1 analysis of seepage prevention and freezing damage of concrete channels
Concrete is composed of sand, stone, water, cement and other materials. These materials have certain water absorption and are in water environment for a long time. Under the condition of negative temperature, the volume of water will expand, and after repeated frost heaving, melting cycle and stress, it will eventually lead to freeze-thaw damage of concrete. Concrete (precast concrete slab) is a rigid material with high compressive strength, but low tensile strength and poor ability to adapt to tensile deformation or uneven deformation. Under the action of frost heaving force or thermal stress, it is easy to be destroyed, and its failure forms are summarized as follows. ① Bulging and cracks. In winter, the concrete slab and the foundation soil of the canal bed freeze into a whole, and bear the frost heaving force, frost heaving force and tensile stress caused by the shrinkage of the concrete slab itself. When these stress values are greater than the ultimate stress of concrete slab at low temperature, the slab will be destroyed. ② Overhead lifting. In the canal section with high groundwater level, the foundation soil of the canal bed is close to the groundwater, and the frost heaving amount is large, while the frost heaving amount of the canal top is small, resulting in a large floating overhead of the concrete lining board. This phenomenon generally occurs at the foot of the slope or 0.5 meters above the water surface, in the middle of the canal bottom. 3 collapse. There are two forms of freezing-thawing collapse of canal lining: first, due to frost heaving, the concrete slab is raised overhead, which destroys the support at the foot of the slope and loses the stable balance of the concrete slab cushion. Therefore, when the local foundation soil melts, the concrete slabs on it slide down the slope, and they are dislocated, infiltrated and overlapped. Secondly, the large-scale landslide during the melting period of the foundation soil of the canal slope led to the collapse of the canal slope, which led to the push of the concrete slab at the foot of the slope and the collapse and slip of the upper concrete slab. 2 concrete canal seepage control measures to prevent freezing injury
Whether the seepage control of concrete channel produces frost heaving damage depends on the water migration and frost heaving when the foundation soil is frozen. These effects are related to local soil quality, soil moisture content, negative temperature and engineering structure at that time. If measures are taken to eliminate or improve one of the factors, it is possible to prevent the frost heaving damage of concrete. However, the seepage control of concrete canals is mostly on cohesive soil, and the canal water is easy to replenish the foundation soil, so the concrete slab is light in weight and weak in frost heaving resistance. Some canal sections cannot avoid natural and man-made unfavorable conditions and are prone to freezing injury. In fact, it is difficult to achieve the goal of not frost heaving by taking a single measure. Practice has proved that comprehensive measures should be taken according to the specific conditions of the project to prevent the freezing injury of concrete channels. From the aspects of canal planning and layout, foundation soil treatment, drainage, thermal insulation, lining structure, materials, construction quality, management and maintenance, etc. Take appropriate anti-freezing measures. Some effective methods to prevent and control freezing injury in practice are introduced as follows.
2. 1 Avoiding frost heaving Avoiding frost heaving is to avoid the natural conditions with large frost heaving or the influence of frost heaving on the channel concrete in the frost heaving soil area in the planning and design of the concrete channel seepage control project. (1) Try to avoid cohesive soil, soft soil layer, muddy swamp and areas with high groundwater level, and choose areas with strong water permeability that are not easy to frost heave or areas with deep groundwater level. Control the frozen layer at the bottom of concrete channel above the recharge height of underground capillary water. ② Fill channels as far as possible. (3) The canal line is selected in the ridge zone with higher terrain. (4) in the canal section with leakage and ground backwater, drainage facilities should be set as far as possible. ⑤ Planning and arranging forest belts and all kinds of willows can improve the soil environment of canal bed foundation and help prevent freezing injury because of the well-developed roots of willows. 2.2 Reduce frost heaving When frost heaving accumulation or deformation occurs in the foundation soil of the canal bed under the repeated action of frost heaving and ablation, appropriate measures can be taken to reduce the maximum frost heaving amount of the foundation soil to the allowable displacement range of the concrete structure. ① replacement method. The method of replacing frost heaving soil under concrete slab with non-frost heaving materials such as Gobi and aeolian sand in freezing depth. Gobi and aeolian sand cushion will not produce frost heaving, but also can eliminate water seepage and prevent the lower water from migrating to the surface freezing zone. Therefore, replacing the cushion can effectively reduce frost heaving and prevent frost damage. In general, the content of clay impurities in the replacement Gobi and aeolian sand cushion should not be greater than 5%, especially when the replacement layer is frozen in saturated state, it must be ensured that there is a drainage outlet for the replacement layer during the freezing period. If the mud content of concrete slab joint leakage or lateral seepage is enough to pollute the replacement layer, a thin geotechnical protection layer should be set around the replacement layer. (2) heat preservation. Laying thermal insulation material behind the concrete slab lining can reduce or eliminate the cold, reduce the depth of replacement cushion and cut off the water supply of the lower soil, thus reducing or eliminating the freezing depth and frost heaving of the canal bed. With the development of chemical industry and new thermal insulation materials such as benzene board, it is widely used in the seepage control project of concrete channels in Xinjiang Corps, which has a good effect on reducing frost depth and frost heaving. This kind of thermal insulation material has the advantages of light weight, high strength, low water absorption, good thermal insulation performance and convenient transportation and construction. ③ Compaction method. It can increase the dry density of foundation soil, reduce porosity and weaken water permeability. When the compacted soil with high density freezes, it has the ability to hinder the migration and accumulation of water, thus reducing or even eliminating frost heaving. 3 concrete seepage control channel repair
3. 1 Repair of cracks in cast-in-place concrete seepage control channel When cracks appear in concrete seepage control channel, as long as the concrete surface is roughly flat and there is no big dislocation, if the joint width is small, the method of sticking vinyl perchloride adhesive coated glass fiber cloth can be used for repair. Larger channel cracks can be repaired by filling. (1) Remove the dirt and sundries in the seam, the seam wall and both sides of the seam to make it clean and dry. (2) Fill the joint with coal tar pitch or plastic and compact it to make the surface smooth.
3.2 Repair the masonry joints of precast concrete slabs in seepage control channels. Masonry joints of precast concrete slabs are mostly cement mortar joints, which are prone to cracks, falling blocks and other diseases. If it is not repaired in time, it will not only increase the leakage loss, but also gradually aggravate the disease and cause greater losses. The repair method is: chisel away the cement mortar block at the joint, flush the joint wall and joint, fill it with cement mortar with the same label as the concrete slab, tamp it and smooth it, and keep it moist for no less than 14 days.
3.3 Repair of surface damage of concrete seepage control board. Surface damage of concrete impervious plate, such as erosion and holes, can be repaired with cement slurry. First of all, all the damaged concrete must be removed, and the repaired parts should be chiseled and rinsed clean. Then, under the condition of keeping the working face moist, use a wood trowel to wipe the mortar on the repaired part, and then smooth it repeatedly, and then use an iron trowel to polish it, and keep it moist for no less than 14 days. When the depth of the repaired part is large, a proper amount of pebbles can be mixed into the cement mortar to reduce the drying shrinkage of the mortar and enhance its strength.
3.4 Repair of concrete impervious layer The concrete impervious layer is seriously damaged, such as fracture, dislocation, sliding and so on. The damaged part should be removed, the soil foundation should be better, and it should be filled again. When filling, special attention should be paid to the joint surface of new and old concrete. After the surface of the joint is chiseled and cleaned, a layer of cement slurry with a thickness of 1mm shall be painted before pouring concrete. Pay attention to the moisturizing and curing of filled concrete. The concrete removed in the decoration should be used as much as possible. For example, the usable part of the cast-in-place slab may not be removed. Prefabricated boards can be used, and should be reused as much as possible. Broken concrete can be made of stone or concrete aggregate.
3.5 During the operation of the seepage-proof channel, when there is a local breach or landslide in the emergency repair channel, the water supply should be stopped urgently or the water level should be lowered, and temporary treatment such as blocking sand with Gobi stones or geotextile bags should be carried out at the same time. After the running water ends, normal maintenance will be carried out. 4 conclusion
In recent years, in the design and construction of concrete seepage control projects of Qianjin Reservoir, Xiaohaizi Middle Main Canal, Inman Branch Canal, 48th Regiment, 50th Regiment and 53rd Regiment, in the comprehensive management of Tarim River Basin in Xinjiang, the supporting and water-saving reconstruction projects of large irrigation areas, technical safeguard measures such as replacing Gobi, aeolian sand cushion and adding benzene board insulation layer have been widely adopted. The concrete seepage control channel basically works well. It has played a role in saving water, improving the utilization rate of water resources, achieving remarkable anti-seepage effect and improving the natural environment.
For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd