Rock slope is a very common slope in highway, railway, water conservancy, mine and other projects. This kind of slope is generally steep, without planting conditions, and it is difficult to restore the original ecological balance by natural forces. Exposed rock slopes (rock slopes supported by shotcrete and bolts will be discussed in later articles) will bring a series of problems, such as the destruction of food chain, the deterioration of local microclimate (heat island effect in summer), and the rock slopes along highways and railways will also cause visual pollution because of the gray and monotonous color of the slope surface. Need to take engineering measures to put green clothes on rock slopes as soon as possible under the premise of ensuring slope stability, so as to reduce ecological deterioration and beautify the environment? Soil and water conservation law? It is necessary. Japan carried out earlier research on greening of rocky slopes and achieved good results, but the project cost is generally high, which is not suitable for China's national conditions. While studying the existing methods of slope greening, this paper puts forward its own views and applies them to engineering practice. 1 Classification of excavated rock slopes and conventional greening methods 1. 1 The rock slopes in the classification project of excavated rock slopes are generally steep slopes with large inclination, with no vegetation conditions or poor vegetation conditions. According to the causes of slope formation, it can be divided into fill slope and excavation slope. The greening of rockfill rock slope will be discussed in the following article, and this paper only discusses the excavation slope. According to the nature related to slope protection and greening, rock slopes are divided into: (1) According to the relationship between structural plane and slope inclination, they are divided into three types: stable, unstable and dangerous. ⑵ According to the groundwater activity on the slope, the slope is divided into four categories: dry, wet, dripping and spring. (3) According to the slope position, the slope can be divided into toe slope, middle slope and top slope. (4) According to the development of cracks, slopes can be divided into complete slopes, relatively complete slopes, broken slopes and broken slopes. 5] According to the water resistance of slope rocks, slopes can be divided into water-stable slopes, water-soft slopes and water-soluble slopes. [6] According to the slope height, it is divided into high slope and low slope, and the division standard is 10m. Once according to the direction of slope, it is divided into sunny slope (facing south), yin-yang slope (facing east or west) and shady slope (facing north). ⑻ According to the slope, it can be divided into: less than 30 is a gentle slope, 30-45 is a slope, and more than 45 is a steep slope. The above division is aimed at local slopes. In engineering practice, a slope often has multiple slope types at the same time. 1.2 The problem to be solved by conventional greening methods is how to fix the planting conditions on steep slopes, that is, exotic soil, to provide water and fertilizer for plants and resist wind and rain. Classification of conventional greening methods for excavated rock slopes: (1) According to different methods of fixed planting conditions, it can be divided into alien soil planting belt greening method, fiber greening method and frame alien soil greening method. ⑵ According to the different plants used, it can be divided into herb greening, vine greening, grass-irrigation mixed greening and grass-flower mixed greening. The greening method of exotic soil vegetation belt refers to the artificial production of a belt with a certain width and thickness, and its cross-sectional structure is generally protective net+waterproof fiber layer+(seeds, fertilizer, soil, improver, water-retaining agent)+non-woven fabric (from top to bottom). During construction, the slope is cleaned first, then planting belts are laid at regular intervals, fixed on the slope with iron wires, and finally the soil containing fertilizer with a certain thickness is sprayed. Cover with non-woven fabric or film, and remove the plant seeds after they grow on the covered slope. For soft slopes, you can hang a net. Simple process and low cost. But it doesn't have the function of slope protection, and the slope can't stand the erosion of heavy rain or long-term rainfall, nor can it stand the drought, so the greening effect is poor. Fiber greening method refers to the method of greening with fibers made of crushed plant straws, fertilizers, seeds, etc. Bonded with organic glue and sprayed on the slope. This method has a certain slope protection function in the early stage and can resist the attack of heavy rain. Disadvantages are no drought resistance and high cost. The frame soil greening method refers to first building a frame with prefabricated frames or stones and concrete on the slope, and then planting greening plants in the soil built in the frame. Because of the small water area of rock slope, there is generally no drainage ditch in mortar frame. In order to prevent the rain from washing away the soil, you can cover it with a grass curtain. This method has the advantages of low cost, simple process and good greening effect, but it has little protective effect on the slope and is only suitable for the slope with a slope less than 30. 2 Vegetation concrete slope protection and greening technology and formula 2. 1 Introduction of vegetation concrete slope protection and greening technology Vegetation concrete is a new technology for rock slope protection and greening with 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 greening additive (patented technology of Three Gorges University) and mixed greening seeds 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 sunscreen and moisturizing. Cement makes the vegetation concrete form a protective layer with a certain strength. After a period of water conservation, grass will cover the slope, remove non-woven fabrics, and 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 the selection and function of materials used in engineering greening technology: the protective net can be made of plastic, iron wire, steel bar and other materials, and the selection of mesh and materials should be based on the protection requirements and characteristics of slopes. The function of the protective net is to protect the slope together with the anchor, and at the same time form the "skeleton" of vegetation concrete, enhance its integrity and prevent it from falling off the slope. Cementing material, generally 425 cement, makes the vegetation concrete mixture cohesive and makes the vegetation concrete have strength. Sandy loam is selected as vegetation soil. Sandy loam has good water, nutrient, gas and heat conditions and coordination ability, and is suitable for plant growth. Sandy loam is the main body and "muscle" of vegetation concrete. Generally, rice husk and sawdust are used as organic matter, which can also increase the fluidity of concrete mixture and facilitate construction. In addition, after decay, it can provide nutrients such as nitrogen, phosphorus and potassium for plants and increase the porosity of vegetation concrete. Humus is made of rice husk, sawdust and distiller's grains by decay. It can improve the physical properties of vegetation concrete-coordinate water, gas, thermal conditions and chemical properties-and enhance its fertilizer retention and buffering performance. At the same time, a large number of microorganisms are introduced into vegetation concrete to improve the physical properties of vegetation concrete-to coordinate water, gas and thermal conditions and chemical properties-and to enhance its fertilizer conservation and cushioning properties. 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, whose main function is to create a growing environment for plants. Mixed green seeds are cold-season grass seeds and warm-season grass seeds, which are optimized according to biological growth characteristics. 2.2 Formula of Vegetation Concrete When determining the formula of vegetation concrete, the following factors should be considered: (1) Ensure that the mixture has good cohesiveness and fluidity, that is, it is easy to construct. (2) The unconfined compressive strength of vegetation concrete is not less than 15Kpa, that is, it can withstand wind and rain without falling off. (3) Vegetation concrete has suitable bulk density and porosity, specifically, the porosity is 50-65% (volume ratio) and the bulk density is 1.3- 1.7g/cm? Such a structure is beneficial to plant growth. (4) Vegetation concrete has good planting conditions, such as good water and fertilizer supply, which can ensure the nutrient supply of plants for many years. Vegetation concrete can supply nutrients for a long time, and plants can also supply themselves, such as dead leaves and grass roots rot, bacterial nitrogen fixation and so on. The total weight of cementitious materials, phytoliths, organic matter and humus accounts for about 80% of the weight of vegetation concrete, so they determine the main properties of vegetation concrete. Cement is the decisive factor affecting strength and workability. Experiments show that when the cement content is greater than 10% (weight ratio, the same below), the unconfined compressive strength of vegetation concrete can be guaranteed to be not less than 15Kpa. The dosage of cement generally does not exceed 25%. Organic matter and humus are collectively called organic matter, and their contents have great influence on the physical properties of vegetation concrete, namely strength, bulk density and porosity, water and fertilizer supply. The greater its content, the smaller its bulk density, the greater its porosity and the lower its strength. Too high content of organic matter will lead to too low strength and too high porosity of vegetation concrete, which is not conducive to moisture retention, and will also reduce the cohesiveness of the mixture and increase the rebound loss during spray construction. Practice shows that the optimum content of organic matter is 8- 16%. The content of concrete greening additives is generally not more than 2%. Too much content is not conducive to reducing costs, and too little can not create the growth substrate needed by plants. The formulation of concrete greening additives produced by Three Gorges University is scientific and reasonable. Many engineering practices show that its content is 1.0-2.0%, which can meet the needs of plants well. 3. Grasp the opportunity of unloading and greening of rock slope excavation. The excavation process of rock slope is essentially unloading process in mechanics. Especially for deep excavation of high slopes, the in-situ stress release is large, the unloading amount is large and the unloading range is wide. With the unloading, unloading cracks and unloading deformation appear on the slope, and the horizontal unloading deformation of some excavated slopes reaches the meter level, which can not be ignored. Based on the theory of rock mechanics, the method and timing of slope protection are determined, and displacement observation points are set on the excavated slope to observe the deformation trend of the slope, which provides the basis for determining the appropriate timing of slope support and greening. Furthermore, the excavation process of rock slope changes or destroys the original natural water and geogas circulation system, which will be aggravated with the increase of exposed rock exposure time. Therefore, it is very important for the protection quality and greening effect of rock slope to support while excavating. 4 Engineering practice Vegetation concrete greening method has the advantages of good protective performance, excellent greening effect and wide application scope. We have adopted this method in many projects, such as the rock slope of Shuibuya Project (15000m? , slope 73), the rock slope of Three Gorges Project (10000m? , slope 75), high rock slope of Gaobazhou Power Plant (12000m? Slope 80), etc. Taking the greening project of high rock slope in Gaobazhou Power Plant as an example, this paper introduces the application of vegetation concrete greening method in rock slope. 4. 1 Geological and climatic overview The high rock slope of Gaobazhou Power Plant is located from the right shoulder of the dam to the downstream Wangjiachong section, parallel to the downstream waterway and close to the ship lift. The bottom of the slope is 200m, the highest point of the slope is 80m, the dip angle is 70-80, the slope strike is 40, and the area is 12000m? Its safety and stability are directly related to the safety of navigation channels and dams. The rock strata exposed in this slope section are the first member of Heishigou Formation of Middle Cambrian, and the lithology is medium-thick argillaceous microcrystalline dolomite, limestone mixed with thin layer and very thin layer argillaceous microcrystalline dolomite, sandy microcrystalline dolomite, a small amount of oolitic limestone and siliceous rocks. Karst is undeveloped and is a relative aquifuge. The strike of the stratum is about 290, the dip angle is SW (inclined to the upstream of the right bank), and the dip angle is about 40. There is a fault in the middle of the slope, striking SN, dipping NW and dipping 80, which is filled with calcite and calcite cemented breccia. The structural cracks in the bedrock on the right bank of the dam are developed, with strike of 23-32, dip mainly NW, dip angle of 50-90, width of 3-8m, maximum width of 40m, length of10-30m-30m, and several meters, all of which are filled with calcite and well cemented. The structural fractures are all high dip tensile fractures, with the development interval of 0.4- 1.5m, the linear density of 5-8 lines /m, the maximum linear density of 3.2%-5%, and the surface fracture rate of 9.94%. Gaobazhou has a subtropical climate, with an annual average rainfall of 1200mm, the hottest average temperature of 28.8℃ in July, and the lowest monthly average temperature of 10 of 65438+3.0℃. Extreme climatic conditions are: extreme low temperature -9.8℃, extreme high temperature 42.0℃, and maximum daily rainfall of 300mm. 4.2 Selection of greening method According to the previous slope classification method, investigate the geological conditions of the slope. The high rocky slope of Gaobazhou Power Plant is a stable, dry and broken slope, and the surrounding rock is weakly alkaline, with locally soft argillaceous limestone and dolomite. Although there will be no large-scale landslide on the slope, rolling stones will be formed locally due to weathering. Considering the safety of navigation channel and dam, the slope must be protected. At the same time, Gaobazhou Power Plant has tourism value because of its elegant environment. Therefore, the slope needs greening. Based on the above factors, the greening mode of vegetation concrete is selected. 4.3 Vegetation concrete construction in winter. First, clean the slope, remove sundries, and drill holes on the slope with a hand-held pneumatic drill. The hole spacing is 800×800, the hole depth is 500, and the hole diameter is φ 18. Insert the rebar with a depth of 700, φ 12, and use the grouting machine to inject 1: 1 expansive cement slurry to fix the anchor rod. Fix Φ 6 barbed wire on the anchor rod with a spacing of 50×50. According to the weight ratio of12%: 74%:12%:12%:1%:1%,425# cement, plant soil, humus, long-acting fertilizer water-retaining agent and concrete greening additive are fully mixed to form.
Concrete greening additive is a patented product produced by Three Gorges University. The grass seed is a mixture of dog bud root, water-saving grass and Leymus chinensis, with the weight ratio of 20%: 60%: 20% and the dosage of 0.05kg per square meter. Organic matter and humus are distiller's grains, sawdust, rice husk and their products, and the planting soil is dry sandy loam. Vegetation concrete is sprayed in two layers by concrete spraying equipment, with the base layer thickness of 90 and the surface layer thickness of 10. Grass seeds are added when spraying on the surface layer, and covered with plastic film after spraying. Sprinkle water for one month and uncover the plastic film when the slope is covered with grass. Construction machinery and, 12m? Air compressor, 5m? /h concrete sprayer, 0.35m? Mixer, 5t dump truck. 4.4 Evaluation of greening effect: After 6 days of spraying construction on high rock slope of Gaobazhou Power Plant, grass seeds germinate and break ground. A month later, the grass covered 80% of the slope and grew happily. Two months later, the grassland was dense and lush, covering 65,438+000% of the slope. Then, after several heavy rains in spring and plum rains for 20 days in April and May, no vegetation concrete fell off the slope, which met the requirements of slope protection and greening. Conclusion 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. Although we have engaged in many engineering practices and gained some experience, we still need to make further quantitative research. Future research topics are: (1) cost research of different greening methods; Screening of greening plants; Establishment and restoration of slope ecosystem; Slope landscape planning; Determination of the best mix proportion of vegetation concrete greening method under different slope and climate conditions (from the aspects of workability of mixture, physical, chemical and biological characteristics of vegetation concrete, water and fertilizer characteristics of vegetation concrete, etc. We believe that there will be more breakthroughs in technology after in-depth research and practice.
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