Wednesday, 4 November 2015

Steel, Website & UAVs

With the flyover at Hammersmith now complete, I have been fortunate to start work as a site engineer with a steel erection company.  28-32 Chancery Lane is a nine storey office development in the heart of London's legal district.

Arriving on site in mid-September, the demolition of the original building to occupy the site was complete and the basement slab was almost finished.

Steel frame erection
With a retained fa├žade and existing adjacent buildings just millimetres away, the installation of the perimeter steelwork has been a challenge.  It is apparent that previous surveys have been carried out to determine the location of these walls and only minor adjustments of the designed structure have been necessary (so far).

Is it bad luck to walk under a tripod?
The website www.brecklandgeomatics.com is now complete and is now live.  This is a showcase of my own Limited Company and the services that I am able to provide as a freelance engineering surveyor.

www.brecklandgeomatics.com

In October, I successfully passed my Unmanned Aerial Vehicle (UAV) flight examination, which means that I am now able to apply for a Permit for Aerial Work to fly "drones" commercially in the UK.  This is the culmination of nearly seven months work involving a two-day aviation ground school (with exam), writing an Operations Manual which covers all aspects of the procedures and safety whilst flying the UAV and also acquiring sufficient flying hours and practice.

DJI Inspire 1 during training



Thursday, 13 August 2015

The End is Nigh

After nearly 20 months of working on Hammersmith Flyover in West London, it only remains to tidy up and leave the bridge "as we found it". Although, hopefully in a better state than it was in 2012 when it was in danger of collapse following years of neglect and had to be closed to traffic!

Today, the flyover has 34 new sliding bearings beneath its piers, over 150 km of steel cables holding it together (the distance from London to Calais - rather apt given that they were installed by Freyssinet, a French company) and a new waterproofed road surface.

Access to the bearings has been improved to allow future inspections to take place and five new door openings have been cut into some of the piers for access into the bridge deck above.

New door opening (without door)
One of the final tasks is to re-instate the covering over the pits surrounding the piers.  These were removed to enable access to the old and rusting bearings upon which the piers sat.

Threaded couplers were cast into the pit wall during their strengthening.  Following a detailed survey of these, bespoke seating cleats were made so that the bolt holes exactly matched the coupler locations.

One of four seating cleats per pit
Next, galvanised (rust proof) steel beams are installed around each pier and a shelf angle is attached to the pier itself.

Steel beams installed
The pit is then covered with a frame and pre-fabricated trench panels - provided by Fibrelite.

Panel installation
The final steps are to replace the tarmac and paving slabs around the piers to blend into the covers. At the pier, another overlapping cover will be fixed to the pier to allow it to move freely.

[to be continued]

Tuesday, 28 July 2015

All quiet on the Western front

The temporary ramps that have been in place at the centre of Hammersmith Flyover for over a year have finally been removed.

The tarmac ramps and hinged covers were put in place to allow work to be carried out at night on the replacement of the expansion joint - before being lowered again in the morning for the rush hour traffic to pass over.

The only problem with this system was the noise created by the cars, lorries and coaches as they clattered over the joint at often more than the regulation 30mph.  Residents in nearby flats overlooking the flyover have had to endure months of disturbance as the works have progressed.

Over the last few weekends, the new expansion joint has been installed - during a full closure of the flyover to allow the concrete to set without any undue vibrations.  Working throughout the 48 hour weekend closures, day and night teams worked continuously to ensure that the road was ready for Monday morning.

Installing the expansion joint - at night
First of all the Eastbound joint was installed and then the Westbound joint was set in place a week later.  At just under a ton each, each metre long segment of the joints had to be aligned and levelled to a high accuracy as cars would be speeding over the joint in all weathers and conditions.

Aligning and levelling the joint
Each steel joint must slope from the verge at the edge of the bridge towards the central reservation at the middle to follow the alignment of the road surface.  This is to allow any rainwater to be collected and removed along drainage channels in the kerb.  In addition, the joint also slopes from East to West to follow the natural "hump" of the brdige.

The specialist joints allow the bridge to expand and contract with changes in temperature and are made up of two interlocking "combs" that are expected to move by 100mm on each side of the bridge between a cold Winter and hot Summers' day.  Movements of 20mm are not uncommon during a single 24 hour period.  The teeth maintain a road surface whatever the gap in the concrete bridge underneath.

Interlocking teeth
Over the last weekend, the ramps and temporary covers were finally removed and a fresh layer of tarmac was laid flat at the same level as the rest of the bridge allowing vehicles to travel over the bridge without even realising that they were "jumping" across a gap between the two halves of the flyover.
The new joint in place
There is still work to be done installing the drainage channels and replacing the central crash barrier, but the local residents can sleep peacefully once again!

Tuesday, 30 June 2015

Expansion Joint Repairs

Hammersmith Flyover is over 600m long and built in two halves with a thermal joint in the middle - actually 6/15th's of the way along from West to East. The expansion joint allows the concrete bridge to "grow" and "shrink" as the bridge temperature changes. During a 24 hour period, the gap at the centre can be 10 to 20mm smaller at night than during the day and over 100mm different between Summer and Winter.

Anyone who has driven over the flyover recently, and especially anyone living nearby, will know that there is a temporary plate covering the joint. This causes cars to have to slow down and makes a loud noise each time a car or lorry passes over it.

Covering over the old expansion joint
Temporary cover and ramp
The temporary covers, which are on hinges, allow works to progress underneath by enabling the plates to be lifted at night, the old concrete to be removed and then being lowered again for normal daytime traffic.

Old and broken out concrete
Surveying the expansion gap
The remedial works are now almost complete and the new expansion joint (a large steel plate with interlocking teeth) to ready to be set into position in the next two weeks.

Once the "steel combs" have been concreted into position, the old covers and temporary Tarmac ramps will be removed and some fresh Tarmac can be laid at the final road level. Job done.

Thursday, 11 June 2015

Awards and UAVs

Another award for Hammersmith

My current project, the Hammersmith Flyover in West London was awarded the CIHT (Chartered Institution for Highways and Transportation Innovation Award on Tuesday. The award was in recognition of the enterprise, ingenuity, design, performance and quality of the project.

Award presented by Robert Llewellyn
Not least were factors such as best-value and cost-benefit.

The re-strengthening of the flyover, working around the existing structure and keeping traffic disruption to a minimum has been a challenge.  Bespoke machinery and techniques have been used to install kilometers of new internal cabling into the bridge to replace the original tendons that have become corroded through use of winter salt and poor maintenance.

Installation of the external "blisters"

French sub-contractor "Freyssinet" was commended for its technological expertise.

UAV Aerial Modelling

As an exercise to determine the method, procedure and results of 3D modelling by use of an unmanned aerial vehicle (UAV), I flew my trusty DJI F550 hexacopter around an old stone building near Thetford, a rabbit Warreners Lodge dating back to about 1400.

DJI F550 with GoPro 4

Approximately 80 photographs were taken from all angles around the lodge and stitched together using Agisoft Photoscan.

Some of the aerial photographs
The photographs are automatically aligned to its neighbour using common points and although there was no positional information, such as GPS data, the software was able to produce a photo-realistic model of the building.

3D model created in Agisoft Photoscan
 
Once created the program could then export the results in 3DS format (3DS max), Wavefront OBJ (3D data modelling transfer format) or even generate a point-cloud which can be imported into AutoCAD via Autodesks ReCap software.

Point cloud in AutoCAD 2014
The finished model is not orientated or scaled.  This must be done from ground dimensions taken independantly.

The quality of the final product reflects the quality of the screen captured stills taken from the original GoPro video.  My next project will use high resolution photographs taken at 3 to 4 second intervals...

Thursday, 28 May 2015

GeoBusiness 2015

Today was the second and last day of The GeoBusiness Show in London. Billed as "The Geospatial Event", it was a chance for anyone and everyone associated with capturing, manipulating and presenting spatial data to meet and exchange new ideas as well as show off their wares.

The exhibition floor was reportedly 64% larger than last years inaugural show and this was evident by the additional stands situated at the entrance of the Business Centre in Angel.

GeoBusiness Show 2015
As ever, the Leica stand took centre stage. However, ironically, having spent the time and money attending the show, the in-joke was that Leica is about to announce a leap forward in technology and all of the Reps were sworn to secrecy before the official announcement on 1st June. Even its distributors, such as Opti-cal, had been instructed not to reveal any information!

Meanwhile, other brands such as Topcon were not so secretive and it was great to meet previous co-worker Peter Roberts, now Technical Support Manager, who enthusiastically demonstrated Topcons new instrumentation.

The show was ideal for company directors such as Steve Ashcroft of Paragon Surveys to discover new products that might be useful in carrying out surveys in ways not possible before now. The event was also a showcase for suppliers to gauge interest by demonstrating working prototypes of new gadgets and gizmos.

Personally, I did not have enough time to fully engage with this years event, but more than made up for this by meeting the legendary Ralph Perez, owner of New York Geomatics, whilst on a rare visit to London. Ralph is a great ambassador for the industry and it was an honour to meet up in person.

The future of surveying is assured and whilst technology is making the collection of data even easier and quicker, it is still driven by the surveyor and his imagination and skill.

Sunday, 17 May 2015

Bearing replacement (2)

The bearings that allow Hammersmith Flyover to expand and contract are situated underneath each of the 15 columns or piers rather than on the top - which not only means that the piers move as well, it also means that the bearings are in a 2m deep pit below the pavement and makes replacing them a very difficult operation.

Construction of a pier pit in 1960
To replace the bearings, it is therefore necessary to firstly lift the pier to remove the old ones. This is easier said than done. Hammersmith Flyover is over 50 years old and the piers are not designed to be lifted. There is a danger that the columns will crack, the pit floor will fail or that the pier will topple over setting off a domino effect and causing the whole bridge to tip over.

So, before any lifting could take place it was necessary to strengthen the base of the pit, by drilling steel rods into the concrete slab, stress more steel bars around and through the base of the pier to prevent it "exploding" apart and also to demolish then rebuilt the top of the pit wall (see below) to allow lateral jacks to be installed to prevent the pier toppling.  All of these operations have taken a year of preparation.

Pier pit wall strengthening

The new bearings are attached to the underside of the piers through large steel plates bolted and grouted to the underneath. As mentioned in an earlier blog, the carrier plates must be installed to a very small tolerance. The two plates have to parallel to less than 1mm. However, "if it can be measured, it can be improved". Using precise Leica theodolites and industrial grade corner cube reflectors, measurements of 0.2mm are achievable. Setting the carrier plates to a tighter tolerance than necessary, maximizes the amount of accuracy that may be lost due to fabrication tolerances.

Installation of the carrier plates
Supplementary jacks at each corner of the pier help to keep the pier level and steady whilst the precise work of setting the carrier plates is undertaken.

Working in tight areas means that Automatic Target Recognition (ATR) is critical. The distances measured are shorter than the minimum normal focusing range of approximately 1.5m. Similarly, ATR does not need ambient light and can be used in dark conditions.

The next step is to pour grout into the gap between the carrier plates and the pier base to ensure full load bearing...