Nothing seems more down-to-Earth than dirt, but scientists are going to space
to understand how earthquakes and related strains and stresses disturb soil
and sand.

When Space Shuttle Columbia lifts off in January, it will carry the Mechanics
of Granular Materials (MGM) experiment, which studies soil behavior under conditions
that cannot be duplicated on Earth — the microgravity, or low-gravity created
as the Shuttle orbits Earth.

Results from this granular mechanics research can lead to improved
foundations for buildings, management of undeveloped land, and handling of powder
or granular materials used in chemical, agricultural and other industries.

ìEven in North Alabama, we experienced an earthquake tremor last year,î said
Buddy Guynes, the experimentís project manager at NASA’s Marshall Space Flight
Center in Huntsville, Ala. " This experiment is relevant to our lives on
Earth. At NASA, we also want to know how soil behaves at different gravity levels,
so one day crews can safely build habitats on Mars and the Moon."

How do earthquakes and other geological activities, like mining, impart stress
to soil causing it to literally become shifting sand? As an earthquake strikes,
it deforms the soil, changing the volume of the soil. If water is present, water
pressure may build up in the pore space between the soil grains.† What was once
a solid foundation begins to flow like a liquid, a process called soil liquefaction.
As the soil moves, foundations become unstable, and Earth’s gravity wins out
— collapsing buildings, bridges and other structures.

Earth’s gravity also makes it difficult for scientists to study the precise
physics of granular mechanics and soil liquefaction.

"On Earth, gravity-induced stresses quickly change the amount of weight,
or loads, a foundation can support," said Dr. Stein Sture, the experimentís
principal investigator at the University of Colorado at Boulder. "We can
use space-based research to perform detailed analyses to understand the physics
that causes water- saturated, but initially firm foundation soil, to suddenly
flow like water."

The strength of sand or any particulate material depends on how the granular
assembly is packed together and interlocked. Moisture or air trapped within
or external loads on the site help determine its weakness or softness. Cyclic
loading and instabilities can cause the soil to loosen and collapse under the
stress of earthquakes or other pressures.

"Computer tomography scans will produce a series of images that help us
study the minute details of individual grains of sand and how they interact
with each other," said Sture. "We can examine the particle arrangement
and structure of soils and learn about the strength, stiffness and volume changes
that occur when low pressures are applied to granular materials."

For the STS-107 experiment, three sand columns held inside latex sleeves will
be used for nine experiment runs. Ottawa sand — natural quartz sand with fine
grains widely used for civil engineering experiments — will be saturated with
water to resemble soil on Earth. Each column holds about 1.3 kilograms (2.8
pounds) of Ottawa F-75 banding sand.

The flight crew will use a laptop computer to send commands to the experiment,
causing the sand to be compressed between two tungsten metal plates. As the
sand is compressed and relaxed, a load cell will measure the applied force,
and three CCD cameras will record changes in shape and position of the soil
inside the column. This compression and relaxation will simulate the loads that
might be imparted to soil via earthquakes and other external forces.

The three columns will be used for nine tests or observations periods. Upon
completion of each run, the samples will be expanded and stretched back to their
original length to create a homogenous mix of sand and water at the start of
each run.

When the Shuttle lands, the sand columns will be imaged using computer tomography
at laboratories at NASA’s Kennedy Space Center in Florida. Then, they will be
injected with epoxy, and the columns will be sawed into thin disks. These will
be sent to experiment investigators in Colorado and Louisiana for inspection
under an optical microscope.

"Our earlier flights showed gravity masked measurements of friction between
grains of sand," said Dr. Khalid Alshibli, project scientist for the experiment
and professor of civil engineering at Louisiana State University and Southern
University in Baton Rouge. "This is an important factor in determining
the amount of weight the soil can support."

The Mechanics of Granular Materials experiment has flown twice†— on Space
Shuttle missions STS-79 in 1996 and STS-89 in 1998. These investigations revealed
soil specimens were two-to-three-times stronger and much stiffer than scientists
had predicted. The16-day STS-107 flight aboard Columbia gives scientist an opportunity
to perform longer, more complex experiments. Future experiments will benefit
from extended tests aboard the International Space Station, including experiments
under simulated lunar and Martian gravity in a science centrifuge.

ìWe anticipate valuable results from the STS-107 experiments,î said Alshibli.
ìWe are using a novel specimen reformation technique that enables us to use
the same specimen for more than one experiment run. This lays the foundation
for more extensive, long-term soil research that can be carried out on the International
Space Station.î

In addition to the Mechanics of Granular Materials experiment, Columbia will
carry 29 more investigations sponsored by NASA’s Office of Biological and Physical
Research. These peer-reviewed and commercial experiments will advance knowledge
in medicine, fundamental biology, fluid physics, materials science and combustion.
The STS-107 mission is a dedicated science mission recommended by the National
Research Council and approved by the U.S. Congress. With more than 80 investigations,
it builds on prior multidisciplinary Shuttle science missions and serves as
a prelude to long-duration investigations that will be possible as science capabilities
grow on the International Space Station.