Estimating Rock Properties Using Sound Levels from Drilling
conditions, whereas noise level can be categorised into the range of observations. Once a vast domain range has been established based on experiments, a great deal can be predicted based on the relationship between noise level, rock properties and drilling parameters.
Drilling conditions may be a permutation of various parameters such as drill machine type, drill bit type, drill bit diameter, feed mechanism and various other drilling parameters such as thrust, RPM, etc. (see Figure 5). Rock properties that can be accounted for while talking about noise produced are compressive strength, density, abrasivity, etc. The most challenging part is understanding the noise produced. Noise produced cannot be assigned a discrete value; rather, it will be represented by a spectrum curve commonly called the frequency–loudness distribution curve. This feature will drag the relationship in two dimensions of frequency and loudness, because variations in domain will vary across the whole spectrum. An example of a noise spectrum curve is given in Figure 2.
It is clear from the above context that experiments will be perfomed with n number of rocks (with distinct properties) subjected to m number of drilling conditions to obtain a range set of n x m number of spectrum curves. A sample of the data that will be obtained is given in Table 4. The main aim is to end up establishing a mathematical equation that satisfies the observations. It is true that the path is very long, but there may be benefits along the way. These benefits are in the form of the database collected. Each time an experiment is performed to add new data to the database, there is an increase in the possibility of predicting the rock type, knowing the conditions and noise spectrum curve. This prediction can be done with a computer program, for which the fuel would be the
Figure 3: Effect of Compressive Strength of Rock on Sound Levels Near the Drill Bit for a Constant Thrust of 160N and Varying Air Pressure1
121.5 122.0 122.5 123.0
121.0 120.5 120.0
1,000
1,200 1,400 1,600 1,800 2,000 2,200 2,400 Compressive strength (kg/cm2
) 5.0 kg/cm2 5.5 kg/cm2 6.0 kg/cm2 7.0 kg/cm2
database. If a microprocessor is brought into picture, the maximum benefit can be obtained by creating a user interface in the program that can help the user to negotiate the field contours in a 3D interactive way.
The programme will have the provision to input drill conditions and determine the drill hole location. For each hole a noise spectrum curve will be input using a suitable device, such as a noise spectrum analyser. These noise spectrum curves may vary with the depth of the hole (especially at the surface where two different rock layers are in contact). All of the input data will be compared with a database (corresponding to a particular drill condition). Based on the result, a 3D
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A-weighted sound level (dB)
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