Highway Research Record

III. GEOTECHNICAL ENGINEERING
COMPLETED PROJECTS
Investigation and Recommendation of Suitable Corrective Measures for Prevention of Road Cut Slopes along Access Road from Naihar Village to Bridge point, Koldam, H.P.

Duration: May 2004 to September 2004
Central Road Research Institute, New Delhi (R)

Present Status and Progress
The National Thermal Power Corporation (NTPC) awarded this project to CRRI as a consultancy project, to investigate the approach road to dam site, starting from Naihar village to bridge point (nearer to the dam site). There are two critical areas namely; at bridge point and another one at a location for proposed dumping fill area near Naihar village, which are facing slope stability problem. The detailed studies have been carried out in field as well as in laboratory and finally remedial measures were suggested for two critical sites. Remedial measures were also suggested location wise for over all improvement of the approach road. The investigations have been completed and final report suggesting measures for slope stability has been submitted to NTPC.

Findings / Conclusions
As a part of the dam construction, the dam authority has constructed an approach road roughly 1.5 km long from Naihar village to bridge point connecting the dam site. This road has been experiencing slope failures and erosion problems. Another problem was to dump the excavated waste material at a suitable location without disturbing the slope stability. Moreover, part of the dumped area can be used as a part of the road. Studies were carried out to design suitable corrective measures for prevention of road cut slopes along approach road from Naihar village to bridge point at Koldam.

Remedial Measures
A Reinforced Earth (RE) retaining wall is suggested to be constructed in place of the 5 m masonry wall at the location of proposed dump area. The RE wall of maximum 14 m suggested height will be able to absorb more filling material and also can withstand more pressure from within. The backfill behind the RE wall should be placed in layers compacting as per MORTH specifications

General Remedial Measures
During the field investigation, it is found that some remedial measures are required to improve the over all slope conditions and the stability all along the dam site approach road. These remedial measures are discussed as:
1. The stream is to be lined at least up to 15m from the road head so that stream bed should not be eroded further near the     valley side.
2. Catch pits are required wherever extra materials come along streams to avoid damage and chocking of the drains and     culvert.
3. On the base of slope gradient on road it was found that a few culverts are also required in the study area.
4. Road side lined drains are required to carry the discharge and to avoid the erosion and infiltration of water into the slope.
5. Catch water lined drains are required uphill side to intercept the surface water seeping into the hill slope.
6. 1-1.5m high stone masonry wall is required all throughout the road with chain link mesh on its top.
7. Cavities/depression on uphill side should be filled with locally available material and compacted properly to avoid infiltration of     surface water from them.
8. The over hang portions either should be supported with gabion wall or removed.
9. Any damage or choking of the culverts, catch pits, road side drains should be repaired or filled material removed immediately.
10. Slope dressing is required at places.
11. Earth fill retaining wall should have back fill material having good drainage characteristics along with weep holes.
12. Tension cracks should be sealed.
13. All slide prone areas should be inspected periodically to check any sign of erosion or movement, if there is any movement       or erosion for effective measures to be adopted immediately without any delay.

Limitations
The area referred from Naihar village to Bridge point is a part of the river terrace. The top of the terrace used for terrace cultivation. Many villages are established on top of it. The discharge of water from the houses and the water used for the agriculture purpose, is not properly chanelized and seeps into the slope.