Viaduct I Failure, Caracas – La Guaira Highway, Venezuela

Ali JabalameliYaút PeñaPattanun Chanpiwat

Introduction

Viaduct No.1 was completed in 1953. The main part of structure consist of three parallel arch ribs of a hollow

box type, with a hinge to hinge span of 152 m and a height of 70 m. The southern pile was founded on vertical concrete shafts and three

inclined concrete piles. The pilaster and the arch on the northern side were founded on a raft

foundation.

Behaviour of the southern slope 1953-1987

Landslide in 1974 that affected many low income houses.

In 1981 a landslide occurred in the upper part of the slope, located 250 m south of the Viaduct.

An asphalt bump formed along southern abutment on April 1987.

Geotechnical investigation, including photogeology, borings and slope instrumentation was carried out.

1974 Landslide

Photogeology

Aerial photographs carried out between 1936 and 1983 were carefully examinated.

Scarps, stepped topography and color tone contrast of the slope were evidence of an ancient , 500 m long landslide.

A meander in the channel of Tacagua creek at the bottom of the slide served as physiographic evidence of the slope movement.

Geology and exploratory borings (prior to 1987)

• Material of the slope: Colluvial material derived from ancient landslides.•Rock Mass: Limestones interfoliated with calcaroues mica schists, quartzites and some amphibolites.

• Main Geological Feature: East - West Fault. Considered geologically active and responsible for some earthquakes in central Venezuela.

•Strike Parallel to strike of slope.•Dip Direction 15-40° North

Colluvium

Limestones

Emergency works in 1987

•245 passive anchors. 1 3/8” diameter grouted bars. 30 – 36 m long. 3 m into rock.

•20 prestressed cable anchors.•Only constructed to divert the landslide thrust from the bridge.

•On both sides:

•On the south abutment:

•Opening of the expansion joints to reduce the positive bending moment on the northern side.

Geological Exploration 1987 - 1988: Observations

• Movement of rock blocks along foliation planes at low dips (10°-20°).

•Tectonic slickensides.•Local fault breccias.

Evidence of the intense tectonic history of the area.

•Fault Breccia 50 m wide in a direction parallel to the displacement vector of the landslide.

Two inclinometers revealed the presence of a well defined failure surface

Surface Movement Monitoring

A) 3 bench marks opposite side of valley

B) 15 control reference points on the surface

C) 56 control points on the deck

D) 4 control points on pilaster s and abutments

Instrumentation

Prediction of failure

Prediction based on* Fukuzono (1985 ) and Voight (1989a,b)*Ration between rate of soil movement & rate of arch

closingMethod*collect rate of soil movement (cm/month)*plot the invert of velocity against time (month/cm)

Effect of landslide thrust on Viaduct No. 1Why does it fail?

*Slope movement of reactive ancient landslide*Moving of Viaduct No.1 southern side increase distress in the structure*The structural geologic setting influence and rainfall infiltration*Structure is designed to resist compression stress not for tension forces

Cause

Action

*Replacement of northern concrete abutment and piers with steel trusses with rollers (allow to move freely )

*Replacement of original concrete rockers with steel struts (resist tension)

*Construction of a cable system placed in U shape grabbing between two piers ( support of transverse shear failure & releasing energy stored in the decks)

Series of Actions

August 2005 December 2005

Question ?

References

Salcedo, Daniel. "Behavior of a landslide prior to inducing a viaduct failure, Caracas-La Guaira highway, Venezuela." Engineering Geology. 109. (2009): 16-30. Print.