Geo-Congress 2023: Geotechnical Characterization

Although geostatistical tools have been available for over 50 years, their implementation is uneven across geotechnical industry. One barrier to more widespread use of geostatistics in practice is the difficulty in knowing which realizations, of many error minimizing realizations, are representative of the actual subsurface conditions. When using a set of subsurface explorations, such as CPT, there can be many viable realizations of conditions. For a highly variable mine tailings pile orthogonal 2D MASW profiles showing material variability via shear wave velocity are compared to geostatistical realizations of materials between CPT soundings. Specifically, orthogonal 2D MASW lines were conducted to image the subsurface for soft and stiff locations potentially indicating rubble or debris in the subsurface, while CPT were performed for geotechnical shallow and deep foundation design. In this work the geophysics are used to “truth” the geostatistical analyses. This paper shows that 2D geophysical profiles and geostatistics can both be used to constrain subsurface uncertainties, drive successful foundation design, and control construction phase obstructions.

Rock material characteristics such as mineral composition, fractures, and rock fabric can be closely related to potential stability issues of underground constructions. The composition, durability, and potential swelling are often diagnosed by use of X-ray diffraction (XRD) analysis; however, this method does not recognize non-crystalline rock components and textural properties of weathered and altered rocks. Hyperspectral imaging (HSI) is an emerging technique in lithological and mineral mapping, which utilizes the spectral reflectance signature of the target materials and can be applied both at laboratory and field settings. A pilot study has been conducted to explore the potential of the HSI-based approach using rock chip samples from swelling rocks down to microscopic scale, using the shortwave infrared (SWIR, 1,000–2,500 nm). By comparing the efficiency between HSI and traditional laboratory methods including XRD analysis and petrographic studies, this study provides insights on using new approaches to study weak rock degradation relevant for site characterization and risk management in civil engineering projects.

Hydro-Quebec owns more than 680 dams and dykes, and a large number of appurtenant structures such as powerhouses, spillways, and water intakes distributed among 100 hydroelectric installations. Such large structures require deep surface and underground rock excavations coupled with rock reinforcement systems that insure stability and safety. The geological context for most of these hydroelectric installations requires ground support design, which mainly relies on permanent mechanically anchored rock bolts, fully grouted after installation. Over the years visual inspections revealed noteworthy corrosion on visible parts of rock bolts in delimited areas. The purpose of this paper is to present the results of an industrial research project initiated to investigate the extent of corrosion, its effect on bolt serviceability, and possible causes of premature rock bolts aging in a hydroelectric setting. This paper will present the importance and benefits of rock bolt environmental characterization, selection of suitable corrosion protection, and implementation of selected protection. The outcomes of this research served for the development of a technical guide to be used for inspection and maintenance.

In the East-Central Florida region, where there is relatively deeper depth of bedrock than north/west of Florida, cone penetrometer tests (CPTs) have been popularly used for sinkhole geotechnical investigation. From the CPTs, an index known as the raveling index (RI) was developed. This raveling index is used to better understand the status of raveling, thus, quantitatively evaluating the susceptibility of sinkholes. However, standard penetration test (SPT) is still the most common subsurface exploration method in geotechnical engineering practice. In areas of shallow bedrock/limestone or where CPT testing is unavailable, SPT testing is necessary, often the case in West-Central Florida. In this paper, a method for calculating the raveling index in known sinkhole locations using SPTs was developed. An analysis of the RIs calculated using CPTs was performed to compare with those calculated using SPTs. The outcome of this analysis is a preliminary result showing a potential benefit of SPT in sinkhole investigation and also a limited correlation between the RI calculations. Subsequently, there may be a possibility of using SPTs in tandem with CPTs for future projects to be effectively used to investigated for sinkhole risk. This study was applied to various sinkhole locations throughout Central and northern Florida.

The downhole method is one of the most widely used in situ seismic tests to determine shear wave velocity (V_S) profiles for site characterization and site response analysis. Although easy to perform in the field, it has always been a tedious task to accurately interpret the downhole data based on the arrival times of shear waves at the borehole receiver. Commonly used methods are the direct, interval, and Snell’s Raypath methods. Snell’s Raypath method has been known to provide the best results for downhole processing at multilayered subsurface sites as it considers the actual travel path of waves considering the refraction along the wave travel path. The direct method is considered better when the soil layers are uniform with reduced chances of refraction. In this study, V_S profiles are estimated for two boreholes 100 m deep at a deep silty deposit underlain by sandstone rocks. The Snell’s Raypath method was observed to be more suitable for shallow subsurface to capture a greater variation in properties and need for a higher resolution in shallow subsurface. The direct method was found suitable for deeper layers where dense soil and rock layers are located, which show more uniform layering with depth.

Karst subsidence or localized cover collapse of subsurface cavities (sinkholes) is a severe hazard in the United States and can be found in all 50 states. Although occurrences of subsidence or sinkholes are challenging to predict, karst areas are more susceptible and conducive to the formation of cover collapse sinkholes. Seasonality and daily conditions in soil moisture, surface temperature, and precipitation collected from satellite-based sensors and remote sensing algorithms can be used to investigate incipient failure factors that initiate a sinkhole: in particular, the NASA Soil Moisture Active Passive (SMAP) Level 4 root zone soil moisture, the Integrated Multi-satellite Retrievals (IMERG) algorithm for the Global Precipitation Measurement (GPM) mission, and the Famine Land Data Assimilation System (FLDAS) Noah Land Surface Model. This study presents a holistic assessment of several known sinkhole occurrences in the United States using coarse low spatial resolution data. It was observed that comparing the spatial and temporal volumetric soil moisture from SMAP_L4 and FLDAS Noah with the precipitation intensity from GPM_IMERG data functioned well in detecting impending conditions at the investigated sites. This research aimed to develop a routine process flow analysis through SMAP L4_SM, FLDAS Noah, and GPM_IMERG data and investigate the normalized difference vegetation index (NDVI) to conduct sinkhole assessment.

The undrained shear strength of clay often increases in an approximately linear manner with depth. This trend can be characterized by an undrained strength at the top of the soil layer (s_u0) and a change in undrained strength with depth (ρ). Because naturally occurring soils are rarely homogeneous and consequently show high variability in undrained shear strength, the measured properties will exhibit scatter about the linear trend. While many studies have examined the variability in undrained shear strength itself, statistical data for describing undrained shear strength as a function of soil depth is sparse to nonexistent in the geotechnical literature. In addition, the slope and intercept parameters would be expected to show significant correlation, which has not been investigated. The analysis presented in this paper estimates the intercept, slope, and statistics of published data sets of undrained shear strength and generates smaller synthesized data sets based on that information. The synthesized data is then used to estimate the mean and standard deviation of the slope and intercept parameters from the linear trends, and to estimate the correlation coefficient between these two parameters. A strong negative correlation is found between s_u0 and ρ. The stability of a homogenous clay slope with linearly increasing undrained shear strength is examined probabilistically. The negative correlation between s_u0 and ρ substantially reduces the calculated probability of failure for the example.

In ground motion prediction equations (GMPEs), site characteristics are usually addressed by the shear-wave velocity of top 30 m (V_S30) or depth to 1.0 km/s shear-wave velocity isosurface (Z_1.0); however, these parameters are either inferred or limited to the shallow depths. Therefore, using other site proxies such as site fundamental frequency is useful. In this study, a data set from the KiK-net strong ground motion network is used to estimate the maximum-likelihood estimate of site fundamental frequency (f_ml) and its corresponding amplitude (A_ml) using the horizontal-to-vertical spectral ratio (HVSR) of surface ground-motions. First, the recorded ground motions with PGA ≥ 0.1% g and Mw > 3 are selected and processed for 100 stations. Second, the HVSR is calculated for each recorded event at each site. Third, f_ml and A_ml are estimated for each site using previously developed automated methodologies by the authors. These automated methodologies provide the uncertainties associated with f_ml and A_ml estimates, whereas the conventional HVSR methods yield one value. Lastly, the results obtained in this study are compared with a recent independent study on a similar data set. The results of automated methods are very consistent with those of the independent study. According to the results, using f_ml can be referred to using the first peak frequency (f₀) and highest peak frequency (f_peak) in the HVSR curve. In addition, the findings show that the Fourier amplitude spectrum and 5%-damped pseudo-spectral acceleration have fairly comparable performance in estimating site fundamental frequency and its amplitude.

Earth pressure cells (EPCs) are typically utilized to measure total soil and water pressures in situ. Installed EPCs exhibit an active stress arching phenomenon in which the stress sensed by the EPC is smaller than the stress in the soil surrounding the EPC. Unfortunately, the hydrostatic calibration factor provided by the manufacturer cannot account for this phenomenon, resulting in the need to independently calibrate a given EPC in the laboratory before it is installed in situ. Though other researchers have conducted their own independent laboratory calibration of EPCs in dry sand, the custom testing setups that have been developed for this calibration procedure have required special apparatus fabrication, which makes these procedures difficult to replicate. In the current study, a simplified testing apparatus and method were developed to calibrate EPCs in dry sand, which utilize standard equipment that is commonly found in most geotechnical testing laboratories. Three 1-MPa-range semiconductor EPCs were calibrated in dry sand at various sand column heights ranging from 5 cm to 30 cm by subjecting them to ten loading cycles at each column height. The goal of this study was to examine the influence of sand column height and load cycles on the EPCs’ associated sensitivity ratio. Overall, the results observed in the current study were consistent with results presented by previous researchers for EPCs calibrated at the same sand column height using larger and more sophisticated testing setups; this indicates the potential utility of the simplified calibration procedure that is described in the current paper for independent calibration of EPCs.

The evaluation of sinkholes continues to present challenges when managing highway infrastructure given current geotechnical subsurface investigation techniques. Typical drilling efforts combined with standard penetration testing (SPT) and cone penetration testing (CPT) provide useful information, but only at a limited number of points throughout the site. Such efforts are also not routinely utilized after the implementation of sinkhole treatment efforts as a means of quality control due to logistical challenges and costs. The horizontal-to-vertical spectral ratio (HVSR) method, which records ambient seismic noise using a single, broad-band three-component seismometer, can be rapidly deployed throughout a site and provides information regarding the stiffness of the subsurface materials. Repeated HVSR measurements at the same locations can potentially identify problematic areas present after the implementation of sinkhole treatment efforts. In this paper, HVSR measurements were collected along a roadway where known sinkholes were present. The HVSR testing locations were collocated with boreholes to allow for a comparison with the inferred subsurface profile from geotechnical investigations. The roadway was then subjected to an extensive grouting program to treat the active sinkholes. HVSR measurements were subsequently repeated at the same pre-grouting locations to investigate changes in the subsurface stiffness. The results exhibited an increase in HVSR amplitude toward lower frequencies when comparing the pre- and post-grouting ambient noise measurements, possibly indicating a stiffening of the soil post-grouting. Despite rejection of time windows that exhibited evidence of near-field anthropogenic waveforms, there was still significant variance in the results attributed to poor coupling of the seismometer (i.e., pavement surface and gravelly fill on the roadway shoulder), adverse weather conditions (i.e., wind and rain), and the complexity of the site conditions (i.e., the extent and spatial variability with which grout flowed into voids and interaction of grout with nearby buried utilities). Use of HVSR as a quality control tool for sinkhole treatment efforts should be further investigated with consideration of the complexities that can affect such variance in the results.

The cone penetration test (CPT) is widely used in geotechnical engineering for subsurface soil characterization due to its nearly continuous profiling, expediency, and repeatability, which are difficult to match with drilling, sampling, and laboratory testing, or other subsurface characterization techniques such as the standard penetration testing (SPT). In addition to obtaining the cone tip resistance, sleeve friction, and pore water pressure, the seismic piezocone penetration test (SCPTu) also provides measurements of shear wave velocities with depth. A series of SCPTu soundings have been completed at several strategic Illinois test locations to characterize the particular response of Illinois soils in terms of stress history, strength, compressibility, stiffness, organic content, and hydraulic properties. Additionally, since the current geotechnical engineering practice in Illinois has a heavy reliance upon the SPT, an evaluation of correlations between paired sets of SCPTu readings and SPT blow counts corrected for energy efficiencies was made at a selected location. The findings of this research will be incorporated into the Illinois Department of Transportation’s (IDOT) geotechnical manual through the development of guidelines for using CPT in the state of Illinois. This effort is geared towards expanding the use of CPT in IDOT practice allowing for higher quality subsurface data that can reduce design costs while increasing sustainability and reducing risk.

Intermediate geomaterials (IGMs) are used as bearing strata in various civil engineering projects. It is important to reliably evaluate the geotechnical characteristics of IGMs to ensure the stability of their associated structures. In the case of IGMs, such as highly or completely weathered rocks and residual soils, it is difficult to obtain undisturbed specimens for laboratory tests. Therefore, field tests are performed to evaluate the design parameters of IGMs. However, it should be noted that conventional field tests are specialized for soils and rocks. In this study, a novel field test device, the borehole pressure shear tester (BPST), was developed to reliably evaluate the deformation and shear strength parameters of IGMs. A 1:1 scale physical model test was conducted to validate the reliability and applicability of the BPST. The test was performed using a calibration chamber, for simulating the stress conditions of the field ground. The test results were compared with laboratory triaxial compression test results and direct shear test results.

The application of geostatistical sequential simulation methods to build geomechanical models and quantify the corresponding uncertainty is well established in the oil and gas industry, whereas the majority of subsoil models created for civil engineering projects utilize deterministic interpolation methods where uncertainty cannot be evaluated. In this paper, the root causes of these uncertainties for subsoil model generation are briefly explained, and a concept for the consideration of these uncertainties by means of probabilistic subsoil modeling is presented. This makes it possible to statistically evaluate geotechnical risks in both the design and construction. Using two case studies, the use of the geostatistical method is demonstrated on the basis of site investigations consisting of (1) CPTs and (2) borehole logs. The case studies illustrate the great potential and advantages of this methodology of subsoil modeling compared to the conventional deterministic approach. Further developments are required for its implementation in practice, which are outlined in a brief outlook.

The variability of solid waste properties is typically greater than observed for natural soils over comparable horizontal and vertical distances. Quantifying this variability is critical to the success of solid waste landfill retrofit and final cover designs. This paper presents data from a combined multichannel analysis of surface waves (MASW) and rotary soil boring investigation of a 60-year-old, 8-hectare solid waste landfill. This investigation provided input to a final cover design project. A comparison of the data illustrates where these technologies complemented each other for characterization of subgrade properties and where they conflicted. In general, the combined use of these technologies yielded valuable insights into subsurface conditions. The data also yielded parameters useful for modeling the spatial variability of old solid waste that can be used for future design analyses.

Cone penetration testing (CPT) is widely used for geotechnical characterization of subsurface materials. Shear wave velocity (Vs) measurements provide very useful information for engineering purposes and can usually be added to land-based CPT testing programs for a relatively minor increase in cost and time. However, performing Vs measurements from a floating platform on submerged materials such as impounded tailings and coal ash is a challenge due to the lack of available equipment required to generate shear waves from the mudline. To solve this problem, the authors developed a new model using machine learning techniques to estimate Vs based on conventional CPT measurements without direct Vs measurements. The model uses a random forest algorithm implemented in Python for solving this regression problem. The new model is shown to provide more accurate estimates of Vs than methods widely used currently. The technique also provides for the possibility of generating continuous Vs profiles with greater vertical resolution than currently obtained using discrete measurements.

This paper reviews the application of magnetic resonance imaging (MRI) for monitoring pore water in different porous media. The physics of MRI and different imaging techniques are first presented in detail, and studies focusing on quantifying water and water flow in porous media are reviewed. Then, we present the results of MRI scans for a poorly graded sand (badger sand), scanned utilizing a 9.4 Tesla MRI scanner. The specimen was saturated with deionized (DI) water in a PVC container, then placed inside the magnetic resonance (MR) scanner for fast low angle shot (FLASH) sequence imaging. The collected 2D images were then processed, and a 3D tomography for the pore water distribution was reconstructed. The volumetric water content (w_c) for the badger sand specimen was then calculated by three-dimensionally segmenting of the pore water component acquired using the MRI. The calculated water content agreed with the water content used to prepare the specimens, validating the adopted scanning parameters and methodology. Such results pave the way for more advanced analysis of pore water in soils under steady state or varying water flow.

In this study, the MASW testing was carried out on asphalt pavement using several accelerometers and geophones to characterize the stiffness profile of the pavement. Park’s phase-shift method was applied to the experimental data to obtain the dispersion image in the frequency-phase velocity domain. Typical pavement structures have high stiffness layers, such as the asphaltic or concrete layer above the underlying less stiff subgrade. The dispersion image for such a case shows an increasing trend of phase velocity with increased frequency, which contrasts with the normally dispersive soil profiles. This obtained dispersion curve can be easily mistaken as a single continuous curve for inversion analysis, leading to errors in the obtained profile of the pavement, which includes shear wave velocity (V_S) and thickness of each layer (h). The predominant modes obtained from the fast delta matrix method for assumed pavement layers are matched with the effective dispersion curves obtained from experiments to obtain the correct results for properties of each layer. The automatic inversion using Monte Carlo-based global search algorithm gives a pavement profile that matches the extracted core sample results.

Over the last several decades, active surface wave testing has received increasing attention in geotechnical engineering and has become a common method for site characterization. Active surface wave testing can be performed using Rayleigh- and/or Love-type surface waves. However, Rayleigh-type surface waves have been the most commonly used wave type among practitioners in the geotechnical community. This paper provides one case study for a site with a very shallow impedance contrast where surface wave data processing, particularly mode assignment, becomes very complex. Both Rayleigh and Love-type surface wave testing was conducted for the case study. The surface wave data were processed using two different scenarios: (1) fundamental mode Rayleigh waves only and (2) multimodal inversion using Rayleigh and Love type surface waves. These results were then compared to the boring to identify the performance of each approach. The results indicate that the first higher mode dominated the Rayleigh-type surface wave dispersion data at many frequencies, while the Love-type surface wave dispersion data were associated with the fundamental mode. Overall, the results indicate that the inclusion of Love-type surface waves and multimodal inversion can significantly improve the reliability of the inversion process and the final 1D shear wave velocity profile for sites with a very shallow impedance contrast. Relying solely on Rayleigh-type surface wave data for such sites would lead to mode misidentification and data misinterpretation. Therefore, it is recommended to employ both Rayleigh and Love-type surface waves for sites with a shallow impedance contrast to avoid data misinterpretation and enhance the reliability of the site characterization using active surface waves testing.

With the accelerating rate of global warming, seasonally frozen ground has been an emerging issue in the Northern Hemisphere. The freeze-thaw cycling of frozen soils is known to be the cause of various engineering failures of infrastructure in cold regions. To better conduct construction in cold regions, ground investigations on soil profile distribution and properties of frozen soils are essential. Researchers found that electrical resistivity method outperforms traditional ground surveying methods in frozen soils for their greater convenience and cost-effectiveness. However, detailed investigation into the relationship between electrical resistivity of soil and a variety of soil properties, especially properties related to the freeze-thaw process, is still needed. In this study, a series of laboratory experiments are conducted to determine the relationship between soil electrical resistivity and soil geotechnical properties such as initial water content, bulk density, and pore fluid concentration under freeze-thaw conditions. Manually prepared soil samples undergo artificial freeze-thaw cycles, and electrical resistivity and temperature values are recorded simultaneously. Measurement results are summarized for curve fitting, and a statistical model showing relationship between electrical resistivity and temperature during freezing and thawing is given. When the temperature was above the freezing point, resistivity has a linear relationship with temperature on a semi-logarithmic plot; when the temperature was below the freezing point, resistivity has a parabolic relationship with temperature on a semi-logarithmic plot. Result patterns during freezing are also different from those during thawing. Impacts from other soil properties are also incorporated in the model through optimization methods. Theoretical basis of the relationships is discussed to reveal changes in the structure of coils at different stages of freeze-thaw cycling. The findings of this study are expected to enhance understandings of frozen soil structure and geophysical surveying in cold regions.

Determining the depth to bedrock is important for a variety of geotechnical engineering applications such as foundation design and slope stability investigations. Direct determination of bedrock depth by drilling often provides only a sparce spatial sampling of depths. Geophysical methods, such as refraction, resistivity, and surface wave measurements, provide reliable estimates of bedrock depths but require extensive equipment deployment and expertise to interpret the data. In recent years, the horizontal to vertical spectral ratio (HVSR) method has found widespread application in seismology, earthquake engineering, and geotechnical engineering. HVSR requires only a single three-component sensor, uses ambient noise as the source, and, importantly, requires little expertise to determine the site frequency. The method is well suited as an inexpensive and non-intrusive complement to geotechnical site investigation programs. Specifically, the HVSR method can be used to estimate the depth of bedrock. Past studies have demonstrated the ability to derive region-specific relationships to estimate the depth to bedrock over depths to several hundred feet. In this study, we investigate the viability of HVSR measurements to determine the depth of shallow bedrock (tens of feet) over a more localized area (about 300 acres) in Central Missouri. Relationships between site frequency and bedrock depth are developed for these conditions, along with prediction bounds. The influence of variable bedrock conditions on the results is assessed and discussed.

A new 3D ambient noise tomography (3D ANT) method is presented for geotechnical site characterization. It requires recording ambient noise wavefields using a 2D surface array of geophones, from which cross-correlation functions (CCF) are then extracted and directly inverted to obtain S-wave velocity (Vs) structure. The method consists of a forward simulation using 3D P-SV elastic wave equations to compute the synthetic CCF and an adjoint-state inversion to match synthetic and field CCFs for extraction of Vs. Compared to conventional passive seismic methods using characteristics of Green’s function (GF), the main advantage of the presented method is that it does not require the energy balance at both sides of each receiver pair to retrieve the true GF. Instead, the source power spectrum density is inverted during the analysis and incorporated into the forward simulation to account for source energy distribution for accurate extraction of Vs profiles. The presented 3D ANT method was applied to 3 h of noise recordings from an array of 196 geophones placed on a grid with 5 m spacing at the Garner Valley Downhole Array (GVDA) site in California. The inverted 3D Vs model is found to be consistent with previous invasive and non-invasive geotechnical characterization efforts at the GVDA site.

Development of infrastructure in areas with poor subsurface soil conditions is often encountered in civil engineering. In these situations, the engineering characteristics of problematic soils can be improved by ground improvement techniques tailored to site-specific constraints. Jet grouting is among the most widely used methods to stabilize poor subsurface soils, particularly for underpinning of existing structures and cutoff walls for excavation support. During jet grouting, a stabilizing fluid (cementitious or chemical grout) is injected into the surrounding soil through small nozzles under very high pressure and velocity. The rotary motion of the injection nozzle creates columnar elements of soilcrete as the nozzle is withdrawn from the subsurface. The columns are often overlapped to create a wall or prevent horizontal movement of unstable soils and/or groundwater. However, local variations in the subsurface conditions can lead to variability in the column diameter. This in turn can cause untreated zones where the columns cease to overlap. Typical quality assurance efforts rely on real-time recording of jet grout parameters such as fluid pressure, flow rate, rotational speed, and rate of withdrawal/insertion. This is combined with a comprehensive test program prior to production efforts that establishes the jet grout column spacing, overlap, and overall depth geometry, typically using destructive methods such as excavations and corings of the soilcrete columns. However, these efforts do not allow for a comprehensive site-wide assessment of the as-constructed column geometry given the significant spatial variability present in the subsurface of many sites. Consequently, there exists demand for a high-resolution non-destructive testing (NDT) method that can reliably identify untreated zones caused by lack of column overlap after jet grouting. This paper numerically examines the use of full waveform inversion (FWI) of seismic data as a potential NDT approach for quality assurance of jet grouting efforts. FWI seeks to optimize the misfit between synthetic waveforms and observed seismic data. An initial model is subsequently updated by a linearized inversion procedure for optimizing the wave propagation properties of the subsurface soils. The current study adopts the spectral element method as a robust forward modeling technique to solve the wave propagation equation and updates the models using a quasi-newton approximation of the inverse Hessian to lower the computational cost of the process. The results of the current study highlighted the potential of the FWI technique to reliably image anomalous conditions in the overlapping jet grout column and detect any untreated zones.

An assortment of algorithms for the processing of surface wave data are presented and utilized to analyze several case studies. Algorithms developed in MATLAB are described for extracting dispersion curves from waveforms for all typical field test scenarios, including SASW, MASW, ReMi, and 2D passive arrays. Geopsy contains a publicly available module that inverts dispersion curves for both shear wave velocity and layer thickness based upon a global search algorithm that provides valuable information on the uncertainty of the profile parameters. A suite of models from Geopsy can be post processed with MATLAB routines for display of inversion results, including important statistical parameters. The algorithms have been used to process various forms of original data from several case studies. Inversions with lowest variability are produced by soft soil sites with gentle variation, whereas sites with sharp contrasts such as soil over rock at shallow depths can produce inversion results with much larger variability. Inversion for that “one true model” can be elusive, even in the case of synthetic data sets where the true model is known; it is possible to come close, but with inversion come both uncertainty and blurriness.

The goal of this study is to summarize the existing state of practice for using geo-acoustic signals in geotechnical and foundation engineering and to further outline potential future directions for this technique. For decades, acoustic signals have been recognized as a feasible geophysical technique to estimate soil properties including, but not limited to, the shear wave velocity in a soil medium, porosity, and relative density. These geophysical acoustic methods rely on signals produced by an external source within the soil mass. Recent studies further suggested potential correlations between acoustic signals produced naturally by soil formations and the physical and mechanical properties of these soils. In this manuscript, we will first summarize current knowledge about the current uses of geo-acoustic signals from the literature. We will then present a brief discussion about existing applications of such technology in geotechnical and foundation engineering.

In bio-mediated geotechnical techniques, the estimation of microbially altered geomechanical properties has mostly been conducted at core-scale due to the complexity of in situ field-scale measurement of biogeomechanical properties. However, the successful in situ field application of this emerging field of geomechanics relies on proper upscaling of this process from core-scale to field-scale (reservoir-scale). Here, we developed and applied a machine learning (ML) algorithm (artificial neural network, ANN) to model and predict the reservoir-scale biogeomechanical-altered properties of shale and carbonate rocks. We first obtained experimental data of the core- and bulk-scale mechanical properties (uniaxial compression strength, UCS) of the core samples impacted by a microbial strain. These core-scale data were then subsequently used as input variables to predict the field-scale biogeomechanical altered properties. The results show a high degree of correlation between the ML-predicted field-scale biogeomechanical properties and the laboratory-obtained bulk-scale biogeomechanical properties in shales (11.2% mean absolute percentage error) and carbonates (13.5% mean absolute percentage error). In addition, the result shows that the degree of correlation in rock mechanical properties and new mineral precipitations may be higher with increasing pore spaces in the tested rock types. This study provides a first leap from the laboratory and core-scale investigations toward field-scale geotechnical and geo-environmental applications of biocementation and biomineralization by predicting in situ biogeomechanical alterations.

In this study, the discrete element method (DEM) is adopted to evaluate the damage and cracking behaviors of sandstone containing two unparallel fissures under freeze-thaw cycles. The rock and water compositions are represented by particles of different sizes and properties, with smaller water particles filled into rock pores. A modified elastoplastic parallel bonded model is developed to describe the accumulation of residual strain caused by the ice-water phase change. The model is calibrated by comparing numerical results [uniaxial compressive strength (UCS), Young’s modulus, and failure pattern] with published experimental data. Compared with published experimental results, similar crack coalescence patterns and similar deteriorating effects of freeze-thaw cycles (FTCs) are observed in the numerical results. This study enhances our understanding of the influence of FTC on the cracking behaviors of sandstone containing fissures and may contribute to the future design and assessment of climate-resilient infrastructure.

Global surface temperatures rose by 1°C in 2020 relative to the average temperatures between 1951 and 1980. A reduction in the extent of the almost 24% of the Northern Hemisphere covered by permafrost will impact the stability of new and existing civil infrastructure in the area. Frozen soil is a multi-phase system consisting of ice, unfrozen water, air, and soil particles. Fluctuations in temperature change the proportions of the constituents significantly impacting the strength of the soil mass. The strength behavior of fine-grained soils will differ substantially from that of frictional soils since fine-grained soils can have high ice contents due to their high-water absorption capacities. However, the lack of commercially available equipment has deterred research efforts in understanding the impact of climate change on the shear strength properties of fine-grained soils. This paper describes the development of a new direct shear box that allows for temperature-controlled testing. Modifications to the temperature-controlled shear box as deemed necessary from validation tests are also described. For example, comparisons of the temperature measurements within the soil sample to the chilled glycol circulating in the modified direct shear box indicated that additional insulation had to be provided to the apparatus. The freezing mechanism applied to the soil sample affected the distribution of ice within the pore spaces and illustrated the need to freeze the sample from all directions. This was incorporated into the modifications that were designed in this study. Shear strength parameters from the newly designed temperature-controlled direct shear box matched well with those from the traditional shear box.

Modulus reduction and damping versus shear strain relationships (hereafter MRD) are essential for nonlinear ground response analyses of soil sites. For sites containing thick deposits of peat, large shear strains that produce pronounced nonlinearity are expected in seismically active regions. Currently, available MRD models for peat have strongly divergent characteristics, particularly with regard to the influence of confining stress. We assembled a large database of test data from literature and proposed a hyperbolic model, similar in form to widely used models for non-organic soils, for application to peat. We related the critical model parameters to stress history-modified effective stress, finding no strong dependence on organic content (OC) and peat composition (fibrous structure) over the parametric range of the database (OC >30%). The new model captures both the weak and strong dependencies of MRD behaviors with effective stress from literature, with weak dependence occurring in normally consolidated peats for ${\sigma }_v^{\prime }/p_a>0.2$ (where ${\sigma }_v^{\prime }$ is vertical effective stress and $p_a$ is atmospheric pressure) and stronger dependence at smaller stresses. We present here a model for OC >30% conditions and its associated aleatory variability, which was established from residuals derived from test results. Compared to previous peat MRD models, the proposed model has more easily interpretable parameters and reduces the model bias and uncertainty.

The use of so-called “transparent soils” as proxy geotechnical materials has allowed for the non-intrusive observation of a variety of models representing different engineered systems. Laponite is one such soft clay surrogate that has seen increased usage in recent years. However, this material has yet to be subjected to a thorough characterization and quantification of its physical and mechanical properties. The study presented herein followed a systematic approach towards the identification of the undrained shear strengths of laponite mixtures across a wide range of mixes and additive dosages. Results from vane shear tests showed that the undrained shear strength increased with (1) increasing laponite colloid content, (2) decreasing additive dosage, and (3) aging time. The base geotechnical characteristics and mechanical properties of the clay surrogate as provided in this study are expected to facilitate proper interpretation of the behavior of this surrogate material in geotechnical physical models involving transparent clays.

The threshold sand content of mixtures of sand and gravel is defined as the sand content at which the mixture of sand and gravel transitions from behaving as a gravel to behaving as a sand. This transition occurs when there is insufficient room in the voids created by the gravel to contain all of the sand grains present in the mixture; at this sand content, the material begins to transition from sand grains contained in a gravel matrix to gravel particles contained in a sand matrix. Below the threshold sand content, the material behaves as a gravel; above the threshold sand content, the materials behave as a sand. This phenomenon of transitional behavior has been extensively studied for mixtures of sand and non-plastic silt, with the silt content at which the behavioral change occurs often being referred to as the “threshold fines content.” As increasing amounts of sand are added to a gravel, the soil mixture transitions from gravel to sandy gravel to gravelly sand and eventually to sand. This change in soil composition leads to changes in the maximum and minimum index void ratios (e_max and e_min) of the soil, as well as changes in the coefficient of uniformity, C_u. As sand is initially added to a gravel, the range of particle sizes increases, the index void ratios decrease and the coefficient of uniformity increases. These trends continue until the threshold sand content is reached. Mixtures that are below the threshold sand content typically have higher friction angles and stiffness. As the sand content continues to increase above the threshold sand content, the range of particle sizes decreases, the index void ratios increase and the coefficient of uniformity decreases. In this study, the changes in strength and stiffness that are predicted to occur at the threshold sand content were investigated for four mixtures of sand and gravel tested at different sand contents. The four mixtures studied consisted of a uniform sand mixed with a uniform gravel, a uniform sand mixed with a poorly-graded gravel, a well-graded sand mixed with a uniform gravel, and a well-graded sand mixed with a poorly-graded gravel. For each combination, specimens were prepared at a constant relative density at various sand contents and were tested in drained triaxial tests. From these tests, the change in shear strength and stiffness that occurred as the sand content increased were determined for each pairing of sand and gravel. At sand contents below the threshold sand content, the strength and stiffness were similar to that of the gravel. At sand contents above the threshold sand content, the strength and stiffness were similar to that of the sand. In each case, the changes in friction angle, ϕ’, and secant modulus, E_s, were found to be statistically significant and to occur at sand contents corresponding to the threshold sand content. This suggests that there is a change in the behavior of sand-gravel mixtures that occurs at the threshold sand content.

Natural soil deposits can consist of particles with a wide range of sizes. In current practice, the assessment of shear strength and stress-dilatancy behavior of coarse-grained soils is based on methods developed for poorly graded sands, without explicit consideration for differences in gradation. This paper investigates the influence of the range of particle sizes on the monotonic shear strength and the stress-dilatancy response of poorly- to well-graded soils. Using the 3D discrete element method (DEM), the applicability of commonly used sand-based stress-dilatancy frameworks is assessed for a range of gradations. This DEM investigation employs clumps of spheres to accurately simulate the particle shapes on specimens with coefficients of uniformity (C_U) varying between 1.9 and 6.9. These specimens were subjected to isotropically consolidated drained triaxial compression at various relative densities and confining stresses with the objective of isolating the effects of particle size distribution from those of particle shape. The peak and critical state shear strengths and the dilatancy responses of the specimens with different gradations are evaluated. For the same state parameter, the results indicate an increase in the shear strength and rate of dilation as the range of particle sizes increases. However, the critical state line shifts downward, and its slope decreases as C_U is increased. The DEM results are compared to Bolton’s stress-dilatancy relationship to highlight the inadequacies of using clean sand-based frameworks in capturing the behavior of well-graded soils.

Offshore pipelines that transport hydrocarbons under high pressure and high temperature are usually thermally insulated to maintain an elevated temperature and prevent any heat loss to the surroundings. However, the temperatures at the outer-wall of the pipes may still be elevated and therefore may potentially affect the interface resistance between the pipeline and the seabed. This study aims at experimentally investigating the drained shear resistance of the soil-pipe interface at elevated temperatures (22–60°C) and low normal stresses typical of field conditions (2.45–6.1kPa). A series of direct shear tests are thus performed using a modified-for purpose direct shear apparatus. Low and high plasticity clays, consolidated from a slurry, were sheared against smooth and rough interfaces to characterize the peak and residual interface shear response under drained conditions. Results indicated that the effect of elevated temperature on the interface resistance is highly complex and dependent on the roughness of the pipe coating, the plasticity of the clay, and the magnitude of the applied normal stress.

Montmorillonite, kaolinite, and quartz were used to prepare 20 samples in the laboratory to have liquid limits ranging from 8 to 486 and plasticity indices ranging from 4 to 431. The samples were normally consolidated to pressures ranging from 25 kPa to 100 kPa and then subjected to bender element tests to determine the maximum Young’s modulus of elasticity and maximum shear modulus. Both the maximum Young’s modulus of elasticity and the maximum shear modulus were observed to depend on the consolidation pressure, the clay mineralogy, and the plasticity characteristics. In particular, an increase in the consolidation pressure would result in an increase in the modulus of elasticity and the shear modulus. At a constant plasticity index, a soil containing montmorillonite had a higher moduli value than a soil containing kaolinite. An increase in the plasticity index corresponded to a decrease in the value of the maximum Young’s modulus of elasticity and the maximum shear modulus. Little variations were observed in the values of the maximum Young’s modulus of elasticity and the maximum shear modulus when the plasticity index exceeded 250 regardless of the consolidation pressure or the clay mineralogy. Figures that can be used to estimate the maximum Young’s modulus of elasticity and the maximum shear modulus as a function of the clay mineralogy, plasticity characteristics, and consolidation pressure are provided.

This paper reports a comparative study of the consolidation behavior of dredged soils by using a standard conventional odometer and a modified conventional odometer. A series of tests were carried out on the dredged soil samples from the Louisiana coastal area. Dredged soils are soft and highly moisturized, and thus form a large strain consolidation settlement. For this reason, the seating load, which is the initially applied load at the consolidation test, is an essential factor for the consolidation test of slurry-type dredged soils. The conventional odometer comes up with a large seating pressure of 0.01 TSF (1 TSF = 107.25 kPa), which would squeeze part of the soft slurry sample out of the odometer cell if the initial moisture content is greater than 70%. Utilizing 3D printing technology, the dial cap was printed out using material polylactic acid (PLA). Then, the seating pressure has been significantly reduced, and the newly achieved seating load turned out to be 0.002 TSF, including the porous stone weight. With the 3D-printed dial cap, dredged soil samples with a moisture content up to 100% could be successfully tested. The laboratory test results of the consolidation properties of Louisiana dredged soils are presented in this study. The results suggest that the modified consolidation apparatus can be used to obtain a reliable relationship between void ratio and effective stress for materials with high initial void ratios.

Thermal loading changes the hydraulic conductivity of the soil medium. This research aims to study the effect of a heating-cooling cycle on the permeability of Kaolin clay. A temperature-controlled triaxial permeameter cell is used in this study to explore the variations of soil permeability at 20°C, 50°C, and 80°C. The hydraulic conductivity at each temperature is measured after 48 h at each temperature during the heating-cooling cycle to make sure the volume change due to thermal loading is stabilized. Evaluation of void ratio change during heating and cooling has been observed to predict the thermal behavior of Kaolin clay. It is observed that the intrinsic permeability during the cooling cycle is 9%–12% lower than the permeability observed during the heating cycle. The obtained results suggest that Kaolin clay’s microstructure can change subject to a heating-cooling process, which creates irrecoverable deformation in the clay and regulates the macro behavior such as permeability of Kaolin clay.

Soil thermal conductivity k plays a significant role in performance assessment of energy geostructures that have direct or indirect thermal interaction with soil. Research presented herein uses a custom-made apparatus to determine both transient- and steady-state values of k from a single test. Results obtained from three different soils suggest that the steady-state k values are consistently higher than their transient-state counterparts. For all tested materials, transient-state k values are sensitive to the rate of soil temperature increment, whereas the values of steady-state k remain constant irrespective of the rate of transient heating. Numerical simulations of laboratory experiments suggest that the use of a time-dependent function of k predicts the experiment results adequately. Moreover, analyses demonstrate that the use of a transient-state k value may significantly underestimate power output from a geothermal pile.

The Federal Highway Administration (FHWA) recently completed an interlaboratory round-robin study that explored the shear strength variability of open-graded aggregates (OGAs) in large-scale direct shear (LSDS) devices. The study found that many participating labs had significantly different device configurations and test procedures. Unlike standard direct shear devices (box width ≤100 mm), there are no unique industry standards for LSDS device design (box width ≥300 mm) or test procedures. Thus, LSDS testing remains the Wild West compared to more established standard direct shear test practices. To explore this frontier, FHWA’s geotechnical laboratory is experimentally and numerically investigating key variables of LSDS device design. This paper presents results from FHWA’s experimental investigation into the influence of upper shear box fixity and the texture of a hinged load platen on the deformation behavior and strength of a selected OGA. Results indicate that box fixity has a significant influence, with mobile boxes producing peak shear stresses approximately half those of fixed boxes. In contrast, platen texture had negligible influence. Ultimately, this paper seeks to begin an in-depth discussion of the questions prompted by the round-robin study—which device configurations produce the most consistent results, and which configurations best represent an aggregate’s true behavior and strength?

The cone penetration test (CPT) is widely used to characterize the behavior and properties of soils ranging from clays to sands. Although the CPT is often used to characterize silts, there exist few methods to interpret CPT data that were specifically developed for silts. This is partly attributed to a limited number of numerical and experimental cone penetration studies that specifically focus on silts. Past studies generally examined either undrained penetration in near-normally consolidated clay or drained penetration in clean sand, whereas cone penetration in silty soils (at the standard penetration rate of 2 cm/s) may be drained, partially drained, or undrained, depending on the soil’s permeability and compressibility. Consequently, uncertainty is introduced into CPT data interpretation for intermediate soils since geotechnical engineering practice lacks an established theoretical basis for evaluating cone penetration data in silts and other intermediate soils such as silty or clayey sands. This study takes a step towards establishing a theoretical basis by examining cone penetration in a non-plastic silt with a direct axisymmetric penetration model and the MIT-S1 constitutive model, calibrated against laboratory element testing and geotechnical centrifuge model tests. The objectives of this study are to (1) validate the numerical model for non-plastic silt with existing experimental cone penetration data from centrifuge tests and (2) use the numerical model to examine how simulated CPT data are affected by drained or undrained conditions during penetration, state-dilatancy relationships, and initial soil state.

Time and rate dependency studies of soil materials have been focused on clayey soils where the viscous effects are more pronounced for low confining pressures. In sandy materials, time-dependent and rate effects are usually considered negligible. Therefore, for practical purposes sands are deemed as non-viscous materials although there is experimental evidence that creep strains of 10% under monotonic loading can be developed. The viscous behavior of granular materials has been demonstrated to be stress dependent. For low confining pressures, it is attributed to particle rearrangement. Most studies on compressibility time-dependent effects of granular soils were developed in one-dimensional or triaxial conditions. The effects of different contents of non-plastic silts have been studied showing that granular soils with fine contents around the transitional limit of approximately 35%–45% start to behave in compressibility testing more like a fine grained material following isotach characteristic behaviors. The objective of the testing program presented herein, which was performed in a constant rate of strain apparatus for low confining pressures, was to evaluate the effects of fines in the material compressibility response of Central Florida silty sands. Control tests on several relative densities were targeted for clean sands. Creep, relaxation, and strain rate effects were evaluated in soil samples reconstituted to several effective axial stress conditions, and fines were added to the clean sand to target void ratios corresponding to the loose state. In this research, the concept of global void ratios versus skeleton void ratios was used to compare the silty sand behaviors up to a 20% of fine content in relation to control tests conducted in clean sands. This research concluded on the relative importance of considering the participation of fines up to 20% weight based on the compressibility response for several sample preparation techniques used to reconstitute the soil samples in the laboratory.

Many advanced soil constitutive models are modifications of the Modified Cam-Clay model. They are based on the concept of critical state theory and use several parameters to simulate the mechanical behavior of soils. Among these, parameters describing the compression behavior of the soil must be determined, even though one-dimensional consolidation tests may not be available, especially for preliminary studies. This information may also be needed to switch from a less complex soil model (e.g., Mohr-Coulomb) to a more complex one (e.g., Modified Cam-Clay). In this paper, the slope of the virgin compression line (λ) was estimated by advancing the existing methods in the literature with rapid laboratory testing equipment, such as the fall cone and miniature vane shear tests. By using this approach, two methods are proposed to estimate the value of λ. Then, these methods were applied on three different soils, and the results were compared and verified using one-dimensional consolidation test. The results obtained from the proposed test methods showed an accurate estimation of the λ parameter for clays, which makes these methods reliable, fast, and economical. But, as the clay fraction of the soil decreases, the methods tend to overestimate the λ values.

Increase in soil salinity is one of the major effects of climate change, which has direct and indirect effects on the chemical, hydraulic, and mechanical behavior of soils. Earlier studies have demonstrated the change in material properties on soils with low-high saline concentrations; however, the transition of low to high threshold values that influence the fundamental properties of the soils is unclear. This study is an attempt to evaluate the threshold of low salt concentrations on changes to soil properties and develop correlations on the geochemical and consistency limits of soil. Characterization tests and geochemical tests including particle size, consistency limits, pH, electrical conductivity (EC), sodium adsorption ratio, and cation exchange capacity were determined. The amount of Ca, Mg, Na, and K present in the soil was evaluated using atomic absorption spectrometry (AAS). Each test was performed on the seven different mixes of varying sodium chloride (NaCl) concentration within a low salinity range to understand its effect on geochemical parameters and consistency limits. Regression analysis was performed on the experimental results which showed a linear relationship between electrical conductivity (EC) and salt concentration whereas liquid limit values were defined by two best linear fit equations for different salt concentrations. A threshold value was defined for the liquid limit above which the effect of salt concentration is limited.

Levees are geologically complex earthen structures that vary laterally and vertically. Current levee inspection practices consist of mainly visual inspections of the surface with limited instrumentation that measures data at discrete locations. To better characterize and monitor the subsurface of these highly complex and spatially distributed systems, non-invasive geophysical methods, such as the multichannel analysis of surface waves (MASW) and electromagnetic induction (EMI), can be used to map the geophysical properties, i.e., shear wave velocity and apparent electric resistivity, respectively. This study focuses on investigating the effect of soil grain size on shear wave velocity and electric resistivity measurements conducted in the laboratory for a range of relative density, water content, and confining stress values. The testing program involved two types of sand: Ottawa C109 sand and Nevada sand, which have different grain sizes, with a D₅₀ of 0.36 mm and 0.18 mm, respectively. It is shown that both shear wave velocity and electric resistivity measurements were affected by grain size and can therefore be used to distinguish between different types of sands at depth. Laboratory testing showed that the coarser sand has higher shear wave velocity at lower water contents and that shear wave velocity decreases with increasing water content. Finer sand particles exhibited lower electrical resistivity for all soil densities and water contents compared to the coarser sand specimens, but the relationship was more pronounced at lower water contents.

Aggregate materials play essential roles in the sustainable performance of engineering applications. Size and shape properties of these aggregates determine the composition and packing of the aggregate assemblies, which impact layer strength, modulus, and deformation response under wheel loading. Current state-of-the-practice methods to evaluate aggregate properties rely on visual inspection, manual measurements, material sampling, and laboratory sieve analysis, as well as ground penetrating radar (GPR) for on-site inspection. Advanced aggregate imaging systems developed to date primarily focused on measurement of separated or slightly contacting aggregate particles, which is not applicable for densely stacked aggregate assemblies under field conditions. In this regard, development of a reliable, accurate, and cost-effective field evaluation technique is crucial. This paper presents an innovative approach using deep learning-based image segmentation techniques for evaluating aggregate materials in the field. The approach requires preparing an image data set comprised of aggregate images collected from various field and laboratory sites, where each image is manually labeled to identify individual particle locations by tracing their boundaries. Then, a state-of-the-art object detection and segmentation framework, called Mask R-CNN, is trained on the task-specific data set to develop the image segmentation kernel. Finally, the trained segmentation kernel is used to segment individual particles, and post-processing provides the morphological indices for the segmented particles. This segmentation approach has been utilized for the field evaluation of large-sized riprap materials and medium-sized ballast materials, with further performance tuning to address various field conditions. The segmentation results show good agreement with the ground-truth labeling and greatly improves the accuracy and efficiency of aggregate field evaluation procedures. Based on the presented findings, the deep learning-based segmentation approach can serve as an efficient and reliable tool for determining aggregate shape and morphological properties in field evaluation applications.

Over the past decades, multiple studies have associated the deformation of coarse-grained soils subjected to temperature variations with complex mechanisms involving particle interactions at the microscale. Despite increasing advances in the understanding of how coarse-grained soils subjected to temperature variations deform at the macroscale, knowledge at the microscale remains limited, with arguably no experimental observations about such particle interactions. This work presents an experimental investigation on particle interactions developing in coarse-grained soils subjected to heating by means of X-ray computed microtomography. Specifically, this work discusses a tomography experiment where particles of F-35 silica sand are subjected to a temperature variation from 30°C to 80°C under zero applied vertical stress in a small container. The displacements of individual particles are analyzed by image analyses on two image scans before and after the heating. The results show that tomography experiments combined with image analyses can provide sufficient accuracy at the microscale to capture particle displacements induced by temperature variations. Heating induces upward particle displacements whose magnitudes increase for particles located at shallower locations in the assembly, suggesting a macroscopic volumetric expansion of sand upon heating that results from the expansion and interactions of individual particles.

Driven precast concrete piles are used as a compelling deep foundation alternative and can be installed below the groundwater table without providing any casing and also unnecessary time delays. Granular materials with relative densities ranging from loose to medium-dense conditions constitute an ideal scenario to install pile foundations using impact driving methods since their bearing capacity might increase due to soil compaction. However, those soil conditions can be highly susceptible to ground deformations induced by pile driving operations mainly due to particle rearrangement and excess pore water pressure buildup and dissipation. Pre-drilling can play a significant role in pile driving-induced deformations and vibrations since the waves emanating from the pile get attenuated prior to reaching the ground surface as the distance between the pile tip and the ground surface increases. This paper presents the effects of pre-drilling installation procedures of prestressed concrete piles on the ground response quantified in terms of deformations and vibrations using a finite element model conducted in PLAXIS 2D. The authors analyzed two configurations of pre-drilling depths selected from bridge construction projects in Florida. The critical-state based hypoplasticity model for sands enhanced with the intergranular strain concept was used as the constitutive soil model for the analyses, thus allowing the program to track changes in the state of stresses and void ratios of the soil as the pile is being driven in the ground in a continuous large-deformation approach. Two diesel hammers and their corresponding forces applied to the top of the pile were used in the numerical models to consider the effects of the selected rated energies in the final response. The results of the numerical analyses indicated that pre-drilling effectively reduces both ground deformations and vibrations quantified in terms of peak particle velocities due to the relative position of the pile tip in relation to the distance to the ground surface.

Frost action in soils causes a significant effect on the performance of roadways. This effect is more pronounced in the regions that are experiencing seasonal subfreezing temperatures as the soil undergoes multiple freeze-thaw cycles. Apart from the subfreezing temperature, the frost action is also affected by the soil type as the void ratio and hydraulic conductivity of soils control the presence and movement of water for the growth of ice lenses. Frost heave is mainly attributed to silty soils, but significant frost heave can also occur in clay and sandy soils under favorable environmental conditions. For the present study, frost heave and thaw settlement of clayey and sandy soils, subjected to a one-dimensional freeze-thaw cycle, is investigated to determine how the frost action varies with soil types. Soil specimens were subjected to ten freeze-thaw cycles. Total heaving, heave rate, and water intake were measured as a function of time during testing. The moisture content of the soils after ten freeze-thaw cycles was also measured. The amount of pore water and external water supply affects the total heave during freeze-thaw cycles. Therefore, the effect of moisture availability during the freeze-thaw cycles was also investigated by comparing the results of specimens with or without an external water supply. Results of the study suggested that significant frost heave occurred in both clay and sandy soils. In addition, the application of ten freeze-thaw cycles provided a better estimation of the total heave than that observed with two freeze-thaw cycles (typical/standard numbers of freeze-thaw cycles). The maximum heave (40.9 mm) and heave rate (5.01 mm/day) were found to be higher in clay soil. The presence of an external water supply contributed to the frost action, and total heave was seven times higher in soils with an external water source. Soil with a free water supply showed 1.1–1.7 times higher moisture content after ten cycles compared to the soils with no external water supply. These results were used in estimating the frost heave potential of soils in different environmental conditions.

Triaxial testing has been routinely used as a standard laboratory test that allows correct determination of soil characteristics. Previously the volumetric strain of the triaxial specimen was considered to be uniformly distributed along with the specimen during the isotropic and deviatoric loading. Although this assumption might hold true under isotropic loading, the effects of restrained ends and disturbance during the procedures of specimen installation and testing can cause nonuniform strains throughout the whole specimen. This paper investigates the effects of specimen preparation and misalignment on the strain uniformity along with the soil specimen during triaxial testing. A series of consolidated drained tests at several stress paths were conducted on sand specimens. A photogrammetry-based method was applied at different stages of specimen preparation and testing to provide a three-dimensional full-field deformation measurement of the surface of the triaxial soil specimen. One commercial camera was used to capture images for the triaxial specimen, and a developed application for data processing and post-processing was utilized to ensure automatic and fast processing of the developed photogrammetric-based method. The local displacement data provided by the photogrammetry-based method enabled the evaluation of the strain localization and the volumetric strain nonuniformity analysis at different heights along with the specimen. The triaxial test results demonstrated that the soil specimen during triaxial testing has deformed nonuniformly in the axial, radial, and circumferential directions. The plots of the strain localization precisely presented the variation of local strains and the magnitude of deformation after the saturation stage. These results prove the soil specimen volume is not constant during saturation, and unavoidable disturbance had occurred during the specimen preparation steps and saturation. The results proved that the specimen misalignment during triaxial testing leads to scattering in the triaxial test results. Further discussion was presented about the shear band characterization including shear band thickness, formation, and propagation.

The small-strain behavior and effects of stress path rotation angle of Hawthorn Group (HG) sands in Central Florida are examined in this paper. A series of directional-stress-probe tests were conducted on high-quality HG sand samples extracted from the deep foundation test site (DFTS) at the University of Central Florida (UCF). The small-strain response was studied under undrained and drained triaxial conditions following compression and extension stress paths using internal instrumentation, bender elements (BE), and Hall effect (HE) displacement transducers. For the entire testing program, the stress history of the material was reproduced during the reconsolidation stage in order to isolate the effects of stress path rotation angle. The discussion is centered on the small-strain behavior with emphasis on shear, bulk, and cross-coupling moduli degradation. The results showed that the small-strain stiffness behavior of this material is affected by the stress path rotation angle.

Calcareous sands have different engineering properties than clays and silica sands due to their high particle angularity and in situ void ratios. The characteristics and stress-strain response of calcareous sands are necessary for the design and long-term maintenance of offshore infrastructure, such as piers, bridges, and offshore renewable energy systems. The monotonic stress-strain response of calcareous sands from Ledge Point Australia is examined in this study, as well as the effect of increasing particle damage and crushing severity on loading behavior. The calcareous specimens were crushed by both consolidation and shearing methods to obtain varying amounts of crushed material. Results indicated that as the content of particle breakage in the sample matrix increased, the crushed sands contracted less and exhibited a stronger dilative behavior during shearing. However, the highest shear strength was obtained by the sample with relative particle breakage (Br) of 0.05, rather than the sample with the highest crushing content.

Increased industrialization, urbanization, and economic growth of developing countries like India have demanded more energy requirements. Currently, thermal power plants are the dominating power generation sources. Accordingly, coal ash management has become a huge challenge in India and globally. Mass utilization of coal ash is possible in geotechnical applications and hence requires a proper understanding of its elastic parameters such as Young's modulus, shear modulus, and bulk modulus. The present study investigated the effect of sample preparation, initial void ratio, confining pressure, and S and P wave travel time measurement on the elastic parameters of coal ash using bender element tests. Additionally, power models for the maximum shear modulus (G_max) and maximum Young’s modulus (E_max) were developed, and the fitting constants, A and n, for the relationship were evaluated. These relationships are useful as input parameters in static and seismic analysis of various geotechnical structures constructed with coal ash.

This study aims to assess the impact of freezing-thawing cycles on the preconsolidation pressure of saturated clays. The effect of elevated temperatures and the impact of freezing on the preconsolidation pressure of clays have been investigated. However, there still exists a lack of understanding about how one extreme temperature, such as freezing, impacts the preconsolidation pressure on the other extreme, such as an elevated temperature. In this paper, a modified temperature-controlled odometer is utilized to determine temperature effects on the preconsolidation pressure. One-dimensional consolidation is first performed on two kaolinite clay specimens, one at room temperature (20°C) and the other at an elevated temperature of 40°C. Moreover, another specimen is exposed to a temperature cycle of 20°C to –15° and to 40°C. Then, the specimen is again incrementally consolidated at 40°C. The preconsolidation pressure for each specimen is estimated using the strain energy. We then assess the impact of the freezing temperature applied to the last specimen on the preconsolidation pressure by comparing the pressure between the three considered specimens. The results suggest that the sample experiencing a freezing temperature prior to a heating stage shows a higher preconsolidation pressure.

This paper describes a simple approach to modify a direct shear test device to perform interface shear tests under constant normal stiffness (CNS) conditions. There is continued interest in the use of piles and pile anchors for both fixed and floating offshore wind structures, particularly in the sandy soils along the East Coast of the United States. Design analyses and modeling may require CNS testing, which closely represents the boundary conditions near the interface of the pile during axial monotonic and cyclic loading. The simple and economical modifications allow for the testing of any pile material-sand interface by mechanically maintaining constant normal stiffness conditions on the sample during shear.

The goal of this paper is to determine the accuracy of US frost depth maps used to determine the foundation depth in cold regions. Estimating the frost depth continues to represent a challenging task to engineers, specifically in cold regions. Frost depth and heave put significant risks on several infrastructure including highways, runways, pipelines, and buildings. It is, therefore, recommended to locate the foundation depth of this critical infrastructure below the expected frost depth at any given location. In the United States, predictions of the frost depth for foundation design have been performed using maps that were developed decades ago prior to the significant climate changes we experience nowadays. In this study, we will revisit these maps with the sole aim of assessing their accuracy considering recent weather trends. We employ existing semi-empirical and fully empirical predictive models to estimate the frost depth at different US locations using recent weather data. These models estimate the frost depth based on correlations between frost depth and the cumulative freezing degree day (CFDD); in this study, the latter is estimated using recent weather data. We then assess the accuracy of existing frost depth maps by comparing the predicted frost depth for the selected locations to those estimated from existing maps. The results of the analysis show that frost depth is a function of meteorological parameters and soil’s dry density and water content. We also conclude that the existing contour maps overestimate the freezing depth when compared to the values predicted by the modified Berggren formula as a representative of semi-empirical equations widely employed to calculate frost depth.

This study investigates the effect of the percentage (f) of finer particles on thermal and electrical properties of binary soil mixtures via well-controlled laboratory tests. Binary mixtures of a fine silica sand (Ottawa F-55 sand) and a medium-coarse sand (ASTM 20/30 sand) were deposited at eight different mixing ratios in a custom-built soil box via air pluviation. After deposition, a thermal needle was inserted into the dry mixture sample to measure thermal conductivity. The thermal needle was then removed, and the mixture sample was saturated with a 0.1% NaCl solution. After completion of the saturation process, electrical resistivity and thermal conductivity of the saturated mixture sample were measured using a Nilsson meter and a thermal needle, respectively. Results from a series of laboratory tests showed that the void ratios of the binary soil mixtures initially decreased with the increasing percentage of finer particles and achieved the densest condition at f = 30%, but further increase in f led to an increase of void ratio. Both thermal conductivity and electrical resistivity increased as f increased, peaked at about f = 30%–50%, and then decreased. Also, the thermal conductivity in the saturated condition was about 8.3 times that in the dry condition.

This study aims to assess temperature effects on the residual shear strength of soft clays. Seasonal variation in temperature changes the engineering properties of soils. Temperature fluctuation seasonally induces the destabilization of the ground near the surface and causes geotechnical hazards such as thermally induced landslides. Therefore, in this study, a modified temperature-controlled ring shear apparatus is used to change the temperature of clays and evaluate the effect of the temperature on the residual shear strength. For this purpose, two clays with two different mineralogies are selected and then residual shear strengths are measured at room temperature (i.e., 20°C), 10°C, as well as at elevated temperatures of 30°C and 40°C. The results for each of the considered clays at different temperatures are compared to assess the temperature effects on the residual shear strength of soils. The results show a negligible impact of temperature on the residual shear strength of Illite and Montmorillonite clay mixture (Rhassoul clay). However, the residual shear strength of Kaolinite clay increases with either heating or cooling. Although more investigation is required, the evolution of residual shear strength with temperature is potentially dependent on the clay mineralogy.

This paper presents an experimental investigation related to the effect of freezing-thawing (F-T) cycles on the volumetric behavior of soils, with particular focus on the impact of the range of freezing temperatures on soils’ response impact. A reconstituted specimen made up from a commercial silt was subjected to F-T cycles in an 1D cell manufactured in a 3D-printer. The soil specimen was fully saturated, and the test was conducted under open system conditions inside an environmental chamber. Volume changes were recorded using a linear variable differential transformer (LVDT) during cyclic F-T. The test results show that the impact of the range of the freezing temperature is only relevant in the higher range of freezing temperatures (i.e., near the freezing point), and it tends to reduce significantly as the minimum temperature reduces. The study also shows that stress-history of the soil has a significant influence on the volumetric behavior soils subjected to F-T cycles.

Crushed rock is a common granular material in civil engineering, mining, and railway applications. Numerous prior studies have shown that design-scale mechanical behavior strongly depends on the morphological features of the particles. In this study an efficient technique to import realistic particle geometries into DEM simulations of bulk granular materials is provided. First, a suite of 300 synthetic 3D particle geometries (referred to as particle avatars) of varying sizes and shapes is prepared using a computational physics engine. Second, relationships between widely used 2D and 3D shape descriptors are obtained for the particle avatars. From the 2D-3D shape relationships it is observed that the true sphericity (3D) is well correlated with perimeter sphericity (2D). Therefore, some 3D shape features can be reasonably estimated from 2D digital images of grains. Finally, DEM simulations are carried out to investigate angle of repose for several clump geometries. The bubble pack technique was used to create pebble clumps with varied numbers of pebbles. Results show that the repose angle is more strongly dependent on the shape of the created clump (collection of pebbles) than by the shape features of the original particle geometry. This research shows that the shape features of the clumps used in simulations affect the results, regardless of the procedures used to get 3D geometries of particles.

This study investigates the mechanical behavior of biogenic carbonate sands from Puerto Rico at grain-scale level. Micro-computed tomography has also been used to get insights on the internal structure of these particles before and after loading. The crushing strength of these particles are smaller comparing to the values reported for silica sands. It has also been shown that these particles have complex internal structure including a network of pores connected with channels. This study also demonstrates the effect of intragrain structure of biogenic carbonate sands and shows how internal grain structure plays a role on particle fracture.

Consolidation testing is an essential part of geotechnical testing, particularly for settlement analyses and staged construction. Two of the most common tests are incremental loading and constant rate of strain tests. Incremental loading tests hold a particular load over a 24-h duration, typically taking about a week to run, providing limited stress-strain data points, and measures secondary compression characteristics. Constant rate of strain tests holds the rate of strain constant throughout the test, can take about two to three days to run depending on the strain rate, provides a near continuous stress-strain diagram, and limited measurements of secondary compression. This paper presents an alternative to these consolidation testing methods. First proposed in the early 1980s, the constant pressure ratio consolidation test varies the strain rate to maintain the ratio of excess pore pressure to total stress constant throughout the test. To maintain this ratio, a computer is required to loop the strain rate to hold the ratio of the excess pore pressure to total stress to the desired level. An experimental program consisting of 16 re-sedimented Boston blue clay compared the results of the three consolidation test methods. The experimental program also examined conditions unique to the constant pressure ratio method, namely the update time interval. The results for the constant pressure ratio test indicate the test finishes within hours, often taking more time to set up and saturate the sample up than to run the test. The constant pressure ratio test provides similar a near continuous stress-strain and similar coefficients of consolidation across the three tests. The constant pressure ratio test provides limited measurements of secondary compression, like the constant rate of strain test. The update time interval tells the software how often to loop and update the strain rate to maintain the pressure ratio. This paper demonstrates that the constant pressure ratio consolidation test provides results faster than the two common consolidation tests, while providing similar results to both tests.

This paper presents nonlinear dynamic analyses (NDAs) of the 1988 Saint Adelphe landslide using FLAC 8.1 with the user defined constitutive models PM4Silt and PM4Sand. The analyses utilized previously characterized and developed laboratory and field data, ground motions, and site conditions. A method was introduced for modeling large sensitivities and high peak strengths using the PM4Silt constitutive model. Calibration of the constitutive model and NDAs of the landslide are presented. The results of the analyses indicate that the numerical methods used could reasonably approximate the observed failure. The results also highlighted the need for the development of models which can directly account for high peak undrained strength ratios and large strength loss in analyses. The implications of these results on practice are discussed.