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72-749: Four types of tessellated pavements are recognized: tessellated pavements formed by jointing ; tessellated pavements formed by cooling contraction; tessellations formed by mud cracking and lithification; and tessellated sandstone pavements of uncertain origin. The most common type of tessellated pavement consists of relatively flat rock surfaces, typically the tops of beds of sandstones and other sedimentary rocks , that are subdivided into either more or less regular rectangles or blocks approaching rectangles by well-developed systematic orthogonal joint systems. The surface of individual beds, as exposed by erosion , are typically divided into either squares, rectangles, and less commonly triangles or other shapes, depending on

144-480: A = half crack length. Fracture mechanics has generalized to that γ represents energy dissipated in fracture not just the energy associated with creation of new surfaces Linear elastic fracture mechanics (LEFM) builds off the energy balance approach taken by Griffith but provides a more generalized approach for many crack problems. LEFM investigates the stress field near the crack tip and bases fracture criteria on stress field parameters. One important contribution of LEFM

216-451: A car windshield or a highly ductile crack like a ripped plastic grocery bag. Rocks are a polycrystalline material so cracks grow through the coalescing of complex microcracks that occur in front of the crack tip. This area of microcracks is called the brittle process zone. Consider a simplified 2D shear crack as shown in the image on the right. The shear crack, shown in blue, propagates when tensile cracks, shown in red, grow perpendicular to

288-445: A constant of proportionality within geology. σ n is the normal stress across the fracture at the instant of failure, σ f represents the pore fluid pressure. It is important to point out that pore fluid pressure has a significant impact on shear stress, especially where pore fluid pressure approaches lithostatic pressure , which is the normal pressure induced by the weight of the overlying rock. This relationship serves to provide

360-533: A few centimeters to several metres. They are often oriented perpendicular to either the upper surface and base of lava flows and the contact of the tabular igneous bodies with the surrounding rock. This type of jointing is typical of thick lava flows and shallow dikes and sills. Columnar jointing is also known as either columnar structure , prismatic joints , or prismatic jointing . Rare cases of columnar jointing have also been reported from sedimentary strata. Joints can be classified according to their origin, under

432-478: A fixed function of θ {\displaystyle \theta } . With knowledge of the geometry of the crack and applied far field stresses, it is possible to predict the crack tip stresses, displacement, and growth. Energy release rate is defined to relate K to the Griffith energy balance as previously defined. In both LEFM and energy balance approaches, the crack is assumed to be cohesionless behind

504-437: A fracture forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel , foundation , or slope construction. Fractures also play a significant role in minerals exploitation. One aspect of the upstream energy sector is the production from naturally fractured reservoirs. There are a good number of naturally fractured reservoirs in

576-555: A large extent on the grain size, texture, and coherence of the rock. This polygonal tessellation is best developed in relatively fine-grained, uniform, and siliceous or silicified sandstones. The most well known example of a tessellated pavement is the Tessellated Pavement that is found at Lufra, Eaglehawk Neck on the Tasman Peninsula of Tasmania . This tessellated pavement consists of a marine platform on

648-519: A lava lake or flood basalt flow or the sides of a tabular igneous intrusion into either lava of the lake or lava flow or magma of a dike or sill. Joint propagation can be studied through the techniques of fractography in which characteristic marks such as hackles and plumose structures are used to determine propagation directions and, in some cases, the principal stress orientations. Some fractures that look like joints are actually shear fractures, which in effect are microfaults. They do not form as

720-440: A patterned pavement after the sediment becomes lithified into a sedimentary rock. The final type of tessellated pavement consists of relatively flat, sandstone surfaces that typically exhibit a complex pattern of five- or six-sided polygons. Typically, these polygons vary greatly in size from 0.5 to 2 m in width. These polygons are defined by well-developed fractures that sometimes have raised rims. They are found within exposures of

792-413: A remote tensile stress, σ n , is applied, allowing microcracks to open slightly throughout the tensile region. As these cracks open up, the stresses at the crack tips intensify, eventually exceeding the rock strength and allowing the fracture to propagate. This can occur at times of rapid overburden erosion. Folding also can provide tension, such as along the top of an anticlinal fold axis. In this scenario

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864-403: A result from shear or tensile stress. Some of the primary mechanisms are discussed below. First, there are three modes of fractures that occur (regardless of mechanism): For more information on this, see fracture mechanics . Rocks contain many pre-existing cracks where development of tensile fracture, or Mode I fracture, may be examined. The first form is in axial stretching. In this case

936-432: A result of vertical gravitational loading. In simple terms, the accumulation of either sediments, volcanic, or other material causes an increase in the pore pressure of groundwater and other fluids in the underlying rock when they cannot move either laterally or vertically in response to this pressure. This also causes an increase in pore pressure in preexisting cracks that increases the tensile stress on them perpendicular to

1008-418: A result, any differences in hydrostatic balance down the well can result in well control issues. If a higher pressured natural fracture system is encountered, the rapid rate at which formation fluid can flow into the wellbore can cause the situation to rapidly escalate into a blowout, either at surface or in a higher subsurface formation. Conversely, if a lower pressured fracture network is encountered, fluid from

1080-475: A rod under uniform tension Griffith determined an expression for the critical stress at which a favorably orientated crack will grow. The critical stress at fracture is given by, σ f = ( 2 E γ π a ) 1 / 2 {\displaystyle \sigma _{f}=({2E\gamma \over \pi a})^{1/2}} where γ = surface energy associated with broken bonds, E = Young's modulus , and

1152-478: A tectonic - hydraulic hybrid. Exfoliation joints are sets of flat-lying, curved, and large joints that are restricted to massively exposed rock faces in a deeply eroded landscape. Exfoliation jointing consists of fan-shaped fractures varying from a few meters to tens of meters in size that lie sub-parallel to the topography. The vertical, gravitational load of the mass of a mountain-size bedrock mass drives longitudinal splitting and causes outward buckling toward

1224-511: A weakened section of rock. This weakened section is more susceptible to changes in pore pressure and dilatation or compaction. Note that this description of formation and propagation considers temperatures and pressures near the Earth's surface. Rocks deep within the earth are subject to very high temperatures and pressures. This causes them to behave in the semi-brittle and plastic regimes which result in significantly different fracture mechanisms. In

1296-435: Is a significant part of understanding the geology and geomorphology of an area. Joints often impart a well-develop fracture-induced permeability to bedrock. As a result, joints strongly influence, even control, the natural circulation ( hydrogeology ) of fluids, e.g. groundwater and pollutants within aquifers , petroleum in reservoirs , and hydrothermal circulation at depth, within bedrock. Thus, joints are important to

1368-438: Is an important part of finding and profitably developing ore deposits. Finally, joints often form discontinuities that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel , foundation , or slope construction. As a result, joints are an important part of geotechnical engineering in practice and research. Fracture (geology) A fracture

1440-755: Is any separation in a geologic formation , such as a joint or a fault that divides the rock into two or more pieces. A fracture will sometimes form a deep fissure or crevice in the rock. Fractures are commonly caused by stress exceeding the rock strength, causing the rock to lose cohesion along its weakest plane. Fractures can provide permeability for fluid movement, such as water or hydrocarbons . Highly fractured rocks can make good aquifers or hydrocarbon reservoirs , since they may possess both significant permeability and fracture porosity . Fractures are forms of brittle deformation. There are two types of primary brittle deformation processes. Tensile fracturing results in joints . Shear fractures are

1512-422: Is called cataclastic flow, which will cause fractures to fail and propagate due to a mixture of brittle-frictional and plastic deformations. Describing joints can be difficult, especially without visuals. The following are descriptions of typical natural fracture joint geometries that might be encountered in field studies: Faults are another form of fracture in a geologic environment. In any type of faulting,

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1584-541: Is less than force required to fracture and create new faults as shown by the Mohr-Coulomb diagram . Since the earth is full of existing cracks and this means for any applied stress, many of these cracks are more likely to slip and redistribute stress than a new crack is to initiate. The Mohr's Diagram shown, provides a visual example. For a given stress state in the earth, if an existing fault or crack exists orientated anywhere from −α/4 to +α/4, this fault will slip before

1656-422: Is observed. To fully understand the effects of applied tensile stress around a crack in a brittle material such a rock, fracture mechanics can be used. The concept of fracture mechanics was initially developed by A. A. Griffith during World War I. Griffith looked at the energy required to create new surfaces by breaking material bonds versus the elastic strain energy of the stretched bonds released. By analyzing

1728-462: Is the stress intensity factor , K, which is used to predict the stress at the crack tip. The stress field is given by σ i j ( r , θ ) = K ( 2 π r ) 1 / 2 f i j ( θ ) {\displaystyle \sigma _{ij}(r,\theta )={K \over (2\pi r)^{1/2}}f_{ij}(\theta )} where K {\displaystyle K}

1800-423: Is the stress intensity factor for Mode I, II, or III cracking and f i j {\displaystyle f_{ij}} is a dimensionless quantity that varies with applied load and sample geometry. As the stress field gets close to the crack tip, i.e. r → 0 {\displaystyle r\rightarrow 0} , f i j {\displaystyle f_{ij}} becomes

1872-518: The Giant's Causeway in Northern Ireland . The third type of tesselation recognized by Branagan is associated with the shrinkage and cracking of fine-grained, either clayey or calcareous , sediments . They consist of polygonal cracking, often associated with individual 'plates' that tend to be concave upward, that characterizes the formation of mudcracks in fine-grained sediments. Often,

1944-806: The Hawkesbury Sandstone within the Sydney , New South Wales, Australia region, exposures of the Precipice Sandstone at the Kenniff Cave Archaeological Site in Queensland , Australia, and in exposures of Upper Cretaceous sandstones of the Boulder, Colorado , U.S., region. The origin of this type of tessellated pavement remains uncertain. The size and shape of these polygons appears to be dependent to

2016-577: The coulomb failure envelope within the Mohr-Coulomb Theory . Frictional sliding is one aspect for consideration during shear fracturing and faulting. The shear force parallel to the plane must overcome the frictional force to move the faces of the fracture across each other. In fracturing, frictional sliding typically only has significant effects on the reactivation on existing shear fractures. For more information on frictional forces, see friction . The shear force required to slip fault

2088-435: The "pans" therefore erodes more quickly than the joints, resulting in increasing concavity. The loaf formations occur on the parts of the pavement closer to the seashore, which are immersed in water for longer periods of time. These parts of the pavement do not dry out so much, reducing the level of salt crystallisation. Water, carrying abrasive sand, is typically channelled through the joints, causing them to erode faster than

2160-492: The United States, and over the past century, they have provided a substantial boost to the nation's net hydrocarbon production. The key concept is while low porosity, brittle rocks may have very little natural storage or flow capability, the rock is subjected to stresses that generate fractures, and these fractures can actually store a very large volume of hydrocarbons, capable of being recovered at very high rates. One of

2232-412: The active fracture experiences shear failure, as the faces of the fracture slip relative to each other. As a result, these fractures seem like large scale representations of Mode II and III fractures, however that is not necessarily the case. On such a large scale, once the shear failure occurs, the fracture begins to curve its propagation towards the same direction as the tensile fractures. In other words,

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2304-411: The angle at which joint sets of systematic joints intersect to form a joint system, systematic joints can be subdivided into conjugate and orthogonal joint sets. The angles at which joint sets within a joint system commonly intersect are called dihedral angles by structural geologists. When the dihedral angles are nearly 90° within a joint system, the joint sets are known as orthogonal joint sets . When

2376-848: The birth of true horizontal drilling in a developmental context. Another example in South Texas is the Georgetown and Buda limestone formations. Furthermore, the recent uprise in prevalence of unconventional reservoirs is actually, in part, a product of natural fractures. In this case, these microfractures are analogous to Griffith Cracks, however they can often be sufficient to supply the necessary productivity, especially after completions, to make what used to be marginally economic zones commercially productive with repeatable success. However, while natural fractures can often be beneficial, they can also act as potential hazards while drilling wells. Natural fractures can have very high permeability , and as

2448-405: The crack tip. This provides a problem for geological applications such a fault, where friction exists all over a fault. Overcoming friction absorbs some of the energy that would otherwise go to crack growth. This means that for Modes II and III crack growth, LEFM and energy balances represent local stress fractures rather than global criteria. Cracks in rock do not form smooth path like a crack in

2520-412: The dihedral angles are from 30 to 60° within a joint system, the joint sets are known as conjugate joint sets . Within regions that have experienced tectonic deformation, systematic joints are typically associated with either layered or bedded strata that have been folded into anticlines and synclines . Such joints can be classified according to their orientation in respect to the axial planes of

2592-417: The direction of the least principal stresses. The tensile cracks propagate a short distance then become stable, allowing the shear crack to propagate. This type of crack propagation should only be considered an example. Fracture in rock is a 3D process with cracks growing in all directions. It is also important to note that once the crack grows, the microcracks in the brittle process zone are left behind leaving

2664-462: The economic and safe development of petroleum, hydrothermal, and groundwater resources and the subject of intensive research relative to these resources. Regional and local joint systems exert a strong control on how ore-forming hydrothermal fluids (consisting largely of H 2 O , CO 2 , and NaCl — which formed most of Earth's ore deposits ) circulated within its crust. As a result, understanding their genesis, structure, chronology, and distribution

2736-411: The fault typically attempts to orient itself perpendicular to the plane of least principal stress. This results in an out-of-plane shear relative to the initial reference plane. Therefore, these cannot necessarily be qualified as Mode II or III fractures. An additional, important characteristic of shear-mode fractures is the process by which they spawn wing cracks , which are tensile cracks that form at

2808-527: The first initial breaks resulting from shear forces exceeding the cohesive strength in that plane. After those two initial deformations, several other types of secondary brittle deformation can be observed, such as frictional sliding or cataclastic flow on reactivated joints or faults. Most often, fracture profiles will look like either a blade, ellipsoid, or circle. Fractures in rocks can be formed either due to compression or tension. Fractures due to compression include thrust faults . Fractures may also be

2880-559: The folds as they often commonly form in a predictable pattern with respect to the hinge trends of folded strata. Based upon their orientation to the axial planes and axes of folds, the types of systematic joints are: Columnar jointing is a distinctive type of joints that join together at triple junctions either at or about 120° angles. These joints split a rock body into long, prisms or columns. Typically, such columns are hexagonal, although 3-, 4-, 5- and 7-sided columns are relatively common. The diameter of these prismatic columns ranges from

2952-422: The fracture face is actually touching the other face. The cumulative impact of asperities is a reduction of the real area of contact' , which is important when establishing frictional forces. Sometimes, it is possible for fluids within the fracture to cause fracture propagation with a much lower pressure than initially required. The reaction between certain fluids and the minerals the rock is composed of can lower

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3024-460: The free air. In addition, paleostress sealed in the granite before the granite was exhumed by erosion and released by exhumation and canyon cutting is also a driving force for the actual spalling. Unloading joints or release joints arise near the surface when bedded sedimentary rocks are brought closer to the surface during uplift and erosion; when they cool, they contract and become relaxed elastically. A stress builds up which eventually exceeds

3096-542: The labels of tectonics, hydraulics, exfoliation, unloading (release), and cooling. Different authors have proposed contradictory hypotheses for the same joint sets and types. And, joints in the same outcrop may form at different times under varied circumstances. Tectonic joints are joints formed when the relative displacement of the joint walls is normal to its plane as the result of brittle deformation of bedrock in response to regional or local tectonic deformation of bedrock. Such joints form when directed tectonic stress causes

3168-408: The least principal normal stress, σ n . When this occurs, a tensile fracture opens perpendicular to the plane of least stress. Tensile fracturing may also be induced by applied compressive loads, σ n , along an axis such as in a Brazilian disk test. This applied compression force results in longitudinal splitting. In this situation, tiny tensile fractures form parallel to the loading axis while

3240-422: The load also forces any other microfractures closed. To picture this, imagine an envelope, with loading from the top. A load is applied on the top edge, the sides of the envelope open outward, even though nothing was pulling on them. Rapid deposition and compaction can sometimes induce these fractures. Tensile fractures are almost always referred to as joints , which are fractures where no appreciable slip or shear

3312-419: The local and regional geology and geomorphology but also in developing natural resources, in the safe design of structures, and in environmental protection. Joints have a profound control on weathering and erosion of bedrock. As a result, they exert a strong control on how topography and morphology of landscapes develop. Understanding the local and regional distribution, physical character, and origin of joints

3384-426: The minimum principal stress (the direction in which the rock is being stretched). If the tensile stress exceeds the magnitude of the least principal compressive stress the rock will fail in a brittle manner and these cracks propagate in a process called hydraulic fracturing . Hydraulic joints occur as both nonsystematic and systematic joints, including orthogonal and conjugate joint sets. In some cases, joint sets can be

3456-457: The minimum principal stress (the direction in which the rock is being stretched). This leads to the development of a single sub-parallel joint set. Continued deformation may lead to development of one or more additional joint sets. The presence of the first set strongly affects the stress orientation in the rock layer, often causing subsequent sets to form at a high angle, often 90°, to the first set. Joints are classified by their geometry or by

3528-548: The most famous examples of a prolific naturally fractured reservoir was the Austin Chalk formation in South Texas. The chalk had very little porosity, and even less permeability. However, tectonic stresses over time created one of the most extensive fractured reservoirs in the world. By predicting the location and connectivity of fracture networks, geologists were able to plan horizontal wellbores to intersect as many fracture networks as possible. Many people credit this field for

3600-455: The most well-consolidated, lithified, and highly competent rocks, such as sandstone , limestone , quartzite , and granite . Joints may be open fractures or filled by various materials. Joints infilled by precipitated minerals are called veins and joints filled by solidified magma are called dikes . Joints arise from brittle fracture of a rock or layer due to tensile stress . This stress may be imposed from outside; for example, by

3672-502: The number and orientation of the joint sets that comprise the joint system. This relatively flat surface of individual beds of sedimentary rocks are frequently altered by weathering along joints as to cause the bedrock along the joints to be either raised or recessed as the result of differential erosion. This type of tessellated pavement is commonly observed along shorelines where wave action has created relatively flat and extensive wave-cut platforms that expose jointed bedrock and keeps

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3744-418: The order of centimeters, meters, tens of meters, or even hundreds of meters. As a result, they occur as families of joints that form recognizable joint sets. Typically, exposures or outcrops within a given area or region of study contains two or more sets of systematic joints, each with its own distinctive properties such as orientation and spacing, that intersect to form well-defined joint systems. Based upon

3816-401: The outlines of the polygons formed by this type of cracking are preserved and accentuated by the infilling of the cracks with material of a different composition from that of either the clayey or calcareous sediments in which the cracks form. The infilling of the cracks by sediments of a different character often preserved the polygonal pattern of the cracking where it can be exhumed by erosion as

3888-407: The plastic regime cracks acts like a plastic bag being torn. In this case stress at crack tips goes to two mechanisms, one which will drive propagation of the crack and the other which will blunt the crack tip . In the brittle-ductile transition zone , material will exhibit both brittle and plastic traits with the gradual onset of plasticity in the polycrystalline rock. The main form of deformation

3960-628: The processes that formed them. The geometry of joints refers to the orientation of joints as either plotted on stereonets and rose-diagrams or observed in rock exposures. In terms of geometry, three major types of joints, nonsystematic joints, systematic joints, and columnar jointing are recognized. Nonsystematic joints are joints that are so irregular in form, spacing, and orientation that they cannot be readily grouped into distinctive, through-going joint sets. Systematic joints are planar, parallel, joints that can be traced for some distance, and occur at regularly, evenly spaced distances on

4032-417: The propagation tip of the shear fractures. As the faces slide in opposite directions, tension is created at the tip, and a mode I fracture is created in the direction of the σ h-max , which is the direction of maximum principal stress. Shear-failure criteria is an expression that attempts to describe the stress at which a shear rupture creates a crack and separation. This criterion is based largely off of

4104-669: The rest of the pavement, leaving loaf-like structures protruding. Joint (geology) A joint is a break ( fracture ) of natural origin in a layer or body of rock that lacks visible or measurable movement parallel to the surface (plane) of the fracture ("Mode 1" Fracture). Although joints can occur singly, they most frequently appear as joint sets and systems. A joint set is a family of parallel, evenly spaced joints that can be identified through mapping and analysis of their orientations, spacing, and physical properties. A joint system consists of two or more intersecting joint sets. The distinction between joints and faults hinges on

4176-528: The result of the perpendicular opening of a fracture due to tensile stress, but through the shearing of fractures that causes lateral movement of the faces. Shear fractures can be confused with joints because the lateral offset of the fracture faces is not visible in the outcrop or in a specimen. Because of the absence of diagnostic ornamentation or the lack of any discernible movement or offset, they can be indistinguishable from joints. Such fractures occur in planar parallel sets at an angle of 60 degrees and can be of

4248-415: The same size and scale as joints. As a result, some "conjugate joint sets" might actually be shear fractures. Shear fractures are distinguished from joints by the presence of slickensides , the products of shearing movement parallel to the fracture surface. The slickensides are fine-scale, delicate ridge-in-groove lineations on the surface of fracture surfaces. Joints are important not only in understanding

4320-400: The shore of Pirates Bay, Tasmania. This example consists of two types of formations: a pan formation and a loaf formation. The pan formation is a series of concave depressions in the rock that typically forms beyond the edge of the seashore. This part of the pavement dries out more at low tide than the portion abutting the seashore, allowing salt crystals to develop further; the surface of

4392-412: The sides of a tabular igneous, typically basaltic, intrusion. They exhibit a pattern of joints that join together at triple junctions either at or about 120° angles. They split a rock body into long, prisms or columns that are typically hexagonal, although 3-, 4-, 5- and 7-sided columns are relatively common. They form as a result of a cooling front that moves from some surface, either the exposed surface of

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4464-444: The strength of the rock is reached and a new fault is formed. While the applied stresses may be high enough to form a new fault, existing fracture planes will slip before fracture occurs. One important idea when evaluating the friction behavior within a fracture is the impact of asperities , which are the irregularities that stick out from the rough surfaces of fractures. Since both faces have bumps and pieces that stick out, not all of

4536-459: The stress required for fracture below the stress required throughout the rest of the rock. For instance, water and quartz can react to form a substitution of OH molecules for the O molecules in the quartz mineral lattice near the fracture tip. Since the OH bond is much lower than that with O, it effectively reduces the necessary tensile stress required to extend the fracture. In geotechnical engineering

4608-402: The stretching of layers, the rise of pore fluid pressure , or shrinkage caused by the cooling or desiccation of a rock body or layer whose outside boundaries remained fixed. When tensional stresses stretch a body or layer of rock such that its tensile strength is exceeded, it breaks. When this happens the rock fractures in a plane parallel to the maximum principal stress and perpendicular to

4680-501: The surface (plane) of the fracture that remains "invisible" at the scale of observation. Joints are among the most universal geologic structures, found in almost every exposure of rock. They vary greatly in appearance, dimensions, and arrangement, and occur in quite different tectonic environments. Often, the specific origin of the stresses that created certain joints and associated joint sets can be quite ambiguous, unclear, and sometimes controversial. The most prominent joints occur in

4752-455: The surfaces of these platforms relatively clear of debris. The second type of tessellated pavement consists of a bedrock surface that exhibits joints that form polygons that are typically regular in size, spacing, and junctions. Typically, these polygons represent the cross-sections of polygonal, typically hexagonal joints, called columnar jointing , that formed as the result of the cooling of basaltic lava . This type of surface can be seen at

4824-407: The tensile forces associated with the stretching of the upper half of the layers during folding can induce tensile fractures parallel to the fold axis. Another, similar tensile fracture mechanism is hydraulic fracturing . In a natural environment, this occurs when rapid sediment compaction, thermal fluid expansion, or fluid injection causes the pore fluid pressure, σ p , to exceed the pressure of

4896-465: The tensile strength of bedrock to be exceeded as the result of the stretching of rock layers under conditions of elevated pore fluid pressure and directed tectonic stress. Tectonic joints often reflect local tectonic stresses associated with local folding and faulting. Tectonic joints occur as both nonsystematic and systematic joints, including orthogonal and conjugate joint sets. Hydraulic joints are formed when pore fluid pressure becomes elevated as

4968-404: The tensile strength of the bedrock and results in jointing. In the case of unloading joints, compressive stress is released either along preexisting structural elements (such as cleavage) or perpendicular to the former direction of tectonic compression. Cooling joints are columnar joints that result from the cooling of either lava from the exposed surface of a lava lake or flood basalt flow or

5040-424: The terms visible or measurable, a difference that depends on the scale of observation. Faults differ from joints in that they exhibit visible or measurable lateral movement between the opposite surfaces of the fracture ("Mode 2" and "Mode 3" Fractures). Thus a joint may be created by either strict movement of a rock layer or body perpendicular to the fracture or by varying degrees of lateral displacement parallel to

5112-558: The wellbore can flow very rapidly into the fractures, causing a loss of hydrostatic pressure and creating the potential for a blowout from a formation further up the hole. Since the mid-1980s, 2D and 3D computer modeling of fault and fracture networks has become common practice in Earth Sciences. This technology became known as "DFN" (discrete fracture network") modeling, later modified into "DFFN" (discrete fault and fracture network") modeling. The technology consists of defining

5184-409: The work of Charles Coulomb, who suggested that as long as all stresses are compressive, as is the case in shear fracture, the shear stress is related to the normal stress by: σ s = C+μ(σ n -σ f ), where C is the cohesion of the rock, or the shear stress necessary to cause failure given the normal stress across that plane equals 0. μ is the coefficient of internal friction, which serves as

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