Research Of Different Construction Methods Diversion Tunnel Rock Stability Of JinpingⅡHydropower Station

The twenty-first century, construction of water conservancy and hydropower often require excavation of underground tunnel, and research of rock stability is of great significance. The project example is Jinpingâ…¡hydropower which the length of diversion tunnel is about 17km, excavation diameter is 13m, maximum depth is 2525m, above ground stress value is more than 70MPa, and the external pressure is greater than 10MPa, with great depth, hole length, diameter large and high stress, high water pressure characteristics. In addition, four diversion tunnels of Jinping Hydropower Station are different from the adjacent construction of drilling and blasting method long exploratory tunnel and auxiliary holes, 1# and 3# diversion tunnels construction using TBM, once a shape, cross sections are circular; 2# and 4# diversion tunnels construction by drilling and blasting method, two steps excavation, horseshoe-shaped section for the four centers of circles. Diversion tunnels'span are large , on-site measurements and observations are difficult, especially in the construction of TBM driving fast and supporting up quickly. In the design and construction stage of diversion tunnels, accurate evaluation of the rock stability is an indispensable condition of economic and rational for rock reinforcement design, fast and safe construction and operation safety of diversion tunnel, in these complex geological conditions, Jinping buried and long diversion tunnel stability problems are more prominent. Therefore, for considering various effect factors as much as possible in the construction and excavation of Jinping diversion tunnels, and researching the stability of rock is very important.For researching of rock stability of Jinpingâ…¡hydropower station, this paper used three ways of a common mechanism of geological processes, rock classification and numerical simulation. First,introduced the engineering geological conditions of diversion tunnels in detail;Second, statistical analysised the rock conditions of diversion tunnels and deformation and failure features of rock using different construction methods, as reference for subsequent papers in research of different construction methods diversion tunnels rock stability of Jinpingâ…¡h ydropower station; Third,analysised the rock stability during the excavation of diversion tunnels in theory by mechanism of geological processes; Fourth, analysised the applicability of in different construction of diversion tunnels by existed rock classification (JPF) system of Jinping,and explored difference lies of rock stability resulted in using different construction methods;Finally,researched of different construction methods diversion tunnesl rock stability through numerical simulation,then summarized different construction processes impacted on rock stability.In summary, this paper used three ways of a common mechanism of geological processes, rock classification and numerical simulation,then analysised and researched the different construction methods diversion tunnel rock stability of Jinpingâ…¡hydropower station,the main results draw the following:First, the geological process mechanism analysis showed that under the stress field in the project area as the excavation of diversion tunnels, the maximum principal stress direction is south spandrel to north arch foot, minimum principal stress is vertical with it, that north spandrel to south arch foot. Therefore, compressive stress concentration at the north spandrel, while tensile stress concentration at the south spandrel, so it caused severe deformation, but the expressions are different, of which the north spandrel prone to burst, high-stress fracture stress-type collapse , south spandrel is prone to collapse, a general destruction of such swap block, and these consistent with the statistical results of rock deformation and failure characteristics of the scene.Secondly, through analysising the applicability of in different construction of diversion tunnels by existed rock classification (JPF) system ,we know that JPF rock classification system's match rate is higher in 2# and 4# diversion tunnels ,and 1#, 3# diversion tunnels which excavated by drilling and blasting, above 80%; but the maximum match rate is 70% in 1#, 3# diversion tunnels which excavated by TBM, it's match rate is lower. Different lithology and depth segment, JPF rock classification system's match rate is lower in TBM than drilling and blasting construction tunnels, and the system of classification which JPHC's result of rock classification coincide with the actual highest, JPQ system's result is lower,and JPRMR system's result is the lowest. Therefore, the existed JPF rock classification system has been applied to construction of tunnels by drilling and blasting method, and in the poor applicability of tunnels construction by TBM,it's need further amendments to improve.Finally, numerical simulation and analysis results show that under the same conditions of depth and rock classification, diversion tunnels'rock by full-face excavation and two steps excavation have the same law of stress, displacement and plastic zone distribution, that the stress concentration and distribution of plastic region are mainly in the north spandrel and south arch foot, while the displacement distribution is mainly in the south spandrel and north arch foot. But the stress concentration, displacement and plastic zone distribution degree is different, compare with the 2# and 4# diversion tunnels excavation ,rock have higher degree of stress concentration and wider distribution of displacement and plastic zone of 1# and 3# diversion tunnels excavation.In addition, in the process of diversion tunnels with full-face excavation and tow steps excavation, the maximum principal stress concentration in the vault and the arch parts in front of the working face both, but the minimum principal stress is reduced, and from the outside increases. After working face within 1 times the hole diameter, the supporting role of tunnel face control the stress concentration,but after 2 times the hole diameter, the maximum and minimum principal stress distribution will not change, indicating that the disappearance of spatial effects, stress released completely and rock deformation close to convergence; under the same condition of depth, the stress concentration degree is higher and the distribution range has been expanded of III rock classification than II rock classification after the tunnel excavation; Under the same condition of rock classification, with the depth increases and the stress level increased, resulting in rock's stress concentration increase seriously and the distribution range expanding; Different excavation manner led to the excavation face spatial effects have some difference, the last crown subsidence is biger by up and down stairs excavation of 2# and 4# diversion tunnels than full-face excavation of 1# and 3# of diversion tunnels. To sum up, excavation by step is benefit to the rock stability.