Ground control in underground mines

Purpose

The purpose of the guideline is to assist employers, workers and other workplace parties with understanding the requirements in Regulation 854 (Mines and Mining Plants) regarding ground control.

This resource does not replace the Occupational Health and Safety Act (OHSA) and its regulations and should not be used as or considered legal advice. Health and safety inspectors apply the law based on the facts in the workplace.

Objective

The objectives of the guideline are to:

• help workplace parties understand the requirements in Regulation 854 – Mines and Mining Plants under the Occupational Health and Safety Act (OHSA) for ground control
• provide best practice recommendations and what to consider when fulfilling those requirements
• provide information on design and operational considerations to prevent ground instability in mines

Legal requirements

Section 53 of the Act and the following sections of Regulation 854 and O. Reg. 420/21 (Notices and Reports under Sections 51 to 53.1 of the Act – Fatalities, Critical Injuries, Occupational Illnesses and other Incidents) under the Occupational Health and Safety Act cover the important requirements:

• Regulation 854
  • Sections 5.1, 5.2 and 5.3 (risk assessments)
  • Section 6 (mine design)
  • Section 6.1 (unsupported openings in underground mines)
  • Section 19 (boundary pillars separating adjacent underground mines)
  • Section 65 (communication program)
  • Section 66 (workplace examinations of ground conditions)
  • Section 67 (procedures for installing ground support)
  • Section 67.1 (scaling)
  • Section 69 (illumination for ground assessments)
  • Section 71.1 (seismic risk management program)
  • Section 72 (records of ground instability)
  • Section 73 (ground support quality control program)
• O. Reg. 420/21
  • Section 4 (requirements for reporting rock bursts and falls of ground)

Background

Many fatalities have occurred because of ground instability in Ontario mines. Understanding the hazards of ground instability and the application of a ground control program is fundamental to managing the hazards associated with ground instability.

Ground stability is the summary of many key factors and is dependent on the geometry, geology and quality of the rock mass as well as mining induced stresses. Managing these factors, as they change over time, is critical to the ground control program to ensure the safety of the opening. Ground instability can result from various types of ground failure mechanisms, the two most common being kinematic, or gravity type failures, and rockbursts.

Kinematic or gravity type failures occur when there are discontinuities within a rock mass where openings or excavations occur. These combine to form release planes, which allow blocks or wedges of rock to fall or slide from the periphery of such openings or excavations. The discontinuities can consist of naturally occurring breaks in the rock mass (faults, joints, contacts between individual components within a rock mass, or bedding planes) as well as mining related breaks (mining induced stress fractures and cracks caused by blasting).

Rockbursts involve the sudden failure of a rock mass in which openings or excavations occur and can result in the release of stored energy, often causing the displacement and violent ejection of detached rock. Generally, the following three categories of rockbursts are thought to exist.

Strain-type rockbursts

Strain-type rockbursts occur in development headings shortly after a round of advance has been blasted, especially where the rock mass is stiff and brittle. They are caused by the rapid build-up of stress concentrations shortly after blasting and result in the sudden failure of the rock mass in the roof, walls, floor or face of the heading.

Fault-slip-type rockbursts

Fault-slip-type rockbursts occur when a rock mass moves along a local fault, thereby releasing energy that can cause rock mass damage around nearby mine openings. Relative movement of rock masses on either side of a fault can occur when the clamping forces that normally prevent such movement are disturbed as a result of ground stress redistributions caused by normal mining activity.

Pillar-type rockbursts

Pillar-type rockbursts occur when pillars (meaning rock remnants that separate openings or mined-out regions) become over-stressed and fail suddenly. Ground stresses in an underground mine cannot be transmitted through openings in the rock mass and are therefore channeled into pillars, which will fail if pillar geometries are under-designed.

Mine life stage

Many of the active underground mines currently operating in Ontario are becoming deeper and are at a mine life stage where pillars are becoming more prevalent. Normally, inherent ground stresses increase with depth and the presence of pillars often elevates the level of mining induced ground stresses. Therefore, many deeper and older mines are becoming more vulnerable to and are more routinely experiencing rockbursts.

Throughout 2014 and the early part of 2015, the ministry led the Mining Health, Safety and Prevention Review (the review) to develop a better understanding of the occupational health and safety needs of the mining sector.

The recommendations that were set out in the final report from the Mining Health, Safety and Prevention Review, included one that the ministry require the mining employers address the priority hazards identified in the risk ranking exercise. One of these priority hazards was enhancing ground control protection by identifying key elements in the control of these hazards and requiring employers to maintain a record of significant seismic events in addition to incidents of ground instability.

Risk Assessment

Sections 5.1 to 5.3 of Regulation 854 require mines to assess hazards and potential hazards and establish controls to eliminate or reduce those hazards. In underground mines, as well as surface mines producing metallic ore, this assessment should include ground instability hazards.

Employers should ensure that appropriate subject matter experts are relied upon when assessing and managing risks and engage the appropriate ground control subject-matter experts (from both engineering and operational backgrounds) when identifying and ranking such hazards.

The assessment of ground instability hazards might include the identification of regions that could become prone to ground instability due to:

• the elevation of ground stresses from expected changes in mine geometry (the presence of diminishing pillars), or mining at deeper horizons
• deteriorating ground support in older excavations
• the expansion of the mine into regions having lower quality rock masses, or problematic geologic structures and joint sets
• the expected mining in close proximity to faults, which could trigger seismicity and rockbursting
• inadequate ground support
• a combination of the aforementioned points

Engineering, work practice or administrative controls should likely be considered to manage these hazards where elimination or substitution is not practicable. Regulation 854 requires that the employer consult with the joint health and safety committee or health and safety representative, if any, about measures to control hazards.

Where new engineering controls are required to manage identified ground control hazards, these should be incorporated into the mine design required by section 6 of Regulation 854. If work practice or administrative controls are needed, they should be incorporated into other procedures or protocols such as those required by:

• Section 65 (the formal communication of ground control information)
• Section 66 (workplace examinations of ground conditions)
• Section 67 (procedures for installing ground support)
• Section 67.1 (scaling)
• Section 69 (illumination for ground assessments)

Relevant controls should also be incorporated into an underground mine’s seismic risk management program, required under section 71.1 of Regulation 854.

For more information regarding this requirement, see the Ministry’s guideline entitled Seismic Risk Management Programs in Underground Mines.

Mine design

Section 6 was included in Regulation 854 following the deaths of four miners in June 1984 after a rockburst at the Falconbridge Mine in Sudbury. It responded to recommendations from the subsequent Provincial Inquiry into Ground Control and Emergency Preparedness in Ontario Mines, known as the Stevenson Inquiry.

The mine design is intended to be a formal analysis of ground stability of both active and proposed openings of the mine. These analyses should attempt to predict the ground failure mechanisms that could arise through the implementation of the mine extraction plan and should define any measures that should be undertaken (the adjustment of opening geometries, the use of more robust ground support systems, or modifications to the planned extraction sequence) to contend with these ground failure mechanisms.

Responsibilities with respect to mine design

The owner of an underground mine or a surface mine producing metallic ore must prepare and maintain a mine design assessing the ground stability of the active and proposed workings of the mine.

Subsection 6(2) of Regulation 854 requires that the mine design be prepared under the direction of an engineer registered or licensed under the Professional Engineers Act. In this capacity, the engineer is confirming that the extraction plan for a mine has been properly evaluated from a ground stability perspective to ensure that all potential ground failure mechanisms have been identified, and that there are measures to contend with any expected ground instability.

Although the mine design must be overseen by an engineer, its preparation is a collaborative effort involving other individuals.

Planners

Planners who design mine excavations, extraction sequences and blasts to identify considerations such as sequencing, ground support and monitoring needs.

Geologists

Geologists who delineate the mine ore bodies, update mine ore reserves, oversee mine exploration programs and map all mine excavations to identify and record all mine lithological units and geologic structures.

Ground control engineers or specialists

Ground control engineers or specialists (typically mining engineers) who perform pre-mining stability analyses to understand the effects that mining induced stresses and geologic structure could have on the excavations and extraction sequences designed by planners, and who design ground support systems for mine excavations and recommend and oversee ground monitoring programs.

Ground control technicians or technologists

Ground control technicians or technologists who work with the specialists and install and collect data from ground monitoring instrumentation and perform quality control tests on ground support systems.

Using external consulting engineers

Not all mining operations, particularly smaller ones, have sufficient in-house technical resources to prepare the mine design. In such cases, these operations should engage the services of qualified external consulting engineers. However, an in-house engineer familiar with the operation should still be responsible for the mine design’s implementation.

What a mine design should include

Subsection 6(2.1) also specifies that the mine design be based upon “sound geotechnical engineering practices” which should include the following:

• A comprehensive methodology to make available all geotechnical information needed to undertake the necessary pre-mining excavation stability analyses. This could include:
  • relevant material property values for all mine lithological units
  • the interpretation and projection of geologic mapping results
  • ground stress measurements
  • pertinent groundwater information
  • relevant ground monitoring data
  • the results from the application of relevant rock mass classification systems
• The routine undertaking of pre-mining stability analyses (including the application of empirical, analytical and numerical modelling methods) and the interpretation of the findings from such analyses (using engineering judgement based on relevant ground control experience) to assess the stability of proposed excavations on both a micro and macro scale (ensuring that proposed excavation dimensions, orientations, extraction sequences and ground support requirements have been analytically rationalized according to relevant engineering design principles, allowing for the necessary design modifications to be made prior to the beginning of mining).
• Backfill design considerations, including the strength requirements for backfill specified in a mine design.

Aspects of the mine design

The mine design must describe the following aspects.

Geological and geotechnical aspects of the mine

The geological and geotechnical aspects of the mine, such as:

• describing the regional geology in the vicinity of the mine
• defining the mine ore bodies in terms of their dimensions (thickness, strike length and height), dip and dip direction and the depth at which they occur
• listing the lithological units in the mine, as well as any local alteration, within the context of the regional geology
• defining the mine structural geology, including all joint sets as well other mine geologic structures (faults, dykes and bedding planes) and characterize them in terms of their orientations (dip and dip direction) and spacing
• characterizing the hydrogeology at the mine, as well as its expected impact on ground stability
• expressing the findings from the application of recognized rock mass classification systems
• describing the in-situ stress regime at the mine (the three principal inherent stresses, in terms of direction and magnitude as a function of depth), as well as the methods that have been used to estimate the in-situ stresses
• providing the results of all tests that have been carried out to determine the material properties (uniaxial strength, shear strength and modulus of elasticity) of the mine lithological units, and how the results haven interpreted and responded to

Geometry of existing and proposed excavations

The geometry of existing and proposed excavations such as specifying the depth, dimensions and orientations of existing and planned openings and indicating the dimensions of existing and planned pillars. The engineering basis and rationale for the geometry of mine openings and pillars should also be provided

Previous occurrences of ground instability

Previous occurrences of ground instability, including details for all reportable and non-reportable instances of ground instability that have occurred at the mine. These descriptions should be consistent with those required in records under section 72 and should include details regarding:

• the time, location and extent of the incident
• records of any monitoring system or devices before the occurrence
• whether workers were present when the incident occurred
• whether there was equipment damage as a result of the incident
• whether installed ground support was damaged as a result of the incident
• the amount of material displaced
• the ground failure mechanism(s) that caused the incident
• the nature of the release planes in the rock mass that resulted in the incident
• any remedial measures that are required in response to the incident

Mining methods

The mining methods including stope sequencing and blasting methods, including:

• a rationale or explanation as to why the method was selected and is used
• an account of the ore extraction sequence that has been adopted and an explanation of how it will optimize ground stability
• a list of types of explosives used at the mine, weight of explosive per delay that is specified, drill holes specifications for both development and production blasting (meaning hole diameters and spacings), and a description of any perimeter or de-stress blasting practices that are applied
• backfill design considerations

Mine ground support systems

The mine ground support systems are comprised of physical elements which are installed to provide ground stability. Examples of ground support could include:

• mechanical anchor rockbolts
• backfill
• resin rebar
• cable bolts
• screen (including weldmesh and chain link varieties)
• shotcrete (including fibre reinforced varieties)
• spray-on liners
• shotcrete posts
• concrete wedges
• timber cribs
• timber or steel sets
• arches (including steel or shotcrete varieties)
• dynamic ground support systems for seismic active areas
• composite systems (systems that consist of combinations of the aforementioned types)

The mine ground control program should list:

• all ground support systems (including components and specifications) that are to be installed at the mine
• the locations where they are to be installed
• the engineering rationale for the design of the ground supports systems (in other words, an explanation of the ground failure mechanisms that the ground support systems are intended to address)

The ground control program should explain whether the ground support is intended to be used as primary or secondary ground support.

The ground control program should define the life expectancy of the ground control system (meaning the duration limit that ground control elements need to be replaced following installation).

Measures used to assess potential ground instability

Measures that have been identified or are used to assess potential ground instability, such as instrumentation and computer modelling, including:

• listing all analytical methods employed to assess the effects of ground stresses and geologic structure of ground stability at the mine, as well as the results from the application of these methods and how the results have been interpreted and responded to
• listing all ground monitoring instruments employed at the mine (including those used to measure ground stresses, ground displacement and mine seismicity), as well as the results from the application of these instruments and how the results have been interpreted and responded to

Records of ground instability at a mine are an important source of information for the mine design. A formal analysis of these records should take place regularly to identify changes in trends in the ground failure mechanisms that are occurring at a mine. Such identified changes should be considered when calibrating numerical models.

As mentioned above, Regulation 854 requires mines to do formal risk assessments. If that assessment determines that new engineering controls are required to manage identified ground control hazards, these should be incorporated into the mine design.

Unsupported openings in underground mines

Workers in an underground mine must be prevented from accessing unsupported excavations unless an engineer has specified in a written report that the excavation is self-supporting. Unsupported excavations should also be identified in the mine design required under section 6.

Subsection 6.1(1) of Regulation 854 prohibits the alteration of an existing, unsupported excavation in an underground mine unless:

• an engineer prepares a written report, in accordance with sound geotechnical engineering practices, on the program alterations; and
• the written report states that workers will not be endangered by the proposed alteration.

Subsection 6.1(2) requires that a new excavation in an underground mine that is planned to be unsupported shall not be developed unless an engineer prepares a written report in accordance with sound geotechnical engineering practices stating that workers will not be endangered by the proposed excavation.

Subsection 6.1(3) requires that any of the engineering reports referred to above must be kept readily available at the mine site and be provided to the joint health and safety committee or health and safety representative, if any.

Boundary pillars separating adjacent underground mines

Section 19 of Regulation 854 is based on the principle that individual mining operations approaching a common boundary need to be informed of each others’ mining plans. Subject to certain requirements, mining of a boundary pillar by either mining operation may be mined if both operations of adjacent mines agree, as per subsection 19(5). Failure to adhere to this principle could present the following risks:

• Blasting within the boundary pillar could induce large unexpected vibrations on the other side of the boundary.
• Excessive extraction of the pillar on one side of the boundary could reduce its size to the point that it incurs high stresses or seismicity and rockbursting that could cause the pillar to fail or become damaged.
• Backfill placed in openings that have been created right up to one side of the boundary could fail or flow into one side of the boundary when it is exposed by mining on the other.

Subsection 19(1) generally requires a 60-metre-thick pillar on either side of a boundary adjoining underground mining properties. Subsection 19(2) generally requires that an engineer prepare or check plans, drawings, specifications, mining methods and procedures for the mining of the boundary pillar before it is mined. As such, the mining of a boundary pillar is expected to be undertaken in accordance with sound geotechnical engineering practices (see the Mine Design section for more information about what constitutes “sound geotechnical engineering practices”).

Subsection 19(3) requires any drawings, plans and specifications, mining methods and procedures pertaining to the extraction of the boundary pillar be maintained and kept up-to-date. The pillar dimensions and mining methods must provide ground support to control pillar failure, rockbursting, ground falls, and withstand an inrush of water or water-bearing materials.

In addition to plans and procedures referred to in section 19, the schedules for mining a boundary pillar should be shared and agreed to by the mining operations on either side of a boundary. Where they exist, boundary pillars should be identified in the mine design required under section 6.

Reporting uncontrolled falls of ground and rockbursts

As a general matter, section 53 of the Act provides that if a premature or unexpected rockburst or other prescribed incident occurs at a mine or mining plant, the owner must give written notice to the joint health and safety committee or health and safety representative, if any, and to a Director of the Ministry of Labour, Immigration, Training and Skills Development. Subsection 4(3) of O. Reg. 420/21 prescribes other events that trigger this notice requirement including: any rockburst that damages equipment or displaces more than five tonnes of material; and, an uncontrolled fall of ground that damages equipment or displace more than fifty tonnes of material.

An uncontrolled fall of ground is one that is not expected to occur. If a fall of ground is expected to occur, then this possibility must be referred to in the mine design, otherwise, it must be reported if it meets the reporting criteria. For example, if sloughing from the walls of an unfilled open stope (including walls made up of backfill) is expected to happen, then the extent to which this can occur without causing regional ground stability must be specified and rationalized in the mine design. Any sloughing that occurs beyond this limit, and meets the reporting criteria, must be reported.

A rockburst will cause damage (loose material to be generated) to a rock-mass. However, if the damaged material is not displaced, but is sustained by installed ground support, then this is not considered to be a fall of ground.

Damage to equipment from a rockburst or an uncontrolled fall of ground would normally consist of damage that renders the equipment unable to fulfill its normal functions or to be operated safely.

These requirements, which specify which forms of ground instability are reportable to the ministry, differ from section 72 of Regulation 854, which requires a record be kept for any incident of ground instability that occurs at a mine.

Communication of ground control information

Section 65 of Regulation 854 requires an employer in an underground mine to develop a written communication program in consultation with the joint health and safety committee, if any. The program is intended to ensure timely communication of information between workers and supervisors in the mine about:

• ground stability
• ground movement
• falls of ground
• ground monitoring equipment
• emergencies

Moreover, the regulation specifies the content of the communication program. It must set out: the measures and procedures for communicating information; the type of information that is to be communicated; and the actions taken by supervisors and workers concerning the information that is communicated to them.

Examples of the types of information that should be reported by workers to supervisors include:

• evidence of a fall of ground, a rockburst or audible seismicity (including when and where such occurrences happened)
• unusual findings from workplace examinations of ground conditions (required under section 66 of Regulation 854)
• situations where excavation geometries are larger than specified in the mine design (a development heading that has gone “off-line” or “off-grade” requiring it to be enlarged)
• evidence of ground support deterioration (due to corrosion in the case of rockbolts or detachment of shotcrete from the rock surface to which it has been applied)
• evidence of ground support ostensibly being exposed to excessive loading
• evidence of excessively bagged screen or screen with broken strands
• evidence of significantly cracked or deformed shotcrete
• evidence of new stress fracturing in mine rock masses
• evidence of new geologic structural features (joint sets, faults or dykes) appearing in mine rock masses
• the identification of rebar resin that it past its specified expiry date
• evidence of water emanating from boreholes or discontinuities in mine rock masses
• evidence of production drill holes or raised bored raises undergoing deformation

Examples of the types of information that should be provided by mine management, technical staff and supervisors to workers include:

• changes to mine ground support types or standards
• findings from ground stability analyses identifying regions of the mine that could be vulnerable to ground instability
• findings from ground monitoring results identifying regions of the mine that could be vulnerable to ground instability
• findings from ground support quality control tests or evaluations
• changes to the mine design
• changes to the mine excavation sequence
• the upcoming adoption of a new mining method
• changes to protocols for mine re-entry following seismic events or rockbursts
• findings from investigations into incidents of ground instability
• hazard alerts prepared by the Ministry of Labour, Immigration, Training and Skills Development or health and safety associations pertaining to ground control
• the occurrence of strong seismic events

Workplace examinations for ground assessments

Section 66 of Regulation 854 requires that, before work is begun, the ground conditions at a workplace in an underground mine must be examined for dangers and hazards, and if required, be made safe.

Ground instability hazards can be identified on a macro basis, such as through formal stability analyses required under section 6. However, it is also essential that such hazards be identified on a micro or local basis through routine examinations of individual workplaces to look for evidence of:

• deteriorating ground support
• excessive quantities of bagged material contained by screen
• the presence of discontinuities in the workplace rock masses that could cause ground instability (joints, faults, bedding planes, mining induced stress fractures or blast induced fractures)
• water emanating from discontinuities or drill holes
• deteriorating workplace rock masses (based on the application of conventional rock mass classification systems)

Findings from these workplace examinations would be reported to mine management, supervision or technical staff under the communication program required by section 65. In addition, proper illumination needs to be provided under section 69 to effectively conduct such examinations.

Procedures for installing ground support

Section 67 of Regulation 854 requires written procedures to be used concerning: activities related to the installation of ground support; and, activities that expose a worker to unsupported ground before ground support is installed.

Installing ground support in an underground mine can present unique health and safety hazards to workers. It ordinarily takes place following the creation of a new opening and occurs at the interface of where ground support has been installed in an excavation rock mass and where it has yet to be installed. In some circumstances, workers may be exposed to unsupported ground while installing ground support in a newly created opening. It is imperative that workers only be exposed to unsupported ground when an engineer has deemed the area to be self supporting and stable.

The requirements in section 67 relate to other provisions in Regulation 854. For example, it is crucial that a proper examination of workplace ground conditions required by section 66 occur and that the workplace is adequately illuminated to allow for proper assessment of ground conditions required by section 69. In fact, these aspects should be incorporated into a mine’s procedures for installing ground support. In addition, section 73 requires that a quality control program be developed to ensure that ground support systems are properly installed and remain effective while in use.

Scaling

Section 67.1 of Regulation 854 states that no other work be done in an underground mine that hinders scaling procedures.

The primary purpose of scaling is to condition a rock mass (remove loose material) to allow for the safe installation of primary ground support. As such, scaling is a vitally important process and requires that no other activities be performed that would interfere with or distract workers who are involved in scaling.

Moreover, serious hazards are associated with the scaling process if it is not executed properly. For example, workers involved in scaling must have a clear path for retreat to ensure they will not be exposed to scaled material that can fall or topple from a rock mass surface.

It is crucial that the workplace is adequately illuminated as per section 69 to allow for proper assessment of ground conditions and that a proper examination of workplace ground conditions required by section 66 has occurred prior to scaling.

Illumination for ground assessments

Section 69 of Regulation 854 specifies the requirements for:

• illumination to assess ground conditions in an underground mine
• cap lamp capabilities
• procedures for assessing cap lamps
• maintaining records of cap lamp maintenance test
• the provision of auxiliary lighting

In order for ground instability to occur, discontinuities (geologic structures such as joints or bedding planes, or stress induced fractures) present in the rock mass must combine to form blocks or wedges of rock that are free to fall, slide or topple from the periphery of mine excavations. Proper illumination allows for such discontinuities to be detected, particularly when activities such as scaling and installing ground support are being carried out.

Adequate illumination is necessary when undertaking certain prescribed activity, such as assessing workplace ground conditions as per section 66 or conducting scaling activities under section 67.1. Procedures for installing ground support required under section 67 should also specify that sufficient lighting be provided when ground support is installed.

Records of ground instability

Section 72 of Regulation 854 requires that a record be kept at an underground mine or a surface mine producing metallic ore in the event of:

• rockbursts
• uncontrolled falls of ground
• seismic events of a magnitude that is likely to cause rock mass damage or may compromise the effectiveness of the ground support system
• seismic events that occur in or near an active area of a mine that is of a magnitude that may cause ground instability.

These records must include:

• the time and location of the incident
• any other relevant information, including the records of any monitoring instruments or devices before the occurrence

Other relevant information includes:

• whether workers were present when the incident occurred
• whether there was equipment damage as a result of the incident
• whether installed ground support was damaged as a result of the incident
• the amount of material (either rock or backfill) displaced
• the ground failure mechanism(s) that caused the incident
• the nature of the release planes in the rock mass that resulted in the incident
• the source location and magnitude (for a seismic event)
• any remedial measures that are required in response to the incident

Sections 6 and 72 are closely connected. As mentioned above under “Mine Design”, records of ground instability at a mine constitute an important input into the ground control mine design. A formal analysis of the contents of such records should take place on a regular basis to identify changes in trends in the ground failure mechanisms that are occurring at a mine. Such identified changes should be considered when calibrating numerical models.

Ground support quality control program

Section 73 of Regulation 854 requires that an employer shall:

• develop a quality control program for an underground mine
• ensure that the mine ground support systems that are specified in the mine design are properly installed and remain effective while in use
• maintain the quality control program and provide a copy of the program and a record of the tests to the joint health and safety committee or health and safety representative

While ground support systems should be properly designed, failure of these systems can still occur if they have not been properly installed or if they become ineffective at some point following installation. For example, the following things should be considered:

• deterioration (from corrosion or exposure to the effects of blasting)
• increasing loading conditions (due to changes in excavation geometries resulting in increased roof spans)
• exposure to unexpected ground failure mechanisms

Excavations may be considered unsupported if the ground support system has become ineffective.

Confirming that ground support systems are properly installed could include:

• preparing formal procedures for the installation of ground support required by section 67
• ensuring that ground support installation crews have been trained in the application of the necessary installation procedures
• ensuring that ground support installation equipment has been properly calibrated and maintained
• conducting spot observations of ground support installation crews to ensure the installation procedures are being properly followed
• performing torque tests (for mechanical anchor rockbolts)
• performing pull tests (for mechanical anchor rockbolts, resin rebar, friction stabilizers and cable bolts)
• measuring drill hole diameters for hole size sensitive ground support systems to ensure that they are within acceptable tolerance ranges (for mechanical anchor rockbolts, resin rebar, some types of friction stabilizers and cable bolts)
• drilling holes into applied shotcrete (to confirm that its thickness meets the design specification)
• conducting uniaxial compression and other strength tests on specimens of shotcrete to be applied to confirm that strength requirements have been met (for shotcrete and shotcrete posts)

Confirming the effectiveness of ground support systems while they are in use should, in part, be addressed at the design stage (selecting ground support systems with life spans compatible with that anticipated for the excavation in which the system is to be installed).

Other post-installation methods for ensuring that ground support systems remain effective might include formal observations and evaluations conducted by ground control specialists, and the use of ground monitoring instrumentation such as multi-point extensometers.

Other forms of ground support quality controls might include specifications for:

• product selection and procurement (to ensure that ground support products meet the required standards)
• supplier certification (to ensure that ground support suppliers hold the proper certification credentials)
• handling and storage of ground support products (ensuring rebar resin is not used beyond its expiry date)

Consultation with the committee or representative

Where the Occupational Health and Safety Act or its regulations require that an action be taken in consultation with another party, including but not limited to the committee or representative, the Ministry of Labour, Immigration, Training and Skills Development expects that the employer will engage in a meaningful interaction (including but not limited to dialogue, discussion and providing all relevant information) with the committee or representative. For example, sections 65 and 67 require that the committee or representative be consulted on the development of the communications program and procedures for installing ground support.

There should be a genuine opportunity for the committee or representative to comment, and those comments should be received and considered in good faith. This includes taking into account any feedback and responses from the committee or representative before taking action (implementing a plan, or program) and responding to any recommendation arising out of the consultation.

Consultation is not simply informing the committee or the representative that the employer intends to take action.