TAG 166 - Geological Society of Australia

Engineering geology advancesThe investigation years by the SMHEA commenced in about 1949 and ateam of geologists was set-up under leadership of Dan Moye as ChiefEngineering Geologist, from 1949 to 1967. He built a team thatpioneered many of the now-accepted practices in the discipline ofengineering geology, including drilling methods, rock-mass classification,rock mechanics applications, tunnel logging methods and waterpermeability testing.Dan Moye (1955) stated in his landmark paper:Engineering geology in practice is a service to civil engineering(including the civil aspects of mining engineering). The engineeringgeologist should be, first and foremost, a well-trained geologist.This statement still holds true today.During the Snowy Mountains Scheme’s site investigations, civildesigns, construction supervision and monitoring, the followingfundamental issues were addressed:l classification of weathering of granitic rocks and strengthestimationl diamond drilling — triple-tube core barrels to improve core recovery,core logging and boxing methods standardised, careful recording ofrock defectsl improvement of the water pressure test (Lugeon) method.During celebrations of ‘The Spirit of the Snowy Fifty Years On’, ProfessorET Brown stated, “… the Snowy’s geological and engineering staff wereahead of their time”.The rocks encountered in the various project areas were commonlygranitic — granites, granulite and gneiss — with variable degrees ofweathering, often to 100 m depth. It was clear that a system for assessmentof the performance of rocks and soils in slopes, foundations andunderground openings was needed. This was when a classification ofweathering was introduced by the engineering geologists, starting from‘fresh’ (unweathered) through to ‘completely weathered’. This and similarsystems, defined internationally by various institutions such as theInternational Society for Rock Mechanics, form a basis for engineeringdescription of rocks today.In addition to weathering, the definitions of engineeringproperties of soil and rock materials were expanded to cover substancestrength, geological structures, groundwater permeability and state ofstress so that predictions could be made about excavatability, foundationsuitability and stability of slopes. As the work proceeded underground,a new set of guidelines became critical for ground support (this isdiscussed later in this article).The engineering geologists also became part of the design team,with contributions to design and tendering, and then to methods ofconstruction and site supervision. During the development, contractswere awarded on a lump-sum basis, as the old government-supervisedday works contracts on large civil projects were being phased out. Thus,the tender packages required a high standard with consistent and highqualitydata. The need to provide geological information was aided bythe discipline of obtaining quality data and standardising thepresentation and rock quality classifications.ABOVE: The bucket test — bucket filledwith crushed rock and model rockbolts used to demonstrate theprinciple to tunnel workmen. Imagecourtesy SMEC collection.RIGHT: Eucumbene–Tumut tunnel,indicating construction activityin 1954. Image courtesy SMECcollection.Advances in rock-bolting technologyAt this time in the 1950s to 1960s, rock mechanics was an emergingdiscipline and development of underground rock engineering wasadvanced during construction of the Tumut 1 and 2 underground powerstations. Early stress analyses were typically done as a two-dimensionalphotoelastic modelling process. It was only after Tumut 1 was excavateddid in situ stress testing start — by the flat jack method.These studies and practical underground excavation work led tohuge advances in rock-bolting technology:l The technique of rock bolting was one of the many innovativeengineering achievements used on the scheme to prevent rockinstability.l The properties and behaviour of rock played a major role indetermining the design and construction programs adopted.l Steel bolts of differing lengths and spacing were inserted, wherethey were found to be an excellent anchorage rock in tunnels.l Grouting of bolts into the rock became the normal practice.In the words of engineer Aubrey Hosking:Previous to the Snowy, rock bolts were put up individually — this is, youput up a rock bolt because there was a bit of rock that was going to falldown, so you put a bolt up and pinned it to the rock behind. You’ve got tohave an anchoring inside, and then you tension the bolt. If you’re compressingit in the direction of the bolt, there is also a lateral force generated.What the Snowy did was to realize [sic.] that this lateral force couldmake the bolt self supporting — that is [if] you had rock bolts in a pattern,instead of individually, they could reinforce one another and create astructural entity, which would support a power station or a tunnel roof.At one stage the underground miners expressed concern aboutworking under a free span of rock with no steel rib support or otherconventional support systems. All they could see were many face platesof the supporting bolts. So a demonstration was made by the geotechnicalteam by placing aggregate in a large steel bucket, then smallmodel bolts were embedded and tensioned against inch-size face plates.The bucket was then upturned and nothing fell out. Whether thisconvinced all miners to get back underground was not recorded but formany years there was a large mine skiff with full-sized bolts hangingupturned near the Snowy Mountains Engineering Corporation (SMEC)laboratories in Cooma.TAG March 2013| 23