Note: Descriptions are shown in the official language in which they were submitted.
CA 03188126 2022-12-22
DESCRIPTION
(1) TITLE OF INVENTION
RAPID CONSOLIDATION AND COMPACTION METHOD FOR SOIL IMPROVEMENT OF VARIOUS
LAYERS OF SOILS AND INTERMEDIATE GEOMATERIALS IN A SOIL DEPOSIT
(2) TECHNICAL FIELD
This application is for applying for a utility patent in a technical field
which includes civil engineering and
geotechnical engineering for soil densification of layers of soils and
intermediate geomaterials in a soil
deposit. This specification/description is complete-in-itself. This invention
is not sponsored or supported
by federally sponsored research or development or by any other organization.
This invention has been
conceived, developed and completed independently by the inventor, Dr. Ramesh
Chandra Gupta, Ph. D.,
P.E, President and Sole Owner of SAR6 INC. The inventor, Dr. Ramesh Chandra
Gupta is a Citizen of
the United States of America.
(3) BACKGROUND OF INVENTION
Sand drain technique to strengthen the weak soils (Kennedy and Woods, 1954)
has been in wide use
from long time. Bowles, 1988 summarized the method of Sand Drains to
strengthen and consolidate
clayey soil layers which cannot support the load of the embankment or
foundation structures. A circular
casing or mandrel is driven vertically into a soft clayey layer to the
required depth. The soil in the casing
or mandrel is removed and the hole is backfilled with clean sand under gravity
to form a loose layer of
sand column in the surrounding weak clayey soil. The mandrel or casing is then
removed by pulling it out
of the ground. The embankment is then constructed on top of the ground surface
up to the full height in
stages. If the full height of embankment is 5 meters, it will develop excess
pore-pressures to about 49
kPa (7.1 psi). After allowing sufficient time for consolidation, to dissipate
the developed excess pore
pressures generally up to 90% consolidation, either embankment if it is for
highway left in place or
otherwise the embankment is excavated and the required structure, such as
buildings or air ports, oil
storage tank etc., is constructed on original ground or at some depth below
the original ground.
Depending on the horizontal spacing of sand drains and coefficient of
consolidation of in-situ clays, the
time for consolidation could vary from six months to a year or more. Recently,
PVC drains or wick drains
have generally replaced the sand drains.
Mars (1978) introduced another method in which a probe pipe with a partially
openable valve in a form
of two halves of a cone at its end is driven by a vibratory probe, assisted by
liquid jets to erode the in-situ
soils around and below the probe and to facilitate its penetration to the
design depth. Vibratory probe is
very light in weight with very low centrifugal force, and therefore, either
pre-auguring or liquid jets to erode
the soil is required. Liquid jet pipes are the integral part of the probe pipe
which pass through at the end
of probe pipe in to the in-situ soil. The probe has bands around the probe at
some spacing vertically.
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When the probe pipe is being penetrated in to the ground, the end valve
remains in closed position, and
the pebbles, stones etc. is filled in the probe pipe by gravity through a
chute achieving a very loose
density. When the probe pipe is pulled out of the ground, the partially
openable valve opens and allows
the pebbles, stones or sand drop through its narrow opening which appears to
be less than 25% inside
area of the probe pipe, thus forming a column of pebbles, stones etc. with its
area of cross-section less
than 25% inside area of the probe pipe, because before additional pebbles etc.
drop in, in the remaining
outside area of probe pipe and bands, the in-situ soil consisting of either
clay or sand will quickly run and
cave-in. Therefore, the pebbles etc. dropped under gravity will only be able
to form a column in very loose
condition with the area of cross-section significantly smaller than the inside
area or outside area of the
probe pipe. No embankment to surcharge the area to compact it, has been
described in this method
(Mars, 1978). Mars (1978) method was developed to compact an area of soil
having initial low bearing
strength, such as an alluvial or sandy area or an area of hydraulic fill. Many
organizations do not allow
vibratory probes to drive pipes in clayey soils. In sand drain technology,
embankment is placed on the site
area to consolidate and densify the area, which also results in densification
of sand drains which consists
of loosely filled sand, but Mars (1978) method does not use the embankment to
be built over the area
where the loosely filled pebbles etc. have been filled in the vertical holes.
Therefore, Mars method could
loosen the area in place of densifying it.
The invention in this application comprises of a rapid consolidation and
compaction method (RCCM) to
produce rapid consolidation of the layer of clayey soil resulting in increase
of its density and consistency.
The RCCM comprises (i) first driving a hollow pipe section to some depth to
minimize heave at the ground
surface or above the layer of soil requiring improvement, (ii) driving a
displacement pile consisting pipe
section with a removable or detachable end plate after filling and compacting
the sandy material in the
pipe section closed with the removable end plate, to the required depth in the
layer of clayey soil through
inside the hollow pipe section previously driven, (iii) because the pipe
section with detachable end plate
performs as a displacement pile displacing the in-situ clayey soil and
creating high excess pore-water
pressures, which are expected to be generally in a range of 100 to 800 kPa,
but could be as high as 2500
KPa; (Note: values of excess pore-water pressures shall depend on the
consistency and depth of the clay
below the ground surface), (iv) before pulling out the pipe section out of the
ground, a heavy weight is
placed top of the compacted material inside the pipe section, (v) now remove
or pull out the pipe section
out of the ground; the heavy weight continues to push down the column of
compacted sandy material and
prevents any necking to form in the column of the compacted material, (vi) the
detachable or removable
end plate opens the 100 percent of the inside area and thus forms a column of
compacted sandy material
equal to inside area of the inside area and weight further imposes the
downward force which further
laterally is displaces to occupy space equal to the outside area of the pipe
section, (vii) thus, the column
of compacted sandy material behaves as a porous displacement pile embedded in
the clayey soil and
allows the excess pore-water pressures to first develop and then rapidly
dissipate them causing excess
pore-water to flow first horizontally to the porous displacement pile and then
vertically flow through it to
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the ground surface or to a sandy layer above or below the porous displacement
pile, and (v) when the
porous displacement piles adjoining to the first one in a grid pattern are
installed, the length of the
drainage path is further reduced to half the spacing between adjoining porous
displacement piles,
allowing rapid consolidation of the layer of clayey soil resulting in its
increase of density and consistency
sufficiently enough to support loads of the required structure, such as
pavement, civil structure, airport or
oil storage tank, etc. Installing the porous displacement piles in the layer
of loose to medium dense sand
layer in a grid pattern results in the instantaneous increase in its density.
Therefore, the rapid
consolidation and compaction method (i.e., RCCM) presented in this application
as an invention,
improves and increases the density of all types of soils and intermediate
geomaterials to support loads of
the structures of a project. The sandy material is compacted to relative
density equal or greater than 70%
or even up to 100% inside the pipe section, depending on the requirement of
supporting loads of the
structure and also the subsurface soil conditions. The maximum value of the
excess pore-water pressures
is on the surface of the cone penetrometer and the value of excess pore-water
pressures rapidly reduces
with radial distance from the cone penetrometer. Same trend of excess pore-
water distribution around
porous displacement piles is expected to occur during penetration of the
porous displacement piles. The
maximum excess pore-water pressures near the face of the porous displacement
shall quickly dissipate
through the porous displacement pile as the length of the path of flow is zero
or very short distance from
the zone of higher excess pore-water pressures. When adjoining porous
displacement piles are installed,
the length of the path for flow shall reduce to half the spacing between
adjoining porous displacement
piles. For example, if the center to center spacing of porous displacement
piles is say, 4 times their radius
of the porous displacement piles, then the distance between faces of the
porous displacement piles shall
be only three times the radius, but from the mid-point between the porous
displacement piles shall be
only 1.5 times the radius, facilitating very quick dissipation of the excess
pore-water pressures. In an
earth dam of 30-meter height, excess pore-water pressures to the extent of 290
kNm2, are developed in
clay zone and therefore, it is required that the sandy material to satisfy a
filter criterion to prevent
migration of fine particles of clayey soil and also to allow free flow of the
excess pore-water pressures. In
view of this, the particle size distribution of the compacted sandy material
in the porous displacement
piles, will also be designed to satisfy the filter criteria (Prakash and
Gupta, 1972).
In many cases, it may not be practical to pull out the pipe section out of the
ground. Therefore, porous
reinforced concrete piles with or without prestress, or porous pipe section
with the end plate, or pipe
section with small holes and the end plate, filled by the compacted sandy
material shall also installed
through inside the non-displacement piles and shall be used as the porous
displacement piles, if (1)
drivable by a pile driving hammer into the soil without exceeding allowable
driving stresses, (2) allow free
drainage and flow of water and prevent migration of fine soil particles of
clays and silts or fine sand, (3)
the holes in the tube or pipe section need to be quite small so as to retain
sandy material during
compaction in the pipe section. These porous displacement piles will not
require pulling out of the pipe
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section out of the ground and the installation will become faster, with no
noise which may happen during
pulling the pipe section.
In the invention presented in this application, constructing the embankment to
create uniform excess-
pore water pressures in clayey soil is not required, as much higher excess
pore-water pressures are likely
to develop by penetration of porous displacement piles.
SUMMARY OF INVENTION
(a) Technical Problem with Existing Geotechnical Methods for Soil Improvement
As explained above, widely used methods for consolidation and for densifying a
layer of clayey or silty soil
are sand drains or wick (PVC) drains, which have been used for more than 50
years. Other methods such
as osmosis etc. are rarely used. Recently, several methods have come up which
do not increase the
consistency or density of the layer of clayey or silty soils, but increase the
load capacity by installing (a)
Geopiers or (b) Stone Columns or (c) Jet Grouted Columns or (d) Lime or Cement
Mixed Columns with
clayey soils installed in a drilled hole by drilling and auguring (Shaefer et
al., 2016). Even bottom feed
stone columns, which do not use drilled holes does not succeed in improving
the density of the layer of
the clayey soils, probably because of very strong vibrations by the vibratory
probe disturbing matrix of
clayey soils and then allowing inflow clayey soils in them. When holes are
excavated using the above
methods, a considerable amount of excavated material spreads around the site
of the project ,which has
to be properly disposed of to prevent any environmental problem. Reinforced
Concrete Piles or H-Piles
overtopped by small footing and several layers of geotextile separated by
sandy material have been used
to support the loads of the embankment on soft to very soft soils. All these
methods do not the density
and/or increase consistency of soft to very soft soils, but support the weight
of road embankment directly,
without permitting load on the soft clay layer. These methods are very costly
involving millions of dollars
per mile (one mile = 1.6 Kilometer). There are no historical case histories
for the above newer
technologies, which may demonstrate their successful long-term behavior.
For compaction of layers of sandy materials in a soil deposit, there are
several methods, which are
being used, such as dynamic deep compaction by dropping a weight from the
selected height, Vibro-
replacement and Vibro-floatation, Geopiers using rammed gravelly materials,
stone-columns as bottom
feed or top feed, etc. The vibro-floatation or stone column equipment has
frequency of 3000 rpm,
centrifugal force of 30000 kg, weight of 9000 kg, height of about 2.5 meter,
and inside diameter of about
38 cm. The vibro-floatation and stone column vibro-equipment has a central
hole through which water jets
are jetted to erode soil when subsurface soil conditions are such that
vibration alone cannot penetrate into
soil any further or when penetration rate becomes very slow. The rapid
consolidation and compaction
method using porous displacement piles is a new method which can be used
successfully to densify the
sandy materials in which excess pore-water pressures do not develop or if
develop then dissipate as fast
as these are generated. The RCCM will generally require readily available
instruments and machinery
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such as cranes and pile driving hammers etc., pullers, surface or plate
vibrators, which could be available
on rent or for leasing at most places or for sale from manufacturers.
(b) Solution to Problem and Advantageous Effects of Invention
As explained above, the rapid consolidation and compaction method is installed
to increase the density of
both sandy and clayey materials. Since the sandy material is very economical
with much lower cost as
compared to jet grouted columns, columns of cement or lime mixed with clayey
material or Geopiers, the
cost of using the rapid consolidation and compaction method shall be much
lower and could save millions
of dollars on a big project. The rapid consolidation and compaction method
shall densify the (i) very soft
to soft cohesive soil to stiff or very stiff cohesive soil, (ii) medium stiff
cohesive soil to stiff or very stiff
cohesive soil, (iii) stiff cohesive soil to very stiff cohesive soil, and (iv)
very stiff cohesive soil to hard or
very hard soil cohesive soil, depending on the selected spacing between the
adjoining porous
displacement piles and relative density of compacted sandy soil in the porous
displacement piles.
Similarly, the rapid consolidation and compaction method shall compact sandy
soil from (i) very loose
(relative density less than 15%) to medium dense (relative density between 35
and 65%) , (ii) loose
(relative density between 15 and 35%) to medium or dense sand (relative
density between 65 and 85%),
(iii) from medium dense to dense sand, and (iv) from dense to very dense
(relative density greater than
85%), depending on the selected spacing between the adjoining porous
displacement piles and relative
density of compacted sandy soil in the porous displacement piles. When
densification to higher densities
of in-situ soils is required then the relative density of the sandy material
in porous displacement piles
more than 70% even up to 100% may be selected for the compacted sandy material
in the displacement
pipe section with removable end plate, which after installation is pulled out
of the ground to form a porous
displacement pile. Both the densified in-situ clayey silty soil and in-situ
sandy soil in a layer to the
selected depth below ground surface shall be capable to provide support to the
foundation of a structure
with adequate bearing capacity and minimum settlements. During construction of
the structure on
densified in-situ soil, if any excess pore-water pressure develops, shall
quickly dissipate and small
settlement shall occur before the structure reaches full height. No embankment
as required for the sand
drains or PVC drains and waiting for consolidation to occur for 6 months to
more than a year shall be
needed when the RCCM has been selected. Therefore, progress of construction
shall become very fast,
which is very important for highway projects for expansion or widening of
existing roads and highways or
also for support of the foundations of various structures.
(4) BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
Fig. 1A: Atypical detail showing installed non-displacement pile (120) and
pipe section (123) with
detachable or removable end plate (124) and filled with compacted sandy
material.
Fig. 1B: A typical detail of pipe section (123) with detachable or removable
end plate (124) driven to
design depth.
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Fig. 1C: A typical detail showing a hammer or weight (126) placed on top of
the compacted sandy
material (125), prior to pulling the pipe section (123) out of the ground.
Fig. 2A: A typical detail of the column of compacted sandy material acting as
a porous displacement pile
(125) after the pipe section has been pulled out of the ground and the hammer
or weight (126) still resting
on the porous displacement pile (125).
Fig. 2B: Atypical detail of completion of installation of the porous
displacement pile (125), with end plate
(124) sitting under it.
Fig. 3A: A typical detail of a setup to provide lateral support to the pipe
section (123) during compaction of
the sandy material in it.
Fig. 3B: Another typical detail of a setup to provide lateral support to the
pipe section (123) during
compaction of the sandy material in it.
Fig. 4A: A typical detail of the hinged connection connecting pipe section
(123) to the removable and
detachable end plate (124).
Fig. 4B: A typical detail showing the end plate becoming vertical during
pulling the pipe section (123) out
of the ground.
Fig. 5A: A typical detail of the pipe section (123) with a removable and
detachable short pipe (132)
inserted inside the pipe section (123) where the short pipe (132) is attached
to end plate (124).
Fig. 5B: A typical detail showing the removable and detachable short pipe
(132) and end plate (124) left
behind while pulling the pipe section (123) out of the ground.
Fig. 5C: A typical detail showing the removable end plate (124) attached to
the connecting rods (133); the
connecting rods (133) which are fastened by bolts (13%) to the top of the pipe
section (123).
Fig. 5D: A typical detail showing the connecting rods (133) and removable end
plate (124), which after
removing the bolts (135) are left behind during pulling the pipe section (123)
out of the ground.
Fig. 6A: A typical detail of removable end plate (124) connected to pipe
section (123) with a hinge (130)
on one side and on opposite side by an angle (137) which is also bolted to the
pipe section (123), for
lifting the pipe section (123) filled with compacted sandy material, to a
location where it is to be driven into
the ground.
Fig. 6B: A typical detail of pipe section (123) bolted to short pipe section
(132) which is attached to the
end plate (124) for lifting the pipe section filled with compacted sandy
material to a location where it is to
be driven into the ground.
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Fig. 7A: A typical plan showing the grid lines (151) and the locations (150)
of porous displacement piles
for soil improvement under a spread footing.
Fig. 7B: Sectional elevation showing the installed porous displacement piles
(125) under the spread
footing.
Fig. 8A: Atypical detail of the installed porous displacement piles (125)
under an embankment.
Fig. 8B: Atypical detail of the installed porous displacement piles under an
embankment with porous
displacement piles at primary locations installed ahead of the embankment and
the embankment
extended on the installed porous displacement piles(125).
Fig. 9: A typical plan showing the grid lines (151) and the locations (150) of
porous displacement piles for
soil improvement under and by the side of foundation of the Leaning Tower of
Pisa.
Fig. 10: Atypical detail showing foundation of the Leaning Tower of Pisa and
subsurface soil layers along
with batter Porous Displacement Piles (125).
DETAILED DESCRIPTION OF INVENTION
The main motivation for the invention of the rapid consolidation and
compaction method (RCCM) is to
develop a method for soil improvement which can densify a layer of the soil or
the intermediate
geomaterial (IGM) in a soil deposit. Cohesionless soils are defined as having
Nco less than 50 blows/0.3
m, whereas cohesionless Category 3 IGMs are defined as having Nco greater than
50 blows/0.3 m
(AASHTO, 2012). Cohesive soils are defined as having undrained shear strength
less than 0.25 MN/m2,
whereas cohesive IGMs Category 1 are defined as having undrained shear
strength greater than 0.25
MN/m2 (AASHTO, 2012). The invention in this application comprises of a rapid
consolidation and
compaction method (RCCM) to produce rapid consolidation of the layer of clayey
soil resulting in increase
of its density and consistency. The RCCM comprises (i) first driving a hollow
pipe section to some depth
to minimize heave at the ground surface or above the layer of soil requiring
improvement, (ii) driving a
displacement pile consisting pipe section with a removable or detachable end
plate after filling and
compacting the sandy material in the pipe section closed with the removable
end plate, to the required
depth in the layer of clayey soil through inside the hollow pipe section
previously driven, (iii) because the
pipe section with detachable end plate performs as a displacement pile
displacing the in-situ clayey soil
and creates high excess pore-water pressures, which are expected to be
generally in a range of 100 kPa
to 800 kPa, but could be as high as 2500 KPa (Note: values of excess pore-
water pressures shall depend
on the consistency and depth of the clay below the ground surface. Pore-water
pressures in the range
between 260 psi (1793 kPa) and 400 psi (2758 kPa) were recorded in Cooper
Marl. Peuchen et al. (2010)
recorded pore-water pressures in the range between 50 kPa (7.25 psi) and 800
kPa ( 261 psi) during
piezocone penetration in heavily overconsolidated cohesive soil.), (iv) before
pulling out the pipe section
out of the ground, a heavy weight is placed top of the compacted material
inside the pipe section, (v)
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while removing or pulling out the pipe section out of the ground, the heavy
weight continues to push down
the column of compacted sandy material and prevents any necking to form in the
column of the
compacted material, (vi) the detachable or removable end plate opens the 100
percent of the inside area
and thus forms a column of compacted sandy material equal to inside area of
the inside area and weight
further imposes the downward force which further laterally displaces compacted
sandy soil to occupy
space equal to the outside area of the pipe section, (vii) thus, the column of
compacted sandy material
behaves as a porous displacement pile embedded in the clayey soil and allows
the excess pore-water
pressures to first develop and then rapidly dissipate them causing excess pore-
water to flow first
horizontally to the porous displacement pile and then vertically flow through
it to the ground surface or to
a sandy layer above or below the porous displacement pile, and (v) when the
porous displacement piles
adjoining to the first one in a grid pattern are installed, the length of the
drainage path is further reduced
to half the spacing between adjoining porous displacement piles, allowing
rapid consolidation of the layer
of clayey soil resulting in its increase of density and consistency
sufficiently enough to support loads of
the required structure, such as pavement, civil structure, airport or oil
storage tank, etc. Installing the
porous displacement piles in the layer of loose to dense sand layer in a grid
pattern results in the
instantaneous increase in its density. Therefore, the rapid consolidation and
compaction method (i.e.,
RCCM) presented in this application as an invention, improves and increases
the density of all types of
soils and intermediate geomaterials (whether, loose condition or dense, soft
or very stiff, to support loads
of the structures of a project. The sandy material is compacted to relative
density equal or greater than
70% or even up to 100% inside the pipe section, depending on the requirement
of supporting loads of the
structure and also the subsurface soil conditions. When footing of a structure
is constructed on the soil
which has been densified by the RCCM, weight of the structure further creates
excess pore-water, which
also gets rapidly consolidated and footing may continue to settle uniformly by
very small magnitude as the
substructure and superstructure is being constructed, but after completion of
the superstructure, there
shall be hardly any settlement and if any, shall occur uniformly. After
completion of installation of porous
displacement piles, the ground surface soils may be compacted by passes of
compaction roller, or sheep
foot roller etc., by general contractor, if needed as per project drawings.
For the above process, a hollow pipe section (120) is driven into soil to the
selected depth (121) to
minimize the heave at the ground surface. A hollow pipe sections have very
small annular area compared
to its outside or inside area, and therefore, for geotechnical purposes, the
hollow pipe piles are called
non-displacement piles. Similarly, piles consisting of HP-section and channel
sections etc. are called non-
displacement piles. After the non-displacement pile (120) has been driven into
the ground, as shown in
Fig. 1A and Fig. 1B, a displacement pile, consisting of the pipe section (123)
with a removable end plate
(124) and filled with compacted sandy material (125) is driven into the layer
to be densified. Since the end
plate is attached at the bottom of the pipe section, when driven into ground,
the pipe section with closed
end displaces the in-situ soil reducing the void volume of the in-situ soil or
develops excess pore-water
pressures and occupies its space; and thereby eventually densifies it. After
placing a weight or hammer
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(126) on the top of sandy material as shown in Fig. 1C, and the pipe section
is pulled out from the ground,
leaving behind the detachable or removable end plate at the bottom of the
column of the compacted
sand, as shown in Fig. 2A. The weight or hammer (126) helps to continue
pushing the column of sandy
soil downwards and even help push sand in the column laterally to occupy the
space left by the thickness
of pipe section. During pulling the pipe section out of the ground, as an
option, few drops of weight after
raising it by a few centimeters may further help in displacing sandy material
in the voids created by pulling
out the pipe section (123). Thereafter, the non-displacement pile (122) is
also pulled out and a few drops
of the weight or hammer further helps in displacing and compacting sandy
material (125) in the voids
created by pulling out the non-displacement pile (120). In this way, the
porous displacement pile (125)
consisting of compacted sandy material, as shown in Fig. 2B, is installed into
the ground in the depth, the
densification or soil improvement is needed.
The hollow pipe or tube section could be round, square or rectangular or any
shape available or made
in the industry. Sometimes, two angle sections or two channel sections welded
together could also be
used as a hollow pipe section. When such sections are attached with a
detachable or removable end
plate and used as a displacement pile to be driven in to ground, then for
geotechnical purposes, it is
called a displacement pile as it displaces the soil by occupying its place.
When these sections without any
end plate at its bottom (i.e., a hollow section) is driven in to ground then
for geotechnical purposes, it is
called a non-displacement pile. The sandy material can be compacted inside the
pipe section at the
location where it is to be driven or at the ground other than the location
where it is be driven or otherwise
in the pipe section after being driven in to ground if the ground below it is
sufficiently dense to limit
settlement to keep the end plate intact at the bottom of the displacement
pile.
The non-displacement pile is driven into the ground first, in order to
minimize heave at the ground
surface or at the top the layer which is to be densified. Ideally, during
driving the displacement pile, there
should not be any heave of the ground surface to achieve maximum lateral
displacement of the soil by
the porous displacement pile, in order to achieve maximum densification. That
is why to minimize heave,
first a non-displacement pile is driven to selected depth and then the
displacement pile is driven through
the non-displacement pile. If this step of driving displacement pile through a
non-displacement pile is
omitted and displacement pile is driven directly, due to economics or for any
other reason such as not
very practical at a particular site, etc., or when non-displacement pile has
not been driven to adequate
depth to minimize or prevent heave, then although full densification of in-
situ soil would not occur
because of some heave at the ground surface, yet it could be considered
satisfactory in certain
circumstances. In such cases, the amount of densification will be less as the
volume of the in-situ soil
displaced by the displacement pile will be sum of the reduction of voids in
the in-situ soil plus the volume
soil which heaved at the ground surface or at the top of the layer to be
densified. The overburden soil
above the depth of the bottom of the non-displacement pile (120) acts to
prevent or minimize the heave at
the ground surface to a reasonable limit, when the weight of the overburden
soil above the bottom of the
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non-displacement pile (120) is sufficient enough to prevent heave at the
ground surface. According to the
presently available research, the overburden depth between 7 to 10 times or
more may be sufficient to
limit heave at the ground surface, depending upon the soil conditions.
However, not enough or substantial
research is available at the present, to predict the reasonable depth (121) in
different types of soils at
various densities or consistencies to prevent or minimize the heave at the
ground surface when a
displacement pile is being driven into the ground. Sufficient research shall
be developed to predict the
reasonable depth (121) in different types of soils at various densities or
consistencies, when the projects
involving ground improvement using the RCCM are being implemented.
The sandy soil (125) is filled in layers in the pipe section (123) and each
layer compacted by a
specified number of drops of a hammer or a weight (118) to achieve a specified
dry density or relative
density. The connecting pipe or rod (127) connects the weight or hammer to a
boom of crane or to a pile
driving hammer system (not shown in the Fig. 1C). Alternatively, either the
sandy soil can also be filled in
layers and then the hammer or the weight (118) placed on top of each layer,
after which vibrated by
attaching a surface vibrator on the sides of the pipe section (123) or the
vibratory probe/weight is placed
on top of each layer for densifying the sandy soil to the specified dry
density or relative density. The pipe
section (123) with detachable or removable end plate is generally maintained
vertical while filling sandy
material in it and compacting it.
It is advisable that the density of the compacted sandy material inside the
pipe section (123) should
generally be based about 70% relative density, because this is the requirement
which is generally
followed for compacting embankments. When densification of stiff to very stiff
clays to hard clayey soils or
medium dense or dense sand to very dense sand is required, then relative
density of compacted sandy
material in the pipe section to about 70% or greater than 70% and even up to
100% may be more
appropriate. In earth quake zones and over faults, or under atomic power
plants, even very stiff clays or
dense sands may require further densification, in such cases, the relative
density of more than 70% to
even up to 100% for the column of compacted sandy soil to perform as porous
displacement pile could be
specified. However, when very soft clays or soft clays to be densified to
medium stiff clays or loose to
very loose sand is to be densified to medium dense sand, then relative density
requirement could be
relaxed, if structural support requirement of the site could be met by lesser
relative density of the porous
displacement piles consisting of compacted sandy material. The relative
density of medium dense sand
varies from 35 to 65%. If the site where its subsurface layers need to be
densified to the relative density
equivalent to medium dense sand condition to meet the structural foundation
support or overall ground
support of the site, then it may be sufficient to install porous displacement
piles consisting of columns of
sandy material to relative density necessary for medium dense sand, therefore
then in such cases, the
sandy soil in the pipe section (123) shall need to compacted to achieve medium
dense condition.
Therefore, the sandy soil in pipe section (123) shall need to be compacted to
achieve the medium dense
or to dense or very dense condition according to requirements at the project
site. Selecting an appropriate
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spacing and diameter of the porous displacement piles is also important to
determine how much porous
displacement piles will displace and compress the in-situ soil to densify it.
To densify to a greater relative
density of sandy soil in the pipe section (123), few extra drops of hammer
shall be needed on each layer
of the sandy soil in the pipe section (123), which is rather easy, less time
consuming and only few extra
dollars. The porous displacement piles with relative density greater than the
density of densified in-situ
soil densified by the rapid consolidation and compaction method, shall work as
a reinforcement to share
more load of an embankment or foundation of a structure than that by the
densified in-situ soil, thereby
reducing the total settlement of the structure and the embankment. All these
technical points should be
considered in design of the porous displacement piles for each project.
Fig. 3A shows a typical example for the support system to maintain the pipe
section (123) in vertical
position during compaction of sandy soil in the pipe section, and therefore,
it is desirable that the pipe
section is laterally supported by horizontal braces (111). The horizontal
braces are attached to vertical
column sections (110) on either side. The column sections are supported on a
concrete pad or a plate
and fastened into it by nails or bolts (114). Alternatively, the pipe section
(123) as shown in Fig. 3B is
maintained vertical by slipping it into another pipe section (116) which has
already been driven into
ground to sufficient depth to remain laterally stable; this pipe section (116)
also protrudes out of the
ground to maintain the pipe section (123) vertical and laterally stable while
compacting the sandy material
in it. The lateral support system shall be especially designed at each project
depending on the length and
size of the pipe section and soil conditions, at which time these typical
examples shall also be considered.
When the soil layers under water in a river or ocean are to be densified from
a boat or floating platform or
a ship, the lateral support system shall be specially designed with discussion
with their owners.
There are various types of hammer/weight available to drop on the sandy soil
placed inside the pipe
section (123) for densifying the sandy soil; any of these hammers/weights and
their attachments can be
used when considered appropriate according to specifications or brochures of
the manufacturers of the
equipment. There are many types of surface vibrators available in the industry
which can be used around
the pipe to densify sand inside the pipe section (123), when the weight or
hammer has already been
placed on top of the sandy material to compact it, or placing the vibrator on
top of a plate or vibrating
weight to densify sandy soil inside the pipe; any of the available systems if
appropriate can be used
following the manufactures' brochure or specification. There are many types of
pile driving hammers
including vibratory hammers available in the industry to drive a non-
displacement or displacement pile;
any of these driving hammers can be used when considered appropriate. There
are many types of pile
pipe pullers including vibratory pullers or pullers with hydraulically
operated jaws to grab the pile available
in the industry to pull the non-displacement or displacement pile out of the
ground; any of these pullers
can be used when considered appropriate. The attachments between the pipe
section or rod (127) and
the crane by U-Bolts or hooks etc., or attachment between the puller and the
pipe section (123) or the
surface vibrator to the pipe section (123) or plate vibrators etc. shall be in
accordance with the
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manufacture's specification and brochure. When the pipe section is being
driven, all attachments of pile
driving hammer shall be in accordance with pile driving specifications. Many
organizations do not allow
vibratory hammers to drive non-displacement or displacement piles in clayey
silty soils, because it is
considered that vibration remolds and disturbs the matrix and lock-in-stresses
of clayey silty soils.
Few typical examples of detachable or removable end plates are shown in Fig.
4A, Fig. 4B, Fig.5A, Fig.
5B, Fig. 5C, Fig. 5D, Fig. 6A and Fig. 6B. Fig. 4A shows a detachable end
plate which is attached by
bolts (131) to a hinge connection (130) on one end to the pipe section (123);
during driving the pipe
section (123), the detachable end plate (124) remains attached to the bottom,
but when pipe section
(123) is pulled out of the ground, the detachable end plate (124) connected by
the hinge (130) becomes
vertical as shown in Fig. 4B, assisting pulling of the pipe section (123) out
of the ground, but maintaining
the compacted sandy material in place. Fig. 5A shows a short piece of pipe
section or a snug corrugated
pipe (132) positioned inside the pipe section (123) but attached to the end
plate (124). During driving
steadily and carefully, a short pipe section (132) and end plate remains in
position at the bottom of the
pipe section (123), but when the pipe section (123) is pulled out of the
ground, the end plate (124)
attached to the short pipe or snug corrugated pipe section (132) is left
behind in the ground, as shown in
Fig. 5B. As an additional option, the section (132) can also be attached by
thin aluminum rivets to pipe
section (123), but these rivets shall break when weight of compacted sand
material exert its weight to
break the aluminum rivets. Fig. 5C shows the end plate (124) attached to a
plurality of connecting rods
(133) which are vertically installed upwards on diametrically opposite
locations outside the pipe section
(123) and held by bolts (135) near the top of the pipe section (123). The
connecting rods (133) pass
through a circular plate (136) supported by a plurality of angle sections
(140) and fastened by bolts (135)
near the top of pipe section (123). During driving the displacement pile, the
end plate (124) remains
attached, but before pulling the pipe section (123), the bolts (135) are
removed and when the section
(123) is being pulled out of the ground, the detachable end plate (124) is
left behind in the ground as
shown in Fig. 5D. In this way the compacted sandy material is left in place
forming a porous displacement
pile. At each project, the removable or detachable end plate may be especially
designed depending on
soil conditions and length and size of the displacement piles at which time
the above typical examples
shall also be considered.
The above details are applicable when the field operations to compact the
sandy material are being
performed at the location where the pipe section (123) is to be driven. When
the sandy material is being
compacted in the pipe section (123) at some other location and then to be
transported to the selected
location where it is to be driven in to the ground, the additional attachments
to end plate (124) are
required. In such cases, the detachable plate arrangement of Fig. 5A and Fig.
5B will still work, but some
improvement in Fig. 4A, Fig. 4B, Fig. 5A and Fig. 5B will be needed. As shown,
in FIG 6A, a plurality of
angle sections (137) is attached by bolt to the pipe section (123) on
diametrically opposite sides to each
other and also to the hinged connection (130). Fig. 6B shows the short pipe
section (132) attached by a
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plurality of bolts to pipe section (123) on diametrically opposite sides to
each other. When the pipe section
(123) has been transported to selected location for driving, it is necessary
to remove bolts (138) and slip
out the angle sections (137). Similarly, bolts (131) as shown in Fig. 6B has
to be removed, when end
plate is touching the ground, after which the crane slings be loosened to
lower down the displacement
pile on the ground.
For pulling the pipe section (123) successfully out of the ground, weight of
the weight or hammer (126)
kept on top of the compacted sandy material, is designed based on the side
frictional resistance
developed between the compacted sandy material inside pipe section (123) and
side frictional resistance
between outside of the pipe section (123) and in-situ soil around it and also
any suction force exerted by
the in-situ soil on the end plate during pulling of the pipe section.
Similarly, weight of the weight or
hammer and number and height of drops is designed to achieve the specified
density. Although,
structural members described for non-displacement and displacement pile
consist of circular section as
shown in the text and Figures, any non-common section of hollow rectangular,
or elliptical section or any
other non-common section will work with the RCCM and can be used on demand by
a client. During
driving the non-displacement or displacement pile, sometimes, it becomes
important to limit noise and
vibrations, in such cases, heavy hammers with very small height drops or
hydraulically pushing the piles
into the ground may become important so as to minimize or limit the damage or
risk to adjoining
structures. To monitor settlement of the adjoining structures, the settlement
readings both at the structure
and at the ground surface and at some depth in the ground may also be made.
Also, it may be advisable
to perform wave equation analyses for driving the pipe section (123) with a
selected hammer (Pile
Dynamics, Inc., 2005). To determine amount of improvement and increase in
density of the improved in-
situ soils, the subsurface exploration using the in-situ testing methods and
laboratory tests on the
extracted samples from the in-situ soil may also be performed before and after
installation of the porous
displacement piles.
The porous displacement pile consisting of the column of compacted sandy
material besides
densifying and improving soil around it, has another important function to
perform, which is to prevent the
passage or migration of clay or silty particles into the compacted sandy
material while allowing free flow of
water through the column of the compacted sandy material in order to dissipate
the excess pore-water
pressure. The gradation of the compacted sandy material to perform a function
of a filter to limit migration
of the fine material and allow free flow of water shall be designed based on
the design criteria for filters or
chimney filters used in earth dams or earth and rockfill dams, using the
Terzaghi's criteria with or without
some modification made by several organization such as US Bureau of
Reclamation, etc. (Prakash and
Gupta, 1972). The sandy material may consist of mixture of sand and little
quantity of small gravel, but
should satisfy requirements of allowing free flow of water and to prevent
migration of fine particle of in-situ
soil into the column of compacted sandy material. The sandy material should
not contain more than
specified quantity of fine particles in order to maintain its property of free
flow of water. Generally, well
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graded clean sands have been used in sand drains; the same type of material,
when meeting the filter
Criteria, could be used for the porous displacement piles.
Briefly Terzaghi's Criteria is briefly described as below:
(1) Piping or Migration of particles criteria: D85(Base) represents the
particle size that must be retained.
D15(Filter) is representative of average pore size. Filter to trap particle
size larger than about 0.1 D15(Filter)
D15 (filter) < 4 to 5 D85 (Base)
Permeability or Free Flow Criteria:
D15 (filter) > 4 to 5 D15 (Base)
Gradation Control
D50(filter) < 25 D50 (Base)
Sandy material in porous displacement pile performs as the filter. In-situ
clayey silty soil which surrounds
the compacted sandy material of the porous displacement pile, performs as the
base in the above criteria.
D15 is the diameter for which 15% of the material by weight is finer and D85
is the particle diameter for
which 85% of the material by weight is finer. In geotechnical engineering, the
focus of engineers is
generally to make the best use of the available soils in the vicinity of the
site. If for any reason, the sandy
soils in the vicinity of the project site are slightly out of the requirements
of the conservative Terzaghi's
criteria, then laboratory tests could be performed such as described by
Prakash and Gupta, 1972 or in
publications of United States Bureau of Reclamation or other publications, to
check whether on-site sandy
soils meet the filtration characteristics of chimney filters.
During piezocone cone penetration sounding in highly stratified and heavily
overconsolidated soft to
stiff soil with cone penetration resistance (qc) between 0.1 and 1 MPa, the
penetration pore-water
pressures ranging from 50 to 1.8 MPa (7.25 to 261 psi), values increasing with
depth below ground
surface were recorded from ground surface to depth of about 22-meter depth
(Peuchen, 2010). During
penetration of displacement piles in cohesive soils, penetration pore-water
pressures of this magnitude
shall be expected. Penetration pore-water pressures of 1.8 MPa equals 183.6
meter of water head from a
183 m (600 feet) high earth/concrete dam reservoir. Therefore, the compacted
sandy soil of the porous
displacement piles could experience such high pore-water pressures and
therefore should meet the
chimney filter criteria as used for earth and rockfill dams. In such cases, if
about a 1" (25 mm) pipe with a
porous disc at its bottom, is driven into porous a displacement pile, then one
can see clear water flowing
out from the top of the pipe.
The porous displacement piles comprising of the column of compacted sandy soil
have been
described above. There is another equally attractive method to install porous
displacement piles to
perform the same type of function, but it is more costly than the method
already explained. Porous
reinforced prestressed concrete piles (or even without prestress), or porous
pipe section with the end
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plate, or pipe section with small holes and the end plate, filled by the
compacted sandy material shall also
be installed through inside the non-displacement piles and shall be used as
the porous displacement
piles, if (1) drivable by a pile driving hammer into the soil without
exceeding allowable driving stresses, (2)
allow free drainage and flow of water and prevent migration of fine soil
particles of clays and silts or fine
sand in to the porous displacement piles, (3) the holes in the tube or pipe
section need to be quite small
so as to retain sandy material during compaction in the pipe section. These
porous displacement piles will
not require pulling out of the pipe section out of the ground and the
installation will also become easier
and faster. In many cases where soil layers consist of very sticky clays or
when batter piles are involved
or when any more vibration or noise cannot be tolerated, pulling out a pipe
section could be difficult or
may not be allowed by authorities.
In many areas such as in earthquake zones, the local building code may not
allow construction unless
the relative density is above a certain value. Table 1 gives liquefaction-
potential relationships between
magnitude of earthquake and relative density for a water table 1.5 m below
ground surface:
Table 1: Approximate relationship between earthquake magnitude, relative
density (Dr)and liquefaction
potential for water table 1.5 m below ground surface (From Seed and ldriss,
1971)
Earthquake High Liquefaction Potential for
liquefaction depends on Low Liquefaction
Acceleration Probability soil type and earthquake acceleration
Probability
0.10g Dr <33% 33% < Dr <54% Dr > 54%
0.15g Dr <48% 48% < Dr < 73% Dr > 73%
0.20g Dr < 60% 60% < Dr < 85% Dr > 85%
0.25g Dr < 70% 70% < Dr < 92% Dr > 92%
In such cases, RCCM shall be used to densify subsurface soil layers as needed
for the areas in 0.10g
zones to Dr of more than 55%, then relative density of sandy soil in the pipe
section may need to be
compacted to a minimum of 55% or greater. In areas of 0.15g zones, RCCM shall
be used to densify
subsurface soil layers to Dr of more than 75%, then relative density of sandy
soil in the pipe section may
need to be compacted to a minimum of 75% or greater. In areas in the 0.20g
zones, RCCM shall be used
to densify subsurface soil layers to Dr of more than 85%, then relative
density of sandy soil in the pipe
section may need to be compacted to a minimum of 85% or greater in order to
bring such areas in low
liquefaction probability. In areas in the 0.20g zones, RCCM shall be used to
densify subsurface soil layers
to Dr of more than 85%, then relative density of sandy soil in the pipe
section may need to be compacted
to a minimum of 85% or greater in order to bring such areas in low
liquefaction probability. In areas in the
0.25g zones, RCCM shall be used to densify subsurface soil layers to Dr of 95%
or more than 95%, then
relative density of sandy soil in the pipe section may need to be compacted to
a minimum of 95% or
greater in order to bring such areas in low liquefaction probability. The
spacing and diameter of the
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porous displacement piles need to be designed in order to achieve displacement
and void volume
reduction of the in-situ soil to achieve required densification and density
for the subsurface layers of the
site. From the above discussions, it is stated that the requirement of
compacting sandy soil in the pipe
section (123) to the particular relative density and spacing and diameter of
the porous displacement piles
shall depend on the subsurface soil conditions at a site, and the requirements
up to which the subsurface
layers are to be densified at that site.
Typical Examples of Industrial Applications of the RCCM
Ground Improvement under a spread footing
When a project requires ground improvement of the layer of soil, the RCCM can
provide an economical
and very useful solution. For example, a spread footing of a bridge foundation
is to founded on soil which
consists of a week layer of soil (140) and needs soil improvement in order to
support the loads from the
bridge superstructure. Fig. 7A shows a typical layout plan of the grid lines
(151) and location of the center
of porous displacement piles(150) consisting of the column of compacted sandy
material (125) in a
square or rectangular grid pattern. The locations marked by number "1" at the
grid intersection (150) are
the primary locations where the porous displacement piles shall be installed
first, using the method
described in the above paragraphs. The locations marked by number "2" at the
grid intersection are the
secondary locations where the porous displacement piles shall be installed
after completing the
installation at the primary locations. The secondary locations are usually
selected at the center of grid of
four primary locations. The locations marked by number "3" at the grid
intersection are the tertiary
locations where the porous displacement piles shall be installed after
completing the installation at the
secondary locations. The locations marked by number "4" at the grid
intersection are the final and last
locations where the porous displacement piles shall be installed after
completing the installation at the
tertiary locations. A similar arrangement for locations of the porous
displacement piles can also be made
in a triangular pattern or quadrilateral pattern as is done for vibro-
replacement columns, or any other
selected grid pattern selected for a particular configuration at a project
site.
Fig. 7B shows a sectional elevation view of the grid pattern shown in Fig. 7A.
In Fig. 7B, reinforced
concrete foundation (146) has been laid over mud mat (147). The porous
displacement piles consisting of
compacted sandy materials are installed to the design depth in the layer,
which in this case lies in the soil
layer (141). CASE 1: Assume top Layer (142) and bottom layer (141) consists of
sandy material and the
sandwiched layer (140) consists soft clay. In this case the pipe section with
detachable end plate can be
driven from the ground surface without driving a non-displacement pile first,
if the layer (142) is sufficiently
thick to reasonably minimize the heave at the top of the weak layer (140),
otherwise, it shall be advisable
to drive non-displacement pile first and then drive the pipe section (123)
with detachable end plate (124)
through inside the non-displacement pile. CASE 2: Assume the top layer (142)
consists of Clay and the
sandwiched layer (140) consists of loose sand and requires densification. In
this case, it is advisable to
drive the non-displacement pile first to the bottom of the top layer (142) or
to some small depth in loose
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sand layer (140). It shall be advisable to auger out the clayey soil from
inside the non-displacement pile
and the drive the pipe section (123) with detachable end plate (124) to the
design depth. This shall avoid
pushing the clayey soil into the loose sand layer, which can prevent
instantaneous densification of the
loose sand layer. Therefore, at each project, the subsurface soil profile
shall be carefully examined and
the installation method carefully designed. In some cases, the design may not
require installation of
porous displacement piles at tertiary (3) or final grid locations (4).
Ground Improvement under Embankments
The RCCM can be used under mechanically stabilized walls (such as
reinforcement earth wall) to reduce
and limit their settlements and also to develop required stability. The slopes
which are found not to have
enough factor of safety based on slope stability analyses when densified by
use of the RCCM, shall be
able to develop required factor safety for slope failures. The road and
highway embankments founded on
very soft layers of soils sink and settle sometimes by several inches or feet
or meters; and slopes of
2H:1V generally provided on opposite sides of the embankment are found to be
unstable, therefore
requiring very flat slopes. In such cases the RCCM shall densify the weak or
soft soils under the
embankments and reduce settlements to the reasonable limits and also improve
the slope stability of the
embankment slopes without requiring flatter slopes. One typical example is
shown in Fig. 8A and Fig. 8B.
As shown in Fig. 8A, a layer (142) of sandy material is first laid over very
soft clayey soil to build an
embankment of low height where the equipment can be brought to install the
porous displacement piles
consisting of the compacted sandy material. After the installation of the
porous displacement piles, the
embankment is further raised to full height by additional layers (143). As
shown in Fig. 8B, the clayey soil
is very weak and it cannot even support the embankment of low height to bring
the equipment on it, then
the porous displacement piles on primary locations (or even on secondary
locations) can be installed
ahead of the embankment of low height and then the embankment is extended
further and then the
porous displacement piles on secondary and tertiary locations can be
installed.
The rapid consolidation and compaction method (RCCM) can also be used in
coastal regions where
embankment is to be further extended into the ocean to build new land for
airports and housing projects
etc., and where the subsurface soils consist of loose sands and soft to very
soft clays. Similarly, new
islands can be built even where subsurface soils consist of loose and soft and
very soft soils underlies as
these subsurface soils can be densified by the rapid consolidation and
compaction method. To reduce
down drag on the piles driven in clayey and silty soils, the sand drains or
PVC (wick) drains are installed
and an embankment is built over them to consolidate the clayey silty layer for
certain time period for
generally up to 90% consolidation and then sometimes the embankment is removed
and the piles are
driven. In place of sand drains or wick drains, the RCCM to install porous
displacement piles can be used,
which shall rapidly consolidate the layer without requiring to build an
embankment and waiting for up to
90% consolidation. The RCCM can be used very economically for any layer of
soils or intermediate
geomaterial where soil improvement to densify it is required and also, where
ever, presently existing
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methods such as jet grouted columns, columns of cement or lime mixed with
clayey material or Geopiers
or vibro-replacement or vibro-floatation using a Vibro-probe, stone-columns as
bottom feed or top feed,
etc., are being used.
Ground Improvement under Tilting or Leaning Structures such as The Leaning
Tower of Pisa
There are many structures throughout the world which have tilted either during
construction or after
completion of the construction. The ground improvement using the rapid
consolidation and compaction
method for installation of porous displacement piles can improve the
foundation soils which will also result
in reducing the angle of tilt significantly and bring the leaning structure
close to about vertical. There are
many other structures in the Town of Pisa, Italy, which are tilting like
Leaning Tower of Pisa, but not to
this extent. First the porous displacement piles should be installed at other
tilting structures of Town of
Pisa to demonstrate the effectiveness of soil improvement in succeeding to
reduce the tilt with underlying
subsurface conditions, before considering to install porous displacement piles
at the Leaning Tower of
Pisa to reduce the tilt. To reduce the angle of tilt of the Leaning Tower of
Pisa, (i) the lead weights have
been placed on the north side on prestressed concrete ring around the
foundation of the leaning tower of
Pisa, (ii) steel cables to anchor the tower on north side to limit movement
towards south, (iii) Drill holes
installed to remove soil from the drilled holes on the north side, and (iv)
some excavation in east-west
direction (Jamiolkowsky, et al., 1993). However, no construction on the
southside has been permitted and
even subsurface exploration consisting cone penetration soundings has been
permitted 10 to 20 meters
from the south edge of the tower in order not to disturb the tower, although
construction as stated above
has been permitted on the north side. Prior to installation of porous
displacement piles, the additional
steel cables to anchor the tower could be considered to further anchor the
tower by steel cables in north-
east and north-west directions. If permission is granted by the concerned
authorities, the scheme of
installation of porous displacement piles as shown in Fig. 9 and Fig. 10 could
be worth consideration to
consolidate and densify the upper clay (named locally as Pancone Clay) between
El. -7 m and -18 m,
which has cone penetration resistance, qc, only between 1 to 1.5 M Pa
(Jamiolkowsky, et al., 1993). The
porous displacement piles are proposed to be installed at a batter of about
1V:2H ( or even between
1V:3H and 1V:1H as considered necessary), in order to achieve densification of
the upper clay (163) and
to possibly lift the foundation of the south side of the Leaning Tower of
Pisa. When Upper Clay (160) is
densified, its bearing capacity shall increase resulting in less settlement on
the south side. When the
angle of tilt is reduced, the bearing pressure on the south side will reduce
and the bearing pressure on
the north side will increase, causing more settlement on north side and
reducing settlement on the south
side of the tower foundation. Also, after stabilizing and densifying the Upper
Clay (163), the tendency to
further tilt on the south side of the tower foundation in future will be
prevented. The following description is
to demonstrate the industrial application of the ground improvement under a
leaning structure to reduce
its tilt. For that purpose, the Leaning Tower of Pisa has been selected.
Following steps are advisable to
implement the scheme:
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1. Perform subsurface investigation near the south side of the tower.
2. Install instruments to monitor vibrations and settlements both on ground
surface and in selected
depths below the ground surface and around the tower above the ground level.
3. Perform radar survey at designated points around the tower above ground
level, before and
during implementation of the scheme.
4. Fig. 9 shows the grid lines (151) and the locations (150) at grid line
intersections, where the
porous displacement piles could be installed.
5. Fig. 10 shows:(a) Ground surface elevation as El. 3.0 m (170), (b)
elevation of the bottom of
Clayey and Sandy yellow silt (162) as El. -7 m (171), (c) the elevation of the
bottom of Upper Clay
(163) as El. -18 m (172), (d) the elevation of bottom of the Intermediate Clay
(164) as El. -22.5 m
(173), ( e) the elevation of the bottom of the Intermediate Sand (164) as El. -
24.5 (173), and (f)
Lower Clay (166) underlies the intermediate sand (165).
6. The outside diameter of tower foundation (162) is 19.58 m with 4.5 m
diameter circular space in
the center. Lower portion of tower is designated as reference number 161 in
Fig. 10. Non
displacement piles (120) at a batter of 1H:2V are proposed to be driven first
up to the bottom level
of the foundation of tower. Pile Section (123) with detachable end plate (124)
and filled with
compacted sandy material shall then be driven through the non-displacement
pile (120) to
penetrate some small distance in the Intermediate Clay (164). After which the
pipe section will be
pulled out of the ground followed by withdrawal of non-displacement pile. The
porous
displacement pile (125) numbering from 1 through 5 shall be driven first as
shown in this Figure.
Pipe section (123) and detachable end plate (124) has not been shown in this
Figure.
7. The porous displacement piles at Grid Intersection Location No. 1, which is
15 meters from the
south edge of the Leaning Tower, and then at Location No.2 about 12 meters
from the south
edge, followed by at Location No. 3 at 9 meters from the south edge, at Grid
location 4 at 6
meters from south edge and Grid intersection location no. 5 at 3 meters from
the south edge
could be installed successively, to monitor and observe the settlement,
vibrations and movements
etc., continuously and to analyze the effects of installing the porous
displacement piles around
the tower when their locations get closer to the tower foundations.
8. When recorded data has been analyzed to determine the safety of the
tower and when found
satisfactory after installation of each porous displacement pile, then only
the installation of the
remaining porous displacement piles could be considered.
9. If permitted by the authorities, the installation at primary location in
the following order could be
considered: primary locations 6 through 13, then 14 through 21.
10. After analyzing the data and considered satisfactory to move ahead, then
installation at tertiary
location in the following order could be considered : Locations 22 through 27,
then 28 through 47
could be considered. Tertiary locations could be considered after evaluating
the reduction in tilt of
the leaning tower.
19
Date Regue/Date Received 2022-12-22
CA 03188126 2022-12-22
11. Subsurface exploration to be done to evaluate the improvement of
properties of Upper Clay after
completion of the construction of porous displacement piles.
12. Although only installing the batter porous displacement piles has been
shown in Fig. 10, the
vertical porous displacement outside the tower foundation in addition to those
shown in Fig. 9 and
Fig. 10 could also be installed to improve the density of upper clay outside
of the tower
foundation. The dispersion of the load of tower or any foundation is
considered to occur at a slope
of about 60 degrees.
13. In place of the installation of porous displacement piles consisting of
the column of compacted
sandy soil, the porous displacement pile consisting of porous pipe section
with attached end plate
or pipe sections with holes and containing compacted sandy material and end
plate can be
considered, as these sections will not need to be pulled out of the ground,
and will not involve the
disturbance and noise which will be associated with pulling the pipe section
out of the ground.
These porous displacement piles shall also be driven through inside the non-
displacement piles.
Densification under a structure undergoing settlement
When a structure such as a building or an oil or water tank is continuously
undergoing settlement on all of
its sides, then batter porous displacement piles on all sides penetrating
under the structure could be
installed to prevent or reduce further settlements significantly. The batter
displacement piles shall be
required to be installed in particular sequence, so that any instant, these
are evenly located symmetrically
around a structure. Porous displacement piles might consist of the column of
compacted sandy soil and
installed as described above. To reduce vibrations, noise and disturbance, the
porous displacement piles
comprising porous pipe section or pipe section with small holes and with end
plate and filled with
compacted sandy soil could also be considered to be installed. All
displacement piles shall be driven
through inside the non-displacement piles. The selection shall be made for a
particular site based on soil
conditions and environment around the structure.
Teachings of this Application
The various aspects of what is described in the above sections, can be used
alone or in other
combinations for other type of applications. The teaching of this application
is not limited to the industrial
applications described here-in-before, but it may have other applications.
Therefore, teaching of the
present application has numerous advantages and uses. It should therefore be
noted that this is not an
exhaustive list and there may have other advantages and uses which are not
described herein. Although
the teaching of the present application has been described in detail for
purpose of illustration, it is
understood that such detail is solely for that purpose, and variations can be
made therein by those skilled
in the art without departing from the scope of the teaching of this
application. Features described in the
preceding description/specification may be used in combination, other than the
combinations explicitly
described. Whilst endeavoring in the forgoing specification/description to
draw attention to those features
of the invention believed to be of particular importance, it should be
understood that Applicant and
Date Regue/Date Received 2022-12-22
CA 03188126 2022-12-22
Inventor claims protection in respect of any patentable feature or
combinations of features hereinbefore
referred to and/or shown in the drawings/Figures whether or not particular
emphasis has been placed
thereon. The term "comprising" as used in the claims does not exclude other
elements or steps. The term
"a" or "an" as used in the claims does not exclude plurality. A unit or other
means may fulfill the functions
of several units or means recited in the claims. As various possible
embodiments might be made of the
above invention, and as various changes might be made in the embodiments above
set forth, it is to be
understood that all matter herein described or shown in the accompanying
drawings is to be interpreted
as illustrative and not in a limiting sense.
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21
Date Regue/Date Received 2022-12-22
