In the construction of water conservancy, highway, railway, mine and other construction projects, there are often a lot of excavations, which destroy the original vegetation, resulting in a large number of exposed soil slopes and rock slopes, leading to serious soil erosion and ecological environment imbalance. Such as soil erosion, landslide, debris flow, local microclimate deterioration, photoacoustic pollution, biological chain destruction and so on. It often takes a long time to restore the ecological balance of the slopes formed by these projects by relying on the power of nature itself. Soil slope can be restored in a short time by artificial protection and greening, but it is difficult to restore the original vegetation on rock slope. With the strengthening of China's economic strength and people's awareness of environmental protection, people pay more and more attention to the protection and research of ecological environment. The Soil and Water Conservation Law promulgated by the state also has explicit provisions on the protection of vegetation environment.
The United States, France, Canada, Australia and other developed countries pay more attention to environmental greening. Slope greening in Japan started relatively early, and their dominant idea in engineering construction is that construction and greening should be carried out simultaneously. Commonly used slope greening methods include reinforced concrete frame method, vegetation cover method, exotic soil vegetation belt method, fiber greening method, ecological porous concrete greening method, thick matrix spraying greening method and so on. Among them, the greening of rocky slopes can adopt the methods of alien soil planting belt, fiber greening, ecological porous concrete greening and thick substrate spraying greening. The same weakness of alien soil planting belt method, fiber greening method and thick substrate spraying greening method is that the strength is very low, and the alien soil planting belt method can only be used for gentle slopes. The disadvantages of fiber greening method and thick substrate spraying greening method are poor water retention and drought tolerance. Ecological porous concrete greening method has higher strength and better protection effect, but there are also two problems; The ability to provide nutrients for plants is poor, and the cost is too high. The cost of slope protection project is about 20,000-30,000 yen /m2. At present, there are few researches on slope protection greening in China, and most of them are limited to imitating and introducing foreign slope protection greening methods, such as alien soil planting belt method, ecological porous concrete greening method, fiber greening method and so on. Due to the superior geographical location, climatic conditions and adaptability to plant growth, these technologies are relatively successful in Japan. Most of China's inland areas are basically in arid climate, so it is an urgent task for engineers and technicians to research and develop a new environmental protection technology which is suitable for China's national conditions, has certain strength and rain erosion resistance, can adapt to plant growth for a long time and achieve the purpose of greening. In this paper, the application of the patented technology of Three Gorges University "Vegetation concrete slope protection greening technology" in high and steep rock slopes is studied.
2. Overview of engineering examples
The high-steep rock slope from the right shoulder of Gaobazhou Hydro-junction dam to the downstream Wangjiachong section is parallel to the downstream waterway and close to the ship lift. The bottom of the slope is 260m long, the highest point of the slope is 80m, the inclination angle is 70 ~ 80, and the area is 14000m2. The rock is limestone, thin and undeveloped. The slope strike is 40 and tends to the northwest. The rock surface is newly excavated rock. The high and steep rock slope is divided into a code track every 12m. The region has a subtropical climate, with an annual average rainfall of1200mm. The average temperature in the hottest month in July is 28.8℃, and the average temperature in the lowest month is 1.0℃. As shown in figure 1 (omitted).
3. Brief introduction of vegetation concrete slope protection greening technology
Vegetation concrete slope protection and greening technology is a new technology for protecting and greening rock slopes by using specific concrete formula and seed formula. It is a comprehensive environmental protection technology integrating rock engineering mechanics, biology, pedology, fertilizer science, silicate chemistry, horticulture and environmental ecology. Vegetation concrete is to determine the composition ratio of cement, soil, humus, water-retaining agent, concrete admixture (patented technology of Three Gorges University) and mixed green species according to the geographical position, slope angle, rock properties and greening requirements of the slope. Mixed sowing of green seeds is optimized by mixing cool-season grass seeds and warm-season grass seeds according to biological growth characteristics. The concrete method of vegetation concrete slope protection greening technology is: firstly, laying barbed wire or plastic net on the rock mass and fixing it with anchor nails and anchor rods. After the raw materials of vegetation concrete are mixed, they are sprayed on the rock slope with conventional anchor and shotcrete equipment to form vegetation concrete with a thickness of nearly 10cm. After spraying, it is covered with a layer of non-woven fabric, which is sun-proof and moisturizing. Cement makes the vegetation concrete form a protective layer with certain strength. After a period of water conservation, the grass will cover the slope, remove the non-woven fabric, and the dense grass will grow naturally. Vegetation concrete slope protection greening technology can solve the problem of rock slope protection greening once and for all. Therefore, we also call it engineering greening technology.
4. Application of vegetation concrete slope protection greening technology in Gaobazhou.
4. 1 Mixture ratio of vegetation concrete in Gaobazhou project
The vegetation concrete of Gaobazhou project consists of seven materials: cement, soil, humus, long-acting fertilizer, water-retaining agent, concrete admixture and mixed green seeds. Cement is a kind of consolidated material with strength to achieve the purpose of engineering protection, and 425# dam cement is generally used; Soil is the basic substance for plants to provide nutrients and store nutrients for a long time, and loam or sandy loam (sand content is less than 5%) is generally used; Humus is the basic substance that gives priority to providing nutrients for plants and creating space for the growth of plant roots. Generally, distiller's grains, sawdust and dried straw fibers are used. Long-acting fertilizer is a long-acting compound fertilizer for plant growth. Generally, urea, biological fertilizer and chemical compound fertilizer are used. Water-retaining agent absorbs water when the water is sufficient and provides water for plants when the weather is dry. Generally, water-retaining agent with particle size of 100 mesh is used. Concrete additive is a patented product of Three Gorges University Lvye Environmental Protection Engineering Co., Ltd., whose main function is to create a growing environment for plants. Mixed sowing of green seeds adopts cold-season grass seeds and warm-season grass seeds, and the mixed sowing is optimized according to the biological growth characteristics.
4.2.2 Spraying thickness of vegetation concrete
The thickness of vegetation concrete should meet the requirements of slope protection strength, rain erosion resistance and long-term plant growth. In order to meet these two requirements, considering that the high-steep rock slope in Wangjiachong section of Gaobazhou is a newly excavated rock surface, we design the spraying thickness of vegetation concrete to be 10cm, and spray it twice at base and surface. The spraying thickness of the base layer is 8cm, and the spraying thickness of the surface layer is 2cm. The mixed plant seeds are only mixed and sprayed on the surface layer.
4.2.3 Determination of mixed plant seeds
The rocky steep slope in Wangjiachong section of Gaobazhou is close to the dam head, which not only meets the requirements of evergreen seasons, but also meets the requirements of landscape design. Therefore, mixed green seeds can be divided into cool-season grass seeds and warm-season grass seeds, which are determined according to biological growth characteristics. Water-saving grass, ryegrass, Bermuda grass, Leymus chinensis and white clover are used.
4.2.4 Main construction machinery
(1) crusher; (2) mixer; (3) air compressor; (4) concrete sprayer; (5) elevators; (6) Hand pneumatic drill; (7) high-pressure water pump; (8) hanging basket.
Construction process flow
The main construction process is shown in Figure 2.
(1) Building gutter and drainage ditch. Around the slope and yard, the longitudinal drainage ditch of the slope is every 20 m. ..
(2) Clean and level the slope. Remove the silt and pumice on the slope, knock out the protruding rocks to make the slope as flat as possible, and then clean the slope with a high-pressure water gun to make the slope beneficial to the complete combination of vegetation concrete and rocks.
(3) laying a fixed composite net. The purpose of laying fixed composite net is to enhance the strength of slope protection and form reinforced vegetation concrete. Generally, 20mm steel bars are used for cross anchorage according to 1.5m× 1.5m, and the length of the anchor rod is 30-80cm.
(4) Mixing vegetation concrete. According to the size of the mixer, measure and mix according to the proportion of vegetation concrete. When spraying the mixture on the surface, add the mixed plant seeds.
(5) Spraying vegetation concrete. It is required that the nozzle of the spray gun is about 1m away from the rock surface, and the amount of water added should ensure that the vegetation concrete does not flow. Sub-base and surface secondary injection, in the process of base injection, attention should be paid to secondary leveling.
(6) Covering non-woven fabrics. After surface spraying, cover with 28g/m2 non-woven fabric to keep moisture, so as to create a rapid teething environment for seeds.
(7) Water spray curing. Vegetation concrete should be kept moist during curing. The water spraying equipment should use the nozzle to move and spray to prevent the high-pressure head from directly spraying water. The general curing period is about 50 days when plants cover the ground.
5, engineering protection and greening effect
5. 1 Plant growth and greening effect
After the spraying construction is completed, after 6 days of moisture preservation, the cold-season grass seeds in the mixed plant seeds have priority to teether, followed by other grass seeds. Due to the rational application of vegetation concrete formula, plants take root quickly and grow vigorously. Due to the reasonable combination of biological growth characteristics of mixed plant seeds, plant growth performs well in drought resistance and pest resistance. In 50 days, the green grass flattened and completely covered the rock slope. After that, it basically does not need manual maintenance and can grow naturally.
5.2 storm erosion resistance and slope protection ability
After the spraying construction is completed and maintained for 48 hours, the vegetation concrete will produce a certain strength. After 6 days, it will be able to withstand the rainstorm. Due to the control of the thickness and density of vegetation concrete, its impermeability is weak. Therefore, it is beneficial to the cementation between rock slope and vegetation concrete. After a year of wind, rain and sun exposure, no cracks and shedding were found in the vegetation concrete.
6. Conclusion
(1) Vegetation concrete slope protection and greening technology has been tested by many engineering applications, natural climate and plant growth cycle, which proves that the protective effect and greening effect of vegetation concrete on rock slope meet the design requirements, and the technology is encouraging.
(2) Rock slope greening is a new frontier discipline, involving rock mechanics, biology, soil science, fertilizer science, silicate chemistry, horticulture, environmental ecology and many other disciplines. This topic has just started in China, and there are few researchers engaged in this topic at present. There are still many work problems that need to be tested, studied and innovated.
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