Research

Bioinspired Geotechnics

Biological organisms have developed elegant solutions for a variety of needs that are analogous to many engineering problems, such as propulsion for efficient mobility and anchorage to resist wind loads. We study the biological strategies employed by organisms that live in or on the ground to develop bio-inspiration for geotechnical applications such as soil-structure interfaces, soil penetration, and site characterization.

Snakeskin-Inspired Surfaces and Piles

Surface profiles of three snake species.

Snakes generate propulsive forces for locomotion while maintaining low friction with the substrate to minimize energy expenditure. The scales on the skin along the underside of the snake compose a surface with frictional anisotropy that mobilizes a larger amount of friction when the substrate is moved against the scales (towards the snake’s head) than when it moves along the scales (towards the snake’s tail). Through laboratory, centrifuge, and field tests and DEM simulations, we have shown that our bio-inspired surfaces and piles mobilize interface shear strengths in monotonic and cyclic loading conditions that are dependent on the direction of displacement relative to the soil (i.e. frictional anisotropy). Our results indicate that implementation of this snakeskin-inspired texturing can enable multifunctionality and increase the efficiency of geotechnical applications such as piles, soil nails, and geomembranes.

Sponsor:
NSF Center for Biomediated and Bioinspired Geotechnics (CBBG), Deep Foundations Institute (DFI)

Bio-Inspired Soil-Burrowing and Penetration

Force chains and normal stresses around a self-burrowing probe from DEM simulation

The objective of this project is to improve current subsurface exploration and infrastructure construction technologies by drawing inspiration from the ability of limbless burrowing organisms, such as earthworms, polychaetes, caecilians, tree roots, and clams, to burrow through soil in an efficient manner. Engineers encounter a similar situation while conducting in-situ testing, where a probe equipped with sensors is advanced through soil. Often times, significant challenges are met when in-situ tests are performed on remote locations with little or no accessibility to drill rigs. Our work consists advances the geomechanical understanding of different self-burrowing strategies and evaluates their efficiency and feasibility for application in geotechnical engineering. We are currently performing numerical simulations, experimental tests, and building a field prototype as part of this project.

Sponsor:
National Science Foundation (NSF), Center for Information Technology Research in the Interest of Society (CITRIS), NSF Center for Biomediated and Bioinspired Geotechnics (CBBG)

Root-Inspired Foundations and Anchorage Systems

3D geometry of root systems subjected to pullout testing, where bottom tree root system mobilized significantly larger loads.

Tree root systems are remarkably efficient at providing anchorage against complex loads. We are working towards developing knowledge and understanding of the mechanisms that contribute to capacity development of nonlinear or branched foundation systems, such as tree root systems, which could lead to improved sustainability in the arena of foundation design. We are exploring the relationship between root system architecture and force-displacement behavior to better understand how to efficiently develop foundation capacity and demonstrates the potential for improvement in material and energy efficiency compared to pile and footing approaches.

Sponsor:
NSF Center for Biomediated and Bioinspired Geotechnics (CBBG)

Fundamental Aspects of Soil Behavior

The behavior of granular media is governed by inter-particle interactions that take place at the microscale. We use experimental and numerical techniques to investigate these interactions and to understand their influence on the element-level behavior on applications such as the development of soil analogs and the shearing behavior of sandy and gravelly soils.

Particle Shape Effects Enabled by 3D Printed Soil Analogs

Particle-Particle Compression Test

We are currently developing the experimental techniques to generate 3D Printed (3DP) soil analogs as well as a framework for the interpretation of results from laboratory tests with these 3DP analogs. Our goal is to create a new experimental tool that allows researchers to design soil analogs to independently study the effects of particle properties (e.g. shape, roughness, and size), constituent material properties (e.g. stiffness,), and soil properties (e.g. gradation) on fundamental aspects of granular materials behavior. Our current work focus is to investigate the effect of particle shape on the strength, stress-dilatancy, and wave transmission behaviors of soils.

Sponsor:
National Science Foundation (NSF)

Particle Size Distribution Effects on the Monotonic and Cyclic Behavior of Coarse-Grained Soils

3D polar plots showing the contact force distribution

The packing of a granular assembly is intimately related to its particle size distribution. The smaller particles in broadly graded soils fill the void in between the larger particles, resulting in larger densities and high numbers of contacts between particles. In turn, the larger particles carry disproportionately large contact forces, largely contributing to the stability to the assembly with aid of the lateral restraint provided by the smaller particles. These aspects control the observed differences in the shear strength, stress-dilatancy, critical state, and cyclic behavior of coarse-grained soils. We are investigating these effects in the context of the monotonic and cyclic behaviors of sandy and gravelly soils.

Sponsor:
National Science Foundation (NSF)

Assessment of Fabric and Stress-Induced Anisotropy with Wave Transmission

DEM simulation of shear wave transmission in granular media

Anisotropy in fabric and stress can lead to anisotropy in the mechanical and hydraulic properties of soils. This anisotropy has previously been shown to impact the response of soils, including its bearing capacity, liquefaction resistance, and hydraulic conductivity. This project's objective is to develop experimental capabilities and an interpretation framework for assessing fabric- and stress-induced anisotropy using wave transmission.

Load Transfer, Foundations, and Soil-Structure Interface Behavior

One of our main research topics is the transfer of load between soils and geotechnical systems. Virtually all of our infrastructure's stability depends on the efficiency with which load is transferred to the underlying or surrounding soil. Our research in this topic includes interfaces with sand and clay, the effects of loading conditions and partial drainage, and applications on deep foundations, offshore anchors, geosynthetics, and soil characterization.

Soil deformations from PIV analysis on sand specimens.

Interface Shear Behavior of Sandy and Clayey Soils

We study the transfer of load across soil-structure interfaces. Our research spans many sub-topics, including the effect of surface roughness on the mechanisms of load transfer (i.e. interface friction versus passive resistances), partial drainage at interfaces with fine-grained soils, axial and torsional shearing around axisymmetric bodies (i.e. piles, CPT friction sleeves), and use of interface shear strength measurements of soil classification using custom modules for CPT probes.

Anchors and Foundations for Offshore Infrastructure

Multi-ring anchor for floating offshore infrastructure

As developments for wind energy productions continue to advance in the US, offshore wind turbines in the Pacific coast and locations with deep waters will be required. In these cases, floating infrastructure offers an advantage over traditional alternatives that rely on monopiles or jacketed structures. At UC Davis, we are performing centrifuge tests to examine the behavior of the shared ring anchors in sand and clay subjected to multi-directional monotonic and cyclic loading.

Sponsor:
National Science Foundation (NSF), Triton Anchors, Department of Energy (DOE)

Static liquefaction and stability assessment of CCPs and mine wastes

Centrifuge Testing of dewatering of fly ash

Stability of Fly Ash Impoundments

Failures of fly ash impoundments have resulted in significant economic and environmental losses. One of the principal causes of the incurred damages is the tendency of saturated fly ash to deform and “flow”, which can cause it to inundate large areas around the impoundment. This study has the goal of characterizing the runout extent and progression of partially dewatered fly ash deposits in a geotechnical centrifuge as they are subjected to modeled impoundment failures. Our objectives also include developing methods to characterize the change in fly ash state and properties (i.e. state parameter, shear strength, stiffness) using advanced in situ testing.

Sponsor:
Electric Power Research Institute (EPRI)