Perennial landslides

By Nagaland Post | Publish Date: 8/5/2019 12:02:15 PM IST

 Even as Nagaland is struggling economically and with a plethora of projects and schemes aimed at the uplift of the socio-economy, the road conditions that impede free movement add to the problem. In an era where other states have four or six lane highways, Nagaland is unable to even have even an all-weather single-lane road. The four-lane road from Dimapur-Kohima Road ( from Km 123.840 to Km 138.775, Km 138.775 to Km 152.490 and Km 152.490 to Km 166.700) covering a total length of 42.48 Kms was approved at a cumulative cost of Rs 1199.11 crore. Of serious concern is the stretch between Kohima and Sechü, particularly the old KMC garbage dumping site. The soil on this particular stretch is unstable and perennially prone to landslides. This particular stretch including some near the unstable soil zone. The particular zone harbours several old landslides that can be better recognised by the proper interpretation of aerial photographs. Clay becomes the potential slip zone in an outcrop causing landslides. Almost every landslide has multiple causes. Slope movement occurs when forces acting down-slope (mainly due to gravity) exceed the strength of the earth materials that compose the slope. One method of tackling the problem is to take a proper aerial photo after which a detailed ground study can reveal further evidence of previous land movement. Having identified an existing landslide, active or latent, the road engineers can then determine whether avoidance is economically practicable; if the slide cannot be avoided the necessary investigation can be made to determine the extent and natural composition of the soil. The cost of controlling one preventable slipout or major landslide on a project will often more than offset the cost of a proper preliminary investigation on the entire project. The behaviour of landslides is mostly influenced by fluctuating water content and stresses in the unsaturated zone. One of the stresses in the unsaturated zone resulted from soil characteristics such as clay content. Methods used to address landslides include: covering the land with impermeable membranes in order to prevent water infiltration in the landslide; directing surface water sources away from the landslides; draining ground water streams away from the landslides and minimizing irrigation on the surface of the soil. The road engineers would be knowing about building better roads but on this issue, there is perhaps another dimension of exploring alternatives to either prevent, minimise or take a detour away from the area. Since the area is susceptible to landslides despite the efforts of previous builders (BRTF), perhaps the agency currently engaged in the four-lane work, the NHIDCL should also explore whether the particular stretch can be avoided by diverting it through another area. Unless something drastic is done to prevent landslide or to explore an alternative route, the four-lane highway will be subject to the dictates of weather. As the fate of the four-lane project between Kohima and Dimapur is likely to be tied with the behaviour of the soil in the particular zone, a greater effort is needed to study every aspect and in this regard there could be additional cost for addressing this problem. Therefore, no efforts should be spared to ensure that landslides do not negate the objective of the project.

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