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.

Accurate predictions of drying rates are desirable to optimize surface deposition of thickened or paste tailings. A series of laboratory and field trials were implemented to study evaporation from tailings at the Bulyanhulu gold mine and were compared with numerical simulations using the unsaturated flow model SoilCover. The laboratory tests included two “large-scale” experiments on 10 cm thick layers of tailings 2 m by 1 m in plan, and a smaller column test on a 20 cm thick and 20 cm diameter sample. Data monitored during these tests included albedo, volume change, degree of cracking, matric suction, water content, and drying rate. Field data included gravimetric water contents and albedo values. The model could reasonably simulate the laboratory experiments when adjustments were made to account for self-weight consolidation and the effect of volume change on the relative permeability function. The model could simulate drying in the field for up to 3 weeks after deposition before the accumulation of gypsum and magnesium sulphate salts began to affect evaporation. Cracking and salt accumulation were observed both in the laboratory and in the field. A general model for simulating drying from paste tailings should incorporate the effects of cracking and salts.

External corrosion is a major factor contributing to the deterioration of cast iron water mains; it weakens the pipe wall, which increases the risk of failure. External corrosion is a function of the interaction between the pipeline and the soil that surrounds it. The aggressiveness of soil towards cast iron is affected by soil properties such as resistivity, pH, and the presence of sulphate reducing bacteria. Water main sections and accompanying soil samples were collected from locations across Toronto within the framework of a comprehensive research project over a 2 year period. After careful examination of the effect of each of the soil properties, it appears that soil resistivity has the largest effect on the observed maximum average pitting rate. Limitations to the practical application of the American Water Works Association soil corrosiveness scoring system are also presented. A preliminary spatial analysis of the data indicates that water mains in the district of Etobicoke have had a higher average rate of external corrosion than those in the district of Toronto. Microbiological corrosion could be an aggravating factor in the district of Etobicoke, since areas exhibiting increased levels of sulphide concentration were identified in soils that had originated from this district.Key words: water mains, external corrosion, soil properties, Toronto, cast iron, pipes.

Hydration occurring in cemented paste backfill (CPB) is shown to generate matric suction through self-desiccation. This complicates determination of the water-retention curve and mechanical properties during curing, which are important in stope design, and renders problematic the use of axis-translation testing procedure to control suctions in strength testing. An alternative is to monitor suction directly during testing. To this end, a miniature tensiometer is inserted into the base of a triaxial cell. A series of unconfined and confined tests are performed on early-age (less than two weeks old) CPB. The observed behaviour is similar to that observed in weakly cemented soils, showing a distinct tendency to dilate during shearing.