What are the technologies and methods for excavating rock slopes to green them? The following Zhongda Consulting Tendering Teacher will give you answers for your reference.
Rock slopes are very common slopes in highways, railways, water conservancy, mining and other projects. This kind of slope is generally steep and has no vegetation conditions. It is difficult to restore the original ecological balance by natural forces. Exposed rock slopes (rock slopes that have been supported by shotcrete anchors will be discussed specifically in future articles) will bring about a series of problems, such as damage to the food chain, deterioration of local microclimate (heat island effect in summer), roads, railways The rocky slopes along the line also cause visual pollution due to the gray and monotonous color of the slope surface. Taking engineering measures to cover the rocky slopes with green as soon as possible while ensuring the stability of the slopes is a need to reduce ecological deterioration and beautify the environment, and is also required by the Soil and Water Conservation Law. Japan carried out research on rock slope greening earlier and achieved good results. However, the project cost is generally very high and is not suitable for my country's national conditions. This article not only studies existing slope greening methods, but also puts forward its own opinions and applies these ideas to engineering practice. 1. Classification of excavated rock slopes and conventional greening methods 1.1 Classification of excavated rock slopes Rock slopes in projects are generally steep slopes with large inclination angles, with no or poor vegetation conditions. According to the reasons for the formation of the slope, they can be divided into Fill slopes and cut slopes. The greening of filled rock slopes will be discussed in a future article. This article only discusses the excavation slopes. Rock slopes are classified according to the properties related to slope protection and greening as follows: (1) According to the relationship between the structural surface and the inclination of the slope, it can be divided into three types: stable, unstable and dangerous. ⑵According to the groundwater activity on the slope, the slope can be divided into four categories: dry, wet, dripping, and spring. ⑶ According to the location of the slope, it can be divided into foot slope, middle slope and top slope. ⑷ According to the development of fracture surface cracks, slopes can be divided into complete slopes, relatively complete slopes, fractured slopes and broken slopes. ⑸According to the water resistance of slope rocks, slopes can be divided into water-stable slopes, water-soft slopes and water-soluble slopes. ⑹ According to the height of the slope, it is divided into high slope and low slope, and the classification standard is 10m. ⑺According to the orientation of the slope, it is divided into sunny slopes (facing south), shady slopes (facing east or west), and shady slopes (facing north). ⑻According to the slope slope, it can be divided into: less than 30° for gentle slope, 30°-45° for slope, and greater than 45° for steep slope. The above division is for local slopes. In engineering practice, a slope often has several slope types at the same time. 1.2 Conventional greening methods The difficult problem to be solved in excavation rock slope greening is how to fix the planting conditions on the steep slope, that is, the guest soil, which can provide water and fertilizer for the plants and can withstand wind and rain. Classification of conventional methods of greening excavation rock slopes: ⑴ According to different methods of fixing planting conditions, it can be divided into soil planting belt greening method, fiber greening method, and frame soil greening method. ⑵According to the different plants used, it can be divided into herbaceous plant greening, vine greening, grass-shrub mixed greening, and grass-flower mixed greening. The soil vegetation belt greening method refers to the artificial production of a belt of a certain width and thickness. Its cross-sectional structure is generally a protective net + waterproof fiber layer + (seeds, fertilizers, soil, improvers, water-retaining agents) + non-woven fabrics (from top down). During construction, the slope is first cleaned, then planting strips are laid at certain intervals, fixed on the slope with wires, etc., and finally a certain thickness of soil containing fertilizer is sprayed. Cover with non-woven fabric or film, and remove the plant seeds after they grow to cover the slope. (For soft slopes cocoa hanging net). The process is simple and low cost. However, it does not have the function of slope protection. The slope cannot withstand the erosion of heavy rain or long-term rainfall, nor can it withstand drought, and the greening effect is poor. The fiber greening method refers to a greening method in which fibers made from crushed plant straw, etc. are cemented with organic glue and sprayed onto the slope surface. This method has a certain slope protection function in the early stage and can withstand heavy rains. The disadvantage is that it is not drought-resistant and the cost is high. The frame-based soil greening method refers to first using prefabricated frames or using stone or concrete masonry frames on the slope, and then planting green plants in the soil inside the frames. Due to the small water-facing area of ??rock slopes, drainage ditches are generally not provided in mortar frames. To prevent rainwater from washing away the soil, it can be covered with straw mats. This method has low cost, simple process and good greening effect, but it has little protective effect on the slope and is only suitable for slopes with a slope less than 30°. 2. Vegetation concrete slope protection and greening technology and formula 2.1 Introduction to vegetation concrete slope protection and greening technology Vegetation concrete is a new technology that uses specific concrete formulas and seed formulas to protect and green rock slopes.
It is a comprehensive environmental protection technology integrating rock engineering mechanics, biology, soil science, fertilizer science, silicate chemistry, horticulture and environmental ecology. Vegetation concrete is based on the geographical location of the slope, slope angle, rock properties, greening requirements, etc. to determine the composition ratio of cement, soil, humus, water-retaining agent, concrete greening additive (patented technology of China Three Gorges University) and mixed greening seeds. Mixed greening seeds are selected from cool-season grass species and warm-season grass species based on biological growth characteristics. The specific method of vegetation concrete slope protection and greening technology is: first lay wire or plastic mesh on the rock mass, and fix it with anchors and anchor rods. The vegetation concrete raw materials are mixed and then sprayed onto the rock slope by conventional shotcrete equipment to form vegetation concrete with a thickness of nearly 10cm. After the spraying is completed, it is covered with a layer of non-woven fabric to protect against sunlight and moisture, and cement makes the vegetation concrete form a protective layer with a certain strength. After a period of watering and maintenance, the grass will cover the slope, and the non-woven fabric will be removed, and the dense grass will grow naturally. Vegetated concrete slope protection and greening technology can solve the problem of rock slope protection and greening once and for all. Therefore, we also call the selection of materials used in engineering greening technology and its functions as follows: The protective net can be made of plastic, iron wire, and steel bars. The mesh degree and material selection should be based on the protection requirements and characteristics of the slope. The function of the protective net is to protect the slope together with the anchor rods, and at the same time form the "skeleton" of the vegetation concrete, enhancing its integrity and preventing it from falling off the slope surface. The cementing material generally uses 425# cement, which makes the vegetation concrete mixture cohesive and gives the vegetation concrete strength. The planting soil is sandy loam, which has good water, nutrition, air, heat conditions and coordination capabilities, and is suitable for plant growth. In vegetation concrete, sandy loam is the main part and the "muscle" of vegetation concrete. Organic matter generally uses rice husks, sawdust, etc., and their use can also increase the fluidity of the concrete mixture and facilitate construction. In addition, after decaying, they provide nutrients such as nitrogen, phosphorus, and potassium to plants, and at the same time increase the void ratio of vegetation concrete. Humic substances are obtained from the decay of rice husks, sawdust and distiller's grains. It can improve the physical properties of vegetation concrete - coordinate water, gas, heat conditions and chemical properties - enhance fertilizer retention and buffering properties, and at the same time contribute to vegetation concrete. Introducing a large number of microorganisms into the plant to improve the physical properties of vegetation concrete - coordinating water, air, heat conditions and chemical properties - enhancing fertilizer retention and buffering properties, and working with plant roots, gradually transforming vegetation concrete into a plant suitable for plants The soil in which it grows. Long-term fertilizers are compound fertilizers that provide long-term effectiveness for plant growth. They generally use urea, biological fertilizers, and chemical compound fertilizers. Water-retaining agents absorb water when there is abundant water and provide water to plants when the weather is dry. Water-retaining agents with a particle size of 100 mesh are generally used. The concrete additive is a patented product of China Three Gorges University. Its main function is to create an environment for plant growth. The mixed greening seeds use cool-season grass species and warm-season grass species. The mixture is optimally formulated according to biological growth characteristics. 2.2 Formula of vegetation concrete The following factors need to be considered when determining the formula of vegetation concrete: ⑴ Ensure that the mixture has good cohesion and fluidity, that is, easy construction. ⑵ The unconfined compressive strength of vegetation concrete is not less than 15Kpa, that is, it can withstand wind and rain without falling off. ⑶ Vegetation concrete has appropriate bulk density and porosity. Specifically, the porosity is 50-65% (volume ratio), and the bulk density is 1.3-1.7g/cm?. This structure is conducive to plant growth. ⑷ Vegetation concrete has good planting conditions, such as a good supply of water and fertilizer, which can ensure the supply of nutrients for plants for many years. (Vegetation concrete can supply nutrients for a long time, and plants can also replenish themselves, such as dead leaves and grass roots rotting, bacterial nitrogen fixation, etc.) The total weight of cementing materials, plant soil, organic matter, and humus accounts for about 80% of the weight of vegetation concrete. Therefore, They determine the main properties of vegetated concrete. Cement is the decisive factor affecting strength and workability. Experiments show that when the cement dosage is greater than 10% (weight ratio, the same below), the unconfined compressive strength of vegetation concrete can be guaranteed to be no less than 15Kpa. The cement dosage generally does not exceed 25%. Organic matter and humus are collectively called organic matter. Their content has a significant impact on the physical properties of vegetation concrete, namely strength, bulk density, porosity, and water and fertilizer supply. The greater its content, the smaller the bulk density, the greater the porosity, and the lower the strength. Excessive organic matter content will cause the strength of the vegetation concrete to be smaller and the porosity to be too large, which is not conducive to retaining moisture. It will also reduce the cohesion of the mixture and increase the rebound loss during spray construction. Practice shows that the optimal 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 content cannot create the growth substrate required by plants.
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