Holdfast Training Services Trial Blog

Figure 1: Superlatch connection system.

Today I used SUPERLATCH to splice the pile reinforcement cages for the first time, and I thought that the overall system is interesting and worthy of a blog. The inventor (Steve Render) was here as the system is in its infancy, so I had a good opportunity to ask a few questions and to get a brochure from him as well.

Superlatch is a highly efficient means of connecting spliced reinforcement cages during the construction of rotary bored piles, and I was assured that it can be used in CFA and diaphragm walls too. It has two main aims, to save time, and to increase safety. I will cover these separately below:

Safety

Traditionally the connections between sections of reinforcement cage have consisted of multiple shackles or u-bolts which are secured by the contractor between the piles. This practice requires that the operatives reach through the gaps in the cages with their hands or even whole arms, whilst the lower cages are suspended on the casing with temporary supports, and the top cage is suspended by a crane. Although this process has been used at BPS for all piles so far without incident, if either of these cages were to move, the arm / hand would be at serious risk. Superlatch is welded to the cage off-site during cage construction, and when the cages are lowered onto the preceding cage, the latch mechanism (covered later) automatically secures the connection with no need for any operatives to reach through the cage. If the cage needs to be dismantled for any reason, there is a release tool (Figure 2) which again does not require an operative to reach through the cage.

Figure 2: Release Tool

Time

In theory, not having to manually splice the cages clearly saves time, however so far my experience of Superlatch (one pile consisting of 5 cages and 4 splices) is that it is slower, although I am confident that it will soon speed up. The cages which it is being used to splice are formed of 44no 40mm diameter bars, spaced equally in pairs. There pairs are welded together in places, the uppermost of which is approximately 1.2m from the end. This results in some pairs having gaps between them at the end, as shown in Figure 3.

Figure 3: Gaps in paired bars.

When lowered, the Superlatch in the upper cage sticks into the lower cage like a fin, as seen in Figure 4. These fins need to be located between the pairs of bars, but it has proved difficult to achieve this, often resulting in many lowers and raises of the cage before it is in the correct position. I have suggested that the pairs of bars are spot welded at the top to mitigate this problem – but no welding of the cages is allowed on site, and attempts with tie wires proved insufficient. The fabricator will be contacted and asked to do this weld at the top, which should improve the time taken on piles where the cages are yet to be delivered. Clearly this will not be an issue when single bars are used. I expect this system to save approximately 10-15 minutes per splice in the near future, resulting in a considerable saving of 40-60 minutes per pile, as well as increasing safety.

Figure 4: Multiple latches per splice protrude like fins into the inside of the cage.

How does it work?

Figure 5: Superlatch Mechanism.

Figure 6: Mechanism in position.

As can be seen in Figure 5 and Figure 6, Superlatch works with a simple spring loaded latch, which is lowered onto a receiving band (shown in yellow on Figure 7) on the cage below. This bands can be substituted with a plate for a diaphragm wall. There must be a minimum of 2 latches per splice, today we had 3 for the lowest splice and 4 for the remainder, due to the load each splice would carry increasing up the length of the cage (the cages are suspended during the pour.) A range of sizes of Superlatch are available, with an individual load range of 1-6 tonne, so it can be suitable and efficient for small to large cages.

Figure 7: Lowering the cages together.

Conclusion

This system is undoubtedly safer, but in my experience of piling (admittedly limited to just 7 weeks) the risk which it mitigates has a very low likelihood already, and potentially does not need further mitigation. However, as a time saving product, I think that it is a really good option. Bauer and their cage fabricators have not used Superlatch before, and the operatives here and the fabricators at the yard are still learning the initial lessons of how to adapt their techniques and designs to maximise the potential benefits. With a little more experience in splicing cages in this way, coupled with an extra / repositioned weld when bars are in pairs, I think that the product will be a success.

I have added the Superlatch brochure here if anyone is interested, and I will reply in 1 to 2 weeks with an updated opinion of time savings once I have used it more and when the modified cages arrive.