Holdfast Training Services Trial Blog

5 weeks down and hopefully something of value to report. It took several weeks for my brain to warm up.

Interesting to see the content of Brad and Dan’s work. The temporary works environment looks excellent in terms of variety and volume of small problems to solve.

I am now working for Robert Bird Group (RBG) in Sydney within one of their structures teams. The Sydney office contains 2 structures teams, a civil design team, and a construction engineering team (temporary works and construction methodology). I am currently working on 2 projects; University of Wollongong (UoW) and Blacktown and Mount Druitt Hospital (BMDH). UoW is in the tender design phase and BMDH is under construction.

The structures team is managed by a principal engineer, with the support of 3 associate engineers.  RBG policy dictates that all associate engineers and above must be chartered engineers. Work packages are assigned to the engineers, including myself, at the team resource meeting which is held every Monday morning.

My responsibilities to date:

Task 1.                  UoW – Structural Steel Frame design on Levels 4 & 5.  I was tasked to develop the concept designs for the entire level 4 and 5 structural steel roofs. In the initial stages, I had to scrutinise the architectural model in Revit as well as the architectural floor plans to produce some initial layouts for a frame. The aim was to create a frame layout that would correspond with the Architect’s floor plan but, also achieve continuity of load run-down through to the concrete frame to avoid load transfer. The level 4 roof was to be built off the level 3 slab, and the level 5 roof off the level 4 slab. You can see the extents of the steel frames for level 4 and 5 in RBG’s structural BIM model below (you can see that level 5 had no structural elements at this stage).  My initial layouts were incorporated into the BIM model and the in-house draftsman created some hasty level 4 and 5 general arrangements (GA) for further design development.

In order to simplify the analysis and design, I decided to consider level 4 & 5 separately. I used a software package called Microstran (I agree with Brad, much easier than STAAD) to complete the analysis for the indeterminate frame. The biggest challenge was ensuring that lateral stability was provided and that the frame included members to support the various architectural features (e.g. curtain walls and façade).  I finally opted for horizontal and vertical bracing in order to provide lateral stability (loads eventually running back into structural slab).  The image below shows my Microstran model for level 4 and the various structural elements that had to be included to support some of the architectural features.

To create a working model, the nodes and members had to be modelled accurately in order to complete analysis. Deciding whether a connection was to be pinned or fixed was very challenging. The process helped me understand how the overall structure and individual members were behaving (e.g. tension only members, what the different connection types would be and what forces could be transferred).  To simulate the interaction between the frames on level 4 and 5, I modelled the connection as pin supports.

Once the associate engineer was satisfied that my model was stable, I then had to calculate the actions and create the design load combinations for the model (22 in total). This included the calculation of wind actions using Australian Standard (AS) 1170.2.2011: Wind Actions. The process was similar to EC; you work out the design pressure and your net pressure coefficients to get a KPa value (extract from my calculations below).

After calculating the actions on the structure, I then assigned section classifications to each member in the model. I started by considering the primary rafter and modelled it as a SS beam to get a ballpark BM. With the primary member assigned, I worked through the structure and reduced the section geometry as I went. I had to go back and change some of the sections, as RBG will typically use particular sections for different purposes (e.g. CHS/SHS for struts and EA for ties).  With more experience, this process would be more intuitive.  The image below shows my final model for level 4, the different section classifications are indicated by different colours (left image). The image on the right is my final analysis and shows the BM envelope for all load combinations. I used the results to complete strength and serviceability checks on the sections I had chosen. Australia didn’t completely copy the English on this one, they have the RED BOOK for their steel section properties and capacities. Deflections and bending capacities were satisfactory (Span/500 was used to be conservative). I did have to incorporate some fly bracing (restraints) to reduce the effective length of the main rafters; to prevent buckling in the wind suction case.

RBG subcontract the final production of structural drawings to RAMTECH software solutions in India. Therefore, I had to produce some marked up GAs and elevations to communicate my design output for final drafting (see examples of my work below). The final drawings will be issued to the competing contractors, via the client, to assist with pricing the job for tender submissions.

Task 2.                  BMDH – Precast concrete façade inspections.  I was also tasked with overseeing the final approval and inspection of some pre-cast concrete façade panels on the BMDH. The panels are essentially SS slabs on the outside of the building. They are supported at the top of the panel by a corbel that sits on the structural slab and is pinned by a dowel connection (see image below).

The design had already been completed for the panels and I just needed to check the details during my inspection. However, I wanted to understand how the panels were behaving and did some simple analysis to identify where the critical points for inspection were. I deducted that the shear load in the dowel connections was critical and that the critical BM would be in the corner of the panel (FBD and quick analysis below). The wind action would also create biaxial bending (so vertical and horizontal reo required in panel).

The panels were being constructed by Hanson in their factory just outside Sydney. The Architect (Jacobs) and Contractor (AW Edwards) were also present during the inspection. The reinforcement was satisfactory; however, honeycombing was identified in some of the corbels, which reduced the cover and durability of the section. Hanson will now provide a product specification and methodology for patching in those areas.

Now firmly settled into Phase 3, I thought it was about time I provided an update of my most recent ponderings.

I am working for Tony Gee and Partners on a new link road near Wigan. The A49 Goose Green to Westwood Park Link Road scheme comprises a new 2.3km highway to relieve congestion and provide future access to a new development – Westwood Park. The scheme consists of a new dual two lane carriageway with new non-motorised user routes, four new road bridges, two new footbridges and culvert repair works. Two new roundabouts will be built as part of the scheme to provide access and distribution into the future development of Westwood Park. The scheme provides design opportunities across highways, structures and geotechnical disciplines.

Proposed A49 Route with Route Sections & Structures

Roles – One of my current responsibilities is for the developed design of Scotsman Canal Bridge. This was tendered as an integral bridge under the ER’s. The design consisted of 8No. 1.6m deep W12, 32.3m long, precast pre-stressed concrete bridge beams supporting a 250mm thick reinforced concrete bridge deck. The bridge has a 13.7° skew. The superstructure is made integral with reinforced concrete abutments supported on reinforced earth embankments atop a 7m wide zone ground improvement.

Integral bridge design solutions (designed without any expansion joints between spans and abutments) offer a host of benefits from increased durability, reduced maintenance and lifecycle costs. However, they can pose the designer several issues to consider from the moment connect between beam and deck to the geotechnical issues of increased earth pressures and deformation behind the abutments. At the moment these are problems for future Al to overcome – so wait out for further blog posts!

A calc or two – Given the rushed nature of tenders, one of my initial tasks has been to verify the tender design for various aspects. These have included;

1. Verifying the abutment pad pressures – The ground improvement works that the proposed abutments are to be sited on have a maximum uniform bearing pressure of 170KN. Assuming the carriageway dimensions in the tender and a precast manufacturer of the W12 beams a permanent load take down was achieved. The tendered ER’s stated an SV 196 variable loading requirement. From BS EN 1991-2 a Group 5 loading regime was assumed with LM1 and LM3. In the same vein as Ex Bridge, the notional lanes and load models were calculated to attain a variable load adequate for the purposes of this rough pressure check. My initial verification checks noted;

122KN (permanent) + 64KN (Variable) ≥ 170KN ∴ Not Okay

However, it is deemed that values used for verification are very conservative and so this could be satisfied later in developed design.

2. Verifying Edge Beam Arrangements – As designers there is a need to design for the execution phase. One of my tasks has been to verify various edge beam arrangements for the contractor to choose as a desired install arrangement. This has involved creating beam arrangements around; beam, parapet and deck elements. From here the permanent load of the system is calculated and then the beam arrangements are checked for global stability / overturning moments allowing for wind and pedestrian effects. A summary sheet is then provided to the contractor in order to allow an informed choice of install arrangement.

Sketch Summary sheet

I have quickly realised that in the design office communication is as important a skill as on site. Communicating assumptions and/or queries early makes for a smooth and productive design phase. However, this information also needs to be succinct and relevant to the recipient.

I hope to provide some details of the developed design in the coming months as I get to grips with LUSAS!

Al

I am working in a team of 10 for the JV that has the main civils contract for Hinkley Point C.  Bouygues-Laing O’Rourke (Bylor) are responsible for the structure(s) that contain the nuclear gubbins for the 3200 MWe reactors, cooling systems, and ancillary buildings. Currently circa. £2bn of contracted scope, and rising.

The TW office responds to requests for scaffold, formwork, lifting calculations and other curios from site on an ad-hoc basis.  They liaise in advance with the pre-construction team (working mostly out of Paris) to design formwork and falsework systems along with bases for the 40-50 tower cranes to be installed.  Large volume packages are let and managed by the TW team to supply chain companies like Sateco, Peri, Doka and Hunnebeck.

I just completed my first task which was re-working some calculations for reinforcement cage lifting and issuing the new lift schedule to site.  Not quite a flume I know Ed!  The cages were for the reactor inner containment structure which consists of a pre-stressed ring and conventional reinforced concrete.  This forms the lower wall of the reactor building(s).  I can’t put up any decent drawings or models, unfortunately.  The re-working was required as the method of installation changed, separating the cages into smaller lifts.

I was surprised at the factor of safety of 1.35 x 1.2 was applied for what is 3 crane lifts.  Onto the wagon, off the wagon and turned vertically prior to installation.  By using some steel designers manual/StaadPro/standard beam formula I managed to reduce quite a lot of the welding on each cage.  The number of ties on the cage was the critical case.

Proposed tie and weld arrangement.  Still less conservative than the original design.

Ties themselves are difficult to quantify although tensile testing exists.  An assumed SWL of 254N (25kg) gave a FoS of 8 from tensile test results.  I couldn’t find out where that SWL was taken from.  It seems rightly high in FoS terms given the risk of corrosion, human error in tying and damage.  Future testing of tied wire is in the offing which should provide data for my TMR on the subject.  I expect the variance between samples to be greater, and still quite difficult to pin down.  However, any improvement in capacity reduces the amount of work for the steel fixers which equals fewer hunchbacks and less knackered wrists!

Working in the office is a noticeable step change from the site.  Namely, that, a lot of people wear headphones all day and there are fewer threats of violence or general harassment. When I told the animals on site that I was going to work in TW they said that I’d be responsible for adding zeros to the budget and making things difficult to construct.  On reviewing a small work package for welding to reinforcing cages I have observed how this can occur.  I have also seen how easy it is to specify something that is overdesigned or even unsafe to construct. Particularly as they do not see many pairs of eyes before heading out the door.

I’ll hopefully have something more coherent and of note to post soon.

Dan

I thought it would be interesting to briefly post about a project I’m working on as it is a little different:

Aquatar is a brand new waterpark development on Etaifan Island in Doha, Qatar. The client is Katara Hospitality, a global developer of the Emir of Qatar. Atkins are delivering the concept design.   The project involves 21 rides and attractions, a 75m iconic tower ride, themed bridges and various dry attractions.  The waterpark site is located on Qetaifan Island, an area of recently reclaimed land on the coast north of Doha. This means the buildings will be subject to high thermal and wind loads, seismic actions and durability requirements of a marine environment.

I am responsible for the design of the Icon Tower which will be a braced steel frame with an internal reinforced concrete core. The tower will take the form of an offshore oil-rig type structure as seen in the picture above and in line with the theming of the waterpark. The height of the building will be around 75m with a base width of around 25m. The tower will have many water rides twisting around and through it meaning that saving space is essential to maximize the flumes passing through. These rides will be supported back to the primary structure by secondary steel bracketry (by others). The tower is located offshore on a separate reclaimed island (Icon Island). Lateral stability will be achieved by a combination of the core walls and action of the braced steel frame that will withstand all design horizontal loads from wind and seismic actions. Gravity loads consisting of self-weight of the structure, super imposed dead loads and live loads will be transferred via the floor plates to the braced steel structure and core, to the structure foundation.

Slide layout. Currently the shape and direction that the slides will go in is not defined. For the flume slides the average angle of a slope is 1:11. The actual path of the slides will be decided by the ride manufacture and will not come at this stage. What I am doing is considering average loads on the structure whilst waiting for a water slide manufacturer to provide me with loadings. The flumes will go around and also through the tower therefore I need to leave sufficient room between the tower bracing to allow this to happen.

Quick calc. Between floors 2 and 3 at 34m and 50m respectively, there are 5 flumes.  Assuming each flume is 2m in diameter, and considering the most simple ride that goes in a circle around the circumference of the tower (they will be more complicated that this and this will cause even greater issues, however simply for this calc they go around the outside). The circumference at the bottom is roughly 78.5m. The height difference between 34m and 50m is 16m. At a 1:11 slope the length of flume needed to go from 34m to 18m is 176m. This means that the flume will go 2.24 times around the structure (176/78.5) within this 16m floor level difference. A single flume will take up 4.48m (2m high x 2.24 loops) of surface area over the structure of the 16m. 5 Flumes will therefore take up 22.4m of the 16m available. Tubes will therefore have to be hanging off the structure 2 wide in some locations, and will need to go through the structure multiple times in other locations. Space may be an issue.

This highlights some of the complexity we are working with and I’m sure will provide good blog material in the coming months.  Now I’m off to dabble in some seismic loading.

Hi all,

Merry Christmas, I trust like me everyone had intentions to do loads of thesis but ended up doing none.

Getting a little bored of working for a management contractor I decided to move to phase 3 mid November. I though now would be a good time to give a little update.

I’ve started at a small office which have recently branched out from Australia into the London market called BG&E. I haven’t yet worked out what that stands for, for those interested here is the website.

Home

There are 9 in the office, 4 structural engineers, 1 BIM technician, 1 CAD technician, 2 RC detailers and me. So far the office has been doing temporary works for some of the big London contractors and some mid rise residential developments in Cyprus.

Since starting, I have been getting bits of work but as can be expected nothing substantial. I’ve outlined what type of stuff I’ve been doing.

Task 1 – Reinforcement rates

Part of a wider package with Getjar, as a second checker I used a mixture of RC intents and details to calculate tonnages for costing as part of a tender return.

Task 2 – Transfer Beams

The Broadway, London is a resi/commercial development with 6 buildings between 14 – 20 stories. The structural engineers, RBG, have detailed a steel section encased in RC as a transfer structure for a line of columns which go the hight of the structure. The step that the beams make is an architectural feature of the building creating large lobbies, see the section through below.

The issue was the contractors crane strategy did not have the lift capacity/radius to lift in the transfer beams. So they engages BG&E to conduct an option study, which was then given to me. There was no information on column loads, just the GAs and floor load diagrams. Unfortunately for me, the column tributary areas are different for each column and also the loads. So I did a column run-down using load reduction permitted in EC1 to get the loads at the base of the supported column. I then used a software called RAPT to ‘play’ with possible options. The most effective solution would have been to increase the depth of the beam and use normal reinforcement, however generally beams cannot be increased in depth due to the other trades. So I increased the width of the beam to 1200mm and it worked with 3 layers of 32s @ 100 (in the bottom), this was proposed to the contractor and we wait for further work. Clearly PT could have been used, but the it is not clear if the floor plates will be PT as they are c300-350mm which is thick for the spans.

Task 3 – Climbing Screens

Wembley Park, is a large resi development to the left of Wembley Stadium for those who have been recently. The contractor has won the job and is trying to work out their climbing screen and back propping strategy, the climbing screens can be seen below. This seems a little late to me, how much floor back propping is required and how quickly it can be struck must surely be known to form a programme. Unless it is a guess….

Getjar ask BG&E to conduct a concept study to see what is required for the climbing screens. Again the RC intent was not available as the design is not that advanced, all that was available was the floor plans and loading diagrams. Looking at the typical floor layout it was clear that there were three different spans. Knowing that the RC slabs would be designed for the loads in the diagrams, i.e. permanent case. I built the spans in RAPT (programme) and calculated the forces and reinforcement required. I then used this to compare to the construction case with the loading from back propping, climbing screens and a construction LL.

This showed that the climbing screens did not need any additional back propping, if the loads where not applied at the same times as the back propping to construct the wet deck. This is unlikely, as the buildings a residential the SDL and LL are low, 1.5Kpa each. The 250mm RC slab exerts a back propping load significantly larger than this and would need back propping over at least two floors. I calculated that for the loads to be combined the reinforcement would need increasing locally by up to 15% above that required in the perm case. It is now up to Getjar to do a cost exercise, material cost v programme to see which is preferred.

As a side note I also check deflections to ensure deflections under construction loading where not excessive. Whilst doing so I noticed that one of the larger spans was deflecting 30mm under permeant loads which is over span/250, which would be bad for internal finishes. I raised this to the contractor and this may come back to BG&E to design a PT slab for this area.

Task 4 – Tower Crane Grillage Cat 3 Check

The foundations for tower cranes are generally considered temporary works and as such fall under the guidance of BS 5975. The level of the required design check is outlined generally on the complexity and consequence of a failure, the category’s can be seen below.

My previous project, One Nine Elms has 5 tower cranes, all supported off grillage which is more complex than normal, I have discussed one at length in a previous post. Clearly the consequence of a failure could be dire, for those with a strong stomach YouTube ‘tower crane collapse Mecca’. It is also bad for business, failures are very public affairs and to make them worst developers/main contractors like to put their company logo on the crane. Anyway, a cat 3 check should be conduct by a person outside of the organisation which did the design. The check should be done without the calculations, just the drawings and any pertinent information, loading etc etc. This task was given to me with the direction to see how far I get…… shit. I was given some information about the crane and Carey’s design drawings.

My first start was to check Carey’s had used the correct loads from the crane supplier, it was slightly concerning to find they had missed the most onerous case a storm hitting the front of the jib. I built the steel grillage in a software called Microstran (similar to STAAD) and applied the loads with a number of different combinations to get forces and deflections. I then realised I have forgotten everything Neil taught us about steel and spent a day going back through section and member checks by hand, the software also does a check which it useful. Clearly somebody sits in the crane cab so a large differential deflections between the legs gets amplified higher up. I also believe the crane suppliers factor up the loads they provide, as a way of reducing deflections to stop Pdelta effects.

By far the most difficult check was the connections, with my main issue being whether to fix or pin the members at the joint. I found the 16mm FW on the fin plate insufficient by some margin in either case and suggested an alternative solution. The solution (see below top) uses and 8mm FW which can also be done with one pass so Saving labour costs. In checking the apex type of connection I found that the plate welded to the plunge column plate resulted in a bearing stress great than the capacity of the section and would also be difficult to weld on site. After some head scratching and advice I came to the solution below.

Quite a bit if stuff in a couple of weeks and I am learning lots quickly. One thing I have noticed is that the engineers do almost everything on some form of analysis software, Excel and Bluebeam with very little being done by hand.

I hope I haven’t bored everybody to much but you already know I’m a geek.

Brad

James, these are the loads supplier by Select for a 70m tower crane. The overturning moment drops to almost nothing when the crane is tied.

Since the last update I’ve continued working on Glen Lyon. It appears that it is something akin to Hotel California, in that you can check out – but can never leave. The list of operational vulnerabilities is growing, with many of the top ones preventing production ramp-up to full potential. As it currently stands they are limited to 87mbd (1000 barrels a day) (87*1000*$62.65~$5.5m a day) when they should be producing at 130mbd. The delta created between these 2 values is quite considerable for a daily profit. Since these figures are so great, intervention was required. This is in the form of a ‘Vulnerability Strike Team’ made up of a multi-discipline team of engineers, in which I am the mechanical/project representative. A quick outline of 2 scopes (8 in total) below:

Rundown cooler change-out

The production of crude oil requires cooling from 90degC to 50degC for storage within the offload tanks. This cooling is achieved through 2-off rundown coolers, consisting of plate heat exchangers. Over the past couple of months the pressure differential across the coolers has increased from the allowable of 0.7bar to it’s current level of 2.7bar. This level displays high signs of fouling/blockage. The current understanding is that through the operating conditions which has been used recently this may have resulted in the build up of wax, where the wax appearance level is 38degC. Both coolers must be online to ramp-up above 87mbd. Current options to solve this were as follows:

1. Perform a chemical de-wax procedure using a solvent based chemical. This was completed but showed no signs of improvement.
2. Accept higher export temperature, as long as it does not exceed the safe working limit of the offload storage tanks. There was even talk of offloading at a higher temperature and chartering a tanker to drive around the North Sea to allow the crude to cool to 40degC so that it can be offloaded in port.
3. Change-out the cooler for the spare unit held in storage.

After a failed attempt at option 1 we pulled the trigger on option 3, which was my bag. This change-out required a 16Te vessel-vessel lift (heaviest lift conducted on Glen Lyon since production started earlier this year) which required a sea state of <2.5m significant wave height. It then involved an unknown weight (based upon unknown quantity of wax) of an inboard lift, over live plant to remove the old cooler. Long story short, they managed to lift the cooler but it was 102kg below the allowable 10904kg safe working limit (~99%). This was an imposed limit by the mechanical handling contractor based upon stress analysis performed on the cooler lifting points. Some photos below to show you what I’m talking about.

Spare unit – lifting point circled

Trial lift conducted after a design of rigging

Offshore cooler – required removal of closing spools and complex lift

Offshore unit – confined lifting space

Heating Medium – leak mitigation

A further scope of work I’ve been SPA for has been the remedial works required to recover from the discovery of unreliable/failed flow transmitters (as described in previous blog). This scope involves the works required to mitigate against the potential of instrument failure of a 16″ and 8″ heating medium line. Both options below are being worked up concurrently:

1. Drain down of approximately 25m3 of heating medium, removal of old flow transmitters and replacement with blank pipe spools. This will require a 7 day outage, which would cost them around $30-40m in deferred revenue. This is not currently acceptable but is the base case.
2. Engineer an external pipe clamp for mounting over the top of the flow transmitters. This involves a case filled with resin. We are currently working up the control of works required to enable this work to be done while the line is hot, reaching temperature of 110-140degC. The 16″ clamp weights around 800kg so stress analysis of the pipe is required, which is still unknown. The decision was to buy these regardless since if this option is feasible it will prevent a 7 day outage.

To provide a little context I’ve included a couple of photos below showing what the flow transmitters look like.

16″ flow transmitters

8″ flow transmitter – bunding in place for potential leaking

8″ – constrained construction

I guess in summary, something that I’ve not been exposed to before is the realities of the importance of production revenue. The vulnerabilities we are currently working on will hopefully help Glen Lyon reach its potential of 130mbd, bringing in ~$8m a day. The pace of life is very different to planned project delivery, but it makes things far more interesting anyway. Although there is currently no time for thesis….

Interesting article in this months issue of ‘The Structural Engineer’ on how engineers can overcome the problems between design and implementation of seismic-resistant schools in rural Nepal.  It covers issues such as skilled labour/quality control, availability of materials, local politics, bureaucracy/design approval, corruption, and perception of materials.  It also proposes the following recommendations:

1) Engage with local politicians. Try to win the trust of individuals in the community who can help you understand the power dynamics. This is as important a preparation as a site survey.
2) Understand the limitations of the local workforce. Even working masons struggle to
understand written plans and new methods. Consider photos and 3D constructions. Expect a diff erent work ethic from labourers, and factor in delays.
3) Source materials carefully: you may need to compromise. Consider the problems of
transportation.
4) Consider innovative materials and methods. See what has been used successfully in
the area.
5) Adapt buildings for safety, but incorporate traditional features and appearance.
6) Anticipate corruption, and devise a strategy for its management from the planning stage.
7) Liaise with and learn from NGOs already working in the area: they will have solved many of the problems you face.
8) Remain optimistic that your efforts are worthwhile, and that children will lead better and safer lives as a result.

Given the environments we may find ourselves working in the future it’s worth a read – there’s also a link in the article to a webinar for the more visual learners!

Link to article:  https://www.istructe.org/journal/volumes/volume-95-(2017)/issue-11-12/complete-issue-(november-december-2017)

Those on Phase 1, if you aren’t already aware, you can get a student membership with the IStructE for free that gives you access to a lot of useful resources.

Link to student membership:  https://www.istructe.org/membership/types-of-membership/student-member

Ed (or anyone else who’s worked out there) – during your time in Nepal was there much consideration given to Earthquake design?  Would be interested to hear your thoughts on the article.

I am trying to specify a connection detail for a 50mm rising foul into a 100mm dia gravity sewer.  Peak flow is 0.05l/s, assuming 50l per person per day and 15 people.  I have read about septicity causing illness in rising mains, Wessex Water describe it as:

• A common problem with foul pumping stations is a combination of low flows and long retention times. This results in bacteria multiplying in the anaerobic conditions. This is called ‘septicity’ and can occur in wet wells or rising mains.

I think that I need to provide a break chamber to slow the flow prior to it entering the gravity manhole.  The design information does not specify how the connection is terminated, and as the design life is 10+ years septicity could cause a problem.  Practically speaking, it will prevent the inside of the manhole becoming ‘splashed’ by high pressure flow.

If anyone has any experience on such connections it would be appreciated.

Thought it would be a useful issue especially for providing such infrastructure overseas and the need to control disease/illness.

Cheers,

Dan

G’day all.

This is mainly a request for help should anyone know of a solution or encountered a similar problem before.

Context

I am working on the Mernda Rail Extension Project (MREP) in Melbourne in the rail construction team for John Holland. The main items of my scope are in the delivery of the traction power to run the trains. This includes three new substations, overhead delivery of traction power and the installation of a new 22kV distribution network (underground and aerial).

22kV distribution

The bulk supply points for the Mernda project are the AusNet Epping Zone Substation and AusNet South Morang Zone Substation. AusNet are the District Network Operator (DNO).  The 22kV supply between AusNet zone substations and the traction substations is via cable. The majority of the supply is by underground cable between traction substations, with the exception of a section of aerials (with a small cable section) between Epping and Hawkstowe Traction Substations. The general network arrangement is provided in Figure 1.

Figure 1 – 22kV Arrangement

The Ariel transmission, depending on its location, be it in the rail corridor, residential area or on a shared user path (walkers and bikes) has different pole types, namely steel or concrete. The choice is driven by cost, construction time and the design standards.

The Rail Operator has stipulated that design must meet standards AS 2067 which includes reference to Standard AS/NZS 60479.1 for calculation of levels associated with the risk of heart fibrillation and Standard ENA Doc025, EG0 providing guidance in establishing risk level.

The bottom line is that the required earth grid resistance of 5 ohms cannot be achieved in all areas using the Rail Operators standard earthing arrangement. This is mainly due to the fact that we have solid rock 300 mm below ground down to 10 m deep along the entire site, which is not great due to the high resistivity levels, which are well over 100 ohms at all locations with the worst being 200 ohms until you get below the rock.

There are 32 concrete poles shown in figure 2 that are in public areas and need the earth grid to achieve 5 ohms. We cannot get to the 5 ohms for any of the poles and just to get near this we would need multiple 10m+ earth stakes at each pole. Not a cost that the project or the rail operator wants to entertain.

Figure 2 – Concrete pole dimensions

Therefore, there are two options for a solution going forward:

1) Apply a probability assessment in accordance with Guide ENA EG-0 referenced in AS2067:2016. – This has been flatly refused by the rail operator.

2) Cladding poles with an insulating medium to a height of 2.4m to mitigate the possible Touch Voltage hazard to meet the requirements of AS60479.1. – This is the preferred option.

Question

My question after being unable to find a product that can conduct the role of “cladding the poles”, does anyone have any experience with this issue and know of a product, or a possible solution that has not been considered?

If there are any other questions about the project, traction power, substations or work in the rail environment I will try my best to answer.