After the April 25, 2015 earthquake, a lot of people have realized a
very scary fact, a house can’t be made strong enough if the soil it
rests is not strong. One of the signs of weak soil is liquefaction
during earthquake. In the recent earthquake, we could observe
liquefaction in different places in Kathmandu, causing a number of
structure to settle and fail.
Liquefaction occurs when vibrations or water pressure within a mass of soil cause the soil particles to lose contact with one another. As a result, the soil behaves like a liquid, has an inability to support weight and can flow down very gentle slopes. This condition is usually temporary and is most often caused by an earthquake vibrating water-saturated fill or unconsolidated soil.
1) loose, granular sediment or fill
2) saturation by groundwater
3) strong shaking
After April 25 earthquake and after shocks that followed, water came
out of the ground in some places, sand and gravel also came out in some
places. These are the signs of liquefaction. This problem was most
pronounced in Gongabu area, Balaju, New Bus Park, Machapokhari, and
Goldhunga areas. In those areas, some buildings have tilted and others
have sunken in the ground. Water and sand had also come out of the
ground in Khumaltar area in Lalitpur and Kharipati area in Bhaktapur.
Other places of high liquefaction potential are the areas near rivers
like Balkhu, Manohara corridor, Bishnumati corridor, and Bagmati
corridor.
Similar liquefaction was observed in the 1934 earthquake. The following text is taken from the only official document written about the earthquake by Brahma Shumsher J B Rana.
When compared to the 1934 earthquake, less amount of liquefaction was
observed in the 2015 earthquake. Liquefaction is a directly correlated
to the duration of the shaking during earthquake.
In a report by Kathmandu Municipality and JAICA in 1998 to 2000, high probability of liquefaction was predicted.
Liquefaction occurs when vibrations or water pressure within a mass of soil cause the soil particles to lose contact with one another. As a result, the soil behaves like a liquid, has an inability to support weight and can flow down very gentle slopes. This condition is usually temporary and is most often caused by an earthquake vibrating water-saturated fill or unconsolidated soil.
Conditions that Cause Liquefaction
Liquefaction most often occurs when three conditions are met:1) loose, granular sediment or fill
2) saturation by groundwater
3) strong shaking
Similar liquefaction was observed in the 1934 earthquake. The following text is taken from the only official document written about the earthquake by Brahma Shumsher J B Rana.
In a report by Kathmandu Municipality and JAICA in 1998 to 2000, high probability of liquefaction was predicted.
Road Damage due to 25th April 2015 EQ in Nepal
Liquefaction in Hetuda due to 25th April 2015 EQ in Nepal
(photo credit: @razzulovely in Twitter)
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