Effects of Soil On Ground Motion

EFFECTS OF
SOIL ON
GROUND
MOTION
LIQUEFACTI
ON
LIQUEFACTION
Soil liquefaction, also called

earthquake liquefaction, ground
failure or loss of strength that
causes otherwise solid soil to
behave temporarily as a viscous
liquid.
LIQUEFACTION
The phenomenon occurs in

water-saturated unconsolidated
soils affected by seismic S waves
(secondary waves), which cause
ground vibrations during
earthquakes.
LIQUEFACTION
Buildings constructed on loose soil
pitch and tilt easily when
liquefaction occurs, since the soil
no longer supports the structures’
foundations.
LIQUEFACTION
When loose saturated sands, silts,
or gravel are shaken, the material
consolidates, reducing the porosity and
increasing pore water pressure. The
ground settles, often unevenly, tilting
and toppling structures that were
formerly supported by the soil.
LIQUEFACTION
For example, the 1964

Niigata earthquake caused
widespread liquefaction in
Niigata, Japan which destroyed
many buildings.
LIQUEFACTION
Partial liquefaction of the soil in

Adapazari during the 1999
Kocaeli, Turkey, earthquake
caused several buildings to settle or
fall over.
LIQUEFACTION
During the 1995 Kobe, Japan,

earthquake, increased pore
pressure pushed the quay wall
near the west end of the bridge
toward the river, allowing the
soil and westernmost pier (Pier
134) to move 1 m eastward.
LIQUEFACTION
San Francisco earthquake of

1906: Soil Liquefaction
Row houses in San Francisco,

California, tilted by soil liquefaction
after the San Francisco earthquake
of 1906.
LIQUEFACTION
1989 Loma Prieta, California

earthquake, liquefaction of the soils
and debris used to fill in a lagoon
caused major subsidence,
fracturing, and horizontal sliding of
the ground surface in the Marina
district in San Francisco.
CAUSES OF
LIQUEFACTI
ON
CAUSES OF LIQUEFACTION
To understand liquefaction, it is
important to recognize the
conditions that exist in a soil deposit
before an earthquake. A soil deposit
consists of an assemblage of
individual soil particles.
If we look closely at these particles,
we can see that each particle is in
contact with a number of neighboring
particles. The weight of the overlying soil
particles produce contact forces between
the particles - these forces hold individual
particles in place and give the soil its
strength.
(a) Soil grains in a soil deposit. The height of the blue column to the right
represents the level of porewater pressure in the soil.
(b) The length of the arrows represent the size of the contact forces between
individual soil grains. The contact forces are large when the porewater pressure is
low.
Liquefaction occurs when the
structure of a loose, saturated sand
breaks down due to some rapidly applied
loading.
As the structure breaks down, the
loosely-packed individual soil particles
attempt to move into a denser
configuration. In an earthquake,
however, there is not enough time for
the water in the pores of the soil to be
squeezed out.
Instead, the water is "trapped" and
prevents the soil particles from moving
closer together. This is accompanied by
an increase in water pressure which
reduces the contact forces between the
individual soil particles, thereby softening
and weakening the soil deposit.
Observe how small the contact forces are because of the high water
pressure. In an extreme case, the porewater pressure may become so high
that many of the soil particles lose contact with each other. In such cases,
the soil will have very little strength, and will behave more like a liquid than
a solid - hence, the name "liquefaction".
EFFECTS OF
LIQUEFACTI
ON
EFFECTS OF LIQUEFACTION
1. Building failure
- In soil liquefaction, the bearing
capacity of soil is being reduced.
- The combination of liquefaction and
earthquake forces causes the buildings to
lose their equilibrium. This causes
buildings on affected land to sink
into the ground.These dangers do not
provide sufficient time for evacuation, Picture: Building failure due to liquefaction after the
resulting in a catastrophic loss of life and Niigata earthquake (1964)
property.
2. Foundation crack
- The uneven settlement of a raft
foundation may damage the
foundation.
- A cracked foundation fails to
distribute the load evenly on the
ground.
- Liquefaction can also cause the Picture: Foundation crack caused by liquefaction
overlying ground to spread and crack
as the liquid sediment forces its way
to the surface.
3. Damage to pile foundation
- The pile foundation acts as a
column that transfers the
structural load to the deeper
strata. The liquefied soil exerts
lateral stress to the pile that
causes buckling. The pile may Picture: Damage to pile foundations from ground liquefaction
distort, and its load-carrying

capacity decreases.
4. Retaining wall failure

- A retaining wall fails by sliding,
tilting, or overturning. The
liquefied soil exerts an
additional force on the retaining
wall that causes it to fail.
Picture: Building wall cracks caused by liquefaction

5. Slope erosion
- Liquefaction destroys the soil
slopes.
- The soil flows down and
settles on the flat ground.
The sliding soil causes a large
fissure formation on the slopes.
Picture: Slope erosion caused by liquefaction
6. Damage to utilities
- Utilities like water lines, sewers,
gas lines, etc., are disturbed due
to liquefaction. The sewer
manholes vertically uplift in the
liquefaction phenomenon.
Picture: Soil liquefaction allowed this sewer to float
upward and breach the pavement during the 2004 Chūetsu
earthquake
7. Sand Boiling
- When liquefaction happens under a
tightly compacted crust, the water
pressure beneath the surface
causes the water to escape in the
form of a bubble. These result in the
formation of boiling water.
Picture: Sand boils due to liquefaction during the 2011
Christchurch earthquake.
THANK YOU
FOR LISTENING!
REFERENCES:
https://dailycivil.com/soil-liquefaction-causes-effects-and-types/
https://depts.washington.edu/liquefy/html/why/why1.html

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EFFECTS OF

Soil liquefaction, also called

The phenomenon occurs in

For example, the 1964

Partial liquefaction of the soil in

During the 1995 Kobe, Japan,

San Francisco earthquake of

Row houses in San Francisco,

1989 Loma Prieta, California

distort, and its load-carrying

4. Retaining wall failure

Picture: Building wall cracks caused by liquefaction

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