Geologists suggest construction of gabion wall to prevent landslide in Majhigaon

IPR, GANGTOK, 3 JULY 2023 : After a geological inspection of Majhigaon (Jorethang) landslide by a team of geologists, the Sikkim Mines and Geology Department has suggested the construction of gabion walls along the damaged road section as a temporary measure so that the rate of the erosion by Rammam Khola can be minimized, especially during heavy rainfall. 

The entire slide area is located at N270 07.896’ latitudes E88016.774’ longitudes at an elevation of 325m amsl. The slide is located approximately 200 meters south of Green Lung Park along Circular road at Majhigaon, Jorethang, Namchi District (valley side). Further, the slide is located opposite to the confluence of Ramam khola and Rangit khola in the area The area is part of river terrace comprising of River Borne Material (RBM) deposits represented by boulders, cobbles, pebbles overlain by sandy soil overburden. The lithology of the area is sedimentary rock represented by dolomitic limestone with sandstone.

Due to the development of hairline cracks on the buildings located on the hill side of the road section, chances of severe damage and collapse cannot be ruled out in the immediate future, says a Press release issued by the Department.

Buildings located on the valley side, along with temporary shelters, should be kept at high alert and the occupants should be shifted to a safer location as the changed course of the river may cause damage, especially during heavy rainfall. The changed course of the river may erode the left bank comprising loosely compacted river bed mineral deposits. This is also a threat to the settlements in the valley side of the road section area. During the dry season, collection of the deposited flash flood materials would help retain the original course of Rammam Khola. 

dumping of muck along streams, river banks to be avoided which increases the volume of runoff during monsoon by several times and results in such flood situations in the downstream area.

The Department has suggested suggested to restore the road formation during the dry seasons so that the footing of the foundation of the wall of the road formation may be done on competent strata/bed rock in the area. Further, deep type foundations such as piling are suggested as a permanent mitigation measure followed by bank protection works with placement of big stone boulders.

According to the report, the main triggering factor behind the Majhigaon landslide was the cutting by the rivers Rangit and Rammam. A flash flood in Rammam Khola on June 28eroded the base of slope of the Circular Road formation. The course of Rammam Khola flow was diverted about 100 metres due to the accumulation of flash flood deposits on the mouth of Rammam, pushing river Rangit towards the left bank of the river.

The increase in the volume of water in Rammam Khola might have been due to bank erosion, slide or the dumping of construction muck materials along the catchment area. The road formation was built on loosely compacted filling materials which on interaction with high flashflood led to the sudden failure of the base of the road formation. About 20metres of road formation have been washed away. Cracks can be observed on the road formation and the buildings on the hill side of the slide.