Number 22, July 1990 – Editorial and society news

Since this is our last editorial before handing over the reins to the Victorian Group we’re inclined to be a little self indulgent and reflect briefly on some of the wins and losses of our spell on the Editorial Panel.

Almost inevitably, the last four issues of Australian Geomechanics have seen more than their fair share of news, views and papers from WA – however we must correct the impression that all geotechnical activity in WA revolves round the UWA centrifuge!! Not so, but the rotating editorship does give individual states the opportunity to do a bit of grandstanding, to push issues of particular concern and to throw the spotlight on geotechnical activity within their state. We would like to think that we’ve succeeded in all three areas.

From the outset, we attempted to standardise journal format by computerising its production using desktop publishing software. This was not without its headaches, however when it was successful, we believe the result was very pleasing. The Journal was intended to be a half yearly publication however problems of work commitments, software incompatibility and unfamiliarity, late copy and last but not least, poorly developed keyboard skills (two digit variety), all contributed to delay publication beyond the deadlines. For this we apologise and wish Victoria, ‘the very best of luck’.

Thanks to Peter May, IEAust Canberra, advertising is now a regular feature in each issue and brings in important revenue, offsetting journal publishing costs.

Our intention to narrow the gap between geotechnical people in the mining and civil engineering areas has met with only limited success if measured in terms of published articles and papers of common interest. However on the local scene, the formation of a separate WA AGS Group in the gold mining town of Kalgoorlie is interpreted as a positive step towards bringing the two disciplines together. So too is the formation of the WA Centre for Geomechanics which will provide an important link between the resource industries and major research institutions in WA. Either initiative could in turn prove to be an important source of technical papers and talks for the wide geotechnical community.

This special issue is devoted almost entirely to Waste Management, fulfilling a commitment we made on first taking over the editorial hot seat. The very existence of this issue is a reflection of the growing concern within and outside the profession about the subject of waste and its safe disposal.

Too often in the past, the waste products of society have been poorly managed and have exerted a heavy toll on the environment. A growing awareness of the problem has lead in recent times to consepts minimising and recycling waste and where these are not possible, disposing of waste safely, i.e. in such a way that is within the capacity of the environment to absorb it. This is consistent with the idea of ecologically sustainable development which forms the subject of our guest editorial from WA-EPA’s Browne-Cooper. His article is particularly timely as it follows closely on the heels of IEAust’s release of its “Environmental Principles for Engineers”. According to one of its authors, the main purpose of the Principles is to get across the importance of ethics in sustainable development and as such it largely complements the previously issued IEAust’s Environmental Code of Practice, first ublished in 1987.

Whilst in recent years there has been a shift in emphasis of production strategies away from waste treatment to waste prevention, management of waste whether from the past, present, or future, will continue to remain a significant problem facing society (sic engineers).

Of the various options for disposal of waste, sea outfalls – dumping at sea, incineration and disposal on land, all have their inheren problems for the environment and their critics. Even recently constructued sea outfalls whose designs are ostensibly on studies of the assimilative capacity of the receiving environment, are showing signs of harmful impacts. Incineration is expensive, frequently produces unacceptable gas emissions and typically encouters its own brand of “nimby” type opposition. Disposal on land is no better off carrying with it the potential for pollution of surface or groundwater resources and sterilising tracts of land.

In some cases however, disposal on land can be beneficial:

The more benign waste such as digested sewage sludge can have value as a fertiliser in agricultural spreading however leaching of nutrients to water courses and soil contamination must be avoided.

Red mud – bauxite residue – has been used to benefit to decrease the permeability of poor agricultural sandy soils making them better able to retain applications of fertilisers.

Other land disposal options of the more ecologically damagaing waste rely on containment to prevent surface or groundwater contamination by leaching. This aspect of waste management is relatively familiar territory to the geotechnial profession and one which sees increasing application of the use of geomembranes. A review of their use in Australia is provided in the paper by Parker and Sadleir.

A companion paper entitled “Geosynthetic Containments in Environmental Protection” by Sadleir discusses the use of both membranes and geotextiles, alone or in conjunction with clay fill, as liners or caps, to provide landfill leachate containment.

Site investigations for proposed waste disposal sites and more particularly, for existing contaminated sites have their own characteristic problems. For contaminated sites, historial site records can give all important clues to likely contaminants and therefore which analytical tests to perform – you need to know what you are looking for to arrive at the correct test for finding it!! Again a prior knowledge of the site can be all important in knowing where to drill to locate any buried contamination.

These and other aspects of site investigation of contaminated land are addressed in “Auditing of Contaminated Land”, a very useful paper by David Parker. Reasons for auditing are given together with key steps and pitfalls in the processes of field investigation, testing and assessing contaminated sites. Answers to ‘What are acceptable levels of contamination for a particular site??’ are discussed and mention is made of Victoria’s statutory audits. One wonders how long it will be before other states follow suit!!

Leacates from waste deposits contain chemicals which may adversely affect the sealing properties of clay liners or foundations. This type of chemical interaction was examined in the comprehensive investigations carried out for a landfill disposal site for aluminium smelter waste – the subject of an interesting paper by Sullivan and Knight. Fortunately in this particular case, batch tests identified good absorbtive capacity in the clay.

Gaining an understanding of the likely migration of containment plumes was achieved by Hensley and Savidou in experimental work using geotechnical centrifuge modelling. Results of the physical modelling according to their paper, compared favourably with numerical modelling and demonstrate yet again the versatility of the centrifuge in engineering investigations.

Mine tailings – the water borne fine waste product from mining activity deposited traditionally in characteristic and frequently unattractive waste dumps – has its own brand of environmental engineering problems:

Traditional tailings disposal involving thickeneing and pumping slurried tailings to dams/lagoons, presents problems for rehabilitation. The deposited tailings have initial high water content, correspondingly weak shear strength and occupy large areas of land which are susceptible to erosion.

A promising alternative disposal technique which overcomes many of these problems, involves mixing the tailings with ‘coarse reject’. The combination of materials has improved engineering properties and behaviour, is easier to rehabilitate and has better future land use capabilities. This technique has been trialled successfully in the NSW coal mining industry and forms the subject of a paper by Williams.

One of the key imponderables in the managent of tailings disposal is the question of how quickly the waste material will consolidate and therefore improve in its properties. Fahey and Toh in their paper have developed a technique for examining and predicting consolidation behaviour of slurried tailings under various filling rates and boundary drainage conditions. For this they used a combination of numerical modelling based on large strain consolidation parameters obtained from geotechnical centrifuge modelling.

By its very nature, waste management frequently requires a multidisciplinary approach. This presents geotechnical engineers with a unique challenge in which they have to work with and have an understanding of many other disciplines. The latter can be achieved not only by training but by encouraging interdisciplinary debate in technical journals and in speciality conferences. One such conference is the forthcoming Conference on Geotechnical Management of Waste and Contamination due to be held in Sydney in March 1993.

The Editorial Panel strongly recommend anyone with an interest in waste management to take up the challenge and contribute to what we are sure will be a very successful conference.