8 research outputs found
Novel assessment test for granular road foundation materials
Drivers for sustainability have made it necessary for the construction industry to adapt
its traditional processes to become both more efficient and produce less waste.
Performance based design and specification in the UK for motorways and trunk roads
permits a very flexible approach to pavement design, material selection and
performance related testing aimed at utilising materials to their maximum potential.
However, it is clear that within the emerging philosophy of using materials that are âfit
for purposeâ there are many technical challenges for design and specification. There is a
need to develop suitable methods of evaluating materials prior to their being used on
site. This project was born out of this requirement, with a particular emphasis on coarse
granular materials due to their common role in capping construction and also their
unique difficulty for measurement under laboratory conditions due to their large range
of particle size.
A novel assessment test for coarse capping materials for roads that can be used to
indicate their likely short-term in situ performance, under controlled laboratory
conditions before construction on site, has been developed during this research
programme. Key findings relating to the behaviour of coarse capping materials, the use
of stiffness measuring devices and variables that influence the measurement of
composite stiffness are discussed in detail. The research highlights the necessity for
adequate drainage and protection of foundation materials against increase in water
content. When adopting a performance specification the timing of the pavement
assessment is critical, both on site and in the laboratory. The performance measured on
site should perhaps only be considered as a âsnapshotâ relating to the stress state in the
material at the time of testing
The assessment of coarse granular materials for performance based pavement foundation design
The need to use more recycled and marginal materials in pavement foundations is
encouraging moves towards performance based specifications. Such an approach needs
data on the fundamental material parameters of stiffness and resistance to permanent
deformation (strength) to allow analytical design and achieve comparable compliance
testing on site. Whilst a number of laboratory and field tests to measure such performance
exist, all have limitations relative to either the particle size of materials that can be tested
and/or correlation between the laboratory and field derived data.
This paper presents the development of a large scale resiliently lined steel laboratory
material box tests proposed for routine material assessment. The test utilises a Lightweight
Deflectometer, similar to that proposed for field compliance testing to provide
performance data from compacted large particle size granular materials. The system
developed utilises a âsoftâ base condition to replicate typical subgrade stiffness and allows
wetting and drying of materials to assess their environmental stability. The results show
that such a test can simply provide suitable data for performance based design, but
consideration needs to be given to the water content of materials, the time of testing after
compaction, and the use of appropriate boundary conditions. These findings have both
implications not only for the developed tests but for field compliance testing of pavement
foundations
Lightweight deflectometers for quality assurance in road construction
The use of Lightweight Deflectometers (termed LWDs in Europe, and occasionally
PFWDs in the USA) for construction quality control or material investigation for road construction
has increased worldwide. In the UK the change in pavement foundation design to a
âperformance based approachâ has brought about the use of Lightweight Deflectometers for
field assessment of stiffness modulus. This paper reviews the LWD as a field evaluation tool. It
discusses in some detail the test variables that can influence and affect the field data quality, and
presents brief summaries of recent fieldwork where an LWD has been used as a quality control
tool. The paper concludes both on the LWD usefulness and also its limitations for a variety of
earthwork and road assessment scenarios, and describes a field test protocol for its use on a variety
of materials. The findings demonstrate the flexibility of the LWD but also show that its determination
of âstiffness modulusâ may differ from that of the conventional Falling Weight Deflectometer
(FWD) to a varying extent. The paper provides a useful reference document for
LWD users, consultants, material specifiers, contractors and clients
Insitu assessment of stiffness modulus for highway foundations during construction
Several portable field devices that measure stiffness modulus are reviewed in detail in
this paper including the German Dynamic Plate Test (also known as the Lightweight Drop Tester),
the TRL foundation tester (UK), the Prima (Denmark) and the Humboldt Soil Stiffness Gauge
(USA, also known as the GeoGauge). Laboratory and field data are presented which explain the
many important influences on the measured data and demonstrate comparative performance with
respect to the Falling Weight Deflectometer. These field data show significant scatter and site
specific correlation. A strategy for compliance testing during construction, as part of a performancebased
specification approach for the UK, is suggested. Conclusions are made regarding the devicesâ
relative merits and limitations, and considerations for their introduction into contractual use for
routine assessment during construction
Geotechnical specifications for sustainable transport infrastructure [published as: Sustainable earthworks specifications for transport infrastructure]
The specification of the materials and methods used in earthworks and foundations for highways, railways and airfield runways can be approached in several ways. However, in part due to the sustainability agenda there is a need to use specifications that make best use of material properties, and a performance-based specification may be considered the best way to facilitate this. The advantages and disadvantages of the different specification approaches is described and discussed in this paper. The functional requirements of a performance-based specification for UK highway foundations are considered. The (recently researched) performance-based specification is explained, demonstrating the steps to its development, determination of the engineering requirements, suitable target values and the potential construction-related implications. It is shown that performance-based specifications offer the advantage of better incorporation of the principles that underpin sustainable construction but also require a fuller understanding of material behavior for their development and implementation. However, contractual issues and implications for construction need to be carefully considered to allow a full performance-based approach to be successfully adopted. It is considered in the UK that a staged implementation of a performance specification is necessary to permit the gaining of experience of both the process and the field measurement methods, some of which are relatively novel, and to reduce the risk of contractual disputes or potential failures and thus a negative reaction from the industry
Review of lightweight deflectometer for routine in situ assessment of pavement material stiffness
The use of a portable lightweight deflectometer (LWD) for construction quality control or
material investigation for earthworks and road construction is increasing around the world.
This paper reviews the LWD as a field evaluation tool, discusses the test variables and data
quality and concludes both on its usefulness and also its limitations for a variety of earthwork
and road assessment scenarios. The paper aims to provide a state of the art reference
document for LWD users, consultants, material specifiers, contractors and clients. It reviews
data from road foundations (subgrades, granular capping and sub-base) and fully constructed
in-service (thinly surfaced) roads, to demonstrate the flexibility of the LWD but also show
that its determination of âstiffness modulusâ may differ from that of the conventional Falling
Weight Deflectometer (FWD) to a varying extent.
A series of laboratory investigations are presented that demonstrate the sensitivity to
uniformity of plate/surface contact, and also limitations in the interpretation of peak
displacement from the device. In conclusion, a good understanding of the device workings
and careful specification of the test variables are required to both analyse the data correctly
and permit comparison between data sets. The device is concluded to be a useful and versatile
field quality control and pavement investigation tool, if an understanding of the device issues
is considered by data users
A review of geotechnical specifications for sustainable transport infrastructure
The specification of the materials and methods used in earthworks and foundations for
highways, railways and airfield runways can be approached in several ways. However,
due to the sustainability agenda there is a need to use specifications that make best use of
material properties. The advantages and disadvantages of different specification
approaches are described and discussed in this paper and a performance-based
specification is considered the best way to facilitate sustainability. The functional
requirements of a recently researched performance-based specification for UK highway
foundations is explained, demonstrating the steps to its development, determination of the
engineering requirements, suitable target values and the potential construction-related
implications. It is shown that performance-based specifications offer the advantage of
better incorporation of the principles that underpin sustainable construction but also
require a fuller understanding of material behaviour for their development and
implementation. However, contractual issues and implications for construction need to be
carefully considered to allow a full performance-based approach to be successfully
adopted. It is considered in the UK that a staged implementation of a performance
specification is necessary to permit the gaining of experience of both the process and the
field measurement methods, some of which are relatively novel, and to reduce the risk of
contractual disputes or potential failures and thus a negative reaction from the industry
Laboratory assessment of coarse granular road foundation materials
A new UK âperformance based specificationâ for road foundations potentially allows any material that is âfit for purposeâ and encourages the wider use of marginal and recycled/secondary materials. The specification provides guidance with respect to a target stiffness, density achieved and maximum allowable rutting depth under construction traffic (to avoid damage to the subgrade during construction). Full-scale field trial sections are currently used and proposed for large schemes to assure as the suitability of proposed foundation materials. However, it is prudent to develop a routine, economical and laboratory-scale means to assess the performance and suitability of the foundation materials before any full-scale trials are undertaken.
This paper presents the findings of recent research work at Loughborough University with regard to the development of a large-scale laboratory assessment test aimed specifically for granular materials. A series of test results on four granular materials are presented in detail, with an emphasis on their stiffness behavior, with some field data for comparison and preliminary validation of the laboratory method. The effects of a soft and rigid base condition, and wetting and drying of the material is shown to have a significant effect on the measured values of both stiffness and strength for the samples tested. However, there appears a reasonable relationship between the laboratory results for the soft base condition and the field data. Several recommendations for further work are made and practical observations and comments for the construction and measurement of these materials on site within a performance specification framework