Stability (Operational Phase)
During operation
The statutory duties of quarry operators to maintain a safe working place are set out in the Health and Safety at Work etc Act (1974) and implemented by the Quarries Regulations 1999 (and associated mandatory Approved Code of Practice) L0292 which were made under that Act and came into force on 1 January 2000.
Slope failures in quarries are responsible for only a small proportion of notifiable accidents in quarries, but the consequences can be extremely severe in terms of the potential for death or injury (as well as cost and, sometimes, viability). The risks associated with such hazards can be minimised through quarry design Pre-operation starts that anticipates adverse geotechnical settings and incorporates mitigation within it (by specifying inherently secure slope angles, heights and orientations). Mitigation of stability risks During operation is achieved through the application, by competent engineering geologists and geotechnical engineers, of established methods of stability analysis, detailed slope design, and also by construction and management of quarry slopes supervised by competent quarry management personnel in accordance with the designs and related excavation and tipping rules.
The Quarries Regulations 1999, the Approved Code of Practice and associated guidance set out in detail the ways in which stability of the excavations and tips in operating quarries is to be assured through compliance with a system that has the following features:
- all tips (including liquid tips, commonly referred to as lagoons) and excavations must be designed (regulations 13 and 30);
- safe methods of working (the working rules) for all excavation and tips must be prescribed by a competent person, written down and implemented (regulation 31);
- quarry excavations must be regularly inspected by a person competent to make the inspections. Where existing or proposed excavations or tips are assessed to represent significant hazards (or, by virtue of their height and/or inclination are defined as such in the regulations), more detailed analysis and reporting is required to be carried out by a geotechnical specialist with appropriate qualifications and experience (regulations 32 and 33).
A slope failure, or the failure of an earth or rock structure, even if it does not cause injury or danger to people, can have profound economic consequences. In the short term, costs may increase or production may be lost arising, for example, from blockage of a haulage route, problems with access to working benches or a need to repair or replace plant damaged by the failure. Even more seriously, a failure could affect the viability of the operation (e.g. by taking out the main haul road and making it impossible to access all of the permitted reserves). This underlines the importance of avoiding adverse geotechnical settings (such as undercut bedding) and incorporating adequate factors of safety as part of an iterative process of quarry design at the outset. Proper attention to stability early in the design stage should avoid the problems that arise when unfeasibly steep final slopes are assumed, leading to over-estimates of recoverable reserves.
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