AU2001279495A1 - Earth anchoring system - Google Patents

Description

TITLE

EARTH ANCHORING SYSTEM

This invention relates to improvements in earth anchoring

systems, improved earth anchors and improved methods of installation

of earth anchors.

The invention is particularly although not exclusively concerned

with earth anchoring systems used in conjunction with sheet piling

systems.

Earth or "ground" anchors are well known and come in a wide

variety of configurations suitable for differing earth formations,

installation systems and/or anchor loads.

Many prior art earth anchors include either pivoted flukes or

arms which engage with the wall of a borehole to resist withdrawal.

Others may include a helical flight to assist in locating the anchor in

the earth formation and then acting as the anchoring means.

Typical anchors of the type having pivotable flukes are

described in United States patents 1 850 1 47, 1 636 61 7 and 4 593

500, United Kingdom patent application 2100314A, United Kingdom

patent 656663 and Russian patents 676-685 and 1 071 -706.

United States patents 1 63661 7, 4593500 and United Kingdom

patent 656 663 require a borehole to be formed to enable insertion of

the anchor into the ground.

United States patent 1 8501 47, United Kingdom patent 21 00314 and Russian patent 1 071 706 require an anchor with

retracted blades to be driven into an earth formation by a percussive

force acting on the anchor head while Russian patent 676685

describes an anchor head with a helical screw flight to enable the

anchor head to be screwed into the earth formation.

Our International Patent Application PCT/AU97/00365

published as WO97/47824 described an anchor system having a

pointed cutting head, pivotal flukes and a tubular driving tool

extending over the anchor rod to rotate the anchor head to cut az

pathway through the earth formation. Rotatable engagement between

a threaded nut and a socket on the driving tool causes the pivotal

flukes on the anchor head to expand outwardly. The tubular driving

tool also acts as a grouting conduit to grout the anchor rod as the

driving tool is withdrawn from the earth formation.

While generally effective for their respective intended purposes,

prior art earth anchors and their methods of installation suffer from a

variety of disadvantages.

Where an earth anchor requires a predrilled borehole, this is time

consuming and weakens the earth formation along the length of the

borehole which later must be filled in.

Percussively driven earth anchors require a driving tool which

extends between the pointed anchor body and the power source for

the driver. Such anchors generally are limited to soft earth formations and shallow penetrations.

Accordingly, with prior art earth anchors, the choice is largely

governed by the geological nature (hardness) of the earth formation

and the depth to which the anchors are required to be located.

A particular disadvantage of prior art earth anchors when used

with sheet piling retention systems in an excavation is that the large

aperture which must be cut in the sheet piling to accommodate an

anchor head and/or driving tool causes a substantial localised

weakness in the sheet piling.

Accordingly it is an aim of the present invention to overcome or

ameliorate at least some of the disadvantages associated with prior art

earth anchors and methods of installing same.

According to one aspect of the invention there is provided an

earth anchor including:-

a hollow body member having a screw threaded aperture

adjacent one end thereof to receivably locate a screw threaded anchor

bar;

a shaped cutting head located at an end of said body opposite

said one end; and,

a helical flight located intermediate the ends of said body.

Suitably said anchor is adapted to be driven rotatably into an

earth formation.

If required said anchor may include one or more drive engagers, in use, engageable with a rotatable driving tool.

The one or more drive engagers may comprise a socket and

spigot engagement associated with said body.

Suitably, the one or more drive engagers comprises a pair of rib-

like projections diametically opposed on an outer surface of said body,

said rib like projections being engageable, in use, with complementary

recesses in a driving tool.

The driving tool may be a tubular member, in use, forming a

casing for a borehole formed by anchor, an inner surface of said

tubular member and an anchor bar attached to said body member

forming an annular cavity therebetween.

Alternatively the driving tool may comprise the screw threaded

anchor bar.

If required a grouting tube may be removably secured over said

anchor bar.

Suitably said grouting tube is removably secured by a screw

threaded nut engaging said anchor bar adjacent an end thereof remote

from said body member.

According to another aspect of the invention there is provided

an earth anchoring system including an earth anchor as described

above wherein the anchor bar is encased in a cementitious grout over

all or part of a buried length of the anchor bar.

Suitably the earth anchoring system is used in conjunction with a sheet piling system utilising lightweight contoured sheet steel piles.

According to yet another aspect of the invention there is

provided a method of installation of earth anchors of the type

described above, said method including the steps of:-

rotatably driving into an earth formation the anchor with a

threaded anchor bar screw threadably attached thereto, said shaped

cutting head forming a first region of fractured and/or loosened earth

through which an inner portion of a helical flight on said body member

rotates, said helical flight in use serving to draw said earth anchor into

the earth formation during rotation and, thereafter, providing an

anchoring abutment resistant to withdrawal by a load applied to said

anchor bar.

If required said anchor is rotatably driven by a tubular driving

tool removably engagable over said body member.

Alternatively, said anchor member is rotatably driven by a

rotational force applied to said anchor bar.

The earth anchor may be installed with a grouting tube

removably located over said anchor bar, said grouting tube in use

permitting encapsulation in a cementitious grout of all or part of a

buried length of said anchor bar.

In order that the invention may be more readily understood and

put into practical effect, reference will now be made to preferred

embodiments described in the accompanying drawings in which:- FIG 1 shows an anchor according to one aspect of the

invention;

FIG 2 shows a method of installing the anchor of FIG 1 into an

earth formation through a contoured sheet piling wall;

FIG 3 shows one method of installing the anchor according to

the invention;

FIG 4 shows another method of installing the anchor according

to the invention.

In the drawings like reference numerals are employed for like

features for the sake of simplicity.

FIG 1 shows a cross-sectional view of an earth anchor 1 and a

sheet piling bearing plate 20 for the purpose of relative size

comparison.

Anchor 1 comprises a tubular steel body 2 having a steel

cutting head 3 welded therein. Cutting head 3 is simply a section of

mild steel plate although if required it could include hardened and

sharpened cutting edges on points 4.

A helical flight 5 is welded onto body 2 and may included a

shaped or sharpened leading edge (not shown) . The shape and

configuration of helical flights for rotary excavators and tubular

foundation members is well known and forms no part of this invention.

On the outer surface of body 2 towards a trailing end thereof

are a pair of diametrically opposed rib-like projections or "dogs" 6 which engage in corresponding slots of a driving tool described later.

Within body 2 is located an annular steel washer 7 to which is

welded an elongate coarse threaded nut 8 of the type utilised with

thread rolled bar employed as tension members in the construction

industry. As shown a portion of a thread rolled anchor bar 9 extends

through nut 8 and the free end 9a thereof rests against the rear edge

3a of cutting head 3.

FIG 2 shows the exposed end of anchor bar 9 when installed in

an earth formation supported by a contoured sheet piling member 1 0.

After a sheet piling member 1 0 is driven into an earth formation

and the front face 1 0 a thereof exposed by excavation of earth, it is

often necessary to anchor the sheet piling to the earth structure

therebehind.

Initially a generally "snail"-like aperture 1 1 (as shown in

phantom) is cut into the sheet piling at the radius of the trough 1 2

between adjacent ridges 1 3. The generally circular portion 1 1 a has a

diameter slightly greater than the body portion 2 of the anchor and the

elongate extension 1 1 b to the aperture 1 1 has a length slightly greater

than the leading edge of flight 5.

It thus can be seen from FIG 1 that as the plane of the sheet

piling face 1 4 in which the elongate extension 1 1 b lies is angled

relative to the rotational axis of flight 5, the leading portion of anchor

1 comprising cutting head 3 and tubular member 2 extends through the aperture 1 1 a. Anchor 1 may then be rotated whereby the leading

edge of flight 5 enters aperture portion 1 1 b and the anchor continues

to rotate, the flight 5 follows through the aperture 1 1 a/1 1 b as the

anchor 1 moves forward into the earth behind the sheet piling.

After the anchor 2 and associated anchor rod 9 is driven into

the earth formation to a desired depth, the driving tool (not shown) is

disengaged leaving a portion of anchor bar extending from aperture

1 1 , which portion can then be cut to a desired protruding length 9a as

required.

A bearing plate 20 having a cross sectional contour

complementary to and nestable with that of the sheet piling member

10, having an aperture 1 5 slightly larger than anchor bar 9 is placed

over the protruding end 9a and is pushed into contact with sheet piling

member 1 0. Bearing plate 20 is then tack welded as required to

secure it to sheet piling member 10.

A shaped bearing washer 1 6 is then placed over the end of

anchor bar 9 and an elongate nut 1 7 is secured on anchor bar 9 and

then is tensioned to a required degree.

It can be seen from FIGS 1 and 2 that the use of a helical flight

associated with the anchor 1 permits an anchor head of relatively large

diameter to be inserted through a minimally sized aperture in the

contoured sheet piling without a substantial compromise to the

structural integrity of the sheet piling. FIGS 3 and 4 show alternative methods of installing earth

anchors according to the invention.

In FIG 3 there is shown an installation method suitable for

anchor bars having a diameter of, say 25mm or less.

Initially, anchor 1 is assembled with a 25mm thread rolled bar 9

secured thereto. Over bar 9 is secured a grouting tube 21 having a

quick release hydraulic coupling 22 at least on the end remote from

anchor 1 . A spacer 23 is then positioned over bar 9 and a threaded

nut 24 compressively secures tube 21 over the bar.

A driving tool 25 comprising a steel tube having opposed slots

26 in one end 25a is secured over the tubular body 2 of anchor 1 to

engage drivingly with dogs 6 and otherwise to enclose bar 9 and

grouting tube 21 . By means of a driving adaptor 27 attached to the

drive shaft 28 of a rotary boring machine or the like (not shown), the

entire assembly as shown is inserted through the sheet piling 1 0 and

driven to a required depth into the earth formation.

For deep anchor installations, each of bar 9, grouting tube 21

and driving tool 25 are adapted by end couplings to be connected to

further lengths respectively as required.

As can be seen, the driving tool tube 25 forms a borehole

casing which serves to compact the earth therearound. When driving

tool tube 25 is withdrawn from the borehole, the wall of the borehole

maintains a considerable degree of integrity depending upon the earth formation. If the borehole is unduly wet or clogged with loose

material, grouting tube 21 may be coupled, after removal of spacer 22

and unit 23, initially to a source of compressed air to blow out loose

material and/or dry the borehole.

Grouting tube 21 thereafter is coupled to a source of flowable

cementitious grout under pressure and, as tube 21 is gradually

withdrawn from the borehole, cementitious grout is introduced to

encapsulate anchor bar 9 and otherwise fill the borehole to greatly

enhance the frictional engagement of the earth anchor assembly with

the earth formation.

FIG 4 shows an alternative embodiment of the assembly of FIG

3.

This embodiment is particularly suited to anchor systems having

an anchor bar of, say, 30mm or greater as it has been found in

practice that the torsional strength of the anchor bar material is

sufficient to enable the bar itself to be employed as the driving tool.

As shown, the anchor body 2 does not require the driving dogs

6 of the arrangement of FIG 3 and thus a grouting tube 21 having a

diameter up to that of tubular body 2 is possible.

Like the arrangement of FIG 3 grouting tube 21 is secured over

anchor bar 9 by means of a spacer 23 and a threaded nut 24

compressively engaged against spacer 23 and tube 21 . A simple

threaded adaptor boss 30 provides a drive coupling with the drive shaft of a rotary boring machine (not shown) . The boss has a blind

aperture 31 whereby the threaded rod 9 locks against the end of blind

aperture 31 during insertion of the ground anchor and it permits ready

disengagement of the adapter 30 simply by reversing the direction of

rotation.

Again, like the embodiment of FIG 3, the grouting tube 21 may

be coupled to a source of compressed air to blow out loose earth

and/or to dry the borehole. Thereafter, flowable cementitious

introduced to fill the borehole and encapsulate the anchor rod as the

grouting tube 21 is gradually withdrawn.

As described with reference to FIG 2, a bearing plate is then

placed over the free end of the anchor rod together with a bearing

washer and the anchor system is tensioned to a desired tension by a

threaded nut as previously described.

It readily will be apparent to a skilled addressee that many

modifications and variations may be made to the invention without

departing from the spirit and scope thereof.

Claims (17)

1 . An earth anchor including:-

a hollow body member having a screw threaded aperture adjacent

one end thereof to receivably locate a screw threaded anchor bar;

a shaped cutting head located at an end of said body opposite said

one end; and,

a helical flight located intermediate the ends of said body.

2. An earth anchor as claimed in claim 1 wherein said anchor is

adapted to be driven rotatably into an earth formation.

3. An earth anchor as claimed in claim 1 or claim 2 wherein said

anchor includes one or more drive engagers, in use, engageable with a

rotatable driving tool.

4. An earth anchor as claimed in claim 3 wherein said one or more

drive. engagers comprise a socket and spigot engagement associated with

said body.

5. An earth anchor as claimed in claim 3 or claim 4 wherein the one

or more drive engagers comprises a pair of rib-like projections diametically

opposed on an outer surface of said body, said rib like projections being

engageable, in use, with complementary recesses in a driving tool.

6. An earth anchor as claimed in any one of claims 3 to 5 wherein the

driving tool is a tubular member, in use, forming a casing for a

Substitute Sheet (Bule26) RO/AU borehole formed by anchor, an inner surface of said tubular member

and an anchor bar attached to said body member forming an annular

cavity therebetween.

7. An earth anchor as claimed in any one of claims 1 to 3 wherein

the driving tool comprises the screw threaded anchor bar.

8. An earth anchor as claimed in any one of claims 1 to 7 wherein

a grouting tube is removably secured over said anchor bar.

9. An earth anchor as claimed in claim 8 wherein said grouting

tube is removably secured by a screw threaded nut engaging said

anchor bar adjacent an end thereof remote from said body member.

1 0. An earth anchoring system including an earth anchor as claimed

in any preceding claim wherein the anchor bar is encased in a

cementitious grout over all or part of a buried length of said anchor

bar.

1 1 . An earth anchoring system as claimed in claim 10 whenever

used in conjunction with a sheet piling system utilising lightweight

contoured sheet steel piles.

1 2. A method of installation of earth anchors as claimed in any one

of claims 1 to 9, said method including the steps of :-

rotatably driving into an earth formation said anchor with a

threaded anchor bar screw threadably attached thereto, said shaped

cutting head forming a first region of fractured and/or loosened earth

through which an inner portion of a helical flight on said body member rotates, said helical flight in use serving to draw said earth anchor into

the earth formation during rotation and, thereafter, providing an

anchoring abutment resistant to withdrawal by a load applied to said

anchor bar.

1 3. A method as claimed in claim 1 2 wherein said anchor is

rotatably driven by a tubular driving tool removably engagable over

said body member.

1 4. A method as claimed in claim 1 2 wherein said anchor member is

rotatably driven by a rotational force applied to said anchor bar.

1 5. A method as claimed in any one of claims 1 2 to 1 4 wherein the

earth anchor is installed with a grouting tube removably located over

said anchor bar, said grouting tube in use permitting encapsulation in a

cementitious grout of all or part of a buried length of said anchor bar.

1 6. A method as claimed in any one of claims 1 2 to 1 5 wherein

said anchor is inserted into an earth formation via an aperture in

contoured sheet piling.

1 7. A method as claimed in claim 1 6 wherein said anchor is inserted

by rotation via an aperture having a cross sectional area smaller than a

cross sectional area represented by a diameter of said helical flight.