WoodsfordQuarry ComesonStream - Agg-Net.com · screens the ‘as dug’ material at 50mm and feeds the –50mm fraction on to a 750mm wide field conveyor for delivery, at a rate of

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August 2010 www.Agg-Net.com 11

Hills Group are an independent, family owned,regional business based in Swindon, Wiltshire,but with operations extending from

Gloucestershire, across Oxfordshire to Berkshireand down to Dorset. Originally founded as a brick-making company in 1900 by Edward Hill, today, fourgenerations later, the multifaceted, multi-millionpound business employs around 385 people andencompasses the production of quarry products(Hills Quarry Products Ltd), waste-management andrecycling activities (Hills Waste Solutions Ltd) and thebuilding of quality new homes (Hills Property Ltd).

The Hills Quarry Products (HQP) division operatesa network of five quarries across south-west England,producing a full range of sand, gravel and limestoneaggregatematerials, as well as three plants producingready-mixed concrete and floor screeds. Several of thedivision’s quarry sites are also licensed for the tippingof inert materials which, in turn, provide a source ofrecycled products and topsoil. This year, as thecompany celebrates its 110th anniversary, Hills havemarked a southward expansion of the business withthe opening of Woodsford Quarry, their first mineralextraction operation in the county of Dorset. �

Woodsford QuarryComes on StreamHills Group open their first mineral extraction operation in Dorset

Hills Quarry Products’ new sand and gravel operation at Woodsford Quarry in Dorset

12 www.Agg-Net.com August 2010

TThhee ssiitteeLocated on agricultural land in the Frome valley about5 miles east of Dorchester, Woodsford Quarry liesbetween the villages of Crossways and Woodsford andcomprises a low-level, state-of-the-art mineralprocessing plant and associated ready-mixed concretefacility. The site had been earmarked as a potentialdevelopment area in the county’s mineral plan for anumber of years before the landowner was finallygranted planning approval from Dorset County

Council, albeit with several conditions relating to noiselevels, hours of work, water discharge, roadimprovements, footpaths, landscaping etc. Withpermission secured, some two years ago competitivetenders were sought for operation of the quarry andthe bid from Hills Group proved successful.The total area of the site is 163.3ha and the

current consented reserve of sand and gravelamounts to 4.2 million tonnes. Based on a targetoutput of around 175,000 tonnes per annum, theoperational life of the site is estimated at 24 years.

The reclaim belt from thesurge pile to the mainprocessing plant

A Rowecon motorized cut-offgate and belt feeder are usedto recover material from thesurge pile

New Quarry


Progressive low-level restoration of the site,incorporating an improved drainage scheme, willultimately return the land back to full agricultural use. Access to the quarry is from the south-west

corner of the site via a new entrance on to theCrossways to Dorchester road. This was constructedearly last year by Bath-based Ikon Construction, whowent on to build the site’s main and internal asphaltaccess roads and processing plant foundationsduring spring 2009. Although the plant and operationsin the north-western part of the site are well screenedby landforms and hedgerows, as part of the site

preparation works, the ground level in the vicinity ofthe plant was lowered by 2m and environmental bundswere constructed along the north-eastern andwestern boundaries of the site to further reduce thevisual and noise impacts of the operation.

GGeeoollooggiiccaall sseettttiinnggThe extraction site is situated close to the westernextent of the Tertiary Reading Beds (Bagshot Bedssequence) on the western margin of the geologicalstructure known as the Hampshire Basin. The valleygravel forming the economic mineral at the site �

The Wileman 2M3 Pnu-Drivecontraflow scrubber barrel

The Hewitt Robins 4.2m x1.25m double-deck horizontalscreen


occurs at low elevations predominantly within thevalley of the river Frome, which flows from west toeast across the region. The mineral itself (a flint sandand gravel) is of Pleistocene Age and composed ofmaterials derived from plateau gravels that occur tothe south of the quarry. The deposit, which varies inthickness from 3m to 5m, overlies beds of the LowerGreensand formation and is considered as an upperaquifer. As such, the water table is affected seasonallywith maximum elevations occurring between Januaryand March, followed by a steady decline during thesummer months. However, groundwater levels at thesite will be controlled by pumping during the wintermonths to allow dry working of the quarry all yearround.

EExxttrraaccttiioonn aanndd ffeeeeddiinnggThe depth of overburden varies across the site butgenerally comprises around 400mm of topsoil/subsoilwith occasional silt/clay lenses measuring100–300mm in thickness. Removal of these materialsis carried out in house by HQP between April andAugust using a Volvo EC290 excavator, two Volvo A25Darticulated dumptrucks and a Komatsu D61PX dozer.As the site is still in its early stages of operation, thetopsoil and subsoil are currently being strippedseparately and stored in amenity bunds until requiredfor restoration purposes. As the site develops,however, the soils will be stripped and directly

placed on previously worked-out areas as part of theongoing restoration programme. The sand and gravel deposit is extracted from the

dry working using a Volvo L150F wheel loader and fedinto a Finlay 595 mobile screener. This unit pre-screens the ‘as dug’ material at 50mm and feeds the–50mm fraction on to a 750mm wide field conveyorfor delivery, at a rate of 180 tonnes/h, to a surge pilewith a live capacity of 800 tonnes. Meanwhile, therejected +50mm material (predominantly large flints)is discharged to a stockpile to await subsequentcampaign crushing using a mobile crusher.

PPrroocceessssiinngg ooppeerraattiioonnssThe main processing plant was designed, installed andcommissioned to Hills Quarry Products’ specificrequirements by Leicestershire-based maincontractors Wileman Engineers Ltd. Erection of thelow-level plant (all elements are less than 8m inheight) was completed during summer 2009, with finalcommissioning taking place during October andNovember. It is designed to wash and size theprimary screened ‘as dug’ sand at a maximumthroughput rate of 180 tonnes/h to produce, inconjunction with a Linatex sand plant, a full range ofwashed sands, single-size gravels and ballastmaterials for supply throughout Dorset andneighbouring Somerset. The plant is equipped witha PLC system, supplied by Bridges Electrical, which

Maximum height of the low-level plant is 8.0m

controls all aspects of its operation, such as feed rateand start/stop sequencing. In addition, all conveyorsare fitted with rotation sensors to facilitate unmannedrunning. The quarry’s weighbridge and ticketingoperations are conducted through a computerizedsystem supplied by Avery Weigh-Tronix. Recovery of material from the surge pile is achieved

via a 30m long x 3m diameter Armco-type tunnel,supplied by Asset International. A rubber-lined chutein the roof of the tunnel feeds material, via a Roweconmotorized cut-off gate, on to a variable-speed beltfeeder which, in turn, discharges on to a 160m longx 800mm wide troughed and part-inclined tunnelreclaim/field conveyor for delivery to the plant. Thebelt feeder is PLC controlled via a Siemens Acumassbelt weigher to maintain a consistent feed from thesurge pile to the processing plant at the desired rate. On arrival at the processing plant, the –50mm

material is fed in to a Hewitt Robins 4.2m x 1.8mdouble-deck washing screen equipped with SCSpolyurethane deck modules. The top deck cuts thematerial at 40mm while the bottom deck cuts at 5mm.Any +40mm rejects are sent, via conveyor, to aground bay for subsequent reprocessing by a mobilecrusher, while the –40mm +5mm fraction is conveyedto a Wileman 2M3 Pnu-Drive 2m diameter x 3m longcontraflow scrubber barrel for attrition to release thesands and clays ahead of the final grading screen.Fresh water feed requirements to the washingsection amount to approximately 1,100 gal/min.The second and final screen is a Hewitt Robins 4.2m

x 1.25m double-deck horizontal screen. Once again,both decks are fitted with SCS polyurethane modules,the top deck cutting at 20mm and the lower deckcutting at 6mm and 10mm. Any 5–6mm product issent to a ground storage bay while the 6–10mm and20–40mm fractions are conveyed to their respectiveground stockpiles by a pair of static inclined conveyors.The predominant 10–20mm fraction is conveyed to itsground stockpile by a radial conveyor.All the stockpiling and transfer conveyors used

within the plant are powered by Renold drives andgearboxes of varying sizes and equipped with either800 or 600mm wide x 500/3-ply all-nylon belts withrubber covers, supplied by RAP Conveyors. Theconveyor drive shafts run in INA FAG self-aligning ballbearing plummer blocks, while the belts themselvestravel on 102mm diameter three-roll, equi-length,drop-in idler sets with sealed-for-life bearingssupplied by Rulmeca UK Ltd. Scraper sets from RHConveyor Services are fitted under all head drums forbelt-cleaning purposes. Meanwhile, the sand and fines released by the

washing screen and the scrubber barrel are pumpedto the holding sump ahead of a Linatex compact sandplant and dewatering screen system. Some 1,150gal/min of water and up to 100 tonnes/h of –5mmsolids are pumped from the sump to the centre of a1.22m diameter Linatex S-Type classifier. Here, thecoarse fraction reports to the base of the classifiervessel and is extracted by a Linatex 200/150mm borepump and fed to a Linatex 660 G4 hydrocyclone. Thisapparatus washes and thickens the product, removing–75 micron material via the overflow while theunderflow discharges ‘coarse’ sand on to a VD15dewatering screen, which removes the free moistureprior to stockpiling via conveyor.Concurrently, the overflows from the S-Type

classifier and the coarse hydrocyclone are directedto a collecting sump and then pumped by a

150/125mm bore pump to a Linatex 375 G4hydrocyclone. As before, this unit washes andthickens the product and removes, via the overflow,any unwanted –75 micron silts and excess water. Thistime, however, the underflow discharges ‘fine’ sandon to the VD15 for dewatering prior to stockpiling. Thesingle dewatering screen is fitted with a dividing platedown its length, to maintain separation between thecoarse and fine sands.Silt and excess water from the sand plant is

discharged to a ground sump where a Warman150SP vertical pump delivers the liquor through 300mof 280mm diameter HDPE fused pipework to thequarry’s silt lagoons. Connected by a series ofchannels and with a potential silt storage capacity of98,000m3, these allow hindered settlement of thesolids and provide clean water for re-use in thewashing process. The clean water pump, a 37kW Flygtelectric submersible, delivers 350m3/h back to theplant via 360m of 250mm diameter HDPE fusedpipework.The loading out and rehandling of the final sand and

gravel products is carried out by a Volvo L120Fwheel loader equipped with an on-board weighingsystem, with deliveries to customers being made bythe company’s franchised vehicle fleet as well asadditional contract hauliers, as required. The �


New Quarry

The Linatex compact sandplant

Volvo L120F loader is also used to feed aggregatematerials to Woodsford Quarry’s on-site ready-mixed concrete plant.

CCoonnccrreettee ppllaannttThe fully enclosed Econocrete C100 combined drybatching and wet-mix plant, supplied by Basford PlantLtd and owned and operated by Hills Quarry Products,has the capacity to process 60–80m3 per hour andfeatures a 4m3 dry batch capability and a 2m3 Teka THZ3000 single-discharge pan mixer.The plant is fed via a 10-tonne capacity loading

hopper and 650mm wide x 30° inclined radial chevronbelt arrangement. Aggregate materials are stored insix overhead bins, each with a capacity of 50 tonnes,while cement products are stored in three 60-tonnesilos which incorporate a silo safety system. The plantalso includes a 32,000-litre recycled water storage and

pumping system, a 4,500-litre clean water header tank, a four-admixture pumping and weighing system and a 4m3 aggregate and cement weighingmachine.An elevated and air-conditioned control room

houses the plant’s automated control system, whichcomprises a Windows-based BPL computerizedbatching system with multi-recipe and batch data-recording facilities. Full independent manual controlis also provided.

OOppeenn ddaayyThe opening of Woodsford Quarry received a positiveresponse from guests who attended an open day atthe site on 12 May 2010. Visitors included localresidents, members of the site liaison committee,representatives of Dorset County Council, suppliers,environmental groups and customers. Those presentwere taken on tours of the site and shown theprocesses involved in extracting minerals andproducing ready-mixed concrete. Thames Valley Archaeological Services were also on hand to provide a display of interesting finds from thequarry.Commenting on the open day, Hills Quarry

Products’ group director, Alan Mackenzie, said: ‘Thistype of event gives us the opportunity to meet withstakeholders and to work together, via future liaisonmeetings, to provide the minerals that society needsto build our schools and hospitals and improve theenvironment we live in. We have a reputation forproviding quality and service to our customers, andI believe the new operation at Woodsford will allowus to continue to do this.’

AAcckknnoowwlleeddggeemmeennttThe editor wishes to thank Hills Group for permissionto visit the site and, in particular, Alan Mackenzie,group director - Quarry Products; Steve Bowman,quarry manager; Andrew Liddle, operations manager;Peter Andrew, business development manager; andMatthew Joyce of Wileman Engineers Ltd, for theirhelp in the preparation of this report.


The Econocrete C100combined dry batching andwet-mix plant

New Quarry

The site office andweighbridge facility

WoodsfordQuarry ComesonStream - Agg-Net.com · screens the ‘as dug’ material at 50mm and feeds the –50mm fraction on to a 750mm wide field conveyor for delivery, at a rate of

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