Central District Projects

Loop 202 (South Mountain Freeway)

Controlled Rock Blasting


SMF Blasting Adverstisement Graphic - WEB-01-01-02

Connect 202 Partners, the developer responsible for building the 22-mile-long freeway for the Arizona Department of Transportation, anticipates that controlled rock blasting will be necessary in some locations west of 24th Street and beyond Desert Foothills Parkway beginning September 2017. For more information about controlled rock blasting, please see the Frequently Asked Questions below.

Controlled Rock Blasting Frequently Asked Questions  (FAQ)

General Information

What is controlled rock blasting?

Crews are using equipment to manually remove rock from the foothills along Pecos Road near Desert Foothills Parkway. If the rock cannot be efficiently broken manually, controlled rock blasting using small amounts of timed charges will be needed to fracture the rock for removal. The broken rock will then be removed and used as fill for the freeway. Controlled rock blasting is a standard construction technique used in many areas of the nation for many years without damage to property.

How will I be notified?

Residents and property owners within approximately 600 feet of the cut location where blasting is needed, will be notified five days prior to the onset of blasting. Once blasting begins in a cut area, it will continue for several weeks. Electronic message signs on Pecos Road and Desert Foothills Parkway will provide information on any temporary traffic restrictions. Information will also be posted to the project website: SouthMountainFreeway.com/Pecos. Residents may also sign-up for weekly traffic alerts online, call 1.855.SMF.L202 or email SMFinfo@C202P.com if they need additional information.

Will this work affect traffic?

To ensure the safety of motorists using Pecos Road and Desert Foothills Parkway, there will be temporary traffic restrictions during blasting activities. Message board signs on Pecos Road and Desert Foothills Parkway will provide advance notice of any traffic restrictions. If access to the Post Office will be interrupted, information will be posted in advance to alert customers.

What can I expect?

Most Ahwatukee residents will not experience any changes to their daily routine. Residents in Ahwatukee may hear sirens, and there will be temporary traffic restrictions on Pecos Road and Desert Foothills Parkway.

On the day of scheduled blasting activities, a siren will sound a five-minute warning, and crews will clear the area. A second siren will provide a one-minute warning. The actual controlled blast will only last a few seconds. Following the controlled rock blast, crews will clear the site, and an all-clear siren will sound. 

Who will conduct the blasting?

Connect 202 Partners, the developer hired to construct the freeway, has hired a blasting engineer, blasting consultant and third party vibration monitoring team with close to 100 years of combined blasting experience in Arizona and across the United States. The Connect 202 Partners’ team will conduct any required controlled blasting activities following industry best practices and in accordance with all applicable laws.

What is the schedule?

While crews are able to remove the rock without blasting at this time, controlled rock blasting may be required in some locations beginning in September 2017 where the rock cannot be efficiently broken manually. Once controlled rock blasting begins in a specific location, multiple controlled blasts may be required daily for several weeks. Residents and businesses within approximately 600 feet will be notified five days prior to the start of controlled rock blasting near their structures.

What do people feel?

Controlled blasting results in air pressure and vibrations.  Air pressure from controlled blasting travels slower than vibrations in the ground). If you are inside your house, you may first sense vibrations beneath your feet, followed by wall and upper structure motion “noise”. Certain structures may readily respond to the low frequency energy of airblast (lightly loaded structures, large exterior walls or highly peak roofs). As such, the duration of structure shaking may be longer than the duration of the ground motions alone. Farther from the blast, you may feel what you perceive as two blasts when indeed the structure may respond separately to the ground, then the air pressure. These vibrations will be similar to wind gusts of approximately 30 miles per hour.

Impact to Adjacent Structures

How will blasting affect adjacent structures?

Controlled rock blasting using modern technology does not adversely impact adjacent structures. Only proven and safe methods will be used.  Blasting companies must comply with standards that mitigate impacts to structures and conform to City of Phoenix ground vibration regulations, which are stricter than federal guidelines.

Property owners within one-half mile of potential blasting areas have been offered a free structure condition survey. These surveys document the current condition of the structure prior to any controlled rock blasting. Additionally, seismographs will be placed near the blast area to monitor vibrations and ensure they remain below regulated limits.

How does the blasting company protect nearby structures?

Blasters are trained, experienced experts in their field. They must comply with many strict safety and security regulations that cover transportation, storage and handling of explosives. Blasters also understand off-site impacts of blasting and know how to design each blast to minimize airblast and ground vibrations, keeping levels as low as practically possible while performing their job.

How will vibrations be monitored?

Blasting seismographs will be placed at the closest structures surrounding the blast site as a control measure to ensure that the amplitudes of airblast and ground vibrations are as expected and well within safe standards. Blasting seismographs are used for quality control and to protect your property. Blasting and seismic reports are reviewed after each blast, and provided to regulatory agencies. Blasting and seismograph records are always retained by the blaster for future reference in the event questions arise about the blasting. 

How will you know the vibrations are not exceeding regulated limits?

Seismographs will be used to measure and record vibrations and noise at structures nearest to the project. This will assure we are generating vibrations within the safe blasting zone. State-of-the-art, digital seismographs will be employed by qualified engineers. Vibration records will be provided to the contractor and permitting authorities. A database of ground vibration measurements will be developed and relied upon to assure compliance with safe criteria for all surrounding structures.

What if I know that cracks have formed since the blasting?

When controlled rock blasting is heard and felt, it is human nature to start looking for cracking around the house. Many homeowners subsequently will find a number of cracks, noted for the first time, and associate them with the blasting activities. Indeed, these cracks were present before blasting began and simply not noticed before. The use of small amounts of timed charges is specifically designed such that ground vibrations remain low, and no cracking will occur in structures. As such, it is important for you to become acquainted with the existing conditions of your home.

Prior to the start of blasting, C202P offered free structure condition surveys to homes within one-half mile of the areas where blasting may occur. This distance is about three times the distance typically surveyed by blasting companies.

If a property owner believes the controlled rock blasting resulted in new cracks, they may request a post-blasting condition survey which will be compared to their pre-blast condition survey report to determine if the cracks existed prior to the controlled rock blasting.

If cracks haven’t formed due to blasting, what is the cause?

Cracking in structures is normal and expected over time.

There are hundreds of reasons why cracks appear in construction materials with age, wear and tear and use of a home. The most common environmental and human factors that lead to cracking in drywall, stucco, masonry, wood and other materials include the following:

  • short- and long-term changes in temperature and humidity (leading to large expansion/contraction material strains)
  • water intrusion through cracks and around foundations from broken water pipes or leaking hose bibs
  • transient wind and earthquake loads
  • soil conditions at time of construction or changes in soils after construction (soft, wet clays, improperly compacted or poorly drained fill, expansive clays)
  • improper foundation design for the range of anticipated soil conditions
  • unsupported upper structure spans
  • inferior or “green” construction materials
  • normal, everyday household activities

All of these forces create strains in construction materials that often exceed those generated in structures from blasting within established safe limits and are often greater than the failure strain of the weaker material (such as drywall and stucco). Remember that minor cracking in construction materials is normal and expected. Extensive cracking may be a sign of structural problems, and an expert should be immediately consulted.

Maybe 10 or 20 blasts will not harm my house, but what about repeated blasting and long-term effects?

Many homeowners accept that ground motions measured outside their home below the safe blasting criteria will not cause cracking today. But what about the future? Do the effects of repeated blasting accumulate in structures such that defects will start showing up long after the blasting is done? This question was carefully researched by the U.S. Bureau of Mines (USBM) in a two-year blasting study. The USBM determined that as long as blasting takes place within the safe criteria, structure wall strains are far below the “elastic” or recoverable limit and do not accumulate or add over time. There has been no evidence that repeated controlled blasting has an adverse effect to structures.
Regulations

What are the safe standards for blasting?

Safe blasting standards were proposed by the USBM (shown below) based on over 40 years of studies that included direct crack observations correlated with ground vibrations. Frequency-based standards limit maximum ground velocity as a function of frequency at the peak velocity. Blasting below this line is safe as this line represents the 100-percentile (or level of assurance) that threshold cracking in wall materials, such a drywall, will not occur. Above this line, damage may occur at increasing intensities as peak velocity increases. These are the standards to which our project blasting will adhere.

These standards have been adopted as law by some state, county and city regulatory bodies for quarry and construction blasting. In the absence of regulations, this criterion is widely employed by blasters when blasting is conducted near structures and now serves as the industry standard for safe blasting in the U.S. for all types of structures and blasting in all types of geology. To this day, there has been no scientific study that challenges these standards. Standards established by the City of Phoenix are more stringent than federal requirements.

blasting-faq-figure1

How do structures respond to blasting?

Ground vibrations and airblast (air vibrations) are felt by persons inside structures even at very low levels of amplitude of 0.01 in/sec, far below levels that could possibly cause cracking. Excitations from blasting contain many different frequencies that may readily transfer into a structure, causing structure components to shake. When the predominant frequencies are close to the structure’s natural frequency (4-12 Hz for whole structures and 18-25 Hz for mid-walls), the structure may respond from motions in the ground and air, depending on the amplitudes. The inside “noise” you may perceive is associated with higher frequencies that may generate mid-wall motions, leading to rattling of loose objects resting on or against walls. These structure motions are very low in amplitude and are not harmful in any way but may startle and alarm you and leave you with the impression that damage may be occurring. However, no damages from blasting will occur at the levels we will be blasting, guided by the safe blasting criteria.

How does blasting relate to the Richter scale?

The Richter magnitude scale was developed in 1935 as a mathematical device to compare the size of earthquakes from a number of monitoring locations to establish the epicenter (origin) of a quake. On the Richter scale, a magnitude 5.3 might be computed for a moderate earthquake, and a strong earthquake might be rated as magnitude 6.3. Except in special circumstances, earthquakes below magnitude 2.5 are not generally felt by humans.

There is no direct comparison of the energy of vibrations from blasting with the Richter scale. The Richter scale is not used to express damage to structures as it does not represent intensity but rather magnitude. Therefore, it is not appropriate to compare Richter magnitude numbers to blasting intensity if cracking potential is being considered.

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Civil RightsTitle VI of the Civil Rights Act of 1964, and the Americans with Disabilities Act (ADA)

Pursuant to Title VI of the Civil Rights Act of 1964, and the Americans with Disabilities Act (ADA), ADOT does not discriminate on the basis of race, color, national origin, age, sex or disability. Persons that require a reasonable accommodation based on language or disability should contact ADOT’s Civil Rights Office at civilrightsoffice@azdot.gov. Requests should be made as early as possible to ensure the State has an opportunity to address the accommodation.

De acuerdo con el título VI de la Ley de Derechos Civiles de 1964 y la Ley de Estadounidenses con Discapacidades (ADA por sus siglas en inglés), el Departamento de Transporte de Arizona (ADOT por sus siglas en inglés) no discrimina por raza, color, nacionalidad, edad, género o discapacidad.  Personas que requieren asistencia (dentro de lo razonable) ya sea por el idioma o por discapacidad deben ponerse en contacto con la Oficina de Derechos Civiles en civilrightsoffice@azdot.gov. Las solicitudes deben hacerse lo más pronto posible para asegurar que el equipo encargado del proyecto tenga la oportunidad de hacer los arreglos necesarios.