Deep foundation pit supporting method

Abstract

The present application relates to the technical field of building foundation pit development, in particular to a deep foundation pit supporting method, comprising marking the position of steel sheet pile according to design drawings, and performing waterproof construction according to the position of steel sheet pile. In response to the verticality of pile machine meeting the standard, the steel sheet pile and the section steel are installed. The verticality of pile machine is measured by using line plumb method, so as to avoid that the hole drilling has a certain inclination angle and affects the supporting strength of deep foundation pit supporting. The drilling hole is formed according to the design hole position, the drilling hole is sprayed by using the jet grouting pipe, and the anchor cable and the steel strand are pressed. The concrete area is established, the concrete is poured into the concrete area to form the counterforce beam, the supporting structure is tensioned and locked by using the anchor cable and the steel strand, and the deep foundation pit supporting structure is completed. At this time, the foundation pit excavation can be performed, the anchor cable, the steel sheet pile and the section steel are further used to form the supporting system which can be used for deep foundation pit, the supporting strength in the deep foundation pit can be ensured when the construction space is reduced, and the construction safety is ensured.

Description

Technical Field

[0001] This invention relates to the field of foundation pit development technology, and more specifically, to a deep foundation pit support method. Background Technology

[0002] Deep foundation pit support refers to the measures taken to support, reinforce, and protect the sidewalls of a foundation pit to ensure the safety of underground structure construction and the surrounding environment. It is a temporary structural engineering project. According to industry regulations, foundation pits with an excavation depth exceeding 5 meters (including 5 meters) or with more than three basement levels are considered deep foundation pits. When the geological conditions of the area where underground structures are being constructed are complex, it is difficult to predict and control the stability and deformation of the foundation pit during the excavation process.

[0003] Most existing deep foundation pit support systems use sheet piles + anchor cables or sheet piles + internal bracing. These two methods not only require a large construction space, but also cannot balance stability and construction efficiency. Summary of the Invention

[0004] This invention was made to solve the above-mentioned technical problems. Its purpose is to provide a deep foundation pit support method, which forms a reaction beam by sequentially setting steel sheet piles and steel sections, and works in conjunction with anchor cables. This method is easier to implement in actual construction, and ensures the rigidity of the entire deep foundation pit support while taking into account construction efficiency.

[0005] To achieve the above objectives, the present invention provides a deep foundation pit support method, comprising: marking the location of sheet piles according to design drawings and carrying out waterproofing construction according to the location of the sheet piles; installing sheet piles and steel sections in response to the verticality of the pile driver meeting the standard; forming boreholes according to the design hole positions, spraying grout into the boreholes using a jet grouting pipe, and pressing in anchor cables and steel strands; establishing a concrete area, pouring concrete into the concrete area to form a reaction beam, and using the anchor cables and steel strands to tension and lock the support structure, thereby completing the deep foundation pit support structure.

[0006] Preferably, the method further includes: excavating the foundation pit in layers based on the deep foundation pit support structure, and constructing the main structure in sequence; after the main structure is constructed, cleaning the bottom of the foundation pit and backfilling the foundation pit; chiseling out the reaction beam, pulling out the sheet piles and the steel sections, and backfilling the gaps where the reaction beam, the sheet piles and the steel sections are located.

[0007] Preferably, the step of forming a borehole according to a designed hole position, spraying grout into the designed hole position using a jet grouting pipe, and pressing in anchor cables and steel strands includes: obtaining the designed hole position and moving the drilling rig to the designed hole position; in response to the error between the drilling rig and the piling machine conforming to a first preset range, starting the drilling rig until a preset depth is reached to form the borehole; inserting the jet grouting pipe into the borehole, starting the jet grouting, and after the grouting stops at the preset depth for a preset time, raising it upwards synchronously with the drill rod of the drilling rig; in response to the jet grouting pipe being raised to a preset height, pulling out the drill rod and pressing the steel strands into the borehole.

[0008] Preferably, obtaining the designed hole position and moving the drilling rig to the designed hole position includes: obtaining the designed hole position of the anchor cable according to the design drawing; moving the drilling rig to a non-working face and starting the drilling rig; and moving the drilling rig to the designed hole position in response to the drilling depth of the drilling rig matching the length marked on the drill rod of the drilling rig.

[0009] Preferably, in response to the error between the drilling rig and the piling machine conforming to a first preset range, the drilling rig is started until a preset depth is reached. Before this, the process further includes: excavating a drainage ditch and a circulating slurry pool according to the designed borehole position.

[0010] Preferably, the step of inserting the jet grouting pipe into the borehole and starting the grouting process, after the grouting has been held at the preset depth for a preset time, and then being lifted upwards synchronously with the drill rod of the drilling rig, includes: inserting the jet grouting pipe into the borehole; starting the grouting process after the nozzle of the jet grouting pipe reaches the bottom of the borehole; synchronously lifting the jet grouting pipe and the drill rod in response to the jet grouting pipe holding at the preset depth for a preset time; increasing the grouting pressure of the jet grouting pipe in response to the jet grouting pipe being within the bottom range of the borehole; and restoring the initial grouting pressure of the jet grouting pipe in response to the jet grouting pipe no longer being within the bottom range of the borehole.

[0011] Preferably, the process of establishing a concrete area, pouring concrete into the concrete area to form a reaction beam, and using the anchor cables and steel strands to tension and lock the support structure to complete the deep foundation pit support structure includes: obtaining reinforcing bars and formwork; binding the reinforcing bars together with the formwork to form a concrete area; pouring concrete into the concrete area to form a reaction beam; calibrating the tensioning equipment; connecting the steel strands and the tensioning equipment; and, in response to the support structure meeting a preset strength, gradually increasing the locking load on the steel strands until the steel strands are completely straight, thus completing the tensioning and locking of the reaction beam.

[0012] Preferably, the step of obtaining the reinforcing bars and formwork, and binding the reinforcing bars together with the formwork to form a concrete area includes: determining the position lines of the reinforcing bars, arranging the reinforcing bar joints in an interlaced manner and binding them; the formwork surrounds the reinforcing bars and the formwork is assembled with each other using steel pipes, and the top of the formwork is finished by applying wire to complete the concrete area.

[0013] Preferably, the step of gradually increasing the locking load on the steel strands until the steel strands are completely straight, in response to the strength of the support structure meeting the preset strength, to complete the tensioning and locking of the reaction beam, includes: tensioning and locking the steel strands with a 20% locking load in response to the strength of the support structure meeting the preset strength; sequentially tensioning and locking the steel strands with 50%, 70%, and 100% locking loads; and tensioning and locking the steel strands with a 110% locking load to make the steel strands completely straight.

[0014] Preferably, before forming the borehole according to the designed hole position, spraying grout into the designed hole position using a jet grouting pipe, and pressing in the anchor cable and steel strand, the method further includes: removing the thick soil on the surface of the working face and slope setting.

[0015] Based on the above description and practice, the deep foundation pit support method of this invention includes: marking the location of sheet piles according to the design drawings, and carrying out waterproofing construction according to the location of the sheet piles. Since deep foundation pit construction and underground building construction take a long time, establishing waterproofing construction based on the location of the sheet piles can prevent sheet pile corrosion due to weather conditions or wear from debris, thereby ensuring the support strength of the deep foundation pit support. In response to the pile driver's verticality meeting the standard, sheet piles and structural steel are installed. The verticality of the pile driver is measured using a plumb line method. After the pile driver is vertical, drilling is performed to avoid drilling at a certain angle, which would affect the support strength of the deep foundation pit support. Boreholes are formed according to the designed hole positions, and grout is injected into the boreholes using a jet grouting pipe, and anchor cables and steel strands are pressed in. Stable underground foundation support is formed through grouting, and anchor cables and steel strands are extended from the boreholes and installed inside the boreholes to facilitate subsequent tensioning and locking of the support structure. A concrete zone is established, and concrete is poured into the zone to form a reaction beam. Anchor cables and steel strands are used to tension and lock the support structure, completing the deep foundation pit support structure. At this point, the foundation pit can be excavated, and anchor cables, sheet piles, and steel sections are used to form a support system that can be used for deep foundation pits. This reduces the construction space while ensuring the support strength within the deep foundation pit and guaranteeing construction safety. Attached Figure Description

[0016] Figure 1 This is a flowchart of a deep foundation pit support method according to one embodiment of the present invention.

[0017] Figure 2This is a flowchart of a deep foundation pit support method according to another embodiment of the present invention.

[0018] Figure 3 This is a flowchart of step S3 of a deep foundation pit support method according to one embodiment of the present invention.

[0019] Figure 4 This is a flowchart of step S31 of a deep foundation pit support method according to one embodiment of the present invention.

[0020] Figure 5 This is a flowchart of step S33 of a deep foundation pit support method according to one embodiment of the present invention.

[0021] Figure 6 This is a flowchart of step S4 of a deep foundation pit support method according to one embodiment of the present invention.

[0022] Figure 7 This is a flowchart of step S41 of a deep foundation pit support method according to one embodiment of the present invention.

[0023] Figure 8 This is a flowchart of step S44 of a deep foundation pit support method according to one embodiment of the present invention.

[0024] Figure 9 This is a schematic diagram of the deep foundation pit support structure in one embodiment of the present invention.

[0025] The attached figures are labeled as follows: 1. Steel sheet piles; 2. Steel sections; 3. Drilling; 4. Anchor cables; 5. Steel strands; 6. Reaction beams. Detailed Implementation

[0026] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0027] Furthermore, the accompanying drawings are merely illustrative diagrams of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. It should be noted that in this invention disclosure, the terms "comprising," "configured with," and "set in" are used to indicate an open-ended inclusion, meaning that additional elements / components / etc. may exist besides those listed; the terms "first," "second," etc., are used only as labels and are not intended to limit the number or order of objects; the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention.

[0028] Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0029] This invention discloses a method for supporting deep foundation pits. For details, please refer to... Figures 1 to 9 This deep foundation pit support method utilizes sheet piles, anchor cables, and structural steel to form a composite support structure. It can be used to support foundation pits of a certain depth, overcoming the problem of large construction space typically required for deep foundation pit support, ensuring sufficient support strength, and preventing safety accidents. Specifically, the deep foundation pit support method includes: Step S1: Mark the location of sheet pile 1 according to the design drawings, and carry out waterproofing construction according to the location of sheet pile 1.

[0030] In some application scenarios, during actual construction, the location of sheet pile 1 is determined by design drawings and marked with lime. Construction personnel can design waterproofing based on the location of sheet pile 1, and prioritize waterproofing design to ensure that the sheet pile 1 and other support structures will not rust due to environmental humidity or rainwater during the implementation of the deep foundation pit support method, thereby affecting the support strength of the entire support structure.

[0031] Step S2: In response to the pile driver's verticality meeting the standard, install sheet pile 1 and steel section 2.

[0032] In some application scenarios, to ensure that borehole 3 is perpendicular to the working face during construction, the pile driver is positioned, ensuring it is stable and level, and nearby obstacles are cleared. The pile driver is then vertically positioned using a plumb line method. After ensuring the pile driver is vertical, a hydraulic excavator is used to install the sheet piles 1 and the steel section 2 to the designated elevation according to the design drawings. The top elevations of the sheet piles 1 and the steel section 2 should be the same and 500mm higher than the top of the capping beam to facilitate subsequent positioning and construction.

[0033] Step S3: Drill hole 3 is formed according to the designed hole position. Grout is sprayed into drill hole 3 using a jet grouting pipe, and anchor cable 4 and steel strand 5 are pressed in.

[0034] In some application scenarios, a drilling rig is used to drill borehole 3, and the jet grouting pipe is simultaneously lowered to spray grout into borehole 3 to form ground piles, ensuring the strength of the entire deep foundation pit support. Furthermore, after grouting, anchor cables 4 and steel strands 5 are promptly pressed into borehole 3, facilitating subsequent reinforcement of the entire deep foundation pit using steel strands 5.

[0035] Step S4: Establish a concrete area, pour concrete into the concrete area to form a reaction beam 6, and use anchor cables 4 and steel strands 5 to tension and lock the support structure to complete the deep foundation pit support structure.

[0036] In some application scenarios, after the installation of sheet piles 1 and steel sections 2 is completed, and the ground piles and steel strands 5 are fixed, a concrete area is built according to the design drawings, and concrete is poured to form a reaction beam 6. The steel strands 5 are connected to the anchor cables 4 and the reaction beam 6, and the steel strands 5 are gradually tightened to tension and lock the entire deep foundation pit support, ensuring the support strength of the deep foundation pit, simplifying the construction steps, and reducing the waste of manpower and material resources.

[0037] Furthermore, to ensure the smooth progress of subsequent sheet pile 1 and anchor cable 4 construction, the following steps are included before step S3: Step S30: Remove the thick soil from the surface of the working face and slope it.

[0038] In some application scenarios, before drilling holes (3) with a drilling rig and driving in sheet piles (1) and steel sections (2) with a pile driver, construction personnel should check for debris on the working surface and manually remove approximately 60cm of soil, removing surface sand, gravel, and hard lumps to facilitate subsequent pile driver and drilling operations. Simultaneously, appropriate backfilling and slope protection should be implemented to prevent collapse during excavation of the foundation pit.

[0039] Understandably, after the deep foundation pit support is constructed, excavators can be used for deep foundation pit excavation, specifically including: Step S51: Based on the deep foundation pit support structure, excavate the foundation pit in layers and construct the main structure in sequence.

[0040] In some application scenarios, after completing the deep foundation pit support, the principles of horizontal segmentation, vertical layering, and support before excavation are followed. For example, when the foundation pit depth is 6.8m, the first step is to excavate to 3m, and the second step is to excavate to 6.5m. When the depth reaches 20-30cm at the bottom of the foundation pit, manual cleaning is required to avoid over-excavation. The excavated soil is transported out by vehicle from near the sheet pile 1.

[0041] Step S52: After the main structure construction is completed, clean the bottom of the foundation pit and backfill the foundation pit.

[0042] In some application scenarios, after the main structure construction is completed in the foundation pit, tree roots, accumulated water, and other debris at the bottom of the pit must be removed, and the water in the pit must be pumped out and the silt removed to prevent backfilling from being incomplete due to debris, which could lead to collapse under the weight of the building and cause safety hazards. The main structure includes the foundation slab, side walls, and roof slab, and after construction, the support strength and surface waterproofing must be ensured. Specifically, during backfilling, the soil material must be selected based on the surrounding soil, and the optimal moisture content must be determined to determine the thickness of the soil layer, the number of compaction cycles, etc. The backfill height should reach approximately 3 meters below the reaction beam 6. When connecting deep and shallow foundation pits, the deeper foundation pit is filled to the elevation of the shallower foundation pit first, and then backfilled simultaneously. When working in sections, the joints should be made into a stepped shape (height-to-width ratio 1:2), with a staggered joint distance of ≥1.0m. After filling, the working surface is leveled by pulling a line, and leveled or supplemented according to the standard line.

[0043] Step S53: Remove the reaction beam 6, pull out the sheet pile 1 and the steel section 2, and backfill the gap where the reaction beam 6, sheet pile 1 and steel section 2 are located.

[0044] In some application scenarios, after the surface is completely leveled, an excavator is used to break the reaction beam 6, and a pile driver is used to pull out the sheet pile 1 and the steel section 2 in one go. Fine sand is then used to fill the original positions of the reaction beam 6, sheet pile 1 and steel section 2.

[0045] After drilling a hole using a drilling rig, the steel strand 5 needs to be placed into the drilled hole 3. Step S3 specifically includes: Step S31: Obtain the designed hole position and move the drilling rig to the designed hole position.

[0046] In some application scenarios, the design hole positions are drawn on a flat working surface according to the design drawings. The drill rig is moved to align with the design hole positions, and the pile driver is leveled and centered to ensure that the pile driver and drill rod correspond to each other.

[0047] Step S32: In response to the error between the drilling rig and the piling machine meeting the first preset range, start the drilling rig until the preset depth is reached to form the borehole 3.

[0048] In some application scenarios, the error between the pile driver and the drilling rig is measured. The first preset range is a deviation of less than 20mm. When the error between the pile driver and the drilling rig is less than 20mm and the verticality error of the borehole 3 is less than 0.15%, the drilling rig is started to drill the borehole 3.

[0049] Step S33: Insert the jet grouting pipe into borehole 3, start the jet grouting, stay at the preset depth for a preset time, and then lift it upwards synchronously with the drill rod of the drilling rig.

[0050] In some applications, after the jet grouting pipe is inserted to the designed depth, the high-pressure pump is started, and then grout is jetted upwards. To ensure the quality of the pile bottom, the nozzle of the jet grouting pipe is lowered to the designed depth for a preset time of 10 seconds. After the grout is flowing normally from the orifice of the jet grouting pipe, it is then jetted and lifted.

[0051] In addition, if the drilling rig malfunctions during construction, the lifting and rotation of the drill rod should be stopped, and the malfunction should be repaired and eliminated immediately. After the accident is resolved, the grouting should be carried out again to ensure that the overlap with the original grouting stop surface is not less than 20cm.

[0052] Step S34: In response to the jet grouting pipe being raised to the preset height, pull out the drill rod and press the steel strand 5 into the borehole 3.

[0053] In some applications, after the jet grouting is raised to the design elevation, the drill rod is pulled out, and the steel strand 5 is pressed into the predetermined depth using the drill rod. During the jacking process, continuous grouting must be maintained, and the pressure must not exceed 1 MPa to prevent flowing mud and sand from clogging the nozzle of the jet grouting pipe.

[0054] Furthermore, to ensure that the indiscriminate discharge of slurry during shotcreting does not affect normal construction, the following is also included between steps S32: Step S320: Excavate drainage ditches and circulating slurry pools according to the designed borehole locations.

[0055] In some application scenarios, before construction, drainage ditches and circulating grout pools are constructed in the site, avoiding the construction areas of sheet piles 1, steel sections 2, and reaction beams 6. The drainage ditches can guide the grout overflowing from the jet grouting pipes back to the circulating grout pool for reuse. Waste grout after grouting can be introduced into a sedimentation tank, where it is sedimented and chemically treated according to actual discharge standards before being discharged. The settled soil can be removed simultaneously during the excavation of the foundation pit.

[0056] To ensure the verticality and accuracy of borehole 3, the drilling rig needs to be pre-started to ensure its normal operation. Step S31 specifically includes: Step S311: Obtain the design hole positions of anchor cable 4 according to the design drawings.

[0057] In some application scenarios, the designed hole positions are drawn on a flat working surface according to the design drawings.

[0058] Step S312: Move the drilling rig to a non-working face and start the drilling rig.

[0059] In some application scenarios, the drilling rig is moved to a non-working area that will not affect the actual construction area, and a test spraying is performed. After the mechanical test run of borehole 3 is normal, pilot drilling begins to ensure the normal operation of the drilling rig.

[0060] Step S313: In response to the drilling depth of the drill rig matching the length of the drill rod marking on the drill rig, move the drill rig to the designed hole position.

[0061] In some application scenarios, during the pre-start drilling process, the length of the drill rod is recorded and compared with the depth of the borehole 3. When the depth matches the length, the drill is moved to the designed hole position, ensuring the accuracy of the borehole 3 depth.

[0062] To ensure the strength of the ground pile formed by grouting through the jet grouting pipe in borehole 3, step S33 specifically includes: Step S331: Insert the jet grouting pipe into borehole 3. After the nozzle of the jet grouting pipe reaches the bottom of borehole 3, start the grouting.

[0063] In some application scenarios, the jet grouting pipe is inserted into borehole 3 until it reaches the bottom of borehole 3. The high-pressure pump is then turned on, and the grout is sprayed out from the hole of the jet grouting pipe, thus starting the grouting process.

[0064] Step S332: In response to the jet grouting pipe remaining at a preset depth for a preset time, simultaneously lift the jet grouting pipe and the drill rod.

[0065] In some applications, when the nozzle is lowered to the designed depth, it is rotated for about 10 seconds at the bottom position. After the grout is flowing out of the hole normally, it is then rotated and lifted to ensure the quality of the bottom end of the pile and avoid breakage due to insufficient strength at the bottom end.

[0066] Step S333: In response to the grouting pipe being located within the bottom range of borehole 3, increase the grouting pressure of the grouting pipe.

[0067] In some application scenarios, in order to prevent the pile bottom from becoming top-heavy due to excessive weight above, the borehole 3 is divided into a bottom area and a shallow area according to the depth of the borehole 3. When the jet grouting pipe is located in the bottom area of ​​the borehole 3, the jet grouting pressure of the drill rod is increased and maintained for a longer time to increase the grout density at the pile bottom, thereby improving the quality of the pile bottom.

[0068] Step S334: In response to the grouting pipe no longer being located within the bottom range of borehole 3, restore the initial jet grouting pressure of the grouting pipe.

[0069] In some applications, when the jet grouting pipe is raised to a shallow area, the initial jet grouting pressure of the jet grouting pipe can be adjusted back and maintained until the grouting is completed.

[0070] To ensure the support strength of the entire deep foundation pit support, step S4 specifically includes: Step S41: Obtain the reinforcing bars and formwork, and tie the reinforcing bars together with the formwork to form the concrete area.

[0071] In some applications, the construction location of the piles is checked according to the design drawings. The location of the reinforcing bars is then determined based on the excavation lines and marked with lime lines. A concrete area is then constructed using the reinforcing bars and formwork. The reinforcing bars must be tested before use, and the formwork must have sufficient strength and rigidity.

[0072] Step S42: Pour concrete into the concrete area to form the reaction beam 6.

[0073] In some applications, when pouring concrete into concrete areas, it is necessary to use an immersion vibrator to compact the concrete to prevent uneven concrete from affecting the strength of the reaction beam 6.

[0074] Step S43: Calibrate the tensioning equipment and connect the steel strand 5 to the tensioning equipment.

[0075] In some application scenarios, the tensioning equipment must meet national standards and must be carried out at least 14 days after the anchor cable 4 is driven into the pile. Tensioning can only be carried out after confirming that the strength of the reaction beam 6 and the anchor cable 4 is sufficient. The steel strand 5 is connected to the tensioning equipment, and the tensioning equipment and the steel strand 5 should be carried out at intervals to avoid affecting the adjacent anchor rods.

[0076] Step S44: In response to the support structure meeting the preset strength, gradually increase the locking load on the steel strand 5 until the steel strand 5 is completely straight, and complete the tensioning and locking of the reaction beam 6.

[0077] In some application scenarios, when the strength of the support structure meets the preset strength, which can be 75% of the overall strength, the locking load on the steel strand 5 is gradually increased using tensioning equipment until the steel strand 5 is completely straight, thus completing the tensioning and locking.

[0078] When using reinforcing bars and formwork to form a concrete area, step S41 specifically includes: Step S411: Determine the position lines of the reinforcing bars, arrange the reinforcing bar joints in an interlaced manner, and tie them together.

[0079] In some applications, the location lines of the reinforcing bars are determined according to the design drawings. The reinforcing bars can be processed according to actual site requirements and tied on-site. When connecting the reinforcing bars, if lap welding is used for the joints, the joints should be staggered by 50%. A protective layer should be provided on the outside of the reinforcing bars; this protective layer can be a spacer block, which should be securely tied to the reinforcing bar to prevent damage from external forces.

[0080] Step S412: The formwork is surrounded by reinforcing bars and the formwork is assembled with each other using steel pipes. The top of the formwork is tied with wire to complete the concrete area.

[0081] In some applications, a release agent needs to be applied to the formwork before splicing to prevent corrosion. This release agent must not come into contact with the reinforcing bars or concrete joints to prevent the oily nature of the release agent from causing slippage between the formwork and the reinforcing bars, which could affect the stability of the entire concrete area. Furthermore, steel pipes are used for auxiliary connections during formwork splicing, and diagonal braces are installed between the formwork sections to prevent deformation under stress. The top of the formwork is reinforced with tension wires to prevent the formwork and reinforcing bars from floating upwards under the force of concrete pouring, thus affecting the quality of the reaction beam 6.

[0082] When tensioning anchor cable 4 to enhance the strength of deep foundation pit support, the force on steel strand 5 should be gradually adjusted. Specifically, step S44 includes: Step S441: In response to the support structure meeting the preset strength, tension the locking steel strand 5 using a 20% locking load.

[0083] In some application scenarios, when the strength of the support structure meets the preset strength, which can be 75% of the overall strength, a 20% locking load is first applied using a tensioning device to connect the reaction beam 6 and the steel strand 5, and then the two are connected and fixed.

[0084] Step S442: Use locking loads of 50%, 70%, and 100% to tension the locking steel strand 5 in stages.

[0085] In some application scenarios, the locking load on the steel strand 5 is gradually increased. Specifically, it can be 50%, 70%, or 100% of the locking load, gradually increasing in stages until the steel strand 5 is straightened. This avoids the steel strand 5 being directly subjected to a large locking load, which could cause the steel strand 5 to break.

[0086] Step S443: Tension the locking steel strand 5 using a 110% locking load to make the steel strand 5 completely straight.

[0087] In some application scenarios, after the steel strand 5 is straightened, on the one hand, it can prevent the steel strand 5 and the anchor from rebounding, reserve a buffer space for retraction, apply a 110% locking load to the steel strand 5, and tension and lock the steel strand 5; on the other hand, the steel strand 5 can hold the load for 2 to 5 minutes, accelerate the stress relaxation of the steel strand 5, and allow it to complete most of the attenuation in a controlled state in advance, thereby reducing its subsequent relaxation loss and further ensuring the support strength of deep foundation pit support.

[0088] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for supporting deep foundation pits, characterized in that, include: Mark the location of the sheet piles according to the design drawings, and carry out waterproofing construction according to the location of the sheet piles; In response to the requirement that the verticality of the piling machine meets the standard, steel sheet piles and structural steel are installed; Drill holes are formed according to the designed hole positions, grout is sprayed into the drill holes using a jet grouting pipe, and anchor cables and steel strands are pressed in. A concrete zone is established, and concrete is poured into the concrete zone to form a reaction beam. The anchor cables and steel strands are used to tension and lock the support structure, thus completing the deep foundation pit support structure.

2. The deep foundation pit support method as described in claim 1, characterized in that, Also includes: Based on the deep foundation pit support structure, the foundation pit is excavated in layers, and the main structure is constructed in sequence. After the main structure construction is completed, the bottom of the foundation pit is cleaned and the foundation pit is backfilled. Remove the reaction beam, pull out the sheet pile and the steel section, and backfill the gap where the reaction beam, sheet pile and steel section are located.

3. The deep foundation pit support method as described in claim 1, characterized in that, The process of drilling holes according to designed locations, applying grout to the designed locations using a jet grouting pipe, and then pressing in anchor cables and steel strands includes: Obtain the designed hole position and move the drilling rig to the designed hole position; In response to the error between the drilling rig and the piling machine meeting a first preset range, the drilling rig is started until a preset depth is reached to form the borehole; The jet grouting pipe is inserted into the borehole, and the grouting is started and held at the preset depth for a preset time before being lifted upward synchronously with the drill rod of the drilling rig. In response to the jet grouting pipe being raised to a preset height, the drill rod is pulled out and the steel strand is pressed into the borehole.

4. The deep foundation pit support method as described in claim 3, characterized in that, The step of obtaining the designed hole position and moving the drilling rig to the designed hole position includes: The design hole positions of the anchor cable are obtained according to the design drawings; Move the drilling rig to a non-working face and start the drilling rig; In response to the drilling depth of the drill rig matching the marked length of the drill rod, the drill rig is moved to the designed hole position.

5. The deep foundation pit support method as described in claim 3, characterized in that, The step of starting the drilling rig until a preset depth is reached in response to an error between the drilling rig and the piling machine falling within a first preset range, before which the following steps are also included: Drainage ditches and circulating slurry pools were excavated according to the designed borehole locations.

6. The deep foundation pit support method as described in claim 3, characterized in that, The step of inserting the jet grouting pipe into the borehole, starting the jet grouting, and then raising it synchronously with the drill rod of the drilling rig after the grout has stayed at the preset depth for a preset time includes: Insert the jet grouting pipe into the borehole, and start grouting after the nozzle of the jet grouting pipe reaches the bottom of the borehole; In response to the jet grouting pipe remaining at the preset depth for a preset time, the jet grouting pipe and the drill rod are simultaneously raised; In response to the grouting pipe being located within the bottom range of the borehole, the grouting pressure of the grouting pipe is increased; In response to the grouting pipe no longer being located within the bottom range of the borehole, the initial jetting pressure of the grouting pipe is restored.

7. The deep foundation pit support method as described in claim 1, characterized in that, The process involves establishing a concrete zone, pouring concrete into the zone to form a reaction beam, and using the anchor cables and steel strands to tension and lock the support structure, thus completing the deep foundation pit support structure, including: Obtain reinforcing bars and formwork, and tie the reinforcing bars together with the formwork to form a concrete area; Concrete is poured into the concrete area to form a reaction beam; Calibrate the tensioning equipment and connect the steel strand to the tensioning equipment; In response to the support structure meeting the preset strength, the locking load on the steel strand is gradually increased until the steel strand is completely straight, thus completing the tensioning and locking of the reaction beam.

8. The deep foundation pit support method as described in claim 7, characterized in that, The process of obtaining reinforcing bars and formwork, and binding the reinforcing bars together with the formwork to form a concrete area includes: The position lines of the reinforcing bars are determined, and the joints of the reinforcing bars are arranged in an interlaced manner and tied together. The template surrounds the reinforcing bar and the templates are assembled with each other using steel pipes. The top of the template is finished with wire drawing to complete the concrete area.

9. The deep foundation pit support method as described in claim 7, characterized in that, The step of gradually increasing the locking load on the steel strands in response to the support structure meeting the preset strength, until the steel strands are completely straight, completes the tensioning and locking of the reaction beam, including: In response to the support structure meeting the preset strength, the steel strands are tensioned and locked using a 20% locking load; The steel strands are tensioned and locked in stages using locking loads of 50%, 70%, and 100% in sequence; The steel strand is tensioned and locked using a 110% locking load to make it completely straight.

10. The deep foundation pit support method as described in claim 1, characterized in that, Before drilling according to the designed hole position, spraying grout into the designed hole position using a jet grouting pipe, and pressing in anchor cables and steel strands, the process also includes: Remove the thick soil from the surface of the working face and slope it.

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