The document discusses the shear strength of discontinuities in rock masses. It defines key terms like basic friction angle (φb), residual friction angle (φr), cohesion (c), and introduces Barton's method for estimating shear strength which accounts for joint roughness coefficient (JRC) and joint compressive strength (JCS). Small scale laboratory tests are used to determine φb, while JRC and JCS are estimated visually in the field. The shear strength of rough surfaces is higher than smooth surfaces due to surface asperities. Shear strength decreases if discontinuities are filled with soft materials like clay.
Gravity anomaly across reagional structuresAmit K. Mishra
Gravity Anomaly across continents and ocean, gravity anomaly across mid-oceanic ridges, gravity anomaly across orogenic belts, and gravity anomaly across subduction zones.
This document summarizes key concepts about sedimentary basins. It defines sedimentary basins as areas of the Earth's crust where sediments accumulate due to tectonic subsidence. Tectonics plays a crucial role in forming sedimentary basins and controlling sedimentation rates and environments. Data on sedimentary basins comes from surface mapping, core sampling, and seismic profiling, which can be used to reconstruct the evolution of basins through cross sections, isopach maps, and backstripping techniques. Paleocurrent measurements provide important clues about sediment dispersal patterns within basins.
Structural geology is the study of the architecture and geometry of the Earth's crust and the processes that have shaped it. It involves analyzing how rock bodies deform in response to tectonic stresses. Structural analysis generally involves descriptive, kinematic, and dynamic analysis. Descriptive analysis describes rock structures like folds and faults. Kinematic analysis evaluates strain and changes in shape and orientation of rocks. Dynamic analysis reconstructs the stresses that caused rock deformation and failure. Stresses in rocks can be tensile, compressive, or shear stresses. Stress is analyzed using concepts like the stress tensor, Mohr's circle diagrams, and the orientation of maximum shear stresses. The main sources of stress that drive deformation are the motions of tectonic
This document provides an outline for a course on sequence stratigraphy. It covers key concepts in stratigraphy including sedimentary depositional environments, facies analysis, sequence stratigraphy principles, and causes of sea level change. Common siliciclastic and carbonate stratigraphic successions are examined. The role of base level and relative sea level changes in controlling sediment accumulation and sequence boundaries is discussed.
This document discusses various mechanisms of rock folding. It defines folding as the bending of rock strata due to compressional forces. There are several types of fold mechanisms including buckling, bending, flexure folding, flexural slip, flexural flow, passive flow, and kink folding. Each mechanism is influenced by factors like temperature, pressure, fluid properties, and the composition and texture of the rock. Buckling involves shortening of rock layers under lateral pressure. Bending involves applying force across layers to produce gentle folds. Flexural slip forms parallel concentric folds through buckling or bending with slip along layering.
Geological structures- التراكيب الجيولوجيه
Geological Structures
What are Geologic Structures?
إيه هيا التراكيب الجيولوجيه؟
Division of Structures
تقسيم للتراكيب الجيولوجيه
A- Primary structures
Ripple marks
Mud cracks
Cross bedding
Graded bedding
Burrows
B- Secondary Structures
Folds
Faults
Joints
Unconformities
What are Geologic Structures?
إيه هيا التراكيب الجيولوجيه؟
Geologic structure is any feature in rocks that results from deformation, such as folds, joints, and faults.
اى شكل فى الصخر ينتج من خلال عملية التشويه مثل : الصدوع والطيات
هى التشققات والتصدعات الضخمة والالتواءات العنيفة التى تشوه صخور القشرة الارضية .
Geologic structures are usually the result of the powerful tectonic forces that occur within the earth. These forces fold and break rocks, form deep faults, and build mountains .
Division of Structures
• Primary (or sedimentary) structures: such as ripple marks, cross-bedding, and mud cracks form in sediments during or shortly after deposition.
هى التراكيب الناتجة من تدخل العمليات الخارجية أثناء الترسيب
• Secondary structures: is that structures formed after the formations of any kind of rocks, such as folds, faults, or unconformities.
Primary structures
They are any structures in sedimentary rock formed at or shortly after the time of deposition: such as:
هى الاشكال التى تتخلف بالصخور تحت تأثير عوامل مناخية وبيئية خاصة مثل الجفاف والحرارة وتأثير الرياح والتيارات المائية وغيرها وبدون أى تدخل من جانب القوى والحركات الارضية أمثلة ذلك:
Ripple marks
علامات النيم: هي تموجات رملية صغيرة تنشأ على سطح الطبقات الرسوبية بواسطة حركة الماء أو الهواء و تكون حروف علامات النيم متعامدة على اتجاه الحركة.
They are wavelike (undulating) structures produced in granular sediment such as sand by unidirectional wind and water currents or by oscillating wave currents.
Wind and current ripples. (Asymmetric
Wave ripples. (Symmetric
Mud cracks
التشققات فى الرواسب الطينية : حيث ينكمش سطح الرسوبيات الطينية مخلفة شقوقا مميزة فى فترات الجفاف
Mud crack is a crack in clay-rich sediment that has dried out.
Cross bedding
التطبق المتقاطع هو النمط الذي تسلكه الرسوبيات الجديدة المتراكمة عند تأثرها بأي من التيارات المائية أو الهوائية. عندما تستق
Mohr circle mohr circle anaysisand applicationShivam Jain
Mohr's circle is a graphical representation used to analyze the state of stress at a point. It relates the normal and shear stresses acting on planes of all orientations passing through that point. The document discusses how to construct Mohr's circle through an example and how it can be used to analyze principal stresses, maximum shear stress, and normal and tangential stresses on any given plane. Applications of Mohr's circle include studying brittle deformation features like faults and fractures, pore pressure effects, and stability of structures like bridges, dams and tunnels.
The document discusses sequence stratigraphy, including concepts of accommodation space, causes of eustatic sea level change, and causes of tectonic subsidence. It also defines parasequences as conformable successions of genetically related beds bounded by marine flooding surfaces that typically shallow upwards. Parasequences represent asymmetric cycles and include facies deposited laterally together based on Walther's Law of facies change.
Gravity anomaly across reagional structuresAmit K. Mishra
Gravity Anomaly across continents and ocean, gravity anomaly across mid-oceanic ridges, gravity anomaly across orogenic belts, and gravity anomaly across subduction zones.
This document summarizes key concepts about sedimentary basins. It defines sedimentary basins as areas of the Earth's crust where sediments accumulate due to tectonic subsidence. Tectonics plays a crucial role in forming sedimentary basins and controlling sedimentation rates and environments. Data on sedimentary basins comes from surface mapping, core sampling, and seismic profiling, which can be used to reconstruct the evolution of basins through cross sections, isopach maps, and backstripping techniques. Paleocurrent measurements provide important clues about sediment dispersal patterns within basins.
Structural geology is the study of the architecture and geometry of the Earth's crust and the processes that have shaped it. It involves analyzing how rock bodies deform in response to tectonic stresses. Structural analysis generally involves descriptive, kinematic, and dynamic analysis. Descriptive analysis describes rock structures like folds and faults. Kinematic analysis evaluates strain and changes in shape and orientation of rocks. Dynamic analysis reconstructs the stresses that caused rock deformation and failure. Stresses in rocks can be tensile, compressive, or shear stresses. Stress is analyzed using concepts like the stress tensor, Mohr's circle diagrams, and the orientation of maximum shear stresses. The main sources of stress that drive deformation are the motions of tectonic
This document provides an outline for a course on sequence stratigraphy. It covers key concepts in stratigraphy including sedimentary depositional environments, facies analysis, sequence stratigraphy principles, and causes of sea level change. Common siliciclastic and carbonate stratigraphic successions are examined. The role of base level and relative sea level changes in controlling sediment accumulation and sequence boundaries is discussed.
This document discusses various mechanisms of rock folding. It defines folding as the bending of rock strata due to compressional forces. There are several types of fold mechanisms including buckling, bending, flexure folding, flexural slip, flexural flow, passive flow, and kink folding. Each mechanism is influenced by factors like temperature, pressure, fluid properties, and the composition and texture of the rock. Buckling involves shortening of rock layers under lateral pressure. Bending involves applying force across layers to produce gentle folds. Flexural slip forms parallel concentric folds through buckling or bending with slip along layering.
Geological structures- التراكيب الجيولوجيه
Geological Structures
What are Geologic Structures?
إيه هيا التراكيب الجيولوجيه؟
Division of Structures
تقسيم للتراكيب الجيولوجيه
A- Primary structures
Ripple marks
Mud cracks
Cross bedding
Graded bedding
Burrows
B- Secondary Structures
Folds
Faults
Joints
Unconformities
What are Geologic Structures?
إيه هيا التراكيب الجيولوجيه؟
Geologic structure is any feature in rocks that results from deformation, such as folds, joints, and faults.
اى شكل فى الصخر ينتج من خلال عملية التشويه مثل : الصدوع والطيات
هى التشققات والتصدعات الضخمة والالتواءات العنيفة التى تشوه صخور القشرة الارضية .
Geologic structures are usually the result of the powerful tectonic forces that occur within the earth. These forces fold and break rocks, form deep faults, and build mountains .
Division of Structures
• Primary (or sedimentary) structures: such as ripple marks, cross-bedding, and mud cracks form in sediments during or shortly after deposition.
هى التراكيب الناتجة من تدخل العمليات الخارجية أثناء الترسيب
• Secondary structures: is that structures formed after the formations of any kind of rocks, such as folds, faults, or unconformities.
Primary structures
They are any structures in sedimentary rock formed at or shortly after the time of deposition: such as:
هى الاشكال التى تتخلف بالصخور تحت تأثير عوامل مناخية وبيئية خاصة مثل الجفاف والحرارة وتأثير الرياح والتيارات المائية وغيرها وبدون أى تدخل من جانب القوى والحركات الارضية أمثلة ذلك:
Ripple marks
علامات النيم: هي تموجات رملية صغيرة تنشأ على سطح الطبقات الرسوبية بواسطة حركة الماء أو الهواء و تكون حروف علامات النيم متعامدة على اتجاه الحركة.
They are wavelike (undulating) structures produced in granular sediment such as sand by unidirectional wind and water currents or by oscillating wave currents.
Wind and current ripples. (Asymmetric
Wave ripples. (Symmetric
Mud cracks
التشققات فى الرواسب الطينية : حيث ينكمش سطح الرسوبيات الطينية مخلفة شقوقا مميزة فى فترات الجفاف
Mud crack is a crack in clay-rich sediment that has dried out.
Cross bedding
التطبق المتقاطع هو النمط الذي تسلكه الرسوبيات الجديدة المتراكمة عند تأثرها بأي من التيارات المائية أو الهوائية. عندما تستق
Mohr circle mohr circle anaysisand applicationShivam Jain
Mohr's circle is a graphical representation used to analyze the state of stress at a point. It relates the normal and shear stresses acting on planes of all orientations passing through that point. The document discusses how to construct Mohr's circle through an example and how it can be used to analyze principal stresses, maximum shear stress, and normal and tangential stresses on any given plane. Applications of Mohr's circle include studying brittle deformation features like faults and fractures, pore pressure effects, and stability of structures like bridges, dams and tunnels.
The document discusses sequence stratigraphy, including concepts of accommodation space, causes of eustatic sea level change, and causes of tectonic subsidence. It also defines parasequences as conformable successions of genetically related beds bounded by marine flooding surfaces that typically shallow upwards. Parasequences represent asymmetric cycles and include facies deposited laterally together based on Walther's Law of facies change.
Joints are fractures in rock where there is negligible displacement. They can range in length from millimeters to tens of meters. Joints form due to tensile or shear failure when rocks experience stress. The orientation and spacing of joints is influenced by factors like bed thickness, stress directions, and proximity to faults or folds in the rock. Joints have characteristic surface features and patterns that provide information about the stresses that caused them and rock properties. Joint patterns are important for applications in mining, construction, and hydrogeology.
The presentation comprises the Gravity Method, It's anomaly, reduction, and its applications. The Gravity method is commonly used in Geology specifically in Geophysics.
The document discusses facies analysis, which involves dividing sedimentary rock bodies into facies units based on their distinctive lithological or biological features. Facies can be defined descriptively based on attributes like rock type, fossils, or sedimentary structures, or interpretively to represent depositional environments. Facies units may represent different scales from thin sections to thick successions. Facies associations represent commonly associated attributes and form the basis for facies models, which explain observed associations. Interpreting facies involves considering factors like the meaning and scales of facies units as well as relationships between facies and depositional environments or processes.
Mid-ocean ridges are underwater mountain systems formed at divergent tectonic plate boundaries where new oceanic crust is generated. They consist of a chain of mountains linked by a central rift valley and result from mantle upwelling and melting in response to plate spreading. As the buoyant magma rises to the seafloor at the plate boundary, it emerges as lava to form new ocean crust upon cooling.
Sequence stratigraphy involves subdividing stratigraphic records based on bounding discontinuities. A depositional sequence is defined as a succession of genetically related strata bounded by unconformities and correlative conformities. During a sequence, systems tracts are deposited in response to changes in relative sea level, including highstand, falling stage, lowstand, and transgressive tracts bounded by surfaces like sequence boundaries, transgressive surfaces, and flooding surfaces.
This document summarizes a seminar on Ramsay classification of folds and folding mechanisms. It introduces Ramsay fold classification, which divides folds into three classes based on criteria like dip isogon patterns and curvature. Class 1 folds have convergent dip isogons and greater inner curvature. Mechanisms of folding discussed include buckling, which can form Class 1b folds of constant thickness, and bending due to intrusion or between boudins. Applications of the classification include hydrocarbon and salt dome exploration.
1. The document summarizes a presentation on magnetic survey methods given on May 21, 2020. It discusses concepts like magnetic susceptibility of rocks, elements that make up Earth's magnetic field like the core and mantle, and how magnetic polarity reversals are recorded in rocks.
2. Key factors that control magnetic susceptibility of rocks are magnetic minerals like olivine and magnetite. Susceptibility can also depend on mineral grain alignment. Magnetic fabrics provide information on rock composition and formation processes.
3. Earth has layers of increasing density, from less dense continental crust to denser mantle and core. The outer core generates convection currents that power the magnetic field, and the inner solid core rotates to produce it.
This document defines sequence stratigraphy and discusses its basic concepts. Sequence stratigraphy studies genetically related rock units bounded by unconformities. It is based on dividing strata into sequences bounded by sea level changes. Key concepts discussed include depositional sequences, parasequences, flooding surfaces, system tracts, accommodation space, and the importance of sequence stratigraphy for understanding basin evolution and resource exploration.
The gravity method involves measuring variations in the Earth's gravitational field to determine subsurface density variations. Gravity surveys measure differences in gravitational attraction at surface locations. After collecting data at regular intervals, corrections are applied for drift, elevation, tides and topography. The corrected anomalies are analyzed to infer subsurface geology, locating structures like faults, voids or buried valleys. Common applications include engineering, environmental and geothermal studies.
This document discusses survey design and procedures for electrical resistivity surveys. It describes three common modes: 1) Sounding mode, where electrode spacing is varied to map resistivity with depth at fixed locations. 2) Profiling mode, where electrode spacing is fixed and the array is moved laterally to map lateral resistivity variations. 3) Profiling-sounding mode, which combines aspects of profiling and sounding modes. Common electrode arrays like Wenner and Schlumberger are described for each mode. Sounding and profiling modes are suited for mapping vertical and horizontal resistivity contrasts respectively.
Stratigraphy establishes relationships between rock layers by classifying them into mappable units called formations, which can be subdivided into members and grouped into units called groups. Correlating rocks means establishing their equivalency using physical stratigraphy techniques like lithostratigraphy (comparing rock types), magnetostratigraphy (comparing magnetic polarity sequences), and sequence stratigraphy (using sea level curves), or biostratigraphy techniques like comparing fossil zones, evolutionary lineages, and index fossils to determine the relative or absolute ages of rock layers.
This document discusses various geological structures including folds, faults, joints, unconformities, and methods to characterize rock mass quality. It describes key terms like dip, strike, anticline, syncline, and classifications of different fold types. Fault types like normal, thrust, and strike-slip faults are outlined. Engineering considerations of these structures are mentioned regarding their suitability for construction projects and impacts. Methods like Rock Quality Designation (RQD) and Rock Structure Rating (RSR) to evaluate rock mass quality are also summarized.
This document discusses different sedimentary environments including terrestrial, marginal marine, and marine settings. Terrestrial environments include fluvial systems like braided rivers and meandering streams, alluvial fans, glacial deposits, lacustrine environments, and aeolian deposits in deserts. Marginal marine environments are located along the continental boundary and include beaches, barrier islands, lagoons, estuaries, and tidal flats. Marine environments discussed are coral reefs, continental shelf, continental slope, continental rise, and abyssal plain. Different sedimentary structures form in each environment providing clues to depositional conditions.
Geophysical prospecting uses physical methods to study the structure of the Earth's crust and locate minerals and ores. It involves collecting data using geophysical methods like seismic, gravitational, magnetic, electrical, and electromagnetic surveys. Seismic methods are commonly used in exploration. They involve generating seismic waves using sources like sledgehammers and analyzing the reflected and refracted waves detected by receivers to characterize subsurface layers and locate resources based on their elastic properties. Proper data acquisition, processing to reduce noise, and geological interpretation of processed seismic data are required to build an accurate model of the subsurface.
Stress is the internal resistance of a material against an applied load or force. There are different types of stress that rocks can experience, including lithostatic stress from the weight of overlying rocks, and differential stress from tectonic forces like tension, compression, and shearing. Rocks deform in response to stress in different ways depending on factors like pressure, temperature, and composition. At low stresses rocks deform elastically and return to their original shape when unloaded. At higher stresses near the surface, rocks deform brittlely and fracture. Deeper underground, higher temperatures cause ductile deformation where rocks flow plastically. The stress-strain behavior of rocks is important for understanding their mechanical properties and failure under stress
The document discusses several failure criteria for rocks, including:
1) The Mohr-Coulomb criterion, which defines shear strength as a function of cohesion and friction angle.
2) The Hoek-Brown criterion, which models the non-linear relationship between principal stresses and incorporates rock mass quality.
3) The Griffith failure criterion, which postulates that stress concentrations at flaws like cracks cause propagation and failure.
It also briefly mentions the Drucker-Prager yield criterion and that empirical criteria tailored to a specific rock type may provide the most precise failure prediction.
Anderson's theory of faulting predicts that the orientation of faults depends on the principal stresses. It assumes reverse faults dip at 30 degrees, normal faults dip at 60 degrees, and strike-slip faults are vertical. However, exceptions like low-angle normal faults exist. Pore fluid pressure or pre-existing weaknesses in the rock can allow faults to form at shallower angles. The rolling-hinge model also explains how low-angle normal faults can develop.
A fabric describes the spatial and geometric relationships that make up a rock at the microscopic to centimeter scale. It includes planar structures like bedding and cleavage, as well as the preferred orientation of minerals. There are different types of fabric including linear fabric formed by elongate minerals, planar fabric formed by platy minerals, and random fabric with no orientation. Foliation specifically refers to any planar arrangement of minerals or structures in a rock. Foliation can be primary, forming during rock formation, or secondary, resulting from deformation. Common types of secondary foliation include cleavage, schistosity, and mylonitic foliation. Lineation describes a preferred linear orientation of features in a rock, often related to deformation processes like intersection of planar
ELECTRICAL METHODS OF GEOPHYSICAL EXPLORATION OF MINERAL DEPOSITS.pptxImposter7
This document discusses various electrical methods used in geophysical exploration of mineral deposits. It describes five main geophysical methods - seismic, gravity, electrical, radioactive, and magnetic. The electrical methods section focuses on self-polarization, equipotential, electromagnetic, resistivity, and induced polarization techniques. Resistivity techniques like Wenner, Schlumberger and dipole-dipole configurations are explained. The document concludes that electrical methods are useful for exploring metallic and sulphide deposits and groundwater, as well as characterizing rock properties.
Shotcrete is a cement-based concrete that is pneumatically projected at high velocity onto underground excavation surfaces for rock support. There are two main types - dry mix, where materials are conveyed dry to the nozzle and water added, and wet mix, where materials are pre-mixed with water. Recent developments include adding steel fibers for reinforcement and microsilica for strength. Shotcrete provides effective support in mining when applied correctly using proper equipment and experienced operators. It is increasingly used for permanent openings and offers advantages over traditional rockbolt and mesh support.
This document discusses design considerations for large underground caverns excavated in weak rock at depths of 100-300m below the surface for hydroelectric projects. It addresses the stability of caverns and surrounding rock mass given in situ stress conditions, effects of nearby slopes, and determining appropriate pillar sizes between excavations. The key design factors are the strength of the rock mass, influence of structural features like joints and bedding planes, sequence of excavation and support, and stress changes induced by nearby slopes and excavations. Pillar size between caverns must consider stresses imposed and stability of the rock mass.
Joints are fractures in rock where there is negligible displacement. They can range in length from millimeters to tens of meters. Joints form due to tensile or shear failure when rocks experience stress. The orientation and spacing of joints is influenced by factors like bed thickness, stress directions, and proximity to faults or folds in the rock. Joints have characteristic surface features and patterns that provide information about the stresses that caused them and rock properties. Joint patterns are important for applications in mining, construction, and hydrogeology.
The presentation comprises the Gravity Method, It's anomaly, reduction, and its applications. The Gravity method is commonly used in Geology specifically in Geophysics.
The document discusses facies analysis, which involves dividing sedimentary rock bodies into facies units based on their distinctive lithological or biological features. Facies can be defined descriptively based on attributes like rock type, fossils, or sedimentary structures, or interpretively to represent depositional environments. Facies units may represent different scales from thin sections to thick successions. Facies associations represent commonly associated attributes and form the basis for facies models, which explain observed associations. Interpreting facies involves considering factors like the meaning and scales of facies units as well as relationships between facies and depositional environments or processes.
Mid-ocean ridges are underwater mountain systems formed at divergent tectonic plate boundaries where new oceanic crust is generated. They consist of a chain of mountains linked by a central rift valley and result from mantle upwelling and melting in response to plate spreading. As the buoyant magma rises to the seafloor at the plate boundary, it emerges as lava to form new ocean crust upon cooling.
Sequence stratigraphy involves subdividing stratigraphic records based on bounding discontinuities. A depositional sequence is defined as a succession of genetically related strata bounded by unconformities and correlative conformities. During a sequence, systems tracts are deposited in response to changes in relative sea level, including highstand, falling stage, lowstand, and transgressive tracts bounded by surfaces like sequence boundaries, transgressive surfaces, and flooding surfaces.
This document summarizes a seminar on Ramsay classification of folds and folding mechanisms. It introduces Ramsay fold classification, which divides folds into three classes based on criteria like dip isogon patterns and curvature. Class 1 folds have convergent dip isogons and greater inner curvature. Mechanisms of folding discussed include buckling, which can form Class 1b folds of constant thickness, and bending due to intrusion or between boudins. Applications of the classification include hydrocarbon and salt dome exploration.
1. The document summarizes a presentation on magnetic survey methods given on May 21, 2020. It discusses concepts like magnetic susceptibility of rocks, elements that make up Earth's magnetic field like the core and mantle, and how magnetic polarity reversals are recorded in rocks.
2. Key factors that control magnetic susceptibility of rocks are magnetic minerals like olivine and magnetite. Susceptibility can also depend on mineral grain alignment. Magnetic fabrics provide information on rock composition and formation processes.
3. Earth has layers of increasing density, from less dense continental crust to denser mantle and core. The outer core generates convection currents that power the magnetic field, and the inner solid core rotates to produce it.
This document defines sequence stratigraphy and discusses its basic concepts. Sequence stratigraphy studies genetically related rock units bounded by unconformities. It is based on dividing strata into sequences bounded by sea level changes. Key concepts discussed include depositional sequences, parasequences, flooding surfaces, system tracts, accommodation space, and the importance of sequence stratigraphy for understanding basin evolution and resource exploration.
The gravity method involves measuring variations in the Earth's gravitational field to determine subsurface density variations. Gravity surveys measure differences in gravitational attraction at surface locations. After collecting data at regular intervals, corrections are applied for drift, elevation, tides and topography. The corrected anomalies are analyzed to infer subsurface geology, locating structures like faults, voids or buried valleys. Common applications include engineering, environmental and geothermal studies.
This document discusses survey design and procedures for electrical resistivity surveys. It describes three common modes: 1) Sounding mode, where electrode spacing is varied to map resistivity with depth at fixed locations. 2) Profiling mode, where electrode spacing is fixed and the array is moved laterally to map lateral resistivity variations. 3) Profiling-sounding mode, which combines aspects of profiling and sounding modes. Common electrode arrays like Wenner and Schlumberger are described for each mode. Sounding and profiling modes are suited for mapping vertical and horizontal resistivity contrasts respectively.
Stratigraphy establishes relationships between rock layers by classifying them into mappable units called formations, which can be subdivided into members and grouped into units called groups. Correlating rocks means establishing their equivalency using physical stratigraphy techniques like lithostratigraphy (comparing rock types), magnetostratigraphy (comparing magnetic polarity sequences), and sequence stratigraphy (using sea level curves), or biostratigraphy techniques like comparing fossil zones, evolutionary lineages, and index fossils to determine the relative or absolute ages of rock layers.
This document discusses various geological structures including folds, faults, joints, unconformities, and methods to characterize rock mass quality. It describes key terms like dip, strike, anticline, syncline, and classifications of different fold types. Fault types like normal, thrust, and strike-slip faults are outlined. Engineering considerations of these structures are mentioned regarding their suitability for construction projects and impacts. Methods like Rock Quality Designation (RQD) and Rock Structure Rating (RSR) to evaluate rock mass quality are also summarized.
This document discusses different sedimentary environments including terrestrial, marginal marine, and marine settings. Terrestrial environments include fluvial systems like braided rivers and meandering streams, alluvial fans, glacial deposits, lacustrine environments, and aeolian deposits in deserts. Marginal marine environments are located along the continental boundary and include beaches, barrier islands, lagoons, estuaries, and tidal flats. Marine environments discussed are coral reefs, continental shelf, continental slope, continental rise, and abyssal plain. Different sedimentary structures form in each environment providing clues to depositional conditions.
Geophysical prospecting uses physical methods to study the structure of the Earth's crust and locate minerals and ores. It involves collecting data using geophysical methods like seismic, gravitational, magnetic, electrical, and electromagnetic surveys. Seismic methods are commonly used in exploration. They involve generating seismic waves using sources like sledgehammers and analyzing the reflected and refracted waves detected by receivers to characterize subsurface layers and locate resources based on their elastic properties. Proper data acquisition, processing to reduce noise, and geological interpretation of processed seismic data are required to build an accurate model of the subsurface.
Stress is the internal resistance of a material against an applied load or force. There are different types of stress that rocks can experience, including lithostatic stress from the weight of overlying rocks, and differential stress from tectonic forces like tension, compression, and shearing. Rocks deform in response to stress in different ways depending on factors like pressure, temperature, and composition. At low stresses rocks deform elastically and return to their original shape when unloaded. At higher stresses near the surface, rocks deform brittlely and fracture. Deeper underground, higher temperatures cause ductile deformation where rocks flow plastically. The stress-strain behavior of rocks is important for understanding their mechanical properties and failure under stress
The document discusses several failure criteria for rocks, including:
1) The Mohr-Coulomb criterion, which defines shear strength as a function of cohesion and friction angle.
2) The Hoek-Brown criterion, which models the non-linear relationship between principal stresses and incorporates rock mass quality.
3) The Griffith failure criterion, which postulates that stress concentrations at flaws like cracks cause propagation and failure.
It also briefly mentions the Drucker-Prager yield criterion and that empirical criteria tailored to a specific rock type may provide the most precise failure prediction.
Anderson's theory of faulting predicts that the orientation of faults depends on the principal stresses. It assumes reverse faults dip at 30 degrees, normal faults dip at 60 degrees, and strike-slip faults are vertical. However, exceptions like low-angle normal faults exist. Pore fluid pressure or pre-existing weaknesses in the rock can allow faults to form at shallower angles. The rolling-hinge model also explains how low-angle normal faults can develop.
A fabric describes the spatial and geometric relationships that make up a rock at the microscopic to centimeter scale. It includes planar structures like bedding and cleavage, as well as the preferred orientation of minerals. There are different types of fabric including linear fabric formed by elongate minerals, planar fabric formed by platy minerals, and random fabric with no orientation. Foliation specifically refers to any planar arrangement of minerals or structures in a rock. Foliation can be primary, forming during rock formation, or secondary, resulting from deformation. Common types of secondary foliation include cleavage, schistosity, and mylonitic foliation. Lineation describes a preferred linear orientation of features in a rock, often related to deformation processes like intersection of planar
ELECTRICAL METHODS OF GEOPHYSICAL EXPLORATION OF MINERAL DEPOSITS.pptxImposter7
This document discusses various electrical methods used in geophysical exploration of mineral deposits. It describes five main geophysical methods - seismic, gravity, electrical, radioactive, and magnetic. The electrical methods section focuses on self-polarization, equipotential, electromagnetic, resistivity, and induced polarization techniques. Resistivity techniques like Wenner, Schlumberger and dipole-dipole configurations are explained. The document concludes that electrical methods are useful for exploring metallic and sulphide deposits and groundwater, as well as characterizing rock properties.
Shotcrete is a cement-based concrete that is pneumatically projected at high velocity onto underground excavation surfaces for rock support. There are two main types - dry mix, where materials are conveyed dry to the nozzle and water added, and wet mix, where materials are pre-mixed with water. Recent developments include adding steel fibers for reinforcement and microsilica for strength. Shotcrete provides effective support in mining when applied correctly using proper equipment and experienced operators. It is increasingly used for permanent openings and offers advantages over traditional rockbolt and mesh support.
This document discusses design considerations for large underground caverns excavated in weak rock at depths of 100-300m below the surface for hydroelectric projects. It addresses the stability of caverns and surrounding rock mass given in situ stress conditions, effects of nearby slopes, and determining appropriate pillar sizes between excavations. The key design factors are the strength of the rock mass, influence of structural features like joints and bedding planes, sequence of excavation and support, and stress changes induced by nearby slopes and excavations. Pillar size between caverns must consider stresses imposed and stability of the rock mass.
The Rio Grande project involves a 1000 MW pumped storage hydroelectric plant located in Argentina. It provides electrical storage for the local power grid. The main underground facilities are located within high quality gneiss rock. Support requirements were assessed during excavation and minimal support was needed due to the excellent rock quality. Rockbolts and shotcrete were used as needed based on geotechnical inspection. The UNWEDGE program was utilized to analyze wedge failures and determine support requirements.
This document discusses soil shear strength, focusing on fine-grained soils. It covers topics like clay mineralogy, bonding mechanisms, structural units of common clay minerals like kaolinite and montmorillonite, double layer water, intergranular pressure, water pressure, the relationship between mineralogy and shear strength, soil fabric, Atterberg limits, ideal soil laboratory testing, and undisturbed Shelby tube sampling. In summary:
1) It describes the mineralogical composition and structure of common clay minerals and how they influence shear strength.
2) It explains concepts like double layer water, intergranular pressure, and how water pressure relates to shear strength.
3) There is a relationship
This thesis examines autonomous excavation of fragmented rock using load-haul-dump (LHD) underground mining machines. It presents results from experimental studies on an LHD machine conducting excavation trials. Cylinder pressure signals were found to contain information about bucket-rock interaction. Dynamics models of the LHD were developed using parallel cascade identification, but were not highly accurate. Finally, an admittance control framework is proposed where the bucket responds dynamically to sensed cylinder forces for autonomous excavation.
1. Shear strength is the ability of soil to resist sliding along internal surfaces and is one of the most important engineering properties of soil.
2. Coulomb proposed that shear strength (s) of soil is equal to apparent cohesion (c) plus normal stress (σ) multiplied by the tangent of the angle of shearing resistance (φ).
3. The direct shear test and triaxial compression test are commonly used laboratory methods to determine the shear strength parameters c and φ of soils, while field methods include the vane shear test.
The document discusses shear strength of discontinuities in rock masses. It introduces concepts like shear strength of planar surfaces, shear strength of rough surfaces, Barton's estimate of shear strength which relates shear strength to joint roughness coefficient (JRC) and joint compressive strength (JCS). It discusses estimating JRC and JCS in the field and how these parameters are influenced by scale. It also summarizes the shear strength of filled discontinuities and the influence of water pressure on shear strength.
Friction is the resistance to motion when one solid body moves over another in contact. There are two main types of friction: dry friction and fluid friction. Dry friction, also called Coulomb friction, occurs between two dry surfaces in contact. Fluid friction occurs between layers of a fluid moving at different velocities.
The document discusses the mechanisms and theories of friction. It explains that friction arises from interactions between surface asperities or roughness. The dominant mechanisms are adhesion between contact areas and plastic deformation. Adhesion contributes to friction through the force needed to overcome molecular bonds between contacting asperities. Deformation friction is the energy required for plastic plowing or deformation of asperities. The total friction force is the sum
Shear Strength Of Rockfill, Interfaces And Rock Joints, And Their Pointsguest963b41
The document discusses the shear strength of rockfill, rock joints, and their interfaces and contact points. It finds that the peak shear strength of rockfill and rock joints have similar non-linear strength envelopes when interpreted from large-scale triaxial tests and direct shear tests, respectively. Index tilt tests can also characterize the extremely low stress-dependent shear strength of rockfill and joints. The actual contact stresses when peak shear strength is reached are very high due to small contact areas. Equations are presented to estimate the shear strength of rockfill, rock joints, and their interfaces using characteristics measured from index tests. The non-linear strength envelopes mean that stability factors of safety will reduce from top to bottom and outside to inside
This document discusses strength parameters for clays, including:
- The peak friction angle for clays decreases with increasing plasticity index and activity. Critical state friction angles range from 20-25° for kaolin clays and 20° for montmorillonite clays.
- The Hvorslev failure envelope models the strength of overconsolidated clays using equivalent friction angle and cohesion parameters.
- Undrained shear strength of clays decreases with increasing liquidity index and increases with overconsolidation ratio. Empirical equations relate strength to plasticity index and preconsolidation stress.
- Shear bands form after peak strength due to strain localization. Their thickness is 7-10 particle diameters
Theoretical study for r.c. columns strengthened with gfrp with different main...Ahmed Ebid
DOI: 10.13140/2.1.3631.9041
It becomes a common practice to strength and repair reinforced concrete columns by wrapping them with GFRP sheets. The aim of this research is to develop a formula to describe the relation between the gain of strength of reinforced concrete square columns, their longitudinal reinforcement and number of warped layers of GFRP sheets. The research is based on simulating loading tests of a set of 12 reinforced concrete columns with different reinforcement ratios and different number of warped layers of GFRP sheets using ANSYS software. The outputs of the ANSYS models are verified using experimental tests results carried out by the author in earlier research. The results of the study are used to develop a proposed formula to correlate the axial capacity of the warped square RC column with its reinforcement ratio and the confining stress caused by the sheets. Values from both proposed formula design and formula of Egyptian Code of Practice (ECP) are compared with ANSYS outputs and experimental results. The final conclusion is that gained strength due to confining equals to (confining stress / Fcu)
FABRICATION AND CALIBRATION OF LARGE SCALE DIRECT SHEAR TEST APPARATUSEditorIJAERD
This research is focused on the Design, Fabrication and Calibration of large scale Direct Shear and Pullout
apparatus to find the shear strength parameters of the soil with large particles under constant normal load. With this
apparatus experiments on fine (loose & dense state), medium (loose & dense state), and coarse (loose & dense state)
sand and also crush aggregate were conducted under different normal loads of 12.7 KN (1.27 ton), 25.4 KN (2.54 ton)
and 38.1KN (3.81 ton). To check the performance of apparatus testing were also done with standard direct shear test
apparatus under the same conditions. As the tests were carried out under different loading conditions without any
problem occur in the equipment assembly hence it was concluded that the equipment design governs. Furthermore it was
observed that there is reasonable difference in the test values of large scale and small scale tests so it was concluded that
the large scale direct shear equipment is calibrated.
This document discusses the shear strength of soils. It begins with an abstract describing shear strength and factors that influence it, such as particle interactions and stresses. It then outlines different methods to measure shear strength in the laboratory and field, including direct shear tests, triaxial shear tests, and vane shear tests. The Mohr-Coulomb failure criteria is also explained as a way to analyze shear strength based on normal and shear stresses. Key parameters that govern shear strength are identified as cohesion and the friction angle.
The document discusses shear strength of soils. It defines shear strength as the soil's resistance to shearing stresses and deformation from particle displacement. Shear strength depends on cohesion between particles and frictional resistance, as modeled by the Mohr-Coulomb failure criterion. Laboratory tests like direct shear and triaxial shear tests are used to determine the shear strength parameters (c, φ) that describe a soil's failure envelope.
1. Slope stability is a major issue for open pit mining. Factors like slope geometry, geology, groundwater, mining method, and dynamic forces can impact stability.
2. Common slope failure types include planar, wedge, and circular failures. Wedge failures occur at the intersection of two discontinuities. Circular failures can be classified as slope, toe, or base failures.
3. Stability analysis methods include wedge analysis using spherical projections, the method of slices for circular failures, and the friction circle method. Each approach considers factors like shear strength and forces on potential failure surfaces.
Vibrational Analysis Of Cracked Rod Having Circumferential Crack IDES Editor
The frequency ratio of torsional vibration of a rod without crack and of rod with crack subjected to torque at the free end for various crack depth and varying crack location is investigated. It is found that even a cracked of small depth is
dangerous at the fixed end, also as the crack depth is increases more than 50% of diameter of rod there is a considerable drop in natural frequency of the rod .
This document provides an overview of shear strength of soils. It defines shear strength as the maximum shear stress a soil can sustain without failure. Several factors that affect shear strength are discussed, including soil composition, initial state, structure, drainage conditions, and loading. The key concepts of principal stresses, Mohr's circle, and the Mohr-Coulomb failure criterion are explained. Common laboratory tests to evaluate shear strength parameters (c, φ) are also summarized, including direct shear testing, unconfined compression testing, and triaxial compression testing.
The document presents a general analytical solution for determining the required anchor force to stabilize rock slopes undergoing toppling failure. It extends previous solutions by considering blocks of infinitesimal thickness, leading to ordinary differential equations that can be integrated for simple slope geometries. For a uniform slope, two failure modes are possible - sliding toe (ST) and tension toe (TT) - depending on the dip, cut slope angle, and friction angle. The solution provides an upper bound for the required anchor force for slopes higher than 20-30 times the average block thickness.
This document provides an overview of lateral earth pressure and slope stability analysis. It defines key terms related to slopes, describes common slope failure mechanisms such as translational and rotational slides, and lists some common causes of slope failure. It then discusses various methods for analyzing slope stability, including infinite slope analysis and circular failure surface analysis. Equations are provided for calculating the factor of safety of infinite slopes made of cohesive-frictional soils with and without seepage, as well as for analyzing rotational failures in undrained cohesive soils. The document is a lecture on soil mechanics and geotechnical engineering concepts.
Analysis of soil arching effect with different cross-section anti-slide pileIJERA Editor
Although the knowledge of soil-arching effect of anti-slide pile become common, the analysis of soil-arching effect with different cross-section anti-slide pile is little. Therefore,this paper choose three typical cross-section piles (rectangular, square, circular), Then do some study about the Mechanism of mechanism, frictional arch and end bearing arch of three cross-section piles and the form of soil arch with different cross-section and the soil arch zone under same condition in order to define the best cross-section, The result show that rectangular section pile and square section pile are composed by frictional arch and end bearing arch, while circular section pile is made up by united arch, finally rectangular section pile has a more effective retaining effect than square section pile and circular section pile through compared soil arch zone with three type section piles.
Okay, here are the step-by-step workings:
a) Plot the Mohr's circle with σx = 20 kPa, σy = 30 kPa, τxy = 10 kPa
b) Determine the pole
c) Draw a line through the pole at 30° from the horizontal
d) It intersects the circle at σa = 26 kPa, τa = 8.66 kPa
e) The major and minor principal stresses are the intersections of the circle with the σ axes:
σ1 = 30 kPa
σ3 = 20 kPa
f) The major principal plane is parallel to the σy axis. The minor principal plane is parallel to the σ
This document discusses techniques for determining the spatial and size distributions of spherical inclusions in mild steel. Planar measurements taken from electropolished surfaces are compared to measurements taken from fracture surfaces. It is found that the average dimple size on fracture surfaces is always greater than the most probable first neighbor spacing from planar measurements. Additionally, the mean inclusion size is smaller on fracture surfaces compared to electropolished surfaces. These differences are believed to arise from the fracture process itself.
This document discusses determining the shear strength of soils. It explains that shear strength is the maximum shear stress a soil can withstand before failing. There are two main types of shear strength - drained and undrained. Laboratory tests like direct shear tests and triaxial tests are used to determine the shear strength parameters (c, φ) by simulating the in-situ stress conditions. The Mohr-Coulomb failure criterion relates shear strength to effective normal stress and describes shear failure. Parameters c' and φ' define the failure envelope in effective stress space.
The document presents an analytical method for determining stress distributions in pin-loaded orthotropic plates. The method assumes a rigid pin, clearance between the pin and plate, and a constant coefficient of friction. Numerical results are shown for normal, tangential and shear stresses on the cavity for different composite layups. The method can predict stresses for varying clearances and a perfectly fitting pin. Experimental validation and improvements to contact modeling are recommended.
This document discusses determining the shear strength of soils. It explains that soils fail in shear and their shear strength can be determined using laboratory tests like direct shear tests or triaxial tests on soil samples. The Mohr-Coulomb failure criterion describes the shear strength of a soil using parameters like cohesion (c) and friction angle (φ). These parameters can be estimated from the results of shear tests and used to assess shear strength and stability of soils under different field conditions.
This document discusses a marketing solution involving Facebook message marketing. It will utilize Facebook mobile, desktop, and profile data as well as page, company and group information to target potential customers. The solution aims to engage customers through personalized messages.
This document describes Edition 3.1 of the Association of Geotechnical and Geoenvironmental Specialists' (AGS) format for the electronic transfer of geotechnical and geoenvironmental data. The AGS format was created to standardize the electronic transfer of subsurface investigation data between different software programs and users. This updated edition includes new groups, fields, pick lists, and determinand codes added based on user suggestions. It aims to incorporate commonly used additions to the format while maintaining compatibility with previous versions.
This document contains 17 references related to rock mechanics and rock engineering. The references span from 1931 to 1994 and include journal articles, conference proceedings, books, theses, and reports. The references cover topics such as rock mass classification systems, shear strength of rock joints, rockfall analysis, tunnel support, and case histories of rock engineering projects.
The document discusses blasting damage in rock excavations and methods to control it. It begins with a brief history of blasting and how the understanding of its effects on rock stability has lagged behind other areas of rock mechanics. Blasting can damage rock through dynamic stresses, gas pressure, and fracturing from the release of compressed rock. Precisely controlling blasting techniques from the initial cut through the full blast sequence is necessary to minimize damage extending several meters into the surrounding rock. Methods discussed include pre-splitting, smooth blasting, and the use of delays to allow broken rock to clear before subsequent holes detonate. Proper blasting design is crucial for ensuring the stability of underground excavations and rock slopes.
The document discusses rock mass properties and the Hoek-Brown failure criterion for estimating the strength of jointed rock masses. It presents the generalized Hoek-Brown criterion equation and describes how to determine the intact rock properties of uniaxial compressive strength (σci) and the Hoek-Brown constant (mi) from triaxial test data or estimates. It also discusses estimating the Geological Strength Index (GSI) of the rock mass.
This document discusses rockfall hazards and analysis. It begins with an introduction noting that rockfalls are a major hazard for mountainous transportation routes and have resulted in numerous deaths. It then discusses the mechanics of rockfalls, noting that slope geometry and surface materials are most important in determining rockfall trajectories. Various measures to reduce rockfall hazards are discussed, including identification of problems, reducing energy from excavation, installing physical barriers like nets and ditches, and the Rockfall Hazard Rating System used to assess slopes.
The document introduces factor of safety and probability of failure in engineering design. It discusses using sensitivity studies to systematically vary parameters over their credible ranges to determine the influence on factor of safety. This allows a more rational assessment of design risks than relying on a single calculated factor of safety. The document then provides an introduction to probability theory and statistical concepts used in probabilistic analyses, including random variables, probability distributions, sampling techniques, and calculating the probability of failure for a slope design example.
The document describes a slope stability analysis of a steep rock slope in Hong Kong located near apartment buildings. Due to heavy rains causing landslides in the 1970s, the stability of this slope was analyzed. A simple limit equilibrium model was used to calculate the factor of safety under normal conditions and during earthquakes or heavy rains. The analysis found that instability could occur if the slope became fully saturated during an earthquake. However, as earthquakes and heavy rains are unlikely to occur simultaneously, it was concluded there was no serious short-term threat to stability. Evacuation of nearby apartments was deemed unnecessary based on this short-term stability assessment.
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.
1. The development of rock engineering began in the late 18th century, but it was not established as a formal discipline until the 1960s after several catastrophic dam failures that demonstrated limitations in predicting rock mass behavior.
2. Early contributors to rock mechanics came from various fields like soil mechanics, mining, and geology. They made important contributions to understanding rock failure even if they did not consider themselves "rock mechanics engineers".
3. Major events like dam failures and mine collapses in the 1950s and 1960s highlighted the need for rock mechanics as a discipline and led to rapid advances in methods for designing rock structures and underground excavations.
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.
This document summarizes three articles related to previous topics in Geotechnical Instrumentation News (GIN). The first article discusses distributed optical fiber sensing, which allows continuous strain measurement along an optical fiber cable. This is useful for geotechnical applications where soil loading is non-uniform. The second article compares different technologies for strain monitoring, including distributed optical fiber sensing. The third article provides examples of using distributed optical fiber sensing to monitor strain in pile foundations and detect cracks.
This study aimed to map forest fire risk zones in Quang Ninh province, Vietnam using remote sensing and GIS. Forest fire data from MODIS and field surveys were compared to validate the analysis. Factors like forest type, proximity to roads and settlements, slope, and aspect were used as inputs to a weighted overlay analysis. This generated a risk map classifying the area into very low to very high risk zones. Most fire locations fell within high or very high risk areas, validating the model. Improving input data resolution and incorporating additional social and weather factors could enhance future analyses. The study effectively mapped forest fire risk to aid decision-making for forest management in Quang Ninh province.
1. 4
Shear strength of discontinuities
4.1 Introduction
All rock masses contain discontinuities such as bedding planes, joints, shear zones and
faults. At shallow depth, where stresses are low, failure of the intact rock material is
minimal and the behaviour of the rock mass is controlled by sliding on the
discontinuities. In order to analyse the stability of this system of individual rock blocks,
it is necessary to understand the factors that control the shear strength of the
discontinuities which separate the blocks. These questions are addressed in the discussion
that follows.
4.2 Shear strength of planar surfaces
Suppose that a number of samples of a rock are obtained for shear testing. Each sample
contains a through-going bedding plane that is cemented; in other words, a tensile force
would have to be applied to the two halves of the specimen in order to separate them. The
bedding plane is absolutely planar, having no surface irregularities or undulations. As
illustrated in Figure 4.1, in a shear test each specimen is subjected to a stress σn normal to
the bedding plane, and the shear stress τ, required to cause a displacement δ, is measured.
The shear stress will increase rapidly until the peak strength is reached. This
corresponds to the sum of the strength of the cementing material bonding the two halves
of the bedding plane together and the frictional resistance of the matching surfaces. As
the displacement continues, the shear stress will fall to some residual value that will then
remain constant, even for large shear displacements.
Plotting the peak and residual shear strengths for different normal stresses results in
the two lines illustrated in Figure 4.1. For planar discontinuity surfaces the experimental
points will generally fall along straight lines. The peak strength line has a slope of φ and
an intercept of c on the shear strength axis. The residual strength line has a slope of φr.
The relationship between the peak shear strength τp and the normal stress σn can be
represented by the Mohr-Coulomb equation:
τ p = c + σ n tan φ (4.1)
where c is the cohesive strength of the cemented surface and
φ is the angle of friction.
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3. Shear strength of planar surfaces 61
Figure 4.1: Shear testing of discontinuities
In the case of the residual strength, the cohesion c has dropped to zero and the
relationship between φr and σn can be represented by:
τ r = σ n tan φr (4.2)
where φr is the residual angle of friction.
This example has been discussed in order to illustrate the physical meaning of the term
cohesion, a soil mechanics term, which has been adopted by the rock mechanics
community. In shear tests on soils, the stress levels are generally an order of magnitude
lower than those involved in rock testing and the cohesive strength of a soil is a result of
the adhesion of the soil particles. In rock mechanics, true cohesion occurs when cemented
surfaces are sheared. However, in many practical applications, the term cohesion is used
for convenience and it refers to a mathematical quantity related to surface roughness, as
discussed in a later section. Cohesion is simply the intercept on the τ axis at zero normal
stress.
The basic friction angle φb is a quantity that is fundamental to the understanding of the
shear strength of discontinuity surfaces. This is approximately equal to the residual
friction angle φr but it is generally measured by testing sawn or ground rock surfaces.
These tests, which can be carried out on surfaces as small as 50 mm × 50 mm, will
produce a straight line plot defined by the equation :
τ r = σ n tan φb (4.3)
4. 62 Chapter 4: Shear strength of discontinuities
Figure 4.2: Diagrammatic section through shear machine used by Hencher and Richards (1982).
Figure 4.3: Shear machine of the type used by Hencher and Richards (1982) for
measurement of the shear strength of sheet joints in Hong Kong granite.
5. Shear strength of rough surfaces 63
A typical shear testing machine, which can be used to determine the basic friction angle
φb is illustrated in Figures 4.2 and 4.3. This is a very simple machine and the use of a
mechanical lever arm ensures that the normal load on the specimen remains constant
throughout the test. This is an important practical consideration since it is difficult to
maintain a constant normal load in hydraulically or pneumatically controlled systems and
this makes it difficult to interpret test data.
Note that it is important that, in setting up the specimen, great care has to be taken to
ensure that the shear surface is aligned accurately in order to avoid the need for an
additional angle correction.
Most shear strength determinations today are carried out by determining the basic
friction angle, as described above, and then making corrections for surface roughness as
discussed in the following sections of this chapter. In the past there was more emphasis
on testing full scale discontinuity surfaces, either in the laboratory or in the field. There
are a significant number of papers in the literature of the 1960s and 1970s describing
large and elaborate in situ shear tests, many of which were carried out to determine the
shear strength of weak layers in dam foundations. However, the high cost of these tests
together with the difficulty of interpreting the results has resulted in a decline in the use
of these large scale tests and they are seldom seen today.
The author’s opinion is that it makes both economical and practical sense to carry out
a number of small scale laboratory shear tests, using equipment such as that illustrated in
Figures 4.2 and 4.3, to determine the basic friction angle. The roughness component
which is then added to this basic friction angle to give the effective friction angle is a
number which is site specific and scale dependent and is best obtained by visual estimates
in the field. Practical techniques for making these roughness angle estimates are
described on the following pages.
4.3 Shear strength of rough surfaces
A natural discontinuity surface in hard rock is never as smooth as a sawn or ground
surface of the type used for determining the basic friction angle. The undulations and
asperities on a natural joint surface have a significant influence on its shear behaviour.
Generally, this surface roughness increases the shear strength of the surface, and this
strength increase is extremely important in terms of the stability of excavations in rock.
Patton (1966) demonstrated this influence by means of an experiment in which he
carried out shear tests on 'saw-tooth' specimens such as the one illustrated in Figure 4.4.
Shear displacement in these specimens occurs as a result of the surfaces moving up the
inclined faces, causing dilation (an increase in volume) of the specimen.
The shear strength of Patton's saw-tooth specimens can be represented by:
τ = σ n tan( φb + i ) (4.4)
where φb is the basic friction angle of the surface and
i is the angle of the saw-tooth face.
6. 64 Chapter 4: Shear strength of discontinuities
Figure 4.4: Patton’s experiment on the shear strength of saw-tooth specimens.
4.4 Barton’s estimate of shear strength
Equation (4.4) is valid at low normal stresses where shear displacement is due to sliding
along the inclined surfaces. At higher normal stresses, the strength of the intact material
will be exceeded and the teeth will tend to break off, resulting in a shear strength
behaviour which is more closely related to the intact material strength than to the
frictional characteristics of the surfaces.
While Patton’s approach has the merit of being very simple, it does not reflect the
reality that changes in shear strength with increasing normal stress are gradual rather than
abrupt. Barton and his co-workers (1973, 1976, 1977, 1990) studied the behaviour of
natural rock joints and have proposed that equation (4.4) can be re-written as:
JCS
τ = σ n tan φ b + JRC log10
σ
(4.5)
n
where JRC is the joint roughness coefficient and
JCS is the joint wall compressive strength.
4.5 Field estimates of JRC
The joint roughness coefficient JRC is a number that can be estimated by comparing the
appearance of a discontinuity surface with standard profiles published by Barton and
others. One of the most useful of these profile sets was published by Barton and Choubey
(1977) and is reproduced in Figure 4.2.
The appearance of the discontinuity surface is compared visually with the profiles
shown and the JRC value corresponding to the profile which most closely matches that of
the discontinuity surface is chosen. In the case of small scale laboratory specimens, the
scale of the surface roughness will be approximately the same as that of the profiles
illustrated. However, in the field the length of the surface of interest may be several
metres or even tens of metres and the JRC value must be estimated for the full scale
surface.
7. Field estimates of JRC 65
Figure 4.2: Roughness profiles and corresponding JRC values (After Barton and Choubey 1977).
8. 66 Chapter 4: Shear strength of discontinuities
Straight edge
Asperity amplitude - mm
Length of profile - m
400 20
Joint Roughness Coefficient (JRC)
300 16
12
200 10
8
6
100 5
4
3
50
Amplitude of asperities - mm
40 2
30
20 1
10 0.5
5
4
3
2
1
0.5
0.4
0.3
0.2
0.1
0.1 0.2 0.3 0.5 1 2 3 4 5 10
Length of profile - m
Figure 4.6: Alternative method for estimating JRC from measurements of surface
roughness amplitude from a straight edge (Barton 1982).
9. Field estimates of JCS 67
4.6 Field estimates of JCS
Suggested methods for estimating the joint wall compressive strength were published by
the ISRM (1978). The use of the Schmidt rebound hammer for estimating joint wall
compressive strength was proposed by Deere and Miller (1966), as illustrated in Figure
4.7.
Average dispersion of strength
for most rocks - MPa
200
250
100
150
50
3
Unit weight of rock - kN/m
+ + + +
32
| | | |
+
|
30
400
350
28
300
250
26
200
Uniaxial compressive strength - MPa
24
150
22
20
100
90
80
70
60
50
40
Hammer orientation
30
20
10
0 10 20 30 40 50 60
0 10 20 30 40 50 60
0 10 20 30 40 50 60
0 10 20 30 40 50 60
0 10 20 30 40 50 60
Schmidt hardness - Type L hammer
Figure 4.7: Estimate of joint wall compressive strength from Schmidt hardness.
10. 68 Chapter 4: Shear strength of discontinuities
4.7 Influence of scale on JRC and JCS
On the basis of extensive testing of joints, joint replicas, and a review of literature, Barton
and Bandis (1982) proposed the scale corrections for JRC defined by the following
relationship:
−0.02 JRCo
L
JRC n = JRCo n
L
(4.6)
o
where JRCo, and Lo (length) refer to 100 mm laboratory scale samples and JRCn, and Ln
refer to in situ block sizes.
Because of the greater possibility of weaknesses in a large surface, it is likely that the
average joint wall compressive strength (JCS) decreases with increasing scale. Barton
and Bandis (1982) proposed the scale corrections for JCS defined by the following
relationship:
−0.03 JRCo
L
JCS n = JCS o n
L
(4.7)
o
where JCSo and Lo (length) refer to 100 mm laboratory scale samples and JCSn and Ln
refer to in situ block sizes.
4.8 Shear strength of filled discontinuities
The discussion presented in the previous sections has dealt with the shear strength of
discontinuities in which rock wall contact occurs over the entire length of the surface
under consideration. This shear strength can be reduced drastically when part or all of the
surface is not in intimate contact, but covered by soft filling material such as clay gouge.
For planar surfaces, such as bedding planes in sedimentary rock, a thin clay coating will
result in a significant shear strength reduction. For a rough or undulating joint, the filling
thickness has to be greater than the amplitude of the undulations before the shear strength
is reduced to that of the filling material.
A comprehensive review of the shear strength of filled discontinuities was prepared by
Barton (1974) and a summary of the shear strengths of typical discontinuity fillings,
based on Barton's review, is given in Table 4.1.
Where a significant thickness of clay or gouge fillings occurs in rock masses and
where the shear strength of the filled discontinuities is likely to play an important role in
the stability of the rock mass, it is strongly recommended that samples of the filling be
sent to a soil mechanics laboratory for testing.
11. Shear strength of filled discontinuities 69
Table 4.1: Shear strength of filled discontinuities and filling materials (After Barton 1974)
Rock Description Peak Peak Residual Residual
c' (MPa) φ° c' (MPa) φ°
Basalt Clayey basaltic breccia, wide variation 0.24 42
from clay to basalt content
Bentonite Bentonite seam in chalk 0.015 7.5
Thin layers 0.09-0.12 12-17
Triaxial tests 0.06-0.1 9-13
Bentonitic shale Triaxial tests 0-0.27 8.5-29
Direct shear tests 0.03 8.5
Clays Over-consolidated, slips, joints and minor 0-0.18 12-18.5 0-0.003 10.5-16
shears
Clay shale Triaxial tests 0.06 32
Stratification surfaces 0 19-25
Coal measure rocks Clay mylonite seams, 10 to 25 mm 0.012 16 0 11-11.5
Dolomite Altered shale bed, ± 150 mm thick 0.04 14.5 0.02 17
Diorite, granodiorite Clay gouge (2% clay, PI = 17%) 0 26.5
and porphyry
Granite Clay filled faults 0-0.1 24-45
Sandy loam fault filling 0.05 40
Tectonic shear zone, schistose and broken
granites, disintegrated rock and gouge 0.24 42
Greywacke 1-2 mm clay in bedding planes 0 21
Limestone 6 mm clay layer 0 13
10-20 mm clay fillings 0.1 13-14
<1 mm clay filling 0.05-0.2 17-21
Limestone, marl and Interbedded lignite layers 0.08 38
lignites Lignite/marl contact 0.1 10
Limestone Marlaceous joints, 20 mm thick 0 25 0 15-24
Lignite Layer between lignite and clay 0.014-.03 15-17.5
Montmorillonite 80 mm seams of bentonite (mont- 0.36 14 0.08 11
Bentonite clay morillonite) clay in chalk 0.016-.02 7.5-11.5
Schists, quartzites 100-15- mm thick clay filling 0.03-0.08 32
and siliceous schists Stratification with thin clay 0.61-0.74 41
Stratification with thick clay 0.38 31
Slates Finely laminated and altered 0.05 33
Quartz / kaolin / Remoulded triaxial tests 0.042-.09 36-38
pyrolusite
12. 70 Chapter 4: Shear strength of discontinuities
4.9 Influence of water pressure
When water pressure is present in a rock mass, the surfaces of the discontinuities are
forced apart and the normal stress σn is reduced. Under steady state conditions, where
there is sufficient time for the water pressures in the rock mass to reach equilibrium, the
reduced normal stress is defined by σn' = (σn - u), where u is the water pressure. The
reduced normal stress σn' is usually called the effective normal stress, and it can be used
in place of the normal stress term σn in all of the equations presented in previous sections
of this chapter.
4.10 Instantaneous cohesion and friction
Due to the historical development of the subject of rock mechanics, many of the analyses,
used to calculate factors of safety against sliding, are expressed in terms of the Mohr-
Coulomb cohesion (c) and friction angle (φ), defined in Equation 4.1. Since the 1970s it
has been recognised that the relationship between shear strength and normal stress is
more accurately represented by a non-linear relationship such as that proposed by Barton
(1973). However, because this relationship (e.g. Equation 4.5) is not expressed in terms
of c and φ, it is necessary to devise some means for estimating the equivalent cohesive
strengths and angles of friction from relationships such as those proposed by Barton.
Figure 4.8 gives definitions of the instantaneous cohesion ci and the instantaneous
friction angle φi for a normal stress of σn. These quantities are given by the intercept and
the inclination, respectively, of the tangent to the non-linear relationship between shear
strength and normal stress. These quantities may be used for stability analyses in which
the Mohr-Coulomb failure criterion (Equation 4.1) is applied, provided that the normal
stress σn is reasonably close to the value used to define the tangent point.
In a typical practical application, a spreadsheet program can be used to solve Equation
4.5 and to calculate the instantaneous cohesion and friction values for a range of normal
stress values. A portion of such a spreadsheet is illustrated in Figure 4.9.
shear stress τ
tangent φi
ci
σn normal stress σn
Figure 4.8: Definition of instantaneous cohesion c i and instantaneous friction angle φi for a
non-linear failure criterion.
13. Instantaneous cohesion and friction 71
Barton shear failure criterion
Input parameters:
Basic friction angle (PHIB) - degrees 29
Joint roughness coefficient (JRC) 16.9
Joint compressive strength (JCS) 96
Minimum normal stress (SIGNMIN) 0.360
Normal Shear dTAU Friction Cohesive
stress strength dSIGN angle strength
(SIGN) (TAU) (DTDS) (PHI) (COH)
MPa MPa degrees MPa
0.360 0.989 1.652 58.82 0.394
0.720 1.538 1.423 54.91 0.513
1.440 2.476 1.213 50.49 0.730
2.880 4.073 1.030 45.85 1.107
5.759 6.779 0.872 41.07 1.760
11.518 11.344 0.733 36.22 2.907
23.036 18.973 0.609 31.33 4.953
46.073 31.533 0.496 26.40 8.666
Cell formulae:
SIGNMIN = 10^(LOG(JCS)-((70-PHIB)/JRC))
TAU = SIGN*TAN((PHIB+JRC*LOG(JCS/SIGN))*PI()/180)
DTDS = TAN((JRC*LOG(JCS/SIGN)+PHIB)*PI()/180)-(JRC/LN(10))
*(TAN((JRC*LOG(JCS/SIGN)+PHIB)*PI()/180)^2+1)*PI()/180
PHI = ATAN(DTDS)*180/PI()
COH = TAU-SIGN*DTDS
Figure 4.9 Printout of spreadsheet cells and formulae used to calculate shear strength,
instantaneous friction angle and instantaneous cohesion for a range of normal stresses.
Note that equation 4.5 is not valid for σn = 0 and it ceases to have any practical
meaning for φb + JRC log10 ( JCS / σn ) > 70° . This limit can be used to determine a
minimum value for σn. An upper limit for σn is given by σn = JCS.
In the spreadsheet shown in Figure 4.9, the instantaneous friction angle φi, for a
normal stress of σn, has been calculated from the relationship
∂τ
φ i = arctan
∂σ
(4.8)
n
14. 72 Chapter 4: Shear strength of discontinuities
∂τ JCS πJRC 2 JCS
= tan JRC log10
+ φb −
180 ln 10 tan JRC log10 σ + φ b + 1
(4.9)
∂σ n σn
n
The instantaneous cohesion c i is calculated from:
ci = τ − σ n tan φi (4.10)
In choosing the values of ci and φi for use in a particular application, the average normal
stress σn acting on the discontinuity planes should be estimated and used to determine the
appropriate row in the spreadsheet. For many practical problems in the field, a single
average value of σn will suffice but, where critical stability problems are being
considered, this selection should be made for each important discontinuity surface.