1. Project overview

The proposed building is located to the east of Luxiang, Wuchang, with Luoyu Road to the north and Block A of Optics Valley World City to the south. The pile type adopts manual hole digging pile, and the strength grade of pile core concrete is C30. The pile diameter is 0.9m.

2. Engineering geological conditions

For the geological conditions of the project site, please refer to the Geotechnical Engineering Investigation Report of Block B of Guanggu World City provided by Central South Survey and Design Institute. The specific strata are as follows:(1) miscellaneous fill;(2) clay;(3) residual soil;(4)-1 strongly weathered shale;(4)-2 moderately weathered shale.

2. Preparation Basis

1. Bidding Documents for Foundation Pit Support Project in Suhe Special Zone

2. Code for Design of Concrete Structures (GB50010-2002)

3. Code for Design of Building Foundation (GB50007-2002)

4. Code for Acceptance of Construction Quality of Building Foundation (GB50202-2002)

5. Code for Acceptance of Construction Quality of Concrete Structures (GB50204-2002)

6. Technical Code for Building Pile (JGJ 94-2008)

7. Technical Code for Testing of Building Foundation Piles (JGJ 106-2003)

8. Load Code for the Construction of Buildings (GB50009-2001)

9. Technical Code for Testing of Building Foundation Piles (JGJ 106-2003)

10. Technical Code for Building Foundation (DB42/242-2003)

11. Other relevant construction and acceptance specifications and procedures.

3. equipment selection

Due to the requirements of construction period and according to the geotechnical investigation data and actual construction experience, rotary drilling rig can be used to drill cast-in-place piles for pile hole formation in this project, and one CSR rotary drilling rig is selected for drilling equipment. If the above equipment cannot meet the requirements of pore-forming quality and construction period due to the influence of stratum, rotary drilling and manual drilling shall be adopted to ensure the engineering quality and construction period.

4. construction scheme

1. Construction technology and method of rotary drilling

a) Construction process

B) Construction method

1) Measurement control

(1) Before the opening, the pile position shall be accurately positioned, and the positioning gantry pile shall be set outside the pile position.

(2) Cross control network and reference point shall be set on the ground for pile position axis. When the drilling rig is in place, ensure that the verticality deviation is not more than 1%.

2) Hole-forming:

1. In the process of drilling, continuous barrel soil is used to drill holes.

2. Rig in place: crawl to the pile position to be drilled through its own crawler, and adjust the rig mast and fuselage horizontally and vertically under the control of the machine's own computer.

3. Embedding casing: after the drilling rig is in place, under the guidance of measurement and construction personnel, the drill tip is aligned with the center of the pile position, and the casing is lowered after the drilling rig is rotary dug to a certain depth to take out the soil. Generally, the burial depth of the casing is 1-2m, and it is advisable that the casing should be about 30cm higher than the ground according to the site conditions.

4. Re-test and correct the deviation between pile position and casing center: after the casing is buried, the surveying personnel and supervision representative shall review and correct the pile position. After the completion of this procedure, the opening notice shall be declared and the drilling shall be carried out.

5. If the rotary drilling rig cannot normally excavate due to formation reasons, it will be replaced by manual pneumatic pick, and the casing will be welded and pressed to the bottom of the hole to serve as a protective wall. Mechanical ventilation must be adopted when the digging depth exceeds 10m. 12V safety voltage and explosion-proof lamp shall be used for lighting in the hole; a firm and reliable safety ladder shall be set in the well hole to facilitate the construction personnel to go up and down. When the digging work is suspended, the hole must be covered.

2. Fabrication and placement of reinforcement cage

a) The reinforcement cage must be carefully processed according to the requirements of the design drawings.

B) The type, steel grade, size and specification of the reinforcement shall meet the design requirements, and the manufacturing deviation shall meet the following requirements:

Spacing of main reinforcement: ± 10mm

Stirrup spacing: ± 20mm

Reinforcement cage diameter: ± 10mm

Reinforcement cage length: ± 50mm

Bending degree of main reinforcement: ≤ 1%

Bending degree of reinforcement cage: ≤ 1%

B) Welding requirements for reinforcement cage:

C) for the reinforcement cage made in sections, the reinforcement length shall be single-sided lap welding, the weld length shall be 10d, the closing hoop and the reinforcement ring shall be single-sided lap welding, the weld length shall be 10d, the joints of the main reinforcement shall be staggered during welding, the number of reinforcement joints in the same section shall not exceed 50% of the total number of main reinforcement, and the spiral stirrup shall be mostly spot welded with the main reinforcement to increase the strength of the strength of the steel cage.

d) During joint welding, the upper and lower main reinforcement shall be aligned to keep the upper and lower axes of the reinforcement cage consistent.

e) Requirements for protective layer of reinforcement cage:

(1) When entering the hole, the reinforcement cage shall be gently placed slowly at the hole position. After entering the hole, the reinforcement cage shall be slowly lowered without rotating left and right. It is strictly prohibited to force the lowering with high ups and downs.

(2) The surface dirt of the welding part shall be removed first.

(3) After the lower hole of the reinforcement cage meets the requirements, the main reinforcement can be spot welded to the hole casing or firmly bound to the hole with iron wire to position the reinforcement cage and prevent movement.

2. Underwater concrete pouring

After pouring the catheter, clean the hole twice to ensure that the sediment thickness at the bottom of the hole meets the specification requirements.

a) For the perfusion catheter, check its completeness, verticality and connection tightness, and carry out water seal test on the catheter on schedule.

B) Lower the bottom of the pipe into the hole 300-500mm from the bottom of the hole, and make records.

c) Water-blocking plug and rubber ball with the same caliber as the catheter. Enough initial irrigation volume and buried depth of 0.8~1.5m shall be guaranteed. For continuous perfusion, the buried depth shall be 2-6m.

d) Assign special personnel to measure the embedded depth of the conduit and make records. In the process of pouring concrete, the rising height of concrete surface should be detected frequently and the depth of buried pipe should be checked. When the concrete rises to more than 4m above the bottom of the framework, lift the conduit to make the bottom of the conduit more than 2m above the bottom of the reinforcement cage framework, which can restore the pouring speed and maintain the normal buried depth. When the pouring is close to the top of the pile, maintain sufficient height of the conduit and adopt measures such as connecting short conduits, the underwater concrete pouring surface is 1.0~1.5m higher than the design elevation of the pile top (this height is tentatively determined by the design, supervisor and the owner according to the development of cracks in the stratum), so as to remove the laitance and ensure the quality of the concrete pile body. The elevation of the concrete surface shall be measured before the removal of the conduit to ensure that the poured concrete reaches the design elevation.

e) The lifting of the conduit shall be kept in the center to prevent it from touching the reinforcement cage, and the removed conduit shall be cleaned in time.

f) The filling coefficient shall be controlled at 1.1 when pouring concrete. According to the test pile concrete filling coefficient is 1.3, but the filling coefficient may be greater than 1.1 when pouring concrete in this stratum, and the excess concrete shall be approved by Party A and the supervisor.

g) When approaching the top of the pile, the height of the funnel shall be increased due to the reduction of the concrete height in the conduit, the pressure drop, and the increase of the specific gravity of the mud consistency outside the pipe, resulting in difficulty in pouring.

h) When the concrete pouring is completed, the casing shall be set aside in a timely manner and the orifice shall be protected to prevent accidents.

I) When pouring concrete, the number of concrete specimens shall be retained according to the design and specification requirements, and the 28d strength shall be measured.

3. Pile foundation inspection and acceptance

1. After 28 days after the construction of engineering piles is completed and the strength meets the design requirements, large and small strain detection of piles shall be carried out according to the requirements of the Technical Code for Building Pile Foundation (JGJ94-2008). Small strain detection shall be carried out for each pile, and a certain number of piles shall be selected for large strain detection. The pile foundation inspection shall be carried out by the qualified unit, and the pile with large strain shall be jointly determined by the supervision and design institute, which shall not only be representative, but also reflect the real situation of construction.

2, pile foundation construction is completed in a timely manner to draw the completion drawing, do a good job of pile position plane review, sort out the completion data, and please quality supervision department in a timely manner to do a good job in the completion of the project pile acceptance, timely delivery of the upper structure construction.

3. The following completion data shall be submitted for pile foundation completion acceptance: pile position measurement layout chart, engineering geological survey, material test record and certificate of approval, construction log, pile construction concealment record, pile position completion layout plan, pile static and dynamic load test data, sub-project quality inspection and evaluation form, and pile foundation project acceptance record file form and pile foundation project completion acceptance certificate shall be submitted at the same time.

4. Technical measures for engineering quality assurance

1) Detailed survey records shall be kept for each setting-out, and each row of marker piles shall be checked. The records of survey results shall be signed and approved by the on-site supervision engineer;

2) Make all quality records in detail and accept the inspection of on-site supervision and design department at any time.

3) Quality inspection and control during construction

(1) The hole-forming process includes hole position, hole diameter, hole depth, verticality, sediment thickness, etc.

Hole position quality inspection and control: after the construction site is leveled, the pile position shall be accurately measured and placed according to the design drawings. The pile position error (D/6, and not more than 100mm) shall be submitted to the supervisor in writing for acceptance. During positioning, the deviation between the center of the casing and the center line of the pile position shall not be more than 50mm. Axis control points shall be set at the position where the drilling is not affected so as to determine the hole position to determine the hole position after completion.

Inspection and control of hole diameter quality: according to the performance and geological conditions of the drilling rig, carefully consider the form and size of the drill bit. It must be considered that the hole diameter shall not be less than the design requirements, nor shall it exceed the design requirements, which will cause waste. For hole diameter inspection, a hole gauge can be made for inspection, and the diameter of the drill bit can be corrected according to the inspection results.

Hole depth quality inspection and control: inspection shall be carried out in combination with measuring rope and original drilling tool records. The design depth must be guaranteed and the hole shall not be terminated in advance.

Verticality inspection and control: before drilling and opening, check that the moving track of the drilling rig is firm and stable. The four corners of the top plane of the track shall be at the same elevation. The drilling rig crown block, rotary table and hole position shall be on the same vertical line before starting. The drill bit shall be firm during drilling and shall be lightly hammered and tightly hit during drilling.

(2) The process of making reinforcement cage includes the type, diameter and quantity of reinforcement: spacing of main reinforcement: spacing of spiral reinforcement; Stirrup spacing; Lap length of reinforcement; Welding condition of reinforcement, diameter and length of reinforcement cage; Length of hanging reinforcement.

Check whether the type, diameter and quantity of steel bars meet the design requirements. After checking, the steel cage can be hung down. When lowering the steel cage, check the bending deformation of the steel bars.

Technical index of steel cage: spacing of main reinforcement: ± 10mm; Stirrup spacing or spiral hoop pitch: ± 20mm, steel cage diameter: ± 10mm; Steel cage length: ± 50mm; Single-sided lap welding is adopted for welding, with weld thickness h greater than or equal to 0.3d and width B greater than or equal to 0.7d; Welding length l is greater than or equal to 10d.

The protective layer of underwater steel cage is controlled by prefabricated concrete blocks. Setting method: one block is set every 3-5M, each block is welded on the steel bar with stirrup steel passing through the prefabricated concrete block with a diameter of 50mm, and at least four blocks are set for each block, which is evenly arranged along the steel cage. When lowering the reinforcement cage, if the reinforcement cage cannot be lowered to the bottom. The cage must be pulled out to sweep the hole, and the reinforcement cage must be lowered again. After the reinforcement cage reaches the design position, during the perfusion process, the conduit must be pulled out to avoid hanging and touching the reinforcement cage, causing the reinforcement cage to float upward.

(3) Check the over-filling amount of concrete. The reason for the overfilling of bored piles is that the drill bit will expand to a certain extent when passing through the soft soil layer. At the same time, when the concrete is injected into the pile hole, a part of it will spread to the soft soil layer. The measures to control the amount of concrete over-filling are mainly to master the drilling speed of each layer of soil. During normal drilling operation, do not stop drilling casually to avoid excessive expansion.

(4) The builder shall insist on sampling with a sampler when the concrete pouring is close to the pile top elevation, strictly control the pile top elevation, and avoid over-filling or under-filling.

4) Quality inspection and control after the completion of the process

(1) Adhere to the process handover inspection system. Adhere to the principle that the next process is not allowed to be carried out after the last inspection of the previous process. After the completion of the previous process, the operation team shall conduct self-inspection first, and the quality engineer shall conduct full-time inspection. After the inspection is qualified, the on-site supervisor shall be notified to be present for inspection. After the inspection is qualified, the next process can be carried out.

(2) If the design change or technical approval is proposed due to the owner's reasons, the supervisor must issue a notice and modify or change the technical parameters in writing.

(3) The completion and acceptance of the pile foundation project shall be carried out in strict accordance with the JGJ94-2008 of the Technical Code for Building Pile Foundation) and the requirements of the Code for Acceptance of Construction Quality of Building Foundation Engineering and the relevant requirements of the Hubei Provincial Project Quality Management Record. Acceptance of cast-in-place pile foundation project.