etude experimentale de la resistance en traction de residus miniers non satures a l'aide d'essais de flexion

The responsible disposal of mining wastes is a challenge that needs to be addressed. Mining operations produce a variety of waste materials such as waste rocks and tailings. Tailings, which contain a high percentage of fine particles, are generally stored in an initially saturated state, in tailing impoundments surrounded by dikes. Over time, such tailings tend to consolidate, and may become unsaturated due to drainage and evaporation, which makes their behavior more complex. It is important to understand the behavior of unsaturated tailings in order to predict their response in the field.;Unsaturated tailings (as well as soils) as submitted to a negative water pressure (suction). This negative pressure creates capillary forces that contribute to the cohesion between particles. This apparent cohesion is not an inherent (intrinsic) property of the material as it varies with the amount of pore water and the related degree of saturation. The apparent cohesion is correlated to the tensile strength and it has a significant impact on the mechanical behavior of unsaturated materials such as mine tailings.;This project focused on the evaluation of the tensile strength of unsaturated mine tailings. Several studies on this subject have been carried out on clayey soils and cemented materials, but granular (cohesionless) materials such as tailings from hard rock mines have not received much attention. Thus, this research aimed at developing a better understanding of the tensile behavior and associated properties (i.e. apparent cohesion and modulus of elasticity) of unsaturated tailings.;The methodology consisted of experimental tests and numerical analyses. The laboratory tests were performed on three types of tailings, with fairly similar properties, obtained from different mine sites. The laboratory testing program included the development of an experimental method, based on bending tests, to assess the tensile strength as a function of the degree of saturation of the tailings. For this purpose, prismatic moulds used to perform shrinkage tests were used to prepare the specimens. The homogeneity of these specimens (in terms of water content) was examined to validate the preparation procedure. The results demonstrated that the water content is relatively constant in the prismatic specimens.;The force and deformation measured up to failure during 67 bending tests are presented in the thesis. The measured data were analyzed using the elastic theory to determine the tensile strength of the samples. These provide relationships between tensile strength and degree of saturation. The experimental study also included the evaluation of effect of the void ratio (initial and final) on the tensile strength. The experimental values of the tensile strength were also compared with results obtained from predictive models.;Young's modulus was also determined using the strength and measured vertical deflection during the bending tests on tailings. The tensile strength values were also used to assess the apparent cohesion as a function of the degree of saturation using the effective angle of internal friction (obtained from another study). The relationship between suction and tensile strength (and apparent cohesion) was also investigated.;In addition, the finite element code SIGMA/W 2007 (Geo-Slope Inc) was used to simulate the results from bending tests conducted on tailings at different water contents. The basic geotechnical properties of the tailings and the measured force up to the specimens' failure were used to reproduce the experimental observations. The numerical simulations were carried out using the linear elastic and elastic-plastic constitutive laws. Calculations resulted in vertical deflection, tensile strain and tensile strength values that are quite close (but usually smaller) to the experimental results. The effect of Young's modulus and apparent cohesion on the specimen behavior was also investigated using the elastic-plastic (EP) model. The results indicate that these two parameters can have a significant influence on the deflection (and deformation) and stress state within the tailings specimens.;The influence of geometrical factors (i.e. thickness h and length L), Poisson's ratio and loading rate was also investigated numerically. The results show that increasing the specimen thickness tends to decrease the time for failure, which is related to the apparition of yield zones in the model. Increasing the specimen length L increases the vertical deflection and the failure time. These simulations indicate that the Poisson's ratio only has a small effect on the response of the material during such bending tests.;This research fulfilled the initial objectives and addressed other important issues related to the strength of unsaturated tailings. The results presented here should be useful for future work on their geotechnical behavior.