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Soil Liquefaction by qmqm wang
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Soil Liquefaction |
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Business,Business News,Business Opportunities
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Earthquake liquefaction
A liquefaction susceptibility map - excerpt of USGS map for the San Francisco Bay Area. Many areas of concern in this region are also densely urbanized.
Earthquake liquefaction is a major contributor to urban seismic risk. The shaking causes increased pore water pressure which reduces the effective stress, and therefore reduces the shear strength of the sand. If there is a dry soil crust or impermeable cap, the excess water will sometimes come to the surface through cracks in the confining layer, bringing liquefied sand with it, creating sand boils, colloquially called "sand volcanoes".
Studies of liquefaction features left by prehistoric earthquakes, called paleoliquefaction or paleoseismology, can reveal a great deal of information about earthquakes that occurred before records were kept or accurate measurements could be taken.
Quicksand
Main article: Quicksand
Quicksand forms when water saturates an area of loose sand and the ordinary sand is agitated. When the water trapped in the batch of sand cannot escape, it creates liquefied soil that can no longer support weight. Quicksand can be formed by standing or (upwards) flowing underground water (as from an underground spring), or by earthquakes. In the case of flowing underground water, the force of the water flow opposes the force of gravity, causing the granules of sand to be more buoyant. In the case of earthquakes, the shaking force can increase the pressure of shallow groundwater, liquefying sand and silt deposits. In both cases, the liquefied surface loses strength, causing buildings or other objects on that surface to sink or fall over.
The saturated sediment may appear quite solid until a change in pressure or shock initiates the liquifaction causing the sand to form a suspension with each grain surrounded by a thin film of water. This cushioning gives quicksand, and other liquefied sediments, a spongy, fluidlike texture. Objects in the liquefied sand sink to the level at which the weight of the object is equal to the weight of the displaced sand/water mix and the object floats due to its buoyancy.
Quick clay
Main article: Quick clay
Quick clay, also known as Leda Clay in Canada, is a unique form of highly sensitive clay, with the tendency to change from a relatively stiff condition to a liquid mass when it is disturbed. Undisturbed quick clay resembles a water-saturated gel. When a block of clay is held in the hand and struck, however, it instantly turns into a flowing ooze, a process known as spontaneous liquefaction. Quick clay behaves this way because, although it is solid, it has a very high water content, up to 80%. The clay retains a solid structure despite the high water content, because surface tension holds water-coated flakes of clay together in a delicate structure. When the structure is broken by a shock, it reverts to a fluid state.
Quick clay is only found in the northern countries such as Russia, Canada, Alaska in the U.S., Norway, Sweden, and Finland, which were glaciated during the Pleistocene epoch.
Quick clay has been the underlying cause of many deadly landslides. In Canada alone, it has been associated with more than 250 mapped landslides. Some of these are ancient, and may have been triggered by earthquakes.
Turbidity currents
Main article: Turbidity current
Submarine landslides are turbidity currents and consist of water saturated sediments flowing downslope. An example occurred during the 1929 Grand Banks earthquake that struck the continental slope off the coast of Newfoundland. Minutes later, transatlantic telephone cables began breaking sequentially, farther and farther downslope, away from the epicenter. Twelve cables were snapped in a total of 28 places. Exact times and locations were recorded for each break. Investigators suggested that a 60-mile-per-hour (100 km/h) submarine landslide or turbidity current of water saturated sediments swept 400 miles (600 km) down the continental slope from the earthquake epicenter, snapping the cables as it passed.
Effects
Liquefaction can cause damage to structures in several ways. Buildings whose foundations bear directly on sand which liquefies will experience a sudden loss of support, which will result in drastic and irregular settlement of the building. Liquefaction causes irregular settlements in the area liquefied, which can damage buildings and break underground utility lines where the differential settlements are large. Pipelines and ducts may float up through the liquefied sand. Sand boils can erupt into buildings through utility openings, and may allow water to damage the structure or electrical systems. Soil liquefaction can also cause slope failures. Areas of land reclamation are often prone to liquefaction because many are reclaimed with hydraulic fill, and are often underlain by soft soils which can amplify earthquake shaking. Soil liquefaction was a major factor in the destruction in San Francisco's Marina District during the 1989 Loma Prieta earthquake. Mitigating potential damage from liquefaction is part of the field of geotechnical engineering.
See also
Paleoseismology
Dry quicksand
Atterberg limits
Mud volcano
Sand volcano or sand blow
Thixotropy
Events
Aberfan disaster
References
^ Jefferies, M. and Been, K. (Taylor & Francis, 2006) Soil Liquefaction
^ Youd, T.L., and Idriss, I.M. (2001). "Liquefaction Resistance of Soils: Summary report from the 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of Soils", Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 127(4), 297-313
^ Robertson, P.K., and Fear, C.E. (1995). "Liquefaction of sands and its evaluation.", Proceedings of the 1st International Conference on Earthquake Geotechnical Engineering, Tokyo
^ Robertson, P.K., and Wride, C.E. (1998). "Evaluating Cyclic Liquefaction Potential using the cone penetration test." Canadian Geotechnical Journal, Ottawa, 35(5), 442-459.
^ http://earthquake.usgs.gov/research/hazmaps/whats_new/workshops/CEUS-WORKSHP/Tuesday/NE-Tuttle.2.pdf
^
^ Bruce C. Heezen and Maurice Ewing, urbidity Currents and Submarine Slumps, and the 1929 Grand Banks Earthquake, American Journal of Science, Vol. 250, December 1952, pp. 849873.
^ Damage Caused by EarthQuakes
External links
Soil Liquefaction
Shaking, Liquefaction on Harbor Island, one of the few known live observations of an earthquake liquefaction event by a seismologist
v d e
Topics in geotechnical engineering
Soils
Clay Silt Sand Gravel Peat Loam
Soil properties
Hydraulic conductivity Water content Void ratio Bulk density Thixotropy Reynolds' dilatancy Angle of repose Cohesion Porosity Permeability Specific storage
Soil mechanics
Effective stress Pore water pressure Shear strength Overburden pressure Consolidation Soil compaction Soil classification Shear wave Lateral earth pressure
Geotechnical investigation
Cone penetration test Standard penetration test Exploration geophysics Monitoring well Borehole
Laboratory tests
Atterberg limits California bearing ratio Direct shear test Hydrometer Proctor compaction test R-value Sieve analysis Triaxial shear test Hydraulic conductivity tests Water content tests
Field tests
Crosshole sonic logging Nuclear Densometer Test
Foundations
Bearing capacity Shallow foundation Deep foundation Dynamic load testing Wave equation analysis
Retaining walls
Mechanically stabilized earth Soil nailing Tieback Gabion Slurry wall
Slope stability
Mass wasting Landslide Slope stability analysis
Earthquakes
Soil liquefaction Response spectrum Seismic hazard Ground-structure interaction
Geosynthetics
Geotextile Geomembranes Geosynthetic clay liner Cellular confinement
Instrumentation for Stability Monitoring
Deformation monitoring Automated Deformation Monitoring
Categories: Environmental soil science Sedimentology Soil mechanics Seismology and earthquake terminology Earthquake engineering I am a professional writer from Cheap On Sales, which contains a great deal of information about tungsten carbide burrs , hydraulic crimping tool, welcome to visit!
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