| Rockfall often occurs on rocky slopes in high mountain valley areas,which is a typical natural disaster formed by fast moving rock masses.Rockfall is characterized by high velocity,high energy and over-concentration of impact.The initiation and movement of rockfall are hidden and complicated,which make the early identification and later treatment of rockfall disasters very difficult.For unstable rocky slopes,especially landslide remnant scarp,rockfall hazards are more frequent which poses a great threat to people,vehicles and construction facilities nearby.Based on terrestrial laser scanning and numerical simulation,this paper takes two landslide remnant scarps,the Huashiya remnant scarp and Hongshiyan remnant scarp,as examples to complete the rockfall analyses from data collection to rockfall source identification and rockfall hazard assessment,and finally to the design and optimization of rockfall mitigation measures.The major results are as follows:(1)The basic concepts and definitions of rockfall and rockfall hazard were illustrated.The concepts of rockfall probability,intensity and frequency were clarified,based on which the definitions and calculation formulas of rockfall susceptibility,hazard and risk were elaborated.Moreover,the role of rockfall inventories and vulnerability of threatened objects in quantitatively rockfall hazard assessment has been illustrated.(2)The differences,characteristics and advantages of two-dimensional and threedimensional rockfall models are compared and analyzed,and the concepts and definitions of rockfall motion were elaborated.The models and calculation methods of free fall,rolling-sliding and collision of rockfall were studied in detail.The influence of terrain resolution,restitution coefficient,friction on the rockfall motion was analyzed.The disturbance of small ground undulation,such as dead wood and isolated rocks,on rockfall movement was illustrated.Then,the basic and probabilistic models of rockfall motion are proposed.(3)The mechanism of plane failure,toppling and wedge failure of rocky slopes was studied,and the initial process,destabilization mode and influencing factors of rockfall are elaborated.The remote identification of structure surface of rock slope was realized by remote sensing technology.The K-clustering fuzzy method was applied to automatically identify the structure plane of large-scale rocky slope.The research results were successfully applied to the Huashiya landslide remnant scarp to realize the accurate identification and localization of rockfall source area.(4)The factors affecting the simulation of rockfall movement were studied,which included the 3D terrain model,the statistics of rockfall history and the mechanical parameters of the ground.The method of terrain data acquisition based on remote sensing technology was introduced,and the advantages and disadvantages of terrestrial laser scanning and UAV technology are compared.A qualitative analysis method of rockfall frequency-magnitude based on limited rockfall inventories is proposed to identify the parameters of rockfall source area in the absence of sufficient historical data.The inversion of 3D rockfall motion parameters based on 3D back analysis was conducted.The research results were successfully applied to the run-out simulation and hazard assessment of the rockfall of the remnant back scarp of the Huashiya landslide and Hongshiyan landslide,revealing the distribution and intensity of the rockfall disaster.(5)Common rockfall control measures including slope-clearing,rockfall protection trench,vegetation protection,cushion layer,flexible protection system,concrete retaining wall and slope reinforcement were illustrated,and the strength limit,capacity limit and application limit of these measures were elaborated.Based on the concept of cost-benefit,a design and optimization method of rockfall prevention and control measures considering various factors such as the terrain,topography,rockfall frequency,rockfall intensity,features of protection area,construction cost and implementation difficulty was proposed.This method made full use of the strength limit of structural protection measures and improved the capacity limit of nonstructural measures,realizing the optimization of rockfall protection system. |
