There are many aspects involved in anti-seepage wall construction technology, such as continuous wall construction technology for deep mixing piles; underground continuous thin anti-seepage wall construction technology; key technology for anti-seepage wall construction; sawing method for wall forming technology and construction technology, etc. According to the actual conditions of the project and the characteristics of these technologies, the appropriate construction techniques can be selected to achieve the desired results.
I. Construction technology of continuous wall building with deep mixing piles
The deep mixing cement soil seepage prevention wall is constructed by single-axis and multi-axis deep pile driver. The principle is to drill the hole to a predetermined depth with a deep pile driver, inject cement slurry into the hole, stir with a spiral bit, try to make the soil and cement slurry forcefully mix and condense to form cement column, and overlap each other. Formed into a wall to prevent seepage.
1. Construction method of double-power three-head deep mixing pile machine
The mixing pile machine is positioned according to the axis of the anti-seepage wall, and the machine base is leveled according to the connecting pipe on the pile machine, and the deviation slope should be less than 5‰. The centering deviation of the pile position is not more than 50mm.
An cement slurry preparation system, the cement slurry is strictly filtered, and a filter is arranged in front of the mortar mixer and the collecting hopper. Pipeline connection: Connect the mortar pump outlet to the feed pipe inlet of the deep mixer with a pressure hose.
Commissioning. Adjust the stirring speed, not exceeding 10% of the designed value; adjust the lifting speed, generally controlled at about 1m/min; the slurry feeding line and the water supply line are unobstructed; all kinds of instruments should be correctly displayed, and the test data is accurate.
The spray is stirred and sinked. Start the slurry pump to the drill bit, then start the main machine to make it rotate forward, and select the drill bit to push the gear down until the design depth.
Spray mixing is promoted. When drilling to the design depth, stop pouring the cement slurry for 30s until the orifice is returned to the slurry, and the drill pipe is lifted in the opposite direction to continue the grouting and keep the orifice slightly slurryed. When the mixing head is lifted to the top of the design pile, stop lifting, stir and spray for a few seconds to ensure uniform and compact pile head.
Stir. After stirring and spraying for a few seconds, the mixing head is rotated forward to the design depth, and then reversely turned to the top of the pile. At this time, the amount of cement slurry to be poured is appropriately controlled (subject to not blocking the pipeline).
Clean the tubing. Injecting clean water into the collecting hopper, and starting the grout pump to clean the residual cement slurry in the pipeline until the mixing head discharges the clean water, and manually removes the soft soil adhered to the stirring head. Then, move the machine to carry out the construction of the next pile.
2. Single head deep mixing pile machine construction method
The single-head machine is the same as the multi-head machine construction step. When the pile machine is walled, the single-head machine has one more cycle than the multi-head machine, and it is not sorted. Each time the machine is moved 44.4cm, the wall thickness is 32.5cm.
3. The application range of deep mixing method anti-seepage wall
The deep mixing method has strong applicability in soft soil foundation reinforcement and anti-seepage treatment, and its bearing capacity and anti-seepage performance can meet the conventional requirements after treatment. Under the current construction conditions, considering the guarantee of economy and quality, the scope of application should be loose sand, silty sand, silty clay and soil with a small amount of gravel, and even soil overhead or caves can be constructed. However, it should be used with caution in the gravel layer, the silt with high organic matter content and the clay layer with less water content.
4. Technical characteristics of deep mixing method anti-seepage wall
High construction efficiency: When the average construction efficiency is up to 13.2m/set, it is a method for building walls with various anti-seepage technologies. The cost of forming a wall is low: the cost of forming a wall is 1/5 of high-spray, which is concrete seepage prevention. 1/3 of the wall; simple construction process: no need to slot, no problems such as collapse, retaining wall, backfilling, compaction, etc., more importantly, not destroying the dam; good wall effect: uniform wall thickness, few joints, wall The body thickness meets the anti-seepage requirements (the diameter of the pile machine head is 400-500mm), the wall depth can reach 22m; no pollution, low noise, etc.
Second, the key technology of anti-seepage wall construction
Verticality
The key technology common to the combination drilling machine slotting method, water jet method and deep mixing pile is verticality. The degree of verticality is related to whether the constructed cut-off wall is on the same wall axis. Therefore, the left and right deviation, axis deviation, and hole slope data during construction should be carefully observed and recorded according to the operating procedures and regulations. If the deflection is found, take measures to correct the deviation and ensure that the impervious wall is on the same axis. Otherwise, it is prone to breakage of the wall or the bottom of the wall is not tight, and the construction gap is too large, causing concentrated leakage.
2. Wall joint connection processing
The joint between the concrete wall and the concrete wall should be repeatedly cleaned up and down the wall joint of the original pouring to ensure that there is no mud at the joint. The wall and the wall are connected in parallel, and the length of the lap should be 1~2m. If it is found that the sealing is not strict and the leakage channel is generated, the leakage can be closed by drilling the cast-in-place concrete to achieve the purpose of interception.
3. Collapse
Reinforcement and collapse are prone to occur due to the mud wall protection process during construction. The main reason for reaming and collapse is that the soil layer contains straw layer, silt layer, voids, cracks and so on. To solve the above problems, the main measures that can be taken are as follows: First, strictly control the concentration of the wall mud, and if necessary, the bentonite can be appropriately added according to the proportion. The second is to encrypt the spacers and increase the supporting force. The third is to shorten the length of wall casting and reduce the flooding time.
4. Drilling and lifting of deep mixing piles
The mixing pile is an anti-seepage wall formed by pumping the cement slurry into the soil through a high-pressure slurry system while drilling and lifting. Its drilling and lifting speed is directly related to wall thickness, width, strength and impermeability. Therefore, in the construction work, the manipulator should strictly implement the control procedures and process flow. The original records and construction logs shall be recorded in detail and the control and supervision of key processes shall be strengthened.
Third, underground continuous thin anti-seepage wall construction technology
Several methods and equipment for underground continuous thin anti-seepage wall construction are bored and grouted into a wall. Its main working principle is to grout the grout into a wall. One type of equipment is a multi-head small diameter deep mixing once into a wall pile machine. The equipment is mainly composed of a hydraulic step to perform a chassis, a special guide frame, a six-head drill pipe, an interlocking unit and the like. The equipment has reasonable structure and high wall-building efficiency, and the maximum wall depth is 22m. The other equipment is a double-powered multi-head deep mixing pile machine. It is mainly composed of hydraulic step to carry out the chassis, special guide frame, wall forming device, three-bar six-head mixing drill bit and other components. Double-powered drive, with multi-step drilling speed adjustment, adjustable drill pipe center distance, three-tube metering grouting, advanced vertical precision control, small environmental impact, etc. The maximum wall depth is 21m. Hydraulic grab ultra-thin concrete Impervious wall. The thickness of the wall is generally 25~30cm. The equipment is made of CH-60 and CH-80 hydraulic grabs produced abroad, and the maximum depth of the groove can reach more than 70m. Because the thickness is only 1/3~1/2 of the conventional concrete anti-seepage wall, under normal circumstances, the hydraulic grab can be directly used to dig into the trough, the mechanization degree and work efficiency of the construction are greatly improved, and a large amount of concrete and other related materials can be saved. Materials, engineering costs have been greatly reduced. At the same time, the verticality and continuity of the wall can be better guaranteed, and the anti-seepage effect can fully meet various design requirements, which truly reflects the good anti-seepage performance of the concrete anti-seepage wall, short construction period, low cost, quick effect, etc. advantage.
Fourth, the sawing method into the wall process and construction technology
The wall forming process adopts the cutter bar of the sawing machine in the pilot hole, and performs the upper and lower reciprocating cutting movement at a certain inclination angle, and moves forward and slot according to the grounding condition according to the formation condition at a speed of 0.8-1.5 m/h. The soil cut by sawing may be discharged from the tank by a reverse circulation slagging system or a positive circulation method, and a mud wall is used to form a slot. When the slotting machine has a slot length of 6 to 11 m, the geophone spacer is used to divide the slot into a slotted section and a rafting section, and then the hole is cleaned and plastically poured to form a cut-off wall having a width of 0.2 to 0.3 m. body. The sawing machine is mainly composed of a walking chassis, a power and transmission system, a shank and bracket pressurization system, a slagging system, a lifting facility and an electrical control system. There are two types of sawing machines, mechanical and hydraulic, depending on the transmission. The sawing machine can be replaced and combined according to different specifications of the cutter bar, so that the slot width is 0.2-0.5m and the depth is 40m. The advantage of the saw-groove method and the construction equipment is continuous groove formation, high work efficiency and wall quality. Good, and deep into the wall, suitable for clay, sand and gravel stratum with a particle size of less than 100mm. Because the method has the characteristics of continuous groove formation, it can also be formed into a wall by using self-condensing mortar and solidifying mortar technology to form an anti-seepage wall with different strength and different impermeability indexes.
Five, special processing technology
1. If the guide wall is severely deformed or the bottom is collapsed, the following treatment methods should be adopted: (1) The damaged part should be rebuilt to guide the wall or other safe construction measures should be taken; (2) Improve the conditions of the ground level and the mud performance in the tank.
2. The ground layer is seriously leaking, and the plugging material should be quickly filled in. If necessary, the tank hole can be backfilled.
3. When the pipe is blocked, pulled out or leaked during concrete pouring, the following methods must be used: (1) Pull out the pipe completely, rinse it, and re-install it, and pump the mud in the pipe to continue pouring; (2) Before proceeding with pouring, the concrete surface elevation and the length of the pipe must be checked to confirm the safe insertion depth of the pipe.
4. When the steel cage floats during the concrete pouring process, the following measures shall be taken: (1) The depth of purchase of the conduit shall be adjusted in time and the rising speed of the concrete surface shall be appropriately reduced; (2) The cage shall be anchored or pressed.
5. In the event of quality accidents during concrete pouring, the following methods can be used for treatment: (1) cutting out the concrete that has been poured into the hole and re-casting; (2) subsidizing a new wall on the upstream side of the wall to be treated; 3) When the ground layer can be well irrigated, it is advisable to grout or high-pressure jet grouting on the upstream side of the wall section to be treated.
references:
[1] Ma Ming, Xu Zanyun, Wu Xueqin, Underground Continuous Wall Joint Form and Leakage Analysis 2008 No. 30
[2]Wang Weidong, Ruan Guoen, Huang Shaoming, Research and Application of Prefabricated Joint Technology for Underground Continuous Wall; Journal of Underground Space and Engineering; 2007, Issue 03
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