This document discusses the key considerations and process for preparing a building site. It outlines that a site analysis should be conducted which includes checking ordinance surveys, measurements, preservation orders, flood potential, and consulting utilities. A soil investigation determines suitability, aids foundation design, and identifies potential difficulties. This involves a desk study, walkover survey, and physical exploration using boreholes or trial pits. Samples are tested in a lab to classify and characterize the soil properties. The document describes common soil types and issues like contaminated soils, water tables, and methods for improving poor soils to support foundations.

1. Preparation of a Site
Part 6
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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 characteristics
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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
soil
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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
ground
Physical exploration and inspection of the
ground by means of boreholes or trial
holes
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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
tested
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6. Soil Types
Sand/gravel- can give good bearing capacity-
good water dissipation
Clay-good ground bearing- prevents water
passing between strata
Rock-hard solid formation- often impervious
such as granite or limestone- excellent
strata on which to build
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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 level
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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 construction
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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.
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10. Contaminated Soils
Typical examples of where
contaminated soils are located;
Landfill sites
Gas work sites
Sewage farms and works
Scrap yards
Industrial areas
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11. Removal of Contaminated
Soils
There 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 deep
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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
foundation
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13. Purpose of Lab testing
 To check classification of soil
 Moisture content
 Liquid limit
 Particle size distribution
 Bulk density
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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-
compaction
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15. Key Terms To Remember
 Bearing Pressure
 Bearing Capacity
 Subsidence
 Settlement
 Compaction
 Consolidation
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