Geotechnical Engineering is a branch of civil engineering that deals with the behavior of earth's material engineering. Geotechnical engineering is important in civil engineering, but also has applications in the fields of military, mining, petroleum, and other engineering disciplines related to construction occurring on the surface or in the ground. Geotechnical engineering uses the principles of soil mechanics and rock mechanics to investigate subsurface conditions and materials; determine the relevant physical/mechanical and chemical properties of these materials; evaluating the stability of natural slopes and man-made soil deposits; assess the risks posed by site conditions; designing ground work and foundation structure; and monitor site conditions, soil work and foundation construction.
Typical geotechnical engineering projects begin with a project review which is necessary to determine the required material properties. Then follow the investigation of the location of the soil, rocks, distribution of faults and the properties of bedrock on and below the area of ​​interest to determine their engineering properties including how they will interact with, on or under proposed construction. Site investigation is necessary to gain an understanding of the area at or where the engineering will take place. Investigations may include assessment of risks to humans, property and the environment from natural hazards such as earthquakes, landslides, drainage pits, soil liquefaction, debris flows, and coral reefs.
A geotechnical engineer then determines and designs the type of foundation, earthwork, and/or pavement required for the artificial structure intended to be built. Foundations are designed and built for various size structures such as high-rise buildings, bridges, medium to large commercial buildings, and smaller structures where soil conditions do not allow code-based design.
The foundations built for structures on the ground include a shallow and deep foundation. Retaining structures include earth-filled dams and retaining walls. Earthworks include embankments, tunnels, embankments and embankments, ducts, reservoirs, the deposition of hazardous waste and sanitary landfills.
Geotechnical engineering is also linked to coastal and ocean engineering. Coastal engineering can involve the design and construction of docks, marinas, and piers. Marine engineering may involve a foundation and anchor system for offshore structures such as oil platforms.
Geotechnical and geological engineering fields are closely related, and have large overlapping areas. However, the field of geotechnical engineering is a specialization of engineering, in which the field of engineering geology is a geological specialty.
Video Geotechnical engineering
History
Humans have historically used land as materials for flood control, irrigation purposes, burial sites, foundations of buildings, and construction materials for buildings. The first activity is related to irrigation and flood control, as shown by the imprint of dikes, dams, and canals dating back to at least 2000 BC found in ancient Egypt, ancient Mesopotamia and the Fertile Crescent, as well as around the early settlements of Mohenjo Daro and Harappa in the valley Indus. As cities expanded, structures were built with the support of a formalized foundation; Ancient Greeks mainly built pad foundations and foundations of strip-and-rafts. Until the 18th century, however, there was no theoretical basis for land design that had been developed and disciplined more than art rather than science, relying on past experiences.
Several engineering problems related to foundations, such as the Leaning Tower of Pisa, prompted scientists to start taking a more scientific-based approach to checking subsurface. The earliest advances occurred in the development of ground pressure theory for the construction of retaining walls. Henri Gautier, a French Royal Engineer, recognized the "natural slope" of different soils in 1717, an idea which came to be known as the stationary corner of the ground. An improper land classification system is also developed based on the weight of the material unit, which is no longer considered a good indication of the soil type.
The application of mechanical principles to the ground was documented as early as 1773 when Charles Coulomb (a physicist, engineer, and captain of the army) developed an enhanced method of determining the earth's pressure on military fortifications. Coulomb observes that, in failure, different slip planes will form behind the sliding wall and he suggests that the maximum shear stress in the slip plane, for design purposes, is the sum of the soil cohesion, , and friction
In the 19th century, Henry Darcy developed what is now known as Darcy's Law which describes the flow of liquid in porous media. Joseph Boussinesq (mathematician and physicist) developed the theory of stress distribution in elastic solids that proved useful for estimating pressure at depth of soil; William Rankine, an engineer and physicist, developed an alternative to Coulomb's earth pressure theory. Albert Atterberg developed a clay consistency index that is still in use today for soil classification. Osborne Reynolds acknowledged in 1885 that shear led to solid volumetric dilatation and contraction of loose granular materials.
Modern geotechnical engineering is said to have begun in 1925 with the publication of Erdbaumechanik by Karl Terzaghi (a civil engineer and geologist). Regarded by many as the father of modern soil mechanics and geotechnical engineering, Terzaghi developed the principle of effective stress, and showed that the shear forces of the soil are controlled by effective pressure. Terzaghi also developed a framework for the theory of the carrying capacity of the foundation, and the theory for the prediction of clay layer completion rates due to consolidation. In his 1948 book, Donald Taylor admits that the interlocking and widening of solid particles contributes to the peak power of the soil. The reciprocal relationship between the behavior of volume change (widening, contraction, and consolidation) and the shear behavior are all connected through plasticity theory using the ground state mechanics of critical state by Roscoe, Schofield and Wroth with the publication of On the Yielding of Soils in 1958 critical is the basis for many contemporary contemporary contemporary models that describe the behavior of the land.
Geotechnical centrifugal modeling is a method of testing the physical-scale model of geotechnical problems. The use of centrifuges increases the resemblance of testing of scale models involving soil because the strength and stiffness of the soil are very sensitive to limited pressures. Centrifugal acceleration allows a researcher to gain great pressure (prototype scale) in a small physical model.
Maps Geotechnical engineering
Train technicians
Geotechnical engineers are usually graduates of a four-year civil engineering program and some hold a master's degree. In the United States, geotechnical engineers are usually licensed and regulated as Professional Engineers (PE) in most countries; currently only California and Oregon have licensed geotechnical engineering specialties. The Academy of Geo-Professionals (AGP) began issuing Diplomate, Geotechnical Engineering (D.GE) certification in 2008. The state government will usually license the engineers who have graduated from ABET-accredited schools, passed the Fundamentals, several years of work experience under the supervision of a licensed Professional Engineer, and passed the Professional Engineering exam.
Soil mechanics
In geotechnical engineering, the soil is considered a phase three material composed of: rock or mineral particles, water and air. Soil cavities, the space between mineral particles, contain water and air.
Soil engineering properties are influenced by four main factors: the dominant size of mineral particles, the type of mineral particles, the grain size distribution, and the relative quantities of minerals, water and air present in the soil matrix. The fine particles (fine) are defined as particles less than 0.075 mm in diameter.
Soil properties
Some important properties of the land used by geotechnical engineers to analyze field conditions and design land work, maintain structures, and foundations are:
- Specific weight or Unit Weight
- The cumulative weight of solid particles, water and air from the unit volume of soil. Note that the air phase is often regarded as no weight.
- Porosity
- Void volume ratio (containing air, water, or other liquids) on the ground with total soil volume. Porosity is mathematically related to the vacancy ratio by
- di sini e adalah kekosongan rasio dan n adalah porositas
- Void ratio
- Racing volume void terhadap volume partikel padat dalam massa tanah. Rask kekosongan secara matematis terkait dengan porositas oleh
- Permability
- Ukuran kemampuan air mengalir melalui tanah. Ini dinyatakan dalam satuan kecepat.
- Compressibility
- Tingkat perubahan volume dengan stres yang efektif. Jika pori-pori diisi dengan air, maka air harus deperas keluar dari pori-pori untuk memungkinkan compresi volumetrik tanah; konsolidasi disebut process.
- Kekuatan geser
- Tegangan geser maksimum yang dapat diterapkan dalam massa tanah tanpa menyebabkan kegagalan geser.
- Batas Atterberg
- Batas car, Batas plastik, under Batas penyusutan. Indeks ini digunakan untuk estimasi properti teknik lainnya dan untuk classikasi tanah.
Investigasi geoteknik
Geotechnical engineers and technical geologists conduct geotechnical investigations to obtain information about the underlying and adjacent (and sometimes adjacent) soil physical properties of a site to design the soil and foundation work for the proposed structure, and to improve pressure on soil and structural work which is caused by subsurface conditions. Geotechnical investigations will include surface exploration and subsurface exploration of a site. Sometimes, geophysical methods are used to get data about the site. Sub surface exploration usually involves in-situ testing (two common examples of in-situ tests are standard penetration tests and cone penetration tests). In addition, site investigations will often include subsurface sampling and laboratory testing of sampled soil samples. Excavation of holes and excavations (especially for finding fault and slide fields) can also be used to study soil conditions at depth. Large diameter drilling is rarely used because of safety and cost issues, but is sometimes used to allow geologists or engineers to be lowered to drill holes for visual and manual checks directly to soil and rock stratigraphy.
Various soil samplers exist to meet the needs of different engineering projects. The standard penetration test (SPT), which uses a thick-walled split-spoon sampler, is the most common way to collect disturbed samples. Piston samplers, using thin-walled tubes, are most commonly used for less disturbed sample collection. More sophisticated methods, such as soil freezing and Sherbrooke block samplers, are superior, but even more expensive.
Atterberg boundary tests, moisture measurements, and grain size analyzes, for example, can be performed on disturbed samples obtained from thick-walled soil samplers. Properties such as shear strength, hydraulic conductivity rigidity, and consolidation coefficients can be altered significantly by sample noise. To measure these properties in the laboratory, high quality sampling is required. Common tests for measuring strength and stiffness include triaxial shear and unlimited compression test.
Surface exploration may include geological mapping, geophysical methods, and photogrammetry; or it could be as simple as an engineer going around to observe the physical conditions at the scene. Geological mapping and geomorphological interpretation are usually completed in consultation with a geologist or engineering geologist.
Geophysical exploration is also sometimes used. Geophysical techniques used for subsurface exploration include measurement of seismic waves (pressure, shear, and Rayleigh waves), surface wave method and/or downhole method, and electromagnetic survey (magnetometer, resistivity, and ground penetrating radar).
Build foundation
The foundations of buildings emit loads from buildings and other structures to the earth. Geotechnical engineers design a foundation based on the load characteristics of the structure and properties of the soil and/or bedrock at the site. In general, geotechnical engineers:
- Estimate the size and location of the load to be backed up.
- Develop an investigative plan to explore the subsurface.
- Determine the required soil parameters through field and laboratory testing (eg, consolidation test, triaxial shear test, shear vane test, standard penetration test).
- Design the foundation in the safest and most economical way.
The main considerations for foundation support are the carrying capacity, completion and movement of the soil under the foundation. Carrying capacity is the ability of soil sites to support the burden imposed by buildings or structures. Settlement occurs under all foundations in all soil conditions, although lightly loaded structures or rock sites may experience insignificant settlements. For heavier structures or softer sites, either the overall settlement relative to an unbuilt area or adjacent building, and differential settlement under a single structure, may be of concern. Particular attention is the settlement that occurs from time to time, since a direct settlement can usually be compensated during construction. Ground movements under the foundation of structures can occur due to shrinking or swelling of expansive soils due to climate change, expansion of soil ice, permafrost melting, slope instability, or other causes. All these factors must be considered during the foundation design.
Many building codes define basic foundation design parameters for simple conditions, often varying according to jurisdiction, but such design techniques are usually limited to certain types of construction and certain types of sites, and are often very conservative.
In areas of shallow rock, most of the foundations can be directly above the bedrock; in other areas, the soil can provide sufficient strength to support the structure. In areas of deeper bedrock with soft soil, deep foundations are used to support direct structures in bedrocks; in areas where bedrock is unavailable economically, a rigid "bearing layer" is used to support the deep foundation instead.
The shallow foundation
A shallow foundation is a type of foundation that transfers the building load to a very close surface, not to the subsurface. Shallow foundations usually have a depth to a width ratio of less than 1.
Folding
Footholds (often called "spreading footholds" as they deploy loads) are structural elements that transfer structural loads to the ground by direct area contact. The footrest can be isolated the foundation for a point or column load, or a stepping strip for a wall or other long (line) load. Footrests are usually constructed of reinforced concrete that is thrown directly to the ground, and is usually implanted to the ground to penetrate the zone of ice movement and/or to gain additional bearing capacity.
Slab Foundations
The variant on a scattered footing is to have all the structures attached to a single concrete slab that underlies the entire area of ​​the structure. The sheets should be thick enough to provide sufficient stiffness to spread a somewhat uniform bearing load, and to minimize differential settlement throughout the foundation. In some cases, bending is allowed and buildings are built to tolerate minor movements of the foundation instead. For small structures, such as single-family homes, the slabs may be less than 300 mm; for larger structures, the foundation slabs may be as thick as a few meters.
The slab foundation can be a slab-on-grade foundation or an embedded foundation, usually in a building with a basement. Slab-on-grade foundations should be designed to allow potential ground movement due to changing soil conditions.
Foundation within
The deep foundation is used for structures or heavy loads when shallow foundations can not provide adequate capacity, due to their size and structural limitations. They can also be used to transfer the building load through a weak or compressible soil layer. While a shallow foundation relies only on the underlying bearing capacity, the deep foundation can rely on end bearing resistance, frictional durability along its length, or both in developing the required capacity. Geotechnical engineers use special tools, such as cone penetration tests, to estimate the amount of leather and end bearings available beneath the surface.
There are many types of deep foundations including piles, drill holes, caissons, piers, and earth stable columns. Large buildings such as skyscrapers usually require deep foundations. For example, the Jin Mao Tower in China uses a tubular steel pile of about 1m (3.3 ft) pushed to a depth of 83.5m (274 ft) to support its weight.
In buildings built and found to live in settlements, a support pole can be used to stabilize existing buildings.
There are three ways to place the pile for a deep foundation. They can be moved, drilled, or installed using auger. Driven stacks extended to their required depth with the application of external energy in the same way hammered nails. There are four typical hammers used to move such a pile: drop the hammer, diesel hammer, hydraulic hammer, and air hammer. Drop the hammer simply drop the heavy load onto the pile to drive it, while the diesel hammers use a single cylinder diesel engine to force the pile through the Earth. Similarly, hydraulic and air hammers supply energy to the pile through the hydraulic forces and air. The energy given from the hammer head varies with the selected hammer type, and can be as high as one million pound feet for large scale diesel hammers, the hammer head is very commonly used in practice. Piles are made of various materials including steel, wood, and concrete. The drilled stack is made by drilling the first hole to the proper depth, and filling it with concrete. Drilled stacks can usually carry more payloads than driven piles, simply because the pile is larger in diameter. The auger mounting method of the pole is similar to the installation of a drill pole, but the concrete is pumped into the hole when the auger is removed.
Lateral earth support structures
The retaining wall is the structure that holds the earth. The retaining walls stabilize the soil and rocks from the movement or erosion of the lower slopes and provide support for vertical or near-vertical class changes. Cofferdams and bulkheads, structures for holding water, are sometimes also regarded as retaining walls.
The main geotechnical concern in the design and installation of retaining walls is that the weight of the retained material creates lateral ground pressure behind the wall, which may cause the wall to damage or fail. The lateral soil pressure depends on the height of the wall, the soil density, the strength of the soil, and the amount of allowable wall movement. This pressure is the smallest at the top and rises downward in a manner similar to hydraulic pressure, and tends to push the wall away from the backfill. Groundwater behind a wall that is not dissipated by the drainage system causes additional horizontal hydraulic pressure on the wall.
Gravitational wall
The wall of gravity depends on the size and weight of the mass wall to withstand the pressure from the rear. Gravitational walls often have slight setbacks, or dough, to improve wall stability. For the short term, landscape walls, gravity walls made of dry stacked mortars (mortars) or segmental concrete units (brick units) are commonly used.
Earlier in the 20th century, higher retaining walls were often gravitational walls made of concrete or large rocks. At present, the higher retaining walls are increasingly being constructed as composite gravity walls such as: geosynthetic backing or precast-reinforced steel facing; bronjong (stacked steel wire basket filled with stones), crib walls (cells built from the cabin-beam style of precast or wooden concrete and filled with free dewater or pebbles) or walls nailed with soil (ground reinforced with stems steel and concrete).
For reinforced soil gravity wall , the ground reinforcement is placed in a horizontal layer along the wall height. Generally, the soil amplifier is geogrid , the high strength polymer, which gives the tensile strength to hold the ground together. The face of the wall is often of precast, segmental concrete units that can tolerate multiple differential motions. The reinforced ground mass, along with the facing, becomes the wall of gravity. The reinforced mass must be built large enough to withstand the pressure from the ground behind it. Gravitational walls typically have to be at least 30 to 40 percent as deep (thick) as the wall height, and may have to be larger if there is a slope or additional cost on the wall.
Cantilever wall
Prior to the introduction of modern soil-reinforced gravity walls, cantilevered walls were the most common type of retaining wall. Cantilever walls are made of relatively thin stems of reinforced concrete, poured concrete in place or castrated stones (often in reverse T shape). These walls contain a cantilever (like a beam) to a large structural footing; change the horizontal pressure from behind wall to vertical pressure in the ground below. Sometimes cantilevered walls are supported on the front, or include counterfort at the rear, to increase their stability against high loads. Buttresses are short wing walls at right angles to the main wall trends. These walls require a rigid concrete foundation under the depth of seasonal ice. This type of wall uses much less material than traditional gravity walls.
Cantilever walls withstand lateral stress by friction at the base of the wall and/or passive earth pressure , the tendency of the ground to resist lateral movement.
The basement is a cantilevered wall shape, but the force in the basement wall is larger than the conventional wall because the basement wall is not free to move.
Excavation Excavation
Shoring up temporary excavations often requires the design of walls that do not extend laterally outside the walls, thus supporting the lengthwise beneath the planned base of the excavation. A common method to support is the use of sheet piles or soldier beam and lagging . Sheet Piles is a staple shape that is driven using interlocked steel sheets to obtain a sustainable barrier on the ground, and is pushed before excavation. Army beams are constructed from large steel sections leading H, which is about 2-3 m, pushed before excavation. When the excavation results, horizontal wood or steel sheet (left behind) is inserted behind the H stack flange.
In some cases, the lateral support that can be provided by supporting walls alone is not sufficient to withstand the planned lateral load; in this case additional support is provided by walers or tie-backs. Waler is a structural element that connects the excavation so that the load from the ground on both sides of the excavation is used to hold each other, or that transfer the horizontal load from the support wall to the bottom of the excavation. Tie-backs are steel tendons that are drilled into a wall surface that extends above the ground that apply pressure to the wall, to provide additional lateral resistance to the wall.
Earthworks
- Excavation is the process of training the earth as needed by removing the soil from the site.
- Filling is the process of training the earth as needed by placing the land on the site.
- Compaction is a process in which the soil density increases and soil permeability decreases. The content of the placement work often has specifications that require a certain degree of compaction, or alternatively, the specific properties of compacted soil. In-situ soil can be compacted by rolling, deep dynamic compaction, vibration, blasting, gyrating, dough, compaction grouting etc.
Upgrade
Ground Improvement is a technique that improves the engineering properties of the treated soil mass. Typically, the modified properties are shear strength, stiffness and permeability. Soil improvement has evolved into a sophisticated tool to support the foundations for various structures. Applied correctly, that is, after giving reasonable consideration to improved soil properties and the type and sensitivity of structures under construction, increasing land often reduces direct costs and saves time.
Stabilization of the slope
Slope stability is a slope-covered ground potential to survive and experience movement. Stability is determined by the balance of shear stress and shear strength. The previously stable slope may be initially affected by the preparation factors, making the conditional slope unstable. The triggering factor of slope failure can be a climatic event which can then create an unstable active slope, leading to mass movement. Mass movement can be caused by an increase in shear stress, such as loading, lateral pressure, and transient forces. Alternatively, shear strength can be reduced by weathering, changes in pore pressures, and organic matter.
Some modes of failure for the slopes include falling, topples, slides, and flow. On the slopes with coarse grained or rocky soils, falls usually occur as rapid degradation of rocks and other loose slope materials. Tilt clumps when large column of land tilts up the vertical axis at failure. The typical slope stability analysis considers shear failure, categorized primarily as a rotational slide or translational slide. As indicated by the name, the rotation slide fails along a generally curved surface, while the translational slide fails along a more flat surface. The slope that fails because the flow will resemble the fluid that flows downward.
Analysis of slope stability
Stability analysis is required for engineered slope design and for estimating the risk of slope failure on natural or designed slopes. The general assumption is that the slope consists of a layer of soil that is above a rigid base. The mass and base are assumed to interact through friction. The interface between mass and base can be planar, curved, or has some other complex geometry. The purpose of slope stability analysis is to determine the conditions under which the mass will slip relative to the base and cause slope failure.
If the interface between mass and slope base has a complex geometry, difficult slope stability analysis and numerical solution methods are required. Typically, the exact geometry of the interface is unknown and the simplified interface geometry is assumed. The limited slope requires a three-dimensional model for analysis. To keep the problem simple, most of the slopes are analyzed assuming that the slope is very wide and can therefore be represented by a two-dimensional model. The slopes can be dried or not dried. Undrained conditions are used in calculations to generate conservative risk estimates.
The popular stability analysis approach is based on principles relating to the concept of boundary balance. This method analyzes the limited or infinite slope as if it would fail along the surface of the shear failure. The equilibrium pressure is calculated along the failure plane, and compared to the shear strength of the soil as determined by the Terzaghi shear strength equation. Stability is ultimately determined by the same safety factor as the shear strength ratio to the equilibrium voltage along the surface of the failure. The greater safety factor than one generally implies a stable slope, a failure that should not occur with the assumption of uninterrupted slopes. The 1.5 security factor for static conditions is commonly used in practice.
Offshore geotechnical engineering
Offshore marine geotechnical engineering deals with the design of the foundation for man-made structures at sea, away from the shoreline (contrary to on land or near the coast ). The oil platforms, artificial islands and submarine pipelines are examples of such structures. There are a number of significant differences between offshore and offshore geotechnical techniques. In particular, increased land (on the seafloor) and more expensive location investigations, offshore structures are exposed to a wider geohazard range, and higher environmental and financial consequences in the event of a failure. Offshore structures are exposed to various environmental loads, especially wind, waves and currents. This phenomenon may affect the integrity or ease of servicing structures and foundations during its operational life - they should be taken into account in offshore design.
In undersea geotechnical engineering, seabed material is considered a two-phase material consisting of 1) rock or mineral particles and 2) water. Structures can remain in place on the seabed - as well as for docks, jettys and fixed-bottom wind turbines - or perhaps floating structures that remain roughly relative to their geotechnical anchor points. The lower belly of a man-made floating structure includes a large number of offshore oil and gas platforms and, since 2008, some floating wind turbines. Two general types of designs engineered for floating structure retrofts include a loose strap-leg and catenary loose system. "Tension leg mooring systems have vertical tethers under tension providing major recovery moments in pitch and roll.Mooring catenary systems provide station keeping for offshore structures but provide little stiffness at low voltage."
Geosynthetics
Geosynthetics is a type of plastic polymer product used in geotechnical engineering that improves engineering performance while reducing costs. These include geotextiles, geogrid, geomembrane, geocell, and geocomposites. The synthetic properties of the product make it suitable for use in soils where high levels of durability are required; Their main functions include: drainage, filtration, reinforcement, separation and containment. Geosynthetics are available in different shapes and materials, each corresponding to a slightly different end-use, though often shared. These products have various applications and are currently used in many civil and geotechnical engineering applications including: roads, airfields, railways, embankments, stacked dams, retaining structures, reservoirs, canals, dams, landfills, bank protection and engineering coast.
See also
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References
Source of the article : Wikipedia
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