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Phase 1 of the site investigation is the desk survey. This is an important part of the process, due to it saving a considerable amount of time and money for the client and contractor and providing key information on the construction site.
ordnance survey (also known as OS) these maps are shown in a two dimensional paper format as well as a digital format. The digital format is commonly used, this has been produced by using satellite mapping which can be accessed via the internet shown in a variety of scale sizes; this could save a lot of time when you are researching information on the potential construction site. According to Chudley et al. (2011) ordnance survey gives details on buildings, structures and boundaries, surrounding roads, footpaths and properties, and often reveal topographical details, existing feature, watercourses, trees (in appendix 1 it states that there are mature trees around a part of the site) and archaeological features. This could have an effect on the property sale once the projects finished.
Past use of the construction site significantly affect its future use. According to Chudley et al. (2011) historical maps and local archives are used to find out the history of the site. Chudley et al. (2011) states it can provide information on
Potential obstructions underground
Boundaries, footpaths and roadways
According to Chudley et al. (2011) Historical document are included in the archives and show photographs, maps and records that are used to research past history of the site.
Legal aspects are an important feature in the desk survey, examples are
Health and safety
As it can be critical as to whether the site will pass the building and planning applications. According to Approved Documents [WWW] there are fourteen parts of approved documents which make up the building regulations, these standards need to be met or exceeded when constructing. According to Health topics in construction [WWW] the health aspects can range from asbestos to hand-arm vibration, with these risks being assessed and managed carefully to stop people being affected. According to Safety topics [WWW] the safety topics include site organisation to mobile plant and vehicles, these areas of risk need to be monitored and assessed constantly to stop people from coming to harm on the construction site.
Phase 2 of the site investigation is the fieldwork survey, as this is also an important part of the process. From the walkover survey you will be able to visually see what is on the site. According to Chudley et al. (2011) the walkover survey could find information such as existing structures, existing services, trees, hedges and boundaries, indication of topography and levels, evidence of groundwater levels and flooding, overhead obstructions such as overhead power lines. This information is crucial as to see whether the site is feasible to construct on.
Soil testing is important to inspect what type of soil you will be constructing upon the site. Emmitt, S. and Gorse, C. (2006) state that there are many different varieties of on-site and laboratory test that are used to determine the soil condition. According to Chudley et al. (2011) soil tests will cover density and compaction, composition, grading profile, moisture content, shear strength and the bearing capacity. Ground contamination on site can be a serious issue. According to Riley, M. and Cotgrave, A. (2008) ground contamination on site can include chemicals, metals, materials, waste and liquids.
Trial pits are extremely useful when it comes to inspecting the soil types on site. According to Chudley et al. (2011) they state that the trial pit is a square pit and the dimensions are 2m x 2m x 2m, then an engineer will inspect the trial pit to determine the ground water level or take sample of the soil if needed. Topliss, S. and Hurst, M. (2010) also states that trial pits are limited to 5 meters or less in depth. Chudley et al. (2011) emphasises that the trial pit are normally excavated using a back-acter excavator. Topliss, S. and Hurst, M. (2010) highlights that a record must be taken alongside the soil profile that will be recorded as the hole is being excavated.
According to Regular Soil Augers [WWW] Hand augers are commonly used in the site investigation. Hand augers are used to extract soil samples from the site. The auger is useful to visually see what is below the subsoil and then take the samples back to the laboratory, and then form a decision on what foundation to use on site.
(1B) clay is a cohesive soil type. According to Riley, M. and Cotgrave, A. (2008) "the more cohesive the soil, the greater the ability to support itself during the process of excavation". This could save money, as this site has firm clay and can support itself if it wasn't then temporary support would be needed to hold the soil type to be excavated and this would be an extra cost.
The likely problems that could occur for clay soil are
Trees those are close to the foundations.
In Appendix 1 the top right photo, it shows the firm clay has been excavated and at the bottom of the excavation its showing ground moisture, this could indicate that the site has a high water table content. According to Riley, M. and Cotgrave, A. (2008) the small particle sizes which makes up clay, has a high amount of small holes between the particles, this will cause the behaviour of clay to show a change in quantity, when it is being affected by the changing moisture content. Riley, M. and Cotgrave, A. (2008) idea is supported by Emmitt, S. and Gorse, C. (2006), who says that firm clay suffers noticeable vertical and horizontal shrinkage when dry, and expands when the clay is wet, as this is due to the changes of the season. This could affect the foundations and cause subsidence due to the shrinking and swelling, this could be prevented if the foundation is reinforced.
Frost heaves occur when the water table is high; in Appendix 1 the top right photo, the clay soil has water content which is close to the surface level, this could swell in the clay soil when the water content is frozen. According to Emmitt, S. and Gorse, C. (2006) when the water in the clay freezes and expands, this "is due to crystals of ice forming and expanding in the soil and so causing frost heave". Emmitt, S. and Gorse, C. (2006) state that in the United Kingdom, the groundwater close to the surface is uncommon to freeze below 0.5 meters. Frost heaves could affect the foundation and cause it to crack due to the water freezing and expanding; to prevent this, the ground needs to be protected and the foundation to a deep depth.
Trees can have a substantial effect on the subsoil; from this it can affect the substructure and superstructure of the site. In Appendix 1 the top left and the bottom right photo, they show that there are mature trees around that part of the site. According to Chudley et al. (2011) states that clay subsoil is susceptible to changes in moisture content. Riley, M. and Cotgrave, A. (2008) states that this has a strong connection to the mature trees being located close to the foundation. Chudley et al. (2011) states that if the mature trees are located close to the foundations of the site at a distance less than the height of the tree, then the roots will be deep in the clay soil, the trees will then take out all of the moisture from the soil and cause the clay soil to shrink, this will cause the foundations to subside. Knowing that the mature trees are close to the foundation, there is a need to take in account the soil properties of the clay soil.
(1C) In Appendix etc. groundwork - formwork, pumping water out of the soil, then where to take the water could filter it in with a watercourse
Task 2 - Foundations
(2A) Appendix etc.
(2B) for the construction site, the foundation type that I will use is trench fill strip foundation, over other suitable alternative such as piles and raft foundation. Emmitt, S. and Gorse, C. (2006) states that trenches are commonly formed using a mechanical excavator and excavated to the width that is needed for the foundation. According to Emmitt, S. and Gorse, C. (2006) the foundation for the trench fill should be at least 0.9 meters in depth to provide a suitable stable foundation. This is so the foundation will be unaffected from the firm clay subsoil, such as swell and shrinkage. (Week 7 PowerPoint) states that for the trench fill strip there is no need to use formwork due the subsoil being firm clay. The advantage of using no formwork is saving money for the client and contractor. (Week 7 PowerPoint) states that apart from using a digger to excavate the trench there is no need to use specialist plant for the excavations. According to (Week 7 PowerPoint) the bricklaying below ground level will be reduced. Emmitt, S. and Gorse, C. (2006) states that the trench should be filled with concrete as quickly as possible, to stop the subsoil changing its moisture content and the clay beginning to shrink.
The other suitable alternative was pile foundation. According to Chudley et al. (2011) there are two types of piling systems that are used on low-rise construction projects. Chudley et al. (2011) states that the two systems are bored or precast driven piles, where the depth they commonly reach up to around 6 meters deep. According to (Week 7 PowerPoint) the pile foundation is useful when the bearing stratum is deep as it will avoid the shrinkage in the clay subsoil. The reason for not choosing this foundation type is that it needs specialist equipment, this process is not cost effective. The cost for this equipment as well as a person to operate the machinery would not be efficient for the construction project.
The other suitable foundation was raft foundation.
(Week 7 PowerPoint) states that the positive for this selection would have been that it is cheap to construction due it not being a deep excavation. The reason why I am not choosing this foundation is (Week 7 PowerPoint) states that raft foundation needs reinforcement below the loadbearing walls. This process of reinforcement can be costly expense if the foundation has already been constructed.
(2C) method statement - Trench Fill Foundation
Site ready to start work
Site clearance complete
Mark out the site foundation boundary
Excavations for the trench fill foundation can start
Trench excavated by mechanical digger
Batter back the trench
Clean the excess soil from the excavation
Make sure there are no digger teeth marks are left
Pour concrete to required level
Compact the concrete to release air bubbles
Build up brickwork and block work to DPC/DPM
Fill the cavity below ground level with weak mix concrete
Floor construction - back fill soil
Avoid the mortar bridging damp proof course
DPC laid at 150mm above ground level
Task 3 - External Walls
(3B) Appendix (week 12 lecture 1 PowerPoint) Timber frame construction is a renewable and sustainable source of timber unlike other construction materials such as concrete and steel.
External thermal properties and performance for timber framed construction are high, due to the thickness of the frame and add insulation to meet the u-value that have been set out. The disadvantage to this is adding more insulation to the building can impact on the footprint of the floor area.
Offsite manufacturing of for timber framed construction is beneficial, as it provides a consistent quality to the material compared to if it prepared on site.
Time frame construction is quick to construct as it's a dry trade and there are no waiting time so other trades can start work quicker, however, timber needs to be stored correctly as the disadvantage is that it could get damp.
Balloon frame construction, according to Chudley et al. (2011) this process uses "full-height studs from ground level to the roof".
The benefits are that it's built to full height and this means that it can be water proof in a relatively short time. The period of time that it takes to construct the balloon frame is a quick process; also it is easier to pack the timber stud with insulation. However, the disadvantage is that there is a need to provide cavity barriers between floors to prevent fire spread as it travels quicker than a timber frame, another issue is that it is hard to move around the site and to transport the material.
Task 4 - Floors
(4B) fire risks
List of references
Chudley, R. Greeno, R. Hurst, M. Topliss, S. (2011) Construction Technology. 5th Edition. Spain: Pearson Education Limited. Chudley et al. (2011)
Topliss, S. Hurst, M. (2010) Construction & The Built Environment Level 3. 1st Edition. Spain: Pearson Education Limited. Topliss, S. and Hurst, M. (2010)
Riley, M. & Cotgrave, A. (2008) Construction Technology 1: House Construction. 2nd Edition. Find Place of Publication: Palgrave Macmillan. Riley, M. and Cotgrave, A. (2008)
Emmitt, S. & Gorse, C. (2006) Barry's Introduction to the Construction of Buildings. 2nd Edition. Find Place of Publication: Blackwell Publishing. Emmitt, S. and Gorse, C. (2006)
Emmitt, S. & Gorse, C. (2006) Barry's Advanced Construction of Buildings. 1st Edition. Find Place of Publication: Blackwell Publishing. Emmitt, S. and Gorse, C. (2006)
Riley, M. & Cotgrave, A. (2009) Construction Technology 2: Industrial and Commercial Building. 2nd Edition. Find Place of Publication: Palgrave Macmillan. Riley, M. and Cotgrave, A. (2009)
Health and Safety Executive (n.d) Health topics in construction [WWW] Available from: http://www.hse.gov.uk/construction/healthtopics/index.htm (Accessed 05/11/2012)
Health and Safety Executive (n.d) Safety topics [WWW] Available from: http://www.hse.gov.uk/construction/safetytopics/index.htm (Accessed 05/11/2012)