What specifically does the treatment of cement powder spray piles include? The following Zhongda Consulting and Bidding Teachers will answer your questions for your reference.
Cement powder spray pile is the abbreviation of "cement powder spray mixing pile". It uses a modified auger drill to drill the drill bit to the designed soil depth, and uses compressed air to pass the cement powder through the inner hole of the drill pipe. It is transported to the drill bit and rotated while spraying powder. At the same time, the mixer is lifted strictly according to the lifting speed determined by the design, so that the cement and soft soil are mixed together to cause a chemical reaction to form a pile. This method is used to improve the bearing capacity of the foundation soil. strength and stability. Powder spray piles were first proposed, promoted and applied by Japan and Sweden in the 1970s, and my country introduced this technology in the early 1980s. Because powder spray piles can effectively reduce the total settlement, withstand a large loading rate, have strong resistance to lateral energy changes, and can greatly shorten the construction period, they are currently widely used in the field of soft foundation treatment. However, because it is an underground hidden project, there are many factors that affect the quality, and project quality problems are prone to occur. Therefore, the construction and supervision quality control of powder spray piles must be strengthened.
1. Quality control in the construction preparation stage
(1) Quality control of raw materials
Powder spray pile cement generally uses 325 or 425 ordinary silicate Cement or slag cement. The type and grade of cement used in construction should comply with the design requirements. For purchased cement, the contractor's self-inspection and supervisory sampling inspection shall be used for review and verification. To meet the requirements of the specification, the manufacturer's quality assurance unit and factory test report must be inspected by the supervision engineer, and those with small output and unstable quality shall be avoided as much as possible. of cement produced by small cement plants. When the cement is put into the tank, it should be sieved. The maximum particle size should not exceed 5mm, and it should not contain paper scraps, plastic sheets, garbage and other debris. The supervision laboratory should also conduct random inspections of the cement materials used in batches to ensure the quality of the cement materials. In addition, the stacking of cement should meet the standards and moisture-proof requirements. It is strictly forbidden to use expired, damp, agglomerated, or deteriorated cement.
(2) Performance control of machinery and equipment
The deep mixer is the key to construction. It is strictly forbidden to use non-standard products or self-modified equipment for powder spray pile drivers. The equipment entering the site must be an ammeter with good performance that can display the current change when the drill pipe is drilled, a pressure gauge that displays the pipeline pressure, and an electronic scale that measures the amount of cement sprayed. (or computer measuring device). All ammeters, pressure gauges, electronic scales (or computer measuring devices) and other measuring instruments and weighing instruments must be calibrated by the measurement department and can be used in engineering construction only after passing the standards.
(3) Control of measurement and setting out
In order to ensure the quality of the cement powder spray pile reinforcement soft soil project, the points must be positioned strictly according to the design requirements. Therefore, the construction site should be leveled in advance and obstacles should be removed. The supervision engineer should work with the construction unit to re-test the project conductor level points, and after meeting the accuracy of the design documents, go through the on-site pile delivery procedures. The construction unit shall adjust and stake out the square grid according to the control points and level points, and measure the distance with a steel ruler. Control positioning deviations as required, fill out the stakeout inspection form, and submit it to the supervision engineer for review and approval. The supervision engineer should conduct retest inspections to ensure the accuracy of the stakeout. The construction unit should assign dedicated personnel to record the engineering control piles, leveling points and stakeout measurements, and properly protect the measured axis and pile layout points for future use.
(4) Conduct indoor proportioning test before construction
Before construction, take samples from locations with large water content to conduct indoor proportioning test to measure the natural moisture content and Porosity ratio, liquid plastic limit, organic matter content, organic matter content, PH value and unconfined compressive strength of various ages of cement and soil with different mixing amounts to test the applicability of powder spray piles for reinforcing this type of soft soil and the design of ash mixing Whether the measured pile body strength can meet the design requirements. During the test process, supervisors should supervise the entire process or conduct parallel tests to ensure that the test results are accurate and reliable.
(5) A process test pile must be carried out before construction
Whether the cement and soil are mixed evenly is one of the key factors affecting the reinforcement effect of cement powder spray piles. Therefore, construction technology tests should be carried out before large-area construction of powder spray piles. Through experiments, various operating technical parameters suitable for the site are determined and the pile forming experience under the site conditions is mastered. According to the construction characteristics of cement powder spray piles, the technological test should achieve the following purposes.
(1) Propose various operating parameters that meet the designed cement injection amount, such as drilling rig lifting speed, mixing blade rotation speed, pipeline pressure, ash tank pressure, etc.;
(2 ) Check the uniformity of cement mixing and pile diameter;
(3) Determine the reasonable amount of ash that meets the quality requirements under the geological conditions;
(4) Understand drilling and the resistance to improvement, and propose corresponding implementation measures;
(5) Determine the method of identifying the strength-bearing layer.
2. Quality control during the construction stage
Powder spray piles are underground hidden projects, and their quality control should be throughout the entire construction process, and all-round and whole-process construction supervision should be adhered to. . The contractor of each construction bid section must be responsible for the quality and progress of the powder-coated piles, and each drilling rig must be operated by a dedicated person. During the construction process, on-site supervision is the most important task. The on-site supervisor should be familiar with the construction technology and various construction parameters, and conduct all-round, all-weather supervision during the entire construction process.
The main construction process of powder spray piles is: cleaning the site → filling the drainage slope → measuring and positioning → placing the powder spray mixing machine in place → pre-stirring and sinking → powder spraying and stirring to lift to 0.3m above the ground → Repeat stirring and sinking → Repeat stirring and lifting until it is 0.3m above the ground → Turn off the stirring machine.
(1) Before the start of construction, level the original ground to the construction elevation of the powder mixing piles, remove all obstacles on the ground and underground at the pile locations, and spray powder on rivers, ponds and structures. Piles should be backfilled with cohesive soil first, then rolled to a certain degree of compaction and with a certain drainage slope.
(2) The drilling rig should be positioned in strict accordance with the designed pile position and specification requirements. Use a total station or theodolite for positioning, and use a spirit level to check the verticality and horizontality in two orthogonal directions of the drilling rig rod or turntable. , the plane error of the pile position shall not exceed 5cm, and the inclination of the drill pipe shall be less than 1.5%. Supervisors should also check the connection of each part of the main engine, the hydraulic system, electrical system, the installation and debugging of each part of the powder spraying system, and the sealed connections of ash tanks and pipelines. Whether the situation is normal, make necessary adjustments and tightening work. The ash tank should be filled with one pile according to the designed input amount to ensure the quality of the pile. After the ash tank is full, the feed port should be covered and sealed to eliminate abnormalities. Construction can only be carried out after the situation is met.
(3) Strictly control the drilling depth, powder spraying elevation and dust stop surface to ensure that the length of the powder spray pile and the powder spraying amount meet the specified requirements. The depth error shall not be greater than 5cm, and the average cement loss shall not be greater than 1kg/m. The powder spray pile must penetrate the soft soil layer to reach the relatively high-strength bearing layer, and penetrate 50cm into the hard soil layer. The depth of the bearing layer shall be determined according to the geological data. In addition, it should also be determined based on the reading value of the ammeter during drilling. When the reading of the ammeter rises significantly while the drill pipe is drilling, it indicates that it has entered the hard soil layer. If it can last for more than 50cm, it indicates that it has entered the bearing layer. Supervisors at the side station should pay attention to the scale marked on the drill pipe to ensure that the designed pile length has been drilled.
(4) Each time the mixer sinks or lifts, the time must be recorded by a dedicated person. The time error shall not be greater than 5 seconds. There must be time to wait for the powder to arrive at the bottom of the pile before lifting to prevent the mixer from lifting without spraying powder. situation, the specific time will be obtained from the process test pile. Stirring should be repeated within the upper 1/3 of the pile.
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