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With the cost of land, materials and energy increasing it is becoming increasingly important for Architects and Engineers to make design choices that will produce the most efficient and cost effective structure and substructure for the money and area that is built upon. This is then interlinked with the practicability of providing the needs and what is expected of a project, services are of the upmost importance to a project and in many cases are considered and provided in a design as one of the first jobs in a building. This is a study into the techniques used on site to provide services to a project, excavation and how a structure performs.
The site that this study is based around is Miller Homes - Royal Gate site as residential development located in Derbyshire.
On this site information used is a generalisation regarding all houses to be built on site although there are a variety of designs on site it is not practical to analyse each method used in foundation building or service provisions however the most common methods have been included and analysed in depth in this assignment.
Services and how they have been provided:
By having access to files provided on site of the most up to date locations of services pre construction and proposed services it was easier to envision and physically see the techniques used for providing the services. The site of Royal Gate is adjacent to the Derby school for the deaf and one of Derby's main roads which already housed mainline services that could be accessed with relative ease with the use of drawings to site these services.
Each service is placed at a specific level underground and has its own unique colour depending on what it is providing this is a health and safety precaution and also makes it easier to find services to maintain and make alterations to.
British Telecom - BT is the supplier of telecommunication in this particular area and provides a basic telephone line and a fibre optic service down Ashbourne road. The service was extended down New Street with a telephone substation placed to extend and bridge the connection. (These cables are at a proposed depth of 450mm as they are located under the road. BT services are identified with a grey line for services in place and a grey dashed line for proposed or in service telephone lines, Fibre Optics are highlighted in green.)
Severn Trent Water - STW has existing water mains running through Ashbourne Road and are tapped into with 90mm HPPE (High Pressure Polyethylene Piping) and located below New Street travelling through the site entrance at which point the piping splits into two directions allowing for either half of the site to receive the water supply.
- All excavations work and laying of pipes are to be completed by STW.
- Tree preservation order at the mouth of the junction of New Street on the west side at point "A".
- Manifolds with 6 ports will be provided by STW to serve particular plots.
- All water meters for service connections to be installed in the boundary boxes by STW.
Connect Utilities Gas Service - Connect utilities is an external contractor for laying services. Ashbourne road houses a high pressure gas main this was then branched off of with medium pressure mains down New Street and once the pipeline had reached the centre of the site it was then connected to low pressure pipes which are connected to the gas meters across the plots. The depth at which the gas mains are outside of the site and inside the site vary with about 250mm due to slopes between the main road and the site level, this is also due to the need for ease of maintenance of the pipes inside the site. These pipes are then protected with tiles over the top to prevent accidental damage to them.
- Service routes should be perpendicular to the front of the property and take the shortest possible route from the meter box to the main source, bearing in mind the limitation specified by the designer that service routes should not be laid in any building that is adjacent to another and under no circumstances should it run parallel to the main pipeline.
- All services are to be laid and installed in full compliance with IGE/TD/4 Edition 4 (Institution of Gas Engineers and Managers)
(These Pipelines are proposed at a depth of 750mm in road reducing to 500mm once in site but this will be offset with the difference in terrain level. Gas piping is highlighted in yellow and pipe width is varied with line weight.)
Connect Utilities Electrical Services - High voltage cables located on Ashbourne Road have been ducted down New Street with the installation of a transformer installed for the use of electricity both on site and in final use of supplying each plot with electricity. Low voltage cabling solutions are used on site with low voltage being defined as anywhere between 50 - 1000V in AC current.
- A maximum of 2 services will use the same service joint/duct to a house.
- Service routes should be laid perpendicular to the front of the property and laid to the nominated main with no more than 25m in length.
- Joint positions in front of driveways must be avoided.
These rules are much the same system as the gas pipelines with the included maximum length of the distance between join and mainline electricity.
Street Lighting Miller Homes - This connects through the transformer supplied by Connect Utilities as above taking a linear path throughout the proposed roads on site.
- Columns are fitted with double pole isolation in the cut-out and fuse discrimination to comply with the British Standard BS7671 (Appendix 1.1)
- Where there are known services in the vicinity of excavations the contractor shall ensure hand digging is carried out with care, the contractor shall arrange for statutory undertakers plant to be marked on site prior to excavations with mechanical excavators.
(These cables are proposed at a depth of 900mm. Electrical cabling is highlighted in red with the transformer represented as an orange square.)
All images used are a not to scale representation of a guideline route that services have been laid at. Service drawings were not available for use in this essay due to copyright disallowing usage in a public domain.
At the beginning of excavation a topsoil strip of about 70mm was removed from site and retained elsewhere due to a guideline in building regulations that topsoil is kept due to its value both monetarily and ecologically.
Topsoil was removed with a 360 degree tracked back actor fitted with a toothed bucket. Trenches of 1500mm deep and 1500mm wide for pad foundations were then dug and supported with mini boxes or will be battered after any excavation past 900mm. In some soils around the site clay boards were used in places with shrinkable soils that may be influenced by local fauna and also rebar is placed into the bottom of the clay board at 500mm to help support the load. All excavations are fenced off with rigid barriers for health and safety precautions. The ground conditions of shallow trenches are assessed for stability before any persons may enter it for works.
The majority of foundations that were set on site were strip foundations but as each buildings foundation was tailored to the ground it was on some buildings had pad foundations supporting part of its walls. Pre fabricated reinforcement cage is used to lay concrete for the strip foundation, concrete is placed directly into the open trenches and is tamped down by workers with a tamping tool then levelled with a rake to remove air bubbles.
In the strip foundation block and brickwork are laid using site mixed or ready mix mortar and in some of the plots 10N blocks may be needed, in this case trench blocks will be too heavy.
The typical foundation found on this site takes the form shown below:
Considering that the trench would take the form of 700mm wide and 1500mm at the strip and 1500mm wide and deep for pad foundations. Drawing is not to scale.
All services are brought through the brick and block work but are required to have a lintel fitted above as to not place load on them.
During construction and after completion a structure different loads will be affect how the building is taking those loads however during construction is not as important to worry about how loads are carried as it is for the final article to handle the loads within its factor of safety due to the addition of imposed and final dead weight. Imposed weights are such things as furniture and live loads that will move around the building independently. Other imposed weights/forces are the weather as such factors as wind, snow, rain and ground water flow.
British Standard BS 7671 "Requirements for electrical installations" is the national standard in the United Kingdom for low voltage electrical installations. It is also used as a national standard by Mauritius, St Lucia, Saint Vincent and the Grenadines, Sierra Leone, Sri Lanka, Trinidad and Tobago, and Uganda, and several other countries base their wiring regulations on BS 7671. The IET (formerly IEE) has published wiring regulations in the United Kingdom since 1882. Since their 15th edition (1981), these regulations have closely followed the corresponding international standard IEC 60364. Today, they are largely based on European CENELEC harmonization documents, and therefore are technically very similar to the current wiring regulations of other European countries. In 1992, the IEE Wiring Regulations became British Standard BS 7671 and they are now treated similar to other British Standards. They are maintained by the Joint IET/BSI Technical Committee JPEL/64, the UK National Committee for Wiring Regulations. Although the IET and BSI are non-governmental organizations and the Wiring Regulations are non-statutory, they are referenced in several UK statutory instruments.
- Terrain and aerial maps provided by (Google Earth - http://earth.google.com/)
- Illustrations created by (Alex Watkiss in Google Sketch Up - http://sketchup.google.com/)
- 6 Port Manifold Picture (http://www.essentialwaterservices.co.uk/images/6port.jpg)
- Strip foundation picture (www.buildstore.co.uk/materials/foundations.html)5
- All information used in this essay is provided by plans provided on site and the site manager of Miller Homes Royal Gate site Allen Marshall.
- Note form information is available on demand if required in this assignment as proof of referencing.