Christianne de Lyra Nogueira

Formation of Secondary Containment Systems Using Permeation of Colloidal Silica

U.S. Environmental Protection Agency (USEPA) regulations require the capture of spills from liquid tanks containing hazardous chemicals by using a secondary containment system. Compacted clay or geomembrane liners are commonly used in secondary containment systems, but they are cumbersome when used in conjunction with existing liquid tanks because of pipeline networks surrounding the tanks. This study evaluates the formation of hydraulic barriers for secondary containment through the permeation of colloidal silica grout. A sim- plified infiltration model is presented to predict the downward movement of the colloidal silica grout into a soil layer, considering the time- dependent increase in dynamic viscosity of the colloidal silica for different concentrations of an electrolyte accelerator. Because the simplified infiltration model cannot predict the soil-grout interaction or the permeation of the colloidal silica by fingering, its results were calibrated by using the observations from a large-scale column test involving the permeation of colloidal silica into sand. The predicted position of the wetting front was found to match that of the experiment when the parameter governing the change in viscosity of the colloidal silica was increased by a factor of 30. The infiltration model calibrated with observations from column infiltration experiments provides a simple approach to the design of the secondary containment systems using permeation of colloidal silica. DOI: 10.1061/(ASCE)EE.1943- 7870.0000345.

Use of the DCP test for compaction control of staged dikes in mining tailings dams

An alternative method for quality control of earthworks in mining tailing dams is described in this article. It is composed by a penetrometer, known by the acronym DCP (Dynamic Cone Penetrometer), and is used primarily in road construction (quality assessment of pavement layers). With this apparatus, strength measurement of superficial layers of natural and compacted soils can be performed, including mine sand tailings, in a fast and efficient manner. The instrument was successfully used in the construction control of an iron ore mining tailings staged dam in the Quadrilatero Ferrifero, in Minas Gerais State, and the results showed distinctly effective densification of the embankment compacted layers, but with a sort of irregularity in their spatial distribution. In addition, field control using the traditional core-cutter method was also performed for comparison between both techniques.

Numerical simulation of hillside mine waste dump construction

In activities involving disposal of mine waste in a dump, it is necessary to carry out a preliminary study of the mechanical behavior of both dump and the foundation materials. Due to the complexity of this problem, numerical techniques are essential for providing an approximate answer to the problem. Thus, the finite element method (FEM) was used to evaluate the stress-strain-strength behavior of a hillside waste dump built on a deformable foundation by the ascending method; the results of which are herein presented. The dump material is considered to be Morh-Coulomb nonlinear elastic perfectly plastic while the foundation material is considered to be linear elastic. The numerical simulation of mine waste dump construction is carried out by the “gravity turn on” technique and the dynamic mesh procedure. Different geometric configurations are analyzed and it is concluded that some requirements established by law should be reviewed and refined.

Non linear elasto-plastic analysis of cylindrical cavity in rock mass using a Hoek-Brown criterion

This paper aims to present an elastic, perfectly plastic, constitutive model based on the Hoek-Brown failure criterion and with non-associative plasticity. The objective is to apply the model to the non-linear analysis of geotechnical problems like excavations in rock mass. The computational implementation was carried out with a computational program called ANLOG (Non-Linear Analysis of Geotechnical Problem) system based on a displacement formulation of the finite element method. Due to the non-linear nature of the constitutive model, the study adopts an incremental iterative Newton-Raphson procedure with automatic load increments to guarantee the global level equilibrium. In addition, to guarantee the consistency condition at the local level, the study adopts, for the stress integration, an explicit algorithm with automatic sub-increments of strain. To validate the computational implementation and applicability of the numerical model, the study uses theoretical results to compare with ones obtained with the numerical simulation of cylindrical cavity in rock mass.

Análise numérica do processo de ressecamento de um rejeito fino da mineração de ferro

To obtain analytical solutions for desiccation analyses of soft soil such as mine tailing slimes is difficult because of the non-linearity of the material constitutive relationships and complexity of the problem boundary conditions. Thus, it is more attractive to use of numerical models to address the desiccation phenomenon. This paper presents a numerical model for desiccation of a fine mine tailings produced by milling processes of iron ore. The modeling is based on the theory proposed by Abu-Hejleh (1993) and uses a finite difference computer code associate to that theory. This model was calibrated using field data from a previous work and results from laboratory tests. Good agreement was found between simulation results and field observations suggesting applicability of the numerical model in future designs to enhance effectiveness of the desiccation process.

Formulação numérica, via MEF, de problemas de adensamento considerando a variação do nível d'água.

A fully coupled isoparametric formulation based on the finite element method to solve consolidation problems due to the drawdown of the water table is presented in this paper. The primary variables of this formulation are displacement and total hydraulic head. The free surface is considered as a changing contour and its location is determined by the use of the residual flow procedure, in which the water, firstly stored in the porous of the soil between two consecutive free surfaces, is imposed as a flow across the actual free surface. A strategy to reduce the permeability, necessary to minimize the flow in regions with negative pore pressure, is adopted. The numerical model is implemented in an ANLOG computational code to solve problems in a plane strain state. Examples to validate this formulation are presented.

Formulação numérica de limite inferior para problemas de estabilidade de taludes em solos reforçados

This paper presents the Lower Bound formulation for stability problems by the finite element method (FEM), and its applicability to continuous media or reinforced soils. In case of reinforced soils, two formulations are described using equivalent continuous model and discrete model. The studied examples show the potentiality of the solution method for practical problems in geotechnical engineering.