| Mountainous areas are characterized by complex terrain conditions and fragile ecological environment,and also face significant geological disaster risks during engineering construction.Ultra-high-steep rock slopes,as the main carriers of geological disasters such as landslides,rockfalls and debris flows,have their rock structure characteristics explored as an effective approach for the smooth implementation of disaster prevention and reduction in mountainous areas.However,the internal structures of rock masses are extremely complex under hundreds of millions of years of crustal movement.The rock masses are characterized by prominent inhomogeneity,anisotropy and discontinuity,which makes the local and global rock mass disaster analysis extremely difficult and hard to break through.As the weak planes of rock masses,discontinuities are the controlling boundaries of jointed rock mass disasters.Therefore,how to efficiently obtain and precisely describe discontinuities is the basis of carrying on the rock mass disasters.In addition,how the complex structures control the local and global disaster modes remains challenging and difficult.In order to deal with the challenges aforementioned,this study focuses on the“controlling theory of rock mass structure” and takes several ultra-high-steep rock slopes above the entrances and exits of a railway tunnel in the southwest China as the research objects.By proposing a multi-angle UAV nap-of-the-object photogrammetry measurement scheme,a major breakthrough in modeling precision from “centimeterlevel” to “millimeter-level” is made.An automatic discontinuity recognition and interpretation platform is built to improve the automatic interpretation efficiency of massive engineering geological models.Aiming at the complex geological phenomena of slopes,the 3D discrete fracture network simulation technology is improved and the3 D geometric boundary reconstruction of slopes is carried out.The multi-scale structural geological model of slopes is constructed,which truly reflects the mechanical influence of discontinuities with different scales on the slope stability.Considering the internal structure of rockfalls,the leap from rigid body dynamics to discrete medium dynamics of rockfall analysis is completed,and the dynamic fragmentation simulation of rockfalls is realized.The main research achievements and conclusions are as follows:(1)Combined with engineering geological elements of rock masses,a multi-angle UAV nap-of-the-object photogrammetry measurement scheme is proposed.The scheme constructs a technology system of “quick shooting – fine shooting – supplementary shooting”.On the basis of quick shooting using traditional nap-of-the-object photogrammetry,the multi-angle fine shooting is specially designed for the complex slope terrain units and different discontinuity development characteristics,and key areas are also considered by supplementary shooting,which can comprehensively ensure the acquisition of high-resolution images of the entire slope surface.The established model using the aforementioned scheme successfully realizes the breakthrough of modeling precision from “centimeter-level” to “millimeter-level”,making the discontinuities “clearly seen and accurately measured”,and promoting the fundamental improvement of the accuracy of structural disaster research.(2)Based on the point cloud domain and connectivity growth,an automatic recognization and interpretation algorithm for rock mass discontinuities is proposed,and a software platform ARFD-RMS(automatic recognization and fine descriptions for rock mass structures)is built.The platform divides the large slope area into several small areas through “parallel computing” to carry out the recognization and interpretation of discontinuities at the same time,which greatly improves the efficiency of automatic discontinuity interpretation.The platform is used to quickly recognize and fine descriptions the rock structures based on the above-mentioned “millimeter-level”realistic model.The results show that the platform successfully realizes the “hour-level”rapid acquisition of huge and complex discontinuity system information and the accuracy is up to 85,which promotes the intelligent development of rock engineering geology.(3)In order to solve the abnormal problem of discontinuity parameters caused by slope vegetation cover and frequent rockfalls,an improved 3D discrete fracture network(DFN)simulation method is proposed.The method is used to correct the discontinuity density by analyzing the different vegetation(stripe,dotted and face-like)developed in the slope surface.The sampling deviation of trace lengths caused by frequent rockfall is corrected,and the distribution characteristics of 3D geometric boundary radius are determined on the basis of “random number generation”.A possible solution to the problem of high sampling frequency of discontinuities parallel to slope surface caused by rockfall is proposed.Finally,based on the improved 3D DFN simulation method,the 3D DFN models of slope rock mass is reconstructed,which provides more accurate controlling geometric boundary information for rock mass disaster analysis.(4)In order to solve the problem that the number of discontinuities of ultra-highsteep slope is too huge and the sizes are various,a multi-scale structural geological model of slope is constructed.This model “explicitly” considers the geometric and mechanical parameters of large-and medium-scale discontinuities and “implicitly”considers the effect of small-scale discontinuities on the deterioration of rock mass strength,which not only embodies the complex structures of ultra-high-steep slope,but also greatly improves the computational efficiency of rock masses.The 3D stability of ultra-high-steep slopes is studied on the basis of the aforementioned model and the results show that large-scale discontinuities have obvious controlling effect on the global deformation of slopes,local unstable blocks are easily formed when large-scale discontinuities cutting with medium-scale discontinuities,so the slope failure often presents the phenomenon of local rockfalls and global instability.In addition,the more obvious the degradation effect of small-scale discontinuities is,the lower the stability of slope rock mass is.Therefore,the consideration of multi-scale discontinuities is an effective way to reasonably and accurately evaluate the stability of ultra-high-steep slope.(5)On the basis of the fine description of the shape,volume and internal discontinuities of the dangerous rock blocks,a method is proposed to simulate the rockfall movement and fragmentation considering the internal structures of rockfalls,which completes the leap from rigid body dynamics to discrete medium dynamics.By constructing a “double” visualization scheme of macro and micro in the dynamic fragmentation process of rockfalls,the fracture mechanism of macroscopical rockfall structures is explained from the perspective of crack propagation.The trajectory and kinetic energy of each fragment are monitored and the preliminary exploration of the slope dynamic response was also made.The results show that the rockfall movement can be divided into three stages:(1)Freely-falling stage;(2)Dynamic balance stage;(3)Accelerated movement stage.The rockfall trajectory is different from the linear trajectory obtained by traditional simulation,but the fan-shaped trajectory composed of many fragments,which has practical significance for the prevention and control of engineering rockfalls. |
