Route Location In High Earthquake Intensity Mountainous Regions Based On Risk Control

Railways and highways in mountainous areas were largely damaged during 5.12 Wenchuan Earthquake. It not only seriously hindered the entry of the rescue team, but also delayed the recovery and reconstruction process of the earthquake-stricken areas. At present, seismic designs of railway and highway are mainly focused on the design of engineering structures. However, hazard avoidance in the source stage of route location and overall risk control of route engineering in the whole life, are the most advanced and effective countermeasure to mitigate seismic damages. Therefore, hazard avoidance line layout and risk control of route engineering in the whole life should be system design of route location in high earthquake intensity mountainous regions.In this dissertation, investigation was carried out on road damages triggered by Wenchuan and Lushan earthquakes. Then, new-built route location technique in high earthquake intensity mountainous regions consisting of transportation corridors selection, space line layout and site structure design, was researched based on the concept of earthquake risk control. After the earthquake, natural environment deteriorates and secondary slope hazards prone to occur. For this post-seismic environment, remediation and reconstruction technologies for seismic damage road were researched. The main works and conclusions are as follows:Through investigation and analysis, seismic damage characteristics of subgrade engineering were summarized, and fundamental countermeasures to mitigate seismic damage of route in mountainous regions were proposed. The damage of subgrade engineering is not very serious. The emergency maintenance is easy to open for traffic. Slope hazard is the primary cause of road damage. Road damage caused by slope hazards triggered by earthquake is much more serious than that caused by the earthquake directly. Slope stabilization measures can effectively reduce the risk of slope hazards. But slope hazards triggered by earthquakes often start from the ridge. Slope hazards caused great damage to roads is beyond the right of way. The prevention of slope hazards can not rely solely on stabilization measures. There need to consider damage mitigation from the stage of route location, which is the beginning of the route design. When through the active fault, any seismic design structure can not resist the earthquake surface deformation. To reduce the damage of the deformation, countermeasures should be taken in the stage of route location.For transportation corridor selection in route location, the primary pattern of road damage by earthquake in mountainous regions was concluded by geomorphology evolution theory. From the tectonic geomorphology theory, landform patterns formed by active faults and seismic disaster were analyzed, and the principles of transportation corridors selection were obtained. Fault tectonic basins usually form wide and flat terrain zonal distributed in steep mountains, which gradually evolve into human settlements and transportation corridors. The transportation corridor has not only favourable topography conditions, but can effectively avoid the slope hazards also. Flexural basin on footwall of reversed faults, rift basin on hanging wall of normal faults, and rift basin and pull-apart basin on strike-slip faults are available geomorphic units of transportation corridors. Considering both seismic risk and topography conditions, the conclusions are:The transition zone from mountain to basin on footwall of reversed faults is available for road. Because the earthquake magnitude of normal faults is not very large, road can pass the rift basin, and resist the seismic risk by seismic design of engineering structures. There has straight and flat terrain along strike-slip faults. By using simple engineering structures which are easy to be remedied, damages can be mitigated.For space line layout in route location, the effect of topography on seismic wave propagation in three-dimensional space is studied, based on the wave motion theory and seismic damage phenomenon. In the principle of passing the site with weak ground motion, the key points of space lines layout were proposed. There is no close relationship between the intensity of ground motion and the elevation in regions. The ground motion intensity of large mountain or terrain ladders is not continued to amplify with the increase of elevation. Elevation amplification effect is not considered at route elevation determination of large sections. The direct and reflected body waves fracture rockmass along the hillside back to the wave propagation direction, and massive slope hazards happen. Along the hillside facing wave propagation direction, surface waves is easier to form and spread away harder than the opposite hillside, and the surface soils slide more. As the result, routes in earthquake near-field with great body waves shall be selected along the hillside facing wave propagation direction, while far-field with great surface waves shall be selected the opposite side. Valley can effectively obstruct the high frequency range of Rayleigh wave propagation in space. The ground motion on the wave incident side is stronger than the other side. Valley routes shall be avoided the incident side of seismic waves, according to the relative position between active fault and valley.For site structure design in route location, simple structures are adopted to reduce losses based on risk control. Embankment, shallow cutting, short tunnel and low bridge are simple structures, which are little cost for construction and easy to remedy. Because of the earthquake surface deformation, road is disconnected with a displacement on the two sides of the fault. Special design for line to mitigate the damage of the deformation is studied. To minimize the recovery project, large radius curves are used to across the fault. After the earthquake, it can recover by diminishing the radius of the curve. To keep the standard of the line, a section of straight line needs to be reserved for the outward deformation side of the curve, when the line is designed. It's not suitable for road through the fault in a straight line. If the road passes through the fault in a straight line, a curve should be design near the fault. Fault creep problem is not critical for space line layout. It can be solve in structure design.Disaster-resilient is the international new concept of disaster mitigation now. The built route system of disaster resilience is also the development direction of our country. Emergency maintenance technology of railways and highways is an important section to achieve the disaster resilience. Based on the investigation of subgrade damages triggered by Wenchuan Earthquake, engineering countermeasures of rescue and security were summarized. The seismic damage mechanism, evaluation and maintenance of retaining structures are studied. Moreover, based on the case analysis of remediation and reconstruction roads after Wenchuan Earthquake, the principle of new-built road and reconstruction valley roads is proposed. In the period of rescue and security, structures damaged a small portion of, or structures with great deformation, are temporarily reinforced with rapid and effective techniques to maintain and improve the road traffic capacity. The foot of retaining walls and the unstable foundation site need to be reinforced. There were two deformation modes of seismic damage for retaining walls, inclined deformation and sliding deformation. The inclined retaining walls could still bear the soil pressure after the earthquake. The lateral strengthening could effectively control development of the deformation, as well as make the overall stability and the foundation stress meet the code requirement. Some of the sliding deformation retaining walls may convert into landslide sites. According to the amount of deformation, the landslide site can be distinguished, and then the right remediation scheme be formulated. For reconstruction roads with the original transportation corridor, the construction needs to avoid the active period of post-seismic hazards. The geological hazards need to be payed attention to and guided route location. For new-built road with the sense of lifeline, the transportation corridor should be separated from the existing one.