Rupture and safety of perilous rock are dominated by control fissure behind perilous rock block. Based on model-Ⅰand model-Ⅱ stress strength factors of control fissure under acting of weight of perilous rock, water pressure in control fissure and earthquake forces, method to calculate critical linking length of control fissure is established. Take water pressure in control fissure as a variable periodic load, and abide by P-M criterion, when control fissure is filled with water, establish the method to calculate fatigue fracture life of control fissure in critical status by contributing value of stress strength factor stemming from water pressure of control fissure in Paris’s fatigue equation. Further, parameters C and m of sandstone with quartz and feldspar in the area of the Three Gorges Reservoir of China are obtained by fatigue fracture testing.

Hitherto，perilous rock is the weakest topic in disasters studies．Specially, damage of control fissure under loads is one key technique in study of develop mechanism of perilous rock．Damage division of end area of control fissure was defined by authors，then calculation methods of timed-Poisson’s ratio and timed-Young’s modulus were established in damage mechanics theory．Further，the authors set up dam age constitutive equation of control fissure．which founds important basis to numerical simulation for control fissure to develop．

Velocities of solid phase and liquid phase in debris flow are one key problem to research on impact and abrasion mechanism of banks and control structures under action of debris flow。Debris flow was simplified as two-phase liquid composed of solid phase with the same diameter particles and liquid phase with the same mechanical features。Assume debris flow was one-dimension two-phase liquid moving to one direction．then general equations of velocities of solid phase and liquid phase were founded in two-phase theory．Methods to calculate average pressures，volume forces and surface forces of debris flow control volume were established．Specially，surface forces were ascertained using Bingham’s rheology equation of liquid phase and Bagnold’s testing results about interaction between particles of solid phase．Proportional coefficient of velocities between liquid phase an d solid phase was put forward，meanwhile，divergent coefficient between theoretical velocity and real velocity of solid phase was provided too．To state succinctly before．method to calculate velocities of solid phase and liquid phase was obtained through solution to general equations．The method is suitable for both viscous debris flow and thin debris flow．Additionally．velocities every phase can be identified through analyzing deposits in-situ after occurring of debris flow．It is obvious from engineering case the result in the method is consistent to that in real-time field observation。

As one weak topic in research of debris flow, abrasion of debris flow shortens obviously application life of control structure composed of concrete. High-speed drainage structure, one of the most effective techniques to control giant debris flow disaster, has shortened one- third application life due to abrasion by debris flow. Based on velocity calculation method founded by two-phase theory, research of abrasion mechanism of debris flow to high-speed drainage structure was made. The mechanism includes both abrasion mechanism of homogeneous sizing and shearing mechanism of particle of debris flow to highspeed drainage trough structure. Further abrasion equations of both sizing and particle were established by Newton movement theory of debris flow. And abrasion amount formula of the high-speed drainage trough structure is set up by dimensional analysis. Amount to calculating in the formula is consistent with testing data in-situ, which is valuable in design of high-speed drainage structure.

Using normal and shear rigid coefficients of intact rock and fracture plane, rigidly normal, shear equivalent rigid coefficients of fissure rock mass are conducted. On the basis of hypotheses of small displacement of rock mass, principle of superposition, irrelevance of strength parameters C and φ and Coulomb theory, formulas to calculate equivalent strength parameters C and φ of equivalent continuous mass from fissured rock mass with anchor piles are given. The achievement is extremely valuable in integral stability analysis of the rock mass slope and important in promoting the research of the rock mass’s constitutive relation.