No abstract

In this study, numerical analysis of an embankment dam was carried out to predict settlement behavior with the use of the Mohr-Coulomb Model (MCM) and of the Hardening Soil Model (HSM). The MCM was applied to all material zones of the dam and the HSM was used for four major material zones that occupied significant volume. The settlement response of the dam was similar for MCM and HSM for three material zones (clay core, sandy gravel and random fill), each having a modulus of elasticity (MOE) in the range of 25000 to 50000kPa. However, it was found that after the end of the construction, the MCM showed about 57% and 50% more settlement as compared to HSM when MOE of sandy siltstone varied from 70000 to 125000kPa respectively. The results regarding the dam settlement predicted with the HSM are in agreement with the findings in previous studies.

No abstract

In an upstream tailings dam, loose layers might occur at different depths due to melting of frozen layers deposited during freezing temperature in Sweden. Reduced shear strength of such layers in a tailings dam might cause stability problems. Due to slow consolidation process, it is unknown, whether self-weight of a high tailings dam could have influence on strength and stiffness of soft tailings located at different depths. For numerical modelling, appropriate strength and stiffness properties of soft tailings are needed. For this purpose, loose layers in an upstream tailings dam were identified based on results of cone penetration tests.Consolidated Drained (CD) triaxial tests were conducted on undisturbed soft tailings collected from different depths of the dam. The results indicated that depth did not have considerable influence on strength and stiffness of tailings. Hardening Soil Model (HSM), at high confining pressures and axial strains underestimated stiffness of soft tailings under CD triaxial state. This study shows that: (i) proper care is needed in evaluating strength and stiffness parameters for soft tailings, and (ii) use of the HSM is likely to predict more deformations which could give an early warning before an actual failure of a tailings dam.Keywords: Soft tailings; Stress-strain behavior; Triaxial tests, Hardening Soil Model, strength and stiffness. IntroductionTailings dams may be constructed using three methods such as: upstream, downstream and centerline [1]. Tailings dams raised using upstream construction method are relatively economical as compared to ones constructed with other two methods [1]. It is generally understood that soil becomes stronger in deep layers as compared to the surface. This implies that lower layers in an embankment dam might be stronger than those at the top. This is because the strength is dependent on the confining pressure coming from the layers above. Materials StudiedThe undisturbed samples of tailings were collected from various locations of Aitik tailings dam. Void ratio and bulk density of tailings obtained from various depths are shown in Table 1. Samples were collected from those layers of the dam which were described as loose according to CPT results. Particle size distribution curves conducted by [6] showed that the tailings particles at shallow depth were more angular than those obtained from deeper depths.All samples were fully saturated having water content from 15 to 44%. The average specific gravity and bulk density of the studied tailings were 2.83 and 1.73-1.98 t/m 3 , respectively.Place Table 1 here.All tests were subject to axial strain rate of 5 × 10 −3 mm/min. The axial strains were measured indirectly by volume changes in lower chamber, and radial strains were calculated from changes in specimen height and volume. Similarly, volumetric strains were calculated from changes in back volume of specimen by measuring amount of water coming into or going out of specimen and initial sample dimensions. The axial deformations in the test s...

For the settlement computation of an embankment dam, the soil stiffness is of great importance. Unfortunately, due to the lack of funds allocated for geotechnical investigation, stiffness parameters are commonly not evaluated as compared to strength properties. As a result, this may create hindrance in the use of advanced constitutive models such as Hardening Soil Model (HSM). In this study, the settlement with respect to depth and long term settlement of an embankment dam computed with Mohr-Coulomb Model (MCM) is compared with that of HSM applied to foundation soil only with limited data on stiffness. The results show that the MCM overestimated settlement in comparison with HSM. The settlement increment of MCM, in comparison with HSM, at the crest and at the depth of 120m was 53% and 82% respectively after the filling of the reservoir. The settlement computed with MCM and HSM were 2.9% and 1.35% of the dam height. It can be interpreted that the settlement predicted with MCM is unrealistically high due to the single constant value of modulus of elasticity (MOE), while the predictions of HSM are in agreement with the literature. In addition, the long term settlement computed using MCM is about 59% higher than that of HSM for the condition after the filling of the reservoir. This paper shows that the settlement of an embankment dam could be predicted reliably by using HSM even when a limited number of stiffness data is available.