Abstract
The aim of this study is to predict peak particle velocity level at a limestone quarry located in Istanbul, Turkey. The ground vibration components were measured for 73 blast events during the bench blast optimization studies during a long period. In blasting operations; ANFO (blasting agent), gelatine dynamite (priming) and NONEL detonators (firing) were used as explosives at this site. Parameters of scaled distance (charge quantity per delay and the distance between the source and the station) were recorded carefully and the ground vibration components were measured by means of vibration monitors for every event.
Then, the data pairs of scaled distance and particle velocity were analyzed. The equation of scaled distance extensively used in the literature was taken into consideration for the prediction of peak particle velocity. At the end of statistical evaluations, an empirical relationship with good correlation was established between peak particle velocity and scale distance for this site. The established relationship and the results of the study are presented.
1. Introduction
Ground vibrations and air blasts are the parts of rock blasting. Therefore, they are unavoidable. With high intensity of wave motion, they can damage nearby buildings. Thus, the technical and economical aspects, such as block size, uniformity and cost, should be taken into consideration together with the elimination of environmental problems resulting from ground vibration and air blast by blasting engineer in bench blast designs. The prediction of ground vibration components has a great importance in the minimization of the environmental complaints. Estimating the particle velocity and other components of ground vibration with reliable approaches will be very useful in blast design [1–3,5].
2. Test site and procedure
2.1. Test site description
An extensive research program was carried out at a quarry named Sarikayatepe which belongs to Akcansa
cement company in order to establish a reliable formula for the prediction of peak particle velocity and to minimize the environmental problems arising from blasting. The test site is located near Istanbul and the layout of the quarry including the shot points and monitoring stations is shown in
Fig. 1.
As it can be seen from Figs. 2 and 3, the blast holes were vertical and 105 mm in diameter for all benches. Hole lengthwas 22 m with 1 m of sub-drilling and 6 m of stemming for first and third benches and was 32 m with 1.5 m of subdrilling and 6.5 m of stemming for second and fourth benches. In blasting operations, ANFO C5% Al (blasting agent), Rovex 650 and gelatine dynamite (priming) were used as explosives for all blasts. Non-electric millisecond delay system was used to initiate the blasts. The blast-timing pattern was designed to allow a 42 ms delay between rows and a 17 ms delay between holes within a row. Inner hole detonator was used as 25 ms interval.
Fig. 1. Layout of the quarry including the shot points and monitoring stations
2.2. Text procedure
The ground vibration components were measured for 73 blast events in order to predict peak particle velocity for this site during bench blast optimization studies over a period of 10 months. In this study, while the parameters of scaled distance (charge quantity per delay and the distance between the source and the station) were recorded carefully, the ground vibration components were also measured by means of two vibration monitors (Nitro Consult UVS 1504 and Instantel Minimate Plus models) for 73 blast events as shown in Fig. 1. The specifications of these monitors are nearly same. However, calibration between two types of vibration monitors should be put into consideration at the beginning. For this reason, some test shots were fired, and acceptable results were obtained. The scaled distance equation suggested mostly for cylindrical charge in the
literature was used for the prediction of peak particle velocity and this equation is given below
where SD, scaled distance; R, distance between the shot and the station (m); Wd, maximum charge per delay (kg).
Peak particle velocities (PPV) have been calculated from the following equation that is widely used in various studies
where K and b represent the influence of blast design and geology.
For predicting the peak particle velocity for this site, the developed blast design was applied accurately for each shot. The maximum amount of instantaneous charges per delay was recorded carefully and the distance between the shot point and the monitoring station was measured accurately by using survey equipment.
Fig. 2. Layout of the test benches of the quarry.
Fig. 3. General blasting pattern for Sarikayatepe limestone quarry.
3. Test results and discussion
The damage from vibration induced by bench blasting has been evaluated on the basis of its peak particle velocity related with corresponding dominant frequency. A large number of blasts (73 events over a period of 10 months) were monitored for recording the peak particle velocity in order to develop a similar formula. The results of ground vibration measurements that were carried out at the limestone quarry, including peak particle velocity, frequency, total charge, charge per delay, distance and scaled distance have been presented in Table 1 for a few events as sample. In order to establish a useful relationship between peak particle velocity and scaled distance, simple regression analysis was carried out by using all data pairs. In simple regression, linear, logarithmic, exponential, reciprocal and power curve fitting approximations were tested and the best approximation equation with highest correlation coefficients was determined.
At the end of the study, this determined equation for limestone zone is found to be in accordance with the literature and the equation can be used to eliminate
Table 1
Results of ground vibration measurements [7]
Table 2
Summary of simple regression output
Fig. 4. Peak particle velocity versus scaled distance.
environmental problems for the events that the vibrations will not be monitored. The formula, which has 95% confidence level, is given below
The empirical factors K and b are determined as 340 and K1.79, respectively, for this site. The results of the
regression and correlation have been presented in Table 2 in detail. The graph of the obtained relations between the particle velocity components and the scaled distances are also presented in Fig. 4.
Table 2 shows the statistical calculations using the full data set consisting of 73 shot events. It shows the standard summary output of the SPSS (statistical analysis software) regression analysis performed within the data analysis tool. The R square quantity is a basic measure of the quality of the fit. In this case, a value of 0.861 indicates that 86.1% of the PPV variability is explained by the linear regression. The intercept coefficient is obtained from the linear regression in the log–log transformed space. It should be noted that 102.532 equals 340.40 which is in agreement with Fig. 4. Finally, the critical slope
Table 3
Calculated and measured values of peak particle velocity
Fig. 5. Comparison of the established formula with some previous PPV prediction approaches [1,8,9]
value of K1.793 is easily extracted from the summary output. Hence, given a particular scaled distance, we offer a best guess as to the PPV as well as upper 95% prediction limit below which we expect future blasts to occur [4,6]. The upper 95% prediction limit line was generated from the standard error and data distribution curve by means of SPSS (version 10) software (Fig. 4).
Additionally, the relation was also tested and it can be seen that the measured and calculated values of PPV were fairly close (Table 3). As it can be seen from Table 3, the established relation at upper 95% prediction bound was also tested and the measured values of PPV were obtained below the line.
Meanwhile, the equation established as a PPV predictor is also compared to some previous ones in Fig. 5. By studying this graph carefully, the comparison shows that the formula developed for limestone zone is also in accordance with the literature. This case has proved that it can be possible to design blasting reliably by using this formula for the site.
4. Conclusions
Environmental constraints will be restrictive more and more on mining activities. So, the measurement of ground vibration induced by blasting is significantly important on controlling and elimination of environmental problems. Since the particle velocity is still one of the most important ground vibration predictors for regulating the blast design, an empirical relationship with good correlation has been established between peak particle velocity and scaled distance for this site where host rock is limestone. Using this relation, practical charts should be prepared for various charge levels and distances to control blasting for this quarry. This empirical formula obtained from 73 data pairs can only be used to provide approximate levels of the particle velocity. It must be taken into consideration that its use in the blast design could give erratic results. In order to support this formula more events should be monitored in various directions and the regression analysis should be updated considering the results of further measurements. Additionally, this formula should also be revised depending upon the time and progressing of the pit.