Quality assurance measures for high-speed exit foundation pit support projects?

Summary of quality assurance measures for high-speed exit foundation pit support projects: Water collection wells are set up at the corner of the foundation pit or every 30 to 40m, with a diameter of 0.5m and a depth of about 1.0m. The well wall can be temporarily supported by a retaining board, and 0.3m thick gravel can be laid at the bottom of the well to prevent mud and sand from clogging the water pump.

Quality assurance measures for high-speed exit foundation pit support projects

1 Project construction quality acceptance standards

1.1 Design drawing requirements

1.2DGJ08 -11-1999 "Code for Design of Foundation Foundation"

1.3GJ79-2002 "Technical Specification for Treatment of Building Foundation"

1.4GB50202-2002 "Code for Acceptance of Construction Quality of Building Foundation"

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1.5CECS96:97 "Technical Regulations for Foundation Pit Support"

2 Construction Management Guarantee Measures

In order to ensure the construction quality of this project, the following management measures are planned to be taken:

2.1 Selection of construction management personnel

(1) Project management team: Based on the specific conditions of this project, our company will form a team of highly skilled workers with high technical qualifications and rich experience in pile foundation construction. The project management team is responsible for managing this project.

(2) Project manager: Appoint a person with national first-level project manager qualifications and rich engineering construction experience as the project manager.

(3) Chief Engineer: Comrades with rich technical construction management experience will be selected to serve.

(4) Other members: Other main project management personnel have rich experience in construction project management.

(5) Certificate status: Ensure that all members of the team hold job certificates.

2.2 Selection of construction operators

(1) Selection of labor team:

Select a professional construction team with rich construction experience, hard work and excellent work style.

(2) Certification status:

Special and technical types of work are guaranteed to hold operation certificates and technical grade certificates issued by the Labor Bureau and the Municipal Construction Committee through unified assessment.

2.3 Technical clarification system

Before construction, technical clarifications and safety clarifications shall be made to the construction management personnel and construction workers. We must be well aware of the requirements for safe and civilized construction, and have a thorough understanding of the technical solutions and ensuring measures adopted and implement them into practice.

2.4 Raw material quality control measures

(1) Strengthen the quality control of materials. All raw materials, finished products, components and equipment required for the project are strictly purchased according to quality standards. Construction materials must have a Shanghai entry permit (except for factories in this city) and a quality guarantee certificate before entering the site. After arriving at the site, the project manager and chief engineer must organize the supervision unit and relevant personnel to conduct sampling inspections. Raw materials and steel materials are overlapped and sent for inspection, and attention should be paid to stacking them separately, with signs, and not to be mixed. It can be used only after passing the test.

(2) Reasonably organize the supply and use of materials and do a good job in storage, transportation, and safekeeping. After the materials arrive at the site, appropriate storage areas should be arranged and designated personnel should be designated for safekeeping.

(3) All material supply departments must provide product certificates. Quality management personnel conduct random inspections and supervision of the products provided. Products that do not meet quality standards and do not have certificates of conformity are not allowed to be used, and necessary sealing measures are taken to remove them from the site in a timely manner.

2.5 Management of testing and measuring equipment

(1) All measuring instruments during construction, such as theodolite, level, steel tape measure, etc., must have mandatory metrological inspection certificates.

(2) Our company’s full-time measurer will be responsible for the periodic identification and random inspection of the measuring equipment used in the construction of this project.

(3) On-site measuring instruments must be kept and used by designated personnel, and a usage account must be established. Others are not allowed to use them at will.

(4) All measuring instruments (including theodolite, level, steel tape, etc.) must be calibrated and identified regularly. Damaged measuring instruments must be reported for repair and replacement in time, and work while sick is not allowed.

7. Steel sheet pile construction technology

1. General requirements for steel sheet pile construction

⑴The setting position of steel sheet piles must meet the design requirements and facilitate the drainage corridor Foundation construction means leaving room for formwork support and removal outside the most prominent edge of the foundation.

⑵ The layout shape of the steel sheet piles for the foundation pit wall protection should be as straight and neat as possible, and irregular corners should be avoided to facilitate the use and support setting of standard steel sheet piles. The surrounding dimensions should comply with the sheet pile module as much as possible.

⑶ During the entire foundation construction period, during construction operations such as excavation, lifting, reinforcing bars, and concrete pouring, it is strictly prohibited to collide with supports, arbitrarily dismantle supports, arbitrarily cut or weld on supports, and do not Heavy objects should be placed on supports.

2. The sequence of steel sheet pile construction

According to the construction drawings and elevation: Place the pile positioning line → Set the pile guide groove according to the positioning line control → Repair and smooth the walking path of the construction machinery → Set the retaining piles → Send the retaining piles to the designated elevation → Excavate the soil → Concrete construction → Fill the soil → Pull out the steel sheet piles.

3. Inspection, hoisting and stacking of steel sheet piles

⑴Inspection of steel sheet piles

After the steel sheet piles are transported to the construction site, they need to be sorted out. Remove debris from the lock (such as welding slag, waste filler, etc.) and repair the defective parts.

① Method for lock inspection: Use a steel sheet pile of the same type and specifications about 2 meters long as a standard, and make all steel sheet piles of the same model pass the lock inspection. The inspection uses a winch to pull a standard steel sheet pile flat car and perform a lock pass inspection from the pile head to the pile tail. Correct the detected lock distortion and "dead bend".

② To ensure that the locks on both sides of each steel sheet pile are parallel. At the same time, try to keep the width of the steel sheet piles within the same width specification. Width inspection is required. The method is as follows: Divide each steel sheet pile into upper, middle and lower parts and measure its width with a steel ruler so that the width of each pile is within the same size. The difference between adjacent numbers of each piece should be less than 1. . Encrypted measurements can be made for local deformations visible to the naked eye. Steel sheet piles that exceed the deviation should be used as little as possible. ③ For other inspections of steel sheet piles, a comprehensive inspection should be carried out for any defects, residues, untidyness, rust, curling, etc. of the pile body, and corresponding measures should be taken to ensure normal use.

④Lock lubrication and anti-seepage measures, for steel sheet piles that have passed the inspection, are to ensure that the steel sheet piles can be inserted and pulled out smoothly during the construction process, and to increase the anti-seepage performance of the steel sheet piles during use. Each steel sheet pile lock must be evenly coated with mixed oil, and its volume ratio is butter: dry bentonite: dry saw foam = 5:5:3.

⑵Steel sheet pile lifting

Two-point crane should be used to load and unload steel sheet piles. When lifting, the number of steel sheet piles lifted each time should not be too many, and care should be taken to protect the lock from damage. The lifting methods include bundle lifting and single lifting. Bundle lifting usually uses steel ropes, while single lifting often uses special spreaders.

⑶Steel sheet pile stacking

The location for stacking steel sheet piles should be selected on a flat and solid site that will not cause large settlement deformation due to pressure, and should be easy to transport to piling. construction site. When stacking, attention should be paid to:

①The order, location, direction and plane layout of the stacking should take into account the convenience of future construction;

②Steel sheet piles should be separated according to model, specification and length. Stack, and set up signboard instructions at the stacking place;

③ Steel sheet piles should be stacked in layers, and the number of each layer should generally not exceed 5. Sleepers should be placed between each layer, and the spacing should be between the layers.

Summary of quality assurance measures for high-speed exit foundation pit support projects: Water collection wells are set up at the corner of the foundation pit or every 30 to 40m, with a diameter of 0.5m and a depth of about 1.0m. The well wall can be temporarily supported by a retaining board, and 0.3m thick gravel can be laid at the bottom of the well to prevent mud and sand from clogging the water pump.

Generally, it is 3-4 meters, and the upper and lower skids should be on the same vertical line, and the total stacking height should not exceed 2 meters.

4. Installation of guide frame

In steel sheet pile construction, in order to ensure the correct position of the pile axis and the verticality of the pile, control the driving accuracy of the pile and prevent the sheet pile from To reduce the buckling deformation and improve the penetration ability of piles, it is generally necessary to set up a certain stiffness and strong guide frame, also known as "construction purlin".

The guide frame adopts a single-layer double-sided form, usually composed of guide beams and purlin piles. The spacing between purlin piles is generally 2.5 to 3.5m. The spacing between double-sided purlins should not be too large, generally slightly larger than The thickness of sheet pile wall is 8~15mm.

The following points should be noted when installing the guide frame:

① Use theodolite and level to control and adjust the position of the guide beam.

② The height of the guide beam must be appropriate, which is conducive to controlling the construction height of steel sheet piles and improving construction efficiency.

③The guide beam cannot sink or deform as the steel sheet piles are driven.

④The position of the guide beam should be as vertical as possible and should not collide with the steel sheet piles.

5. Steel sheet pile driving

Steel sheet pile construction requires the correct selection of piling methods, piling machinery and flow section divisions, so that the sheet pile wall after driving has sufficient stiffness and It has good waterproofing effect and the sheet pile wall surface is straight to meet the requirements of foundation construction. Closed sheet pile walls are also required to be closed and closed.

According to the on-site construction conditions, the separate driving method is adopted.

This method starts from one corner and drives each piece of steel sheet pile piece by piece without stopping in the middle. Therefore, the pile driver has a short traveling route, simple construction, and fast setting speed. However, since a single block is driven in, it is easy to tilt to one side, the cumulative error is difficult to correct, and the flatness of the wall is difficult to control.

⑴ First, the surveyor determines the axis of the steel sheet pile cofferdam. Guide piles can be set at certain distances. The guide piles directly use steel sheet piles, and then hang ropes as conductors. Use the conductors to control the steel plates during piling. When the axis of the pile is required to be axially normal, a guide frame is used.

⑵ Prepare pile caps and deliver piles: The pile driver lifts the steel sheet piles and manually sets them in place.

⑶ Single piles should be driven continuously one by one, paying attention that the pile top elevation should not differ too much.

⑷ During the driving process, measure and monitor the slope of each pile at any time to not exceed 2. When the deflection is too large and cannot be adjusted by the pulling method, pull it up and drive again.

6. Excavation

6.1 Construction sequence of earthwork excavation for foundation pits

⑴Earth excavation should be carried out continuously in layers and in symmetrical excavations.

⑵ Before earth excavation, carry out well point dewatering outside the foundation pit to keep the foundation pit water-free to facilitate excavation. The mechanical entrance and exit channels and surrounding areas are filled with steel plates to spread the pressure and reduce side effects. pressure.

⑶ Provide drainage measures on the ground and in the pit.

(4) Pay attention to the deformation observation of the support system during excavation.

⑸When working in the foundation pit, a full-time safety officer is responsible.

⑹The order of excavation of earthwork is as follows:

After driving the steel sheet piles, dig the first layer of soil (the excavation depth of each layer of soil shall not exceed 2 meters), and then dig Installation of the second layer of soil support, excavation of the third layer of soil, excavation of the bottom soil and base cleaning

Subsequent process construction. Start digging from the north (towards the entrance of Shenzhen). Park the excavator in the middle of the foundation pit and exit toward the roadside in order while digging.

The excavator excavation route map is as follows:

6.2 Precautions for foundation pit excavation:

①The excavation depth should be carried out strictly in accordance with the foundation pit structure construction drawing .

② Excavating machinery shall not be located directly on concrete supports that have not been backfilled and paved with subgrade boxes.

③ Strictly control the slope of the longitudinal grading of the excavation section, making sure that the slope of the soil slope is not greater than the safe slope (1:1.5), and always pay attention to timely elimination of water flowing to the soil slope to prevent soil landslides .

④ Strengthen the management of ground drainage facilities and set up retaining walls around the foundation pit to prevent ground water from flowing into the foundation pit and affecting the stability of the foundation pit.

⑤ If after excavation of the foundation pit it is found that the soil quality at the bottom of the pit is inconsistent with the survey report, report it to the owner, supervisor and design unit in a timely manner.

⑥ Strengthen the treatment of water accumulated at the bottom of pits, and assign dedicated personnel to be on duty 24 hours a day to pump water.

6.3 Possible problems and corresponding treatment measures during foundation pit excavation

6.3.1 Emergency measures for foundation pits:

In order to prevent sudden accidents In order to ensure that the underground structure construction of this project proceeds smoothly, the following measures will be taken to ensure the safety of the entire foundation pit and the surrounding environment. The following emergency measures are specially formulated:

① Before excavation, a certain amount of Materials and equipment include sand bags, steel pipes, wooden cubes, hemp wire, sacks, and 2-3 anchor hole forming machines and grouting machines each.

② If it is found that the local displacement of the supporting structure is large and exceeds the permitted range during excavation, the excavation should be temporarily suspended, and steel pipes or steel pipe cables should be used for diagonal bracing in the vertical plane. The outside of the supporting structure is unloaded to reduce active earth pressure, and anchor rods can also be laid for reinforcement.

③When cracks appear in the support structure, steel pipes or steel pipe cables can be used to reinforce the support structure and the support piles.

④ If there is water leakage between supporting piles, if the leakage point is not large, the leakage can be blocked with early-strength cement after being drained by a catheter, or the leakage can be blocked by driving in wood cubes, hemp silk or sacks; when the water inflow is large, In large cases, in addition to the aforementioned methods, measures such as local compaction grouting outside the pit will be combined.

6.4 Foundation pit drainage

When excavating deep foundation pits in areas with high groundwater levels, since the aquifer is cut off, groundwater will inevitably seep in continuously under the pressure difference. If the foundation pit is not dewatered and dewatered, the foundation pit will be flooded, which will worsen the on-site construction conditions and reduce the bearing capacity of the foundation. Under the action of dynamic water pressure, it may also cause phenomena such as quicksand, piping, and slope instability. , Therefore, in order to ensure the safety of foundation pit construction, effective precipitation and drainage measures must be taken.

Generally, the following conditions should be met when carrying out deep foundation pit excavation:

1) The foundation pit should be kept dry during excavation;

2) Maintain the stability of the foundation pit slope and the stability of the foundation pit floor;

3) Do not affect the normal use of adjacent buildings and underground pipelines.

6.4.1 Foundation pit dewatering scheme design

6.4.1.1 Depth depth requirements

Because the foundation pit retaining structure of this project uses manually dug piles, To ensure the safety of artificial development of pile rows, when designing dewatering, the dewatering of the foundation pit and the construction dewatering of the supporting pile rows should be considered uniformly. It is necessary to ensure that the required drop S at the center line of the foundation pit should be no less than 0.5m below the excavation base. . Taking all factors into consideration, the minimum depth of descent is 8.7m.

6.4.1.2 Precipitation scheme

The only commonly used methods for dewatering deep foundation pits in Shenzhen are open trench dewatering and tube well dewatering. Since open ditch dewatering in foundation pits is suitable for projects with small precipitation depths, this project adopts tube well point dewatering. At the same time, open ditches should also be designed for foundation pit excavation, but it only collects groundwater and groundwater that seep out locally in the foundation pit and pit walls. Groundwater during other construction operations. The well point is set outside the foundation pit.

(1) Calculation of foundation pit water inflow and well point design

The water inflow from foundation pit precipitation is related to the hydrogeological conditions of the site, the shape and size of the foundation pit, and the boundary conditions of the supply water, etc. . The ratio of the length to width of this foundation pit project is greater than 2, and it is not a narrow and long foundation pit. According to the engineering hydrogeological conditions provided in the engineering geological survey report, the precipitation in this project is calculated as a pressureless complete well.

a. The minimum required depth reduction is S. S=8.7m

b. Influence radius R0 is found in Table 12.2.5 of "Technical Specifications for Deep Foundation Pit Support of Buildings in Shenzhen Area" (SJG05-96) and R=100m. The permeability coefficient K is the weighted average of the permeability coefficients of each soil layer within the precipitation depth range. After calculation, K=1.0m/d.

c. Determine the burial depth of well point pipes, assuming that the distance between well point pipes is 20m;

HO=H1 ib/2 L0=10.2 (m),

d. Water inflow from foundation pit.

The large well method is used to predict the amount of water inflow from the foundation pit.

Consider the long and narrow foundation pit as a "big well", and its calculated radius

X0=L/4=8.95 (m)

The amount of water inflow from the foundation pit is:

Q=1.366K(2H-S)S/(lgR/X0)=2247(m3/d)

e. Calculate the maximum water output of each well point.

n=1.1Q/q=6(root)

f. Determine the number of well points.

g. Depth calculation.

If the depth reduction requirements are not met, the number of well point pipes should be increased.

After further calculations, the number of well point pipes needs to be increased to 9.

Meet the depth reduction requirements. In the above formulas:

Q--water inflow volume of foundation pit, m3/d;

K--aquifer permeability coefficient, m/d;

L--Length of foundation pit, m;

H--Height of head of phreatic aquifer, m;

S--Required depth of groundwater level drawdown, m;

S′--depth of groundwater level drop, m;

R--radius of influence, m;

H0--burial depth of well point pipe, m;

H1--The distance from the buried surface of the well point pipe to the bottom of the foundation pit, m;

i--The slope of groundwater drop;

B--The width of the foundation pit, m;

X0--imaginary radius of the foundation pit, m;

q--water output of a single well, m3/d;

l0--filter Length of the working part, m;

r0--radius of the well point pipe, m;

ri--distance between each well point pipe and the water level drawdown verification point, m.

h. Selection of pumping equipment.

Tube well point dewatering. Each tube well uses a separate water pump to pump water to lower the groundwater level. Due to the large precipitation depth of this project, deep well pump-type submersible pumps can be used in consideration of the simple installation, low energy consumption, high efficiency and low cost of the submersible pump. According to the water inflow at the tube well point, the submersible pump number is selected: 1500QJ20-39/6.

(2) Plan formulation

Based on the theoretical calculation of the water inflow in the foundation pit and the results of the depth calculation, combined with the characteristics of this project, a row is arranged longitudinally around the foundation pit. Well points, each row of well points is 1m away from the row of piles, 9 well point pipes are arranged at 20m intervals, and 2 observation wells are arranged in the center of the foundation pit to observe the water level drop.

(3) Drainage scheme design

1) The drainage ditch and water collection well are set 1m outside the pile enclosure structure.

2) The open ditch and water collection well in the foundation pit will gradually deepen with the continuous excavation of the foundation pit, and their distance from the pile row shall not be less than 0.3m. The cross-section of the open ditch shall be trapezoidal, and the width of the ditch bottom shall be 0.3m. .

3) Water collection wells are set at the corner of the foundation pit or every 30 to 40m, with a diameter of 0.5m and a depth of about 1.0m. The well wall can be temporarily supported by a retaining board, and 0.3m thick gravel can be laid at the bottom of the well to prevent mud and sand from clogging the water pump.

4) Maintain a certain height difference between the drainage ditch and the water collection well. The water collection well should be 0.5~1.0m lower than the drainage ditch, and the drainage ditch should be 0.3~0.5m lower than the excavation surface.

5) Use pumping equipment to drain the water from the water collection well to the outside of the foundation pit. It is strictly forbidden for the discharged water to flow back into the foundation pit. 6) Before construction during rainy season, the drainage system on site should be checked to ensure smooth water flow.

7) During the excavation and construction of the foundation pit, the precipitation is mainly from the tube well, supplemented by the open drainage of the sewage pump in the open ditch, pumping and digging at the same time

① In order to facilitate the construction in the pit, The pit is drained using blind ditches and water collection wells. The blind ditches are backfilled with large-sized gravel or pebbles, which are interconnected so that the water is concentrated through the drainage ditches into the water collection wells or deeper caps, and then the collected water is discharged through the sewage pump. pit. Drainage ditches and water collection wells at the bottom of the pit are set up on the inner side of the retaining piles.

②Outer drainage of the pit: Set up a 400×400mm ground drainage open ditch along the edge of the pit on the outside of the retaining piles, plaster the inside with cement mortar, and arrange a water collection well at the corner to drain the water through a water pump. Enter the municipal drainage system. Prevent surface water from flowing into the pit and keep the foundation pit from accumulating water during basement construction.

③ Strengthen the maintenance and cleaning of the intercepting ditches on the pit surface and the water collection ditches and wells at the bottom of the pit to prevent rainwater from entering the foundation pit and to quickly drain groundwater.

④ When cracks appear on the surface or sides of the pit, they should be filled and sealed immediately with cement sand to prevent rainwater from penetrating.

Erect steel pipe ladders for construction workers to get up and down.

7. Support installation

A. Production and installation of support steel pipes

①Preparation work before the production of support steel pipes

a. Inspect pipes, fittings, etc. one by one according to design requirements.

For pipe fittings, check their model, specifications, and nominal diameter.

Steel pipe: Its pipe diameter, wall thickness, single pipe pressure test record, internal and external anti-corrosion layer (appearance, anti-corrosion thickness, spark, etc.) geometric size allowable deviations, etc. should be checked.

Permissible deviation of geometric dimensions of straight welded coil pipe sections

Project allowable deviation (mm)

Perimeter D≤600±2.0

Dgt; 600±0.0035D

Roundness pipe end 0.005D; other parts 0.01D

End face verticality 0.001D, and not greater than 1.5

The arc is measured using an arc plate with arc length πD/6 and the gap formed at the longitudinal seam on the inner or outer wall of the pipe. The gap is 0.1t 2 and not greater than 4; the gap at the longitudinal seam 200mm away from the pipe end is not greater than 2

Note: 1..D is the inner diameter of the pipe (mm), t is the wall thickness (mm);

2. Roundness is the maximum and minimum diameters of the pipe mouths at the same end that are perpendicular to each other. The difference in diameter.

B． Optional welding rod: According to the material of the base material and the welding method, the T422 welding rod is selected, and its quality complies with the current national standards "Carbon Steel Welding Rods" and "Low Alloy Welding Rods".

Machines equipped with welding tools and pipe lowering: According to the length and diameter of the pipe, the welding method and the construction environment, appropriate welding tools and pipe lowering machinery are equipped.

For steel pipe welding work, welders with a certain technical level and practical experience, and who hold corresponding certificates, are selected to perform the welding work.

Longitudinal welds: When facing each other, the longitudinal welds of pipes should be placed in the 45° direction above and left and right, and the longitudinal welds between two adjacent pipes should be staggered by no less than 300mm.

Spot welding: Spot welding is performed after the steel pipe has passed the inspection. Spot welding standard requirements should be in accordance with the requirements in the GB50268-97 standard.

Spot welding length and spacing

Pipe diameter (mm) Spot welding length (mm) Circumferential spot welding point (place)

350～50050～605

600～70060～706

≥80080～100 The welding distance should not be greater than 400mm

⑥Pipeline welding

Welding: Double welding is preferred Face welding. Before manual arc welding, the rust, grease, dirt, etc. on both sides of the welding joint should be cleaned to make the welding seam metallic luster. During the welding process, effective measures should be taken to prevent it from being corroded by wind, rain and rain. When the ambient wind force is greater than level 5 or the relative humidity is greater than 90, protective measures should be taken during welding; when welding, the weld should be allowed to expand and contract freely, and the welding joint should be slowly cooled down;

When welding multiple layers , the root of the first layer of weld must be evenly penetrated and must not be burned through; when welding subsequent layers, all slag from the previous layer should be removed. The thickness of each layer of welding seam is generally 0.8 to 1.2 times the diameter of the electrode, and the arc starting points and arc extinguishing points of each layer should be staggered.

When welding pipe interfaces, the welding sequence and operating methods should be considered to prevent internal stress caused by concentrated heat. The current should be adjusted for flat welding, vertical welding, horizontal welding and overhead welding. The flat welding current is larger and the overhead welding current is smaller.

In order to ensure the welding quality, carbon arc gouging should be used to remove the slag contained in the coating before welding in the pipe, and the metallic luster should be exposed before welding. Carbon arc gouging construction should comply with Article 4.1.16 of the "Welding Regulations for Building Steel Structures" (JGJ81-91): Carbon arc gouging workers must be trained and qualified before they can operate. When planing, the appropriate power polarity, carbon rod diameter and current should be selected based on the properties and thickness of the steel.

Carbon arc gouging should use a DC power supply and requires the electrode to be connected in reverse (that is, the workpiece is connected to the negative pole of the power supply). In order to avoid defects such as "carbon inclusion" or "slag sticking", in addition to using a suitable planing speed, the carbon arc gouging should also be There is a suitable tilt angle between the rod and the workpiece, see the table below.

Suitable inclination angle between carbon arc gouging carbon rod and workpiece

Going depth (mm) 2.534567～8

Inclination angle (°) 253035404550

If "carbon inclusion" is found, re-planing should be done 5 to 10 mm from the edge of the "carbon inclusion". The depth should be 2 to 3 mm deeper than the carbon inclusion. The slag can be polished with a grinding wheel. When working in the open air, work should be done at an upwind outlet. When working in a closed environment, ventilation measures must be taken. The process parameters are shown in the table below.

Commonly used process parameters for carbon arc gouging

Carbon rod diameter (mm) arc length air pressure (MPa) polarity current

(A) gouging speed

（m/min）

51～20.39～0.59 DC reverse connection 2500.5～1.0

61～20.39～0.59 DC reverse connection 280～3000.5～1.0

71～20.39～0.59 DC reverse connection 300～3501.0～1.2

81～20.39～0.59 DC reverse connection 350～4001.0～1.2

101～20.39 ~0.59 DC reverse connection 450~5001.0~1.21.0~1.2

The thickness of the weld fillet should comply with the technical requirements for the height and width of the weld bead reinforcement surface and undercut and misalignment in the table below in GB50268-97 and standards.

Appearance quality of welds

Project technical requirements

There must be no molten metal flowing to the unmelted base metal outside the weld, and the weld and heat There should be no defects such as cracks, pores, arc craters, and ash on the surface of the affected area; the surface should be smooth and uniform, and the weld bead and base metal should transition smoothly

The width of the welding groove edge should be 2 to 3 mm

Surface

The reinforcement should be less than or equal to 1 0.2 times the groove edge width, and should not be greater than 4mm

The undercut depth should be less than or equal to 0.5mm, and the weld seam should be less than or equal to 0.5mm. The total length of the undercut on both sides shall not exceed 10% of the weld length, and the continuous length shall not be greater than 100mm

The misaligned edge shall be less than or equal to 0.2t, and shall not be greater than 2mm

Not welded Fully allowed

B. Installation of supporting steel pipes

Use a crane to lift the supporting steel pipes. According to the sequence of earth excavation, support the steel pipes when the installation support position is dug. For the installation of the crane, the following provisions are made for the hoisting of the crane:

1. The company must have a professionally qualified inspection and testing agency for all construction hoisting machinery used to issue an inspection and testing certificate for the construction hoisting machinery and equipment. Book.

2. When the crane is operating, the working site should be flat, solid, and have drainage measures; there should be no obstacles within the lifting radius of rotation (see Table 2-6 for the minimum distance between hoisting operations and transmission lines) ). Adequate lighting equipment is required for night operations.

Minimum distance table between hoisting operations and transmission lines

Transmission line voltage 1kv1-35kv360kv

Minimum distance (m) 1.530.1 (v-50) 3

The crane operator and the signal commander must cooperate closely. The commander must be familiar with the performance of the hoisting machinery under command and the actual weight of the hoisted object; the operator must execute the signal command of the commander.

Safety protection devices such as the hoisting machinery's amplitude indicator, torque limiter, and travel limit switch must be complete, sensitive and reliable, and must not be adjusted or dismantled at will. It is strictly forbidden to use limit devices instead of mechanisms. operate.

During lifting operations, no one is allowed to stay or pass under the heavy objects; no matter what the circumstances, it is strictly forbidden to use lifting equipment to lift people. It is strictly prohibited to pull, lift or lift heavy objects buried underground or solidified on the ground. The lifting components should be stable when hanging. Use snap rings and do not use hooks.

The hanging position point should be selected at an appropriate place or at a marked position, and the angle between the wire rope and the suspended object should be greater than 45°.

The wire rope used must have a quality certificate from the manufacturer. The specifications, diameter, and strength of the wire rope must meet the requirements of this type of crane; the wire ropes on the drum should be firmly connected and arranged neatly. When the wire rope is paid out, More than three turns must be left on the reel. The wire rope must not be looped, knotted, bent or jointed.

Crane operators should strictly implement various rules and regulations when entering the construction site. Workers should be briefed on hoisting safety techniques and implement a certificate-based employment system for special operators to ensure the safety and reliability of hoisting equipment.

3. The crane should be parked 3 meters away from the edge of the foundation pit for operations to ensure that the stability of the foundation pit wall is not disturbed and to reduce the lateral load on the steel sheet piles during the hoisting operation.

The schematic diagram of the crane hoisting operation is as follows:

8. Removing the supporting steel pipes and steel sheet piles

(1) From the completion of the foundation pit shear wall construction to the steel pipe support After the designated position at the bottom and the foundation pit at that position are backfilled, the steel pipe support must be pulled out for reuse. Before removing the steel pipe support, you should carefully study the sequence of the steel pipe support method and the time of removing the steel pipe support. Remove the steel pipe support in the order of first the middle and then both sides. The specific operations are as follows:

1. When unloading the steel pipe support Unloading from the middle to both sides, the operator must follow the operating requirements of gas cutting and welding;

2. The crane operator and the signal commander must cooperate closely, and the commander must be familiar with the performance of the hoisting machinery under command and the actual weight of the hoisted object; the operator must execute the signal command of the commander.

Safety protection devices such as the hoisting machinery's amplitude indicator, torque limiter, and travel limit switch must be complete, sensitive and reliable, and must not be adjusted or dismantled at will. It is strictly forbidden to use limit devices instead of mechanisms. operate.

During lifting operations, no one is allowed to stay or pass under the heavy object; no matter what the circumstances, it is strictly forbidden to use lifting equipment to lift people. It is strictly prohibited to pull, lift or lift heavy objects buried underground or solidified on the ground. The lifting components should be stable when hanging. Use snap rings and do not use hooks. The hanging position point should be selected at an appropriate place or at a marked position, and the angle between the wire rope and the suspended object should be greater than 45°.

The wire rope used must have a quality certificate from the manufacturer. The specifications, diameter, and strength of the wire rope must meet the requirements of this type of crane; the wire ropes on the drum should be firmly connected and arranged neatly. When the wire rope is paid out, More than three turns must be left on the reel. The wire rope must not be looped, knotted, bent or jointed.

Crane operators should strictly implement various rules and regulations when entering the construction site. Workers should be briefed on hoisting safety techniques and implement a certificate-based employment system for special operators to ensure the safety and reliability of hoisting equipment.

(2) After the foundation pit is backfilled, the steel sheet piles must be removed for reuse. Before pulling out steel sheet piles, the sequence of pile pulling methods and pile pulling time should be carefully studied. Otherwise, due to the vibration effect of pulling out piles and excessive soil on the piles, ground settlement and displacement will be caused, which will cause harm to the underground structure under construction. , and affect the safety of adjacent original buildings, structures or underground pipelines. It is very important to try to reduce the amount of soil carried by pulling out piles. At present, water and sand filling measures are mainly used.

First use a pile driver to clamp the head of the steel sheet pile and vibrate it for 1 to 2 minutes to loosen the soil around the steel sheet pile and produce "liquefaction" to reduce the frictional resistance of the soil to the pile, and then slowly move it toward the pile. Up vibration pull. When pulling out piles, pay attention to the load of the pile driver. If you find it difficult or impossible to pull out the pile, you should stop pulling out the pile. You can first drive down a little, and then pull up. Repeat this to pull out the pile.

Things to note when pulling out piles:

① Starting point and sequence of pulling out piles: For closed steel sheet pile walls, the starting point for pulling out piles should be at least 5 away from the corner piles. The starting point for pile extraction can be determined according to the situation during pile sinking, and the jumping method can also be used when necessary. It is best to pull out the piles in the reverse order to driving them.

② Vibration and vibration pulling: When pulling out piles, you can first use a vibrating hammer to vibrate the lock mouth of the sheet pile to reduce soil adhesion, and then pull out while vibrating. For sheet piles that are difficult to pull out, you can first use a diesel hammer to vibrate the pile down 100-300mm, and then alternately vibrate and pull out the pile with a vibrating hammer.

③ For steel sheet piles with large pulling resistance, use intermittent vibration method, each vibration is 15 minutes, and the vibrating hammer does not exceed 1.5 hours continuously.

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