UCLA Civil and Environmental Engineering

A Clear Zone (CZ), the unobstructed roadside area with highly compacted soil, naturally accumulates high concentrations of pollutants from traffic activities. These pollutants are washed off by road runoff and enter waterways. In situ, treatment of polluted runoff from the CZ could not only protect water resources but also provide an opportunity to recharge groundwater. However, the soil in the CZ requires compaction, which limits the natural infiltration and treatment of road runoff. In this study, we examine whether and how amending the soil in the CZ with sand, a common bulking agent used in road design, and Expanded Shale, Clay, and Slate (ESCS) aggregates, a novel light-weight engineered bulking agent, could help treat stormwater in situ. ESCS-amended soil media infiltrated 220% more water than sand-amended soil under compaction, indicating that the addition of ESCS would make the CZ better at treating road runoff generated during high-intensity rainfall. Compared to sand-amended soil in the CZ, ESCS-amended soil provided 58% more plant-available water during prolonged drying, indicating that ESCS addition would help maintain vegetation, thereby minimizing maintenance needs. Finally, replacing sand with ESCS improved the soil capacity in the CZ to remove pollutants, including heavy metals and E. coli, indicating the performance life of ESCS-amended soil would be longer than that of sand-amended soil in the CZ. Collectively, these results indicate that the addition of ESCS as an alternative bulking agent to sand in compacted soil in the CZ could potentially treat road runoff in situ and prevent pollution originating from road infrastructure.

Designing and printing metamaterials with customizable architectures enables the realization of unprecedented mechanical behaviors that transcend those of their constituent materials. These behaviors are recorded in the form of response curves, with stress-strain curves describing their quasi-static footprint. However, existing inverse design approaches are yet matured to capture the full desired behaviors due to challenges stemmed from multiple design objectives, nonlinear behavior, and process-dependent manufacturing errors. Here, we report a rapid inverse design methodology, leveraging generative machine learning and desktop additive manufacturing, which enables the creation of nearly all possible uniaxial compressive stress‒strain curve cases while accounting for process-dependent errors from printing. Results show that mechanical behavior with full tailorability can be achieved with nearly 90% fidelity between target and experimentally measured results. Our approach represents a starting point to inverse design materials that meet prescribed yet complex behaviors and potentially bypasses iterative design-manufacturing cycles.

In structural vibration response sensing, mobile sensors offer outstanding benefits as they are not dedicated to a certain structure; they also possess the ability to acquire dense spatial information. Currently, most of the existing literature concerning mobile sensing involves human drivers manually driving through the bridges multiple times. While self-driving automated vehicles could serve for such studies, they might entail substantial costs when applied to structural health monitoring tasks. Therefore, in order to tackle this challenge, we introduce a formation control framework that facilitates automatic multi-agent mobile sensing. Notably, our findings demonstrate that the proposed formation control algorithm can effectively control the behavior of the multi-agent systems for structural response sensing purposes based on user choice. We leverage vibration data collected by these mobile sensors to estimate the full-field vibration response of the structure, utilizing a compressive sensing algorithm in the spatial domain. The task of estimating the full-field response can be represented as a spatiotemporal response matrix completion task, wherein the suite of multi-agent mobile sensors sparsely populates some of the matrixs elements. Subsequently, we deploy the compressive sensing technique to obtain the dense full-field vibration complete response of the structure and estimate the reconstruction accuracy. Results obtained from two different formations on a simply supported bridge are presented in this paper, and the high level of accuracy in reconstruction underscores the efficacy of our proposed framework. This multi-agent mobile sensing approach showcases the significant potential for automated structural response measurement, directly applicable to health monitoring and resilience assessment objectives.

When the shock load is applied, materials experience incredibly high temperature and pressure conditions on picosecond timescales, usually accompanied by remarkable physical or chemical phenomena. Understanding the underlying physics that governs the kinetics of shocked materials is of great importance for both physics and materials science. Here, combining experiment and large-scale molecular dynamics simulation, the ultrafast nanoscale crystal nucleation process in shocked soda-lime silicate glass is investigated. By adopting topological constraints theory, this study finds that the propensity of nucleation is governed by the connectivity of the atomic network. The densification of local networks, which appears once the crystal starts to grow, results in the underconstrained shell around the crystal and prevents further crystallization. These results shed light on the nanoscale crystallization mechanism of shocked materials from the viewpoint of topological constraint theory.

A simplified analytical solution is derived for the dynamic response of a flexible vertical retaining wall supported on a rotationally compliant footing, subjected to vertically-propagating harmonic S-waves under plane-strain conditions. The wall retains a semi-infinite, homogeneous viscoelastic soil layer of constant thickness and material properties. The proposed solution is based on the Veletsos-Younan simplifying assumption of zero vertical normal stresses in the soil, and negligible variation of vertical displacements with horizontal distance from the wall. A modified integration technique is employed, inspired by the seminal work of Vlasov and Leontiev, which simplifies the analysis by suppressing the vertical coordinate and transforming the governing partial differential equation into an ordinary one that admits an elementary solution. Both cantilever and top-hinged walls are studied. Closed-form solutions are derived for lateral soil displacements, dynamic soil pressures, and equivalent Winkler springs connecting the wall to the far-field soil. It is shown that for cantilever conditions even a small amount of wall flexibility leads to a strong reduction in soil thrust, while the rotation at the wall base causes an additional decrease in thrust. The predictions of the method are in good agreement with available solutions, while new results for combined wall flexibility and rotational compliance are presented. The proposed approach offers a simpler alternative to the complex elastodynamic solutions of Veletsos and Younan.

The seismic analysis of bridge structures is often performed using the substructure method in which the foundation is replaced by an equivalent "spring" representing foundation impedance. Ground motions from seismic hazard analyses correspond to a free-field condition, and therefore should be modified to account for kinematic soil-structure interaction effects before being used as input to the springs. This paper presents closed-form analytical solutions for the response of an elastic pile subjected to harmonic seismic excitation in uniform elastic soil. We use these solutions to compute transfer functions relating foundation input motion to free-field ground motion and use the results to verify predictions from a beam-on-Winkler-foundation numerical model. The two approaches show good agreement, indicating that the numerical modeling method is appropriate for investigating more complex effects such as soil and pile nonlinearity. Ground motion deamplification due to kinematic SSI is demonstrated to be significant for stiff foundations in soft ground conditions. Numerical simulations using recorded ground motions demonstrates that transfer functions can be computed only from frequency bands for which the motions contain adequate energy.