Report No. : GEO Report No. 260

Report Title : Study on Methods and Supervision of Rock Breaking Operations and Provision of Temporary Protective Barriers and Associated Measures (2011), 250 p.

Author : Halcrow China Limited

Abstract

This report documents the findings of reviews of local and international practice, published and unpublished literature, experience of study team members and liaison with industry with respect to excavation of rock slopes. It also provides recommendations on good practice for rockfall hazard assessment, rock slope excavation, contractual arrangements and the use and design of temporary rockfall mitigation measures, with particular emphasis on roadside slopes.

The study emphasises that rockfall hazard assessments should be carried out throughout a project with a view to the prevention of rockfalls or mitigation of their impacts. Three stages of assessment have been defined. It is emphasised that it is impossible to predict all hazards through any method of rock mass assessment and that, in high consequence situations, extreme measures such as road closure during critical periods of construction should be considered.

Several aspects of the formation of rock slopes using mechanical, chemical and blasting methods are reviewed and discussed. The study reviews the advantages and disadvantages of each type of method with respect to ease of excavation and contribution to risk. The study recommends a number of improvements that could be made to the general and particular specifications.

The study recommends that barriers may be selected according to specific parameters derived from simulations of a specific design rockfall event. It is concluded that both rockfall prevention (insitu slope treatment) and rockfall protection (roadside barriers) should be considered. In the case of roadside slopes, temporary traffic management measures should always be considered and put in place where necessary to mitigate the risk.

Finally, the Report recommends improvement to rockfall hazard assessment, site supervision and traffic management. Conclusions are drawn concerning excavation methods, use of rockfall mitigation measures and the use of well-conceived contract clauses at all stages of a project. The study concludes that good and safe practice is best achieved when all of these issues are monitored, appropriately revised and addressed throughout the various stages of a project.

GEO has incorporated the recommendations relating to safe breaking of rock on roadside slopes in the Highway Slope Manual (GEO, 2000) and Technical Guidance Note No. 14.

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