Evaluation of a new grain breakage factor based on the single grain crushing strength

In granular soils subjected to high-level shear stress, a micro-damage occurs in the soil's internal structure, referred to as grain breakage. The main factors controlling grain breakage are the applied stress level and the single grain crushing strength of the individual grains (σ_f). This paper presents a laboratory study on ballast grains' single grain crushing behavior. Double-plate grain crushing tests were carried out on dolomite, calcerous, and basalt origin grains, having sizes ranging from 2.00 to 37.50 mm. Factors affecting the single grain crushing strength, such as grain shape, loading rate, and grain size, were investigated. Individual grains' single grain crushing strength was observed in three phases related to granular soils' 3-staged one-dimensional compression behavior. An equation that considers grain shape in terms of grain sphericity (form) has been proposed to determine the single grain crushing strength. One-dimensional compression tests were performed on uniformly graded soil samples consisting of calcerous and basalt origin grains. The single grain crushing strength of the calcerous origin soil sample's mean grain-sized grains was determined to be 12.7 MPa, and this value was determined to be 25.6 MPa for the sample consisting of basalt origin grains. One-third/fourth of this single grain crushing strength value was obtained as the virgin compression line (VCL) initial stress of the soils’ one-dimensional compression curve (4.3 and 6.0 MPa for calcerous and basalt origin soil samples, respectively). The final stress of the VCL was determined to be close to 1–1.25 times of this specified single grain crushing strength (16 and 26 MPa for calcerous and basalt origin soil samples, respectively). The change in the mean grain size of the soil samples (d₅₀) during one-dimensional compression was defined as an exponential function. A new grain breakage factor depending on the single grain crushing strength of the soils’ mean grain-sized grains has been proposed to determine the grain breakage that develops under one-dimensional compressional conditions.