CN115897600A - Construction method for newly-built foundation pit close to existing subway station deep foundation pit proximity area - Google Patents

Abstract

The invention discloses a construction method for a new foundation pit adjacent to an existing deep foundation pit approach area of an existing subway station, which includes site treatment of a new foundation pit, construction of diagonally braced support piles in the proximity area, construction of a shared enclosure pile waist beam, and construction of supports Pile caps, oblique bracing construction in the adjacent area, earthwork excavation in the adjacent area, construction of underground structures in the adjacent area of the new foundation pit, backfilling of plain concrete under the oblique braces in the adjacent area, removal of oblique bracing inside the underground structure, and support piles used as anti-corrosion structures for underground structures. Steps such as pile extraction and backfilling of the adjacent area to the design elevation. The present invention forms the surrounding protection piles of the new foundation pit by borrowing the existing surrounding protection piles of the foundation pit of the subway, and by setting the supporting structure of the cap-slant bracing-waist beam, it avoids the impact of the excavation of the new foundation pit on the subway project and other surrounding underground The impact of the structure of the building; on the basis of ensuring the overall stability and safety of the foundation pit, the entire support system also plays a very good role in controlling the displacement deformation of the foundation pit and the deformation effects of surrounding buildings and the environment; the invention effectively controls engineering investment, Greatly shorten the construction period.

Description

A construction method for a new foundation pit adjacent to the deep foundation pit adjacent area of an existing subway station

technical field

The invention relates to the technical field of foundation pit surrounding protection pile construction, in particular to a construction method for a newly built foundation pit adjacent to an existing foundation pit.

Background technique

Affected by the limited land resources of urban planning, some new projects must be constructed in close proximity to existing subway stations. Excavation of foundation pits of existing subway stations will have an impact on the soil in the adjacent area, resulting in the original stress of the soil in the adjacent area. Variety. Similarly, when excavating the foundation pit of a new project, in order to prevent the collapse of the disturbed soil in the adjacent area from affecting the stability of the two foundation pits, it is therefore necessary to excavate all the disturbed soil in the adjacent area when excavating a new foundation pit After completion, certain support measures shall be taken to prevent excessive displacement of the new foundation pit at the beginning. For the support methods of general deep foundation pits, surrounding protection piles, anchor cables, and internal supports are mostly used. For the construction method of the adjacent area of the two foundation pits, the surrounding protection piles of the foundation pit of the shared original ground station and steel support can be used for support. protection to ensure the stability of the proximity zone.

Contents of the invention

The purpose of the present invention is to solve the shortcomings in the prior art, and proposes a construction method for a new foundation pit adjacent to an existing foundation pit approach area.

In order to achieve the above object, the present invention adopts the following technical solutions:

The construction method of the new foundation pit adjacent to the existing foundation pit adjacent area includes the following steps:

1. New foundation pit site treatment

Due to the special geographical location and specific regional influence of the project, all stages of the project from foundation pit support, earthwork excavation to diagonal brace construction are very important. Foundation pit excavation is the first stage of the project implementation. It is especially important to measure and release the corner points of the side line according to the positioning piles, and then measure and release the inner side line or slope bottom line of the foundation pit according to the width of the operation surface and the width of the drainage ditch. Excavate the first layer of earthwork to the bottom position of the design elevation of the waist beam of the shared enclosure pile (1500mm below the ground surface).

2. Construction of diagonally braced piles in the proximity area

The support piles are constructed by skip-digging: first construct No. 1, 3, 5, 7 and 9 piles, and then construct No. 2, 4, 6, 8 and 10 piles, and so on. The top of the support pile is located 8750mm below the surface, the bottom of the pile is 12750mm below the surface, the pile length is 4000mm, and the pile diameter is 800mm. After the support pile construction is completed, in order to prevent workers from falling into the hole of the support pile, the soil is used for backfilling, and the excavation will be carried out when the support pile cap is constructed.

1) Positioning and setting out

According to the positioning axis of the building, the full-time surveyors will accurately stake out the positions of the supporting piles to the site according to the plan of the supporting piles, and the wooden short piles will be used as the identification of the supporting piles for the stakes on site;

2) Pile position into hole

After the pile position is accepted, the drilling rig is in place and the fuselage is adjusted. The front and rear vertical benchmarks of the drilling rig tower are used to check the guide rod, and the position is corrected so that the drill rod is vertically aligned with the pile center to ensure that the vertical deviation of the pile body is not greater than the allowable deviation;

3) Reinforcement cage placed

In order to ensure that the reinforcement cage is not deformed during hoisting and lowering, a φ20 welded reinforcement is added every 2m in the reinforcement cage. The reinforcement hoop and the main reinforcement are welded. Less than 5cm; the steel cage is hoisted by a long auger drilling rig auxiliary winch. Before lifting the steel cage, check that there are no high-voltage lines and obstacles on the site to ensure safe construction of the steel cage. The steel cage is installed by docking the wellhead. Positioning, the allowable error of the positioning elevation is ±5cm, and the length of the reinforcement cage anchored into the cap is not less than 35d;

4) Concrete pouring

When pouring concrete, the concrete slump should be measured, and the slump is required to be 16-18cm, and the concrete should have good workability; in order to ensure the quality of the concrete pile body, during the pouring process, the conduit should be continuously moved up and down to make the concrete dense . When necessary, vibrating rods should be used for vibration; in order to ensure the quality of the pile top, the pipe should be slowly pulled out of the concrete at the end of pouring to prevent the formation of cavities.

3. Construction of waist beams of shared enclosure piles

When excavating the earthwork to the height of the purlin, the construction of the obliquely braced waist beam and the jacking seat requires that the side wall of the waist beam and the side wall of the cap be parallel to facilitate subsequent diagonal bracing;

Remove the protective layer on the upper part of the subway shared retaining pile to expose the reinforced steel bars, clean the surface of the reinforced bars, weld the waist beam reinforcement with the main reinforcement of the original retaining pile body, and then pour concrete into the formwork for maintenance;

The waist beam construction process is as follows:

Excavate the earthwork on the top of the waist beam → chisel away the laitance layer of the cast-in-place pile to the design elevation of the pile top → cushion layer concrete → tie reinforcement → formwork support → pouring the waist beam concrete (C30) → maintenance;

4. Construction of pile caps

When the concrete of the supporting pile reaches the design strength, continue to excavate the foundation pit to the top of the supporting pile, and leave soil in the adjacent area of the two deep foundation pits to make the supporting pile cap.

1) Binding of steel bars on the platform

After the construction of the support piles is completed, a steel bar binding frame should be set up before binding, and the steel bars of the cap should be bound above the anchor bars reserved at the top. When binding, the upper main bars are placed first, and then the stirrups. Binding vertically, the spacing of stirrups conforms to the design and specifications; after the upper layer is bound, pass through the main reinforcement of the lower layer and tie it with the stirrups in time; after the main reinforcement of the side is penetrated, place the inner stirrups and tie bars one by one and tie them firmly. Surface lap welding, the length of the steel bars after welding meets the design requirements, and the steel bar pads are bound in time after the steel bars are bound;

3) Form support and concrete pouring

The concrete is commercial concrete with a strength grade of C30. It is transported to the construction site by a concrete transport vehicle. The pouring of the concrete should be carried out continuously. If it must be intermittent, the intermittent time should be shortened as much as possible. During the pouring process, it should be vibrated in time and a plug-in vibrator should be used. It should be inserted quickly and pulled out slowly, and the insertion points should be evenly arranged, moved point by point, in sequence, without omission, so as to achieve uniform vibration, and the moving distance should not be greater than 1.5 times the radius of the vibration effect (generally 30-40cm). Use a wooden trowel to smooth the beam surface for the first time in time. After the initial setting and before the final setting, use a steel trowel to finish the beam surface. After the platform is poured, cover it with straw bags and send special personnel to water and maintain it every day;

4) Form removal and maintenance

Within 12 hours after the concrete pouring is completed, the caps should be watered and maintained in time. The number of maintenance is based on keeping the surface moist. The caps can be dismantled after 24 hours. Affect the overall look and feel, the removed formwork should be cleaned up in time and stacked neatly for the next use;

5. Diagonal bracing construction in the proximity area

The steel support of the main body adopts a 600×600 steel lattice diagonal brace, and the top of the steel support is welded with a 700×700×16 steel plate for sealing; It is connected with the pre-embedded steel bars on the sloped side wall of the cap, and the jack is applied evenly through the jack; the steel support is welded to the waist beam of the shared enclosure pile, and the other end is a movable support. The pre-loaded axial force of the steel support is completed by two hydraulic jacks, and the capacity of the jacks meets the requirements of the designed pre-loaded axial force. The jack is installed between the embedded plate 406 and the jacking seat 303 . When the steel support is installed, the axes of the waist beam, the end and the jack are kept on the same axis. In order to ensure straightness, the locking pieces on the steel support should be tightened in diagonal order at the same time. The final eccentric value of assembly is not greater than 20mm. The diagonal brace should be tightened before welding. When the jacking force reaches the designed pre-loading force, install the locking plate on the locking section and remove the jack after welding. The pre-loaded axial force of the jack must be symmetrical and synchronous to ensure that the supporting axis is stressed. Before the oblique support is welded dead, a pre-jacking force of not less than 400KN must be applied;

6. Earthwork excavation in the proximity area

Retain the earthwork under the diagonal braces to carry out the construction of the basement structure of the library. After the construction of the basement structure is completed, the retained earthwork will be cleared and transported. The earthwork between the steel braces is excavated by an excavator, and the earth near the steel braces and the bottom of the braces is manually excavated to prevent mechanical excavation from causing the braces to be unstable and damaged.

7. Underground structure construction in the vicinity of the new foundation pit

For the deconstruction of the basement, only the structure from the bearing pile cap to the common retaining pile is constructed first, and the side wall and the steel bars at the junction of the bottom plate and the side wall are bound and concrete is poured. When the concrete strength of the side wall reaches the design strength, the opposite side Apply waterproof material to the outer surface of the wall. The rest of the basement structure will continue to be constructed after the steel diagonal braces are removed.

8. Plain concrete backfill under the diagonal braces in the adjacent area

After the construction of the basement structure is completed, remove and retain the earthwork, cut off the oblique supports, and carry out plain concrete backfill. When the earthwork is removed and the oblique supports are removed, the surrounding protection piles will completely lose the support and the lateral pressure of the earthwork. Will it affect the surrounding protection piles and If the subway structure is adversely affected, if this part of the earthwork is retained and only the concrete on the upper part of the earthwork is backfilled, it will have a certain protective effect on the surrounding retaining piles;

9. Removal and waterproofing of diagonal braces inside the underground structure

After cutting off the oblique bracing of the steel lattice, it is necessary to seal and waterproof the openings of the oblique bracing through the basement floor and outer wall. The plain concrete backfill between the retaining piles has a certain waterproof effect, and it is only necessary to use concrete to seal the opening of the steel support on the side wall. After the steel support of the basement floor is cut off, the waterproof sheet is laid first and then the concrete cushion is poured. On the concrete cushion, the steel bars are continuously bound and concrete is poured to complete the unfinished basement floor structure and reinforce the waterproofing of the floor wall to achieve Eliminate the effect of leakage, that is, complete all construction.

10. Bearing piles are used as uplift piles for underground structures

In the area where the groundwater is relatively abundant, after removing the steel diagonal braces inside the basement structure, the bearing pile caps can be chiseled out to expose the stressed steel bars, and the stressed steel bars are welded to the basement structural bottom plate steel bars and poured with concrete, so that the bearing piles become the basement The overall structure of the bottom plate is used as an anti-floating pile in the basement, which greatly saves the construction cost.

11. Backfill the adjacent area to the design elevation.

When the construction of the entire basement structure is completed and the concrete strength reaches the design elevation, the underground soil shall be backfilled. Before backfilling the outdoor foundation pit, it is necessary to check the underground waterproof layer and protective layer, and repair the damage in time, clean up the garbage and other sundries at the bottom of the foundation pit, and bounce the horizontal line on the outdoor waterproof protection plate before backfilling to control the backfill soil. the height of.

Preferably, the construction process of step 1 is: site leveling → foundation pit positioning → pile position setting out → support pile construction → compaction grouting → waist beam construction → brick arch retaining wall construction → earthwork layered excavation → Soil nailing→hanging steel mesh→spraying anchor→maintenance.

Preferably, the mortar supply and masonry operations in Step 1 are as follows: commercial concrete C30 is used for the supporting pile concrete, the mortar is manually mixed on site, and the masonry is constructed.

Preferably, the pile foundation construction in step 1: drilling and grouting construction is adopted, steel cages are hoisted down, earth and stones are transferred in the site by excavators, and dump trucks are used for external transportation.

Preferably, in step 2, the drill pipe is drilled to a predetermined depth, and the on-site construction technicians check whether the soil layer required by the design is reached according to the geological survey report and the actual drilling unearthed observation analysis; The construction will adopt the construction method of long spiral post reinforcement cage.

Preferably, in step 2, before drilling, the valve of the drill bit is sealed, and the drill pipe is moved down until the drill bit touches the ground, and the drill rig is started to rotate the drill bit; generally, it should be slow first and then fast. When it is shaking or difficult to drill, stop the machine or slow down the footage, stop drilling when encountering obstacles, analyze the reasons, and prohibit forced drilling.

Preferably, in step 2, the protective layer made of concrete pads is made into an arc shape on the side of the hole wall, generally arranged vertically at intervals of about 2m, and each row is symmetrically arranged with four blocks along the circumference.

Preferably, the concrete spacer can also be made into a cylindrical shape, and there are holes in the middle to be worn on the stirrups.

Preferably, in step 3, when placing the steel bars, the surveyor should lay out the wires on the cushion in advance, and the steel cages should be placed close to the wires. The horizontal error should not exceed 3cm, and the vertical error should not exceed 2cm. The installed steel bars should look straight .

Preferably, in step 3, before pouring concrete, the rubbish, soil and other sundries in the formwork and oil stains on the steel bars should be removed, and it is checked whether the cement mortar pads of the steel bars are well placed.

Compared with prior art, the beneficial effect of the present invention is:

1. The present invention forms the surrounding protection piles of the new foundation pit by borrowing the surrounding protection piles of the existing subway foundation pit, and avoids the impact of the excavation of the new foundation pit on the subway project and others by setting the supporting structure of the cap-slant brace-waist beam. Structural influence of surrounding underground buildings.

2. The invention effectively controls project investment and greatly shortens the construction period. Due to the limited construction site, the starting point of this support plan is to minimize the impact of foundation pit excavation on surrounding buildings and the environment. On the basis of ensuring the overall stability and safety of the foundation pit, the entire support system also plays a good role in controlling the displacement deformation of the foundation pit and the deformation effects of surrounding buildings and the environment, while also taking into account the economy.

Description of drawings

Fig. 1 is the flow chart of the new foundation pit that the present invention proposes next to the existing foundation pit approach area construction method;

Fig. 2 is the structural diagram of groove installation diagonal brace operation in the construction method of the present invention;

Fig. 3 is the structural diagram of earthwork excavation to the bottom process in the construction method of the present invention;

Fig. 4 is the structural diagram of backfill plain concrete operation in construction method of the present invention;

Fig. 5 is the structural diagram of the stirrup (trapezoidal) of the platform in the present invention;

Fig. 6 is the structural diagram of the main reinforcement of the platform in the present invention;

Fig. 7 is a cross-sectional structure diagram of a diagonal brace in the present invention;

Fig. 8 is a connection structure diagram of the diagonal brace and the waist beam in the present invention;

Fig. 9 is a structural diagram of the connection between the brace and the cap in the present invention.

In the figure: protection pile 1 for subway foundation pit, waist beam 2, embedded plate A201, diagonal brace 3, steel support 301, steel plate 302, jacking seat 303, bearing platform 4, well-shaped main reinforcement 401, square closed hoop 402 , longitudinal reinforcement 403, trapezoidal closed hoop 404, transverse reinforcement 405, embedded plate B406, prestressed tendon 407, anchor 408 cap, support pile 5, basement structure 6.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention.

This project: Hefei Central Library is located at the intersection of Qimen Road and Feicui Road. Line intersections and transfer points. According to the foundation pit support design drawings, the original enclosure piles of the subway project will be shared during the excavation and foundation pit support of the library. In order to prevent the shared enclosure piles from tilting to the side of the newly excavated foundation pit, the following is proposed Construction method, refer to Figure 1.

1. Construction of diagonal support piles, refer to Figure 2:

1.1 Construction preparation

(1) The entire set of construction equipment should be inspected before officially entering the site to ensure that the equipment is in good condition, and it is forbidden to enter the site with faulty equipment. Assist Party A in the layout of water and electricity pipelines related to the construction of support piles, and ensure that they can be put into construction immediately after entering the site. The roads and foundation pit ramps on the construction site should meet the driving requirements of equipment transport vehicles and truck cranes to ensure transportation safety.

(2) When the equipment is assembled, an isolation area should be set up, commanded by a special person, and assembled in strict accordance with the procedures. Non-installation personnel are not allowed in the assembly area to prevent safety accidents.

(3) Arrange materials to enter the site, and conduct material re-inspection and concrete proportioning test as required.

(4) Make quality and safety technical disclosure before starting construction, and fill in the "Technical Disclosure Record".

1.2 Positioning and setting out

After the construction unit provides the positioning axis of the building, both parties should conduct a joint inspection, and both parties should sign the "Handover Inspection Record" for confirmation. According to the building positioning axis provided by the construction unit, the full-time surveyors accurately set out the positions of the support piles to the site according to the plan of the support piles. On-site pile position setting out uses wooden short piles as the identification of support pile positions.

After the construction unit, the supervisory unit and the designer jointly inspect the pile position and sign it, the next process can be carried out.

1.3 Drilling

After the pile position is accepted, the drilling rig is in place and the fuselage is adjusted. The front and rear vertical benchmarks of the drilling rig tower are used to check the guide rod, and the position is corrected so that the drill rod is vertically aligned with the center of the pile position to ensure that the vertical deviation of the pile body is not greater than the allowable deviation.

Before drilling, seal the drill bit valve, move the drill pipe down until the drill bit touches the ground, and start the drilling rig to rotate the drill bit. Generally, it should be slow first and then fast. If the drill pipe is found to be shaking or difficult to drill during the hole forming process, stop the machine or slow down the footage. Stop drilling when encountering obstacles, analyze the reasons, and prohibit forced drilling.

According to the design pile length, determine the drilling depth and make eye-catching notes on the corresponding position of the drilling rig tower, as the basis for controlling the pile length during construction. When the bottom surface of the power head reaches the mark, the pile length meets the design requirements.

The drill pipe is drilled to the predetermined depth, and the on-site construction technicians analyze whether the soil layer required by the design is met according to the geological survey report and the observation and analysis of the actual unearthed holes. In case of special geological conditions, the designer of the support pile should comprehensively determine it according to the drawings and the actual geological conditions on site, and notify the supervisor in time.

During the construction process, the "Record of Supporting Pile Construction" should be filled in timely and accurately. If it is found during construction that the long spiral can not be constructed through dry hole formation, the construction method of long spiral post reinforcement cage will be adopted.

1.4 Manufacture and installation of reinforcement cage

(1) Fabrication of reinforcement cage

a) In order to ensure that the reinforcement cage does not deform during hoisting and lowering, a φ20 welded reinforcement is added every 2m in the reinforcement cage. The reinforcement hoop and the main reinforcement are welded. The thickness of the reinforcement protection layer around the pile is determined according to the size of the pile hole. But not less than 5cm.

b) The types, models and dimensions of steel bars should meet the design requirements. If there is any replacement, it should be replaced according to the specification requirements, and the design and supervision should be approved and recorded.

c) Binding sequence of reinforcement cage: first arrange the main reinforcement at equal intervals, and then install the stirrups according to the specified spacing after the stiffening hoops are fixed. The joints between stirrups, stiffening stirrups and main bars are fixed by arc welding.

d) Concrete pads or other effective measures shall be adopted on the outside of the reinforcement cage to ensure the thickness of the reinforcement protection layer. The thickness of the protective layer of the main reinforcement should be ≥ 50mm, and the thickness of the protective layer at the bottom of the platform cap should be ≥ 100mm.

(2) Steel cage stacking

a) The production site of the reinforcement cage can be determined according to the actual situation of the site, but it must be within the coverage of the tower crane so as to be used for stacking the reinforcement cage.

b) Reinforcement cages should be stacked in the order of installation. Those installed first should be stacked on the upper layer, and those installed later should be stacked on the lower layer. Only two layers can be stacked at most.

c) When stacking the reinforcement cage on the lower floor, the sides of the reinforcement cage should be padded with stones to prevent rolling.

(3) Install the reinforcement cage in place

a) The steel cage is hoisted by the auxiliary winch of the long auger drilling rig. The pulling force of the auxiliary winch of the long auger drilling rig is 20kN (2T). The longest pile position of this project is Z1, the effective pile length is 15m, and the weight of a single pile is 0.932T. The auxiliary hoist meets its lifting weight. Before hoisting the steel cage, check that there are no high-voltage lines and obstacles on the site to ensure the safe construction of the steel cage. The steel cage is installed by docking the wellhead. The length of the platform is not less than 35d.

b. Protective layer

①At the upper and lower ends of the reinforcement cage and in the middle, set four steel bar “earrings” symmetrically on the same section at a certain distance (generally about 2m), and the diameter of the steel bar is generally 10-12mm.

②Use concrete blocks as protective layer. The side close to the hole wall is made into an arc shape, generally arranged vertically at intervals of about 2m, and each row is symmetrically arranged with four pieces along the circumference; the concrete spacer can also be made into a cylindrical shape, and there are holes in the middle that can be worn on the stirrups.

1.5 Concrete pouring and support pile detection

a) After the acceptance of the hole formed by the dry operation, the concrete should be poured within 1 hour using the conduit as the chute. The distance between the bottom of the conduit and the bottom of the hole is about 1m.

b) When pouring concrete, the concrete slump should be measured, and the slump is required to be 16-18cm, and the concrete must have good workability.

c) In order to ensure the quality of the concrete pile body, during the pouring process, the conduit should be continuously moved up and down to make the concrete dense. Vibrate with a vibrator if necessary.

d) In order to ensure the quality of the pile top, the conduit should be slowly pulled out of the concrete at the end of pouring to prevent the formation of voids.

After the construction of the support piles is completed, the maintenance age reaches 70% of the strength, and the integrity of the support piles is tested. The design drawings require that the number of test piles should not be less than 20% of the total number of support piles, and not less than 5. The site requires The integrity of the support piles is tested at 100% to ensure construction safety. Only after passing the inspection can the next process cap platform construction be carried out.

2. For the construction of the oblique support bearing platform, refer to 5 and 6. One side of the platform 4 is composed of a well-shaped main reinforcement 401, and the main reinforcement 401 is welded with a square closed hoop 402. The inner side of the square closed hoop 402 is bound with a longitudinal reinforcement 403. 4. A trapezoidal closed hoop 404 is formed inside the other side, and the inner side of the trapezoidal closed hoop 404 is bound with transverse reinforcement 405, and the formed steel cage is tied to the top reinforcement of the support pile 5, and finally cast into the cap 4;

2.1 Platform construction technology

Cut off the upper protective layer of the subway shared retaining piles to expose the stressed steel bars, clean the surface of the steel bars, weld the waist beam reinforcements to the main bars of the original guard piles, and then pour concrete into the formwork for maintenance.

Excavate the earthwork on the top of the cap → chisel away the laitance layer of the pouring pile to the design elevation of the pile top → cushion concrete → tie reinforcement → support the formwork → pour the cap concrete (C30) → maintenance.

2.2 Construction preparation

1) The foundation trench soil has been excavated to the design elevation, and the soil between the piles has been excavated clean.

2) Use a level to mark the elevation of the pile top on the pile body, and mark it with red paint.

2.3 Precautions for construction

1) When using the machine, check and confirm that the motor, cables, etc. are normal, the protective grounding device is in good condition, and the protective device is safe and effective before starting the machine.

2) During the pile head demolition process, construction personnel should be equipped with corresponding labor protection articles to prevent concrete debris from splashing and causing harm to construction personnel; personnel not related to construction should not approach the construction site.

3) When the pile head is hoisted away, the steel wire rope should be used to bind it firmly, and it can only be hoisted after the tying personnel evacuate.

2.4 Binding of steel bars for caps

2.4.1 Main materials and tools

Reinforcement: There should be a certificate of conformity from the factory, and a retest of mechanical properties shall be carried out according to the regulations, and it can be put into use only after passing the test. Steel bars should be free from old rust and oil stains.

Iron wire: No. 20-22 iron wire (fired wire) or galvanized iron wire (lead wire);

Concrete Cover: Mortar Pads

Tools: rebar hooks, crowbars, rebar spanners, lashing frames, wire brushes, trolleys, chalk, rulers, etc.

2.4.2 Steel bar processing

Correctly select the steel bar level and specification according to the drawings, and carry out blanking processing. The length of the longitudinal reinforcement should be preferentially welded, and the reinforcement with d≤20 is allowed to be overlapped (d is the diameter of the reinforcement), and the length of the overlapping section is ≥0.7L, and should not be less than 200mm. The joint area percentage should be ≤ 50%. Trial welding is carried out before formal welding, and batch welding can only be carried out after passing the test. The overlapping areas of steel bars are staggered, and the distance between two adjacent joints is not less than 1m. The number of overlapping main reinforcements in the same section shall not exceed 25% of the total number of reinforcements, and the external angle shall be staggered by more than 1m. The circle should be straightened before blanking can be used to process stirrups, and the blanking size should be strictly in accordance with the drawing size. The processing of stirrups should be carried out by skilled workers, and the processing dimensions should be checked frequently during the processing to avoid unusability due to excessive errors.

2.4.3 Binding of steel bars

Before binding, a reinforcement binding frame should be set up, and binding should be carried out above the anchor bars of cast-in-place piles to improve efficiency. When binding, place the upper main reinforcement of the cap first, and then place the stirrups. When binding according to the spacing of the drawings, the stirrups and the main reinforcement are bound vertically, and the spacing of the stirrups meets the design and specification requirements; after the upper layer is bound, the main reinforcement of the lower layer of the cap is pierced and tied with the stirrups in time; Tie the tendons and tie them securely. The lap of the main reinforcement adopts single-sided lap welding, and the length of the steel bar after welding meets the design requirements. After the steel bars are bound, tie the steel bar pads in time.

2.5 Cap formwork support

First prepare 2 sets of cap side formwork in the processing area according to the design requirements, drive 1.2m long 48*3 steel pipes with a depth of 500mm into the soil between every two piles, put the prepared formwork inside the steel pipe, and use wooden boards at the joints After the connection is completed, the inner seam of the joint is pasted with adhesive tape to prevent slurry leakage, and the protective layer pads are placed at the same time. After confirming that all the steel bars have been bound and the pads are well placed, use horizontal steel pipes to connect the steel pipes between the piles with fasteners, and Use 48*3 steel pipes to horizontally connect along the side of the formwork at a place 150mm below the elevation of the cap platform, and strengthen the connection with the columns. After all installations, use diagonal braces to reinforce the columns.

2.6 Pouring of platform concrete

Before pouring, the garbage, soil and other sundries in the formwork and the oil stains on the steel bars should be removed, and the cement mortar pads of the steel bars should be checked to see if they are well placed.

Concrete is commercially available concrete with a strength grade of C30, which will be transported to the construction site with a concrete truck. When pouring concrete, it should be carried out continuously. If it must be intermittent, the intermittent time should be shortened as much as possible. During the pouring process, it is necessary to vibrate in time. When using a plug-in vibrator, it should be inserted quickly and slowly. The moving distance is not greater than 1.5 times of the vibration radius (generally 30-40cm). After vibrating, use a wooden trowel to smooth the beam surface for the first time in time. After the initial setting and before the final setting, use a steel trowel to finish the beam surface. water maintenance.

2.7 Formwork removal and maintenance of caps

Within 12 hours after the concrete pouring is completed, the beam surface should be watered and maintained in time, and the maintenance times should be based on keeping the surface of the cap platform moist. After 24 hours, the side formwork of the platform cap can be removed. During demolition, the demolition tool shall not touch the concrete, so as to avoid damage to the water chestnut of the bearing platform, so as not to affect the overall appearance. The dismantled formwork should be cleaned up in time and stacked neatly for the next use.

3. Slant braces are installed with grooves, referring to Figure 2, 7-9, the braces 3 are composed of a steel support 301 at the main body, a steel plate 302 at the top and a jacking seat 303 at the bottom, and the steel support 301 is a welded lattice column ;

The side of the waist beam 2 close to the steel support 301 is chiseled, exposing the embedded plate A201 and fully welded with the steel plate 302;

The side of the platform 4 close to the steel support 301 has been chiseled to expose the pre-embedded plate B406 and the prestressed tendons (407), the prestressed tendons (407) pass through the jacking seat 303, and a plate of the jacking seat 303 is connected to the pre-embedded The plate B406 is fully welded and connected, and the prestressed tendons (407) are stretched and locked with the other plate of the jacking seat 303 through the anchor 408.

When the earthwork is excavated to the height of the purlins, the waist beams and supports shall be constructed obliquely, and internal oblique braces shall be set on the retained earthwork.

1) The steel support is made of Q235B steel, the welds at the welding joints are all fully welded, the weld height hf≥8, and shall meet the requirements of the design and relevant specifications;

2) The positions of the diagonal braces are arranged according to the plan, which must be reviewed on site, and beams and columns of the main structure should be avoided;

3) The earthwork in the cross-section must be retained during the construction of the diagonal braces, and the excavation can be layered and segmented until the construction of the diagonal braces is completed. The diagonal braces should be constructed one by one. Hour;

4) Where steel lattice braces pass through the bottom plate and side walls of the main structure, one or more water stop plates can be installed at the bottom plate and side walls, and the number of water stop plates is determined according to the waterproof requirements of the foundation bottom plate and side walls . If the water-stop plates on each single-leg angle steel overlap, they should be staggered from each other;

5) After the foundation pit of the basement is backfilled, the steel lattice braces inside the basement can be cut off;

6) The diagonal brace should be tightened before it is welded to death.

Diagonal brace jacking construction: There is a special jacking seat at the end of the steel brace, and the jacking is applied evenly with a jack. When the jacking force reaches the designed pre-stressing force, install the locking piece on the locking section and weld it dead, then remove the jack. The pre-loaded axial force of the jack must be symmetrical and synchronous to ensure the force on the supporting axis. Before the oblique support is welded, a pre-jacking force of not less than 400KN must be applied.

4. Excavate the earthwork to the bottom, refer to Figure 3,

Keep the earthwork under the diagonal braces, and carry out the construction of the basement structure of the library. After the construction of the basement structure is completed, the retained earth shall be cleared and transported.

5. Backfill plain concrete, refer to Figure 4,

Keep the earthwork under the diagonal braces, and carry out the construction of the basement structure of the library. After the construction of the basement structure is completed, remove and retain the earthwork, cut off the oblique supports, and backfill with plain concrete. When clearing and transporting the retained earthwork and cutting off the oblique supports, the surrounding protection piles will completely lose the support and the lateral pressure of the earthwork. Will it have an adverse impact on the surrounding protection piles and the subway structure? The retaining piles play a certain protective role, and the feasibility of this scheme is studied.

6. Support internal cutting and waterproofing

After cutting off the diagonal braces of the steel lattice, it is necessary to seal and waterproof the openings of the diagonal braces passing through the basement floor and the outer wall. There are 29 diagonal braces underground, which will generate 58 hidden leakage points. Improve the technology of the diagonal brace, add welding water-stop sheet and reinforce the waterproofing of the outer wall to achieve the effect of preventing leakage.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (9)

1. The new foundation pit is close to the existing foundation pit approach area construction method, it is characterized in that, comprises the following steps: 1. New foundation pit site treatment Due to the special geographical location and specific regional influence of the project, all stages of the project from foundation pit support, earthwork excavation to diagonal brace construction are very important. Foundation pit excavation is the first stage of the project implementation. It is especially important to measure and release the corner points of the edge line according to the positioning pile, and then measure and release the inner edge line or slope bottom line of the foundation pit according to the width of the operation surface and the width of the drainage ditch; excavate the first layer of earthwork to the bottom of the design elevation of the waist beam of the common enclosure pile Location (1500mm below the surface); 2. Construction of diagonally braced piles in the proximity area The support piles are constructed by skip-digging: first construct No. 1, 3, 5, 7, and 9 piles, and then construct No. 2, 4, 6, 8, and 10 piles, and so on. The position is 8750mm below the ground surface, the bottom of the pile is 12750mm below the ground surface, the pile length is 4000mm, and the pile diameter is 800mm. Excavation shall be carried out when the pile cap of the supporting pile is installed; 1) Positioning and setting out According to the positioning axis of the building, the full-time surveyors will accurately stake out the positions of the supporting piles to the site according to the plan of the supporting piles, and the wooden short piles will be used as the identification of the supporting piles for the stakes on site; 2) Pile position into hole After the pile position is accepted, the drilling rig is in place and the fuselage is adjusted. The front and rear vertical benchmarks of the drilling rig tower are used to check the guide rod, and the position is corrected so that the drill rod is vertically aligned with the pile center to ensure that the vertical deviation of the pile body is not greater than the allowable deviation; 3) Reinforcement cage placed In order to ensure that the reinforcement cage is not deformed during hoisting and lowering, a φ20 welded reinforcement is added every 2m in the reinforcement cage. The reinforcement hoop and the main reinforcement are welded. Less than 5cm; the steel cage is hoisted by a long auger drilling rig auxiliary winch. Before lifting the steel cage, check that there are no high-voltage lines and obstacles on the site to ensure safe construction of the steel cage. The steel cage is installed by docking the wellhead. Positioning, the allowable error of the positioning elevation is ±5cm, and the length of the reinforcement cage anchored into the cap is not less than 35d; 4) Concrete pouring When pouring concrete, the concrete slump should be measured, and the slump is required to be 16-18cm, and the concrete should have good workability; in order to ensure the quality of the concrete pile body, during the pouring process, the conduit should be continuously moved up and down to make the concrete dense ;If necessary, use a vibrating rod to vibrate; in order to ensure the quality of the pile top, the pipe should be slowly pulled out of the concrete at the end of pouring to prevent the formation of cavities; 3. Construction of waist beams of shared enclosure piles When excavating the earthwork to the height of the purlin, the construction of the obliquely braced waist beam and the jacking seat requires that the side wall of the waist beam and the side wall of the cap be parallel to facilitate subsequent diagonal bracing; Remove the protective layer on the upper part of the subway shared retaining pile to expose the reinforced steel bars, clean the surface of the reinforced bars, weld the waist beam reinforcement with the main reinforcement of the original retaining pile body, and then pour concrete into the formwork for maintenance; The waist beam construction process is as follows: Excavate the earthwork on the top of the waist beam → chisel away the laitance layer of the cast-in-place pile to the design elevation of the pile top → cushion layer concrete → tie reinforcement → formwork support → pouring the waist beam concrete (C30) → maintenance; 4. Construction of pile caps When the concrete of the support pile reaches the design strength, continue to excavate the foundation pit to the top of the support pile, and leave soil in the adjacent area of the two deep foundation pits to make the support pile cap; 1) Binding of steel bars on the platform After the construction of the support piles is completed, a steel bar binding frame should be set up before binding, and the steel bars of the cap should be bound above the anchor bars reserved at the top. When binding, the upper main bars are placed first, and then the stirrups. Binding vertically, the spacing of stirrups conforms to the design and specifications; after the upper layer is bound, pass through the main reinforcement of the lower layer and tie it with the stirrups in time; after the main reinforcement of the side is penetrated, place the inner stirrups and tie bars one by one and tie them firmly. Surface lap welding, the length of the steel bars after welding meets the design requirements, and the steel bar pads are bound in time after the steel bars are bound; 3) Form support and concrete pouring The concrete is commercial concrete with a strength grade of C30. It is transported to the construction site by a concrete transport vehicle. The pouring of the concrete should be carried out continuously. If it must be intermittent, the intermittent time should be shortened as much as possible. During the pouring process, it should be vibrated in time and a plug-in vibrator should be used. It should be inserted quickly and pulled out slowly, and the insertion points should be evenly arranged, moved point by point, in sequence, without omission, so as to achieve uniform vibration, and the moving distance should not be greater than 1.5 times the radius of the vibration effect (generally 30-40cm). Use a wooden trowel to smooth the beam surface for the first time in time. After the initial setting and before the final setting, use a steel trowel to finish the beam surface. After the platform is poured, cover it with straw bags and send special personnel to water and maintain it every day; 4) Form removal and maintenance Within 12 hours after the concrete pouring is completed, the caps should be watered and maintained in time. The number of maintenance is based on keeping the surface moist. The caps can be dismantled after 24 hours. Affect the overall look and feel, the removed formwork should be cleaned up in time and stacked neatly for the next use; 5. Diagonal bracing construction in the proximity area The steel support of the main body adopts a 600×600 steel lattice diagonal brace, and the top of the steel support is welded with a 700×700×16 steel plate for sealing; It is connected with the pre-embedded steel bars on the sloped side wall of the cap, and the jack is applied evenly through the jack; the steel support is welded to the waist beam of the shared enclosure pile, and the other end is a movable support; the pre-loaded axial force of the steel support is completed by two hydraulic jacks , the capacity of the jack meets the requirements of the design pre-loaded axial force; the jack is installed between the embedded plate 406 and the jacking seat 303; when the steel support is installed, the axes of the waist beam, the end, and the jack are kept on the same axis. Straight, the locking pieces on the steel support should be tightened in diagonal order at the same time; the final eccentricity of the assembly should not be greater than 20mm; the diagonal brace should be tightened before welding, and when the jacking force reaches the designed pre-loading force, install and lock at the locking section After the piece is welded, remove the jack. The pre-loaded axial force of the jack must be symmetrical and synchronized to ensure that the supporting axis is stressed. Before the oblique support is welded, a pre-jacking force of not less than 400KN must be applied; 6. Earthwork excavation in the proximity area The earthwork under the diagonal braces is reserved for the construction of the basement structure of the library. After the construction of the basement structure is completed, the retained earthwork is removed; the earthwork between the steel braces is excavated by an excavator, and the earthwork near the steel braces and the bottom of the braces is manually excavated. The method of excavation prevents mechanical excavation from causing instability and damage to the diagonal brace; Underground structure construction in the adjacent area of new foundation pit For the deconstruction of the basement, only the structure from the bearing pile cap to the common retaining pile is constructed first, and the side wall and the steel bars at the junction of the bottom plate and the side wall are bound and concrete is poured. When the concrete strength of the side wall reaches the design strength, the opposite side Apply waterproof material to the outer surface of the wall; the rest of the basement structure will continue to be constructed after the steel diagonal braces are cut off; Plain concrete backfill under the diagonal braces in the adjacent area After the construction of the basement structure is completed, remove and retain the earthwork, cut off the oblique supports, and carry out plain concrete backfill. When the earthwork is removed and the oblique supports are removed, the surrounding protection piles will completely lose the support and the lateral pressure of the earthwork. Will it affect the surrounding protection piles and If the subway structure is adversely affected, if this part of the earthwork is retained and only the concrete on the upper part of the earthwork is backfilled, it will have a certain protective effect on the surrounding retaining piles; Removal and waterproofing of diagonal braces inside underground structures After cutting off the oblique bracing of the steel lattice, it is necessary to seal and waterproof the openings of the oblique bracing through the basement floor and outer wall. The plain concrete backfill between the enclosure piles has a certain waterproof effect, and it is only necessary to use concrete to seal the opening of the steel support on the side wall; On the concrete cushion, continue to bind steel bars, pour concrete, complete the basement floor structure that has not been completed, and reinforce the waterproofing of the floor wall to achieve the effect of preventing leakage, that is, complete the entire construction; Bearing piles are used as uplift piles for underground structures In the area where the groundwater is relatively abundant, after removing the steel diagonal braces inside the basement structure, the bearing pile caps can be chiseled out to expose the stressed steel bars, and the stressed steel bars are welded to the basement structural bottom plate steel bars and poured with concrete, so that the bearing piles become the basement The overall structure of the bottom plate is used as an anti-floating pile in the basement, which greatly saves construction costs; 11. Backfill the adjacent area to the design elevation; When the construction of the entire basement structure is completed and the concrete strength reaches the design level, backfill the underground soil; before backfilling the outdoor foundation pit, the underground waterproof layer and protective layer must be inspected, and any damage is found to be repaired in time. Clean up, and before backfilling construction, play a horizontal line on the outdoor waterproof protection board to control the height of backfilling. 2. The construction method according to claim 1, wherein the new foundation pit is adjacent to the adjacent area of the existing foundation pit, characterized in that the construction process of the first step is: site leveling → foundation pit positioning → pile position setting → support Pile construction→compaction grouting→waist beam construction→brick-laying arch retaining wall construction→earth excavation in layers→soil nailing→hanging steel mesh→spray anchor→maintenance. 3. The method for constructing a new foundation pit next to an existing foundation pit according to claim 1, characterized in that the mortar supply and masonry operations in the first step are as follows: commercial concrete C30 is used for supporting pile concrete , The mortar is manually mixed and built on site. 4. The new foundation pit according to claim 1 is close to the existing foundation pit approach area construction method, it is characterized in that, the pile foundation construction in the described step 1: adopt borehole perfusion construction, hang the reinforcement cage, in the field Earth and stone transfer is carried out by excavators, and dump trucks are used for external transportation. 5. The new foundation pit according to claim 1 is close to the existing foundation pit approach area construction method, it is characterized in that, in said step 2, the drill pipe is drilled to a predetermined depth, and the on-site construction technicians are based on the geological survey report and Observation and analysis of the actual borehole unearthed to see if the soil layer required by the design is met; if it is found during construction that the long spiral dry hole cannot be constructed, the construction method of the long spiral post-installed reinforcement cage will be adopted. 6. The construction method according to claim 1, wherein the new foundation pit is adjacent to the adjacent area of the existing foundation pit, characterized in that, in the second step, before drilling, the drill bit valve is sealed to move the drill pipe down to the drill bit When touching the ground, start the drilling rig to rotate the drill bit; generally, it should be slow first and then fast. If the drill pipe is found to be shaking or difficult to drill during the hole forming process, stop the machine or slow down the footage. When encountering obstacles, stop drilling and analyze the reasons , It is forbidden to force drilling. 7. The new foundation pit according to claim 1 is close to the existing foundation pit approach area construction method, it is characterized in that, in the described step 2, the protective layer that the concrete spacer is done is made into an arc shape by one side of the hole wall, Generally, one line is arranged vertically at intervals of about 2m, and each line is symmetrically arranged with four blocks along the circumference. 8. The new foundation pit according to claim 1 is close to the existing foundation pit approach area construction method, it is characterized in that, in described step 3, when laying steel bar, lay out line on cushion layer in advance by surveyor, steel bar cage Place it close to the line, the horizontal error shall not exceed 3cm, the vertical error shall not exceed 2cm, and the installed steel bar will look straight. 9. The new foundation pit according to claim 1 is close to the existing foundation pit approach area construction method, it is characterized in that, in the described step 3, the rubbish, earth and other sundries in the formwork and the steel bars should be placed on the concrete before pouring. Clean up the oil stains and check whether the cement mortar pads of the steel bars are properly cushioned.

Images