The waterproof curtain of triaxial cement mixing pile can improve the stability and impermeability of foundation pit slope and achieve the effect of stopping water and retaining soil. Cement-soil mixing pile is suitable for treating soil slopes with loose gravel, coarse sand, silt or groundwater less than 80 m/d. Cement-soil mixing pile has the advantages of no vibration, low noise, no pollution, low cost and safe construction operation.
I. Overview of the Project:
The civil engineering of a city's raw water intake pump station is located at the upstream of the original intake pump station 100m on the bank of douhe reservoir, surrounded by water on three sides, about 350m away from the Luanhe River estuary, with a construction area of 2319.6m2.
The total length of diversion open channel is199.6m, the easternmost end is10m rubble protection section, and the open channel1-0/0m is cast-in-situ reinforced concrete structure with a clear width 1- 10/0m, a wall thickness of 700mm, a wall height of 7-9.2m and a floor thickness. The basement is located below the natural terrace 10m, and the excavation depth is large, the groundwater level is high, and the permeability coefficient of soil layer is large, so the precipitation can not meet the construction requirements, so the triaxial cement mixing pile is used as the water-stop curtain retaining wall. As shown in the figure:
Next, taking this project as an example, the construction technology of water-stop curtain of triaxial cement mixing pile is introduced.
Second, the operating conditions:
1. According to the geological survey, triaxial cement mixing pile curtain should be used to stop the water in this soil.
2, the construction site completes the three links and one leveling, and determine the construction material storage area, drainage ditch, at the same time decorate safety and environmental protection facilities.
3. According to the red line position, structural coordinates and absolute elevation leveling points given by Surveying and Mapping Institute, do a good job in positioning the axis position and leveling points of cement-soil mixing piles in diversion open channel, and the axis and leveling points should be obviously firm. draw
4. Laying a steel slag road with a width of 8m and a thickness of 0.5m along the mixing axis as the working face of cement-soil mixing pile construction equipment.
5. Sufficient lighting facilities should be provided during construction at night, and obvious signs should be set in dangerous areas. Temporary cables must be erected more than 2 meters.
6. Carry out pile test on the machinery entering the site to check whether it meets the technical parameters such as nozzle speed, shotcrete lifting speed, cement dosage, water-cement ratio, etc.
Third, the mechanical properties:
Model 1, HP-5 mobile deep cement mixing pile machine (automatic leveling)-Mud is transported to the bit blade through the center of drill pipe and sprayed by two nozzles with power of 45KW.
2.BW 150 electromagnetic governor controls two gunite pumps with a power of 7.5KW.
3. Two mortar mixers with power of 4.5KW.
4, catheter 120m (high pressure hose) φ25mm.
Fourth, the construction technology:
1, positioning
Two mobile deep cement-soil mixing pile drivers are located on the pile axis on the east side of the diversion canal, and they are constructed from the midpoint of the pile axis to both sides respectively. Two mortar mixers are installed outside the diversion canal 10 meter, near the temporary cement silo. Each set of equipment * * * has two operators: 1 professional technicians control the cement-soil mixing pile driver to pile; 1 Pump driver, control mortar mixer and mud pump, and make construction records.
The designed pile diameter is 500mm, and double-row piles are driven along the pile axis. The total number of construction piles is 2 128.
Signal command: the foreground and background rely on the sign signal to command. Red flag means stop spraying, blue flag means start spraying, and yellow flag means mechanical failure.
2. Slurry mixing and shotcreting
(1) Pump Worker 1, responsible for preparing mortar and pumping mud, counting material consumption and recording pumping time, contacting the front desk signal, maintaining mortar equipment and cleaning mud conveying pipeline.
(2) When preparing cement slurry, mix P.O32.5 ordinary portland cement and water according to the ratio of 1: 0.6.
(3) Fill the soil with cement slurry at the construction site in strict accordance with the work and vertical speed of the mixing pile machine at the front desk. According to the sinking speed of 1.7m/min and the lifting speed of 1.8m/min, the electromagnetic governor is adjusted at any time in the background to control the pressure of the shotcrete pump, the shotcrete conveying pipeline is within 60m, and the control pressure at the outlet of the shotcrete pump is 0.3-0.4mpa; ; If the conveying conduit is more than 60m and within the range of 100m, the slurry discharge pressure of the slurry jet pump should be controlled at 0.4-0.6MPa, and it will rotate while spraying and sink while lifting.
The prepared mortar shall not be isolated, and the pumping must be continuous, and the mortar shall be prepared step by step. The prepared slurry must be used up within 2 hours, and the slurry exceeding 2 hours is unqualified. If continuous slurry supply is not possible for some reason, a signal must be sent to the front desk immediately, and the mixer bit should be 0.5m above and below the slurry stop point to re-spray slurry to prevent slurry shortage and pile breakage. At the same time, make a good record of cement mixing pile construction.
3. Stir in piles
Professional operators shall be responsible for the verticality of cement-soil mixing pile construction to ensure the continuous and complete operation of the water-stop curtain, and regularly check whether the drill bit size meets 500 mm.
The flatness of the equipment and the verticality of the guide frame must be effectively controlled at any time. When mixing sinks to 8m, it is necessary to check and adjust the verticality of the machine again to ensure that the finished pile 100% is qualified.
After the mixing pile machine is started normally, shift gears to control the rotation speed of the mixing pile machine to work normally, and mix at a speed of 60 rpm according to the soil quality of the site (clay and sand). The drill bit automatically sinks along the guide frame to cut the soil. The drill bit of the mixer is operated in the foreground. After sinking to the foundation soil of 50cm, the blue flag will be displayed in the background to signal the start of concrete spraying (due to the high water level at the scene, the mud will easily flow out of the ground after the drill bit is buried). When the mixing shotcrete sinks to the designed depth of 8m, the shift position is reversed, and the shotcrete is stirred up along the guide frame at a speed of 55 rpm. The second time, mix and spray concrete at the same sinking speed to the designed depth of 8m, and use up the prepared mortar. In order to ensure the uniform and dense mixing of pile foundation soil and mud, slow lifting is adopted for the last time, and the mixing speed is 0.5m/min, and only mixing without shotcreting is carried out until the drill bit comes out of the ground to form a pile. The verticality error of finished pile is not greater than 1%, the diameter deviation of pile is not greater than 4%, the depth error of pile is not greater than 100mm, and the pile location arrangement error is not greater than 50 mm. ..
Verb (short for verb) shift:
Repeat steps 2 and 3 in the construction technology for the construction of the next pile. The piling construction must be carried out continuously, with three shifts every day until the construction is completed. Two piles intersect 100mm, the second row of piles intersects with the first row of piles by 40 mm, and the spacing between adjacent piles shall not exceed 10h and 24h. Otherwise, measures should be taken to fill piles to ensure the effective lap between piles and the water stop curtain.
Six, the use of triaxial cement mixing pile water curtain to create value:
In view of the characteristics of high groundwater level and large permeability coefficient of sandy soil layer in this project, the cement-soil water-stop curtain has good water-stop effect, which ensures the large-area excavation of the foundation trench of the approach channel, and has been unanimously recognized and highly praised by Party A, design and supervision units, laying a good foundation for the smooth progress of the project.
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