Tokyo, 13 May 2015 Preliminary damage survey report on 2015 Nepal Gorkha Earthquake Pokhrel R.M., Chiaro G., Kiyota T., Katagiri T. Institute of Industrial Science, University of Tokyo, Japan Goda K. Bristol University, UK Sharma K. PhD Student, Alberta University, Canada
Advance Party of Japanese Investigation Team for the 2015 Nepal Earthquake Disaster JSCE: Japanese Society of Civil Engineers JGS: Japanese Geotechnical Society ATC3, ISSMGE: Asian Technical Committee, Int. Society of Soil&Geotech. Eng. Survey team
Damage survey Day 1 (5/1): Kathmandu city (Heritage area) Day 2 (5/2): Trishuli & Melamchi Day 3 (5/3): Kathmandu city (Structural & Geotechnical damage) Day 4 (5/4): Epicenter area (Baluwa) Day 5 (5/5): Pokhara valley Pokhara Baluwa Mw=6.6 (4/25) Mw=7.8 (4/25) Trisuli Mw=6.7 (4/26) Melamchi Kathmandu 3
1. Introduction Geology of Nepal Mw=7.8 Epicenter 4
1.1. Geology of Kathmandu valley and surroundings (Source: Department of Mines and Geology (DMG, 1998) 5
1.2. Geology of Kathmandu Valley Bed rock Soft soil Bed rock Schematic geologic cross-section of the Kathmandu basin sediments during the late Pleistocene (Sakai et al., 2002) 6
1.3. Morphology of Kathmandu Valley Kathmandu valley is an intermountain basin (600 sq km) filled by lacustrine deposits derived from the surrounding mountains Kathmandu Valley The elevation of the Kathmandu valley varies from 1270m to 1400m 7
2. Kathmandu city F E A. Heritage buildings B. Highway damage C. Liquefaction D. Road failure E. & F. Building collapse A D B C Distance from epiceter: 78 km from Mw=7.8 (4/25) 71 km form Mw=6.6 (4/25) 65 km from Mw=6.7 (4/26) Structural issues Geotechnical issues 8
2.1. Heritage buildings collapse (location A) 9
Basantapur Tower Before Maju Dewal Before After After Most of the temples are more than 500 years old 10
Heritage building collapsed but no damage to nearby RC building 11
2.2 City center 12
2.3. Building collapse (North-west of Kathmandu) Silt and sand Alluvial deposit Clay F E Silt and sand Study area D B 13
Along the Ring Road (location F) Local ground motion amplification and/or loss of bearing capacity, poor quality of non-engineered RC buildings 14
Study area (location E) Alluvial soil Alluvial soil (Holocene) Pleistocene soil Pleistocene deposit RING ROAD At least 28 buildings totally collapsed or should be demolished Most heavily damaged buildings are located on the alluvial soil deposit 15
2.4. Damage along Araniko Highway (location B) LOKANTHALI Ground fissures Tilted buildings A A Road damage Kathmandu side Tilted buildings Bhaktapur side 16
Embankment settlement Photo source: Google map May 2013 Before earthquake During survey Bhaktapur side Kathmandu side Extension completed in 2011 Just after earthquake Photo source: wordpress.com 17
2 Reinforced retaining wall Southern side Kathmandu side Northern side Kathmandu side Reinforced retaining wall Masonry gravity retaining wall Sloped ground Sloped ground Bhaktapur side Bhaktapur side 18
Section A-A A A Settlement Temporary filling Retaining wall cracks and fissures Temporary filling 19
Retaining walls cracks 20
Road pavement failure Main road Bus stop area 40-60cm Damage due to poor compaction of the filling soil 21
Ground failure nearby embankment 60 cm 120 cm 80 cm 22
Ground-failure-induced tilting and subsidence of buildings 70 cm 23
2.5. Soil liquefaction (location C) IMADOL Sand boiling Karmanasa river 90 m No damage induced to surrounding buildings Water table very low during dry season 24
2.6. Road failure (location D) AIRPORT 25
3. Trishuli & Melamchi Trishuli Team A Melamchi Kathmandu Team B 26
On the way to Trishuli Rock fall Shallow landslide Cracks on the road 27
Villages encountered: Ranipauwa Nipala Battar (Bidur) Gerkhu Ranipauwa > 80% houses damaged Gerkhu Battar 28
Damage to Trishuli earth dam Liquefaction Cracks River bed Hydro-power plant Trisuli River 29
Upstream Embankment road Downstream river Compacted gravelly soil 30
Soil liquefaction Liquefaction-induced lateral spreading 29 m Sand boiling 52 m 31
On the way to Melamchi 90 km from Mw=7.8 (4/25) 40 km from Mw=6.7 (4/26) Melamchi Kathmandu 32
14 Melamchi 37 69 33
61 Shallow landslide 5 Retaining wall failure 4 36 Shallow landslide Unstable boulders 34
4. Epicenter area Baluwa Barpak Epicenter Mw=7.8 (USGS) Kathmandu 35
1 2 3 Typical damaged building Landslide Weathered rock 8 9 10 Weathered rock Boulder of banded gneiss Weathered limestone 36
Cut slope 37
Landslides 38
Landslide #1 45m 58m 62m Looking from the road down to the river 39
Landslide #2 33m 71m 38m 40
Landslide #3 To Barpak (5 km) Jholunge Blocking access to Barpak village Darauda Khola River Baluwa 41
70m 107m 20m 300m 42
Very unstable!!! 43
5. Pokhara valley Marginal damage only to few houses Distance from epiceter: 71 km from Mw=7.8 (4/25) 86 km from Mw=6.6 (4/25) 205 km from Mw=6.7 (4/26) 44
Armala area - sinkhole Muddy water was observed after the earthquake 45
No new sinkholes and no change in sinkholes size Nov 2014 May 2015 46
6. Bridges Trishuli Kathmandu Melamchi Baluwa (Epicenter) 47
7. Summary Survey damage was conducted in Kathmandu city, Trishuli, Melamchi, Epicenter area and Pokhara city In Kathmandu city, most of structural damage was observed in the city center (heritage buildings and old masonry houses) and in the north-west area along the ring road (non-engineered RC building, loss of bearing capacity of soft soils) Ground failure induced the settlement of an embankment along the Abariko highway, sinking and tiltin f a number of RC buildings In Trishuli, liquefaction was observed. However, most significantly, cracks along the upstream side of the earth dam are of concern. 48
In Melamchi, damage to houses and landslides were widely observed (close to Mw=6.7 epicenter of 4/26) In the epicenter area, many villages were completely devastated and a number of landslides could be observed In Pokhara valley, only minor damage to houses were observed. In Armala area, no new sinkholes were formed No damage to bridges was observed during the survey 49
8. Concluding remarks House inspection should be done as early as possible Inspection of the landslide area is also important because damaged rocks as well as large cracks still remain on the slope. Survived slopes could have further damage (during rainy season) We couldn t reach the mountain area where a natural landslide dam is reported. Need helicopter or a long trekking The damage to the roads and buildings in the Kathmandu valley would be linked with ground condition Damage distribution in the fault area corresponds well with the characteristics of the earthquake (i.e. heavy damage in the east area while no damage in east (and south) area from the epicenter 50
Thank you very much for your kind attention! Acknowledgement 51