Building demolition waste (BDW) has been massively stockpiled due to increasingly rapid urbanization and modernization. The use of recycled BDW as unbound granular base/subbase materials is among the sustainable, cost-effective, and environmentally friendly pavement construction alternatives. The resilient modulus is an important mechanical property of BDW-derived aggregates and mechanistic design input of pavements incorporating BDW. This paper presents the results of a comprehensive laboratory study on the shear strength and resilient modulus characteristics of BDW-derived aggregate materials. A series of monotonic triaxial compression tests and repeated-load triaxial (RLT) tests were conducted with five different gradations representing particle breakage and different stress paths. The apparent cohesion and internal friction angle of recycled BDW aggregates under consolidated drained conditions ranged from 35.3 to 57.5 kPa and from 30.2° to 54.3°, respectively. The apparent cohesion and internal friction angle also increased and decreased non-linearly with the increasing relative content of fine particles, respectively. The resilient modulus of recycled BDW aggregates gradually decreased with increasing relative content of fine particles at the same stress level. Both the deviator stress and confining pressure exhibited significant influences on the resilient modulus, while the effect of confining pressure was more profound. Based on laboratory testing data, a mechanistic-empirical model was developed to predict the resilient modulus of recycled BDW aggregates from gradation and stress-state variables. The findings could be useful for extended engineering applications of BDW in unbound granular pavement base/subbase construction.

The high-speed railway (HSR) subgrade has a strict settlement-control standard at the mm level, but its deformation stability is significantly threatened on permafrost with poor thermal stability and in susceptible-to-thawing settlements. Therefore, the filler suitable for permafrost regions needs to be explored and determined. In this study, the frost heaves, permeabilities and static strength characteristics of three coarse fillers were experimentally investigated, and the optimal subgrade filler was determined for the certain HSR, the first HSR in permafrost regions around the world. The test fillers include pure fillers, 5% cement improved fillers and 5% cement + 3% modifier improved fillers, and the effects of curing time, modifier content and freeze–thaw cycles were analyzed. The test results show that: (1) the frost heave rate and permeability coefficient decrease with the increase of curing time and modifier content, while increasing with the freeze-thaw cycles; (2) After six freeze–thaw cycles, the cement + modifier improved filler’s frost heave rate and permeability coefficient are 0.51 and 0.00331 cm/s, a larger decrease in the frost heave rate (more than 50%) and the permeability coefficient (about one order of magnitude) than that of pure filler; (3) The cement + modifier improved filler shares the highest compressive strength under different curing times and freeze-thaw cycles. In summary, the modifier has a more significant influence on the engineering characteristics than the curing time or freeze-thaw cycles, and the cement + modifier improved filler has the best comprehensive performance. This study will provide a technical reference for the foundation-treatment and disease-prevention of HSRs in island permafrost regions.