Geo-Congress 2023: Geotechnical Systems from Pore-Scale to City-Scale

Relief wells are commonly used to reduce the pore water pressure on the river-side of levees which will eventually reduce the risk of levees and embankments failure. Two-dimensional slope stability analyses, which are commonly used, tend to smear the three-dimensional relief well water influence. Two-dimensional (2D) analyses assume that relief wells have infinite length normal to the 2D plane of the model. Three-dimensional (3D) analysis more accurately captures the seepage flow around the relief wells and considers the spacing effects of these wells on the overall groundwater analysis. This study considers a full 2D and 3D steady state finite element seepage analyses of a typical levee with different relief well setups. The pore water pressure distributions of these cases were used for 2D and 3D limit equilibrium analyses to find the slope factor of safety and probability of failure. A full comparison of the effect of relief wells is presented for the 2D and 3D models for cases with and without relief wells.

On March 9, 2018, south of the town of Orange in Central West New South Wales, Australia, the tailings dam at the Northern Tailings Storage Facility (NTSF) of Cadia Valley failed. At the time of failure, buttresses were being constructed on the downstream slope of the dam to increase the factor of safety. The upper buttress, towards the crest, was completed in March 2018 while an excavation at the toe to remove accumulated tailings was left open from January 2018 until failure. The cause of the failure was determined to be a low-density or weak zone in the Forest Reef Volcanics (FRV) unit-A that was exposed in the toe excavation. The FRV unit-A is a highly weathered, relatively weak, compressible, and strain weakening volcaniclastic material that underlies parts of the NTSF dam. Using values of Atterberg limits for the FRV unit-A from the failure area, peak, fully softened, and residual shear strength envelopes were estimated using existing empirical correlations. The estimated stress-dependent strength envelopes were then used in an inverse 2D limit equilibrium analysis to evaluate the mobilized strength of the FRV unit-A. The mobilized strength envelope was then compared to the shear strength models used in the design limit equilibrium analysis for the NTSF dam. This comparison shows that correlations yielded a reasonable fully softened strength envelope for the FRV unit-A that could have been used for the design of the subject slope. This could have prevented the over-estimate of the factor of safety using the design strength models because of the potential for softening during the toe excavation. A similar analysis should be conducted for future projects to evaluate tailings dam foundation stability.

Load distribution in an embankment built over a soft foundation soil has always been a concern for engineers. Sharing the load with another load-bearing system will aid in improving the overall load distribution. The objective of this study is to monitor the mid-term performance of Recycled Plastic Pins (RPP) in load transfer behavior for an embankment. For this study, two field sections were constructed. One section was reinforced with RPPs having a cross-section of 15 cm × 15 cm and a length of 3 m, and the other section was left unreinforced, termed as the control section. For transmitting the load from the embankment to the RPPs, a load transfer platform (LTP) of geogrid and recycled crushed concrete aggregate (RCCA) was placed above the RPPs. The field sections were instrumented with inclinometers, piezometers, and pressure plates. The field data for the settlement, pore water pressure, and pressure variation on RPP and adjacent soil were collected and monitored for more than three years. A 2.4 m embankment height was applied which was constructed in three phases. The maximum settlement was found to be 35 mm in the reinforced section whereas in the control section it was significantly higher (73 mm). The dissipation of excess pore water pressure was found faster in the control section compared to the reinforced section resulting in more consolidation settlement in the control section. Based on the pressure plate data, RPPs carried about 14 times more load than the adjacent foundation soil in between RPPs. The higher value of load sharing implies that RPPs act as an effective system in distributing embankment load to the stronger soil strata. The use of recycled plastic pins over soft soil, thus, can be considered as a viable approach for ground improvement.

An analytical method is commonly used to design relief well systems by assuming the well line extends an infinite distance parallel to the dam or levee. This assumption may be met in some cases, but when a well line is of finite length, this can severely underestimate excess heads. Although these consequences have been historically recognized, a practical graph-based analytical approach for finite well line design has not been developed. Finite well lines exist and continue to be installed at many locations, so this study developed a practical design method for such systems. Analytical solutions and numerical models were used to improve understanding of the performance of partial and full penetration finite well systems. Performance was found to be dependent on well system geometry, the ratios of effective seepage entry and exit distances to well spacing, and the number of wells. Model results were used to develop new uplift factors that more accurately define excess heads along and landward of finite well systems that fully or partially penetrate the aquifer.

Sluiced Coal Combustion Residual (CCR) materials have inherent vulnerabilities due to their tendency to have low unit weights and their state of deposition, and they can potentially exhibit highly contractive or dilative behavior during shearing. Flow failure and slope instability of surrounding dikes (typically built with CCRs or clays) due to dewatering are typically considered as potential failure modes (PFMs). The objective of this paper is to review the undrained behavior of CCR material during shearing due to dewatering, evaluate the potential consequences of dewatering (i.e., removal of free water) existing facilities, and provide general recommendations to mitigate PFMs associated with dewatering activities. Changes in shear stresses and strains, pore water pressure, and slope stability are evaluated for a representative containment dike as a result of dewatering activities. For the slope evaluated, the results show that the variation in shear stresses and pore water pressures due to dewatering are expected to be small and, therefore, the expected influence on the stability of the slopes to be small. However, known incidents of instability at CCR impoundments with gentle slopes have occurred across the industry and warrants careful examination of the loading mechanisms and material behavior during loading. Based upon this evaluation, this paper includes specific recommendations to reduce risks during construction dewatering.

Field compaction control is arguably the most common yet critical quality control procedure in geotechnical engineering. Since the early 1930s, the Proctor-based process for performing quality control of compacted soils has consisted of comparing the in-place dry unit weight (or density) and in-place moisture content of the soil with a laboratory reference. However, the current practice overlooks several facts that stand out by comparing compacted soil prepared in the laboratory versus compacted soil placed in the field. These issues mainly stem from overlooking the differences in the compaction energy in the lab versus what is applied in the field, and the unsaturated nature of compacted soil in assessing compaction performance. To address some of these issues, a new saturation-based framework for compaction quality control is compared to the traditional Proctor-based with the goal of providing practicing engineers with further insight into the key engineering attributes of compacted soils. The proposed saturation-based system builds upon advances in unsaturated soil mechanics and recent studies that relate normalized dry unit weight of the as-compacted soils that can significantly reduce the variation of laboratory-prepared reference specimens. The presented comparison is developed with the same field and laboratory data collected in most earth fill projects. For illustration purposes, the saturation-based framework is applied to a case history of compaction control data for an earth dam and compared to the conventional method.

To evaluate the seismic response in high-profile tailings storage facilities (TSF), Nonlinear Deformation Analyses (NDAs) using advanced constitutive models are typically performed. To date, however, few of these advanced models have been validated against field conditions during significant earthquakes. NDAs were used to simulate a well-documented case history response of a 160 ft height TSF during a moment magnitude (M_w) 5.7 earthquake with recorded peak ground accelerations (PGA) of 0.12–0.35 g around the TSF, a recorded PGA of 0.25 g on the TSF. First, estimates of input ground motions at depth were obtained, along with validation of nonlinear procedures, through a suite of 1D equivalent linear and nonlinear deformation analyses using the GQ/H model in DEEPSOIL. Second, 2D fully coupled NDAs in FLAC using the PM4Sand and PM4Silt effective stress, critical state compatible, bounding surface plasticity models to evaluate the 2D system dynamic response at a critical TSF section. Fully coupled NDAs provided reasonable ranges of acceleration response, displacements, and pore water pressure generation in the tailings impoundment that were consistent with field observations. The results demonstrate the benefits of nonlinear models for evaluating the seismic performance of dams during earthquakes.

The onset of static liquefaction in anisotropically consolidated soils is of relevance in assessing the performance of geotechnical systems. Previous studies have also highlighted the role of inherent soil fabric. This study derives an analytical instability criterion for granular materials under undrained loading by using the relatively new anisotropic critical state theory (ACST). The criterion is established using the SANISAND-F model, and it is amenable to incorporating consolidation anisotropy and fabric effects. We assess different numerical strategies for simulating the instability onset on materials sheared from initially anisotropic conditions. Our assessments indicate that simulations that consider consolidation followed by shear better represent the response observed in laboratory tests. It is observed that the degree of anisotropic consolidation has no significant effect on the instability stress ratio, but a very high degree of anisotropic consolidation results in a spontaneous collapse. It is also observed that the anisotropic consolidated specimens have a higher instability stress ratio in triaxial compression than in triaxial extension, highlighting the effect of loading direction relative to the existing fabric.

According to the National Centers for Environmental Information (NCEI), the US was impacted by 20 separate billion-dollar disasters in 2021, including inland floods, severe storms, and tropical cyclones. Shallow landslides are common on earthen infrastructure that contains high plasticity clay due to its swelling nature, particularly when exposed to moisture during extreme weather events. As severe weather becomes more common due to climate change, levee slopes are further compromised. Vetiver grass implanted as a bio-inspired slope stabilization method in levees built using marginal soils, such as Yazoo clay in Mississippi, provides an economically and environmentally sustainable solution. Vetiver has deep grassroots that can exceed 10 ft (3 m) in depth; this makes it ideal for water conservation and stormwater management. The current paper presents a 40 ft (12.2 m) × 30 ft (9.1 m) study area of a test levee slope improved using vetiver grass. A finite element (FE) seepage analyses and limit equilibrium stability analysis considered the effect of seepage, flooding, and rainfall on the stability of a comparable levee design with and without vetiver implantation. This research demonstrates that planting vetiver in Yazoo and loess clays is feasible and can improve the stability of the levee. With increased probability of extreme weather, vetiver’s use on levees holds promise as a climate-resilient solution.

Nonlinear dynamic finite element simulations are used to study field case histories of Japanese levees shaken by past earthquakes. The Ministry of Land, Infrastructure, Transport, and Tourism (MLIT) in Japan instrumented various levees with ground motion sensors, and in one case a piezometer, and inspected the levees for damage following a series of earthquakes for which recordings are available. In this study, these levees are analyzed using finite element simulations in OpenSees using constitutive models capable of capturing liquefaction effects combined with an element formulation that models groundwater flow. Measured and predicted responses are compared, including (1) the pseudo acceleration response spectrum for the horizontal motion of the levee crest, (2) pore pressures in a sand layer that exhibited liquefaction, and (3) permanent levee crest settlement. Small-strain levee response was first calibrated using the recorded response from earthquakes with small amplitude. We then moved forward with analysis of larger ground motions. Predictions of crest settlement agree reasonably well with observations, with significant damage predicted correctly. However, settlements larger than 1 cm are predicted for a number of motions for which no damage was reported. It is unclear whether these are over-predictions, or whether settlements larger than 1 cm may have gone undetected in post-earthquake inspections. This study provides validation that nonlinear effective stress analyses are capable of predicting levee deformations due to soil liquefaction, and may therefore play an important role in future assessments of the seismic response of levee systems.

Highway embankments built with expansive soils often undergo shallow slope failure due to permanent deterioration of soil’s hydromechanical properties owing to its shrink-swell behavior. The alternate wetting and drying cycles result in the development of desiccation cracks, increase in water infiltration, and subsequent reduction in shear strength. This study provides an overview of the forensic analysis of the rehabilitation work performed on a failed highway embankment near North Texas. The rehabilitation of the embankment was performed by considering the detrimental effects of wet–dry cycles, and perched water table in the slope during rainfall events. The surficial layer was treated with lime and a subsurface drainage system was installed during the rehabilitation. A post-rehabilitation data-monitoring framework was developed and comprehensive analyses are presented to validate the effectiveness of treatment considering the temporal deformation and moisture content. Vertical deformation was monitored using Terrestrial LiDAR Scanners (TLS) and total station. Temporal deformation data showed marginal vertical deformation of embankment and the overlying pavement. Moisture sensor data illustrated minimal changes in volumetric water content of the treated layer, below the treated layer, and of the native soil. The deformation and moisture results align well with the expected performance and validate the efficacy of the surficial lime treatment with a drainage system for a long-term durable performance of the rehabilitated embankment.

Lightweight aggregate has a low self-weight and a high friction angle; therefore, it has great potential to be used in column-supported embankments to reduce loads over soft soils. However, the effect of lightweight fill on load transfer, especially soil arching in the load transfer mechanism, is not well investigated. This study performed numerical simulations using the Discrete Element Method (DEM) to investigate the soil arching evolution of lightweight aggregates in column-supported embankments simulated by two-dimensional (2D) trapdoor tests considering different densities. The micromechanical parameters were calibrated using the repose angle tests of lightweight aggregates. The gravity deposit method was used to obtain a dense assembly of the embankment fill and the settlement of soft subsoil was simulated by the downward movement of a trapdoor. The fill deformation was analyzed and the stress acting on the trapdoor and its corresponding soil arching ratio were calculated. Numerical results showed that the lightweight fill had smaller deformations than a normal-weight fill. In addition, the lightweight fill resulted in lower vertical stresses acting on the trapdoor and soil arching ratios as compared with the normal-weight fill. This study demonstrates the lightweight aggregate had favorable performance in 2D numerical simulations of trapdoor tests.

This case study describes the results of a monitoring program conducted during the construction of a preload and final levee tie-in embankment in Terrebonne Parish, Louisiana. The overall project included a floodgate, floodwall, and a levee embankment tie-in situated within the Louisiana Gulf Coastal Plain. Site exploration revealed thick deposits of very soft clay with layers of organic clay and peats. In general, near surface soils were very soft and compressible. Due to subsurface conditions, achieving sufficient settlement during the construction of the tie-in through a ground improvement program was essential to reduce the negative impact of drag settlement on structural features installed at the end of the preload. Geotechnical instrumentation of the levee tie-in comprised of settlement plates, settlement gauges, magnet extensometers, and piezometers. The monitoring program was conducted to assess rates and magnitudes of settlement for the levee tie-in and effectiveness of the prefabricated vertical drains (PVDs). Piezometric data was used to monitor pore water pressure response to the addition of fill and the dissipation of pore water pressure in the months after fill placement. This study presents the results of the instrumentation and monitoring program as well as key lessons learned.

The whole behavioral spectrum of jointed rock slopes should be investigated to analyze the stability and post-failure state of these geostructures that host a variety of civil infrastructure. This study aims at understanding the mechanical behavior of jointed rock slopes, which emerges from the interaction between the newly generated fractures and the complex network of pre-existing fractures. We use a hybrid finite-discrete element method to analyze the failure and post-failure states of several jointed rock slope models with different joint patterns. The initial failure is triggered by a strength reduction mechanism. This method of analysis can indicate the failure mechanism and other important parameters for the analysis and design of sustainable and resilient infrastructure surrounding the slopes. These important parameters include, for example, the runout distance and volume, and the kinetic energy of the failed materials. The results show that jointed rock geostructures do not have a single factor of safety. This is because the contributions of the rock matrix and discrete fracture network in the failure mechanism and extent of these structures are different and depend on their initial and evolving properties with the given environmental perturbations.

In 2018, the Caisse de Dépôt et Placement du Québec (CDPQ) awarded a $6.3 billion design-build contract to the Joint Venture (JV) team NouvLR for the design and construction of a 67-km light rail system called the REM in Montreal, which will be one of the largest automated transportation systems in the world. The complexity of the project posed unique geotechnical challenges on many levels. Part of the alignment was constructed over peatland where low bearing capacity and excessive settlement obstacles needed to be overcome. Many small and large diameter utilities, running in the vicinity of proposed embankments, required the design of a protection system by mean of column supported embankment. Part of the alignment was to be constructed over an old landfill where the subsurface investigation indicated up to 9 m of solid waste. Presence of over 10 m of soft to firm silty clay required ground improvement using semi-rigid inclusions (such as Controlled Modulus Columns) to minimize settlement. Numerous segments along the project alignment were found to be underlain by potentially liquefiable soils where laboratory cyclic direct simple shear (DSS) tests were performed to assess liquefaction potential. Furthermore, over 25 km were constructed on 650-span elevated structure founded on single drilled shafts socketed into rock. To optimize the shaft design, three full-scale, bidirectional (Osterberg Cell) static load tests and two fully instrumented lateral load tests in critical areas were performed. The paper discusses the static load tests results as well as the different issues and concerns raised during the geotechnical design and how these were addressed.

A commonly used composite pile is a precast, prestressed concrete pile with an H-pile stinger, which consists of a lower section of steel H-pile embedded in an upper pile section of precast, prestressed concrete. During the construction of Fireboat Station No. 15 Project at the Port of Long Beach (POLB), driven concrete-steel composite piles were used to penetrate surficial obstructions at the toe of an existing rock dike, and concrete piles were used at the area further away from the dike. Driving behavior and performance of those two pile types were observed and compared at locations, where similar subsurface conditions presented. Dynamic pile tests, using Pile Driving Analyzer (PDA), were performed to evaluate soil resistance, pile driving stresses, and hammer performance. Case Pile Wave Analysis Program (CAPWAP) analysis was performed to evaluate pile capacity and soil resistance distributions. Matching wave equation results to field observations and PDA measurements were performed with the specific parameters of the hammer, driving system, soil model, and pile types using Refined Wave Equation (GRLWEAP) Analysis. Based on the matching data, the pile driving behaviors for the two different toe conditions were simulated and compared with the field observation. This paper demonstrates the site conditions, construction methods, load test results, driving performance, and comparison with or without steel H-pile stingers in design and construction perspectives. It demonstrates that using H-pile stingers at the lower section of a precast concrete pile helps increase pile driving efficiency, reduce pile stresses during driving, maintains similar ultimate capacity, and results in cost savings.

This paper presents a method to estimate tunneling-induced ground movements by connecting the earth pressure balance tunnel boring machine (EPBM) operation data to the ground monitoring data. The proposed method requires no prior assumptions, such as the ground loss and the geologic parameters. This study was conducted using a data set from the State Route 99 (SR99) tunnel project in Seattle, WA. The prediction models were developed using (1) ordinary least squares (OLS) as a parametric linear regression method; and (2) random forests (RF) as a nonparametric nonlinear machine learning method. Segmentation and feature importance analyses were carried out to investigate the influence of EPBM features on the induced ground movements in different ground-machine interaction mechanisms. This study shows that various tunneling-induced ground responses can be estimated solely based on the EPBM feature data and the tunnel spatial geometries. The segmentation and feature importance analyses reveal that each ground response segment has different governing parameters. Features related to the steering and pressure controls appear to influence the induced ground movements during the EPBM passing strongly. These features are not typically considered in conventional tunneling-induced ground movement prediction methods.

The County of Los Angeles is implementing several green infrastructure projects within public roadways. The primary objective of these projects is to capture and infiltrate the stormwater by diverting flows out of the existing storm drains and/or capturing surface flows before entering the storm drain system. Green infrastructure proposed typically consists of a series of large diameter drywells that store and infiltrate stormwater runoff and provide groundwater recharge. As part of the designs, geotechnical evaluations of the subsurface conditions are necessary, including evaluations of depth of groundwater, infiltration characteristics and capacities of the ground, and effect of drywell spacing, etc. The geotechnical engineering aspects are discussed in the paper using the preliminary design of the San Pedro Street Green Improvement Project as a case study. The infiltration capacities were evaluated through drywell infiltration testing. The effect of well spacing was evaluated by numerical modeling that was calibrated by test results; the modeling shows that for a well depth of 38 ft and a well spacing of 100 ft, 96% of well efficiency can be achieved.

The Los Angeles (LA) Metro Purple Line (D-Line) Extension project requires the design and construction of deep station excavations and tunnels for rail transit from downtown to west LA. The tunnel alignment for Reach 2 of the Westside Purple Line Extension 1 construction transects naturally-occurring tar-infused soils, which have been known to cause challenging construction conditions in southern California, as well as many other locations around the world. Two stations in similar geology but located within and outside tar soils were compared. The soil investigations of the tunnels and station excavations consisted of subsurface exploration including deep soil borings, Cone Penetration Testing (CPT), seismic velocity measurements, pressuremeter testing, and gas measurements, among others. The results of CPT and shear-wave velocity testing provide extensive data in tar soils unique to Southern California and an opportunity to increase our understanding of four-phase soil materials and the effects of tar on soil behavior interpretation and engineering properties. CPT correlations for conventional (non-tar-infused) soils were found to be inadequate for tar soils in the Los Angeles basin. The CPT based Soil Behavior Type Index (SBTn) determined in tar soils suggested the presence of much finer-grained material than determined from laboratory testing and field observations. Additionally, the presence of tar soils amplified the difference between CPT correlations for shear wave velocity (V_s) and direct V_s seismic CPT measurements.

The Port of San Diego’s B Street Pier facility (Pier) is the busiest cruise terminal in the City of San Diego with over a hundred ship calls annually (pre-COVID). The Pier is an approximately 9.4-acre bulkhead faced mole extending about 1,000 ft into San Diego Bay and approximately 400 ft wide. On the three offshore sides of the bulkheaded mole are marginal pile supported wharfs constructed in 1923. The upland side of the mole is a concrete gravity seawall constructed in 1900. The mole soils consist of hydraulically placed dredge spoils and are susceptible to liquefaction.The existing Pier containment walls are deemed inadequate for seismic loading, mainly due to the presence of liquefiable materials both in front of and behind the existing containment wall. A solution consisting of an improved Deep Soil Mixing (DSM) zone coupled with the installation of a new steel sheet bulkhead was selected to retrofit and upgrade the Pier to current seismic standards. A key aspect of the design was to minimize loading induced from the wharf onto the existing curtain wall during an earthquake. The DSM zone is intended to serve a triple purpose, that is to improve shear strength of the soils behind the curtain wall, to mitigate the impact of liquefaction, and to provide sufficient bearing for potential future lightly loaded structures which may be constructed on the Pier. To obtain a cost-effective design and limit the DSM zone extents, the design also needed to limit the seismic load contributions to the DSM from the marginal wharves during seismic conditions. A development plan consisting of a multi-phased construction plan was determined to meet the Port’s capital improvement needs and budget. Phase I development will install the DSM zone and steel sheet pile bulkhead along the south and west face of the mole. Future work will include wharf pile and deck replacement along with completing curtain wall replacement along the north face of the mole. This paper presents the geotechnical design challenges and considerations associated with the design of the DSM and sheet pile system comprising Phase I of the development plan. Key aspects of the geotechnical design included the selection of appropriate liquefaction resistance of the DSM improved zone, designing for the lateral spread of the slope in front of the curtain wall, assessment of stability and deformation of the proposed sheet pile, and the determination of the seismic earth pressures.

It has been observed that some organisms such as Erodium seeds, snakes, and sandfish skink can bury themselves in the ground effectively and efficiently. These self-burial behaviors are achieved by one or multiple modes of locomotion including rotation, twisting, and undulation of an asymmetric body. To better understand the fundamental mechanism of these biological burrowing strategies, a series of upward and downward rotational penetration tests were conducted to evaluate the effects of rotational motion, asymmetric shape, and different properties of granular media on the penetration resistance using a robotic arm and 3D printed motorized penetrators. The results confirm that the downward penetration force decreases with the increase of rotational speed and that it further decreases if the penetrator is of a helical shape, highlighting the effects of asymmetric kinematics. It can be concluded that the penetration resistance of a helical penetrator depends on the rotational direction. For a right-handed helical penetrator, clockwise rotation resulted in significantly lower penetration force than counterclockwise rotation and required lower torque, although both reduced penetration force compared to non-rotational penetration. It was found that by coordinating the motions of the helical body, the penetration forces, and anchorage forces can be tuned to achieve self-burrowing.

This paper presents a computational modeling effort carried out during the construction of an underground cavern to predict the ground and structural deformations. The Regional Connector Transit Corridor (RCTC) project consists of an 89-m long, 17.7-m wide, and 11-m high span crossover cavern constructed beneath critical infrastructure using the sequential excavation method (SEM) at relatively shallow depth (15 m below ground surface) in downtown Los Angeles. The cavern construction involved a complex three-drift, two-sidewall configuration and was excavated in the Fernando formation, a weak clayey siltstone. A 3D finite-difference model was developed to simulate the SEM construction explicitly considering 3D multi-face excavation effects and ground-structure interactions. Due to limited field/lab data available, the estimation of geotechnical parameters to be used in the model contains great uncertainty. During SEM construction, as field measurements were obtained continuously, the uncertain parameters were updated through a progressive back-analysis procedure. The predictions of the ground and structural deformations were updated accordingly. The performance of the analysis is demonstrated by comparing the computational results to the field observations. This provides a deliberate application of the observational method in urban SEM construction by quantifying and updating the knowledge of risk along the entire construction process.

This paper presents a detailed analysis of ground deformation that occurred during earth pressure balance tunnel boring machine (EPBM) construction through cohesive and cohesionless soils in Washington, DC. Settlements of 25 mm were observed during the first 1,000 m of tunneling, whereafter, settlements reduced to nearly 0 mm for the next 1,000 m. EPBM data suggests shield annulus and tailshield grouting as the cause of the settlement. 3D computational model results, using TBM parameters, matched well with observed settlement.

A previous study by the authors showed that the rotational movement of a cylindrical cone penetrator could significantly reduce penetration resistance. The effects of penetrator geometry and penetrator-particle interface friction are studied to shed light on the design of a self-burrowing robot in this study. The penetrator-granular media interactions were investigated at different scales by using the discrete element method. Generally, the penetration force on the cone increases with the penetration depth but decreases with the relative slip velocity (the ratio between the rotational velocity and the vertical velocity, v_r/v). The penetration force on the cone increases in the sequence of square, decagon, and flat-end penetrators under the same conditions due to the cross section areas. Besides, the penetration force on the cone also increases with the interface friction. Force chain network and particle trajectory visualize the rotational effect at particle-scale with different penetrator geometries. Overall, the normalized penetration force on the cone decreases dramatically at first and then gradually with the increase of the relative slip velocity. The normalized penetration force on the cone for flat-end penetrator is higher than that for square and decagon penetrators under same relative slip velocity. The normalized penetration force on the cone decreases further with the increase of the interface friction under the same relative slip velocity.

The Silver Springs State Park in Marion County has played a tremendous role in the development of Central Florida’s national image of beautiful natural resources and unique eco-tourism attractions. However, with an increase in urbanization in the surrounding area, the groundwater emitted from Silver Springs has seen a drastic increase in pollutant concentrations, in turn severely affecting the water quality and ecosystems within the Silver River. A major contributing role for the increase in groundwater pollutants is the increase in sinkhole occurrences within the recharge basin for the springs. Sinkholes essentially provide a “direct connect” to the Floridan aquifer, allowing nutrient-rich surface water to enter the aquifer without any natural filtering or biological degradation processes. This study investigates the influences of subsurface conditions to sinkhole formation within the area surrounding Silver Springs through implementing in situ soil laboratory testing and numerical modeling. Through simulations of various subsurface and hydrogeological conditions, stability hazard charts were developed to estimate the critical subsurface and stormwater conditions leading to a potential sinkhole. This methodology presented will greatly benefit future decision making when designing stormwater management structures (i.e., ponds or roadway swales) to ensure less potential of pollutant groundwater entering the groundwater aquifers-particularly in a sensitive environment such as Silver Spring’s.

Soil classification is a fundamental step prior to any design procedure in every geotechnical project. However, the soil testing required for classification purposes is expensive, time consuming, and resource-intensive; making it difficult to conduct accurate and enough testing on a routine basis. Engineers and researchers have carried out soil testing for many years, leading to the development of a huge dataset. Artificial Intelligence (AI) and Machine Learning (ML) which have become more popular in the civil and geotechnical engineering fields in the past few years provide a great opportunity to use the collected data for the development of evolutionary prediction models. In this paper, machine learning algorithms are used to build a model which can classify the soil using Cone Penetration Testing (CPT) data, focusing on three regions in the US (southeastern, central, and western). Random Forest, Support Vector Machine, K Nearest Neighbors, and Extreme Gradient Boosting algorithms are the four ML approaches used in this study for the prediction of the Soil Behavior Type (SBT) zone classification which is widely used for classifying the soil behavior based on CPT results. The performance of the adopted models is compared using different accuracy metrics and the confusion matrix. In this study, the Random Forest classifier and Extreme Gradient Boosting models are found to perform better in terms of soil prediction and total model training.

Results of experiments involving rapid impact and penetration of projectiles in sand targets are presented. A vertical firing range is used to launch aluminum rods having a diameter of 14.3 mm and a length-to-diameter ratio of 5.3 at an impact velocity of approximately 150 m/s into dry and partially saturated sand targets prepared at precise densities. Very loose and very dense sand targets are prepared by means of dry pluviation. Direct measurements of penetration velocity-time history are obtained using a photon Doppler velocimeter (PDV). The results of the experiments reveal that penetration resistance exhibits two regimes in dense sand, separated by a transition velocity of approximately 45 m/s. Furthermore, it is observed that saturation affects penetration differently at high velocities compared to low velocities. High-velocity penetration of partially saturated dense sand is accompanied by cavitation, which reduces the role of the pore fluid in penetration resistance. At lower velocities, penetration into partially saturated sand produces negative pore water pressures, resulting in an increase in penetration resistance. These observations are used to develop a phenomenological framework for predicting the depth of burial of high-speed projectiles in sand.

“Wiggling,” rotational and oscillatory motions are often adopted by many living organisms to penetrate into or burrow in the soil. For example, seeds of the Erodium cicutarium and Pelargonium can bury themselves into the ground for future germination with a continuous rotational motion. The angled worm lizards (Agamodon anguliceps) make tunnels by oscillating their head along the long axis of the trunk. Our previous numerical simulations indicate that both rotational modes lead to comparable reductions of penetration resistance of a rod with a conical tip. In this study, both modes of rotational penetration were further investigated through laboratory experiments. The penetrator consists of a cylindrical shaft and a conical tip with an apex angle of 60°. A gear motor is integrated into the penetrator for rotational motion control: both continuous rotation and oscillatory rotation can be achieved. The penetrator assembly is connected to a six-axis robotic arm, which controls the vertical penetration and collects the force/displacement data. A series of rotational penetration tests were conducted in Ottawa sand F65 with different combinations of vertical and rotational velocities while the resultant velocity was kept as a constant. Different oscillation amplitudes were used under the same rotational velocity for the oscillatory rotational penetration cases. The results confirmed the conclusions drawn from the numerical simulations: for both rotational penetration modes, the rotational penetration forces decrease with the relative slip velocity (ratio between the rotational and vertical velocity); comparing with the non-rotational case, the reduction of penetration force is about 80% for the whole-body-continuous-rotation (WCR) case and 60% for the cone-continuous-rotation (CCR) and cone-oscillatory-rotation (COR) when the relative slip velocity reaches 20. Under the tested conditions, the penetration forces were not affected by the oscillation amplitudes. Comparing with continuous rotational penetration, oscillatory penetration achieved less reduction of penetration force, but it is easier to be implemented in cone penetration tests or self-burrowing robots.

This paper presents the effect of soil-structure interaction on tall buildings’ design and straining actions. This investigation was carried out by analyzing a multi-story building via a direct approach using a 3D finite element model for the soils and the structure. The results are compared with traditional sub-structuring methods that use linear subgrade reaction springs to represent the soil. The results are also compared with the less common sub-structuring approach that adopts nonlinear springs to represent the soil-structure interaction. Two parametric analyses are performed under gravity loads considering different soil characteristics. The effects of soil-structure interaction and the induced differential settlement are presented for various loading conditions and straining actions on the structure-supporting elements. The conclusions include the limitations and advantages of the common sub-structuring approach and the effects of soil non-linearity on the behavior and design of tall buildings.

In situ stabilisation of existing pavement materials is a valuable rehabilitation treatment for secondary and local roads that are generally comprised of a gravel base course with a thin bituminous surface. However, sometimes the required stabilisation depth exceeds the existing base course thickness, meaning some portion of the underlying subgrade is incorporated into the stabilised material. The aim of this research was to determine the effect of subgrade inclusion on the unconfined compression strength (UCS) of the stabilisation material, as an indicator of the performance of stabilised base course and subgrade blends. It was found that three different subgrades, each at 20%–50% of the total granular material, achieved acceptable UCS values with 3%–7% of a triple-blend cementitious binder. Furthermore, it was found that pre-mixing of the hydrated lime component into the granular material was more beneficial when reactive clay subgrades were encountered. In the future, in situ cementitious stabilisation of combined base and subgrade materials (referred to as ‘basegrade stabilisation’) should not be resisted, as long as the associated UCS values are generally in the acceptable range of 1–2 MPa.

Foamed bitumen stabilisation is a valuable technology that allows standard, as well as marginal (or non-standard) materials to be significantly improved by incorporating a relatively low (2%–4%) content of bitumen and a lower (1%–2%) content of a cementitious binder. The mixing/compacting moisture content is critical to the workability and compaction of these materials during construction, with most materials being compacted at approximately 70% of the optimum moisture content associated with the unstabilised granular material. However, some marginal materials have a higher portion of fine particles, greater plasticity, and higher reactivity to moisture, and these often require additional mixing/compaction moisture. One standard granular material and three typical marginal materials were stabilised with foamed bitumen at mixing moisture contents set to 70% and 85% of the granular material optimums. After standard laboratory production, compaction, and curing, specimens were tested for modulus and for tensile strength. For the most marginal granular materials, the visual tightness and uniformity of the samples was clearly improved by the additional mixing moisture, and both the modulus and tensile strengths increased significantly. In contrast, for the standard granular material, the increased mixing moisture adversely effected both the modulus and tensile strength. It was concluded that when marginal materials are being stabilised with foamed bitumen, a workability trial should be performed to ensure the mixing moisture content is set appropriately. Otherwise, the standard 70% of granular optimum rule will likely create an unworkable material in the field.

This paper presents novel solutions for increasing the stability and resiliency of track structures by developing a synthetic energy-absorbing layer (SEAL) using recycled rubber products based on large-scale laboratory tests (i.e., drop-hammer impact tests and cubic triaxial tests). This includes (1) installing recycled rubber mats under ballast, and (2) using SEAL composed of a mixture of rubber crumbs, steel furnace slag, and coal wash with changing amounts of rubber: 0%, 10%, 20%, 30%, and 40% (by weight) to replace traditional rockfill as subballast. The test results confirm that the inclusion of a recycled rubber mat underneath the ballast layer actively reduces ballast deformation and the propagation of impact loading within the depth of the substructure. Also, the SEAL mixture with 10% rubber reduces the track lateral dilation, reduces ballast breakage and load distribution, and also maintains an acceptable settlement.

This is a case history of the design and construction of a geogrid stabilized unpaved roadway used for the construction of a wind farm facility in eastern Oregon where the only source of water is located 25 mi away. The final decision on the roadway section was based on the reduced consumption of water and cost. The sustainable roadway design saved 120,000 gal. of water and 400 dump truck trips. The challenge was quantifying the design with the geogrid and proposed aggregate base course thickness. Typically, engineers use empirical methods such as the Design Method for Geogrid-Reinforced Unpaved Roads by Dr. J. P. Giroud and Dr. Jie Han or the US Army Corps of Engineers software PCASE for un-paved road design. Given the limitations of these methods, the authors used a newly developed Mechanistic-Empirical Method to justify the sustainable design. The method is called the Lees Approach to Applied Mechanical Stabilization (LAAMS). This paper will discuss the project, give a brief overview of the steps in creating and implementing the LAAMS method, and the achieved sustainable benefits.

Interlocking block pavement (IBP) consists of discrete blocks, joint and bedding sands, base, and subbase. Among others, joint sand plays an important role in the overall performance of an IBP, because it facilitates the load transfer between the blocks. Previously, researchers have performed IBP model test in order to determine the appropriate joint width. The proposed value, however, varies depending on the researchers because the geotechnical information (relative density and shear strength) of the joint sands is often neglected and not clearly defined. Therefore, in this study, a laboratory block pavement test was carried out by varying the joint width while considering the geotechnical properties of the paving materials. In addition, the model test was conducted in a newly designed 2D model chamber which enables particle image velocimetry (PIV) analysis. The test results show that the IBP settlement resistance and load dispersion ability are greater for IBPs with narrow joint widths owing to their higher load transfer efficiency (LTE).

Laboratory-based repeated load triaxial testing (a.k.a., resilient modulus or M_r testing) has been widely used for characterizing pavement unbound materials consisting of different mineral compositions, gradations, angularities, and other index properties, fines and moisture contents, and other variants. The M_r testing is usually conducted on a small cylindrical specimen by applying confining pressures and repeated axial stresses, mimicking the possible stress stages due to traffic. However, it is challenging to truly represent the actual field condition in the laboratory due to the absence of all bound and unbound pavement layers forming a pavement system, and due to the presence of a thick, extremely stiff, and unyielding base plate of the cylindrical specimen. As such, the M_r measured in the laboratory may not directly correlate with the M_r measured in the field. An Automated Plate Load Testing (APLT), a field-based plate load testing system for applying dynamic loads and measuring permanent and resilient deformations, offers an opportunity to close a gap between lab and field measured M_r. This paper aims to evaluate composite resilient moduli of geogrid stabilized pavement foundations measured through the APLT system. APLTs were conducted on several test sections consisting of different aggregate base course (ABC) thickness, ABC material types, geogrids, and subgrade conditions. A series of regression models were developed to predict a composite resilient modulus based on ABC thickness, subgrade stiffness, and other parameters. The regression model using the independent variables ABC thickness, subgrade CBR, gradation parameters D50, D85, and % fines performed better than the other models.

Many uncertainties are associated with traffic, climate, structural, and material inputs in the pavement design. Over years, numerous efforts have been dedicated to developing methods to account for these uncertainties in the pavement design. While the traditional AASHTO design guide for rigid pavement design is able to quantify the effect of input uncertainties on the designed pavement service life, the selected design is still highly affected by the accuracy of statistical characterization of the uncertainties. Following AASHTO design guide, the slab thickness of the pavement is chosen without considering the uncertainties in the input parameters which can lead to over-design or under-design. In the past decade, in geotechnical engineering, a new approach called Robust Geotechnical Design (RGD) was developed to find a design which is less affected by the uncertainties in input parameters and the adopted models (called robust, herein). The core of this approach is based on quantifying the resiliency of the design to changes (referred to as robustness, herein). Once the robustness measure is defined, RGD considers safety, design robustness, and cost efficiency, simultaneously. To account for the existing uncertainties affecting the AASHTO design of rigid pavements and reduce their effect on the system response while being cost-efficient, this paper adopts the reliability-based robust design approach. And, to ease the calculation of multi-objective optimization considering cost, robustness, and safety, the simplified RGD approach is used herein. The results obtained from this analysis are compared with the current practice to show the benefits of the proposed approach.

The stiffness characteristics of pavement foundation layers are one of the major factors affecting long-term pavement performance. Resilient modulus (M_R) is a key parameter to evaluate the behavior of geomaterials when they are subjected to continuous traffic loads. Therefore, a reliable characterization of the stress-strain behavior of geomaterials through laboratory tests is crucial for pavement design. In this study, a cyclic true-triaxial device that has the capability of conducting M_R tests on prismatic specimens with mixed rigid and flexible and six rigid boundary conditions was used to determine the effects of boundary type and stress history on the stiffness characteristics of an unbound geomaterial. The test results revealed that the rigid boundary condition yielded higher M_R in both vertical and horizontal directions regardless of the applied stress history. The anisotropy ratios for mixed-type and rigid boundary conditions were determined as 0.09 to 0.21 and 0.05 to 0.41, respectively.

This paper provides guidance on how to balance matters related to the environmental stewardship, market sources, origin and uses, material properties, performance, and economic impact, of using slag materials in pavements. Literature has numerous references on use of slag materials for specific applications, and this paper aims to make us of those references alongside other data from the authors to describe slag materials in a holistic perspective and provide some suggestions for balancing several factors that affect optimal use of this resource within pavements and geo-infrastructure. Discussion is given to the increased importance of recycling of other materials into the infrastructure and benchmarking those materials against recycling of steel slag. Ensuring adequate performance of pavements while increasing recycled materials usage and maintaining safety is a successful measure relative to green initiatives and only occurs due to careful planning, cooperation, and field validations.

Several pavement distresses are associated with excess water in the pavement system. Hence, controlling subsurface water is crucial to pavement’s long-term performance. Improving pavement drainage is commonly used to control the water content in pavement layers. Conventional drainage systems can work under saturated conditions but cannot effectively drain capillary water. A new type of wicking geotextile has been developed that can drain water under both saturated and unsaturated conditions. In this study, the performance of this new type of geotextile in draining water from a paved road shoulder is evaluated. A full-scale test section along Interstate 44 was constructed and instrumented. More than three years of continuous monitoring proved that the wicking geotextile effectively reduced the moisture content of the improved section.

This study presents a mechanistic method that can simultaneously design all three primary length scales (i.e., mixture components, mixture, and structure) in highway/airfield pavements. It directly links the properties of bituminous mixture components and mixture design to pavement structural design via a two-way coupled multiscaling. The details to demonstrate how the approach can design all three length scales simultaneously are given. The bituminous mixture variables include the gradation and elastic properties of aggregates, the viscoelastic properties of fine aggregate matrix, and the fracture properties of the fine aggregate matrix, all of which can be obtained from small-scale tests. The modeling concept was applied to the Federal Highway Administration-Accelerated Loading Facility (FHWA-ALF) test section. The preliminary results imply that pavement structural design and mixture design can be conducted concurrently in a purely mechanistic way with only mixture component properties, which will lead to significant cost-time savings compared to other currently available approaches.

Inspired by the geometric characteristics of mangrove roots, we propose to use a group of skirt-piles around a monopile foundation as a scour mitigation measure. In this study, the effect of the submerged height of the skirt piles on the scour process was evaluated using laboratory flume experiments. Images of the scoured bed were processed based on the photogrammetric method, from which the three-dimensional topography maps were reconstructed and quantitative analyses were performed. The results demonstrate that there is an optimum height of the submerged skirt piles above the mudline which approximates the diameter of the monopile at which the scour depth reaches a minimum. Up to 80% reduction in the volume of scour hole was achieved by using the mangrove-inspired skirt piles at the optimal submerged height. It was found that although the height of the skirt pile affects the maximum scour depth, it has limited effects on the location of the sediment deposition. The presence of the skirt-piles was found to result in a steeper slope of the scour hole in front of the monopile. Furthermore, the slope also slightly changes at the position of skirt piles, which suggests that the sediments between the skirt piles were densified as a result of pile-sediment interaction.

There has been a growing concern in recent years about the effects of anthropogenic noise due to pile driving on underwater wildlife. Over the past three years, investigators have collected several datasets of noise-levels during pile driving from sites throughout the state of Florida using a unique buoy-mounted instrumentation system first presented at Geo-Congress 2020. In this paper, a new empirical sound attenuation model is presented using these data. Included in this model are unique design parameters for driven concrete piles, driven steel piles, and vibrated steel piles. Interestingly, this new model appears to show some dependency between sound amplitude and attenuation efficiency regardless of drive-type, although the reasons for this dependency remain unclear.

This paper presents the design and hydraulic analysis of a stream diversion channel over the lower Santa Ana River in Riverside County, California, which is used to divert stream in the main channel of the river and create space for constructing the pier nose extension structures for the BNSF railroad bridge over the river. The hydraulic characteristics of the river at construction site are obtained from on field observations and the flow information at nearby National Water Information station of the USGS, and they are used to design the diversion channel. The advanced hydraulic (open channel) analyses, using HEC-RAS River Analysis System, are performed to verify the satisfaction of diversion channel to the project specifications and criteria. In addition, the design of stream diversion system also requires the stability assessments of its several components, including temporary diversion dam, channel bank slope, and bridge sheet pile abutment wall in front of the channel. With thorough evaluations of theses design aspects, the diversion channel is designed successfully and functions well as expected.

Failure of power poles during ice storms routinely disrupts the power distribution network, which is costly and can lead to loss of life. Such events are exacerbated by climate change, of which the effects on the power pole distribution network are two-fold. Firstly, climate change is causing more extreme weather and influencing the frequency and occurrence of extreme events. Secondly, drought and excessive rainfall events change the soil moisture; hence, the soil suction increases or decreases affecting the overturning stability of the poles. The role and seasonality of soil moisture content and suction are not routinely considered in the evaluation of power pole systems. This paper evaluates the role of antecedent moisture conditions and soil suction on the behavior of power poles during ice storm loading. The research expands on the current body of research by incorporating soil-structure interaction in the analysis. Analyses were carried out in the commercial software LPILE using p-y curves modified to incorporate the effects of soil suction. Modification to the p-y curves was completed using the concept of apparent cohesion. The variation in soil suction with depth along the embedded portion of the power pole is also considered in the analysis. To incorporate these effects, unsaturated seepage analysis was completed using the commercial software PLAXIS LE Groundwater for the study soils. The seepage analysis used past daily recorded precipitation for a testbed. The study found that while the groundline deflection is impacted by including soil and soil moisture conditions in the analysis. The maximum bending moment developed in the power poles was governed by the above ground loading, wind, and ice, and was not significantly impacted by soil conditions.

In this study, the effect of the embedment ratio of the pipe was investigated using the PIV method. The difference in this study compared to the literature is that in the case of the surcharge load, the failure surfaces were determined experimentally depending on the burial depth of the pipe. In addition, the load-displacement relationship was determined by footing load. The stresses on the pipe were measured by using strain gauges placed on the pipe. The results show the ultimate bearing capacity increases with the increasing depth of the pipe from the strip footing. The results of the PIV analysis show that the failure mechanism of the soil is affected by the embedment ratio of the pipe.

Estimating excavation-induced ground surface displacements in urban areas is needed to assess potential structure damage. Empirical settlement distribution models have been widely used to estimate the zone of influence and ground response behind braced excavation walls. Three underground station excavations, part of the Los Angeles Metro’s K Line Crenshaw/LAX Transit Project, offer a unique opportunity to collect field instrumentation data to improve estimates of ground deformations. One excavation employed cross-lot braces and soldier piles and wood lagging while the other two were supported by cross-lot braces and stiffer Cutter-Soil-Mixing (CSM) walls. For the excavations with stiff support systems and relatively small wall movements, upward surface displacement or heave governed the ground surface response, while surface settlement was measured at the excavation with the more flexible wall system. This heave behavior is often masked by settlement caused by relatively large wall movements, and is thus commonly disregarded. By idealizing the excavation unloading as an upward strip load at the ground surface, the Boussinesq solution for elastic upward movement can be used in combination with a settlement component resulting from lateral wall movements to estimate the magnitude and distribution of excavation-induced surface displacements.

Empirical methods for estimating tunneling-induced ground movements have been widely adopted in the tunneling industry. The transverse surface settlement profile can be described by a Gaussian curve or a modified Gaussian curve whose maximum value and trough width are related to volume loss. Volume loss in turn is related to soil type, tunnel geometry, and construction techniques. Several empirical equations have been developed based on the Gaussian curve and the assumptions of (1) trough width dependency on tunnel depth and ground condition; and (2) volume loss dependency on the ground type and construction techniques. For Earth Pressure Balance Machine (EPBM) tunneling, a volume loss of 0.5% in granular soils and 1%–2% the soft clay has been assumed in the past as an initial estimate. However, with complete filling and pressurization of both the shield (overcut) gap and the grouted tail gap around the lining, volume losses below 0.1% to 0.2% are being achieved in the alluvial granular and clay soils on current Los Angeles Metro tunneling projects. The LA Metro K Line Crenshaw/LAX transit project, tunneled from 2016 to 2018, has provided an opportunity to acquire and organize data on compatible data management systems, and evaluate the extensive field monitoring data for ground conditions specific to predominately granular soils in Old Alluvium. These data allow for the improvement of current empirical methods and correlations for predicting surface settlement induced by EPBM tunnels. The approximately 1-mi (1.6-km)-long, 20.6-ft (6.5-m)-diameter twin tunnels were excavated by an EPBM in a dense sand layer overlain by a silt/clay layer. The cover-to-diameter ratio was consistently about 2. The settlements and volume losses are observed to be heavily dependent on the face/shield pressures. In general, maintaining continuous pressures can significantly reduce settlements. An equation for estimating the volume loss based on the measured EPBM shield pressures is proposed. This equation can be used with the existing empirical methods to estimate the surface settlement profile transverse to the longitudinal axis of the tunnel.

The behavior of soil relaxation in the ground produced by numerous reasons such as cavities, sinkholes, and tunnel excavation in the ground was confirmed in an experiment. To imitate the two-dimensional model ground in the experiment, the geometry was made out of carbon rods. It comes in three different diameters and is distributed at random. The ground’s relaxation was indicated by the structure at the bottom of the experiment, which was used to induce deformation. During the experiment, taken pictures, particle image velocimetry (PIV) analysis was used to examine the behavior of soil particles during ground relaxation. The ground strain is used to express the deformation, and the critical range can be established. Visual confirmation of the results is possible by following the movement and deformation of carbon rod particles. Surface sinking and the behavior of the surrounding ground were confirmed by vectors and contours by simulating the onset of relaxation at various depths of the ground. It is feasible to comprehend the behavior and relaxation range of the surrounding ground using the methods described above when the ground relaxes according to depth. It is feasible to comprehend the issues created by ground relaxation in the subsurface space by doing so. Furthermore, if an underground structure exists, it is possible to identify and predict the movement and deformation of the structure as a result of ground relaxation, as well as to design a cost-effective and stable tunnel by predicting the behavior of the surrounding structures.

Mechanical response of corrugated steel culverts buried in shallow cover depth and subjected to service load conditions has been studied using finite element analysis (FEM) and the Canadian Highway Bridge Design Code (CHBDC). The nature of the surface load critically influences the internal stresses and deformations and finite element analyses have been conducted to investigate the internal forces due to backfill and CL-625 Truckload for wheel and axle loading for 1-, 2-, and 3-lane configurations. The results of the numerical simulations are compared with the recommended internal forces in the CHBDC. The results indicate that the culvert experiences the maximum values of these responses at the crown. In the numerical simulation, multi-lane loading increases the thrust and bending moment magnitude, but this effect is not considered in the bending moment equations used based on the Canadian code. The results of normalized thrust indicate the considered increment in thrust responses due to the multi-lane loading is consistent and conservative relative to the FEM results.

When excavating a vertical shaft in clay, basal heave may occur as depth increases. Basal heave can be hazardous to workers by destabilizing the excavation surface and causing ground deformation that deteriorates the stability of the surrounding ground. Therefore, before constructing a vertical shaft in clay, the behavior of the surrounding ground owing to basal heave should be investigated. Herein, the behavior of the ground surrounding a vertical shaft owing to basal heave was numerically simulated by assuming specific excavation conditions of a vertical shaft for different excavation depths in soft clay. The thickness of the shaft embedment was a variable used to improve the stability of the vertical shaft base; the effects of this parameter on the deformation of the basal heave and surrounding ground were analyzed. The result revealed that the installation of the shaft embedment reduced basal heave displacement, thereby suppressing the deformation of the surrounding ground.

The failure of the tunnel and the ground collapse due to the gas migration and release in the gas-bearing confined stratum during the tunnel project construction are the geotechnical problems that may be encountered in the shallow gas geological area. In this study, a parallel tunnel and the cross-passage failure caused by gas-bearing formation near the Nak-Dong River in South Korea were evaluated through numerical simulation employing multiphase fluid and mechanical coupling equations via COMSOL Multiphysics. Based on the modeling results, it is found that the high-pressure gas in the gas-bearing formation migrates into the deep cement mixing (DCM) to potentially expand fractures. Accordingly, after the tunnel is excavated, the water–gas mixture in the gas-bearing formation overflowing along the DCM fracture can cause stress disturbance around the tunnel, which leads to damage and formation subsidence. In addition, this study analyzes the effect of different gas pressures on the extent of the failure, and the effect of the location and number of potential cracks on tunnel failure was analyzed. This study shed light on the failure modes of tunnels caused by gas migration in gas-bearing soils and the DCM fracture, emphasizing the importance of quality control for DCM when reinforcing in situ soils in gas-bearing areas.

The structural response of moment-resisting frame buildings adjacent to a deep excavation in soft to medium clays is presented. Results of 54 advanced numerical simulations of linear-elastic and nonlinear-inelastic buildings adjacent to a deep excavation were employed to derive a mathematical expression that includes building-soil-excavation interactions and post-yielding behavior of the structural members. The location of the building within the primary influence zone, the fundamental elastic period of the building, the structural aspect ratio, and the underlying settlement troughs are used to describe the vertical structural response of moment-resisting frame buildings. The structural response is hypothesized to be controlled by the internal redistribution of forces computed during the numerical analyses and parametric studies.

This study focuses on the investigation of thermally induced hydraulic hysteresis due to freezing and thawing of an unsaturated silty soil layer. Hydraulic hysteresis is relevant with the quantification of volumetric water content in soils that needs to be included in the subsurface modeling in cold regions. Experimental results from existing literature support hydraulic hysteresis for different type of soils; however, results are controversial. To provide a better understanding of the initial and boundary conditions through a well-defined and systematic approach, a series of freeze-thaw experiments are performed at two different laboratory scales and the effects of initial volumetric water content, dry density, sample size, and number of freeze-thaw cycles on hydraulic hysteresis are investigated. During the experiments, temperatures and volumetric water contents are measured using capacitance sensors embedded in silt layers. The results show that the magnitude of hydraulic hysteresis and unfrozen water content in frozen soils increase with increasing initial volumetric water contents for a given dry density. It is observed that the hysteresis depends on sample size and boundary conditions, which is not investigated before. In addition, a critical temperature for the maximum hysteresis for different samples is identified. It is found that the critical temperature is affected by the initial water content. The results from this study will provide accurate constitutive relationships for fully coupled thermo-hydraulic modelling of unsaturated subsurface layers.

Soil column collapse has been widely studied in the dry condition due to its applicability to natural phenomena such as landslides, avalanches, and debris flows. Given the prevalence of unsaturated soils in nature, in this study, we apply a recently proposed nonlocal poromechanics formulation to study three-dimensional unsaturated soil column collapse. For accuracy and robustness in modeling large deformation and plasticity, an updated Lagrangian framework is adopted in which the equation of motion is formulated in the current/deformed configuration. Numerical simulations are conducted to explore the influence of aspect ratio of the column on the flow characteristics of unsaturated soil. The results are validated using experimental data of collapsed deposit morphology and final height. We also study the influence of initial matric suction in the soil on the final deposit shape.

Compacted embankments are usually found to be in unsaturated condition. In this study, a shallow footing resting on an unsaturated compacted embankment modeled using Barcelona Basic model (BBM) was numerically analyzed. BBM was implemented in FLAC to consider the variation of strength and stiffness with the change in suction. A comparison of the observed responses in the footing-loaded embankment upon infiltration using BBM was made with Mohr-Coulomb model. It was observed that BBM accurately models the collapse load and shows higher settlement compared to the Mohr-Coulomb model as it considers the loss of suction upon infiltration. This involved two phases, viz, loading the embankment by footing and second with infiltration. It was found that net stresses affect the loading, and load-displacement curves are observed while suction is the dominating factor during infiltration and pore pressure variation is observed.

The freeze-thaw (F-T) behavior of saline soils is critical to transportation and geotechnical infrastructure in the regions subjected to seasonal changes and low-temperature conditions. This study conducts laboratory tests on clayey saline soil to investigate its surface morphology, volumetric evolution, and cracking behaviors under F-T cycles. Soils with different levels of NaCl concentrations [0M (Deionized Water), 1M, 2M, and 3M] are prepared and tested for Freeze-Thaw (F-T) and Wet-Freeze-Thaw-Dry (W-F-T-D) conditions. A high-resolution camera and 3D structured light scanner are placed above the samples to capture their 2D and 3D responses at the end of each cycle. Then the image processing techniques are used for 2D and 3D analysis. The results show that the water evaporation rates decrease with time and the water evaporation rate decreases with the increasing salt concentration due to the decrease in capillary potential and salt crystallization at the surface. Overall, the crack area, length, and fractal dimension decreased with increased NaCl concentration for F-T and W-F-T-D. The 2D analysis showed that crack area, crack length, and fractal dimension increased with cycle number for F-T cycles. The 3D analysis results showed that sample volume reduced over time, but the surface area and fractal dimension increased with continuous F-T cycles. The W-F-T-D samples showed that all the parameters were relatively closer to each other at individual salt concentrations except for the volume change. This can be attributed to the wetting and re-freezing, which bring the soil sample closer to the original intact soil sample.

Desiccation cracking in expansive soils is critical to their hydraulic and mechanical properties and affects the long-term performance of various geotechnical infrastructure. In recent years, bio-mediated methods such as bio-cementation have been explored as a possible approach for ground improvement. This study explores the potential of using Enzyme Induced Calcite Precipitation (EICP) for desiccation cracking remediation in clayey soils. EICP uses biologically derived material (plant-based urease enzyme) without requiring bacteria incubation. In this study, crude extract from soybean (Glycine max) is used for urea hydrolysis. Three different enzyme concentrations (10, 30, and 50 g/L) are used to evaluate the effect of calcite precipitation on desiccation crack. According to the analysis of soil cracking images, this technique significantly induces calcite precipitations and effectively reduces the extent of desiccation cracking in clayey soils. The EICP-treated sample demonstrated that the crack area, crack width, and crack length decrease for the higher concentration of urease enzyme with the increasing W–D cycle. The lower concentrations (10 g/L) have minor effects on crack remediation but effectively limit the growth of new cracks. Moreover, when the enzyme concentration increases, calcium carbonate precipitations tend to form a crust on the soil surface, gradually increasing soil surface roughness. This study is expected to improve the fundamental understanding of the EICP technique and provide new insights into its potential application for soil improvement.

A previous study showed mud dauber nests have high densities and high penetration resistance. The high density and penetration resistance of mud dauber nests were attributed to the vibratory compaction technique used by mud daubers (i.e., repetitive tapping produced by their legs and vibrating mandibles) and the well-graded grain size distributions of nest soils. However, the high density and strength of mud dauber nests are also attributed to soil drying under the atmospheric temperature and humidity level (i.e., drying-induced soil consolidation and hardening). This study investigated the mechanical properties of nest soils used by mud daubers with varying moisture conditions to assess the effect of drying on the mechanical properties of mud dauber nests. The suction stress characteristic curve (SSCC), soil water retention curve (SWRC), elastic modulus, and soil shrinkage curve (SSC) of the nest soils under drying were measured using the drying cake (DC) method. Furthermore, direct shear tests were performed under different moisture contents. The SSCCs showed the magnitude of suction stress increased with decrease of degree of saturation. Shear strengths of nest soil with 2% moisture content were significantly higher than saturated nest soil.

Unsaturated soils that exhibit significant volume reduction under wetting or mechanical loading are referred to as collapsible soils. The main objective of this study is to investigate the time-dependent response of an unsaturated sand-bentonite mixture under coupled hydro-mechanical loading conditions. For this purpose, a modified osmotic oedometer device was employed to determine soil volume change properties such as the compressibility coefficient, creep index, and collapse potential under controlled matric suctions. The results demonstrate the interaction of the stress history and the long-term behavior of the tested soil, suggesting that creep and consolidation deformations strongly depend on the preceding hydraulic loadings. Incomplete collapse incidents were observed in the specimens confined in the oedometer ring in which the specimens did not collapse laterally. As a result, the volume states of the collapsed samples were located above the saturated normal consolidation line. The higher void ratios led to higher creep deformations in saturated samples that experienced the collapse phenomenon. This behavior is attributed to the meta-stable condition of samples, which eventually tends to evolve toward the stable virgin consolidation curve. Moreover, the creep index and collapse potential increased with the net stresses within the range of applied loads. Findings confirm the reverse relationship between the creep index and applied matric suction.

Modified tempe cells equipped with time-domain reflectometry (TDR) sensors can measure dry-out curves for sands over the complete range of saturation. The water content measured from TDR sensors is estimated from directly measured dielectric constant and electrical conductivity using empirical calibration relationships. However, the commonly used calibration equations were developed from test data in conditions different from the tempe cell test. In this study, a tempe cell with a self-fabricated TDR sensor was used to evaluate the TDR-measured water content estimated from Topp’s equation and one-step method. The tempe cell was placed on two digital scales to record mass change and, thus, the water content change during the test. ASTM fine-graded sand of two different densities was tested for dry-out curves of dielectric constant and electrical conductivity. The results show that both empirical relationships can not perform satisfactorily for both tests over the complete range of saturation, and a new calibration relationship is needed to improve water content measurement from TDR sensors for tempe cell test.

The p-y curve method is widely used in geotechnical engineering to understand the behavior of laterally loaded piles. Relatively little experimental research has been done to assess the lateral response of piles in unsaturated sands using the p-y curve method. This paper presents p-y curves obtained from centrifuge tests to show the influence of the unsaturated soil on the lateral resistance and, consequently, the p-y curves. A solid cylindrical steel pile was used to evaluate the lateral response of piles when embedded in F-75 Ottawa Sand. The centrifuge test setup was subjected to 50 g at the mid-depth of the embedded pile length to assess the lateral behavior of the pile in the prototype scale. Thus, a prototype pile with a diameter of 0.5 m and an embedded length of 9.5 m was simulated. The pile was laterally loaded using a loading actuator mounted on the centrifuge setup. The p-y curves were obtained using the strain gauges instrumented along the circular pile surface. The lateral resistance was obtained by double differentiation of the bending moment profile, while the lateral displacement profile was obtained by double integrating a fitted curve on the curvature data with the necessary boundary conditions. Experiments included saturated and a mix of unsaturated-saturated soil. The water table was lowered to the desired elevation in-flight prior to lateral loading for the unsaturated-saturated soil test. This paper discusses a fundamental understanding of how water table fluctuation can influence the behavior of laterally loaded piles for a performance-based design.

The objectives of this study were to identify the optimal soil water retention curve (SWRC) equation for unsaturated fouling ballast and to evaluate unsaturated fouled ballast peak shear stress. Ballast fouling degrades the track and results in poor performance. However, there is limited research on the sensitivity of the mechanical behavior of ballast fouling to variations in water content. In this research, clay and coal fouling materials were mixed with the clean ballast to varying degrees of fouling. For the hydraulic behavior, a custom large-scale system was developed to measure the specimen volumetric water content at various suctions during drainage. A nonlinear least squares method was used to determine best-fit parameters for four common empirical equations for water content versus suction of five fouled ballast specimens. All soil water retention models were subjected to mathematical correction techniques to incorporate high soil suctions up to 10,00,000 kPa. For the mechanical behavior, large-scale direct shear tests were performed on fouled ballast at the volumetric water content beyond air-entry value and over much of the unsaturated region. The study highlights how SWRC characteristics and different fouling materials impact peak shear stress. As the degree of fouling increased, the percentage of fines increased which extends the fouled ballast capillarity. However, the highest peak shear stress was observed at the dry condition for all experiments, likely because the wet fouling material lubricates the ballast aggregates. Unsaturated coal fouling resulted in greater peak stress compared to clay fouling. The parametric model used to determine the residual water content reduces uncertainty in describing the results. Additionally, the selected model will be used to develop a constitutive model to describe the unsaturated strength of fouled ballast. Such a model will improve the fundamental understanding of ballast degradation characteristics so that the likelihood of fouling can be predicted and managed versus identified and repaired.

Underground geo-structures and climate change can trigger heat, moisture, and vapor flow and may induce volumetric shrinkage in clays. This drying phenomenon is a multiphysical process and is accompanied by alterations in the thermal, hydraulic, and mechanical states of the multiphase system. Reversible and irreversible characteristics of shrinkage deformation have been observed experimentally in clayey for different ranges of moisture contents. An accurate evaluation of the drying process helps to study the drying-induced damage of geomaterials. In this study, a finite element model that considers the thermo-poroelastoplastic constitutive framework is developed. The developed thermo-hydro-mechanical (THM) model can accurately analyze the transversely isotropic behavior of natural clays in unsaturated conditions. Results indicate that 82% of the total volumetric deformation in dying-induced shrinkage is irrecoverable. In addition, it is observed that most of the plastic volume change occurs within the early stage of drying when the soil’s unsaturated condition is in a funicular state.

The use of appropriate tortuosity factor in determining D_v (diffusion coefficient) leads to an accurate estimation of vapor fluxes from porous medium like soil. Tortuosity is the representation of interconnectedness of the pore space, and it accounts for the convoluted flow path traversed by the water (liquid/vapor) to diffuse into the atmosphere. As the soil desaturates into funicular and pendular regime from the saturated regime, reorganization of water takes place making the path less easy and more tortuous for its movement. Many researchers proposed several tortuosity models to predict the diffusive flux, but the applicability of a single tortuosity model (either as a function of volumetric air content/volumetric water content or an empirical value) for the entire suction range remains questionable. As the dominant mode of water transport (liquid and vapor) varies with desorption, the movement is dependent upon the interconnectedness of voids. Available relations to estimate τ based on idealized pore structure, porosity, and volumetric air content, led to large variations between experimental and predicted moisture vapor flux. A new simple relation based on experimentally derived data of a residual soil is proposed to predict τ from volumetric water content (θ).

The mechanical response of unsaturated soil is controlled by the two stress state variables of matric suction and net normal stress. Modern geotechnical laboratory devices allow for the direct measurement of unsaturated soil volumetric response under controlled conditions of both stress state variables. The oedometer pressure plate device (OPPD) is one apparatus that can impose suction-induced partial wetting conditions under constant or varying vertical stress conditions while measuring vertical deformations. This study brings together three extensive laboratory investigations of the mechanical response of fine-grained soil specimens to variations in both matric suction and net normal stress, which were conducted using a series of OPPDs located at Arizona State University’s Geotechnical Laboratory. The effects of differing soil index properties, sample preparation, and stress path history on the moisture-driven volumetric response is evaluated. A comparison between the suction-volume change indices of reconstituted clay specimens to those of relatively intact clay specimens is also included.

Expansive soils cause damage to many types of construction throughout the world, however, their presence is not always well recognized. Expansive soils are generally clayey soils that undergo swelling and shrinkage in cycles with changes in moisture contents. Many classification techniques exist to identify expansive soils, with use of the Atterberg Limits and Hydrometer testing being the most prevalent. A direct measurement test, the Expansion Index (ASTM D4829), exists to classify expansive soils in a consistent manner. Due to its relative quick testing time and low cost, the EI is often used in practice as a screening tool to identify the presence of expansive soils, as required by the building code, for sites with variations in soil composition, without a direct incorporation in design formulae. Conversely, the Atterberg Limits and Hydrometer Tests, despite their costs and longer time for testing, are often required to be determined to accomplish the foundation design per the Wire Reinforcement Institute (WRI) method, or the Post Tensioning Institute (PTI) method, as required by code. In practice, not all samples collected for EI testing are used for Atterberg Limits and Hydrometer Tests. Therefore, a correlation between the two index tests may be useful. A direct correlation between the Expansion Index (EI) and the Atterberg Limits (LL and PI) has not been previously established. Laboratory test data on samples where both EI and Atterberg Limits (LL and PI) have been conducted for the same sample have been collected. Correlations between the two have been determined and are reported within. Additionally, some samples where hydrometer tests were also conducted have been used to further understand the correlations between the two primary index test types. Results indicate there is a general linear trend between the EI and the LL and PI values; however, there is a wide scatter in the ranges of the data indicating the correlation is variable and only loosely correlated. Reasons for the results are discussed.

Coded targets have been widely used for solving the corresponding problem in photogrammetry for high-accuracy three-dimensional measurements. Accurate and efficient recognition and identification of coded targets are of great importance in coded target-based photogrammetry. In this paper, an efficient and accurate method for coded target decoding was developed. In this method, blob analysis was performed to recognize the coded targets. Then, image processing, the RANSAC algorithm, and the interpolation technique were applied respectively to decode the coded targets, identify falsely identified coded targets, and recover missing coded targets. Interpolation was also performed on the membrane, which can significantly increase the density of the points on the membrane and produce more representative 3D results for the soils specimen. This method was implemented into a MATLAB program and all computation was done automatically by the computer program. This method takes advantage of the prior knowledge of the geometric arrangement of the coded targets. The effectiveness and accuracy of the proposed method are validated by implementing it into three-dimensional reconstruction of soil specimens during triaxial testing in geotechnical engineering. Experimental validation results indicate that the proposed method can achieve accurate and efficient coded target recognition and identification results.