Experimental investigation on porosity reduction of a coarsely crushed rock layer subject to vertically cyclic loading

- Porosity monitoring in samples with vertically cyclic loading was conducted.
- Cyclic loadings can cause breakage and abrasion of aggregates or their edges.
- Factors affecting on porosity reduction with cyclic loading are examined.
- Porosity reduction weakens quickly till stable with cyclic loading.
- Long-term cyclic loadings can weaken the cooling capability of embankment.

The long-term cyclic loadings from traffic and maintenance may weaken the occurrence of buoyancy-driven natural convection of the pore air in the coarsely crushed rock layer during winter months and the effectiveness of cooling down the embankment and underlying foundation soils, thus resulting in instability and failure of the highway/railway embankment structure. Obviously, successful application of the coarsely crushed rock embankments in cold regions has to study both theoretically and experimentally the impact of cyclic loadings on the particle shape, grain size distribution and rearrangement of the crushed rock aggregates and the porosity variation of coarsely crushed rock layer. Therefore, some experiments on the crushed rock samples with dimensions of 75 × 75 × 87 cm under vertically cyclic loadings have been carried out. Three coarsely crushed rock samples with initial grain sizes of 16-40, 25-50 and 50-80 mm were used to measure the related parameters to study their variations in cooling capability after the vertically cyclic loadings, respectively. The experimental approach on examining the particle shape and grain size distribution variations and the rearrangement of the crushed rock aggregates and the porosity reduction of the crushed rock layer under vertically cyclic loadings is developed. The porosities of three crushed rock samples with vibrating loading cycles have been measured using the water flooding approach.The results show that the cyclic vibrating loadings can cause the breakage and abrasion of the particles and their edges in the coarsely crushed rock layer and the particles also tend to be rounding and non-angular. These result in rearranging of particles and decreasing of particle size and increasing of fines content in the coarsely crushed rock layer, thus reducing the porosity of the crushed rock layer. Compared with the initial average porosities before cyclic loading, the reduction rates of final average porosity in three crushed rock samples after cyclic loading with 18,000 cycles reach to 6.53, 7.45 and 8.08% corresponding to initial grain sizes of 16-40, 25-50 and 50-80 mm, respectively. These reduction rates of the final average porosities in the vibrated crushed rock samples after cyclic loading increase relatively with increasing of an initial grain size. Under such conditions, the long-term cyclic loadings from traffic and maintenance can weaken the effectiveness of cooling down the embankment and underlying foundation soils due to natural convection in the coarsely crushed rock layer during winter months.