Ground Vibration and Air blast
It is common for measurements of ground and air vibrations to be made during blasting, to ensure compliance with statutory requirements. Although these measurements are sometimes essential from a public comfort and damage point of view, they provide little useful information for blast performance evaluation.
One measure of blasting performance is the size distribution of rock fragments. Practical methods for distribution of rock fragmentation vary from simple visual estimates to more complex photographic techniques.
The ideal way to assess fragmentation is to pass all of the rock through a series of calibrated screens. This technique is suitable for small test blasts, but is not appropriate for production blasts in mines.
The most common method of assessing fragmentation is a simple visual estimate of fragments on the surface of the muck pile. This may adequate for detecting gross problems, but is too subjective for a thorough blast assessment program.
Muck pile Displacement
1. The maximum throw, which is a measure of the horizontal disc placement;
2. The horizontal displacement of the centre of gravity, which is a measure for the average forward displacement and
3. The muck pile well which is a measure of the over all movement and loosening of the rock mass.
Hence parameters are usually quantified by surveying the muck pile after the blast, and comparing those to pre-blast measurements. Laser profiling equipment can be used to collect this information more quickly and safely than conventional surveying techniques.
Blasting may produce unwanted damage, in the form of over break beyond the design limits of the blast.
Digging Equipment performance depends on the fragmentation, position, shapes and looseness of the muck pile. Productivity of draglines, shovels, excavators and front-end loaders can be monitored to provide an overall measure of blast performance. As performance of this equipment depends on individual operators, measurements should be made over an extended period of time.
The functions of digging and loading equipment which can be monitored, to assist with blast performance assessment, are:
1. Bucket fill factors
2. overall productivity
3. time lost in handling oversize
4. Downtime for clean up, maintenance on buckets etc.
Measurement and recording these parameters are labour-intensive and time consuming as it is difficult to automate the collection of useful data. On-board monitoring equipment can now be used to record relevant information for production and maintenance planning, and is developing to a stage where it is possible to assess blast performance by measuring digging rates.
Effective blast performance assessment can be achieved only if adequate information is collected before, during and after the blast. To understand the factors which produce different results, including unwanted side-effects, information must be recorded for later analysis.
Simple report sheets can be used to record the essential information, to avoid any misunderstanding or reliance on memory alone. The relevant information for each operation depends to some extend on local conditions and requirements, but some factors are common to all blasting operations. Once a recording system has been established, it is relatively simple to develop it into a comprehensive data base, using a computer to store, manipulate and report relevant information. Such systems allow input of downstream actives such as diggability and could calculate a bottom line cost.
A video tape of each blast is simple and powerful recorded image that can easily be tagged and kept for future reference.