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Direct Extraction

As working faces move closer to localcommunities, the direct extraction ofweaker rocks is often the only option

if quarrying is to continue. Direct extractioncan also be referred to as free digging — theextraction of virgin or unblasted material.If the rock has to be hauled any distance,

the possibility of using solely a dozer (crawlertractor) with ripper is eliminated. Therefore,unless a dozer rips and an excavator loads,essentially the following possibilities remain:1. An excavator extracts and loads the rockusing a bucket only.

2. One excavator continuously rips and asecond unit loads. Obviously, byemploying a second excavator, costs willbe increased, but production shouldremain high and can match,approximately, that obtained when usingdrilling and blasting.

3. Rip and load, whereby one excavatoralternates between using a ripper toothand a bucket by means of a quick-

coupler. This can be an excellentmethod, but to obtain similar productionlevels to those achievable if drilling,blasting and loading, a larger excavatorwill be required at increasedpurchase/running cost.

4. Use of a hydraulic breaker, although thiswill require a second excavator to loadthe material.

Bucket onlyTo remove rock using the bucket only, one ormore of the following must be evident: therock must have a relatively low uniaxialcompressive strength; must have beensubjected to extensive weathering and/orcontain sufficient natural faults, fractures,laminations; and must have relatively lowbonding strength. If so, the use of anexcavator of suitable proportions and bucketcapacity may be possible, depending onproduction requirements.If a considerably larger unit is required,

then its associated costs (ie purchasing andrunning) will often prove more expensive thandrilling and blasting, although this might bethe only acceptable method.Sedimentary rocks such as limestone

and sandstone can often be extracted withoutthe use of (or with lesser use of) explosives,although it is important to emphasize thatsites and material within the same rockclassification can vary considerably. Forexample, Carboniferous limestone is oftenmore difficult to extract than Jurassiclimestone, having been compressed formany millions of years longer, althoughboth are frequently extracted without the useof explosives.However, a possible problem when using

the bucket only is the potential to removeunsuitably large fragments. While thesecan be reduced by means of a drop ball, forexample, frequent use of this tool can provetime-consuming and, therefore, reduceefficiency. ‰

In situations where urban encroachment places limits on drilling andblasting, ripping and loading using excavators can be a viable alternative, asRob Sinclair explains

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The Liebherr RH120-E shown in figures 1and 2 extracts two specific types of materialin close proximity in one area of a site; thestronger and considerably more demandingmaterial is known locally as jura (Jurassic),zeta, hangende bauk kalke, and the secondas mergel.The stronger, homogenous zeta exhibits

few laminations, fractures or natural faultsand has a uniaxial compressive strength ofapproximately 220MPa. Initially, the site’sCaterpillar D11R ripped the material downto 7m (23ft). However, beyond this the rockis further compressed and a maximum ofonly 200 tonnes/h was achievable – some 600tonnes less than required.As a result, two possible methods

remained. Although the use of explosives ispermitted, due to the location of a residentialarea and the risks of subsidence, the velocityof detonation would not be permitted toexceed 1,000m/s (3,280ft/s), and would,therefore, be largely ineffective. In addition,the site wanted to ensure its continuedgood-neighbour policy, so a decision wasmade to utilize a hydraulic excavator fordirect extraction.The solution was to acquire an excavator

that could achieve either 800 tonnes of zetaor 1,500 tonnes of mergel per hour. Unusuallyfor a large mining-class model, the machinewas installed and had to prove its ability toattain the required production before beingpurchased. During its evaluation, the RH120-E averaged 848 tonnes of zeta per hour using121 litres of fuel; thus, the machine remainedon-site, a decision that subsequently provedvery successful.

Ripping processRipping was, for many years, the preserve oflarge dozers (horizontal ripping), usually withsingle-shank rippers. However, over thepast decade hydraulic excavators performingvertical ripping with a ripper tooth haveincreasingly been seen as a viable alternative,usually undertaken by 60- to 120-tonneclass machines. With ripping, the fragmentation is

influenced by the ripper tooth width and,therefore, the operator has greater influenceover the size of the material than if it had beenblasted. Thus, a more uniform size that canbe processed by the crusher is produced,while fines, lower value or waste materials arealso reduced.Two methods can be employed; first,

continuous ripping whereby one excavator isdedicated to ripping the material and followedalong the bench by a second, usually smallerunit, which loads the material into dumptrucksor an in-pit crushing system. Occasionally, anexcavator rips and then, using the bucket,casts the material aside to be rehandledusing a wheel loader, which loads into the in-pit crusher.The second method is referred to as ‘rip and

load’. As the name suggests, the excavatorrips the material, usually for aggregate ordimension stone purposes, subsequentlyloading it into trucks by use of the bucket.

Dedicated rippingExcavators of 30 to 45 tonnes are sometimesused to rip in small quarries but this is a rarity.More often, excavators weighing at least 70tonnes are used because of their extra massand power to produce reasonably high volumes,together with sufficient durability to withstandthis type of demanding application.If continuously ripping, a 70-tonne-class

excavator is quite capable of matching a 70-tonne-class dozer in terms of material ripped,while the amount of fuel consumed by the mostfrugal examples in this class is noticeably less.Furthermore, their initial purchase price is alsoless.In a ripping application, the excavator is, not

surprisingly, subjected to considerablestresses, but so too is the dozer and itsundercarriage wear will be greater than thatof the excavator.The dozer, though, will prove advantageous

if the ripped material is to be moved to a

Fig. 1. With its 8.6m3 bucket, the RH120E’s cycle times are completed within 25s. This materialcontains about 66% limestone intersected with clays and a silica content of up to 18%. A V-edge lip andpenetration teeth are used to maximize cycle times and the latter, on average, last 600h. Side adaptorsare subject to breakage but the bucket, in general, withstands the application very well

Fig. 3. A Liebherr R984C rips chalk for thepurpose of cement production

Fig. 2. The RH120-E has to extract 800 tonnes of zeta per hour – a sedimentary limestone containingiron oxide, silica and nitrates

Special Report

stockpile up to about 100m (300ft) away. Thisis because, once ripped, it can push thematerial to the desired location. In contrast, ifripped by an excavator, the rock must beloaded into trucks by a second unit, significantlyincreasing the cost per tonne.

Rip and loadDuring this process, the excavator alternatesbetween the ripper and bucket by use of aquick-coupler.Depending on the size of the excavator, the

material being ripped, and siteconditions/efficiencies, a 45-tonne-classmachine can rip and load into haulers atabout 150 to 250 tonnes/h. The 70- to 85-tonneclass can rip and load about 200 to 400 tonnesand the 110- to 120-tonne class about 400 to600 tonnes. Although an excavator performingrip and load will, of course, never achieve thesame hourly production as it would loadingblasted material, an ability to penetrate thematerial using the ripper tooth means it hasthe potential to replace a larger excavator thatworks the site using the bucket only. Thus, itmay be possible to reduce purchase andoperating costs.Assuming the rock can be ripped, if it must

be hauled by truck (ie primarily due to distance)the rip and load technique is the most effectiveripping method. However, the question remainsas to whether the excavator can achieve therequired tonnage previously achieved using asmaller excavator to load the pre-blastedmaterial.Increasingly, quarries are reaping the

benefits of direct means of extraction. Althoughdrilling and blasting costs are either eliminatedor significantly reduced, there are risks,particularly when using one machine to rip andanother to load; thus, it may prove impossibleto offset their associated costs. In addition,because use of the bucket only or rippingnormally requires an over-sized excavator, its subsequent costs are significantly higher.As such, its premium may again prove

uneconomical in comparison with drilling andblasting, unless a single machine undertakesboth ripping and loading duties, ie ‘rip and load’.If production requirements can be achieved,

vertical ripping can be an excellent alternativeto drilling and blasting, not only in terms ofreducing or eliminating costs, but also inminimizing disruption to production and bettermeeting environmental needs. However, toascertain if ripping may provide desirablebenefits at a specific site, a site evaluation isrequired.Rob Sinclair is the author of the book

Hydraulic Excavators: Quarrying & MiningApplications (Sinclair Publishing, 2012, ISBN9781906148355). He has worked in thequarrying industry for more than a decade,variously as an assistant plant manager, salesengineer and excavator product specialist.This article first appeared in the October

2012 edition of Quarry, the official journal of theInstitute of Quarrying Australia, and isreproduced here by kind permission.

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Fig. 4. Once sufficient amounts of material are ripped, the ripper tooth is released

Fig. 5. The quick couplerallows the switch fromripper tooth to bucket

Fig. 6. The bucketcan be attached inless than 30s. Thecoupler hooks on tothe bucket pin;once in position,the locking pins areextended