Study On Engineering Geology Of Red Bed Soft Rock Tunnel In Yintao Project

Yintao project,a large scale inter-basin artesian diversion work,is the biggest hydraulic engineering in Gansu province.Its engineering geological conditions are very complicate,including the red beds of the Cretaceous and the Tertiary,the large deformation of tunnel's surrounding red-bed soft rock,the stability of surrounding rock and so on.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 physical,mechanical and water reasonableness properties of the Cretaceous and the Tertiary red beds are systematically studied by field exploration, direct shear testing,in-situ test of elasticity modulus of rock mass,sonic wave testing of rock mass,laboratory rheological test,grain size analysis and XRD of clay minerals relying on 7^# experimental tunnel.On the basis of above researches, the rational engineering geological parameters were obtained.Those parameters can be used to design tunnel,predict tunnel's surrounding rock deformation accurately, and choose reasonable reserved deformation.Some countermeasures and recommendations are proposed according to the engineering geological problems arose from TBM construction in 7^# and 9^# tunnel.The research results can be applied to Yintao project directly,providing geological support for the optimization design,and providing reference for similar projects.Meanwhile,the research enriched and developed the theory of red beds engineering geology.The main research contents and results are as follows:(1)Based on the existing research achievements,the regional geological environment,topography and geomorphology,neotectonics and formation lithology of Yintao project are analyzed and evaluated with the theoretical guidance of tectonic theory and geological system theory.By means of the investigation and analysis,the distribution of red beds was checked out in Yintao project area.(2)Applying the past engineering investigation datum and research results of the Yintao project,the physical and mechanical indexes of the Cretaceous and the Tertiary red beds are systematically studied and determineded(identified)by field exploration and laboratory tests.On this basis,the red beds lithology and engineering geological petrofabric are evaluated quantitatively and classified objectivly.(3)By the laboratory rheological test,the stress - strain - time relationship curve of red-bed soft rock was obtained and the rheological characteristic was analyzed. After model identification research,the results shown that the rheological characteristics of red-bed soft rock conform to the Burgers model.Using Marquardt iterative method,rheological parameters were obtained under different load and deformation conditions.The rheological parameters are far lower than the hard rock. The results reflect that neogene argillaceous siltstone and silty mudstone has remarkable rheological property.(4)On the basis of above research results,the quantitative engineering geology conceptual model of red bed soft rock was established.This kind of rock mass is made up of mudstone,argillaceous siltstone and silty mudstone,and its outward appearance is red.It has the following characteristics:loose structure,low mechanical strength,large deformation and remarkable rheological property.Its saturated uniaxial compressive strength is less than15MPa,elastic modulus is less than 10GPa,viscosity coefficient ranges from 1.0×10¹²to 1.0×10¹⁴pa·s.Engineering manifestations of the rock has the characteristics of plasticity,swellability,disintegrability,rheology and ion-exchange.If the soft rock or the weak interlayer in the soft-hard alternant bed controlled entire rock mass's deformation and strength characteristic,this kind of rock mass belongs to the category of red rock soft rock.(5)Combining with the deformation monitoring results and using the physical and mechanical parameters obtained from field test and laboratory experiment,the deformation characteristic of red bed soft rock tunnel was analyzed under different depth condition by engineering geology analogism,theoretical calculation and numerical calculus methods(applying the Mohr-Coulomb criterion,the Drucker-Prager criterion and Burgers model).Then,the maximum deformation of red bed soft rock tunnel was forecasted under different condition.(6)The advantages and disadvantages of TBM construction and drilling & blasting method,as well as the feasibility of use the TBM construction in 7^# and 9^# red bed soft rock tunnel of Yintao project were analyzed based on engineering geological conditions,engineering design,construction organization design,project investment,technology and economy.The possible engineering geological problems in TBM construction will be large deformation and sudden water inflow depending on statistical analysis of engineering geological problems occurred in TBM constructions and red bed soft rock tunnels.According to the engineering geological problems brought by TBM construction in 7^# and 9^# tunnel,some countermeasures and recommendations are proposed to solve the rational reserved deformation,which should range from 9 to 13 cm.The research results provide a fundamental basis for TBM design and construction.