The small range of moisture contents measured with typical filter paper media in test method ASTM D5298 Measurement of Soil Potential (Suction) Using Filter Paper, require that the mass of the paper be measured to 0.0001 g. The accuracy and resolution of several readily available filter papers was investigated, along with investigating a polymer material as a possible alternative media. The importance of calibrating the filter paper was supported by the study, and suggested that because the slope of the calibration curve varies from paper to paper, the filter papers with the capability of measuring a broad range of water contents (low slope of the water content suction calibration curve) provide increased measurement resolution. The polymer media strips were found to have a much greater range of the moisture content than any of the filter papers, providing even greater resolution in the prediction of suction. The polymer strips performed just as well as the filter papers and showed repeatability in the measured suction values. The primary limitation in using polymer material is the lack of mass production of the material in a form suitable for suction measurements.

A seasonal monitoring program of flexible pavement performance has been performed in Tennessee since 1996, in which the water content of the subgrade is measured by Time Domain Reflectometry (TDR) probes. Five-segment probes were chosen to increase the number of measurements and volume of soil monitored. The variations of water content measured in the subgrade and the base course closely follow the temperature trends. This finding suggests the significance of temperature effects on TDR measurement. A laboratory calibration program was thus carried out to study the temperature effects on TDR measurement of volumetric water content. Temperature effects on TDR measurement are related to the energy of the signal. After correcting for temperature effects, the field TDR measurements of volumetric water content appear to track a seasonal variation.

A comprehensive instrumentation system was installed at four sites across the state of Tennessee to monitor long-term seasonal changes in subgrade water content. This paper summarizes the instrumentation and evaluates each of the monitoring methods. The instrumentation included a complete weather station, time domain reflectometry probes, temperature sensors in the pavement and subgrade, free-drainage pan lysimeters, and resistivity probes. The paper describes problems encountered, how they were resolved, the value of the data obtained, and provides recommendations based on the lessons learned from the 5-years of data collection.

Vertical loads on concrete box culverts under high embankments are examined, where a high embankment is defined herein as one where the height of the fill above the culvert is greater than the width of the culvert. Results from an instrumented culvert are described, with results from pressure cells, strain gages in the wall, and strain gages in the roof showing reasonable agreement. There was strong correlation between the height of fill and the pressure and internal forces in the culvert, suggesting that the soil-structure interaction factor is independent of the H/B ratio. The results of the instrumented culvert were compared to those of other instrumented culverts under high embankments. The measured roof pressures were significantly greater than the pressure due to the soil overburden, with the measured pressures averaging 1.5 times the soil overburden pressure. Although the soil-structure interaction factor recommended by the American Society of Highway and Transportation Officials specification tends to under-predict the loads acting on concrete culverts, a simplified reliability analysis suggests that the Specification provides a sufficient level of safety. DOI: 10.1061/(ASCE)1084-0702(2005)10:6(643)

A comprehensive instrumentation system was installed at four sites across the state of Tennessee to monitor seasonal variations in the environmental factors affecting flexible pavement response. This paper presents some selected findings obtained from over five years of continuous data collection. The data included temperature and water content of the various pavement layers, and weather information. Falling weight deflectometer (FWD) tests were used to observe the pavement response during different seasons. The measured seasonal variations in subgrade and base water content were observed to be small. Consistent with these observations, the seasonal variations in FWD back calculated subgrade modulus were small, suggesting that these effects may not be important in the design of pavements in moderate climates. Since the pavement systems were anew construction, little pavement distress was observed over the study period. However, as the pavements age, water infiltration may increase leading to greater water content changes in the unbound materials.

Multisegment time domain reflectometry (TDR) probes are an attractive alternative to single-segment probes when used for the in situ measurement of water content changes in pavement systems. Because several independent measurements are made along the length of the multisegment probe, these instruments offer several advantages over the more traditional TDR probes. These include the ability to obtain measurements over a greater volume of soil, the ability to install the probe into relatively undisturbed soils, and the redundancy provided by multiple measurements from the same instrument. However, because of the difference in signal strength along the probe, all segments do not provide the same level of accuracy. Several factors that must be considered when using these probes are discussed, including the sources of measurement error and the temperature dependence of the measurements in some segments. A method is described by which the results from lower accuracy segments can be used when higher accuracy segments fail during service, taking advantage of the redundancy provided by multisegment probes. The method is demonstrated on data from a site from which over 4 years of continuous water content measurements have been obtained.

Free-drainage lysimeters, commonly used in agriculture to monitor evapotranspiration and solute transport, were installed at three highway test sites in Tennessee. The lysimeters were installed below flexible pavement systems just beneath the coarse-graded asphalt stabilized base. The lysimeters collect water infiltrating the unbound aggregate (stone base) and monitor the quantity of infiltration by diverting the flow into tipping bucket rain gauges. One test site indicated infiltration beneath the longitudinal joint in the first several months of monitoring. A second test site, where the dense surface layer was not in place, indicated infiltration correlating with rainfall. Data from this site were used to develop a model to predict the measured infiltration based on the recorded rainfall. The monitoring method and modeling approach may be applicable in the investigation of pavement permeability, drainage system efficiency, and the role of infiltration in the seasonal variation of water content of unbound pavement layers.

Subgrade resilient modulus is highly dependent on water content, which can vary significantly with a number of environmental factors. Four sites across the state of Tennessee were instrumented with comprehensive monitoring systems that collect meteorologic, subgrade water content, infiltration, and temperature data. These data will be used to develop a rational method to account for environmental effects (e.g., seasonal changes in subgrade water content, in flexible pavement design). Multiple-segment TDR probes were placed horizontally in the soil subgrade, in the stone subgrade, and in the asphalt stabilized base, and single-segment probes were placed in the asphaltic concrete of the roadway sections. Tension-free pan lysimeters were installed at three of the test sites to measure infiltration through the pavement layers. Temperature sensors were installed in the soil subgrade and in the stone base at the same elevations as the TDR probes, and at three elevations in the top 200 mm of the pavement. Each site was instrumented with a weather station that monitors relative humidity, air temperature, rainfall, wind speed, and solar radiation. The preliminary data indicate changes in water content in the stone base layer that correlate with rainfall, and a small seasonal change in subgrade water content. Data from a test site where the pavement surface layer is not in place indicate that the asphaltic layers below the surface layer are permeable during significant rainfall events and that water appears to move freely through the asphalt stabilized base layer.

Since the late 1970s there has been increased interest in understanding groundwater movement and solutetransport in the vadose zone. While it is widely recognized that the potential for significant lateral flow exists as waterperches above impeding layers in the vadose zone, conducting meaningful research on this phenomenon requires controlof land management over large areas. A 7500-ha holding available to the Tennessee Agricultural Experiment Station atthe Ames Plantation in West Tennessee provides such an opportunity for extensive vadose zone monitoring over largeareas. In 1991 an interdisciplinary team of researchers at The University of Tennessee began developing a researchfacility in a 994-ha agricultural watershed to monitor off-site movement of agricultural chemicals. A 10-ha no-tillage testsite was equipped with a centrally located 0.4-ha test plot and a monitoring system to characterize surface andsubsurface hydrology. Shallow wells to collect perched water, with screens at the loess-paleosol interface (1.8 to 2.8 mbeneath the soil surface), were installed at 23 locations on concentric circles with radii of 45, 60, 90, and 150 m from thecenter of the 0.4-ha test plot. Potassium bromide was surface applied on 9 March 1993 to the 0.4-ha test plot at the rate of 300 kg/ha of Br. Datafrom shallow wells at the Ames Plantation Water Quality Project indicated extensive lateral movement of water in thevadose zone. Based on the spatial distribution of the shallow wells that yielded bromide, 17 additional shallow wells wereinstalled in March 1995 to more accurately characterize water movement at the loess-paleosol interface. An automaticsampling system was installed to collect samples from the 17 new wells as well as from four of the original wells. Thesampling system uses a liquid level switch and a datalogger to open a solenoid valve allowing vacuum from supply tanksto extract the sample from the well into sample collection jugs and to record the time the samples are extracted. Thesampling system is working well and is easily maintained by the field technician.