Designing a local deformation gauge for one-dimensional compression testing in sand

This research focuses on developing a Local Deformation Gauge (LDG), inspired by the design concept of a proving ring for force measurement. The LDG is employed to measure vertical strain (ε_v) in a sand sample compacted within a CBR mold during one-dimensional (1D) compression tests. The primary objective is to assess the constrained modulus (M) of the sand sample under varying vertical stress (σ_v) levels, subsequently examining different bulk stress (θ) levels. The M value is determined separately from the ε_v value measured using the LDG (ε_v,LDG) and an external gauge (ε_v,EXT). A comparative analysis is conducted between the M-θ relationships derived from the two distinct M values. The study reveals that M values obtained from ε_v,LDG and ε_v,EXT increase with rising θ. Notably, when compared at the same θ, the M value derived from ε_v,LDG is significantly greater than that from ε_v,EXT. This discrepancy in M values is attributed to bedding errors occurring at the contacts between the sand sample and the cap and base. The development of an arching effect within the sand sample leads to imperfect movement synchronization between the LDG and the sand sample.