Thoughts on road design for reconstruction of hydropower station reservoir area?

As an important part of the resettlement project of hydropower station, the road reconstruction in the reservoir area of hydropower station plays an important role in the whole hydropower station construction. According to the characteristics of road reconstruction in the reservoir area of hydropower station and the principles of road design, various factors that should be comprehensively considered in the design are analyzed, and on this basis, possible problems and solutions are put forward.

1. Overview

With the infrastructure construction and social development in China, the demand for energy is increasing. At the same time, the international community and our government pay more and more attention to the importance of environmental protection. Choosing clean and renewable energy sources (such as hydropower, wind power and photovoltaic power generation) has become the focus of China's energy construction. However, hydropower is one of the main energy sources in China because of its advantages of little influence from the external natural environment, long sustainable utilization period, basically no impact on the environment and adjustable peak. In recent years, the state has invested heavily in the construction of hydropower stations.

The main roads for hydropower station construction are: external traffic, internal traffic and road reconstruction in the reservoir area. Foreign transportation mainly studies foreign transportation routes, and selects the appropriate routes through economic and technical argumentation. According to the traffic needs of the general layout of power station construction, the appropriate route and slope are selected to arrange the traffic in the field to meet the needs of power station construction. The roads in the reservoir area discussed in this paper belong to the field roads of hydropower station construction, and the original roads in the reservoir area flooded by the reservoir are mainly rebuilt according to the "three principles" of the reservoir (original scale, original standard and original function). According to the reservoir "three principles" and traffic volume analysis, the standards and grades of road reconstruction are determined.

As the main road of reservoir construction, the reconstruction road of hydropower station reservoir area plays a vital role in the construction of resettlement sites, resettlement and even hydropower station water storage and power generation.

2. Principles of road design in reservoir area of hydropower station

The overall design feature of the reconstructed road in the reservoir area of hydropower station is to reconstruct the existing traffic engineering submerged by reservoir water according to the standard of "original grade, original scale and original standard" for reservoir reconstruction in combination with the resettlement sites and market towns arranged on both sides of the reservoir area. Its design features are as follows: firstly, on the basis of meeting the design specifications, it meets the safety requirements of reservoir water storage, that is, the normal water level and design flood level should be the primary design considerations in subgrade design; Secondly, the project is to serve the local people in the reservoir resettlement site, which not only meets the requirements of road construction clearance near the village, but also meets the travel needs of the people, taking into account the needs of production and life, and is better than the existing field tractor roads, village roads and irrigation settings. However, the surrounding human and geological conditions are generally complex, which has become the focus and difficulty in the design process.

Affected by the impoundment of the reservoir, the reconstruction route of the reservoir area has been improved, with steep terrain, complex geological conditions, more bad geological sections and great design difficulties. The influence of reservoir impoundment and topographic and geological conditions should be considered in the design. Moreover, in the design of cross-mountain route, we should make use of natural terrain to develop lines and try to avoid setting turning curves. In view of the fact that the roads in the reservoir area can't get the required distance and overcome the height difference of the natural development line, the transition curve can be designed in appropriate places to reduce the engineering quantity. When setting a turning curve, the line shape of the turning curve should be continuous, uniform and good visibility, and transition curves should be set at both ends, and speed limit signs and traffic safety facilities should be set up.

3. Problems and solutions in construction.

(1) Most of the reconstruction roads in the reservoir area of hydropower station are subgrade along the river. After the impoundment of the hydropower station reservoir, the water level changes greatly, and the scouring along the river will cause the foot of the submerged subgrade to retreat, which will seriously threaten the stability of the subgrade slope along the river. The subgrade along the river needs to be prevented to ensure the functional reliability of the subgrade under water scouring and water level fluctuation. According to its structure and function, the protective measures of the concave bank subgrade along the river can be divided into two forms: one is direct protection, that is, the slope of the concave bank subgrade is directly covered with anti-erosion materials to resist the collapse caused by water scouring; The second is indirect protection, such as groins. By arranging groins or groins on concave banks, the nature of water flow is changed and the effect of water flow on subgrade is reduced.

(2) As a channel connecting the resettlement sites, the reconstructed roads in the reservoir area of hydropower station should communicate with other related professions in the process of survey and design to meet the requirements of the construction of resettlement sites, and be connected with the main roads of resettlement areas according to the planning and layout of resettlement sites.

(3) In the design site investigation stage, we should communicate with the local government to understand the wishes of local residents. Avoid obstructing the construction because the wishes of local residents are inconsistent with the design ideas, so that the construction cannot be carried out, and changes have to be made to meet the wishes of local residents, resulting in waste of investment or even abandonment of the project.

(4) Pay attention to the influence of the bank collapse area of the reservoir, because during the operation of the hydropower station, the water level of the reservoir fluctuates within a certain range due to the season, climate and the regulation requirements of the cascade hydropower stations. However, the reservoir banks in this area are in the state of water storage and over-storage all the year round and are in an unstable state. If the subgrade passes through this section, it may be in an unfavorable unstable state. Therefore, when passing through the reservoir bank collapse area, we should avoid it according to the scope of the reservoir bank collapse area determined by the geological report to ensure that the safety distance is not less than 10m.

(5) Fully consider the needs of farmland irrigation. Combined with the local irrigation system and topographic conditions, a complete drainage and irrigation network will be formed to avoid destroying the original irrigation system due to highway construction. The low-fill subgrade (1 ~ 2m) passes through the subgrade in the farmland section, and culvert communication is made on the subgrade irrigation canal, which can not only ensure the integrity of the irrigation system, but also deal with some road wastes.

(6) Pay attention to geological exploration. Highway reconstruction in hydropower station reservoir area is generally affected by reservoir water storage, and the line position is raised. The route often goes out of the steep slope, and the excavation and filling height of the slope is high. In the geological exploration stage, we should focus on the exploration of high-filling and deep-digging sections to avoid increasing the number of protection projects or even adjusting the route because of the great difference between the actual geological situation revealed during construction excavation and the geological exploration report.

(7) Pay attention to subgrade protection design. Generally speaking, the highway reconstruction in the reservoir area has strong internal and external geological functions and complex geological structure. Neotectonic movement is characterized by large-scale overall intermittent rapid uplift, rock mass fragmentation, strong weathering, heavy rain concentration and steep mountain slopes, and various external dynamic geological phenomena are developed. The main adverse geological phenomena are weathering, collapse and landslide.

Weathering and fragmentation mainly occur in various exposed rock slopes of some roads and trails. Due to severe weathering, weathering and fragmentation are common, but the scale is small and easy to remove, which has little impact on the project.

Collapse mainly occurs on both sides of river valleys and gullies. The exposed hard rock slopes of some roads and paths destroy the integrity and stability of rock mass due to the development of criss-crossing joints and cracks, and it is easy to collapse at steep slopes, but it is only related to individual construction sites, with the characteristics of low frequency, small scale, easy removal and little impact on engineering.

Most of the reconstructed road sections in the reservoir area are mountain slopes, with steep transverse slopes, large rock surface undulations, thick slope cover, completely weathered bedrock and frequent rainfall concentration. Under the concentrated erosion of the slope toe by rainwater and ditch water, shallow loose accumulation layer often collapses (soil slip), but the scale is small, and the design and construction are easy to dismantle or deal with, which has little impact on the reconstructed road.

The thickness of overburden along the highway varies greatly, and there may be problems such as uneven settlement of subgrade and expansion of red clay in some areas.

The following protection forms are mainly adopted for deep excavation subgrade and high fill immersed subgrade: shotcrete and bolt support for slope; SNS active and passive protective nets are set on the slope; The top of the excavated slope is provided with a drainage ditch; Geogrids are used to treat high-fill flooded subgrade; Rock-filled subgrade is used for high-fill submerged subgrade; Retaining wall shall be set for the filled subgrade.

(8) Pay attention to the layout of road safety facilities. The design index of road route in the reservoir area is low, and there are many practical problems such as submerged water level, complex geology, mountainous hills, resettlement and so on. Doing well the layout of its safety facilities is an important guarantee for traffic safety and public safety. If the signs that are not set separately need to be set side by side, the prohibition and indication signs should be set first.

5. Summary

In the construction of hydropower station, road reconstruction in reservoir area, as an important part of resettlement planning, plays a vital role in resettlement, relocation, travel, construction of resettlement sites, water storage and power generation on schedule. In the design of highway reconstruction of hydropower station, we should comprehensively consider natural conditions and human factors, do a good job of on-site investigation, and meet the needs of hydropower station and local construction according to relevant codes and regulations.

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