1. The document describes the failure of pit slopes at the Deilmann Tailings Management Facility (DTMF) due to collapse of loose outwash sand deposits when resaturated during flooding.
2. Finite element modeling was used to model the stress paths in the sand and ensure stresses did not reach the collapse surface during remediation activities or final flooding. A designed rock buttress was added to prevent triggering of collapse.
3. Geotechnical analyses including limit equilibrium and finite element modeling were used to design slope remediation including flattening slopes and adding a rock buttress to achieve long-term stability with factors of safety over 1.3 and prevent localized collapse triggering.
(2010) - Yates M, Krzeminski M, Berthier D, Hamidi B - The Application of Jet...Michal Krzeminski
Jet grouting was used to construct the Runway End Safety Area for Sydney International Airport. It was needed to bridge over existing structures in a way that stabilized the ground, provided bearing capacity, and created an impermeable barrier. A complex design of jet grout columns with varying diameters, lengths, and reinforcement was implemented based on detailed modeling. Over 1,600 jet grout columns totaling over 13,000 meters in length and 5,100 cubic meters in volume were constructed using a double fluid system to meet the project's geotechnical requirements.
This document provides guidance on ensuring geotechnical slope stability for post-mining landforms. It discusses designing stable slopes for landforms such as low wall spoil, out-of-pit dumps, and final void batters. It emphasizes the importance of geotechnical investigations and slope design to prevent issues like lost production, safety risks, and remediation costs. Data collection should consider factors like foundation strength, slope stability, and drainage for dumped materials.
Mine water risk in open pit slope stabilitySafdar Ali
The document discusses mine water risk and its impact on open pit slope stability. It analyzes the slope stability of a chromite mine in India under three conditions: dry, drained, and undrained. Slope stability analysis was performed using the SLOPE/W software. The factor of safety was highest for the dry condition (1.277) and lowest for the undrained condition (1.230). Proper drainage is required to maintain stability as water can reduce shear strength and increase pore pressure.
The document summarizes the design and construction of the foundations for the Rion Antirion Bridge in Greece. An innovative foundation concept was adopted using steel tubular piles driven into the seabed to reinforce the soil, with a gravel layer between the piles and the concrete caisson foundation. This concept provided seismic capacity and minimized differential settlement risks. Close cooperation between designers, contractors, and reviewers was essential to developing and implementing this challenging foundation solution.
The document discusses various factors that affect slope stability and methods to determine slope stability. It addresses how gravitational forces, water, earthquake activity, slope angle, and rock structures can impact stability. Specific triggers for landslides include rainfall, erosion, construction activities, and earthquakes. Slope stability is determined by calculating the factor of safety, which compares resisting and driving shear forces based on a slope's cohesion, internal friction, and other properties. A factor of safety below 1 indicates a slope is unstable.
R16 41013.2 stability analysis of slopesPoorna Nagidi
The document discusses slope stability analysis. It defines slopes and describes types of natural and man-made slopes. Slope stability is important for earth dams and natural slopes to prevent catastrophic failures. Factors that cause slope instability include gravitational forces, seepage water, surface erosion, lowering of adjacent water levels, and earthquakes. Common types of slope failures are rotational, translational, compound, and wedge failures. Rotational failures occur along a circular or non-circular slip surface. Translational failures occur along failure surfaces parallel to infinite slopes. Compound failures combine rotational and translational slips. Wedge failures involve separation of soil blocks along inclined planes of weakness.
The document provides information about slope stability analysis. It defines a slope and describes natural and man-made slopes. It discusses causes of slope failure such as gravitational forces, seepage, erosion, and earthquakes. Methods of slope stability analysis are described including infinite slope analysis, finite slope analysis using wedge failure, friction circle, and Swedish circle methods. Factors of safety are defined with respect to shear strength, cohesion, and friction. The aims of slope stability analysis are to assess stability, understand failure mechanisms, and design preventive measures.
(2010) - Yates M, Krzeminski M, Berthier D, Hamidi B - The Application of Jet...Michal Krzeminski
Jet grouting was used to construct the Runway End Safety Area for Sydney International Airport. It was needed to bridge over existing structures in a way that stabilized the ground, provided bearing capacity, and created an impermeable barrier. A complex design of jet grout columns with varying diameters, lengths, and reinforcement was implemented based on detailed modeling. Over 1,600 jet grout columns totaling over 13,000 meters in length and 5,100 cubic meters in volume were constructed using a double fluid system to meet the project's geotechnical requirements.
This document provides guidance on ensuring geotechnical slope stability for post-mining landforms. It discusses designing stable slopes for landforms such as low wall spoil, out-of-pit dumps, and final void batters. It emphasizes the importance of geotechnical investigations and slope design to prevent issues like lost production, safety risks, and remediation costs. Data collection should consider factors like foundation strength, slope stability, and drainage for dumped materials.
Mine water risk in open pit slope stabilitySafdar Ali
The document discusses mine water risk and its impact on open pit slope stability. It analyzes the slope stability of a chromite mine in India under three conditions: dry, drained, and undrained. Slope stability analysis was performed using the SLOPE/W software. The factor of safety was highest for the dry condition (1.277) and lowest for the undrained condition (1.230). Proper drainage is required to maintain stability as water can reduce shear strength and increase pore pressure.
The document summarizes the design and construction of the foundations for the Rion Antirion Bridge in Greece. An innovative foundation concept was adopted using steel tubular piles driven into the seabed to reinforce the soil, with a gravel layer between the piles and the concrete caisson foundation. This concept provided seismic capacity and minimized differential settlement risks. Close cooperation between designers, contractors, and reviewers was essential to developing and implementing this challenging foundation solution.
The document discusses various factors that affect slope stability and methods to determine slope stability. It addresses how gravitational forces, water, earthquake activity, slope angle, and rock structures can impact stability. Specific triggers for landslides include rainfall, erosion, construction activities, and earthquakes. Slope stability is determined by calculating the factor of safety, which compares resisting and driving shear forces based on a slope's cohesion, internal friction, and other properties. A factor of safety below 1 indicates a slope is unstable.
R16 41013.2 stability analysis of slopesPoorna Nagidi
The document discusses slope stability analysis. It defines slopes and describes types of natural and man-made slopes. Slope stability is important for earth dams and natural slopes to prevent catastrophic failures. Factors that cause slope instability include gravitational forces, seepage water, surface erosion, lowering of adjacent water levels, and earthquakes. Common types of slope failures are rotational, translational, compound, and wedge failures. Rotational failures occur along a circular or non-circular slip surface. Translational failures occur along failure surfaces parallel to infinite slopes. Compound failures combine rotational and translational slips. Wedge failures involve separation of soil blocks along inclined planes of weakness.
The document provides information about slope stability analysis. It defines a slope and describes natural and man-made slopes. It discusses causes of slope failure such as gravitational forces, seepage, erosion, and earthquakes. Methods of slope stability analysis are described including infinite slope analysis, finite slope analysis using wedge failure, friction circle, and Swedish circle methods. Factors of safety are defined with respect to shear strength, cohesion, and friction. The aims of slope stability analysis are to assess stability, understand failure mechanisms, and design preventive measures.
The document summarizes the design and construction of the foundations for the Rion Antirion Bridge in Greece. Key points:
- The foundations had to withstand severe environmental conditions like weak soil, earthquakes, and tectonic movements. An innovative concept was adopted using large diameter caissons resting on reinforced natural ground with steel pipe inclusions.
- Under each caisson, 150-200 steel pipe inclusions 2m in diameter were driven into the soil in a 7m grid to reinforce it. A 2.8m thick gravel layer separated the caisson from the inclusions.
- This concept provided capacity design by allowing sliding at the gravel interface during large seismic forces, limiting forces on the super
This document summarizes a case study of a slope failure that occurred on the Kimola Canal in Finland in 1965. The slope failure involved 90,000 cubic meters of clay sliding into the canal. Researchers analyzed the geotechnical conditions and concluded that the failure was caused by redistribution of excess pore pressures after excavation. New analyses using finite element modeling and measured pore pressure data found a factor of safety close to 1, consistent with the failure. The slope failure highlighted issues with assuming undrained strength parameters for design, as effective stress analysis better explained the failure. Inhomogeneity and anisotropy in the clay properties likely contributed to the upward extension of the failure surface.
Slope stability analysis: The term slope means a portion of the natural slope whose original profile has been modified by artificial interventions relevant with respect to stability. The term landslide refers to a situation of instability affecting natural slopes and involving large volumes of soil.
This document summarizes a thesis seminar presentation on slope stability analysis. It discusses different types of slope failures in rocks, including rock falls, rock slides, planar failures, wedge failures, circular failures, and toppling failures. It also outlines various methods for analyzing slope stability, including the Swedish circle method, ordinary circle method, Bishop's method of slices, and numerical modeling approaches like continuum modeling, discontinuum modeling, and hybrid/coupled modeling. The objectives and steps of conducting a rock slope stability analysis are also summarized.
1) A magnitude 7.6 earthquake struck Gujarat, India in 2001 near the city of Bachau, causing widespread damage.
2) Two embankment dams, Chang Dam and Fatehgadh Dam, within 150 km of the epicenter were examined. Chang Dam experienced almost a complete collapse likely due to liquefaction of its shallow foundation soils, while Fatehgadh Dam experienced less severe but still significant damage.
3) Analysis of the foundation soils beneath the dams found they were susceptible to liquefaction when saturated, which likely contributed to the observed damage during the earthquake when reservoir levels were low but foundation soils remained saturated.
This document provides an overview of slope stability and analysis. It defines different types of slopes as natural, man-made, infinite and finite. Common causes of slope failure like erosion, seepage, drawdown, rainfall, earthquakes and external loading are described. Key terms used in slope stability are defined, including slip zone, slip plane, sliding mass and slope angle. Types of slope failures are identified as face/slope failure, toe failure and base failure. Methods for analyzing finite slope stability, like Swedish circle method, Bishop's simplified method and Taylor's stability number are introduced. Infinite slope analysis is described for cohesionless, cohesive and cohesive-frictional soils. Example tutorial problems on slope stability calculations are
This document provides lecture notes on slope stability analysis. It begins with an introduction to slopes, defining slopes and discussing natural and man-made slope failures. It then discusses various methods of slope stability analysis, including infinite slope analysis for cohesionless, cohesive, and cohesive-frictional soils, considering factors like seepage. Finite slope analysis methods are also introduced, including total stress analysis for cohesive and c-φ soils. Key concepts covered include factor of safety, failure surfaces, driving and restoring moments. Factors affecting slope stability like rainfall, earthquakes, and tension cracks are also summarized.
This document discusses slope stability and different types of slope failures including translational and rotational. It describes factors that affect slope stability such as erosion, water seepage, earthquakes, and gravity. Methods for analyzing slope stability are presented, including infinite slope analysis, Culmann's method, friction circle method, method of slices, Bishop's method, and Spencer's method. The key parameters in analyzing slope stability are the factor of safety and stability number.
Topographic influence on stability for gas wells penetrating longwall mining ...legend314
Gas wells that penetrate mineable coal seams may be subject to distress caused by ground movements due to longwall mining. Especially important are the lateral shear offsets and axial distortion, which are most damaging for wellbores. To replicate typical conditions in the Appalachian basin, a geological model that considers the combined effects of topography, weak interfaces between monolithic beds and various mining depths is presented in the foregoing. These conditions adequately represent the principal features of the anticipated response of gas wells that are near-undermined by longwall panels. We examine the magnitudes of longitudinal distortions, lateral shear offsets, delaminations, and vertical and lateral strains along vertical wells drilled to intersect the seam at various locations within the longwall pillar. We analyze the distribution of these deformations and predict areas where the most severe deformation would occur.
This document discusses different types of braced excavation systems used to support deep excavations, including soldier beams with lagging, sheet piles, and slurry trenches. It describes the design process for braced cuts, which involves analyzing stability, ground movements, and structural elements like sheet piles and struts. Methods for determining loads on structural elements using tributary area and equivalent beam approaches are presented. Factors affecting stability like heaving in soils are discussed. Design of structural components like struts, wales, and sheet piles is also covered.
Detailed Slope Stability Analysis and Assessment of the Original Carsington E...Dr.Costas Sachpazis
A 1225 m long, 35 m high zone earth filled embankment was being constructed from 1981 to 1984 from a British Regional Water Authority to regulate flows in the River Derwent in England. The Carsington Dam was planned to be one of the largest earth filled dams in Britain. Its reservoir capacity was 35 million m3 and the watertight element was Rolled Clay Core with an upstream extension of boot shaped and shoulders of compacted mudstone with horizontal drainage layers of crushed limestone about 4 metres apart and a cut-off grout curtain (Davey and Eccles, 1983).
The downstream slope was 1:2.5 and the upstream slope 1:3. Fill placing began in May 1982 and took three summers, with winter shutdowns. In August 1983 a small berm was placed at the upstream toe to compensate for a faster rate of construction. Earth filling restarted in April 1984 and was one metre below the final crest level on 4 June 1984 when the upstream slope slipped (Skempton, 1985). Observations of pore pressure and settlement were made during construction at four sections and horizontal displacements were observed from August 1983. The Carsington Dam was almost completed on 1984.
However, at the beginning of June 1984, a 400-m length of the upstream shoulder of the embankment dam slipped some 11 m and failed. At the time of the failure, embankment construction was virtually complete with the dam approaching its maximum height of 35 m. Horizontal drainage blankets were incorporated in both the upstream and the downstream shale fill shoulders. Piezometers had been installed and pore pressures were being monitored in the foundation, in the clay core, and in the shoulder fill. The failure surface passed through the boot shaped rolled clay core and a relatively thin layer of surface clay in the foundation of the dam. Investigation of the events at Carsington has made important contributions to the fundamental understanding of the behaviour of large earthworks of this type (Vaughan et al., 1989; Dounias et al., 1996).
The objective of this research is to evaluate a detailed slope stability assessment of the Carsington Earth Embankment Dam in the UK used to retain mine tailings.
By using and applying advanced geotechnical engineering analysis tools and modelling techniques the Carsington Earth Embankment Dam, which is considered a particular geotechnical structure, is analysed.
In the current detailed slope stability analyses the total and effective stress state soil properties / parameters were used, and the most critical slip circle centre according to Fellenius - Jumikis method was initially determined. Subsequently, the Carsington Earth Embankment Dam and its foundation was analysed and examined against failure by slope instability. Considerations of loading conditions which may result to instability for all likely combinations of reservoir and tailwater levels, seepage conditions, both after and during construction were made, and hence three construction and / or loading condit
This document discusses types of rock slope failures. It describes four main types: plane failure, wedge failure, toppling failure, and rotational failure. For each failure type, it explains the structural conditions and geometry required for that specific failure to occur. Diagrams provide visual examples of how each failure mode appears. The document also briefly discusses methods for stabilizing unstable rock slopes, including drainage, excavation, reinforcement, and protective measures.
There are several types of slope failures that can occur in open pit mines. Plane failures occur along a planar discontinuity when the dip of the discontinuity is less than the slope angle. Wedge failures result from the intersection of two discontinuity sets dipping out of the slope. Circular failures have a curved failure surface and generally occur in weak soils or rocks. Toppling failures involve the overturning of rock columns formed by steeply dipping discontinuities. Slope stability is influenced by factors that increase shear stress, like excavation, or decrease shear strength, such as weathering. Accurately predicting slope failures is important for safety in open pit mining.
This document discusses soil arching in granular soils. It begins with an introduction to soil arching and how it occurs when stress is transferred from yielding soil to rigid adjacent zones. It then discusses experimental evidence of arching from previous studies. Finally, it covers the mechanism of arching, factors that affect it, theories about arching stresses and shapes, and limit state analysis used to analyze arching.
A presentation about on-site slope monitoring methods to detect early slope failures and prevent any expected damage on site. Also presents a few scientific methods.
The document is a student paper on slope stability analysis. It was prepared by Riyaz Ahmad Bhat, a civil engineering student at the Department of civil engineering and technology. The paper discusses slope stability analysis, including the objectives of analysis, conventional methods like limit equilibrium, and numerical methods. It also describes visiting mountain slopes in Kashmir to study the effects of tectonic activity and an earthquake in 2005. The conclusion is that the paper helps understand basic concepts and procedures of slope stability analysis.
There are four main types of slope failures: plane, wedge, toppling, and rotational. Plane failures occur along planar discontinuities like bedding planes or joints. Wedge failures form when two discontinuity sets intersect perpendicularly to the slope. Toppling failures involve the forward rotation of rock columns about a fixed point. Rotational failures involve movement along a curved failure surface within the soil. Each failure type has specific structural conditions required, such as the dip direction and angle of discontinuities compared to the slope face.
Regarding Types of Foundation, Methods, Uses of different types of foundation at different soil properties. Methods of construction of different types of foundation, Codal Provisions etc.
The document provides information on shallow foundations, including definitions, design criteria, methods for determining bearing capacity, and modes of failure. It discusses Prandtl's analysis, Rankine's analysis, and Terzaghi's bearing capacity theory. Terzaghi's theory assumes a shallow strip footing fails along a composite shear surface through five zones: an elastic zone under the footing, two radial shear zones, and two linear shear zones forming a triangular shape. The theory is used to derive an expression for ultimate bearing capacity considering the soil's shear strength properties.
This document discusses rock slope stability analysis and engineering. It describes a rock slope in Hong Kong supported with tensioned rock anchors and shotcrete. The principles of rock slope design concern the orientation and characteristics of discontinuities like joints and faults. Slope stability analysis requires determining the friction angle and cohesion of potential sliding surfaces. Shear strength testing is used to define the cohesion and friction angle parameters in the Coulomb failure criterion for analyzing rock slope stability.
Este documento presenta información sobre ambientes virtuales de aprendizaje (AVA). Incluye un plan de trabajo con temas y actividades para un curso de AVA que se llevará a cabo en junio. También describe algunas plataformas AVA como Chamilo, Schoology y Edmodo, y herramientas que pueden enriquecer un AVA como Cacoo, Animoto, Drive y YouTube. Finalmente, ofrece lineamientos generales para la elaboración de cursos virtuales en una plataforma que incluyen solicitar el espacio, materiales de apoyo, admin
This document is a curriculum vitae for Manabela Mashudu Robert. It provides his personal details and contact information, as well as an overview of his educational qualifications and work experience. Robert has tertiary qualifications in firefighting and first aid from Impact Firefighter and Emergency College. He also has computer literacy and business management certificates from Phangami Technologies. His work experience includes managerial and sales assistant roles at various retailers. He provides three references from former employers.
The document summarizes the design and construction of the foundations for the Rion Antirion Bridge in Greece. Key points:
- The foundations had to withstand severe environmental conditions like weak soil, earthquakes, and tectonic movements. An innovative concept was adopted using large diameter caissons resting on reinforced natural ground with steel pipe inclusions.
- Under each caisson, 150-200 steel pipe inclusions 2m in diameter were driven into the soil in a 7m grid to reinforce it. A 2.8m thick gravel layer separated the caisson from the inclusions.
- This concept provided capacity design by allowing sliding at the gravel interface during large seismic forces, limiting forces on the super
This document summarizes a case study of a slope failure that occurred on the Kimola Canal in Finland in 1965. The slope failure involved 90,000 cubic meters of clay sliding into the canal. Researchers analyzed the geotechnical conditions and concluded that the failure was caused by redistribution of excess pore pressures after excavation. New analyses using finite element modeling and measured pore pressure data found a factor of safety close to 1, consistent with the failure. The slope failure highlighted issues with assuming undrained strength parameters for design, as effective stress analysis better explained the failure. Inhomogeneity and anisotropy in the clay properties likely contributed to the upward extension of the failure surface.
Slope stability analysis: The term slope means a portion of the natural slope whose original profile has been modified by artificial interventions relevant with respect to stability. The term landslide refers to a situation of instability affecting natural slopes and involving large volumes of soil.
This document summarizes a thesis seminar presentation on slope stability analysis. It discusses different types of slope failures in rocks, including rock falls, rock slides, planar failures, wedge failures, circular failures, and toppling failures. It also outlines various methods for analyzing slope stability, including the Swedish circle method, ordinary circle method, Bishop's method of slices, and numerical modeling approaches like continuum modeling, discontinuum modeling, and hybrid/coupled modeling. The objectives and steps of conducting a rock slope stability analysis are also summarized.
1) A magnitude 7.6 earthquake struck Gujarat, India in 2001 near the city of Bachau, causing widespread damage.
2) Two embankment dams, Chang Dam and Fatehgadh Dam, within 150 km of the epicenter were examined. Chang Dam experienced almost a complete collapse likely due to liquefaction of its shallow foundation soils, while Fatehgadh Dam experienced less severe but still significant damage.
3) Analysis of the foundation soils beneath the dams found they were susceptible to liquefaction when saturated, which likely contributed to the observed damage during the earthquake when reservoir levels were low but foundation soils remained saturated.
This document provides an overview of slope stability and analysis. It defines different types of slopes as natural, man-made, infinite and finite. Common causes of slope failure like erosion, seepage, drawdown, rainfall, earthquakes and external loading are described. Key terms used in slope stability are defined, including slip zone, slip plane, sliding mass and slope angle. Types of slope failures are identified as face/slope failure, toe failure and base failure. Methods for analyzing finite slope stability, like Swedish circle method, Bishop's simplified method and Taylor's stability number are introduced. Infinite slope analysis is described for cohesionless, cohesive and cohesive-frictional soils. Example tutorial problems on slope stability calculations are
This document provides lecture notes on slope stability analysis. It begins with an introduction to slopes, defining slopes and discussing natural and man-made slope failures. It then discusses various methods of slope stability analysis, including infinite slope analysis for cohesionless, cohesive, and cohesive-frictional soils, considering factors like seepage. Finite slope analysis methods are also introduced, including total stress analysis for cohesive and c-φ soils. Key concepts covered include factor of safety, failure surfaces, driving and restoring moments. Factors affecting slope stability like rainfall, earthquakes, and tension cracks are also summarized.
This document discusses slope stability and different types of slope failures including translational and rotational. It describes factors that affect slope stability such as erosion, water seepage, earthquakes, and gravity. Methods for analyzing slope stability are presented, including infinite slope analysis, Culmann's method, friction circle method, method of slices, Bishop's method, and Spencer's method. The key parameters in analyzing slope stability are the factor of safety and stability number.
Topographic influence on stability for gas wells penetrating longwall mining ...legend314
Gas wells that penetrate mineable coal seams may be subject to distress caused by ground movements due to longwall mining. Especially important are the lateral shear offsets and axial distortion, which are most damaging for wellbores. To replicate typical conditions in the Appalachian basin, a geological model that considers the combined effects of topography, weak interfaces between monolithic beds and various mining depths is presented in the foregoing. These conditions adequately represent the principal features of the anticipated response of gas wells that are near-undermined by longwall panels. We examine the magnitudes of longitudinal distortions, lateral shear offsets, delaminations, and vertical and lateral strains along vertical wells drilled to intersect the seam at various locations within the longwall pillar. We analyze the distribution of these deformations and predict areas where the most severe deformation would occur.
This document discusses different types of braced excavation systems used to support deep excavations, including soldier beams with lagging, sheet piles, and slurry trenches. It describes the design process for braced cuts, which involves analyzing stability, ground movements, and structural elements like sheet piles and struts. Methods for determining loads on structural elements using tributary area and equivalent beam approaches are presented. Factors affecting stability like heaving in soils are discussed. Design of structural components like struts, wales, and sheet piles is also covered.
Detailed Slope Stability Analysis and Assessment of the Original Carsington E...Dr.Costas Sachpazis
A 1225 m long, 35 m high zone earth filled embankment was being constructed from 1981 to 1984 from a British Regional Water Authority to regulate flows in the River Derwent in England. The Carsington Dam was planned to be one of the largest earth filled dams in Britain. Its reservoir capacity was 35 million m3 and the watertight element was Rolled Clay Core with an upstream extension of boot shaped and shoulders of compacted mudstone with horizontal drainage layers of crushed limestone about 4 metres apart and a cut-off grout curtain (Davey and Eccles, 1983).
The downstream slope was 1:2.5 and the upstream slope 1:3. Fill placing began in May 1982 and took three summers, with winter shutdowns. In August 1983 a small berm was placed at the upstream toe to compensate for a faster rate of construction. Earth filling restarted in April 1984 and was one metre below the final crest level on 4 June 1984 when the upstream slope slipped (Skempton, 1985). Observations of pore pressure and settlement were made during construction at four sections and horizontal displacements were observed from August 1983. The Carsington Dam was almost completed on 1984.
However, at the beginning of June 1984, a 400-m length of the upstream shoulder of the embankment dam slipped some 11 m and failed. At the time of the failure, embankment construction was virtually complete with the dam approaching its maximum height of 35 m. Horizontal drainage blankets were incorporated in both the upstream and the downstream shale fill shoulders. Piezometers had been installed and pore pressures were being monitored in the foundation, in the clay core, and in the shoulder fill. The failure surface passed through the boot shaped rolled clay core and a relatively thin layer of surface clay in the foundation of the dam. Investigation of the events at Carsington has made important contributions to the fundamental understanding of the behaviour of large earthworks of this type (Vaughan et al., 1989; Dounias et al., 1996).
The objective of this research is to evaluate a detailed slope stability assessment of the Carsington Earth Embankment Dam in the UK used to retain mine tailings.
By using and applying advanced geotechnical engineering analysis tools and modelling techniques the Carsington Earth Embankment Dam, which is considered a particular geotechnical structure, is analysed.
In the current detailed slope stability analyses the total and effective stress state soil properties / parameters were used, and the most critical slip circle centre according to Fellenius - Jumikis method was initially determined. Subsequently, the Carsington Earth Embankment Dam and its foundation was analysed and examined against failure by slope instability. Considerations of loading conditions which may result to instability for all likely combinations of reservoir and tailwater levels, seepage conditions, both after and during construction were made, and hence three construction and / or loading condit
This document discusses types of rock slope failures. It describes four main types: plane failure, wedge failure, toppling failure, and rotational failure. For each failure type, it explains the structural conditions and geometry required for that specific failure to occur. Diagrams provide visual examples of how each failure mode appears. The document also briefly discusses methods for stabilizing unstable rock slopes, including drainage, excavation, reinforcement, and protective measures.
There are several types of slope failures that can occur in open pit mines. Plane failures occur along a planar discontinuity when the dip of the discontinuity is less than the slope angle. Wedge failures result from the intersection of two discontinuity sets dipping out of the slope. Circular failures have a curved failure surface and generally occur in weak soils or rocks. Toppling failures involve the overturning of rock columns formed by steeply dipping discontinuities. Slope stability is influenced by factors that increase shear stress, like excavation, or decrease shear strength, such as weathering. Accurately predicting slope failures is important for safety in open pit mining.
This document discusses soil arching in granular soils. It begins with an introduction to soil arching and how it occurs when stress is transferred from yielding soil to rigid adjacent zones. It then discusses experimental evidence of arching from previous studies. Finally, it covers the mechanism of arching, factors that affect it, theories about arching stresses and shapes, and limit state analysis used to analyze arching.
A presentation about on-site slope monitoring methods to detect early slope failures and prevent any expected damage on site. Also presents a few scientific methods.
The document is a student paper on slope stability analysis. It was prepared by Riyaz Ahmad Bhat, a civil engineering student at the Department of civil engineering and technology. The paper discusses slope stability analysis, including the objectives of analysis, conventional methods like limit equilibrium, and numerical methods. It also describes visiting mountain slopes in Kashmir to study the effects of tectonic activity and an earthquake in 2005. The conclusion is that the paper helps understand basic concepts and procedures of slope stability analysis.
There are four main types of slope failures: plane, wedge, toppling, and rotational. Plane failures occur along planar discontinuities like bedding planes or joints. Wedge failures form when two discontinuity sets intersect perpendicularly to the slope. Toppling failures involve the forward rotation of rock columns about a fixed point. Rotational failures involve movement along a curved failure surface within the soil. Each failure type has specific structural conditions required, such as the dip direction and angle of discontinuities compared to the slope face.
Regarding Types of Foundation, Methods, Uses of different types of foundation at different soil properties. Methods of construction of different types of foundation, Codal Provisions etc.
The document provides information on shallow foundations, including definitions, design criteria, methods for determining bearing capacity, and modes of failure. It discusses Prandtl's analysis, Rankine's analysis, and Terzaghi's bearing capacity theory. Terzaghi's theory assumes a shallow strip footing fails along a composite shear surface through five zones: an elastic zone under the footing, two radial shear zones, and two linear shear zones forming a triangular shape. The theory is used to derive an expression for ultimate bearing capacity considering the soil's shear strength properties.
This document discusses rock slope stability analysis and engineering. It describes a rock slope in Hong Kong supported with tensioned rock anchors and shotcrete. The principles of rock slope design concern the orientation and characteristics of discontinuities like joints and faults. Slope stability analysis requires determining the friction angle and cohesion of potential sliding surfaces. Shear strength testing is used to define the cohesion and friction angle parameters in the Coulomb failure criterion for analyzing rock slope stability.
Este documento presenta información sobre ambientes virtuales de aprendizaje (AVA). Incluye un plan de trabajo con temas y actividades para un curso de AVA que se llevará a cabo en junio. También describe algunas plataformas AVA como Chamilo, Schoology y Edmodo, y herramientas que pueden enriquecer un AVA como Cacoo, Animoto, Drive y YouTube. Finalmente, ofrece lineamientos generales para la elaboración de cursos virtuales en una plataforma que incluyen solicitar el espacio, materiales de apoyo, admin
This document is a curriculum vitae for Manabela Mashudu Robert. It provides his personal details and contact information, as well as an overview of his educational qualifications and work experience. Robert has tertiary qualifications in firefighting and first aid from Impact Firefighter and Emergency College. He also has computer literacy and business management certificates from Phangami Technologies. His work experience includes managerial and sales assistant roles at various retailers. He provides three references from former employers.
1) Formula 1 racing generates large revenues through broadcasting rights, race hosting fees, corporate hospitality, advertising, and sponsorship deals. In 2014, F1's parent company Delta Topco reported record revenues of $1.8 billion, up 3.2% from the previous year.
2) F1 has been successful in expanding to new markets like Russia and Austria, driving further revenue growth. Hosting fees for new races have reached over $60 million annually as countries use F1 to promote tourism.
3) Long-term contracts that increase 10% annually have stabilized F1's finances and insulated it against economic downturns. This steady revenue growth has increased the valuation of F1's parent company to an
Este documento describe tres tipos de licencias para obras creativas: Creative Commons, que permite a los usuarios acceder a recursos según las condiciones establecidas por el autor; Coloriuris, que permite a los autores autogestionar si su obra es gratuita o remunerada; y GPL, que protege la libre distribución, modificación y uso de software como los programas de GNU y paquetes de software libre.
Este libro trata sobre descubrir y utilizar el poder interior que todos tenemos. Enseña que el amor propio es la clave para sanar la vida y mejorar la calidad de vida. Al amarnos a nosotros mismos incondicionalmente, podemos superar obstáculos, expresar sentimientos de forma positiva, y crear relaciones satisfactorias.
El documento presenta un plan de trabajo para la identificación y selección de plataformas virtuales de aprendizaje. Incluye una agenda con diferentes actividades a realizar como la explicación general del tema, socialización y retroalimentación, alimentación de un AVA con aspectos indicados, elaboración de cuestionarios, consulta sobre ventajas y desventajas de plataformas, y publicación de presentaciones y pantallazos en blog. También presenta lineamientos generales para la elaboración de cursos virtuales en plataformas que incluyen solicitar el espacio,
El documento presenta un plan de trabajo para un curso sobre MOOC. Incluye una introducción al tema, seguida de sesiones para conceptualizar los MOOC, realizar un curso práctico, diseñar un curso propio, discutir derechos de autor y formular un trabajo virtual. También resume brevemente la historia de los MOOC y características como su acceso masivo y gratuito. Explica las diferencias entre MOOC y e-learning y presenta varias plataformas populares para crear y publicar MOOC.
The document is the 2016 annual report for the Institute of Noetic Sciences (IONS). It summarizes IONS' mission to advance the science of consciousness and human potential through rigorous research. It describes IONS' work in 2015-2016, including publishing over 20 papers on topics like parapsychology, meditation, and mind-body interventions. It highlights IONS' team of 7 in-house scientists and 6 research fellows from fields like neuroscience, genetics, and physics. It also discusses IONS' educational programs that apply scientific findings to enhance lives and benefit society.
Patient satisfaction is important for hospitals and healthcare providers. It is measured using surveys like HCAHPS which assess patient perceptions of care. High patient satisfaction is important for hospitals as it influences reimbursement and can incentivize improving quality. Nurses play a key role in patient satisfaction through fundamentals like communication, personalized care, and accountability. Hospitals should focus on initiatives that empower nurses and improve organizational culture to boost both patient satisfaction and nurse satisfaction.
2015 CDA-Frederickhouse Erosion Controlshiqiang Ye
This document summarizes the bank erosion control measures implemented at the Frederickhouse Dam in Ontario. Significant erosion was undercutting the 28m high left bank downstream of the dam due to turbulent discharge. Monitoring after a large landslide identified the need to stabilize the slope. Tests were conducted to determine soil properties, and a Flow-3D model was used to simulate flow patterns and evaluate design options. The final design included a stabilizing berm and armourstone riprap to arrest further erosion and meet safety standards, with construction completed in 2014.
Explosive Compaction of Foundation Soils Seymour Falls DamDario Gnoato
The document summarizes the explosive compaction project used to densify foundation soils for the seismic upgrade of the Seymour Falls Dam in Vancouver, BC. Explosive compaction involved drilling over 800 blast holes and detonating sequential charges to induce compaction through liquefaction and reconsolidation of soils. Strict limits were placed on explosives selection, blast designs, and monitoring to minimize impacts to nearby structures and fish hatchery. The project successfully achieved the targeted 2-5% volumetric strain in soils through a bottom-up sequence of three blast passes across 18 panels using electronic detonators and emulsion explosives.
This document summarizes the landslide remediation and slope stabilization project for the Tauroa residential subdivision in Havelock North, New Zealand. The project involved removing an existing shallow landslide that was less than 10 meters deep and replacing it with an engineered fill slope. Additional geotechnical investigations were conducted to inform the design of the engineered fill slope. The slope design incorporated seismic considerations based on New Zealand standards to allow for limited deformation during a design-level earthquake while keeping deformations within tolerances for the planned structures.
1) Sand production from unconsolidated reservoirs can be triggered during initial flow or later due to pressure changes and can vary in severity, sometimes requiring remedial action and sometimes being tolerated.
2) The article reviews methods for predicting, controlling, and preventing sand production, focusing on gravel packing as the most popular method for completing sand-prone wells.
3) Factors like inherent rock strength, stress levels, fluid turbulence, and pressure changes can cause sand production by detaching and transporting sand grains. The challenge is to control sand without reducing well productivity.
1) The paper discusses new hydraulic fracturing techniques used to stimulate shallow wells in the Sacatosa oil field in Texas. Traditional techniques resulted in horizontal fractures that impaired performance.
2) The new techniques aimed to create vertical fractures through changes in perforation strategy, pump schedules, and staged stimulation. They were tested on 26 injectors and 8 producers.
3) Analysis found evidence of strong vertical fractures and injectivity tests matched design objectives. Producers stimulated with the new techniques saw higher initial production than those using legacy methods.
The Rion Antirion bridge in Greece connects the Peloponnese peninsula to the mainland across the Gulf of Corinth. Its foundations had to withstand severe environmental conditions including weak soils, earthquakes up to magnitude 7.0, and long-term tectonic movements. The innovative foundation concept adopted reinforced the natural ground with steel tubular piles and included a gravel layer between the piles and foundation raft. This provided capacity to resist the large seismic forces while minimizing differential settlement hazards. Extensive site investigations characterized the poor soil properties to ensure compatible design of seismic demand and foundation capacity.
This document discusses when a rock engineering design can be considered acceptable. It notes that there are no universal rules and that each design is unique based on the site conditions, loads, and intended use. Acceptability is based on engineering judgment guided by analyses and studies. Tables provide examples of typical problems, parameters, analysis methods, and acceptability criteria for different rock structures. Case histories are also discussed to illustrate the factors considered and criteria used to determine acceptability, including ensuring stability and reducing deformation. One case examines slope drainage works to improve stability of landslides in a reservoir area. Another evaluates deformation control for a power tunnel by locating a replacement in a zone of small movements.
Auvinet exc foundations and geotechnical hazards cfpbolivia
The document provides an overview of geotechnical hazards and challenges for excavations and foundations in Mexico City, where the soft lacustrine clays are highly compressible and susceptible to subsidence. Three key points:
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Geotechnical analysis of gravity flow during block cavingMbarrera Guerra
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3) Numerical analysis of single and multiple draw points shows stress concentrations and ellipsoidal draw zones similar to field observations. Draw zone size depends on material friction angle.
The document describes a major project presented by 7 students on assessing bearing capacity and liquefaction of shallow foundations. It includes sections on introduction, significance, factors affecting liquefaction, and consequences of liquefaction. The literature review summarizes several papers on liquefaction evaluation methods, constitutive models for simulating liquefaction in software, and effective stress approaches for predicting liquefaction behavior. The overall project aims to understand liquefaction hazards and their impact on geotechnical engineering design.
Rock Melting: A Specialty Drilling System for Improved Hole Stability in Geot...swilsonmc
A Los Alamos National Laboratory team is actively reevaluating a
drilling system that uses electrically-heated graphite, or molybdenum
penetrators to melt a hole as it is slowly pushed through rock. The
primary result of a rock melting penetrator is to form molten material
that consolidates into a rugged glass lining, thus preventing hole
collapse and minimizing the potential for cross-flow and lost
circulation. Drilling fluid requirements are reduced or eliminated,
and the penetrator does not rotate.
Laboratory bench tests are being coupled with time-dependent
thermomechanical models to understand the physics of the process
and adapt rock melting to a variety of field environments.
The potential geothermal drilling applications include a wellbore seal
in lieu of intermediate casing particularly in areas of lost circulation
or borehole wall collapse. Additionally, by modifying the penetrator
tool, the system could be designed to melt through a stuck pipe or
bit, thereby eliminating cementing and redrilling. Modification of the
rock melting drill to allow injection of reagents and thinners into the
melt to increase penetration rates, and enhance glass liner properties
is also under investigation.
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Buffer blasting presentation for Coal 2016.rev1John Latilla
Targeted buffer blasting is used at Ukhaa Khudag coal mine in Mongolia to stabilize slopes containing bedding plane shears by disrupting the shear planes. Buffer blasts increase slope stability by raising the cohesion and friction angle of the rock mass. Analysis shows buffer blasting can allow slopes up to 13 degrees above the dip of the coal seams. Of the cases studied, 86% of buffer blasts successfully stabilized slopes. Improved planning is needed to proactively identify areas needing buffer blasts.
The document summarizes the design and construction of the foundations for the Rion Antirion Bridge in Greece. Key points:
1) The foundations used an innovative design of large diameter gravity caissons resting on reinforced natural ground, with steel tubular inclusions and a gravel layer, to address weak soil conditions, seismic activity, and tectonic movements.
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The document describes a study that tested the shear strength of clay soil samples from the Rattlesnake Gulf landslide in New York's Tully Valley. The study used an Autoshear device to measure shear stress, vertical displacement, and horizontal load in order to analyze shear strength parameters. The results will help understand what makes the area susceptible to landslides and inform slope stability analysis. A literature review covers concepts of slope stability, shear strength testing, and factors influencing landslides in the Tully Valley region.
C Sachpazis: Soil liquefaction potential assessment for a ccgt power plant in...Dr.Costas Sachpazis
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In this area, a Combined Cycle Gas Turbine (CCGT) Power Plant is planned to be constructed and its foundation stability and durability reassurance is of utmost importance to structural engineers. In the study of the geotechnical ground investigation for the foundation design of the CCGT project, a number of field and laboratory tests were carried out.
For evaluating its foundation soil liquefaction potential and risk during an earthquake, some internationally accepted guidelines are available based on soil density, void ratio, plasticity index, standard penetration test values, and other simple soil properties.
The liquefaction behavior and potential of this kind of foundation soils stratified in the alluvial deposits has been studied thoroughly based on both Seed’s and Idriss’s procedure / relationships as well as Prakash’s limit state methodology, using S.P.T. results and an algorithm program / software code, that was developed and published by the author. The S.P.T. tests were executed inside the twenty investigation - sampling boreholes of a depth range from 10 up to 50 meters each one, in an 100.000 s.m. plot, where a Combined Cycle Gas Turbine (CCGT) Power Plant is planned to be constructed.
According to the results of these analyses and assessments the well documented and argued necessity is deduced either for transferring the project foundation loads to underlying deeper and more competent bearing strata and layers, or for strengthening, geotechnically upgrading (ground improvement), stabilizing and cement grouting the foundation ground of the CCGT Power Plant using jet grouting piles techniques.
Finally, the exact depth range under the CCGT Power Plant foundation site that is prone and dangerous to be liquefied in the event of a strong seismic shock and vibration was determined and diagrammatically presented and the remedial measures to be taken were suggested. Hence, in this way the liquefaction risk can be mitigated or even deterred from the incompetent upper natural soil layers of the project foundation ground.
IRJET- To Study Behavior of Pile in Liquefaction of Soil using AnsysIRJET Journal
This document summarizes a study that uses ANSYS software to analyze the behavior of pile foundations in liquefied soil. The study models different pile group configurations (varying number of piles and spacing between piles) embedded in soils of varying density (loose, medium, dense sand). The analysis seeks to determine the optimal pile configuration for minimizing settlement under load for each soil density condition. Results show that settlement decreases with increasing soil friction angle and increasing number of piles. Settlement also decreases with increasing relative density of the soil. Load-settlement response is similar for medium and dense sands. The study aims to better understand pile-soil interaction effects to improve design of pile foundations in liquefiable soils.
This document discusses various topics related to seismic design, including:
- Seismicity and plate tectonics, which show that most earthquakes occur at plate boundaries.
- Different types of earthquakes like intraplate and reservoir-induced seismicity. Reservoir-induced seismicity can occur due to rapid reservoir filling or fluctuations in water level.
- Effects of soil conditions like basin effects that can amplify seismic ground motions. Soft soils in large basins like Mexico City significantly amplified motions from a distant earthquake, contributing to extensive damage.
- Key geotechnical aspects impacting seismic design like liquefaction, plasticity index, and shear wave velocity and how they relate to soil behavior during earthquakes
1. 1 INTRODUCTION AND BACKGROUND
The Deilmann Tailings Management Facility (DTMF) at the Key Lake uranium mill in northern
Saskatchewan is a former open pit mine that has been the receptor for tailings since 1996. Ap-
proximately 70m of outwash sand overlying sandstone bedrock is exposed in the west wall of the
west cell in the DTMF. Tailings were first deposited in the east cell of the DTMF in January 1996.
Sub-aerial deposition was used in the east cell between January 1996 and December 1998. The
first tailings in the west cell of the DTMF were sub-aerially deposited in April 1999. In mid-2000
a new pit crest tailings distribution system was commissioned, the old in-pit tailings distribution
system was decommissioned, and flooding of the DTMF commenced. The objectives in flooding
of the pit included preventing the freezing of deposited tailings, reduction of dewatering volumes
and stabilization of the pit walls under a deep water cover. Flooding was achieved by pumping all
Deilmann dewatering flow into the pit, as well as by allowing horizontal drain flow to report
directly to the pit. Figure 1 presents a schematic section of the DTMF design, showing the main
elements. Figure 2 presents a view of Deilmann pond during the early stages of flooding, with a
tailings deposition barge in the foreground and the outwash sand visible above the sandstone bed-
rock on the far west wall.
Finite Element Effective Stress Path Modeling of Collapsible
Outwash Sand for Pit Slope Mitigation Design
T. Meyer, P.Eng.
BGC Engineering, Montrose, Colorado, USA
Hari Mittal,
H.K. Mittal and Associates, Saskatoon, Saskatchewan, Canada
Pat Landine,
Cameco Corporation, Saskatoon, Saskatchewan, Canada
ABSTRACT: The Deilmann Tailings Management Facility (DTMF) at Key Lake is a former open
pit mine that has been the receptor for tailings since 1996. The west wall of the DTMF exposes
approximately 70m of outwash sand overlying sandstone bedrock. The first tailings were depos-
ited in the east cell of the DTMF in January 1996 and initial flooding of the DTMF began in 1998
by allowing various existing horizontal drains to flow directly into the pit. Pit slope sloughing
began to occur in mid-2001 and continued until pit flooding was stopped. Field studies have
concluded that very loose to medium dense sands are present in the DTMF outwash sand deposit
at depth. Interpretation of CPT and SPT test data indicated void ratios above the steady-state line,
indicating a loose state that could collapse upon loading. The failure mechanism was identified
as structural collapse of the loose outwash sands upon re-saturation followed by flow liquefaction.
Finite element (FE) modeling was used to compute insitu stresses within the outwash sand slope
under various conditions. The FE model was developed for discrete stages (both historic and
proposed) to estimate stress conditions in the outwash sand from “flat ground” pre-mining condi-
tions through dewatering, mining, pit flooding, unloading due to slope failures and planned slope
flattening excavation and loading due to final pit flooding to a final pond elevation. The primary
objective of the modeling was to evaluate the effective stress path of soil elements to provide a
level of confidence that loads produced by construction and final pit flooding do not result in
stress states in the slope that are on or above the collapse surface, thereby indicating that collapse
triggering would not be expected to occur.
Proceedings Tailings and Mine Waste 2016 | Keystone, Colorado, USA | October 2-5, 2016
115
2. Figure 1. DTMF Schematic Section
Figure 2. DTMF Initial Pit Flooding
In August 2001, as the water level rose above the toe of the lowermost sand overburden slopes in
the west cell above approximately elevation 465 m, some pit sloughing began to occur. By the
time water levels reached an elevation of about 475 m in October, 2001, the rate and extent of
sloughing in this area and others was well beyond original expectations and threatened some of
the infrastructure near the pit crest.
Geotechnical Considerations
116
3. There were two significant slope failures: one in February 2002; and a second one in February
2003. By August 2003, the slope crest had receded a total of approximately 31 m to 46 m, de-
pending on the location around the pit perimeter. Then on November 11, 2003, a major sloughing
event occurred causing pit crest regressions on the order of 15 m to 21 m in some areas and span-
ning about 1000 m of the perimeter of the DTMF in the West cell.
This unexpected failure, and the magnitude of the failure, forced Cameco to re-evaluate the
strategy of quickly flooding to elevation 510 and prompted a series of actions beginning with
stabilization of the water level at about 497 m Figure 3 presents a photograph of the DTMF out-
wash sand slope in 2009 after water levels had been stabilized and slope sloughing substantially
abated. Figure 4 presents a photograph of the same slope area following remediation which in-
volved excavation of the slope to a stable angle and placement of a rock fill toe buttress.
Figure 3. Original DTMF Pit Slope.
Figure 4. Remediated DTMF Pit Slope.
Proceedings Tailings and Mine Waste 2016 | Keystone, Colorado, USA | October 2-5, 2016
117
4. 1.1 Failure Mechanism
Under saturated conditions loose sands can develop a mobilized peak strength that is less than the
conventional effective friction angle at critical state condition. This is sometimes referred to as a
“collapse mechanism” with an associated mobilized soil strength referred to as a “collapse friction
angle” or “collapse strength”. Research has shown that the sand grain structure can collapse dur-
ing fully drained loading, as well as during undrained loading with a mobilized friction angle well
below the conventional effective friction angle (Sasitharan et al. 1993). Hanzawa (1980) hypoth-
esized a similar mechanism for liquefaction of loose sands.
Laboratory testing of the DTMF outwash sands indicated volumetrically contractive behavior,
which under undrained conditions produces a potential for pore pressure increases and consequent
liquefaction, or void ratio decrease followed by stress redistribution in a drained response. Either
case can lead to slope failure.
It was postulated that the outwash sand pit wall failures occurred as a result of: re-submergence
of the sand slope, resulting in loss of suction strength in the saturated sand; reduction of the ef-
fective stress accompanied by a suppression in shear resistance below the water level; and yielding
of the sand in the toe area when the ground stress approaches or equals the strength of the soil.
This reduced available shear strength (collapse strength) of the sand is less than the peak effective
value. It was postulated that sand grain structure collapse occurs in the re-submerged sand, fol-
lowed by a rapid undrained response and liquefaction leading to flow slide failure.
This failure mechanism was adopted for the detailed geotechnical analyses to support the
remediation design. Methodology for finite element modeling incorporated the collapse surface
related to loose sand collapse behavior.
1.2 Design Criteria and Methodology
Based on a review of industry standards and a project-specific risk evaluation, a minimum factor
of safety (FoS) of 1.3 was selected for establishing safety setbacks during construction as well as
long-term stability of the remediated pit slope.
In addition to limit equilibrium (LE) analyses performed to determine the minimum factors of
safety for the design, the project team considered it desirable to demonstrate the robustness of the
design through finite element (FE) stress path modeling. Given the postulated failure mode of
structural sand grain collapse leading to slope failure, localized areas of stress could develop in
the slope during final pit flooding which may be indicative of localized sloughing of the final
slopes. These localized sloughs have been known to be retrogressive in nature based on project
history. It was recognized that conventional LE analyses may indicate an acceptable FoS against
slope instability, but not account for localized stress conditions. This is an inherent limitation of
LE analyses. The primary goal of the FE modeling was to demonstrate that the onset (triggering)
of collapse stress conditions in the slope, would not occur during slope remediation or subsequent
flooding.
It is important to distinguish between the two criteria for long-term reliability of the facility.
A minimum FoS of 1.3 (as calculated by LE analyses) provides an adequate reserve resistance
against overall collapse and can be viewed as a “conventional” factor of safety against slope fail-
ure. For most geotechnical projects evaluating slope stability, this type of criteria is normally
applied. However, the DTMF project was somewhat unique due to the meta-stable nature of the
outwash sand requiring an adequate remedial design with reserve resistance against the trigger of
local collapse, as determined through rigorous finite element modeling of the final slopes during
pit flooding. This was achieved by modeling the loading history beginning with the pre-mining
state and ending with a flooded pit. This analysis determined the stress states in the sand mass,
as well as effective stress paths of elements in the slope. The established design criteria dictated
that the stress states in the outwash sand slope must remain below the collapse surface (defined
by a collapse friction angle) during each step of the remediation process and subsequent flooding.
Geotechnical Considerations
118
5. 1.3 Subsurface Conditions
The overburden deposits in the Key Lake area are dominated by glacially derived materials. Gla-
cial till deposits in the general DTMF area, include both ground moraine and drumlin forms. The
till is typically a poorly sorted, unstratified mixture of sand, gravel, cobbles and boulders with
lesser amounts of silt and clay. Till is generally present in the eastern two thirds of the DTMF. In
contrast, the west wall overburden slope is comprised of outwash deposits, with minimal (if any)
till. Outwash sand deposits would have formed during glacial retreat, as a portion of the till carried
in the glaciers was washed out and deposited adjacent to the retreating ice. This mode of deposi-
tion is known to result in loose deposits. Outwash sand deposits in the project area are up to 70
meters in thickness and generally consist of stratified, poorly to well sorted sand with minor
amounts of gravel. Coarser (gravel to cobble size) deposits are also found in some areas near the
base of the outwash sand above the sandstone contact. These coarser deposits were encountered
in boreholes completed in the western portion of the project area in the thickest sand sections.
The geotechnical conditions encountered in the 2010 geotechnical exploration program were
fairly consistent across the site and indicative of the glacial outwash geology of the area. The
outwash material encountered consisted mainly of interlayered clean sands of various sizes with
some silty layers. The major types of material can be grouped in four categories: 1) clean fine
sand, 2) clean fine to medium sand, 3) fine to coarse sand with trace fine gravel, and 4) silty fine
sand / sand with silt. The moisture content of the sand above the water table was typically low,
indicating a fairly well drained condition. A zone of variable thickness consisting of gravel and
cobble sized material, typically mixed with sand or in a sand matrix, was encountered just above
the outwash/sandstone contact. A zone of weathered sandstone was typically encountered below
the contact.
2 GEOTECHNICAL ANALYSES
2.1 General
The analyses included evaluation of multiple study sections spaced at regular intervals around the
west cell of the DTMF. The work involved the following primary elements:
Development of study sections around the project area.
Evaluation of field and laboratory physical data to determine appropriate material param-
eters for the analyses.
Back-analysis of the November 2003 slope failure event to verify geotechnical parame-
ters.
Geotechnical sensitivity analysis of a typical mining bench and current outwash sand
slopes for verification of back-calculated parameters.
Finite element modeling of insitu conditions at various slope configurations and water
table elevations to evaluate the effective stress path of points within the outwash sand
behind the slope.
Geotechnical limit equilibrium analyses to establish initial construction safety setback
distances at each study section for current conditions.
Calculation of long-term (following slope flattening and pit flooding to elevation 510m)
factors of safety against slope failure.
Establishment of an excavation line for slope flattening around the entire project area
based on results of geotechnical analyses.
2.2 Material Properties
The average critical state friction angle of the outwash sand, was estimated to be about 33 degrees
with a range of 32 to 35 degrees based on triaxial compression testing. The mobilized (collapse)
friction angle at onset of instability during undrained tests was found to range from about 20 to
27 degrees, with a majority of the values in range of 22 to 24 degrees. Conventional triaxial
drained testing indicated a peak shear strength of about 31 to 35 for the sand.
Proceedings Tailings and Mine Waste 2016 | Keystone, Colorado, USA | October 2-5, 2016
119
6. Back-analyses were also conducted on cross-sections of the pit wall with data from well docu-
mented failure events to estimate the field-scale shear strength of the sand. The results of this
analysis revealed a fairly good agreement with the laboratory derived data mentioned above.
Based on the laboratory testing and back-analysis results, the selected outwash sand engineering
parameters for final detailed slope remediation design are presented in Table 1. Rockfill proper-
ties were taken from literature values (Leps 1970). Leps’ empirical strength model of the weakest
type of rockfill was conservatively adapted for stability analyses.
Table 1 - Material Properties for Detailed Design Analyses
Material Name
Unit Weight
(kN/m3
)
Cohesion (kPa)
Phi
(Degrees)
Upper Sand 16.5 6 32
Lower Sand 19.7 0 24
Rockfill 22.0 0 38
Bedrock No potential for slope instability
2.3 Determination of Safety Setbacks
Slope stability analyses were performed at nineteen study sections in the project area to establish
safety setbacks around the west wall crest behind which slope remediation work could be safely
performed. The study sections evaluated the following:
Existing conditions (existing ground surface with water level at 497m) to calculate cur-
rent FoS and required safety setback based on the design criteria (FoS > 1.3).
Proposed final slope conditions based on safety setback criteria plus 20m (work zone
width behind safety setback line) or as needed to provide a final FoS > 1.3 with the wa-
ter level at 510m.
The resulting average calculated safety setback was about 42 meters.
2.4 Slope Remediation Design
Each section was also evaluated for long-term factor of safety for the final (post-remediation)
slope configuration with the water table elevation at 510m. The final slope configuration was
based on the calculated safety setback plus 20m and the “bench and slice” construction method-
ology for two final slope configuration cases:
1. Configuration based solely on LE analyses with a bottom bench elevation of 505m and a
thin riprap rock layer for wave protection (see Figure 5)
2. Configuration based on FE analysis with a constructed lower rock zone to prevent trig-
gering of sand collapse upon re-saturation (see Figure 6).
Geotechnical Considerations
120
7. Figure 5 – Final Slope Configuration Without Rock Zone
Figure 6 – Final Slope Configuration with Rock Zone
3 FINITE ELEMENT MODELING
3.1 General
Finite element (FE) modeling was used to compute insitu stresses within the outwash sand slope
under various conditions. FE modeling was conducted using SIGMA/W, a computer program
developed by Geoslope International (Geoslope, 2010b). Stresses were computed at various
stages (eg. pit mining, initial pit re-flooding, loss of mass due to slope failures, slope flattening
excavation, and further pit re-flooding).
The primary objective of the modeling was to evaluate the effective stress path of soil elements
to provide a level of confidence that, loads produced by construction and final pit flooding would
not result in stress states on or above the collapse surface. Although LE analyses results indicated
acceptable factors of safety against slope instability for the remediated and flooded slope config-
uration, these analyses only considered average conditions along evaluated slip surfaces and did
not consider localized stress zones that could develop within the sand mass due to loading.
The pit slope sloughing history suggests that localized sloughing can lead to retrogressive slope
failure. Since the failure mechanism has been identified as: structural collapse of the loose sands
upon re-saturation followed by flow liquefaction, the triggering of collapse must be avoided to
provide a reliable design.
Proceedings Tailings and Mine Waste 2016 | Keystone, Colorado, USA | October 2-5, 2016
121
8. 3.2 Methodology and Parameters
The FE model was developed for discrete stages (both historic and proposed) to estimate stress
conditions in the outwash sand from “flat ground” pre-mining conditions through dewatering,
mining, pit flooding, unloading due to slope failures and planned slope flattening excavation and
loading due to final pit flooding to 510 m elevation.
The generalized “collapse surface” concept proposed by Sladen, D’Hollander and Krahn
(1985) was utilized by Geoslope in previous studies and was adopted for the purposes of this
study. When deviator stress (q) is plotted with mean effective stress (p’) in an undrained triaxial
test, the collapse surface can be determined from a straight line through the maximum deviator
stress points for each test.
A collapse surface angle of ranging from 22 to 24 degrees was used for the analysis based on
the results of laboratory testing back analyses. The intersection point of the collapse surface with
the critical state line is referred to as the steady state strength (Css) and its value is estimated to be
approximately 10 kPa from field observations of the flow failure runout angles (about 5 to 15
degrees).
3.3 Model Configuration
The model geometry is based on ground survey data at various states as shown on Figure 6. The
mesh consists of 3-meter quadrilateral and triangular elements with secondary nodes. Boundary
conditions (BC’s) include fixed stress/strain along the model border. A fluid load BC was estab-
lished on the slope to account for free water pool loading, where applicable. Figure 6 presents the
model configuration at proposed final remediated slope conditions. This configuration is referred
to as the “Base Case” and represents a possible remediated slope configuration based solely on
LE analyses results. Figure 7 presents the finite element mesh and boundary conditions used. A
one-meter thick zone of rockfill (riprap) has been added to the final slope from elevation 498m to
511m for protection of the slope against wave action. Five selected mesh nodes are shown as
points A through E, which were used to track effective stresses in the outwash sand mass at these
areas of interest.
Figure 7 – Finite Element Model Mesh and Boundary Conditions
The outwash sand materials were modeled as elastic, perfectly plastic with values of the initial
tangent modulus determined from consolidated-drained (CD) triaxial testing (Mittal 2007).
3.4 Physical Modeling Sequence
The FE modeling steps were developed to simulate fourteen distinct configurations of the slope
from pre-mining conditions (step 1a) through dewatering (step 1b), pit development (step 2a),
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122
9. tailings infill and reflooding (step 2b through 2d), slope failures (steps 3a and 3b), pond water
level changes (steps 4a and 4b) and future highwall configurations (5a to 5d). The modeling steps
were linked within SIGMA/W resulting in staged analyses where results of a new stage depend
on the solution of the previous stage. Stress conditions are carried through the model allowing
capture of the stress history from flat ground conditions to current conditions, accounting for water
level changes and loss of soil mass due to slope failures based on field information provided by
Cameco. The final (proposed) slope configuration was then created by removing the excavated
material and raising the pond level in several stages.
3.5 Results
Initial results indicated development of overstressed areas near the slope face between elevation
497m and 511m. The stress conditions predicted in the model indicate unstable conditions which
could lead to progressive slope sloughing. This condition did not meet the stated design criteria
of preventing the onset of collapse conditions in the slope. Rock fill was then added to the lower
slope area until the model indicated safe conditions.
Figure 8 presents the rock zone configuration established through iterative FE modeling. Con-
struction of the rock zone involves excavation of outwash sands to create a minimum 10m wide
bench at elevation 497.5m. Following sand excavation, the rockfill is placed uncompacted to the
dimensions shown. The rock zone improves the performance of the remediation by providing
mass for “containment” of stresses near the slope face thereby preventing the onset (triggering)
of collapse stress conditions. The effective stress paths for the rock replacement scenario are
shown on Figures 9 through 13. The rock zone mass provides effective stress confinement result-
ing in the stress paths remaining below the collapse line during the final flooding stages. This
provides confirmation that the proposed rock replacement meets the stated design criteria.
Figure 8 – Rock Zone Configuration
Proceedings Tailings and Mine Waste 2016 | Keystone, Colorado, USA | October 2-5, 2016
123
10. Figure 9 – Rock Replacement FE Model Stress Path – Point A
Figure 10 – Rock Replacement FE Model Stress Path – Point B
0
100
200
300
400
500
600
0 100 200 300 400 500 600
DeviatorStress-q
Mean Effective Stress - p'
CSL
Collapse
PointA
3a
2a
5a
1b
3b
4b
1a5d
0
100
200
300
400
500
600
0 100 200 300 400 500 600
DeviatorStress-q
Mean Effective Stress - p'
CSL
Collapse
PointB
5a
3a
2a
5d
1b
3b
4a
1a
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124
11. Figure 11 – Rock Replacement FE Model Stress Path – Point C
Figure 12 – Rock Replacement FE Model Stress Path – Point D
0
50
100
150
200
250
300
350
400
450
500
0 50 100 150 200 250 300 350 400 450 500
DeviatorStress-q
Mean Effective Stress - p'
CSL
Collapse
PointD
5d
3a
5a
1b
3b
1a
0
50
100
150
200
250
300
350
400
450
500
0 50 100 150 200 250 300 350 400 450 500
DeviatorStress-q
Mean Effective Stress - p'
CSL
Collapse
PointC
3a 2a
5a
1b
4a
1a
5d
Proceedings Tailings and Mine Waste 2016 | Keystone, Colorado, USA | October 2-5, 2016
125
12. Figure 13 – Rock Replacement FE Model Stress Path – Point E
4 CONCLUSION
Finite Element (FE) stress analyses were performed to evaluate the effective stress path of soil
elements within the slope under excavation unloading and pit flooding conditions to further vali-
date the final design parameters and demonstrate a margin of safety against the onset of sand
collapse conditions. FE modeling results indicated collapse stress conditions developing near the
slope face during final pit flooding for the Base Case slope configuration established through LE
analyses. In order to improve the slope remediation design to meet the design criteria, rock re-
placement of overstress sand near the slope face creating a rockfill zone along the lower slope was
evaluated. Iterative FE analyses were utilized to obtain a rock replacement design providing suf-
ficient confinement of the sand in the lower slope to provide a robust design. A margin of safety
(calculated by the Strength Reduction Factor technique) of over 1.6 was calculated for the final
configuration with rock replacement and a final pond water elevation of 510m.
0
50
100
150
200
250
300
350
400
450
500
0 50 100 150 200 250 300 350 400 450 500
DeviatorStress-q
Mean Effective Stress - p'
CSL
Collapse
PointE
5a
3a
5d
1b
4a
1a
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126