Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02944709 2016-10-07
STRUCTURAL SUPPORT
TECHNICAL FIELD
[0001] Supports for ground supported structures.
BACKGROUND
[0002] A traditional method of densifying base soils to provide support
for ground
supported structures, called pressure grouting or permeation grouting,
involves forcing a
high density cementitious material under high pressure into the base soils
with a view to
increase the bearing capacity of the soils. However, in the case of weak soils
there is no
controlling of the amount of grout that is required and as such, extreme
amounts of grout can
be pressure pumped into the soils with limited or no positive results. This is
especially true in
the case of highly saturated soils. Methods are known for injecting polymeric
foam into bags
underground for supporting weak soils, for example as disclosed in US
published application
no. 20150016897 published January 15, 2015.
SUMMARY
[0003] A method of imparting strength to earth or soil is disclosed. A
confinement
unit is placed in the earth below a ground surface, the confinement unit
having a first end
oriented towards the ground surface, a second end opposite the first end, and
the first end
having an opening. Granular material is released into the confinement unit
through the
opening to at least partially fill the confinement unit with granular
material. Expandable
polymeric resin is injected into the confinement unit to at least partially
fill the confinement
unit to compress earth around the confinement unit.
[0004] In various embodiments, there may be any of the following: the
confinement
unit is filed with granular material until full; the method further comprises
injecting gas to at
least partially fill the confinement unit prior to releasing granular material
into the
confinement unit; injecting expandable polymeric resin comprises injecting the
expandable
polymeric resin initially at the second end of the confinement unit; placing a
confinement
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unit in the earth comprises putting the confinement unit onto the end of a
tube and pushing
the tube into the earth; the method further comprises drilling a hole in the
earth prior to
placing the confinement unit in the earth; placing a confinement unit in the
earth comprises
placing the confinement unit at the bottom of the hole.
[0005] A confinement unit is also disclosed for use in imparting strength
to earth
below a ground surface. The confinement unit comprises at least an opening, a
first end and
a second end opposed the first end. The confinement unit is located in earth
under the ground
surface and at least partially filled with granular material and expandable
polymeric resin to
compress the earth around the confinement unit. In various embodiments, the
confinement
unit may include the following: the opening further comprises a backflow
prevention valve
to prevent material contained within the confinement unit from passing out of
the
confinement unit when the opening is unobstructed, the confinement unit is
water-resistant,
the confinement unit is waterproof, and the granular material is gravel.
BRIEF DESCRIPTION OF THE FIGURES
[0006] Embodiments will now be described with reference to the figures, in
which
like reference characters denote like elements, by way of example, and in
which:
[0007] Fig. Ito Fig. 4 are side elevation views, in section and not to
scale, of earth
below a ground surface and illustrating a process forming a confinement unit
packed with
gravel and resin in earth below a ground surface.
[0008] Fig. 5 is a flow diagram that illustrates a method of imparting
strength to earth
below a ground surface.
DETAILED DESCRIPTION
[0009] Immaterial modifications may be made to the embodiments described
here
without departing from what is covered by the claims.
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[0010] This document relates to the construction of in-situ expandable
vertical/horizontal support member(s) in weak base soils as a means of
densifying the weak
base soils for supporting and under-pinning structures on these soils. For
example, these
methods and apparatuses may carry out the densification of foundation soils
support systems
for buildings, walks, bridge approaches, concrete or asphalt paved roads, rail
beds, and any
other structure requiring a base support system or requiring enhancement or
strengthening of
the existing soil-based support system.
[0011] The present disclosure is directed to providing a controlled method
of
densifying soils at depth to increase bearing capacity of the weak soils as an
alternative to
pressure grouting and to direct injection of expanding polymer resins into
weak base soils.
Weak alluvial soils and silts replete with peat, hog fuel, and other weak
sediments that may
be highly saturated and demonstrative of Standard Penetration Test N-values of
5 or lower
are examples of soils that this disclosure relates to.
[0012] In many types of weak soils, such as weak alluvial soils, silts,
clay, peat, hog
fuel, wood chips, and water saturated soils for example, the inherent strength
of the earth
below the ground surface is limited. Soils of these types are known to have
caused hazardous
situations such as standing derailments of trains, and the cracking of
foundations of various
structures. In order to stabilize these types of soils, and prevent such
incidents from
occurring, the earth below the ground surface must be strengthened.
[0013] Fig. 1 to Fig. 4 show apparatus used in an embodiment of a method of
forming a structural support in earth 10 below a ground surface 12. In Fig. 5,
a method of
forming a structural support in earth below a ground surface is outlined. In
stage 100 of Fig.
5, a water-resistant or waterproof confinement unit or bag 14 is placed in the
earth 10 under
the ground surface 12, the confinement unit 14 having a first end 16 oriented
towards the
ground surface 12, a second end 18 opposite the first end 16, and the first
end 16 having an
opening 20. Injector tubes 26 are placed in the confinement unit before,
during or after
installation of the confinement unit in the ground, so that at some stage
there are injector
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tubes 26 in the confinement unit as illustrated in Fig. 2.
[0014] In stage 102, granular material 22 is released or dropped into the
confinement
unit through the opening 20 to at least partially fill the confinement unit 14
with granular
material 22 such as gravel. Filling the confinement unit 14 may include
dropping gravel in
the confinement unit 14 until no more gravel is able to fit in the confinement
unit.
[0015] In stage 104, expandable polymeric resin 24 is injected into the
confinement
unit 14 through the opening 20 to at least partially fill the confinement unit
14 to compress
earth 10 around the confinement unit 14. The expandable polymeric resin 24
reacts to form
foam which expand and fill confinement unit 14, encapsulating the granular
material 22 and
compressing and densifying the earth 10 around it as it expands. By densifying
and
strengthening the weak adjacent soils, the weight bearing capacity of the
ground surface 12
is increased, and overlying structures may be more easily stabilized and built
on top. The
gravel and resin packed confinement unit forms a structural support within the
earth that is
capable of supporting a structure above the ground surface.
[0016] Confinement unit 14 may be made of non-expandable material, for
example
thick polymer material. The material may resist the expansion of the
confinement unit itself,
thus compressing the inside and outside of the confinement unit while
maintaining structural
integrity. In some embodiments, the confinement unit is made of resilient
material. The
confinement unit 14 may be placed in the hole 28 before or with one or more
injections tubes
26. Gravel 22 may be placed in the confinement unit 14 through opening 20 or
through the
injection tubes 26 if they are large enough. The one or more injection tubes
26 may be used
to inject expandable polymeric resin 24 into the confinement unit 14 after
gravel 22 is placed
in the confinement unit 14. The gravel 22 may be placed in the confinement
unit 14 by
dropping the gravel from a tube, chute or shovel (not shown). The confinement
unit 14 acts
to contain the gravel 22 and polymeric resin from escaping into the earth 10
around the
confinement unit 14.
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[0017] The one or more injection tubes 26 may be located at different
depths within
the confinement unit 14. Each injection tube 26 may be used for injection of
resin and gas
and may provide access for granular material.
[0018] Hole 28 may be created by any suitable means such as drilling with
metal
devices or with a hydrovac unit. The drilling device (not shown) may be
removed upon
completion of the hole and prior to placement of confinement unit 14, and tube
26. In other
embodiments, hole 28 may be drilled in the earth using a hollow drill stem
connected to a
sacrificial drill bit. In some embodiments, injection tube 26, along with the
confinement unit
14 is placed in the hollow drill stem under the ground surface 12. In some
weak soils, the
hollow drill stem may be required to prevent the drilled hole from collapsing
prior to
placement of the confinement unit. In some embodiments, the confinement unit
may be
driven through the weak earth without requiring a hole.
[0019] Prior to releasing gravel into confinement unit 14, gas, for example
compressed air, may be injected to at least partially fill the first
confinement unit 14. Gravel
may be released into the confinement unit 14 multiple times. Between each
addition of
granular material, further injections of air may be made to expand the
confinement unit 14.
As the confinement unit 14 is inflated, the granular material accumulates near
the second end
of the confinement unit 14. Re-inflation of the confinement unit by injection
of gas may be
required depending on the composition of the earth 10. For example, where re-
inflation may
be required where earth 10 are very weak, such as when the earth is super-
saturated and acts
like water. The confinement unit may be expanded in-situ as much as possible
using
compressed air to allow as easy as possible filling of each confinement unit
with granular
material and expandable polymeric resin.
[0020] Referring to Fig. 2, releasing of granular material 22 may be
through inserting
the granular material through the one or more injection tubes 26. Granular
material 22, gas
and resin 24 may each be provided through the same injection tube 26. Gravity
may act on
the granular material to bring the granular material to the second end 18 of
the confinement
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unit 14. The amount of granular material 22 required may be determined by
comparing the
volume of the confinement unit 14 to the volume of granular material 22
accepted by the
confinement unit. Injection of the expandable polymeric resin may proceed
first with the
injection end of tube 26 near the second end 18 of confinement unit 14. Spaces
in between
the granular material 22 may be filled by the resin as the resin moves within
the confinement
unit and the confinement unit may expand as the resin is injected. The
granular material may
be enveloped by the resin 24, and the resin 24 may bind the granular material
together. The
water-resistance or waterproof nature of the confinement unit may allow the
resin to bind
with the granular material with limited or no water to interfere with the
binding. Once
confinement unit 14 has begun to accumulate resin 24, the injection tube or
tubes 26 may be
gradually drawn up towards opening 20 or each injection tube 26 may be left at
the same
level in the confinement unit 14 during injection of polymeric resin, then
left embedded in
the gravel and polymer composite. The resin may be hydro-insensitive
polyurethane for
example.
[0021] Prior to injecting expandable polymeric resin into the confinement
unit 14,
gas may be injected to further expand the confinement unit to facilitate
injection of the resin.
In some embodiments, the expandable polymeric resin is added as a liquid and
fills the
confinement unit through the expansion of the polymeric resin, the balloon
effect on the
confinement units compacting and compressing the base soils surrounding the
confinement
unit. By filling the confinement unit 14 with air prior to injection, the
expandable polymeric
resin is allowed to freely flow into confinement unit 14 between the granular
material 22 and
properly fill, yet be confined by, the dimensions of confinement unit 14 upon
expansion.
[0022] Referring to Fig. 2, after gravel 22 is placed in the confinement
unit 14 and
polymeric resin 24 is injected into the confinement unit 14, the resulting
structure may be
used as a structural support 54 for a ground surface 12 or a building placed
on the ground
surface 12. The support 54 comprises confinement unit 14 located in earth 10
under the
ground surface 12 and at least partially filled with granular material 22 and
expandable
polymeric resin 24 to compress the earth 10 around the confinement unit 14.
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[0023] In some of the embodiments of methods disclosed herein, the earth
comprises
at least one of weak alluvial soils, silts, clay, peat, hog fuel, wood chips,
and water saturated
soils. It should be understood that each method disclosed herein can
incorporate all the
characteristics of the other methods.
[0024] In the embodiments of the methods disclosed herein, the expandable
polymeric resin may be expanding polymeric resin that comprises a high
density, closed cell
expanding two component polyurethane foam system. The resin may be hydro-
insensitive. In
some embodiments, the polymeric resin is a high density, two-part, closed cell
expanding
polymeric resin system, such as a polyurethane system which is injected into
the
confinement unit or array of confinement units. The particular foam system
used may be
tailored to meet specific design applications relating to tensile strength,
compressive
strength, shear strength, flexural strength and other structural
characteristics to meet the
specific design applications of the controlled foam densification system. It
is also possible to
use other expandable substances having similar properties.
[0025] The expansion rate of the freely blown polymeric resin system is
known as is
the approximate relationship of the expanding polymeric resin system under
confinement in
a weak soils condition and hence the amount of resin can be pre-estimated to
minimize resin
usage and maximize soils densification around the confinement unit or array of
confinement
units.
[0026] The shape and size of containment units, constructed of natural or
synthetic
fibers for example, will be determined depending upon the soils conditions.
The weaker the
soil's condition, the larger the containment unit may be in both width and
depth. The
containment bags will typically not be symmetrical in shape to enhance the
stability of the
filled bag in the weak soils as well as enhance any "friction" effect the
containment unit may
have. The containment units may be designed to meet specific soils needs, for
example using
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a containment unit in a specifically weak soil strata that has been designed
to more so
compact the weak soil as compared to the soils above and below the weak
strata.
[0027] The use of a bag to confirm the polymeric resin is mainly beneficial
for
densification of weak and very weak base soils with N-values being no larger
than 5. Any
base soil condition with N-values greater than 5 can be directly injected with
an expanding
polyurethane to densify these base soils. Direct injection into weak and very
weak base soils
proves ineffective and uneconomical as tremendous amounts of expanding polymer
resin can
be injected into these weak soils and the tendency for the material is to set
up in vertical
wing patterns that really do not compact and compress the base soils to
increase density and
load bearing capacity. Accordingly, a confinement unit is required to be
placed in and
through the weak soils strata and then filled with an expanding polymer resin
to effectively
compact the base soils laterally and provide support vertically as well. There
is a direct
relationship between the strength of the base soils being treated and the
lateral
compressibility of these weak soils.
[0028] It has been determined that the design of any confinement unit has
limitation
in terms of the diameter of the unit. The maximum diameter to effectively
produce a
contiguous column of solid polyurethane is in the order of 2' ¨ 2.25'. A
larger diameter
confinement units would only be applicable in very, very weak soils which are
determined to
be quite compressible. Another mitigating element against larger diameter
confinement units
is the polyurethane foam system employed because of the way the system
actually expands ¨
le: larger volume areas are not as effectively filled especially when injected
into rather
lengthy confinement units. Further, because the polyurethane system tends to
follow the
route of least resistance it will tend to move vertically instead of laterally
thus mitigating the
effect of laterally compacting the weak base soils.
[0029] It may be difficult to effectively fill a long confinement unit by
simply
employing one injection port. To ensure proper and effective fill of a
confinement unit the
confinement should be compartmentalized, for example, at 7' ¨ 8' intervals
with injectors
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located within each compartment. In some embodiments, the compartments are
defined by
the location of the injectors within the gravel. The gravel resists movement
of the polymeric
resin from a specific nozzle or injector tube. The polymeric resin then stops
moving when it
encounters the confinement unit or polymeric resin from another nozzle or
injection tube. In
another embodiment, the confinement unit may be compartmentalized with one or
more
dividers 30, shown in Fig. 3A. The divider 30 may be formed by material such
as tape, paper
or other fragile membranous material that extends across the confinement unit.
The divider
may be placed during filling of the confinement unit with gravel. After a set
amount of
gravel is placed in the confinement unit, the divider is inserted, then
additional gravel added.
The divider used to make the compartments may be be very weak so when the
expanding
resin hits that area it will actually tear the tape and completely fill the
confinement unit. The
diameter of the confinement unit will be determined by the compressability of
the base soil.
The weaker the base soil and more compressable it is the larger the diameter
of the
confinement unit.
[0030] Different polyurethane systems have different coefficients of
expansion and
thus depending upon the density of the polyurethane system the amount of
material to be
injected into each compartment of the confinement unit can be predetermined.
The denser
the polyurethane system the less expansion is realized upon injection and thus
more material
is required to effectively fill the confinement unit. Additionally, since the
polyurethane foam
is confined it will densify itself to a degree as a result of this confinement
¨ ie: it compact
and compresses itself in confinement thereby requiring more material to
effectively fill the
confinement unit. This densification of the foam results in a stronger column
of foam within
the confinement unit as well as requiring lower density foam systems to effect
the same job.
Depending upon the volume of the confinement unit; the compressibility of the
soils being
treated and the foam system being used determines the amount of material that
will be
injected into each compartment to provide an effective fill of the confinement
unit.
[0031] A challenge in the densification of weak soils using a confinement
unit is
what grid pattern needs to be employed to effectively densify the weak soils.
For structures
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that are lineal in nature such as rail beds, building foundations and the like
a tighter grid
pattern and may be required depending upon the weakness of the base soils and
other factors.
Weak liquefiable soils can also be treated using confinement units and a much
tighter
staggered grid pattern is required to give assurance that the weak typically
saturated silts and
sands will not liquefy in the event of seismic activity.
[0032] In the claims, the word "comprising" is used in its inclusive sense
and does
not exclude other elements being present. The indefinite article "a" before a
claim feature
does not exclude more than one of the feature being present. Each one of the
individual
features described here may be used in one or more embodiments and is not, by
virtue only
of being described here, to be construed as essential to all embodiments as
defined by the
claims.
