Holdfast Training Services Trial Blog

CPD/what I wish I’d known about the thesis

This is just a quick blog to follow on from the very useful blog by Rich Garthwaite on CPD and then talk a bit about the thesis.

ICE events.

There lots of presentations at One Great George Street which generally start at 18.30 so can be a good excuse for leaving site at a sensible time. There are a few annual talks which I have attended and thought were interesting for those in London or for those not, logging in online.

Joint Professional Meeting between the Royal Engineers and ICE, this year on 28 April 2016.

James Renie Medal – this is the top 3 successful CPR candidates from the previous year vying to demonstrate that they best reflect Renie’s principles.

ICE tour and history presentation. I did not hugely rate the presentation but having been to a few more things since, knowing a bit about the background to the creation of the ICE as well as seeing more of the institution’s home is only of benefit. The tour is by all accounts good.

Flemming Award, Smeaton lecture and John Mitchell lecture. These annual lectures which cover a geotechnics (and other topics) and two were recorded.

https://www.ice.org.uk/eventarchive/the-2015-fleming-award-competition

https://www.ice.org.uk/eventarchive/smeaton-lecture-2015

For those more geotechnically minded the Rankine lecture at Imperial College is pretty much the top end of geotechnical discussion and worth going along to hear about current themes in academia and industry. Next year (March) will be an overseas presenter. Don’t under estimate how popular it is!

These all help both towards CPD hours as well as attribute 9 in terms of participating in ICE events.

Thesis

The second point of this blog is just to point out some of the ‘what I wish I’d knowns’ regarding the thesis writing. Perhaps something others have found similar things, or not. I have got 4 points. Might be useful for Phase Twos now, albeit at preparation stage only.

Format. Slightly dull point but if anyone has resisted making use of the word styles, auto-format templates I would strongly encourage getting on board early. With 4 x TMRs, 5 x AERs and a thesis it will save hours on formatting if all of the lists of contents, figures, tables and most usefully references are all done for you. Also internal referencing within the document becomes easy as the document will self update. Highly recommended.

Timing. I found there was no time between TMRs, AERs and site work to start writing the thesis much before Christmas – clearly possible, you would just have to be more organised. Therefore the likelihood is you may choose a topic related to site and be writing it when not on site. However, it will help if you know what it is you are doing much before Christmas to allow primary data collection – as per the coursework timeline.

Primary data collection. For the reason above, if doing a site related thesis, collecting primary data from site is critical. If it’s tests on concrete or monitoring data or something else, I would advise deciding in sufficient time to get the information you need. You probably won’t manage to capture it all, so get all the details of people you might need to pull favours from afterwards.

Keeping a record. The biggest thing I am finding is not remembering quite what happened and when it happened. This is practically in terms of why some of the primary data is as it is (so I recommend keeping a site diary for sole thesis purpose of recording activities relating to the data). This is also cerebrally; trying to remember what you discussed or wrote on a notebook, 5 notebooks ago, did not work so well for me. I would have kept a better electronic record (text, photos,) of discussions, events and even thoughts to help remember everything when coming to put pen to paper a few months later.

Just my thoughts anyway.

Jet Grouting

Jet grouting is a construction process which employs a high kinetic energy jet of water to break down a soil formation into suspended particles and mixes the in-situ soil with cement grout.  This process of hydrodynamic erosion of the soil and mixing forms a soil-cement mix which has improved properties.  There are three distinct phases to the process (see Figure 1):

1. Breakdown of soil formation using high-pressure jet. A borehole (90-150mm) is drilled to depth and fluid is pumped at a pressure >450bar to the base of the drilling rods to breakdown the soil formation.
2. Introduction of grout. The rods are rotated slowly as they are extracted from the borehole and cement is pumped from the base of the rods simultaneously.  This creates a column of soil-cement mix, evenly distributed through the treated volume. This phase of the process uses a computer to control to extraction speed, rotation, grout pressure and grout flow.
3. Displacing of excess material. All excess soil-cement mix exits freely to the top of the borehole and removed.  The pressure is stopped 500mm below ground level.

Figure 1  Jet Grouting Technique

Requirement at Australia 108

The scope of works for the Australia 108 project was to provide a jet grout plug from RL -7.0m to RL -8.0m to act as a strut against the core retaining wall and reduce estimated deflection during excavation.  This would enable a 6m deep excavation from RL -1.0m to RL -7.0m without the requirement for walers and struts.  It would also serve as a plug to reduce water ingress into the excavation. In total 106 jet grout plugs were placed varying in diameter from 1.4m to 2.2m, (see Figure 2).  The ground conditions from RL 0m to RL – 17.0m is Coode Island Silt which is soft to very soft silty clay with high plasticity.  The GWL sits at RL 0m.   Menard Bachy secured the contract for these works.

Figure 2  Jet Grout Column Arrangement

Trial Works

The strength of the grout mix will be tested to confirm that 2MPa has been achieved at 28 days based on cubes sampled daily from the spoil return.  It is possible to core the jet grout plug in situ and test but it is preferrable not to.  Instead trial works were done prior to production of the core plug.  The aim of the trial was to allow commissioning of the grout batching, pumping and drilling equipment and to ensure that the columns are consistent with the design assumptions.

Six jet grout columns were arranged as per Figure 3 to achieve overlaps of 400mm between 1.4m and 2.2m columns, and overlaps of 300mm between 2.0m and 2.2m columns.  The trial columns were installed at the same depth approximately 10m away from the permanent location.  The overlaps were cored and visually inspected to check for integrity prior to commencing the permanent works (photo of core sample at Figure 4).  It was assessed that close to 100% of the Coode Island Silt had been replaced by grout and that the overlaps have been achieved.

Figure 3  Trial Column Arrangement

Figure 4  Photo of Trial Column Cores

Risks

The greatest risks with this method are as follows:

1. Not achieving required depth.
2. Not achieving column depth.
3. Incorrect drill location resulting in insufficient overlap between columns.
4. Damage to near-by structures and uplift due to the high pressure and flow rate.

To mitigate these risks, the jet grouters rely heavily on computer control and monitoring.  The operators are given design parameters from the engineers and they ensure the equipment is calibrated and they adhere to these parameters; they provide a drilling record for every column as part of the QA process. They also drill approximately 100mm above and below the target depths to ensure there is a consistent band at the required depth.  They also use GPS and surveyors to locate the boreholes pre drilling and provide an as built post drilling record.  If a column is installed in the incorrect location or depth, the process can be repeated in the correct location as the pressure is sufficient to erode the soil-cement mix.

Method Statement and photographs

I have included below a simplified method statement to demonstrate the how the jet grout plug is installed prior to the core raft,  as well as numerous photos so you can see how the actual construction process looks.  In practice, it took a lot of co-ordination on site as the site set-up and trenches to remove the fluid spoil were a  considerable laydown.  Interestingly though, one thing I couldn’t capture well on photo was how much the ground bubbled due to the sub-surface pressures created by the process. 

Flow Net

Flow Net Take 2

We are finally building! After weeks of delays waiting for the demolition contractors to handover the basement area and only have sketches of what will be built to look at, we finally got hold of area 1.1 (number 1 of 21 areas) where we will be constructing a 1.25m raft slab. This area in particular has a lot going on; temporary and permanent drainage, a tower crane, two sumps and several columns.

The initial task once handover hand been completed was to waterproof the area of the pour. This involved laying ‘egg crate’ (drainage membrane) on the ground where it will act to  diffuse pore pressure and stop any water that enters underneath the slab from building up enough head to affect the slab. The waterproof system that is being used is SIKA. From what i can see this system seems to be a licence to print money. SIKA will only provide their 15 year warranty after one of there representatives has inspected it, and will only sign it off if their products have been used.

   This ‘egg crate’ will be laid across the entire site.

Once the egg crate had been installed, a 50mm layer of blinding was placed on top before the steel fixers moved in. Unfortunately one of my duties at the moment is ordering and managing all rebar for the basement. After initially laughing off suggestions that this was one of the harder/stressful things for an engineer to manage ( I believe I said “how hard can it be?”) it has become the absolute bane of my life. After 6 deliveries there has been something wrong with almost every one; late, wrong or has bits missing. This would not be so bad if the site has stock rebar lying around, however the QS department will not allow such a thing and we are only allowed to have the exact bars that we need on site. This means that when a bundle of 50 bars is left in the yard in Wales and doesn’t  make it to London it becomes a major issue. The construction manager does not want to hear the word ‘delay’ at any time!

When the correct rebar is on site the steel fixers throw it in very quickly. This pour alone had just over 35 tonnes of rebar.

Bottom mat being installed alongside one of the sumps.

Further work on top and bottom mat. Drainage being installed on the foreground, crane base can be seen in the background.

The crane base was particularly tricky to install. Four concrete plinths had to be cast into the bottom mat and the base lifted into position on top of them. There is a 0mm tolerance between the four legs. Therefore this required a lengthy exercise of adding/removing steel shims from underneath the legs and tightening the leveling screws. This is much easier said than done and it took a few hours before there was a 0mm difference between all four legs.

Plinths ready for a crane.

crane base in position.

After 6 days of of steel fixing, carpentry, welding and lots of other things the area was ready for concrete. 320m³ was poured in one very hectic day, it took around 12 hours to get it finished and this is not the biggest pour on this project by a long shot. At peak periods we will be pouring around 3 slabs a week.

The area ready for some concrete

About 10hrs into the pour.

the pour would need to be power-floated. Note the large puddles forming due to the torrential rain that came down all day. The gaps between the crane base and the concrete will be grouted at a later date.

A busy few weeks on site and only set to get busier. The main issues encountered so far have been:

• Stores – Expanded operate by using a ‘just in time’delivery philosophy. The materials they need will turn up at the right time in the right place, therefore removing the need for large stock piles of equipment on site. In theory this is a good way to go about it, however, in practice there are many times when the right stores do not turn up or are sent to the wrong place thus creating a threat to the project timeline.
• Logistics – the site is very restricted and has a complex logistics system that goes with it. The gatesmen will turn away a vehicle if it is not on their list so all deliveries have to be booked in a week in advance. Again, this does not work well in practice as there are always last minute deliveries and changes to the schedules. I have had to sweet talk them on more then one occasion to get them to let a last minute delivery in.
• Overzealous construction manager – not really that much of an issue, more a minor bugbear. The is a very specific schedule with pours taking place simultaneously and lots of moving parts. One of those moving parts is the construction manager. He has been a coiled spring waiting to start work and now that we have it is hard to reign him in. Everything must be done NOW, regardless of whether there is the stores or manpower with which to do so. He has been nicknamed the Tasmanian Devil as he sweeps through the area and causes havoc and confusion but somehow manages to get the job done.

On a separate note, today I brought another cat. I am one step closer to becoming a crazy cat person.

Figure 1 – The design for the R&D Building

Having now been on site for the grand total of two weeks, I thought it was time to post my first blog and explain the project to set the scene for future blogs.

PROJECT OUTLINE

The project I am working on is the construction of a 56,000m² Research and Development (R&D) facility North of London. The build covers two sites, with a main R&D building to the North and an Energy Centre to the South with a public road dissecting the two sites. A 4m wide, 150m long, services tunnel runs under this road, connecting the R&D building to the Energy Centre to provide mechanical and electrical services and data. The road running through the site is an important ‘blue lights’ route for the emergency services and the South Site has a high speed railway running along its Western boundary – both of which create significant environmental challenges and places a number of constraints on the Project. Skanska Construction UK Ltd are the Principle Contractors for the Project.

Figure 2 – The Energy Centre

PROPOSED DESIGN

The R&D Building is a 4 storey reinforced-concrete building comprising a basement level and ground level accommodation, consisting of six glass boxes, supporting a two-floor disc. The disc contains two floor plates and has a staggered vertical façade and saw-tooth roof. Upon the roof there are six small external open plant rooms. The R&D building is still in the construction phase with the majority of the basement concrete pads still to be constructed although work has started on the ground floor with some of the Eastern concrete floor pads being poured.

Figure 3 – Construction of the R&D Building

The Energy Centre is a 3 storey steel frame building traditionally built and enclosed in cladding of different types. It has a lower basement area to only one part of the building and one side of the building is allocated to Facility Management and so includes a number of offices and control rooms. The building has a flat roof which will be used to house some mechanical plant including cooling towers and AHUs. Two large flues will run from the roof to the basement to provide an exhaust for the Cooling Towers, boilers, generators and combined heat and power (CHP) unit. The steel frame for the Energy Centre is still under construction. The tunnel connecting the R&D building to the Energy centre ‘broke through’ last week and so work is underway reinforcing and completing the tunnel walls.

Figure 4 – Construction of the Energy Centre

 CONTRACTURAL ARRANGEMENTS

Due to the well-developed relationship between the Client and the Principal Contractor (Skanska UK), the project is being conducted under a cost plus JCT contract with the client retaining the design and ground risk. I am working for Skanska Rashleigh Weatherfoil (SRW) who are the Building Services arm of Skanska Construction UK Ltd. This means that Skanska UK sub-contracts the building services installation to SRW who in turn manage the building services projects and then contract the installation work out to sub-sub-contracts.   The various mechanical and electrical supply and installation packages are conducted under fixed lump sum contracts.

Figure 5 – The services tunnel linking the Energy Centre to the main R&D Building

SO FAR SO GOOD……

As a project manager in the MEP (Mechanical, Electrical and Plumbing) Team for the Energy Centre, I will be involved in both the electrical and mechanical fit out of the Energy Centre and services tunnel which is due to start in Aug 16. Currently I am managing a package to plan, tender and contract out the off-loading, moving and placing of the various plant (boilers, generators, transformers, chillers, large pumpsets, CHP etc) and so I am getting plenty of exposure to the tendering and procurement process. This is proving to be a valuable first role as it means studying all of the technical drawings and developing an understanding of the wider M&E packages – all of which this package will support.

This project is very innovative and is utilising several interesting design features such as a 270m deep ground source heat pumps, a new revolutionary, highly-efficient, baffled cylindrical heating shunts (first time this technology has been used in the UK) and stainless steel rebar to name but a few; and so I already have a few TMR titles in the making!

Gary Jackson

The Calder Highways Overtaking Lanes (CHOTLs) project is to construct 2 overtaking lanes on a stretch of very straight, sleep-inducing, 2 lane – 2 way road some 550kms from Melbourne in rural Victoria.

As Design Manager for the CHOTLs, I held a kick-off meeting with the Client (a local highways authority) to nail down what was in my scope of works and what was out.  I then drove the 6 hours to the proposed locations to do a site walkover (lessons learned from the Amaroo project).

I am to deliver a detailed design to the Client by the end of June.  Drainage and pavement structural design are not included in the scope of works.  The OTLs are to tie into and match the existing pavement structure with subsurface drainage excluded from design.  Essentially, I am delivering the geometric design.

So, Q1; “what is the enemy doing and why”?    Remembering the triple bottom line (people, profit and planet), my enemy is the planet, and it does what mother nature says it must.

The stretch of road where the OTLs will be constructed is extremely environmentally sensitive.  Buloke trees and the mallee emu wren make planning construction in this area a challenge and has already resulted in a re-visit to site to seek alternative OTL locations.

Mallee-emu-wren

Buloke Tree

Traditionally it was accepted that if you veered off a highway at 110km/h and hit a tree within 9m, you could be fatally injured.  The solution was to remove any trees within 9m of the road verge.  Increasingly stringent environmental legislation has made it illegal to remove certain trees. The environmentally friendly solution is to install Wire Rope Safety Barriers (WRSBs) in the pavement verge.

Wire Rope Safety Barrier (WRSB)

So that’s the trees, the birds and drivers looked after.  The benefits of the WRSB seem flawless, unless you are a kangaroo.  Kangaroos are stupid and routinely get cleaned up by trucks and cars.  The issue with installing WRSB is that if a Kangaroo is to jump into the road, they are not as likely to jump out of it when WRSBs are installed.  Areas with the WRSBs have seen an increase in the number of collisions between vehicles and kangaroos.  You’d be forgiven for thinking that kangaroos are a dime a dozen and therefore expendable.  The problem is that they grow to 6ft and hitting one with your car will write off the kangaroo, the car, the WRSB, and potentially yourself.

Public enemy #1

In my opinion, it would seem that the order of importance is planet, followed by people and then maybe profit.  There is no 100% solution to designing out the risk of nature and man crossing paths, but ensuring the sustainability of protected trees and birds is a higher priority than looking after the kangaroos.  It’s no wonder most trucks and utes have bull bars.

Kangaroo defence

Battersea Power Station

In the last few days I managed to get on a visit to the actual Battersea Power Station (part of phase 2 within the wider Battersea project) after I hosted some of the Phase 2 engineers around the NLE site. I took some pictures and thought they might be interesting.

The Power Station itself will become home to a whole myriad of things, from multi million pound apartments, roof top gardens, a hotel, cinema, restaurants, office space and event space.

I floated the idea of a fly through drone video sequence of our site to the Project Manager but he didn’t seem to interested.

Battersea Power Station walk through model

Model of Battersea Project Phase 3 buildings. I have marked out the extent of the NLE Station and Crossover Boxes

Luxury Appartments … one day

Roof of Turbine Room A – Future Roof garden

Turbine Room A

Middle space between the chimneys.

Middle Space

Turbine Room B

NLE Update

Project milestone achieved, on the completion of diaphragm wall piling within the Crossover Box. Other than the release of funds to have a beer or two on the project it means that we can hand over some space and start the excavation. We dont the whole box as rotary bored piles still have 4 weeks left to finish so we are chasing them out of the box as we continue to excavate.

Having excavated from 101m ATD to 97m ATD the diaphragm wall need breaking out to expose the starter bars. Maximum effort to break concrete as quickly as possible without bending any bars. We are quite content with the lack of bent bars so far.

Crossover Box Excavation

Breaking down of the Diaphragm Walls and exposing of Starter Bars

The sheet piles have started springing a few leaks. They did not have any bitumen in the clutches before they were driven. We now have a problem to either construct a small sump into the blinding layer at 97m ATD or try and seal them (very difficult to do). So far we think welding might be an option but will then require digging back out to break the weld before the piles are pulled out. Not a massive issue, but interested if anyone knows how to plug a dam? water level is at 100m ATD so no more than 3m of head.