot, the pre-construction platform cannot be built on the site outside the boundary, which seriously increases the construction difficulty and slows down the anchor cable construction progress.

[0005] Therefore, there is an urgent need for a reverse anchor cable pre-construction method to solve the problem that anchor cable construction in the existing technology easily encroaches on the land outside the red line. Summary of the Invention

[0006] The technical problem this invention aims to solve is: how to avoid occupying land outside the red line during anchor cable construction. To solve this problem, this invention provides a reverse anchor cable pre-construction method, comprising the following steps:

[0007] S1. Construct and form support piles at the construction red line;

[0008] S2. Determine the anchor hole opening position, and excavate and level a multi-layer stepped anchor pre-construction platform within the construction red line according to the anchor hole opening position;

[0009] S3. Based on the determined anchor hole opening position, construct and clean the corresponding anchor hole on the anchor pre-construction platform;

[0010] S4. Install anchor cables in the anchor cable holes corresponding to the Nth layer of the anchor cable pre-construction platform, and pre-embed steel sleeves after the anchor cables are installed.

[0011] S5. The earthwork is backfilled in layers from bottom to top up to the N+1th layer anchor cable pre-construction platform, and then grouting is carried out on the anchor cable holes after the Nth layer is installed.

[0012] S6. Install anchor cables in the anchor cable holes corresponding to the anchor cable pre-construction platform of the N+1th layer, and pre-embed steel sleeves after the anchor cables are installed.

[0013] S7. Repeat steps S5 and S6 until all anchor cables are installed in all the anchor holes. Then, backfill the soil in layers to the top of the support piles. After the cement slurry reaches the required strength, start the anchor cable tensioning and locking construction.

[0014] Preferably, the support piles in step S1 include cast-in-place piles and square piles, a transfer beam is constructed between the cast-in-place piles and the square piles, a cap beam is constructed at the top of the square piles, and a center hole for anchor cable installation is provided in the middle of the square piles corresponding to the anchor cables.

[0015] Preferably, the distance between the elevation of the support pile and the center hole at the highest point is not less than 1.5m.

[0016] Preferably, in step S2, the vertical distance between each platform layer and the corresponding anchor cable center hole in the anchor cable pre-construction platform is not less than 2m.

[0017] Preferably, the installation angle between the anchor cable and the corresponding anchor cable pre-construction platform is 20° to 30°.

[0018] Preferably, the anchor cable is made of multiple bundles of unbonded steel strands, the strength of the steel strands is not less than 1860 MPa, the anchorage length of the anchor cable is not less than 10 m, the standard value of the axial tensile force of the anchor cable is not less than 380 kN, and the locking value is not less than 350 kN.

[0019] Preferably, the anchor cable installed in step S4 includes the following manufacturing steps:

[0020] S41. Each bundle of steel strands in the anchor cable is isolated and protected by a resin sleeve.

[0021] S42. Use anti-corrosion coating to fill the gap between the steel strand and the resin sleeve, and use grease-soaked cotton yarn to fill both ends of the resin sleeve. At the same time, use iron wire to fix it to prevent the resin sleeve from falling off.

[0022] S43. Anti-corrosion treatment shall be carried out on the exposed parts of the anchor cable tensioning section.

[0023] Preferably, the resin sleeve is made of polyethylene and the wall thickness of the resin sleeve is not less than 1 mm; the depth of the pre-embedded anchor cable hole in the steel sleeve is not less than 1 m.

[0024] Preferably, in step S5, the thickness of each backfill layer in the layered backfill is not greater than 0.5m, and the backfill compaction coefficient is not less than 0.93.

[0025] Preferably, in step S7, when the anchor cable is tensioned and locked, the strength of the cement grout anchor body must be greater than 20 MPa and reach more than 80% of the design strength.

[0026] Compared with the prior art, the reverse anchor cable pre-construction method provided in this embodiment of the invention has the following advantages:

[0027] In this embodiment, after determining the anchor hole locations according to the design drawings, a multi-tiered, stepped anchor pre-construction platform is excavated and leveled within the construction boundary. The corresponding anchor holes are then constructed based on this platform. After installing the corresponding anchors on the Nth layer of the leveled platform, backfilling is performed on the (N+1)th layer. Grouting is then carried out on the anchors installed on the Nth layer. The corresponding anchors are then installed on the (N+1)th layer of the platform, and this process is repeated until all anchors are installed. After completion, the earthwork is backfilled to the elevation of the support piles. Once the cement grout anchor body reaches the required strength, the anchor cable tensioning construction begins. In this invention, according to the design drawings, a multi-tiered anchor cable pre-construction platform is excavated and leveled within the construction boundary. After installing one layer of anchor cables, the earthwork is backfilled to the next anchor cable pre-construction platform. The entire anchor cable construction process is gradual and less difficult, eliminating the trouble of occupying space outside the construction boundary to build an anchor cable construction platform in existing technologies, and avoiding the problem of slow construction progress caused by complex sites outside the construction boundary. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the construction structure using existing technology;

[0029] Figure 2 This is a construction schematic diagram of the cast-in-place pile in this invention;

[0030] Figure 3 This is a construction schematic diagram of the anchor cable pre-construction platform in this invention;

[0031] Figure 4 This is a construction diagram of the anchor cable tensioning and locking process in this invention;

[0032] Figure 5 This is a schematic diagram of the process flow in this invention.

[0033] In the diagram: 1. Support pile; 11. Cast-in-place pile; 12. Square pile; 13. Transfer beam; 14. Cap beam; 15. Central borehole;

[0034] 2. Anchor cable pre-construction platform;

[0035] 3. Anchor cable;

[0036] 4. Steel sleeve;

[0037] 5. Backfill earthwork; 6. Site outside the red line; 7. Anchor cable construction platform; 8. Cast-in-place pile construction platform; 9. Anchor cable construction equipment. Detailed Implementation

[0038] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0039] like Figure 4 and Figure 5 As shown, a preferred embodiment of the present invention provides a method for pre-construction of reverse anchor cables, which includes the following steps:

[0040] S1. Construct and form support pile 1 at the construction red line;

[0041] S2. Determine the location of the anchor cable hole opening, and excavate and level the anchor cable pre-construction platform 2 into a multi-layered stepped structure within the construction red line according to the location of the anchor cable hole opening;

[0042] S3. Based on the determined anchor hole opening positions, construct and clean the corresponding anchor holes on the anchor pre-construction platform 2.

[0043] S4. Install anchor cable 3 in the anchor cable hole corresponding to the Nth layer of anchor cable pre-construction platform 2. After the anchor cable 3 is installed, the corresponding steel sleeve 4 is pre-embedded.

[0044] S5. The earthwork is backfilled in layers from bottom to top to the N+1th layer anchor cable pre-construction platform 2, and then grouting is carried out on the anchor cable holes after the Nth layer is installed.

[0045] S6. Install anchor cable 3 in the anchor cable hole corresponding to the anchor cable pre-construction platform 2 of the N+1th layer, and pre-embed steel sleeve 4 after the anchor cable 3 is installed.

[0046] S7. Repeat steps S5 and S6 until all anchor holes are installed with anchor cables 3. Then, backfill the soil in layers to the top of the support piles 1. After the cement slurry reaches the required strength, start the tensioning and locking construction of the anchor cables 3.

[0047] See Figure 1In existing technologies for anchor cable 3 construction, an anchor cable construction platform 7 is typically created by backfilling earthwork outside the construction boundary. Anchor cable construction equipment 9 is then installed on the platform 7 to drill anchor cable holes in the soil or rock within the boundary. Following this, the anchor cables 3 are installed, grouted, and tensioned. However, when the site outside the boundary 6 is unusable or the terrain is too steep, it is difficult to backfill and level a suitable anchor cable construction platform 7. This increases the difficulty of anchor cable 3 construction and slows down the construction progress. In this invention, according to the design drawings, the construction site within the boundary is excavated, and a multi-tiered pre-construction platform 2 is leveled according to the locations of the multiple designed anchor cable holes. Then, the anchor cables 3 are installed layer by layer from bottom to top, with earthwork backfilling performed. This eliminates the need for the site outside the boundary, avoiding the impact of the site outside the boundary 6 on the construction process. This makes the entire anchor cable 3 construction process more orderly and the construction progress faster and smoother.

[0048] In some embodiments, the support pile 1 in step S1 includes cast-in-place pile 11 and square pile 12. A transfer beam 13 is constructed between the cast-in-place pile 11 and the square pile 12. A cap beam 14 is constructed on the top of the square pile 12. A center hole 15 for installing the anchor cable 3 is provided in the middle of the square pile 12 corresponding to the anchor cable 3.

[0049] See Figure 2 Specifically, in the actual construction process, according to the design requirements of the elevation of C30 concrete transfer beam 13 in the construction drawings, the rotary drilling and grouting pile construction platform 8 is first excavated at the red line. The rotary drilling and grouting pile construction platform 8 is used as the construction foundation for the excavation and grouting construction of the grouting pile 11. After the grouting pile 11 is completed, the C30 concrete transfer beam 13 is excavated. After the transfer beam 13 is completed, the square pile 12 and the capping beam 14 are constructed according to the site environment. During the construction of the square pile 12, the center hole 15 needs to be reserved according to the distance between the square pile 12 and the anchor cable 3 hole, the installation tilt angle of the anchor cable 3, and the design requirements on the drawings, so that the anchor cable 3 can pass through the center hole 15 for installation during the installation process.

[0050] In other embodiments, when the site conditions or construction progress are insufficient to expedite the construction of the square piles 12, the construction of the square piles 12 can be carried out simultaneously with the installation of the anchor cables 3. Specifically, after the completion of the transfer beam 13, the construction of the square piles 12 and the installation of the anchor cables 3 can begin concurrently. During the concurrent construction of the square piles 12, a center hole 15 is also reserved to facilitate the installation of the anchor cables 3 and subsequent grouting. The construction of the square piles 12 and the capping beam 14 on them is carried out concurrently with the earthwork backfilling. When the strength design of the square piles 12 meets the requirements, and the anchor body strength of the cement grout also meets the requirements, the tensioning and locking of the anchor cables 3 can begin. Furthermore, in some embodiments, the cross-sectional dimensions of the square piles 12 are 1200mm x 1200mm.

[0051] In some embodiments, the distance between the elevation of the support pile 1 and the highest point of the center hole 15 is not less than 1.5m. Specifically, if the distance between the elevation of the support pile 1 and the highest point of the center hole 15 is too low, it will affect the normal progress of the grouting process after the anchor cable 3 is installed. If the distance between the elevation of the support pile 1 and the center hole 15 is too low, the grouting process is prone to mud leakage due to excessive cement grout injection pressure.

[0052] In some embodiments, in step S2, the vertical distance between each platform in the anchor cable pre-construction platform 2 and the corresponding anchor cable 3 center hole 15 is not less than 2m.

[0053] See Figure 3 Specifically, during the construction of anchor cable 3, the installation angle between anchor cable 3 and the corresponding anchor cable pre-construction platform 2 is 20° to 30°. If the vertical distance between the anchor cable pre-construction platform 2 and the corresponding anchor cable 3 center hole 15 on the square pile 12 is too small, the anchor cable 3 will not be able to pass through the center hole 15 on the square pile 12 correctly during the installation process, thus failing to complete the installation of anchor cable 3. In addition, if the distance between the two is too small, it will also increase the difficulty of placing and tensioning anchor cable 3 during the installation process.

[0054] In one specific embodiment, the anchor cable 3 is made of multiple bundles of unbonded steel strands with a strength of not less than 1860 MPa. The anchorage length of the anchor cable 3 is not less than 10 m, the standard value of the axial tensile force of the anchor cable 3 is not less than 380 kN, and the locking value is not less than 350 kN. Since the anchor cable 3 is installed at an angle, the length of the free section of the anchor cable 3 varies depending on its location. In one embodiment, the length of the free section of the anchor cable 3 ranges from 7 m to 14 m, and the longitudinal spacing between the anchor cables 3 is 3.2 m. In actual construction, the specific data can be determined based on the actual construction conditions on site, as well as the number and spacing of the anchor cables 3.

[0055] In some embodiments, the anchor cable installed in step S4 includes the following manufacturing steps:

[0056] S41. Each bundle of steel strands in anchor cable 3 is isolated and protected with resin sleeves to avoid corrosion problems after grouting.

[0057] S42. The gap between the steel strand and the resin sleeve is filled with anti-corrosion coating, and the two ends of the resin sleeve are filled with grease-soaked cotton yarn. At the same time, the resin sleeve is fixed with iron wire to prevent it from falling off. The anti-corrosion coating can better protect the steel strand and avoid the corrosion of the steel strand by cement slurry. The grease-soaked cotton yarn at both ends of the resin sleeve can also protect the steel strand and slow down the rate at which cement slurry penetrates into the gap between the resin sleeve and the steel strand, thus protecting the steel strand.

[0058] S43. Anti-corrosion treatment shall be carried out on the exposed parts of the anchor cable tensioning section 3.

[0059] In some embodiments, the resin sleeve is made of polyethylene, and the wall thickness of the resin sleeve is not less than 1 mm; the depth of the steel sleeve 4 embedded in the anchor cable 3 hole is not less than 1 m. If the wall thickness of the resin sleeve is too small, it is prone to rupture under grouting pressure, leading to damage and erosion of the steel strand by the cement grout. If the depth of the steel sleeve 4 embedded in the anchor cable hole is too small, it is prone to instability. During grouting, the steel sleeve 4 is easily pushed out of the anchor cable 3 hole by the cement grout under grouting pressure, thus causing the steel sleeve 4 to fail in protecting the anchor cable 3.

[0060] In some embodiments, in step S5, the thickness of each layer of backfill soil 5 in the layered backfilling is not greater than 0.5m, and the backfill compaction coefficient is not less than 0.93. See also Figure 4 Specifically, during the backfilling process, if the compaction of the backfill soil 5 is insufficient, it will affect the increase of the grouting coefficient, leading to cement grout leakage. In the later stage, backfill soil settlement may also cause the anchor cable 3 to break. The layered backfilling of the soil, with each layer of backfill soil 5 having a thickness of no more than 0.5m, is also to improve the compaction of the backfill soil and make the backfilled soil layer as stable as possible. At the same time, a more stable backfill soil 5 can also form a more stable anchor cable pre-construction platform 2. During the construction of the anchor cable 3, the construction equipment located on the anchor cable pre-construction platform 2 can also be more stable and less prone to tilting due to vibration, which could lead to construction errors.

[0061] In some embodiments, during step S7, when the anchor cable 3 is tensioned and locked, the strength of the cement grout anchor body must be greater than 20 MPa and reach more than 80% of the design strength. See also Figure 4Specifically, when tensioning and locking anchor cable 3, the anchor cable 3 can be tensioned in stages according to the design requirements to avoid damage caused by excessive tension. When tensioning and locking anchor cable 3, a crane can be used to suspend a basket to assist in the tensioning construction. The crane can be set at the top of the backfill layer inside the red line to avoid using the site outside the red line.

[0062] In summary, this invention provides a reverse anchor cable pre-construction method, which can, during the anchor cable 3 construction process, treat the site within the construction red line, excavate and level it to create an anchor cable pre-construction platform 2 with a multi-layered stepped structure, thereby achieving a gradual construction of the anchor cable 3. This avoids the trouble of frequently occupying the site 6 outside the construction red line during the anchor cable 3 construction process, and also avoids the problems of complex construction process, low construction efficiency, and slow construction progress caused by the site 6 outside the red line.

[0063] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A method for pre-construction of reverse anchor cables, characterized in that, Includes the following steps: S1. Construct and form support piles at the construction red line; S2. Determine the anchor hole opening position, and excavate and level a multi-layer stepped anchor pre-construction platform within the construction red line according to the anchor hole opening position; S3. Based on the determined anchor hole opening position, construct and clean the corresponding anchor hole on the anchor pre-construction platform; S4. Install anchor cables in the anchor cable holes corresponding to the Nth layer of the anchor cable pre-construction platform, and pre-embed steel sleeves after the anchor cables are installed. S5. The earthwork is backfilled in layers from bottom to top up to the N+1th layer anchor cable pre-construction platform, and then grouting is carried out on the anchor cable holes after the Nth layer is installed. S6. Install anchor cables in the anchor cable holes corresponding to the anchor cable pre-construction platform of the N+1th layer, and pre-embed steel sleeves after the anchor cables are installed. S7. Repeat steps S5 and S6 until all anchor cables are installed in all the anchor holes. Then, backfill the soil in layers to the top of the support piles. After the cement slurry reaches the required strength, start the anchor cable tensioning and locking construction.

2. The reverse anchor cable pre-construction method according to claim 1, characterized in that, The support piles in step S1 include cast-in-place piles and square piles. A transfer beam is constructed between the cast-in-place piles and the square piles. A cap beam is constructed on the top of the square piles. A center hole for anchor cable installation is provided in the middle of the square piles corresponding to the anchor cables.

3. The reverse anchor cable pre-construction method according to claim 2, characterized in that, The distance between the elevation of the support pile and the center hole at the highest point shall not be less than 1.5m.

4. The reverse anchor cable pre-construction method according to claim 1, characterized in that, In step S2, the vertical distance between each platform in the anchor cable pre-construction platform and the corresponding anchor cable center hole is not less than 2m.

5. The reverse anchor cable pre-construction method according to claim 4, characterized in that, The installation angle between the anchor cable and the corresponding anchor cable pre-construction platform is 20° to 30°.

6. The reverse anchor cable pre-construction method according to claim 1, characterized in that, The anchor cable is made of multiple bundles of unbonded steel strands with a strength of not less than 1860 MPa, an anchorage length of not less than 10 m, a standard value of axial tensile force of not less than 380 kN, and a locking value of not less than 350 kN.

7. The reverse anchor cable pre-construction method according to claim 6, characterized in that, The anchor cable installed in step S4 includes the following manufacturing steps: S41. Each bundle of steel strands in the anchor cable is isolated and protected by a resin sleeve. S42. Use anti-corrosion coating to fill the gap between the steel strand and the resin sleeve, and use grease-soaked cotton yarn to fill both ends of the resin sleeve. At the same time, use iron wire to fix it to prevent the resin sleeve from falling off. S43. Anti-corrosion treatment shall be carried out on the exposed parts of the anchor cable tensioning section.

8. The reverse anchor cable pre-construction method according to claim 7, characterized in that, The resin sleeve is made of polyethylene and the wall thickness of the resin sleeve is not less than 1 mm; the depth of the pre-embedded anchor cable hole in the steel sleeve is not less than 1 m.

9. The reverse anchor cable pre-construction method according to claim 1, characterized in that, In step S5, the thickness of each backfill layer in the layered backfill is not greater than 0.5m, and the backfill compaction coefficient is not less than 0.

93.

10. The reverse anchor cable pre-construction method according to claim 1, characterized in that, In step S7, when the anchor cable is tensioned and locked, the strength of the cement grout anchor body must be greater than 20 MPa and reach more than 80% of the design strength.

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