Study On Geological Engineering Problems In Yufengsi Deep-Buried Tunnel Along Yunnan-Tibet Railway

On the basis of collecting and analyzing predecessor's information, filed geological work,remote sensing, indoor examination analysis and simulative calculation, using multidisciplinary theory like engineering geology, rock body mechanics and so on, this dissertation, combining with practical project, studies the important engineering geological problems of the Yufengsi tunnel of Yunnan-Tibet railway. In the light of general analysis in many aspect such as region geology, crust stability, activity fault, seismic hazard and engineering geology conditions of tunnel site, combining with the analyzing region stress field and 3-D FEM simulation of tunnel site, the dissertation gives general studies and prediction about rock burst and water bursting of Yufengsi tunnel , and besides , it studies the rigidity criterion for rock burst of tunne wall. By more than three years'study, we have obtain some progress and conclusion as follows: 1.Based on analyzing the region geology condition and crust stability in the NW of Yunnan, the dissertation studies the features of arel neotectonic and activity faults, and then classified activity faults to four kinds as pre quaternary faults, early-mid pleistoncene activity faults, late pleistoncene activity and Holocene faults. A preliminary evaluate criterion for instability crust region is put forward, in which the velocity of fault movement and the seismic magnitude are parameters by which the activity of faults can be divided into four degree.2.Region present stress field analysis shows:1 the present region stress field in the NW of Yunnan is mainly in the NNW direction extrusion(about 340°),and intersects at small angle with Yufengsi tunnel of N310°W direction, which is propitious to the tunnel's stability. 2,in the tunnel site ,the stress value is high and is influenced by region stress field and landform. In the light of 3-D simulation for tunnel site, two stress type can be partitioned off. On the two end of the tunnel, stress field featured that the principle stress alters quickly and the discrepancy between maximum principle stress and minimum principle stress is large. In the mid tunnel, stress field featured that main stress alters slowly and the discrepancy between maximum main stress and minimum main stress is small .3.On the basis of systemically analyzing eight influencing factors of rock burst occurrence, using multi-criterions for rock burst occurrence such as stress criterion, burst potential and rigidity criterion, coupling with rock mechanical property test and stress field simulation, many parameters of rock burst have been worked out suck as Wet index, Wcf index, Barton index and Russenes index. Considering these parameters and engineer geology conditions of tunnel site, the plat of rock burst occurrence and intensity class at Yufengsi tunnel in three levels as follows: lithology, tunnel segment and section of tunnel, are predicted emphatically. The prediction results shows: middle-strong rock burst occurs at basalt tunnel segment which is 3500m length, about 32% of the total tunnel length. Among the basalt tunnel segment, strong rock burst may concentrates on the segment from 1000m to 1500m which is about 4% of the total tunnel. None but light or middle rock burst is likely to occurs at thick bedded sandstone in the middle of tunnel with layered clastic rock. Among the rest ,it need attention to the exit end of the tunnel with thick bedded limestone without karst water in which the light or middle rock may occur. In tunnel section, the intensity of rock burst is high at arch top. The bottom and arch springing is light. the side wall has no rock burst.4.The rigidity criterion for rock burst is studied and applied in Yufengsi tunnel of Yunnan-Tibiet railway based on the minimum energy theory. Firstly, the three kinds rock failure process in different confining pressure is analyzed according to the complete stress-strain curves experiment of rock specimens, in-situ stress data and digital simulation results. Secondly, the rigidity curves of either tunnel plastic rockmass or elastic rockmass is obtained by the analysis and simulation results. Finally, the tunnel rockburst hazard of three kinds rockmass are estimated by rigidity criterion. The basalt rockburst hazard is the most heavily, and the layered sandstone rock burst hazard is the most light.5.The plats where water gushing occurs in Yufengsi tunnel are predicted and evaluated. The result shows: the segment where industrial scale water gushing occurs mostly concentrates on the Wenhai fault zone and scyncline structure segment on the exit end of the tunnel. Wenhai fault zone, which is fault and karst and rock boundary multiple-unit control plats, may occurs middle-large scale gushing water and results in a set of environment problems. Moderate or below scale water gushing is occurs in the scyncline structure on the tunnel exit segment.