Tikou Belem

Chemical factors that influence the performance of mine sulphidic paste backfill

Sulphide-rich tailings from four Canadian mines were sampled (Mines A1, A2, B and C) to prepare several different paste backfill mixtures. The sulphur grade within these tailings samples range from 5 to 32 wt.%. The binders used were Portland-cement-based binders, fly-ash-based binders and slag-based binders with proportions ranging from 3 to 6 wt.%. The study was carried out in two stages. Stage I allowed us to understand the effects of binder type, binder proportion and tailings properties on compressive strength development of paste backfill during the course of curing time. It was pointed out that for high sulphide tailings, neither the slag-based binders nor the fly-ashbased binders were effective, whereas the sulphate-resistant-based binder (mix of Type I [TI] and Type V [TV] Portland cements) gave good long-term strength. However, the slag-based binders gave the best strength for low and medium sulphide-bearing tailings for which the Portland- and the fly-ash-based mixtures have a relatively low strength. Stage II allowed us to study the early stage strength acquisition of the various mixtures. It was found that the chemical composition of the mixing water plays a role on the mechanical behavior of certain cemented backfills. D 2002 Elsevier Science Ltd. All rights reserved.

Geometric analysis of damaged microcracking in granites

Abstract Practically identical samples are tested at the same confining pressure and temperature but at different deviatoric stress levels. Thin sections are observed using an optical microscope and recorded as images in order to study the crack network evolution. The compound cracks are decomposed into elementary cracks (right segments) with constant orientation and then reassembled in order to determine crack length and cumulated crack length. The results of crack observations are discussed in the light of the mechanisms of crack evolution at microscopic level compared to the stress–strain curves. It results from our observations that mean crack length increases only moderately in comparison with maximal crack length and the number of cracks. Zhao reports similar results (cf. Zhao, Y., 1998. Crack pattern evolution and a fractal damage constitutive model for rock. Int. J. Rock. Mech. Min. Sci. 35 (3), 349–366). The evolution of microcracking can be attributed more to new crack nucleation rather than to growth of the pre-existing cracks.

Relationship between wood porosity, wood density and methyl methacrylate impregnation rate

Abstract Mercury intrusion porosimetry (MIP) was used to evaluate the impregnation mechanisms of wood by methyl methacrylate (MMA) through examining the changes in porosity, pore volume, pore size distribution and bulk density of solid wood before and after MMA impregnation. Porosities of MMA-impregnated (hardened) wood samples were lower than those of solid wood samples for six studied species, five hardwoods and one softwood. Densities of hardened wood were enhanced from 45 to 130% depending on the species. The pore volume available for mercury intrusion was shifted from pore d>0.1 µm for solid wood to pore d≤0.1 µm for hardened wood. A pore diameter of 0.1 µm was used as the transition point for MMA impregnation and the increased mercury penetration below this point was attributed to the MMA polymer pore structure. Porosity as an intrinsic property of wood appears to be the main determinant of impregnation rate and polymer retention, especially for porosity with pore diameter >0.1 µm. The results indicate that the MIP technique is an effective tool with which to study the impregnation process.

Assessment of the Modified CUAPS Apparatus to Estimate In Situ Properties of Cemented Paste Backfill

This paper evaluates some improvements in the design of a laboratory apparatus called curing under applied pressure system (CUAPS) designed to estimate in situ properties of cemented paste backfill (CPB). This apparatus is effective in conducting the following tests on samples during curing: (i) One-dimensional consolidation test with or without pore water pressure (PWP) measurement, (ii) PWP dissipation test, (iii) saturated hydraulic conductivity (permeability) test, and (iv) curing under constant or variable vertical pressure. Unconfined compression tests can be also performed on consolidated CPB samples after each of these tests. The modified CUAPS apparatus is assessed in this paper. Preliminary results are promising and validate the functionality of the CUAPS apparatus, which will contribute to the knowledge on consolidation behaviour of in situ CPB material.

Auscultation of a Dam for Mining Restoration in Quebec, Canada

The tailing management is a long term concern for environment and social security. Following the discovery of a new gold mineralization, a mining company aims at reusing one of tailings storage facility at the mining site. However, there is a small treated water reservoir (polishing pond) downstream of the Northwest dam. It is therefore important to know the present state of the Northwest dam’s internal structure. Geophysical methods of electrical resistivity and georadar were used for the auscultation of the Northwest dam. Numerical models were subsequently used to assess the geotechnical behavior of the dam in different deposition situations by simulating the restoration. The image processing results of georadar data show a layered structure near the surface. Changes in electrical resistivity offer deeper information than georadar. The lateral variability of the electrical resistivity corresponds to heterogeneity within each layer. As we cannot collect samples for the characterization of materials, the geophysical interpretation results help to estimate the compositional structure of the dam; ultimately it helps in numerical modeling on the safety factor estimation.