U.S. patent number 3,824,797 [Application Number 05/267,753] was granted by the patent office on 1974-07-23 for evacuated tube water hammer pile driving.
This patent grant is currently assigned to Orb, Inc.. Invention is credited to Serge S. Wisotsky.
United States Patent |
3,824,797 |
Wisotsky |
July 23, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
EVACUATED TUBE WATER HAMMER PILE DRIVING
Abstract
Driving long piles into submerged lands with a liquid ram or
spear generated in an evacuated tube. Various drivers are enclosed.
In one embodiment, the pile itself is used as at least a portion of
the working chamber for generating water hammer.
Inventors: |
Wisotsky; Serge S. (Sharon,
MA) |
Assignee: |
Orb, Inc. (Marion, OH)
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Family
ID: |
26859633 |
Appl.
No.: |
05/267,753 |
Filed: |
June 30, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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163422 |
Jul 16, 1971 |
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Current U.S.
Class: |
405/228; 175/56;
173/1; 181/120 |
Current CPC
Class: |
E02D
7/26 (20130101); E02D 7/28 (20130101); E02D
7/00 (20130101); E02D 7/02 (20130101) |
Current International
Class: |
E02D
7/00 (20060101); E02D 7/28 (20060101); E02D
7/02 (20060101); E02D 7/26 (20060101); E02d
007/10 (); G01v 001/38 () |
Field of
Search: |
;61/53.5,63,46.5 ;173/1
;181/.5H ;114/206 ;175/56 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Shapiro; Jacob
Attorney, Agent or Firm: Priddy; Robert R.
Parent Case Text
CROSS-REFERENCE
This is a continuation-in-part of an abandoned prior copending
application Ser. No. 163,422, filed July 16, 1971 and now
abandoned, the disclosure of which is hereby incorporated by
reference.
Claims
What is claimed is:
1. In the driving of piles underwater, wherein the pile has its tip
embedded in the subsoil of a body of water and an evacuatable
enclosure with side walls and a lower barrier is effectively
coupled with the tip of the pile for transmitting driving forces
exerted upon said barrier to said tip, the method which comprises:
evacuating at least a portion of said enclosure, thereby removing
water and at least a portion of any gases or any vapors which may
be present in the evacuated portion and evacuating sufficiently to
provide space for acceleration and deceleration of a mass of water
adequate to produce the necessary force and energy for driving said
pile; accelerating along the axis of said pile a mass of water
which moves substantially independent of said pile in said
evacuated portion of said enclosure; suddenly decelerating said
mass against said barrier, thereby converting hydraulic kinetic
energy to a water hammer driving pulse for driving said pile into
said subsoil; and repetitively evacuating, accelerating,
decelerating and driving as aforesaid.
2. A method in accordance with claim 1 wherein said evacuatable
enclosure is beneath the surface of said body of water, and the
mass of water accelerated along the axis of said pile is
accelerated under the influence of the hydrostatic head in said
body of water.
3. A method in accordance with claim 1 wherein said evacuatable
enclosure is in communication with a reservoir, and the mass of
water accelerated along the axis of said pile is accelerated under
the influence of a hydrostatic head in said reservoir.
4. A method in accordance with claim 3 wherein said reservoir is
pressurized with gas or vapor.
5. A method in accordance with claim 1 wherein said enclosure is
within said pile.
6. A method in accordance with claim 1 wherein the walls of said
enclosure are defined at least in part by the walls of said
pile.
7. A method in accordance with claim 1 wherein the driving force is
applied to said pile through a coupling which is below the top of
the pile.
8. A method in accordance with claim 7 wherein the coupling is
closer to the subsoil of said body of water than to the top of said
pile.
9. A method in accordance with claim 1 wherein the enclosure is
evacuated by pumping.
10. A method in accordance with claim 1 wherein said enclosure is
evacuated with a condensable vapor.
11. A method in accordance with claim 10 wherein said condensable
vapor is condensed, and the acceleration of said mass of water is
commenced, by spraying cool water into the condensable vapor.
12. A method in accordance with claim 1 wherein said enclosure is
evacuated with combustion gases that are at least partially
condensable.
13. A method in accordance with claim 1 wherein said enclosure is
evacuated by forcing the water away from the barrier with piston
means.
14. A method in accordance with claim 13 wherein said piston means
is moved by pressure exerted thereon by condensable vapor, and said
condensable vapor is then condensed to commence the acceleration of
said mass of water along the axis of said pile.
15. A method in accordance with claim 1 wherein the acceleration of
said mass of water along the axis of said pile is commenced by the
rapid opening of valve means communicating between said enclosure
and a source of water under pressure.
16. A method in accordance with claim 15 wherein said valve is
retained closed during evacuation of said enclosure and opens in
response to the water reaching a predetermined level in the
evacuation of said enclosure.
17. A method in accordance with claim 15 wherein a hydrostatic head
in said source of water is applied to said valve for assisting in
the rapid opening thereof.
18. A method in accordance with claim 15 wherein the water hammer
intensity is controlled by controlling the rate at which said valve
is opened.
19. A method in accordance with claim 1 wherein said pile is driven
in either direction by valves at both ends of said enclosure and by
controls for driving along the tube axis in either direction.
20. A method in accordance with claim 1 including selectively
retarding the axial velocity of said mass of water for varying the
pressure and time characteristics of the water hammer driving pulse
to compensate for varying strata and driving conditions.
21. A method in accordance with claim 20 wherein said axial
velocity is retarded by retarding the opening of a valve which
commences the acceleration of said mass of water.
22. A method in accordance with claim 20 wherein said axial
velocity is retarded by baffle means in said enclosure.
23. A method in accordance with claim 20 wherein said axial
velocity is retarded by imparting a twisting motion to the mass of
water which moves along the axis of said enclosure.
24. A method in accordance with claim 1 wherein the mass of water
accelerating along the axis of said enclosure substantially fills
the cross section of said enclosure.
25. A method in accordance with claim 1 wherein the water
decelerated against said barrier has substantially theoretical bulk
density on impact.
26. A method in accordance with claim 1 wherein the mass of water
decelerated against said barrier has less than one-fourth the mass
of said pile.
27. A method in accordance with claim 1 wherein said pile has a
length to diameter ratio of equal to or greater than 15, said pile
is submerged in water 200 feet deep or deeper, said evacuatable
enclosure is beneath the surface of said body of water, and the
mass of water accelerated along the axis of said pile is
accelerated under the influence of the hydrostatic head in said
body of water.
28. In the dirving of piles underwater, wherein a pile having a
length to diameter ratio of equal to or greater than 15 has its tip
embedded in the subsoil of a body of water 200 feet deep or deeper
and an evacuatable enclosure with side walls and a lower barrier is
effectively coupled with the tip of the pile for transmitting
driving forces exerted upon said barrier to said tip, the method
which comprises: evacuating at least a portion of said enclosure,
by removing water and at least a portion of any gases or any vapors
which may be present in the evacuated portion and evacuating
sufficiently to provide space for acceleration and deceleration of
a mass of water adequate to produce the necessary force and energy
for driving said pile; accelerating along the axis of said pile a
mass of water which moves substantially independent of said pile in
said evacuated portion of said enclosure; selectively retarding the
axial velocity of said water mass for varying the pressure and time
characteristics of a water hammer driving pulse to be generated by
impact of said mass against said barrier; suddenly decelerating
said mass against said barrier, thereby converting hydraulic
kinetic energy to said water hammer driving pulse for driving said
pile into said subsoil; and repetitively evacuating, accelerating,
decelerating and driving as aforesaid.
29. A method in accordance with claim 28 wherein said axial
velocity is retarded by retarding the opening of a valve which
commences the acceleration of said mass of water.
30. A method in accordance with claim 28 wherein said axial
velocity is retarded by baffle means in said enclosure.
31. A method in accordance with claim 28 wherein said axial
velocity is retarded by imparting a twisting motion to the mass of
water which moves along the access of said enclosure.
32. In the driving of piles underwater, wherein a pile having a
length to diameter ratio of greater than or equal to 15, a diameter
of three feet or larger and a length of 200 feet or longer has its
tip embedded in the subsoil of, and is completely submerged in, a
body of water at least about 200 feet deep, and has an evacuatable
enclosure beneath the surface of said body of water with side walls
and a lower barrier effectively coupled with the tip of the pile
for transmitting driving forces exerted upon said barrier to said
tip, the method which comprises: evacuating at least a portion of
said enclosure, by removing water and at least a portion of any
gases or any vapors which may be present in the evacuated portion
and evacuating sufficiently to provide space for acceleration and
deceleration of a mass of water adequate to produce the necessary
force and energy for driving said pile; accelerating along the axis
of said pile under the influence of the hydrostatic head in said
body of water a water ram or spear having a length to diameter
ratio of 10 or more which moves substantially independent of said
pile in said evacuated portion of said enclosure; suddenly
decelerating said mass against said barrier, said water being at
substantially theoretical bulk density on impact, thereby
converting hydraulic kinetic energy to a water hammer driving pulse
for driving said pile into said subsoil; and repetitively
evacuating, accelerating, decelerating and driving as
aforesaid.
33. A method in accordance with claim 32 in which the evacuated
portion of said enclosure is 50 feet in length or longer.
34. In the driving of piles underwater, wherein the pile has its
tip embedded in a subsoil of a body of water and an evacuatable
enclosure with side walls and a lower barrier is effectively
coupled with the tip of the pile for transmitting driving forces
exerted upon said barrier to said tip, the method which comprises:
evacuating at least a portion of said enclosure, by removing liquid
and at least a portion of any gases or any vapors which may be
present in the evacuated portion and evacuating sufficiently to
provide space for acceleration and deceleration of a mass of the
liquid adequate to produce the necessary force and energy for
driving said pile; accelerating along the axis of said pile a mass
of said liquid which moves substantially independently of said pile
in said evacuated portion of said enclosure; suddenly decelerating
said mass against said barrier, thereby converting hydraulic
kinetic energy to a liquid hammer driving pulse for driving said
pile into said subsoil; and repetitively evacuating, accelerating,
decelerating and driving as aforesaid.
Description
BACKGROUND
The kinetic energy output of a pile driver is the product of its
driving mass and its velocity at the instant of impact with a pile.
The emplacement of piles in the ground by pile driving is
accomplished by transmitting the kinetic energy of a hammer or
other driving mass to a pile in sufficient quantity to cover
nonproductive energy consuming factors such as impact stresses,
radiation, reflection and ground quake, and to overcome the
friction, elasticity and inertial impedence components of the pile
and ground.
Increasingly larger land-based and offshore structures are
constructed year after year. Larger structures demand longer and
more massive piles for their foundations, more deeply embedded in
the ground. This requirement is particularly severe in the case of
large off-shore installations such as ship terminals, and oil
drilling, production and storage facilities. Without suitable
foundations, such structures weighing tens of thousands of tons can
be readily dislodged and toppled by heavy storms, large vessels
bumping, earthquakes, ice floes, often with catastrophic loss of
life, damage to the environment and loss of invested capital. Thus,
to provide adequate load-bearing and to prevent pull-out,
requirements exist for driving piles hundreds of feet long, several
feet in diameter, weighing hundreds of tons, and for continuing the
driving to depths of soil penetration where driving resistance is
severe.
A complex series of relationships pertaining to pile and soil
characteristics, driving environment, economics and materials
governs the design of a pile driver. However, generally speaking,
the advent of piles of greater mass and conditions productive of
more severe driving resistance require drivers of increasing
kinetic energy output. In the absence of adequate driving energy,
that which is available is consumed largely or completely by the
aforementioned nonproductive energy consuming factors, leaving
little or no energy to drive the pile. Under such conditions, some
help is obtained by palliatives such as drilling a pilot hole,
water jetting or grouting into an over-size hole, but these
measures normally reduce load-bearing capacity. Thus, as each new
generation of more massive piles and more severe driving conditions
arises, drivers of greater energy output must be designed.
The kinetic energy output of an existing hammer can be increased by
increasing either its mass or its impact velocity. The latter
alternative is unattractive for a number of reasons.
First, there is the matter of the efficiency with which the hammer
transfers energy to the pile. In a complete inelastic collision
between a hammer and pile, the kinetic energy remaining after
impact for overcoming the nonproductive factors and driving the
pile is in proportion to the ratio of the hammer mass divided by
the total mass of hammer plus pile. An increase in pile mass
without a corresponding increase in hammer mass results in a
reduction of driving efficiency.
Also, higher hammer velocities are more predisposed to product high
local impact stresses. When the latter exceed the yield point of
the pile material, kinetic energy is wasted and efficiency
reduced.
For these and other reasons, manufacturers discourage the use of a
pile driver in which the hammer's mass is less than one-fourth that
of the pile, and a mass ratio of one-half is generally recommended
for land-based operations.
This presents a dilemma in off-shore pile driving. The largest
steam hammer pile drivers currently in use in off-shore/marine work
are limited, practically, by safety considerations relative to
their handling in stormy weather, to weights on the order of 60
tons (hammer mass about 30 tons). Consequently, they usually are
inadequate to drive the larger piles due to mass-mismatch.
For instance, with a 200-ton pile, the energy transfer efficiency
of a 30-ton hammer would be 100 percent .times. 30/(30 + 200) or
about 13 percent. Moreover, even this relatively small amount of
energy transferred to the pile is not altogether effective in
driving for other reasons stated below.
The picture is further complicated by the fact that the energy in a
pile is effective to penetrate the soil only if there is a proper
impedance match between the force-time-displacement characteristics
of the driver and corresponding parametric thresholds of the soil.
The available alternatives for varying the force-time-displacement
characteristics of a steam hammer are limited, and this presents
practical problems as the tip and sides of a pile often pass
through strata of widely varying characteristics as the pile
penetrates the earth.
Thus, under the severest conditions, pile driving is an arduous,
time consuming and expensive task which sometimes ends in failure
to achieve design load-bearing capacity or depth. Also, the
inability to drive large piles to sufficient depths often
necessitates driving a larger number of smaller piles, so that as
many as eight or 16 piles may be required for the foundation of a
single log of a multi-leg offshore structure.
Bearing in mind the storm-weather safety considerations mentioned
above, it is of interest that at least one pile driver manufacturer
has proposed for offshore operations a pile driver, nominally rated
at almost 500,000 ft. lb., weighing on the order of 230 tons,
equivalent to the weight of several locomotives. Lifting this
gigantic mass and adequately securing it during storm conditions
present major challenges. Nevertheless, the fact that at least some
of those active in the art seem ready to accept these formidable
challenges suggests the severity of the problems and limitations
with which the pile driving art is now struggling.
SUMMARY OF THE INVENTION
The method of the present invention is carried out in a long,
massive pile which is, or is intended to be, part of the foundation
for a large offshore structure. The pile has its tip embedded in
the subsoil of a body of water. An evacuatable enclosure with
sidewalls and a lower barrier is effectively coupled with the tip
of the pile for transmitting driving forces exerted upon said
barrier to said tip. The method comprises: evacuating at least a
portion of said enclosure, by removing water and at least a portion
of any gases or vapors which may be present in the evacuated
portion and evacuating sufficiently to provide space for
acceleration and deceleration of a mass of water adequate to
produce the necessary force and energy for driving said pile;
accelerating along the axis of said pile a mass of water which
moves substantially independent of said pile; suddenly decelerating
said mass against said barrier, thereby converting hydraulic
kinetic energy to a water hammer driving pulse for driving said
pile into said sub-soil and repetitively evacuating, accelerating,
decelerating and driving as aforesaid. Using this method, it is
possible to generate powerful mechanical impulses whose force-time
characteristics can be tailored over a wide range of values to
better match the driving requirements of various pile and soil
conditions. Other advantages will be discussed along with certain
preferred embodiments of the invention as illustrated in the
accompanying drawings and text.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical elevation, foreshortened and partially broken
out, showing an evacuated tube water hammer driver in which the
evacuatable enclosure is a tube other than the pile itself.
FIG. 2 is a schematic diagram of a driven similar to that shown in
FIG. 1, but provided with a pipe coupler and alignment means for
securing the driver within a pile.
FIG. 3 is a sectional view of a coupler for the FIG. 2 driver.
FIG. 4 is a schematic diagram in which the evacuatable enclosure is
defined at least in part by the walls of the pile, the motor-pump
combination, water hammer valve and control means being similar to
that described in FIG. 1.
FIGS. 5 and 6 are schematic diagrams of steam-reset water hammer
pile drivers in which the evacuatable enclosure is defined at least
in part by the walls of the pile.
FIGS. 7 through 9 are schematic diagrams of condensable vapor reset
pile drivers in which the evacuatable enclosure is a tube separate
from but coupled to the pile, and in which various different kinds
of condensable vapors are employed.
FIGS. 10 through 12 are schematic diagrams of means insertable in
the evacuatable enclosures of the previously described water
hammers for varying the water hammer impulse.
FIGS. 13 and 14 are schematic diagrams of free-piston evacuatable
enclosure water hammers in which the pistons are reset by
mechanical and fluid pressure means respectively.
DESCRIPTION OF PREFERRED EMBODIMENTS
In accordance with the invention, the enclosure walls can be at
least partly or wholly, defined by a tube separate from the pile
being driven, as disclosed by FIGS. 1-3, 7-9 and 14 hereof. FIG. 1
represents a configuration of a pile 1 driven underwater into the
ground 100 by a top-mounted hammer. The pile 1 is securely fastened
to the hammer 3 by a coupling means 2. This coupling 2 may take the
form of simply bolted flanges or a more sophisticated mechanical
clamping arrangement similar to the scroll- or
pneumatically-operated machine tool lathe chucks which are
well-known and will not be described further. The pile hammer 3 in
the present case includes hammer tube 4, made of flanged sections
of heavy-walled tubing bolted together and contains a shock-mounted
electric motor 5 - hydraulic pump 6 combination near its bottom.
(The motor-pump positions may be interchanged.) The pump 6
evacuates the water out of the hammer tube 4 through a
center-mounted pipe 7 discharging vertically out its top. The pump
6 axially supports the discharge pipe 7 or, in other
configurations, vice versa. On the top-most section of the water
hammer tube 4 is mounted the fast-opening water control valve 8 and
its pneumatically operated actuator 9. When open, valve 8 freely
admits water from the surrounding body of water through the valve
body and its inlet 12 into hammer tube 4. A wire rope sling 10
supports the entire assembly from the surface and also conveys the
power and control harness 11 thereto.
The design of the water control valve 8 may be such that rapid
opening thereof is aided by the force generated by the ambient
hydrostatic head acting on the valve. In order to prevent the
inrushing water from exerting any drag forces on the pump 6 and
motor 5 assembly, the liquid level is controlled to prevent the
draw-down of water to the pump level. The casings of the pump,
motor and discharge pipe should be made strong enough to withstand
the resulting water hammer pressure. When required, the
motor-pump-discharge pipe assembly can be made free-floating and
mechanically shock-isolated axially from the water hammer tube by a
lower compression spring (not shown) which supports the static air
weight of the motor-pump-pipe assembly and an upper compression
spring (not shown) which helps the gravity return of the pump
assembly to its normal mid-position. A hydraulic type shock
absorber (not shown) can be used to provide viscous damping to
reduce oscillations. Further shock resistance can be provided by
making the motor pump critical components neutrally buoyant in
their respective liquid by means of low density construction
materials and high density liquids incorporated in their respective
frames. Motor conductors and control cables pass from the surface
to the motor 5 and valve 8 through the water-tight power and
control harness 11.
When the pile is of sufficient length and diameter, and also to
facilitate the handling of long assemblies, the hammer tube 4 may
be located internally within the pile as shown in FIG. 2, using any
internal coupling, such as that (40) shown in FIG. 3. This permits
incremental upward repositioning of the hammer as the pile 1 is
driven into the bottom 100. It also permits coupling of the driver
to the pile at a position which is closer to the sub-soil 100 than
the top of the pile, giving an improved driving action.
Concentricity alignment rings 42 may be secured to each water
hammer tube flange joint as shown in FIG. 2.
To secure the hammer within the pile high pressure fluid is fed
into the lower cylindrical cavity 53 of the pile coupled 40 through
port 54, FIG. 3. This flow causes the cylinder frame 55 to move
downward over the piston 56. The piston shaft is secured to the
base 57 that is bolted to the bottom flange 48 of the water hammer
tube 4. When the cylinder frame 55 moves downward it creates a
toggle action in the multiplicity of links 58. The resultant
mechanical advantage varies as the cotangent of the angle between
the link and the radial normal. Consequently, hard-tooth shoes 59
slide radially outward in T slot guides in the base 57 and bite
into the pile walls. Simultaneously, the fluid in the upper
cylindrical cavity 60 is exhausted through port 61. A four-way
electrically controlled valve (not shown) can be used to control
the influx and efflux of the pressurized fluid, which may be
hydraulic or air. To release the pile coupled, the influx and
efflux ports on the piston base are interchanged by control valve
action. The compression spring 62 in the upper cylinder 60 retracts
the entire mechanism when the air pressure is off. This pile
coupler also can be used in the end-drive configuration.
In accordance with the invention, the enclosure walls can be at
least partly, or wholly, defined by the walls of the pile being
driven, as disclosed by FIGS. 4 through 6, and 13, hereof. FIG. 4
represents a configuration of a pile 1 driven underwater into the
ground 100 with the aid of a module which includes parts similar to
the pile driver of FIG. 1, and which therefore bear like reference
numerals.
Extending axially through the control valve 8 and actuator 9 is a
discharge pipe 7 which communicates with and supports a pump 6 by
the pump discharge outlet. The pump in turn supports an electric
drive motor 5. The valve 8, actuator 9, pipe 7, pump 6, motor 5,
and cap 120 to which they are secured constitute a unitary module
which can be mated temporarily, during driving, with each of a
series of piles.
Cap 120 is in water-tight sealing engagement with the pile mouth 1
and may be provided if desired, with means for remote-controlled
release, e.g., a latch and trip-wire (not shown) to the surface,
for releasing the module from the pile when driving has been
completed. A wire rope sling 10 is provided for lowering and
lifting the module onto and off of the piles, and also conveys the
power and control cable harness 11 thereto. The module is serviced
by a barge 124 having a winch 125 and cable 126 for lifting and
lowering the module and a drum 127 for paying out and winding up
the power and control cable harness 11.
When the module is mated to a pile, the pile performs the function
of the hammer tube of the FIG. 1 embodiment, and the operation is
the same. In this case, the evacuatable enclosure is defined by the
cylindrical walls of the pile 1 and the inner surface 121 of the
pile tip 122. The enclosure is coupled with the tip through the
wall material of the pile.
During the operation of the device, water is evacuated from that
portion of the enclosure which is at or above the level of pump
inlet 123 and discharged through the discharge pipe 7. Upon opening
of the fast acting valve 8, water is drawn through valve inlet 12
and is accelerated inwardly along the axis of the pile by the
ambient hydrostatic head. Because the valve is provided with a
large opening, the mass of water moving along the axis of the pile
substantially fills the cross-section of the evacuated portion of
the enclosure. The water is unrestrained and therefore continues
moving substantially independent of the pile until it is suddenly
decelerated against the barrier provided by the inner surface 121
of the pile tip, the water being substantially at its theoretical
bulk modulus when decelerated. In this connection, it should be
noted that the mass of water can be decelerated against the barrier
either directly or "per se" (if provision were made for completely
emptying the pile before admitting the water) or indirectly, such
as by contacting the water accumulated in the lower portion of the
pile. As a result of such deceleration at the water's theoretical
bulk modulus, the hydraulic kinetic energy is converted to a
powerful water hammer driving pulse for driving the pile into the
sub-soil.
The pile hammer 3 can be freely modified, as desired. For instance,
the motor 5 and/or pump 6 may be located outside hammer tube 4 or
pile 1 provided the pump inlet is in communication with the
interior of the tube at a position spaced along the tube axis from
water control valve 8. Hammers can be employed which have water
control valves at both ends and controls which would permit driving
along the tube axis in either direction. Configurations may be
fabricated for horizontal driving.
Different kinds of valves also may be used. Such others include
spring-loaded, hydraulically -- and electromagnetically -- actuated
linear and rotary shear varieties; metal, plastic and elastomeric
pinch-off forms, free jet and fluidic submerged jet and
pressure-switched groups; and, change-of-state valving techniques.
Specific models are identified as spool and gridiron, sliding and
rotary shear valves; conventional globe, gate, plug, ball,
balanced/eccentric-pivoted poppet and butterfly, and flapper
valves; resilient sleeve hydraulically, pneumatically, and
mechanically squeezed pinch valves; jet pipes; electroviscous and
magnetoviscous forms.
Any other design of evacuatable water-hammer driver may be used in
the present invention. Included are those in which evacuation of
the water is accomplished by condensable vapors or gas injected
into or generated within the chamber. In such cases, a water
control valve is not essential to start the flow of liquid in the
hammer tube. These are illustrated in FIGS. 5-9, which also show
that the enclosure walls may or may not be at least partly defined
by the walls of the pile itself.
IN FIG. 5, a barge 124 is anchored above the pile 1, having a tip
122 embedded in the subsoil 100 and an upper end 130 which is
submerged and in open communication with the ambient sea water
surrounding it. On the barge is a steam generator 105, control
valve 127 for metering steam flow through the insulated steam hose
11, a winch 125, and a cable 126. The steam hose extends downwardly
to the pile, along with cable 126, which by an appropriate sling
131 supports and retrieves an insulated rigid steam pipe 132
pre-positioned inside the pile by surface-released latching spiders
133. The latching mechanism (not shown), and spiders must be strong
enough to withstand the bottom of the steam pipe 132 terminates in
a steam check valve 134 fitted with steam nozzle 135 open downward.
Thus, when the valve 127 opens for a predetermined interval to emit
a burst of high pressure steam (which of necessity must be of
substantially higher pressure than the hydrostatic head) an
expanding steam bubble is produced which forces upwardly that water
which is present in the pipe above the level of the steam nozzle
135.
Preferably, the volume of the steam burst is regulated to just
evacuate the pile 1 of water. The steam is preferably of superheat
quality and released in sufficient quantity to just evacuate the
pile 1 of water. The efflux upward momentum generates a
corresponding down thrust. It also causes a sudden vapor
condensation when the tube pressure is driven negative The
attendant evacuation by change of the physical state of the steam
results in reversing the water flow to generate the downdriving
water hammer impulse to the pile 1. If a non-condensable gas like
air were used to the exclusion of steam, a spring-like compliance
would be imparted to the water, severely reducing the power of the
hammer blow. A Helmholtz type of damped oscillation is then
generated, whose frequency depends on the volume of entrapped air,
hydrostatic head, and mass of water in the tube.
FIG. 6 represents a similar arrangement which operates in the same
manner. However, in this case, the pile 1 has an open-ended tip
136, and the barrier 140 is a remote-controlled incrementally-moved
gripper assembly (similar in construction and operation to FIGS. 3
and 2, respectively). Said assembly secures check valve 134
terminating steam pipe 132 feeding steam nozzle 135 (of folded horn
construction) which exhausts upwards. As the pile is driven
downward the water which is entrapped in cavity 143 between the
barrier 140 and soil plug 144 exhausts out through drain pipe 142.
The gas-filled compliant balloon 141, precharged to ambient
pressure, absorbs the momentary volumetric increments of the water
displaced during driving. The hydraulic tightness of the water
barrier 140 is not critical when leakage absorbed by the compliance
141 subtracts only an insignificant amount from the total dynamic
pressure.
FIG. 7 discloses a condensable vapor reset driver in which the
evacuatable tube is defined by a tube 4 other than the pile 1
itself. The tube 4 is coupled, to the pile, for instance, by a
coupler (not shown) similar to that in FIG. 3. The controls for the
coupler, the steam generator 105 and control valve 104 may be
mounted on a surface barge (not shown) and may pass to the pile in
any desired manner, such as for instance as disclosed in FIG. 5. In
the operation of this embodiment, the steam control valve 104 is
open momentarily to meter the proper amount of steam from generator
105 to the interior of the pile. The operation is the same as the
FIG. 5 embodiment.
FIG. 8 represents an arrangement similar to FIG. 7, utilizing a
two-phase combustible mixture consisting of a pressurized fuel such
as hydrogen, or a hydrocarbon as kerosene or alcohol, in container
106, a fuel-metering valve 107, a pressurized oxidizer such as
oxygen in container 108, and its corresponding metering valve 109.
The fuel combustion chamber 110 is located within the water hammer
tube 4. The component 111 represents either the external ignition
source, such as a spark plug, or proprietary catalyst for the
monopropellent type rocket fuels such as hydrogen peroxide or
hydrazine. For hypergolic (spontaneous combustion upon mixing) type
propellants the igniter 111 may be eliminated. On the other hand,
liquid (water)borne particles of solid type propellants or
explosives may be metered via the valve 107, caught in the screened
combustion chamber, and fired off by means of the igniter 111. The
products of combustion are used to expel the water as previously
discussed. These combustion products will be condensable, or at
least partly so, due to their water vapor content.
Similarly, FIG. 9 also represents the use of socalled rocket fuels
wherein the combustion chamber 110 is external to the water hammer
tube 4. The combustion products' metering valve 112 controls the
water evacuation cycle and also acts as a check valve against the
water hammer pressure. The remaining parts are similar to those
shown in FIG. 8.
Practically, the principal limitation on the generation of larger
values of water hammer within a single pipe may be the
circumferential tensile or hoop stress. As will be shown, the
generation of water hammer at a 1,000 ft. depth in a 2-foot
diameter steel pipe requires a wall thickness of 2.34 inches in
order to keep the stress down to 69,000 psi While this is not an
excessive working stress for modern alloy steels, it still exceeds
structural grade ratings. Since the invention is normally used in
limited access or restricted environments, a low safety factor can
be employed. To avoid the use of excessively massive pipe walls,
reinforcement in the form of filament winding or an axial series of
external or internal spaced reinforcing rings is recommended. The
distributed spring mass configuration of the latter also reduces
the transonic velocity of wave propagation along the pipe. Two
advantages follow, namely, reduction of hoop stress and increase of
impulse duration. The use of pipe wall materials with a lower
elastic modulus like aluminum or resinated fiberglass achieves a
reduction in water hammer pressure by lowering the transonic
velocity. For these to be fully effective under water, additional
acoustic pressure release material like cork may be applied at the
ambient water interface in order to preclude acoustic loading.
Another method of reducing wall stresses, by slowing down the axial
velocity, is to use a series of truncated cone baffles 150 and 151
as illustrated in FIG. 10 or to spiral the water in the tube by
uni-directionally twisted or alternately twisted bundles of smaller
diameter tubes or baffles. Thus, the water hammer tube 4 of any of
the preceding embodiments may be provided with a plurality of
twisted tubes 152 within the tube 4 and extending axially of at
least a portion of the tube which defines the evacuatable
enclosure. Where the tube 4 includes a discharge pipe 7 or other
equipment along its axis, the spiral tubes 152 may be arranged
around or above them. Similarly, baffles 155 and 156 of varying
rotation may be used, as disclosed in FIG. 12. The longer travel
path provided by these various means proportionally creates a
longer pulse.
Where the water hammer device is provided with a valve to start the
water flow, the water hammer intensity can be reduced by retarding
the rate at which the valve goes from full closed to full open
position.
Thus, for a given driving application (assuming a given depth, pile
mass and soil conditions) it is possible to tailor the force-time
characteristics of the water hammer impulses by a suitable
selection of the length and diameters of th water hammer tube, and
the reinforcement and material of construction thereof. Also, one
may employ the acoustic pressure release material, baffles and
valve opening rate as discussed above. Thus, it will be seen that
the method has far more flexibility than is provided by the
conventional steam hammer.
When the water hammer tube is provided with a unidirectional helix,
a component of mechanical torque and rotation can be generated by
the checked angular momentum of the falling mass of water. This can
increase the penetrating power of the pile driver in certain soils.
The "screw" vs. the "nail" action also improves a friction pile's
load bearing capacity, especially when the "lead" or helix angle is
optimized for the soil conditions.
FIG. 13 discloses one example of that class of evacuatable tube
water hammer drivers which include one or more "free" pistons. In
the present context, a free piston is one which, during at least a
portion of its movement between the extreme limits of its travel,
is not directly coupled to or is at least substantially independent
of, the pile. Configurations are possible in which the free piston,
provided with means to raise it in the evacuatable chamber, can
replace the pump-motor combination. In the preferred mode of
operation, the piston will replace both the pump-motor combination
and the water control valve.
In FIG. 13 a barge 134 is anchored over a pile 1 having its tip 122
embedded in sub-soil 100. The pile's open mouth 130 is submerged.
From a winch 125 on the barge descends a cable 126 through pile
mouth 130 to a piston 160. The latter fits closely enough within
the pile walls to at least partially and preferably substantially
completely bar the entry of water into the space below the piston
as it is raised, the need for or desireability of packing 161 being
determined in part by the speed at which the piston is to be raised
and lowered.
Operation of this embodiment simply involves repetitively and
alternately raising the piston 160 with winch 125 and dropping the
piston, which may, if desired come to rest against a cushion block
163. Raising of the piston evacuates an enclosure defined by the
pile tip and side walls. Quick release of the piston and rapid
descent thereof through the pile accelerates a mass of water above
the piston. This mass is suddenly decelerated by indirect contact
through the rigid piston with the barrier provided by th cushion
block 163 when the piston strikes the latter. This, in turn,
generates the water hammer impulse which drives the pile.
To minimize drag and inertia forces which would retard the fall of
piston 160, a clutch may be used to disengage the winch reel from
its drive motor during the fall of the piston. For large piston
loads a multi-sheaved block and tackle, mounted on the top of the
hammer tube, may be employed. The main hook made in the form of a
bull gear may be disengaged from the piston by rotation, pivoting
around a bushed holding pin. The required mechanical power may be
provided by a small electric or hydraulic motor-driven pinion. A
small rope which follows the piston down its stoke may act as a
guide for reengaging the lifting hook. Other quick make-break
configurations are the commerically available wireline overshot
latching clips for removing downhole core barrels from diamond bits
left inside petroleum wells.
A guided long rack and motor-driven pinion means may also be used
to raise the piston. A high pressure-angle stubby gear tooth
profile facilitates the easy disengagement of the pinion from the
rack by a guick-acting cam or hydraulic piston means. The rack can
ride down with the piston and the pinion assembly remain fixed at
the top of the hammer tube.
Similarly, another piston-raising means may employ a split nut
fastened to hydraulically or cam-actuated chuck jaws to engage and
quickly disengage a long, threaded screw fastened to the piston.
The nut is rotated by a motor driven pinion meshing with a bull
gear made integral with the chuck, all mounted in top of the water
hammer tube.
Another method would use a hydraulically-actuated cylinder to lift
the piston. A hydraulic chuck, on the end of the cylinder rod,
latches and disengages the piston.
For shorter and faster piston hammer strokes a tube-mounted
electric or hydraulic motor-driven cam is used to provide a
relatively slow lift and free drop to the piston.
Instead of packing or piston rings, a rolling diaphragm type seal
may be used to keep the water out of the interior of the water
hammer tube. A suitably-shaped fillet at the bottom of the stroke
supports the elastomeric-impregnated fabric against the
high-amplitude water hammer pressure pulse.
In the above-described embodiments, the water hammer tube has been
entirely submerged in the water in which it is operating, the
preferred mode of carrying out the invention. This makes use of the
hydrostatic head available in the water to power the driving
impulse. Also, the submerged-operation feature of the invention
offers the possibility of easier handling during storm conditions.
However, in other cases, especially shallow water applications, the
water hammer tube may be at least partially above the surface of
the water. Whether the evacuatable enclosure is defined by a tube
separate from the pile, or by the pile itself, the water for
generating the water hammer pulses may be provided by an upward
extension of the pile or the tube, which is filled with water, or
by a reservoir located above the hammer tube as shown in FIG.
14.
IN FIG. 14 is shown a pile 1 partially embedded in sub-soil 100 and
having its upper end 130 protruding above the water's surface. A
driver 171 is releasably secured in the top of the pile by a
coupler 40 similar to that disclosed in FIG. 3, like parts of the
respective couplers being identified in the drawings by the same
reference numerals. To the base 57 of the coupler is secured the
base 172 of the driver.
Extending upwardly from the base 172 is an upright, elongated water
hammer tube 4. A reservoir 188 is supported by the tube 4 and
connected thereto by flared walls 189 to promote smooth flow of
water 190 between the tubes and reservoir. The reservoir may be
pressurized if desired by forcing in gas or vapor through inlet
192. A central column 173 is suitably secured to the base 172 and
extends upwardly and coaxially with the water hammer tube 4 and
thence at least part way into reservoir 188, where it may be
supported by a three-legged spider 191 secured to the reservoir
walls, only one leg of which is shown in the drawing.
Piston 174 is mounted for vertical or axial reciprocation on column
173 between base 172 and stop 180 secured toward the upper end of
the column. Both the piston and base 172 are reinforced to
withstand the mechanical shock associated with water hammer
pressures. The piston itself may of course contribute some driving
momentum during operation, but normally, during driving, the mass
of the piston is less, and usually substantially less than half,
the mass of the fluid (water) which is above it or which enters the
tube 4 during the down stroke.
The piston has a central aperture 177 of slightly greater diameter
than the outside of column 173, and has an outer diameter slightly
less than that of the inner diameter of the water hammer tube 4.
Suitable seals may be provided if desired in the clearances between
the piston on the one hand and the pile and column on the other.
However, when operating with a small pressure differential across
the piston, e.g., 1 atmosphere or less, leakage of water and steam
past the piston will be minimal. Thus, it is possible to fabricate
the apparatus in a way which provides a close but essentially
drag-free relationship between the piston and the other parts.
Also, making the piston neutrally buoyant relative to water may
reduce the pressure differential and discourage leakage.
Connected to a suitable steam supply (not shown) is a steam conduit
178 with control valve 123. Conduit 178 feeds passages in base 172
terminating in steam outlets 179. When the control valve 123 is
opened to emit a burst of steam from the outlets 179 at a pressure
greater than the ambient water pressure above piston 174, it will
be forced upwardly in tube 4. When the piston retains sufficient
upward momentum after control valve 123 closes, the resultant
further expansion of the space beneath the piston can super-cool
the steam and condense it, thus evacuating the space beneath the
piston. Where, because of insufficient momentum or other reasons,
there is not sufficient auto-cooling of the steam, cool water may
be sprayed into the space beneath the piston by water conduits and
spray nozzles (not shown) fitted into the central column and/or
base, or into the side walls of tube 4.
In order to keep the evacuatable enclosure free of steam
condensate, and possibly of cooling water where such is used, the
base 172 may be fitted with a drain pipe 182 and valve 181. Valve
181, like steam valve 123, will normally be opened during the
raising of piston 174 and closed on the down stroke.
In certain apparatus, e.g., that having a cam-actuated free piston,
it may be found desirable to adjust the actuation of the valve to
maintain the hydraulic pulse repetition rate at an operational
resonance of the system. This can be accomplished by placing
sensors on the driver and/or pile and/or ground and automatically
actuating the valve in response to signals from the sensors.
Although water is used as an example, the working fluid is not
necessarily limited thereto. In a closed system, any liquid may be
used.
EXAMPLE
When working with water hammer tubes of about 50 feet and longer,
one can obtain driving pulses which are approximately two or more
times as long as with the large steam hammer described in the
comparison example, Longer pulses are obtained with a hammer tube
of 100 feet in length. This may be illustrated with a water hammer
tube of 24 inch diameter schedule 160 (2.343 inch wall) steel pipe
100 feet long and weighing 54,209 pounds. Ancillary equipment
includes a pump to evacuate the tube at some convenient rate, a
water-tight cap at one end of the tube, and a fast acting valve at
the other end.
After the pipe is evacuated and the control valve is suddenly
opened, the water entrance velocity "U.sub.1,000 " at the 1,000 ft.
depth "h" is
U.sub.1000 = .sqroot.2gh = .sqroot.[2 .times. 32.2 ft./sec.sup.2
(1,000 + 34)ft.] = 259 ft./sec.
The external, upward force on the capped bottom end of the pipe due
to the difference between the ambient pressure and internal vacuum
is
F.sub.v = .rho.ghS.sub.I = 64 lbs./ft..sup.3 .times. 1,034 ft.
.times. 2.03 ft..sup.2 = 134,500 lbs.
The weight of the evacuated water and resultant buoyancy is
F.sub.W = .rho.gS.sub.I L = 64 lbs./ft..sup.3 .times. 2.03
ft..sup.2 .times. 100 ft. = 13,000 lbs.
The transonic velocity in the pipe is ##SPC1##
The water hammer pressure is
p.sub.WH = .rho.v U = 1.99 slugs/ft.sup.3 .times. 4,679 ft/sec
.times. 259 ft/sec = 16,700 psi.
The corresponding simple tensile hoop stress in the pipe walls
is
s = pD/2t = (16,700 psi .times. 19.3 in)/(2 .times. 2.34 in) =
69,000 psi.
The water hammer impulse force is
F.sub.WH = p.sub.WH S.sub.I = 16,700 psi .times. 293 in..sup.2 =
4,900,000 lbs.
The time duration of the impulse force on the capped end is
T.sub.WH = 2L/v = (2 .times. 100 ft.)/4,670 ft/sec = 0.0428
sec.
The hydraulic momentum of the incoming water, just before impact,
is
(MU).sub.H = .rho.S.sub.I LU = 1.99 slugs/ft.sup.3 .times. 2.03
ft.sup.2 .times. 100 ft .times. 259 ft/sec
= 104,500 slug-ft./sec = 104,500 lb-sec.
The hydraulic kinetic energy of the incoming water is
KE.sub.H = 1/2 .times. 13,000 lbs./32.2 ft/sec.sup.2 .times. (259
ft/sec).sup.2
= 13.5 .times. 10.sup.6 ft.lbs. = 18.3 Mega Joules
The incoming hydraulic power is
W.sub.H = .pi./8.rho. D.sup.2 U.sup.2 = .pi./8 .times. 1.99
slugs/ft..sup.3 .times. (1.61 ft).sup.2 .times. (259
ft/sec).sup.3
= 35 .times. 10.sup.6 ft.lbs./sec = 47.5 Megawatts
As a check, the work required to evacuate the pipe against the
ambient hydrostatic head, or the potential energy of its cavity
is
PE.sub.H = ambient pressure .times. pipe volume = .rho. g h S.sub.I
L
= 64 lbs/ft.sup.3 .times. 1,034 ft .times. 203.5 ft.sup.3 = 13.5
.times. 10.sup.6 ft.lbs.
The water hammer power is
W.sub.WH = .pi./8.rho. D.sup.2 U.sup.2 v = .pi./8 (1.99
slugs/ft.sup.3) (1.61 ft).sup.2 (259 ft/sec).sup.2 (4,670
ft/sec)
= 631 .times. 10.sup.6 ft.lbs./sec. = 855 Megawatts
COMPARISON
An example of the contemporary state-of-the art is referenced for
comparison. One of the largest, commercial single-acting steam/air
hammers for land-based or offshore piledriving is the 060 size
rated at 180,000 ft.lbs. The practical underwater operational limit
is 200 ft. The striking energy, obtained by a 60,000 lb. weight
free-dropping 3 ft., is 1/75th of the water hammer value from the
two foot pipe example. At the theoretical terminal velocity of
U.sub.SH = .sqroot.2gh = .sqroot.2 .times. 32.2 ft/sec.sup.2
.times.3 ft = 13.9 ft/sec, its momentum, (MU).sub.SH = 60,000
lbs/32.2 ft/sec.sup.2 .times. 13.9 ft/sec = 25,900 lb.sec. or
one-fourth of that acquired by the water hammer example. The
principal feature of the water hammer, however, is in the
relatively long time duration of the impulse force. In order to
improve on this desirable characteristic, the steel piledriving
hammer uses an expendable wooden or resinated-fabric cushion block
insert between the ram and the pile to diminish the impact shock.
Wave propagation theory, using computerized solutions of finite
difference equations, has been applied to a math model describing
system behavior of "What happens when (the) hammer hits (the)
pile," Eng. News Record, 5 Sept. 1957, Edw. A. Smith; also, refer
to E.A.L. Smith, "Pile-Driving Analysis by the Wave Equation," J.
Soil Mechanics and Foundations Div., Proc. ASME, Aug. 1960. A
further investigation, correlating piledriving characteristics with
its load bearing capacity, (Forehand and Reese, "Pile-Driving
Analysis Using the Wave Equation," Princeton Univ., M.S.
Engineering Thesis, 1963), discloses that the impulse duration,
defined as "the time the velocity remains positive," is of the
order of 10 milliseconds for the steel hammer blow or one-fourth of
that in the water hammer example. If so, then the 30 ton steel
hammer impulse force is
F.sub.S = 25,900 lb.sec./0.01 sec = 2,600,000 lbs.
or roughly one-half of the water force. The mechanical power
transfer rate of the steel hammer is, roughly, W.sub.S = 180,000
ft. lbs./0.01 sec. = 24.4 M W, or 1/35 of the water hammer power.
If the impulse duration of the steel hammer blow is shorter, the
force obviously increases in inverse proportion, but then a new
difficulty arises in establishing compression, and displacement,
simultaneously along the entire length of a long pipe. For example,
in a steel pile 200 ft. long, even with an undamped (unclamped)
sound velocity of 16,600 ft/sec. in steel, it takes 12 milliseconds
for the impulse to reach the tip. With concrete piles, this trouble
is further aggravated because sound velocity in concrete is
one-third slower. Some contemporary offshore foundation designs
call for loads up to 2,000 tons from piles 200-600 ft. long, 3-8
ft. in dia., weighing 100-200 tons, in up to 1,000 ft. of water.
Without supplementary techniques involving pre-drilling or jetting
such piles are practically undrivable by the steam-air hammer even
when spliced to extend to the surface.
From the foregoing, it may be seen that the invention provides many
advantages. It makes feasible a large increase in driving
capability. And this can be done using a smaller mass ratio
(driving mass versus pile) than has heretofore been thought
advisable in steam hammer operations. That is, larger impulses can
be generated using a driving mass which is less than one-fourth
that of the pile. This, in turn, makes it possible to drive piles
without the use of palliatives such as pilot hole drilling, water
jetting and grouting into an oversized hole, which measures can
reduce pile load-bearing capacity.
The pressure-time characteristics of the water hammer impulse can
be tailored over a wide range of values to match corresponding
requirements of the pile and soil. Thus, driving impedance can be
better matched to that of the earth than when operating with for
instance a steel hammer.
Under the longer impulses which can be generated by a water ram or
spear having a length to diameter ratio of 10 or more, long piles,
e.g., L/D .gtoreq. 15, move more nearly as a unit, e.g., their
driving action is more like that of a nail, rather than a worm, in
which one part moves ahead while other parts are held back. Thus, a
greater fraction of the driving energy is usefully expended in
overcoming displacement skin friction, to advance the pile, rather
than being tied up in the rubber-like ground "quake." With the long
pulses which may be provided with water hammer if desired, unwanted
standing wave conditions in the pile can be prevented more
effectively. The invention renders unnecessary the use of a cushion
block, as sometimes required with a steel hammer, thereby
eliminating the inelastic collision energy loss associated
therewith.
Certain important advantages are associated with the convenient
manner in which the invention may be applied under water. With the
driver submerged, it may be handled with greater safety and ease
during storm conditions. Coupling of the driver to the pile at a
point below its top end helps to reduce losses of driving energy
attributable to the mechanical compliance of the pile. Submerged
operation provides inherent capacity for generating larger pulses
as submergence increases, and particularly a depths greater than
200 feet where hydrostatic back pressure aggravates the venting
problem of the air operated hammer, where thermal line losses
preclude the steam driven hammer and where conventional vibratory
driving requires such a relatively large back-mass for preload and
such low frequencies that reaction forces necessary for driving
become ineffective without excessively large excursions. Handling
is facilitated because the driving mass can be drained from the
apparatus when it is being transported and lifted above the
surface.
Moreover, water hammer operation makes it convenient to twist the
pile as it is driven downward, such as by including helical baffles
in the water hammer tube which impart a twisting motion thereto. In
some cases, especially where the "lead" or helix angle is optimized
for the soil conditions, this can improve the pile's load bearing
capacity.
In view of the foregoing, it is apparent that the present invention
is a broad one, and that many changes may be made in the foregoing
embodiments without departing from the spirit of the invention.
* * * * *