JBV Demolition received a call from their valued client Addison’s Projects on Monday 28th August.
At the time, Addison’s were project managing a groundwork’s contract within Blackpool Pleasure Beach. The project for Addison’s involved the instillation of piles and pile caps including building concrete bases ready for the installation of a new ‘roller coaster’ within the main complex.
Addison’s had installed approximately 900 piles and 300 pile caps. They had encountered various challenges through the project, however the biggest came at the very end.
With all pile caps installed, Addison’s and the Pleasure Beach employed two independent surveyors to ensure that the pile caps and specifically the mounting plates for the rides steelwork were all set out correctly.
Unfortunately, approximately 10% of the mounting plates were outside of the limit of tolerance of 15mm. it transpired that these plates had moved during the settlement of the concrete pour.
The solution; re-set steelwork at fabrication stage or break out the cast pile caps and recast.
Addison’s contacted the fabricators and fortunately managed to alter the design of all but 11 of the bases.
Due to the amount of space available, a 5 tonne excavator was largest machine which could access any area within the footprint of the new ride. This being without causing any damage to the mounting plates of those correctly set.
Conventional breaking using this type of machine could potentially have taken 3-5 days. Therefore a minimum project extension of 33 days (7 working weeks).
The secondary challenge would then be removing the concrete such that the piles or the tie in rebar was not damaged.
Again, using conventional breaking techniques of a machine mounted breaker, it is highly likely that piles and the rebar will be damaged. The consequence of this; cut the pile off, re expose rebar, redesign the pile caps.
This adds far more time and cost;
• approximately ½ a day per pile = 15 days (3 working weeks)
• redesign of pile caps is the critical path prior to ordering any of the rebar structure = estimated 15 days (3 working weeks)
The challenge therefore is to reduce a potential programme of 13 working weeks to as minimal as possible.
The reason for this;
• the recasting of pile caps must also allow for a curing time of the concrete of 28 days minimum (4 working weeks)
• the steelwork had already been fabricated and was being shipped from Germany, arriving on site, ready for instillation from the 25th September (just 4 working weeks following a call being received at JBV Demolition offices).
JBV Demolition Engineers visited site on Tuesday 29th August and met with Addison’s, the Pleasure Beach and the contractor involved in setting the bases.
The challenge was presented and JBV Demolition engineers suggested that the use of Autostem would be the best way forward.
Autostem is a non-detonating, self-stemming blasting cartridge designed for civil’s applications amongst others.
The Autostem cartridge offers almost the same calorific value (in terms of Jules of energy) however without the high velocity of detonation of traditional explosives used in the same application. This means essentially that Autostem works by rapidly expanding gas and not the percussive shockwave of traditional explosives
A problem solved
The JBV Demolition Engineers believed that using auto stem would present the following benefits to the client;
o the use of Autostem would fragment the concrete from the inside, and in JBV estimates would reduce the time taken for removal of each pile cap to less than 1 day
o drilling time was estimated at 12-16 cores per day, with 6 cores on average per pile cap meant that JBV Demolition could prep and burst at least 2 pile caps every day
o after each burst, the pile cap could be removed. Therefore pile caps could start being removed just one day following JBV Demolition commencement on site
• Saving the piles
o The way in which Autostem works means that the concrete will split at its weakest point. Traditionally this is at the connection points between the reinforcement and the concrete itself. This means that the concrete is effectively stripped form the rebar
o With the concrete being shattered from the inside out, there is less work required for the breaker. Therefore less percussive vibration and instead all that is required is to remove the rebar and let the concrete fall away from itself. In this way, the piles and their tie in bars are not damaged and are immediately available for reuse
An added bonus
There were predominantly two types of pile cap on site at Blackpool
1. A single unit with one mounting plate in the shape of a triangle
2. A double unit with two mounting plates in the shape of a rectangle
Now, unfortunately for Addison’s on all of the double units which were out of tolerance for the steelwork of the ride (4 number), only one of the mounting plates to the double pile cap were out. Traditionally, this would mean breaking both mounting plates out and recasting a large base once again.
Using auto stem, JBV Demolition were able to create a split between the two mounting plates by stitch drilling. The stitch drilling did not involve the removal of the cores. Instead all that was required was to create a line of weakness between the mounting plate and concrete which was to remain and the one with was to be removed.
Remembering the way in which Autostem works, having a line of weakness allows the gasses to escape, meaning that even with the cores left in, there would be no transfer of the destructive energy into the block which is to remain.
JBV Demolition commenced works on site on Tuesday 12th September. The first test burst was performed on Wednesday 13th September with another burst completed the same day once the test had proven the methodology to all stakeholders.
In total, 137 cores were drilled from 13th through 21st September. That was an average of 17 cores drilled per day. The last burst was completed by 8:30AM on Friday 22nd September with the concrete being removed that same day.
The quickest time of removal of a single pile cap unit was 3 hours
The methodology works so well that Addison’s asked JBV to complete another 4 bursts on single units. This was complete by Wednesday 27th September. A mere 3 working days following completion of the original scope.
The principal risks of using Autostem are in the preparation works and during the bursting.
• The preparation works involve drilling holes into the concrete. This has an inherent risk of hand arm vibration.
o This risk is managed by using a drill mast stand. This completely eradicates the risk of hand arm vibration and was used on this project to great effect
• The use of Autostem itself only presents risks during detonation. The risk here is fly rock. Concrete is a brittle substance and can shatter into many small pieces, which, if unmanaged could potentially cause striking injuries
o This risk is managed in two ways;
1. Conveyor matting – layers of conveyor matting are used to contain any fly. The conveyor mats are made of 20mm thick steel reinforced rubber. Laying these over the burst area contains any potential fly
2. In the event that any fly did escape, an exclusion zone of 40 meters from the centre of the burst area is enforced. This exclusion zone is managed by JBV Demolition staff and can be further reduced by the use of hording or something similar.
Furthermore, this exclusion zone is only required for approximately 15 minutes – whilst the area is checked and made safe, followed by the burst itself. Once the burst is complete, there is no further risk and thus the area is once again safe for occupation
You may be asking yourself, ‘what are the risk of the product in carriage, storage?’, ‘can the product be accidentally detonated?’.
In fact, you may be surprised to hear that Autostem is classified by the United Nations under UN Code 1.4s. This qualifies the cartridge outside the conventional explosives class. Instead, the closes specification which this product comes to is a shotgun cartridge.
As a result, there are no obligations to notify authorities of its use or storage. Instead, we notify the local authorities of its intended use and the times and dates under its use out of courtesy.
The product cannot be accidentally detonated either. There is a special detonator which must be connected to the cartridge in order to set it off. This detonator has a dead man’s switch as well as a covered initiator. All of this means that to detonate a cartridge, it must be done so purposefully.
The final point of explanation is what happens if a cartridge does not detonate?
It is important at this point to note that in the history of use of Autostem, there has never been a reported case of a failed cartridge. However, if there is, this doesn’t present a real issue.
With no detonator connected, the cartridge is effectively inert. Instead, to dispose of the failed cartridge, you can simply remove it and open it up. Burn off the contents (not explosive and less volatile than paper) and dispose of the plastic in the relevant recycling bin.
If the cartridge cannot be removed, then a second cartridge is simply let off over the top of it. This will initiate the other cartridge and thus it is disposed of.
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