Mineral Mines & Quarries Inspectorate | Bulletin | No.202 V 1 | 10 June 2022
Integrity of Structures at Mineral Mines and Quarries
Since 2011 there have been 129 reported incidents involving the failure of structures in the mineral mines and quarries sector, with 19 of those occurring in the last 12 months. These structural failures have resulted in uncontrolled movements, and falls of objects, persons and, in some circumstances, whole structures. All of these incidents had the potential to cause serious harm to persons.
Five of the recent incidents included:
- Corrosion of steelwork: A 1.5m long section of steel, weighing 10-12kg, detached from a beam and fell 10m from an overhead structure to the floor.
- Failure of a cement silo structure: The support structure for a cement silo failed, causing the silo to collapse, striking the control room and causing damage to the surrounding equipment.
- Failure of conveyor structure: Failure of the truss section of a stacker conveyor caused the head end of the conveyor to droop approximately 2m before coming to rest on the top of the stockpile.
- Handrail failed: A worker was exposed to a 12m fall to the ground when the stanchions of a handrail they were leaning on cracked, allowing the handrail to move.
- Failure of raw water tank: A structural failure of a large capacity water tank caused a significant release of water and collapse of the tank structure, resulting in injuries to a worker and damage to surrounding equipment.
The Mineral Mines and Quarries Inspectorate has issued 17 compliance actions to control hazards associated with failure of structures across Queensland in the last 12 months.
How did it happen?
Though there were a number of contributing factors to the incidents identified above, a common issue has been the failure to identify 'loss of structural integrity' as a hazard and to implement effective controls.
Sites with structures must ensure they have identified the failure of those structures as a hazard. Controls should be based on the likelihood and potential consequences of damage to mechanisms and failure modes of the structures on site.
Damage mechanisms can include:
- Corrosion (from environmental or chemical sources, particularly in underground mines)
- Vibration (from environmental or operational sources)
- Fire and heat
- Interaction with mobile and other plant
- Adverse weather effects
- Rot and pest damage (e.g. termites, rodents)
- Wear and loss of section from operational sources (such as flow of material/fluids)
- Subsidence or erosion
- Damage and overload from operational sources (such as spillage, used in a way other than originally intended)
- Damage and overload from maintenance sources (such as landing of heavy items for shutdown maintenance, placing mobile equipment on structures, removal of sections and members)
- Improper design, construction, installation, modification and repair of structures.
- Site Senior Executives must ensure the failure of structures is identified as a hazard on site and implement effective controls to protect persons.
- Site Senior Executives should develop a Structural Integrity Management Plan in consultation with a suitably qualified person (such as a Structural Engineer) that includes requirements for periodic inspections, audits, testing and reporting on the condition and risk of structures on site.
Structures at mines and quarries can include the following:
- Walkways, platforms, fixed ladders and stairs
- Retaining walls
- Processing plant support structures for conveyors, mills, solvent extraction and electrowinning plants, grinding, gravity and floatation cells
- Storage bins, tanks, hoppers and silos
- Bridges and culverts
- Cooling towers and ventilation fan structures
- Winding equipment infrastructure such as headframes, sky-shafts and towers
- Support structures for mine services (surface and underground)
- Shade structures (igloos and similar)
- Dredges, pontoons and ship-loading facilities.
The failure modes of structures can include:
- Collapse and sudden failure
- Partial collapse and instability
- Failure of individual sections or members
- Permanent deformation (e.g. buckling and bending) of sections or members
- Cracking in members and weldments
- Failure of connections and fasteners
- Spalling and cracking failures on concrete.
It is recommended that sites engage competent persons (typically engineering consultancies with RPEQ certified structural engineers) to assist them in first establishing a baseline audit of their structures. The results of the audit should be used to identify the risk of any defects found, and repairs prioritised accordingly (from items requiring immediate attention to items requiring attention in several years).
Management plans can then be created to manage structures as part of the site's preventative maintenance strategy. Typical industry strategies for structures can involve periodic in-house and external third-party inspections, with the interval of these inspections set based on likely damage and failure mechanisms and the associated level of risk.
Some useful questions to ask when establishing a structural integrity program on site are as follows:
- What structures do I have on site?
- How are the structures on site registered or otherwise identified?
- What design, installation, commissioning, modification and repair records do I have for the structures on site?
- Does the site have a set of as-built drawings for the structures?
- How have structures changed or been modified since installation?
- What environmental effects, operational or maintenance activities can damage structures on site?
- How do I know the current condition of my structures?
- What controls do I currently have to prevent failure of structures?
- Are persons currently engaged to inspect structures competent to do so?
- How do persons on site know when a structure is unsafe?
- How do persons on site report when a structure is unsafe?
- How does the site identify and track work carried out on structures?
A management plan for structural integrity can be used to give a systematic approach to managing the structures on a mine site. Typical plans within industry include consideration of at least the following elements:
- Scope and purpose
- Applicable structures on site and how these will be divided into manageable portions
- Design of structures
- Construction/Installation of structures
- Modification of structures
- Inspections and audits
- Defect reporting and management process
- Decommissioning and demolition of structures
- Records management
- Training and competency requirements of personnel with roles in managing structures/inspections
- Roles and responsibilities.
Applicable standards (non-exhaustive list):
- AS/NZS 1170 Series - Structural design actions
- AS 1657:2018 - Fixed platforms, walkways, stairways and ladders - Design, construction and installation
- AS 1720 series - Timber structures
- AS 3600:2018 - Concrete structures
- AS 3700:2018 - Masonry structures
- AS 3990-1993 - Mechanical equipment - Steelwork
- AS 4100:2020 - Steel structures
- AS 4678-2002 - Earth-retaining structures
- AS 5100 series - Bridge design
- AS 5104:2017 - General principles on reliability for structures
- AS ISO 13822-2005 - Basis for design of structures - Assessment of existing structures.
Contact: Rob Henson, Inspector of Mines , +61 7 4745 4105 QldMinesInspectorate@rshq.qld.gov.au
Issued by Resources Safety & Health Queensland
Placement: Place this announcement on noticeboards and ensure all relevant people in your organisation receive a copy, understand the content, findings and recommendations as applicable to their operation. SSEs should validate that recommendations have been implemented.