| Debris flow is a common geological phenomenon, loose material and water is a necessary condition for the formation of debris flow. Numerous studies show rainfall, snowmelt, melting ice make the water content of the loose debris increase and strength reduction, which breaks the original system of force balance, is the inner reasons for the formation of debris flow. The strength of the deposits is determined by its own characteristics. The study on the strength of the deposits can provide the foundation for the establishment of the mechanical model of debris flow. Therefore, the paper based on lab large-scale direct shear test and particle flow simulation program to study the strength characteristics of debris flow deposits, has important theoretical significance and practical engineering value.Papers in Nanjiao gully, Mentougou district of Beijing fangshan district of Damo gully debris as the research object, through a series of physical test, X-ray diffraction test and lab large-scale direct shear test, the strength of the particle composition, analyzed composition mineral composition and deformation characteristic sand the strength and deformation characteristics,used PFC2 D program for numerical simulation of direct shear test, combined with the results of laboratory tests were studied microscopic mechanical properties. The studies suggest that:(1) Two kinds of debris particle size composition of gravel content is higher, and the fine grain content is low. Two kinds of debris mineral composition is basically the same, Nanjiao gully debris is given priority to with primary mineral, its content is much higher than the primary mineral content of the Damo gully.(2) The shear stress and shear displacement relationship curve shape of the deposits of Nanjiao gully and Damo gully is largely the same, into three stages: in the shear deformation stage began, the shear stress and shear displacement curve form a straight line approximation; with the increase of shear displacement, curve tends to be gentle and gradually reached peak intensity; in the latter part of the shear process, the curve is gradually decreased and when the vertical stress is 100 kPa, curve showed a significant strain softening phenomenon.(3) Contrast two kinds of deposits soil samples shear strength parameters in four kinds of water rate can be found, when the moisture content is 1%, 3%, 5%,to Damo gully deposits, the internal friction angle of Nanjiao gully deposits is larger; when moisture content is 7%, the two kind of deposits soil internal friction angle are basically the same; when the water content is the same, Damo gully deposits cohesion is much larger than the deposits of Nanjiao gully.(4) By shear stress simulation test was- shear displacement curve, the shear strength envelope curve fitting and comparing the results of laboratory tests can be found, the degree of agreement with the experimental simulation curve is better explained by particle flow code can be more accurately simulate the direct shear tests. When the moisture content is the same, compared with the simulation test laboratory test, the internal friction angle was slightly larger, while the cohesion was slightly smaller.(5) In different water cut conditions in the simulation, the direct shear test appeared different degree in the process of the shear dilatancy phenomena and apparent shear zone. The shear zone of the simulation of the shear direct test occurred mostly in the height of 16 cm ~ 23 cm range, the influence of the vertical stress and moisture content is smaller, and the width of the shear zone is about 6cm ~ 8cm The model’s internal contact force significant changes have taken place in the shear process, there has been stress concentration in the lower left and upper right of the boundary forming a plurality of main chain of stress,and stress direction undergone significant tilt. |
PDF Full Text Request