III. GEOTECHNICAL ENGINEERING

A. COMPLETED PROJECTS
2. Investigation Instrumentation and Monitoring of Patalganga Landslide on NH-58, Uttaranchal (phase-I)
Duration

March 2002 to June 2005
(i) Central Road Research Institute, New Delhi (R)
(ii) Department of Science & Technology, New Delhi (S)

 

Present Status and Progress
Completed
 
Findings/ Conclusions
Morphometric statistical analysis of the profiles along the streams indicate that the sine values of the slope angle of all the profiles have been found to be more than 0.5 (critical values of the Crozier, 1973) in most of the cases suggesting instability. Furthermore the analysis of the profiles along the streams and the slope indicate that mostly the type of movement is slumps/flow, which coincides with the monitoring results during the investigation.

Rock sequence in the valleys dominated by dolomitic limestones and slates with quartzites and metabasics. Besides the bedded rocks, the basin has a huge thickness of quaternary sediments largely composed of assorted morainic and hill wash material probably of Late Pleistocene glacial origin. Two right lateral strike-slip faults namely the Patalganga fault, which follows the drainage course towards the basin mouth and Nauligwar fault, off setting obliquely to the Patalganga Fault near the confluence of Patalganga (Semkura nadi) and neo-Ganeshganga, have been mapped. A localised development of anticlinal (Semkura) structure, oriented at an angle to the N-S oriented second-generation anticline, is also mapped around confluence site. A majority of rose plots having consistent NW-SE maxima represents the release of strain to the right angle of the NW-SW (direction of maximum compressive stress).

The structural features recorded in the main slide body indicate a strong north-south extension. This resulted in E-W running dilational fracture having dilation from less than 8 cm to over 30 cm. Shear fractures wherein throw of 88 cm to more than 2.52 m has been observed, mostly run parallel to E-W; however oblique planes are also noticed with significant relative movement showing hanging wall as well as footwall collapse.

Slope movement monitoring through steel pedestals indicate that the slide has differential shallow slide movement .The movement ranges from 2 m to 13 m. Most of the movement vectors indicate dominant direction of sliding towards SW and WNW directions coinciding mainly with the main direction of general sliding along Patalganga valley.

 
Limitations

Detailed mapping of the slide areas and exploration for getting the realistic slope profile is needed for design of remedial measures. It is difficult to access some of the slide locations for detailed mapping/survey and also the subsoil exploration using bore log to know the subsoil strata.

 
Recommendations

Based on the study during the course of the project following recommendations are made:

• Some of the landslides identified inside the Patalganga valley partially damaged a few of the villages and still threatening their existence. It is recommended to take quick measures, so that further damage as well as the loss of life can be prevented as suggested in the report.

• Patalganga landslide which is situated at the mouth of the Patalganga watershed can block the river if a bigger magnitude of slide takes place and a tragedy, as appeared in 1970, can be repeated again, thus, after next monsoon, remedial measures should be implemented to avoid the landslide.