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

- A model was designed to investigate the strength properties of backfill in a stope.
- The strength presents a wave-type change along the flow direction in the model.
- The strength decreases gradually from the bottom to the top in the model.
- Some analysis methods and theories were selected to explain the results.

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.