1. Ground Improvement Issues & Techniques
CE1203 Geotechnical Properties & Construction Methods

2. Definition of Ground Improvement
Ground treatment is the controlled alteration of the state, nature or mass behaviour of ground materials in order to achieve an intended satisfactory response to existing or projected environmental and engineering actions.
Mitchell, J M and Jardine, F M (2002)
‘A Guide to ground treatment’
CIRIA

3. Main Improvement Techniques:
• temporary
e.g. dewatering or ground freezing, where the improvement is only during the application
• short-term
e.g. some forms of grouting, or use of diaphragm walls for ease of construction with longer term benefits
• long-term
e.g. soil nailing, vibro-replacement, curtain grouting of a dam, where the treatment is integral to the permanent works.

4. Benefit to the Construction Work
Reduction and control of deformation & settlement
Reduction, control and exclusion of groundwater to aid safety and buildability
Reduction of susceptibility to erosion and improving life-span.

5. Effect on the Ground • Change of state;
i.e. the same ground but made stronger, stiffer, denser, more durable
• Change of nature;
i.e. the ground becomes a different material by inclusion of other materials
Change of response;
i.e. through the incorporation of other materials, the ground becomes a composite material with enhanced load-carrying or deformation characteristics.

6. Main Improvement Techniques:
• by vibration
• by adding load
• by structural reinforcement
• by structural fill
• by admixtures
• by grouting
• by specialist dewatering

7. Benefit Technique ◊◊◊ ◊ Higher Bearing Capacity Less/ more Even
◊◊◊ = Main benefit
◊ = Secondary benefit
Benefit
Technique
Higher
Bearing
Capacity
Less/ more
Even
settlement
Faster
Settlement
Ground water
control
Reduced
Liquefaction
potential
Increased
Erosion
resistance
Improved
slope / face
stability
Vibro-replacement
◊◊◊ ◊
Dynamic Compaction
Pre compression
Vertical Drainage
Reinforcing soil / soil nailing
Structural fill
Lime/cement admixture
Permeation grouting
Cavity grouting
Ground freezing
Slurry cut off trench & pumping
Well pointing

8. Vibroflotation Plant
Mitchell, J M and Jardine, F M (2002)

9. Use of Vibration Techniques
Mitchell, J M and Jardine, F M (2002)

10. Vibro-Replacement
Principles of column construction using the dry top-feed process
1. Vibrator penetrates
weak soils under action
of vibrations and
‘compressed air’ jetting
medium and forms a
hole to design depth,
usually a competent
bearing stratum
2. After being held at
depth for a short time,
the vibrator is
withdrawn and a
charge of stone is
placed into the hole
3. The vibrator is
reintroduced into the
hole, the stone is
compacted, forced out
and tightly interlocked
with the surrounding
ground
4. By adding
successive charges of
stone and compacting
each one, a column of
very compact stone is
built up to ground level
Animation Clip
Palm Island Dubai

11. Dynamic Compaction Plant
Specialist Rig to reduce noise and environmental disturbance

12. Dynamic Compaction
It involves the repeated dropping of a large weight (15 tonnes or so) from a height of up to 15 metres.
The site is usually covered at first with a wide grid, followed by a smaller grid using a lighter weight or a reduced fall.
This technique can effectively compact the ground down to a depth of a few metres 
Not suitable for small sites or sites where vibration, impact etc can affect adjacent buildings or building service in the ground
Video Clip

13. Summary – Factors Effecting Ground Improvement
Suitability of existing geotechnical materials?
Size of improvement area?
Availability of specialist plant / equipment?
Proximity to existing habitation / buildings?
Access & safety considerations?
Cost effective cf: traditional methods?

14. Activity
Examine the following situations and state what ground improvement method would be suitable & why:
A deep vertical shaft construction in an area of high ground water.
An area of ground with shallow soft man-made fill materials, such as mining waste, for housing development.
An area of previously drained and reclaimed silt with low bearing capacity for road construction.
The stabilisation of a rock face overhanging a busy railway.
A previous land fill tip used for domestic waste.
Ground Freezing
Dynamic Compaction / vibro-flotation
Pre-compression
Cement grouting / nailing
Importing structural fill