According to the British Geotechnical Association, the
annual spend on earthworks in the UK is believed to be
in the region of £1bn – £1.5bn. It is reasonable to surmise
that a significant portion of this spend is occurring during
the remediation of Brownfield sites to enable their
redevelopment using recycled or re-used materials
that are complex in their composition, properties and
mechanical behaviour.
In principle, subject to the necessary approvals, anyone
can conduct earthworks to cut and fill land to meet
desired topographic levels. However, if the materials
used as fill are not properly compacted, or if the land is
already poorly compacted, long-term settlement can
cause significant and costly damage to buildings and
infrastructure in the years after the redevelopment has
been completed.
Controlling compaction during earthworks is therefore
very important to engineers, contractors, their clients
and third-party stakeholders who may have some
vested interest or liability associated with the final
development (e.g., the National Housebuilding Council,
Local Authority Highways and Building Control).
Manual testing of placed and compacted materials by
competent professionals has long been a common method
of compaction control during earthworks implemented
by reputable contractors. Moisture content, dry density,
air voids, undrained shear strength and stiffness moduli
are parameters that are often advocated in earthworks
specifications (both within end product specifications and
to a lesser extent method specifications) as metrics for
on-site field engineers to verify compliance with associated
criteria at a required frequency.
Unfortunately, these metrics are measured using field
techniques with limitations that often lead to delays
and reduced earthworks productivity. I have personally
witnessed many working hours lost due to human error
and equipment failure relating to these techniques;
not to mention the countless hours spent unravelling
the reasons for recorded false positives and/or false
negatives due to the complexity of the recycled or
re-used earthworks materials that are commonplace in
Brownfield land remediation.
It is therefore not surprising the several years ago
VertaseFLI strategically invested in our own earthworks
compaction plant (a 26 tonne Bomag roller with an
interchangeable drum), that was equipped with
continuous compaction control using the BOMAP
system. During operation, the roller provides a
continuous measure of ground stiffness (based on
a vibration modulus), which can be correlated with
other compaction control metrics (e.g. density) as
required. Furthermore, the roller is currently fitted with
a polygonal drum that imparts compactive effort via
an ‘impact’ force rather than a ‘static’ force, providing
the opportunity to explore the compaction of thicker
layers and increase productivity.
This continuous compaction control technology
reduces reliance on manual field testing, which
can bring significant cost savings to our Brownfield
remediation projects involving earthworks. These cost
savings may be particularly notable for more complex
recycled or site-won earthworks materials intended
for re-use, for which compaction is more challenging
to verify using standard field techniques.
