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    Question Trench Spot Shores

    Anybody out there have any experience with or comment on the use of Airshore or Paratech Spot Shore Rails in a trench wall collapse without using strongbacks or trench panels?
    Last edited by CANFF2706; 12-31-2010 at 08:09 PM. Reason: typos

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    Quote Originally Posted by CANFF2706 View Post
    Anybody out there have any experience with or comment on the use of Airshore or Paratech Spot Shore Rails in a trench wall collapse without using strongbacks or trench panels?
    Are you referring to the Paretech wailer system?
    Mike
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    No, I'm actually referring to this technique:
    Attached Images Attached Images  

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    Quote Originally Posted by CANFF2706 View Post
    No, I'm actually referring to this technique:
    Gotcha.
    I haven't seen any rescue teams shore a trench like this. This technique is sometimes used by contractors when the soil is believed to be dense, compact and safe (a good class A soil) If rails aren't used most contractors will use pieces of 2x12 that measure 12'' long.(more cost effective)
    Trench panels may not do a lot in the way of providing much shoring force however they do add a mental sense of security for us the rescuers.
    Hope This Helped,
    Mike Donahue
    "Training Prepares You...For Moments That Define You

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    That's what I thought and have always been taught too but then I came across this article at the following website. ( See link below - I tried to attach it to protect the innocent but it was too big...)

    Some of the photos show "skip shoring", which is fine in Type A & B soils for contractors while others show no strongbacks used, just "spot shore rails" or plywood. Would a trench that has had a slough in or lip in collapse (or any type of soil collapse for that mater) still be considered to have Type A or B soil?

    If anyone knows the author/s of the article, I'd love to hear from him/them and hear further what their rationale was for coming up with their techniques and see what engineering data they have to back them up.

    http://www.bothellfire.org/TechRescu...potshoring.pdf

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    This was an interesting article, I sent it to a few guys I know to get there thoughts on it. I looking forward to reading the responses to this thread.
    Nice Post,
    Mike
    "Training Prepares You...For Moments That Define You

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    Their is absolutely nothing wrong with placing shores like in the picture. The tabulated data supports it in all classes except flowing soil.
    The arch effect is what keeps the soil in place not fin forms.
    When you look at the data we place shores much closer then the data allows. The use of the mini whale plates is a good choice for initial operations where a heavy rescue may not have fin forms.
    On our heavy rescue we can place a protective box around a victim down to 10 feet or a single row to the limits of the shores. It is meant as a preventative measure for secondary collapse that would kill the victim.

    So download the tab data from Airshore, Prospan or Paratec. The fireservice uses the 4X4 grid for simplicity, the manufactures tabulated data will prevent a collapse as well as properly placed wood or hydraulics off of the OSHA charts.

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    Default Spot Shores

    Using skip shoring or "spot shores" at a trench rescue (cave in) is an inherently BAD idea with the exception of using it as a rapid means to protect the victim from an impending secondary cave in. We call this victim protectionconcept "Primary Shoring". At a cave in type rescue the soil has proven to be unstable and should be treated as worse case scenario soil or Type C-60. I have spoken with a head technical person at Paratech and he assures me that their "spot shore" rail was not intended to be used as shown in the picture in this thread. It was intended to be used with .75" Finform as an alternative to a bolted on wood strongback. I also see in the Paratech and Hurst (Airshore) shoring charts that Fin form should be used to shore unstable (C-60) soil.
    A lot of myths about shoring exist in the rescue community. If enough people hear it and repeat it it becomes gospel. One such myth suggests that Finform only provides a pyschological comfort to the rescuers/victim. We have done several years of destructive testing on trench rescue shoring systems and I can tell you that Finform is stronger and more ductile than 2"x12" lumber (strongbacks). While you may have been told that the shores are the columns, the strongback are the beams and the Finform is merely decking our tests prove otherwise. In most cases (with bolted on strongbacks) the Finform should be considered the structural component and the strongback as a nailing block. When the Finform and the strongback (2"x12") are glued together they enhance each others strength.
    Finform also distributes the force of the struts compression force over a larger surface area. This is very important in unstable soil but less important in stable and dense soil conditions.
    Our brothers and sisters in Seattle have written an article about their use of spot shores. My question to them is "Has it been tested under C-60 cave in conditions"? This will be one of the topics of destructive teasting planned for the Spring of 2011.

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    Read in the article that they have used spot shoring in soil rated C60. I dunno, seems like a pretty large risk. Then again, someone said on here once that we are in the job or risk management, who better to judge the ammount of risk. Still, I'd feel better with Fin Form in place.

    They do talk about tossing the spot shores over the patient area, and panel shoring the flanks to give a zone of safety. My biggest concern is that once you shoot the strut, is it going to push into the soil and cause a secondary collapse?
    ~Drew
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    Just rechecked the current data from airshore. Fin-form is required for C-60 soil...the picture is not C-60 soil.
    Tabulated data should ALWAYS be referenced at your operation since the data requires closer then 4X4 in some situations when you use the spot shores.
    Bottom line is that you can, and should, follow the tab data. You can use more protection the the data suggests, but going from memory on a call is not a good practice.
    My area has hard packed clay and layered soil as a norm, so we really don't see class C-60 or C-80 soil here. We use spot shores all the time with no problems.
    Remember to always check (and update) your tabulated data and you'll be successful.

    The tab data for airshore is here: http://www.jawsoflife.com/Downloads/Default.aspx

    Good topic, our tab data book was made only a year ago and these sheets are different.

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    My thought is regardless of soil type, once it collapses it is classified as TYPE C! What ever type of shoring teams use, I completely feel that I am placing the system in there to protect my rear first then the patient.

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    Default Soil Type

    It seems that a lot of firefighters are comfortable discussing soil classification. I wonder how many really have the training and experience needed to make such determinations. At underground construction sites soil classification may only be determined by a highly trained and experienced employee called a competent person. These people typically have thousands of hours of experience at “live” excavation sites. They have seen many types of soil and have witnessed passive and active soil conditions. They have experienced the effects of weather, vibrations, surcharged loads and work activities around the trench site.
    Even with all that experience a competent person would never classify a soil solely based only on a visual test or observation. Manual tests would have to be completed to determine the accuracy of the visual tests. The visual tests need to include an analysis of the soil properties, an evaluation of the performance (stability) characteristics and an identification of the environmental exposure conditions. Shear strength and unconfined compressive strengths must be determined to classify soil. Recognized manual tests include textural soil classifications (jar test), shear vane, pene-trometer and thumb penetration tests, plasticity tests, ribbon tests and drying tests. All of this testing takes time, equipment and well trained and experienced personnel. At a rescue scene that amount of time, equipment and personnel is seldom if ever present. While I have met some firefighters who have taken a competent person course but I can count on one hand the number of firefighters that are really qualified (experience and training) enough to make this potentially life and death decision.
    According to OSHA, Type A soil is considered very stable with good shear strength and unconfined compressive strength to resist the relatively low lateral forces being exerted on the trench wall. Type B soil is less stable and has higher lateral forces being exerted. Type C soil is unstable with the most lateral forces. Soil that is active (moving) and has caved in should not be considered as even moderately stable. If it has caved in the soil should always be considered unstable soil. If the soil is unstable then you should design your shoring system for worse case scenario forces. Worse case scenario forces (trench walls that are not falling in as fast as you dig them) are considered to be 60 pounds per square foot. Shoring manufacturers call this C-60 soil.
    Using the “worst case scenario” approach to rescue shoring provides for a reasonable level of firefighter safety. With a tiered and prioritized approach (Primary Shoring, Secondary Shoring etc.) shoring systems that are based on “worse case scenario soil” can be accomplished in a timely and safe manner. Shoring systems that do not provide for lateral force protection of at least 60 psf but instead rely on soil classification decisions made by firefighters are dangerous at best. If you are counting on the construction or repair crew to classify the soil for you don’t forget that it was their
    mistake(s) that brought you to the scene in the first place.
    At a cave in... rescuers should always design their shoring system for "worse case" (TYPE C-60) soil.

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    Quote Originally Posted by rescuezman View Post
    It seems that a lot of firefighters are comfortable discussing soil classification. I wonder how many really have the training and experience needed to make such determinations.
    ...

    At a cave in... rescuers should always design their shoring system for "worse case" (TYPE C-60) soil.
    This. Unless you have a certified dirt man, all soil is Type C.
    ~Drew
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    Quote Originally Posted by FiremanLyman View Post
    This. Unless you have a certified dirt man, all soil is Type C.
    Well said Lyman....Well said.
    Mike
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    So you don't do soil testing? No thumb penetration test? No penetrometer? You just assume it is "C" soil?
    That is unproductive and unprofessional. The manufacturers tabulated data and the OSHA charts use more shores and they are closer together, in some cases closer then 4X4. By not testing the soil you are increasing the time of the rescue and wasting resources.
    We are professionals (or should be) why wouldn't you do what is appropriate. When I started in this business we used wood, screwjacks and hydraulics. The airshores were not anything like we have now and far weaker. You came to appreciate the shoring system and its components.
    It is called size up and knowing your job, I'm guessing you don't pull a 2.5" on every fire "just in case" then why apply that logic to a trench rescue?
    With that being said, you almost never have class "A" soil because you drop 1 level due to prior collapse. You could have "A" if you had a medical emergency in an unshored trench, and in that case it is vital that we don't screw around with shores we don't need.

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    Soup is this you?? Randy

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    There is a bit more to it than sticking your thumb or penetrometer into the soil when you arrive at the scene of a rescue. The sample must be taken from a fresh spoil. That means you would have to be there when it is being dug. The tests should be repeated to confirm accuracy. If the soil is layered you need a fresh sample from each layer and then must rate the entire soil as the worst layer. What you are betting on when you use soil classifications to determine your shoring design is that your Type B soil shoring plan (which can be 33% weaker) will hold the forces of the active soil you are dealing with. If you error in your soil assessment, the shoring system could fail.
    Quickly put a shoring system in place to protect the victim then beef it up to hold 60 psf (worst case scenario soil). If you error its on the side of safety and really doesn't take all that much more time than setting up a system for soils with less lateral force.
    Having been a guy who has had to make that call several times in my career I'd have to argue with you about being unprofessional and unproductive.

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    It is all part of size-up, to disreguard the soil class is leaving a large part of your size up out.
    It isn't much different then not doing a 360 at a structure fire because you "know" the neighborhood. You are possibly missing an important piece of the puzzle. Unless your on a 1 person rescue unit you sould be sizing up, number and status of patients, soil type, checking the tabulated data and formulating a plan of action for the rescue. We shouldn't just start our 4X4 grid and assume it is "C" soil.

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    I must respectfully disagree with you on this point. While you certainly need to do an assessment and size up you can eliminate a very difficult part of the evaluation (soil classification) by always using a "worst case scenario soil" standard profile. Its similar to always considering a firefighter on a rope system as weighing 300 pounds and a two person load at 600 pounds. You don't need to bring out a scale and weigh everyone during your size up. You use the standard and match the equipment and system design to provide the desired safety ratio.
    Sixty pounds of lateral force per square foot times depth should be the standard for rescue shoring. The rope guys set a standard we should too.
    I have yet to find a firefighter who is experienced enough to accurately determine soil forces from visual or manual tests. I have personally conducted every type of visual and manual soil test available and do not consider myself expert enough to determine existing soil forces based on those tests. Most firefighters have very limited training and experience with soil testing and should reconsider their ability to determine soil forces.

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    Obviously, I won't change your mind over a computer, so I'm fine with agreeing to disagree.
    What does your team do for the unshored trench without a collapse? "C" soil with a 4X4 grid? or do you follow the soil class and tabulated data?
    My problem with not looking at the data is you may be able to safely shore the trench and give yourself some more room to work. We've had these scenarios and it is very nice to have the ability to not be forced into a 4X4 grid.
    I've done this long enough to have done it without the nice pneumatic shores. I can guarantee that pounding wedges into wood shoring didn't apply the same force to the trench as a modern pneumatic shore. The numbers are confirmed by thousands of contractors over many, many years. The more we become familiar with our trade the better we become. 95% of the time you'll see a 4X4 grid in our trenches treated like it is class "C" soil, however we should be backing our decision based on actual data. I wouldn't want to be talking to an IDOL investigator and not be able to give a definitive answer to what class soil we are working in or why our struts are spaced the way they are.

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    Quote Originally Posted by ADSNWFLD View Post
    With that being said, you almost never have class "A" soil because you drop 1 level due to prior collapse. You could have "A" if you had a medical emergency in an unshored trench, and in that case it is vital that we don't screw around with shores we don't need.
    Just curious ADSNWFLD, where is it written that a prior collapse lowers the soil classification 1 level? That's the first time I have ever seen that stated.

    I have always been taught that a collapse indicates unstable soil conditions and should be treated as Class "C" soil. If the trench has collapsed once there is a high risk that it could collapse again.
    Last edited by CANFF2706; 02-25-2011 at 12:39 PM.

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