Second coming

Stonehenge, Buckingham Palace and the Clifton Suspension Bridge are testament to the engineering and construction skills of bygone eras. But how easily could they be replicated today? Kier London, Faithful & Gould and Mott MacDonald put forward their proposals.

STONEHENGE

Tender

To: Wiltshire County Council

From: Kier London

Presented by: Kevin Coyle, James Catchpole, Blessing Gwena, Nick Miller

Additional cost advice: Realstone, Blockstone, Natural Welsh, Ainscough Crane Hire

Introduction

The Kier design team’s proposals seek to deliver a successful modern day Stonehenge in terms of costs, methods of construction, and programme. to bring Stonehenge into the 21st century, we propose to rebrand it as public art in the same vein as the world famous Angel of the North in gateshead.

Our approach is based on a new build project on an unspecified site in south Wiltshire, with a design team consisting of engineers, architects and draughtsmen.

We have taken a holistic approach to the design process by maintaining focus on practical delivery, affordability and long-term performance. We are keen to deliver a Stonehenge project that requires minimal maintenance and is sustainable.

We have selected the most appropriate foundation solutions for the design, taking into account the existing ground conditions in south Wiltshire and topography. The site levels have also been carefully considered to minimise waste removal from the site. cost, speed of construction and the impacts on overall construction programme were all taken into account.

Sustainability is at the heart of our design. We are aiming for a ceeQUAL (civil engineering environmental Quality Assessment & Award Scheme) “excellent” rating.

Special attention will be paid to environmental impacts of elements such as water, noise, dust and energy.

Furthermore, while the original stone was transported from as far away as Wales, we propose to use local quarries for stone and minimise transport costs where possible.

Construction 

The success of a faithful rebuild of Stonehenge rests on our ability to source the original materials and our methods of construction. in ancient times, transportation of the stone was the biggest challenge and very labourintensive.

We have opted to transport all stone by road. We explored rail and water, but the local infrastructure in Salisbury would not be able to support our project.

We have calculated a programme of 15 weeks 2 days, an improvement on the millions of manhours needed in prehistoric times.

Lifting techniques would also have been a major challenge when Stonehenge was first built. extensive archaeological studies have concluded that rope would have been the main material used for lifting the stones into upright positions – inch by inch.

We propose the use of a 160t mobile crane to lift stones, the largest of which is 50 tonnes, into position. With no detailed information of the ground conditions, we have opted to build a piling mat along the avenue to accommodate the crane. this will be positioned in the centre of the inner circle for the majority of construction and is designed to achieve a maximum reach of 17m. Lifting eyes will be set into the stone to enable attachment to the crane and slings will be used for extra support.

Buildability

We explored how we could erect the stones safely and achieve stability. The weight of the stones would provide stability and keep them in place. the main concern was the horizontal forces. We assumed a uniform wind load before deciding on the depth of our pits – 1m deep for the smaller Bluestone megaliths, and 2m for the sarsen trilithons (two uprights supporting the stone lintels). The pits would later be backfilled using excavated material.

The position of our tower crane is key to ensuring we deliver our project in the quickest time possible. it was important that we minimised the risk of crane standing due to associated costs and loss of programme. We have devised a strategy that allows lorries to drive onto the site with the stone already laid in the correct position and park as close to the crane as possible.

This process will help eliminate storage issues and will limit the number of vehicles entering the site. each stone will be numbered and delivered according to the sequence of construction. 

Health, safety and environment

We will reduce labour by employing mechanical methods of excavation and compacting. We have allowed for excavators to dig the pits and trenches. We have also allowed for remote controlled compactors, which will help eliminate human input when it comes to the backfilling process. 

Excavating and moving large amounts of soil presents many challenges, mainly storage and disposal. therefore, all material excavated will be used as backfill and for the mound.

Costs

In assessing costs, the most difficult task was to locate a local quarry which could provide the stone. Following numerous enquiries, and after eliminating those suppliers who sourced their stone from china, it was decided that the smaller Bluestones would be sourced from a quarry in Wales, with the sandstone used for the sarsen trilithons being sourced from Derbyshire.

We contacted quarries to provide a cost per tonne for each type of stone, and calculated indicative haulage costs which covered the transportation of the stones from the quarry to site. the rates in the cost plan refer to an amalgamation of these two sources of cost data to deduce a realistic estimate for the cost of the stone. the rates also include an allowance for stone working as the stones would be cut larger in all dimensions as the quarries could not guarantee exact sizing.

Our main contractor preliminaries appear very inflated, due to the fact that almost 40% are made up from the costs of the crane. Another factor in the high preliminaries cost is the quantity of site hoarding, as it is a very large site with a relatively small build area.

To achieve best value for the client, we attempted to calculate the wholelife costs associated with the structure.

However, no whole-life cost model existed for a structure with a lifespan in excess of two millennia. Factors such as a couple of world wars per century and the severe effects of weathering due to climate change would need to be taken into account. Bearing all this in mind, it was decided that the whole-life costs would be astronomical.

BUCKINGHAM PALACE

Tender

To: the London Borough of Westminster

From: Faithful & Gould

Presented by: Mat Fenner, Richard Stocking, Bill Bladen

Introduction

After an initial brief discussion, we concluded that nearly two centuries after the original Buckingham Palace was created in the approximate form we see today, it would be very difficult to replicate in its original construction. 

The industry has not retained the traditional craft skills that were commonplace in the 18th century, or where those skills still exist there are far fewer artisans practising. Prime examples are the joinery for the moulded door frames and sash windows, or the traditional lathe and plasterwork for the ceiling mouldings. 

By incorporating these skills into the project, the construction costs and programme timeline would be significantly increased. We therefore decided to use a mix of traditional and modern methods of construction to make the programme far shorter, and use off-the-shelf materials that the majority of workers in today’s construction industry would be familiar with.

Method

We would construct a concrete and steel frame, making it wind and watertight as soon as possible. the next step would be the internal works, fitting the windows, and then fixing the stone cladding. then we would construct the roof by laying natural slates over a steel and timber construction.

Sustainability

Because of its heritage status and traditional design, Buckingham Palace is regarded as one of the worst energy performers in London. the estimated annual utilities bills are in the region of £2.2m. to address that we looked at priorities that would give us the maximum payback on energy conservation while not damaging the Palace’s aesthetic appeal.

We would replace all 760 traditional sash windows with modern versions. These would give us a huge saving on heat loss and combined with heavy insulation of the walls and ceilings, we would be creating a far more energy efficient structure.

Additionally we looked at technologies we could deploy to enable the palace to generate its own energy. these included photovoltaic cells, which would supplement electricity drawn from the grid. We would also install a ground source heat pump. these additions cost around about £10m but even in the reasonably short term the Royal household would notice the payback.

Fit-out

Inside the palace there are 19 state rooms, 52 principal bedrooms, 188 staff bedrooms and 92 offices. We would commission plaster replicas of the moulded ceilings and finishes.

We estimate the project would take around three years, though that could be shortened by running some activities concurrently.

This proposal excludes landscaping, the reconstruction of marble Arch, which was originally part of the Palace under the John Nash scheme, but later relocated, and fitting of corgi dog flaps to the internal doors (although we anticipate that we could get a supplier to donate these).

CLIFTON SUSPENSION BRIDGE

Tender

To: Bristol City Council

From: Mott MacDonald, Franklin & Andrews

Presented by: Bridges team: Ian Palmer, Chris Tait, Raghu Nair. Estimator: Ian Mansfield

Introduction

We would employ modern materials, construction and manufacturing methods to create a facsimile of Isambard Kingdom Brunel’s “darling”, the iconic Clifton Suspension Bridge. But the stone masons, archers shooting ropes between the towers and a forest’s worth of timber scaffolding used in the original would be replaced by steel-fi xers, helicopters and tower cranes.

The brilliance of Brunel and the simplicity of a suspension bridge means there would be few changes in the construction sequence. But today’s techniques and available equipment would accelerate the construction programme and avoid the two deaths reported when building the original.

Method

We would use modern ground strengthening techniques to ensure the integrity of the brittle rock and use modern plant to prepare the rock for foundations. The Somerset rock had to be built up some 30m as it slopes towards the Avon Gorge. We would use reinforced concrete keyed into the rock rather than an intricate series of brick vaults. 

We would then construct the towers. To minimise bearing pressures on the cliff top rock, the heavy masonry towers would be replaced with a reinforced concrete shell and clad in a masonry skin to recreate the traditional “Egyptian” appearance. Modern self-climbing scaffolding and tower cranes would replace the timber scaffold used to haul the pennant stone used in the 1800s.

We would crane into place a modern, cast steel “saddle” onto the tops of the towers – a half-wheel shaped feature allows some movement in the suspension chains that run across the top of each tower to prevent damage.

Demonstrating an early example of sustainable construction, the original wrought iron chains were recycled.

Hungerford Bridge across the River Thames was being replaced at the time of construction and its chains transported to Bristol and used on the Clifton bridge.

We would replace the wrought iron chains, the strongest material available then, with modern, high-strength steel.

The erection of the chains would be similar to the original method, except that the hemp rope used to drag up the first catwalk cables – rumoured to have been fired between the towers by bow and arrow – would be replaced by a small wire flown across by helicopter. These cables were used to lift in a temporary wooden bridge that was used as a platform from which to attach the actual cables.

Materials

In Brunel’s design, the side span chains – which extend from the tops of the towers to ground level at either side of the bridge – are anchored deep in the rock with iron castings. But we would replace these with reinforced concrete gravity anchors on either side of the bridge.

Despite its poor aerodynamics, we would faithfully replicate the original road deck, although the wrought iron girders suspended from wrought iron hangers attached to the chains would be replaced by modern steel equivalents. The use of stronger, modern materials would remove the current weight and traffic flow restrictions. However, clogging the bridge with lorries and buses would certainly remove the charm of one of the most recognisable structures in the world.

We believe the original construction period would be reduced dramatically. But as with the original bridge, rioting Bristolians could affect such bold claims.