Open Cut » Drilling & Blasting
ACARP Project C14057 is an investigation into the effects of blasting on mine infrastructure. The objectives of the project were to provide:
· A methodology for the assessment of infrastructure types and the establishment of realistic vibration limits for the prevention of damage based on structural integrity and responsible factors of safety;
· A methodology for the establishment of clearance distances to ensure prevention of damage and safety to infrastructure from blast vibration and flyrock; and
· A report giving realistic range of strengths for infrastructure types of concern to the coal mining infrastructure.
The infrastructure types chosen by the advisory committee were:
· Public roads;
· Railway lines;
· Concrete bridges;
· Conveyor structures;
· Power lines with timber poles;
· Power lines with concrete poles;
· Steel transmission pylons;
· Electrical substations;
· Fixed mine plant and industrial buildings;
· Underground workings;
· Buried communication cables;
· Dams; and
· Heritage structures.
Most of the listed infrastructure is constructed of concrete, timber and steel and the emphasis is placed on these materials.
The methodology for the assessment of vibration limits for the infrastructure items without
further detailed analysis can be summarised as follows:
· Ground motion from vibration results in a deformation of the ground surface that can be expressed as 'strain' within the elastic range of surface movement;
· The ground strain is transferred to structures as follows:
- Buried structures with a reduction of ground strain eg. Buried pipelines, underground workings.
- Elevated structures with a possible increase due to amplification by structure response e.g. buildings, towers.
- Structures sitting on the surface have a direct transfer e.g. roads.
· The strain on some structures can be expressed in strength of material terms which can be compared to working strains permitted by relevant Standards and Codes and used to determine either 'safe' PPV levels or factors of safety for applied limits.
· Ground strain is difficult to measure but it can be estimated from PPV by the following approximations:
- Plane wave strain theory (Dowding)
- Ground deformation (Angular Distortion)
· The amplification of the ground strain by different structures can be conservatively estimated from derived curves.
· Direct measurements of strain on structures usually lie between those given by the two approximations; plane wave strain approximations are usually higher than measured strain;
· The maximum strains on structures can therefore be conservatively determined if the PPV on the ground is known.
· The strains induced can be compared to strength of material methodology or serviceability criteria to determine 'safe' vibration limits to prevent damage.
The recommended 'safe' vibration limits for the infrastructure items investigated are tabulated in the final report.
THE FINAL REPORT IS AVAILABLE FROM THE ACARP WEB SITE