Highway Research Record

III. GEOTECHNICAL ENGINEERING
COMPLETED PROJECTS
Sinking of Road at km 209.170 on Aizawl – Lunglei Highway (NH-54) in Mizoram

Duration: January 2003 to December 2004
Central Road Research Institute, New Delhi (R)

Present Status
Border Roads Organisation offered the opportunity to CRRI to carry out detailed investigations of the landslide affected area at km.209.170 on NH-54 in Mizoram. At this location, sinking as well as sliding had affected the hill slope. Failure of hill slopes at various locations in the down hill region further aggravate the problem. Detailed investigations of the entire affected hill slope was carried out to understand the causes and mechanism of failure of the hill slope so as to suggest suitable remedial measures to improve the slope stability.

Findings / Conclusions
Failure mechanism of the hill slope was predicted by carrying out detailed engineering geological studies of the entire hill slope area. Overall failure mechanism has been predicted by using stereonet diagram. Nature of behavior and safety factor of the debris materials resting on different probable failure planes at different depths were determined with the help of structural geological properties of the rock formation in the area. The predictions of depth of failure plane are quite difficult in this area because of high influence of past tectonic activity in the rock formation. Continuous monitoring will be needed after the implementation of remedial measures.
The studies predicted the recurrence of slope instability problem even after the implementation of remedial measures. Considering the probability of recurrence of failure, three alternate bye passes have also been suggested for the purpose of emergency use especially during heavy monsoon.

Limitations
Non availability of contour map of landslide affected area and difficult terrain conditions.

Recommendation
On the basis of investigation of the entire hill slope area different types of remedial measures were suggested on the plan such as sealing of cracks like plugging / filling and sealing of pot hole type feature and tension cracks; provision of various types of drainage including surface, subsurface and their combination etc.; retaining structures including heavy as well as light retaining structures; ground improvement by erosion control, lime column installation techniques and compaction of loose debris mass.