Highway slope protection safety and ecological beautification?

With the changes in people's concepts of environmental protection and traffic safety, the design and construction of highway slope protection has attracted more and more people's attention. To ensure the stability and safety of highway slopes and protect the environment, it is necessary to Strengthen comprehensive research on highway slope protection. The design of highway protection projects should closely grasp the geological, hydrological, climatic and other characteristics of the design object, flexibly adopt different protection types, and increase the greening area of ??vegetation while ensuring the stability and safety of highway slopes, so as to build ecological highways. A good foundation has been laid to make the main body of the highway both safe and environmentally friendly. The following is a brief introduction to the common protection forms of highway slopes:

1. Main types and mechanisms of slope damage

1. Highway lower slope: The lower slope of the roadbed is generally filled Dirt embankment. The damage to a stable embankment slope mainly manifests itself as erosion of the slope surface and slope toe. Slope erosion mainly comes from the direct erosion of the slope by atmospheric precipitation and the erosion of the slope runoff, causing the roadbed slope to form gullies along the direction of the slope flow. The continuous development of the gullies leads to the destruction of the roadbed; embankments along the river and those built on the river beach The embankments in the flood detention area are also threatened by floods. This threat is manifested in the erosion of the embankment foot and the damage to the slope.

Slope damage is also related to the nature of the subgrade filler, the height of the subgrade slope, and the degree of compaction of the subgrade. Generally speaking, sandy soil slopes are more susceptible to erosion and damage than clay soil slopes. Higher subgrade slopes are more susceptible to erosion by running water than lower subgrade slopes. Slopes with better compaction are more susceptible to erosion than lower subgrade slopes. Less compacted slopes are resistant to erosion.

2. The upper slope of the highway

The upper slope is a manually excavated slope, and its strength should meet the requirements for a stable slope. Such a stable slope will be affected by rainfall, snowmelt, and frost heaving. , and other forms of weathering, the main damage forms of slopes are erosion, collapse, etc.

Scouring damage generally occurs on gentle soil slopes, such as sandy soil slopes, loess slopes, loess slopes, etc. Under the action of atmospheric precipitation, many slopes are formed along the runoff direction. Small gullies, if no protective measures are taken, tend to expand year by year; at the foot of the slope, snow often occurs in winter, causing the foot of the slope to become soft and soft, reducing the strength, and the upper soil loses support, causing damage; at the same time, high-speed The rain and snow water splashed by the moving cars also washed away at the foot of the slope. In short, the foot of a soil slope is the weakest link of the slope.

Slope collapses are generally divided into three categories: rockfall type, landslide type, and flow type. Sometimes, these three forms may appear simultaneously in one collapse.

Rockfall type generally refers to steep rock slopes. The rock formations prone to rockfall must have cracks developed under the influence of joints, bedding, or faults, and are divided into weak fault blocks by crack surfaces of different sizes. , these crack surfaces are wide, smooth, and directional. Rockfalls and rock slides tend to occur along steep crack surfaces. The extent of the opening of the cracks may not be identifiable with the naked eye, but water can seep in. Due to repeated freezing and thawing, and long-term micro-movement, the cracks gradually expand. Due to rainfall, the cracks are filled with water, which generates lateral hydrostatic pressure and causes collapse. Generally, rock masses with developed fissures are more prone to rockfall. In addition, this phenomenon can also occur when hard rock lies beneath a weak layer. This type of damage must be strictly controlled, as falling rocks can easily pose a threat to driving.

Landslide collapse means that the rock layer is sheared under the action of external force and slides along the soft rock between layers. It mostly occurs in rock masses that tend to be on the roadbed and have weak interlayers between layers. In addition, when the bedrock is overlain by loose accumulations such as debris layers and rock piles, the accumulations are prone to collapse along the bedding planes, joint planes or fault planes of the rock formations.

Collapses during heavy rains are mostly of the flowing type. Loose sedimentary soils such as sand, rock debris, shale weathered soil, etc. are often affected by water and produce flowing collapses. There is no obvious shear in the flowing collapses. Sliding surface.

Obviously, when the slope height is large, the above types of slope failure are more likely to occur on lower slopes.

From the above analysis, it can be seen that in the slope protection design, it is necessary to do a good job in slope protection design, drainage and waterproof design, and water control issues, and also according to the geological conditions, rock mass properties, and rock strata. The shape and height of the slope should be carefully designed for the slope surface.

Second, protective measures are required

Currently, the highways in Hebei Province mainly have the following protective measures:

1. Plant protection

The use of plant protection is to use vegetation to cover slopes and plant roots to reinforce slopes to protect roadbed slopes from erosion by atmospheric precipitation and surface runoff.

Using plant protection to increase the vegetation area and reduce surface runoff can fundamentally reduce soil and water loss in the roadbed. Plant coverage has a great slowing effect on surface runoff and soil erosion. The leafy canopy can intercept part of the precipitation, and the huge root system can directly absorb and store part of the water, and can also stabilize the surface soil. In places without vegetation coverage, all precipitation falls on the ground surface, forming runoff, causing water and soil erosion and erosion. The root system of vegetation can be closely combined with the soil layer. The intertwined root system and root system make the surface soil form a strong stable layer with different depths, thereby effectively stabilizing the soil layer, fixing the ditch slope, blocking erosion and collapse, and having mechanical protection. Protective effect.

In the warm and rainy southern region of my country, plant protection has been widely used in the protection of upper and lower soil slopes, which not only protects the slopes, but also beautifies the environment. In the northern region, plant protection measures are limited to the protection of lower slopes. Upper slopes are often dry and short of water, making it difficult to maintain. Moreover, the steep slope is not conducive to plant growth. In the northwest loess area, loess road cutting slopes are often steeper than 1:0.75, and slow down to 1:1 when the slope is higher. In Hebei, the slope of soil slopes is generally 1:1, and natural precipitation on the slope is often used to maintain plant growth. It is more difficult because the slope is steep, water is difficult to maintain, and the vegetation survival rate is low.

In recent years, many greening experts have tried to protect the greening of highways on steep upper slopes in the north, using measures such as three-dimensional geonets, but they have not been widely promoted on highways. Therefore, the issue of plant protection on upper slopes still needs further research to cover the bare upper slopes in the northern region with green clothing.

Plant protection includes planting grass, turf, and trees on slopes. In Hebei, due to the lack of turf for digging in general areas, it is more convenient to plant grass and trees. Generally, perennial, cold-resistant, drought-tolerant grass species with well-developed root systems are selected for grass planting, and tree species (including shrubs) that are easy to survive are preferred for tree planting.

Rye and crown flower are both cold- and drought-tolerant plants. The joint planting technology of rye and small crown flower has been successful in some colder and arid areas in the north, and is more suitable for the climatic conditions in the north. Rye grows quickly and can be established in the same year, but its roots are shallow and suitable for short-term protection; crown flower grows slowly and can only mature after a year, but its roots are deep and is especially drought-resistant, and its ability to spread and reproduce is strong. It is suitable for long-term protection of roadbed slopes. The combination of the two can achieve the purpose of combining short-term protection and long-term protection.

In terms of tree planting, Hebei Province has gained a lot of valuable experience in planting Amorpha purpurea on the slopes of many highways over the years, such as the Beijing-Shijiazhuang Expressway, the Tangshan Section of the Daqin Railway, and the Shihuang Expressway. etc., have all adopted this protective measure and achieved success, not only protecting the slopes, but also beautifying and greening the highway.

2. Frame protection

Frame protection uses concrete, mortar blocks (flakes) and other materials to form a skeleton on the slope, which can effectively prevent the roadbed slope. Gullies are formed under the erosion of water on the slope surface. At the same time, the surface roughness coefficient of the slope surface is increased and the water flow speed is slowed down. Generally, scour is limited to a local area within the frame. The method of combining frame protection with grass protection improves the protection effect and beautifies the environment at the same time.

Frame protection is mostly used on the lower slope of the roadbed. It is an auxiliary protective measure. In addition to having a certain protective effect on the roadbed slope, it also has a beautifying effect on the road surface, especially at interchanges. Slopes are the most widely used within the scope. In recent years, people have paid more and more attention to the impact of highways on the environment and the beautification of road appearance, so this form of protection is often used.

The shape of the frame can be made into various shapes according to people's imagination and people's pursuit of beauty, such as large frames with an angle of 45 degrees, hexagonal concrete prefabricated block protection, and mortared stone arches. Protection, wheat ear type made of mortar rubble or prefabricated blocks, etc.

Some sections of the Shanghai-Nanjing Expressway and the lower slope of the Guiyang-Huangguoshu Expressway, which is about to be completed and opened to traffic, use mortar masonry arch protection. Some sections of the lower slope of the Beijing Badaling Expressway adopt large 45-degree frames. The small frames with hexagonal concrete prefabricated blocks inside the grid and the wheat ear-shaped sections of the Shihuang Expressway in Hebei Province all give people a beautiful enjoyment.

Frame protection measures can also be used to protect the upper slope of the soil, which not only increases the aesthetic effect, but also prevents the slope from being eroded. However, since the frames need to be slotted into the upper slope, the construction is difficult. It is only used in important scenic spots and is generally rarely used.

3. Slope protection

Pave (mortar or dry) rubble, rubble or concrete prefabricated blocks on a stable slope to prevent surface runoff or slope water from flowing against it. The erosion of the slope is called slope protection. The paving method generally adopts mortar paving. When the erosion is slight, dry paving can be used.

Subgrades located in riverbanks or flood detention areas are often under direct threat from floods. Therefore, slope protection measures must be adopted. The protection height should be at least 0.5 of the subgrade design flood level plus wave height, backwater height and 0.5 meters above the safe value. In addition, when the roadbed is along the stream and the roadbed slope encroaches on the river, slope protection measures must also be taken.

For embankment slope protection on soft soil foundation, when there is no impact of water erosion, dry-laid rubble slope protection can be used to adapt to the deformation of the embankment slope caused by foundation settlement.

4. Cover

Cover includes protective forms such as plastering, hammering, spray grouting, and shotcrete.

1) Due to their short service life, surface wiping protection and surface beating protection are rarely used on highways of all grades, especially on the slopes of highways. The author believes that when When the roadbed is low, plastering is used for protection and reasonable mixing of grass seeds can not only play a protective role in the early stage of construction, but also play a protective and greening role during the operation period. It can be tried in future construction.

2), Shotcrete protection and shotcrete protection

Shotcrete protection and shotcrete protection are suitable for rock edges where the slope is prone to weathering, cracks and joints are developed, and the slope is uneven. The main function of the slope is to seal the cracks in the slope rocks to prevent the intrusion of atmospheric precipitation and slope water, thereby preventing lateral water pressure and ice cracking in the cracks, preventing the slope rocks from continuing to weather, and protecting the slope from rockfall collapse.

The cover protection measure widely used on highways is shotcrete. This protection requires setting up a diamond-shaped metal mesh or high-strength polymer geogrid within the concrete and fixing it to the slope through anchor rods or anchor piers. This is mainly to prevent concrete from hardening and shrinking to cause cracks or spalling. The treatment of rock slopes with fissures on the Shitai Expressway in Hebei Province and the Taijiu Expressway in Shanxi Province has been very effective. In particular, it has been very successful in treating altered andesite slopes in Hebei Province. After treatment, rockfalls and collapses no longer occur. However, when shotcrete was used for protection on a certain section of the slope, spalling also occurred. The rock mass is fully weathered limestone, and the new shotcrete does not combine well with it, the contact is uneven, and the local strength is very low. In addition, the shotcrete does not have a metal mesh or geogrid, and the integrity is not good, thus creating a double connection between the interior and the outside. Under the action of factors, local peeling occurs.

Therefore, before construction of shotcrete protection, there should be no weathered debris and weathered soil on the slope surface; shotcrete protection measures should not be used for fully weathered rocks; in order to prevent cracks or spalling from the hardening and shrinkage of shotcrete , it is necessary to add anti-cracking metal mesh or high-strength polymer geogrid. When the rock mass has the potential risk of sliding along the rock layer inclined to the road surface, anchoring measures with shear anchors should also be taken.

5. Protective walls

In order to cover the excavation slopes of various soft rock formations and relatively broken rocks, as well as the soil slopes that are prone to erosion, they are designed to protect them from the influence of the atmosphere. The wall built is called a protective wall.

Retaining walls are mostly used for easily weathered mica schist, chlorite schist, argillaceous limestone, phyllite and other severely weathered soft rock formations and relatively broken rock sections to prevent continued weathering. It can effectively prevent slope erosion and prevent sliding, flowing and rockfall slope collapse. It is the most common protection type for upper slopes.

Except for its own weight, the protective wall does not bear other loads, nor does it bear the soil pressure behind the wall. Therefore, the slope of the excavation slope protected by the protective wall should meet the requirements of the ultimate stable slope.

The protective walls include solid protective walls, window-type protective walls, arched protective walls, etc. The solid protective wall is used for general soil and broken rock slopes; the hole-window type protective wall is used for slopes with a gentler slope than 1:0.75, and the hole window can be hammered (when the slope is dry) or dry-laying rubble; arch Type protective wall is used when the rock formation at the lower part of the slope is relatively complete and the upper slope needs to be protected. The slope of the excavation protected by a protective wall should not be steeper than 1:0.5.

In order to enhance the stability of the protective wall, when the protective wall is high, it should be built in stages. Depending on the quality of the bedrock on the cross-section, every 6 to 10 meters high will be regarded as a grade, and the level of the wall should be A platform of ≥1 meter is installed on the top; an ear wall is set up every 4 to 6 meters high on the back of the wall, and the ear wall is 0.5 to 1 meter wide.

The top of the protective wall should be compacted or paved with original soil to prevent water from the slope from being washed away and causing damage after penetrating into the wall. Before building a protective wall, loose rocks and loose soil should be removed from the protected slope. For slopes with rapidly weathering rock formations such as mica rock, chlorite schist, etc., a protective wall should be built immediately after digging out the fresh rock surface.

Among the protective facilities of high-grade highways in mountainous areas in my country, protective walls are the most common form of protection for upper slopes, and most of them are solid protective walls. Generally, they are based on the height of the slope and the degree of weathering of the rocks. and the engineering geological characteristics of the rock and soil to adopt semi-protective or full-protective measures. In semi-protective measures, slope toe protection walls are sometimes used. Due to the excavation of road cuttings, the flow direction of the air is changed, forming a rotating airflow in the road cutting. In rainy and snowy weather, this airflow carries the erosion and damage ability of rain and snow to the slope toe. At the same time, rain and snow water splashed by high-speed cars also directly wash away at the foot of the slope; natural precipitation flows downward from the top of the slope along the slope. When it flows to the foot of the slope, the speed is the largest and the erosion is the most severe. Therefore, it is best to set up a low wall at the foot of the slope. Minimal protective measures. On the other hand, setting up a protective wall at the foot of the slope also plays a role in inducing driving sight lines. For soil slopes, when technical and economic conditions permit, greening can also be carried out, and some vines can be planted to beautify the environment.

In short, to do a good job in highway construction, ensure the stability and safety of highway slopes, and protect the environment, we must have a deep understanding of the types and mechanisms of highway slope damage, and analyze the soil quality, hydrology, climate, etc. of different project objects. Characteristics: flexibly adopt different protection types, strengthen design, strengthen construction management, and build safe, ecological, and beautiful roads.

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