|
|
Liquefaction Resistant
Structures
|
A structure that possesses ductility, has the
ability to accommodate large deformations, adjustable supports for correction of
differential settlements, and having foundation design that can span soft spots can
decrease the the amount of damage a structure may suffer in case of liquefaction
(Committee on Earthquake
Engineering, NRC, 1985). To achieve these features in a building
there are various aspects to consider.
|
Shallow foundation
Aspects
It is important that all
foundation elements in a shallow foundation is tied together to make the
foundation move or settle uniformly, thus decreasing the amount of shear
forces induced in the structural elements resting upon the foundation. The photo
to the right shows a house wall under construction in Kobe, Japan. The
well-reinforced perimeter and interior wall footings
(KG) are tied together to enable
them to bridge over areas of local settlement and provide better resistance against
soil movements. A stiff foundation mat (below) is a good type of shallow foundation,
which can transfer loads from locally liquefied zones to adjacent stronger ground.
|
|
Buried utilities, such as sewage and water pipes, should have
ductile connections to the structure to accommodate the large movements and settlements
that can occur due to liquefaction. The pipes in the photo connected the two
buildings in a straight line before the earthquake
(KG).
|
Deep foundation
Aspects
Liquefaction can cause
large lateral loads on pile foundations. Piles driven through a weak,
potentially liquefiable, soil layer to a stronger layer not only have to
carry vertical loads from the superstructure, but must also be able to resist
horizontal loads and bending moments induced
by lateral movements
if the weak layer liquefies. Sufficient resistance can be achieved by piles of
larger dimensions and/or more reinforcement. It is important that the piles are
connected to the cap in a ductile manner that allows some rotation to occur without a
failure of the connection. If the pile connections fail, the cap cannot resist
overturning moments from the superstructure by developing vertical loads in the piles
(see figure below).
|
|
|