Appraisals and Geotechnical Assessment
Persons in or near a quarry should not be at risk due to the collapse of a quarry face or from the movement of all or part of an excavation, tip or lagoon. This section provides an overview of the main points and legal requirements for a more detailed explanation refer to Part 6 Excavations Including (Quarry Faces), Tips and Lagoons of the SAFE QUARRY GUIDELINES TO THE SAFETY, HEALTH AND WELFARE AT WORK (QUARRIES) 78 REGULATIONS 2008
An appraisal is intended to be a straightforward exercise to determine which excavations tips and lagoons, proposed or existing, would pose a significant risk if they failed, or in the case of a tip or lagoon, move significantly more than that allowed in the design, and so merit an assessment by a geotechnical specialist.
The appraisal should be carried out with enough detail and sufficient expertise to decide if an excavation, tip or lagoon poses a significant risk from collapse or movement. It is not normally necessary for appraisals to be carried out by a geotechnical specialist, though advice from one is appropriate where the level of hazard is unclear.
In some cases it is obvious that any failure of an excavation, tip or lagoon could prove fatal, for example, an excavation, or tip or lagoon near a public roadway, house or above quarry offices. In these cases the initial appraisal can be very brief as a geotechnical assessment by a geotechnical specialist will be needed.
Areas where no one is at risk from a collapse of part of an excavation must be included in the appraisal because failure in such areas could affect the stability of the remainder of the excavations. Appraisal of such areas may also provide information relevant to the safety of other parts of the excavation. Amongst other things, the appraisal should take account of the material to be excavated or tipped, its structure, water content/drainage, the proximity of watercourses, roadways, workplaces, residential accommodation or abandoned workings, and any evidence or history failures.
Records of the conclusions of appraisals are required to be kept available at the quarry. The conclusions of the appraisal should be included in the safety statement. Where the excavation, tip or lagoon is considered to be unsafe or likely to become unsafe in the near future, there should be a clear recommendation as to what action should be taken and when.
Little needs to be recorded in other cases where the appraisal is to be followed by a geotechnical assessment.
Where there is no significant hazard, the detail should be sufficient to explain the conclusions and how they were reached.
The appraisal should be reviewed at appropriate intervals and in particular in light of:
- significant changes to working methods;
- experience of the geology and hydrology on site;
- changes outside the site which significantly increase the hazard, for example, the construction of houses or roadways near the boundary;
- evidence of significant failure or movement; or
- discovery of incorrect assumptions or errors in the appraisal.
The hazard should be considered significant or potentially significant if such a failure would directly or indirectly, be:
- liable to endanger premises, roadways or other places where people are likely to be found offsite; or
- likely to cause serious or fatal injuries to persons on or off-site.
If the degree of hazard is not clear at the excavation, the advice of a geotechnical specialist should be sought. Where an appraisal of any excavation, tip or lagoon identifies a potential significant hazard that cannot be rectified immediately, the operator must engage a geotechnical specialist to carry out a site investigation to establish if a full geotechnical assessment is required. Even where a significant hazard or potential significant hazard can be rectified immediately by the operator, it may still be necessary to have a site investigation and/or a geotechnical assessment carried out to identify what caused the development of the hazardous condition, what if any effects it had or may have on the overall stability of the excavation, tip or lagoon and what actions are needed to prevent reoccurrences.
A geotechnical assessment means an assessment carried out by a geotechnical specialist identifying and assessing all factors liable to affect the stability and safety of a proposed or existing excavation, tip or lagoon. A geotechnical assessment may be preceded by a site survey and site investigation to establish critical information to assist in any full geotechnical assessment.
Further geotechnical assessments must be carried out at least every 2 years or as specified by the geotechnical specialist or in the event of:
(a) significant changes to the working methods;
(b) new information about the geology or hydrology of the site;
(c) changes outside the site which significantly increase the hazard, for example, the construction of houses or roadways near the boundary;
(d) evidence of significant failure or movement; or
(e) discovery of incorrect assumptions or errors in the site investigation and/or assessment.
The level of expertise required to carry out a geotechnical assessment depends on the complexity of the site and properties of the materials being worked, tipped or stored. The geotechnical specialist must have sufficient expertise and practical experience of similar conditions to adequately assess the safety of the excavation, tip or lagoon and the precautions required to make and keep it safe. The operator must ensure that any remedial work identified during a geotechnical assessment is carried out by the date specified by the geotechnical specialist. When deciding how long to allow for remedial measures, the geotechnical specialist should consider the risk involved. The greater the risk, the sooner the work needs to be completed.