PRE-BLAST
SURVEYSAre You Getting The Real Thing???
Preblast surveys are conducted on homes, structures, schools, churches or any structure within ½ mile of proposed blasting. The structures could be cell phone towers, bridges, concrete driveways, out buildings, most any man made structure. The purpose is to show existing condition before any blasting is done.
The federal and state laws require preblast surveys to be completed before any blasting is completed. Most anyone can conduct a preblast survey and the guidelines vary from state to state.
Prices range from as little as $25.00 upwards of $1,000.00 per structure. I've seen many surveys that were not worth the paper the report was written on. These surveys should be conducted by persons with construction knowledge, blasting technique, and as much blasting experience as possible. Just because you maybe a real estate appraiser doesn't mean you could be a good preblast surveyor. There are a lot of people doing these surveys who have no blasting experience or know the difference between normal settling conditions or blasting damage.
Most structures will have defects and sometimes these defects are seen as a blasting cause.The type structure, the ground the structure is built upon, the time of year you are looking at the structure, the materials used and other factors can give false assumptions. Most cases it is nearly impossible to tell if blasting is a cause of change. Structures with shallow foundations react to changing weather conditions as well as ones constructed on soft ground. Just because your structure is built on solid rock doesn't mean it won't settle. The bearing walls and floors react to weather, weight and surrounding conditions. Take for instance a structure built close to the rail road tracks or highways maybe subject to vibrations from trains and trucks that could cause certain conditions to take place in the condition of a structure. Over time most structures will show signs of age or settling, or other defects that were not present when the structure was first constructed. Blasting is often blamed for these normal structural changes that appear over time. Sometimes the change could be more rapid due to workmanship, materials or the ground the structure is built upon. Just because a crack appears over night doesn't mean that the cause was from blasting down the road on the local strip job. It could be that the crack is but a structural defect that was bound to happen, it's just happened during the period Joe Coal Company was conducting blasting operations. These surprises do happen and it is important for preblast surveys to identify any defects that are present so a company's blasting doesn't get the blame for something that was not related to any blasting. Most cases people never notice anything until something arrouses their curiosity and then they start looking for changes or may notice something that has been there awhile but just now noticed it. Then they try and come up with a cause and in most cases the local blaster is blamed.
Good pre-blast surveys, persons knowledgeable of blasting practices, construction technique, geology and experience that conduct these surveys are your best bet. If you just want a quick report so you can start blasting then the $25.00 worthless survey maybe what you deserve. Proper surveys cannot be conducted for $25.00 dollars. First off if a survey fails to note the existing condition, it is not a pre-blast survey. Second structures should be examined from the outside and the inside, under the floor, taking note of basements, foundations, walls, and anything that doesn't appear normal. Plus because there maybe no cracks in a wall doesn't mean you don't document it. You take video, lots of photo's of everything, walls, floors, ceilings, whether they are in perfect condition or not. The keywords here are existing condition. If you fail to note all surfaces, rooms, ceilings, floors then you have failed the pre-blast survey. You should take photo's that show the living conditions, such as heavy furniture in place, other factors that could cause a change in structure appearance over time. You are like a forensic scientist collecting data to prove your theory. This data, information you collect depends on whether any attorney or insurance company may loose a blasting case and pay for damages they should not be paying for. If you don't collect it, don't show it, then you failed the survey. Good pre-blast surveys protect the structure owner, the blasting company, the insurance company and your reputation as a pre-blast surveyor.
More is better. The more photo's you have the better, different angles, in various lighting conditions and overlapping is a good practice. I've seen surveys that had two photo's , one of the front and back outside and that was it. Totally worthless and a waste of the owners and companies time. There should be video and several hundred photo's to back up a pre-blast survey. Simply taking a few photo's with sketches is not worth very much. Sketches by their self are not worth much, now a photo of the same thing is worth a lot more. Video, photo's and sketches and notes are worth the most together.
Distance and closeups of the same area are important. Brick walls should be examined from a distance and then eyeballed within a few inches. You can't see all the cracks several feet away. You must view at a distance, then up close , and then at different angles, to catch the true condition. Light and angle can hide structural defects if your not in the right spot to view. Knowing how concrete reacts to changing weather conditions is a must. Knowing how concrete cures is a must as well. Take for instance where a concrete slab is poured on top of a concrete block or brick porch. If the contractor did not use felt or plastic or other material to separate the new concrete from the block or brick, when the concrete cures and seasons it will shrink and it will pull the block or brick with it. The concrete bonds to the block or brick and before long the top row or two of brick or block will develop a separation between mortar joints in the older joints. Weather has the same reaction as well over time. Most materials will shrink and expand and a barrier between the different materials is needed to keep the other materials from being affected. Shallow foundations with footers not deep enough will freeze and the ground will expand thus taking the foundation with it causing cracks. Extreme dry seasons are also bad for foundations as the ground dries up it develops cracks and of course any foundations in this ground could also be affected. When it comes down to changing conditions, blasting is one of the most least causes when you take into consideration the other forces that enact on structures. To say blasting is the only cause is incorrect, one must look at every possible effect. Blasting may enhance or cause certain effects to appear earlier under certain conditions. If the blasting is not within three hundred feet (300') then as the distance increases the less likely the blasting is the cause and affect.
Most blasting cases are heard by a Jury in a Trial. The burden of proof is thrust upon the attorneys to convince that blasting is or is not the cause. Most jurors have no idea about the case they are to preside over. They do not know anything about blasting except that it blows things up. The misconception is blasting will cause damage. Controlled blasting technique is less likely to cause damage than a jet plane crashing into a house. The odds are quite high for a jet to crash into a house. Take for instance that the blaster has conducted blasting operations many times using accepted blasting technique to achieve fragmentation of rock. It's not a trial and error, but a controlled science. The blasters have the backing of the blasting industry and the expertise of the powder companies selling them blasting materials. They follow approved blasting plans are licensed to blast and are experienced.
The problem is people waiting for your mine site to get close to them so they can claim damage or try and extort money from your company. They feel a little vibration for a split second and right away they think you have damaged them. They go around and start looking for anything that they can say is blasting damage. Most times they find defects they never noticed before. The pre-blast survey records these defects so a property owner cannot claim it as blasting damage. It protects the company and the property owner. It records the existing condition and if there are any changes then this can be investigated and determine the cause. It's proof that this is new and not existing. So it works both ways, it shows existing problems and if there are changes then there is proof that the problem never existed at the time of the survey. Some people believe they have been damaged, the pre-blast survey is a tool that shows change or no change.
When you pay for a pre-blast survey you want the best possible survey and the best possible price. If your paying on the low end your not getting much and that will come back to haunt you. The pre-blast survey requires the expertise of an experienced person who has blasted and designed shots and knows construction technique. They know what to look for and how to document it. They give no opinions, they just show existing condition by using video and lots and lots of photo's. They provide the tools for attorneys and experts in geology, structural engineering and other professionals to determine the cause of an a problem. Twenty five photo's and a little paper work isn't worth much. Pre-blast surveys must consist of photo's of every room, every wall, ceiling, floor with overlapping photo's even if there are no cracks. The purpose of the PRE-BLAST SURVEY is to RECORD EXISTING CONDITION not cracks only. If your pre-blast survey fails to do this then you don't have a pre-blast survey. You have nothing.
