Issue Six - Winter 2000
Welcome to the sixth edition of 'Engitect'. Through your feedback we are pleased to hear that readers enjoy 'Engitect'. In this issue we describe some of the major engineering work carried out for Waitrose Malvern, a recent addition to Waitrose' portfolio, and also our work over the last 70 years on Euston House, as well as the regular features such as the caption competition and the 19th Century construction cartoons
The Great Wall of Malvern
The residents of Great Malvern have recently enjoyed the benefits of a brand new Waitrose store built in the centre of the town. What shoppers may not appreciate when they park their cars in the car park is the amount of engineering work that was necessary in order to create the space in which the store now lies.
The site was formerly a car park comprising two terraces cut into a steeply sloping site just to the north of the main high street. Those of you who know the Malvern area will recall the steep wooded slopes of the Malvern Hills around the town.
In order to create a level area for the store and the car park it was clear that it would be necessary to cut further into the hillside. In fact some 47,000m3 was excavated. The ground investigation report by Soil Consultants Ltd found that it would be possible to use much of the excavated material as fill to make up the car park levels including a new vehicular access ramp.
A phased construction programme was developed in conjunction with the construction management contractor, Costain Construction Ltd., where the excavation was carried out in stages across the site taking into account the restricted site confines.
Retaining walls up to 8 metres high were required to uphold the hillside around the development and to retain the fill material along the north elevation. These comprise timber crib walls and reinforced earth retaining structures.
Timber crib walls comprise an interlocking timber framework which is gradually backfilled with granular material as the wall is erected. The walls rely on their self-weight to provide resistance to sliding and overturning, and the timber is pressure treated with preservative to ensure longevity. Phi Group undertook the design and installation of these walls. The reinforced earth retaining structures comprise granular fill, compacted in layers, over polyethylene strips laid on the ground as 'reinforcement'. This reinforcement layer is repeated as the wall is raised. The wall elevation is faced with Malvern stone with an attractive raised pointing known locally as 'snake' pointing or more commonly as 'ribbon' pointing.
One particular area of the site presented the design team with a number of difficulties. The area in question lay on the site boundary, and a retaining wall some 8,5 metres high, cut into the declivity, would be required. Just a short way up the slope lay a 5-storey block of flats. In addition the requirement to achieve 240 car parking spaces meant that the excavation could not be cut back at a safe angle to allow construction of a timber crib wall.
Some form of temporary works was clearly required to retain the excavated face in the short term so that the permanent wall in the form of crib wall could be erected. To make matters worse, however, a spring issued from the ground near the base of the excavation, and an existing sewer ran across the site at the top.
Options including reinforced concrete piles embedded deep in the ground were explored and discounted on the grounds of cost, due to the presence of rock at a relatively shallow depth. The final solution was developed by Costain Construction Ltd., their sub-contractors, Phi Group, and Thomas Vale, who were responsible for design and installation of sheet piles.
The solution involved the installation of soil nails, which comprise small diameter holes drilled deep into the embankment, which are filled with cement grout into which a steel rod id driven. The 'nails' thus constructed were designed to reinforce and stabilise the bank and were installed in stages as the excavation proceeded. Working in this way it was possible to stabilise the bank at an angle of 600 to the horizontal, whereas the natural angle of the ground would have been nearer 300. The steeper slope reduced the space taken to construct the wall to approximately one third of that required without the nails.
A sheet piled wall was installed at the base of the excavation because planning requirements dictated that this section had to be faced with Malvern stone. Only a limited embedment was possible due to the presence of rock, so the top of the wall was tied with a soil anchor installed in a similar way to the soil nails. Once the sheet piles were in place a timber crib wall was erected to form the permanent retaining structure, as the nails were designed to act in the short-term only. The structural form of the wall is illustrated in the diagram, together with photographs showing the site during and after construction.
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Fastrack Building Comes of Age
Euston House, a 154,760sq ft storey office block was completed in 48 weeks from commencement of demolition to occupation. The building comprises a steel frame with reinforced concrete floors, which were laid at the rate of one a week. If I say that the floors are of the ï¿½Diespekerï¿½ type then some of you will recognise that I am not referring to a modern building. So much for fast track construction being a modern idea as the building was, in fact, erected in 1933 for the London Midland and Scottish Railway. We have the dated construction photograph to prove it.
Not only do we have the progress photographs, we also have a full set of structural drawings as, Bertram Hurst, our founding partner, was the Engineer for the project.
So, when we were asked by William Verry Ltd to provide structural engineering advice for a major refurbishment, we were able to compliment our expertise in the refurbishment of old buildings with a saving in excess of ï¿½10,000 as exploratory work to determine beam, column and foundation sizes was unnecessary.
We have archive records of nearly all the ten thousand or so buildings upon which we have worked plus many other buildings where we have advised on party walls or checked alterations by others. So the next time you are thinking of altering or developing a building a five minute call to us to check to see if we have any records could pay dividends (see following article and Euston House and HPM Archive).
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Over the last 3 years we have assembled a database of all our jobs, which data back to 1910. All our staff are able to search for buildings at the touch of a button, given a street name or other reference. The project data sheet records details of the project including whether any archive material is held and where to find it. For projects since 1997 we operate a fully computerised contact, time, cost and document management system with a place for every file and every file in its place.
This allows rapid information and document retrieval and automatic fax or e-mail issues to the project team.
Andrew Dutton has put a great deal of time and effort into this development of the system, which all our staff now agree they would be bereft without.
See HPM Archive
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CDM And All That
Regular readers will recall the picture taken by Lawrance Hurst showing an existing party wall foundation with an unusual inclusion. We invited readers to submit captions for what Lawrance's Instructing Surveyor might have said upon encountering this unusual 'reinforcement' in the wall footing. We were pleased to receive a number of entries including:
"Lawrance, could 'Thisbe' reinforcement? 'Pyramus' know, I'll ask him."
For those of you who are unfamiliar with party wall legislation and party wall surveyors, their association goes under the title Pyramus and Thisbe Club, which comes from the affair conducted by Pyrmus and Thisbe through the Wall in Shakespeare's 'A Midsummer Night's Dream'.
Peter Offord sent us the following:
"The 'Instructing' Surveyor would ask himself and say:
Q. When is a Special Foundation not a Special Foundation?
A. When it's got a shovel in it.
Q. When is a Special Foundation a Special Foundation?
A. When it's got a shovel and an iron mattress in it. Because that assemblage should comfortably distribute the load."
Those of you who are familiar with the Party Wall etc. Act 1996 will know Section 20 of The Act which defines Special Foundations as foundations in which an assemblage of beams or rods is employed for the purpose of distributing any load.
Surveyors appointed by building owners will normally advise strongly against the incorporation of 'Special Foundations' in their projects because of the potentially onerous obligations in The Act with building owners and their successors in perpetuity.
Finally, Johnny Johnson erstwhile of Hillier Parker sent us his suggestion from New Zealand:
"The system may well be referred to in one of your collection of late 19th Century brochures but my friend its still a bloody shovel."
The judges deliberated for some time before agreeing that Richard Thelwell's entry was the most appropriate. A bottle of champagne is on its way to him and our thanks are extended to the other entrants for the time and trouble they took in submitting their entries.
We would like you to put your mind to the next caption competition. Lawrance Hurst took this view recently, in Central London.
We are all aware that recent changes to health and safety legislation including the CDM Regulations have increased awareness of safety issues. Even so, the wording on the sign is somewhat unusual. Perhaps readers would like to submit captions speculating on the nature of the hazard bearing in mind the environment and neighbours.
A bottle of champagne will be awarded to the winning entry.
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For HPM the beginning of Y2K saw the start of the renovation of Peter Jones in Sloane Square, London. The store, for which HPM were involved in the 1030s rebuild of a large part of it, is the flagship of the John Lewis Partnership.
Essential works were carried out in the previous year whilst Planning and English Heritage Approvals were obtained. The project, programmed over five years at a cost of ï¿½80M plus, required trading space to be provided elsewhere whilst the centre of the store is being gutted and renovated.
A fast conversion of part of one of the stores two warehouses in nearby Draycott Avenue was needed before departments could be re-arranged in the main store under Phase 1. Starting in January, Bovis Lend Lease transformed over 30,000sq ft. into a department store complete with a new window frontage, customer staircase and well, passenger lift, associated M & E services and an interior design in keeping with the warehouse features. It opened on the 2nd of May with the provision of two courtesy buses circulating back and forth to the main store, and is now known as PJ2.
The enabling works carried out during this year in the main store, including the movement of over 350 departments and the temporary alterations to the M & E services, has allowed the store to be split into three. Trading continues at both the East and West ends with an external steel framed link along the Kings Road, whilst the renovation of Phase 2 has now begun.
A team of four from HPM integrated into a multi-disciplined project office of over fifty personnel at the beginning of the year, and set up on the seventh floor of the building to produce the working information. It has been a very worthwhile exercise from our point of view, having not only the existing structural information on our doorstep but also the other consultants looking over your shoulders...
Hard work and dedication from both the Partnership's project team and Bovis Lend Lease's management team, of which HPM are pleased to be a part, has enabled Phase 2 projects to be commenced four months ahead of schedule.
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We extend a warm welcome to Alan Merison, who joins us from Bylander Waddell, Colin Bowden and John Cook who join us from Owen Williams (R. T. James & Partners), Nadeem Masued, John Parkhouse who takes over as Accounts Manager, Stan Ritter who has taken over our work checking license applications for a number of the major estates in London, and Tom Newby, who has been working on our computer system and internet site.
All members of staff can now be reached via personal e-mail addresses. The address comprises of the first letter of their Christian name followed by their full surname and then @hurstpm.co.uk, all in lowercase. For example, Andrew Dutton's e-mail address is email@example.com. Our receptionist will be pleased to help if you have any queries. Of course you can also contact anyone via the general e-mail address: firstname.lastname@example.org
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A further entry in our series from the 19th Century building practices and hazards to health, here is one that some of our engineers can relate to; particularly the reference to 'slack baked bricks'. There is at least one street in London where our engineers would resist proposals to remove the plaster in order not to destabilise the wall. In one particular instance the clay from the bricks can be removed with a teaspoon! Slack baked indeed! The article is taken from 'The Complete Builder' by J. F. Sullivan, published in 1880. Things are better now, aren't they? Answers on a postcard to the editor please.