<p><p><strong>References:<br></strong><em>Elseifi (2003)<br>Christopher et al. (2010)</em></p><p><strong>Method Summary</strong></p><p>This method assesses the moisture content in the encapsulated soil using Ground Penetration Radar (GPR) and Time Domain Reflectometer (TDR) probes. Falling Weight Deflectometer (FWD) or Light Weight Falling Weight Deflectometer (LFWD) tests can also be performed to evaluate resilient moduli of the subgrade before, during, and after construction. In GPR, the moisture content is measured by sending electromagnetic waves through the surveyed structure and then analyzing the reflected signal. The scan of the pavements, presented as a colored map, shows the distribution of the moisture content in the soil. The TDR probes measure the soil moisture content by sending a pulsed signal in the host material and examining the reflection of the signal. The FWD and LFWD methods consist of applying an impulse load to the paved or unpaved surface using a falling weight, typically between 4 and 107 kN (1,000 and 24,000 lbs), dropped on a plate resting on the surface. The deflection profile along the project site may be examined to determine if changes exist in the pavement structural response (i.e., due to moisture changes in the encapsulated subgrade layer). The FWD and LFWD data can be analyzed to back-calculate the resilient moduli of the subgrade and other pavement layers.</p><p>The measurement of the moisture content and/or FWD in the encapsulated and control sections (without membrane) can demonstrate the effectiveness of the partial encapsulation technique. These test methods are more suitable for the post construction monitoring of the moisture content (Elseifi 2003) or resilient modulus (FHWA 2010).</p><p><strong>Accuracy and Precision</strong></p><p>The GPR measurements indicate the relative moisture content within the pavement scan. The accuracy of TDR probes relies on the conversion factor of dielectric constant of the soil to the moisture content. Generally the conversion factor is supplied by the manufacturer and with an accuracy of ±2%. FWD tests over-predict the resilient modulus and a factor is applied based on empirical evidence to correct the result. Thickness and temperature measurements are also important elements in obtaining correct interpretation. Repeated tests in the same location under similar temperature conditions can produce consistent results.</p><p><strong>Adequacy of Coverage</strong></p><p>The GPR and FWD tests can be implemented to cover the entire improved soil in a reasonable time. The TDR probes should be installed at each location of the moisture content measurement. Sufficient evaluation coverage requires many TDR probe measurements.</p><p><strong>Implementation Requirements </strong></p><p>Some experience and specialized equipment is necessary.</p><p><strong>General Comments</strong></p><p>Greater accuracy can be achieved by developing calibration equations from comparisons between moisture contents using TDR and gravimetric methods. Likewise, the FWD accuracy in obtaining resilient modulus values can be improved by comparing field data to laboratory test results.</p></p>