Developing Mechanism And Mitigation Techniques Of Massive Collapse

Perilous rock is a global and widely generated geologic hazard, which has a great geological hidden danger for the safety on mining product, mountainous highway, shipping traffic and mountainous towns. The direct economic loss exceeds two billion Yuan per year. For instance, on 5th, June, 2009, in Wulong County, Chongqing City, Jiwei Mountain had a oversized collapse, it caused over 80 dead. On 25th, July, 2009, on the Chediguan Bridge, position 44km+200, the highway from Dujiangyan to Wenchuan in G213, Wenchuan County, Sichuan Province, it arose mountainous landslip, and the rockfall broke the bridge pier, collapsed the bridge deck, caused 2 trucks fell into Min River, 6 dead and about one hundred million Yuan economic loss. Obviously, to take research on the formation mechanism and disaster reduction technology of massive collapse by single rockfall system is the national demand for the disaster reduction of mining, traffic and urban construction and the logical demand for the development of safety and disaster mitigation science.This paper adopts some research methods, such as, field survey, model experiment, numerical simulation, geomorphology, fracture mechanics, kinematics, wave theory, sensor technology, etc., to process some scientific problems on perilous rock systematically, for example, evolutional rules of rock avalanche, stability of perilous rock, ringing effect of massive collapse, movement routes of landslip rocks, mechanism of movement mechanics on massive collapse, technology on the emergency response, disaster mitigation and safety alarm, etc. The main innovative achievements are as follows:(1) According to the large-scale rock slope in the syncline structural zone within soft-hard interphase sandstone (limestone) and mudstone around Three Gorges Reservoir area, it reveals the developing mechanism of rock cavity, including difference weathering mechanism and fracturing weathering mechanism. It proposes concepts of macroscopic chain and microcosmic chain about landslip in rock slope with gentle inclined angle. Based on that, it posts the chained evolution rule of massive collapse, and divides the rules into two types, simple model and composite nested model.(2) It constructs the stability analysis method of perilous rock systematically, with the limit equilibrium theory, load types and combination on rock mass, stability evaluation standard and calculating methods on the coefficient of stability for different perilous rocks, etc. To focus on the fracture propagation at the dominant structural plane of perilous rock, is a scientific cognition for the essence of perilous rock failure. This article adopts the fracture mechanics to build stability analysis method of perilous rock's fracture, this method can reflect the online stability of perilous rock mass continuously, and it is the scientific basis for the emergency safety alarm of abrupt collapse hazard.(3) It analyzes the interactional mechanics relationship among perilous rock masses on the cliff, it discusses the rock avalanche sequence of packets collapse by damaage and fracture mechanics and it tests and verifies chained regular of perilous rock ,and it constructs the mechanics equations for dynamic vibrating on the ringing effect of perilous rock avalanche to the adjacent rock mass. It confirms ringing effect of perilous rock Landslip through the experiments, for that, the theoretical calculation is basically consistent with the experimental value, and the established dynamic vibrating formula accords with the objective reality.(4) Based on the dynamic recovery coefficient test on the lower cushion geotechnical medium, through the established maximal impact force formula to inverse the normal recovery coefficient of gravel cushion. The coefficient value lies between 0.258~0.314 and it accords with the objective reality. This paper divides the movement of landslip into four steps, free fall, initial collision, in-flight state and subsequent collision. It establishes calculating methods of the rock masses'motional velocity and distance under different motional forms. It proposes the discrimination standard of rockfall motional forms. And it confirms those conclusions by field experiments and numerical simulation.(5) This paper deduces the air compression equations for the bottom air of massive collapse. Through the air compression characteristic test of landslip rock mass, it primarily obtains the relation curve between air leakage coefficient at the bottom of collapse and the speed of collapse, and by the model of air compression experiment, it gains load of air cushion, air leakage coefficient and critical leakage coefficient at different height and different pore ratio. The production takes important positive significance for the further study on the movement process of packets collapse.(6) To aim at the emergency and hazard mitigation demand for the abrupt rock avalanche hazards of perilous rock, it develops a series of new technology and special equipment, such as, jury anchorage for perilous rock, borehole stress sensor of strain-type, borehole stress sensor of piezoelectric-type, energy dissipation shed-hole of rockfall and the safety alarm system, etc. It provides technical support for the emergency safety alarm and prevention of collapse hazard.To condense the above main research production into 4 innovations:(1) According to the mechanical relationship between the chained evolution rule of landslip and perilous rock mass in Three Gorges Reservoir area, this thesis adopts fracture mechanics, the produced stress intensity factors and equivalent stress intensity factors by the effect of equivalent bending moment, etc. to construct the time equation about the rockfall of perilous rock. And it reveals the collapse sequence of perilous rock on the cliff with soft base.(2) To take falling perilous rock as an aim, it establishes the vibrating model of rock avalanche. Based on fracture mechanics and wave theory, it constructs the formula of stress intensity factors under ringing effect. According to the collapse energy, it builds the calculating methods of transient departure speed, particle displacement speed and vibrating wave intensity for landslip. And it reveals the ringing effect of perilous rock systematically.(3) Through experiments, this thesis reveals that the normal recovery coefficient value of gravel cushion lies between 0.258~0.314, and it divides the movement of landslip into free fall, initial collision, in-light state and subsequent collision forms. Hereby, it puts forward some new calculating methods for the movement route of rockfall.(4) To aim at the prevention demand for the abrupt rock avalanche hazards of perilous rock, it develops a series of new technology and special equipment, such as, jury anchorage for perilous rock, borehole stress sensor of strain-type, borehole stress sensor of piezoelectric-type, energy dissipation shed-hole of rockfall and the safety alarm system, etc.