![Based on field and laboratory measurements, Gardner [1] established an empirical
relationship between density ρ and P-wave velocity α. Known as Gardner’s formula
for density, this relationship given by ρ = cα0.25, where c is a constant that depends
on the rock type, is useful to estimate density from velocity when the former is
unknown. With the exception of anhydrites, most rock types — sandstones, shales,
and carbonates, tend to obey Gardner’s equation for density.](https://image.slidesharecdn.com/group-4-geology-ppt1-231015071408-b4c2cd5e/85/Group-4-GEOLOGY-ppt-1-ppt-37-320.jpg)
Group-4-GEOLOGY-ppt (1).ppt
- 2. ATTITUDE OF BEDS • Geologists take great pains to measure and record geological structures because they are critically important to understanding the geological history of a region. One of the key features to measure is the orientation, or attitude, of bedding. We know that sedimentary beds are deposited in horizontal layers, so if the layers are no longer horizontal, then we can infer that they have been affected by tectonic forces and have become either tilted, or folded. We can express the orientation of a bed (or any other planar feature) with two values: first, the compass orientation of a horizontal line on the surface—the strike —and second, the angle at which the surface dips from the horizontal, (perpendicular to the strike)—the dip
- 3. DIP – IT IS DEFINED AS THE AMOUNT OF INCLINATION OF A BED WITH RESPECT TO A HORIZONATAL PLANE. THIS IS MEASURED ON A VERTICAL PLANE LYING AT RIGHT ANGLED TO THE STRIKE OF THE BEDDING.
- 4. TYPES OF DIP True Dip – It is the maximum amount of slope along a line perpendicular to the strike, in other words, it is the maximum slope with respect to the horizontal. It may also be stated as the geographical direction along which the line of quickest descent slopesdown. Apparent Dip – Along any direction other than that of the true dip, the gradient is scheduled to be much less and therefore it is defined as the apparent dip. The apparent dip of any bed towards any direction must always be less than its true dip.
- 5. STRIKE Strike is generally defined as the line of intersection between a horizontal plane and the planar surface being measured. It is found by measuring the compass direction of a horizontal line on the surface.
- 6. Strike and dip are often easier to see on an exposure of rock than on a map, as the above photograph shows. Geologists use strike and dip symbols on geologic maps to show strikes and dips measured in the field. The geologic map (left) shows many strike and dip symbols. A GEOLOGIC MAP is used to show rock units or geologic strata that are exposed at the surface. Bedding planes and structural features such as faults, folds, foliations, and lineations are shown with strike and dip or trend and plunge symbols which give these features' three- dimensional orientations.
- 7. IMPORTANCE OF DIP AND STRIKE - To determine the younger bed of formation. It is well known that younger beds will always be found in the direction of dip. If we go in the direction of dip, relatively beds of younger age will be found to out-crop and older rocks in the opposite direction. - In the classification, and nomenclature of folds, faults, joints and unconformities, the nature of dip and strike is of paramount significance. Thus the attitude, which refers to the three dimensional orientation of some geological structures, is defined by their dip and strike
- 8. MEASURING STRIKE AND DIP The strike and dip of planar geologic structures, such as bedding, faults, joints and foliations, can be determined by several methods with the Brunton compass. MEASURING STRIKE MEASURING DIP
- 9. FOLDS, FAULTS , JOINTS
- 10. FAULT A fault is a break in the rocks that make up the earth's crust, along which on either side rocks move pass eachother. Larger faults are mostly from action occuring in earth's plates. A fault line is the trace of a fault, or the line of intersection between the fault line and the earth's surface Stike-slip faults are vertical (or nearly vertical) fractures where the blocks have mostly moved horizontally. If the block opposite an observer looking across the fault moves to the right, the slip style is termed right lateral; if the block moves to the left, the motion is termed left lateral.
- 11. Dip-slip faults are inclined fractures where the blocks have mostly shifted vertically. If the rock mass above an inclined fault moves down, the fault is termed normal, whereas if the rock above the fault moves up, the fault is termed reverse A transform fault is a special variety of strike-slip fault that accommodates relative horizontal slip between other tectonic elements, such as oceanic crustal plates. Often extend from oceanic ridges.
- 12. FOLD S A fold is when one or more originally bent surfaces are bent or curved as the result of permanent deformation. Folding and Warping Syncline and anticline are terms used to describe folds based on the relative ages of folded rock layers. A syncline is a fold in which the youngest rocks occur in the core of a fold (i.e. closest to the fold axis), whereas the oldest rocks occur in the core of an anticline.
- 13. TYPES OF FOLDS Anticline: Linear with dip away from the center Syncline: Linear with dip towards the center Monocline: Linear with dip in one direction between horizontal layers on each side. Basin: Non-Linear with dip towards all center directions. Dome: Non-Linear with dip away from center in all directions.
- 14. JOINT S a joint is a fracture dividing rock into two sections that moved away from each other. A joint does not involve shear displacement, and forms when tensile stress breaches its threshold. In other kinds of fracturing, like in a fault, the rock is parted by a visible crack that forms a gap in the rock.
- 15. TYPES OF JOINTS SYSTEMATIC JOINTS: have a subparallel orientation and regular spacing JOINT SET: joints that share a similar orientation in same area JOINT SYSTEM: two or more joints sets in the same area NONSYSTEMATIC JOINTS: joints that do not share a common orientation and those highly curved and irregular fracture surfaces.
- 16. Bedding planes are of great importance to Civil engineers. They are planes of structural weakness in sedimentary rocks, and masses of rock can move along them causing rock slides. Since over 75 percent of the earth’s surface is made up of sedimentary rocks, civil engineers can expect to frequently encounter these rocks during construction. Undisturbed sedimentary rocks may be relatively uniform, continuous, and predictable across a site. These types of rocks offer certain advantages to civil engineers in completing horizontal and vertical construction missions. They are relatively stable rock bodies that allow for ease of rock excavation, as they will normally support steep rock faces. Sedimentary rocks are frequently oriented at angles to the earth’s “horizontal” surface; therefore, movements in the earth’s crust may tilt, fold, or break sedimentary layers. Structurally deformed rocks add complexity to the site geology and may adversely affect construction projects by contributing to rock excavation and slope stability problems. Engineering Construction and The Study of Beds
- 17. ROCK MECHANICS PHYSICAL AND MECHANICAL PROPERTIES OF ROCKS
- 18. PHYSICAL PROPERTIES a. POROSITY- is the percentage of void space in a rock. It is defined as the ratio of the volume of the voids or pore space divided by the total volume. It is written as either a decimal fraction between 0 and 1 or as a percentage. For most rocks, porosity varies from less than 1% to 40%
- 19. b. PERMEABILITY is the property of rocks that is an indication of the ability for fluids (gas or liquid) to flow through rocks. High permeability will allow fluids to move rapidly through rocks. Permeability is affected by the pressure in a rock. DENSITY varies significantly among different rock types because of differences in mineralogy and porosity. Knowledge of the distribution of underground rock densities can assist in interpreting subsurface geologic structure and rock type. Rocks are generally between 1600 kg/m3 (sediments) and 3500 kg/m3 (gabbro).
- 20. CLASSIFICATION OF ROCK HARDNESS CLASSIFICATION FIELD TEST RANGE OF COMPRESSSIVE STRENGTH (MPa) Very soft rock Can be peeled with a knife, material crumbles under firm blows with the sharp end of a geological pick. 1-3 Soft rock Cannot be scraped with a knife, indentations of 2-4 mm with firm blows of the pick point. 3-10 Medium hard rock Cannot be scraped or peeled with a knife, hand held specimen breaks with firm blows of the pick. 10-25 Hard rock Point load tests must be carried out in order to distinguish between these classifications. These results may be verified by uniaxial compressive strength tests on selected samples 25-70 Very hard rock 70-200 Extremely hard rock >200 c. HARDNESS is the subjective description of the resistance of an earth material to permanent deformation, particularly by indentation (impact) or abrasion (scratching) .
- 21. d. STRENGTH-Strength is the ability of a material to resist deformation induced by external forces. The strength of a material is the amount of applied stress at failure (ASTM D653). The laboratory uniaxial (unconfined) compressive strength is the standard strength parameter of intact rock material. • Tensile strength- is extremely difficult to measure: It is direction- dependent, flaw-dependent, sample size-dependent,… • An indirect method , the Brazilian disk test is used. The Brazilian test is a technique used to evaluate the tensile strength of brittle materials like concrete or rocks. The experiment consists in compressing a circular disk along its vertical diameter in order to induce tensile failure at the center of the disk
- 22. Compressive strength- Compressive strength or compression strength is the capacity of a material or structure to withstand loads tending to reduce size, as opposed to tensile strength, which withstands loads tending to elongate. The Uniaxial Compressive Strength of Soft Rock. Soft rock is a term that usually refers to a rock material with a uniaxial compressive strength (UCS) less than 20 MPa. Uniaxial compressive test equipment
- 23. Shear strength- shear strength is the strength of a material or component against the type of yield or structural failure when the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a material along a plane that is parallel to the direction of the force. When a paper is cut with scissors, the paper fails in shea
- 24. e. ELASTICITY- Elasticity is the property of matter that causes it to resist deformation in volume or shape. Some of the deformation of a rock under stress will be recovered when the load is removed. The recoverable deformation is called elastic and the non-recoverable part is called plastic deformation. Commonly, the elastic deformation of rock is directly proportional to the applied load. The ratio of the stress and the strain is called modulus elasticity.
- 25. f. PLASTICITY - ability of certain solids to flow or to change shape permanently when subjected to stresses of intermediate magnitude between those producing temporary deformation, or elastic behavior, and those causing failure of the material, or rupture (see yield point). Plasticity enables a solid under the action of external forces to undergo permanent deformation without rupture. Elasticity, in comparison, enables a solid to return to its original shape after the load is removed. Plastic deformation occurs in many metal-forming processes (rolling, pressing, forging) and in geologic processes (rock folding and rock flow within the earth under extremely high pressures and at elevated temperatures).
- 26. For example, a solid piece of metal being bent or pounded into a new shape displays plasticity as permanent changes occur within the material itself. In engineering, the transition from elastic behavior to plastic behavior is called yield. Plastic deformation is observed in most materials, particularly metals, soils, rocks, concrete, foams, bone and skin.
- 27. ELASTIC WAVES AND ROCK PROPERTIES
- 28. Stress is force per unit area. Imagine a particle represented by an infinitesimally small volume around a point within a solid body with dimensions (dx, dy, dz) Strain is deformation measured as the fractional change in dimension or volume induced by stress. Strain is a dimensionless quantity. Static -concerned with bodies at rest or forces in equilibrium. Dynamic- a force that stimulates change or progress within a system or process. Terminology
- 29. DETERMINING DYNAMIC ROCK PROPERTIES I-Typical Rock Properties • Modulus of Deformation – Young’s Modulus - E • Modulus of Rigidity – Shear Modulus – G • Modulus of Volume Expansion – Bulk Modulus - K • Poisson’s Ratio - μ • Bulk Density – ρ • Compressive Strength – σC • Tensile Strength – σT II-Rock Properties Referenced to Blasting Actions • Young’s Modulus is a measure of the resistance of a solid to transmit load allows transmission of longitudinal stress from shock wave impact • Bulk Modulus is a measure of the resistance of a solid to change in volume allows transmission of transverse stress resulting from shock wave impact • Poissons’ ratio defines the amount of borehole expansion that can occur under dynamic loading just before rock/ore failure maximum amount of ‘hoop’ stress that can be tolerated before cracks are generated • Compressive strength dictates the level of crushing that will occur at the borehole wall • Tensile strength dictates the level of tensile stress when crack formation will occur Can have supersonic cracking as well as interstitial cracking
- 30. III- Dynamic or Static • Fragmentation of rock/ore is a dynamic process, not a static one • Rock/ore appears to be much stronger in the dynamic case, than the static one (rule of thumb is to assume that dynamic such as compressive and tensile strength are twice the values of static properties) • Degree of fit (correlation with measurement properties) is better with dynamic rock/ore parameters • Easier and less expensive getting dynamic rock properties using dynamic loading such as detonating explosive charges • Rock/ore core strength values do not appear to correlate well with dynamic values • Dynamic properties are preferred in computer models relating the dynamic processes of blasting action to dynamic properties of the material being blasted
- 31. Wave velocities in a rock are computed from wave propagation travel times from sonic logs. Elastic wave velocity is a powerful parameter used to interpret the physical properties underlying the rock. However, a range of geological rock properties affect wave velocities. Understanding the microstructural, fluid, stress, and mineralogical controls on elastic wave velocities is at the center of laboratory experiments on the rock core. WAVE VELOCITIES IN A ROCK
- 32. SEISMIC WAVES TYPES Seismic waves--- are elastic waves that propagate in the earth. P-waves ---(or equivalently, compressional waves, longitudinal waves, or dilatational waves) are waves with particle motion in the direction of wave propagation. S-waves--- (or equivalently, shear waves, transverse waves, or rotational waves) are waves with particle motion in the direction perpendicular to the direction of wave propagation.
- 33. Seismic wave velocities change over a wide range in nature, even for the same rock type, since several factors control the velocity of a specified medium. This phenomenon generally prevents defining the subsurface lithology by seismic velocities only. Velocity Analysis
- 34. For instance, measured P wave velocities of sandstones range from 1.8 to 4.8 km/s depending on several factors, including • Lithology • Saturation and fluid type • Porosity • Cementation, grain size and pore shape • Age of the rock • Pressure/compaction or depth • Density of the medium • Temperature • Frequency of the seismic signal • Anisotropy and fractures • Clay content • Consolidation
- 35. From the definitions of the P- and S-wave velocities , note that both are inversely proportional to density ρ. At first thought, this means that the lower the rock density the higher the wave velocity. A good example is halite which has low density (1.8 gr/cm3) and high P-wave velocity (4500 m/s). In most cases, however, the higher the density the higher the velocity This is because an increase in density usually is accompanied by an increase in the ability of the rock to resist compressional and shear stresses.
- 36. So an increase in density usually implies an increase in bulk modulus and modulus of rigidity. Note that the greater the bulk modulus or the modulus of rigidity, the higher the velocity.
- 37. Based on field and laboratory measurements, Gardner [1] established an empirical relationship between density ρ and P-wave velocity α. Known as Gardner’s formula for density, this relationship given by ρ = cα0.25, where c is a constant that depends on the rock type, is useful to estimate density from velocity when the former is unknown. With the exception of anhydrites, most rock types — sandstones, shales, and carbonates, tend to obey Gardner’s equation for density.
- 38. THREE INDIRECT WAYS TO ESTIMATE THE S-WAVE VELOCITIES The first approach is to perform prestack amplitude inversion to estimate the P- and S-wave reflectivities and thus compute the corresponding acoustic impedances (analysis of amplitude variation with offset). The second approach is to record multicomponent seismic data and estimate the S-wave velocities from the P-to-S converted-wave component (4-C seismic method). The third approach is to generate and record S-waves themselves.
- 39. STATIC AND DYNAMIC MODULI OF ELASTICITY -The dynamic moduli of rock are those calculated from the elastic- wave velocity and density. Usually refers to the elastic stiffness that can be derived from elastic wave velocities in combination with density. -The static moduli are those directly measured in a deformational experiment. Also refers to the elastic stiffness that relates deformation to applied stress in a quasi-static loading situation, that is the slope of the stress–strain curve.
- 40. Modulus of elasticity : The ratio of the stress in a body to the corresponding strain (as in bulk modulus, shear modulus, and Young's modulus) — called also coefficient of elasticity, elastic modulus. An elastic modulus is a quantity that measures an object or substance's resistance to being deformed elastically when a stress is applied to it. The elastic modulus of an object is defined as the slope of its stress–strain curve in the elastic deformation region: A stiffer material will have a higher elastic modulus. The three types of elastic constants are: Modulus of elasticity or Young's modulus (E), Bulk modulus (K) and. Modulus of rigidity or shear modulus
- 41. GROUTING WHAT IT IS: Rock grouting is the injection of specially formulated cement-based mixes into the ground to improve its strength or reduce permeability. The principle of grouting is to fill the open voids existing in a rock mass in introducing, by pressure through boreholes, a certain amount of a "liquid" matter, in fact a suspension, that will harden later on. The properties of the grouted rock complex should be modified in the desired way.
- 42. HOW IT WORKS: It’s most commonly performed by drilling holes into the underlying rock to intercept open cracks, joints, fissures or cavities, then pumping under pressure balanced and stabilized grout mixes using a combination of cement, water, and additives. For larger, more complex projects, enhanced quality control is available through real-time computer monitored grouting software called GROUT I.T. WHY YOU NEED IT: Rock grouting can be used to decrease water flow through fractured rock, plus it can be performed in areas with space constraints. It is mostly used for dams, tunnels, reservoirs and shafts.