Current best practice in the quarryingindustry is conducted in accordancewith the Quarry Regulations 1999,

which require that operators carry outappraisal and assessment of significantgeotechnical hazards. There is, of course,older legislation (Mines and Quarries (Tips)Regulations) which deals with the particularproblems associated with substantial tipsites, whether active, closed or abandoned.However, past mineral working activity was

often piecemeal in nature. In many casesrecords were poor and memories areunreliable. Developers faced withuncertainties associated with theirgroundworks, but looking for secure budgetsand reliable timelines, need to tread verycarefully when dealing with former quarrysites. Natural processes of plant growthand animal occupation of sites, as well asformer reclamation works, can cause groundrisks to be missed as ‘greening up’ occursover timescales of ten to a few hundred years.

DDeesskk ssttuuddyyKey to any successful investigation strategyis a full and proper desk study. Regrettably,these days it is easy to download a set ofhistorical maps, obtain a BGS site report and

a Coal Authority report, bind them togetherand call them a desk study. Unfortunately,reliance on such ‘off-the-shelf’ investigationreports poses potentially considerable risksin that, all too often, critical pieces ofhistorical context may be missing.One of the key items of historical

information frequently not present instandardized desk study packages is themid-19th Century tithe map. This is typicallyavailable at county library institutions andpredates Ordnance Survey first-editionmapping. It is often a source of valuableinformation on former land usage,particularly when read in conjunction with the

accompanying apportionment. Somecounty libraries offer online side-by-side scanning of tithe plans withmodern mapping, and in some casesaerial photography. The quality ofinformation available is illustratedin figure 1. This is an extract fromthe 1847 tithe map for the Haltonarea of Widnes, published on theCheshire West and CheshireRecords Office website:( h t t p : / /maps . c he sh i re . g o v.uk/tithemaps).The accompanying apportionment

records Plot No. 127 as being bothowned and occupied by JohnTomkinson, and to be the ‘Scite of oldquarry now occupied with spoil’.The land use is classified as ‘Waste’.There are many other potential

sources of information which can �

May 2011 www.Agg-Net.com 15

Development Work atAbandoned Quarry SitesThe need for thorough ground investigationBy K.H. Nicholls, Geotechnics Ltd

Site shown on the extract from 1847 tithe plan (see fig. 1) viewed from east looking south-westwards, as at March 2011

Fig. 1. Extract from 1847 tithe plan

shed light on local quarry history. Thesemay include published historical documents,information in private collections (landedestates), industrial/museum archives,archaeological collections etc. In reality, theonly way to ensure that as wide a range aspossible of good-quality sources is consultedis to utilize the skills of locally basedindividuals who are best able to locate useful,relevant information.

WWaallkk--oovveerrA thorough walk-over is also an essentialweapon in the engineering arsenal. Again, itis possible to obtain a reasonableunderstanding of the site via computerswithout leaving the desk. Google Earthoffers aerial views of the site, and GoogleStreet View allows viewers to drive past thesite entrance. There is, however, nosubstitute for a site visit, where an old shafthidden beneath the tree canopy may beapparent, or remnants of past tipping activitycan be inspected. The act of walking the siteitself allows a judgement to be made as tothe conditions underfoot (critical informationfor planning investigation works), the natureof vegetation cover and the potentialpresence of contaminants. To a geologist,much can be made from the physical ‘lie ofthe land’. A lot of information can becomeapparent in a walk-over, from the observationof street names (eg Sand Pit Lane), publichouse names (eg Quarryman’s Rest) and, ofcourse, the observations of members ofthe local community who may provideinformation, some more accurately thanothers, as to who worked in the quarry andwhen, how backfilling operations werecarried out, and even sometimes offeringdetailed knowledge of backfill materialsand handling procedures.

SSiittee iinnvveessttiiggaattiioonnA thorough desk study and walk-over surveyshould allow the planning of a good siteinvestigation, which will allow the developerto establish ground-related risks associatedwith the site’s previous usage. For typicallow-rise developments on former quarrysites, critical issues are likely to be:• The depth of the original excavation.• The location of former quarry highwalls.

• The groundwater regime.• The ground gas regime.• The nature of any quarry backfillmaterials.

• The stability of exposed quarryhighwalls.

• The stability of former tip sites.Site investigation is likely to comprise

some or all of the following works: trial pitexcavation (fig. 2); window sample operations(fig. 3); cable percussion drilling (fig. 4); rotarydrilling, both open-hole and cored (fig. 5);geotechnical and chemical testing; andgroundwater and ground gas installationsand monitoring. Where appropriate, thesestandard investigation techniques may needto be supplemented with site-specificinvestigation techniques, such asdiscontinuity surveys, geophysical explorationand in-situ testing.

CCoommmmoonn ddeevveellooppmmeennttiissssuueess Some of the key issues that developers takingon old quarry sites will need to address

16 www.Agg-Net.com May 2011

Fig. 2. Trial pitting operations; these can revealmuch about the nature of old backfill materials

Fig. 3. Window sampling equipment

Fig. 4. Cable percussion drilling

May 2011 www.Agg-Net.com 17

Geotechnics & Hydrogeology

include: • Slope risk reassessment.• Total and differential settlements.• Contamination (human health).• Contamination (controlled waters).• Gas-generation potential.These are considered briefly in turn:

Slope risk reassessmentIn working quarries, face layouts and slopedesign are intended to provide an appropriate

level of security during the excavationworks. Within this framework, slopesgenerally stand as steep as possible,as by doing so the volume of winnablematerial is maximized. Modernplanning procedures for quarryoperations will include provision forend-of-life design, with slopes madesafe for the envisaged end-of-lifeland use. However, old abandonedquarries are often left with faces ina condition unsuitable for the majorityof alternative land uses. It is certainlythe case that slopes such as thoseshown in figure 6 would have beenacceptable in the environment of aworking quarry, but it is unlikelythat they would be deemedsatisfactory for any land use allowingunrestricted public access to thetoe of the slope. In developing thesite, it is likely that extensive rockengineering will be required to bringslopes of this nature to a conditionsuitable for alternative uses involvingpublic access.

Total and differentialsettlements

Many old abandoned quarries will have beenbackfilled with poor-quality materials (see fig. 2). While the existing surface mayhave reached some level of equilibrium, theaddition of any new loads may renewsettlement of the backfill materials. Suchsettlements are entirely dependent on thenature of the material incorporated within thequarry void, and the amount of compactionor treatment applied to that material, eitherat the time of placement, or since.Settlements are likely under any newly

placed fill or loaded ground. As well asposing risks to new-build structures,serviceability issues can be significant forroads, pavements and buried serviceinstallations. While sound engineering designcan deal with many of the issues arising fromthe compressible nature of loose fillmaterials, extensive investigation will benecessary to properly characterize thematerials present.A particular problem regarding differential

settlement (ie the difference between theground settling the most and that settling theleast) will be associated with the line of anyformer quarry high wall. Structures whichspan this feature will need to be carefullydesigned, potentially involving differentfoundation solutions at different locations inthe building.Designers will also need to be aware of the

potential impact of time-related settlementcriteria, particularly when dealing with acombination of granular materials (wheresettlements are rapid, almost to the point ofinstantaneous) and cohesive materials(where settlements can take many years tocomplete).

Contamination (human health)In less environmentally aware timesexcavations in the ground were attractiveplaces to deposit unwanted materials. Inmany cases this deliberate tipping was seento be a ‘win-win’ option, allowing worked-outvoids to be reclaimed from standing water byraising land locally, while at the same timeallowing disposal of waste from the local gasworks, refuse destructor, foundry orslaughter house. This unrecorded andfrequently entirely uncontrolled tipping givesconsiderable cause for concern for any new-build development taking place on, or in closeproximity to, backfilled quarry sites.New-build development schemes that

require planning permission will passthrough the planning regime and should,therefore, pass through the local authorityplanning regime, which is responsible forprotecting matters of human health. Fewauthorities will have completed their task ofidentifying all ‘contaminated land’ within theirarea, but will utilize ‘conditioned’ approvalor advice notes to ensure that potentialcontaminated land is dealt with utilizingcurrent practice. This is likely to include aphase-one desk-study report, a phase-twointrusive investigation (if required followingthe findings of the phase one assessment),preparation of formal remediation strategiesand submission of verification reports uponcompletion.

Contamination (controlledwaters)The Environment Agency is the regulatorcharged with protecting controlled watersfrom potential contamination. As such,developers taking on liabilities for existingold quarry sites need to be completelysatisfied that the nature of the ground is �

Fig. 5. Rotary drilling rig

Fig. 6. This abandoned quarry face in Carboniferous limestone is perfectly acceptable in a working quarryenvironment but probably unacceptable in a development allowing public access to slope toe or crest

18 www.Agg-Net.com May 2011

not likely to cause the regulator to identifythe developer or future landowners aspotentially responsible persons in the eventof potential future contamination.

As discussed previously, old quarries can be full of many different sources of contamination, anddisturbance during constructionand redevelopment has thepotential to release suchcontamination, currently secureon site, into the widerenvironment and specificallyinto controlled waters. Also, itshould be stressed that thereare very real dangers thatinadequately plannedinvestigation work can, itself,contribute significantly topotential risks by, for example,drilling through a clay-sealedquarry into an underlying sandaquifer.

Gas-generationpotentialThe degradation of organicmaterials entrained within fills,due to the work of bacteria,leads to old quarry sites being asignificant potential source ofmethane and carbon dioxide.The actual quantity of gas ‘make’will depend on the nature of thematerials incorporated withinthe body of the landfill. However,

sites where active landfilling of waste hasoccurred could be anticipated to have high flowrates and high concentrations of landfillgases. Even quarry sites that have not been

backfilled as active landfills, but are simplypart-occupied by deposits of made ground,can generate significant gas concentrationsand flow rates.Investigation of the local gas regime will

require the installation of a number ofboreholes with gas-monitoring equipment,and monitoring of the devices over a periodof months, in the general case.Methane is the landfill gas of most concern

due to its potentially explosive nature in air.Carbon dioxide is an asphyxiant gas. Otherorganic gases can be generated in landfillsalong with non-organic problematic vapoursand gases (such as sulphur dioxide, nitrousoxides and ammonia). Monitoring will need tobe designed to search for gases appropriate to the ground conditionsencountered.

CCoonncclluussiioonnssA properly thought through groundinvestigation is a fundamental prerequisite forthe successful redevelopment of formerquarry sites. This will include a stagedapproach to the investigation following alogical sequence comprising a desk study andwalk-over, on-site pitting, drilling and testingworks, laboratory testing and formalreporting.Failure to undertake such an investigation

in a thorough manner could expose thedeveloper to a wide range of ground-relatedrisks, and even potential litigation.For further information contact Geotechnics

Ltd on tel: (01244) 671117; or email:knicholls@geotechnics.co.uk

Fig. 7. Spent oxide gas works waste, known as ‘Blue Billy’,uncovered in a former sand and gravel pit. Blue Billy is highlyacidic and can contain (typically) around 2% by weight cyanide(hence the name – cyan = blue)

Geotechnics & Hydrogeology

Fig. 8. Early 20th Century refuse destructor waste beneath hardcore at a former brickworks and clay pit excavation. These sorts of waste may show highconcentrations of metal contaminants, such as lead, nickel, zinc and arsenic, as well as potential organic contaminants such as benzo[a]pyrene