Large-span deep foundation pit steel-concrete combined supporting structure and construction method thereof

Abstract

The invention relates to a large-span deep foundation pit steel-concrete combined supporting structure and a construction method thereof. The large-span deep foundation pit steel-concrete combined supporting structure comprises profile steel enclosing purlins arranged on the edge of a foundation pit; the concrete side truss structures are arranged on the two opposite sides of the foundation pit; the profile steel supports are connected between the oppositely arranged concrete fringe truss structures in a supporting manner; the multiple profile steel angle braces are obliquely arranged at the corners of the foundation pit in a supporting mode, and the ends of the profile steel angle braces are connected with the corresponding profile steel enclosing purlins and the concrete fringe truss structures; and the axial force servo system is connected to the profile steel support and the profile steel angle brace and is used for applying axial force to the profile steel support and the profile steel angle brace. The concrete fringe truss structure has good deformation control capacity and serves as a force transmission buffer strip between the prestressed profile steel support and the enclosure structure coping beam, and the problems that a foundation pit cracks, bends, inclines and the like due to the fact that concentrated axial force is too large are solved.

Description

Technical Field

[0001] The invention relates to the field of foundation pit construction engineering, and in particular to a large-span deep foundation pit steel-concrete combined supporting structure and a construction method thereof. Background Art

[0002] With the rapid advancement of urbanization in my country, the number of deep foundation pit projects has also increased dramatically, and the deformation control requirements of foundation pits have become increasingly stringent. In order to ensure the safety of underground engineering construction, the selection of a reasonable and efficient foundation pit engineering support plan is of utmost importance. Among them, the large-span deep foundation pit in Linjiang has a high water level outside the pit, a large support span, and high deformation control requirements, which makes the foundation pit support requirements higher than other types of deep foundation pits. Traditional reinforced concrete supports have strong rigidity and are suitable for different foundation pits, but they have poor flexibility and economy, the materials cannot be reused, and they are prone to safety and environmental problems during installation and dismantling. Summary of the invention

[0003] The purpose of the present invention is to overcome the defects of the prior art and provide a large-span deep foundation pit steel-concrete composite support structure and a construction method thereof, so as to solve the problems of the existing reinforced concrete support such as poor flexibility, poor economy, non-reusable materials and easy safety and environmental problems during installation and dismantling.

[0004] The technical solution to achieve the above purpose is:

[0005] The present invention provides a large-span deep foundation pit steel-concrete composite supporting structure, comprising:

[0006] Steel purlins installed at the edge of the foundation pit;

[0007] Concrete side truss structures located on opposite sides of the foundation pit;

[0008] Supporting steel supports connected between oppositely disposed concrete side truss structures;

[0009] Multiple steel angle braces are provided at the corners of the foundation pit for oblique support, and the ends of the steel angle braces are connected to the corresponding steel perimeter purlins and the concrete side truss structure;

[0010] The axial force servo system connected to the section steel support and the section steel angle support is used to apply axial force to the section steel support and the section steel angle support.

[0011] A further improvement of the large-span deep foundation pit steel-concrete composite support structure of the present invention is that it also includes a plurality of pairs of support columns driven into the foundation pit along the setting positions of the steel supports and the steel angle braces, and a support beam is connected between a pair of support columns, and the support beam supports the corresponding steel supports and steel angle braces.

[0012] A further improvement of the large-span deep foundation pit steel-concrete composite supporting structure of the present invention is that the concrete side truss structure is provided with a concrete triangular structure corresponding to the steel support and the steel angle brace, and one side of the concrete triangular structure is butt-connected to the end of the corresponding steel support and steel angle brace.

[0013] A further improvement of the large-span deep foundation pit steel-concrete composite support structure of the present invention is that a pair of diagonal braces are provided at the end of the steel support close to the end of the concrete side truss structure, and the pair of diagonal braces are obliquely supported between the steel support and the concrete side truss structure.

[0014] A further improvement of the large-span deep foundation pit steel-concrete composite supporting structure of the present invention is that a steel triangle structure is provided on the steel purlin corresponding to the steel angle brace, and one side surface of the steel triangle structure is butt-connected to the end of the steel angle brace.

[0015] The present invention also provides a construction method for a large-span deep foundation pit steel-concrete composite support structure, comprising the following steps:

[0016] Install steel purlins at the edge of the foundation pit;

[0017] Concrete side truss structures are cast on opposite sides of the foundation pit;

[0018] Providing a steel support, and connecting the steel support between oppositely disposed concrete side truss structures;

[0019] Providing a steel angle brace, obliquely supporting the steel angle brace at the corner of the foundation pit, and connecting the end of the steel angle brace with the corresponding steel perimeter purlin and concrete side truss structure;

[0020] An axial force servo system is provided, and the axial force servo system is connected to the steel support and the steel angle support, and the axial force servo system is used to apply axial force to the steel support and the steel angle support.

[0021] A further improvement of the construction method of the large-span deep foundation pit steel-concrete composite support structure of the present invention is that before setting the steel support and the steel angle brace, support columns are first provided, and the support columns are driven into the foundation pit in pairs along the setting positions of the steel support and the steel angle brace;

[0022] A supporting crossbeam is provided, and the supporting crossbeam is connected between a pair of supporting columns, and the supporting crossbeam is used to support the corresponding steel support and steel angle brace.

[0023] A further improvement of the construction method of the large-span deep foundation pit steel-concrete composite support structure of the present invention is that when the concrete side truss structure is cast, a steel bar of a concrete triangle structure is arranged at a corresponding position on the side of the concrete side truss structure, and an embedded part that is butt-connected to the end of the corresponding steel support and steel angle brace is arranged on the corresponding side of the concrete triangle structure.

[0024] A further improvement of the construction method of the large-span deep foundation pit steel-concrete composite support structure of the present invention is that when the steel support is provided, a pair of diagonal braces are provided between the steel support and the concrete side truss structure.

[0025] A further improvement of the construction method of the large-span deep foundation pit steel-concrete composite supporting structure of the present invention is that when installing the steel purlin, a steel triangular structure is set at the position of the steel purlin corresponding to the steel angle brace, and the steel angle brace is connected by using the set steel triangular structure.

[0026] The beneficial effects of the large-span deep foundation pit steel-concrete composite support structure and the construction method thereof of the present invention are:

[0027] The concrete side truss structure adopted in the present invention has good deformation control ability, and serves as a force transmission buffer zone between the prestressed steel support and the top beam of the enclosure structure, avoiding problems such as cracking, bending, and tilting of the foundation pit caused by excessive concentrated axial force.

[0028] The present invention sets a concrete triangle structure on the side truss structure to connect with the steel support, increases the safety factor of the joint between the steel support and the support, sets an axial force servo system on the steel support, accurately applies prestress, and realizes the functions of automatic low-pressure compensation and automatic high-pressure alarm.

[0029] The large-span deep foundation pit steel-concrete composite support structure and the construction method thereof of the present invention effectively improve work efficiency, shorten construction period, save costs, and achieve the purpose of safe and efficient construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a flow chart of the construction method of the large-span deep foundation pit steel-concrete composite support structure.

[0031] Figure 2 It is a cross-sectional view of the connection between the medium-shaped steel support and the concrete side truss structure of the large-span deep foundation pit steel-concrete composite support structure of the present invention.

[0032] Figure 3 It is a top view of the steel-concrete composite supporting structure for a large-span deep foundation pit according to the present invention.

[0033] Figure 4 It is a schematic diagram of the layout of the axial force servo system in the steel-concrete composite supporting structure of the large-span deep foundation pit of the present invention.

[0034] Figure 5It is a schematic diagram of the connection between the corresponding parts of the concrete triangle structure and the side truss structure in the steel-concrete composite supporting structure of the large-span deep foundation pit of the present invention.

[0035] Figure 6 The figure is a schematic diagram of the steel bar arrangement inside the concrete triangle structure in the steel-concrete composite supporting structure for a large-span deep foundation pit of the present invention.

[0036] Figure 7 The present invention is a schematic structural diagram of the embedded parts arranged at the concrete triangle structure in the steel-concrete composite supporting structure of the large-span deep foundation pit.

[0037] Figure 8 The present invention provides a model diagram of a corbel bracket in a large-span deep foundation pit steel-concrete composite supporting structure and a construction method thereof.

[0038] Fig. 9 It is a model diagram of installing steel purlins in the large-span deep foundation pit steel-concrete composite supporting structure and its construction method of the present invention.

[0039] Fig.10 This is a model diagram of installing support columns and beams in the large-span deep foundation pit steel-concrete composite support structure and its construction method of the present invention.

[0040] Fig.11 It is a cross-sectional view of the joint of the support columns in the large-span deep foundation pit steel-concrete composite support structure and the construction method thereof of the present invention.

[0041] Fig.12 This is a model diagram of the template and steel bar layout of the concrete side truss structure in the large-span deep foundation pit steel-concrete composite support structure and its construction method of the present invention.

[0042] Fig.13 It is a structural schematic diagram of installing steel angle braces in the large-span deep foundation pit steel-concrete composite supporting structure and its construction method of the present invention.

[0043] Fig.14 It is a structural schematic diagram of installing an axial force servo system in a large-span deep foundation pit steel-concrete composite supporting structure and a construction method thereof of the present invention.

[0044] Fig.15 This is a model diagram of the large-span deep foundation pit steel-concrete composite supporting structure of the present invention.

[0045] Fig.16 The present invention provides a flow chart for the installation, use and removal of the axial force servo system in the large-span deep foundation pit steel-concrete composite support structure and its construction method. DETAILED DESCRIPTION

[0046] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0047] See also Figure 1The present invention provides a large-span deep foundation pit steel-concrete composite support structure and a construction method thereof. Aiming at the pain points of deep foundation pit construction such as near pipelines, high water levels, and large spans, the traditional process is to use reinforced concrete support, but its flexibility and economy are poor, the materials cannot be reused, and it is easy to cause safety and environmental problems during installation and dismantling. In view of this, the present invention adopts a support system of steel support, angle bracing, and concrete side trusses as support in the foundation pit. The concrete side truss structure has a good ability to control deformation. It serves as a force transmission buffer zone between the prestressed steel composite support and the top beam of the enclosure structure to avoid cracking, bending, tilting and other problems caused by excessive concentrated axial force in the foundation pit. The first vertical line adopts a single-piece and the second vertical double-piece steel support, which can effectively solve the problem of large deformation in the middle area of ​​the enclosure structure. The steel support is connected to the concrete side truss structure through a force transmission piece, and a concrete triangle structure is set at the anchor end of the purlin and the force transmission piece along the force direction to increase the safety factor of the joint between the steel support and the support. At the same time, the steel composite support is combined with the axial force servo system to accurately apply prestress, in which the second double-piece is applied simultaneously up and down, and the axial force servo system is used for 24-hour real-time monitoring to realize the functions of automatic low-pressure compensation and automatic high-pressure alarm. The construction method of the large-span deep foundation pit steel-concrete composite support effectively improves work efficiency, shortens construction period, saves costs, and achieves the purpose of safe and efficient construction. The large-span deep foundation pit steel-concrete composite support structure of the present invention and its construction method are described below in conjunction with the accompanying drawings.

[0048] See also Figure 3 , showing a top view of the large-span deep foundation pit steel-concrete composite support structure of the present invention. Figure 4 , showing the layout schematic diagram of the axial force servo system in the large-span deep foundation pit steel-concrete composite support structure of the present invention. Fig.15 , showing the model diagram of the large-span deep foundation pit steel-concrete composite support structure of the present invention. Figure 3 , Figure 4 and Fig.15 , the large-span deep foundation pit steel-concrete composite supporting structure of the present invention is explained.

[0049] like Figure 3 , Figure 4 and Fig.15As shown, the large-span deep foundation pit steel-concrete composite support structure of the present invention includes a steel purlin 21, a concrete side truss structure 22, a steel support 23, a steel angle brace 24 and an axial force servo system 25, wherein the steel purlin 21 is arranged at the edge of the foundation pit, and the steel purlin 21 is arranged on one side of the foundation pit; the concrete side truss structure 22 is arranged on the opposite sides of the foundation pit, and the concrete side truss structure 22 is arranged on both sides where the steel support 23 needs to be arranged; the steel support 23 is supported and connected between the relatively arranged concrete side truss structures 22; there are multiple steel angle braces 24, and the steel angle braces 24 are obliquely supported and arranged at the corners of the foundation pit, and the ends of the steel angle braces 24 are connected to the corresponding steel purlin 23 and the concrete side truss structure 22; the axial force servo system 25 is connected to the steel support 23 and the steel angle brace 24, and is used to apply axial force to the steel support 23 and the steel angle brace 24.

[0050] like Figure 2 As shown, before the foundation pit is excavated, a retaining structure 10 is first set up around the foundation pit. The retaining structure 10 can be a ground-connected wall or a water-stop curtain. A capping beam 11 is set on the top of the retaining structure 10. After the foundation pit is excavated to a certain depth, the first concrete side truss structure 22 can be constructed. The first concrete side truss structure 22 is connected to the capping beam 11. When the foundation pit is dug to the setting height of the second support, a concrete purlin 12 is set on the inner side of the retaining structure 10, and the second concrete side truss structure 22 is connected to the concrete purlin 12. Preferably, the steel bar part of the concrete side truss structure 22 can be implanted into the corresponding capping beam 11 and concrete purlin 12 to achieve an effective fixed connection.

[0051] In a specific embodiment of the present invention, Figure 8 and Fig. 9 As shown, before installing the steel purlin 21, a corbel bracket 212 is installed on the inner side of the top beam 11, and then the steel purlin 21 is installed on the corbel bracket 212, and a steel triangle structure 211 is set at the connection between the steel purlin 21 and the corresponding steel angle brace 24. Fig.13 As shown, one side of the steel triangle structure 211 is butt-jointed with the end of the steel angle brace 24 .

[0052] In a specific embodiment of the present invention, Fig.12 and Fig.15 As shown, when constructing a concrete side truss structure, steel bars are tied at corresponding positions and formwork is set up, and then concrete is poured to form a concrete side truss structure.

[0053] Furthermore, if Figure 3 As shown, the concrete side truss structure 22 is provided with a concrete triangular structure 222 corresponding to the steel support 23 and the steel angle brace 24, and one side of the concrete triangular structure 222 is butt-connected with the end of the corresponding steel support 23 and the steel angle brace 24.

[0054] Combination Figure 5 and Figure 6 As shown, the concrete triangular structure 222 is integrally cast with the concrete side truss structure 22. When the formwork and reinforcement of the concrete side truss structure 22 are set, the formwork and reinforcement of the concrete triangular structure 222 are butt-connected with the formwork and reinforcement of the concrete side truss structure 22. Specifically, the concrete triangular structure 222 includes a plurality of triangular bars 2223. The bending angle of the triangular bars 2223 matches the angle of the concrete triangular structure 222. The triangular bars 2223 are arranged at intervals along the thickness direction of the concrete triangular structure 222. The concrete triangular structure 222 also includes a plurality of U-shaped stirrups 2221. The U-shaped stirrups 2221 are inserted into the triangular bars 2223 and partially extend into the concrete side truss structure 22. The concrete triangular structure 222 also includes a plurality of closed stirrups 2222. The closed stirrups 2222 are arranged on the triangular bars 2223 and the U-shaped stirrups 2221. The setting direction of the closed stirrups 2222 is perpendicular to the setting direction of the U-shaped stirrups 2221.

[0055] An embedded part 2224 is provided on one side of the concrete triangular structure 222 connected to the steel angle brace 24. The embedded part 2224 is connected to the triangular reinforcement 2223, the U-shaped stirrup 2221 and the closed stirrup 2222 in the concrete triangular structure 222 via the connecting reinforcement 2225. Figure 7 As shown, the side plate of the embedded part 2224 is connected to the bolt 2227, and the end of the bolt 2227 is connected to the steel bar connector 2226, and the steel bar connector 2226 is connected to the embedded bar 2225, so that the embedded bar 2225 extends into the interior of the concrete triangle structure 222.

[0056] After the formwork and reinforcement of the concrete triangle structure are set, concrete is poured to form the concrete side truss structure 22 and the concrete triangle structure 222 .

[0057] Furthermore, in order to improve the structural stability of the concrete side truss structure 22 , vertical lattice columns 221 are provided in the foundation pit. A plurality of vertical lattice columns 221 are provided and supported on beams corresponding to the concrete side truss structure 22 .

[0058] In a specific embodiment of the present invention, Fig.10 and Fig.15As shown, before the steel support 23 and the steel angle brace 24 are set, a plurality of pairs of support columns 261 are driven into the foundation pit along the setting positions of the steel support 23 and the steel angle brace 24, and the support columns 261 are set on both sides of the corresponding steel support 23 and the steel angle brace 24 to be set, and a support crossbeam 262 is connected between a pair of support columns 261, and the support crossbeam 262 is used to support the corresponding steel support 23 and the steel angle brace 24. That is, when the steel support 23 and the steel angle brace 24 are set, the steel support 23 and the steel angle brace 24 are placed on the corresponding support crossbeam 262.

[0059] Combination Fig.11 As shown, when driving the support column 261, the driving depth of the support column 261 needs to be a certain distance below the bottom of the foundation pit, so the support column 261 is formed by butt welding of multiple steel columns. During welding, corresponding connecting plates are set at the joints and meet the welding quality requirements. The support column 261 is formed by connecting multiple steel columns. When driving the support column 261, it should be ensured that no welding joints appear above the bottom elevation of the bottom plate of the foundation pit.

[0060] In a specific embodiment of the present invention, Figure 3 , Figure 4 and Fig.15 As shown, a pair of diagonal braces 231 are provided at the end of the steel support 23 near the end of the concrete side truss structure 22, and the pair of diagonal braces 231 are obliquely supported between the steel support 23 and the concrete side truss structure 22. The ends of the diagonal braces 231 are fixedly connected to the embedded parts on the corresponding concrete triangular structure 222.

[0061] When the steel support 23 is set, the end of the steel support 23 is vertically connected to the beam corresponding to the concrete side truss structure 22. The diagonal brace 231 is set in the same direction as the diagonal chord on the concrete side truss structure 22 to ensure the consistency of force transmission.

[0062] In a specific embodiment of the present invention, Fig.14 and Fig.15 As shown, the axial force servo system 25 includes a monitoring station, an operating station, a field control station, a hydraulic servo pump station system, a bus system, a power distribution system, a communication system, a mobile diagnostic system, a compensation section (servo combination booster jack), a wireless distributed CNC hydraulic station junction box device and a software system (operating platform). Depending on the number of servo hydraulic jacks, the axial force servo system can be divided into several wireless distributed CNC pump stations, and each CNC pump station is independently controlled and does not affect each other.

[0063] Each CNC pump station has 4 independent oil channels, realizing independent control of 4 groups of supports, and one channel can control 6 servo hydraulic jacks. The CNC oil pump of each servo hydraulic jack has built-in oil pressure and displacement sensors to realize dual control of oil pressure and stroke, so as to achieve the purpose of regulating axial force.

[0064] The foundation pit of the present invention is provided with two layers of prestressed steel composite supports, the first layer is single-piece support, and the second layer is double-piece support. The prestressed steel composite supports using the servo system have 2 groups of composite supports on the first layer and 4 groups of composite supports on the second layer. Each group of prestressed steel composite supports using the servo system uses 6 jacks. During the construction of each group of supports, the pre-axial force of the supports is determined according to the design value combined with experience, and during the excavation of the foundation pit, the support axial force is adjusted according to the axial force and deformation monitoring data.

[0065] The present invention also provides a construction method for a large-span deep foundation pit steel-concrete composite supporting structure, and the construction method is described below.

[0066] like Fig.15 As shown, the construction method of the present invention comprises the following steps:

[0067] Install steel purlins at the edge of the foundation pit;

[0068] Concrete side truss structures are cast on opposite sides of the foundation pit;

[0069] Providing steel support and connecting the steel support between oppositely disposed concrete side truss structures;

[0070] Provide steel angle braces, obliquely support the steel angle braces at the corners of the foundation pit, and connect the ends of the steel angle braces to the corresponding steel perimeter purlins and concrete side truss structures;

[0071] An axial force servo system is provided, and the axial force servo system is connected to the steel support and the steel angle support, and the axial force servo system is used to apply axial force to the steel support and the steel angle support.

[0072] The large-span deep foundation pit steel-concrete composite supporting structure of the present invention is applied to the construction project at the intersection of Qiantang River and Beijing-Hangzhou Grand Canal. The construction project includes 3 sewage trunk pipes outside the pit close to the Qiantang River, carrying nearly 50% of Hangzhou's daily sewage volume. The sewage pipe is less than 6m away from the edge of the foundation pit excavation. In order to ensure its stable settlement, precipitation is prohibited outside the pit. The water pressure outside the pit is high and the deformation requirements of the foundation pit are high. The foundation pit of the carrier project is relatively regular, with a span of 134.5m and an average excavation depth of 14.95m. Some pits reach 6m, with a large span and a deep excavation depth.

[0073] like Figure 1As shown, the construction method of the present invention includes construction preparation, carefully familiarizing with the design drawings, organizing professional subcontracting units to review the drawings and obtain the minutes of handover; according to the verified support drawings and the minutes of handover of the drawings, the professional subcontracting units carry out the detailed design of the steel support; before the steel support is detailed, combined with the construction situation of the vertical retaining structure, the deviation of the constructed vertical retaining structure is reviewed, and combined with the actual deviation situation, the detailed design of the steel support is coordinated to ensure the accuracy of the size and reduce the difficulty of closing during the support installation.

[0074] Lattice columns can be used for available engineering piles, and steel columns can be used for on-site installation if engineering piles are not available.

[0075] Next, the bracket installation and support column insertion can be carried out simultaneously.

[0076] Insertion of support columns: The support columns are made of steel, such as I-beams. If they need to be butt-welded, it should be ensured that there are no welded joints above the bottom elevation of the base plate. The steel is inserted directly by a manipulator. The depth, angle, and verticality of the steel are strictly controlled during the construction process to facilitate the subsequent connection of the support and beam. After the piles are in place, two theodolites are used to cross each other at 90° to detect the verticality of the pile body. The verticality deviation of the pile inserted into the soil shall not exceed 1% of the pile length. When delivering the piles, an S3 level is configured, and marks are pre-marked on the delivery rod to control the pile top elevation (the pile top elevation error is controlled at about +2cm), and it is strictly forbidden to pull up after over-driving. When inserting the steel column pile, if the pile position is not aligned, the pile should be pulled up and re-inserted. If it deviates from the pile position due to underground obstacles, the column pile should be pulled up immediately, the underground obstacles should be cleared, the hole should be backfilled, and then the stake should be re-set and inserted. If the steel section can be easily driven to the designed pile bottom elevation (especially for projects in silty soil layers), it should be reported to the supervision unit as soon as possible. The supervision unit will contact the support design unit and take measures to lengthen the columns to ensure that the bottom of the steel section column enters a better soil layer (to reduce the sinking of the steel section column).

[0077] Installation of the corbel bracket: The position and elevation of the corbel bracket set along the perimeter of the foundation pit should be determined according to the design drawings. The surface elevation of the corbel bracket (elevation deviation is not more than ±2mm) should ensure that the steel purlin (center line) on it is on the same horizontal plane, straight and beautiful. Before welding the corbel bracket, the connection parts (such as embedded parts, H-shaped steel, etc.) must be thoroughly cleaned of rust, oil stains, concrete residues and other debris within a range of not less than 200mm×200mm. The welded corbel bracket must ensure that the connection parts are firm and reliable, with sufficient stability, and no distortion or cold welding; the upper surface elevation of the corbel bracket is controlled within 2mm and its elevation angle should be controlled ≥90 degrees, and shall not exceed 95 degrees. When welding the steel corbel bracket, it must be hoisted, positioned and welded by an excavator. The hoisting can be stopped only after the lower or upper fulcrum is fully welded to ensure the safety of the operation.

[0078] Installation of steel purlin: setting of reference points and positioning of wire pulling. Before installing the purlin, the axis reference point must be determined. The reference points on the inner side of two adjacent corners of the foundation pit are measured and set by a total station or theodolite through coordinate calculation. The plane installation positioning is performed by hanging wire through the reference point. The actual installation axis deviation is required not to exceed ±10mm. The wire used for pulling wires is generally string or cotton wire, with a diameter of 0.8-1.0mm, which is determined by the distance of the wire pulling on site; the wire sinker is used for centering, with uncertain specifications, and a diameter of 25-50mm is usually appropriate. The tip of the wire sinker should be accurate so as to align with the center point. Install the gallows firmly at a location other than the reference center point, hang the string or cotton wire and use tension to straighten it (the tension should be 40%-60% of the wire breaking force). After positioning, mark the corbel for the control of the installation position of the purlin. The single-side positioning line of the inner purlin of the foundation pit must meet the basic requirement of being in a straight line. The purpose is to ensure that the outer retaining structure is evenly stressed after the prestress is applied. The installation of purlins should follow the principle of "long first, short later, reduce the number of joints, and stagger the joints". Longer purlins should be used first to reduce the number of joints. The purlins are hoisted in sections according to the order of support erection. The steel purlins are placed on the brackets by manual cooperation with the crane. After the purlins are in place, check whether the steel brackets are loose due to impact. If they are loose, immediately weld and reinforce them.

[0079] Installation of brackets and beams: The installation of brackets must control their horizontal elevation. The horizontal elevation of the top surface can be inferred from the positioning elevations of the angle braces, braces, and H-shaped steel. The bracket surface elevation = the center elevation of the supporting structure - (1 / 2 of the height of the supporting member + the height of the beam). The deviation of the bracket surface elevation (elevation deviation is not more than ±2mm) should ensure that the elevation of the beam surface of the corresponding support is on the same plane; the bracket and the steel column are fastened with no less than 6 high-strength bolts (Note: the installation direction of the bolts connecting the column and the bracket must be consistent). The installation of brackets requires strict control of verticality. Even if the steel column is offset, the bracket must meet the vertical requirements by adding steel plates. If the elevation positioning of the steel column deviates, channel steel can be used instead of the bracket (temporary adjustment method) to connect with the support beam. When using oxygen acetylene to drill holes on site on the support beam and the original bracket, pay attention to controlling the hole size to avoid the bolts from slipping after being stressed; the installed bracket must be firmly fastened to the steel column pile, and the torque of the friction type high-strength bolts must meet the specified requirements. The elevation deviation of the bracket surface of each steel column shall not exceed 5mm. After the bracket is installed and the surface elevation is verified, the beam can be installed; the specifications of the beam should meet the requirements of the design drawings, and there should be no butt joints (materials should be inspected and accepted one by one when they arrive on site); when adjusting the positioning of the steel column (structural beams, walls, columns and other components should be avoided), the span of the beam shall not be increased without authorization.

[0080] Concrete side truss structure construction: top beam (purlin), concrete triangle, and steel support are constructed according to the connection node details. After the steel bar binding is completed, the steel bar embedded parts are installed and passed the acceptance, pouring can be carried out.

[0081] Installation of steel supports and steel angle braces: Before installing each steel composite support beam, if conditions are met on site, pre-joining should be carried out on the ground and the straightness of the support after pre-joining should be checked. The eccentricity of the center line of the two ends of the jointed support (including the jack and TO component) should be controlled within 2 cm. After passing the inspection, the whole support should be hoisted into place according to the position. For projects that do not have the conditions for pre-joining on site, a total station (theodolite) should be used for positioning, and a control line of the support beam should be made on the beam. Then, pre-joining should be carried out along the control line from one end (from both ends if the length exceeds 100 meters). Be sure to ensure that the steel composite support beam is straight in the plane. During pre-joining, WA components, special jacks, TO components, etc. are firmly connected by high-strength bolts. In addition, the cross lock buckle of the special jack must be set in the middle, that is, three wires are left in front and behind to facilitate the removal of prestress during dismantling. During the assembly of the steel composite support beam, if there is extra space in the SC placement gap, a steel plate of corresponding thickness must be used to pad it tightly to prevent the overall eccentricity of the support system after being stressed. Before the steel composite support beam is assembled and pressurized, it should be temporarily connected to the beam with a hoop, and the joint bolts can be tightened only after passing the inspection.

[0082] Installation of the axis force servo system: installation, use and removal process as follows Fig.16 As shown, equipment debugging: After the system is powered on, test the system pressure, pressure maintenance, solenoid valve switching, manual loading, automatic loading, communication distance, etc. to ensure that the pump station equipment is normal.

[0083] Jack hoisting installation: The steel support involving the axial force servo should be assembled in combination with the node construction requirements of the servo part during the installation of the support, and the jack should be located at the center of the pressure part after meeting the following requirements:

[0084] ① A crossbeam is provided under the support of the servo node (generally realized by a crossbeam in a crisscross pattern) to ensure that the support node does not sink under the action of its own weight;

[0085] ② The pressure parts at the servo node are in natural contact with the force box or the gap is no more than 5mm (the width of the protection box is 400mm, and the size of the servo hydraulic jack is Φ455×359mm), and the force box and the pressure parts are connected by bolts with a length of not less than 200mm (all bolts must not be tightened, and the same and large expansion space should be maintained);

[0086] ③ Except for the servo nodes, the joints of other supports should be tight (if there are gaps, wedges should be inserted before pressurization) to avoid uneven force on the supports caused by the gaps during pressurization;

[0087] ④ The horizontal support members and the beams are connected by clamps (to avoid lateral deviation of the beams when pressure is applied), and other support members (including channel steels and cover plates) are bolted and fastened in place.

[0088] Oil pipe data line connection: The oil pipe and data line are connected from the corresponding oil circuit and data interface on the pump station, and reach the jack position along the side of the vertical enclosure structure and the support side. Install the ultrasonic sensor, and its end face is flush with the installation end face, and then connect the displacement line to observe whether the indicator light of the ultrasonic sensor is normal. Then connect the oil pipe, connect the oil inlet pipe to the lower cavity of the jack, and connect the oil return pipe to the upper cavity of the jack, and add a gasket. Then use a cable tie to tie the displacement line and oil pipe to the support head so that the joint is not under stress.

[0089] Apply axial force: After the jack is in place and before applying axial force, the two sides of the jack should be firmly attached to the pressure pieces in the "0" stroke state (the gap should not be greater than 5mm. If the gap is too large, it may cause insufficient pressure even at the maximum stroke). Adjust the oil pressure so that the jack piston presses against the pressure piece to generate axial force. At this time, when the piston stroke is large, it should be adjusted using a wedge.

[0090] Set the axial force control value: After pressurizing to the design pre-added value, set the axial force design value, upper and lower limit design alarm values, etc. under each design condition in the central monitoring system according to the design requirements. If the design has requirements, set the upper and lower limits according to the design requirements. If there are no design requirements, set the upper limit alarm value as 1.05-1.1 times the support pre-added value (for silty soil layers, set the upper limit as 1.3-1.5 times), and set the lower limit alarm value as 0.85-0.95 times the support pre-added value (for silty soil layers, set the lower limit as 1.0 times the pre-added value).

[0091] On-site measurement and control: The system measurement and control adopts closed-loop continuous measurement and control. If the measurement and control method is changed, it must be reported to the design unit for approval. While the system is being measured and controlled, it is supplemented by manual monitoring, monitoring in the monitoring room and manual inspections. The monitoring room ensures that someone is on duty 24 hours a day (or remote online duty) to respond to data abnormalities in the first time.

[0092] Pressure relief and exit: Pressure relief can be started after receiving the support removal order. In order to avoid excessive instantaneous prestress release that may cause local deformation and cracking of the structure, a step-by-step unloading method is adopted. The unloading is divided into three levels. When the pressure is relieved to 0, the jack piston is retracted.

[0093] Support removal, removal principles:

[0094] (1) The side truss is dismantled according to the principle of "replacing the support first, then removing the support". When the strength of the replaced support structure reaches 100%, the support can be removed.

[0095] (2) According to the principle of "corner brace first, then opposite brace, long corner brace first then short corner brace", the overall demolition of each support is carried out in the order of "symmetrical demolition, secondary components first, then primary components", gradually retreating from small to large, and from the middle to the two ends.

[0096] (3) On the side close to the subway tunnel and sewage main, static cutting method is used for demolition to ensure the safety of the foundation pit and reduce disturbance to the surrounding environment.

[0097] Support pressure relief:

[0098] (1) The support pressure relief should be carried out slowly and in stages (first relieve 50% of the pressure, then stabilize for 1 hour and then relieve the pressure to zero). Rapid pressure relief is strictly prohibited.

[0099] (2) If any abnormal conditions such as cracks in the floor slab force transmission belt or the top beam are found during pressure relief, pressure relief should be suspended; if the monitoring data is abnormal, pressurization should be temporarily resumed.

[0100] In a specific embodiment of the present invention, before the steel support and the steel angle brace are arranged, support columns are provided first, and the support columns are driven into the foundation pit in pairs along the arrangement positions of the steel support and the steel angle brace;

[0101] A supporting beam is provided, and the supporting beam is connected between a pair of supporting columns, and the corresponding steel support and steel angle brace are supported by the supporting beam.

[0102] In a specific embodiment of the present invention, when the concrete side truss structure is cast, the steel bars of the concrete triangle structure are arranged at the corresponding positions of the side parts of the concrete side truss structure, and the embedded parts that are butt-connected with the ends of the corresponding steel support and steel angle brace are arranged on the corresponding sides of the concrete triangle structure.

[0103] In a specific embodiment of the present invention, when the steel support is provided, a pair of diagonal braces are provided between the steel support and the concrete side truss structure.

[0104] In a specific embodiment of the present invention, when installing the steel purlin, a steel triangle structure is arranged on the steel purlin at a position corresponding to the steel angle brace, and the steel angle brace is connected by using the arranged steel triangle structure.

[0105] The present invention is described in detail above in conjunction with the embodiments of the drawings, and those skilled in the art can make various variations of the present invention according to the above description. Therefore, certain details in the embodiments should not constitute limitations of the present invention, and the scope of protection of the present invention shall be defined by the scope of the attached claims.

Claims

1. A large-span deep foundation pit steel-concrete composite support structure, characterized in that: include: Steel purlins installed at the edge of the foundation pit; Concrete side truss structures located on opposite sides of the foundation pit; Supporting steel supports connected between oppositely disposed concrete side truss structures; Multiple steel angle braces are provided at the corners of the foundation pit for oblique support, and the ends of the steel angle braces are connected to the corresponding steel perimeter purlins and the concrete side truss structure; The axial force servo system connected to the section steel support and the section steel angle support is used to apply axial force to the section steel support and the section steel angle support.

2. The large-span deep foundation pit steel-concrete composite support structure according to claim 1 is characterized in that: It also includes a plurality of pairs of support columns driven into the foundation pit along the setting positions of the steel supports and the steel angle braces, a pair of support columns are connected with a support beam, and the support beam supports the corresponding steel supports and steel angle braces.

3. The large-span deep foundation pit steel-concrete composite support structure according to claim 1, characterized in that: The concrete side truss structure is provided with a concrete triangular structure corresponding to the steel support and the steel angle brace, and one side surface of the concrete triangular structure is butt-connected with the end of the corresponding steel support and the steel angle brace.

4. The large-span deep foundation pit steel-concrete composite support structure according to claim 1, characterized in that: A pair of diagonal braces is provided at the end of the steel support close to the end of the concrete side truss structure, and the pair of diagonal braces is obliquely supported between the steel support and the concrete side truss structure.

5. The large-span deep foundation pit steel-concrete composite support structure according to claim 1, characterized in that: A steel triangle structure is provided on the steel purlin corresponding to the steel angle brace, and one side surface of the steel triangle structure is butt-connected with the end of the steel angle brace.

6. A construction method for a large-span deep foundation pit steel-concrete composite support structure, characterized in that: The steps include: Install steel purlins at the edge of the foundation pit; Concrete side truss structures are cast on opposite sides of the foundation pit; Providing a steel support, and connecting the steel support between oppositely disposed concrete side truss structures; Providing a steel angle brace, obliquely supporting the steel angle brace at the corner of the foundation pit, and connecting the end of the steel angle brace with the corresponding steel perimeter purlin and concrete side truss structure; An axial force servo system is provided, and the axial force servo system is connected to the steel support and the steel angle support, and the axial force servo system is used to apply axial force to the steel support and the steel angle support.

7. The construction method of the large-span deep foundation pit steel-concrete composite support structure according to claim 6, characterized in that: Before setting the steel support and the steel angle brace, first provide support columns, and drive the support columns into the foundation pit in pairs along the setting positions of the steel support and the steel angle brace; A supporting crossbeam is provided, and the supporting crossbeam is connected between a pair of supporting columns, and the supporting crossbeam is used to support the corresponding steel support and steel angle brace.

8. The construction method of the large-span deep foundation pit steel-concrete composite support structure according to claim 6, characterized in that: When the concrete side truss structure is cast, the steel bars of the concrete triangle structure are arranged at the corresponding positions on the sides of the concrete side truss structure, and the embedded parts that are butt-connected with the ends of the corresponding steel supports and steel angle braces are arranged on the corresponding sides of the concrete triangle structure.

9. The construction method of the large-span deep foundation pit steel-concrete composite support structure according to claim 6, characterized in that: When setting the steel support, a pair of diagonal braces are set between the steel support and the concrete side truss structure.

10. The construction method of the large-span deep foundation pit steel-concrete composite support structure according to claim 6, characterized in that: When installing the steel purlin, a steel triangle structure is arranged at a position on the steel purlin corresponding to the steel angle brace, and the steel angle brace is connected by using the arranged steel triangle structure.

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