Journal of Geotechnical and Geoenvironmental Engineering

The particle-scale shear and tensile strength measurements of microbial-induced calcite precipitation (MICP) treatment have been investigated in this paper. Glass beads were used to represent sand particles. Three particle-scale test setups were developed to measure the tensile, shear, and cyclic shear strength of MICP-treated ${\mathrm{CaCO}}_3$ bonds between glass beads. Sporosarcina pasteurii bacterial cells were introduced to precipitate ${\mathrm{CaCO}}_3$ and form cementation bonds between glass beads. The preliminary particle-scale test (Test setup 1) was designed to measure the shear and tensile strength of ${\mathrm{CaCO}}_3$ bonds precipitated between glass beads mounted on optical fiber sensors with known properties. Shear and tension loads were applied to the ${\mathrm{CaCO}}_3$ bonds by the displacement actuators controlling the movement of movable stages. The improved particle-scale test setup (Test setup 2) was developed using a larger and stable reaction chamber, an automated injecting system, and stiff bending elements (instead of optical fibers) that were connected to glass beads to improve measurements. Deflections of the bending elements were measured to calculate the tensile and shear strength of the ${\mathrm{CaCO}}_3$ bonds using the beam theory. The enhanced particle-scale test setup (Test setup 3) was developed to directly measure the shear and tensile forces generated in ${\mathrm{CaCO}}_3$ bonds using load cells and LVDTs to investigate the monotonic and cyclic response of the ${\mathrm{CaCO}}_3$ bonds. For the tests using Test setup 3, the shear and tensile strengths were 378 and 446 kPa, respectively.

In the prefabricated vertical drain (PVD) treatment of dredged slurry with high water content, fine slurry particles move toward the PVD membrane and accumulate around it due to the vacuum gradient. This process results in the formation of an almost impervious clogging column. The clogging column is cylindrical and symmetric about the vertical PVD axis, and it impedes vacuum consolidation of high water content slurry. A radial filtration model was created to describe the formation and growth of the clogging column using the equilibrium, continuity, kinematic, and constitutive equations in a cylindrical coordinate system. Essential components of the model are the moving boundary conditions for the clogging column–slurry interface and for the outer boundary surface of the slurry. The model accurately predicts temporal variation in the radius of the clogging column. Model predictions were compared to particle image velocimetry test results to validate the model. Real-time distributions of the void ratio, permeability, and effective stress for soil within the clogging column were also quantified and analyzed. The expansion of the clogging column was accompanied by compression of the soil skeleton. The distributions of the void ratio and permeability within the clogging column were highly nonlinear. The drainage rate of PVD was governed by the portion of the clogging column surrounding the PVD membrane.

This paper explores the use of a variational autoencoder to predict the embankment settlement and pore water pressure based on monitoring data. A variational autoencoder can learn intrinsic patterns in embankment behavior through unsupervised deep machine learning. The proposed approach implemented the observational method efficiently because updating soil parameters was no longer a necessary step, unlike in previous research. The embankment response was predicted directly through Gibbs sampling, which involves an iterative encoding and decoding process in the variational autoencoder. The variational autoencoder was trained using simulated embankment responses from the numerical (Plaxis) model. The approach was applied at the Ballina site to predict the embankment response, based on monitoring data with varying time periods. The prediction intervals captured the actual trends satisfactorily, with the intervals becoming more aligned with actual values as more monitoring data were incorporated. The predictions were also more reasonable, compared to those based entirely on representative soil parameters from laboratory or in-situ tests. The variational autoencoder was also applied to another case involving synthetic monitoring data based on the Ballina site, which demonstrates the capability of the variational autoencoder to predict multiple scenarios of embankment behavior.

Centrifuge testing data are presented to elucidate the influence of particle size and gradation on cone penetration resistance. The physical, index, and material properties of nine test soil mixtures, sharing a common geologic origin and ranging in $D_{50}$ from 0.18 to 2.58 mm and $C_u$ from 1.53 to 9.86, were quantified and compared to the range of values exhibited by clean sands in the literature. Each centrifuge model was subjected to dynamic loading and characterized by six cone penetration test (CPT) soundings performed at $D_R$ values ranging from 23% to 96%. The coarser soils exhibited higher cone penetration resistances than clean sands under comparable conditions due to the continuum failure mechanism becoming compromised (more likely as $D_{\mathrm{CPT}}/D_{85}$ decreased) and the variation in mechanical properties with particle size (e.g., $G$ and ${\varphi }_{pk}^{\prime }$). This study provides insight into the multifaceted influence of soil gradation on penetration resistance, which can be leveraged in engineering practice to improve the in situ characterization of coarse-grained gravelly soils.

The main objective of this paper is to develop equations correlating the erosion resistance of a soil to its common geotechnical properties. A total of 975 erosion tests and approximately 13,600 associated common geotechnical properties were organized in a database called Texas A&M University (TAMU)-Erosion. About 300 of the 975 erosion tests and approximately 4,200 associated common geotechnical property tests were performed at Texas A&M University over the past 20 years. In parallel, an additional 675 erosion tests and approximately 9,400 corresponding common geotechnical properties were collected from the open literature. The erosion tests include mostly the erosion function apparatus test (EFA), jet erosion test (JET), and hole erosion test (HET). The raw data for all tests are embedded in TAMU-Erosion, along with an inquiry operation manual that allows the user to search the database. This database was used along with a standard statistical regression method and a probabilistic representation to develop the best equations correlating the erodibility parameters to the geotechnical properties. The best fit for each equation was quantified using standard goodness of fit indices. The best equations are presented along with probability curves conveying to the user the probability that the predicted value will be overpredicted or underpredicted.

Multiple barriers have become popular to mitigate debris flows worldwide. Existing guidelines only recommend the minimum spacing based on volume retention, and the influence of flow–barrier interaction is ignored. It is obvious that understanding the flow–barrier interaction for a multiple-barrier system is imperative for safer and more economical designs. In this study, a physical experiment of debris flow impacting a dual rigid barrier system conducted in a 28-m-long flume is presented. The experimental results are used to calibrate a numerical model based on the lattice Boltzmann method (LBM) with a new Voellmy-like rheology. A numerical parametric study is then conducted to investigate the influence of the barrier heights and of the spacing between the barriers on the overflow mechanisms, the material depositions, and the impact dynamics. A new method to estimate the launching angle using the ratio between the barrier height and the flow thickness is proposed to calculate the overflow distance $L^{+}$. Furthermore, the existing volume retention criterion can be used when spacing $L$ is between 2 and 5 times the overflow distance $L^{+}$ (i.e., $L/L^{+}\approx 2–5)$ and both barriers have a similar height. Whereas, when $L/L^{+}>10$, a smaller first barrier results in reduced impact force due to flow thinning and spreading between barriers.

During its service life, railway ballast degrades. Individual grains are abraded, asperities may break off, and the assembly loses performance as the finer material created progressively fouls the assembly. The causes of this are the repeated cyclic loading from passing trains and the major damage caused to ballast by tamping operations to restore track geometry. Eventually the ballast bed requires complete replacement, and recovered trackbed material is disposed of as waste or downcycled. However, modern ballasts often are formed from stronger parent rocks than in the past, and a proportion may retain sufficient characteristics for reuse. This paper investigated the reuse of recovered life-expired ballast. A series of tests using fresh and reused ballast was carried out using the Southampton Railway Testing Facility (SRTF) and a large triaxial testing apparatus to compare performance. The properties of individual ballast grains were characterized in terms of their shape and petrographic make up. The results show that the type of recovered life-expired ballast used in this study has good performance and similar strength to fresh ballast despite having reduced surface roughness. The petrographic analysis showed that a majority of the recovered ballast was formed of granite, with a significant minority of basalt. These findings may be in contrast to those of some previous studies in which different life-expired rock sources were used, and highlights the importance of the source material.

Site-specific subsurface conditions are known to significantly influence the frequency content and amplitude of seismic ground shaking. When attempting to model these effects, known as seismic site effects, most studies have focused on the importance of vertically characterizing subsurface geomaterials. However, laterally characterizing the geomaterials’ variability has generally either been overlooked or oversimplified. As such, little is actually known about the spatial area that influences seismic site response. In this article, we discuss insights that have been gained regarding the spatial area that influences site response from performing two-dimensional (2D) ground response analyses (GRAs) for the Treasure Island Downhole Array (TIDA) site. In these numerical analyses, we use a site-specific, large-scale, three-dimensional (3D) shear wave velocity ($Vs$) model that has been developed to a depth of 150 m over the entirety of Treasure Island (an area of approximately $1.6\times 1.0{\mathrm{km}}^2$). We investigate the lateral extent influencing site response and its azimuthal variability using: (1) four cross sections with increasing lateral extent along the same azimuth; and (2) 12 cross sections with different azimuths that uniformly sample the full 3D $Vs$ model. By comparing 2D GRA predictions to recorded earthquake ground motions at TIDA, we systematically highlight the large spatial area that influences site response, which extends to distances as much as 1 km from the TIDA sensors. Although the TIDA site is often assumed to be archetype of one-dimensional (1D) site conditions, our findings support the idea that there may not be many truly 1D sites due to the large spatial area that influences site response. While some sites can be reasonably modeled using 1D GRAs, moving the engineering profession forward requires focusing our efforts on developing site-specific subsurface models over larger areas to better understand and accurately model seismic site response.

This study presents the results of a laboratory test program that serves to improve the understanding of the liquefaction susceptibility and cyclic response of intact silts that span sand- and clay-like behaviors. Specimens were prepared from samples characterized with a plasticity index (PI) ranging from 0 to 39, fines content (FC) ranging from 29% to 100%, and overconsolidation ratio (OCR) ranging from 1.0 to 4.2, retrieved from five silt deposits in Western Oregon and Southwest Washington. The roles of PI, FC, and OCR on the 1D compression and monotonic and cyclic strength of nonplastic to plastic silts are identified. Hysteretic metrics proposed to quantify cyclic behavior provided an objective means to distinguish between qualitative judgments of sand-like, intermediate, and clay-like behavior. Prior soil index test-based liquefaction susceptibility criteria exhibited good to poor accuracy; modifications to existing criteria aligned with quantified hysteretic behavior, which together indicate that sand- and clay-like behavior is subject to the intensity and duration of cyclic loading. The variation of cyclic resistance ratio (CRR) and cyclic strength ratio, ${\tau }_{\mathrm{cyc}}/s_{u,\mathrm{DSS}}$, with the number of loading cycles, $N$, to reach single amplitude shear strain, $\gamma$, of 3% and 3.75% is presented. The ${\tau }_{\mathrm{cyc}}/s_{u,\mathrm{DSS}}$ for $N_{\gamma =3\%}=10$ and 30 appeared constant for $\mathrm{PI}\le 11$ and $\mathrm{PI}\ge 18$ and equal to 0.63 and 0.54, and 0.82 and 0.76, respectively, with an apparent linear trend for $11<\mathrm{PI}<18$. Despite higher void ratios, intact overconsolidated specimens exhibited greater CRR than their mechanically normally consolidated counterparts, highlighting the effects of OCR and natural soil fabric on cyclic resistance. Cyclic tests conducted on specimens consolidated using a quasi-stress history and normalized soil engineering properties (SHANSEP) method exhibited larger CRR than those tested using the recompression method, which is attributed to the smaller void ratios and potentially greater lateral stresses. The recompression technique is preferred for establishing the cyclic response to capture in-situ conditions when testing high-quality samples and where quantification of the preconsolidation stress is uncertain.

A series of axial load tests in tension has been carried out on open-ended driven steel pipe piles with a diameter of 406 mm and lengths of 70 and 40 m. At the test site, the ground consists of layers of loose fluvial sand and soft silty marine clay deposits. One test pile was well instrumented with strain gauges. The main scope of the test program was to verify design methods including time effects for pile foundations for new bridges at the site. To verify time or aging effects, the piles were load tested 3, 9, and 18 months after installation. The test results are presented in some detail and compared to bearing capacity and load-displacement response predicted prior to pile installation. An unexpected result of the test program was that several days of stops in driving due to welding of the pile segments and connecting of the instrumentation had a major negative impact on the ultimate bearing capacity of the instrumented pile, which failed at about 50% of the predicted values. Noninstrumented test piles with shorter stops due to welding of segments gave bearing capacities in reasonable agreement with predicted values.