National Building Research Organisation

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Rock fall observed on 20-02-15 in between culverts 55/3 and 55/6 on 20-02-2015

Kandy Mahiyangana road (A026) is subjected to continuous disruptions due to rock falls. Apart from road closures, there is a constant threat to the safety of the road users due to unstable hanging rock boulders on the roadside hills. One such event was the massive rock fall occurred on 20^th February 2015 between culvert No 41/9 and 55/6 causing obstructions for transport for almost one day.

Realizing the need of ensuring safety of the road users through mitigating the rock falls, NBRO submitted a conceptual proposal for most vulnerable three locations along the Kandy Mahiyangana road (A026) to the RDA by recommending rock fall mitigation work done under World Bank funded Climate Resilience Improvement Project (CRIP) as a Design and Built Contract

Under this project, NBRO identified three most vulnerable locations for rock falling along Kandy Mahiyangana road and recommended five different types of countermeasures against rock falls after considering the site-specific geological and geomorphological conditions of these three locations.

NBRO Team headed by Director General, Eng. (Dr.) Asiri Karunawardena had a technical visit to monitor the ongoing construction work of the above rock falling sites on 29^th December 2020. One of these locations were a 100m road section between the culvert 41/9 and 41/10. The rocky cliff on the road-side in this area is steep and has horizontal and vertical cracks with hanging rock masses. For this site, NBRO recommended a Bisto fence to catch rock boulders detached from rock cliff and on slope.

Location 2 had two areas of concern. Area A has a 30m high vertical weathered bedrock facing the road. The proposed mitigation measure was to cover this rock with a rock net to protect road from potential rock falls. Area B, the other vulnerable area of the second location, has a 60 degree road-facing slope having a mix of exposed and vegetation-covered bedrock. Besides this unstable slope, there is a boulder fallen from a failure happened on 11^th September 2019. After a thorough investigation conducted by NBRO experts, a curtain net was proposed to this area.

Location 3 is the 115m long road section between culverts 55/3 and 55/6. There is a vertical rock cliff separated into blocks by joints and cracks. Removing these unstable rock pieces would disrupt the stability of the surrounding area and might lead to further rock fall events. Therefore, NBRO recommended a rope net to cover the whole rock outcrop along with wired rope fixes to hold the unstable rock fragments to its original position. In addition, unstable rocky particles in the area were to be fixed using rope hooking method.

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