Research My team's research interests are focused on developing intelligent geosystems that can sense and adapt to improve performance. Our current projects described below deal with how instrumentation, signal processing and data analysis techniques can improve geotechnical engineering and geoconstruction. We are also pursuing research in improving mechanically-stabilized earth wall construction, extracting additional information from pile driving, and advancing the adapting aspect of intelligent geosystems through feedback control. Please check back periodically for project updates.
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Venice Lagoon Vibratory Compaction Monitoring |
 As part of the Italian effort to safeguard Venice and its lagoon from flooding, mobile flood gates are being designed and constructed at the three inlets to the Venice lagoon. The gates will rise during storm surges and otherwise remain lowered to maintain tidal fluctuations and preserve the lagoon ecosystem. Approximately 1-2 m of granular fill will be deposited and compacted beneath the gate structures. We are researching techniques to monitor the compaction of the granular fill at the seabed floor using the real time vibration signature from the vibratory plate. We are specifically exploring the real time estimation of soil modulus during the vertical and rocking mode vibration behavior observed from the vibratory plate as well as understanding the nature of pore water pressure generation. The research aims to de-couple the dynamic behavior of soil skeleton and the pore water. Ultimately, with real time assessment of soil stiffness, the compaction process can be optimized to produce the desired result in a more time efficient manner. Our research is being funded by the National Science Foundation. We are also working with the lead geotechnical consultancy company Technital. |
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Monitoring Roller Vibration During Earthwork Compaction |
 The instrumented vibratory roller compactor has tremendous potential to improve the quality of earthwork compaction. As a dynamic soil stiffness measuring device, the instrumented roller provides a continuous measure of mechanistic soil properties and a more direct link to geotechnical design parameters, e.g., layer moduli for pavement design. Furthermore, the integration of monitoring with the compaction operation enables so-called intelligent compaction where the roller speed, path, vibration frequency and amplitude can be modified via feedback control to improve and expedite compaction. In this study, we explored the relationship between roller vibration characteristics and the underlying soil stiffness. An Ingersoll Rand roller was outfitted with instrumentation and data acquisition to monitor drum and frame acceleration, and eccentric excitation force. The study documented the sensitivity of key vibration parameters (drum and frame acceleration, drum phase lag) to soil stiffness in homogeneous and heterogeneous test beds, and demonstrated the capability of the instrumented roller as a proof rolling device. See the paper recently published in ASCE's J. Geotech. & Geoenv. Engineering. |
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In-ground Stress-Strain Behavior During Vibratory Compaction |
 Soil modulus is dependent upon stress path, strain rate and stress magnitude. Therefore, the connection between roller-measured soil stiffness and constitutive soil modulus for layered analysis requires a thorough understanding of stress-strain behavior beneath a traveling vibratory roller. This study seeks to measure the in-ground stress strain response and to characterize the observed constitutive behavior in both compacted cohesive and non-cohesive materials. Measuring in-situ stress and strain is challenging; the resulting measurements are often error-prone. The initial development of the stress-strain measurement approach and the key issues involved was published in the proceedings of GeoDenver 2007. Results from the relationship between roller-measured soil stiffness and in-situ constitutive behavior will appear here soon. |
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Modeling Nonlinear Vibratory Roller Behavior |
 Continuous monitoring of soil properties requires robust numerical models that capture the essential features observed during drum/soil vibration. This study investigated lumped parameter modeling of the drum/soil system to mimic complex behavior observed experimentally during vibration on sandy soil. Two, three and four degree of freedom (DOF) models with linear and nonlinear soil elements were investigated. The research revealed that a 3-DOF model incorporating the soil, drum and frame was successful in capturing behavior during coupled drum/soil vibration and during drum/soil de-coupling. Modeling the soil with constant spring stiffness was reasonably successful; however, the addition of nonlinear soil stiffness due to the curved drum effect and due to strain hardening was effective in matching experimental data. This work was recently published in the ASCE Journal of Engineering Mechanics. |
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Exploring Light Weight Deflectometer Response |
 Light Weight Deflectometers (LWDs) are increasingly being used during earthwork quality assurance of soil compaction. Similar to the Falling Weight Deflectometer, a drop mass imparts a force to a plate resting atop the soil. The measured (or assumed) impact force and computed peak displacement (integrated from plate acceleration or velocity) are used to estimate soil stiffness/modulus. In current practice, soil modulus is estimated using peak values of force and deflection, and by assuming static loading on an isotropic linear elastic half-space. A detailed experimental and analytical investigation showed that isotropic linear elastic half-space theory is not appropriate and that the contact stress distribution varies with soil type. This study was reported in this ASCE Journal of Geotechnical & Geoenvironmental Engineering paper. We are currently exploring the combination of LWD and surface seismic wave testing to capture nonlinear modulus parameters required for mechanistic-empirical pavement evaluation. |
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Profiling Soil Modulus with Surface Waves |
 Surface wave analysis has been successfully used to profile the moduli of pavement systems. Working with our colleague Dr. Nils Ryden from Lund University in Sweden, we are exploring a number of issues related to surface wave analysis of earthwork compaction. One aspect is using shear wave velocity profiles to better understand the dependence that vibratory roller amplitude has on roller measurement values. Some very preliminary findings from this research were presented at SAGEEP 2007 held in Denver in April 2007. |
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Evaluation of Wireless Sensor Nodes for Measuring Slope Inclination |
 Digital inclinometers are used in geotechnical engineering to monitor lateral deformations of excavation walls, retaining walls, embankments and landslide areas. Current conventional slope inclination measurement requires a person to manually lower a probe into a grooved casing and record inclination at prescribed intervals as the probe is drawn upwards. Developing an automated inclinometer system would enable continuous monitoring for use in intelligent construction as well as provide significant savings in terms of equipment, material and labor costs. This research study investigated the use of low-cost wireless sensor nodes as an alternative to traditional inclinometer systems used in geotechnical engineering applications. The findings were published in the Proc. 2005 Intl. Symp. on Automation and Robotics in Construction. |
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