CN116104101A - Foundation pit prestressed supporting system and construction method thereof - Google Patents

Abstract

The application provides a foundation pit prestress support system and a construction method thereof, wherein the foundation pit prestress support system comprises a steel support, lattice columns, joists, portal frames, connecting beams, hanging plates and supporting arches. The steel support applies horizontal prestress to the foundation pit support structure along the axial direction; the lattice column is of a cavity structure and is used for being placed in the foundation pit to carry out vertical bearing on the supporting system; the joist is erected on the lattice column to carry out bearing on the steel support; the door type frame is arranged on the joist and surrounds the steel support to limit the movement of the steel support; the connecting beams respectively connect adjacent steel supports to enhance the rigidity of the support system; the hanging plate is used for connecting the end part of the steel support with the foundation pit support structure; the supporting arch is arranged at the position of the lattice column bearing joist. The prestress support system and the construction method thereof can carry out safe and effective support protection on the enclosure structure of the large-span foundation pit, ensure construction safety, and improve engineering construction efficiency, economic benefit and environmental benefit through modularized recyclable components and standardized installation methods.

Description

Foundation pit prestressed supporting system and construction method thereof

Technical Field

The invention relates to the technical field of building construction, in particular to a foundation pit prestress supporting system and a construction method thereof.

Background

The foundation pit engineering is widely applied to the fields of urban construction engineering, subway engineering, underground comprehensive pipe gallery engineering and the like. In actual construction, because the surrounding environment of a construction site is complex, local adjacent areas around the foundation pit often have underground structures, and in order to protect the original underground structures from being influenced, the supporting mode of conventional supporting piles and prestressed anchor cables cannot be used due to the limitation of the site, and corresponding supporting structures are needed to be adopted for further supporting the foundation pit.

For example, in the construction of large buildings, specific supporting structures are designed by comprehensively considering site conditions, construction period, stratum conditions and the like. Firstly, the foundation ditch span is big, and in the work progress, bearing structure has important influence to foundation ditch stability, support stake displacement deformation, and foundation ditch building envelope's stability is crucial to engineering's construction and surrounding environment safety, consequently, in order to ensure to carry out safe effectual support protection to large-span foundation ditch, need consider bearing structure's continuity and overall structure's atress stability. Secondly, the construction and the dismantling of the supporting structure can affect the construction period of the whole engineering, for example, the supporting structure adopting a reinforced concrete mode often needs to be cast in situ and wait for the concrete to harden and then continue to be constructed, and the reinforced concrete structure wastes time and labor when being dismantled, so that the design of the supporting structure is convenient for the on-site installation and the later dismantling as much as possible so as to reduce the engineering workload. Thirdly, under the national 'double carbon' call and the concept of green sustainable development, the design and construction of the supporting structure are from the perspective of recycling, so that the reusability of building materials is improved as much as possible, the economical use of building raw materials is realized, and the economic benefit and the environmental benefit are improved.

Therefore, for the support of the large-span foundation pit in the building construction process, a safe and effective support system and a construction method are required to be developed so as to solve the problems of continuity and stability of the large-span foundation pit support structure, construction efficiency of the support structure and recycling of building materials in the building construction process and improve the construction quality and construction safety of the building structure.

Disclosure of Invention

In order to solve the problems of continuity and stability of a large-span foundation pit supporting structure, construction efficiency of the supporting structure and recycling of building materials in the building construction process, the application provides a foundation pit prestress supporting system and a construction method thereof, which can safely and effectively support and protect an enclosure structure of the large-span foundation pit, ensure construction safety, and improve engineering construction efficiency, economic benefit and environmental benefit through a modularized recyclable assembly and a standardized installation method.

The technical scheme adopted by the embodiment of the application for solving the technical problems is as follows: a foundation pit prestressed support system is used for providing horizontal support force for a foundation pit support structure of an on-building body and is characterized by comprising steel supports, lattice columns, joists, portal frames, connecting beams, hanging plates and supporting arches.

The steel support applies horizontal prestress to the foundation pit support structure along the axial direction.

The lattice column is of a cavity structure and is used for being placed in a foundation pit to vertically bear the supporting system.

The joists are erected on the lattice columns to carry the steel supports.

The door type frame is arranged on the joist and surrounds the steel support to limit the movement of the steel support.

The tie beams interface respectively with adjacent steel supports to enhance the rigidity of the support system.

The hanging plate is used for connecting the steel support end part and the foundation pit support structure.

The supporting arch is arranged at the position of the lattice column bearing joist.

In a specific embodiment, the steel support is of a segmented structure and comprises a middle section, a fixed end and a movable end, wherein the fixed end and the movable end are positioned at two ends and are respectively connected with the hanging plate; the movable end of the steel support is provided with a telescopic adjusting piece for adjusting the steel support to a required length and applying prestress.

In a specific embodiment, the hanging plate comprises a vertically arranged attaching plate for realizing contact stress, the upper end of the attaching plate, which is contacted with the steel support, is provided with an extension flat plate extending towards the outer side of the enclosure structure and used for realizing fixed connection, and the lower end of the attaching plate is provided with an inward extension flat plate extending towards the inner side of the enclosure structure.

In a specific embodiment, the construction method of the foundation pit prestress supporting system is characterized by comprising the following steps:

s1, designing a supporting system and processing each component;

s2, constructing and installing lattice columns in the foundation pit;

s3, excavating earth downwards to construct a first-layer supporting system, constructing a crown beam at the top of the foundation pit support structure, and mounting hanging plates on the crown beam;

s4, installing a supporting arch, a joist, a steel support, a portal frame and a connecting beam on the lattice column, and applying prestress to the steel support;

s5, continuously excavating earthwork downwards, constructing an enclosing purlin on the inner side of the foundation pit support structure, installing a hanging plate on the enclosing purlin, and constructing a next layer of support system according to the step S4;

s6, repeating the step S5 to finish the final layer support system;

s7, continuously excavating earthwork downwards, constructing anchor rods and waist beams at corresponding positions of the foundation pit support structures, and constructing a bottom plate of a building body at the bottom of the foundation pit;

s8, constructing the floor slab, backfilling the foundation pit fertilizer grooves of the floor, pouring a concrete force transmission belt, and dismantling the support system after the strength requirement is met;

s9, repeating the step S8 until the first-layer support system is removed, and then removing the lattice columns.

In a specific embodiment, in the step S4, the steel support is pre-stressed in stages to reach the design value of the pre-stress and eliminate the deformation of the components of the support system; and after the prestressing force is applied, the steel support is subjected to repeated prestressing force according to the monitored prestress change of the steel support and the deformation degree of the foundation pit support structure so as to improve the safety.

In a specific embodiment, in the step S8, a double-wall structure is further disposed in the foundation pit fertilizer groove, the double-wall structure includes a buttress disposed outside the side wall of the building, an end plate, and a cover plate, one end of the buttress is connected with the side wall of the building, the other end of the buttress is connected with the end plate disposed along the direction of the side wall of the building, and the cover plate is connected to the tops of the buttress and the end plate; and backfilling the inside of the double-wall structure before construction of the cover plate.

In a specific embodiment, the steel support, the crown beam and the enclosing purlin are in an oblique mode, and convex bodies are arranged at the joint positions of the crown beam and the enclosing purlin and the steel support so as to be matched with the mounting hanging plate and bear the prestress applied by the steel support.

In a specific embodiment, the enclosing purlin is provided with a bearing piece connected to the enclosing structure so as to improve safety; the end part of the steel support connected with the enclosing purlin is provided with a hanging piece connected with the foundation pit enclosing structure so as to prevent the steel support from falling off.

In a specific embodiment, the bottom of the lattice column is penetrated in a column pile arranged in the foundation pit, and the lattice column is connected with a reinforcement cage arranged in the column pile.

In a specific embodiment, the waterproof construction of the joint of the lattice column and the bottom plate of the building body comprises the following steps:

t1, pouring a cushion layer, paving a waterproof coiled material on the cushion layer, turning the waterproof coiled material upwards along a lattice column, and arranging a waterproof protective layer on the waterproof coiled material;

t2, binding a bottom plate steel bar, welding with a lattice column, and arranging a water stop steel plate with a downward water facing surface at the position of the upper flanging edge of the waterproof coiled material of the lattice column;

a hollow groove is reserved at the upper part of the connection position of the bottom plate and the lattice column, and a water stop steel plate with the downward water facing surface is preset at the side wall position of the hollow groove;

t4, pouring bottom plate concrete, and arranging waterproof paint at the joint position of the lattice column and the bottom of the empty slot reserved on the bottom plate;

and T5, pouring concrete in the empty groove reserved in the bottom plate.

The embodiment of the application has the advantages that:

1. this prestressing force braced system is through the steel support of design section structure, and the processing of being convenient for and on-the-spot equipment, the scalable regulation of steel support expansion end not only is convenient for arrange load equipment and carries out prestressing force and applys, has improved the regulation flexibility when steel support assembly is connected simultaneously and the convenience when dismantling.

2. The components of the prestress support system can be rapidly installed in the early engineering processing and on site, so that the influence of the reinforced concrete support structure on the construction period is avoided, and meanwhile, the demolition workload is small after the use is finished, so that the engineering construction speed is further improved. The components of the prestress support system can be further recycled after being disassembled, so that the construction raw materials are saved and used, and the economic benefit and the environmental benefit are improved.

3. The construction method of the prestress support system normalizes and systemizes the operation flow of the modular assembly, can realize the safe support of the large-span foundation pit in the horizontal direction, and can be applied to the support construction operation of the deep foundation pit support structure.

4. The waterproof measures in the construction method of the prestressed support system can effectively avoid the influence on the waterproof performance of the building in the assembly construction process of the support system and avoid the later waterproof reworking, thereby further improving the engineering construction quality of the support system and the construction method thereof.

5. The construction method of the prestress support system is used for the double-wall structure and the concrete force transmission belt arranged on the foundation pit fertilizer groove, so that adverse effects of excessive soil pressure around the foundation pit on the building body structure are avoided, and the strength of the building structure and the engineering construction safety are improved.

Drawings

FIG. 1 is a schematic diagram of a foundation pit prestressed supporting system according to the present invention;

FIG. 2 is a schematic diagram of a foundation pit prestressed bracing system steel bracing frame of the present invention;

FIG. 3 is a schematic view of a foundation pit prestressed bracing system portal frame installation in accordance with the present invention;

FIG. 4 is a schematic view of a steel support fixed end and a movable end of a foundation pit prestressed support system according to the present invention;

FIG. 5 is a schematic view of a middle section of a steel support of a foundation pit pre-stress support system according to the present invention;

FIG. 6 is a schematic view of a foundation pit prestressed bracing system tie beam of the present invention;

FIG. 7 is a schematic view of a foundation pit prestressed bracing system column pile and lattice column according to the present invention;

FIG. 8 is a schematic view of a partial cross section of a foundation pit prestressed bracing system column pile and lattice column according to the present invention;

FIG. 9 is a schematic view of a foundation pit prestressed bracing system lattice column and floor joint waterproof;

FIG. 10 is a schematic illustration of a lifting rib of a purlin carrier of the foundation pit prestressed bracing system of the present invention;

FIG. 11 is a schematic view of a reinforcement bar of a foundation pit prestressed bracing system surrounding purlin bearing member of the present invention;

FIG. 12 is a schematic illustration of a foundation pit prestressed bracing system of the present invention;

FIG. 13 is a schematic view of working conditions P1-P6 of a foundation pit prestressed supporting system construction method according to the present invention;

FIG. 14 is a schematic view of working conditions P7-P12 of a foundation pit prestressed supporting system construction method according to the present invention;

FIG. 15 is a schematic view of working conditions P13-P17 of a foundation pit prestressed supporting system construction method according to the present invention.

The main reference numerals illustrate:

1-a convex body; 2-lattice columns; 3-steel support; 301-active end; 302-a fixed end; 303-an intermediate section; 4-connecting beams; 5-joists; 6-enclosing structure; 7-water stopping steel plates; 8-lacing plates; 9-waterproof paint; 10-a bottom plate; 11-upright posts; 12-a waterproof protective layer; 13-waterproof coiled materials; 14-cushion layer; 15-empty slots; 16-bracing arch; 17-portal frames; 18-crown beam; 19-enclosing purlin; 20-foundation pit construction depth; 21-anchor rod; 22-a concrete force transmission belt; 23-floor slab; 24-hanging bars; 25-planting tendons; 26-hanging plate.

Detailed Description

The embodiment of the application solves the problems of continuity and stability of a large-span foundation pit supporting structure in the building construction process, construction efficiency of the supporting structure and recycling of building materials by providing a foundation pit prestress supporting system and a construction method thereof, and the overall thinking is as follows:

referring to fig. 1, the present invention provides a foundation pit prestressed supporting system for providing horizontal supporting force to a foundation pit enclosure 6 of an on-building structure, which comprises steel supports 3, lattice columns 2, joists 5, portal frames 17, contact beams 4, hanging plates 26 and supporting arches 16. The steel support 3 applies horizontal prestress to the foundation pit support structure 6 along the axial direction; the lattice column 2 is of a cavity structure and is used for being placed in a foundation pit to carry out vertical bearing on the supporting system; joists 5 are erected on the lattice columns 2 to carry the steel supports 3; the portal frame 17 is arranged on the joist 5 and surrounds the steel support 3 to limit the movement of the steel support 3; the connecting beams 4 respectively connect the adjacent steel supports 3 to strengthen the rigidity of the support system; the hanging plate 26 is used for connecting the end part of the steel support 3 with the foundation pit support structure 6; the brace arches 16 are arranged at the positions where the lattice columns 2 bear the joists 5. The prestress support system can be rapidly installed in the early engineering stage and on site through the modularized recyclable component design, is convenient to disassemble in the later stage, can safely and effectively support and protect the enclosure structure 6 of the large-span foundation pit, and improves the engineering construction efficiency, economic benefit and environmental benefit.

The steel support 3 in this example is of a segmented structure, and comprises a middle segment 303, a fixed end 302 and a movable end 301 which are positioned at two ends and are respectively connected with the hanging plate 26, wherein the movable end 301 of the steel support 3 is provided with a telescopic adjusting piece for adjusting the steel support 3 to a required length and applying prestress. Specifically, referring to fig. 2-5, in this example, the steel support 3 adopts a tubular structure, the fixed end 302, the movable end 301 and the middle section 303 are connected in the axial direction through a flange structure, and the fixed end 302 of the steel support 3 can be connected with the hanging plate 26 through a flange, so that modular processing and field installation are facilitated, and installation can be realized through a mode of custom processing and field splicing. Further, the middle section 303 of the steel support 3 may have a single-section structure or a segmented structure along the axial direction, so that a more flexible assembly length is realized by designing and processing standard sections, and when the middle section 303 has a segmented structure, the segmented structures can be connected by bolts through flanges arranged at two ends. The steel supports 3 can be pre-assembled on the ground according to the width of the actually measured foundation pit, the movable end 301 head of each steel support 3 is provided with a telescopic adjustment allowance so as to adapt to the requirement of the width change of the section of the foundation pit and the support length, and the steel supports 3 and the telescopic adjustment movable ends 301 of the sectional structure are convenient for arranging load equipment to apply prestress, and meanwhile, the adjustment flexibility of the steel supports 3 during assembly connection and the convenience of the steel supports during disassembly are improved.

The axis deviation, deflection deformation and end face perpendicularity error of the assembled steel support 3 are required to be within the allowable range. The installation of the steel support 3 may be accomplished by providing and placing a pre-stressing force means at the movable end 301 to apply a pre-stressing force, for example, by placing a hydraulic jack at the pressing position of the movable end 301, and after the pre-stressing force is applied to a predetermined value, by providing a spacer block at the movable end 301 and fixing the spacer block firmly, and then unloading the hydraulic jack.

In this example, the lattice column 2 is formed by welding 4 angle steels and the batten plates 8, please refer to fig. 2, the position of the batten plates 8 is finely adjusted according to specific conditions during construction, deformation under hoisting load is strictly controlled during hoisting, and installation and positioning are ensured to be accurate, for example, in this example, deviation of center line of the lattice column 2 is +/-5 mm, deviation ranges of elevation of column top and column bottom of the lattice column 2 are 0-20 mm, and deviation of perpendicularity of the lattice column 2 is not greater than 1/200 of the length of the lattice column.

Referring to fig. 2 and 3, the lattice column 2 is provided with a brace 16 welded at the positions of the batten plates 8 at two sides corresponding to the positions below each steel support 3 to bear the joists 5, and the brace 16 can be formed by processing steel plates. In the embodiment, the joist 5 is made of 2H-shaped steel, and is firmly welded with the supporting arch 16, and rib plates are welded at the welding connecting plates and the web plates of the upper and lower flange plates of the H-shaped steel of the joist 5, so that the structural strength of the joist 5 is enhanced.

Referring to fig. 3, the portal frame 17 is a frame structure welded to the joist 5, and may be made of angle steel, which serves to fix the steel support 3 against movement. Further, referring to fig. 6, contact beams 4 are provided to adjacent steel supports 3 and respectively cross to prevent deformation of the steel supports 3.

In this example, the steel support 3 and the foundation pit support structure 6 are connected and prestressed by the hanging plate 26, referring to fig. 4, the hanging plate 26 includes a vertically arranged bonding plate for realizing contact stress, an extension flat plate extending towards the outer side of the support structure 6 is arranged at the upper end of the bonding plate contacting with the steel support 3 and used for realizing fixed connection, and an inner extension flat plate extending towards the inner side of the support structure 6 is arranged at the lower end of the bonding plate. In the use, the laminating board closely pastes the vertical face of foundation ditch building enclosure 6 to with the prestressing force conduction that contacts with steel support 3 receives for building enclosure 6 of foundation ditch, the extension flat board overlaps with the upside horizontal plane of foundation ditch building enclosure 6 mutually, and accessible sets up through-hole structure and expansion bolts on the extension flat board and realizes further fastening connection, and the interior extension flat board can prevent that steel support 3 from unstably falling. In some embodiments, the fixed end 302 and the movable end 301 of the steel support 3 may be connected to the hanging plate 26 by bolts.

The embodiment also provides a construction method of the foundation pit prestress support system, which comprises the following steps:

s1, designing a supporting system and processing each component;

s2, constructing and installing lattice columns 2 in the foundation pit;

s3, excavating earth downwards to construct a first-layer supporting system, constructing a crown beam 18 at the top of the foundation pit support structure 6, and mounting a hanging plate 26 on the crown beam 18;

s4, installing a supporting arch 16, a joist 5, a steel support 3, a portal frame 17 and a connecting beam 4 on the lattice column 2, and applying prestress to the steel support 3;

s5, continuously excavating earthwork downwards, constructing an enclosing purlin 19 on the inner side of the foundation pit support structure 6, installing a hanging plate 26 on the enclosing purlin 19, and constructing a next layer of supporting system according to the step S4;

s6, repeating the step S5 to finish the final layer support system;

s7, continuously excavating earthwork downwards, constructing anchor rods 21 and waist beams at corresponding positions of the foundation pit support structures 6, and constructing a bottom plate 10 of a building body at the bottom of the foundation pit;

s8, constructing the floor slab 23, backfilling the foundation pit fertilizer grooves of the floor, pouring the concrete force transmission belt 22, and dismantling the support system after the strength requirement is met;

s9, repeating the step S8 until the first-layer support system is removed, and then removing the lattice columns 2.

In this example, referring to fig. 7 and 8, the bottom of the lattice column 2 is inserted into a column pile 11 disposed in the foundation pit, and the lattice column 2 is connected with a reinforcement cage disposed in the column pile 11. The steel support 3, the crown beam 18 and the enclosing purlin 19 are in an oblique mode, and the crown beam 18 and the enclosing purlin 19 are provided with convex bodies 1 at the joint parts of the steel support 3 so as to be matched with the mounting hanging plate 26 and bear the prestress applied by the steel support 3. Specifically, referring to fig. 12, the convex body 1 is formed by a crown beam 18 or an enclosing purlin 19 protruding outwards from one side of the foundation pit to form at least one vertical plane for contacting and bearing with a bonding plate of the hanging plate 26, and an upper horizontal plane overlapping with an extension flat plate of the hanging plate 26, a steel plate can be embedded in the convex body 1 and integrated with the crown beam 18 or the enclosing purlin 19 through concrete pouring, and the connection mode of the crown beam 18 or the enclosing purlin 19 and the steel support 3 with corresponding oblique angles can be realized by the protruding body 1.

During construction, according to the design planning, the upright post pile 11 is constructed before foundation pit earthwork is not excavated, and checking is carried out before construction, so that the arrangement position of the upright post pile 11 is prevented from overlapping with structural columns, walls and the like, and the perpendicularity error of drilling the upright post pile 11, pile foundation settlement, horizontal displacement and differential settlement are ensured to meet the design requirements. When the bored pile construction mode is adopted, measures are taken to ensure that the reinforcement cage of the upright pile 11 is not deformed and is placed in the center of the pile body of the upright pile 11. The lattice column 2 and the steel reinforcement cage of the upright post pile 11 are welded and connected, verticality is controlled during installation, the bottom of the lattice column 2 is inserted into the concrete of the upright post pile 11 to a certain depth, the insertion depth is strictly controlled, the reliable anchoring depth of the lattice column 2 is ensured, and in the overlapping depth of the lattice column 2 and the steel reinforcement cage of the upright post pile 11, stirrups of the steel reinforcement cage can be encrypted to be configured so as to enhance structural connection stability. The axial direction of the lattice column 2 is controlled, the lattice column 2 can be suspended and protected by arranging temporary lifting appliances on the ground, the temporary lifting appliances can be removed after the concrete of the upright post pile 11 reaches 70% of the design strength, the pile holes above the building bottom plate 10 are filled with sand, when a foundation pit is excavated, the excavation speed and the excavation sequence are controlled within the range of 2 meters around the lattice column 2, and the lateral additional soil pressure to the lattice column 2 is avoided.

After the lattice column 2 is constructed and installed, earthwork is excavated downwards in a foundation pit to construct a first-layer supporting system, when the earthwork is excavated to the bottom of the designed installation position of the first-layer steel support 3 by a certain distance, positioning measurement paying-off is carried out, the position of a crown beam 18 butted by the first-layer steel support 3 is determined according to design requirements, the crown beam 18 can be constructed on the top of the foundation pit enclosure structure 6 by adopting a concrete integral pouring method, the central position of the steel support 3 is determined on the crown beam 18, and the steel support 3 can be accurately positioned by adopting a cross-bullet line method, so that the erection and installation of the steel support 3 are facilitated. The hanging plate 26 is arranged on the convex body 1 of the crown beam 18, and the hanging plate 26 and the convex body 1 are fixed through expansion bolts.

The supporting arch 16 is welded at the positions of the two batten plates 8 with the same elevation as the steel support 3 of the lattice column 2, and then the joist 5 which is processed is installed on the supporting arch 16 and welded firmly. Then, the steel support 3 is erected on the joist 5, and the steel support 3 is erected on site by hoisting equipment in a splicing mode so as to adapt to the requirement of the width change length of the section of the foundation pit. During installation, coaxiality and end face verticality of the steel support 3 are required to be checked to meet the use requirements, the steel structure is free of welding damage, cracking and other quality defects, the movable end 301 and the fixed end 302 of each layer of steel support 3 are required to be uniformly arranged on the same side, and all flanges are connected by adopting high-strength bolts.

In this example, each layer of support system is constructed with 7 steel supports 3 with different lengths, after the steel supports 3 are laid and installed, the portal frame 17 is further installed at the corresponding planning position to fix the steel supports 3 to prevent displacement, and the portal frame 17 and the joist 5 are firmly welded during installation. And then, a connecting beam 4 made of profile steel is arranged between the adjacent steel supports 3, and the two ends of the connecting beam 4 are of hoop structures, so that the adjacent steel supports 3 are held tightly and clamped to prevent the displacement deformation of the adjacent steel supports, and the rigidity of a support system is enhanced.

When the prestress is applied to the first layer steel support 3, in order to prevent the steel support 3 from generating excessive deflection when the prestress is applied, the dead-weight deflection of the steel support 3 is corrected to be horizontal before the prestress is applied to the steel support 3. The prestress can be applied in stages to reach the design value of the prestress and eliminate the component deformation of the supporting system; and after the prestressing is finished, the steel support 3 is subjected to repeated prestressing according to the monitored prestress change of the steel support 3 and the deformation degree of the foundation pit support structure 6 so as to improve the safety. Specifically, two hydraulic jacks can be symmetrically arranged at the movable end 301 of the steel support 3 to synchronously apply prestress, initial prestress can be firstly applied to the steel support 3, and a cushion block is arranged at the movable end 301 and is firmly fixed, so that the steel support 3 is installed and fixed. The design prestress can be applied in 5 stages, 20%, 40%, 60%, 80%, 100% of the prestress design value. The prestressing force applied in the first stage is smaller and is kept for 2 minutes, and the rest stages are kept for 5 minutes, so that the deformation of the component is eliminated, the effectiveness of prestressing force is ensured, and the stress loss is reduced. In this example, an axial force gauge for measuring the magnitude of the prestress is provided at the free end 301 of the steel support 3. When the stroke of the jack is insufficient, a steel wedge structure can be inserted, so that the jack is secondarily forced to design prestress, after the prestress is applied in place, the cushion block at the movable end 301 is firmly fixed, and then the jack is unloaded.

Increasing the monitoring frequency within 12 hours after the first prestressing, and finding that the prestressing loss or the deformation rate of the enclosure structure 6 is obviously converged, and re-stressing to a design value is needed; when the temperature difference between day and night is too large and the prestress of the steel support 3 is lost, the prestress should be added to the design value again in the low-temperature period of the day; the detection of the prestress of the steel support 3 is enhanced in the earth excavation process, and when the prestress loss occurs in the detection and the horizontal displacement rate of the pile body of the enclosing structure 6 exceeds the warning value, the prestress of the steel support 3 is increased to control the deformation; when the prestress change of the steel support 3 is more than 3%, the repeated prestressing is implemented, and the repeated prestressing is required to meet the design safety requirement.

The prestressing force braced system of this embodiment is three layer construction, after having built first layer braced system, continues to excavate the earthwork downwards in the foundation ditch to the layering, segmentation mode excavation prevent the machinery collision, adopt the manual work to cooperate small-size machinery to excavate, reduce the no support exposure time. When the steel support 3 is excavated to the bottom of the designed installation position of the second layer of steel support 3 for a certain distance, constructing an enclosing purlin 19 on the inner side of the foundation pit support structure 6, and in some embodiments, arranging a steel structure bearing part connected with the foundation pit support structure 6 on the enclosing purlin 19 to enhance bearing safety; for example, the bearing member of the present embodiment includes a hanging rib 24 and a planting rib 25, refer to fig. 10 and 11, wherein the lower end of the hanging rib 24 is embedded in the structure of the enclosing purlin 19, and the upper end is welded with the pile body main rib of the enclosing structure 6 along the vertical direction; one end of the planting bar 25 is embedded in the structure of the enclosing purlin 19, and the other end is connected in the pile body of the enclosing structure 6 adjacent to the enclosing purlin 19 along the horizontal direction. Further, the steel support 3 may be provided with a hanger attached to the pit enclosure 6 at the end that is attached to the enclosure 19 to prevent the steel support 3 from falling off.

When the enclosing purlin 19 is constructed, the pile body of the enclosing structure 6 can be constructed and planted with the steel bar 25, the hanging steel bar 24 is welded on the main pile body of the enclosing structure 6 above the enclosing purlin 19, and the pile body of the enclosing structure 6 at the position of the enclosing purlin 19 is subjected to roughening treatment so as to enhance the connection stability of the structure. The hanging plate 26 is structurally installed on the convex body 1 of the enclosing purlin 19, and the construction and the prestress application of the second layer supporting system are completed according to the assembly installation method of the first layer supporting system. It should be noted that, after the construction of the second layer supporting system is completed, the prestress of the upper layer supporting system is rechecked and adjusted to meet the design requirement, and the adjustment is performed according to the deformation and stress monitoring conditions of the site enclosure structure 6.

Similarly, the construction steps described above are followed to continue to excavate earth downward, construct the purlin 19, install the relevant components and pre-stress the third layer, i.e., the final layer support system in this example. It should be noted that, along with the construction of the lower layer in turn, the related components of the prestress supporting system can increase the specification of the materials layer by layer to enhance the structural strength, for example, the engineering project in this example can be to the steel supporting 3 material specification of the first layer supporting system which is a pipe with the diameter of 609mm and the wall thickness of 16mm, the steel supporting 3 material specification of the second layer is a pipe with the diameter of 800mm and the wall thickness of 16mm, and the steel supporting 3 material specification of the last layer, namely the third layer, is a pipe with the diameter of 800mm and the wall thickness of 20mm, so as to meet the requirement of the foundation pit supporting force changing along with the depth and improve the engineering safety coefficient.

In this embodiment, after the installation of the final layer supporting system is completed, the earth is excavated down to the elevation of the first anchor rod 21, and the construction of the first anchor rod 21 and the wale is performed; and then, continuously excavating the earthwork to the elevation of the second anchor rod 21 to perform the construction of the second anchor rod 21 and the waist beam, thereby further enhancing the stability of the foundation pit structure. After the second anchor rod 21 is constructed, the earth is excavated to the bottom of the foundation pit for tower crane installation and construction, the bottom plate 10 of the building body is constructed at the bottom of the foundation pit, and then the floor slab 23 at the last layer is constructed. It should be noted that, in constructing the floor 10 of the building, a further waterproofing operation may be performed at the junction between the floor 10 and the lattice column 2, referring to fig. 9, in this example, the waterproofing operation performed at the junction between the lattice column 2 and the floor 10 of the building includes the steps of:

t1, pouring a cushion layer 14, paving a waterproof coiled material 13 on the cushion layer 14, turning up the waterproof coiled material 13 along the lattice column 2, and arranging a waterproof protective layer 12 on the waterproof coiled material 13;

t2, binding steel bars of the bottom plate 10, welding the steel bars with the lattice column 2, and arranging a water stop steel plate 7 with a downward water facing surface at the upper flanging edge position of the waterproof coiled material 13 of the lattice column 2;

a hollow groove 15 is reserved at the upper part of the connection position of the bottom plate 10 and the lattice column 2, and a water stop steel plate 7 with the downward water facing surface is preset at the side wall position of the hollow groove 15;

t4, pouring concrete of the bottom plate 10, and arranging waterproof paint 9 at the joint position of the lattice column 2 and the bottom of the empty groove 15 reserved on the bottom plate 10;

and T5, pouring concrete in the empty groove 15 reserved in the bottom plate 10.

In the embodiment, the waterproof coiled material 13 is a 4mm thick SBS waterproof coiled material, the waterproof coiled material 13 is turned up at the position of the lattice column 2 for 300mm to be paved, the waterproof protective layer 12 is 5mm mortar, the waterproof coating 9 is 4mm thick permeable crystallization waterproof coating, and the C40 micro-expansion concrete is adopted to pour the empty groove 15.

When backfilling the foundation pit fertilizer groove at each layer, considering that the surrounding backfill soil pressure can act on the building body, the concrete strength of the outer wall and the floor slab 23 of the building body is not stable at the moment, meanwhile, the floor slab 23 has a large span space, the bearing capacity is small, the excessive soil pressure can generate irreversible influence on the structure, and in order to ensure the structural stress safety of the building body, a double-wall structure is further arranged in the foundation pit fertilizer groove at each layer, and comprises a buttress, an end plate and a cover plate which are arranged outside the side wall of the building body, wherein one end of the buttress is connected with the side wall of the building body, the other end of the buttress is connected with the end plate which is arranged along the direction of the side wall of the building body, and the cover plate is connected to the top of the buttress and the end plate; backfilling the inside of the double-wall structure before construction of the cover plate, wherein the backfilling material is fluid solidified soil in the example. Further, supporting piles are arranged on supporting piles of the foundation pit supporting structure 6 to strengthen supporting stability of the supporting structure 6. And after the backfilling of the final-layer fertilizer groove is finished, pouring a concrete force transmission belt 22, such as pouring a C20 specification concrete force transmission belt 22 with the thickness not smaller than 1m at the corresponding height position of each layer of floor slab 23 in the example, and dismantling the layer of steel support 3, joist 5, portal frame 17, connecting beam 4 and other components after the concrete force transmission belt 22 meets the strength requirement. When the steel support 3 is removed, crane equipment is used, a steel wire rope is bound on the steel support 3, a jack is arranged at the movable end 301 to exert a jacking force, a cushion block is removed, then the jacking force is relieved, after the jack is removed, high-strength connecting bolts of a flange plate of the steel support 3 are removed, and then the steel support 3 is lifted out in sections so as to be recycled. And each monitoring on the foundation pit support structure 6 is enhanced in the dismantling process of the steel support 3, the dismantling scheme is adjusted according to the monitoring condition, and the grading unloading is adopted, so that the adverse effect of stress mutation on the support structure 6 and the main body structure of the building body is avoided. And (3) sequentially completing construction of the floor slab 23 of the second layer and the first layer, double-wall structure setting, foundation pit fertilizer groove backfilling, pouring of the concrete force transmission belt 22, dismantling of related components such as the steel support 3, the joist 5, the portal frame 17, the connecting beam 4 and the like according to the same steps, cutting and removing constructional columns, cleaning the constructional columns left in the floor slab 23, and pouring by using micro-expansion concrete with one mark higher than the constructional columns.

The specific construction method is shown in working conditions P1-P17 in FIGS. 13-15. In the working condition P1, constructing an enclosure structure 6, upright posts 11 and lattice posts 2 of the foundation pit; in the working condition P2, excavating earthwork to the required foundation pit construction depth 20, namely the construction elevation of the first-layer supporting system, constructing a crown beam 18 and erecting the first-layer supporting system; in the working condition P3, continuously excavating earthwork to the required foundation pit construction depth 20, namely the construction elevation of the second layer supporting system in the example, constructing the layer of enclosing purlin 19 and erecting the layer of supporting system; in the working condition P4, continuously excavating earthwork to the required foundation pit construction depth 20, namely the construction elevation of the final layer supporting system in the example, constructing the layer of enclosing purlin 19 and erecting the layer of supporting system; in the working condition P5, continuously excavating the earthwork to the required foundation pit construction depth 20, namely the construction elevation of the first anchor rod 21 in the example, and constructing the anchor rod 21 and a waist beam at the position; in the working condition P6, continuously excavating the earthwork to the required foundation pit construction depth 20, namely the construction elevation of the second anchor rod 21 in the example, and constructing the anchor rod 21 and the waist beam at the position; in the working condition P7, continuously excavating earthwork to the required foundation pit construction depth 20, namely the bottom elevation of the foundation pit; in the working condition P8, constructing the bottom plate 10 and the last floor 23 of the building body; in the working condition P9, backfilling the foundation pit fertilizer groove to a preset position below the floor slab 23 at the last layer, and casting a concrete force transmission belt 22; in the working condition P10, after the concrete force transmission belt 22 reaches the design strength, removing relevant components of the final layer support system; in the working condition P11, constructing a second-layer building structure and a floor slab 23 of the example; in the working condition P12, continuously backfilling the foundation pit fertilizer groove to a preset position below the floor slab 23 of the second layer, and then casting a concrete force transmission belt 22; in the working condition P13, after the concrete force transmission belt 22 reaches the design strength, removing the related components of the second layer of supporting system; in the working condition P14, constructing a first-layer building structure and a floor slab 23 of the embodiment; in the working condition P15, continuously backfilling the foundation pit fertilizer groove to a preset position below the first floor slab 23, and then casting a concrete force transmission belt 22; in the working condition P16, after the concrete force transmission belt 22 reaches the design strength, removing the related components of the first layer supporting system and the lattice column 2; and in the working condition P17, the building body structure and the floor slab 23 are continuously constructed upwards, and backfilling of the foundation pit fertilizer groove is completed.

In summary, the invention provides the foundation pit prestress supporting system and the construction method thereof, which can safely and effectively support and protect the enclosure structure of the large-span foundation pit, ensure the construction safety, and improve the engineering construction efficiency, the economic benefit and the environmental benefit through the modularized recyclable assembly and the standardized installation method.

Finally, it should be noted that: it is apparent that the above examples are only illustrative of the present invention and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. And obvious variations or modifications thereof are contemplated as falling within the scope of the present invention.

Claims (10)

1. A foundation pit prestressed bracing system for providing horizontal bracing force to a foundation pit enclosure of an in-building structure, comprising:

a steel support which applies a horizontal prestress to the foundation pit support structure along the axial direction;

the lattice column is of a cavity structure and is used for being placed in the foundation pit to vertically bear the supporting system;

joists which are erected on the lattice columns to carry the steel supports;

the portal frame is arranged on the joist and surrounds the steel support to limit the movement of the steel support;

a tie beam that interfaces adjacent steel supports respectively to enhance the stiffness of the support system;

the hanging plate is used for connecting the steel support end part and the foundation pit support structure; and

and the arch is arranged at the position of the lattice column bearing joist.

2. The foundation pit prestress supporting system of claim 1, wherein the steel support is of a segmented structure and comprises a middle section, a fixed end and a movable end which are positioned at two ends and are respectively connected with the hanging plate; the movable end of the steel support is provided with a telescopic adjusting piece for adjusting the steel support to a required length and applying prestress.

3. The foundation pit prestress supporting system of claim 2, wherein the hanging plate comprises a vertically arranged attaching plate for realizing contact stress, an extension flat plate extending towards the outer side of the enclosure structure is arranged at the upper end of the attaching plate, which is contacted with the steel support, for realizing fixed connection, and an inner extension flat plate extending towards the inner side of the enclosure structure is arranged at the lower end of the attaching plate.

4. A method of constructing a foundation pit prestressed bracing system according to claim 3, comprising the steps of:

s1, designing a supporting system and processing each component;

s2, constructing and installing lattice columns in the foundation pit;

s3, excavating earth downwards to construct a first-layer supporting system, constructing a crown beam at the top of the foundation pit support structure, and mounting hanging plates on the crown beam;

s4, installing a supporting arch, a joist, a steel support, a portal frame and a connecting beam on the lattice column, and applying prestress to the steel support;

s5, continuously excavating earthwork downwards, constructing an enclosing purlin on the inner side of the foundation pit support structure, installing a hanging plate on the enclosing purlin, and constructing a next layer of support system according to the step S4;

s6, repeating the step S5 to finish the final layer support system;

s7, continuously excavating earthwork downwards, constructing anchor rods and waist beams at corresponding positions of the foundation pit support structures, and constructing a bottom plate of a building body at the bottom of the foundation pit;

s8, constructing the floor slab, backfilling the foundation pit fertilizer grooves of the floor, pouring a concrete force transmission belt, and dismantling the support system after the strength requirement is met;

s9, repeating the step S8 until the first-layer support system is removed, and then removing the lattice columns.

5. The method for constructing a foundation pit prestressed supporting system according to claim 4, wherein in said step S4, prestress is applied to the steel support in stages to reach the design value of prestress and eliminate component deformation of the supporting system; and after the prestressing force is applied, the steel support is subjected to repeated prestressing force according to the monitored prestress change of the steel support and the deformation degree of the foundation pit support structure so as to improve the safety.

6. The construction method of a foundation pit prestressed supporting system according to claim 5, wherein in the step S8, a double-wall structure is further provided in the foundation pit fertilizer tank, the double-wall structure comprises a buttress, an end plate and a cover plate, the buttress, the end plate and the cover plate are arranged outside the side wall of the building body, one end of the buttress is connected with the side wall of the building body, the other end of the buttress is connected with the end plate arranged along the direction of the side wall of the building body, and the cover plate is connected to the tops of the buttress and the end plate; and backfilling the inside of the double-wall structure before construction of the cover plate.

7. The method for constructing a foundation pit prestressed supporting system according to claim 6, wherein said steel supports are inclined with respect to said crown beams and said purlin, and said crown beams and said purlin are provided with projections at the connection portions with said steel supports for fitting and mounting the hanging plates and for supporting the prestress applied by said steel supports.

8. The method of constructing a foundation pit prestressed bracing system according to any one of claims 5-7, wherein said purlin is provided with a bearing member connected to the enclosure structure to improve safety; the end part of the steel support connected with the enclosing purlin is provided with a hanging piece connected with the foundation pit enclosing structure so as to prevent the steel support from falling off.

9. The method for constructing a foundation pit prestressed supporting system according to claim 8, wherein the bottoms of said lattice columns are penetrated in the column piles arranged in the foundation pit, and said lattice columns are connected with the reinforcement cages arranged in the column piles.

10. The method for constructing a foundation pit prestressed supporting system according to claim 9, wherein said waterproofing of the joint of said lattice column and the floor of the building comprises the steps of:

t1, pouring a cushion layer, paving a waterproof coiled material on the cushion layer, turning the waterproof coiled material upwards along a lattice column, and arranging a waterproof protective layer on the waterproof coiled material;

t2, binding a bottom plate steel bar, welding with a lattice column, and arranging a water stop steel plate with a downward water facing surface at the position of the upper flanging edge of the waterproof coiled material of the lattice column;

a hollow groove is reserved at the upper part of the connection position of the bottom plate and the lattice column, and a water stop steel plate with the downward water facing surface is preset at the side wall position of the hollow groove;

t4, pouring bottom plate concrete, and arranging waterproof paint at the joint position of the lattice column and the bottom of the empty slot reserved on the bottom plate;

and T5, pouring concrete in the empty groove reserved in the bottom plate.

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