John Peter Lambert

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. LWD is reviewed as a field evaluation tool, the test variables and data quality are discussed, and the usefulness and limitations for a variety of earthwork and road assessment scenarios are described. A state-of-the-art reference document is provided for LWD users, consultants, material specifiers, contractors, and clients. Data from road foundations (subgrades, granular capping, and subbase) and fully constructed in-service (thinly surfaced) roads were reviewed to demonstrate the flexibility of the LWD and to show that its determination of stiffness modulus may differ from that of the conventional falling weight deflectometer to a varying extent. A series of laboratory investigations was undertaken to demonstrate the sensitivity to uniformity of plate-surface contact and the limitations in the interpretation of peak displacement from the device. A good understanding of the device workings and careful specification of the test variables are required both to analyze the data correctly and to permit comparison between data sets. It is concluded that the device is a useful and versatile field quality control and pavement investigation tool if an understanding of the device issues is considered by data users.

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. There is a need for a more sustainable use of resources, and specifications that make best possible use of material properties are required. A performance-based approach is considered the best way to achieve this. The functional requirements of a performance-based specification for UK highway foundations were considered. The recently researched performance-based specification, demonstrating the steps to its development, determination of the engineering requirements, suitable target values, and potential construction-related implications, is explained. Performance-based specifications offer the advantage of better incorporation of the principles that underpin sustainable construction and require a fuller understanding of material behavior for their development and implementation. However, contractual issues and implications for construction need t...

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 utilizes a light–weight deflectometer, similar to that proposed for field compliance testing to provide performance data from compacted large particle size granular materials. The system developed utilizes a “soft” 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.