Introduction of flat ribbon cable (FRC) sensor for density measurement of road materials using time domain reflectometry (TDR)

Moisture content and density of unbound granular pavement materials are important properties for compaction control providing a great influence on pavement performance. Time domain reflectometry (TDR) usually uses rod probe sensors, which can provide pointwise readings of density. However, pointwise readings might not be representative enough for a complete road section. This paper introduces the application of flat ribbon cable (FRC) sensor, which can be extended up to 6 meter to measure moisture and density of road materials. Soil specific calibration is done in the laboratory considering the variation of moisture and density of materials where sensors of three different lengths are considered to enable the development of length normalized calibration. The electric parameter used to derive soil density is the voltage drop, which occurs after the passage of an electromagnetic wave along the sensor embedded in the soil. Soil moisture is related to the permittivity of the soil sample, which is obtained from the travel time of the TDR signal. Laboratory results indicate that calibration functions are independent of moisture and density. These soil specific calibration functions are useful in measuring long term pavement performance and managing rutting of roads

Strength analysis of a partially-flooded pavement using falling weight deflectometer test before and after maintenance

Frequent flooding and wet weather events are the challenges for managing road infrastructure. In this study, falling weight deflectometer (FWD) equipment is employed to investigate the effect of moisture consequence of January 2011 flood at Queensland, Australia on a flooded road. The impacts of the flood on the structural strength were obtained for the whole section as well as different layers individually. These two sets of data provide a clear picture of the road condition as sound, severe or warning before and after the maintenance of the road. Furthermore, the moisture content of the spotted road at field condition providing the structural stiffness was obtained with a correlation of FWD data. These analysis and investigations play an essential role in optimizing the maintenance method for the roads suffering from the flood

Anisotropy in volume change behaviour of soils during shrinkage

It has been long recognised that some of the fundamental and engineering properties of soils exhibit a certain degree of anisotropy that eventually dictates their directional geoengineering behaviours. Consideration of the importance of the volume change behaviour of soils during shrinkage and a critical review of the literature suggests scopes for further research for the development of a better understanding of the anisotropy in volume change encountered during soil shrinkage. In this paper, anisotropy in volumetric shrinkage behaviour of soil is depicted with the theory of geometry factor and shrinkage strains. A systematic investigation and analysis on the evolution of geometry factors and shrinkage strains of several geomaterial samples during evaporative dewatering is reported herein. A theoretical framework for evaluating shrinkage geometry factors of a cylindrical soil specimen undergoing volume change during progressive moisture loss is described in this paper. Furthermore, based on experimental and literature data, shrinkage geometry factors of several specimens differing in terms of gradational properties, specimen size, evaporative boundary condition and pore fluid salinity are evaluated and discussed in detail in accordance with the theoretical framework. Linkages between shrinkage process, shrinkages strains and geometry factor are also analysed to underpin the usage of geometry factor and shrinkage strains to characterise anisotropy during soil shrinkage

Application of time domain reflectometry method in monitoring state parameters of subgrade soil in pavement

Moisture content has a direct influence on structural performance of pavement. Every year in Australia, heavy vehicles damage roads when the moisture content of the pavement layers reaches a critical value because of heavy rainfall or flooding. When the moisture content changes, increased moisture contents often lead to premature pavement damage under cyclic loading. Time domain reflectometry (TDR) is a noninvasive technique for measuring moisture content. The existing and newly developed TDR sensors are calibrated in the laboratory with materials of subgrade layer from the pavement. These calibrated sensors are installed in both the shoulder and wheel paths of a newly constructed pavement to monitor the dielectric characteristics of the materials. The dielectric characteristics are further utilized to calibrate in situ moisture of the pavement materials as well as transverse moisture distribution across the pavement. Moreover, the electrical conductivity and density of the materials are estimated based on the information of dielectric properties. Finally, the state parameters, namely moisture content, electrical conductivity, and density are obtained from the road instrumentation that would improve the pavement management in terms of damage, like surface deformation or rutting