Nicolas Truong
Supervisor: Luc Chouinard
McGill University, Department of Civil
Engineering and Applied Mechanics
Montreal, Canada
LIQUEFACTION MAP
of LAVAL
Introduction
Methodology
Montreal has been subject to many studies about
earthquakes, but Laval has almost no data on the
consequences of an earthquake and more specifically,
liquefaction. To remediate this situation, the goal of this
project is to create a map of the island of Laval where the
probabilities of liquefaction of any given area can be
calculated, for a certain magnitude of earthquake.
The HAZUS methodology, which was created by the
Department of Homeland Security of the US, was used to
create this map.
Background
Liquefaction occurs when earthquakes impose a cyclic
loading to the soil, forcing it to contract. In cases in which
the soil is saturated with water, and the water unable to
drain, the soil transfers normal stresses onto the water
pores. This results into a loss of the strength and stiffness of
the soil, or a liquefaction of the soil.
Liquefaction can be seen when the soil starts to crack and
boil. A manifestation of the phenomenon can also be
confirmed by mud spouts. Liquefaction can have great
consequences on buildings. Since the soil cannot support the
weight of the buildings, they sink into it as if in quick sand. A
good example of this would be buildings tilting after one of
the first earthquakes that drew attention on liquefaction in
Niigata, Japan in 1964.
From the equation, a grid map can be created, calculating the
probability of liquefaction.
This methodology gives an equation to calculate the
probability of liquefaction. The equation itself has four
variables: a conditional liquefaction probability, the
earthquake magnitude correction factor, the ground
correction factor and the proportion of map unit
susceptible to liquefaction.
P[Liquefactionsc]=
P[Liquefactionsc|PGA=a] . Pml / Km . Kw
The conditional liquefaction probability is found by found by
determining the age and type of sedimentary deposits which
composes the ground of Laval. Depending on this
susceptibility of liquefaction ranging from very low to very
high and on the peak horizontal ground acceleration, a value
can be given to the conditional liquefaction probability.
Results
The maps show that the sediments of Laval are mostly made
of alluvial fan and plain sediments or glacial tills. This gives the
soil a susceptibility of liquefaction ranging from none to low.
For an earthquake of magnitude 6, the highest probabilities
are around 3%, situated in the low liquefaction susceptibility
zones.
Since the above equation was designed for an earthquake
with a 7.5 magnitude, with a water depth of five feet, two
correction factors must be added in the formula using two
equations. Using the ground altitude and water altitude, the
water depth can be found and used to calculate a correction
factor.
Acknowledgement
Prof. Luc Chouinard
Dr. Philippe Rosset
Umma Tamima