Abstract
Crushed waste rock can be used as backfill in goafs to allow re-use of otherwise solid waste and to control surface subsidence. If a certain lateral stress is applied to crushed waste rocks beforehand, they are densified. Therefore, this research investigated the effects of lateral stress on compaction characteristics of waste rocks for backfilling by utilising a self-designed bidirectional loading test system for granular materials. Furthermore, this study tested the changes in the mechanical parameters on lateral and axial loading of waste rocks for backfilling and measured the influence of lateral stress on lateral strain, axial strain, porosity, and lateral pressure coefficient during compaction. The test results demonstrate that (1) lateral stress affects porosity, strain, and the lateral pressure coefficient of crushed waste rocks for backfilling in lateral and axial loading. (2) In lateral loading, the greater the lateral stress, the larger the lateral strain and the reduction in lateral porosity. (3) Under axial loading, for the samples on which a high lateral stress is applied, because the porosity of waste rocks is decreased in advance, the density increases, thus finally resulting in a lower axial strain. (4) After compaction, the particle size distributions of the samples of the crushed waste rocks under four lateral stresses all shift upwards compared with those before compaction, implying that particles are crushed. However, lateral stress does not reach the crushing strength of waste rock particles, which exerts only a small influence on the crushing of particles before and after compaction.
Highlights
In large-scale mining of coal resources in China, solid waste rock is produced and the discharge thereof accounts for about 10–15% of coal production [1,2,3,4]
Waste rock dumps lead to serious geological disasters, such as collapses and landslides [12,13,14,15]
Waste rocks are filled into underground goafs, which processes otherwise waste and controls stratum movement and surface subsidence [18]
Summary
In large-scale mining of coal resources in China, solid waste rock is produced and the discharge thereof accounts for about 10–15% of coal production [1,2,3,4]. Waste rock dumps occupy large areas of land and pollute the air by spontaneous combustion, and contaminate soil and underground water as a result of rainfall [8,9,10,11]. Waste rocks are filled into underground goafs, which processes otherwise waste and controls stratum movement and surface subsidence [18]. Such a method for backfilling has significant social, economic, and environmental benefits, so it is of wide interest. After filling crushed waste rocks into goafs, crushed waste rocks are gradually deformed due to compaction under the Minerals 2018, 8, 552; doi:10.3390/min8120552 www.mdpi.com/journal/minerals
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
