Research On The Major Engineering Geological Problems Of The Dali-Ruili Railway Through Gaoligong Mt.

The Dali-Ruili railway is one of the most important planning and construction railways of China, and it is an important part of the Great Passageway of Southwest Yunnan. Being located in the south part of Hengduanshan Range with extremely complex terrain and geological conditions, there will be a series of important engineering geological problems during the railway construction process. How to safely pass through Gaoligong Mt. for the railway is the key problem that restricts the railway construction. Therefore, on the basis of region engineering geology background analysis, this study selects the Gaoligong Mt. section of Dali-Ruili railway as the study area and applies multi-subjects theories and methods to study the major engineering geological problems of the active fault dislocation effect, deep-buried rockburst, geohazards and the engineering site safety and so on, which can provide technical support for the railway route selection and important engineering geology problems solving. In this paper, the main progress and achievements obtained are as follows:1. Based on the analysis of the region geological background and field geological investigation, this paper deeply analyzes the engineering geological conditions of the Gaoligong Mt. section of Dali-Ruili railway, and discusses the engineering geological problems which may possibly met in the railway construction, such as active fault, high ground temperature, high geostress, deep-buried tunnel rockburst, large deformation, slope stability and so on, as well as their possible effects to the railway construction.2. According to the active faults investigation and comprehensive analysis, it is revealed that Huangcaoba fault and Zhen’an fault are the late Pleistocene-Holocene active faults, with strong activity. Combining with the railway engineering characteristics, adopting numerical simulation analysis method, this paper systematically studies the active fault engineering dislocation effect. Results indicate that, due to the horizontal distance between the Huangcaoba fault and Gaoligong deep-buried tunnel is 2.09km, Huangcaoba fault dislocation effect has less influence to the tunnel under steady creep and stick slip condition. Zhen’an fault is nearly perpendicular to the Gaoligong deep-buried tunnel, the fault engineering dislocation effect may cause tunnel produce certain distortion damage, and the damage extent of 8m coseism dislocation> the damage extent of 3m coseism dislocation> the damage extent of 2.51m steady creep dislocation.3. The geostress value is high at the Gaoligong deep-buried tunnel site, and the tunnel surrounding rock is mainly of marble and granite, with high possibility of rockburst. The rockburst physical experimental results reveal that both pure unloading and loading-unloading styles can lead to rockburst, but the rockburst intensity of the latter is obviously higher than the former. The process of rockburst usually has a character of gradual rupture, lagging and instantaneous character. The sound radiation monitoring data show that the granite samples have extensive sound radiation, while it is not obvious of the marble.4. The geologic structure is an important factor that affects the rockburst, and the rockburst intensity has some relationship with the position between the tunnel and the geologic structure body:when the tunnel axis is parallel to the fold axial line, and the tunnel is located at the anticlinal-shaft or fold limb department, the rockburst possibility is likely to be the biggest; but when the tunnel axis is vertical to the fold axial line, the rockburst possibility is likely to be low; the strike-slip fault have great affects to the stress redistribution after tunnel excavation, and the partial rockburst possibility is big. The tunnel plan and construction may select the position that the tunnel axis is vertical to the fold axis or the position that far away from the strike-slip, which is advantageous for weakening the rockburst. Under complex geological conditions, the tunnel shape also has important effect to the rockburst.5. Field geology investigation indicates that the geohazards of landslip, landslide and the debris flow are intensively developed in the study area, and it has obvious regional and seasonal characteristics. Both sides of Nujiang River and Longchuanjiang River are of high geohazards developing, and some individual geohazard is of huge scale and serious harm, which have tremendous influence to the railway bed, bridge bed, tunnel import and export side slope and so on.6. Using the AHP method based on GIS theory, this paper makes ground and underground engineering site safety comprehensive evaluation of Gaoligong Mt. section separately, and divides the engineering site safety into 4 levels of good, medium, poor and bad, and make comprehensive engineering site safety evaluation on the recommend line scheme of C12K, which has important directive effect to the line optimization, investigation, design and construction.The methodology, techniques and process used in this study can be referenced when studying the engineering geological problems of ridge crossing railway in complex geological conditions.