Experimental investigation on the strength characteristics of cement paste backfill in a similar stope model and its mechanism

The strength comparison of cement paste backfill (CPB) in situ and laboratory exhibit contrary results both in some publications and case-based data. Based on this issue, this paper investigates the strength characteristics of CPB in a stope. A group of experiments in a large similar stope model (SSM) was designed for simulating the consolidation of CPB in a stope, then the unconfined compressive strength (UCS) test on specimens cored in the different position of CPB sample in SSM was conducted. Moreover, macrostructure (high-definition photography and borehole imaging) and microstructure (scanning electron microscopy, SEM) were carried out to help to explain the mechanism. The results indicate that: (i) the strength presents a wave-type change along the horizontal flow direction of paste; (ii) in the gravity direction, the strength decreases gradually from the bottom to the top of the SSM, and there exists sharp changes at some top sections of the SSM; (iii) SEM analyses indicated that the specimens of higher strength showed more compact structure and denser hydration products of Aft, C-S-H and Ca (OH). The strength characteristics of CPB in SSM can be explained by sediment dynamics combined with the macrostructure, microstructure, and 4 strength zones can be concluded accordingly. The studies may guide both backfill study and design. (C) 2017 Elsevier Ltd. All rights reserved.