Engineers' Worst Fear - When Earth Boils

Tarun Nongthombam *

Other than our naharols, which we all should be thankful; there is another which scares the living daylights out of engineers and that is when mother earth gets angry. This is because whatever they build, be it buildings or bridges, roads or railways, dams or dikes all stands on soil or earth. Where there is human settlement, it is generally safe to build. If there are problematic soils, engineers exercise maximum caution to make sure that the soil on which building stands is improved and stable. In Imphal, engineers with go with little more caution if he is asked to construct in places like Lamphel or areas which is swampy .You don't like the earth to move away when your building is ready, if that happens you can do very little but start all over again!

In Manipur landslide and rock fall are very common in our hills, which could also include the whole hillock movement resulting in destroying houses and roads. Recently, we have added mudslide, thanks to our nonstop cutting of trees and shifting cultivation.

Exhibit: -1 shows the mudslide in Keithelmanbi in Manipur, which resulted in NH-39 being affected and much property loss. This reminds people living in hills the need to maintain healthy natural environment.

Exhibit-1: Keithelmanbi mudslide, which was an ecological mishap.
Source: E- Pao Gallery

In Exhibit-2, what you see is a massive earth shift at the Yallourn coal mine in Australia. You can see a railway line and a road ripped apart by the landslide. In Landslide of this scale, there is very little an Engineer can do but sit and watch and save human lives.

Exhibit-2: Landside in Yallourn coal mine in Australia.
Source: -The Sun, UK

There is another phenomenon, which we know very little of and that is when the earth starts boiling or simply it is called as liquefaction. Soil or Earth is able to bear the load of any big building standing on it because of the cohesiveness or the friction between the soil particles. The moment you separate the particles, its bearing capacity vanishes and becomes similar to quicksand. It is on this principle liquefaction works.

Exhibit: 3 Earthquake induced liquefaction resulting in sand blows
Source-M. Tuttle and Associates

Exhibit-3 shows earthquake induced liquefaction. The earthquake shaking generates pressure in the water between the soil particles and causes it to flow up rapidly to the ground surface carrying soil particles along with it. You can see in the figure soil is deposited in the form of sand volcanoes or sand boils. This phenomenon completely makes the soil under building ineffective in bearing the load and thus resulting in loss of property and human lives.

What about an important question which we want to know by now? Are we in Manipur likely to experience this type of severe earth conditions? Answer to this is probably not. We have had many earthquakes in the past, some even of big magnitude and never heard of any of those quicksand conditions. Our soil, which is generally clay dominant, helps in maintaining the cohesiveness, which in loose sandy environment could be difficult.

Thanks to the wonderful reporting on liquefaction in Christchurch by Rakhal Ebeli of Ten News. Click the link below or you might have to paste it to your browser address bar to see what really liquefaction is. Don't forget to put on your speaker.

- Source: www.tennews.com.au -