CN111305220A - Concrete support and structural top plate combined building system based on permanent and temporary combination and construction method thereof - Google Patents

Abstract

The invention relates to a concrete support and structural roof combined building system based on permanent and temporary combination and a construction method thereof, wherein the system comprises an underground structure, fender piles, waist beams and concrete supports; the fender pile is positioned at the outer side of the periphery of the underground structure, the pile top is positioned above a top plate of the underground structure for a certain distance, and the pile bottom is positioned below a bottom plate of the underground structure for a certain distance; the inner side of the fender post is provided with a waist beam, the concrete support is rigidly connected with the waist beams at two sides, and the concrete support is positioned above the top of the underground structure. The invention relates to a concrete support and structure top plate combined system based on 'permanent temporary combination', wherein a temporary concrete support in a foundation pit is taken as a part of a structure top plate, and the temporary concrete support and the structure top plate jointly bear external loads according to the permanent structure, so that the concrete support is prevented from being chiseled out at the later stage of being taken as a temporary component, the process is simplified, the progress is accelerated, the size of the structure top plate is reduced, the integral stress requirement of the structure is met, a new thought of overall consideration of the temporary concrete support and the permanent structure top plate is provided for the first time, and the long-term durability of the foundation pit safe excavation and the underground structure is met.

Description

Concrete support and structural roof joint construction system and construction method based on the combination of permanent and permanent

technical field

The invention belongs to the technical field of underground engineering, and in particular relates to a combined construction system of a concrete support and a structural roof based on a permanent combination and a construction method thereof.

Background technique

For underground projects that are widely constructed at present, foundation pit engineering is the preferred space construction method for all kinds of underground buildings with large buried depths, large spaces, and special-shaped structures. , The inner support is widely used, mainly considering that the inner support has the characteristics of high rigidity, strong deformation resistance, and mature technology. When deep or special-shaped foundation pits are close to important structures, concrete inner support is usually the first choice.

The conventional foundation pit support structure design scheme, whether it is concrete support or steel support, is considered as a temporary structure. After the foundation pit is excavated to the bottom of the pit and the main structure is rebuilt, it will be demolished one after another. However, due to the large volume of the concrete support, The quality of the cut concrete blocks is large, and there are major safety hazards in the process of cutting and lifting, and the on-site construction is time-consuming and labor-intensive.

During the construction of deep and large foundation pits, the dismantling and hoisting of concrete supports have become one of the important factors that restrict the construction period and affect the investment. The breaking, cutting and outbound transportation of concrete supports generally occur after the main structure is poured and the maintenance age is reached. Generally, the foundation pit project is about to be completed. At this time, the requirements for process conversion and step connection in the foundation pit are high, and the construction period pressure is large. The conventional concrete support is only considered as a temporary component, which has seriously restricted the health of the underground project under the concept of green and environmental protection. develop.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a combined construction system of concrete support and structural roof based on the permanent combination and construction method thereof. The elevation of the concrete support is adjusted to the elevation of the permanent structure roof. Pre-embedded steel bar connectors in the pre-cast concrete support, and interface treatment at the joint of the two structures, through the mechanical connection of the stressed steel bars and the bonding of epoxy resin at the structural joint, the connection between the concrete support and the roof of the post-cast structure is realized. The effective superposition of the concrete support and the underground structure forms an organic whole, forming an overall stress system, avoiding the dismantling and external transportation of the concrete support, and effectively reducing the size of the structural roof components, which not only saves the construction period and investment, but is more important. The main thing is to avoid the hidden safety hazards during the cutting and outbound transportation of large concrete supports, better meet the construction concept of safety, green and environmental protection for deep and large foundation pit projects, and at the same time, it is also more conducive to achieving the safety goals of the surrounding environment.

The technical scheme adopted in the present invention is:

The combined construction system of concrete support and structural roof based on the combination of permanent approach is characterized by:

The system includes underground structures, enclosure piles, waist beams and concrete supports;

The enclosure pile is located outside the underground structure, the top of the pile is higher than the roof of the underground structure, and the bottom of the pile is below the bottom plate of the underground structure;

The inner side of the enclosure pile is provided with a waist beam, and the top of the pile is provided with a crown beam. The concrete support is rigidly connected to the waist beam to effectively transmit force, and the concrete support is located at the top of the underground structure.

The underground structure includes the structural top plate, the structural middle plate, the structural bottom plate, the structural side wall and the structural central column. The enclosure piles are located around the outside of the underground structure, and the waist beam and the concrete support are located above the structural top plate.

The top of the retaining pile is provided with a crown beam at the top of the pile, and the retaining pile and the crown beam are effectively connected by planting reinforcement or reserved reinforcement.

The waist beam is located on the inner side of the enclosure pile and is connected by planting bars; the inner side of the waist beam is reserved for stressed steel bars or pre-embedded steel bar connectors.

Concrete support reinforcement bars are arranged in the concrete support, and both ends of the concrete support are connected with the reserved stress reinforcement bars or pre-embedded reinforcement bar connectors on the inner side of the waist beam through the concrete support reinforcement bars.

The upper surface of the structural roof is in a regular gear-shaped concave-convex structure, and the concrete support is located on the upper surface of the structural roof, and is mechanically engaged with the structural roof in a concave-convex shape;

A transverse reinforcing rib is arranged in the concrete support, and steel bar connectors are reserved at both ends of the reinforcing bar.

The contact surface between the concrete support and the structural roof is chiseled and coated with an interface agent.

The structural top plate, the structural bottom plate and the outside of the structural side walls of the underground structure are all provided with waterproof materials for all-inclusive waterproofing.

Backfill is set above the structural roof, and the backfill is backfilled in layers.

The construction method of the joint construction system of the concrete support and the structural roof based on the combination of forever and ever, is characterized by:

Include the following steps:

Step 1: Based on the outline of the underground structure, set up a dewatering well outside the outline of the foundation pit, and carry out dewatering construction 1 month before the excavation of the foundation pit;

Step 2: Stake out according to the coordinates of the enclosure piles and the construction error, and then carry out the construction of the enclosure piles, and carry out the enclosure piles in the order of drilling rig in place, forming holes, clearing holes, lowering the reinforcement cage, pouring concrete, and cleaning the floating slurry on the top of the pile. construction;

Step 3: excavate the trench at the top of the enclosure pile, construct the crown beam on the top of the pile, and then carry out the excavation of the foundation pit according to the principle of digging and supporting;

Step 4: When the foundation pit is excavated to 0.5m below the concrete support, the concrete waist beam shall be constructed in time, and the concrete waist beam and the enclosure pile shall be connected by planting reinforcement. Buried rebar connector;

Step 5: According to the arrangement of the concrete support and the size of the section, the soil in the foundation pit is excavated by grooving, then leveling, laying the cushion, tying the steel skeleton of the concrete support in situ, arranging the reinforcing bars of the concrete support, and setting the reinforcing bars. The position of the reinforcing bars corresponds to the reinforcing bars of the roof, and steel bar connectors are reserved on both sides of the concrete support; the connection between the waist beam and the concrete support is carried out by pre-reserving stressed bars or pre-embedded bar connectors on the waist beam. connect;

Concrete supports are poured as required and maintained as required;

Step 6: After the concrete support reaches the specified curing age and design strength, continue to excavate the foundation pit based on the principle of digging and supporting until the bottom of the foundation pit. Manual excavation is used for 0.5m above the pit bottom, and then the pit bottom is dug in time. Leveling, laying waterproof layer, plain concrete cushion, binding steel bars and pouring structural bottom plate, structural side wall and structural middle plate, during the pouring process of the main structure, remove the internal support at the corresponding position in time;

Step 7: Chisel the surface of the concrete support at the contact part between the structural roof and the concrete support, and then apply the interface agent 2-3 times. Based on the steel bar connector reserved on both sides of the concrete support, the reinforcing ribs set in the middle of the concrete support are connected with the concrete support. Roof reinforcement is mechanically connected, and then the structural roof is poured as required;

The distance between the bottom of the concrete support and the bottom surface of the structural bottom plate shall not be less than 300mm;

Step 8: Backfill the soil in layers above the structural roof, and the density of the backfill is not less than 93%;

Step 9: Remove all structures within 3m below the surface, and reserve a laying path for the later underground structures such as municipal pipelines.

The present invention has the following advantages:

The invention transforms the concrete support in the foundation pit from a temporary structure into a permanent structure, and superimposes it with the structural roof to form a permanent combined construction process of the concrete support and the structural roof. The concrete involved in the concrete support, waist beam, enclosure pile and the underground structure is conventional waterproof concrete, all kinds of steel bars and steel bar connectors are ordinary Q235 steel, and the waterproof materials laid on the outside of the underground structure are conventional waterproof membranes and waterproof coatings. The interface agent between the support and the structural roof is a conventional epoxy resin, and its corresponding size is a conventional type, which is convenient for processing and manufacturing; the diameter and length of the pre-embedded connector in the concrete support can be determined according to the position of the main reinforcement of the structural roof and the overall load. The force requirements are comprehensively determined. The main force-bearing reinforcement is made of threaded steel bars, and the connection with the connector is made of thread. The distance between the bottom of the concrete support and the bottom of the structural roof is generally not less than 300mm, which can be flexibly adjusted under the premise of meeting the requirements of the structural roof’s stress and durability. The technology is simple, the concept is clear, the construction is simple, and it has high economic and social benefits.

Description of drawings

Figure 1 is a plan view of the superimposed arrangement of the concrete support and the structural roof.

Figure 2 is a cross-sectional view of the underground structure.

Figure 3 is a longitudinal sectional view of the underground structure.

Figure 4 is a large sample view of the connection between the concrete support and the structural roof.

In the figure, 1-enclosure pile, 2-pillar crown beam, 3-concrete support, 4-underground structure, 5-structure roof, 6-backfill, 7-concrete support reinforcement, 8-reinforcing bar, 9 - Rebar connector, 10- Interface agent, 11- Roof reinforcement, 12- Waist beam.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments.

The present invention relates to a combined construction system of concrete support and structural roof based on the combination of permanent and imposing conditions, proposes a design idea of internal support as a permanent structure in the existing deep foundation pit engineering, and enriches the functions of the deep foundation pit support system.

The system includes an underground structure 4 , an enclosure pile 1 , a waist beam 12 and a concrete support 3 . The enclosure pile 1 is located on the outer side of the underground structure 4, the top of the pile is located at a certain distance above the top plate of the underground structure 4, and the pile bottom is a certain distance below the bottom plate of the underground structure 4; The side waist beams 12 are rigidly connected and effectively transmit force, and the concrete support 3 is located at the position of the top plate of the underground structure 4 .

The underground structure 4 includes a structural top plate 5, a structural middle plate, a structural bottom plate, a structural side wall and a structural center column.

The top of the enclosure pile 1 is provided with a pile top crown beam 2, and the enclosure pile 1 and the pile top crown beam 2 are connected by planting bars.

The waist beam 12 is located on the inner side of the enclosure pile 1, and is connected by planting bars or reserved stress steel bars in the enclosure pile 1; connect. The concrete support 3 is provided with longitudinal concrete support reinforcement bars 7, and both ends of the concrete support 3 are connected with the reserved stress reinforcement bars or embedded reinforcement connectors on the inner side of the waist beam 12 through the concrete support reinforcement reinforcement bars 7. One or more rows of concrete supporting tendons 7 can be arranged according to the structural stress requirements.

The concrete support 3 is embedded in the top surface of the structural roof 5 of the underground structure 4 . A transverse reinforcing rib 8 is arranged in the concrete support 3, and steel bar connectors 9 are arranged at both ends of the reinforcing bar 8. The reinforcing bar 8 in the concrete support 3 is connected with the corresponding roof steel bar 11 in the structural roof 5 through the steel bar connector 9. . The distance between the bottom of the concrete support 3 and the structural bottom plate 5 is not less than 300mm, which meets the requirements for the penetration and force transmission of the reinforcement bars 11 of the roof. The structural contact surface between the concrete support 3 and the structural roof 5 is chiseled in advance, and the interface agent 10 is coated two to three times. The concrete support 3 is constructed when the foundation pit is excavated to the corresponding elevation, and is considered as a superimposed member with the structural roof 5 in the later stage, and is jointly carried as a part of the permanent underground structure 4 .

The upper surface of the structural top plate 5 has a regular gear-shaped concave-convex structure, and the concrete support 3 is located on the upper surface of the structural top plate 5, and is mechanically engaged with the structural top plate 5 in a concave-convex shape.

The number of concrete supports 3 needs to be comprehensively determined according to the force and durability requirements of the overall member, as well as the stability during foundation pit excavation and the requirements for surrounding environmental protection. Generally, the longitudinal spacing of concrete supports 3 along the underground structure 4 is ≥6m.

The structural top plate 5 , the structural bottom plate and the outside of the structural side walls of the underground structure 4 are all provided with waterproof materials, so as to realize all-inclusive waterproofing. The waterproof material on the outside of the structural side walls and the bottom plate can be pre-laid with anti-stick waterproofing membrane, and the waterproof material on the outside of the structural top plate 5 can be made of waterproof paint.

The backfill 6 is set above the structural roof 5, and the compaction is layered.

The concrete involved in the enclosure pile 1, the concrete support 3, the underground structure 4, the pile top crown beam 2 and the waist beam 12 is ordinary waterproof concrete, and the steel bars involved can be made of Q235 steel.

As shown in Figures 1-4, the underground structure 4 is generally composed of a cast-in-place reinforced concrete structure including the structural roof 5 and the concrete support 3. The dimensions of the structural roof 5 and the concrete support 3, the bottom of the concrete support 3 and the structural roof 5 The vertical distance between them, the number of reinforcing bars 8 inside the concrete supports 3 and the type of reinforcing bars can be comprehensively determined according to the connection of components and the stress requirements of the permanent structure. According to the comprehensive consideration of the force and durability of the composite members of the permanent structure roof 5, it also needs to be comprehensively determined according to the stability during the excavation of the foundation pit and the surrounding environmental protection requirements. Generally, the longitudinal spacing between the concrete supports 3 is ≥6m.

The concrete involved in all reinforced concrete components is ordinary waterproof concrete, the steel bars and connectors are Q235 steel, and the interface agent between the concrete support and the structural roof can be epoxy resin.

The invention takes the temporary concrete support in the foundation pit as a part of the structural roof, and considers the permanent structure to jointly bear the external load. On the one hand, the concrete support needs to be removed as a temporary member, which simplifies the process, speeds up the progress, and saves the investment. The size of the roof of the structure is reduced to meet the overall stress requirements of the structure. For the first time, a new idea of considering the temporary concrete support and the permanent structure is put forward, and the original intention of the concrete support design of "permanent combination" is realized. The design concept of "concrete support and structural roof co-construction technology based on the combination of forever and ever" is a great improvement to the design of the support system in the existing deep and large foundation pit, and provides a brand-new foundation for the practice of green, environmentally friendly and safe underground engineering. At the same time, the construction process is simple, the concept is clear, and the construction is simple, which provides a new idea for the realization of underground energy-saving projects.

The co-construction process method of the concrete support and the structural roof combined with Yonglin includes the following steps:

Step 1: Based on the outline of the underground structure 4, set up a dewatering well outside the outline of the foundation pit, and carry out dewatering construction 1 month before the excavation of the foundation pit;

Step 2: Stake out according to the coordinates of the enclosure pile 1 and the construction error, and then carry out the construction of the enclosure pile 1, in accordance with the main sequence of drilling rig in place, hole formation, hole cleaning, lower reinforcement cage, cast-in-place concrete, pile top laitance cleaning, etc. Construction of enclosure pile 1;

Step 3: excavate the trench at the top of the enclosure pile 1, construct the crown beam 2 on the top of the pile, and then carry out the excavation of the foundation pit according to the principle of excavation and support;

Step 4: When the foundation pit is excavated to 0.5m below the concrete support 3, construct the concrete waist beam 12 in time. Stressed steel bar or pre-embedded steel bar connector;

Step 5: According to the arrangement and cross-sectional size of the concrete support 3, the soil in the foundation pit is excavated by grooving, then leveling, laying the cushion, tying the steel skeleton of the concrete support 3 in situ, arranging the reinforcing bars 7 of the concrete support, setting Reinforcing rib 8, the position of reinforcing rib 8 corresponds to roof steel bar 11, and steel bar connector 9 is reserved on both sides of concrete support 3; the connection between waist beam 12 and concrete support 3 is reserved in advance on waist beam 12 Stressed steel bars or embedded steel bar connectors are used for connection;

Concrete support 3 is poured as required, and maintenance is performed as required;

Step 6: After the concrete support 3 reaches the specified curing age and design strength, continue to excavate the foundation pit based on the principle of follow-up and follow-up support until the bottom of the foundation pit. Manual excavation is used for 0.5m above the pit bottom, and then the bottom of the pit is dug in time. Carry out leveling, laying waterproof layer, plain concrete cushion, binding steel bars and pouring structural bottom plate, structural side wall and structural middle plate, and dismantle the internal support in corresponding positions in time during the pouring process of the main structure;

Step 7: The surface of the concrete support 3 at the contact position between the structural roof 5 and the concrete support 3 is chiseled, and then the interface agent 10 is brushed 2-3 times. Rebar connectors 9 are reserved on both sides of the concrete support 3, and the concrete support is 3. The reinforcing ribs 8 arranged in the middle are mechanically connected with the roof reinforcement bars 11, and then the structural roof 5 is poured as required;

The distance between the bottom of the concrete support 3 and the bottom surface of the structural bottom plate 5 is not less than 300mm;

Step 8: Backfill the soil in layers above the structural roof 5, and the density of the backfill 6 is not less than 93%;

Step 9: Remove all structures within 3m below the surface, and reserve a laying path for the later underground structures such as municipal pipelines.

It is still quite difficult to theoretically find out the temporary inner support of the foundation pit that can also be used as the main underground structure under any conditions. In the same way, the depth of the foundation pit and the erection position of the inner support are not the same, and the stress and durability requirements of the main structure are not completely consistent. The existing underground engineering construction should still follow the basic concept of "permanent combination". The inner support is superimposed and subjected to overall force, and at the same time, it meets the requirements of structural bearing capacity and durability, and ensures that the space above the structure meets the needs of municipal engineering. The concrete support at the roof of the structure is designed as a permanent stress member to ensure the safety of the foundation pit, the reliable stress of the underground structure and the long-term stability to the greatest extent. The current Yonglin combined concrete support and structural roof co-construction process still needs to adhere to the basic principles of function first, adapting measures to local conditions, prescribing the right medicine, and flexible application.

The invention uses the temporary concrete support in the foundation pit as a part of the structural roof, and shares the external load with the permanent structure. On the one hand, the concrete support needs to be removed as a temporary member, which simplifies the process and speeds up the progress. On the one hand, the size of the structural roof is reduced. , to meet the overall stress requirements of the underground structure, and for the first time put forward a new idea of considering the temporary concrete support and the permanent roof as a whole, which improves the safety, green and environmental protection design concept of underground engineering, and has high economic and social benefits. Rail transit, railway, highway and other projects have a wide range of application prospects.

The content of the present invention is not limited to those listed in the embodiments, and any equivalent transformations taken by those of ordinary skill in the art to the technical solutions of the present invention by reading the description of the present invention are covered by the claims of the present invention.

Claims (10)

1. The combined construction system of concrete support and structural roof based on the combination of Yonglin is characterized in that: The system includes an underground structure (4), an enclosure pile (1), a waist beam (12) and a concrete support (3); The enclosure pile (1) is located outside the underground structure (4), the top of the pile is higher than the top plate of the underground structure (4), and the bottom of the pile is below the bottom plate of the underground structure (4); The inner side of the enclosure pile (1) is provided with a waist beam (12), the top of the pile is provided with a crown beam (2), the concrete support (3) is rigidly connected with the waist beam (12) and effectively transmits force, and the concrete support (3) is located in the underground structure (4) Top position. 2. The combined construction system of concrete support and structural roof based on the combination of permanent proximity according to claim 1, is characterized in that: The underground structure (4) includes a structural top plate (5), a structural middle plate, a structural bottom plate, a structural side wall and a structural central column, the enclosure piles (1) are located around the outside of the underground structure (4), and the waist beams (12) and concrete support (3) Above the structural roof (5). 3. The concrete support and structural roof joint construction system based on the permanent combination according to claim 2, is characterized in that: The top of the enclosure pile (1) is provided with a pile top crown beam (2), and the enclosure pile (1) and the crown beam (2) are effectively connected by planting reinforcement or reserved reinforcement. 4. The combined construction system of concrete support and structural roof based on the combination of permanent proximity according to claim 3, is characterized in that: The waist beam (12) is located on the inner side of the enclosure pile (1) and is connected by planting reinforcing bars; the inner side of the waist beam (12) is reserved for stressed steel bars or pre-embedded steel bar connectors. 5. The combined construction system of concrete support and structural roof based on the permanent combination according to claim 4, is characterized in that: Concrete support stress bars (7) are arranged in the concrete support (3), and the two ends of the concrete support (3) pass through the concrete support stress bars (7) and the reserved stress bars or pre-embedded steel bars on the inner side of the waist beam (12). Connector connection. 6. The combined construction system of concrete support and structural roof based on the permanent combination according to claim 5, is characterized in that: The upper surface of the structural top plate (5) has a regular gear-shaped concave-convex structure, and the concrete support (3) is located on the upper surface of the structural top plate (5), and is mechanically engaged with the structural top plate (5) in a concave-convex shape; A transverse reinforcing rib (8) is arranged in the concrete support (3), and steel bar connectors (9) are reserved at both ends of the reinforcing bar (8), and the reinforcing bars (8) in the concrete support (3) pass through the steel bar connector (9). ) are connected to the corresponding reinforcement bars (11) in the structural roof (5). 7. The combined construction system of concrete support and structural roof based on permanent combination according to claim 6, is characterized in that: The contact surface between the concrete support (3) and the structural top plate (5) is chiseled and coated with an interface agent (10). 8. The combined construction system of concrete support and structural roof based on permanent combination according to claim 7, is characterized in that: The structural top plate (5), the structural bottom plate and the outside of the structural side walls of the underground structure (4) are all provided with waterproof materials for full waterproofing. 9. The combined construction system of concrete support and structural roof based on permanent combination according to claim 8, is characterized in that: The backfill (6) is arranged above the structural roof (5), and the backfill (6) is backfilled in layers. 10. A method for constructing a joint-construction system of concrete support and structural roof based on the combination of forever and ever, which is characterized in that: Include the following steps: Step 1: Based on the outline of the underground structure (4), set up a dewatering well outside the outline of the foundation pit, and carry out dewatering construction 1 month before the excavation of the foundation pit; Step 2: Stake out according to the coordinates of the enclosure pile (1) and the construction error, and then carry out the construction of the enclosure pile (1), according to the drilling rig in place, hole formation, hole clearing, lower reinforcement cage, cast-in-place concrete, pile top floating slurry cleaning Carry out the construction of the enclosure piles (1) in the sequence; Step 3: Excavate trenches at the top of the retaining piles (1), construct the crown beams (2) on the top of the piles, and then carry out the excavation of the foundation pit according to the principle of excavation and support; Step 4: When the foundation pit is excavated to 0.5m below the concrete support (3), construct the concrete waist beam (12) in time. The other side of the waist beam (12) is reserved for stressed steel bars or pre-embedded steel bar connectors; Step 5: According to the arrangement and cross-sectional size of the concrete support (3), the soil in the foundation pit is excavated by grooving, then leveling, laying the cushion, binding the concrete support in situ (3) Rebar skeleton, arranging the concrete support to bear the force Ribs (7) are provided with reinforcing ribs (8), the positions of the reinforcing ribs (8) are corresponding to the roof reinforcement bars (11), and steel bar connectors (9) are reserved on both sides of the concrete support (3); waist beams (12) The connection with the concrete support (3) is performed by pre-reserving stress-bearing steel bars or pre-embedded steel bar connectors on the waist beam (12); Concrete support (3) is poured as required, and maintained as required; Step 6: After the concrete support (3) reaches the specified curing age and design strength, continue to excavate the foundation pit based on the principle of digging and supporting until the bottom of the foundation pit. Manual excavation is used for 0.5m above the pit bottom, and then the pit is excavated. The bottom shall be leveled in time, the waterproof layer and the plain concrete cushion shall be laid, the reinforcement shall be bound, and the structural bottom plate, structural side wall and structural middle plate shall be poured, and the internal support at the corresponding position shall be removed in time during the pouring of the main structure; Step 7: Chisel the surface of the concrete support (3) at the contact position between the structural roof (5) and the concrete support (3), and then apply the interface agent (10) 2-3 times. Retain the steel bar connector (9) to mechanically connect the reinforcing bar (8) set in the middle of the concrete support (3) with the roof steel bar (11), and then pour the structural roof (5) as required; The distance between the bottom of the concrete support (3) and the bottom surface of the structural bottom plate (5) shall not be less than 300mm; Step 8: Backfill the soil in layers above the structural roof (5), and the density of the backfill (6) is not less than 93%; Step 9: Remove all structures within 3m below the surface, and reserve the laying path for the later underground structures such as municipal pipelines.

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