Presentation on theme: "PRESENTATION FOR LAFARGE CANADA INC. LAFARGE BATH QUARRY CONTROLLED QUARRY BLASTING TECHNIQUES AND EFFECTS AND IMPACTS OF BLASTING-VIBRATION AND NOISE."— Presentation transcript:
PRESENTATION FOR LAFARGE CANADA INC. LAFARGE BATH QUARRY CONTROLLED QUARRY BLASTING TECHNIQUES AND EFFECTS AND IMPACTS OF BLASTING-VIBRATION AND NOISE Presented by Salvatore Oppedisano, P. Eng. Dury Consultants, division of Inspec-Sol Inc.
CONTROLLED QUARRY BLASTING TECHNIQUES During the past 80 years or so, there have been many innovative changes to the explosives industry and to quarry operations The changes involve product development, manufacture and ultimately final use. Many of the changes have contributed greatly to safety in the handling of explosives and to the flexibility of use for different applications. There are many more regulations and restrictions than existed even a few decades ago. The quarry operator is instructed, guided and restricted for the protection of persons and their property.
CONTROLLED QUARRY BLASTING TECHNIQUES (cont’d) The quarry operator must properly design each of his blasts. Many factors and parameters affect the proper fragmentation and impacts of blasting. Some of these factors and parameters include: Explosive type, loading densities and weights; detonator delays and firing sequence; decking lengths; rock type and jointing (geology); spacing of holes; distance between holes and free face (burden); depth of inert stemming. Controlled blasting is a term that describes all techniques to reduce impacts and effects of blasting and damage to unfragmented rock. The Standard Operating Procedures of the Lafarge Canada Inc (Bath Quarry) have been created with Quality Control in mind and meet the objectives of controlled blasting operations.
EFFECTS AND IMPACTS OF BLASTING-VIBRATION AND NOISE Human response is a factor that is primarily responsible for an entire branch of the explosives industry. Earthquake seismoscopes were known in China centuries ago (B.C.) “How big was that blast on the Richter Scale?” People exposed to blasting operations ask this question quite often. The following is a rough estimate of Richter magnitudes for various explosive weights. VIBRATION 200,000 20,000 2, Pounds of Explosive Richter Magnitude
EFFECTS AND IMPACTS OF BLASTING-VIBRATION AND NOISE (cont’d) The Loma Prieta earthquake of 1989 in San Francisco of magnitude 7.0 could be duplicated if you detonated a billion 200 pound charges. All blasts create ground vibrations. When explosives detonate in a borehole it creates shock waves that crushes material adjacent to the borehole. As this wave travels outward, in becomes a seismic or vibration wave. The situation is similar to the circular ripples produced on the surface of a pool of calm water when it is struck by a rock. Under typical conditions, the blasting vibration intensity dies out (like on water) to become about 1/3 of its previous value each time the distance is doubled. e.g.,250 ft1 full wave 500 ft1/3 of wave 1000ft1/9 of wave etc. Eventually, the wave completely dies out and has zero intensity. VIBRATION (cont ’d)
EFFECTS AND IMPACTS OF BLASTING-VIBRATION AND NOISE (cont’d) It is false to allege that the vibration wave by passes the nearest property and intensities further away. As a reference, the approximate vibrations caused by common everyday activities would be the following: Door slamming – 12.5 mm/sec. Jumping on the floor – 25.0 mm/sec. The following is a comparison of regulations. The Office of Surface Mining (OSM) in the U.S., has recommended guidelines to follow to conform to its regulatory limitations. This is a simplified approach. The following are the peak particle velocities: 0 to 300 ft from blast – 32 mm/sec. 301 to ft from blast – 25 mm/sec. > ft from blast – 18.5 mm/sec. In Quebec, the Ministry of Environment limits vibrations to 40 mm/sec. at 30 m from any structure. In Ontario, the MOE recommends a vibration of 12.5 mm/sec. at the structure. VIBRATION (cont ’d)
EFFECTS AND IMPACTS OF BLASTING-VIBRATION AND NOISE (cont’d) The OSM guidelines were intended to eliminate the likelihood of damage to structures and reduce level of complaints from neighbours. These guidelines include safety factors. In Ontario, the limit was reduced to 12.5 mm/sec. (from 18.5 mm/sec. in U.S.) to add an additional safety factor and reduce complaints further. To put this level into context, blasting operations were carried out on Parliament Hill in 1997 and the general vibration limit used was 17.5 mm/sec. for blasts with quarry type frequencies and all structures were intensely monitored during the operations. After 300 blasts, no visible changes or extension of cracks were noted. Ground vibrations caused by quarry blasting operations can be controlled by adjusting certain parameters in the blast design as mentioned previously. VIBRATION (cont ’d)
EFFECTS AND IMPACTS OF BLASTING-VIBRATION AND NOISE (cont’d) A comprehensive vibration monitoring program has to be part of every quarry operation to be used as an effective tool for finding the best balance of stone production vs. the impact on the neighbours. A review of vibration intensities for blasts in 1999 – 2000 – 2001 reveals that vibrations recorded at neighbouring properties fall in the less than 5 mm/sec. range which conforms to MOE recommendations. VIBRATION VIBRATION (cont ’d)
EFFECTS AND IMPACTS OF BLASTING-VIBRATION AND NOISE (cont’d) In any well controlled blasting operation, the presence of marked air blast effects increases public response and the possibility of complaints. Air blast effects originate from quarry operations particularly when the rate at which the explosive gases escape from improperly stemmed holes or from a plane of weakness (seam, joint, fault) in geology in the free face of the blast. The air displacement (air pressure) propagates at the speed of sound and has an audible noise level. Thus air blasts are measured in decibels. Many structures have natural resonant frequencies close to or equivalent to the air pressure wave. This possibility of resonance causes repetitive pressures on the structure which produces the vibration effects of ground transmitted vibration. NOISE (AIR BLAST)
EFFECTS AND IMPACTS OF BLASTING-VIBRATION AND NOISE (cont’d) Weather conditions such as the presence of temperature inversions (low clouds, ceiling) and strong winds blowing towards populated areas can magnify the levels of air pressures measured in decibel. Studies by the U.S. Bureau of Mines have concluded that if an air blast is under 134 dB, the probability of damage is near zero. Furthermore, an air blast does not exert a force on basement walls of structures. An air blast of over 140 dB is needed to cause damage to the weakest element of the structure, the windows. The air pressure limit of 134 dB is equivalent to a wind velocity of 20 mph. Pressure limits for 70 mph winds fall in the 149 dB level. Therefore, this is consistent with conclusions that damage probability is near zero for less than 134 dB air pressures. In Ontario, the MOE recommends that air blasts resulting from quarry blasts be kept to a level of 128 dB or less. Once again this level is below OSM and U.S. Bureau of Mines recommended levels. NOISE (AIR BLAST) NOISE (AIR BLAST) (cont ’d)
EFFECTS AND IMPACTS OF BLASTING-VIBRATION AND NOISE (cont’d) The review of air pressure measurements from blasts in reveal that when recorded at the structures of neighbouring properties these were generally below the 128 dB target. Air blasts caused by quarry blasting operations can be controlled by properly supervised drilling and loading operations, proper inspection for geological deficiencies and regular verification with national weather services so that timing of blasts could be optimised for reduction of air blasts. Studies have shown that vibrations without marked air blast effects are perceptible by humans at a level of 1.5 mm/sec. The blasts with marked air blast effects are perceptible at 0.5 mm/sec. (refer to graph). NOISE (AIR BLAST) NOISE (AIR BLAST) (cont ’d)
in/sec safe structure limit Intolerable Unpleasant Perceptible Unpleasant 10 mm/sec Unpleasant Complaints Likely 5 mm/sec Perceptible 1.5 mm/sec Perceptible 0.5 mm/sec 50 mm/sec FREQUENCY. cps PARTICLE VELOCITY in/sec STEADY STATE MOTION IMPULSIVE VIBRATION WITHOUT MARKED AIR BLAST EFFECTS IMPULSIVE VIBRATION : WITH MARKED AIR BLAST EFFECTS SUBJECTIVE RESPONSE OF HUMAN BODY TO VITRATORY MOTION
EFFECTS AND IMPACTS OF BLASTING-VIBRATION AND NOISE (cont’d) So the question is “What causes damage to a structure?” Excessive vibrations can cause damage to a structure, but other typical environmental forces do cause damage to structures. These forces include: Changes in temperature; changes in moisture (relative humidity); differential application of internal heat; ageing involving both chemical and physical deterioration; gravitational loads; water in soil. A sudden change of 12°F can cause stress on the elements of a structure which are the equivalent to vibration levels more than 50 mm/sec. A Swedish study conducted from 1965 to 1980 on several buildings concluded normal ageing of structures exposed to environmental constraints (no blasting) resulted in the formation of new cracks or deterioration of existing cracks on a yearly basis (see graph). NOISE (AIR BLAST) NOISE (AIR BLAST) (cont ’d)
Line added Apartment House 1 Apartment House 2 NUMBER OF CRACKS YEARS NUMBER OF CRACKS VERSUS BUILDING AGE (HOLMBERS ET AL, 1981)
CONCLUSION Quarry blasting operations can be conducted with minimised impact to the surrounding neighbours and taking into consideration the economics of quarry operator. Ground vibrations and air blast effects are in fact waste energy left over after the explosive products have performed their intended use which is properly fragmenting the rock. Therefore, for economic reasons and establishing good public relations, quarry operators strive to minimise these effects. When it comes to a quarry operation in proximity of inhabited areas, the technical and scientific knowledge is available to properly address a situation that exists in many communities across North America.