Geotechnical Engineering

Large shafted helical piles are becoming increasingly popular in large scale construction projects as a viable foundation alternative. Recent helical piles have become larger and can resist much higher axial loads. The main installation parameters to consider are the specified torque and anticipated embedment depth. It is common during installation that the torque is not achieved at the design embedment depth predicted from an average soil property. For helical piles supporting structures and facilities that are deflection governed, it is necessary to verify the serviceability limit and the current field verification methods.

In this work, a total of 3,557 proof load tests, associated designs, and soil information from over 800 soil borings were reviewed and utilized to create an empirical formula to predict axial tensile pile capacity at a 5% helix diameter deflection limit. The correlations and empirical formula resulting from the data analysis was verified with full scale performance load testing from other projects, current industry accepted design methods, and current field verification methods. Implementing a deflection-based field verification will, for the first time, provide numerical and theoretical evidence that the installation of a large diameter helical pile is acceptable. The increased confidence in the pile capacity will enable a more effective and efficient design by lowering the design factor of safety or strength reduction factor.

Metal additive manufacturing (AM), also known as three-dimensional printing, is a fast-developing technology for the production of a wide variety of solid components from steel powders. An essential prerequisite of creating solid parts from this technique is to effectively spread the steel powders on a deposition surface. Therefore, the quality of the parts and manufacturing efficiency depends heavily on the spreadability of the powder, which is a function of the powder gradation, particle morphology, environmental factors, and boundary conditions.

In this project, the inter-particle capillary and van der Waals force effects are considered using a novel three-dimensional discrete element model (DEM). Powder spreading and rotary drum tests are performed to evaluate the flowability of the fine metallic powder.

Gabion baskets are the preferred rockfall mitigation method from an economic, environmental, and maintenance perspective due to their low cost to build, more natural appearance, ability to be covered with landscaping, and ease of repair by maintenance crews. However, there is considerable risk and liability issues in deploying gabion barriers owning to the general inability to characterize the serviceability and efficacy post-impact. In this project, a numerical approach based on the discrete element method is developed to address the issue involving transient dynamic rockfall impacts. The model proposed focuses on reproducing the energy loss characteristics during impacts and the post-impact rock fragmentation in the gabion barriers. Two extreme loading patterns are examined: 1) near-simultaneous impacts by multiple bodies; and 2) sequential impacts with full energy dissipation. Finally, the performance of the gabion barriers subject to impact loads is evaluated based on fragmentation size and post-impact deformation.

Rock particle shape plays a crucial role in influencing shear resistance and energy consumption during transient loads. The dynamics of such granular materials are complex and cannot be properly described using closed-form solutions when the problem involves more than a few particles. Thus, for the sake of computational efficiency, it is common practice to implement simplified numerical models that involve a limited number of particle interactions. In this study, a novel approach is used to capture realistic particle shapes while maintaining a relatively high simulation efficiency. The geometry of the particles is determined by a Delaunay triangulation which operates on a set of vertices and returns the corresponding network of facets and grid connections. Inertial and material properties are assigned to the rock prototype which are representative of realistic gravel particles. The algorithm is validated by performing a series of numerical simulations for various particle configurations, demonstrating that mass and momentum are conserved. A potential application of this work is related to rockfall barriers and their response to rigid boulder impacts. This innovative model, based on the discrete element method (DEM), is shown to be capable of simulating rock particles with realistic shapes and complex physical interactions.

Rock excavation is the first step of mineral production that plays a critical role in supporting the growth of electronics and microchips industry. As the demand increases rapidly, underground mining activities have gradually dug to a deeper depth of the earth crust for a higher production. As a result, the mining industry has been facing mechanical, environmental, and technical challenges that have seriously complicated the efficiency and economic efficacy of deep mining. Particularly, the high rock mass stress, high temperature, and high mud/water pressure during excavation have a great impact on the drilling performance and rock failure mechanism. In this project, a three-dimensional thermal-mechanical coupled discrete element model (DEM) is investigated to explore the tool-rock interactions under deep mining conditions. In addition to the index property tests, the rock cutting tests are simulated to investigate the failure mode transition as a function of drilling operation conditions.