Major challenges in £22 million residential redevelopment
All Foundations faced some major challenges creating foundations for the new Great Central development in Chatham St, Sheffield.
The ground consisted sandstone, limestone, coal measures and millstone grit, and the rock is hard to drill without using a heavy rotary equipment.
Potentially requiring to drill down to 15 metres, we carried out a series of Trial Bores on the site using a CFA rig, a Casagrande B175XP.
To the delight of the whole project team, they were able to penetrate deep enough without the need to bring in far heavier and more expensive rotary drill equipment.
“It was a concern from the very outset and something that was causing concern across the board as to the best way of carrying out the job,” said Neal Willis, All Foundations’ Operations Director.
“We offered to mobilise to site with a CFA rig in advance of the works to carry out a series of trial bores.
“We were able to achieve the depths required, which was great as it meant we didn’t have to bring in a rotary rig.”
But this wasn’t the only challenge facing the contractor ahead of building the foundations for Great Central, which when complete will feature a residential development comprising of 131 apartments spread over blocks of up to nine storeys, set around a courtyard and sitting just north of the city centre. It has already been heralded as “raising the bar” for city-centre living in Sheffield.
Operating in a relatively small area, the site was not just on a slope but on three different platforms with a significant difference between the levels – almost six metres in total.
Sequencing was crucial as the contiguous walls were needed to enable the full platform to be excavated to allow all of the piles to be installed.
And the rig had to travel up and down ramps, to access the different platforms, which presented its own set of challenges.
Once the job was up and running, quick progress was made. The company inserted 333 No 450mm diameter CFA Bearing Piles, which were all around 6m long, and 56 No 450mm diameter CFA Contiguous Wall piles, which varied between 5.7m and 7m in length.
The piles were reinforced full length with a cage comprising of between 6B16mm and 7B20mm main bars with B8mm helicals at pitches of between 115mm and 170mm.
Willis added: “Given the very testing landscape, the most pleasing part was that all the planning works benefitted the scheme significantly with the installation works running incredibly smoothly, exactly to the timings planned. This really demonstrated that the commitment of the team in the pre-construction phase paid dividends.”
Oliver Jeffs, from KDS Construction, said: "Great Central is the definition of a project that needs significant planning and collaboration. The challenges of the site demanded the best of out of the project team, and it was pleasing to see the months of effort pre-start pay off with the smooth installation of piles and foundations."
LIPS is ideal for three-storey timber framed apartments
Demolition of two detached dwellings and replaced with two blocks of 3 storey timber framed apartments.
Due to the close proximity of a number of trees and subsequent roots, P W Roxburgh Building Contractors decided to approach All Foundations with a view to determine if our Level Innovative Piled slab (LIPS) solution would be more suitable than traditional foundation methods.
After discussing the project in-depth with our Head of LIPS, Mike Dorman, it became clear that LIPS would be the best option for the foundations from both an economic point of view and an environmental one.
Supported Living Accommodation - Saffron Walden, Essex
East Thames Housing Association identified a real need for the development of new ‘Supported Living Accommodation’ for parents of children and young adults with specific needs. The site at Everitt Road in Saffron Walden in Essex was deemed to be the most suitable for such a development.
Due to the unique shape of the site, East Thames wished to develop an aesthetically pleasing building which would, itself, lend aid in creating a harmonious environment for all residents. Therefore the building was designed in a fan shape rather than a traditional two storey terraced building.
The front of the building was required to be a focal point and as such was designed in the shape of a rotunda. The aesthetically pleasing design meant that many traditional forms of foundations actually became very expensive and difficult to utilise due to the curved shapes required.
Selwyn House restricted access piling
We were contracted to provide foundation piles to support a 7.5m deep sub-basement extension to the former Royal Sun Alliance Headquarters, Selwyn House, next to Green Park in London, which is now a single residence.
Due to the location of the building - a high security area adjacent to St James’ Palace and Clarence House, with a very narrow access road surrounding the building - Ian Cull, our Senior Estimator for the Southern division, visited the site to determine the available access and concluded that restricted access piling would be the best solution, given very tight restrictions on the site and in the surrounding area.
The challenge was to design and install piles to support compressive loads of between 300-700KN and tension loads of 325KN. The ground conditions were water-bearing sand and gravel to a depth of 11.0m, overlying London clay. The working area was 12m x 10m, set 3.0m below pavement level.
Due to the confines of the site, Engel Construction originally envisaged the need to erect a crane to lift the piling rig and equipment into the basement area.
However, we suggested designing and installing 450mm diameter x 22.5m deep, SFA (Segmental Flight Auger) piles using our Klemm 702 min rig, with the rig and equipment being lifted into the basement using our 15T capacity Hiab wagon, hence making substantial savings against crane hire.
Derek Corcoran, Project Manager for Engel, said: "The site was very tight and the preplanning had to be accurate so as not to cause delays to the project and traffic problems on the street outside when we the piling team were mobilising.
"All Foundations compiled a plan for this and executed it well. Once mobilised, the piling team got started in what were tight, difficult conditions. We encountered some obstacles along the way you do in every job but the team were positive and proactive in overcoming any problems and had foresight to eliminate other problems we could have encountered.
We would not hesitate to work with All Foundations in the future."
Two-storey restaurant regeneration project
As part of a refurbishment project the original, single-storey, café was to be demolished to make way for a more aesthetically pleasing, two-storey restaurant with a public roof terrace, which would complement the prestigious surroundings in the Duke of York Square. The design of the new restaurant has already won a New London Architecture Award for its state-of-the-art design.
After an intense tender process to identify the main contractor to deliver this new establishment, Westgreen Construction Ltd was chosen due to its expertise in delivering successful projects of this type. Westgreen then contacted us to seek our advice on the piling aspect of the project.
After reviewing the information and visiting the site, All Foundations decided to utilise a CFA piling rig, a CM-50, to install the 92 No. 600mm diameter piles, which would make up the contiguous piled wall required for the basement.
The CM-50 was identified to be the most suitable rig to install the piles due to the access restrictions and exclusion zones related to the site.
Due to our significant experience of piling in London, we used a number of innovative measures to ensure that the project remained as cost effective as possible.
These measures included using a stronger concrete mix (C-40 strength) to ensure that the piles required could be kept well under the maximum depth of 13 metres, with the majority of piles only needing a depth of 8 metres. This reduction in length provided a significant saving on both time and cost for the project., which took just 13 days of the originally expected three weeks.
Billy Wilkinson, Contracts Manager at Westgreen Construction, said: "The piling service and advice provided by the All Foundations team was professional and helpful, they were always quick to respond to questions and pro-active in offering suggestions to improve the project."
£120 million regeneration project in the Lansdowne area of Bournemouth
As part of a £120 million regeneration project in the Lansdowne area of Bournemouth, Watkin Jones were contracted to replace existing, largely vacant, buildings with new “design and build” multi-storey buildings for a variety of regeneration purposes.
The new buildings to be developed include:
A 454 bedroom student accommodation block
128 bedroom hotel, 10 storeys high for Premier Inn
2000ft2 of new retail space
70,000ft2 of high grade office space over 9 storeys
All of the above were to be developed over a 2 level basement car park with parking for up to 196 vehicles and 290 cycles.
Due to the technical & complex aspects of the large scale excavations required on the project, Watkin Jones structural engineers sought out our advice due to having worked together previously. We were asked to assist in identifying cost-saving measures for constructing the ground retaining structures of the project.
We identified a number of cost-saving measures which had the effect of significantly reducing not only the cost of the scheme but also the disruption to the local communities infrastructure as a whole.
Our solution was a contiguous piled retaining wall, using 600mm dia, heavily reinforced and “temporary berm propped” piles to depths varying from 10 to 13 metres.
The “berm prop” method system (natural earth banking) was chosen to negate any major internal temporary propping works that would hinder the construction of vital main foundation works and/or the requirement for external tie anchors that would be required to be installed into adjacent local government / highway agency-owned land.
In addition the 600mm dia piles provided the ability to carry and transfer the heavy external load-bearing element of the structure below the final basement levels in a suitable and costs effective manner.
Simon Cowell, Construction Director at Watkin Jones, said: "From the very start of the project, All Foundations were fully engaged with ourselves and their allocated site manager was in close communication with our team to ensure that everyone knew what was transpiring at all times.
"It was a pleasure to work with such a pro-active partner who provided dynamic solutions to, often unforeseen, issues. The cost saving options All Foundations provided were very much appreciated, as were the disruption reduction measures.
"All in all the project, in relation to the foundation and piling, went without any major hitches and we would not hesitate to use All Foundations again as their expertise and ability to offer such a comprehensive service benefits all parties involved."