Study On The Great And Important Geological Problems Of Yintao Project In Gansu Province

Yintao project, which is a large scale flowing automatically diversion conservancy project across different drainage areas, and is the biggest water project in Gansu province. Its engineering geological conditions are very complicate, including the great and big engineering geological problems brought by the deep and thick covers of riverbed, the fault zone of the northern margin of Qinling, the high stress of deep-buried tunnel, the red stratums of the Cretaceous and the Tertiary, the collapsible Loess, the saturated loess etc.Through the comprehensive analysis of the engineering investigation datum and the results of scientific research of the "Yintao" project accumulated over the last several decades, the main engineering geological problems be analyzed and evaluated basing on engineering geological and mechanical view, and geological and structural theory and geological system theory. The main contents are as below:(1) Engineering geological problems of 3# tunnel across the fault zone of the northern margin of Qinling. The fault zone of the northern margin of Qinling is one of the six plates strips combination in China and is a regional active fault zone. Summarized up the results of past study, the distribution in earth surface, the structure in section, activities, the fault rock features of the fault zone, the relation with 3# tunnel and other aspects have been researched. It has concluded that the wall rocks of 3# tunnel through the fault zone have a poor stability and the construction will be difficult. The main engineering geological problems include the stability, washing, and the influence of the future faulting activities on the project, we should pay more attention to the gushing water, deformation, declination press, the expandability of wall rocks and other problems about stability and emphasized geological prediction, adjusting design and construction according to conditions in situ..(2) Engineering properties of the deep and thick cover of riverbed in "Jiu-dian-xia" dam site. The dam site has a narrow riverbed and deep trench. The general thickness of the riverbed cover is 40～50m, and the maximal thickness is 54～56 m. According to its particle composition and structure, the cover can be divided into three layers, the upper one should be excavated because it is improper to be foundation, so it should be pay more attention to the study on the middle layer and substratum. Basing on the drilling and sampling, laboratory test, lateral pressure test and loading test in situ, the basic physical and mechanical properties of the cover be determined comprehensively. Then the stabilities of the dam foundation on the thick and deep riverbed cover be analyzed and evaluated, and the formation mechanism of deep trench and the thick cover of the river be researched through the environments of rock mass and its geometric integrity. The main engineering geological problems in project area are infiltration, stability and vibration liquefaction.(3) The problem of tunnel stability which is made up of detrital rock of Cretaceous and tertiary: it summarized distributing characters of red stratums in China, basic described characters of red stratums in Gansu; and estimated its geological engineering characters, such as components, the physical, mechanical and hydrological properties, etc. It have been confirmed that red stratums is low bearing capacity, and large deformation. The main geological engineering problems are weathering, deformation, dispensability, leakage, washing, sliding, water erosion. It has been proved that stability of tunnel is mainly controlled by intensity of rock wall, water content and initial stress, and the type of deformation is of plastic, and NATM technology will be adopted in the construction of tunnel.(4) The problem of constructing technology on tunnel which is made up of saturated loess: No.13-15 tunnels of main cannel are located on saturated loess and 5608 meters in length. It examined and discussed relationship between engineering properties and granularity, microstructure, chemical and mineral ingredients. It also analogized stability of tunnels by traditional method with principal of Drucker-Prager associated flowage. As a result, the rock wall is very weak and shield structured method must be adopt in the construction.