Liquid discharge describes a phenomenon in which the saturated or partially saturated soil substantially loses strength and stiffness in response to the applied stress, usually earthquake shocks or other sudden changes under stress conditions, causing it to behave like a liquid.
In soil mechanics, the term "thawed" was first used by Allen Hazen in reference to the 1918 failure of the Calaveras Dam in California. He described the mechanism of liquefaction of the dam dams as follows:
If the water pressure in the pores is large enough to carry all the loads, it will have the effect of holding the particles apart and producing a practical condition equivalent to suction sand... the initial movement of some part of the material may produce accumulated pressure, first on one point, and then on the other, respectively, as the starting point of the concentration is thawed.
This phenomenon is most often observed in saturated, loose (low density or uncompressed), sandy soil. This is because loose sand has a tendency to compress when the load is applied; Solid sand instead tends to expand in volume or 'dilatation'. If the soil is saturated by water, a condition that often exists when the soil is below the surface of the groundwater or sea level, then the water fills the gap between the soil grains ('pore space'). In response to soil compression, this water increases pressure and tries to flow out of the ground into low pressure zones (usually up to the ground). However, if loading is applied quickly and large enough, or repeated many times (eg earthquake shocks, storm surge) so that water does not flow out in time before the next load cycle is applied, water pressure can build to the extent to which they exceed the force ( contact pressure) between the grains of the soil that keep them in touch with each other. The contacts between these grains are the means by which the weight of the building and the topsoil is moved from the soil surface to the soil layer or stone at a greater depth. The loss of this soil structure causes it to lose all its strength (the ability to transfer the shear stress), and it can be observed to flow like a liquid (hence 'liquefaction').
Although liquefaction effects have long been understood, it is more thoroughly brought to the attention of the engineers after the 1964 Niigata earthquake and the 1964 Alaska earthquake. It was also a major factor in the destruction of the Marina District of San Francisco during the 1989 Loma Prieta earthquake, and in the Port of Kobe during the Great Quake Hanshin in 1995. More recent disbursements are largely responsible for extensive damage to residential properties in the eastern suburbs and Christchurch city of Christchurch, New Zealand during the Canterbury 2010 earthquake and more broadly after the Christchurch earthquake that occurred in early and mid-2011.
Building codes in many developed countries require engineers to consider the effects of liquefaction in building designs and new infrastructure such as bridges, dike dams and retaining structures.
Video Soil liquefaction
Definisi teknis
The soil 'liquefaction' occurs when the effective soil stress decreases substantially zero, corresponding to the total shear loss. This can be initiated by loading monotonic (ie single occurrence, abrupt from stress changes - examples including increased load on the embankment or loss of sudden leg support) or cyclic loading (ie repetitive changes in stress conditions - eg including wave or shock loading earthquake). In both cases, the soil is loosely saturated, and which can produce significant pore pressures on the load changes is most likely to melt. This is because loose soil has a tendency to compress when shaved, resulting in large pore pressures because the load is moved from the soil skeleton to adjacent pore water during undrained loading. As the pore pressures rise, the progressive loss of soil strength occurs when the effective pressure decreases. Melting is more likely to occur in sandy or non-plastic soils, but may be in rare cases in gravel and clay (see quick clay).
'Flow failure' can begin if soil strength is reduced under the pressure required to maintain slope equilibrium or foothold structure. This may occur due to monotonic loading or cyclic loading, and can be abrupt and catastrophic. Historical example is the Aberfan disaster. Casagrande refers to this phenomenon as 'flow liquefaction' although ineffective state is not necessary for this to happen.
The term 'cyclic suitability' refers to the occurrence of soil conditions when large shear strains have accumulated in response to cyclic loading. A typical reference strain for estimating the occurrence of zero effective stress is 5% double shear amplitude strain. This is a definition based on soil tests, usually carried out through cyclic triaxial, simple direct cyclic shear, or a cyclic shear torsional type device. This test is performed to determine the resistance of the soil to liquefaction by observing the number of load cycles at a particular shear stress amplitude before 'failure'. The failure here is determined by the previously mentioned shear stress criterion.
The term 'cyclic mobility' refers to the mechanism of progressive reduction of effective stress due to cyclic loading. This may occur in all soil types including dense soils. However, when it reaches a state without effective pressure, such land widen immediately and regain strength. Thus, the shear strain is significantly less than the actual condition of soil liquefaction where loose soil indicates flow type phenomena.
Maps Soil liquefaction
Genesis
Disbursements are more likely to occur in loose to moderate granular soils with poor drainage, such as sand or muddy sand and gravel containing sediment that can not be decomposed. During wave loading, usually loading without cyclic cycles, ie. seismic loading, loose sand tends to decrease volume, resulting in an increase in their pore water pressure and consequently a decrease in shear strength, ie effective stress reduction.
The most vulnerable deposits to liquefaction are young sand (Holocene-age, deposited in the last 10,000 years) and sand of the same grain size (well ordered), in beds less than one meter high, and saturated with water. Such deposits are often found along riverbeds, beaches, sand dunes, and areas where loess and sandbanks have been accumulated. Some examples of soil liquefaction include quicksand, quick clay, turbidity flows, and liquefaction caused by earthquakes.
Depending on the initial vacancy ratio, the soil material can respond to loading either strain-softening or strain-hardening . Softened soft soil, eg. loose sand, may be triggered to collapse, either monotonic or cyclically, if static shear stress is greater than the final shear strength or steady state of the soil. In this case the flow liquefaction occurs, in which the soil is deformed at constant low shear stress. If the filter soil hardened, for example, the sand is solid enough to solid, the flow liquefaction generally will not occur. However, cyclic softening may occur due to cyclic non-cyclical loading, e.g. earthquake loading. Deformation during cyclic loading will depend on the soil density, magnitude and duration of cyclic loading, and magnitude of the shear tensile reversal. If a stress reversal occurs, the effective shear stress can reach zero, then cyclic liquefaction may occur. If no voltage reversal occurs, zero effective pressure can not occur, and cyclic mobility occurs.
The resistance of the cohesive soil to liquefaction will depend on the soil density, the limited pressure, the soil structure (fabric, age and cementation), the magnitude and duration of cyclic loading, and the extent of shear stress reversal.
Earthquake melt
The pressure generated during a major earthquake can force underground water and liquid sand to the surface. It can be observed on the surface as an effect known as "sand boils," "sand blows" or "sand volcanoes".
Other common observations are instability in the soil - cracks and land movements down the slope or towards the banks of rivers, rivers, or beaches that are not supported. Soil failure in this way is called 'lateral spread', and can occur on very shallow slopes with angles of only 1 or 2 degrees from the horizontal.
One positive aspect of land liquefaction is the tendency of earthquake shock effects to be significantly muffled (minus) for the remainder of the earthquake. This is because the liquid does not support shear stress and once the soil is melting due to trembling, subsequent quake shocks (transferred through the soil by shear waves) are not transferred to the building at ground level.
Studies of liquefaction features left by prehistoric earthquakes, called paleoliquefaction or paleoseismology, can reveal much information about earthquakes that occurred before the recording was kept or accurate measurements could be taken.
Disbursement of earthquakes caused by earthquakes is also a major contributor to the risk of the city's quake.
Effects
The effect of liquefaction in the built environment can be very destructive. Buildings whose foundations are directly overlaid in melted sand will experience a sudden loss of support, which will result in drastic and irregular building settlements that cause structural damage, including the cracking of foundations and damage to the structure itself, or may make structures not functioning thereafter, even without structural damage. Where a thin crust of non-melting soil exists between the foundations of the building and the liquid soil, the failure of a 'sliding punch' foundation may occur. Irregular soil settlement can also damage underground utility lines. Upward pressure applied by movement of the liquid soil through the crust layer can break the weak foundation of the foundation and enter the building through the service line, and allow water to damage the building's contents and electrical services.
Large bridges and buildings built on the foundations of the pole may lose support from adjacent ground and clashing, or rest on a slope after trembling.
Ground and tilted soil beside rivers and lakes can shift to liquefied soil layers (called 'lateral spread'), open large cracks or gaps in the soil, and can cause significant damage to buildings, bridges, roads and services such as water, gas nature, sewerage, electricity and telecommunications installed in the affected land. Buried tanks and manholes can float on diluted soil due to buoyancy. Earth dikes such as flood embankments and earth dams can lose stability or collapse if materials consisting of embankments or foundations melt.
During geologic time, liquefaction of earth-shaped soil material can provide a dense parent material in which fragments can thrive through pedogenesis.
Mitigation methods
Methods to reduce the effects of liquefaction have been designed by earthquake engineers and include various soil compaction techniques such as vibro compaction (soil compaction by a depth vibrator), dynamic compaction, and vibro stone columns. These methods produce soil densification and allow the building to withstand liquefaction of the soil.
Existing buildings can be reduced by injecting grout into the soil to stabilize liquefied soil layers.
![Cool soil liquefaction. [VIDEO]](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_sC99Y7z85IAbZ83z0IpATiNNadKUFWq3pBJNykwfcz69DViF0YsrCvfgWA2zjLgZTvQbCVJekU0JxljDGIqtrifluXfIv_ZKNkstMF4gqypbcG9yJWP80g2B2_7IV1_LJdbecB6CfKqQ=s0-d "Cool soil liquefaction. [VIDEO]")
Quicksand
The suction sand is formed when the water saturates the area of ​​loose sand and unusually restless sand. When water trapped in a pile of sand can not escape, it creates a liquefied ground that no longer supports the weight. Suction sand can be formed by standing or (up) underground water flows (such as from underground springs), or by earthquakes. In the case of the flow of underground water, the strength of the water flow defies the force of gravity, causing the sand grains to become lighter. In the case of an earthquake, shock strength can increase shallow groundwater pressure, liquefy sand and mud deposits. In both cases, the liquefied surface loses strength, causing the building or other objects on the surface to sink or fall.
The saturated sediments may appear solid enough until the pressure changes or shock start liquefaction, causing the sand to form a suspension with each grain surrounded by a thin layer of water. These bearings provide quicksand, and other liquid sediments, textures such as sponges, such as liquids. The objects in the sand-sink sink to a level where the weight of the object is equal to the weight of the sand/water mixture removed and the floating object due to its buoyancy.
Fast clay
The fast clay, also known as Leda Clay in Canada, is a water-saturated gel, which in its solid form resembles a unique form of highly sensitive clay. This clay has a tendency to change from a relatively rigid condition to a liquid mass when it is disrupted. The gradual change in form from solid to liquid is a process known as spontaneous liquefaction. The clay maintains a solid structure even though the water content is high (up to 80% by volume), since the surface tension holds the water clay clay together in a fine structure. When the structure is damaged by sufficient shock or friction, it turns into a liquid state.
The fast clay is found only in northern countries such as Russia, Canada, Alaska in the US, Norway, Sweden, and Finland, which are glaciated during the Pleistocene epoch.
The fast clay has been the main cause of many deadly landslides. In Canada alone, it has been linked to over 250 mapped landslides. Some are ancient, and probably triggered by an earthquake.
Turbidity Flow
The submarine landslide is a turbidity stream and consists of water-saturated sediments that flow down the slope. An example occurred in the 1929 Grand Banks earthquake that struck the continental slope off the coast of Newfoundland. A few minutes later, the transatlantic telephone cord began to break in sequence, further and further down, away from the epicenter. Twelve wired cables total 28 places. The exact time and location are recorded for each break. Researchers suggest that submarines along 100 miles/h (100 km/h) of landslides or turbidity currents from water-saturated sediments sweep 400 miles (600 km) down the continental slopes from epicenter earthquakes, snapping current wires through.
See also
- Aberfan disaster
- Atterberg Limitations
- Drysand is dry
- Earth Stream
- Earthquake engineering
- Mud volcano
- Mud Smud
- Network for Earthquake Engineering Simulation # Research of ground liquefaction
- Paleoseismology
- Sand boils
- Thixotropy
References
Further reading
- Seeds et al., Recent Progress in Soil Dissemination Techniques: Integrated and Consistent Framework, 26 September ASIA Geotechnical Spring Seminar Los Angeles, Long Beach, California, April 30, 2003, Research Center Earthquake Engineering PDF
External links
Media related to Land disbursement in Wikimedia Commons
- Soil Liquefaction
- Disbursement - Northwest Pacific Seismic Network
- The video shows the liquefaction process
- Land disbursements were recorded during the 2011 Tohoku earthquake
Source of the article : Wikipedia
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