High-pressure jet grouting pile is to inject cement slurry into the soil layer by using high-pressure rotary nozzle and mix it with soil to form continuous overlapping cement and solid. Then, in the case of high-pressure jet grouting pile quality control, the basic quality control points of construction unit personnel are as follows:
Construction technology of high-pressure jet grouting pile;
(1) Measuring and setting-out: Measure the setting-out construction axis according to the design and construction drawing and coordinate network points.
(2) Determine the hole position: determine the hole position on the construction axis, code the pile number, hole number and serial number, and measure the ground elevation of each orifice according to the datum point.
(3) Drilling with drilling rig: rotary drilling with mud wall protection, impact casing drilling and impact rotary casing drilling can be used.
(4) Measuring hole depth: when drilling the final hole, measure the length of drill pipe and drilling tool; When the hole depth is more than 20m, the hole inclination is measured.
(5) Lower the jet pipe: high-pressure jet grouting can be carried out only after the drilling experience is qualified. Check the following items before lowering the nozzle.
(6) Stirring pulping: The rotating speed and stirring capacity of the mixer should be adapted to the type of slurry being stirred and the displacement of grouting pump respectively, and the slurry should be uniformly and continuously stirred. Ensure the continuous supply of slurry for high-pressure jet grouting.
(7) Water supply and gas supply: the flow and pressure of high-pressure water and compressed gas for construction shall meet the engineering design requirements.
(8) Jet grouting: The high-pressure jet grouting method is a continuous operation from bottom to top. Nozzle can be divided into single nozzle, double nozzle and multi-nozzle.
(9) Slurry leakage: The amount of slurry leakage at the orifice of high-pressure jet grouting can reflect the grouting effect of the stratum cut by jet grouting. Whether the outlet slurry can be recycled depends on the engineering design and slurry quality, and recycled slurry should be used as much as possible in the project.
(10) Rotary swing lifting: single nozzle swings 360 for rotary spraying; Less than 360 is arc spraying; Less than or equal to 180 is arch spraying; Less than or equal to 90 degrees for swing spraying; When the swing angle is 0, it is unidirectional fixed injection. The coaxial double-nozzle nozzle swings180 for rotary spraying; Less than 180 is bidirectional arch spraying; When the temperature is less than or equal to 90 degrees, it is a two-way swing spray; When the swing angle is 0, it is a two-way fixed spray. Non-coaxial double-nozzle nozzle has an included angle of 90,120 and150, which can be used for oscillating spray and fixed spray. Multi-nozzle nozzle has not been widely used in China at present. Pendulum is a mechanical pendulum and an artificial pendulum in special environment.
(1 1) Pile-forming and wall-forming: The solidified body by high-pressure jet grouting can be formed into the shape required by the design, for example, the rotary jet can be formed into a cylindrical shape and a disk shape, the oscillating jet can be formed into a fan shape, a bell shape, a trapezoid shape, a cone shape and a wall shape, and the fixed jet can be formed into a plate shape.
(12) Filling and reinjection: After the completion of high-pressure jet grouting in each hole, the cement slurry in the hole will settle quickly, so it should be filled and grouted in time until it is full, and the slurry surface at the orifice will no longer sink. Filling and grouting after final injection is a very important work, and the quality of recharge will directly affect the quality of the project, so it is necessary to do a good job of filling and recharge.
(13) Completion of cleaning: After the completion of high-pressure jet grouting for each hole, the grouting pump and the slurry conveying pipeline should be cleaned in time to prevent the slurry from settling and caking in the slurry conveying pipeline due to untimely and incomplete cleaning, blocking the slurry conveying pipeline and nozzle and affecting the construction of the next hole.
Key points of quality control of high-pressure jet grouting pile;
Quality control of high-pressure jet grouting pile before construction;
(1) The construction principle of high-pressure jet grouting pile technology is that under the action of high pressure, grouting pipe with nozzle is first taken to the designated soil layer by the drilling rig, and at this time, the cement slurry will be sprayed from the nozzle, break through the soil layer and penetrate into the soil. According to the different nozzle forms, the spraying process of jet grouting pile can be divided into two ways: directional spraying and rotary spraying. Among them, rotary spraying means that the nozzle rotates while spraying and gradually increases its height, and its consolidated object is cylindrical. The characteristic of jet grouting pile technology is that it will not cause great damage and deformation when the upper structure keeps increasing the load on the soil. Therefore, this technology has an important application in strengthening foundation. It can not only improve the compressive performance of soil, but also improve the shear strength of foundation. However, due to the high cost of high-pressure jet grouting pile, it is still rarely used in practice.
(2) Before construction, carefully check the construction drawings, carry out construction operations in strict accordance with the requirements of construction drawings and design specifications, and then examine and approve the construction organization design. Find out the design defects and coordinate with them to improve. At the same time, it is necessary to strengthen the management before construction, improve the awareness of quality management, and clarify the rights and responsibilities between departments in order to better promote the construction of high-pressure jet grouting piles. Second, the preparation of high-pressure jet grouting pile construction materials. Construction equipment required for high-pressure jet grouting pile construction includes: high-pressure pump, mud mixer, drilling rig, etc. Auxiliary machinery and equipment include: high-pressure pipeline system, operation control system, material storage system, etc. , as well as pipes, valves, joint safety facilities and other auxiliary appliances; In addition, there are necessary materials such as soil, stone and earth-rock mixture.
Quality control in the construction of high pressure jet grouting pile;
(1) rig installation and drilling depth control
The installation of drilling rig is the primary process of high-pressure jet grouting pile construction. Before installation, the specific position of drilling hole should be determined, and then the drill bit should be aimed at the preset drilling center position. After alignment, it should be corrected to ensure that the drill pipe axis can be vertically aligned with the drilling center. In order to ensure its verticality, when the drilling rig is fixed, it should form a 90-degree angle with the preset drilling hole. At the same time, ensure that the error between the drilling center and the drill bit is within 50 mm Generally speaking, the appropriate drilling method should be selected according to the geological and hydrological conditions of the construction site, the required reinforcement depth and the existing construction conditions at the site. If it is a single-pipe high-pressure jet grouting pile, the depth of drilling can reach 30 meters. If the stratum is hard, geological drilling rig can be used to drill holes, and double-pipe and three-pipe jet grouting methods can be used in construction.
(2) Quality control of intubation construction
This technology is an important part of the whole high-pressure jet grouting pile construction, that is, grouting pipe is inserted into the corresponding stratum. In this process, we should always pay attention to the strength of water pressure, and control it within the range of 65438±0 MPa to prevent the phenomenon of hole wall collapse by rotary jet grouting.
(3) Quality control of sprayed concrete
Insert sprinkler irrigation into the stratum to a certain depth, control the flow rate and rotation speed of grouting from top to bottom, check the initial setting time of slurry, and pay attention to increasing the rotation speed in time. The order of deep injection should be spraying first, then turning, and increasing speed, so as to avoid the phenomenon of grouting pipe twist-off. The operation order is the same as above. Before injection, the following inspections should be carried out, including flowmeters and pressures of high-pressure equipment and pipelines, to ensure that all parameters meet relevant design requirements. Pay attention to the flow, pressure, rotation speed, lifting speed and air volume of grouting to ensure that it is highly consistent with the design requirements. When the slurry supply in the backcourt is stopped due to insufficient raw materials or mechanical operation errors, it should be communicated with the front desk in time to avoid pile breakage. When supplying the slurry for the second time, put the mixer 50 cm below the slurry stop point first, and then lift it after the slurry supply is normal; The distance between the high-pressure pump and the jet grouting hole should be kept within a suitable range. Ensure that the injection speed meets the construction requirements. When the pile top reaches the elevation, the speed should be slowed down and controlled within the range of10cm per second to improve the construction quality. After the injection, in order to avoid the downward flow of liquid level, the injection hole should be filled with static pressure. If grouting occurs in the construction process, it may be because there is too much grouting, so it is necessary to reduce the nozzle diameter and increase the rotation speed and injection pressure.
In order to control the engineering quality effectively, the errors of various engineering parameters such as rotation, drilling and lifting speed can be reduced by experiments. When drilling, prevent the vibration of drill pipe of drilling rig vibrator from swinging; At the same time, it is necessary to ensure the plumpness of sprayed concrete, check the depth of the hole, and be ready for early warning at any time. It is also necessary to strengthen the supervision of the construction process and make records of each construction.
Quality control of high pressure jet grouting pile after construction;
(1) On-site supervision technical disclosure.
Many parameters need to be controlled during the construction of high-pressure jet grouting pile. Therefore, in the geological exploration stage, these parameters should be investigated in detail first. Therefore, the supervisors on the construction site are required to have keen observation, scientifically organize the supervisors on the site and accurately determine the parameters of the test pile. Strengthening the supervision of technical disclosure is conducive to improving the construction personnel's understanding of various parameters, thus strengthening quality control in subsequent projects. (2) establish the project supervision system
Various detailed and highly reliable engineering supervision systems should be formulated, and the construction process of high-pressure jet grouting pile should be defined. Only in this way can we ensure that the construction personnel strengthen the quality control of key working procedures in the construction process. In the supervision system, the authority and responsibility of the engineering quality control department should be clearly defined, and the quality control measures and procedures should be clearly written. At the same time, we should also strengthen the ability to deal with emergencies and formulate various effective solutions for quality problems in engineering.
(3) do a good job in the acceptance of high-pressure jet grouting pile construction projects.
After the construction is completed, the engineering quality inspection and acceptance shall be carried out. According to the relevant testing requirements of high-pressure jet grouting foundation in Technical Specification for Testing of Building Pile Foundation (JGJ06-2002), at least 1/5 should be sampled for general and non-mandatory testing items. Check and recheck the concrete strength, pile location center, reinforcement and pile top elevation to ensure compliance with corresponding standards. Generally speaking, when high-pressure jet grouting is completed for nearly one month, its construction quality should be checked in time. The inspection should be targeted, and some consolidated bodies with relatively complex geological conditions and many abnormal phenomena during shotcreting are usually selected for inspection. After the inspection, the supervision unit shall prepare the quality evaluation report and set up the relevant parties of the project construction for acceptance.
(4) Improve the quality awareness of construction technicians.
All units should strengthen the education of construction quality, improve the awareness of construction personnel on engineering quality, and make them fully realize the importance of engineering quality, so as to facilitate the construction and ensure the construction quality.
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