Soil mechanics is a branch of soil physics and applied mechanics that describes the behavior of soils. It differs from fluid mechanics and solid mechanics in the sense that soils consist of a heterogeneous mixture of fluids and particles but soil may contain organic solids and other matter. Along with rock mechanics, soil mechanics provides the theoretical basis for analysis in geotechnical engineering, a subdiscipline of civil engineering, engineering geology, a subdiscipline of geology. Soil mechanics is used to analyze the deformations of and flow of fluids within natural and man-made structures that are supported on or made of soil, or structures that are buried in soils. Example applications are building and bridge foundations, retaining walls and buried pipeline systems. Principles of soil mechanics are used in related disciplines such as engineering geology, geophysical engineering, coastal engineering, agricultural engineering and soil physics; this article describes the genesis and composition of soil, the distinction between pore water pressure and inter-granular effective stress, capillary action of fluids in the soil pore spaces, soil classification and permeability, time dependent change of volume due to squeezing water out of tiny pore spaces known as consolidation, shear strength and stiffness of soils.
The shear strength of soils is derived from friction between the particles and interlocking, which are sensitive to the effective stress. The article concludes with some examples of applications of the principles of soil mechanics such as slope stability, lateral earth pressure on retaining walls, bearing capacity of foundations; the primary mechanism of soil creation is the weathering of rock. All rock types may be broken down into small particles to create soil. Weathering mechanisms are physical weathering, chemical weathering, biological weathering Human activities such as excavation and waste disposal, may create soil. Over geologic time buried soils may be altered by pressure and temperature to become metamorphic or sedimentary rock, if melted and solidified again, they would complete the geologic cycle by becoming igneous rock. Physical weathering includes temperature effects and thaw of water in cracks, wind and other mechanisms. Chemical weathering includes dissolution of matter composing a rock and precipitation in the form of another mineral.
Clay minerals, for example can be formed by weathering of feldspar, the most common mineral present in igneous rock. The most common mineral constituent of silt and sand is quartz called silica, which has the chemical name silicon dioxide; the reason that feldspar is most common in rocks but silica is more prevalent in soils is that feldspar is much more soluble than silica. Silt and Gravel are little pieces of broken rocks. According to the Unified Soil Classification System, silt particle sizes are in the range of 0.002 mm to 0.075 mm and sand particles have sizes in the range of 0.075 mm to 4.75 mm. Gravel particles are broken pieces of rock in the size range 4.75 mm to 100 mm. Particles larger than gravel are called boulders. Soil deposits are affected by the mechanism of deposition to their location. Soils that are not transported are called residual soils—they exist at the same location as the rock from which they were generated. Decomposed granite is a common example of a residual soil.
The common mechanisms of transport are the actions of gravity, ice and wind. Wind blown soils include dune loess. Water carries particles of different size depending on the speed of the water, thus soils transported by water are graded according to their size. Silt and clay may settle out in a lake, gravel and sand collect at the bottom of a river bed. Wind blown soil deposits tend to be sorted according to their grain size. Erosion at the base of glaciers is powerful enough to pick up large rocks and boulders as well as soil. Gravity on its own may carry particles down from the top of a mountain to make a pile of soil and boulders at the base; the mechanism of transport has a major effect on the particle shape. For example, low velocity grinding in a river bed will produce rounded particles. Freshly fractured colluvium particles have a angular shape. Silts and gravels are classified by their size, hence they may consist of a variety of minerals. Owing to the stability of quartz compared to other rock minerals, quartz is the most common constituent of sand and silt.
Mica, feldspar are other common minerals present in sands and silts. The mineral constituents of gravel may be more similar to that of the parent rock; the common clay minerals are montmorillonite or smectite and kaolinite or kaolin. These minerals tend to form in sheet or plate like structures, with length ranging between 10−7 m and 4x10−6 m and thickness ranging between 10−9 m and 2x10−6 m, they have a large specific surface area; the specific surface area is defined as the ratio of the surface area of particles to the mass of the particles. Clay minerals have specific surface areas in the range of 10 to 1,000 square meters per gram of solid. Due to the large surface area available for chemical and van der Waals interaction, the mechanical behavior of clay minerals is sensitive to the amount of pore fluid available and the type and amount of dissolved ions in the pore fluid. To
Rock mechanics is a theoretical and applied science of the mechanical behavior of rock and rock masses. Rock mechanics forms part of the much broader subject of geomechanics, concerned with the mechanical responses of all geological materials, including soils. Rock mechanics, as applied in engineering geology, mining and civil engineering practice, is concerned with the application of the principles of engineering mechanics to the design of the rock structures generated by mining, reservoir production, or civil construction activity such as tunnels, mining shafts, underground excavations, open pit mines and gas wells, road cuts, waste repositories, other structures built in or of rock, it includes the design of reinforcement systems, such as rock bolting patterns. Engineering geology Geotechnical engineering Rock mass classification Slope stability analysis Rock mass plasticity SMR classificationRock mechanics is a theoretical and applied science of the mechanical behavior of rock and rock masses.
Rock mechanics is concerned with the application of the principles of engineering mechanics to the design of structures built in or of rock. The structure could include-but not limited to- a drill hole, a mining shaft, a tunnel, a reservoir dam, a repository component, or a building. Rock mechanics is used in many engineering disciplines, but used in Mining, Geotechnical and Petroleum Engineering. Jaeger and Zimmerman. Fundamentals of Rock Mechanics. Blackwell Publishing. ISBN 9780632057597. CS1 maint: Multiple names: authors list Brady, B. H. G. Brown, E. T. Rock Mechanics For Underground Mining, Kluwer Academic Publishers
Classical mechanics describes the motion of macroscopic objects, from projectiles to parts of machinery, astronomical objects, such as spacecraft, planets and galaxies. If the present state of an object is known it is possible to predict by the laws of classical mechanics how it will move in the future and how it has moved in the past; the earliest development of classical mechanics is referred to as Newtonian mechanics. It consists of the physical concepts employed by and the mathematical methods invented by Isaac Newton and Gottfried Wilhelm Leibniz and others in the 17th century to describe the motion of bodies under the influence of a system of forces. More abstract methods were developed, leading to the reformulations of classical mechanics known as Lagrangian mechanics and Hamiltonian mechanics; these advances, made predominantly in the 18th and 19th centuries, extend beyond Newton's work through their use of analytical mechanics. They are, with some modification used in all areas of modern physics.
Classical mechanics provides accurate results when studying large objects that are not massive and speeds not approaching the speed of light. When the objects being examined have about the size of an atom diameter, it becomes necessary to introduce the other major sub-field of mechanics: quantum mechanics. To describe velocities that are not small compared to the speed of light, special relativity is needed. In case that objects become massive, general relativity becomes applicable. However, a number of modern sources do include relativistic mechanics into classical physics, which in their view represents classical mechanics in its most developed and accurate form; the following introduces the basic concepts of classical mechanics. For simplicity, it models real-world objects as point particles; the motion of a point particle is characterized by a small number of parameters: its position and the forces applied to it. Each of these parameters is discussed in turn. In reality, the kind of objects that classical mechanics can describe always have a non-zero size.
Objects with non-zero size have more complicated behavior than hypothetical point particles, because of the additional degrees of freedom, e.g. a baseball can spin while it is moving. However, the results for point particles can be used to study such objects by treating them as composite objects, made of a large number of collectively acting point particles; the center of mass of a composite object behaves like a point particle. Classical mechanics uses common-sense notions of how matter and forces interact, it assumes that matter and energy have definite, knowable attributes such as location in space and speed. Non-relativistic mechanics assumes that forces act instantaneously; the position of a point particle is defined in relation to a coordinate system centered on an arbitrary fixed reference point in space called the origin O. A simple coordinate system might describe the position of a particle P with a vector notated by an arrow labeled r that points from the origin O to point P. In general, the point particle does not need to be stationary relative to O.
In cases where P is moving relative to O, r is defined as a function of time. In pre-Einstein relativity, time is considered an absolute, i.e. the time interval, observed to elapse between any given pair of events is the same for all observers. In addition to relying on absolute time, classical mechanics assumes Euclidean geometry for the structure of space; the velocity, or the rate of change of position with time, is defined as the derivative of the position with respect to time: v = d r d t. In classical mechanics, velocities are directly subtractive. For example, if one car travels east at 60 km/h and passes another car traveling in the same direction at 50 km/h, the slower car perceives the faster car as traveling east at 60 − 50 = 10 km/h. However, from the perspective of the faster car, the slower car is moving 10 km/h to the west denoted as -10 km/h where the sign implies opposite direction. Velocities are directly additive as vector quantities. Mathematically, if the velocity of the first object in the previous discussion is denoted by the vector u = ud and the velocity of the second object by the vector v = ve, where u is the speed of the first object, v is the speed of the second object, d and e are unit vectors in the directions of motion of each object then the velocity of the first object as seen by the second object is u ′ = u − v. Similarly, the first object sees the velocity of the second object as v ′ = v − u.
When both objects are moving in the same direction, this equation can be simplified to u ′ = d. Or, by ignoring direction, the difference can be given in terms of speed only: u ′ = u − v; the acceleration, or rate of change of velocity, is th
The term landslide or, less landslip, refers to several forms of mass wasting that include a wide range of ground movements, such as rockfalls, deep-seated slope failures and debris flows. Landslides occur in a variety of environments, characterized by either steep or gentle slope gradients: from mountain ranges to coastal cliffs or underwater, in which case they are called submarine landslides. Gravity is the primary driving force for a landslide to occur, but there are other factors affecting slope stability which produce specific conditions that make a slope prone to failure. In many cases, the landslide is triggered by a specific event, although this is not always identifiable. Landslides occur when the slope undergoes some processes that change its condition from stable to unstable; this is due to a decrease in the shear strength of the slope material, to an increase in the shear stress borne by the material, or to a combination of the two. A change in the stability of a slope can be caused by a number of factors, acting alone.
Natural causes of landslides include: saturation by rain water infiltration, snow melting, or glaciers melting. Slope material that becomes saturated with water may develop into a debris mud flow; the resulting slurry of rock and mud may pick up trees and cars, thus blocking bridges and tributaries causing flooding along its path. Debris flow is mistaken for flash flood, but they are different processes. Muddy-debris flows in alpine areas cause severe damage to structures and infrastructure and claim human lives. Muddy-debris flows can start as a result of slope-related factors and shallow landslides can dam stream beds, resulting in temporary water blockage; as the impoundments fail, a "domino effect" may be created, with a remarkable growth in the volume of the flowing mass, which takes up the debris in the stream channel. The solid–liquid mixture can reach densities of up to 2,000 kg/m3 and velocities of up to 14 m/s; these processes cause the first severe road interruptions, due not only to deposits accumulated on the road, but in some cases to the complete removal of bridges or roadways or railways crossing the stream channel.
Damage derives from a common underestimation of mud-debris flows: in the alpine valleys, for example, bridges are destroyed by the impact force of the flow because their span is calculated only for a water discharge. For a small basin in the Italian Alps affected by a debris flow, estimated a peak discharge of 750 m3/s for a section located in the middle stretch of the main channel. At the same cross section, the maximum foreseeable water discharge, was 19 m3/s, a value about 40 times lower than that calculated for the debris flow that occurred. An earthflow is the downslope movement of fine-grained material. Earthflows can move at speeds within a wide range, from as low as 1 mm/yr to 20 km/h. Though these are a lot like mudflows, overall they are more slow moving and are covered with solid material carried along by flow from within, they are different from fluid flows. Clay, fine sand and silt, fine-grained, pyroclastic material are all susceptible to earthflows; the velocity of the earthflow is all dependent on how much water content is in the flow itself: the higher the water content in the flow, the higher the velocity will be.
These flows begin when the pore pressures in a fine-grained mass increase until enough of the weight of the material is supported by pore water to decrease the internal shearing strength of the material. This thereby creates a bulging lobe which advances with a rolling motion; as these lobes spread out, drainage of the mass increases and the margins dry out, thereby lowering the overall velocity of the flow. This process causes the flow to thicken; the bulbous variety of earthflows are not that spectacular, but they are much more common than their rapid counterparts. They develop a sag at their heads and are derived from the slumping at the source. Earthflows occur much more during periods of high precipitation, which saturates the ground and adds water to the slope content. Fissures develop during the movement of clay-like material which creates the intrusion of water into the earthflows. Water increases the pore-water pressure a
Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field includes studies of earthquake environmental effects such as tsunamis as well as diverse seismic sources such as volcanic, oceanic and artificial processes such as explosions. A related field that uses geology to infer information regarding past earthquakes is paleoseismology. A recording of earth motion as a function of time is called a seismogram. A seismologist is a scientist. Scholarly interest in earthquakes can be traced back to antiquity. Early speculations on the natural causes of earthquakes were included in the writings of Thales of Miletus, Anaximenes of Miletus and Zhang Heng. In 132 CE, Zhang Heng of China's Han dynasty designed the first known seismoscope. In the 17th century, Athanasius Kircher argued that earthquakes were caused by the movement of fire within a system of channels inside the Earth. Martin Lister and Nicolas Lemery proposed that earthquakes were caused by chemical explosions within the earth.
The Lisbon earthquake of 1755, coinciding with the general flowering of science in Europe, set in motion intensified scientific attempts to understand the behaviour and causation of earthquakes. The earliest responses include work by John Michell. Michell determined that earthquakes originate within the Earth and were waves of movement caused by "shifting masses of rock miles below the surface". From 1857, Robert Mallet laid the foundation of instrumental seismology and carried out seismological experiments using explosives, he is responsible for coining the word "seismology". In 1897, Emil Wiechert's theoretical calculations led him to conclude that the Earth's interior consists of a mantle of silicates, surrounding a core of iron. In 1906 Richard Dixon Oldham identified the separate arrival of P-waves, S-waves and surface waves on seismograms and found the first clear evidence that the Earth has a central core. In 1910, after studying the April 1906 San Francisco earthquake, Harry Fielding Reid put forward the "elastic rebound theory" which remains the foundation for modern tectonic studies.
The development of this theory depended on the considerable progress of earlier independent streams of work on the behaviour of elastic materials and in mathematics. In 1926, Harold Jeffreys was the first to claim, based on his study of earthquake waves, that below the mantle, the core of the Earth is liquid. In 1937, Inge Lehmann determined that within the earth's liquid outer core there is a solid inner core. By the 1960s, earth science had developed to the point where a comprehensive theory of the causation of seismic events had come together in the now well-established theory of plate tectonics. Seismic waves are elastic waves that propagate in fluid materials, they can be divided into body waves. There are pressure waves or primary waves and shear or secondary waves. P-waves are longitudinal waves that involve compression and expansion in the direction that the wave is moving and are always the first waves to appear on a seismogram as they are the fastest moving waves through solids. S-waves are transverse waves.
S-waves are slower than P-waves. Therefore, they appear than P-waves on a seismogram. Fluids cannot support perpendicular motion, so S-waves only travel in solids. Surface waves are the result of P- and S-waves interacting with the surface of the Earth; these waves are dispersive. The two main surface wave types are Rayleigh waves, which have both compressional and shear motions, Love waves, which are purely shear. Rayleigh waves result from the interaction of P-waves and vertically polarized S-waves with the surface and can exist in any solid medium. Love waves are formed by horizontally polarized S-waves interacting with the surface, can only exist if there is a change in the elastic properties with depth in a solid medium, always the case in seismological applications. Surface waves travel more than P-waves and S-waves because they are the result of these waves traveling along indirect paths to interact with Earth's surface; because they travel along the surface of the Earth, their energy decays less than body waves, thus the shaking caused by surface waves is stronger than that of body waves.
The primary surface waves are the largest signals on earthquake seismograms. Surface waves are excited when their source is close to the surface, as in a shallow earthquake or a near surface explosion, are much weaker for deep earthquake sources. Both body and surface waves are traveling waves; this ringing is a mixture of normal modes with discrete frequencies and periods of an hour or shorter. Motion caused by a large earthquake can be observed for up to a month after the event; the first observations of normal modes were made in the 1960s as the advent of higher fidelity instruments coincided with two of the largest earthquakes of the 20th century – the 1960 Valdivia earthquake and the 1964 Alaska earthquake. Since the normal modes of the Earth have given us some of the strongest constraints on the deep structure of
Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, the processes by which they change over time. Geology can include the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology overlaps all other earth sciences, including hydrology and the atmospheric sciences, so is treated as one major aspect of integrated earth system science and planetary science. Geology describes the structure of the Earth on and beneath its surface, the processes that have shaped that structure, it provides tools to determine the relative and absolute ages of rocks found in a given location, to describe the histories of those rocks. By combining these tools, geologists are able to chronicle the geological history of the Earth as a whole, to demonstrate the age of the Earth. Geology provides the primary evidence for plate tectonics, the evolutionary history of life, the Earth's past climates. Geologists use a wide variety of methods to understand the Earth's structure and evolution, including field work, rock description, geophysical techniques, chemical analysis, physical experiments, numerical modelling.
In practical terms, geology is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources, understanding of natural hazards, the remediation of environmental problems, providing insights into past climate change. Geology is a major academic discipline, it plays an important role in geotechnical engineering; the majority of geological data comes from research on solid Earth materials. These fall into one of two categories: rock and unlithified material; the majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth. There are three major types of rock: igneous and metamorphic; the rock cycle illustrates the relationships among them. When a rock solidifies or crystallizes from melt, it is an igneous rock; this rock can be weathered and eroded redeposited and lithified into a sedimentary rock. It can be turned into a metamorphic rock by heat and pressure that change its mineral content, resulting in a characteristic fabric.
All three types may melt again, when this happens, new magma is formed, from which an igneous rock may once more solidify. To study all three types of rock, geologists evaluate the minerals; each mineral has distinct physical properties, there are many tests to determine each of them. The specimens can be tested for: Luster: Measurement of the amount of light reflected from the surface. Luster is broken into nonmetallic. Color: Minerals are grouped by their color. Diagnostic but impurities can change a mineral’s color. Streak: Performed by scratching the sample on a porcelain plate; the color of the streak can help name the mineral. Hardness: The resistance of a mineral to scratch. Breakage pattern: A mineral can either show fracture or cleavage, the former being breakage of uneven surfaces and the latter a breakage along spaced parallel planes. Specific gravity: the weight of a specific volume of a mineral. Effervescence: Involves dripping hydrochloric acid on the mineral to test for fizzing. Magnetism: Involves using a magnet to test for magnetism.
Taste: Minerals can have a distinctive taste, like halite. Smell: Minerals can have a distinctive odor. For example, sulfur smells like rotten eggs. Geologists study unlithified materials, which come from more recent deposits; these materials are superficial deposits. This study is known as Quaternary geology, after the Quaternary period of geologic history. However, unlithified material does not only include sediments. Magmas and lavas are the original unlithified source of all igneous rocks; the active flow of molten rock is studied in volcanology, igneous petrology aims to determine the history of igneous rocks from their final crystallization to their original molten source. In the 1960s, it was discovered that the Earth's lithosphere, which includes the crust and rigid uppermost portion of the upper mantle, is separated into tectonic plates that move across the plastically deforming, upper mantle, called the asthenosphere; this theory is supported by several types of observations, including seafloor spreading and the global distribution of mountain terrain and seismicity.
There is an intimate coupling between the movement of the plates on the surface and the convection of the mantle. Thus, oceanic plates and the adjoining mantle convection currents always move in the same direction – because the oceanic lithosphere is the rigid upper thermal boundary layer of the convecting mantle; this coupling between rigid plates moving on the surface of the Earth and the convecting mantle is called plate tectonics. The development of plate tectonics has provided a physical basis for many observations of the solid Earth. Long linear regions of geologic features are explained as plate boundaries. For example: Mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, are seen as divergent boundaries, where two plates move apart. Arcs of volcanoes and earthquakes are theorized as convergent boundaries, where one plate subducts, or moves, under another. Transform boundaries, such as the San Andreas Fault system, resulted in widespread powerful earthquakes.
Plate tectonics has provided a mechan
Earthquake engineering is an interdisciplinary branch of engineering that designs and analyzes structures, such as buildings and bridges, with earthquakes in mind. Its overall goal is to make such structures more resistant to earthquakes. An earthquake engineer aims to construct structures that will not be damaged in minor shaking and will avoid serious damage or collapse in a major earthquake. Earthquake engineering is the scientific field concerned with protecting society, the natural environment, the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels. Traditionally, it has been narrowly defined as the study of the behavior of structures and geo-structures subject to seismic loading. However, the tremendous costs experienced in recent earthquakes have led to an expansion of its scope to encompass disciplines from the wider field of civil engineering, mechanical engineering and from the social sciences sociology, political science and finance.
The main objectives of earthquake engineering are: Foresee the potential consequences of strong earthquakes on urban areas and civil infrastructure. Design and maintain structures to perform at earthquake exposure up to the expectations and in compliance with building codes. A properly engineered structure does not have to be strong or expensive, it has to be properly designed to withstand the seismic effects while sustaining an acceptable level of damage. Seismic loading means application of an earthquake-generated excitation on a structure, it happens at contact surfaces of a structure either with the ground, with adjacent structures, or with gravity waves from tsunami. The loading, expected at a given location on the Earth's surface is estimated by engineering seismology, it is related to the seismic hazard of the location. Earthquake or seismic performance defines a structure's ability to sustain its main functions, such as its safety and serviceability, at and after a particular earthquake exposure.
A structure is considered safe if it does not endanger the lives and well-being of those in or around it by or collapsing. A structure may be considered serviceable if it is able to fulfill its operational functions for which it was designed. Basic concepts of the earthquake engineering, implemented in the major building codes, assume that a building should survive a rare severe earthquake by sustaining significant damage but without globally collapsing. On the other hand, it should remain operational for less severe seismic events. Engineers need to know the quantified level of the actual or anticipated seismic performance associated with the direct damage to an individual building subject to a specified ground shaking; such an assessment may be performed either experimentally or analytically. Experimental evaluations are expensive tests that are done by placing a model of the structure on a shake-table that simulates the earth shaking and observing its behavior; such kinds of experiments were first performed more than a century ago.
Only has it become possible to perform 1:1 scale testing on full structures. Due to the costly nature of such tests, they tend to be used for understanding the seismic behavior of structures, validating models and verifying analysis methods. Thus, once properly validated, computational models and numerical procedures tend to carry the major burden for the seismic performance assessment of structures. Seismic performance assessment or seismic structural analysis is a powerful tool of earthquake engineering which utilizes detailed modelling of the structure together with methods of structural analysis to gain a better understanding of seismic performance of building and non-building structures; the technique as a formal concept is a recent development. In general, seismic structural analysis is based on the methods of structural dynamics. For decades, the most prominent instrument of seismic analysis has been the earthquake response spectrum method which contributed to the proposed building code's concept of today.
However, such methods are good only for linear elastic systems, being unable to model the structural behavior when damage appears. Numerical step-by-step integration proved to be a more effective method of analysis for multi-degree-of-freedom structural systems with significant non-linearity under a transient process of ground motion excitation. Numerical analysis is conducted in order to evaluate the seismic performance of buildings. Performance evaluations are carried out by using nonlinear static pushover analysis or nonlinear time-history analysis. In such analyses, it is essential to achieve accurate non-linear modeling of structural components such as beams, beam-column joints, shear walls etc. Thus, experimental results play an important role in determining the modeling parameters of individual components those that are subject to significant non-linear deformations; the individual components are assembled to create a full non-linear model of the structure. Thus created models are analyzed to evaluate the performance of buildings.
The capabilities of the structural analysis software are a major consideration in the above process as they restrict the possible component models, the analysis methods available and, most the numerical robustness. The latter becomes a major consideration for structures that venture into the non-linear range and approach global or local collapse as the numerical solution becomes increa