1 Seepage prevention of water conservancy channels is very important.
The anti-seepage quality of water conservancy channels is directly related to the normal water delivery of channels and the full play of irrigation efficiency. The canal seepage control treatment can not only save water but also control groundwater. But also can reduce the dredging workload, save labor, and achieve the purposes of improving irrigation efficiency and increasing production and income. Therefore, the seepage control of water conservancy channel engineering is very important. Canal seepage control is the most widely used technical measure of water-saving irrigation project at present, which can greatly reduce the waste of agricultural irrigation water. After taking anti-seepage measures, the utilization rate of irrigation water can be improved, the contradiction between supply and demand of agricultural water can be alleviated, and the saved water can expand the irrigation area and further promote the development of agricultural production. It can reduce the occupied area of the canal, prevent the erosion, siltation and collapse of the canal, save the operation and management expenses, and be beneficial to the management of the irrigation area; It can reduce the groundwater level, prevent soil salinization, and is beneficial to the ecological environment and agricultural modernization.
2 Current problems in canal seepage control technology
Due to insufficient attention and less investment to canal seepage control engineering, the research on seepage control engineering has been affected. Until today, there are still many problems to be solved. At present, concrete and other anti-seepage materials are widely used in water conservancy channels in China, which have the advantages of good waterproof effect and fast water flow. But it is not frost-resistant, and it still needs to be improved in northern China. If it is not solved, it will greatly limit the development of canal seepage control engineering. In the aspect of seepage control, the composite use of various seepage control materials is the future development direction. How to combine the advantages and disadvantages of various materials well, organically combine materials with good anti-seepage performance and low cost, learn from each other's strengths and make up for each other's shortcomings, and obtain the greatest economic benefits.
3 Anti-seepage technology of water conservancy channels
Canal lining is the main content and goal of canal water conservancy project reconstruction. Therefore, the project plan is relatively concentrated, mainly the comparison and design of lining methods, including the form, thickness and superelevation of canal lining. The design and construction of lining is an extremely important link in the construction of farmland seepage control channels. Generally speaking, the design and construction of trapezoidal channel is the most important link in farmland water conservancy construction.
3. 1 Gravel cushion construction
After the sloping wall of cohesive soil in the channel is filled, the excavator roughly cuts the slope and manually carries out fine treatment. When processing, hang the line for leveling according to the design elevation. After the slope trimming is completed, the gravel cushion construction will be carried out after the acceptance. After the gravel is transported to the site, it is piled on the top of the dike and evenly spread on the slope from bottom to top. After the gravel paving is completed, rough slope cutting is carried out with backhoe, and then fine slope cutting is carried out manually. When manually repairing the slope, control piles are set at the toe, shoulder and slope respectively, and a row of piles are set along the river. These piles are connected by ropes, and the slope of the passage is divided into several small pieces. Sliding ropes are hung between ropes, and the cutting thickness is controlled by manually moving the sliding ropes, and the slope flatness is strictly controlled. After the slope is trimmed, it will be compacted with a flat vibrating rammer. In the process of compaction, the potholes will be filled up manually in time. Manual slope repair, manual slope repair only needs to control the elevation of slope top, slope elevation, flatness and excavation elevation of canal bottom according to the survey lofting sheet.
3.2 composite geomembrane laying
1) construction procedure
The construction procedure of geosynthetics is: leveling slope (bottom)-laying composite geomembrane-concrete pouring.
2) geosynthetics laying
Composite geomembrane is used as seepage prevention and reinforcement material for import and export channels, in which polyethylene geomembrane is used as the membrane; Wide polyester filament needle-punched geotextile is selected. The physical and mechanical design of composite geomembrane should meet the actual requirements of design. Before geosynthetics are laid, the foundation surface shall be inspected and accepted, and all the roots, weeds and sharp stones on the laid surface shall be removed, and the surface shall be smooth without unevenness and compacted. Geosynthetics shall be laid smoothly and moderately, and shall not be stretched too tightly. Geosynthetics should be pressed on the foundation and supporting layer to avoid overhead and eliminate bubbles to ensure safety.
3) Mechanical lining
Mechanical lining is an important link in channel construction, which ensures the service life of the channel. Before concrete pouring, adjust the slope ratio and elevation of the lining frame, and then pour after inspection. The concrete mixture is transported by the concrete mixer to the feed inlet of the distributor, and the distributor evenly scatters the concrete clinker on the lining surface. After paving is completed, the plug-in vibrator equipped with the cloth machine is started to vibrate and compact the concrete, and then the slurry is lifted, leveled and further compacted by the vibration molding machine. During the pouring process, a special person will be assigned to direct the scene, observe the paving situation, transmit information to the mechanical operators, and master the vibrating time and mechanical walking speed. Mechanical leveling and calendering shall be carried out in time after concrete cloth is vibrated. Close to the formwork and corners are the weak points of mechanical vibration, so manual plug-in vibrator and flat vibrator are needed for supplementary vibration. Artificial calendering should grasp the time to make the surface smooth and smooth.
3.3 Control of flatness and thickness
Generally, the smoothness is controlled from the manual slope repairing process, and then leveled with sand or fine sand when laying insulation board. The flatness control of concrete lining is the most difficult to control and the most prone to problems. After the concrete lining is completed for 20 minutes, the grinding work should be slowed down and the slope should be kept flat as far as possible. Uneven places should be leveled. If it is done by a polishing machine, it should be plastered by hand after completion. The thickness of concrete is directly related to the construction quality and project cost. Because the flow velocity in the irrigation canal is not too large, the design and construction should meet the actual requirements, mainly depending on whether there is underexcavation during slope excavation and the working condition of the lining machine. In the process of concrete construction, assign a special person to measure the thickness of concrete when paving. If the over-poured part is found, adjust the height of the lining machine within the required error range in time.
3.4 Construction treatment of water stop joint
In the design and construction of trapezoidal concrete lining, the design of channel water-stop joint is a crucial link, which is an isolation joint reserved by professional technology according to the specific design and construction requirements during the design and construction of channel lining. Isolation joints can effectively release the energy that causes the stress and deformation of the channel, and prevent random cracks from occurring in the channel due to the temperature change of the gas in the atmosphere or the defects of the foundation itself. In addition, the water stop can also reduce the leakage of the channel and enhance the anti-seepage function of the channel.
3.5 Quality Control of Water Conservancy Canal Seepage Prevention Project
The strength of concrete should be measured when it is used. Because of the discreteness of concrete, even if it reaches the standard, it may change qualitatively during construction, so it is necessary to measure the strength. The discreteness of concrete is mainly related to raw materials, and the variation of raw materials will directly lead to the decline of concrete strength. Therefore, the management of raw materials is very important, and there can be no unqualified raw materials and long-term storage. The procurement and storage of raw materials should be reported in time, and corresponding management schemes should be adopted to ensure the quality of raw materials and the strength of concrete.
Reduce harmful substances in concrete. These raw materials contain some harmful substances. If it exceeds the specified range, the hydration of raw materials will be reduced, and the strength of concrete prepared in the later stage will also be greatly reduced. Reducing harmful substances in raw materials can reduce the abnormal changes of concrete raw materials during hydration and prevent concrete from caking and uneven hardness. If there are loose particles in concrete, it is necessary to increase the water consumption, and some organic water must not be used for mixing, which will form salt frost on the surface of concrete. As for the raw materials of concrete, the strength of concrete is reduced due to the deterioration of raw material ratio, which is mainly affected by the change of water content and specific gravity of sand and gravel.
Strengthen the quality of concrete. The quality and discreteness of concrete have great influence on construction. The discreteness difference of concrete will lead to the decrease of concrete strength and low stability. The influence of concrete quality can not be ignored. The decline of concrete quality will lead to the change of concrete gradation, the viscosity and water absorption of newly prepared concrete are poor, and the strength of concrete can not be guaranteed. In order to ensure the quality of concrete, the management of raw materials must be done well in the early stage of construction, the quality of raw materials must be strictly controlled, and the technical indicators must be met.
4 abstract
So far, the seepage control project of water conservancy channels has achieved good results. The selection of anti-seepage materials and the treatment of poor soil quality involved in anti-seepage engineering affect the anti-seepage effect of the channel. It is an important task for canal seepage control of water conservancy projects to actively implement seepage control projects and reduce canal leakage.
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