Common diseases of subgrade and pavement in highway engineering and their prevention countermeasures?

With the development of economy and the improvement of people's living standards, the role of highways is becoming more and more important. It not only facilitates the development of transportation, but also ensures economic development. Therefore, in the construction of highway engineering, the quality requirements of subgrade and pavement should also be improved accordingly. At the same time, increase economic investment and increase the technical requirements of subgrade and pavement construction in management. Strict construction standards should be formulated to effectively avoid the occurrence of common diseases.

A, highway subgrade pavement disease types

1, slope collapse

Slope collapse is the most common subgrade disease, which can be divided into landslide and landslide according to the soil quality, failure cause and scale of slope. Landslides are caused by the downward movement of soil slopes. It is mainly caused by water damage and improper construction. Landslide makes a part of soil slide along the sliding surface under the action of gravity. The main reason is the damage caused by bad geological conditions. The mechanical properties of rock (soil) determine the loss mode of slope stability. For example, the instability of hard rock slope is mainly controlled by collapse and structural plane, while the instability of soft rock slope is mainly controlled by stress. The better the engineering geological properties of rock (soil), the higher the slope stability. The slope is too steep, the slope chosen for filling is incorrect, the soil is too wet, and the foot of the slope is washed away by water.

2, subgrade deformation

Deep fill, high fill and semi-fill-semi-excavation fill often appear subsidence after opening to traffic for a period of time, mainly for two reasons. On the one hand, due to poor compaction control, thick layering, improper construction measures and high water content, the subgrade is easily deformed due to insufficient compactness. On the other hand, it often lies in material factors, such as incorrect maximum dry capacity and optimum water content, excessive compressibility of materials, and the use of cohesive soil with high plasticity index. This problem will lead to pavement deformation, cracking and subsidence. With the development of transportation industry, the increase of large overweight vehicles and overloaded vehicles will cause the existing roads to be too low to meet the requirements of overweight vehicles and be deformed by heavy pressure.

3. Subgrade settlement

Subgrade built on soft soil foundation is the easiest to sink. Soft soil has high water content, low alkali resistance and low bearing capacity. Because the bottom of subgrade is eroded by water, a large area of gap will be formed under the pavement, and the toe of slope will not be supported. Under the action of subgrade self-weight, the pavement will settle and collapse. The whole problem is partly caused by natural causes, but there are also human factors. During the initial construction of the highway, the staff did not fully consider the pavement conditions and preventive measures for some problems, did not combine the local actual situation, and did not guarantee the preloading time of the soft soil foundation section, which led to the settlement of the highway subgrade. At the same time, we also see that subgrade collapse will bring great hidden dangers to people's lives and property safety, especially at night, which will easily cause vehicle damage and casualties.

4, the surface is uneven

The construction quality of asphalt pavement largely depends on the proportion of asphalt mixture. If the asphalt mixture ratio is improper, such as the asphalt aggregate is relatively large, it may lead to the road surface bulging, and the asphalt aggregate is too small, which will lead to the road surface loosening. Similarly, if other materials are used unreasonably, it will also cause a series of pavement problems. However, when the asphalt mixture is stirred unexpectedly, such as high water content, high temperature and uneven mixing, it will make the pavement difficult to spread, and the asphalt will age if the temperature is too high, which will not guarantee the quality of the pavement.

5. Early pavement damage

If the construction is improper, the pavement will be easily damaged in the early stage of highway project completion. Due to various reasons, the construction quality and the temperature of the final compacted asphalt mixture are not strictly controlled in the paving and rolling of asphalt mixture, which leads to the occurrence of transverse cracks. Due to one-sided pursuit of individual unreasonable indicators, the comprehensive strength, safety and durability of pavement are not fully considered, resulting in unnecessary damage to pavement. In addition, because the local natural environment factors were not comprehensively considered, some unexpected problems were caused, which caused great damage to the pavement.

Second, the treatment measures of highway subgrade and pavement diseases

1, subgrade treatment

The quality of subgrade construction, to a great extent, is the key to the whole highway project. It must stand the test of time, vehicle overload, rainy season and cold winter, so the quality should be strictly controlled when subgrade engineering is carried out. According to different soils, especially soft soil, we should do well in three aspects. First of all, we must ensure that the compaction degree of subgrade meets the requirements and reach the construction quality standard of soft soil subgrade compaction. Secondly, when filling subgrade, gravel and soil with high plasticity and water content should be used as far as possible, and silt, soil containing turf, organic soil and soil containing domestic garbage should not be used. We must never cut corners in the choice of filling type. Third, improve the drainage measures. In order to ensure that the roadbed is always in a dry, solid and stable state, it is necessary to control the content of water that destroys the stability of the roadbed and discharge it out of the scope of the roadbed to prevent overflow and infiltration. Therefore, we should attach great importance to the drainage of subgrade and strive to achieve optimization. For the subgrade diseases that have occurred, there are mainly several methods such as digging and backfilling, filling, bridge crossing and grouting. Among these methods, excavation and backfilling are usually used, excavation and backfilling measures are taken for subgrade and pavement with minor damage, filling measures are mainly taken for subgrade with serious damage, and bridge span and grouting are sometimes used in other cases.

2. Treatment of pavement problems

Fundamentally speaking, to prevent the occurrence of pavement problems, we must start with ensuring the quality of subgrade. However, due to various reasons, there are still many pavement damage problems. Therefore, while ensuring the quality of subgrade, we should also be prepared for pavement treatment. About pavement treatment, we should also pay attention to three aspects.

2. 1 Try to take simple measures for the unevenness of the road surface.

2.2 For pavement cracks, when the number of cracks is small, the cracks can be washed with clear water and repaired with cement slurry. When the crack is large, the weak part should be chiseled away from the crack before construction.

2.3 attention should be paid to the details in the process of pavement treatment to avoid improper treatment and pavement damage from happening again.

3. Slope protection and reinforcement treatment

Subgrade and pavement treatment should be closely combined with local natural environment. First of all, engineering protection should be combined with the local environment and take different measures according to different regions. Wall protection, anchor protection and geosynthetics protection should be combined with the actual situation. Secondly, in the case of project management, we should also pay attention to plant protection. Plant protection is a long-term measure, which can not only beautify the highway, adjust the temperature, but also reinforce the stable slope and effectively protect the stability of subgrade.

4, slope deformation and instability control measures

Slope is a general term for natural slope and artificial slope. Slope is formed under the action of complex geological forces in highway engineering construction, and the slope deformation is mainly manifested in the displacement and inclination of dangerous rocks, subgrade and pavement. For severely damaged slopes, effective measures must be taken to control slope deformation and instability. Subgrade protection is one of the important measures to ensure subgrade stability. In the process of controlling the deformation of subgrade and pavement slope in highway engineering, measures should be taken according to local conditions according to the adverse engineering geological characteristics of slope and the characteristics of landslide reinforcement and protection engineering, combined with the actual situation of highway engineering. When building roads in mountainous areas, measures with strong applicability, simple operation and little negative impact are mainly selected to prevent mountain or slope deformation such as collapse, rockfall, landslide, collapse and debris flow, such as anti-slide piles, anchor rods (cables), retaining walls, slope cutting and grouting, so as to adapt to different physical and mechanical conditions and geological conditions of landslides and landslides respectively.

5, karst area subgrade treatment measures

Karst landforms are distributed in soluble rock areas all over the world, and the foundation problem in karst areas is a prominent problem in highway engineering construction. For the treatment of subgrade in karst area, we should grasp the general situation of subgrade in karst area as a whole, and combine with the actual geological situation to find out the development law and distribution law of karst, so as to formulate a reasonable treatment scheme for subgrade and pavement diseases of highway engineering in karst area. The landform in karst areas is mainly divided into the following situations: first, large-scale and local serious karst subgrade and pavement diseases; Second, it is not serious in small and medium-sized karst subgrade and pavement diseases; Third, karst springs and water caves in the subgrade basement; The fourth type is an open and dry cave in the subgrade base. Specifically, for the treatment of large-scale and local serious karst subgrade and pavement diseases, we should find out the specific location of karst areas and try to avoid highway engineering construction. For the treatment of subgrade and pavement diseases in small and medium-sized karst areas that are not too serious, in highway construction, we should choose the narrowest and easiest-to-take-measures section to pass through, mainly to divert karst water, and adopt the method of adapting measures to local conditions and improving the situation, which should not be blocked. Generally, drainage ditches and drainage tunnels can be used to divert karst water.

In the construction of highway engineering projects, various subgrade and pavement construction problems are often encountered. If reasonable and scientific construction technology is not adopted for targeted treatment, it may have a serious impact on the normal use function of highways and traffic safety. Therefore, we should strengthen the research and discussion on common highway subgrade and pavement construction problems, and take corresponding technical treatment measures to effectively control according to local conditions, so as to ensure the good realization of highway engineering construction quality and construction progress.

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