What is a foundation

1
Agenda

• What is a foundation?
• Types of foundation
• Types of soil
• The purpose of a Site Investigation
• What to do and when

2
What Is A Foundation?

• A foundation is a system which transfers the load
  of a structure to a suitable bearing stratum
  below ground, while taking into account the
  settlement characteristics of that stratum and
  the possible effects of ground heave, subsidence,
  creep or negative skin friction that may be
  imposed on the system.

Piled Foundation Traditional Trench
Fill Raft Foundation
3
Traditional Trench Fill Foundations
Typical Section

• Advantages
• Technically easier (advised by building
  inspector)
• Economical for depths up to 2.0m
• Disadvantages
• Very expensive even impossible in some ground
  conditions
• Expensive and slow for depths greater than 2.0m
• Health and Safety implications
• Expensive on a contaminated site
• Severs tree roots

4
Traditional Pile And Ring Beam
Pile and Beam Typical Section
Pile and Beam Layout
5
Traditional Pile and Ring Beam

• Advantages
• Well known system most groundworkers are
  capable
• Economic for depths greater than 2.0m
• Disadvantages
• Pile positions are relatively fixed (problematic
  for tree roots or other obstructions)
• Excavations generate risks of collapse, water
  ingress and
• Not good for contaminated sites due to production
  of spoil
• Takes longer than Proprietary Systems
• Takes more management than Proprietary Systems

6
Housedeck vs Traditional Pile Beam
7
Types Of Ground
8
Site Investigation - 1

• A Site Investigation is an exploration of the
  conditions you are likely to encounter in the
  ground when constructing the foundations to your
  property.

• Walk Over Study
• Have a look Trees, flora, fauna, water courses,
  elevation, condition of nearby buildings, place
  names (eg. Gravel Pit Rd., Pond St., Spring Lane
  etc)
• Local knowledge
• Desk Study
• Maps dating back to when records were taken. Can
  include searching records of previous uses of
  site and mining records
• Geological survey maps
• Planning departments Local Libraries
• On-site Groundbreaking Work
• Trial pits by hand or excavator
• Lightweight and Heavyweight boring and
  testing equipment
• Laboratory soil testing (eg. plasticity of Clays)

• N.B.
• Ground conditions can change over very short
  distances so a Site Investigation is not a
  guarantee of the ground conditions that will be
  encountered. The risk of encountering unforeseen
  conditions is reduced with a more extensive
  investigation.
• You pay for your Site Investigation whether you
  have it or not!

9
Site Investigation - 2

• According to the NHBC standards chapter 4.1, all
  sites must be assessed by a Desk Study and
  Walkover Survey (Clauses D1-D3).
• When hazards are not suspected a basic
  investigation must be undertaken (Clause D4). At
  a minimum this will involve

• Geotechnical Investigation
• Trial pits
• Boreholes if necessary
• Physical tests such as Clay Plasticity

• Contamination Investigation
• The use of sight and smell to identify
  contaminants
• Sampling of soil from trial pits
• Laboratory testing of samples for example for
  Radon

• This testing must be undertaken by an
  appropriately qualified person to the
  satisfaction of the NHBC.

10
What To Do And When
Make sure you know the build costs before making
an offer. (With the exception of foundations,
most developers know the costs of the whole build
to the nearest penny allow some contingency)
Make an offer for the plot subject to planning
approval and site investigation
If accepted, undertake some form of site
investigation
Satisfied that traditional foundations will
suffice and knowing the cost, proceed subject to
planning approval
Unsure as to foundation cost and type
More Site Investigation
Severe ground conditions withdraw offer
Traditional foundations are the most cost
effective
Piled foundations are the only way forward,
possibly reduce your offer for the plot
Approach builder for firm prices and build-in
contingency know where any additional costs may
arise
Appoint an Engineer to design scheme and obtain
quotations for piling, beams, substructure
brickwork and flooring
Approach specialist foundation provider eg. Abbey
Pynford for a One-Stop Foundation Solution