With the rapid development of China's economy, the transportation industry is also progressing, and the highway construction technology is facing great challenges. At present, highway traffic is developing rapidly, and the driving speed is also increasing. With the gradual increase of vehicle load, the requirements for the quality of highway subgrade and pavement are constantly improving. As the basic engineering of pavement, the quality technology of subgrade also affects the use of pavement. Because the quality problems of subgrade will directly lead to problems such as pavement subsidence and frost boiling, resulting in abnormal traffic of vehicles, it is necessary to strictly control the quality and improve the construction technology in the process of highway subgrade construction, so as to promote the subgrade to achieve a stable purpose.
Keywords: highway subgrade construction technology
Subgrade construction, as the main body of highway, is also the bearing of pavement and the main support. As the basic engineering of pavement, subgrade is a structure built according to certain route position and technical requirements, and bears the traffic load transmitted by pavement. Therefore, the strain characteristics and stress of subgrade soil will have a great influence on the stiffness and strength of the whole pavement structure. Subgrade engineering construction has several characteristics: wide coverage, large labor force and large engineering quantity. Therefore, it is necessary to require quality control during subgrade construction, which is also an important factor in highway construction. Therefore, the quality control requirements of subgrade construction play a very important role in highway construction, and subgrade construction is of great significance. There are many factors that affect the quality of subgrade. The main problem is the construction technology, which not only affects the safety and smoothness of traffic roads, but even causes accidents. Therefore, it is necessary to strengthen the technical management of highway subgrade construction.
1, the significance of highway subgrade
Highway subgrade generally includes cutting and embankment. Its basic operation is through digging, transporting and filling, which is relatively simple. However, the conditions in construction are relatively complicated. Because highway construction and design often work outdoors, the conditions are poor, the construction work is difficult, the traffic is inconvenient and the construction supply conditions are difficult. At the same time, in the process of highway subgrade construction, due to the scattered construction sites and narrow working faces, it is easy to encounter some special circumstances. Therefore, if we encounter this complicated situation, we should pay attention to the construction quality, focusing on efficient, fast and safe construction, and at the same time pay attention to the management and technical problems of subgrade construction. At the present stage of subgrade construction, it is necessary to equip a stable construction professional team with certain technical force and mechanical equipment, and establish a perfect construction technical operation standard system to ensure the improvement of highway subgrade construction technical means.
2. Subgrade treatment
Because the stability and strength of highway subgrade largely depend on the nature of subgrade filler and the compactness of subgrade, it is also the best method and means to ensure the quality of subgrade in order to better improve the requirements of filling and compaction conditions.
2. 1 In the process of highway subgrade construction, the rollers commonly used are large tonnage, so the rolling effect is obvious, which plays a very good role in improving the compactness of subgrade soil.
2.2 In special wet areas, the road subgrade should be compacted. Usually, it is very difficult to deal with the compaction of subgrade in wet area, and some adjustments have been made in the specification: ① The value of compaction degree can be determined according to the test data. ② The natural consistency should be less than 1. 1, the liquid limit should be greater than 40, and the plasticity index must be greater than 18. (3) It is necessary to improve the performance of the filler, so it is necessary to mix quicklime into the soil, which can generally achieve the expected ideal effect.
2.3 Compaction treatment of loess subgrade. In the construction of loess subgrade, it is necessary to deal with the interface of filling and excavation. If the water content of loess is small, it needs to be evenly added with water and then rolled. If the water content is high, it needs to be turned loose and dried before rolling. If it is found that the old loess is difficult to adjust its wet and dry because of its poor water permeability, and because large pieces of soil are not easy to crush, it is necessary to decide the treatment method through experiments in application. On the other hand, it is necessary to build water retaining ditches and other structures at the edge according to the design requirements, and it is necessary to guide the water from the foot of the slope. When the height of the embankment is more than 20m, the compression settlement caused by the self-compacting consolidation of the completed rear embankment shall be reserved according to the design requirements. Special attention should be paid to the drainage of subgrade in loess area. The principles of dispersion, interception, erosion prevention and leakage prevention should be implemented for surface water, and the outlet should be strengthened at the same time.
3. Subgrade drainage treatment
In highway subgrade construction, we must pay attention to the drainage treatment of construction, mainly to avoid unfavorable factors caused by various reasons and have a direct impact on subgrade construction.
3. 1 The main task of pavement drainage is to quickly remove the precipitation within the pavement, so as to reduce the infiltration of water along the pavement and stop scouring the subgrade slope. There are two ways to make rainwater drain off the road surface: the first way is to adopt centralized drainage, and it is necessary to set a water stop across the cast-in-place asphalt concrete outside the hard shoulder to form a triangular water collection tank with the hard shoulder road surface. At the same time, the embankment slope is provided with a drainage outlet and a chute every 20-50m, so that rainwater can be directly discharged into the drainage ditch at the foot of the slope. The second method is decentralized drainage, which is generally applied to long sections with relatively flat terrain and longitudinal slope less than 0.3% in northwest China. 3.2 Common facilities for surface drainage include intercepting ditch, side ditch, rapids and surface drainage pipes. However, for the drainage ditch on the expressway, it is usually necessary to lay protection. Mortar rubble is generally used for reinforcement, and cement concrete precast slabs are also widely used.
4, the technical requirements of highway subgrade construction
4. 1 In the construction technology of pavement cushion, the better material is graded macadam, but the quality of macadam material itself will affect the use of cushion and the construction quality of the whole pavement. Therefore, as a supervisor, it is necessary to master the requirements and standards of gravel technology and control the engineering quality assurance of graded gravel cushion. The general construction process of graded macadam cushion can be divided into transportation leveling, road groove rolling, plastic spraying rolling, initial maintenance and other processes, and graded macadam is mainly a loose material. As a supervisor, it must be reminded that when implementing the construction scheme, it is necessary to adopt a semi-open way to avoid traffic chaos caused by construction. The graded macadam cushion has poor flatness and loose surface.
4.2 The construction technology of cement stabilized macadam base is divided into two types. (1) The cement stabilized macadam base is constructed by road mixing method, and the main procedures are: initial leveling of macadam, paving cement, paving cement, mechanical stirring, leveling, and sprinkling water after rolling. (2) Cement-stabilized gravel base construction adopts factory mixing method. The main construction needs gravel preparation, proper cement dosage, water mixing, road transportation, paving and rolling, and watering.
5. Conclusion
In short, in the process of highway engineering construction, highway subgrade, as a basic project, plays a very important role in all projects. Therefore, in the future subgrade work, we must constantly strengthen our efforts, improve construction technology, find problems as early as possible and solve them in time. Construction must be completed in strict accordance with the requirements of highway construction and carried out in accordance with the requirements of highway design specifications to ensure excellent quality of highway engineering construction and remarkable social benefits.
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