Analytical solutions for the design of shotcreted waste rock barricades to retain slurried paste backfill

Abstract Over the past decades, filling underground mined-out openings (stopes) with slurried backfills has witnessed a significant growth in the mining industry. To do so, retaining structures frequently called barricades should be built in access drifts near draw points to keep the slurried filling materials in place. Barricades made of waste rock (often produced from underground development) are constructed in a more convenient and sustainable manner at lower cost, compared to traditional barricades made of high-strength man-made materials. In recent years, a few analytical solutions have been developed for sizing waste rock barricades (WRB) based on limit-equilibrium analysis. These solutions correspond to such cases when there are no reinforcements made to WRBs except for compaction. A full cover of the entire surface of downstream slope may result in poor drainage and built-up of high pore water pressures behind WRB. Shotcrete is thus usually sprayed over the upper part. More commonly, when constructing a WRB, shotcrete is sprayed on the downstream slope over the upper part (about one third) of a barricade to promote its stability as a whole and to prevent local failures at the barricade top, especially for a WRB with limited top length. To take this aspect into account, new analytical solutions are proposed here to design the integrated backfill barricade built with waste rock and shotcrete. The proposed solutions can be used to estimate the dimensions of shotcreted WRB and strength of shotcrete. An instability criterion, based on the first occurrence among displacement jump of the barricade top or coalescence of currently yield zones, is introduced to help judge the onset of instability of a shotcreted WRB structure. The validity and predictivity of the proposed analytical solutions were calibrated and verified using numerical simulations. Sample calculations are also conducted to illustrate the shotcreted WRB design (i.e., required cohesion and top length) by considering global and local stability. The proposed solutions correlate well with numerical simulations for representative stope height, barricade and shotcrete geometries and properties of waste rocks and shotcrete. The proposed solutions can thus be used to evaluate the required cohesion cs and top length LSL of shotcrete, based on the global and local stability analysis. The proposed solution can also be used to estimate the size of WRB when the parameters of shotcrete are known.