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Earthwork excavation and foundation pit support scheme for the basement of the clubhouse

I. Overview of the Project

Greentown Guihua City Club Project is located in Zone A of Chunxiaoyuan in Guihua City. There are existing residential buildings on the west side of this project and construction passages on the east side. The north and south sides are relatively empty, and there are no underground pipelines around the foundation pit. The foundation pit covers an area of 3800m2 and the excavation depth is about 2.5-5.0m.

Second, the engineering geological conditions

1. The groundwater in this site is shallow, belonging to pore diving, and the buried depth is 0.5m below the natural ground, which is mainly replenished by atmospheric precipitation and surface water infiltration. The excavation scope of foundation pit mainly includes miscellaneous fill, silty clay and silty clay, in which silty clay is located at the bottom of foundation pit, which is not conducive to foundation pit excavation.

2. See table 1 for the thickness of each soil layer and its physical and mechanical properties.

Table 1 Thickness and physical properties of each soil layer

soil layer

Natural gravity number name of soil layer

KN/m3 internal friction angle

() cohesion

Thickness (kPa)

Height (meter)

1 miscellaneous fill18.012.08.00 0.4m-2.2m.

2 Silty clay19.316.517.3 0.7m-2.4m.

Silty clay18.110.09.07.1m-13.2m.

Three, earthwork excavation and support scheme selection

According to the above characteristics of this project, the basement earthwork is excavated in layers, the basement foundation pit is supported by shotcrete anchor net, and the local area is reinforced by cement mixing pile.

Fourth, the construction sequence

Cement mixing pile Cement mixing pile maintenance for 28 days Earthwork layered excavation, shotcrete anchor net layered construction Earthwork layered excavation, shotcrete anchor net layered construction.

Verb (abbreviation of verb) earthwork excavation

1. Excavators are used for large-scale excavation of the basement earthwork, and manual excavation is used for the basement pile caps and ground beams. Large-scale earthwork trimming and pile cap earthwork excavation are carried out simultaneously.

2, earthwork excavation should be carried out when there is no water, foundation pit support and earthwork excavation should be coordinated, layered and segmented excavation along the periphery of foundation pit from top to bottom, and shotcrete anchor net support construction should be carried out in time.

3. According to the number of shotcrete rods supported by shotcrete-anchor net, the earthwork is excavated in two layers (local three layers), the surrounding supporting working face is excavated first, and then the intermediate earthwork is excavated. Surrounding earthwork excavation must be closely coordinated with shotcrete-anchor net construction, and the excavation length of each surrounding section should not exceed 20m on the first floor and 15m below the second floor. When digging silt layer, each digging shall not exceed 7m. If the construction length in one day is too long, job-hopping excavation should be adopted. The next layer of earthwork excavation should be carried out after the upper cement mortar and shotcrete reach a certain strength (generally 2 days according to the current climate). The excavation depth of each layer of earthwork should be controlled within 30cm below the anchor pipe, and no overbreak is allowed.

4, earthwork excavation to the design elevation, immediately with pond slag backfill back cover, and cast cushion concrete, cushion and supporting structure to form a rigid fulcrum, so as to effectively prevent the deformation of foundation pit side wall, it is forbidden to basement exposure time is too long.

5. The engineering piles of this project are immersed cast-in-place piles with small diameter and weak lateral resistance. When excavating, the excavator should try to avoid the pile-intensive parts, and the excavation depth of the earthwork in the middle part should not exceed 2M per layer, and the excavation should be carried out in two or three layers. According to the soil conditions, the basement soil after the first-floor earthwork excavation is no longer suitable for excavators and trucks to pass through. Therefore, after the first-floor earthwork excavation, a 4-meter-wide and 0.5-meter-thick pond slag passage should be laid in the middle of the foundation along the north-south direction (between the axes of 14~ 15) and the east-west direction (between the axes of H~G), and the passage should avoid the pile position as much as possible.

6. According to the requirements of basement construction, a working face with a width of 1.0M is reserved around the basement, open ditches are dug around, collecting wells are set at four corners, and four sewage pumps are prepared for timely drainage.

7. Because the earthwork of foundation pile cap and ground beam needs manual excavation, and the earthwork handling after excavation needs tower crane to complete, it is necessary to install tower crane before foundation earthwork excavation. According to the site conditions, the supporting structure is not allowed to be used as the tower crane foundation, and the stacking load around the foundation pit should not exceed 15M. Tower crane foundation should be located on the base plate. According to the layout and excavation elevation of foundation pile caps and piles, the middle of foundation slab with axis 23~29 /D~F is determined as the tower crane foundation position. The depth of earthwork excavation in this position is about 2.5M, and the minimum pile spacing is 9M. Earthwork excavation will basically not affect the deviation of pile position. The elevation of tower crane foundation (6M×6M) is the same as that of foundation slab, and the slab is 600MM thick. The foundation slab and foundation beam reinforcement shall be overlapped in the construction of foundation reinforcement. (Attached with tower crane foundation plan)

Six, supporting structure construction

1, cement mixing pile construction (see cement mixing pile construction scheme for details)

2. Construction technology, technology and site management of shotcrete-anchor net supporting structure

(1) After earthwork excavation, the slope shall be trimmed according to the slope angle required by the design, and the surface shall be loose and smooth before the first concrete spraying (initial spraying). The initial spraying thickness shall not be greater than 30mm, and markers for controlling the thickness of sprayed concrete shall be buried before the initial spraying.

(2) The soil nail anchor pipe shall be carefully constructed according to the requirements of GBJ-86-85 specification. The soil nails are arranged in plum blossom shape, and the aperture is 1 10 mm. Luoyang shovel is used to make holes, and the reinforcement is φ 20. The centering bracket is made of φ6.5 steel bars, and the spacing is not more than 2M. If Luoyang shovel is inconvenient to punch holes, use φ48×3.0 steel pipe to make it into a plum blossom shape, and make three holes every 0.3m around the steel pipe 120 degrees.

When grouting the anchor hole, add triethanolamine early strength agent, the dosage is 1.5% cement, and the grouting ratio is cement: sand: water = 1: 0.2: 0.5, and mix and use. The mixed pulp is used up before initial setting, and the unused pulp cannot be used again to prevent caking. Grouting pressure should be strictly controlled for anchor pipe grouting, and the general soil layer should be > > 0.5MPa.

(3) Set the steel skeleton at the anchorage position. In this project, two φ 12 long steel bars are welded on the upper and lower sides of the soil nail, and two φ 20L = 100 mm short locking steel bars are set at the end of the soil nail. After laying Φ 6 @ 200× 200 steel mesh, it will be bound by people, and the upper and lower layers of steel bars will be welded. Then the second layer of concrete is sprayed to make the thickness of the whole sprayed concrete reach100 mm. In order to better connect the upper and lower layers of sprayed concrete, the lower layer is sprayed with a 45-degree slope. 2 hours after the final setting of sprayed concrete, water curing will be started for 3-7 days.

(4) Five displacement and settlement monitoring points are set at the top of the plane slope supported by shotcrete-anchor net. In the earthwork excavation area, it should be monitored once a day, once every 3-5 days after the shotcrete-anchor net support and earthwork construction are stable, and once a week after the concrete pouring and the concrete pouring of the bottom plate are completed. Guide earthwork excavation and shotcrete anchor construction according to the monitoring situation every day, and control the deformation of foundation pit in a safe state. It is generally considered that the daily displacement increment is less than 3mm and the cumulative displacement at the top of the supporting structure is less than 40mm, which is a safe state. Observation points are also set in the residence on the west side of the foundation pit to ensure safety.

(5) After digging below the second floor, ensure that there is an excavator in the site, which can be called at any time. If it is found that the displacement at the top of the slope increases beyond the specified value and does not converge after excavation, the back pressure at the toe of the slope shall be backfilled with an excavator immediately until the displacement is stable. After taking reinforcement measures, continue excavation. Dig to the last floor, and the excavator has been evacuated from the site, so it is impossible to backfill the back pressure with the excavator, and then backfill the back pressure with sandbags.

Seven, the construction control points

(1) Strictly abide by the construction procedures, and carry out every construction link according to the drawings and requirements, such as anchor rod spacing, length, net hanging, welding, etc. Grouting should reach the standard pressure and the grouting amount should be full.

(2) Strictly control the quality of materials, especially the quality of bolts, anchor pipes, cement and sand.

(3) Strengthen supervision. Every working procedure should be strictly inspected, and problems found should be handled in time.

(4) Strictly control the excavation depth to ensure the stability of the side wall, and then continue the excavation after the soil layer shotcrete and anchor support is stable.

(5) After close monitoring, it is found that the local seepage is large or the side wall of the foundation pit is deformed greatly, so measures should be taken in time, such as high-pressure grouting to block water and changing anchor parameters to ensure the safety and stability of the side wall.

(6) Strengthen personnel and construction management, organize meticulously, carry out scientific construction, and put an end to all accidents.

Chapter I Project Overview

I. Overview of the Project

Greentown. Zhoushan Cheng Guihua Club Project is located in Lincheng New District, Zhoushan City, on the north side of National Highway 329 and on the east side of A 1 A3# commercial and residential buildings in Cheng Guihua. The foundation pit support of the basement of the proposed building is designed by Hangzhou Survey and Design Institute, and the project construction is contracted by Zhoushan Dachang Construction and Installation Engineering Co., Ltd. ..

According to the general description of engineering supporting structure design, 0.000 of the engineering site is equivalent to an absolute elevation of 5.350m, the absolute elevation of the natural ground is 2. 15 m, and the relative elevation of the ground is-3.20m. The excavation elevation of the basement foundation pit is designed according to the civil structure, and the elevation difference is -5.7 m, -6.5 m, -7.2 m and-8.2m. The foundation pit design. The lower cement mixing pile is covered with soil nails and steel mesh sprayed with fine stone concrete; Local full slope and bottom soil nailing steel mesh sprayed with fine stone concrete cover.

Second, the construction preparation

1. The construction area shall be leveled to ensure the normal walking and construction of mechanical equipment.

2, organize construction personnel and mechanical equipment comes into play.

3. Connect the power supply, set up wires according to the construction requirements, set up an electric box, and establish the on-site power consumption and lighting system.

4. Connect construction and domestic water.

5, organize engineering and technical personnel to learn construction drawings, design specifications and related construction specifications.

6. Participate in the blue prints.the design, and make the blue prints.the design minutes. All employees involved in the construction should carry out the disclosure of construction organization design and safety operation.

7. Organize surveyors to locate and pay off the foundation pit.

Chapter II Construction Machinery and Main Construction Methods

A, construction machinery

According to the supporting structure construction drawing, 12 air compressor WC-65438 and 1 WC-9 air compressor WC-9 air compressor WC-9 air compressor WC-9 air compressor WC-9 air compressor WC-9 air compressor WC-9 air compressor backhoe excavator carry out earthwork excavation. While digging, do initial spraying, anchor nail, net hanging and re-spraying. Ensure the construction progress and safety. (See main construction machinery table for details).

Second, the envelope construction sequence

Cement mixing pile Cement mixing pile curing for 28 days Current layer earthwork excavation and soil nailing support Current layer earthwork excavation and soil nailing support.

Third, the main construction methods

(a) cement mixing pile construction (see cement mixing pile construction scheme)

(2) Earthwork excavation

1. The relative elevation of the buried depth of the foundation of this project is between -5.70 m and -8.20 m, and the relative elevation of the natural ground is about -3.20 m, so the excavation depth is about 2.50 m~5.0 m, and the foundation is reinforced concrete floor with bearing platform and ground beam. Therefore, excavators are used for large-scale excavation, dump trucks are used for transportation, and foundation pile caps and ground beams are excavated manually. Large-scale earthwork trimming and earthwork excavation of pile cap beam are carried out simultaneously. The earthwork excavation of this project is about 13000m3.

2, earthwork excavation construction process

Measure the lofting, measure the excavation elevation, remove the pond slag with a thickness of 0.6m around the foundation pit, reserve earthwork transportation, build an open drain outside the car pit, and excavate the collecting well. Soil nails and shotcrete nets are used for earthwork excavation of the first layer of slope protection, and soil nails and shotcrete nets are used for earthwork excavation of the second layer of slope protection.

Earthwork excavation of the second floor foundation pit, the third floor slope protection earthwork excavation, the third floor foundation pit earthwork excavation, the third floor foundation pit earthwork excavation, local 3-3 sections earthwork excavation, the fourth floor earthwork excavation, the third floor foundation pit soil nail, shotcrete anchor net concrete pile cap and ground beam.

3. The surface water level of the project site is high, and there is a river on the southwest side of the foundation pit. Before earthwork excavation, the water in the river channel should be drained. In order to prevent surface water from flowing into the foundation pit, a 1.0 m× 1.0 m drainage ditch shall be dug around the foundation pit, and four drainage collecting wells shall be set at the four corners of the drainage ditch, and each collecting well shall be equipped with a φ 150 sewage pump, which shall be timely.

4. Before earthwork excavation, the peripheral positioning and lofting of soil nailing support should be carried out according to the design drawings, and grey lines should be set. The general principle of earthwork excavation should be carried out when there is no water, and the foundation pit support and earthwork excavation should be closely coordinated. In order to prevent the foundation pit from gushing soil, the core soil should be used for excavation, and the earthwork around the foundation pit should be excavated first, and then the earthwork in the middle of the foundation pit should be excavated after the current layer of soil nailing and shotcrete mesh concrete are completed and reach a certain strength. Earthwork excavation around the foundation pit should be carried out in layers and sections from top to bottom. The actual excavation depth and slope of earthwork should meet the requirements of design drawings, and pay attention to the overbreak shall not be greater than 30cm, and the one-time or local excavation shall not be too deep. After the excavation of the first layer is completed, nail the soil nail of the current layer and construct the shotcrete anchor net immediately. When excavating the concentric soil in the middle, the excavation shall be carried out from south to north in turn, and the excavation depth shall follow the depth of the soil nailing wall after the current layer is constructed, and the earthwork excavation of each layer shall be carried out step by step with the construction progress of the soil nailing wall. After each layer of earthwork excavation is completed, the engineering piles higher than the earthwork should be leveled.

5. According to the design drawings and combined with soil nailing construction, earthwork excavation is divided into three layers (local four layers). First, the earthwork excavation of slope protection is divided into south and north areas. The south area starts from the section of axis 024 1- 1 in the southeast corner, and the north area starts from the section 3-3 of axis 04 in the east. The first layer of slope protection earthwork excavation without soil nailing wall slope (section 1- 1, 3-3, 4-4, 7-7) design depth 1.9 m, slope grading coefficient 1.2, with soil nailing wall slope (2-2, 5 The length of each earthwork in soil nailing construction around the foundation pit shall not exceed 20m. After the completion of each earthwork excavation, soil nailing and shotcrete mesh concrete construction shall be carried out immediately within the corresponding scope. After the construction of soil nailing and shotcreting anchor net is completed, the first layer of concentric soil will be excavated from south to north.

-3.20 -3.20

1: 1.2~ 1:0.7 -4.50

(single slope)

Schematic diagram of earthwork excavation of the first floor

6. After the upper soil nail support is completed and reaches 80% of the design strength, and the uplift force of the soil nail meets the design requirements, the second layer of slope protection earthwork excavation will be carried out. The design depth of the slope without soil nail wall (sections 3-3 and 4-4) is 1.5 m, and the slope release coefficient is 1.0. The slope surface of soil nailing wall (section 1- 1, 2-2, 5-5, 6-6, 7-7) has a design depth of 0.9 m, 1.65438+30cm, 1.30m and a slope coefficient of 0.7. The length of each earthwork in the soil nailing construction around the foundation pit shall not exceed 15m. After the completion of each earthwork excavation, soil nailing and shotcrete mesh concrete construction should be carried out immediately within the corresponding scope. After the construction of soil nailing and shotcreting anchor net is completed, the second layer of concentric soil will be excavated from south to north.

-3.20 -3.20

-4.50 -4.50

-5.701:1~1:0.7 (slope of the second floor)

Schematic diagram of earthwork excavation on the second floor

7. After the upper soil nail support is completed and reaches 80% of the design strength, and the soil nail uplift meets the design requirements, the earthwork excavation of the third slope protection will be carried out. The excavation depth of the third slope protection earthwork shall be less than 30cm below the soil nail elevation according to the design drawings, and the slope grading coefficient shall be in accordance with the design drawings. Therefore, this layer of soil is silt, and the excavation length of each section shall not be more than 7m. If the construction length of one day is too long, the excavation method should be adopted, and the corresponding scope should be carried out immediately after each earthwork excavation is completed. After the construction of soil nailing and anchor net, the third layer of core soil will be excavated from south to north.

-3.20 -3.20

-4.50 -4.50

-5.70 -5.70

1: 1 (three-layer slope) -6.50 cement mixing pile

Schematic diagram of earthwork excavation of the third floor

8. Earthwork excavation of the fourth floor within the local section 3-3 must be carried out after the previous layer of soil nailing support is completed and reaches 80% of the design strength. Due to the small number of cement mixing piles, this layer of earthwork excavation can be completed at one time, and soil nailing and shotcrete anchor net construction can be carried out immediately after earthwork excavation.

-3.20 -3.20

-4.50 -4.50

-5.70 -5.70

-6.50 -6.50

Double row cement mixing pile

-8.20

Schematic diagram of earthwork excavation of local four-story 3-3 section

9. After the bottom soil nailing support is completed and reaches 80% of the design strength, and the uplift force meets the design requirements, the cap, ground beam and basement shall be leveled by manual excavation. After the earthwork excavation reaches the design elevation, the cushion construction should be carried out in time, so that the cushion and the supporting structure can form a rigid fulcrum, which can effectively prevent the deformation of the side wall of the foundation pit, and it is strictly forbidden to expose the basement for too long.

10. Slope shall be placed in strict accordance with the requirements of design drawings during earthwork excavation. After the excavator is excavated, it shall be repaired manually. When excavating in sections, the adjacent sections of earthwork can only be excavated after the soil nailing support construction in the excavation section is completed and reaches a certain strength. During excavation, it is forbidden to overbreak or excavate the next layer before the upper soil nailing construction is completed. The excavation of the next earthwork can only be carried out after the upper soil nailing reaches 80% of the design strength and the uplift force meets the design requirements.

1 1, after the earthwork is dug to a certain elevation, it will be driven into the basement with a 0.5 m long bamboo stick, and leveled with a level meter as the elevation for cushion. After the foundation pit is cleaned, please ask the relevant departments to check the groove in time and make records of it, so as to carry out cushion construction in time and prevent the basement from being exposed for too long.

12, according to the construction needs, leave a working face with a width of 1.0M around the basement, dig open drains around the foundation trench, set collecting wells at the four corners, and prepare enough sewage pumps for timely drainage. In order to prevent rainwater and surface water from flowing into the foundation pit, waterproof berms are built around the top of the foundation pit to prevent the foundation pit from being soaked by water.

13. The engineering piles of this project are immersed cast-in-place piles with small pile diameter and weak lateral resistance. When excavating, the excavator should try to avoid the dense parts of piles and excavate in layers. According to the soil conditions on site, the basement soil after the first layer of earthwork excavation is no longer suitable for excavators and trucks. Therefore, after the first layer of earthwork excavation, a temporary tunnel with a width of 4M and a thickness of 0.5M is laid in the north-south direction between the 08 axis and the 0 18 axis of the foundation pit, which is beneficial to the excavator operation and the truck earth transportation. Considering the poor soil quality on site, in order to prevent the quality of engineering piles from being affected by excavator operation and truck moving soil on the temporary tunnel, iron plates can be used to cushion the height when necessary.

14. Because the earthwork of foundation pile caps and ground beams needs manual excavation, and the earthwork transportation after excavation needs tower crane to complete, it is necessary to install tower crane before foundation earthwork excavation. According to the site conditions, the supporting structure is not allowed as the foundation of tower crane, and the stacking load around the foundation pit should not exceed15mpa. According to the layout of foundation pile caps and piles and the excavation elevation, with the consent of the design, the foundation slab of the foundation ○23~○29 axis /○D~○F axis is determined as the tower crane foundation position. The depth of earthwork excavation in this position is about 2.5M, and the minimum pile spacing is 9M. Earthwork excavation will basically not affect the deviation of pile position. The elevation of tower crane foundation (4.8M×4.8M) is the same as that of foundation slab, and the thickness of tower crane foundation slab is 600MM. First, the tower crane foundation slab, foundation slab and foundation beam reinforcement are reserved.

15, after the foundation pit support is completed, it is forbidden for heavy vehicles to drive on the surrounding roads, and materials should be piled up at a certain distance from the foundation pit to ensure safety.

(3), soil nailing wall construction

1 construction process of soil nailing wall

1), according to the drawing pay-off positioning soil nailing wall periphery, accurately grasp the soil nailing wall interface position.

2) Unload the soil in a large area to a depth of about 1.0M, construct plain concrete spray surface, and drill soil nail holes with a small drill, with the aperture of 1 10MM, and the depth and angle are as required by the drawings. Then install φ 20 steel bars at the hole-forming position, and set φ6.5 centering brackets on the steel bars every 3M or so.

3) Initially spray C20 fine stone concrete with a thickness of 30~40㎜.

4), cloth steel mesh, the second spray C20 fine stone concrete 50~60㎜.

5) Wash the steel pipe after the sprayed concrete reaches the initial setting, and inject pure cement slurry with water cement ratio of 0.3~0.4 into the pipe with a low-pressure pump.

6) After the grouting and curing of the upper row of anchor pipes reach 80% of the design strength and the uplift of soil nails meet the design requirements, the second stage of earthwork excavation will be carried out, and the excavation will be 20~30㎜ below the elevation of the second row of soil nails. After the earthwork excavation with the length of 10~20M is completed, the soil nailing wall shall be constructed in the corresponding range immediately.

7) After the constructed soil nailing wall reaches 80% of the design strength, dig the soil to the third row of soil nails.

Construction personnel configuration table

Number of managers and operators

Number of positions and job types

Project leader 1 piling 2

The builder 2 sewing worker 5.

Quality Engineer 1 Welder 1

Safety Officer 1 Reinforcement Worker 2

Documentary 1 electrician 1

Material Clerk 1 Other Work 25

Total 7 36

List of entry machinery and equipment