TRENCH SHORING FOR ARCHAEOLOGISTS AND THE RANDWICK GRAVE DIGGING
COURSE
M. A. Smith
Archaeology shares some common safety concerns with
other trenching operations such as grave digging and pipe
laying. Foremost amongst these are the dangers of working in unshored or inadequately shored excavations. It is
not uncommon far archaeological excavations to be more
than 1.5 m deep and deep shafts 4-6 m deep have occasionally been dug (e.g. at Devils Lair, Koonalda Cave,
Malakunanja 11 and Mushroom Rock). Shoring has been
used in some cases. For instance, Jones used it in his
excavations at Rocky Cape in 1%5-67 (R. Jones pers.
comm.), at Nauwalabila 1 in 1981 (Jones and Johnson
1985) and most recently at Allens Cave (R. Jones and
S. Cane p m . comm.). Dortch installed an internal scaffolding of pipe-work and heavy duty timber shoring in the
deep trench at Devils Lair (Dortch 1984). Sim used a
series of nested prefabricated boxes in her excavations on
King Island (Sim and Thorne 1990) and Horton and
Wright used timber soldier sets in trenches at Trinkey
(Wright pers. comm.). These however are the exceptions
and it is still all too rare for shoring to be used on prehistoric sites. The usual practice is to install some form of
shoring only when deposits are demonstrably loose and
unconsolidated or where slumping or fretting of the sections is actively taking p k e . In cases where shoring has
been used there is also some question as to whether it has
been adequately engineered for the lateral stresses that
would be imposed should the trench fail catastrophically.
Many of us are reluctant to shore because it is seen as
time-consuming, expensive and it interferes with access to
the faces of an excavation. This is exacerbated by the fact
that most Australian-trained field archaeologists lack direct experience in the proper installation of shoring and
that the industrial shoring equipment available for hire
(e.g. acrow props, drag boxes, steel sheet pilings and
trench linings) is clearly not suitable for most archaeological applications. However, excavating in deep unshored
trenches is a form of 'Russian roulette' in which we stake
our lives on a rather casual assessment that the trench
walls will continue to be self-supporting. Sooner or later a
trench wall will fail and without the safety margin p m
vided by shoring, someone will be killed (cf. Hayward
1968; Patchell 1990).
Up to now no-one has been seriously injured in an
archaeological excavation in this country. This is partly
because the deeper excavations are generally those dug
into undisturbed ground, made up of ancient consolidated
sediments, and tend to be stable and self-supporting. And
partly it is because there is a professional concern with
Division of Archaeology and Nanual History, Research School of Pacific
and Asian Studies, The Australian National University, Canberra, ACT
0200, Australia
Present address: Department of Archaeology and Anthropology, The
Faculties, The Australian Naticmal Univenity ,Canberra, ACT 0200,
Australia.
protecting sections and the exposed edges of trenches. But
in large measure it may be that this safety record is due to
nothing more than the fact that the number of deep archamlogical excavations is low when compared to industrial
or commercial trenching operations. If I am right, we
need to take steps to improve the safety measures routinely
taken on excavations before our luck runs out.
A new course - Grave Digging (Basic Shoring) - developed at the Randwick Campus of the Sydney Institute of
Technology (see Sydney Morning Herald March 24 1993
'Grave-diggers ensure they don't dig their own') offers
practical instruction in basic shoring techniques and goes
some way towards meeting the technical needs of archaeologists and fieldworkers in related disciplines. The threeday course was completed recently by a group of academic
and technical staff from The Australian National University. Before discussing what the course offers I think it is
useful to draw attention to the legal requirements affecting
excavations and to briefly summarise the risks involved in
working in unshored excavations.
Legal requirements
It is not my intention here to comprehensively review
State and Federal legislation that may have a bearing on
archaeological excavations. However, there are various
regulations that cover safe practice in excavations and
presumably these also cover archaeological excavations.
Provisions vary from state to state but in general there is a
legal requirement to shore up excavations more than
1.5 m deep or to batter the sides of such excavations.
Considerable discretion is allowed in the case of excavations less than 1.S m deep, provided that they are made
safe.
In New South Wales, archaeologists would be well
advised to consult the provisions of the Workers Compensation Act' (1987). and the safety regulations (1988)
that accompany the 'Construction Safety Act' (1912).
The Building Industry Guide (1992) issued by the NSW
Workcover Authority is also worth consulting. In Victoria, the 'Occupational Health and Safety Act' (1985)
provides for codes of practice for various industries and
the relevant Code of Practice for Safety Precautions in
Trenching Operations (1988) is available from the Occupational Health and Safety Authority. In the Northern
Territory, the Industrial Safety Branch of the Department
of Mines and Energy puts out an information sheet on
Guidelines for Safety in Excavations. My copy is dated
1980. More recent versions may be available. Federal
Government 'Construction Safety (Australian Standards)
Rules' are also worth consulting, particularly Regulation
No. 37 (1978) which includes a table specifying the grade
of timber necessary for shoring trenches of various widths
or depths.
Australian Archaeology, Number 39,1994
Smith
Apart from penalties specified in the legislation there
are other risks for unwary archaeologists who fail to comply with the relevant safety regulations. In the event of a
workers compensation claim, for injuries sustained in a
trench collapse, an insurance company might well seek to
recover its losses from either the university or archaeologist responsible if it were established that the excavation
was not shored to current safety standards.
Killer trenches
The walls of an excavation are subject to lateral
stresses equivalent to the weight of the sediment removed.
Given that a m' of sediment weighs -1.5 tonnes, the lateral stresses on the side walls of a 1 m2 by 2 m deep trench
will be about 0.75 tonne, and on the side walls in the mid
section of a longer trench will be 1.5 tonnes. In deeper
excavations the lateral stresses can be tremendous.
Spoil heaps, nearby boulders, or machinery can create
additional stresses near an excavation, technically known
as surcharged ground, and this can produce very dangerous conditions even in excavations less than 1.5 m deep.
Surcharged ground is of course a particular problem for
excavations on urban sites where nearby buildings or embankments add to the risk of trench failure.
Ground under hydrostatic pressure, as in cases where
there are problems with ground water or impeded drainage
(e.g. Wyrie Bog, Tarnbar Springs) is particularly dangerous and in such circumstances it might be advisable to
lower the surrounding water-table using tube wells and
immersion pumps. It is better to place these away from
the trench, rather than pump directly from a sump in the
trench itself and risk generating a flow of water into the
excavation.
Particular risks exist where a new excavation cuts
through the backfill of an older excavation, as is sometimes the case in re-opening archaeological trenches, or
where only a thin baulk separates unconsolidated backfill
from a new excavation. On urban sites, excavations into
'made' ground pose similar risks.
If trench failure occurs it can happen very quickly
giving a digger virtually no time to escape. A recent
article in Plumbing and Mechanical Connection (Patchell
1990) summarises the mechanics of a trench collapse. The
surface of the ground next to the trench may subside
slightly. Tension cracks appear on the ground surface running parallel to the edge of the trench and back from the
edge a distance equal to about 113 to 2/3 the depth of the
trench. These cracks develop as part of the trench wall
shears away from the adjacent deposit. The lower part of
the trench wall usually fails fust. Normally a wedge of
sediment slabs off one wall and breaks against the opposite
wall. This can bury or crush a person. Would-be rescuers
are often killed by further collapse of the now unstable
face.
Although some form of shoring becomes obligatory at
depths greater than 1.S m there will be situations when
much shallower excavations will need some support. In an
article in the British Journal of Occupational Safety
Hayward (1%8:444) offers some sensible advice:
the regulations themselves say, in effect, that if
Austra&zn Archaeology, Number 39, 19%
'
a person can be injured from a fall of more than
four feet, it should be timbered. This may be
the law, but I can quote examples where there
have been falls or collapses from heights of less
than 4 ft 6 in and men have been killed instantly
... It must be remembered that the most vulnerable part of the body is the lower abdomen.
There is no protection by ribs or other bones,
and I have attended inquests following incidents
where men have been buried no deeper than
their stomach and the blow of the earth has
killed them instantly ... It is therefore my considered opinion that any type of ground ... needs
some sort of timbering. This does not mean that
I would advise close boarded timbering in every
case, but those in charge should know and understand the nature of the ground and what its
reactions are likely to be under all sorts of climatic and other conditions, and decide accordingly on the amount of timbering that should be
used.
Grave digging at Randwick
The Grave Digging (Basic Shoring) course offered
at the Randwick campus of the Sydney Institute of Technology was developed originally for grave-diggers employed by Waverley Council in Sydney. In the closelypacked cemeteries in Sydney's eastern suburbs existing
graves are too close together to allow excavation with
machinery such as a back hoe or JCB. New graves therefore are still dug by hand and there is an ever present risk
of injury fiom trench collapses, given the unstable sandy
soil and the presence of heavy tombstones on adjacent
graves. As the piece in the Sydney Morning Herald put it,
'Ashes to Ashes, dust to dust, if the collapsing soil doesn't
get you then the headstone must' (SMH March 24 1993). I
have often discussed with colleagues the need for formal
training in shoring techniques. The Randwick course,
with its emphasis on traditional timber shoring methods,
seemed to meet many of our requirements. A professional
development grant from The Australian National University made it possible to have the three day course specially
run for a small group of academic and technical staff
drawn from several departments: Prehistory (RSPAS),
Biogeography and Geomorphology (RSPAS) and Archaeology and Anthropology (The Faculties).
The course teaches basic closed-sheet timber shoring
(Fig. 1) for use in loose, wet, running or otherwise unstable ground (Mutch 1992). It is run by the School of
Plumbing in the drainage yard at the Randwick TAFE. In
our case the first day dealt with closed-sheet shoring
techniques as applied to a regulation 2 m X 0.75 m X 1.8 m
grave. We proved more physically robust than the plumbers had expected and were able to complete this section of
the course in good time. The remaining two days were
spent in learning how to extend the shoring both horizontally and vertically and how to deal with obstacles protruding from the trench wall. With great gusto the class dug
2 m 2 x 2 m pits (Figs 2 and 3), 4mx0.75mx 1.8m
trenches and dug smaller pits into the base of the larger
Trench Shoring for Archaeologists and fhe Randwick Grave Digging Course
work) supported in place on cleats nailed to runners in the
corners of the trench. As the trench deepens it is necessary to install a second set of walings and struts to support
the lower part of the trench. And so on. For excavations
deeper than 2 m the process is repeated with a second set
of shoring nested in the base of the trench.
Getting the shoring in is only half the work. The safe
way to retrieve the timber is to remove it gradually from
the base up as the trench is backfilled. If this is not done
in a strict order the unsupported walls can collapse instantly - as we found by uncontrolled experiment.
Figure 1 Cbsedsheetshoring (after Hayward 1968).
trenches (technically known as double sets) until the
drainage yard looked like the front line at Gallipoli.
'Ihe basic technique is illustrated in Figures 1,2 and 3.
A heavy timber fiamewnk (a set) comprised of walings
and struts is laid out. Hardwood planks (known as runners) are sunk veatically along the outside of this frameWO* (Fig. 2). nKse are progressively dropped as the
trench is deepened leaving the set (the horizontal frame
Figure 2
Discussion
The Randwick course gives a practical introduction to
basic timber shoring techniques which could be adapted to
suit the needs of archaeologists. Obviously closed-sheet
shoring will not be the most appropriate method of shoring
for many archaeological situations. It requiies a large s u p
ply of heavy timber shoring, something that would be difficult to transport to a site in remote country or in a difficult
location (e.g. a cliff face sea-cave). From the start it also
cuts off access to the vertical facesof an excavation. However the Randwick course is essentially aimed at the worstcase scenario; excavating in loose or running sediments.
Closed-sheet shoring would defmitely be useful for unconsolidated coastal sands, previously disturbed ground or
swamps.
For archaeological excavations in consolidated sediments, an open sheeting technique would be more appropriate (Fig. 4). Jones used a variant of this in the Nauwal-
Seling out the runners. Emeritus Professor R.V.S. Wriight contemplates his future as a grave digger.
Australian Archaeology. Number 39.1994
Smith
archaeological excavations has recently come onto the
market (Patchell 1991). This is the 'Safety Link trench
support system' manufactured by Trade Link Engineering
in Ballarat. It consists of soldier sets of form ply held
apart by an extendable pivotal clamp and would seem to
have many archaeological applications.
If excavations are to be on an industrial scale one
could well consider using one or another of the patent
shoring systems using steel sheeting and hydraulic struts
manufactured by companies such as Krings or Jayville.
These can be hired through Shorco Hire Pty Ltd. For
geomorphic trenching into flood plain deposits or other
landforms a lightweight drag-box or trench-shield would
be ideal.
In some archaeological situations shoring may be
ruled out by either the practical difficulties of installing
it (as in the case of a shelter with a low mf) or the logistic difficulties of getting the requisite materials to the
site. If this is the case the simplest option consistent
with some degree of trench safety is to progressively step
the excavation so that no vertical face is more than l m
high.
Figure 3
C W s h e e t timber shoring extended to deal with a 2 m'X
2 m deep pit with a smakr side trench. The walings and
struts comprising both upper and lower sets can be seen.
abila 1 excavations (Jones and Johnson 1985). For very
stable sediments one could dispense with the walings and
just use soldier sets at 1.5 m intervals (Fig. 5). A new
trench shoring system suitable for small conventional Figure 5
Figure 4
Open-sheet shoring (afler Hayward 1968).
Austrahn Archaeology. Number 39. 1994
Soldier set with acrow props or trench jacks.
Conclusion
Arguably the weakest aspect of professional training in
this country is in the technical aspects of archaeological
excavation. One aspect of this is that most archaeologists
go into the field without any instruction in basic trench
shoring techniques. One of the problems has been that
industrial shoring equipment is not suitable for most archaeological situations. Another is that courses providing
practical training in traditional timber shoring techniques
have been few and far between. That niche has been filled
to some extent by a course now available at the Randwick
campus of the Sydney Institute of Technology. This
course was originally developed to train grave-diggers in
the use of closed-sheet timber shoring techniques suitable
for unconsolidated sandy soils in eastern Sydney. With
modification it provides the sort of training in basic shoring techniques that most field archaeologists could benefit
Trench Shoring for Archueologists and the Randwick Gruve Digging Course
from. The course is offered in the School of Plumbing and
coordinated by Peter Mutch and can be run on request.
The maximum number of participants is twelve with an
overall cost of -$2500.
Dortch, C . 1984 Devil's Lair: A Study in Prehistory. Perth:
Western Australian Museum.
Hayward, J.A. 1968 Unshored excavations are killers. The
British Journal of Occupational Safety 7:441-5.
Jones. R. and Johnson, I. 1985 Deaf Adder Gorge: Lindner
site, Nauwalabila 1. In R. Jones (d.)
Archaeological ReAcknowledgements
search in Kakadu National Park, pp.165-227. Canberra:
I wish to thank Professor Rhys Jones for drawing my
Department of Prehistory, Research School of Pacific
attention to the Grave Digging course, Eugene Wallensky
Studies. The Australian National University and Austra
who organised things from the Canberra end and Peter
lian National Parks and Wildlife Service. Special PubliMutch for his assistance at the Sydney end. The course
cation 13.
was taught by Paul Minogue. Funding was provided by Mutch, P. 1992 Shoring for Grave Diggers. Sydney: TAFE
the Occupational Health and Safety Office (ANU), the
Commission (NSW).
Department of Prehistory, Department of Biogeography Occupational Health and Safety Authority 1988 Code of
Pructice for Sgety Precautions in Trenching Operations.
and Geomorphology and the Centre for Educational
Melbourne. Codes of Practice No. 8.
Development and Academic Methods (ANU). For those
interested in industrial shoring equipment, Shorco Hire Patchell, J. 1990 A grave mistake: Working in unshored
trenches continues to kill plumbers. Plumbing and MechPty Ltd has offices in Sydney, Newcastle, Melbourne and
anical Connection. Summer 1 W O :1 5 1 -4.
Brisbane. The new Safety Link trench system is available Patchell, J. 1991 In the trenches. Plumbing and Mechanical
from Trade Link Engineering in Ballarat (Telephone: 053
Connection. Winter 1991 :142.
333955). Photographs are by the author. Ian Faulkner Sim, R. and Thorne. A. 1990 Pleistocene human remains from
drew the remaining figures. I thank D. Buckle, M. Datar,
King Island, southeastern Australia. Australian ArchaeR. Jones and E. Wallensky for their comments on an
ology 31:44-51.
earlier draft of this paper.
WorkCover Authority of New South Wales 1992 Building
Industry Guide: A Workcover Guide to Workers CompenReferences
sation, Rehabilitation. Worksite Health and Safety and
Department of Mines and Energy (Northan Territwy) 1980
Certification. Sydney.
Guidelines for Sdety in Excavations. Darwin: Industrial Zuel, B. 1993 Gravediggers ensure they don't dig their own.
Safety Branch.
Sydney Morning Herald, March 24 p.3.
A 6700 BP DATE FOR ISLAND USE IN THE WEST KIMBERLEY, WESTERN
AUSTRALIA: NEW EVIDENCE FROM HIGH CLIFFY ISLAND
Sue O'Connor
In a recent paper on island use around Australia I drew
a series of broad comparisons between northeast and
northwest Australia (O'Connor 1992). It was suggested
that although dated sites for island use in the northwest
were currently of an order of magnitude younger than
those in the northeast (see Barker 1989, 1991) future research in northwest Australia was likely to prove that
occupation in the two regions was of a similar order of
antiquity. It was argued that this was because islands
played a similar role in the coastal economy of the occupants of both areas.
This paper reports on a 6700 BP date for an open occupation site on High Cliffy Island. Although High Cliffy
Island still lacks a continuous sequence, the date of 6700
BP post-dates the insulation of the island from the mainland and therefore goes some way towards substantiating
the proposition that island use in the northwest occurred
Division of Archaeology and Nanval History, Research School of Pacific
and Asian Studies, The Australian National University, Canberra,ACI'
0200, Australia
early, as it appears to have in the northeast. Recent results
h m the Montebello group of islands off the Pilbara coast
further corroborate early is1and use in northwest Australia
(Veth 1993).
The island referred to here as 'High Cliffy' is actually
the largest of a group of islands known collectively as the
High Cliffy Islands (Fig. 1). It is only 1 km long and
500 m wide. It sits on the landward edge of the most
extensive inshore reef on the Kimberley coast; the Montgomery Reef, approximately 8 km from the present coastline. The reef encircles two larger sandy islands, known
as the Montgomery Islands. At low tide the reef connects
the small rocky islands to each other and only a narrow
water channel separates them from the Montgomery
Islands. The combined landmass of all these islands at
high tide is less than 20 km2; but at low tide, with the reef
exposed they cover about 300 km2. Blundell (1975153)
records that the largest High Cliffy island belonged to a
clan Erom the Montgomery Islands who gave it the name
Ngalanguru.
Australian Archaeology, Number 39-1994