Discussion on monitoring of soil and water conservation measures in expressway engineering?

The following is the related content of monitoring soil and water conservation measures of expressway project brought by Zhong Da Consulting for your reference.

As a pillar industry of national economy, expressway construction is developing rapidly all over the country. With the large-scale highway construction, the environment along the highway will be seriously affected, especially in ecological damage, soil erosion and other aspects, and its harm is often immeasurable. In order to master the dynamic changes of soil and water loss in the construction process, understand the implementation and prevention effects of various soil and water conservation measures, and rebuild the ecological environment around the expressway as soon as possible, soil and water conservation monitoring is particularly important. The monitoring results of soil and water conservation are the basis for judging the effectiveness of various soil and water conservation measures and the basis for project completion acceptance.

1 monitoring range and monitoring partition

The monitoring range is 1. 1

The soil erosion monitoring area of expressway project is the responsibility area of soil erosion prevention and control in engineering construction, including the project construction area and the directly affected area. Among them, the land occupation for engineering construction refers to the scope of land acquisition and land lease for engineering construction, including the permanent land occupation for the main project, the temporary land occupation for the main project, the land occupation for earth borrowing and mining, the land occupation for waste soil and slag, and the land occupation for the management service area; The directly affected area refers to the scope of soil erosion and its direct harm caused by development and construction activities outside the project construction area, mainly for resettlement and land occupation.

1.2 monitoring partition

Because of the different degrees and characteristics of soil erosion in disturbed areas, the soil and water conservation measures adopted are also different. According to the different types of ground disturbance, the monitoring scope of soil erosion in this project is divided into several monitoring areas, mainly including the main project monitoring area, the borrow site monitoring area, the waste residue site monitoring area, the management service land monitoring area and the construction temporary site monitoring area.

2 main monitoring contents of soil and water conservation measures for expressway projects

Soil and water conservation measures mainly include slope protection engineering, slag retaining engineering, drainage interception engineering, land remediation engineering, vegetation restoration engineering and temporary protection engineering. Mainly monitor the quantity, self-stability, operation of soil and water conservation protection projects and the benefits and effects of reducing water, sand and slag; Stability and landform restoration of slopes and other protected objects; Area and quality of cultivated land restoration.

2. 1 Monitoring of Slope Protection Project

In order to ensure the safety of subgrade engineering itself and beautify the environment, slope protection engineering is implemented at high and steep slopes. According to the different protection objects, construction techniques and protection purposes, slope protection projects have formed various forms of slope protection. At present, there are mainly the following types of expressway slope protection projects (the monitoring indicators of slope protection projects include slope protection projects and slope protection quantities).

2. 1. 1 turf slope protection. Turf paving is a common technology for slope protection and greening. It is to shovel the cultivated lawn with excellent growth and strong strength with a flat shovel or a plotter, transport it to the slope that needs greening, and replant it according to a certain size and specifications, so that the slope can quickly form a lawn. The production of turf can be divided into ordinary turf production and carpet turf production.

2. 1.2 Vegetation belt slope protection. Planting belt is a product with a certain scale made by using special machinery and equipment to plant grass seeds, fertilizers and water-retaining agents. It is made of natural degradable non-woven fabrics or other materials according to a certain density by machine rolling and needle punching.

2. 1.3 Three-dimensional vegetation net slope protection. Three-dimensional vegetation net, also known as soil consolidation net mat, is a three-dimensional structure net mat with a high modulus foundation layer at the bottom, which is made of thermoplastic resin and formed by extrusion, stretching and other processes. The basic layer of three-dimensional vegetation network consists of 1 ~ 3 layers of uniform square grid obtained by biaxial stretching.

2. 1.4 hydraulic spray seeding and grass planting for slope protection. This technology is to spray a mixture of grass seeds, wood fibers, water-retaining agents, adhesives, fertilizers and dyes. The construction of slope protection technology by planting grass is completed by spraying water on the slope surface with a special sprayer. Hydraulic spray seeding and grass planting slope protection is generally used for soil embankment and cutting slope, and soil-rock mixed slope can also be applied after treatment.

2. 1.5 Ecological vegetation bag biological slope protection. The biological protection technology of ecological vegetation bag is to attach selected plant seeds to the inside of degradable fiber woven bag through two layers of wood pulp paper. During construction, the nutrient soil is packed into vegetation bags, sealed and packaged according to the requirements of slope protection. After water conservation, the purpose of slope protection and greening can be realized.

2. 1.6 slope protection by filling soil and planting grass in reinforced concrete frame. Planting grass in reinforced concrete frame for slope protection refers to pouring reinforced concrete frame on the slope or laying prefabricated components on the slope to form a frame, backfilling miscellaneous soil in the frame and taking measures to fix the miscellaneous soil in the frame, and then planting grass in the frame to achieve the purpose of slope protection and greening.

2. 1.7 thick sprayed vegetation revetment substrate. Thick-layer substrate spraying vegetation slope protection is a kind of slope protection technology, in which the mixture of substrate and plant seeds is sprayed evenly on the engineering slope to be protected according to the designed thickness with a concrete sprayer. Its basic structure includes anchor rod, net and matrix mixture.

2.2 Monitoring content of slag retaining project

A large amount of soil and slag will be produced in expressway tunnels and high excavation sections. After the earthwork backfilling of the fill section is completed, the remaining slag will be discharged nearby. In order to prevent the loss of waste residue and affect the ecological environment, it is necessary to pile it in the designated place and build a slag retaining project. According to the position of waste slag, it can be divided into valley slag yard and non-valley slag yard. The valley slag yard is generally selected in ravines, hillsides and other places, and the slag retaining dam and wall are often selected as the forms of slag retaining. The slag retaining dam is suitable for the waste dump with a large amount of waste slag built in the ravine, and the slag retaining wall is located at the waste dump at the foot of the hillside. Slag retaining dikes are generally built in non-valley flat waste yards, and waste residue is enclosed in the dikes. The monitoring indicators of slag retaining engineering mainly include slag retaining engineering and slag retaining engineering quantity.

2.2. 1 slag dam.

(1) location of slag dam. Generally, it should be selected in a ravine near the slag source, which requires narrow terrain, large volume, gentle slope, good geological conditions, easy access to building materials, convenient construction, less soil erosion and sediment, less cultivated land and little impact on the surrounding environment. Gully catchment area should not be too large, which will not endanger the safety of downstream towns and roads.

(2) Drainage facilities of slag dam. After the completion of the slag dam, the original gully runoff outlet was cut off, and mountain torrents overflowed along the slag surface, destroying the slag body. Therefore, drainage works must be arranged. Drainage engineering forms are generally divided into two categories. One is culvert type, which is buried at the bottom of the ravine below the slag body, passes through the slag dam and connects with the river outlet ditch, and is suitable for slag storage with large catchment area and large design flood flow. The other is a drainage ditch, which is arranged at the intersection of the slag surface and the toe of the slope, and the outlet is at the dam head on both sides of the slag dam, and then communicates with the original river. It is suitable for slag storage with small catchment area and small design flood flow.

2.2.2 Slag retaining dike.

(1) Location of the slag dam. It should be selected at the toe of the slag slope on the beach or terrace not far from the slag source and with open terrain. It is required that the foundation condition is good, and it has the function of water retaining and flood control. It is suitable for the local spoil ground with less sand and gravel and less waste slag, and will not affect the flood control safety of downstream towns, villages and farmland.

(2) Slag stacking method of slag retaining dike. Generally, the slag has only one track, and the slope is related to the particle size of the slag, which is generally 1: 1.5 ~ 2.5, and the height of the slag pile should not be greater than 5m. In order to prevent rain from washing the slag surface and slope, drainage ditches are set on the slag surface and slope edge, and trees and grass are planted on the slag surface to prevent waste residue from running off.

2.3 Monitoring content of interception and drainage project

A complete drainage system is formed by setting drainage structures such as kerbs, shoulder chutes, longitudinal drains, rectangular side ditches, transverse drains and trapezoidal intercepting ditches. The main monitoring indicators of interception and drainage engineering are flood control engineering and flood control engineering quantity.

The water retaining kerbs are set on the earth shoulders with the height of filling more than 5m, and the road surface water is concentrated at the kerb opening and discharged into the drainage ditches or side ditches on both sides of the subgrade through the kerb rapids.

Longitudinal blind ditches are set in the central separation zone for embankment section and soil cutting section. Blind ditch is set below the top surface of subgrade, with longitudinal plastic drainage pipe inside. Generally, a horizontal drain pipe is set every 50cm to drain water.

Longitudinal drainage ditches are set for embankment sections with embankment slope height > > < 0.6m on both sides of the highway, and rectangular side ditches are set for cutting sections and embankment sections with embankment height < 0.6m.. ..

In the section above the cutting groove or where the low embankment and zero fill are connected with the subgrade, a intercepting ditch is set at 5m outside the groove to discharge the surface water outside the subgrade.

At the junction of intercepting ditch, side ditch, outlet of longitudinal drainage ditch and natural ditch, canal, river and pond, structures such as rapids, falling transition and stilling basin are used for protection.

2.4 Monitoring content of land consolidation projects

In the process of highway construction, due to excavation, dumping, temporary occupation and other activities, borrow yard, slag yard and spoil yard are formed. These occupied areas need to be backfilled, leveled and covered with soil to restore land productivity and become land for agriculture, forestry, fisheries and other industries. The main monitoring indicators of land consolidation are land consolidation projects (quantity) and land consolidation area.

The land restoration method of borrow site depends on the type of borrow site. According to the landform conditions, the borrow sites can be divided into three categories: hill borrow sites, hillside borrow sites and underground dig borrow sites. After taking the soil, the terrain of the borrow site is relatively flat. After the pit is backfilled, the ground can be further leveled, and the surface layer is covered with soil as agricultural land. At the same time, flood control and drainage facilities should be built around. After the hillside borrow yard is completed, the land remediation method can be arranged according to the specific conditions of the borrow yard. If the slope is steep, the land can be leveled and covered to develop forestry; After the slope is cut and released, if it meets the conditions of agricultural cultivation, land consolidation can be carried out according to the requirements of agricultural reclamation. For the land use recovery of underground digging pits, it can be converted into reservoirs or developed fishery breeding if conditions permit.

On the basis of the slag retaining project, the dump should be rectified after stopping the discharge. The flat slag yard is paved with a layer of clay to form an impermeable layer, and then covered with topsoil. As agricultural land, the soil thickness is generally 0.8 ~1m; For forestry, the soil thickness should exceed 0.5m.. According to the needs of reconstruction and utilization, gentle slopes with certain water conservancy conditions and slopes with good soil quality can be used as agricultural land. Slope land with large ground slope or poor soil quality should be used as land for agriculture, forestry and animal husbandry.

Most of the original land use types in the temporary construction area are cultivated land. Due to compaction, separation, excavation or trampling, the topsoil is destroyed, the natural ecosystem is disturbed by human beings, the ecological function is degraded, and soil erosion is serious. Therefore, after the completion of the highway, some ecological restoration measures for soil and water conservation must be implemented. After the completion of the main project, the temporary construction area should be demolished, and the hardened layer should be removed and stripped to restore the original land productivity of the site.

Land remediation is a link that is easily overlooked in expressway construction, but it is the key point of monitoring in soil and water conservation, because the object of land remediation is the most disturbed and damaged partition in project construction, and it is also the most difficult area for ecological restoration and reconstruction. If the ecological restoration is not carried out in time, it will have a negative impact on the ecological environment, water system and residents' life in the local and surrounding areas.

2.5 Monitoring content of vegetation restoration project

The monitoring of expressway vegetation restoration project can be divided into the following monitoring areas: central separation zone, roadside greening zone, interchange greening zone, management and protection service greening zone and spoil ground greening zone. The main monitoring indicators of vegetation restoration project include vegetation restoration project (quantity), green area, forest and grass coverage rate and vegetation restoration coefficient.

Sampling survey was carried out by standard plot method, and several standard plots were taken for observation, and the distribution, area, species and communities of forest and grass vegetation were recorded, and the indexes such as shading and coverage were calculated. Canopy projection method can be used for canopy, transect method for shrub coverage and grid method for grassland coverage. Vegetation growth and development should be carried out in three months after planting (maintenance period) and in spring and autumn every year, mainly to investigate the survival rate and preservation rate of vegetation within the scope of engineering prevention and control responsibility.

2.6 Monitoring of Temporary Protection Works

The excavation and filling of subgrade is large, and the construction period is long. During the construction process, single projects such as embankment, cutting, bridge foundation and tunnel entrance are eroded by raindrops and runoff, which is easy to cause soil erosion. Specific measures include: temporary grit chamber, geotextile fence, temporary water retaining weir, rapids, temporary flood drainage ditch and engineering slope protection. Temporary slag retaining wall is set on the slope at the connecting end of subgrade, and bagged soil slag or stone can be used. Cut off the tunnel before the tunnel construction.

Ditches and intercepting ditches are connected with surrounding flood drainage ditches to ensure smooth drainage. During the bridge construction, the earth and stone excavated for pier foundation are piled up at a higher position on the shore, and temporary measures such as covering ponchos are taken, which are used as backfilling materials for pier foundation after pouring. During the construction of the dry bridge, the earthwork excavated for the pier foundation will be piled up in a centralized way, and the surrounding area will be temporarily blocked with bagged soil slag, which will be used for backfilling after the pier foundation is poured, and the rest will be transported to a nearby slag yard for stacking, or used for leveling nearby low-lying land. In the protection zone of the construction sidewalk, because the construction sidewalk is an important channel for transporting soil materials, it bears a lot of traffic load and traffic volume, and it is easy to be damaged by precipitation and erosion. Therefore, the drainage measures in the construction of construction access roads are very important to prevent soil erosion. It is a common drainage measure to set up temporary drainage ditch at the end of high slope and grit chamber at low-lying place. The construction access road should be set according to the actual terrain and construction conditions. The access road is usually higher than the original ground and paved with gravel or crushed stone.

In the waste dump and waste dump prevention and control areas, reasonable arrangements should be made for the transfer of waste soil and waste soil, and transport vehicles should be covered with tarpaulins or take other measures to prevent scattering along the way to avoid man-made soil erosion. The waste residue should be compacted by layers in the process of accumulation, and the general compaction degree should reach 85%. Abandoning soil and slag should be blocked first and then discarded. In addition, the period of taking soil and abandoning soil is long. If it crosses the flood season, temporary flood discharge measures should be taken. The high gravel content in the waste dump is an important factor for the long-term waste of waste residue and the failure of vegetation restoration. The recovery of waste residue should consider improving the surface soil and restoring vegetation as soon as possible.

3 Conclusion

At present, the expressway construction in China is developing rapidly. According to the laws and regulations related to soil and water conservation, the monitoring work of expressway soil and water conservation has begun to be market-oriented. Expressway brings convenience and quickness to our work and life, but it also brings disaster and misfortune to our home. The development and introduction of soil and water conservation monitoring provide technical support and guarantee for the standardization construction of expressway construction. How to monitor soil and water conservation is the key to deal with expressway construction and ecological environment protection. Therefore, in highway construction, we should attach importance to soil and water conservation monitoring, actively explore the problems existing in soil and water conservation monitoring, restore vegetation as soon as possible, restore ecological balance, minimize the harm of soil erosion, make highway construction in China develop towards ecological roads, and finally realize the purpose of developing economy and benefiting mankind.

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