Condition of a soil to be liquefiable

Seed and Idriss (1982) consider that a soil can liquefy if:

• - The weight percentage of particles <0.005 mm is less than 15%.

• - LL<35.

• - w/LL>0.9.

This criterion was known as the Chinese criterion.

Calculation

The seismic liquefaction studies of Seed (1966) led to postulate the following conditions:

• - If the pore pressure induced by the dynamic or cyclic action of the earthquake reaches the value of the confining pressure, the soil will reach the state of initial liquefaction.

• - If the sand subjected to cyclic action reaches 20% deformation, total liquefaction will be achieved.

The susceptibility to soil liquefaction can be estimated by different methods, although the most used are those based on the work developed by Seed and Idriss[6]​ and Youd and Idriss.[7]​ These methods establish that the soil liquefies when the cyclic shear stress ratio (CSR, cyclic shear stress ratio, in English) produced by an earthquake is greater than the tangential resistance ratio of the soil (CRR, cyclic resistance ratio, in English). English). The calculation of CSR and CRR is defined in the technical regulations of each country, showing small particular adaptations to each region or application case.[8]​.

The limited knowledge regarding this phenomenon is largely due to two factors:

• - Difficulty in observing its characteristics in real conditions.

• - Complexity of the phenomenon, since in addition to being the result of a highly variable seismic action, it induces a strongly non-linear and hysteretic behavior in the soil, with strong degradation of the mechanical characteristics of the soil of each cycle determined by the generation of neutral pressures in the sample under seismic action.

One of the fundamental problems is the rudimentary knowledge about the breakage and deformation mechanisms associated with the liquefaction phenomenon, which limits the use of elementary tests to study it.

• - There is no single definition for the phenomenon of liquefaction.

• - A general and qualitative definition would be that it is a phenomenon capable of producing large deformations in the land and the existing structures therein, associated with great degradation of the mechanical characteristics of granular soils due to the generation or migration of excess neutral pressure resulting from the cyclic action produced by earthquakes in at least partially undrained conditions.

Earthquake-induced liquefaction is one of the main contributors to urban seismic risk. Shaking causes the water pressure in the pores to increase which reduces the effective stress and therefore decreases the shear strength of the sand. If a dry soil crust or impermeable cover exists, excess water can sometimes rise to the surface through cracks in the top layer, carrying liquefied sand in the process, producing sand bubbles, commonly called "sand volcanoes."

The study of liquefaction characteristics in traces of earthquakes that occurred in prehistoric times, called paleoliquefaction or paleoseismology, can provide a great deal of information about earthquakes that occurred before historical records existed or precise measurements could be made.[9]​.

Quicksand occurs when an area of ​​loose sand that is saturated with water is disturbed. When the water trapped in the sand block cannot escape, the soil liquefies and loses its ability to support weight. Quicksand can form from a rising flow of groundwater (such as from a natural spring), or from earthquakes. In the case of an underground water flow, the force produced by the water flow opposes the force of gravity, causing the sand grains to float. In the case of earthquakes, the force of the shaking can increase the pressure of groundwater near the surface, and in the process liquefy deposits of sand and sediment on the surface. In both cases, the liquefying surface loses resistance, which destabilizes buildings and other structures on the surface, causing them to tilt or collapse.

Saturated sediments can appear extremely solid until a change in ground pressure or shaking triggers the liquefaction process, which causes the sand to form a suspension in which each grain becomes surrounded by a thin film of water. This configuration gives quicksand and other liquefied sediments a spongy texture similar to the consistency of a fluid. Objects that are engulfed in quicksand will sink to the level at which the weight of the object equals the displaced weight of the sand-water mixture and the object “floats” according to Archimedes' principle.

The so-called fast clays or marine clays, also known in Canada as Leda clays or quick clays, are a particular type of extremely sensitive clay, which when disturbed has the tendency to change its state from a relatively rigid one to a liquid state. At rest, fast clays look like a hydrosaturated gel. However, if you take a block of clay and hit it, it instantly takes on the constitution of a fluid, through a process known as spontaneous liquefaction. Fast clays behave this way because, although they are solid, they have a very high water content, which can be up to 80%. Clay retains a solid structure despite its high water content because the surface tension of water holds clay "flakes" together in a delicate structure. When the structure is broken by a blow, the clay changes its state and transforms into a fluid.

Fast clays are generally found in regions located in the northern hemisphere in countries such as Russia, Canada, Alaska in the United States, Norway, Sweden, and Finland, all areas that were covered by glaciers during the Pleistocene.

Fast-moving clays have been the underlying cause of many deadly landslides. In Canada alone they have been associated with more than 250 identified earthworks. Some of them are old and could have been confused with earthquakes.[10]​.

Submarine landslides are turbidity currents and consist of the movement of saturated sediments by water that flows into the deep sea. An example of this phenomenon occurred during the 1929 Grand Banks Earthquake, which occurred on the continental shelf near the coast of Newfoundland. Within minutes of the event, several submarine cables began to break in sequence, at increasingly distant points along the slope, and moving away from the epicenter. In total twelve cables snapped in a total of 28 locations. The exact times and locations at which each break occurred were precisely determined. The researchers suggested that a submarine landslide or turbidity current of sediments saturated by water that moved at a speed of 100 km/h (kilometers per hour) and propagated down the continental shelf along a route of 600 km, breaking the cables in its path.[11]​.

Liquefaction can cause damage to structures in several ways. Buildings whose foundations are directly in the liquefying sand experience a sudden loss of support, resulting in drastic (absolute settlement) and irregular settlement (differential settlement) of the building. Liquefaction causes uneven settlements in the liquefied area and this can damage buildings and break underground utility cables where differential settlements are large. Water and gas distribution pipes and other pipelines can float and move to the surface. Sand mounds can erupt into buildings through utility connections, allowing water to enter and damage the structure or its electrical systems. Soil liquefaction can also cause platform collapses. Environmental soil reclamation areas (landfills) are prone to liquefaction because many are reclaimed with hydraulic fill, and often sit on soft soils that can amplify shaking from earthquakes. Soil liquefaction was a major factor in the destruction of the San Francisco Marina District during the 1989 Loma Prieta earthquake.

Mitigating potential damage due to liquefaction is part of the field of geotechnical engineering.

• - Atterberg limits.

• - Solifluction.

• - Thixotropy.

• - Mud volcano.

• - Earthquake.

• - Tsunami.

• - Soil liquefaction.

• - Harbor Island liquefaction, one of the few situations where a seismologist has been able to witness an earthquake-induced liquefaction event in person.

Condition of a soil to be liquefiable

Seed and Idriss (1982) consider that a soil can liquefy if:

• - The weight percentage of particles <0.005 mm is less than 15%.

• - LL<35.

• - w/LL>0.9.

This criterion was known as the Chinese criterion.

Calculation

The seismic liquefaction studies of Seed (1966) led to postulate the following conditions:

• - If the pore pressure induced by the dynamic or cyclic action of the earthquake reaches the value of the confining pressure, the soil will reach the state of initial liquefaction.

• - If the sand subjected to cyclic action reaches 20% deformation, total liquefaction will be achieved.

The susceptibility to soil liquefaction can be estimated by different methods, although the most used are those based on the work developed by Seed and Idriss[6]​ and Youd and Idriss.[7]​ These methods establish that the soil liquefies when the cyclic shear stress ratio (CSR, cyclic shear stress ratio, in English) produced by an earthquake is greater than the tangential resistance ratio of the soil (CRR, cyclic resistance ratio, in English). English). The calculation of CSR and CRR is defined in the technical regulations of each country, showing small particular adaptations to each region or application case.[8]​.

The limited knowledge regarding this phenomenon is largely due to two factors:

• - Difficulty in observing its characteristics in real conditions.

• - Complexity of the phenomenon, since in addition to being the result of a highly variable seismic action, it induces a strongly non-linear and hysteretic behavior in the soil, with strong degradation of the mechanical characteristics of the soil of each cycle determined by the generation of neutral pressures in the sample under seismic action.

One of the fundamental problems is the rudimentary knowledge about the breakage and deformation mechanisms associated with the liquefaction phenomenon, which limits the use of elementary tests to study it.

• - There is no single definition for the phenomenon of liquefaction.

• - A general and qualitative definition would be that it is a phenomenon capable of producing large deformations in the land and the existing structures therein, associated with great degradation of the mechanical characteristics of granular soils due to the generation or migration of excess neutral pressure resulting from the cyclic action produced by earthquakes in at least partially undrained conditions.

Earthquake-induced liquefaction is one of the main contributors to urban seismic risk. Shaking causes the water pressure in the pores to increase which reduces the effective stress and therefore decreases the shear strength of the sand. If a dry soil crust or impermeable cover exists, excess water can sometimes rise to the surface through cracks in the top layer, carrying liquefied sand in the process, producing sand bubbles, commonly called "sand volcanoes."

The study of liquefaction characteristics in traces of earthquakes that occurred in prehistoric times, called paleoliquefaction or paleoseismology, can provide a great deal of information about earthquakes that occurred before historical records existed or precise measurements could be made.[9]​.

Quicksand occurs when an area of ​​loose sand that is saturated with water is disturbed. When the water trapped in the sand block cannot escape, the soil liquefies and loses its ability to support weight. Quicksand can form from a rising flow of groundwater (such as from a natural spring), or from earthquakes. In the case of an underground water flow, the force produced by the water flow opposes the force of gravity, causing the sand grains to float. In the case of earthquakes, the force of the shaking can increase the pressure of groundwater near the surface, and in the process liquefy deposits of sand and sediment on the surface. In both cases, the liquefying surface loses resistance, which destabilizes buildings and other structures on the surface, causing them to tilt or collapse.

Saturated sediments can appear extremely solid until a change in ground pressure or shaking triggers the liquefaction process, which causes the sand to form a suspension in which each grain becomes surrounded by a thin film of water. This configuration gives quicksand and other liquefied sediments a spongy texture similar to the consistency of a fluid. Objects that are engulfed in quicksand will sink to the level at which the weight of the object equals the displaced weight of the sand-water mixture and the object “floats” according to Archimedes' principle.

The so-called fast clays or marine clays, also known in Canada as Leda clays or quick clays, are a particular type of extremely sensitive clay, which when disturbed has the tendency to change its state from a relatively rigid one to a liquid state. At rest, fast clays look like a hydrosaturated gel. However, if you take a block of clay and hit it, it instantly takes on the constitution of a fluid, through a process known as spontaneous liquefaction. Fast clays behave this way because, although they are solid, they have a very high water content, which can be up to 80%. Clay retains a solid structure despite its high water content because the surface tension of water holds clay "flakes" together in a delicate structure. When the structure is broken by a blow, the clay changes its state and transforms into a fluid.

Fast clays are generally found in regions located in the northern hemisphere in countries such as Russia, Canada, Alaska in the United States, Norway, Sweden, and Finland, all areas that were covered by glaciers during the Pleistocene.

Fast-moving clays have been the underlying cause of many deadly landslides. In Canada alone they have been associated with more than 250 identified earthworks. Some of them are old and could have been confused with earthquakes.[10]​.

Submarine landslides are turbidity currents and consist of the movement of saturated sediments by water that flows into the deep sea. An example of this phenomenon occurred during the 1929 Grand Banks Earthquake, which occurred on the continental shelf near the coast of Newfoundland. Within minutes of the event, several submarine cables began to break in sequence, at increasingly distant points along the slope, and moving away from the epicenter. In total twelve cables snapped in a total of 28 locations. The exact times and locations at which each break occurred were precisely determined. The researchers suggested that a submarine landslide or turbidity current of sediments saturated by water that moved at a speed of 100 km/h (kilometers per hour) and propagated down the continental shelf along a route of 600 km, breaking the cables in its path.[11]​.

Liquefaction can cause damage to structures in several ways. Buildings whose foundations are directly in the liquefying sand experience a sudden loss of support, resulting in drastic (absolute settlement) and irregular settlement (differential settlement) of the building. Liquefaction causes uneven settlements in the liquefied area and this can damage buildings and break underground utility cables where differential settlements are large. Water and gas distribution pipes and other pipelines can float and move to the surface. Sand mounds can erupt into buildings through utility connections, allowing water to enter and damage the structure or its electrical systems. Soil liquefaction can also cause platform collapses. Environmental soil reclamation areas (landfills) are prone to liquefaction because many are reclaimed with hydraulic fill, and often sit on soft soils that can amplify shaking from earthquakes. Soil liquefaction was a major factor in the destruction of the San Francisco Marina District during the 1989 Loma Prieta earthquake.

Mitigating potential damage due to liquefaction is part of the field of geotechnical engineering.

• - Atterberg limits.

• - Solifluction.

• - Thixotropy.

• - Mud volcano.

• - Earthquake.

• - Tsunami.

• - Soil liquefaction.

• - Harbor Island liquefaction, one of the few situations where a seismologist has been able to witness an earthquake-induced liquefaction event in person.