Experimental Examination of the Arching Mechanism on the Micro Level

Abstract

The arching phenomenon is manifested through the reduction of stresses experienced by underground structures. Arching plays an important role in geotechnical engineering construction, such as excavations, retaining structures, pile groups, tunnel boring machines, culverts and underground facilities. The arching mechanism is intrinsic to granular material/rock mass independent of scale effect. Its fundamental mechanism relates to the ability of discrete units to transfer loads through interaction in a preferable geometry, and thus to bridge between the zone (or point) of load application to the zone (or points) of reaction. Though investigated extensively, very little work has been done to address the fundamental mechanism related to the discrete particles interaction. Testing results of an advanced experimental technique is presented and analyzed. A model of granular material made of photoelastic particles is utilized. The model and the sophisticated image and global data acquisition system allow one to track the development of the arching within ideal granular material during a trap door experiment by following the motion of each particle and the contact forces between the particles. Visual and quantitative analyses are presented demonstrating the relationship between the global arching phenomenon and the particle interaction on the micro-level. The information allows one to observe the changes associated with the arching mechanism and the stress variation resulting from it. Comparisons are possible between DEM and the test results.