Comportement mécanique des remblais en pâte cimentés en compression et en cisaillement et étude du frottement aux interfaces remblai-remblai et remblai-roche

RÉSUMÉ Le remblai en pâte cimenté (RPC) une fois acheminé sous terre peut jouer le rôle de support secondaire des terrains encaissants. Grâce à cette fonction de contrôle de terrain, il est possible d’améliorer la récupération des piliers secondaires minéralisés tout en maintenant un bon niveau de sécurité pour les travailleurs et les engins. Le RPC peut également servir de plancher de travail ou de circulation d’engins lourds. Cependant, après sa mise en place dans les chantiers ouverts souterrains, les propriétés mécaniques du RPC évoluent au cours du temps. Cela peut être dû à des facteurs internes liés à la nature et à la quantité des composants du remblai. D’autre part, des facteurs externes comme le massif rocheux encaissant agissent sur le RPC. Toutes ces modifications du comportement mécanique du RPC, si elles ne sont pas connues et mesurées,peuvent causer sa rupture, par exemple lors de l’ouverture d’une face du remblai. Les conséquences pourraient être la dilution du minerai, des dégâts matériels (pertes économiques,des blessures et/ou voire des pertes en vies humaines.----------ABSTRACT The cemented paste backfill once routed underground can act as secondary support of mine stopes. This improves the recovery of secondary mineralized pillars while maintaining a good level of safety for workers and equipment. The cemented paste backfill (CPB) can also serve as working platform or circulation of heavy machines. However, after their incorporation in underground, the mechanical properties of the CPB evolve over time. This may be due to internal factors related to the nature and quantity of the CPB components. Furthermore, external factors also act as the bedrock in which the CPB is placed. All these changes in the mechanical behavior of the cemented paste backfill can create failure inside the CPB or at its interface. This can cause economic and human life loss

Direct shear tests on cemented paste backfill–rock wall and cemented paste backfill–backfill interfaces

This paper presents the results of the shear strength (frictional strength) of cemented paste backfill-cemented paste backfill (CPB-CPB) and cemented paste backfill–rock wall (CPB-rock) interfaces. The frictional behaviors of these interfaces were assessed for the short-term curing times (3 d and 7 d) using a direct shear apparatus RDS-200 from GCTS (Geotechnical Consulting & Testing Systems). The shear (friction) tests were performed at three different constant normal stress levels on flat and smooth interfaces. These tests aimed at understanding the mobilized shear strength at the CPB-rock and CPB-CPB interfaces during and/or after open stope filling (no exposed face). The applied normal stress levels were varied in a range corresponding to the usually measured in-situ horizontal pressures (longitudinal or transverse) developed within paste-filled stopes (uniaxial compressive strength, σc ≤ 150 kPa). Results show that the mobilized shear strength is higher at the CPB-CPB interface than that at the CPB-rock interface. Also, the perfect elastoplastic behaviors observed for the CPB-rock interfaces were not observed for the CPB-CPB interfaces with low cement content which exhibits a strain-hardening behavior. These results are useful to estimate or validate numerical model for pressures determination in cemented backfill stope at short term. The tests were performed on real backfill and granite. The results may help understanding the mechanical behavior of the cemented paste backfill in general and, in particular, analyzing the shear strength at backfill–backfill and backfill-rock interfaces