The main construction technology of underground continuous wall construction is: firstly, build reinforced concrete guide wall, install equipment on site, divide unit groove and guide hole construction, set up and stir mud pit for wall protection (and circulate mud), then use hydraulic grab to carry out groove-forming operation, let earthwork cool and dry, load and transport, clear bottom, change slurry and require opening (and brush slot joints), then hang reinforcement cage and connecting pipe (make reinforcement cage), arrange concrete pouring conduit, and.
Taking the construction of the diaphragm wall of a bridge foundation as an example, the construction scheme and technology of the diaphragm wall are formulated. It is preliminarily determined that the thickness of diaphragm wall is 70cm, the maximum wall depth is 30m, the minimum wall depth is 10m, and the diaphragm wall is 30m_50m rectangle. It is preliminarily proposed that the wall-forming machine is a hydraulic grab and the joint form of the wall is a joint pipe.
A, underground continuous wall construction method and construction technology:
1, construction organization design
The construction design should be based on the engineering geological survey report and field survey data, so as to determine the design, construction scheme and working performance of the underground continuous wall after completion, mainly including the selection of excavation method, slurry circulation process scheme, fabrication and hanging method of reinforcing cage, joint type of trough section, concrete pouring method and drawing method of joint pipe.
2. Preparation before construction: ① Site preparation: determine and arrange the working area of required machinery, mainly including mud mixing equipment (mud mixing equipment is mainly water tanks, and the total amount of water tanks is about 2-3 times of the earthwork volume of the unit trench, that is, 300-450m3); Reinforcement cage processing and temporary stacking site (its foundation is reinforcement); Temporary storage site for joint pipes and concrete pouring conduits and Artux land. (2) Foundation reinforcement: In the construction of underground continuous wall, mechanical trench digging, steel reinforcement cage hanging and concrete pouring are adopted. The ground foundation on which the trencher is installed has a great influence on the accuracy of the underground wall trench, so the ground foundation on which the machinery is installed must be able to withstand the vibration and pressure of the machinery, and the foundation reinforcement measures should be taken (replacing the surface soft soil layer, leveling the rolled foundation, using asphalt concrete as a simple pavement as a temporary sidewalk, etc.). ); (3) Water supply and drainage and power supply equipment: according to the construction scale and equipment configuration, calculate and determine the power supply required by the construction site, and consider the living lighting. , set up transformer and distribution system. The construction of underground continuous wall is a huge project, and the water supply source and water supply pipeline system are designed and constructed comprehensively.
④ Stability of mud wall protection: the main function of mud is wall protection, followed by sand carrying, cooling and lubrication. Mud has a certain density and generates a certain hydrostatic pressure on the tank wall, which is equivalent to a kind of liquid support. The mud level in the tank is 0.6 m- 1.2 m higher than the groundwater level, which can prevent the collapse of the tank wall. For the stability of the diaphragm wall, we can determine the formula of the critical height of the tank stability by calculation, such as Meyerhof formula.
3. Trenching project:
Division of cell slots:
The construction of underground continuous wall is to divide the underground continuous wall into several construction units with a certain length along the length direction of the wall, that is, unit grooves. According to the design and construction conditions (trenching machine performance, slurry storage tank capacity, influence of adjacent buildings, quantity of machinery and equipment, concrete supply capacity and geological conditions), the plane length of the unit tank is preliminarily determined to be 3.8m-7.2m ..
4, mud construction:
The mud implementation plan needs to be tested before it can be determined.
A, mud test:
Mud test includes: ① stability test (physical stability and chemical stability test); ② There are two methods to measure density, namely mud densimeter method and density calculation method;
③ Determination of mud fluidity;
④ filtration test;
⑤ Determination of sand content;
⑥ Determination of pH value;
⑦ Determination of montmorillonite content;
⑧ Calculation method of solid matter content.
B, mud preparation method and mud regeneration treatment:
Procedures and main contents of mud preparation:
① Investigate the foundation and construction conditions;
② Selection of mud materials: bentonite, CMC, dispersant, weighting agent and leak-proof agent;
③ Determining the funnel viscosity of mud: determining the most easily collapsed foundation and the viscosity necessary to maintain stability;
(4) Determining the basic mixture ratio: determining the concentration of slurry and the addition concentration of various additives; ⑤ Mud preparation, test and correction, and finally determine the construction mixture ratio;
⑥ Mud regeneration treatment.
C, mud production cycle:
Fresh mud mixing → fresh mud storage → wall protection of construction tank section → coarse screening to remove soil residue → mud sedimentation tank → mud purification treatment → mud adjustment and storage.
D, hydraulic grab mud tank control index in each construction stage:
Mud type funnel viscosity s density g/cm3Ph value water loss ml sand content% mud skin thickness mm
Fresh mud 22-301.05-1.107-8.5 <10 < 3 <1.5.
Regenerated mud 30-401.08-1.157-9 <15 < 6 < 2.0.
Mud 22-601.05-1.207-10 < 20 is unpredictable.
Mud after hole cleaning is 22-401.05-1.157-10 <15 < 6 < 2.0.
5, guide wall:
Before the underground continuous wall is grooved, the guide wall should be built first. Guide wall is an indispensable temporary structure in underground continuous wall construction. In the process of reconstruction, the guide wall often bears static and dynamic loads such as reinforcing cage, concrete-filled conduit and drilling rig, and it must be carefully designed and constructed before the formal construction of underground continuous wall can be carried out.
1). Guide wall form: simple reinforced concrete guide wall is used in the section with good surface foundation (see figure 1). The L-shaped reinforced concrete guide wall (see Figure 2) is cast in place in the area with weak surface soil.
2) In order to keep the topsoil stable, temporary wood supports and cross braces are added every 1-3m between guide walls; The construction accuracy of the guide wall is directly related to the accuracy of the diaphragm wall, so when constructing the guide wall, we must pay attention to the static space size, vertical and horizontal accuracy and plane position of the inner side of the guide wall.
The horizontal reinforcement of the guide wall must be connected to make the guide wall a whole to prevent accidents due to insufficient strength or poor construction.
In order to ensure the construction accuracy of the underground wall and facilitate the operation of the trencher, the dead zone in the guide wall should be slightly larger than the thickness of the underground wall (5cm larger than the design value), the top of the guide wall should be 5cm above the ground, and the depth of the guide wall should be 1.5m (see the guide wall structure diagram for details).
The construction error standard of guide wall is: centerline error10 mm; The elevation error within the total length of the top surface is 65438 00 mm. ..
3), guide wall construction sequence:
The construction sequence of guide wall is as follows: ① Level the site; (2) measuring position; (3) Trenching and soil disposal; (4) Binding steel bars: (5) Erecting formwork for guide wall. In order not to loosen the soil behind, concrete can be directly poured outside the guide wall without formwork support, and the soil wall can be used as a side formwork; ⑥ pouring guide wall concrete and curing; ⑦ Dismantle the formwork and set the cross brace; ⑧ Backfill the gap outside the guide wall and roll it tightly. If there is no external template, this process can be omitted.
6. Guide hole:
During dredging with hydraulic grab, a vertical guide hole is drilled every 3.8m-7.2m at the axis position of laying out the underground continuous wall, and the aperture is the same as the wall thickness. When the excavated foundation is weak, pilot holes may not be drilled. Steering drilling rig adopts rotary drilling rig.
7. Trenching construction:
Trenching machinery adopts hydraulic grab to form a trench with a length of 3.8m—7.2m, which is completed by 2-3 times of grabbing. The sequence of grabbing and digging is shown in Figure 4.
In order to ensure the quality of the groove, the hydraulic grab should check whether the instrument is normal, whether the correction push plate works normally and whether the hydraulic system leaks before opening and entering the groove.
When the trench begins to form 2-7 meters, the excavation speed should not be slowed down too fast to prevent encountering underground obstacles, and the display accuracy of the instrument should be kept at about 1/500. In the whole groove forming process, the deviation is corrected at any time, so that the display accuracy is always kept in a good range.
After the whole trough section is dug to the bottom, it is necessary to sweep the hole, remove the wall surface of the grab part, remove the sediment at the trough bottom, and eliminate the settlement of the sediment at the trough bottom to the future wall surface. The construction method is: shovel orderly from one end to the other, and control the grasping depth at the same design elevation every 50cm.
8. Clean the bottom:
After digging and sweeping the hole, the interval is 1h, and the mud is drained by a mud suction pump, and the bottom is cleaned and the slurry is changed. The bottom of the hole cleaning pipe is controlled at 10-20cn, and the position changes (the interval is 1m- 1.5m). The time for hole cleaning and slurry changing shall be subject to the qualified export pulp index.
9, reinforcing cage construction:
Reinforcing cages are made on site. The design and calculation of wall reinforcement should not only meet the needs of stress, but also meet the needs of hanging safety, and the grid should have enough stiffness.
According to the design drawings, the reinforcing cage is made, in which the distance between the bottom of longitudinal reinforcement and the bottom of trough is above 10cm-20cm, and the gap between the end of transverse reinforcement and the concrete surface is 5cm- 15cm.
In order to prevent the vertical collision between the groove wall and the reinforcing cage when the reinforcing cage is lowered, a steel plate with a thickness of 3.2mm(30cm_50cm) is used as a positioning pad and welded on the reinforcing cage, that is, three positioning pads are arranged on the front and rear surfaces of the reinforcing cage in each unit groove section at a horizontal and longitudinal interval of 5 m..
According to the length of the unit tank, determine the position of the reserved concrete pouring conduit for the reinforcement cage (the position of the reserved concrete pouring conduit for every13 in the tank section is 3.2m-5.4m, the position of the reserved concrete pouring conduit for every14 in the tank section is 5.4m-7.2m, the distance between the reserved conduits is not more than 3m, and the joint position between the reserved conduit and the end of the tank section is not more than 65433.
Weld the grid into a skeleton. When hoisting, don't directly tie a thousand-kilo rope for hoisting, but use a pole beam for auxiliary hoisting. For a long steel skeleton, consider the method of two cranes to assist hoisting.
10, joint project construction:
After cleaning the bottom, insert the nozzle with the same diameter as the wall thickness for vertical installation. According to the hardening speed of concrete, pull the nozzle appropriately in turn. After about 2 hours of concrete pouring, in order to separate it from concrete, rotate the connecting pipe and pull it out about 10 cm. After pouring for about 2-3 hours, slowly pull out the nozzle from the wall section with a crane and jack. First pull out 10cm to 0.5m- 1.0m, then pull out 0.5- 1.0m every 30min, and finally pull out completely according to the condensation state at the top of concrete. The nozzle position forms a semi-circular tenon and groove.
After digging the groove at the joint of the unit groove section, remove the sediment stuck on the joint surface. The attachment will be removed by inserting a professional tool with a cutting angle along the surface of the joint. So as to avoid concrete strength reduction and water leakage at the joint.
1 1, concrete pouring engineering construction:
After the bottom of the unit tank is cleaned, a reinforcing cage and a connecting pipe are set, and the concrete of the unit tank section is poured. The concrete of the diaphragm wall is poured under the slurry conduit of the retaining wall, and the concrete pouring of the diaphragm wall is prepared and poured according to the concrete poured underwater.
The mixture ratio of concrete is determined by experiments according to the design requirements. Ordinary portland cement or slag portland cement shall be used as the cement, the water cement ratio shall not be greater than 0.6, the cement dosage shall not be less than 370kg/m3, and the slump shall be kept at 18cm-22cm. According to the concrete pouring speed, retarder can be added appropriately. The aggregate for preparing concrete shall not be greater than 40mm.
After the nozzle and reinforcing cage are in place, concrete shall be poured within 4 hours after the sediment at the bottom of the tank is detected not to exceed the design requirements. The conduit is a steel conduit with a diameter of 30cm. Before pouring concrete, the conduit should be tested for strength and tightness, and it can be used only after it is qualified. According to the length of the unit tank, determine the number of pipes (2 pipes in the tank section of 3.2m-5.4m, 3 pipes in the tank section of 5.4m—7.2m, the distance between the pipes is not more than 3m, and the position between the pipes and the terminal joint of the tank section is not more than 1.5m). Initially, the conduit is 30-40 cm away from the bottom of the pool, and the depth of concrete burial is 2-6 meters. The concrete pouring of two or three conduits shall be balanced and continuous. The top surface of pouring concrete is 300mm-500mm higher than the design elevation, and it will be chiseled by pneumatic pick after the initial setting of concrete. After pulling out the connecting pipe, enter another unit slot section for construction.
Second, the labor organization and safety:
List of labor organizations for single-machine operation
Work quantity, main work content, minimum number of people, remarks
1 The excavator driver installed the excavator, excavated the trough section and hoisted three cranes.
2 Hoisting operation, groove formation and positioning of crane 3
3 Mudman's mud system installation and mud production cycle all contents except electromechanical installation.
4. All the work of concrete workers to dismantle concrete conduits and pour concrete and clean up the site 12.
5 All the work of the steel bar worker is about half of that of the 14 welder.
6. The welder shall cooperate with the production of reinforcing cage and undertake all welding work on site. eight
7. Installation, maintenance, hoisting and unloading of electrical equipment nozzles at the mechanical electrician site; four
8 survey inspector lofting and construction monitoring, ultrasonic wall measurement, etc.
9 Management personnel on-site command, technology, quality, materials and life management 14
Generally, 50-65 people go it alone.
Safety measures:
1, establish a safety assurance management system, and implement it in accordance with Safety Regulations for Building Engineering and Underground Engineering;
2. When slotting and opening holes, a special person shall be assigned to command. When turning, pay attention to whether the tail power cord collides, and check whether the cable is damaged before digging;
3. When the operation is suspended during slotting, the grab bucket is hoisted to the ground for parking, and the equipment is suspended from the slotting section for a long time (10m);
4. Don't lift the grab into the lifting slot too fast to prevent the grab from hooking the root of the guide wall and causing an accident;
5, the whole construction process should pay attention to mud deterioration, such as heavy rain, etc.
Three, the main mechanical equipment:
Serial number equipment name usage and dosage remarks
1 Mud mixer of mud system stirs and adjusts the mud for wall protection 1 4m3 /2_3kW.
2 5 pieces of 3LM4PL are pumped, mixed and recycled by mud.
3. There are 24 "and 2.5" mud supply, mixing and recovery pipelines respectively.
Improvement of Mud and Sand Separation Treatment of 2DD-9 18 1 Vibrating Screen
5 cyclone slurry separator reduces slurry density 1 group 4 only includes pump body.
6 waste mud treatment equipment exceeds the standard. 1 set of waste slurry can also be transported by tanker.
7. The crawler crane for trench casting is equipped with KH- 18050t excavator 1 set.
8. Hoist the crawler crane, paint the wall, hang the reinforcing cage, and connect the pipe 1, 35t 35t-100t.
9. The wall brushing device cleans the 1 joint between the groove webs.
10 set 1 set shall be isolated when casting the slot width of the nozzle.
1 1 Jacking-in pipe drawing equipment is pulled out 1 sleeve joint pipe.
12 concrete pouring conduit is poured with 3 sets of cement slurry D30 under the concrete wall.
13 other quality inspection equipment: mud sampling and testing equipment: wall detector; Settlement tester
14 other necessary equipment steel processing equipment; Concrete mixing station and supply system, etc.
Fourth, the quality standard:
Allowable deviation of underground continuous wall
Project specified value or allowable deviation
The strength of concrete is within the acceptable standard.
Axis position (mm) 30
Overall dimension (mm) 0, +30
Inclination 0.5%
Top elevation (mm)+,-10
The sediment thickness meets the design requirements.