COST EFFECTIVE DRIVING SHOES FOR PRECAST CONCRETE
PILES IN BRIDGE CONSTRUCTION
H.H. Lob, B.E.(Civil)
Design Engineer, VIC ROADS
SUMMARY
Studies have revealed that generally during the drivmg ot a flat-ended pile in cohesive or sandy
soil, a cone of earth compresses under the flat tip and acts to a large extent as a point-ended
extension of the pile. This 'cone-of~failure ' mechanism in the soil may largely explain why,
in some tests, there appeared to be no significant advantage from driving a point-ended pile to
that of a flat -ended one. Furthermore, flat -ended piles are more easily kept in line while driving
and provide better bearing for end-bearing piles. Pointed ends add little, if any, to the rate of
penetration.
This paper presents an overview of pile shoe practices within VIC ROADS and other State
Road Authorities, pile-toe requirements of three national highway bridge design codes and a
literature review. A better understanding of the pile-soil interaction has led to the use of cost
effective shoes and significant cost savings in pile manufacture.
ACKNOWLEDGEMENT : The author wishes to thank the Chief Executive of VIC ROADS
for his permission to publish this paper. The views expressed in the paper are those of the author
and do not necessarily reflect the views of VIC ROADS .
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
297
Henry Loh is an Engineer in the Development Section of the Bridge
Department of VIC ROADS. He joined the organisation in 1969 and
has extensive experience in the design of bridges and other road
structures. Prior to joining VIC ROADS he worked with the Rural
Water Commission of Victoria in the area of town water supply. He
is now working on durability of concrete and other development
projects.
298
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
INTRODUCTION
1. Commercial precasters in Victoria have, within the past few years, pushed for the use
of a simpler and cost effective pile-toe protective treatment in bridge construction from the
currently specified concrete tapered toe details. In particular, flat-ended RC piles
incorporating steel flat plate and cruciform-tipped driving shoes have been proposed and
tendered for a number of large VIC ROADS bridge projects, at significant lower costs.
2. Design engineers, it appears, intuitively believe that tapered point-ended piles drive
easier and align better during driving than flat-ended ones. This belief seems to have been
supported and reinforced by the tapered toe requirement of both the NAASRA and
AASHTO bridge design specifications to date. This requirement has been strictly adhered
to in the overwhelming majority of bridge construction piling applications in all State Road
Authorities, including VIC ROADS until recently.
However, the Ontario HBDS 1983 advises that 'Concrete piles are usually provided with
a steel plate cast into the pile and connected to the concrete by means of reinforcing
dowels'.
3. The perceived differences in Code requirements, and the desire to realise the
significant cost savings inherent in the manufacture of flat-ended precast concrete piles
incorporating cost effective driving shoes, have provided the impetus for this investigation.
This paper serves as a record for VIC ROADS use of flat-ended precast RC piles in lieu
of the tapered point-ended ones.
OBJECTIVF.S
4.
The objectives of the investigation are as follows:
(a) Summarise experiences and practices of VIC ROADS and other State Road
Authorities.
(b) Present and discuss requirements for pile-toe protective treatments of three national
Bridge Design Codes.
(c) Assemble some historical and available information on the use and performance of pile
shoes.
(d) Gain some understanding of the pile-soil interaction and soil failure mechanism ahead
of the driven pile.
(e) Provide guidelines for the use of various types of pile shoes in different ground
conditions (Fig. la, 2 and 3).
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
299
VIC
600
_._~~I2~4J
PITCH FOR 0 . 3 ... "A .
I
/'000
ROADS
I .2
125 x 3 Inn
THICK PLATE
4 NO. 20 Inn DIA .
x 600 Inn LONG
BOND BARS
20 x 20 Inn
CHAMFER
FULL STRENGTH
BUTT WELD
90 x 90
60 Inn DIA. x 2BO Inn LONG
HIGH TENSILE STEEL PIN
WI TH CONCAVE END
nm
PLATE
32 Inn PLATE
SOIL CONDITION
FOR VERY HARD DRIVING THROUGH BOULDERY SOILS AND ONTO OR INTO
STEEPLY SLOPING HARD ROCK SURFACES .
PILE SHOE
THE PILE SHOE SHALL BE BALKEN ROCK SHOE OR APPROVED EQUIVALENT.
FIG. 1. - ROCK SHOE DETAIL
SOO
COVER VAR I ES
2S TO 40 mn
P I LE SHOE
: :SP. :;A~Cc;.I, -NG: . . :.F. : OR.; . ;6: . ;•..::3,-","=..::Oc;.I:..;A.:..._ _6.::;0"-111
LIGATURES
10 AT 4S
0
II
.
PITCH FOR 6 . 3"," OIA . HELICAL LIGATURES
1000
80"," PITCH
ELEVATION
PILE SHOE
PILE SHOE SHALL BE CAST IRON AND COMPLY WITH AS 1830/ 187
THE ANCHORAGE BETWEEN THE CAST IRON SHOE AND THE ANCHOR ROO
SHALL RESIST A TENSILE FORCE OF 75 KN
DETAIL
THIS DETAIL IS TO 8E PHASED OUT WHEN EXISTING STOCK IS EXHAUSTED .
PILE SHOE DETAIL
FIG. 1b - TAPERED POINT -ENDED PILEITOE DETAIL
300
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
VIC ROADS
4 NO . 16 mm DIA .
REINFORCEMENT BARS
5 mm PLATES
SECTION A-A
350 OR
400
50 -100
A
l
A
0
0
J
<t
Q:
0
0
•
on
,..,
•
VENT HOLES
REFER~
' - - - 20 x 20 rrm CHAMFER
11
NOTE:!/
OR APPROVED RADIUS
PLAN
FLAT PLATE DRIVING SHOE
350 x 350 mm AS SHOWN
NOTES
SCALE 1
10
REINFORCEMENT
1.
REINFORCEMENT SHALL COMPLY WITH AS 1302 GRADE 400Y
2.
ALL WELDS SHALL COMPLY WITH AS 1554 PARTS 1 AND 3 AND SHALL BE PERFORMED
BY A WELDER APPROVED BY THE ROADS CORPORATION .
STEELWORK
3.
PILE SHOE STEEL SHALL COMPLY WITH AS 367B GRADE 250.
4.
EXPOSED SURFACES OF STEELWORK SHALL BE GIVEN ONE COAT OF AN APPROVED
ZINC PHOSPHATE PRIMER WITH MINIMUM THICKNESS OF 50 ~m.
SOIL CONDITION
5.
TO BE USED IN ALL SOIL CONDITIONS EXCEPTING WHERE LARGE OBSTRUCTIONS
ARE EXPECTED IN THE GROUND, THROUGH OVERLYING SOFT LAYER OR TRASH, IN
DENSE SANDY OR GRAVELL Y MATERIAL, OR FOUNDING INTO STEEPLY SLOPING
HARD ROCK SURFACES .
FIG.2 - FLAT PLATE DRIVING SHOE DETAIL
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
301
VIC
ROADS
4 NO . 16 mm DIA .
REINFORCEMENT BARS
o
o
5 mm PLATES
v
2 No 10 mm DIA . VENT HOLES
(TOP SURFACE AT CASTING)
ww
...J...J
' - - - - - - - 12 mm PLATE
11.11.
~ ~
SECTION A-A
00
100
""v
x x
00
100
,..,V
350 OR
400
5
50 -100
A
o
o
J
V
Q:
o
o
,..,
10
VENT HOLES
REFER
NOTE 2
NOTES
REINFORCEMENT
PLAN
CRUCIFORM DRIVING SHOE
350 x 350 mm PILE AS SHOWN
20 x 20 mm CHAMFER
OR APPROVED RADIUS
SCALE 1 , 10
1.
REINFORCEMENT SHALL COMPLY WITH AS 1302 GRADE 400Y
2.
ALL WELDS SHALL COMPLY WITH AS 1554 PARTS 1 AND 3 AND SHALL BE PERFORMED
BY A WELDER APPROVED BY THE ROADS CORPORATION .
STEELWORK
3.
PILE SHOE STEEL SHALL COMPLY WITH AS 367B GRADE 250.
4.
EXPOSED SURFACES OF STEELWORK SHALL BE GIVEN ONE COAT OF AN APPROVED
ZINC PHOSPHATE PRIMER WITH MIN IMUM THICKNESS OF 50 pm .
SOIL COND ITION
5.
TO BE USED IN SOIL CONDITIONS WHERE LARGE OBSTRUCT IONS ARE EXPECTED
IN THE GROUND BEFORE REACHING SPECIFIED TOE LEVELS OR DRIVING THROUGH
OVERLYING SOFT LAYER, TRASH, DENSE SANDY OR GRAVELLY MATERIAL AND
INTO DECOMPOSED ROCK.
FIG.3 - CRUCIFORM DRIVING SHOE DEtAIL
302
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
HISTORY
GENERAL
5. The idea of using metal shoes to protect the ends of driven piles is not new. Fahy
(1984) has reported on a metallurgical investigation of a small piece of metal shoe extracted
from a wooden pile of a timber bridge known to have existed since approximately 300 BC
on the Via Appia between Rome and Naples.
6. Since then there has been a proliferation of the varieties and intricacies of driving
shoes (e.g. see Fig.3.4 in Chellis 1961) for timber, steel and concrete piles for use in all
sorts of ground conditions. However, the trend now appears to shift towards fewer
varieties of simpler efficient and cost effective shoes for the bulk of the precast concrete
piling applications.
FLAT-ENDED PILES
7. Precast concrete piles with flat tips have been used in Scandinavia for the past 35
years (Badholm and Gravare 1977). These piles are also permitted for use by the SAA
Piling Code AS 2159-1978 in the Australian building construction industry. They are
generally not used in bridge construction in Australia as the current NAASRA BDS 1976
specifically requires the toe of a precast RC or prestressed concrete pile to be tapered.
Flat tips have long been an established practice in other forms of driven piles. Some
examples are the Franki Cast-in-situ concrete driven piles or in steel shell piles driven with
open ends.
VIC ROADS
8. Since the end of 1991, and as a result of this investigation, ViC ROADS has adopted
flat-ended precast RC piles incorporating steel flat plate and cruciform-tipped driving shoes
as standard options.
OTHER SRA'S
9. To the author's knowledge, all other SRA'S except one have not used flat-ended piles.
Department of Transport - Queensland has driven some Balken flat-ended piles, but only
in situations subjected mainly to axial loading with very little bending. The author
understands that this is because of the limited amount of longitudinal reinforcement
provided in the standard Balken piles.
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
303
VIC ROADS PILING PRACTICES
GENERAL
10. All VIC ROADS standard piles (350 x 350 or 400 x 400 mm x 15 m max. standard
lengths) are exclusively of the precast reinforced concrete variety. Precast prestressed
concrete piles were last used some five years ago. Timber piles were last used in timber
bridges on State highways in the early 1940's and in the Municipalities in the early 1950's.
Composite RC piles with fabricated 250UBP85 tips have not been used for the past three
years. Their use will be discontinued and replaced by the much cheaper Balken or
equivalent rock shoes (Fig. 1a). These rock shoes are to be used in very hard driving
through bouldery soils and founding onto or into steeply sloping hard rock surfaces.
Flat-ended RC piles have been successfully driven to capacity at a number of VIC ROADS
bridge projects in Victoria for the past four years. For reason of cost benefits, the previous
standard tapered point-ended toes fitted with cast iron shoes (Fig. 1b) will be phased out
when existing stock is exhausted. They will be replaced by cost effective steel flat plate
(Fig. 2) and cruciform-tipped (Fig. 3) shoes for soil conditions as indicated in the Figures.
The cruciform provides additional strength to the tip to penetrate hard layers and helps to
break up hard ground.
SHOE UNIT COSTS
11. Approximate comparative unit shoe costs, excluding installation by manufacturers,
are shown in Table 1.
TABLE I
SHOE UNIT SUPPLY COSTS ($)
Cast Iron
Point
Balken Rock
Shoe
*25
300
250UBP85
*750
Flat Plate
Cruciform
40
100
* Use to be discontinued when existing stock is exhausted.
COST BENEFITS
12. Removal of the concrete end taper has resulted in an estimated cost saving in
manufacture (including cruciform shoe) of about $150 per pile, or about $150,000 p.a. for
VIC ROADS. This cost saving has been achieved through easier forming of the pile end,
simpler reinforcement detailing by eliminating cranked main bars and reinforcement
congestion at the toe. Flat ends also facilitate mass production of piles which are now cast
in horizontal adjacent forms with tapered sides for easier stripping.
304
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
OTHER SRA'S PILING PRACTICES
13 . Tapered point-ended toes with cast iron shoes are used almost exclusively by other
State Road Authorities. Timber piles with typical cast iron points and mild steel straps are
still in use in Tasmania and Western Australia. Both Western Australia and Queensland
have phased out RC piles and use only precast prestressed concrete piles. Steel shell piles
are driven open-ended in Western Australia. In Tasmania, they are driven with concrete
plugs or precast concrete cone-shaped shoes at the ends.
Only in extremely hard driving conditions, in general, would the other State Road
Authorities consider using UBP-tipped concrete piles or steel 'H' pile. In Tasmania, steel
UBP or UC piles are fitted with cast steel shoes or with flanges shaped to a point to assist
driving. They have also used 'Oslo' cast steel points for anchorage into hard rocks.
CODE REQUIREMENTS
NAASRA BDS 1976
14. Clause 4.5.7.3
Shapes:
Precast Reinforced Concrete Piles, Sub-clause (b) Size and
Unless the pile is to be wholly driven in soft soils (with 'N' values of 2-4), the toe
of a reinforced concrete pile shall be tapered and shall be fitted with a steel or cast
iron driving shoe.
This requirement is generally based on the AASHTO specifications.
It is of interest to note in part in Clause 1.1 Design Analysis that:
.... where it is proposed to depart from other requirements of this Specification,
details of the proposal shall be submitted for the approval of the road authority
concerned.
AUSTROADS DRAFf BDC 1987, 1989
15.
Clause 4.7.6.4 Driving Shoes, Rings and Toe Reinforcement:
Unless a pile is to be wholly driven in soft soils, the toe shall be protected from
damage.
For hard driving conditions, timber reinforced concrete and prestressed concrete piles
shall be fitted with a steel or cast iron driving shoe of truncated cone or pyramid
shape or suitable alternative. The shoe shall be concentric with the axis of the pile
and shall be designed to be integral with the pile.
Consideration shall also be given to the need for reinforcement of the toes of steel H
section piles and open-ended tubular piles.
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
305
Clause 4.7.6.5 Design Details Relevant to Specific Types of Piles:
Size and Shape:
Reinforced concrete piles:
Prestressed concrete piles:
Timber piles:
Steel Piles:
Toe shall be tapered.
As for RC piles.
No toe shape requirements specified.
In cases where steeply sloping bedrock is known to
exist, the toe of steel 'H' section pile shall be suitably
bevelled so that a wedge action develops on
penetration into rock. In all other cases, the toe of
the pile shall be cut square to the pile axis.
AUSTROADS BDC 1992
16. This new bridge design Code is now available (since August 1992) and will be fully
implemented by VIC ROADS by the 1 January 1993.
Content of Clause 4.7.6.4 of the draft Code has been retained in full as Clause 3.7.6.5 of
the new Code. However, there is no longer a requirement for the toe of a reinforced or
prestressed concrete pile to be tappered in Clause 3.7.6.5 of the new Code.
SAA PILING CODE AS 2159 - 1978
17. Clause 4.6.1 Types and Dimensions (d) states that 'The ends of the pile shall be
at right-angles to the length of the pile' .
Clause 4.6.2 Design and Manufacture (g) states that 'Piles shall be provided with a steel
or cast iron shoe at the toe' .
AASHTO HBDS 1989
18.
For precast concrete piles, Clause 4.3.9.4 states:
Piles preferably shall be cast with a driving point and, for hard driving, preferably
shall be shod with a metal shoe of approved pattern.
and Clause 4.3.9.5 states:
Where steel points are not used, points shall be not less than 6 inches in diameter and
the pile shall be bevelled, tapered, or sloped uniformly from the point to 2 feet from
the point.
306
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
ONTARIO HBDS 1983
19.
Clause 6 - 8.3.12 Driving Points of shoes:
Driving points of shoes shall be used unless it is known from previous experience
or special investigation that they are not necessary. The use of rock points shall
be considered for short end-bearing units driven to hard rock surfaces, and for any
units driven to an inclined hard rock surface where slippage of the tip could occur.
The author thinks that this simple open-ended approach is preferable to the specific and
rigid requirements in both the NAASRA BDS 1976 and the AUSTROADS DRAFT BDC
1987.
There is an opportunity to elaborate more on pile shoe requirements in general in the
commentary to the AUSTROADS DRAFT BDC. The author believes, therefore, that it
is of interest to quote in full the 'Commentary' of the Ontario Code on this aspect.
Clause C6 - 8.3.12 Driving Points and Shoes :
Pile ends must be sound and undamaged after driving, because a pile with a damaged
end:
•
•
•
will drive to a capacity that is smaller than that of a sound pile.
could drift and bend in the soil, or
could twist and deviate from its intended location at the cut-off elevation.
Damage to the pile end can be minimised by means of a suitable pile end protection.
For closed-end steel tube piles, a flat steel plate is normally sufficient protection. For
steel H-piles, a separate shoe made of cast steel or ductile iron is needed. Methods,
such as welding steel plates to the flanges and web of the pile, are rarely adequate.
Concrete piles are usually provided with a steel plate cast into the pile and connected
to the concrete by means of reinforcing dowels. Often, however, a regular rock shoe
is required, which consists of a thick steel plate and a tip (dowel) made of hardened
steel. Such rock shoes (rock points) are necessary for all piles driven to hard rock
surface, where slippage of the pile end could occur.
The occurrence of pile end damage is frequent when driving in bouldery soils or into
very dense soil layers. It is difficult to predict damage from borehole information
and even to detect it from indirect observations during test driving or test loading.
Severe tip damage can be discovered on wave traces from dynamic measurements.
The best method to assess damage and to determine the necessity of pile end
protection is to extract piles for direct visual inspection.
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
307
FLAT-ENDED PILES (LITERATURE REVIEW)
20.
According to Chellis (1961) :
It apparently makes little difference whether shoes are open or closed at the end.
Piles with square ends are more easily kept in line while driving and provide better
end bearing for end-bearing piles. Points add little, if any, to the rate of penetration.
The stress may govern, particularly in the case of tapered piles or end bearing piles
and therefore the use of small tips should be avoided with materials having low
strengths in compression. The use of large tips in wood piles is generally advisable.
21.
An extract from the American Wood Preservers Institute Publication (1967):
Preparing tips of piles
For ordinary driving conditions tips of the piles should be cut square or perpendicular
to the axis. Such points are less likely to be damaged in driving, and the pile is
easier to keep in line. During the driving of such a pile a cone of earth compresses
under the blunt tip and acts to a large extent as a point. This practice has been
confirmed repeatedly by the excellent condition of many blunt tips when the piles
were pulled out of foundations for examination or for re-use elsewhere.
As a typical example, a creosoted timber foundation pile driven with a blunt tip at the
Julien Dubuque Bridge in 1941, to a bearing of 35 tons, and thereafter pulled for
inspection, showed an unmarred tip.
22.
ACI S43R-74 (Reaffumed 1980)
Section 5.6.1 Tips:
Flat tips drive straighter and truer than pointed tips. Pointed or wedge shaped tips
may aid penetration through overlying trash, etc., and may also be used to help
penetration into decomposed rock. However, such tips may guide the pile off axial
alignment. Blunt (rounded) tips will often accomplish the penetration through rock,
etc., with a minimum of misalignment and point breakage. (See Section 5.2.8)
Section 5.2.8 Distortion of tips :
Distortion of tips occurs as the tip encounters hard or irregular materials, such as a
nest of boulders overlying firm material. Reinforcement of the tip is recommended.
This may be by flat steel plates or by a fabricated shoe.
308
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
23 .
Tomlinson (1980) commented that:
The Authors' observation that (the rate of) penetration was not increased by the use
of rock shoes is a most valuable one. These shoes with the cast-steel 'Oslo' point
represent quite an appreciable proportion of the cost of a pile, and if their use can be
limited to sites where piles are driven on to a steeply sloping surface, there should
be quite useful savings in cost.
Balken rock shoes could be used as an effective and much cheaper alternative for the 'Oslo'
points in similar application.
24. Williams et al. (1980) have conducted static load testing to failure on large diameter
socketed cast-in-place RC piles in weak rock (mudstone). They found a Terzhagi-type
failure mechanism in the rock for ratio of embedment length (L) to pile diameter (D) of
zero, that is at the ground surface. A punching failure mechanism was always observed
for LID ratio equal or greater than 2.
25. Evans (1987) discussed the performance of driven precast prestressed (tubular)
concrete piles in the different ground conditions (boulders, coarse gravel, medium to very
dense sandy silt) encountered in Hong Kong.
Of interest is the examination of the performance of different types of pile shoes, in
particular a comparative driving test between using a cast iron flat crosshead shoe and a
conical shoe. These two piles were driven one-and-a-half metres on either side of a logged
borehole.
It was expected that the conical shoe would require fewer blows to penetrate hard layers
and this would lead to faster installation. This, however, was not confirmed by the initial
tests which showed that the rate of penetration of each pile was very similar.
The Author concluded that:
At the site studied, there appeared to be no significant advantage from driving a pile
with a conical point, although it was completely satisfactory. In very hard conditions
however, such as crushed rock filling, the conical point should be less susceptible a
damage than the flat crosshead shoe, but this has yet to be proven. Further
cbd;pmt
in pile shoe design would be useful:
•
to improve the penetration rate in cobbles and boulders
•
to increase the depth of penetration in silty sand where piles stop at relatively
low SPT'N' values.
26. Rowlands (1989) gave an account of a small-scale model study to examine the
influence of four different types of piles shoes on the behaviour of piles driven into sand
overlying a layered clay in a container.
It was concluded that the final shape of the plug of sand driven ahead of the pile is
independent of the shape of the pile shoe in every case.
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
309
27. VIC ROADS Geotechnical Group uses the computerised program 'PENPILE' to
calculate the pile capacity for RC piles using the full cross-section of the pile, neglecting
the concrete toe taper length .
The failure mechanism by Meyerhof is assumed where a triangular soil wedge at the end
of the pile is considered to be in an elastic state of equilibrium, and therefore can be
considered as an extension of the pile.
The taper of the standard RC pile toe is only marginally larger than the soil wedge.
Therefore the calculations in 'PENPILE' assume a full cross-section of the RC pile and the
taper is disregarded. This approach is only marginally conservative.
SHOES OR NO SHOES ?
28. The author's view is that there is no reason why a plain high strength concrete toe
finish cannot be used provided that driving stresses in the pile are within acceptable levels.
This applies especially in cohesive soils of uniform consistency with no large obstructions,
in which pile capacity is derived mainly through shaft friction where toe resistance and
therefore stresses in the pile would be low.
ACI 543R-74 (1980) Section 5.6.2 Shoes says that:
Modem high strength concrete usually requires no shoe except in such special cases
as:
(a) In driving through riprap, comer protection is desirable to prevent spalling
(b) To aid in penetration into bedrock or decomposed rock.
29. The use of protective pile shoes should not lead to the conclusion that the pile will
not be damaged (Chellis 1961). Others have advocated that for all piles, especially those
that cannot be examined in the ground - H, timber and precast - it is essential that the tip
be protected. Where 'there may be obstructions in the ground, driving is to sloping rock
or through soft material abruptly on to rock, tip protection is especially needed (Cheney
1981).'
30. VIC ROADS has accepted that shoes are a low-cost insurance to ensure the integrity
of driven piles. They provide a safeguard against possible damage during handling and
unexpected driving difficulties.
310
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
DESIGN OF SHOES
31. The search for some established simple and practical way to design the pile shoe itself
proves elusive. Shoe design appears to be largely an empirical process involving a
combination of laboratory testing and a large reservoir of accumulated practical on-the-job
pile driving experiences.
Nevertheless, for those who are interested, Anon. (1980) describes the results of a finite
element analysis of four types of iron shoe.
TESTING
32. The author believes that it is worthwhile to obtain some quantitative data to compare
the driving resistance and performance of flat-ended and point-ended piles. This
comparative testing using the Pile Driving Analyser (PDA) could be arranged to be carried
out as a part of the actual bridge construction program.
CONCLUDING REMARKS
33. Studies have been shown that end tapers add little to the effective performance of
driven concrete piles in most soil conditions. The concept of the 'cone-of-failure' in the
soil could largely explain the similar rate of penetration for both flat-ended and point-ended
piles. As well,flat tips have been claimed to drive straighter and truer, and less likely to
deviate from axial alignment when floaters are encountered than pointed tips. Flat-ended
precast RC piles have been successfully driven to capacity at a number of VIC ROADS
bridge projects. By eliminating the concrete end taper, significant annual productivity gain
and cost reduction have been achieved in the manufacture of the piles through simpler
reinforcement detailing and casting operduulIs.
Removal of the end taper has also resulted in the use of simple and cost effective driving
shoes. Although shoes are shown to be not necessary in all soil conditions, VIC ROADS
has accepted that shoes are a low-cost insurance for the integrity of the piles. VIC ROADS
has adopted flat-ended precast RC piles with shoes as standard options. Three standard
shoes are specified. These are steel flat plate, cruciform and Balken (or equivalent) rock
shoes. Shoe details and soil conditions for their use are shown in
Figures la, 2 and 3.
Shoe design at present is much more an art than a science. And the author is of the opinion
that comparative PDA testings on flat-ended and point-ended piles in different ground
conditions, wherever opportunities arise, is worth considering. The ONT ARlO HBDS
contains good simple guidelines on shoe and pile-toe treatment.
Bridges are an integral part of the transport network. The cost saving inherent in the
manufacture and use of flat-ended precast concrete piles incorporating simple cost effective
driving shoes will contribute to bridge construction efficiency.
PROCEEDINGS 16th ARRB CONFERENCE, PART 3
311
REFERENCES
ACI 543R-74 (Reaffirmed 1980).
Installation of Concrete Piles.
Recommendations for Design, Manufacture and
American Wood Preservers Institute (1967). Pressure Treated Timber Foundation Piles
for Permanent Structures, p. 68 .
Anon. (1980). FEM Elasto-Plastic Analysis of Iron Bridge Shoe Protrusion. Permanent
Way V22 June, pp. 25-37.
BADHOLM, C. and GRAVARE, C-J. (1977). Precast Segmental Concrete Piles.
Production and Installation. Aag-och vattenbyggaren.
CHELLIS, D.R. (1961). Pile Foundations, 2nd Edition. (McGraw - Hill: New York.)
CHENCY, R. (1981). Benefits of Pile Research to Pile Contractors.
Conference 81 March 4-5, pp. 117-130.
APF Geo-Pile
EVANS, G.L. (1987). The Performance of Driven Pre-Stressed Concrete Pile. Hong
Kong Engineer V15 N3 March, pp. 9-16.
FAHY, F .W. (1984) Abstract: Metallurgy and Archaeology. Metals Australasia V16 N3
April, pp. 6-8.
ROWLANDS, G.O. (1989). Influence of the Shape of a Pile Shoe on a Model Pile
Penetrating Layered Soil: Geotechnical Testing Journal V12 N4 Dec., pp.317-322.
SAA PILING CODE AS2159-1978
TOMLINSON, M.J. (1980). Discussion: Paper 1-4. Recent Developments in the Design
and Construction of Piles. Proc. Institution of Civil Engineers, London, p. 45.
WILLIAMS, A.F. , JOHNSTON, I.W. and DONALD, I.B. (1980). Design of Socketed
Piles in Weak Rock. International Conference on Structural Foundations on Rock, Sydney
May, pp. 327-345.
BRIDGE DESIGN SPECIFICATIONS/CODES:
312
•
NAASRA BDS 1976
•
ONTARIO HBDS 1983
•
AASHTO HBDS 1989
•
AUSTROADS DRAFT (LIMIT STATE) BDC 1987, 1989
•
'92 AUSTROADS BRIDGE Design Code
PROCEEDINGS 16th ARRB CONFERENCE, PART 3