Prof Vinod Lalljee, Soil scientist at the Faculty explains the cracks in Terre Rouge-Verdun link road

 

 
News on Sunday wants to know the reasons behind the cracks and breakup of the recently built Terre Rouge\Verdun link road at a cost of more than a billion rupees and which caused much concern to the general public. In this context, Dr Bhanooduth Lalljee, who holds a PhD in Soil Science, explains the causes. He was previously the Director of Consultancy and Contract Research at the University of Mauritius. He has more than 30 years of experience in teaching, research and consultancy in soil and environmental issues. He is currently the Head of the Department of Agriculture and Food Science at the Faculty of Agriculture, University of Mauritius.

We have seen a number of press reports these days about collapses and cracks in roads and buildings. What are the reasons?
It is important to note that most of these infrastructural damages are occurring on mountain slopes and in valleys. The explanation behind such events is quite technical and complex. I will try to simplify them as much as possible. In those regions, where the newly built roads are opening up, the top soils are of a very specific nature. They are known as Smectite clays. Smectite clays have very peculiar properties – one unit of this clay consists of a natural silica sheet between two natural alumina sheets. Such a structure attracts and retains water, which then causes the clay material to expand. There are various types of Smectite clays, some of which can expand up to a certain limit only (technically called Vermiculite clays), while others can undergo almost unlimited expansion (technically called Montmorillonite clays). Both these groups of clay exist in several regions of Mauritius, like in Vallee des Pretres, Vallee Pitot, Baie du Cap, Quatre Soeurs, Deux Freres, Champ de Mars, Montagne Longue, Valton….The soils are also known as Dark Magnesium Clays (DMC). They have a very large surface area and are highly plastic, for example, one gram of such a clay may occupy 800 m2! In addition, these clays have a very high charge, are very sticky when wet, and have an immense capacity to hold water. Anyone who has been to the Champs de Mars on a rainy day must have experienced the stickiness of the soil. That is why, when they are dry, they are shrunken and cracked, but when they get wet, they expand hugely, generating massive forces that can crack the most solid foundation of bridges, roads, buildings and other infrastructures.
 

One of the most overlooked ingredients in farming exists right beneath farmers’ feet—healthy, fertile soils.

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One of the most overlooked ingredients in farming exists right beneath farmers’ feet—healthy, fertile soils.

Unfortunately, this vital ingredient is being degraded and eroded at unprecedented rates across the world. According to the U.N. Food and Agriculture Organization (FAO), 25 percent of the planet’s land is highly degraded and only 10 percent is improving.

All continents are experiencing land degradation, and the loss of soil quality is not only an issue for farmers, but for all of us.

Deforestation, for example, is causing China's Loess Plateau to erode rapidly. Overgrazing of grassland in the Western United States is reducing soil depth and creating desertification. In India, overcutting trees and crops is reducing soil fertility and threatening wild medicinal plants. And farmland ploughed for commercial agriculture around the world exposes topsoil and increases erosion. In fact, Brazil loses 55 million tons of topsoil every year because of soybean production.

But agriculture doesn’t have to degrade soils—it is possible for food production to enrich the Earth, restore nutrients, conserve water, and prevent further erosion.