Note: Descriptions are shown in the official language in which they were submitted.
CA 02556015 2006-08-04
1 "METHOD FOR INSTALLING A SCREW PILE"
2 FIELD OF THE INVENTION
3 The present invention relates to a screw pile and to a method for
4 installing it in conjunction with injection of grout.
6 BACKGROUND OF THE INVENTION
7 Screw piles have long been commonly used in connection with
8 foundation underpinning, pipeline tie-downs and in other applications.
9 In one known embodiment, the screw pile comprises:
= an open ended tubular shaft having one or more helixes externally
11 mounted thereon adjacent its pointed lower end;
12 = the shaft usually comprises a bottom anchor section carrying the
13 helixes and one or more extension sections;
14 = the shaft has means, such as pin holes, at its upper end, for insertion
of locking pins to connect the shaft with a drive head assembly which
16 functions to rotate the pile into the ground.
17 A screw pile will be characterized by load-carrying and lateral
18 deflection capacities, once implanted in the ground.
19 The load-carrying capacity of a screw pile can be increased by
increasing its length and/or diameter or increasing the number of helixes.
21 However these changes will require that greater torque be applied by the
22 drive head assembly in order to rotate the pile into place at the desired
landed
23 depth. There are finite limits on the amount of torque that can be applied
to
24 the pile and on the capability of the drive head assembly to deliver it.
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CA 02556015 2006-08-04
1 In addition, the nature of the ground into which the pile is implanted will
2 also affect the load-carrying capacity of the pile.
3 It is known to inject grout, such as cement slurry, at low pressure, down
4 through the bore of the hollow shaft and out, through ports in its side
wall, into
the sub-surface formation or stratum in which the pile has been landed, to
6 thereby increase the stiffness of the formation and enhance the load
7 capacities of the pile.
8 The present invention is concerned in one aspect with providing a
9 modified screw pile and in another aspect with providing a method of
installation, which have the objective of increasing the load capacities of an
11 implanted pile.
12
13 SUMMARY OF THE INVENTION
14 In a preferred embodiment, a screw pile is provided having one or
more internal grout pipes extending down into the bore of the tubular shaft.
16 Each grout pipe is connected at its lower end with a side-opening port
17 extending through the shaft side wall. The grout pipe and port combine to
18 provide a grout conduit. The grout conduits each have a small diameter
19 selected with the objective of promoting high pressure grout injection -
that is,
injection at a pressure greater than about 200 psi. The ports are suitably
21 located so that, when the pile is at landed depth, the ports will be
positioned
22 opposite a target formation into which the grout has been injected.
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CA 02556015 2006-08-04
1 In an alternative embodiment, a small diameter shaft, having side-
2 opening ports in its lower end, can be used. The grout is injected into the
3 target formation at high pressure through the bore of the shaft and the
ports.
4 In the course of installation, grout is injected as the pile is being
rotated
into the target formation, to thereby distribute the grout through a vertical
6 interval of the formation.
7 By combining high pressure grout injection and injecting while rotating
8 the pile into the target formation, it has been demonstrated that the load
9 capacities of the screw pile may be increased relative to a non-grouted pile
and relative to a pile which has been grouted, but only when stationary and in
11 place at total depth.
12 In one aspect, the invention is therefore concerned with a method for
13 installing a load-bearing pile in the ground, comprising: providing a screw
pile
14 comprising a tubular shaft having a side wall forming an internal
longitudinal
bore, the side wall having a lower end portion carrying at least one
externally
16 mounted helix, the end portion forming at least one side-opening port
17 extending therethrough; rotationally driving the screw pile into the ground
to
18 penetrate a sub-surface formation in which the end portion is to be landed
at a
19 total depth; and injecting grout into the formation through the shaft and
ports
at high pressure as the screw pile is rotated into the formation.
21
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CA 02556015 2006-08-04
1 DESCRIPTION OF THE DRAWINGS
2 Figure 1 is a side view showing a screw pile, having internal grout
3 pipes, being rotatively driven into a sub-surface ground formation with
4 concomitant grout injection;
Figure 2 is a side view showing grout being injected into the ground
6 formation in the course of rotating a small diameter screw pile into the
7 formation;
8 Figure 3 is a side view of a 10 3/" diameter screw pile equipped with
9 1/2" diameter internal grout conduits terminating at different elevations
along
the length of the shaft;
11 Figures 4, 5, 6 and 7 are sectional views of the screw pile of Figure 3,
12 taken at different elevations along the shaft;
13 Figure 8 is a side view of a 3 1/2" diameter screw pile having side-
14 opening ports;
Figure 9 is a side view showing a drive kelly, a head assembly and the
16 upper end of the screw pile; and
17 Figure 10 is similar to Figure 9, showing the components connected.
18
19 DESCRIPTION OF THE PREFERRED EMBODIMENT
Having reference to Figure 3, a modified, large diameter screw pile 1 is
21 shown.
22
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1 The screw pile 1 comprises an open-ended tubular steel shaft 2 whose
2 side wall 3 forms an internal bore 4 extending longitudinally therethrough.
3 The shaft side wall 3 further forms side-opening ports 5 at spaced intervals
4 along the length of the lower end section 6 of the shaft 2.
A plurality of small diameter grout pipes 7 extend down through the
6 bore 4 and connect with the ports 5 to form internal grout conduits 8.
7 By way of example, the shaft 2 and grout conduits 8 may have
8 diameters of 10 3/ " and 1/2 " respectively.
9 A plurality of helixes 9 are externally mounted to the lower section 6 of
the shaft 2.
11 The shaft 2 may include one or more upwardly extending, tubular
12 extensions 34 connected with the lower end section 6.
13 The shaft 2 and helixes 9 combine to form a screw pile that can be
14 rotatively screwed into the ground 11 to land the lower end section 6 in a
subterranean target formation 12. The implanted screw pile 1 then serves to
16 support and/or anchor an applied load.
17 The grout conduits 8 provide sealed passageways 13 through which
18 streams of grout may be pumped at high pressure (preferably at least 200
psi)
19 by grout pump assembly 29 from ground surface 14, thereby injecting the
grout into the target formation 12.
21 Having reference to Figures 9 and 10, a head assembly 15 is provided
22 for attachment to the top end 16 of the shaft side wall 3.
23
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1 The head assembly 15 comprises an apertured bulkhead plate 17,
2 positioned in the top end 16 of the shaft bore 4. The bulkhead plate 17
3 receives the upper ends of the internal grout pipes 7 and seals around them
4 and between them and the shaft side wall 3.
The head assembly 15 further comprises an open-bottomed, tubular
6 drive can 19. The drive can 19 is adapted to slide over the top end 16 of
the
7 shaft side wall 3. The drive can 19 has pin holes 20 extending through its
8 side wall 21 for registering with pin holes 22 formed through the top end 16
of
9 the shaft side wall 3. Drive pins 18 may be inserted into the holes 22, 20
to
lock the drive can 19 to the shaft top end 16. The drive can 19 comprises
11 internal 0-rings (not shown) for sealing against the outer surface 23 of
the
12 shaft 2.
13 The head assembly 15 also includes a swivel 24, connected with the
14 upper end of the drive can 19. The swivel 24 has an inlet 25 for connection
with a hose 26 and grout pump 27. The grout pump 27, mixing tanks 28 and
16 hose 26 provide an assembly 29 for supplying cement grout, pumped at high
17 pressure. The swivel 24 enables the grout to enter the internal chamber 30
of
18 the drive can 19 from the stationary hose 26, when the drive can is
rotating.
19 The head assembly 15 further comprises a kelly adapter 31 connected
to the swivel 24. The kelly adapter 31 is connectable with the kelly joint 32
of
21 a conventional drive head 33 which functions to rotatively drive the drive
can
22 19 and screw pile 1. The drive head 33 is shown attached to the boom of a
23 mobile installation unit 34.
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1 In the method for installing the screw pile 1, the following steps are
2 practised:
3 = the drive head 33 is connected to the kelly adapter 31 and the hose
4 26 of the grout supply assembly 29 is connected to the grout inlet
25 of the swivel 24;
6 = the drive head 33 is actuated to rotate the screw pile 1 into the
7 ground 11;
8 = when the bottom 41 of the rotating shaft 2 begins to penetrate the
9 interval of formation 12 to be stiffened, the grout supply assembly
29 is activated to begin injecting grout through the grout conduits 8
11 at a pumping pressure greater than 200 psi; and
12 = high pressure grout injection, while rotating the screw pile 1, is
13 continued until the pile approaches landed depth, at which point
14 injection is terminated.
In an alternative embodiment, the invention may be practised by
16 injecting the grout at high pressure through the bore 50 of a rotating,
small
17 diameter (e.g. 3'/2" diameter) screw pile 51 (shown in Figure 8). In this
case,
18 the shaft 52 of the pile 51 has only side-opening ports 53.
19 Comparative Example
This example demonstrates the benefit in pile load capacity obtained
21 by injecting grout at high pressure while rotating a screw pile into the
ground.
22
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1 Three screw piles A, B and C were prepared as follows:
2 = Pile A had a shaft diameter of 10.75 inches and two externally
3 mounted, 20 inch helices spaced 60 inches apart. The pile had a
4 length of 20 feet. Pile A had no internal grout conduits;
= Piles B and C were identical to pile A but each of B and C had four'/~
6 inch grout conduits installed inside the shaft. The ports of the grout
7 conduits were located between the helices at 12 inch intervals;
8 = All three piles were rotated into place and landed 18 feet beneath
9 ground surface by applying torque of 144,000 ft-lbs;
= Pile A was installed without grouting. Pile B was grouted separately
11 through each grout conduit, once the pile was landed at total depth of
12 18 feet by injecting Chem Grout 60T"" (a cement grout) at a pumping
13 pressure of about 300 psi. Pile C was rotated to a depth of 10 feet and
14 then the same type of grout was simultaneously injected through the
four grout conduits as the pile was rotated to total depth of 18 feet.
16 The pumping pressure was maintained at about 200 psi during the
17 installation of the last 8 feet of pile;
18 = The three piles A, B and C were tested to failure (1 inch of settling)
for
19 a compressive load capacity, according to the ASTM D 1143 test,
commencing one week after installation;
21 = The non-grouted pile A failed at 400 kN; grouted pile B failed at 650
22 kN; and grouted pile C failed at 800 kN;
23
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1 = In addition the three piles were tested for lateral load capacities
2 according to the ASTM D 3966-81 test. For a pile lateral movement of
3 15 mm, pile A required 50 kN, pile B required 80 kN and pile C required
4 120 kN.
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