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College of North West London presentation; for the National Diploma in Construction

College of North West London presentation; for the National Diploma in Construction

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  • 08/03/12 John Fox, College of North West London Preparation of a Site

Transcript

  • 1. Preparation of a Site Part 6February, 2012 John Fox, College of North West London 1
  • 2. Site Analysis Before purchasing a plot of land the following considerations must be taken into account; Refer to Ordinance survey Measurement survey Preservation orders/conservation area Flood potential Design of buildings in area Consult utility providers Surface characteristicsFebruary, 2012 John Fox, College of North West London 2
  • 3. Purpose of a soil investigation To determine the suitability of the soil for the proposed project To determine an adequate and economic design of foundation To ascertain any potential difficulties that may arise in construction To determine the cause of changes in the soilFebruary, 2012 John Fox, College of North West London 3
  • 4. 3 Basic stages of soil investigation Desk study- takes into account any existing information such as its topography, geology, vegetation, etc Walk over survey- a direct inspection of the groundPhysical exploration and inspection of the ground by means of boreholes or trial holesFebruary, 2012 John Fox, College of North West London 4
  • 5. Trial holes/pits Foundations up to 3m deep – trial holes are dug by hand or small excavator Typical size of trial holes are 1.2x1.2x3m Foundations up to 30m deep- mechanically bored by a crane mounted auger machine Foundations over 30m- deep borings All samples are sent to the lab to be testedFebruary, 2012 John Fox, College of North West London 5
  • 6. Soil TypesSand/gravel- can give good bearing capacity- good water dissipationClay-good ground bearing- prevents water passing between strataRock-hard solid formation- often impervious such as granite or limestone- excellent strata on which to buildFebruary, 2012 John Fox, College of North West London 6
  • 7. Soil Types Peat-permeable and unsuitable for foundations- can indicate the presence of a high water level Filled or made ground- good quality, clean hard core rubble compacted in layers to engineers levelFebruary, 2012 John Fox, College of North West London 7
  • 8. Non Cohesive Soils When increasing the loads on soil the water content squeezes out, and this can lead to the settlement of a structure.In non-cohesive soils such as sands and gravel the water movement is more rapid and settlement normally occurs during constructionFebruary, 2012 John Fox, College of North West London 8
  • 9. Cohesive soils Cohesive soils such as clay or silt lose their water content far more gradually and buildings may slowly settle for many years before equilibrium is reached.February, 2012 John Fox, College of North West London 9
  • 10. Contaminated SoilsTypical examples of where contaminated soils are located;Landfill sitesGas work sitesSewage farms and worksScrap yardsIndustrial areasFebruary, 2012 John Fox, College of North West London 10
  • 11. Removal of Contaminated SoilsThere are 2 ways in dealing with contaminated soil;2. Removal- this is a costly process as licences are expensive and this may not be viable for the project.3. Capping- this involves the sealing of the material by a layer of clean material e.g. gravel, of approx. 1m deepFebruary, 2012 John Fox, College of North West London 11
  • 12. Water Table Water table- this is the level of water held in the soil which varies in wet and dry periods A high water table can cause problems such as flooding especially in trench excavation A high water table can also have a sulphate content which can lead onto a chemical reaction with the cement in the concrete and then cracking in the foundationFebruary, 2012 John Fox, College of North West London 12
  • 13. Purpose of Lab testing To check classification of soil Moisture content Liquid limit Particle size distribution Bulk densityFebruary, 2012 John Fox, College of North West London 13
  • 14. Foundations on Poor Soils Poor ground with insufficient strength can be dealt with in 2 ways; To excavate until ground of good load bearing capacity is reached To improve it so that it can accept the load by means of vibro- compactionFebruary, 2012 John Fox, College of North West London 14
  • 15. Key Terms To Remember Bearing Pressure Bearing Capacity Subsidence Settlement Compaction ConsolidationFebruary, 2012 John Fox, College of North West London 15