Study On Crack Propagation Characteristics And Reinforcement Method Of Freeze-thaw Rock Mass Test In Cold Region

In the cold area slope engineering,the slope rock mass is subjected to intense freeze-thaw cycle effect,which causes the expansion of the rock fracture development greatly affects the construction and safe operation of the project.In recent years,most research of rock fracture propagation under freeze-thaw cycle conditions are based on the experience of conventional engineering,but few theoretical support.Therefore,it is very important to study the crack propagation characteristics of rock mass under freeze-thaw cycle and the reinforcement method in cold regions.This paper relies on supervisor's program,takes the dacite of a hydropower station dam area in Tibet as the research object,through the freeze-thaw cycle test,uniaxial compression test,similar material test,x ray 3D laser scanning test,similar material fracture reinforcement.This paper studied systematically the macroscopic fracture extension rule and the physical mechanics properties of the similar materials under freeze-thaw conditions.Combined with the two studies and their physical mechanics properties,this paper discusses the reinforcement method of rock mass fracture in cold region engineering.The main conclusions are as follows:(1)With the increase of the number of freeze-thaw cycles,the quality of rock samples increases first and then decreases,and finally tends to be stable.The quality is slightly higher than the initial after freeze-thaw cycle;(2)It is concluded that the primary porosity and fissure of the study area are very rare,but its mineral grains will precipitate with different degree under the condition of freezing and thawing cycle because of the weak consolidation of the mineral grain.As a result,there are rules that a one-way extension,two-way extension and expansion extension about the pores inside of the sample,while the larger cracks will be around the smaller cracks around the extrusion effect,resulting in some small cracks closed;(3)There are three types of the fractured rock mass of freeze-thaw damage degradation modes :grain spalling mode,crack mode,the original fracture crack mode;It can be divided into five stages that the Single freeze-thaw cycle rock ring to the strain change over time : the cold stage,internal water freezing stage,frost heave stage,Melting shrinkage stage and stability of equilibrium stage;(4)Fracture reinforcement method study: In the cold area reinforcement engineering,the angle will affect the role of anchoring force to a certain extent.The smaller the angle between anchor fracture,the lower the anchor force acting on the fracture,therefore should be perpendicular to the fracture in the anchor support.Using inorganic ultrafine particles composed of high-performance grouting material pressure grouting,the slope of the rock can play a series of anchor and prevent water infiltration;(5)It is suggested that the fractured rock mass should be excavated and graded,as well as the drainage hole and the cutoff ditch are arranged.The slope of the excavation area is mostly fragmented,combined bolting and shotcrete net protection.In addition,the design should consider freeze-thaw conditions on the reinforcement effect of the bolt and shorten the displacement monitoring period to prevent the occurrence of anchor failure.