Investigation of intelligent pad foot soil compaction method through the development of in-situ elasto-plastic material characterization devices

Abstract

Proper soil compaction is critical to providing adequate structural support in any geoconstruction project, and is particularly relevant to road construction. However, current quality control/ quality assurance practices often evaluate only 0.1% of the compaction area, which can be problematic for a heterogeneous material like soil. For example, in roadways, improper soil compaction can lead to potholes and cracking. The limitation in coverage is due to dependence on spot testing devices, such as the nuclear density gage or sand cone test. In addition to providing sparse coverage, these devices create a disparity between design and construction engineering by measuring density, whereas soil foundations are designed in terms of an elastic modulus and yield strength (i.e., stiffness and bearing capacity). There is a need for soil compaction monitoring with greatly increased coverage, and mechanistic measurements (i.e., parity with design engineering parameters). This research contributes to advances in intelligent compaction, the goal of which is to provide 100% coverage with mechanistic measurements through machine integrated devices. No such technology exists for static pad foot compaction, which is the focus of this research. This thesis develops novel in-situ material characterization devices and methodologies to enable continuous, mechanistic monitoring of soil compaction for static pad foot soil compactors. In addition to researching the technical challenges of advancing compaction monitoring, this thesis goes one step further to investigate the policy pathways and barriers to adoption of these technologies. Towards intelligent static pad food compaction, I pursue the development of a strain gage instrumented pad, integrated into the pad foot soil compactor. Through numerical modeling, laboratory testing, and field evaluation, I develop a contact force measuring instrumented pad that is sensitive to soil compaction, i.e., contact force increases with compaction. This provides the potential to greatly increase the coverage of pad foot soil compaction monitoring, but remains an empirical approach that does not provide mechanistic parameters. I then take the strain gage instrumented pad towards mechanistic measurements through the investigation of instrumented plates, the simplified geometry of which allows for more robust analysis. Methods for using plate strain measurements to estimate elastic modulus and yield strength are developed through numerical and analytical modeling and evaluated through experimental testing. Improving on previous plate measurement techniques, these approaches develop inverse models based on finite element modeling to extract constitutive parameters from plate strains. Development of these plate-based mechanistic measurement methods benefits pad food soil compaction monitoring due to the similarity in the geometry of a pad and these plates. The mechanistic inverse models developed for the plates serve as a model for an inverse model for the pad. Furthermore, plates may be able to replace pads on a deployed soil compactor to act as monitoring devices. Finally, this thesis addresses the pathways and barriers to innovation adoption in the highway construction industry, which is historically an inertially bound industry. The adoption of intelligent vibratory compaction, which is at very different levels of progress in different states, is investigated. Through interviews with a wide range of industry professionals, I draw attention to the key roles/individuals within this industry that must be aligned to create an environment conducive to adoption.