In situ measurements of cemented paste backfill at the Cayeli Mine

Abstract

Cemented paste backfill (CPB) is accepted as the optimal backfilling material for many underground mines. However, the lack of in-stope backfill pressure data poses fundamental problems from both operational and research standpoints. In response to the requirement for in situ data, a comprehensive field instrumentation project has been conducted. Results are presented here for two stopes at the Cayeli Mine, where geotechnical instruments were installed at the barricades and throughout the stopes. Measurements from a large (slow rise rate) stope with high binder content CPB demonstrated a rapid departure from hydrostatic loading, resulting in relatively low barricade pressures. Conversely, data from a smaller (fast rise rate) stope with lower binder content CPB demonstrated that when cement hydration is retarded, high barricade pressures occur. These examples illustrate the relationship between CPB rise rate and the moderating effect of cement hydration on in situ pressures, which ultimately control barricade pressures. Once CPB gains shear strength, arching of pressures occurs. In situ pressures were reduced with proximity to stope walls and further, under stope access brows, demonstrating that barricade location influences barricade loads. The application of real-time pressure monitoring of pastefill barricades has been demonstrated as an important tool in optimizing operational backfilling efficiency.

Temperature Change and the Total Stress Anomaly in Paste Backfill

“…The arching causes the total vertical stress to reduce from 12 kPa to about 6 kPa (50% reduction) in 6 minutes. This consolidation phenomenon has also been found in the full scale monitoring [3][4][5][6][7][8][9][10]. Figure 6d shows that there is no change in the total vertical stress after the consolidation is completed.…”

“…The general observation in Figure 3 is summarized from several full scale monitoring reports [3][4][5][6][7][8][9][10]. However, stress anomalies are found in some reports [3][4][5][6][7][8], where the total vertical stress increases during the rest period as illustrated by dash dot lines in Figure 3.…”

“…However, stress anomalies are found in some reports [3][4][5][6][7][8], where the total vertical stress increases during the rest period as illustrated by dash dot lines in Figure 3. This is obviously not expected since there is no paste is poured during the rest period.…”

Stress Distribution in a Cohesionless Backfill Poured in a Silo

“…6079 succursale Centre-ville, Montreal, Quebec, H3C 3A7 Canada; Tel: 1-514-340-4711 #2408; Fax: 1-514-340-4477; E-mail: li.li@polymtl.ca conduits buried in trenches. Since then, the arching theory has been widely used in stress estimation within backfill placed in municipal trenches [6][7][8], in powder silos [2,[9][10][11], behind retaining walls [12][13][14], and in mining stope [15][16][17][18][19][20][21][22][23][24][25][26][27][28]. The occurrence of arching is also a well-known phenomenon in dam cores confined by granular soils [29], around piles driven in soft soils [30], in soft soils above a tunnel [31,32], and beneath a stockpile [33,34].…”

“…Under field conditions, several influencing factors, such as irregular geometry, physical and hydraulic properties evolution in the fill and along the fill-wall interfaces, temperature, displacement of confining walls, dynamic loading due to the passage of vehicles for municipal infrastructures or production blasting in mining stopes, could be concurrently involved. This makes the interpretation of experiments a great challenge [2,25,27,40,41]. In contrast to field tests, laboratory experimentations allow the control and measurement of the main influencing factors.…”