Holdfast Training Services Trial Blog

The area on site known as the grout box is due to be handed over from ourselves Laing O’Rourke working on the C502 contract to another contractor working on the c510 contract. The C510 contract is responsible for tunnelling through to the Liverpool street station ticket halls. As part of their contract they are required to carry out ground stabilisation through the use of injection grouting. The area requiring grouting is accessed from the C502 site and as a result we have been busy excavating a shaft and preparing the area for them. The grout that is to be injected behind the pile shaft wall first has to be piped into the grout box and this required the removal of a pile. The removal of the pile threw up a number of questions around the stability of the pile and ground given that it would effectively be suspended and relying on skin friction to stop it moving downwards and closing the gap. In addition and probably more importantly the pile would have no active pressure that it could use to resist the passive pressure of the soil and water behind the pile. To overcome this a reinforced concrete beam was cast into the piles to act as a whaler beam and fix the now free end of the pile. The task of organising the team to cut the pile and remove the concrete was given to the new boy (only once tea making duties were completed). After a period of scratching my head, I decided that the best means to attack the pile would be to get my old friend the diamond core drill and to stich cut the top and bottom of the pile and then to use the 3T excavator to break up the concrete in situ to then be removed in smaller pieces. First question to myself “where is the risk” and from what I could deduce it was more of a question of “where wasn’t the risk”. Working underground, confined space, removing a reinforced concrete pile section, pile failure, recent weather and ground conditions significant water ingress never mind the crushing injuries to persons operating in the shaft. As this was my first major task I felt a little military precision (oh the oxymoron) was required and not the John Moran approach of hitting everything with a stick. Following a detailed planning period during which the task was planned, risks assessed and planned out, reduced to acceptable levels and residual risk communicated, team briefs rehearsals completed the team was ready to go…. And it was then called off as C510 decided it wasn’t required.

In other news I have enclosed my fag packet calcs for those interested from the inclinometer drilling. While useful to plead my case with other engineers on site that the Heath Robinson clutch system was not sufficient I would not rely on them in court. Ultimately this proved to be a project contract and management issue as the contractor was summoned to prove calcs that proved his system worked and as he couldn’t the drilling was stopped and we have gone back out to tender for another contractor to complete the works.

Outside of work I have signed up to cycle London to Paris for some charity or other, more details to follow and I have been invited to sit on the board of a charity of a board called Engineers for Overseas development. The charity challenges young engineers to use their skills to design resource and construct a development projects overseas. The chairman felt that I might have a little bit of experience that would be useful…well you know I just might…pull up a sand bag and I’ll tell you all about it.

My fear with sustainability goals is that they are often the first casualty of cost saving exercises. It is very easy for a consultant to suggest all manner of intricate sustainability measures that if made a reality would no doubt be groundbreaking and win lots of awards, but when the client is paying for it, it is a different story.

At the Perth children’s hospital the Environmental and Sustainability plan (ESP) listed many methods of achieving a Greenstar rating (which I later found out was not a mandatory element of the government contract so was shelved). These included:

• Stormwater harvesting,
• Rooftop gardens,
• Animal bridges from the adjacent park to the rooftop gardens
• Automatic shading devices on window
• Automatic airflow management systems to take advantage of daily temperature ranges
• Solar panels
• Cement replacement materials
• Post Tensioning
• Etc

Of these the majority have been left by the wayside (especially the animal footbridge (or pawbridge) which somebody was obviously smoking crack when they wrote it), with reasons cited as too expensive to implement. It appears that sustainability, if not mandatory must as a minimum be cost neutral and PR positive to have any chance of coming to fruition.

The same can be said of the Perth Gateway project. The project is a AS$1bn national priority scheme to construct a landmark road structure around Perth airport and road and rail freight terminals to make the region an efficient industrial hub.  In summary, for BG&E it is a big road project to design 5 major highway interchanges to improve the traffic flow in the area.

Gateway Project Schematic

I became aware of the issue today when eavesdropping on an engineer ranting about how he was annoyed that the client (Airport) was not listening to him. Though not completely related to the gateway project it is linked.  I investigated a little further and intend to get on a site visit to see what is going on. Essentially during a 1 year storm, the airport receives a flood flow of about 8m3/s (from upstream and its own drainage) but only releases 4m3/s which is good as it is attenuating the flow and reducing the impact downstream. It is also bad for the airport however as now that they own the land (it was recently privatized) they want to develop areas of it for commercial property, the bulk of the water flow that is supposed to go under the runway through 1x1200mm culvert barrel, doesn’t, it floods the potential commercial area, a lot.

One option was to increase the size of the culvert but disruption to air traffic, issues downstream meant this was a non-starter. Another was to re-route the waterway around the bottom of the runway through a swamp (imaginatively known as runway swamp and formed back in the day when they didn’t care for sustainability and were happily excavating peat). It turns out that the swamp because it is so old (1960’s) is now heritage listed an cannot be disturbed so that option is out. Another option was to re-route the flow an make a living stream to the nearest existing water course. This option was picked up on by BG&E and the plan was the extend the living stream another 4km to 6km to tie in with the interchange drainage and no doubt boost the sustainability rating. The airport saw this as additional cost and decided to attenuate the flow in an up-steam basin away from the commercial property and do away with the living stream.

The engineers issue was that although the flow difference between the 1 year storm and 100 year storm was only likely to be 2m3/s (not huge) it was still possible to design the drainage to incorporate the features of a ‘living stream,’ but the client wanted the design changed to be more efficient and hence act as a drainage ditch. The point of a living stream is to slow the passage of water by implementing a more natural channel shape with more gentle channel profile and meanders to inspire vegetation growth that will slow the passage of water by increasing the mannings number and energy losses. This creates a more hospitable environment for wildlife.

The second drainage sustainability aspect of the gateway project is the attenuation of the stormflows around the interchanges. The main interchange has been designed with 7 basins which can hold a capacity of approximately 30,000m3 which is approximately the 100year storm. At low flows the water runs through the basins to a channel that terminates below the outlet in order to allow low levels of water to be absorbed into the ground. At higher flows the channels outflow to fill the other basins before backing up. The maximum outflow of the system is only 200l/s which if operating at capacity would only take about 40hours to clear. I am told that through modelling and a reducing water head this figure is actually over a week. As Perth is effectively a sand based city the water can leach into the ground, but with a relatively high water-table there is not much opportunity for this, so it was not factored into the design.

Gateway Intersection and Drainage Basins

To prevent water-flow sedimenting the soil channels the basins are grassed, and are planted at 130% the required density to ensure that there will be enough to stabilize the soil after inevitable losses to heat and wash out. It feels a little ironic but entirely necessary that they have to install a reticulation system to the basins to ensure the vegetation doesn’t die in the summer months.

In other news I went East to the Wheatbelt region to conduct a few site investigations of bridges that require a waterway analysis. We stayed in the town Quairading in the arse-end of nowhere, in the only hotel which I can confirm without shadow as the worst hotel I have ever stayed in. I don’t want to go into detail (I’m still having flashbacks), but suffice it to say, I have stayed in Blackpool before.  As an added incentive, the ex-trucker female bar manager, with bingo wings that would rival Harry Potters wizard sleeves for looseness, took a shine to me. We started work early, finished work late and funnily enough the week long recce took 2.5days. I have now seen rural Australia and no longer feel the need to see it again.

Me, Bridge and Ute

Quairading Hotel (The picture does not do it justice)

The weather has turned. It was 25 today and biting cold. Coming back to the UK is going to be a shock!