Reliability analysis of block sliding in large brown coal open cuts
- Authors: Xue, Jianfeng , Tolooiyan, Ali
- Date: 2012
- Type: Text , Conference paper
- Relation: The 2012 World Congress on Advances in Civil, Environmental, and Materials Research (ACEM'12) p. 1578-1587
- Full Text: false
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Measurement of pore water pressure properties of unsaturated brown coal using triaxial test
- Authors: Couling, Catherine Elizaebth , Tolooiyan, Ali , Mackay, Rae , Xue, Jianfeng
- Date: 2014
- Type: Text , Conference paper
- Relation: 6th International Conference on Unsaturated Soils, UNSAT 2014 p. 1531-1535
- Full Text: false
- Reviewed:
- Description: Skempton's B parameter characterises the effect of fluid compressibility on the time dependent deformation of materials during isotropic loading. The Skempton B-parameter has been determined for a sample of Victorian brown coal for a range of confining pressures, corresponding to the range of conditions which the coal experiences below the ground water table. The relationship between the change in the B-parameter with respect to time and pressure has also been examined. It has been found that a high back pressure (more than 400 kPa) is required in the material to achieve a degree of saturation close to 100+ACU-. The set of data from these tests is able to provide important evidence of the depth and stress dependent behaviour of the coal.
Experimental study of brown coal hydraulic behavior at low confining stress
- Authors: Liu, Kan , Mackay, Rae , Xue, Jianfeng , Tolooiyan, Ali
- Date: 2014
- Type: Text , Conference paper
- Relation: 6th International Conference on Unsaturated Soils p. 1125-1130
- Full Text: false
- Reviewed:
- Description: The hydraulic behavior of Victorian brown coal has been studied under low pressure confining conditions. A triaxial constant head permeameter was constructed to carry out permeability tests under alternative confining conditions. Test results from alternative constant head test methods were found to be different indicating higher than expected internal storage due to the possible existence of gas in the coal matrix and/or compressibility of the coal grains. A conceptual model of brown coal with disconnected gas bubbles was proposed to explain the observed variation of hydraulic behavior. In this model, the compressible gas bubbles are assumed to be trapped between compressible coal particles. A numerical model was developed to gain insights into the hydraulic influence of these factors and the model was used to simulate the test process. Constant hydraulic conductivity was assumed. The results from the model and the tests are found to compare well. The model explains most but not all of the observed behavior.
Performance of a geogrid reinforced soil wall on PVD drained multilayer soft soils
- Authors: Chen, Jianfeng , Tolooiyan, Ali , Xue, Jianfeng , Shi, Zhenming
- Date: 2016
- Type: Text , Journal article
- Relation: Geotextiles and Geomembranes Vol. 44, no. 3 (2016), p. 219-229
- Full Text: false
- Reviewed:
- Description: A geogrid reinforced soil wall was built on Prefabricated Vertical Drain (PVD) improved multilayer soft soils at the end of a road embankment in Shanghai, China. One day after the last loading stage, an arc shaped settlement was observed on the embankment surface with little observable cracks on the side slopes, and sudden increase of pore water pressure was observed in the piezometers installed in the PVD improved zone. A three dimensional finite element analysis was carried out to compare the performance of the wall with PVDs functional and dysfunctional. The comparison supported the assumption that the PVDs may have failed during construction due to bending or kinking of PVDs caused by the large settlement and lateral movement in the ground. The analysis showed that the movement of the wall toe is very sensitive to its location in the cross direction. Therefore attention should be paid while using toe movement as an indication of wall stability. It shows that the failure had mainly taken place in between the shoulders of the embankment rather than the whole wall. For a full slide to develop, pull out or tensile failure may occur in the reinforcements on the side slopes. Large stresses can be generated in the geogrids in the cross embankment direction due to the uneven settlement observed in the ground. Considering this, biaxial geogrid should be considered if the stress is too high and the inclusion of wrap around geogrids on the side slopes may help to increase the integrity and stability of the wall. © 2015 Elsevier Ltd.
Measurement of water pressure properties of unsaturated brown coal using triaxial test
- Authors: Couling, Catherine Elizabeth , Xue, Jianfeng , Tolooiyan, Ali , Mackay, Rae
- Date: 2014
- Type: Text , Conference paper
- Relation: Unsaturated Soils: Research & Applications Vol. 1
- Relation: Proceedings of the 6th International Conference on Unsaturated Soils, UNSAT 2014
- Relation: Sydney, Australia, 2-4 July, 2014
- Full Text: false
- Reviewed:
- Description: Skempton used the B-parameter (see Equation 1) to represent the degree of saturation of a material, such that, B → 0, when the degree of saturation = 0 and, B → 1, when the degree of saturation = 1 Δ Δ Δu B[ (Δ A+ )]σ3 1σ 3 (1) where, Δu is change in pore water pressure, A and B are pore-pressure coefficients, and σ3 and σ1 are minor and major principal stresses.
Measurement of the tensile strength of organic soft rock
- Authors: Tolooiyan, Ali , Mackay, Rae , Xue, Jianfeng
- Date: 2014
- Type: Text , Journal article
- Relation: Geotechnical Testing Journal Vol. 37, no. 6 (2014), p.
- Full Text: false
- Reviewed:
- Description: 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, 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 100 kPa. 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.