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
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