Geo-Congress 2020: Biogeotechnics

Biogrouting using microbially induced carbonate precipitation (MICP) has advantages over cement grouting for rock joints as the particles of biogrout are much smaller than cement particles and thus can penetrate into very fine rock joints. In this study, we evaluate the performance of biogrout for the sealing of rock joints using model tests. A joint formed by two granite sheets of 0.07 m wide, 0.4 m long, and 0.01 m thick was biogrouted. The formation of biogrout in the joint was examined using 3D scanning and image reconstruction technology. The permeability reduction due to biogrouting was evaluated using the image analyses and numerical simulation. To evaluate the shear strength of the joint, direct shear tests conducted on cylindrical rock samples consisting of a horizontal joint treated using biogrout were also carried out. The tests have shown that the flow rate through rock joints can be reduced by up to 90% with 2~3 rounds of injection. The direct shear tests also demonstrated that peak shear strength of 4~7 MPa could be obtained after biogrouting for a planar rock joint with initially little shear strength. This study has shown that biogrout can be potentially used for rock joints to reduce seepage or enhance stability.

Microbial induced calcite precipitation (MICP) and enzyme induced calcite precipitation (EICP) have been widely studied in laboratories over the last 20 years. In conventional bioaugmentation MICP and EICP treatments, either the bacterium S. pasteurii or the plant-derived urease enzyme, respectively, is combined with a nutrient broth-urea-calcium solution and applied to a soil. Rarely, however, has microbial or enzyme bio-cement technology been taken out of the laboratory and evaluated at field scale under real-world conditions. In this paper, three case histories of full-scale use of surface applied bio-augmentation MICP treatments in rural South Dakota are presented. In all three case histories, MICP was used to provide short-term surface erosion mitigation against rainfall and wind (fugitive dust control). These case histories show the effectiveness of surface applied MICP in surface erosion control along with lessons learned for future research. These case histories also show the environmental effects of MICP on growth of native grasses and plants. In these case histories, the interaction of MICP and vegetation for erosion control is highlighted while MICP and vegetation methods are compared directly.

Several studies have been performed by researchers worldwide on the effective cementation of soils via microbially induced calcite precipitation (MICP). As part of these studies, the focus has generally been on the compressive strength, shear strength, shear wave velocity, and hydraulic conductivity of the treated soil as a function of treatment level. A few studies have also shown that MICP treatment of sandy soils contributes to reduced internal or surface erosion. Other studies, have shown that MICP may be effective for fugitive dust control. In this study, burned soil samples from forest fires in Western South Dakota were treated with several different concentrations of Sporosarcina pasteurii bacteria and growth media. Treated specimens were then subjected to turbulent wind flow of varying velocities in an innovative soil wing erosion testing device. During testing, mass loss of specimens was measured over the wind exposure time to determine surface erodibility of the treated materials as a function of MICP treatment level, fluid velocity, and fluid exposure time. This study shows that for both burned soils, that use of MICP has promise for reduction of surface erosion treated in unsaturated conditions under laboratory conditions.

The foundation systems of mega-flora (i.e. very tall or large trees), have long been used as an analogy for modern shallow and deep foundations. Terzaghi referenced trees as the model for footings and pilings. However, the topology, form, materials, distribution, and function of the natural foundation system have very little in common with the shallow and deep foundation systems that geotechnical engineers design and construct. These natural foundation systems are resilient, robust, and adaptable; ideal templates for a new generation of anthropogenic foundation systems and new understanding of soil-structure interaction. In an effort to further biomimetic geotechnics, this paper will present a review of the actual topology, form, materials, distribution, and function of mega-flora foundations, highlighting key differences with man-made foundation systems, materials, and designs. This paper will dispel common myths about these natural structures, giving engineers insights into their performance under complex and extreme loads. Several key species will be highlighted, with unique aspects of each species’ foundation system highlighted. Field measurements and observations of several natural foundation systems are included in the paper to highlight recent findings about these remarkable systems.

Microbial induced calcium carbonate precipitation (MICP) has attracted attention as a sustainable alternatives of soil improvement and construction materials in recent years. This paper is to develop bio-sandy brick through the MICP and to enhance it with discrete randomly distributed fiber. Four different fiber proportions (0.1%, 0.2%, 0.3%, and 0.4% by weight of dry sand) were used. The four-point bending tests were conducted. Results showed that adding fiber in the MICP treated bio-sandy brick can increase its ductility. The optimum fiber content was around 0.3%. Addition of 0.3% fiber can significantly prevent the post peak flexure strength loss and improved the ductility of bio-sandy brick that still had 400 kPa residual strength at 15% failure strain. The failure strain of fiber-reinforced bio-sandy brick reached the highest as 6.0% at 0.3% fiber addition.

Microbial biopolymers have recently been widely studied as a new class of environmentally friendly materials that can be used to enhance the strength of geotechnical engineering structures but also to reduce the use of cement. This study aims to investigate the feasibility of using microbial biopolymers to reduce water-induced erosion of cohesionless soils. Water erosion was simulated by inducing overtopping hydraulic flow on small-scale levee models under different surface treatment conditions using a laboratory hydraulic flume apparatus. The results show that a microbial biopolymer has significant potential to improve surface erosion resistance of sand due to their interparticle bonding and infiltration control characteristics. Thus, a microbial biopolymer can be beneficial in reducing surface erosion of waterfront earthen structures such as dams, levees, and dikes.

Microbially induced calcite precipitation (MICP), or bio-cementation, is a bio-mediated, environmentally-conscious soil improvement technology that can improve the engineering properties of granular soils through the precipitation of calcium carbonate (CaCO₃) on soil particle surfaces and contacts. While past studies have shown the potential of bio-cementation to improve the resistance of granular soils to earthquake-induced soil liquefaction, the spectrum of behaviors during the transition from the uncemented to lightly cemented conditions has remained poorly characterized. In this study, a series of direct simple shear tests were performed to improve our understanding of the effect of CaCO₃ bio-cementation on the liquefaction triggering and post-triggering strain accumulation behavior of loose sands. A poorly-graded Ottawa F-65 sand material was treated to varying degrees of very light bio-cementation and subjected to undrained cyclic shearing events. All specimens were cemented and sheared under a vertical effective stress of 100 kPa and subjected to cyclic stress ratios (CSR) of 0.1 and 0.2. During these tests, shear wave velocity (V_s) measurements were completed to non-destructively monitor cementation progression and degradation during shearing. Results suggest that even very light levels of bio-cementation (ΔV_s ≈ 0 to 100 m/s) can significantly increase the number of cycles needed to trigger soil liquefaction (3% single amplitude shear strain), e.g., a 10-fold increase in the number of cycles needed to trigger liquefaction was observed when V_s values were increased by only 25 m/s. Despite this significant improvement in small-strain pre-triggering behavior, little improvement was observed with respect to strain accumulation before and after initial triggering. While additional testing is needed, results from this study can improve our understanding of the behavior of lightly bio-cemented and naturally-cemented soils subjected to earthquake-induced undrained cyclic loading.

The field of soil bio-improvement, through microbial-induced calcite mineralization, has gained significant momentum in scientific literature in the past years. The phenomenon, which is inspired from natural environments, has been extensively applied at laboratory bench-scale, leading to a surge of expectations around its potential fit as a mainstream solution to real-world construction and environmental problems. The present study aims to break out of the laboratory and deliver a benchmark, large-scale application of ground bio-reinforcement which was designed and implemented in the canton of Vaud, Switzerland. The work aims to mitigate landslide risk in a slope hit by extreme rainfall in early 2018. This resulted in increased pore water pressure within the failure surface, therefore reducing the soil’s effective shear strength and triggering the slip of roughly 3,000 cubic meters of earth mass. A grouting solution was designed to induce the bio-mineralization of calcite binders within the targeted slip zone. In order to present obtained results in the best possible light, we combine laboratory tests, in situ monitoring, microstructural inspections, and post-stabilization aerial surveillance. Obtained data reveal slower displacement rates for the bio-stabilized zone compared to the rest of the slope. Overall, our global analysis aims to offer new prospects towards bio-mediated geotechnical practice under real-life conditions.

The field of geotechnics is moving fast towards benefiting from new methods and tools to improve the understanding of couplings among complex transport, chemical and biological phenomena. Calcite bio-mineralization, result of bio-grouting, stands out as such a problem where solute and solid transport phenomena, cell attachment, and cell/crystal growth mechanisms hold the key towards the formation of new, improved geo-materials. In the present study, focus is put on the real-time monitoring of the critical evolution of calcite precipitation within long trajectories in microfluidic chips. The total transport path, across which these phenomena are captured and interpreted, ranges between 1 and 1.5 meters to evaluate at which extend calcite crystal growth and deposition varies along the infiltrated porous chips. Results reveal varying number and sizes of crystals which precipitate across the flow path while qualitative characteristics are also discussed. Overall, the study aims to shed light into the previously underexplored, activation of the bio-cementation reaction, which governs nucleation, transport, and growth of calcite mineral binders and, therefore, influences the mechanical response of geo-materials subjected to bio-grouting applications.

Numerous laboratory studies in the past decade have demonstrated the ability of microbially induced calcite precipitation (MICP), a bio-mediated soil improvement method, to favorably transform a soil’s engineering properties including increased shear strength and stiffness with reductions in hydraulic conductivity and porosity. Despite significant advances in treatment application techniques and characterization of post-treatment engineering properties, relationships between biogeochemical conditions during precipitation and post-treatment material properties have remained poorly understood. Bacterial augmentation, stimulation, and cementation treatments can vary dramatically in their chemical constituents, concentrations, and ratios between researchers, with specific formulas oftentimes perpetuating despite limited understanding of their engineering implications. In this study, small-scale batch experiments were used to systematically investigate how biogeochemical conditions during precipitate synthesis may influence resulting bio-cementation and related material engineering behaviors. Aqueous solution chemistry was monitored in time to better understand the relationship between the kinetics of ureolysis and calcium carbonate precipitation, and resulting precipitates. Following all experiments, precipitates were evaluated using x-ray diffraction and scanning electron microscopy to characterize mineralogy and morphology. Results obtained from these investigations are expected to help identify the primary chemical and biological factors during synthesis that may control bio-cementation material properties and influence engineering performance aspects including long-term resilience.

A 0.3 m-diameter×0.9 m-long bio-cemented soil column was created in a 0.6 m×0.6 m×1.2 m box filled with dry quarry sand using enzyme induced carbonate precipitation (EICP). The bio-cemented column was created using controlled rate injection through a tube-a-manchette pipe. The EICP solution had concentrations of 1.5 M urea, 1 M calcium chloride, 9,900 U/l urease enzyme, and 4 g/l of nonfat milk powder. Three treatment cycles were applied. After three days, the bio-cemented column was exposed. The column was measured to be within 10% of the design diameter, but was 20% longer. As the column was deconstructed, needle penetrometer tests performed on various layers indicated that the design unconfined compressive strength of 500 kPa was achieved. While UCS tests on specimens sub-sampled from the column had an average strength of 154 kPa, the specimens appeared to have been disturbed during the sub-sampling process as they exhibited local failure at the ends or outer surface. Overall, these results demonstrate that EICP has potential as a ground improvement method because it can be designed and implemented in the field to strengthen soil using installation methods similar to conventional permeation grouting techniques. Potential applications at greenfield sites or underneath existing structures/infrastructure include bearing capacity improvement, settlement mitigation in loose sands, and prevention of running sands during excavations and tunneling.

Soil erosion is one of the main challenges of today’s geotechnical engineering discipline along rivers, coastlines, and after major storm and hurricane events. The use of vegetation cover is one of the most cost-effective methods for soil erosion control, however, it does not provide long-term ground improvement since the method does not improve soil properties. The study presented in this paper explored the use of the bacterial enzyme induced calcite precipitation (BEICP) technique to reduce the erosion susceptibility of silty sandy soil. The BEICP technique was applied to the surface of sand specimens via a spraying method. The specimens were treated at four different enzyme concentrations (0 mg/mL-control, 0.3 mg/mL, 0.7 mg/mL, and 1.5 m/mL) and tested for erosion susceptibility. The specimens were subjected to water erosion in a recirculating flume with mean flow velocity of 23.2 cm/s. The amount of soil erosion was measured via weight loss of the soil specimen. In addition, scanning electron microscope (SEM) analyses were conducted on specimens. Results of the erosion tests demonstrated that the soils treated with high enzyme concentrations experienced almost no soil weight loss while the weight loss increased significantly (from 2.4% to 15.5%) with a decrease in enzyme concentrations. SEM analyses showed that top 2.54 cm (1-inch) layer of the soil specimen had the highest calcite precipitation formation than the lower level which could help to reduce the erosion susceptibility of the silty sand specimens. Overall, results of this study indicate that the BEICP technique has a potential act as an effective solution to reduce the erosion susceptibility sandy soils when applied through a spray application to the surface of the material.

This paper presents the results of a field implementation of microbial induced calcite precipitation to stabilize expansive soils in Marsing, Idaho. The field test was done by drilling 2.5” (6.35 cm) diameter holes at a spacing of 16” to 30” (40.6 cm to 76.2 cm) into the ground and, injecting bio-enrichment followed by bio-cementation solutions to stimulate the native bacteria and subsequently achieve calcite precipitation. The pH level of the soil, the calcite content, and free swelling potential were monitored over time by collecting periodic soil samples from the injection points. An increase in pH from 8.3 to 9.7 was seen in the first seven days after the injection of bio-enrichment solution. The calcite content in the soil increased and the free swelling potential decreased consistently with each subsequent injection of bio-cementation solution. The calcite content increased from 3% to 8% and the free swell index dropped from 114% to 29%. The results show that microbial induced calcite precipitation can be successfully replicated in the field for the stabilization of expansive soils.

A bio-mediated ground improvement technique known as microbial-induced desaturation and precipitation (MIDP) via denitrification can be used to introduce biogas and bio-minerals into the soil matrix. A feasibility study was performed to assess the potential of MIDP to stabilize sediments under an embankment along the Fraser River in Richmond, a coastal city in Canada. Locally collected sediments were subjected to multiple MIDP treatment cycles under similar stress conditions as expected in the field using a modified triaxial test set up. The hydraulic conductivity was determined after each treatment cycle. The mechanical response of the treated soil was evaluated under undrained loading conditions. Results show that with increasing treatment cycles, the hydraulic conductivity decreased significantly. The original tangent modulus increased with the number of treatment cycles as did the slope of the straight line passing through the phase transformation point in the effective stress path plane. The effective stress paths of treated samples almost merged, and they lie somewhere between the drained and undrained lines.

Testing was conducted to evaluate the effect of including a hydrogel in the treatment solution on the performance of a wind erosion-resistant crust formed using enzyme induced carbonate precipitation (EICP). Samples of a fine sand highly susceptible to wind erosion were treated by spraying their surface with a baseline EICP solution and with an EICP solution enhanced by the addition of xanthan gum hydrogel (XEICP). Treated samples were cured, saturated, and tested for bulk hydraulic conductivity. The bulk hydraulic conductivity was reduced from 2.01×10^-2 cm/s for the untreated dry control specimen to 9.87×10^-3 cm/s for the XEICP treated specimen. Water erosion testing showed XEICP treatment forms a crust more durable to water erosion than treatment with the EICP solution or with xanthan gum treatment alone. These test results indicate that XEICP treatment can create a wind erosion-resistant crust with a minimal decrease to surface hydraulic conductivity.

Sandy slopes and levees in coastal areas are subjected to heavy rains and large storm events, which makes such structures susceptible to surface erosion and failure. Microbially induced calcium carbonate precipitation (MICP) is an emerging soil improvement technique that has shown promising results in scour reduction, liquefaction mitigation, and dust control, among other applications. This method utilizes natural soil bacteria to hydrolyze urea and induce calcium carbonate to bond soil particles together and improve soil matrix’s properties. The study presented herein discusses the implementation of the MICP treatment using surface percolation on a 1 m×8 m plot located on a coastal sandy slope. To make the field application more economically feasible, instead of using laboratory-grade chemicals, industrial-grade urea and calcium chloride were used for the treatments. At the end of the treatment, dynamic cone penetration (DCP) tests were performed on the treated plot and mass of calcium carbonate samples were taken from different elevations along the slope to have an estimation of the improvement of soil and precipitation distribution pattern with depth.

Soil improvement methods applied to reduce permeability of soils are associated with high application cost and produce large carbon footprints. Biofilm-induced permeability reduction is a bio-mediated soil improvement method that can reduce permeability up to two or more orders of magnitude. This study investigates the application of two different treatment strategies, pumped flow with a constant flow rate and gravity flow with a maximum hydraulic gradient of i=2.5, to induce biofilm formation and reduce permeability in two sizes of silica sand. The pumped flow treated columns reduced permeability at a steady rate compared to the gravity flow columns which demonstrated more variability in permeability reduction through treatment. Additionally, the biofilm formation in the pumped flow columns was more resistant to changes in hydraulic pressure.

The soil permeability plays an important role in durability of channels because it controls the rate of entry of moisture that may contain aggressive chemicals and the movement of water from irrigation channel joints. The use of plastic concrete as a waterproofing material and to reduce shrinkage crack was investigated. The main goals of this paper are to investigate the influence of biopolymer addition on mechanical and permeability characteristics of bentonite-sand-cement mortar as an engineered material. A combination of soil mixtures consist of three different amount of bentonite and sand proportions (i.e., 15%:85%, 20%:80%, and 25%:75%) was selected. The cement proportion was selected at 10, 20, and 30% of the total weight of bentonite and sand mixture. Various amount of xanthan gum (i.e., 1, 3, and 5% by mass) as biopolymer material was added to the mixtures. A series of permeability and unconfined compressive strength tests were conducted on samples after 3, 7, and 28 days of curing. The test results showed that the biopolymer addition has a high potential in increasing the strength of the samples and in decreasing the permeability. An optimum composition containing 85% sand, 15% bentonite, 10% cement, and 1% xanthan gum biopolymer with lowest permeability, the lowest shrinkage value, and suitable unconfined compressive strength was suggested as the most suitable mixture for practical applications.

This paper investigates geomechanics of post-fire mudflows and proposes slope erosion prevention by treating the hydrophobic soil with a biopolymer. Exposure of organic matter in shallow soil layers to high temperatures produces gasses that make soil grain surface hydrophobic. Change in hydrological process, loss of vegetation, increase in the erosion rate, flooding, and recently seen catastrophic mudslides are consequences of post-fire water repellency in soils. This study uses experimental laboratory approaches to better understand the onset of soil erosion and fluid-particle interaction in a water repellent slope. Environmentally friendly xanthan gum is proposed to treat the hydrophobic sand with a hypothesis that the highly hydrophilic biopolymer powder will balance water repellency in hydrophobic soil. Rain simulation tests are conducted on natural, hydrophobic, and treated poorly graded fine sand. It is observed that the xanthan gum decreases the rate of erosion and consequently has a potential for reducing the risk of mudslides.

An MICP field trial was performed at the Integrated Field-Scale Subsurface Research Challenge (IFRC) site, at Rifle, Colorado, USA. Non-destructive geophysical tests were used to monitor changes in soil properties as a function of time, while groundwater was sampled and tested for chemical indicators, including pH and dissolved iron content. During the field trial, the measured concentration of dissolved iron (Fe²⁺ ferrous iron) increased, which implied that the increased microbial activity resulted in dissolution of naturally occurring iron oxides, which are naturally occurring cementation agents. Column tests were performed to compare dissolved iron concentrations in the effluent of MICP tests performed in silty sands to sands with iron oxide. Release of ferrous iron was observed in the columns with iron oxide mineral phases; however, no observable differences were detected in the distribution of mass of calcite precipitated within the soil columns.

Microbially induced carbonate precipitation (MICP) is an innovative approach to improve loose soil using bacteria to hydrolyze urea and facilitate the precipitation of calcium carbonate. In this paper, a proposed double wall pile delivery system is introduced to improve submerged sand adjacent to a pile foundation system using MICP. The implementation of MICP delivery system was conducted via the double wall model pile under various constant head differentials in a large-scale soil box. The level of cementation was spatially monitored during treatment using bender elements for shear wave velocity measurements. After the completion of the treatment, cone tip resistance was measured to assess the improvement with distance from the injection source. The cementation profile was also assessed by acid washing the treated sand at key locations. Stabilization results based on the use of the proposed double wall pile delivery system and associated challenges are presented and discussed.

Mature fine tailings (MFT) are by-products from oil sands extraction processes and pose a challenge to the geo-environmental community. Large impoundments are required to store MFT due to physical characteristics of the material, namely the high volume of the water in tailings and large-strain consolidation behavior. Microbial induced calcium carbonate precipitation (MICP) treatment has been previously demonstrated to effectively accelerate the dewatering process of the MFT; however, the change to the consolidation behavior of the MFT after MICP treatments has not been examined. In this paper, slurry consolidometers are constructed to evaluate the compressibility and permeability properties of MFT after MICP treatment. The presented test results indicate MICP can help accelerate the settlement of MFT by developing the soil skeleton with a minimal decrease in permeability.

The end goal of this research is assessing the feasibility of using enzyme induced carbonate precipitation (EICP) to create a cemented top layer to control runoff erosion in sloping sandy soil. The paper presents the results of an experimental study of bench-scale tests on EICP-treated sands to determine a treatment method feasible for field placement for this application. The soils tested were two natural sands and Ottawa 20–30 sand used as control. The EICP application methods were percolation by gravity, one-step mix-compact, and two-step mix-compact. Other conditions considered were pre-rinsing the sand prior to treatment, adjusting soil pH prior to treatment, and changing the EICP solution concentration. Promising results for this field application were obtained using the two-step mix-compact when the soil was first mixed with the urease enzyme solution before compaction. Considering that the EICP reaction starts once all components are added, this method would ensure that the reaction does not take place before the protective layer of treated soil has been installed. The effect of pre-rinsing the natural sand was not consistent throughout the testing conditions and its role in improving soil cementation in natural sand needs further study.

Cohesionless soils such as sandy or silty soils are more susceptible to landslides, slope failures, and erosion in comparison with cohesive soils containing clayey fraction. While vegetation roots are known to provide erosion resistance, shear strength properties of cohesionless soils with grass roots and their effect on slope stability needs more investigations. Therefore, it was decided to test soil specimens of cohesionless soils with and without grass roots in the laboratory. The objective of the testing program was to quantify the effect of grass roots on cohesion and angle of internal friction of the sandy soils. Direct shear tests were conducted on specimens (with and without grass roots) consisting of three types of soils: (i) natural fine silty sand, (ii) clean sand with medium and subangular particles, and (iii) clean sand with angular coarse-grained particles. The effect of grass root was more pronounced in fine silty sand with about 210% increase in cohesion and about 13% increase in the angle of internal friction. The test results indicated that the presence of grass roots increased the cohesion by an average of 119% while the angle of internal friction was found to have increased by an average of 12% among the soils tested. For the tested sands, the inclusion of grass roots was found to increase the factor of safety by 550% for slopes in dry conditions, whereas the factor of safety increased by 525% for slopes with seepage conditions.

A self-penetrating bio-inspired probe is under development for performance of in situ tests in sites typically inaccessible to conventional drill rigs. This bio-inspired probe consists of a radially-expanding shaft section (i.e. anchor) that provides anchorage and an axially-elongating section (i.e. tip) that measures soil penetration resistance (CPT q_c). Self-penetration can be achieved and sustained as long as the anchorage force is greater than the penetration resistance force. The analysis presented herein consists of discrete element modeling (DEM) simulations with the objective of evaluating the self-penetration ability of the bio-inspired probe. The DEM simulations investigate the effects of the anchor length and expansion magnitude on the mobilized reaction and resistance forces. The results highlight the effects of the shaft expansion and tip advancement on the surrounding soil’s state of stresses. In addition, expansion of the anchor induced a reduction of the tip resistance, while simultaneous loading of the anchor and tip resulted in a reduction of the shear reaction force. Overall, an increase in anchor length or expansion magnitude increased the self-penetration ability of the simulated probe.

Application of bio-inspired design to geotechnics is still in the early stages of development. Bio-inspiration methods employed herein are centered on advancing understanding of biological systems from form-level (physical structures), to behavior-level (processes and mechanisms), to principle-level (why the forms and behaviors are or are not effective). This paper details the connection from the study of natural root system forms and behaviors, to direct study of the biological analog, to extraction of principles for development of engineering designs. Ten three-year-old fruit trees with different rootstocks were subjected to vertical pullout tests in the UC Davis Plant Science Department teaching orchard. Measurements during pullout testing included load, displacements, ground accelerations, and photos for 3D model development using photogrammetry. Analysis focused on the progression of failure mechanisms in the root systems through analysis of load, displacement, and distributed accelerometer measured time histories. Results show that trunk displacements associated with peak resistance are smaller than those associated with mobilization of much of the distal root system. Methods for improving strain compatibility will be important for design of nonlinear and branched foundation systems.

Interface friction is a governing parameter in the design of piled foundations. Multifunctional and more efficient piles may be developed based on interfaces that develop higher shear resistances in one loading direction than another. This could be achieved using a biological adaptation present in the skin of many snake species which gives them the characteristic of frictional anisotropy or directionality. The scales along the underbelly of snakes (ventral scales) mobilize less frictional resistances during forward (i.e. caudal) movement than during backward (i.e. cranial) movement. This paper presents the results of a series of interface shear tests on sand specimens subjected to monotonic and cyclic loading against snakeskin-inspired surfaces. The experimental results show a dependence of the mobilized shear resistances on the direction of shearing and asperity height in both monotonic and cyclic loading. The results presented herein provide evidence of the frictional anisotropy that can be mobilized by bioinspired surfaces.

The transfer of load across soil-structure interfaces is of significant importance for the stability and service life of most geotechnical structures. Soil-continuum interfaces are relevant to many human construction activities; however, they also impact the likelihood of survival of numerous plants and animals. Through the process of evolution, many organisms have optimized load transfer across interfaces to fulfill their daily needs, such as hunting and feeding. The biological adaptation used in this research comes from the ventral scales on the underbelly of snakes. When a snake moves on a soil surface it generates enough propulsion force to initiate or maintain forward movement while it simultaneously minimizes the friction that opposes this movement. This feature is enabled due to the greater friction coefficient mobilized during backward (i.e. cranial) than during forward (i.e. caudal) movement. This characteristic is typically referred as friction anisotropy and is produced by the shape, stiffness, and angle of attack of the scales on the snake’s skin. This research explores the effect of asperity compliance and angle of attack of snakeskin-inspired surfaces on the shear strength and deformation behavior of sand-structure interfaces. The idealized snakeskin surface models are composed of asperities made from flexible plastic film of different stiffnesses embedded into a rigid base. The results from shear box interface shear tests highlight the effect of initial asperity angle, scale stiffness, and overburden stress on the shear strength and frictional anisotropy mobilized by the snakeskin-inspired surfaces.

Numerous engineering designs were inspired from nature. Recent researchers have used 3D printing technology to optimize soil reinforcement. In this research, a bio-inspired geogrid shape, from the concept of honeycomb structure was investigated and compared with conventional commercial geogrid. 3D printing technology was used to investigate the feasibility of the proposed geogrid shape and its ability to enhance the bearing capacity of the soil under foundations. Optimization was conducted to improve the performance of the proposed geogrid. This was conducted by studying the use of the proposed geogrid to improve bearing capacity. In this paper a parametric study was conducted by printing physical models of geogrid changing the geogrid depth, thickness, and cell aperture width while measuring the distribution of strains due to loading. Optimum design found for the honeycomb like geogrid was for thickness over cell aperture width of 2.66% and depth over cell width of 13%, have shown the highest improvement of bearing capacity compared to unreinforced case with bearing capacity ratio (BCR) of 1.59. In conclusion, the proposed honeycomb inspired geogrid demonstrated enhanced soil confinement behavior due to its unique shape. The 3D printing technique can be used to test new geogrid designs and geometries due to the flexibility this technique offers in terms of geometries and material stiffness and texture.

The razor clams alternately inflate the shelled body and the muscular foot when burrowing down to the ground. It is found from previous numerical simulations that inflation of the shelled body not only forms a firm anchor for the foot penetration, but also reduces penetration resistance; on the other hand, further foot penetration relaxes the shell anchorage, which may compromise the burrowing effectiveness and efficiency. This study utilizes a photoelasticity-based technology, augmented with image processing, to validate the numerical findings. A simplified penetrator model composed of an expandable rectangular shell and a protrusible triangular foot is designed and incorporated into a transparent cell containing more than four thousand photoelastic disks. Sequential images are then taken during the model penetration, which include an initial foot penetration, followed by shell expansion, and then another foot penetration. An image processing algorithm is developed to detect the evolution of grain contact forces (orientation and magnitude of contact forces) during the shell expansion and foot penetration of the model. Results from this study confirm the existence of the mutual influence between shell expansion pressure and foot penetration resistance: that is, increasing one causes reduction of the other and vice versa.

Many organisms rely on dual-anchor strategy to burrow. A prominent biological role model is the Atlantic razor clam. By concerting the shape changing of various body parts: opening/closing of a rigid shell, extension/contraction of the muscular foot, and inflation/relief of the distal pedal, razor clams can burrow very effectively and efficiently. Using 3D discrete element method modeling, the interactions between two clam inspired dual-anchor penetrators and the surrounding granular media were captured at multiscale. A penetrator includes two major parts: a slender “shell” with time-varying diameter, and a conical “foot”. Two different penetrators were considered: one with a uniform cylindrical shell and the other with a fusiform shell. The granular material consists of spherical particles with an upscaled particle size distribution of Ottawa F65. Microscale parameters are calibrated and validated with experimental triaxial test data. The impact of shell morphology is studied. It is found that opening of the shells compresses the soil around the shell to form anchorage, and at the same time releases the stress around the foot. A fusiform shell morphology is found to have limited influence on the penetration resistance and the shell anchorage during the foot penetration process. A systematic parametric study is still needed to test the hypothesis that a streamlined shell improves the burrowing performance of razor clams.

Seeds of some flowering plants such as Erodium and Pelargonium can bury itself into the ground for future germination. The self-burial behavior is realized due to hygroscopic coiling and uncoiling of the awns. It is hypothesized that the rotating motion due to the changing of the helical structure of the awn reduces penetration resistance of the seed via breaking the local force chains in soil. In this study, this hypothesis is tested using a DEM model, which allows investigating the interaction between a penetrator and the granular material at different scales. The DEM model was first calibrated and validated using existing laboratory triaxial test data of Ottawa sand. A cone was then penetrated into the calibrated soil sample vertically with different rotational speeds. It was observed that the rotational movement can significantly reduce the penetration resistance, and the reduction becomes more pronounced at higher rotational speeds. From particle scale analysis, the force chain and particle velocity field of the soil sample were investigated, and comparisons were made among cases, which shed light on the fundamental mechanism of the reduction effect.

Environmental remediation of contaminated sites, which involves several energy and resource intensive activities resulting in undesirable emissions and waste streams is one of the significant contributors to the global climate change. Thus, a small intervention in the remedial designs which are environmentally sustainable could substantially contribute towards global efforts for sustainable development. Many researchers have and still use life cycle assessment (LCA) as a common tool to evaluate and quantify the environmental impacts of design alternatives. Although the impact assessment is performed to site-specific and problem specific conditions there is no accord if the results from these analyses are representative and reliable due to significant uncertainty within the input parameters used for the analyses. In this regard, an uncertainty analysis is imperative for any LCA to apprise of the variability in the input data and consequently its influence on the environmental impacts evaluated. In this study, a case study involving the remediation of contaminated sediments is discussed. A baseline LCA of different remedial design options was conducted using the site-specific data. Further, an uncertainty analysis was performed using Monte-Carlo simulations approach to estimate the range of expected values of the environmental impacts for the specified variability of the uncertainty in transportation distances involved in the remedial option implementation. The results show that, for the given site-specific conditions, monitored natural attenuation resulted in the least negative environmental impacts with or without considering the variability in transportation distances in the LCA. However, there was significant variability in environmental impacts of a remedial option based on the uncertainty in the input parameters. Hence, incorporating the sensitivity and uncertainty analysis in LCA is imperative for to more reliably inform the practitioners and design professionals of the range of values for the environmental impacts to be expected.

Decisions about risk intervention, such as ground improvement to mitigate soil liquefaction, should be made based on the expected cost and lifecycle benefit (i.e., reduction in loss over the life of an infrastructure asset). In the jargon of performance-based earthquake engineering, vulnerability functions predict loss, and thus, are central to risk management strategy. However, field measurements of loss due to liquefaction have historically been poorly quantified, slowing the development of vulnerability functions requisite for studying the lifecycle economics of ground improvement. Accordingly, aided by engineering and economic data from the 2010–2011 Canterbury, New Zealand, earthquakes—the quantity and combination of which are unprecedented—this study proposes practical functions for predicting liquefaction-induced loss. These functions are: (i) applicable to lightweight structures on shallow foundation systems; (ii) developed as extensions to CPT-based liquefaction analytics already in popular use; and (iii) allow for lifecycle benefits to be quantitatively weighed for a range of intervention strategies. Ultimately, these functions can be used to decide whether, and how, liquefaction should be mitigated, or to demonstrate the economic feasibility of a new type of ground improvement (e.g., bio-inspired and bio-mediated technologies). Towards this end, the proposed functions are demonstrated via application to a liquefiable site in the SODO district of Seattle, USA, wherein a lifecycle cost-benefit analysis of ground improvement is performed.

As part of the development of the emerging technology of enzyme induced carbonate precipitation (EICP), a hotspot, attributional life cycle analysis (LCA) was performed. EICP is a ground improvement technology that binds soil particles together with calcium carbonate precipitation via hydrolysis of urea. EICP seeks to replace traditional soil improvement methods. The purpose of this hot spot LCA was to proactively assess environmental benefits and costs and identify potential unintended consequences for the EICP process. This LCA considered the main components of the EICP treatment solution (urea, calcium, urease enzyme, and nonfat milk powder) with the aim to see if a particular component stood out in the assessment for three environmental impact indicator areas: energy use, CO₂-equivalent air emissions, and eutrophication potential. The results show that urea is responsible for 63% of energy use and 37% of CO₂-eq air emissions, nonfat milk powder is responsible for 38% of CO₂-eq air emissions, and the ammonium byproducts of the EICP process is responsible for 97% of eutrophication potential of EICP. Means for reducing these impacts include finding greener sources of urea, using waste milk as the source for nonfat milk powder, and extracting ammonium chloride from the ground after completion of EICP treatment.

Geotechnical infrastructure projects consume large quantities of energy and resources and can have significant impacts on the environment. Life cycle sustainability assessment (LCSA) provides a more holistic approach compared to current geotechnical design decision making by providing a framework for quantitatively evaluating and weighing the sustainability tradeoffs of viable alternatives for a given application. This paper describes the LCSA evaluation tool developed and employed by the Center for Bio-mediated and Bio-inspired Geotechnics (CBBG), which serves to guide sustainability-oriented research, development, and deployment of CBBG technologies and inform CBBG leadership funding decisions. The framework for and methods of the LCSA review process are described, and three examples of how LCSA has driven decision making and advancements in CBBG research are given. The examples demonstrate how the LCSA evaluation tool can be applied to a diverse portfolio of projects at different stages of development and with different applications. Finally, the paper proposes ways in which the LCSA evaluation tool could be implemented by others in academia or industry.