Building Construction 2

Dr Nabil El-Sawalhi

Associate professor

Engineering Projects Management

Site Analysis and Set-up

• Function of the site analysis

• The main purpose of site analysis is to identify and hence reduce the risks associated with the development by recording site features and soil characteristics, helping to determine the design and cost of suitable foundations and structure.

• A thorough site analysis is an essential first step that will assist development, design and construction decisions.

• The site analysis helps:

• ❑ The client to assess whether the project is viable

• ❑ The client, designer, structural engineer and contractor to locate the best position for the building, avoiding identified problems where possible and making the best possible use of physical features and environmental conditions

• ❑ The engineers to design the most suitable foundation system

• ❑ The mechanical and electrical consultants to design the service provision

• ❑ The designers and contractor to ensure that safe construction methods are used

• ❑ The environmental consultants to identify the most suitable way of dealing with any contaminants and problem materials, e.g. remediation works, material re-use, on-site treatment and disposal options.

The ‘desk-top’ study • The ‘desk-top study’ is a vital element in any site

analysis exercise. • The study involves the collection of all documents

and materials that can be obtained without having to visit the site.

• There is a considerable amount of information available from local and national authorities, museums, private companies and research groups.

• The client or previous owners may also have relevant information to hand.

Information required

• Ownership(s) and legal boundaries

• The client should provide, via a legal representative, information pertaining to the exact location of the site boundaries and responsibilities for maintaining the boundaries.

• These will need to be checked against a measured survey and any areas of uncertainty checked by the legal representative.

• Other issues to be determined by the client’s legal representative include:

• ❑ Rights of way

• ❑ Rights of light

• ❑ Rights of support (for adjoining properties)

• ❑ Legal easements

• ❑ Ownership of land (essential where parcels of land are being assembled to make a larger site)

• ❑ Rights of tenants, etc.

Ground conditions

• collect information on soil and subsoil conditions from the county and local authority, whose local knowledge from maps, geological surveys.

• In addition geological maps from , information from local geological societies, Ordnance Survey maps, mining, river and coastal information may be useful.

• Services

• All suppliers of services should be contacted to confirm the position of pipes and cables and the nature of the existing supply.

• Contaminated land and methane

• Previous use of land can give some clues as to the likely contaminants to be found and the local authority may have records that can help.

• However, extensive soil testing should be carried out to ascertain the nature and extent of any contamination.

• Methane is associated with landfill sites, and local knowledge of old tips can prove useful at an early stage.

• Flooding

• Factors include heavy rainfall, buildings sited on flood plains and inadequate maintenance of rivers and watercourses.

• Thorough checks should be made about previous flooding of the proposed site (if any) and any special requirements suggested or required by the various authorities.

Site reconnaissance

• Written permission should be acquired from the client and/or owners before entering the site and especially before any investigations are carried out (which may require separate written permission).

• Obvious considerations are related to trespass and criminal damage, although the prime concern must be the safety of those doing the investigations.

Identification and physical location of services

• Before undertaking any digging, e.g. for trail holes, it is necessary to clearly identify the nature of the services on the site and their actual position.

• Unfortunately, the majority of the plans provided by the services providers only give an approximate location of their pipes and cables, therefore some detective work is required on site.

• Handheld sonic and magnetic detecting devices are available

Setting out the building

• When setting out building lines, the first step is to measure the building line from the boundary or existing building.

• Then you need to determine the approximate length and position of the string line, together with the building clearance measurement at each end, for locating the hurdle.

• Pegs and hurdle profiles are installed, then the location for the line is accurately marked with nails on the profiles and the line set taut into position so it is correctly aligned with the boundary.

• Once this has been completed, the right angled corners can be set out, the other building lines installed and finally the lines checked for square and measurements checked for accuracy.

Setting out the first line

Set up the first line for the building! • Your first task is to measure the building line from the

boundary or existing building, as determined from site drawings.

• This is often referred to as Step 3 • A corner is chosen to position the first peg Peg A. It must be

positioned the correct distance from front and side boundaries, using measurements obtained from the site plan.

• A square or relatively square corner is usually selected. A nail is partly driven into the top of Peg A to mark the exact position.

• Remember that this is only the starting corner, and may not be completely accurate so final checking for square should be carried out over the whole shape once it is set up.

• In Step 4

• the next peg—referred to as Peg B—is then set up, generally to form a line along the side boundary in a new construction.

• To correctly position Peg B, the distances are measured from Peg A and the side boundary with measurements taken from the site and floor plans.

• A nail is partly driven into the top of Peg B to mark the exact position.

Checking for levels

• Note that, if the site is not level, there are many methods for checking the levels.

• The simplest is to transfer heights using a straight edge and spirit level which is accurate for small set outs.

• You can also use a water (or hydrostatic) level which is accurate for medium-sized set outs.

• For accuracy on larger set outs, you can use a Dumpy or Automatic level which needs two people, one to hold the staff and one to take the reading.

• The laser level is very accurate and only needs one person to operate the electronic receiver staff: it’s suitable for larger set outs as well. However, remember that the laser beam can damage your eyes

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Creating right angles

• Step 5

• is to place a third peg—Peg C—at a third corner, adjacent to Peg A at the other side of the front of the site, next to the other side boundary.

• To correctly determine the position of Peg C, it is assumed that the triangle formed by Pegs A, B and C is a right-angled one, with the right angle at Peg

• A. Step 6 • is the positioning of the last peg at the fourth corner, Peg D. • How do you ensure that the angle at Peg A is a right angle?

There are a number of different methods. • Once you have completed setting up all the lines, the most

common method to check for square is to measure the diagonals. When you are checking for square in a quadrilateral shape, both the diagonals will be exactly the same length, provided that the opposite sides are the same length and are parallel. This is explained in more depth later.

• Here are a number of methods for setting out a right angle.

Fixed type builders square

• Step 1: Using a fixed type builders square, usually about 3 m (3 m, assume that the base line is from Peg A to Peg B.

• Step 2: Drive a peg into the line between Peg A and Peg B, placing a nail in the top centre to coincide with the base line.

• Step 3: Place the outside edge of one arm of the square along the base line, with the right angled corner directly over the nail in Peg C.

• Note : At least one arm of the square must be level for more accurate results.

• Step 4: Peg D is placed south of the line between Pegs A and B, Peg E north, both in line with Peg C so that when a line is fixed between them, it will lie directly over the nail at Peg C and in line with the outside edge of the second arm of the square.

• The builder’s square then gives you a direct measure of whether the two lines are at right angles.

• It is possible to use a folding type builders square, but requires more pegs and a judgement of a 45 degree angle, so is more complex.

3-4-5 Method

• Here you are using the triangle method, where Peg A is 4 units from Peg B, and Peg C is at a right angle in line with Peg A measured at 3 units away using a measuring tape.

• Then the measuring tape from Peg B to Peg C must be 5 units. Make sure that the units are all the same.

• Isosceles triangle method • Here you set up the base line from Peg B to Peg C, placing

Peg A in the middle, at the required location of the right angle. Pegs B and C are equidistant from Peg A. Attach a measuring tape to Peg B and another one to Peg C. Extend the tapes out to any length, provided that they both measure the same. The longer the length (say around 5 m) the greater the accuracy of the angle formed.

• Where the two tapes cross will be the centre position for Peg C. Attach a string line to the nail on Peg A and pull it tight over Peg D, forming a right angle to either side of Peg A on the base line.

• Checking diagonals

• After you create the right angle, all other lines are produced parallel to the original line.

• To check whether the building is square, the diagonals are measured to ensure they are the same length.

• If you find they are not, then there is an error either in the original right angle or in the measurements of the parallel sides.

• Installing hurdles/profiles

• Where do you place the profiles? They should be placed at least 1 m away from the proposed excavation when manual excavation methods are used (pick and shovel) and at least 1.5 m away when mechanical excavation methods are used (backhoe or trench excavator). This space allows for ease of access and prevents the profiles falling back into the excavated area.

• Step 7

• Profile boards are erected at a convenient distance from the pegs, for example, one metre to allow for manual excavation work or at least 1.5 for mechanical, keeping them parallel to the pegs.

• Establish a profile close to the ground at the highest point of the setout, which is assumed to be at Peg A. Use any of the levelling instruments to transfer a height measurement from this profile to all other profiles to maintain a constant height.

• The first profile is set up at right angles to the side boundary, then the next parallel to it, usually labelled 1 and 2.

• Step 8 • Now position string lines between profile boards. Start

by pulling a line, attached to the nail in Peg A, exactly plumb over the nail in Peg B. Use a spirit level to plumb the position up to the profile. Profile 3 is parallel to the side boundary, in line with 2, while the fourth is parallel to 1, at right angles to the side boundary.

• Mark the position on profile 4, release the string line then partly drive a nail in at this mark. Attach a line to the nail on profile 4 and pull it back plumb over the nail in Peg A and mark the position on profile 1. Partly drive a nail at this mark and tie off the line.

• Carry out the same procedure between pegs A and C, where profile 7 is parallel to the side boundary and profile 2, where profile 8 will be parallel to 1 at right angles to 7. Use profiles 2 and 7 next.

• Note : These first two lines will form a right angle. • You may choose to have corner profile at the two rear

corners with only one central post corresponding to pegs B and D, with a post on either side, to which the hurdle or saddle is attached, rather than having four posts.

• This makes it easier by removing one vertical post on either side of the corner.

• Position marks on all other profiles by measuring the correct parallel distances from the marks on the profiles 1, 2, 4 and 7, and position the remaining string lines. Profile 9 will be halfway between Peg A and Peg B, parallel to profiles 2 and 3; profile 10 will be on the other side between pegs C and D, opposite profile 9; profile 11 will be between pegs D and B while the last profile, 12, will be between pegs A and C.

• Step 9: Checking diagonals

• Are the diagonals correct? This is the point at which you check all the diagonals. If the difference is more than 10 mm, you will need to adjust some of the nails on the profiles.