2
Liquid-Sand. That is a savings of more than 700 gallons of
water per cubic yard of backfill material. Because it so dras-
tically reduces the amount of water used on a jobsite, the
use of foam transportation technology also eliminates the
need for an impoundment pond on the jobsite.
In addition, because air is lighter in weight than water,
the transportation of foamed material requires less energy
than is required for the transportation of material in water.
While 50% solids with water weighs approximately 81
pounds, 50% solids with foam weighs only approximately
53 pounds.
Another benefit of using foam transportation technol-
ogy is that it allows for the use of a variety of granular mate-
rials in the production of the backfill product. This means
that many materials otherwise considered waste from
other industries (such as tailings, slag, culm, and crusher
fines) can be resourced in these applications. This not only
reduces materials being placed in landfills but also mini-
mizes transportation costs and utilizes local sources.
Economic Benefits
In addition to providing many environmental advantages,
the use of foam transportation can also reduce jobsite
costs significantly. One way in which foam transportation
reduces cost is by minimizing the amount of equipment
needed on the jobsite.
Because foam suspends appropriately sized fill material
during transportation without segregation, the need for a
high pumping velocity on the jobsite is eliminated. This
further reduces the energy demand and also allows for more
flexibility in the pump equipment used onsite. This ability
to operate at a lower flow velocity (velocity and pressure
vary by project) and plug flow pattern also reduces abra-
sion that can occur on the pipeline and minimizes potential
future degradation.
Due to the fact that more solids per unit area can be
pumped with foam transportation when compared to water
transportation (because of the significantly lighter weight of
the foam), application of the backfill material when using
foam transportation is significantly faster than application
with materials that are transported with water. This both
shortens the production schedule and reduces labor costs.
TYPES OF APPLICATIONS FOR FOAM
TRANSPORTATION TECHNOLOGY
Subsidence Mitigation and Abandoned Mine Land
Applications
Subsidence mitigation is an ideal application for the use
of foam transportation technology. The environmental and
economic benefits of this technology are highlighted in a
mine reclamation project in Colorado.
The Country Club Circle subdivision in Colorado
Springs, Colorado, experienced several subsidence events
that had caused significant damage to structures in the
neighborhood. These subsidence events indicated large
underground voids that had been created by an abandoned
mine that existed more than 60 feet below the ground
surface.
The abandoned mine had created between eight and
nine feet of void space underneath the 60-foot strata of
sand and rock. The voids were found and evaluated with
the use of a borehole camera, sonar scanning, and cross-
hole tomography. The largest void was filled with 267
cubic yards of foamed sand slurry that was injected into
the mine entry. The foam was generated on site, using a
foam generator and foaming agent, and then mixed with
the sand backfill material in a concrete mixer. The sand was
mixed with foam in proportions of seven to 10 cubic feet
of foam per yard of sand. The foamed sand slurry was then
dropped by gravity flow down the four-inch PVC casing in
the borehole.
Subsidence Mitigation with Foamed Sand Backfill
The advantages of using foamed backfill material in subsid-
ence mitigation was recently tested in a field study Liquid-
Sand (Hallman 2017). There are many specific benefits to
using Liquid-Sand.
When the foam and sand are mixed in the produc-
tion of Liquid-Sand, they are mixed at high sand-to-foam
ratios, which means that the resulting mixture acts as a
non-Newtonian fluid and enables control of the suspen-
sion, transportation, and placement of the granular sand
material. Once the foamed sand backfill material is placed,
the foam degrades and compresses from the weight of over-
lying material, allowing the backfill to settle and completely
fill the void space into which it is placed. For example, in
the Hallman field study, the sand backfill traveled 72 feet
from its injection point to completely fill the void.
Because of this unique engineering, a wide variety of
granular materials can be used in the production of Liquid-
Sand material. The backfill material must be well-graded
and non-plastic for the mixture to compact and be effec-
tive. Materials of various granular sizes can be used, as long
as no more than 10% of the material passes through a No.
200 sieve.
A test application of Liquid-Sand was conducted at an
abandoned coal mine in Glenrock, Wyoming. This particu-
lar site featured highly caved and rubbelized conditions, as
Liquid-Sand. That is a savings of more than 700 gallons of
water per cubic yard of backfill material. Because it so dras-
tically reduces the amount of water used on a jobsite, the
use of foam transportation technology also eliminates the
need for an impoundment pond on the jobsite.
In addition, because air is lighter in weight than water,
the transportation of foamed material requires less energy
than is required for the transportation of material in water.
While 50% solids with water weighs approximately 81
pounds, 50% solids with foam weighs only approximately
53 pounds.
Another benefit of using foam transportation technol-
ogy is that it allows for the use of a variety of granular mate-
rials in the production of the backfill product. This means
that many materials otherwise considered waste from
other industries (such as tailings, slag, culm, and crusher
fines) can be resourced in these applications. This not only
reduces materials being placed in landfills but also mini-
mizes transportation costs and utilizes local sources.
Economic Benefits
In addition to providing many environmental advantages,
the use of foam transportation can also reduce jobsite
costs significantly. One way in which foam transportation
reduces cost is by minimizing the amount of equipment
needed on the jobsite.
Because foam suspends appropriately sized fill material
during transportation without segregation, the need for a
high pumping velocity on the jobsite is eliminated. This
further reduces the energy demand and also allows for more
flexibility in the pump equipment used onsite. This ability
to operate at a lower flow velocity (velocity and pressure
vary by project) and plug flow pattern also reduces abra-
sion that can occur on the pipeline and minimizes potential
future degradation.
Due to the fact that more solids per unit area can be
pumped with foam transportation when compared to water
transportation (because of the significantly lighter weight of
the foam), application of the backfill material when using
foam transportation is significantly faster than application
with materials that are transported with water. This both
shortens the production schedule and reduces labor costs.
TYPES OF APPLICATIONS FOR FOAM
TRANSPORTATION TECHNOLOGY
Subsidence Mitigation and Abandoned Mine Land
Applications
Subsidence mitigation is an ideal application for the use
of foam transportation technology. The environmental and
economic benefits of this technology are highlighted in a
mine reclamation project in Colorado.
The Country Club Circle subdivision in Colorado
Springs, Colorado, experienced several subsidence events
that had caused significant damage to structures in the
neighborhood. These subsidence events indicated large
underground voids that had been created by an abandoned
mine that existed more than 60 feet below the ground
surface.
The abandoned mine had created between eight and
nine feet of void space underneath the 60-foot strata of
sand and rock. The voids were found and evaluated with
the use of a borehole camera, sonar scanning, and cross-
hole tomography. The largest void was filled with 267
cubic yards of foamed sand slurry that was injected into
the mine entry. The foam was generated on site, using a
foam generator and foaming agent, and then mixed with
the sand backfill material in a concrete mixer. The sand was
mixed with foam in proportions of seven to 10 cubic feet
of foam per yard of sand. The foamed sand slurry was then
dropped by gravity flow down the four-inch PVC casing in
the borehole.
Subsidence Mitigation with Foamed Sand Backfill
The advantages of using foamed backfill material in subsid-
ence mitigation was recently tested in a field study Liquid-
Sand (Hallman 2017). There are many specific benefits to
using Liquid-Sand.
When the foam and sand are mixed in the produc-
tion of Liquid-Sand, they are mixed at high sand-to-foam
ratios, which means that the resulting mixture acts as a
non-Newtonian fluid and enables control of the suspen-
sion, transportation, and placement of the granular sand
material. Once the foamed sand backfill material is placed,
the foam degrades and compresses from the weight of over-
lying material, allowing the backfill to settle and completely
fill the void space into which it is placed. For example, in
the Hallman field study, the sand backfill traveled 72 feet
from its injection point to completely fill the void.
Because of this unique engineering, a wide variety of
granular materials can be used in the production of Liquid-
Sand material. The backfill material must be well-graded
and non-plastic for the mixture to compact and be effec-
tive. Materials of various granular sizes can be used, as long
as no more than 10% of the material passes through a No.
200 sieve.
A test application of Liquid-Sand was conducted at an
abandoned coal mine in Glenrock, Wyoming. This particu-
lar site featured highly caved and rubbelized conditions, as