Representative elementary surface for morphology and permeability of natural rock fractures

摘要

Fracture surface morphology, mechanical and hydraulic properties are related to fracture size. One of the core issues in thesize effect is the representative elementary surface, which determines the size of the test specimens in the laboratory andfacilitates the application of test results to the field. In this study, the size effect on surface morphology and permeability ofrock fractures is investigated, and the representative elementary surface size for the surface morphology and the permeabilitywas determined based on the asperity height data of fracture surfaces obtained by 3D laser scanning in the field. The roughnessof fracture surfaces varies significantly at small fracture surface sizes. As the fracture surface size continues to increase,the fracture surface roughness tended toward a relatively stable state. The critical size for fracture surface roughness stabilityin the study, which is called the representative elementary surface, is 300-400 mm. The size effect on the permeability ofrock fractures was investigated, and the results show that fracture permeability tended toward a relatively stable state withincreasing fracture size, which was the same as the fracture surface roughness. The representative elementary surface sizefor fracture permeability is less than 100 mm in the study, which is also less than that for fracture surface roughness withthe same coefficient of variation. This result indicated that a lower coefficient of variation might provide the best estimateof the representative elementary surface for fracture permeability compared with the fracture surface roughness.