Study On The Discriminant Model Of The Movable Critical Depth Of Soild Matter In The Source Area Of Debris Flow

Solid source is one of the three basic conditions for the formation of debris flow.The existence of solid source is related to the occurrence,development process and scale of debris flow.Movable solid matter is a concept with clear physical meanings proposed by predecessors.It aims to study the solid matter of debris flow from a mechanical point of view.The determination of the movable critical depth is the core of the quantification of the movable solid matter.Based on this,the relevant research is carried out around the determination of the movable critical depth,and the main research results are as follows:(1)Based on mechanical analysis,a discriminant model for the critical depth of solid matter movable under the action of saturated seepage,seepage and runoff is established.and the different discriminant models were analyzed;Secondly,the influence of the slope type(concave,convex)on the initiation of solid matter and the relationship between the corresponding critical depth of initiation and the movable critical depth of the straight slope type are discussed.The analysis results show that:(1)For the discriminant model of solid matter start-up under saturated seepage conditions:the action force of seepage water body on solid matter includes the seepage force and the scouring force due to the high seepage velocity;(2)For the solid matter start-up discrimination model under the combined action of seepage and runoff:(a)Under saturated seepage and runoff conditions,for an almost inviscid solid material,the ratio of the critical start-up depth to the runoff depth has a boundary,and it varies with increasing slope and runoff depth increase;(b)Under unsaturated seepage and runoff conditions,for viscous solid materials,the initiation critical depth decreases with increasing slope;(3)The relationship between the initiation critical depth H_a(H_t)of different slope types and the movable critical depth H_p of straight slope type is:H_a(H_t)=H_p-2/3h_m,where h_m is the distance between the bottom of the concave slope and its corresponding chord.(2)Carrying out physical simulation tests to verify the established discriminant model;at the same time,the water-soil coupling characteristics and seepage,erosion and other regularities under the changing conditions of the slope,incoming flow,solid matter composition and slope type are discussed.The results show that:(1)For uniform non-sticky debris:(a)The erosion pattern is traceable erosion;(b)The height of the head parallel to the direction of the slope decreases with the increase of the slope,and increases with the increase of the inflow;(c)the seepage velocity and hydraulic gradient in the slope body have a power function relationship,and the seepage state is turbulent;(d)The sum of the hydrostatic gradient of static pressure and dynamic pressure increases with the increase of the incoming flow,and decreases first and then increases with the increase of the slope;(2)For inhomogeneous and non-sticky debris materials:(a)The erosion pattern is runoff erosion;(b)The erosion rate has an exponential relationship with energy slope gradient and hydraulic radius,it has a positive correlation with incoming flow and residual shear stress;(3)For saturated solid matter containing viscous materials:(a)The initiation pattern is traceable and runoff erosion;(b)The anti-scouring ability of the material is higher,the greater the inflow and slope,the greater the turbulent energy of the water flow,the greater the scouring rate and range;(4)The scouring rate of solid material increases with the increase of fine clay content;(5)The solid material in the groove is difficult to start,and the side proves that the relationship between the critical depth of different slope types and the movable critical depth of a straight slope is reasonable;(6)The solid material initiation discrimination model under saturated seepage and the combined action of saturated seepage and runoff critical depth models are all well verified by the test data.(3)A typical debris flow case is selected to verify the discriminant model.First,hydrus software is used to simulate the rainfall infiltration characteristics of solid matter in the debris flow source area to obtain the hydrodynamic conditions and initiation pattern.According to the hydrodynamic conditions and initiation pattern,the corresponding discriminant model is selected to calculate the amount of possible starting solid matter in the source area,and compared with the previous results.The relative error between the two is 18.1%.The result shows that the established model is reasonable.