U.S. patent number 3,691,776 [Application Number 04/886,550] was granted by the patent office on 1972-09-19 for expansive base pile construction.
This patent grant is currently assigned to Raymond International, Inc.. Invention is credited to Judd R. Hull.
United States Patent |
3,691,776 |
Hull |
September 19, 1972 |
EXPANSIVE BASE PILE CONSTRUCTION
Abstract
Pile installation with expansive base wherein the soil in a
desired bearing strata in the vicinity of the pile tip is displaced
by the tip into a region confined by a rim or skirt so that the
soil forms a solid plug between and frictionally locked to the pile
and rim or skirt.
Inventors: |
Hull; Judd R. (Pleasanton,
CA) |
Assignee: |
Raymond International, Inc.
(New York, NY)
|
Family
ID: |
25389242 |
Appl.
No.: |
04/886,550 |
Filed: |
December 19, 1969 |
Current U.S.
Class: |
405/232; 52/297;
52/298 |
Current CPC
Class: |
E02D
5/54 (20130101); E02D 5/72 (20130101) |
Current International
Class: |
E02D
5/00 (20060101); E02D 5/72 (20060101); E02D
5/22 (20060101); E02D 5/54 (20060101); E02d
005/54 (); E02d 005/72 () |
Field of
Search: |
;61/53,53.68,53.6,53.5,46 ;52/297,298 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
185,752 |
|
Jun 1956 |
|
OE |
|
461,146 |
|
Feb 1937 |
|
GB |
|
4,648 |
|
Jan 1920 |
|
NL |
|
31,604 |
|
Dec 1933 |
|
NL |
|
Primary Examiner: Shapiro; Jacob
Claims
What is claimed is:
1. In combination, a displacement pile positioned in the earth with
the lower end of the pile in a region characterized by
substantially non-cohesive granular soil, a perimeter defining rim
of substantial tensile strength also positioned in the earth and
surrounding a mass of soil around the lower end of said pile, the
soil surrounded by said rim being tightly packed by the
displacement of said pile and thereby having a higher density than
the surrounding soil, said soil surrounded by said rim further
being subjected to lateral compressive forces imposed thereon by
said rim, said lateral compressive forces being sufficient to
maintain a shear strength in the soil surrounded by the rim which
is substantially greater than that of the surrounding soil whereby
the soil within the rim is enabled to sustain column loading
imposed thereon by said pile.
2. A combination according to claim 1 wherein said interconnecting
means comprise spaced apart spokes extending between said pile
member and said rim.
3. A combination according to claim 2 wherein said spokes are
inclined with respect to the plane of the lower edge of said
rim.
4. A combination according to claim 2 wherein said spokes are
tilted with respect to the longitudinal axis of said pile.
5. A combination according to claim 2 wherein said spokes are
tapered from a maximum width at said pile to a minimum width at
said rim.
6. A combination according to claim 2 wherein said spokes are
embossed to increase their frictional interlock with a plug of soil
formed therebetween.
7. A combination according to claim 1 wherein said rim includes a
perimeter defining skirt integral therewith and extending upwardly
therefrom.
8. A combination according to claim 7 wherein said skirt is
embossed to increase its frictional interlock with a plug of soil
formed therein.
9. A combination according to claim 7 wherein said skirt is formed
with spiral grooves to permit movement thereof down through loose
soil by rotation therein.
10. A combination according to claim 7 wherein said rim is formed
by folding and hemming a lower edge of said skirt.
11. A combination according to claim 7 wherein said skirt is
strengthened by folds and hems about its circumference at different
distances from its lower edge.
12. A method of installing a displacement pile having a soil
displacing pile member and having at the lower end thereof a
perimeter defining rim of substantial tensile strength comprising
the steps of driving said pile down into the ground through an
upper strata of soft soil while said soft soil passes through the
space between the soil displacing pile member and the rim, and
thence driving said pile further into the ground into a different
bearing stratum characterized by a substantially non-cohesive soil,
while displacing the soil surrounded by the rim laterally in a
direction toward the rim by an amount sufficient both to compact
the ground between the pile member and the rim and to subject said
rim to substantial tension so as to cause said rim to impose
lateral compressive forces on said soil of sufficient magnitude to
produce a plug of said soil having a density and a shear strength
substantially greater than that of the surrounding soil for
frictionally interlocking said plug with said pile and effectively
forming an expanded base for said pile capable of sustaining column
loading imposed by said pile.
13. A method of installing a pile according to claim 12 wherein
said pile and rim are interconnected and are driven together.
14. A method of installing a pile according to claim 12 wherein the
rim is placed in the ground in advance of said pile.
15. A method of installing a pile according to claim 12 wherein
said rim is placed in the ground at the level of a bearing strata
which is primarily of non-cohesive granular soil of greater density
than the soil thereabove.
16. A method of installing a pile according to claim 12 wherein
said pile and rim are placed in the ground by vibrating said pile
at a frequency which tends to fluidize the soil between the pile
and rim in the regions above a desired bearing stratum and then
vibrating the pile at a frequency which tends to compact the soil
between the pile and rim at said desired bearing stratum.
Description
This invention relates to supporting of structural loads and more
particularly, it concerns novel pile arrangements providing
increased loading capacity in certain strata at various depths in
the earth.
Piles are elongated structural elements which are driven or
otherwise placed vertically in the ground; and they serve to
transfer a load, such as from the footing of a building, to a
stable region in the earth. In general, the extreme upper surface
of the earth is too soft and unstable to provide a sufficiently
firm and permanent support for a heavy structural load such as a
large building. Thus, in most heavy construction, piles are sunk
into the earth and are used to transmit the surface load down to
subsurface strata or layers which have a great supporting
capability.
In many locations, several strata of different densities and load
bearing capacity occur at different levels and at different
thicknesses between the surface of the earth and bedrock. Often,
certain of the more dense strata would suffice to support a given
load, except that they are of insufficient thickness; and the pile
pierces through them before sufficient load resistance is built up
between the bearing stratum and the pile. As a result, the pile
must be driven to a deeper supporting stratum, or even to bedrock,
before sufficient load resistance is achieved. This, of course, can
become quite expensive since piles of extraordinary length must be
employed and considerable driving is required.
Attempts have been made in the past to make effective use of
intermediate earth strata in the support of pile members. Such
attempts have involved the use of so-called "bulb" piles which are
elongated members having a bulbous configuration at their lower
end. The enlarged lower end of the pile serves to spread out its
earth contact area, thereby reducing the stress imposed on the
earth through the pile. Bulb piles, however, are expensive to
construct. Also, it is difficult to produce a balanced
properly-shaped bulbous configuration at the lower end of these
piles. Also, such piles are limited to concrete or other castable
material; and they must be formed on site.
According to the present invention there are provided novel pile
arrangements which make use of the support potential of
intermediate earth strata by reduction of the unit stress produced
by the pile on the earth. Moreover, these novel pile arrangements
do not require on site formation of the piles, nor are they subject
to the difficulties of construction associated with conventional
bulb piles.
In one aspect, the present invention involves selective
densification of the earth in the immediate vicinity of the pile
tip at the desired bearing stratum. This densification is such as
to make the surrounding earth effectively an integral part of the
pile base, thereby providing an enlarged base for distributing the
load carried by the pile.
According to the present invention, a soil displacement pile (i.e.,
a pile which forces aside the earth as it moves through the earth),
is driven into a region in which there is located a perimeter
defining tension element such as a rim or sleeve. The earth
displaced by the pile is forced into the space between the pile and
the rim. The rim is thus placed in tension and serves to maintain
the displaced soil under pressure. This compacts and densifies the
soil and increases its shear or rupture strength. At the same time,
the pressures developed serve to increase the frictional contact
between the soil, the pile and the rim. By proper choice of the rim
and pile diameters and rim height, the soil density and frictional
characteristics can be increased to a point where the soil between
the pile and the rim actually forms a solid plug locked to the
pile, thereby providing an effective enlarged base between the stem
and rim.
The present invention also permits selective soil densification at
different levels by taking advantage of the different soil
characteristics in different strata. For example, the pile system
of the present invention can be driven through upper earth layers
where the soil is not very dense and would not provide adequate
support. Thereafter, when the pile system reaches a more dense
strata, the above-described plugging action will take place to form
an enlarged pile tip at a location where it can most effectively
function.
This selective plugging is achieved with the present invention
because the spaces between the rim and pile in the softer less
dense strata are such that the soil displacement which takes place
as the pile is driven has relatively little effect on plugging or
friction characteristics. However, when the pile reaches a stratum
of more dense soil, the soil displacement produced by the pile has
a much greater effect on plugging and friction characteristics so
that a soil base is effected at the level where the soil has
greates support potential.
Various further and more specific objects, features and advantages
of the invention will appear from the description given below,
taken in connection with the accompanying drawings, illustrating by
way of example preferred forms of the invention.
In the drawings:
FIG. 1 is a diagramatic representation of a soil cross-section
showing a conventional pile and a pile according to the present
invention;
FIG. 2 is an enlarged perspective view, partially cut away, of the
base portion of the pile according to the present invention shown
in FIG. 1;
FIG. 3 is a section view taken along line 3--3 of FIG. 2;
FIG. 4 is a diagramatic representation of a slug of soil and forces
acting thereon for use in explaining the principles of the present
invention;
FIG. 5 is a graph used in explaining the operation of one aspect of
the present invention;
FIGS. 6 and 7 are cross-section views similar to FIG. 3 showing
modifications to the base construction of FIG. 3;
FIG. 8 is a perspective view similar to FIG. 2 showing a modified
base construction;
FIG. 9 is a fragmental section view, taken in elevation, of an
alternate base configuration;
FIGS. 10-13 are plan views of various configurations of the base
portion of the pile according to the present invention shown in
FIG. 1;
FIG. 14 is a view similar to FIG. 3 showing a modified spoke
configuration for the pile base of the present invention; and
FIG. 15 is an elevational view showing in outline, a multiple base
pile according to the present invention.
In FIG. 1, there is diagramatically represented an illustrative
earth profile which extends from an upper surface 20 down to
bedrock 22. The distance between these regions and the number, the
thickness and the characteristics of various intermediate strata
will vary depending on the geographical location and the geological
history of the site. In the illustrative case, however, the bedrock
22 is indicated as being approximately 160 feet below the upper
surface 20. There is shown an upper layer 24 of "soft soils" which
extends down from the surface 20 to a depth of about 60 feet. Below
this, and extending downwardly about 10 additional feet is an
intermediate stratum 26 of "medium dense to dense soils". Finally,
a lower layer 28 of "fine sandy silty clay" extends downwardly an
additional 90 feet to the bedrock 22.
A conventional 12 inch square cross-section pile 30 is shown on the
left side of FIG. 1. This pile is indicated as being designed to
support a load of two hundred tons. The upper "soft soils" layer 24
is of insufficient density or continuity to provide any reliable
support for the pile 30 and accordingly, no indication of load
resistance is shown in this region. Actually, there are surface
soils which produce a negative load resistance and tend to pull a
pile down. In such case, the extend of such downward pull must be
added to the load support requirements for the pile.
The intermediate stratum 26 and the lower layer 28 cooperate to
provide a frictional resistance to downward pile movement equal to
about 180 tons. It will be appreciated that this frictional
resistance will increase as the pile is driven deeper into these
layers since then more pile surface area is exposed to the
frictional action of the soil. There is also indicated an end
bearing restraint of 20 tons which completes the load resistance
for the pile. The amount of end bearing restraint depends upon the
density of the soil in this region and on the cross-sectional area
of the lower end of the pile. In the present case, because the pile
cross-section is one square foot and the load is 20 tons, the
pressure exerted on the soil is somewhat less than 300 pounds per
square inch.
It will be appreciated that in the situation described, the pile
makes no particular use of the potential end bearing support
characteristics of the relatively high density intermediate stratum
26. In this situation, only the comparitively minor frictional
restraint available from this stratum is utilized. The reason for
this is that when the pile tip reaches the intermediate stratum,
there is, up to this point, no significant frictional resistance
available. Thus, the end bearing requirements would equal
substantially the entire loading restraint, i.e., about 200 tons.
Moreover, since the pile tip has a cross-section of only 1 square
foot, the pressure exerted on the soil in this stratum would equal
nearly 1 and 1/2 tons per square inch. This is in excess of the
loading limits of the stratum and the pile tip will break through
and will proceed down into the lower layer 28 toward the bedrock
22.
On the right side of FIG. 1, there is shown a pile 32 constructed
according to the present invention and designed to support a
similar load of about 200 tons. As shown, the pile 32 comprises a
stem portion 34, of 12 inch square cross-section, and a base
portion 36 of enlarged configuration. As indicated, the enlarged
base portion is 31/2 feet in diameter and thus possess a bottom
area in excess of 91/2 square feet. This enlarged base then
distributes the 200 ton load so that the pressure exerted on the
soil is less than 300 pounds per square inch, or about the same as
the pressure produced in the softer lower layer 28 by the bottom of
the left hand pile 30. Thus, the denser intermediate stratum 26 is
rendered capable of supporting the same two hundred ton load using
a far shorter pile than would normally be required.
The structural configuration of the base portion 36 of the pile 32
is illustrated in FIGS. 2 and 3. As there shown, the base portion
comprises an outer rim 38, connected by a plurality of radial
spokes 40, to a central hub 42. The hub 42 is configured to
accommodate the lower tip of the pile stem portion 34 and to
receive downward driving and loading forces from the stem. These
forces are transmitted via the spokes 40 to the rim 38. A
cylindrical skirt 44 is attached, as by welding, to the rim 38 and
extends upwardly therefrom.
The pile 32 is installed by assembling the stem portion 34 on the
base portion 36 and driving downwardly on the stem portion to force
the entire assembly down through the earth.
During driving of the pile down through the upper layer 24 of soft
soils, the soil will readily pass through the spaces between the
spokes, hub and rim of the base portion 36. Thus, no substantial
restraint to driving is offered by the soil in the upper layer 24.
When, however, the base portion 36 reaches the denser soil
comprising the intermediate stratum 26, the soil packs more tightly
in the spaces between the spokes, hub and rim. This results in a
plugging or arching action whereby the soil becomes held so tightly
by frictional engagement with the spokes, hub and rim that it
effectively becomes an integral part of the pile base itself. The
base portion is thus enlarged or completed by the earth plug
between the hub 42 and the rim 38. As a result, the base portion
serves to distribute the loading force of the pile over an area
corresponding to the cross section enclosed by the rim.
FIG. 3 illustrates the manner in which the plugging action occurs.
As the pile stem 34 moves downwardly through the earth, it
displaces soil laterally along paths indicated by the arrows 46. As
can be seen, this displace soil enters the spaces between the pile
stem 34 and the rim and skirt 38 and 44. In addition, the soil
directly under these spaces also enters them as the assembly moves
down. It will be appreciated that the soil passing through the
spaces thus becomes compacted. This compaction has relatively
little influence on friction where the soil is soft, as in the
upper layer 24. HOwever, in the intermediate stratum 26, where the
soil is already medium dense to dense, the compacting results in a
rapid pressure rise which greatly increases the friction between
the soil and the various surfaces of the spokes, rim and skirt and
the pile stem. The unit friction is thus increased by this
pressurization. At the same time, the total friction is increased
as the pile is driven further down since greater amounts of rim,
spoke, skirt and stem surfaces are subjected to the action of the
pressurized soil. Eventually, the total frictional restraint comes
to exceed the total end resistance of the base portion 36. At this
condition, if the pile stem and base assembly are forced further
down, the soil in the spaces between the stem, rim and spokes will
not slide up, but instead, will force down against the underlying
soil and cause it to fail. However, at this condition, the total
loading is now spread over a substantially greater area and the
unit loading on the underlying soil is considerably reduced.
In order for plugging action to occur, it is necessary also that
the shear strength of the soil performing the plugging action be
sufficiently high to sustain the load to which the pile is
subjected. Otherwise, a shearing action will occur within the soil
itself between the stem, rim and spokes of the pile base. It is an
important feature of the invention that the combination of the soil
displacing stem portion 34 and the perimeter defining and pressure
retaining rim 38 and skirt 44 serves, by mutual cooperation of
these elements, to increase the shear strength of the soil between
these elements to a point where the soil will act as a solid
structural portion of the pile base and will not fail under pile
loading.
The manner in which shear strength of the soil between the stem,
spokes and rim of the pile base is increased by the present
invention can be seen in FIGS. 4 and 5. FIG. 4 shows
diagramatically a cylindrically-shaped slug 50 of granular,
non-cohesive soil. All soils can be classified as either cohesive
or non-cohesive. In general, non-cohesive soils are those which are
made up of solid rock particles which may vary in size from gravel
down to fine sand. Such soils are generally pervious enough to
permit the water occupying the interstices between the soil
particles to escape as the pile penetrates the soil, thereby
allowing densification of the soil to occur. When the particles
become much smaller than silty sand and become shaped in a special
way, however, they do interact with water and retain it. The soil
then becomes cohesive and sticks together. Clay is a classic
example of a cohesive soil. To a certain extent, the presence in
soil of organic materials will contribute to cohesiveness. Most
soil is a blend of cohesive and non-cohesive components, the
relative amounts varying from location to location and from depth
to depth. For structure supporting purposes, a large non-cohesive
characteristic is desired since it is not subject to hydrostatic
effects and it will not shift in time to the extent that most
cohesive soils will. While the present invention can be used in
many cohesive soils, its action in increasing soil shear strength
to improve plugging is especially effective in the case of
non-cohesive soils.
The slug 50 of FIG. 4 being of a granular non-cohesive soil may be
considered as being made up of a large number of small solid
particles, for example very small marbles. The particles are
confined circumferentially by lateral stresses illustrated by
lateral arrows .sigma..sub.3. These stresses may be supplied from
the surrounding soil, or in the case of the present invention, they
are supplied by the rim 38 and the skirt 44. At the same time, the
soil is subjected to longitudinal loading stresses illustrated by
the vertical arrows .sigma..sub.1. These stresses, in the case of
the present invention, are the pile load, applied via the pile
stem, spokes and rim acting downwardly, and the underlying soil
acting upwardly. Now when the longitudinal loading stresses
.sigma..sub.1 exceed the shear strength for the soil, the soil will
fail and in the present case, will push through the spaces between
the stem, rim and spokes.
The relationship between the lateral restraining stresses
.sigma..sub.3, the longitudinal loading stresses .sigma..sub.1, and
the shear stress in a non-cohesive granular soil are shown
graphically in FIG. 5. The rupture envelope is defined by a
straight line which begins at the origin O of the Mohr diagram and
rises upwardly at an angle .phi.. The angle .phi. increases with
soil density so that, as shown, the rupture line A for a less
densely packed soil will have a shallow angle .phi..sub.1, whereas
the rupture line B for a more densely packed soil will have a
steeper angle .phi..sub.2.
It can be seen in FIG. 5 that the maximum longitudinal stress is a
function of the lateral stress and the angle .phi.. For example,
for the angle .phi..sub.1 and the lateral stress .sigma..sub.3 the
corresponding maximum longitudinal stress is .sigma..sub.1. Note
that the maximum longitudinal stress .sigma..sub.1 is related to
the lateral stress .sigma..sub.3 and angle .phi..sub.1 by a circle
M.sub.1 whose center is located on the abscissa to the right of
.sigma..sub.3 which is tangent to the rupture envelope defined by
.phi..sub.1. If the angle were to remain equal to .phi..sub.1 but
the lateral stress increase to .sigma..sub.3 ', then there is a
substantial increase in maximum longitudinal stress as shown by
.sigma..sub.1 ' in FIG. 5. M.sub.2 is the circle which determines
the location of.sigma.of .sigma.1'. Now if in addition to an
increase in lateral stress from .sigma..sub.3 to .sigma..sub.3 '
there was an increase in .phi. from .phi..sub.1 to .phi..sub.2,
there would be an even greater increase in maximum longitudinal
stress .sigma..sub.1 " as determined by circle M.sub.3.
The pile driving arrangements of the present invention increase the
rupture shear stress or longitudinal load bearing capacity of the
soil between the pile stem, spokes and rim in both of the two ways
described above. Firstly, because the pile stem displaces soil and
forces it into the spaces surrounded by the rim 38 and skirt 44,
the soil becomes more densely packed. Thus, the characteristic
angle .phi. is raised from .phi..sub.1 to .phi..sub.2. Secondly,
the rim and skirt each have substantial tensile strength and thus
restrain the outward radial movement of the soil displaced by the
pile stem. This causes an increase in the lateral restraining force
.sigma..sub.3. As a result of these two factors, the shear strength
of the soil between the stem, rim and spokes is very substantially
increased, and a very positive plugging action can be achieved.
As indicated above, effective plugging which will permit the soil
between the pile stem, spokes and rim to act as an integral part of
the pile base and contribute to its support, depends upon both an
increase in the shear strength of the soil and an increase in the
friction between the soil and the surfaces of the pile stem, spokes
and rim.
The friction increase can be provided by increasing the surface
area of the spokes and rim. In this connection, the skirt 44 forms
an extension of the rim 38 and contributes to an increase in
frictional surface area. In addition, the number and vertical
height of the spokes 40 may be increased to raise the total
friction level. The relative sizes of the soil displacing pile stem
and of the spaces between the stem, spokes and rim required to
introduce plugging and the total friction surface area of the stem,
rim and spokes required to secure the plug to the pile depends, of
course, on the nature of the soil at the depth plugging is desired.
This information can be obtained by means of soil tests made at the
location where the pile is to be installed.
There are a number of modifications of the present invention which
may enhance its effectiveness under different installation
conditions. FIG. 6, for example, shows an arrangement for the pile
base 36 wherein the spokes 40 between the hub 42 and the rim 38 are
inclined downwardly away from the hub at a negative angle (-.alpha.
). This positions the rim 38 and skirt 44 ahead of the stem 34.
This serves to enhance the plugging action since it ensures that a
greater portion of the soil displaced by driving the stem will be
restrained by the rim and skirt.
FIG. 7, on the other hand, shows an alternate arrangement where the
spokes 40 are inclined upwardly away from the hub 42 at a positive
angle (+.alpha.). This positions the rim 38 and skirt 44 behind the
stem 34. While the effectiveness of plugging is reduced with this
arrangement, it permits a more stable interconnection between the
base and stem for driving the base with the stem.
FIG. 8 shows a modification wherein the spokes 40 are tilted at an
angle .beta. relative to the longitudinal axis of the stem-base
combination. Also, pins 60 are provided to secure the hub 42 to the
stem 34 in a manner permitting them to rotate together. Thus, by
turning the stem, the base can be made to rotate and the tilted
spokes 40 will bore through the softer upper soils in auger-like
fashion. They will also assist more effectively in the soil plug
formation and friction lock action when the pile is later driven
down into the bearing stratum. The auger action may also be
enhanced by the provision of spiral corrugations on the outer
surface of the rim and skirt as illustrated at 62 in FIG. 8. Also,
either the skirt 44, or the spokes 40 may be roughened or provided
with an embossed surface, as indicated at 63, to enhance their
frictional characteristics.
The rim and skirt may be formed from a single piece as illustrated
in FIG. 9. As there shown, a sheet metal skirt 64 of light gage
steel is folded and hemmed along its lower edge to form a stiff rim
66. Similar crimping 68 may be provided at various levels to
provide additional stiffness where needed. Also, vertical ribs 70
may be added or formed by crimping where reinforcing is needed in a
vertical direction.
FIGS. 11--13 show alternate rim and spoke configurations. In FIG.
10, a pair of concentric rims 72 and 74, interconnected by spokes
76, are provided to increase the number of spaces in which soil
plugs may be formed. This is advantageous where a base of large
cross-section is to be formed in soil which requires relatively
small spaces to form effective plugs. FIGS. 11 and 12 illustrate
the use of rim and skirt configurations which form square and
triangular perimeters 77 and 78 to provide the soil pressure
retention required for plugging action. While square and triangular
skirt configurations are illustrated, others may also be employed.
It is important, however, that they provide a perimeter defining
enclosure to maintain sufficient pressure retention to achieve soil
plugging in the vicinity of the pile stem.
FIG. 13 illustrates an arrangement wherein the spokes 40 are of
different lengths so that the hub 42 is not centered in the rim 38.
This serves to offset the rim with respect to the pile stem; and is
useful, for example, in driving close to existing structures and
footings.
FIG. 14 shows a pile base 34 with modified or tapered spokes 40a.
As can be seen, the spokes 40a are widest where they connect to the
hub 42, and are narrowest at the rim 38. This helps to counteract
the higher moments produced at the spoke-hub junctions when the
pile system is driven downwardly by means of the stem.
FIG. 15 shows a pile system comprising a common stem 80 and a
plurality of base portions 82a, 82b at different levels. Each base
portions is of a construction similar to those described above and
each makes use of a plugging action as above-described. By use of
plural base portions, the loading may be distributed among
different bearing strata at different levels.
It will be appreciated that the pile construction arrangements of
the present invention may be employed in the case of tension or
anchor piles which are required to resist upward forces.
Although the various base configurations described herein have been
shown as arranged to be driven by the pile stem, it should be
understood that the rim and skirt may be independently drive; and
in fact, need not have any physical connection to the stem except
via the soil plug formed between them. In such case, the spokes may
be eliminated entirely. For example, the base may simply consist of
a rim and/or a skirt driven in place by some means, such as a
vibrator. The stem may thereafter be driven as an ordinary pile;
and when it reaches the level of the base, the soil confining and
pressure retention characteristics of the base will cause the soil
displaced by the stem to form a load supporting soil plug
frictionally interlocked with the stem.
The base, including the rim, skirt, spokes and hub, may be made of
metal or some other material which is capable of being driven into
the soil and which is capable of restraining the soil displaced by
the stem sufficiently to maintain the lateral pressure restraint
necessary for the plugging action. The base material should also be
capable of resisting the corrosive effects of a subterranean
environment. Some materials which may be employed are steel
masonry, concrete, certain plastics, ceramics and wood or paper
products, as well as combinations thereof.
Various driving techniques may be employed with the present
invention. For example, conventional hammers or vibrators, or a
combination of both may be used. In the event that vibrators are
employed, the stem and/or base may be vibrated at one frequency
down to the desired bearing stratum and at another frequency at the
bearing stratum. The first vibratory frequency would be that which
induces fluidization of the soil through which the stem and/or base
are being driven. This allows free flow of soil through the spaces
between the stem, rim and spokes. Thereafter, at the desired
bearing stratum, the elements are vibrated at a different frequency
known to induce compaction and of the soils thereby to effect
plugging of the spaces between the stem, spokes and rim.
It will be appreciated that there has been described novel pile
installation arrangements whereby a pile of an enlarged base may
easily be formed by causing the soil adjacent the base to become
effectively an integral part of the base.
* * * * *