Between November 2019 and May 2021, controlled blasting was used to excavate bedrock on the Paskapoo Slope and another small area south of Crestmont Boulevard S.W. As of April 2021, a total of 211 controlled blasts have cleared 1.7 million cubic metres of rock.
The excavation to the designed grades is now complete and daily controlled blasts are no longer needed. Localized, intermittent blasting will still be required to excavate two stormline trenches on both sides of Stoney Trail between the Trans-Canada Highway and Old Banff Coach Road S.W.
None of the daily blasts in April 2021 generated ground vibrations of a sufficient amplitude to produce a seismograph waveform report (associated values are still retrieved from the histogram data and published on this page). Given this, the shallow depth of the localized blasts and the sporadic timing, notice will not be provided for intermittent blasts going forward. However, seismographs will continue to monitor ground vibrations and the reports will continue to be published each week.
Controlled blasting involves drilling into the rock and placing a controlled amount of explosive charges below ground at engineered locations to fracture the rock. Quantity of charges, drill lengths, locations and cover are all engineered to minimize or eliminate impacts like flying debris, vibrations, sound and dust.
Controlled blasting was used on the West Calgary Ring Road where the excavation could not be completed using conventional heavy construction equipment. While this method of fragmenting rock for excavation is less common in Calgary, particularly near residential areas, it is very common in Ontario and British Columbia where the landscape is rocky.
Daily controlled blasting in this area is now complete. Localized, intermittent blasting to excavate two stormline trenches on both sides of Stoney Trail between the Trans-Canada Highway and Old Banff Coach Road S.W. will continue until Fall 2021.
A small area south of Crestmont Boulevard S.W. was excavated using controlled blasting between April and September 2020. Blasting in this area is now complete.
What to expect
Most of the explosive energy during a controlled blast is expended in fragmenting and heaving the heavy rock, but a small portion of this energy passes beyond the immediate blasting area in the form of elastic ground vibrations and air overpressure.
If blasting is occurring near your home, you can expect to feel vibrations and perhaps hear some noise. However, the vibration levels are normally lower and no more potentially damaging to your building than those caused by slamming a door, windstorms and thunderstorms, or children running and jumping around the house.
The energy in a blast which does not contribute to breaking rock is dissipated in the form of vibration either travelling through the ground (ground vibrations) or through the air (air overpressure). Ground vibrations are elastic waves that cause ground particles to displace momentarily, however, at the frequency and intensity of vibrations created by blasting, the ground particles rarely experience any permanent change in their relative position. As in, once the ground stops vibrating, it will be situated in the exact same position as where it began. Ground vibrations are complex and are measured by intensity (velocity) and frequency in three dimensions.
Intensity (velocity) is the speed at which the ground vibration waves cause particles to move. This is called Peak Particle Velocity (PPV) and is measured in millimetres per second.
Frequency is the number of ground vibration waves within one second. This is measured in Hertz (Hz) (cycles per second).
Air overpressure is the vibrations caused by the blast that travel through the air. Typical residential structures will respond to the air overpressure wave by producing higher frequency secondary noise on internal walls. It is this response along flat walls in a structure that causes much of the rattling and other observed effects such as movement of pictures, clocks, etc. This experience is often mistaken for ground vibrations.
In technical terms, the air overpressure generated by controlled blasting is quite similar to the effects of wind. However, the rapid pressure change produced by an air pressure wave can be startling and much more noticeable compared to a more constant and sustained period of wind. A 40 km/h wind can generate equivalent stress on a structure as a blast-generated air overpressure of 131.7 dB(L). To provide context, the seismographs installed in the Cougar Ridge blasting area since November 2019 have regularly measured air overpressures just from wind exceeding 130 dB(L).
While the blast design will dictate the levels of air overpressure generated, the dissipation of overpressure energy compared to ground vibrations is heavily dependent on environmental conditions such as wind, temperature and other current weather conditions.
We heard residents near the blasting area were uneasy about the vibrations resulting from the blasts and noticed increased rodent activity in their yards. We also heard residents would like advanced notice about when blasting will occur and more communication. In response, Alberta Transportation:
- Established a consistent blasting schedule so residents knew when to expect vibrations.
- Committed to publishing the seismograph reports for the previous week every Tuesday.
- Held four information sessions for residents to speak with the experts.
Determining a threshold for damage
The United States Bureau of Mines (USBM) conducted substantial research to understand and document the impact of blast vibrations on structures. This research is documented in the Report of Investigations 8507 Structure Response and Damage Produced by Ground Vibration From Surface Mine Blasting.
Report of Investigations 8507 (RI8507) established baselines for measuring, analyzing and mitigating blast-induced vibrations. RI8507 outlined a threshold for damage caused by vibrations called the ‘USBM Z-Curve’. These guidelines are the most extensive and factually supported scientific research to date on the effects of blasting vibrations on structures and have been almost universally adopted as the industry standard for blast vibration control. In the years since RI8507 was released, countless additional studies have confirmed the accuracy of the findings.
The Z-Curve line establishes a limit above which damage becomes possible, but it is crucial to note that damage does not automatically occur once this limit is breached. Damage would not actually occur in the average residence until ground vibrations reached significantly higher intensities than those outlined by the USBM Z-Curve. If the Z-Curve criteria is exceeded, the probability of damage is merely introduced and will incrementally increase with higher and higher vibration amplitudes.
Vibrations are occurring around us every day and are highly subjective. Each individual’s perception and tolerance will influence the degree to which vibrations are a nuisance or objectionable. Humans and animals are far more sensitive to vibrations than a two-storey timber framed house, bridge or other structures.
Blasting in close proximity to buildings
Explosives are commonly used across North America in close proximity to man-made structures. For example, blasting is often used to install utilities (gas lines, watermains, telecommunication lines) beside existing roads and buildings or create swimming pools adjacent to existing houses. Urban blasting operations are frequently used in dense downtown cores to construct underground parking garages on new high-rise developments within 5m to 10m of adjacent structures. Blasting has even been successfully undertaken directly beneath Canada’s historic Parliament Buildings as part of the recent West Block Rehabilitation.
The intensity and frequency of vibration is what can initiate damage to a structure, not the physical distance between the blasting and the structure. Blast designs and regulations account for complying with guidelines at the distances to the closest adjacent structures.
The intrinsic nature of blast induced vibrations is to decrease as distance from the blast increases. While the nature of the transmitting medium (rock, soil, etc.) and the presence of geological features can impact how quickly the ground vibrations dissipate, vibration intensity diminishes with increasing distance.
Effects of repeated blasts
The United States Bureau of Mines (USBM) studied the repeated effect of vibration on structures and found that fatigue effects from typical blasting operations are negligible. The USBM conducted two studies using full-sized homes to specifically delineate the effects of fatigue associated with recurrent blasting. When continuously vibrated at an equivalent ground particle velocity of 12mm/s, no adverse response was observed until 52,000 cycles was attained, at which point a taped drywall joint potentially cracked. To reach 52,000 cycles on the West Calgary Ring Road project would take more than 165 years at an average of six blasts per week.
The USBM RI8507 limits account for cumulative or fatigue effects associated with recurrent blasting.
Predicting and measuring vibrations and overpressure
Experienced Blasters can predict the extent of ground vibrations and air overpressure which will be produced based on the amount of explosives being detonated and the distance between the controlled blast to the adjacent structures.
Sophisticated seismographs that measure and record both ground vibration and air overpressure have been installed at several locations along the property line of the closest homes to the blasting area (please see the controlled blasting area map for locations). Each seismograph is thoroughly tested to verify its accuracy (calibrated to National Institute of Standards and Technology (U.S. Department of Commerce) (NIST) and United States Nuclear Regulatory Commission (NRC) standards) before being approved for installation in the field. An independent engineering consulting firm also performs tests in the field once the seismographs are installed to check for any instrumentation failures.
Following each blast, the seismograph recordings are analyzed by an independent consulting engineering firm specializing in explosives and their associated environmental effects. Should discrepancies appear during the analysis of the records, the independent consulting company immediately notifies the blaster and contractor so the instrument can be rechecked. If the instrument is found to be operating incorrectly, it is replaced.
Instrument accuracy is critical for all project stakeholders. Safe blasting that adheres to regulations and protects public safety and property is paramount. Consistent monitoring also allows the blasting designers to adjust and improve the blasting operation.
The seismograph locations have been strategically designed by the independent consulting engineering firm to obtain a representative sample of ground vibration and air overpressure at the properties closest to the blast. The seismographs are measuring the experienced vibration levels at the buildings where they are placed but also serve to represent the ground vibrations and air overpressure for neighbouring structures. As a result, a seismograph is not needed at every structure to accurately measure vibrations within a particular area.
Humans are sensitive to vibrations
If blasting is occurring near your home, you can expect to feel vibrations and perhaps hear some noise. However, the vibration levels are normally lower and no more potentially damaging to your building than those caused by slamming a door, windstorms and thunderstorms, or children running and jumping around the house. Research has shown that a seismograph inside a home can often record higher vibration levels from resident activity than from blasting operations in the vicinity.
Vibrations from blasting can feel stronger than other similar vibrations that are more common.
- Blast vibrations are sudden and startling which amplify the perceived intensity.
- Humans are generally sensitivity to vibrations, and some are more sensitive than others. Individual perception and responses can vary from person to person, building to building or situation to situation.
- The type of surroundings at the time of the blast also influence individual perception (outside, inside, upper or lower floor of your house).
The unique position, orientation and design of each blast on the construction site can also cause the perception of one blast to be stronger than another.
The USBM RI8507 report noted these anecdotal responses to varied intensities of vibrations:
|Peak Particle Velocity||Human response|
|Greater than 0.5 mm/s||Noticeable|
|Greater than 5.0 mm/s||Troublesome|
|Greater than 17.8mm/s||Severe|
The important point is that people are more sensitive to blasting vibration than their homes. The unfortunate suddenness coupled with sensitivity to concurrent vibrating floors, walls and windows worsens the perception and the blast seems more harmful than it really is. This is why scientific instruments, seismographs, are used to accurately evaluate the relative blast effect and amount of motion generated.
Disruption of small wildlife population
Some residents in Cougar Ridge, adjacent to the road right-of-way, reported an increase in moles, voles and other small wildlife entering their property around the same time as controlled blasting began. Alberta Transportation set several vole traps along the Transportation Utility Corridor boundary (with the approval of Alberta Environment and Parks) to address the concerns about increased rodent activity.
Moles, voles and other wildlife are natural to the environment; their populations and location are not managed by the Province or The City of Calgary. Wildlife management on private property is the responsibility of individual homeowners. This includes all costs associated with the removal and repair to gardens or landscaping as a result of these rodents.
Signs of voles include chewed fruit, golf ball-sized holes and tunnels that look like cracks in your lawn. If you think you have voles, here are some general tips for getting rid of them:
- Limit potential food sources like vegetables left in the garden
- Keep any seeds and/or bird feed in rodent-proof containers and regularly clean below bird feeders
- Clear snow over problem areas and/or collapse any tunnels noticed beneath the snow
- Remove mulch from the base of fruit trees in winter
- Place gravel or cinder barriers around garden plots
- Limit desirable habitat by keeping lawns short and remove loose vegetation debris (i.e. grass clippings, leaves)
- Use rodent repellents, such as castor oil or “Critter Ridder” sprays/granules, in the spring
- Wrap chicken wire or mesh around the base of trees to help prevent tree girdling
This City of Calgary webpage has some additional information about controlling voles.
Damage claims process
Homes or businesses are identified for voluntary inspections based on industry best practices. Depending on the depth of the blasting, typically homes or businesses within 150 metres or less of controlled blasting operations are offered voluntary inspections.
For the controlled blasting near Cougar Ridge, which started in November 2019, voluntary home inspections were offered to residents within a specific area (shown on the Cougar Ridge controlled blasting area map) prior to the start of blasting. The home inspections included video and photographic documentation.
For the controlled blasting near Crestmont, no homes or businesses are within 150 metres of the controlled blasting operation. Voluntary inspections are not required in this area.
If you have questions about blasting or are concerned about damage to your home, please email firstname.lastname@example.org. A response will be provided in one business day.
An independent consulting engineering firm specializing in blasting and its associated environmental effects will review each claim and provide a professional opinion about whether or not the damage was caused by West Calgary Ring Road construction. If the damage is proven to have resulted from construction, Alberta Transportation will ensure the situation is resolved in a timely manner.
Required qualifications for a Blaster
Under Alberta’s Occupational Health and Safety Regulation and Occupational Health and Safety Code, anyone who handles, prepares, fires, burns or destroys an explosive for non-mining work must hold a valid permit from Alberta Labour. Through courses, written exams, experience and apprenticeships, blasters learn how to properly design blasts that control rock breakage, influence rock fragmentation and account for ground vibration and air overpressure levels.
Blasting company experience
McCaw’s Drilling & Blasting Ltd. was incorporated in 1977 and has worked on numerous projects in the pipeline, construction and mining industries, including highway projects, marine crossings, permafrost piling and rock blasting projects.