Posts Tagged ‘blasting’

Decade Long Eleven State Study of Blasting Damage Claims

Friday, November 7th, 2008

 Recently, VCE Inc. completed a 10 year, 11 state engineering study of 2,250 blasting damage claims from 1999 to 2008. These investigations were made in Tennessee, Kentucky, Virginia, Nevada, California, Georgia, South Carolina, North Carolina, Alabama, Arizona and Utah. The investigations were made over the last decade and intended to determine if blasting vibrations, or other related forces, were responsible for claimed damages. It was determined that blasting damage claims resulting from ground vibrations damage are valid less than 1.3 percent of the time.

I decided to publish this information in an article in order to address a reoccurring question I have received from many adjusters and homeowners. “Does blasting ever cause damage to structures?” The details of this study and the examples of specific blasting damage and non-blasting related damage causation conditions are best detailed in a short seminar where numerous photos could be used to illustrate some of the study’s findings.

It was determined that valid blasting damage occurred as a result of impact damage associated with fly rock, air concussion stressing, instantaneous reverse stressing associated with ground vibration and crater zone soil shifting related stressing.

The majority of the claimed blasting damages were found to be caused by something other than blasting. These non-blasting causes have included constructions defects, wind damage, thermal and moisture related stressing, differential settlement or other soil related issues, cross grain contraction and seasoning of wooden members, termites, carpenter ants and other insect related wood damages, as well as hydrostatic pressure in the soil. This study examines in detail damages from fly rock, air concussion, ground vibration and soil shifting on numerous residential and commercial structures.

The study contains 1,872 blasting claims in Tennessee, a state whose geology requires blasting for most utility line installations, mass grading for site preparations, highway construction and mining. The valid blasting damage claims have occurred in vibration ranges consistent with previously documented levels for various structural materials.

The study established that valid blasting damages resulting from any direct or indirect blasting related force occur less than 3.5 percent of the time. Blasting damage occurred in the studied structures as a result of fly rock 0.27 percent of the time, they resulted from air concussion 1.82 percent of the time, they resulted from ground vibration 1.29 percent of the time, and they resulted from soil shifting within the crater zone 0.09 percent of the time. It is important to note that this study was simply based on investigations of structures that had a blasting damage claim and did not include the countless number of structures in the areas adjacent to the same blasting activities that not only did not have any damage, but who also did not file a blasting damage claim.

While blasting was not often found as a cause of damages associated with many blasting damage claims, it was on occasion responsible for the damages. Competent experts with direct experience in blasting related stresses and damage forces can identify these damages when they occur.

 Wade Hutchison

Understanding Tennessee Blasting Standards Act Changes in 2008

Monday, July 7th, 2008


In 1975 Tennessee enacted their first Blasting Standards Act. At that time a 2.0 peak particle velocity vibration limit was set. Compliance with this limit allowed blasting contractors to monitor with a seismograph capable of measuring peak particle velocity in 3 mutually perpendicular directions. A blasting contractor could also comply with this limit by loading their blasts in accordance with a standard table of distance, which prescribed the maximum load of any 8 millisecond delay period giving the closest exposure distance to a particular blast.

 In January of 2008 the vibration standard for this law has been changed. Since 1975 several administrative changes have been made to the law; however, this is the first time that the vibration standard has changed. The Tennessee Blasting Standards Act still allows a blaster to comply with the vibration standard portion of the law by utilizing a standard table of distances for all blasts located within 300 feet of a structure; however, now the law utilizes two different formulas for blasting in areas located between 300 – 5,000 feet and for blasts located in areas greater than 5,000 feet from a particular blast. These formulas are shown in Figure 1.

 The vibration standard is no longer a flat 2.0 inches per second (in/s). The vibration standard has been divided into 2 sections. The first standard is strictly based on distance. If blasting occurs within 300 feet of a structure, the contractor is allowed to blast up to 1.25 in/s. If blasting occurs between 300 and 5,000 feet of a structure, a blasting contractor is allowed to shoot up to 1.00 in/s, and if blasting occurs at distances greater than 5,000 feet a blasting contractor is allowed to shoot 0.75 in/s. Each of this vibrations measurements are made in in/s peak particle velocity. The law also allows an alternate standard. The blasting contractor has the option of using the OSM frequency based curve for compliance. This frequency based curve allows a blasting contractor to shoot up to 2 in/s for those blasts where the vibrations occur in a higher frequency range above 30 hertz. The following graph shows the alternate OSM frequency based vibration limit.

 

Previously, the Tennessee Blasting Standards Act has not mandated an air blast level for any blasting activity; however the new law enacted on January 1, 2008, specifies that all blasting will be conducted at levels not to exceed 140 decibels. As a result of current changes VCE, Inc. and PMT, Inc. have cooperated in manufacturing a new version of seismograph software. This software allows seismograph users to identify compliance of measured data with the new law. The message of noncompliance will also be displayed on LCD, which will allow fast and affective blasting adjustment throughout the project for the explosive companies.

 

Eric Grigoryan

  

Earthquake vs. Blasting

Thursday, February 17th, 2005

There are fundamental differences between earthquake activity and blasting activity. Blasting activity has a relatively small crater zone. The definition of crater zone is identified as the area where the hearth is actually physically displaced in a permanent fashion. The principle effect from blasting is the transmission of energy through the ground in the form of vibration. An earthquake has a more significant area where the ground is permanently displaced or shifted. The magnitude of an earthquake is considerably larger than that of conventional blasting. A different scale has been designed to measure the energy associated with an earthquake. This scale is called the Richter Scale (Modified Mercalli Scale). The Richter Scale is set up to define seismic events that increase with tremendous magnitude. Each number on the Richter Scale represents approximately 10 times more energy than the previous number. This relationship is set up to define a magnitude of earth motion event as it relates to its impact on a house.

Peak particle velocity is the normative measurements for blasting operations and is designed to measure the intensity of ground motion. On the peak particle velocity scale we slightly more than double the energy as we move from 1.0 inch per second to 2.0 inches per second peak particle velocity as contrasted with an increase 10 times when we move from 1.0 to 2.0 on the Richter Scale. The Richter Scale and Peak Particle Velocity are both curvilinear in nature; however, their curves characteristics are tremendously different. These differences are evidenced by the table below.

Richter Scale Magnitude Energy (Pounds of Explosives) Peak Particle Velocity
4 200,000,000 1457.47
3 20,000,000 230.99
2 2,000,000 36.61
1 200,000 5.80
0 20,000 0.91
-1 2,000 0.15
-2 200 0.02
-3 20 0.004
-4 2 0.0006

The physical soil displacement from an earthquake is tremendously different than the physical soil displacement from a blast. Earthquakes can generate significant physical displacement over a great distance while soil displacement are on the order of a few then thousandths of an inch when you are outside the crater zone of a blast. Based on this disparity of between blasting vibration and earthquake vibration it is easy to see that blasting requires specialized analysis, calculations and definitions, apart from the Richter Scale used to measure earthquakes effects on a structure. Analysis, calculations and definition associated with earthquakes do not directly transfer to blasting due to differences of frequency, intensity, and magnitude.

Peak particle vibration calculations prepared from Dupont formulas based on average distance for energy values that coincide with published earthquake data relating Richter Magnitude with pounds of explosive energy.

Wade Hutchison

Terrorism Impacts Blasting Industry Record Keeping

Tuesday, February 1st, 2005

During the last several years the events of September 11th have significantly impacted record keeping requirements of every blasting operation. ATF Regulations mandate a close tracking be maintained for all explosives.

The new ATF Regulations require Blast Logs, Travel Manifests, and Blasting Magazine Inventory Sheets to balance precisely. The additional record keeping requirements of the new laws can be laborsome. However, they are worthwhile. Contractors failing to comply with these changes have been penalized with fines and revocation of their licensure.