Bijie Xiaoba-Songlinzhai Highway is 4.64km long, which is an urban road with a design speed of v = 60 km/h, with a total land requisition of 38.33hm2 and a drainage protection project of 25500m2 for demolished buildings * * * 4.376×104m3; Asphalt concrete pavement is adopted, * * * 7.73x104m2; * * * Bridges 14 10m/2, accounting for 30.39% of the total length of the line; Culvert13; There is no tunnel in this section; Separation interchange and plane intersection 1; The project investment is 536.68 million yuan, and the average cost per kilometer is115.66 million yuan; The construction period is 24 months, from April 20 1 1 year to April 201year. The area of responsibility for prevention and control of this project is 5 1.82hm2, of which the project construction area is 44.3hm2, and the directly affected area is 7.52hm2 The earthwork volume of the project excavation is 99× 104m3, the backfill earthwork volume is104.3x104m3, and the borrower is 5.3x.. The project area is dominated by Zhongshan landform. The climate type is subtropical humid monsoon climate, with an average annual rainfall of 954mm and an average annual temperature of 12.8℃. The forest and grass coverage rate in the project area is about 40%.
2 Overview of soil erosion and soil and water conservation of highway engineering projects
2. 1 Division of key prevention and control areas of soil erosion
The project area belongs to the middle and upper reaches of Chishui River in Wujiang River, which is a national key governance area and a provincial key governance area and key supervision area announced by Guizhou Provincial People's Government. This area is dominated by hydraulic erosion and belongs to moderate erosion area. According to relevant regulations, the prevention and control standard of soil erosion in this project shall be the first-class standard.
2.2 Prediction results of soil erosion
During the construction period, the original vegetation and landforms are destroyed or buried in the construction links such as engineering excavation, land occupation, construction site, construction road, temporary storage yard and spoil yard layout, which will damage the original water and soil conservation facilities to varying degrees and may reduce their water and soil conservation functions. Construction excavation, filling and other work are mainly concentrated in the construction period, which will disturb the original surface vegetation, ground composition and topography, make the surface bare, and lose the anti-corrosion and soil consolidation ability of the original vegetation. It also destroys its natural stability, and may cause erosion and collapse, increasing new soil erosion. The original landform will be affected. The damaged area is 44.3hm2, the damaged soil and water conservation facilities are 44.3hm2, the original surface soil and water loss is 4,799 t, the predicted soil and water loss is 879 1t, and the new soil and water loss is 3992t t. According to the feasibility study report, the earthwork volume of the project construction is 99×104m3. The backfill earthwork volume is104.3x104m3.
2.3 scope of responsibility for prevention and control of soil erosion
The total area of responsibility for prevention and control of soil erosion in this project is 5 1.82hm2, of which the construction area is 44.3hm2, and the directly affected area is 7.52hm2 According to the jurisdiction, Bijie section is 30.33hm2, and Dafang section is 21.49hm2.: According to the nature of land occupation, it covers an area of 38.3hm2 permanently and 6hm2 temporarily, and the affected area covers an area of 7.52hm2.
2.4 Soil and water conservation measures
Soil and water conservation measures designed in the scheme: the length of drainage ditch is 4640m, and the slope protection is 81100m2; 3 intercepting ditches and 3 grit chambers; Greening 3230m, planting grass and slope protection 3 places; Tree planting 12000 plants; Stripped topsoil1.562×104m3; Set up 5 temporary bagged soil retaining walls and 9 temporary drainage ditches.
3 Analysis of soil and water conservation measures
3. 1 engineering measures
It is necessary to stop soil erosion in the prevention and control areas, reduce gravity erosion and most hydraulic erosion, and control soil erosion; The drainage in the prevention and control area is smooth, which can reduce soil erosion caused by hydraulic erosion; In order to improve the surface, slope, slope and drainage facilities in the prevention and control area to meet the basic conditions of vegetation restoration.
3. 1.65438+ The cross section of the drainage ditch is trapezoidal, lined with M7.5 mortar rubble with a thickness of 30cm, and a gravel cushion with a thickness of 10cm is laid under the ditch. Through calculation, the bottom of the drain ditch in the construction site and temporary dump is 30cm wide and 40cm deep, with a slope ratio of 1∶0.6, a slope ratio of 5‰ and a water volume of 0.19m3/s; The bottom of the soil yard and waste residue intercepting ditch is 50 cm wide and 50 cm deep. Slope ratio 1: 1.0, slope ratio of ditch bottom is 8‰, and water quantity is 0.54m3/s. ..
3. 1.2 The principle of "stop before discarding" should be followed when discarding slag. Before the slag is abandoned, a M7.5 masonry retaining wall with a height of 200cm, a top width of 100cm, a foundation buried depth of 0.5m, an outer slope of 1: 0.20, and an inner slope of vertical is set downstream. The retaining wall is provided with drainage holes, with a distance of 0.5m from the ground, a distance of 2m and an aperture DN 10 (φ 100 mm), and the upstream side of the drainage holes is provided with a filter layer. Slag piling on the back of the wall: firstly pile the slag to the top elevation of the retaining wall to form a platform, and then pile the slag with a slope of 1∶2.0.
3. 1.3 grit chambers shall be arranged at the outlet of the drainage ditch connected with the water system in the construction site and the dump to prevent the sediment from flowing out of the site. The grit chamber adopts a rectangular structure, with a length of 4m, a width of 2m and a depth of1.5m. It is lined with M7.5 mortar masonry, and the bottom lining of the chamber is 30cm thick. The surrounding lining adopts trapezoidal section, with a top thickness of 30cm and a bottom thickness of 67.5cm, and an external slope ratio of 1: 0.25.
3. 1.4 temporary drainage and retaining measures should be strengthened when filling temporary subgrade to prevent soil erosion from affecting surrounding farmland. Before embankment filling construction, water retaining ridges and drains should be built on both sides of embankment slope bottom to intercept soil erosion caused by precipitation. Clay should be selected for the ridge as far as possible. The cross-sectional dimensions of the ridge are: height 0.3m, top width 0.3m, bottom width 0.75m and slope 1∶0.75. Lay colored strips on the ridges and drains to prevent rain erosion and water erosion. Figure 1 is a schematic cross-sectional view of the temporary drainage ditch.
3.2 Factory measures
According to the principle of "suitable for the ground and suitable for the trees", select excellent native tree species and grass species, or introduce tree species and grass species that have adapted to the local environment after years of planting, adjust measures to local conditions, highlight key points, improve standards and make overall arrangements. Choose tree species that are barren-resistant, sand-resistant, strong in soil fixation and easy to manage, and grass species that are easy to propagate, well-developed in root system and strong in stress resistance. Combined with engineering measures, trees, shrubs and grass are reasonably matched, needles and broad-leaved trees are organically combined, and greening and beautification are unified, which is in harmony with the vegetation and environment around the project area and has good landscape effect, so as to restore damaged plants as soon as possible and improve the surrounding ecological environment.
3.2. 1 Afforestation According to local natural conditions, greening purposes and protection objectives, the selected plant measures should not only consider the function of soil and water conservation, but also take into account the requirements of greening and beautification, so the tree species are mainly suitable for local fast-growing and barren-tolerant trees. Schima superba and Lespedeza are mixed in the woodland and unused land in the original land use types of construction site, construction road, temporary spoil ground and waste residue yard, with plant spacing 1.5m× 1.5m, soil preparation, Schima superba aperture, aperture depth of 0.5m, Lespedeza aperture, aperture depth of 0.3m .. seedling size requires DBH 3cm and seedling height/. Planting in spring, soil preparation and planting, applying compound fertilizer 0. 1kg/ plant as base fertilizer before planting, and planting after ploughing. Before planting, the seedlings should be pruned and soaked, and the roots should be stretched and practical when put into the hole. After planting, strengthen tending management, loosen soil and weed, control pests and diseases, and ensure the survival rate of planted seedlings and grass. After one year, check the growth of seedlings and find that dead plants should be removed in time and replanted with seedlings of the same age.
3.2.2 After planting trees, Bermuda grass seeds should be planted on the ground in the grass planting construction site, construction road, temporary dump and muck yard, so as to achieve the functions of consolidating soil, greening, beautifying and preventing heavy rain from washing away the exposed surface. Sowing density 150kg/hm2, slightly covered with thin soil, and applying 225~300kg of phosphate fertilizer and potash fertilizer as base fertilizer per hectare. The seedlings and seeds used in the plant measures for soil and water conservation in this scheme require first-class seedlings and first-class species, and must have "one sign and three certificates", that is, labels, business licenses, certificates of conformity and quarantine certificates. There is a large amount of rainfall in the project area, and the natural rainfall can basically meet the needs of forest and grass growth and restoration. During the restoration of forest and grass vegetation, in areas where human activities and plant measures are carried out, billboards should be set up in areas where forests and grass are planted or planting boundaries should be simply enclosed to avoid being trampled by pedestrians.
3.3 Soil and Water Conservation Monitoring
The main monitoring contents of this project include the changes of soil erosion, vegetation factors and other soil erosion factors, such as road engineering, construction sites, construction roads, temporary storage yards and garbage dumps. The key monitoring points are excavation and fill slope, and these parts should also be monitored in typical areas and areas where soil erosion is most likely to occur. In key monitoring areas, monitoring methods such as setting up runoff plot, establishing observation plot, collecting sediment in grit chamber and piling can be adopted to measure the amount of hydraulic erosion, and pay close attention to the dynamics of soil erosion in key areas in combination with on-site inspection. At the same time, strengthen the investigation and inspection of other areas, and predict the possible soil erosion and its harm according to the construction progress of the main project, so as to take targeted control measures for each part, effectively control soil erosion and protect and beautify the ecological environment. According to the prediction results, the amount of soil erosion generated during the project construction period is the largest, and the monitoring period of soil and water conservation is two years. The key period of monitoring is the construction period, and the key period of annual monitoring is the rainy season. The monitoring section in each period should be inspected according to the construction situation, and the monitoring equipment in each area should be inspected before the rainy season to ensure the smooth monitoring.
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