10-19-2021, 11:12 AM
What are the factors that can cause soil liquefaction at a site during earthquake shaking?
The factors that make a site vulnerable to liquefaction during strong earthquake shaking are:
(1) Soil stratum with poorly graded fine-grained cohesionless soil, like sand with most particles of same size,
(2) High ground water table, and
(3) Occurrence of an earthquake of large magnitude in the near vicinity of the site, and that too for a long duration.
When these conditions are met with, the solid soil suddenly becomes liquid soil. This is called soil liquefaction. In the liquid state, the Archimedes Principle comes into force – the weight of the liquid displaced by a body floating in a liquid is the weight of the floating body. This implies that when the said soil below a heavy object placed close to the ground surface or below a light object buried at large depths below ground surface, is shaken by an earthquake of large ground intensity for an extended period of time, the heavy object may sink and the light object is thrown upwards. Therefore, structures built on earth can sink, float, tilt or even collapse when soil underneath them liquefies. If the above factors are likely at a site, a competent Geotechnical Engineer should be consulted. She/He will examine the type of soil and the height of water table, and thereafter do the required calculations.
If the calculations show that liquefaction is expected at the site, two options are available, namely:
(1) Strengthen the soil underneath, and
(2) Adopt pile foundations, if feasible.
Both of these options can be expensive, and may not give satisfactory results, if the earthquake shaking exceeds the design value. Thus, in general, it
is best to choose sites that do not liquefy during strong earthquake shaking. Further, the said liquefaction hazard affects the potential for landslides.
Also, when undertaking seismic microzonation, both liquefaction potential of a site and landslide hazard at that site should be integrated, when arriving at the land use zoning. This aspect should be addressed by the Municipal Authority.
for more details
The factors that make a site vulnerable to liquefaction during strong earthquake shaking are:
(1) Soil stratum with poorly graded fine-grained cohesionless soil, like sand with most particles of same size,
(2) High ground water table, and
(3) Occurrence of an earthquake of large magnitude in the near vicinity of the site, and that too for a long duration.
When these conditions are met with, the solid soil suddenly becomes liquid soil. This is called soil liquefaction. In the liquid state, the Archimedes Principle comes into force – the weight of the liquid displaced by a body floating in a liquid is the weight of the floating body. This implies that when the said soil below a heavy object placed close to the ground surface or below a light object buried at large depths below ground surface, is shaken by an earthquake of large ground intensity for an extended period of time, the heavy object may sink and the light object is thrown upwards. Therefore, structures built on earth can sink, float, tilt or even collapse when soil underneath them liquefies. If the above factors are likely at a site, a competent Geotechnical Engineer should be consulted. She/He will examine the type of soil and the height of water table, and thereafter do the required calculations.
If the calculations show that liquefaction is expected at the site, two options are available, namely:
(1) Strengthen the soil underneath, and
(2) Adopt pile foundations, if feasible.
Both of these options can be expensive, and may not give satisfactory results, if the earthquake shaking exceeds the design value. Thus, in general, it
is best to choose sites that do not liquefy during strong earthquake shaking. Further, the said liquefaction hazard affects the potential for landslides.
Also, when undertaking seismic microzonation, both liquefaction potential of a site and landslide hazard at that site should be integrated, when arriving at the land use zoning. This aspect should be addressed by the Municipal Authority.
for more details
