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. 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. 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.
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.
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