Road subsidence at km. 104 Near Kud-Patnitop, Jammu and Kashmir, Prepared by
Pushpendra Kumar, Deputy Manager, Geology,
Rodic consultants Private Limited, RAMBAN-BANIHAL
Disclaimer: Any part of this report should not
be used, updated in any form without the prior permission of the Author.
This report included the following CONTENTS
1. Introduction
2. General Geology of the Site
3. Visually Inspection of Site and Problem observed
4. Proposal for Stabilization Measures
5.
Conclusion
1.Introduction: Cheneni to Patnitop highway passes through rough and steep terrain of lower Himalayas. The kud land slide location falls at 33°05´ 15.04”N and 75° 18´ 8.6”E at km 104 on Cheneni to Patnitop highway. Geologically the area falls under Muree structural belt of Lower Himalayas which is named on Muree, located in Pakistan. The area is tectonically very sensitive due to Muree and Panjal Thrust and very prone to slope failure during snow time and rainy season.
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| Subsidence at Jammu to Patnitop Highway, Lower Himalaya |
2.General
Geology: General Geology
of the area belongs to rocks of Lower Muree formation comprises a sequence of interbedded sandstone and
siltstone/claystone layers, Lower tertiary in age. The tectonic domain of this area is bounded by main
frontal thrust (MFT) in south and main boundary
thrust in north (MBT). Along the nallah, red clay stone is exposed which is
highly weathered on surface and much fined grained. The Rock exposures along
the nallah have dipped towards NE direction. The strike of rock unit is
sub-parallel to the nallah and road at this location.
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| Sequence of interbedded sandstone and siltstone/claystone |
This the Arial view of the site
which is prepared with the help of google map. The map shows the existing protection
works related to old slide. The main causes of this subsidence exactly decided after
details Geo technical investigation but at the site it seems that it is
triggered due to toe cutting of the slope by flooded water during monsoon.
 |
| Arial view of Site from Google Map |
3.Visually
Inspection of Site and Problem observed: The site have been visited on June 26,2018. It have been observed that
the area is under slope instability from long time and some protection measure
already adopted at this location as concrete retaining wall and Gabion Wiremesh
structure. The current subsidence is occurred due to Toe erosion/Scouring of
bed level in the nallah during rain. Due to toe erosion of side slope of the
nallah, the creep movement is triggered. Tilted tree at the slope is an
indication of slow mass movement at this location. It is also define the
lateral boundary of creeping area.
 |
| Rain Cut Below foundation Of RCC cladding wall |
Above photograph shows the toe cutting of existing wall due to flood water on bed level. It should be repaired
immediately to avoid further damage to the road.
Second problem is observed at existing Culvert and culvert return wall which are damaged badly due to erosion of exposed clay stone. Some
cracks are already noticed at floor and side wall of the existing culvert. So
it is immediately needs to be repaired without further delay.
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| Damaged Culvert and Guard wall |
Photograph shows the cracks which are
developed at floor and side wall of the culvert.
 |
| Cracks developed on the floor and wall |
4.Proposal for Stabilization
Measures: There is two
action are required immediately at site to escape further damage of road and
Culvert. First the culvert foundation needs to be repaired immediately
including supporting wall next to return wall. And second are the bed rock
investigation to know the exact sub surface strata and depth of failure plane
within creeping area.
After decided the creeping plane we can installed
micro pile to stop the creep movement within the existing strata.
On the other hand we should remove all loose
materials. The eroded bed level of nallah should be filled by boulders/Pebbles
with help of gabion wire mesh up to desired level and plug its top with lean
concrete to support the eroded toe of
the slope at creeping area. As well as toe of retaining wall should also be
repaired. The top of the gabion structure or boulder layer must be plug
perfectly with lean concrete to prevent the seepage/ingress of water within the
bedding strata. The Side wall throughout the nallah must be constructed to
proper channelize the water flow in desired direction.
5.Conclusion: It is concluded that the
subsidence on road is occurred due to toe cutting of the slope by rain. The
following measures should be required at this location-
- First the Cracks of culvert and retaining wall must be repaired without further delay.
- Cracks on the road should be filled with lean concrete without further delay.
- A Bore hole should be conducted at failure slope to know about subsurface strata and creeping plane.
- The eroded bed level should be retained up to desired level to support the slope base and toe of retaining wall.
- Side wall within the nallah should be constructed to proper channelized of water flow.
- Loose materials on the slope should be removed and geometry of the slope should be updated.
References:
•
IRC:78-2000, Standard Specification
and code of practice for road bridges
• IRC:SP:48-1998, Hill Road manuals
• Duncan C. Wyllie & Christopher W. Mah, Rock Slope Engineering
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