Ali Tolooiyan

Measurement of the Tensile Strength of Organic Soft Rock

Understanding all potential slope failure mechanisms is a pre-requisite for predicting the likelihood of batter movements during excavation in open cut mines. The tensile behavior of soils and rocks may be a significant contributor to a slope failure and must be known in order to quantify the risks of slope failure. The contribution can be particularly significant for Intermediate Geotechnical Materials (IGMs) that possess characteristics of both soils and rocks and where the failure mechanisms are complex due to the interplay between ductile and brittle behavior. Brown coal is such an intermediate geotechnical material. Recent batter movements in the brown coal mines in the Latrobe Valley, Australia have raised doubts about the current understanding of the mechanisms of slope failure in this material. Research is underway to re-evaluate all properties of the brown coal applicable to slope failure. This paper describes the investigation of brown coal tensile strength. There are alternative test methods available to determine the tensile behavior of materials, including direct tensile tests, beam bending tests and Brazilian compression tests. The applicability of each test method is material dependent and, as such, it is necessary to confirm the validity of the methods for each material. Beam bending tests have achieved mixed results for both rocks and IGMs previously. Thus, the present work has explored only the use of Direct tensile and Brazilian test methods. Both methods were implemented using a modified direct shear apparatus and valid test procedures for both test methods were developed. Each test procedure has been verified by Finite Element Modelling (FEM) using ABAQUS 6.12.1 FEM code. The results from the laboratory test methods are in good agreement and show that brown coal is a predominantly brittle material with a peak tensile strength slightly greater than 100u2009kPa. The finite element analyses confirm that non-uniformity of the tensile stresses during sample loading tends to lead to the underestimation of tensile strength for both tests, but the Brazilian test has less bias for brown coal. It is observed that the rate of loading of low stiffness, low permeability, and saturated samples in the Brazilian test is an important test design parameter for the accurate determination of tensile strength of IGMs in the laboratory.

Optimisation of strength reduction finite element method codes for slope stability analysis

One of the modern methods for estimating the factor of safety for the stability of slopes is the strength reduction method. In recent times, computer codes have utilised the strength reduction method in conjunction with finite element analysis. This paper explores the implementation of a strength reduction finite element method with FORTRAN and Python codes in conjunction with the computer-aided engineering package Abaqus, incorporating a modified strength reduction definition, allowing for a refinement of the factor of safety search space. The computational efficiency of the modified method is compared with the traditional technique, for both 2D and 3D analysis. The algorithm results are compared for contrasting FEM element types and geometries and benchmarked against proprietary geotechnical finite element solvers.