The majority of quarry structures existin a hostile environment; they areconstructed mainly of steel and areexposed both to the elements and to acombination of water and abrasive materials.Coarse-grained sand, graded sandstone,limestone and, even worse, dredged marinedeposits, when combined with water, have an unrelenting impact on structureswhich contain and/or transport such materials within the confines of aquarry.In the author’s experience, condition

monitoring of quarry structures prior to theyear 2000 was, at best, carried out on an ‘adhoc’ basis. This was illustrated in his March2000 paper, entitled ‘Bunkers and Bins’,which was published in Quarry Management and highlighted the poorcondition of some quarry structures at thattime.

BackgroundIn the late 1990s and early 2000s, a numberof major structural failures occurred atquarry sites (eg fig.1.). By good fortune, noone was seriously injured or killed but theconsiderable interest shown by the Healthand Safety Executive and ensuing pressurefrom insurance companies played asignificant role in encouraging thoseresponsible for the safety of quarrystructures to put in place a regime ofstructural inspections.

Quarry structuresNumerous types of structures are found atquarry sites, some of steel construction,some with concrete frameworks and someconventional brick buildings. Examples of commonly found structures include:

Conventional structuresBoth open and steel-clad structures,including open, shed-like structures andstructures supporting silos and bunkers aswell as crusher units, shakers and hoppers,are commonplace (figs 2a, 2b, 2c & 2d).Buildings of concrete portal frame

construction are less common but areregularly found at sites which produceconcrete blocks.As might be expected, buildings of brick

construction and Portakabin-type buildingsare found at almost all quarries. They include office blocks, gatehouses, laboratories and canteenfacilities.

Steel bunkers, bins andhoppersAlmost always of steel construction, bunkersand silos take many forms, however mosthave conical or truncated bases and the

latter are generally considered as ‘high-risk’structures (figs 3a, 3b,3c, 3d, 3e & 3f).

Conveyor structures withintegral walkways togetherwith supporting trestles andtowersConveyor supporting structures areinvariably of steel construction; they can beof galvanized or non-galvanized constructionand either bolted or welded. The bolted typesare classified as ‘high-risk’ structures,since these have in the past been the mostat risk of collapse (figs 4a, 4b & 4c).The structures are almost always of

lattice girder construction and alwaysincorporate a walkway which is eithercantilevered from one side or locatedcentrally between twin conveyors.

Other structuresMany other items also are classified asstructures by the quarry industry, such asweighbridges, various types of retaining walls,

16 www.Agg-Net.com June 2013

Structural IntegrityInspections over the last 10 years highlight significant improvementin the condition of quarry structures

By Ken Irish, principal consultant, Irish & Walker Structural Investigations Ltd

Fig. 1.

Fig. 2a. Fig. 2b.

Fig. 2c. Fig. 2d.

Structural Investigation

June 2013 www.Agg-Net.com 17

oil and water tanks, bund walls, stairs, laddersand handrails (figs 5a & 5b).Other major structures such as jetties,

piers, bridges and chimneys are lesscommon but are, nevertheless, present atsome quarry sites.

Objective of inspectionsThe prime objective of structural inspectionsis, of course, to identify both actual defectsand potential defects. Defects might includefaults such as minor impact damage or theoccasional missing bolt, fractured weld orfoundation defect, where no action isrequired other than to monitor the situation.Alternatively, they might include majorproblems which could result in the failure ofstructural elements, structural collapse orspillage of product, or even, in a worst-casescenario, injury or death. Having identified

Fig. 3a.

Fig. 3b.

Fig. 3c.

Fig. 3d. Fig. 3e.

any major defects, the objective is torecommend remedial action indicating a suitable timescale for implementation.

What to look forThe following photographs, mostly taken inthe early 2000s, show the somewhatneglected state of many quarry structures atthat time but illustrate the types of problemswhich inspections are intended to identify.The prime defects fit into three main

categories:

Loss of section or ‘holing’ dueto corrosion and/or abrasionCorrosion affects, to a greater or lesserextent, just about every steel structure inquarries. The worst effects of corrosion tendto be on external and internal stiffenersand on the truncated sections of bunkers. The

bottom sections of main support columns formost elevated open structures can also beaffected, as can structural elements forminglattice girders. Chequer-plate flooring, safetybarriers, handrails, stairs and ladders arealso affected by corrosion (figs 6a, 6b, 6c &6d).Abrasion mainly tends to affect the internal

elements of bunkers and, to a lesser extent,certain elements of conveyors. Corrosion andabrasion often combine and the most seriouseffects of such a combination occur insidebunkers and bins.

Impact damageVehicular impact affects external structuralelements at or near ground level, oftenincluding the main support columns of whatare extremely heavily loaded structures(figs 7a, 7b, 7c, & 7d). ‰

Fig. 3f.

Fig. 4a. Fig. 4b. Fig. 4c.

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Removal and/or repositioningof structural membersStructural members are sometimesremoved and/or repositioned for theconvenience of vehicular access or for theinstallation of conveyors, and this is oftendone without any kind of check on structuralintegrity (figs 8a, 8b & 8c).

Other typical problems • Crushing of steel connections, whereheavy impact occurs from crusherunits (fig. 9a)

• Handrail defects caused by eithercorrosion or impact (fig. 9b)

• Foundations being undermined if to tooclose workings (fig. 9c)

• Missing bolts• Fractured welds• Spalling or cracking of concrete on both foundations and above-groundstructural members

• Excessive vibration.

Typical inspection regimeDuring the past decade many quarryoperators have adopted a system of regularstructural inspections.Inspection procedures vary somewhat

throughout the industry but a typicalapproach is for non-engineering staff to betrained and authorized to carry out visualinspections on an annual basis, with trainedengineering personnel inspecting structuresevery three years.The annual inspection tends to cover

items ranging from the safety of barriers tothe condition and safety of major itemssuch as bunkers and silos, their supporting

structures and the lattice structuressupporting the conveyors and walkways,together with their tower and trestle

supports. The results of these inspectionsare recorded in a simple report format.Triennial inspections cover the same

Fig. 5a.

Fig. 5b.

Fig. 6a. Fig. 6b.

Fig. 6c. Fig. 6d.

Fig. 7a. Fig. 7b.

Fig. 7c. Fig. 7d.

June 2013 www.Agg-Net.com 19

Structural Investigation

ground but with the addition of non-destructive testing, which can include the physical measurement of platethicknesses and the withdrawal of bolts forinspection.The reporting process for both annual

and triennial inspections includesrecommendations for remedial work orwork of a preventative nature and/or, inspecific cases, the need to call on theservices of a chartered structural engineer.The report usually sets down the timescalefor the implementation of eachrecommendation.

Follow-up work In the author’s experience, follow-upworksrecommended in the reports preparedby engineering personnel, ie the triennialreports, tends to be carried out diligently andwithin the timescales set down; however,recommendations made in annual reportsare not always given the same priority withthe result that recommended work is eithernot carried out within the set timescales or,in some cases, not carried out at all. Fortunately, the works which tend to be ignored are often items of lesser importance.

In the author’s experience, these systemshave led to significant improvements in thecondition of structures over the past decade,a fact illustrated by a recent survey carried out by him at a privately ownedquarry.The three-day survey of more than 50 silos

and hoppers, together with approximately 30conveyors, as well as numerous items ofplant, retaining walls and other structures,revealed no significant defects. Only minorimpact damage, a few missing bracings andsome issues regarding excessive spillage onwalkways were recorded. One significantobservation was that the vast majority of the structures were made of galvanizedsteel; clearly, lessons have been learnt.

Possibilities for furtherimprovementConsideration could be given to introducing

a formal Code of Practice for the inspectionof structures throughout the quarryingindustry. This could have significant healthand safety benefits, particularly in respectof small quarry operators.The industry’s reluctance to use paint,

recognized by the author more than 10years ago, continues and is one area whereimprovement could be made, particularly onnon-galvanised structures. More regularpainting could assist greatly by deceleratingthe rate of corrosion on external surfaces and thus prolonging their workinglife. QMAbout the author: Ken Irish has been

deeply involved with quarry structures forthe past 15 years, having worked closely with a number of quarry operators. Helectures regularly on ‘The Inspection ofStructures’.

Fig. 8a.

Fig. 8b. Fig. 8c.

Fig. 9a. Fig. 9b. Fig. 9c.