Holdfast Training Services Trial Blog

Just before my summer leave I attended the most frustrating meeting I think I will ever endure…it made a TFH ISTAR planning co-ord appear proactive!

The background

The embankment that approaches each bridge abutment has a series of piles called CMCs (Continuous Modulus Columns). These piles are placed on a 1m grid over the width of the road for around 50m. They do a number of things but mainly they stiffen the embankment material as they are displacment concrete piles and secondly they transfer some of the load through the constructed embankment to the stiff clay below. They contain no ReBar and are designed to fail if heavily overloaded.

The Problem

Given that the CMCs are not reinforced, they are designed to work in a specific way. Any structural movement will eat in to the tolerance of the CMCs, this means that it would be crazy to install the CMCs whilst our site is still undergoing large amount of settlement we’re still experiencing. Whilst the settlement is starting to slow it has not reduced to the level the Vibro Minard, the subby that is installing them has specified.

The Sticking Point

• Vibro will not give a warranty on the potential for differential settlement of the installation until the ground is at the strength originally specified.
• WSP, the designer, will not check the original spec or conduct any alteration without a FULL check of the whole scheme (big £££). Clearly they can see we’re over a barrel and know something has to give. Their argument is that a reduction in platform strength may have a fundamental impact elsewhere and that requires checking.
• We only have a six week window to get this done before it takes over as the critical path and causes programme delays.
• Kent Council are unlikely to accept the embankment without warranty (we don’t want to ask the question as it will likely open up a huge amount of questions and interest).
• We don’t have the budget to cover the warranty as the project is heavily in debt and this sort of warranty would be for an unknown sum given that no one internally really understands the actual design enough to predict what may happen.

We left the meeting looking at each other saying ‘so what now’.

So What

Quite simply we’re having to wait for the ground to ‘Get A Grip’ and toughen up.

We’ve conducted a number of onsite tests to check the current strength in the ground. The good news is that it’s higher than we expected based on the original model and pizo data however it’s not quite as high as we need.

We have asked the designer look over the findings a predict what the ground strength will be by the time Vibro mobilise if we give them the thumbs up now. It’s looking good, so fingers crossed.

The Disappointment

The sad thing was, everyone sat around that table knew how to solve the problem but hid behind lines like ‘this is what my design manager has said…’! Whilst I understand the requirement to make money, I will never understand the mentality that it is ok to do so whilst others fail, sink and lose out. What made it worse was the lack of spine demonstrated, if you’re going to represent your company then embrace the policies they set, don’t hide behind people who are not present in an attempt to deflect the criticism away from yourself.

The Good News

We have a structure that is starting to look like a bridge, peirs and all!

I’d like to echo Damian’s point when he said that it’s important to question the design.  It’s not just that the design might be wrong, although it often is, but also that when it is right, it could still be better.  I’ll give two examples…

The next evolution of the blockwork saga takes us into the construction of a double skin wall that separates the car park area (a class 2 basement) with the clubhouse area (a class 3 basement). The difference in the classes comes down to a range of measures intended to make the space more inhabitable, such as ventilation, acoustic insulation and (the focus of this rant/blog) waterproofing.

Waterproofing is hugely important to the client because it you don’t get it right first time it cost loads of money to put right. Since SRM would ultimately foot the bill, there has consistently been a lot of pressure to get it right.

The clubhouse area has an additional waterproofing measure in the way of a cavity drainage system. The system interfaces with the block work wall as shown below:

It’s worth noting that this does not align with the architects drawing, or the waterproofing designer’s drawing. But it does reflect reality and therefore I’m building it that way.

Now onto the point about questioning the design…

The bottom of the inner skin is sat onto engineering brick. The bricks are 205mm long and the blocks are 140mm wide. Therefore the bricks were to be cut down then laid side by side (as opposed to end to end) to give a 140mm strip to lay the blocks on. At the base of the cavity there is a void former that the dpc runs over the top of. So why are we cutting the bricks down? Cutting the bricks would cost more and take longer, and you also have to pay for more void former. I suggested laying full bricks to the architect and he was happy for us to do so, as was the waterproofing designer. So why did the additional design call for the bricks to be cut? Because the architect thought the drawing looked neater. I wish I was joking.

So to hark back to Damo’s point, I’ve just saved money by saving time without affecting quality.

The other example is that the inner skin will be dry lined, the only bit of block work that will. Yet the design still calls for paint grade block work. Why? It isn’t painted! I think I remember Pete having a similar thing with a ridiculus concrete finish on a bridge pier that would only ever be seen by a dingo…

In the beginning we had a lot of quality issues with the block work so we’ve got piles of blocks all around the place that we’ve taken down. So I’ve had it agreed that I can use them for the inner skin since it won’t be seen. So I’ve saved material and therefore money without affecting time or quality, and for good measure I’ve wrapped it in sustainability by reducing waste.