Land Slide Control Measures: A Case Study Of Jumja Land

Slide In Western Bhutan

S K Pradhan,Border Roads Organisation,New Delhi

Land Slide Control Measures In BRO

JUMJA SLIDE

PHUENTSHOLING-THIMPHU ROAD IN BHUTAN

JUMJA

AH-48

ANOTHER VIEW OF JUMJA LSIDE

JUMJA SLIDE • This slide is located at Km 41.00 on

Phuentsholing- Thimpu road in Bhutan.

• This is over 50 years old and has been regularly damaging the road stretch.

• This slide is basically a rock slide due to planar failure attributed to adverse jointing pattern.

• The slide has totally denuded the vegetative cover of the hill right from the crown to the toe.

• Due to this, during monsoons the slide tends to slip down because of unstable slope along the wedge.

• Presently, most of the slide comprises of overburden material consisting of huge boulders mixed with soil.

Jumja slide

jumja

S/No Year Damages occurred in Jumja

Restoration work carried out 

1 2005-06 Fmn Sinking Km 41.30 to 41.60 (300x2.60x2.10)

Fmn cutting SMB 300x2.60x2.30 mtr

 

Km 41.60 to 41.75 (150x2.60x3.00)

Fmn cutting HR 150x2.60x4.20 mtr

 

2 2004-05 Fmn Sinking Km 41.370 to 41.550

Km 41.370 to 41.550 Sausage carpeting 180 mtr x 5.50 mtr

 

Km 41.55 to 41.650 Km 41.550 to 41.650 Sausage carpeting 100x11 mtr

 

Fmn damaged Km 41.730 20x3.10 mtr

Sausage T/wall 20x5 mtrSausage R/wall 24x6 mtr

 

3 2003-04 NIL

4 2002-2003 Fmn Breached at Km 41.70 of size 20x3.50 mtr

S/Wall 20x12 mtr

5 2001-02 Fmn Breached at Km 41.55 of size 24x3.00 mtr

C/R/Wall 24x6 mtrS/B/Wall 70x3 mtr

6 2000-01 Fmn Washed away from Km 41.400 to 41.800 400x6 mtr

Fmn cuttings 400 mtrGSB 15 Cm D/Layer 400 mtrS/R/Wall 75x3 mtr (in 3 Steps)S/R/Wall 75x4 mtr (in 4 Steps)S/B/Wall 50x2 mtr (in 2 Steps)

Detailed Investigation for Long Term Solution.

Reccomndations by CRRI

• The boulders from the crown rocky bed falls onto the Western part of the slide area and also rolls onto the road stretch. Scaling of boulders from this zone should be carried out. Only the boulders resting on the surface may be removed.

Reccomndations by CRRI

• The highly fractured and fragmented rock slope should be regraded/restructured and subsequently measures like shotcreting/rock bolting may be implemented to stabilize the exposed rocks.

Reccomndations by CRRI

• The debris mass above road level has acquired angle of repose, however, the non cohesive material in the soil-boulder matrix is expected to be eroded away due to surface runoff. This material has basically developed from the metamorphic gnessic rocks and has affinity with water. Benching of slope using gabion walls and suitable drainage measures on each bench need to be adopted in this zone.

Reccomndations by CRRI

• The boulders resting on the surface of slope may be removed, however, no querrying should be allowed from this zone as this will make cavities as well as loosen the debris material leading to further erosion and debris flows

Reccomndations by CRRI

• The downhill slope on the extreme West side has exposed rock which may get toppled. Plugging of this zone by suitable retaining structures may be carried out.

Reccomndations by CRRI

• The debris mass on the uphill of road level has acquired angle of repose, however, the non cohesive material in the soil-boulder matrix is expected to be eroded away due to accumulated surface runoff. Flexible boulder fencing, benching of slope in reinforced gabion walls and provision of rock collection trench between the slope and the fence must be made .

Reccomndations by CRRI

• The downhill slope on the extreme left has a large natural drain which has been experiencing channel erosion leading to damages on the road stretch. The rocks on the side of the channel comprises of transported boulders or debris mass. The channel should be provided check dams at a few locations. Ballie check dam construction with horizontal reinforcement and pre anchoring would be of help as there hardly any location in the gulley to support the foundation of check dams..

Reccomndations by CRRI

• Scaling of boulders from left flank i.e. the eastern side of the slide, which is presently affected by rockfall problem from the highly fractured and fragmented rock slope. Collection pit should be made just below the rocky zone on the Western zone and also at the road level, wherever possible

Reccomndations by CRRI

• Considering the state of land slide and other conditions, it is suggested to explore the possibility of construction of a tunnel to by pass the slide area.

OPTIONS

• To stabilise the slope with elaborate protective works.

• To explore possiblity of a tunnel

Scope of works

• Rock-bolting (14,060 Nos)

• Gabion-wall in 3 steps, 131 m length

• Gabion-wall in 3 steps, 126 m length

• Water-chute 2m wide 25m both sides

• Water-chute 2m wide 30m both sides

• Lined derain 645 m length

• 2m wide benching 2 Nos 131m length

Scope of works

• 2m wide benching 1 No, 126m length

• Gabion Wall 16m in 4 steps

• Collection pits

• 4 Nos causeway 10 mtr length

• Check dam with bally 8X3m

• Shotcreting 50mm thick with 50mmX50mm wire mesh.

Conclusion

• Land slide areas along major highways pose real logistic problems inso far as they tend to affect the economy of the region in more than one ways. BRO has been battling with many such areas which are ever so prone to landslide in states of Sikkim,Himachal Pradaesh ,J&K and whole of North East.We have been able to reasonably contain slide zones by attending to basics like arresting toe-erosion, improving drianage characterstics etc. However there is a need to undertake a multi-agency in-depth sutdy of chronic cases like Jumja for an effective and expeditious solution of the issues.