Narayangarh-Muglin, a crucial highway connecting the terai with the valley in Nepal, faces frequent slope instability during the monsoon season. This road section, stretching from Chitwan's Ramnagar to Muglin Bazar, holds significant importance as it facilitates the transportation of over 90% of daily consumer goods, commodities, industrial raw materials, and fuel. Additionally, it plays a vital role in the country's export activities. Consequently, the day-to-day economy of the nation relies heavily on the uninterrupted functioning of this road.
This
36km road with chainage CH10-17, CH17-28, CH28-35 is highly affected due to
landslide every year. Places like Gaighat, Mauri
Khola, Ghumaune, Bhaludhunga, Jalabire, Char Kilo, Topekhola and Kalikhola are
among the highly vulnerable areas. According to Geo mechanical survey, the main
reason is due to geomorphology, geology, climate, human activities and their
combinations.
The
hills serve as an important sources of spring water and groundwater, with
natural drains existing within the rock masses. During the monsoon season, the
water level in these areas rises, leading to an increase in groundwater levels
and subsequent movements. This phenomenon is accompanied by the building-up of
pore-water pressure, caused by the presence of water in the pores of the rocks.
However, the implementation of well-designed retaining walls and gabion walls
along the section can effectively control these factors.
Other important factor is that the hills slope contains a lot of clay minerals
that swells up with the contact of water causing unstable slopes. Hence, torrential rain is a main triggering factor. Haphazard
slope cutting is another main reason.
Credit: Timilsina, Manita, and R. K. Dahal
The chainage CH10-17 are mostly dominated by debris slides/mud slides, CH 17-28 by several large scale landslides and CH upto 35 is characterized by rock toppling. Narayangarh-Muglin
road section passes through the Precambrian Lesser Himalayan rocks. Precambrian
means before the geologic age where modern atmosphere and continents were formed,
abundantly characterized by sedimentary rocks. The main rocks in these areas are mudstones, limestones, sandstones, slates, phyllites and quartzites. Quartzites and slates are prominent to rock toppling. A number of instabilities were present along different formations of geological time scale. Among them, Nourpul Formation has a greater number of instabilities. The indicated Jalbire Syncline(rock layers having downward curve) suffer from the toppling effect. However, they are less in southern limb. High dip angle (direction of flow of rain water) is observed from all sides of the syncline, in addition to the road cuts and river undercutting have created unstable and steep slope. Hence, the high attitude of foliation plane is also the reason. Further, the upper reach of the region is subjected to debris and lower one with debris fan making it prone to largescale landslides. Pore water pressure in the discontinuities further aids up in landslide in making. Also, the weathered rocks along the section are more susceptible to small triggering effects like vechicle movements. Furthermore, the section is divided into a number of thrust (major separating boundary breakage subjected to (faults, folds and discontinuities) where in-situ rock stresses, sheared zones and minor faults are present which aggravates landslides.
-Raj K.C.
.jpg)
0 Comments