Advanced Construction Technology
By Professor Chris Gorse & Ian Dickinson – licensed under the Creative Commons Attribution – NonCommercial – Share Alike License
http://creativecommons.org/licenses/by-nc-sa/2.5/
Chris Gorse
Ground and soil stabilisation
Chris Gorse and Ian Dickinson
These slides should be read in conjunction with Emmitt, S. and Gorse,
C. (2010) Barry’s Advanced Construction of Buildings. Oxford, Blackwell
Publishing
General problems of ground
instability include:
•
•
•
•
Landslip
Surface flooding and soil erosion
Natural caves and fissures
Mining and quarrying
• Landfill
• Natural geological variation – faults,
changes in geology – differential settlement
Chris Gorse
Improving the ground
• There are a number of different methods
that can be used to increase the strength and
stability of the ground.
Chris Gorse
Ground stabilisation
• Dynamic compaction
• Vibro compaction - Vibro displacement
• Vibro flotation - high pressure water jets
(improves penetration of hard substrates)
• Pressure grouting
• Surcharging
• Geotechnic membranes
• Soil modification and stabilisation
Chris Gorse
Dynamic compaction
• This involves dropping heavy weights onto
the ground.
• The weight causes the ground to compact.
Chris Gorse
Dynamic compaction
• Ground is consolidated by repeatedly dropping
dead weights and specially designed tampers
• Weights include: Flat bottomed and cone tampers
• Traditional weights are flat bottomed with cable
• Modern systems use cones with guide rails
• Dynamic compaction is suitable for granular soils,
made-up and fill sites
• Using dynamic compaction bearing capacities of
50 to 150kN/m2 can be achieved
Chris Gorse
Dynamic
compaction
Chris Gorse
Typical cone type tampers
(adapted from www.rogerbullivant.co.uk)
Chris Gorse
Dynamic compaction rig
Chris Gorse
Vibro compaction or displacement
• Vibrating rods are forced into the ground
causing the surrounding ground to compact
and consolidate.
Chris Gorse
Vibro compaction or vibro
displacement
• Vibrating mandrels (poker, shaft or rod)
penetrates, displaces and compacts the ground.
• Void Created is filled with stone and recompacted
• Produces stone columns in the ground, compacts
surrounding strata enhancing the ground bearing
capacity and limiting settlement
• Typical applications include support of
foundations, slabs, hard standings, pavements,
tanks or embankments.
Chris Gorse
Vibro compaction - continued
• Used in soft soils, man made and other strata, can
be reinforced to achieve improved specification
• On slopes it can limit the risk of slip failure.
• Ground bearing capacities, for low to medium rise
buildings and industrial developments, is in the
region of 100kN/m2 to 200kN/m2.
• Improved ground conditions may allow heavier
loads to be supported.
• Used in granular and cohesive soils
Chris Gorse
Benefits of vibro-compaction
• Buildings can be supported on conventional
foundations (normally reinforced and shallow
foundations).
• Work can commence immediately following the vibro
displacement. Foundations can be installed straight
away.
• The soil is displaced. No soil is produced.
• Contaminants remain in the ground – reduces disposal
and remediation fees.
• Economical, when compared with piling or deep
excavation works.
• Can be used to regenerate brownfield sites
Chris Gorse
• Can use reclaimed aggregates and soils.
Vibrofloatation
• Vibro floatation uses a similar process to
vibro compaction
• Water jets at the tip of the poker
• Water jets help the vibrator penetrate hard
layers of ground
• Major disadvantage is that the system is
messy and imprecise, thus rarely used
Chris Gorse
Vibro displacement - Typical
sequence
1. A grid is marked out and the
vibrating mandrel (poker) is
inserted to the required depth
2. As the mandrel drives into
the ground the soil is
displaced (surrounding
granular soil is compacted.
Chris Gorse
Vibro displacement - Typical sequence
Chris Gorse
Mandrel
positioned ready
to compact and
displace
Chris Gorse
Ground
displaced
Chris Gorse
Ground compacted void remains
Chris Gorse
Void filled with stone
Chris Gorse
Hardcore is repeatedly displaced and
compacted
Chris Gorse
Chris Gorse
Grouting
• Grouting may be used to fill the voids in the
ground increasing the strength of the
ground.
Chris Gorse
Pressure grouting
• In permeable soils, pressure grouting may be used
to fill the voids.
• Holes drilled using mechanically driven augers.
• As the auger is withdrawn cement slurry is forced
down a central tube into the bore under pressure.
• Pressures of up to 70,000 N/mm2 can be exerted
by the grout on the surrounding soil.
• Slurry contains cementious additives, e.g.
pulverised fuel ash (pfa), microsilica, chemical
grout, cement or a mixture.
Chris Gorse
Soil modification and stabilization
• Machines are available that can break-up
the ground, mix the ground with new
cementious material and improve the
ground quality.
Chris Gorse
Soil modification and recycling
• Additives used in soil stabilisation increase the
strength better, improve compacted and maximise
bearing capacity and minimise settlement.
• The technique can be used to provide stabilised or
modified materials for earthworks, or may be used
to provide permanent load transfer platforms or
hard standings.
• Can be used to treat and neutralise certain
contaminants or encapsulate the contaminants,
removing the need for expensive removal and
disposal.
Chris Gorse
Soil modification, stabilisation
and recycling machine
Working direction
Unstable soil
Milling and mixing chamber
Stable or modified
soil ready for
compaction
Chris Gorse
Schematic of
soil modification and mixing chamber
Chris Gorse
Soil modification and stabilization rig
www. roger-bullivant.co.uk
Chris Gorse
Soil modification and stabilization
plant
www. roger-bullivant.co.uk
Chris Gorse
www. roger-bullivant.co.uk
Chris Gorse
Soil modification and stabilization
plant
www. roger-bullivant.co.uk
Chris Gorse
Surcharging
• This involves placing heavy loads on the ground
for long periods of time.
• Over time the ground will compact.
• Surcharging is time consuming and ties up the
land
• Can be used if long lead-in time available
• Can be used on roads
• May be used on investment land (land bank). The
increase in strength will increase the value of the
land.
Chris Gorse
Surcharging
• Excavated material, quarried stone or other
heavy loads.
• Settlement and compaction period 6 months
to a few years.
• For economics the surcharging acts as a
temporary storage facility
Chris Gorse
Geotechnical membranes
• Geotechnical membranes provide a sheet of
reinforcing material that can be added to the
ground. This increases the stability and
tensile strength of the ground.
Chris Gorse
Geotecnic membrane
Chris Gorse
Geotechnical membranes
• Natural
• Plastic manmade
• Built up in layers compacted between
ground hardcore
• Sheets, fibres and strips
Chris Gorse
Further information supporting these slides can be
found in the following publication and websites.
Emmitt, S. and Gorse, C. (2010) Barry’s Introduction to Construction of Buildings.
Oxford, Blackwell Publishing
Emmitt, S. and Gorse, C. (2010) Barry’s Advanced Construction of Buildings.
Oxford, Blackwell Publishing
Virtual Site (2010) Virtual Site at Leeds Met University
http://www.leedsmet.ac.uk/teaching/vsite
Virtual Site Gallery (2010) Virtual Site Gallery at Leeds Met University
http://www.leedsmet.ac.uk/teaching/vsite/gallery
Chris Gorse