DAMAGES OBSERVED IN THE 2010 CONCEPCIÓN EARTHQUAKE RELATED TO SOIL PHENOMENA

Felipe Villalobos1, Efraín Ovando2, Manuel Mendoza3 andPaulo Oróstegui4

1 Lecturer, Dept. of Civil Engineering, Catholic University of Concepción, Chile, avillalobos@ucsc.cl2 Professor, Instituto de Ingeniería, UNAM, México, eovs@pumas.ii.unam.mx3 Professor, Instituto de Ingeniería, UNAM, México, mjm@pumas.ii.unam.mx4 Geotechnical Engineer, Constructora Lancuyen Ltda., Concepción, Chile, orostegui@lancuyen.cl

INTRODUCTION• Strong earthquake on 27/02/2010, Mw = 8.8,

3.34am (local time), 90 s of duration• Hypocentre100 km north of Concepción, 30 km

deep, extended approx. 450 km long and 150 km wide

• Slip estimated of around 10 m to 12 m• More than 300 aftershocks above 5 Richter and

more than 20 above 6 Richter• Measured max. accelerations in San Pedro de la

Paz between 0.5g and 0.6gBarrientos (2010)

Studied area• Important

metropolitan area of the country

• Around 1 million inhabitants

• High seismicity, previous destructive earthquakes (1570, 1657, 1730, 1751, 1835, 1939, 1960)

San Pedro de la Paz

Dichato

Penco

Hualpén

Bío Bío River

City move afteryear 1751

Concepción Bay

San Vicente Bay

GEOLOGY AND GEOTECHNICS OF THE GREAT CONCEPCIÓN

• Presence of a coastal mountain chain, the Ocean Pacific and the Bío Bío River 2 km wide

• Coastal plain with island hills, lakes, rivers and swamps• Complex conditions due to variety of soils and rock units• Metamorphic rocks, schist and phyllite (SE) in Andalué• Igneous rocks, tonalite, granite and granodiorite (Pzg) in

Chiguayante, Caracol hill, Penco, etc.• Sedimentary rocks, sandstones and siltstones (Ec) in

Lomas de San Andrés, Santa Sabina, Interportuariamotorway, Lenga, etc.

• Rocks are highly weathered, fine soil deposits are mostly of marine origin and fluvial transported sediments

Caracol

Lo P

equé

n

Anda

lué

San Pedro de la PazPzg

La Pólvora

Amarillo

Chepe

Bayona

San Ignacio school

toSanta Juana

Curves of equal period in Concepción centre Geology units (Gajardo 1981)

(Ramirez & Vivallos 2009)

COLLAPSED STRUCTURES

1

2

4

3

1 Alto Río apartment building, no observable soil failure. Weak structural line at ground floor failed

2 Silos, 1950 built row did not present damage, 1970 built row had broken bolts connecting steel shells to footing, no soil failure found

3 Old Bío Bío Bridge 1940, domino effect, decks falling and destroying piers, possible liquefaction, although foundation damage not observable

4 O’Higgings Tower, no soil failure found

Ground floor Alto Ríoaxis with few vertical resistant elements

Deep foundations, stiffness and continuity of foundations specially when there are in plan and in elevation eccentricities

Damage due to liquefaction• Presence of fine cohesionless materials in

saturated low lands• In San Pedro de la Paz liquefaction occurred in

originally wetland areas (Los Batros) without appropriate soil improvement or foundations

• San Ignacio School suffered liquefaction despite the use of geogrids and geotextiles with 3 m compacted sand

• Singular architecture, offset room with different roof height could not follow the soil and structure deformation due to weak connections

• Lack of confinement towards the swamp, it is suggested to extend compacted soil fill or build a retaining structure

San Ignacio School

detaching and rotating of offset part of the building

Santa Juana Road, restaurant settled due to ground displacement towards the river

sand found in the bottom of cracks

1 m

2 m

Santa Juana Road lateral spreading

• Lateral spreading along Santa Juana Road next to the Bío Bío River

• Reclaimed land made of silt and clay not well compacted used to avoid flooding

• Big open cracks parallel to the river damaging seriously structures, piping, etc.

• Reclaimed material slid over liquefied sand towards the river

a)

c)

b)

d)

Steel company harbour in San Vicente Bay

a) Pre-cast piled foundation of the wharf, 1945

b) Portal crane tilted due to derailing

c) Several pile caps broken in 1972 wharf extension (driven steel tubes concreted inside, plus annular concrete cover and bars)

d) View of 400 m long wharf

Advance state of corrosion

Foundations scoured by tsunami• After the earthquake a series of tsunami flooded

coastal towns• Dichato was one of the most devastated and

only a few houses were standing• Standing houses in front of the shore had their

foundations exposed • Tsunami strong current scoured footings

in cantilever

Conclusions and recommendations

• Failures and damages are not necessarily caused by only one reason

• There is a lack of available acceleration recordings in the most affected areas

• It is necessary to study possible amplification effects due to presence of soft soil layers

• Geology research is needed to determine deeper stratigraphy and the existence of faults

• Restrained drain conditions jeopardise well performance against excess pore water pressure increase

• A variety of soil improvement techniques and deeper foundations should be considered as possible solutions to avoid significant damages to structures

Thank you for your attentionSpot the collapsed building