A Type of Asymmetric Distributed Deep-seated Crack Formation Mechanism–以白鹤滩水电站坝址区深部变形破裂为例
A type of asymmetric distributed deep-seated crack(DSC)formation mechanism has been uncovered.Based on DSC distributed in Jingping first stage hydropower station and Shenxigou hydropower station,the generalized characteristics and relationship of asymmetric distribution and river evolution mode has been revealed by field survey and in-situ test.The distribution,failure characteristics,deformation mode,geostress evolution and formation conditions of asymmetric DSC distributed in Baihetan hydropower station has been analyzed by integrated approaches of field survey,morphological analysis and in-situ stress test.The triaxial cyclic test designed according to geostress evolution has been carried out,and the deformation,strength and energy evolution process of aphanitic basalt has been uncovered.The statistical damage constitutive model(SDCM)based on statistical damage mechanics,Griffith strength criterion and test results mentioned above has been established,secondary developed and embedded in FLAC3 D by C++.The formation process including geostress variation,plastic zone distribution and energy evolution of DSC distribted in Baihetan hydropower station has been simulated by FLAC3 D.The results show that:(1)The DSC is a kind of special geological phenomenon which is tensional and tenso-shear failure and loosening belt with fresh no-filling or mud-intercalated slight weathering,banding and interval locally distributed in near surface action zone of high steep rock slope.(2)The spatial range of DSC distributed locally between 1/3~3/5 slope height and 50~225m in horizontal and vertical direction from slope surface.Furthermore,the distribution range had no obvious increasing trend with increase of elevation.(3)The synchronism relationship of river evolution process and distribution range of DSC suggests that the fluvial deviation-undercutting evolution mode accounts for asymmetric distribution of DSC.The DSC had located within the influence scope of high stress zone of river valley bottom,and it seems that the stress evolution of DSC had not been monotonous unload process,but rather cyclic load-unload process.(4)The DSC of Baihetan hydropower station has been located above large staggered zones and formed based on tectonic joint.Three types of deformation modes including shear type,tensile type and expansion type had been divided according to mechanics property and macroscopic geological characteristics.(5)Under triaxial cyclic condition,the total input energy(U)and releasable elastic energy(Ue)has increased power exponent with cyclic numbers increased,and dissipated energy(Ud)is larger in high confining pressure than low confining pressure.On the contrary,Young modulus has nonlinear decreased with cyclic numbers increased,generally and maximum drop is 20~30% and 40% respectively.The sample strength with drastic acoustic emission(AE)energy is obviously less than other samples.All the mentioned above suggest that the damage degree of aphanitic basalt is evidently violent under triaxial cyclic condition than conventional triaxial condition,and the damage degree is increased with cyclic numbers.(6)The statistical damage constitutive model(SDCM)has been established by statistical damage theory and Griffith strength criterion.SDCM is rational due to involve intermediate principal stress and only relate to stress-strain relationship based on micro-unit strength expressed by Griffith strength criterion.The preferable match of SDCM and test results suggests that SDCM can convey pre-and post-peak deformation process of aphanitic basalt.(7)Compared with multiple,homogeneous and cumulative energy release of intact rock mass,the DSC energy induced by high stress zone of river valley bottom is intensely one-off release.Single energy release quantity of DSC is 3~4 times of intact rock mass.Combined with the test results,the drastic energy transformation suggests that damage degree and strength reduction of rock mass is more remarkable and rock mass is more apt to failure.(8)The formation process of asymmetric distributed DSC has been divided into 3 stages successively: energy accumulation,energy release and failure extension.The formation conditions contain hard rocks,tectonic structure,high geostress background and fluvial deviation~undercutting evolution mode.The cyclic load-unload process induced by high stress zone of river valley bottom and intensive release subsequently,which give rise to damage accumulation and strength reduction of rock mass,accounts for the asymmetric distribution of DSC.