Geo-Congress 2020: Engineering, Monitoring, and Management of Geotechnical Infrastructure

Seismic evaluations of embankment dams and levees often involve synthesis and idealization of site investigation data in a simplified spatial structure with equivalent uniform properties assigned to each soil layer or category. The process of assigning equivalent single property values to entire soil layers and categories significantly simplifies the detailed information obtained during the site investigation. This study examines the potential benefits of incorporating the spatial variability of liquefiable soils captured in site investigation data into nonlinear deformation analyses (NDAs) of embankment dams using conditional random fields. Parent models (PMs) are analyzed using unconditional random fields to represent “true” subsurface conditions of a spatially variable, liquefiable soil layer under different size embankments. From each parent model, single continuous columns of soil data are extracted and used to simulate data obtained during site investigations. Conditional embankment models are created using random fields conditioned on the simulated site investigation data to represent possible subsurface conditions. Deformations obtained from sets of conditional model NDAs are compared to those obtained from their parent model NDAs for different embankment sizes and scales of fluctuation to examine the deformation prediction ability of the conditional models.

Three inertia measurement unit devices (denoted as Sensors A, B, and C) from different manufacturers were systematically evaluated for their performances in terms of data stability, reliability, and accuracy. A series of laboratory still, constant rotation, and platform tilt experiments were completed to assess the performances of these sensors. Still experiment was performed to compare the data noise from each sensor device, while platform tilt experiment was used to understand and verify gravitational acceleration readings in three-dimensional space at different slope angles. The constant rotation experiment was used to understand and verify gyroscope readings based on their orientation and the direction of rotation. Sensor selection for landslide monitoring application was conducted by comparing the pros and cons of the sensors as well as their capabilities. This study concludes that Sensor C provides the most accurate and reliable data with the least noise for slope movement monitoring.

Failures of fly ash impoundments have resulted in significant economic and environmental losses, with increased impacts due to the tendency for saturated fly ash to deform and ‘flow’. Dewatering of fly ash ponds could potentially mitigate the risks associated with impoundment failure and the consequences due to fly ash runout. In this study, centrifuge modeling is used to explore changes to the bulk material properties of fly ash deposits resulting from dewatering. Changes to the water content across the deposit height were measured and linked to the measured suction in the pore fluid. These results were also used to estimate changes to the effective stress profile resulting from dewatering. A miniature CPT and bender elements showed that the fly ash shear strength and stiffness increase significantly as the water table was lowered within the model deposit. The potential improvement to the pond stability was highlighted by these centrifuge tests, with further research being undertaken to study the optimization of dewatering practices for ensuring both safety and economic feasibility.

The operation of dams at times requires a sudden decrease in the existing reservoir level. This abrupt change in the upstream water level, known as rapid drawdown, results in the development of unbalanced forces and occasionally causes catastrophic failure of the upstream shell. The drawdown-induced slope stability analyses are typically performed assuming that geomaterials used to build the dam exhibit isotropic permeability; even though, in reality, the geomaterials mostly exhibit anisotropic properties. The principal objective of this study is to comprehend the impact of anisotropic permeability on the drawdown-induced stability analysis of earthen dams and assess the impact of erroneously assuming isotropic permeability properties for numerical analyses. The influence of dam geometry, rate of drawdown, and depth of reservoir water before drawdown were also studied. The results of this research study highlight that the assumption of isotropic permeability inevitably leads to erroneous estimation of deformations incurred during drawdown. The extent of error was observed to increase with an increase in the dam slope and drawdown velocity.

Although wildfires are common globally, California has been experiencing significant loss due to the wildfires. Examples of such losses include frequent landslides and debris flow events. Although most of such post-wildfire debris flow events do not always cause human casualties, the 2018 Montecito debris flow event not only caused over $200M property loss, but also caused a death toll of 21 people in addition to full or partial damage of over 500 buildings. A few bridges were washed away due to the blockade of their waterways by debris and tree branches. The debris basins overflowed and the debris mass was diverted from the natural flow channels. The main reason for the debris flow was a short duration but concentrated rainfall that the area got even before a full containment of the Thomas Fire, one of the worst wildfires in the history of California. This study includes geotechnical properties of the debris flow soil, comparison of several wildfire induced debris flows in Southern California, statistical evaluation of the rainfall threshold for triggering wildfire induced landslides in Southern California, and analysis of rainfall pattern for a few years preceding the disaster. The Montecito debris flow disaster can be attributed to the high intensity rainfall prior to the debris flow event and the low residual shear strength of the ash deposited on the soil matrix.

In June 2012, over 10 inches of rain fell within 24 hours in northeastern Minnesota, causing massive slope failures along a section of scenic Highway 210 through Jay Cooke State Park. The damage was so extensive that officials considered permanently closing the highway. However, local residents indicated their strong desire to re-open the highway and restore it to its natural appearance. The Minnesota Department of Transportation (MnDOT) solicited bids for a $21.3-million fixed-cost, variable-scope, design-build reconstruction project with three primary requirements: innovative slope-stability design methods that blended with the area’s natural setting, a three-year warranty on the repairs, and an extensive slope monitoring system to evaluate performance. The unique contract required stabilizing 74 slopes using innovative techniques along three miles of the steep terrain. Performance monitoring was of particular importance and advanced the limits of slope-monitoring instrumentation and communication in this remote project location through the use of 927 sensors and almost 2,700 monitoring points generating more than 20 million automated readings to date. This paper focuses on the development of the performance monitoring program through the design, installation and commissioning, construction, and three-year warranty periods.

The purpose of this study is to analyze the stability and deformation behaviors of earth slopes subjected to common natural hazards such as rainfall, toe erosion induced by the flood, earthquake, and simultaneous occurrence of rainfall-erosion and rainfall-earthquake. A coupled geotechnical-hydrological finite element software, PLAXIS 2D which is capable of coupling deformation and flow behavior of soil with varying degree of saturation was used. First, a two-dimensional (2D) plane strain model was analyzed by applying a single hazard: rainfall, toe erosion induced by the flood, and earthquake and then dual hazards: rainfall-erosion and rainfall-earthquake. The results showed that slope movements due to dual hazard were higher compared to a single hazard. The factor of safety against slope stability from the dual hazard analysis was found to be lower than that of single hazard analysis. The percentage decrease in the factor of safety for the dual hazard rainfall-erosion compared to single hazard rainfall is 16.1% for SR1, 19.7% for SR2, and 17.3% for SR3. Further, from the parametric study, it can be observed that the factor of safety for the slope ratio 2:1 is 27.67% larger than the slope ratio 1.5:1 and for the slope ratio 3:1 is 78.05% larger than the slope ratio 1.5:1.

Geosynthetic-reinforced pile-supported (GRPS) embankments, as an economic and effective construction technique to reduce total and differential settlements, have been widely used in soft soils. Soil arching and tensioned membrane effects are two main load transfer mechanisms for this GRPS embankment system. Most studies have been done so far to investigate the GRPS embankment under uniform surface loading. However, embankments (e.g., highway and railway embankments) are often subjected to localized surface loading. In this study, two three-dimensional (3-D) finite element models were adopted to investigate the effect of different surface loads (uniform and localized) on the load transfer mechanisms in the GRPS embankments. A basic 3-D model was first established and verified against an existing laboratory test. A series of 3-D numerical analysis considering different surface loads was conducted. Simulation results showed that the GRPS embankment system performed better under uniform surface loading than under localized surface loading in terms of its deformation and load transfer. The load transferred by soil arching under localized surface loading was lower than that under uniform surface loading, while the load transferred by the tensioned membrane effect under localized surface loading was higher than that under uniform surface loading.

Along a portion of Highway 73 west of Lake Sakakawea in the Missouri River badlands of North Dakota, landslide activity had been observed for several years. This activity damaged the heavily traveled roadway, causing temporary closure or constraints on the maximum allowed speed. This large, deep-seated landslide includes high-plasticity clays with limited long-term shear strength and lignite seams carrying groundwater that also contributed to the slope failures. A stabilization design was developed to capture groundwater and route it away from the failure, and drilled shafts were installed as reinforcement to increase the factor of safety and limit long-term displacements. The paper addresses the field mapping, geotechnical investigations, laboratory testing, performance monitoring, design, and construction of the remedial measures.

The role of vegetation in the stability of slopes has expanded recognition in the last few decades. Performance of plants in stabilizing slopes is closely linked to the variation of the shear strength of root-reinforced soils. Vetiver grass (locally known as binna or binna shoba) is mostly available in Bangladesh. An attempt has been made in this study to develop a mathematical model for predicting the shear strength contribution by root of vetiver rooted soil. The mean tensile strength of matured vetiver root was found to be 27 MPa. The shear strength parameters of vetiver rooted soil were determined by in situ shear strength tests. Tests were conducted in the field on 9 block samples under same normal load at same soil depth using a special device developed in the study. Additional shear strength for rooted soil was determined by comparing with bare sample. The obtained relationship between the additional shear strength provided by roots (Δs) and the tensile strength of roots per unit area of soils (t_R) is approximately linear. Based on the experimental observation, a mathematical model (Δs=5.14t_R) was developed to predict the additional shear strength of soil-root system. This simple, straightforward model will provide a convenient mean for stability analysis of vegetated slopes.

Vetiver grass (Vetiveria zizanioides) is easily available in Bangladesh and widely known for its long fibrous roots which significantly increases shear strength of soil. This paper aims to numerically analyze the stability of hill slopes and effectiveness of vetiver for protection of slopes using PLAXIS 2D software. Soil samples were collected from four different hill slopes in Chittagong Hill Tracts (CHT) which were prone to landslides. Three soil samples were classified as sandy soil (SM, SC, and SM-SC) and another one was lean clay (CL). Results from numerical analysis showed that the factor of safety (FS) decreases with the increase in slope angle and for soft clay soil, slope fails at different slope angles. However, presence of vetiver grass on hill slopes increases FS by 2%–15% for sandy soils but for clay the increase in FS is insignificant because of deep seated base failure. Although vetiver alone cannot stabilize a hill slope but can protect the slopes from rain cut erosion which leads to failure. Additionally, analysis has been performed for different root zone depth considering the age of the plantation. Therefore, for sandy mild hill slopes, vegetation can be an effective and green solution for slope protection.

Lateral spreading design of column-supported embankments (CSE) requires estimating the driving lateral thrust as well as the portion of this thrust that should be resisted by geosynthetic reinforcement. A three-dimensional (3D) numerical parametric study was conducted for 128 scenarios using the finite difference method to investigate the lateral thrust distribution in CSEs. For each scenario, a 3D slice of the half-embankment geometry was analyzed, beginning with an undrained embankment loading and followed by the dissipation of excess pore water pressures. Incremental lateral earth pressures were calculated and integrated over depth at the embankment centerline and toe locations to obtain the driving and resisting thrusts produced by embankment loading, respectively. These were compared to the resisting geosynthetic tension at the centerline. Results show that: 1) the centerline driving thrust is largest in the undrained end-of-construction condition and is approximately two times larger compared to the long-term dissipated condition; 2) the foundation passive resistance at the toe is approximately 50% of the centerline thrust in the undrained condition; and 3) for geosynthetic stiffness in the range of 300 kN/m to 900 kN/m, the maximum resisting tension ranges from 2% to 7% of the driving centerline thrust in the undrained and dissipated conditions, respectively. Implications of these results for practice are discussed.

Slope movements and instability present a costly geo-hazard throughout the State of Kentucky. Pipeline going through hilly areas are vulnerable to slope failure or ground movements due to natural features, slope geometry, and disturbance caused by the right-of-way construction. Slope movements may induce additional stresses on the pipeline, which increases the displacement demand that may endanger the pipeline integrity, causing pipe fractures, leakages, fires, and even explosions. Reinforcing the slope at the early signs of movement can reduce the risk of a costly pipeline failure. In this paper, a case history is presented for site assessments, geotechnical study, monitoring, and reinforcement of a slope within a natural gas pipeline right-of-way using steel plate piles. The reinforced slope was monitored using slope inclinometers for post-construction movement. A finite element analysis was conducted to analyze the performance of the reinforcement. The monitoring data were in agreement with the analytical results and design criteria.

The Zone II slope of Doña Juana Municipal Solid Waste (MSW) Landfill became instable two years after commencing with MSW filling. The slope failure resulted in displacing about 1.5 million ton of municipal solid waste toward the Tunjuelito River. Zone II was designed with a leachate recirculation system. The original failure investigation in 1997, utilized instrumentation data and back calculation of the safety factor using limit equilibrium methods to investigate the possible cause(s) of failure. In this paper, the Doña Juana slope failure was investigated utilizing a coupled hydro-mechanical 2D numerical simulation, which allowed to qualitative understanding on the importance of secondary drainage slots. The analysis results, in terms of safety factor and location of the failure surface, are in general agreement with the data collected from field instrumentation and conclusions presented in previous studies. The results demonstrate that the filter to liner area ratio has significant effect on the factor of safety against slope instability. Recommendations on the proper design and operation of a landfill with a leachate recirculation system are provided.

The improvements in imaging technology within a borehole were developed originally for the petroleum industry. However, they have great application to geotechnical projects in characterizing the foundation conditions and for QA/QC (quality assurance/quality control) programs of grouting and cutoff walls. The optical televiewer (OPTV) provides high resolution imagery of borehole walls, allowing for logging and accurate definition of the in-situ conditions within rock or concrete. The acoustical televiewer (ATV) has applications where the OPTV has issues and borehole fluids are not clear, allowing imagery to be generated even in oily or cloudy boreholes. The closed-circuit television (CCTV) technology can also be effectively used to define the subsurface conditions in rock and in concrete works by allowing a video recording of the subsurface conditions. Use of these tools has allowed USACE to better define subsurface conditions as well as better assess grouting programs and barrier wall construction. This has not only added to the project overall quality control but has also provided for cost savings where simple repairs could be realized rather than full replacement of barrier wall elements.

Periods of prolonged rainfall events give rise to sloughing and surficial failures of slopes underlain by expansive clayey soils, resulting in significant maintenance costs for various transportation agencies. Recycled plastic pins (RPP) are a sustainable and cost-effective solution to stabilize such surficial slope failures due to their long-term endurance against degradation. The objective of the current study is to evaluate long term performance of shallow slopes stabilized with recycled plastic pins. Two highway embankments in North Texas, where cracks were observed along the shoulder due to surficial movement of the slopes, were stabilized using RPPs. Inclinometer casings were installed in the slopes to monitor the lateral movement, while topographical surveying was carried out regularly for monitoring the vertical settlement. The long-term performance of the stabilized sections was evaluated between 4 years and 7 years. Based on the study, it was concluded that RPP can be utilized as a sustainable solution for shallow slope failure.

At landfall in Yabucoa, Puerto Rico, on September 20, 2017, the National Hurricane Center classified Hurricane Maria as a strong Category 4 hurricane on the Saffir-Simpson hurricane wind scale. This paper summarizes the geotechnical impacts and consequences from Maria, documented by the Geotechnical Extreme Events Reconnaissance (GEER) team sent to the island in its aftermath. The intense rainfall and strong winds associated with Maria directly or indirectly resulted in over 3,000 fatalities, severe infrastructure loss, over 40,000 landslides, and considerable coastal erosion in Puerto Rico. Hurricane Irma preceded Hurricane Maria by two weeks and this paper addresses the importance of antecedent rainfall and geomorphology on the magnitude of damage. Geotechnical impacts described in the paper include coastal erosion events, bridge abutment scour, the impact of debris flows on the island’s highway system, and foundation failures. The geotechnical failures presented in our article provide insight on the likely modes of failure when major hurricanes affect slopes that have been pre-soaked and are thus especially vulnerable to geotechnical failures. Since global warming will likely increase the intensity and frequency of extreme events like Hurricane Maria, understanding the impacts and aftermath of Maria in Puerto Rico should assist the engineering community in addressing geotechnical vulnerabilities, as well as improve design and construction practices, to improve resiliency.

This paper presents a review of the factors impacting the stability of riverbanks slopes along the Red River of the North which involve Lake Agassiz clays. In particular, the impact of the presence of fissures and micro-fissures and the role of fully softened shear strength in slope stability is discussed. The paper also presents and discusses the results of laboratory testing on disturbed and undisturbed Brenna Formation clay and its relevance to instability. It was found that at the field scale the fully softened shear strength can be a representative lower bound of the strength of the sliding mass not subjected to prior shearing.

An investigation into the practices regarding research of relief wells for pressure relief was conducted to ascertain the origins of the current state of practice within the U.S. Army Corps of Engineers (USACE). Relief well research was reviewed, emphasizing the history of experimentation, usage, and the current state of practice within USACE. The devastating flood of the Mississippi River in 1927 lead to a change in the levee profile along the lower Mississippi. High water nine years later during the 1937 flood gave witness to dangerous seepage conditions and large sand boil activity behind the newly rebuilt levee sections and demonstrated the need for a comprehensive underseepage research program for its control. Early research methods included physical models, well tank, field experiments, and electrical analogy studies. Starting in 1940, filter criteria and well screen compatibility were assessed based on Terzaghi’s recommendations, and results from field and well tank experiments aligned well with this theory. Based on the conditions witnessed during the 1937 flood, field experimentation were conducted to assess the limitations and advantages of different well configurations. A case history from an emergency condition at Fort Peck Dam in 1942 showed that relief wells could be installed in emergency situations and were capable of providing immediate pressure relief. Responses from a 2016 survey of the USACE districts that have large inventories of installed relief wells further defined the current state of practice within USACE. A better understanding of where relief well research has been and what challenges face the levee or dam engineer will better focus future investigations into improving this widely used seepage remediation method.

Weak layers in a slope can undermine its stability over time, particularly when the slope is subjected to rainfall and seismic activities. A challenging task for engineers is to properly identify the presence and extent of such layers. Conventional investigation methods such as cone penetration test and standard penetration test only focus on the localized region surrounding the measurement location and may not provide adequate information by which to evaluate the spatial extent of the layer. Nondestructive/geophysical testing methods can overcome this limitation and can assist practitioners with their assessment of the subsurface. In this regard, full waveform inversion (FWI) is a high-resolution seismic method that builds velocity models by minimizing the residuals between observed and synthetic waveforms. In a pure numerical framework, this study presents a case that studied the effectiveness of FWI to identify a single weak layer with a stiffness of 1/3 of that of the competent material of a slope. Results from the FWI approach provided a promising image of the location and geometric extent of the weak layer that aided in assessing the overall stability of the slope.

Removal of contaminated sediment along a river bank at the base of over-steepened slopes required mitigation of slope impacts to permit the remedial action. The shoreline slopes were, at best, marginally stable as evidenced by near vertical banks, leaning trees, and visible shallow failures at multiple locations. The project has severe constraints due to very high upland slopes, multiple private owners of the upland areas, such that the stabilization measures could neither extend into the upland in many areas, nor could they reduce the river cross section to prevent increased flood hazards, as well as a need to preserve the character of the existing shoreline. This paper will discuss the evaluation and investigation of conditions as well as the selection and design of slope stabilization measures to mitigate the impact of dredging in consideration of competing objectives. This evaluation also considered social, political, hydrological, and technological issues as well as accessibility, and constructability aspects. The design basis development of performance-based specification and construction limitations will be presented. The process resulted in the selection of structural mitigation measures including piling, combi-walls, and submerged rock buttressing with no permanent impact to the upland from the in-river work.

A computational platform for the performance-based probabilistic assessment (PBPA) of seismically-induced slope displacements (D) is presented, which allows to estimate D hazard curves for a wide range of earth systems and natural slopes subjected to earthquakes in different tectonic settings. Procedures in the PBPA framework should be preferred in engineering practice, because they enable a hazard-consistent and rational seismic design. However, they are not commonly used in practice, because they are thought to be too cumbersome to be used in non-critical projects. The computational platform is developed as an object-oriented MATLAB GUI, and it features a variety of different seismic slope displacement models. It provides novel implementations for the full treatment of existing uncertainties (i.e., epistemic and aleatory) in the estimation of D hazard curves. In addition, the platform is fully integrated with state-of-the-art probabilistic seismic hazard assessment tools for one or multiple intensity measures, which allows its direct application in engineering practice. An illustrative example for the application of the platform in the context of an engineering project is presented.

Many of the stormwater tunnels in the Twin Cities area are within the weakly cemented St. Peter sandstone. Although its friable nature makes it conducive for tunneling, the presence of water flow induced piping features can result in unpredictable groundwater behavior and unstable ground conditions, which are often not detected by conventional geotechnical drilling. Many of the stormwater tunnels constructed during the early–mid 20^th century are undersized for storm events which results in surcharging. Cyclic surcharging has led to damage of the concrete tunnel liner and in many instances has resulted in erosion of the Sandstone behind the liner. The authors present in this paper a unique approach to solve the challenge of groundwater inflow during new access shaft construction. By using the hydraulically conductive nature of the Sandstone, drainage holes were installed along the invert of the existing stormwater tunnel, dewatering the shaft, and allowing the project to continue.

The Fremont Siphon Replacement Project included twin 2.15-meter (84-inch) diameter, 141-meter (464-foot) long microtunnel bores beneath the Lake Washington Ship Canal in Seattle, Washington. In addition to the microtunnel bores, the project included two secant pile shafts up to 9.8 meters (32 feet) in diameter and up to 24.4 meters (80 feet) deep, two near-surface connections to the existing trunk sewer system, and a new odor control facility. To mitigate microtunnel risk on the project, King County (the project owner) selected a unique baselining approach where baseline geotechnical conditions for the shafts were described in a traditional geotechnical baseline report, while baseline conditions for the microtunnel drives were presented in the project specifications, with values limited to a cobble and boulder strength range, and a maximum boulder size. The baseline also described the ground as highly abrasive, with the number of cobbles and boulders encountered being incidental to tunneling. To facilitate collaboration with the contractor and mitigate the county’s financial risks associated with differing site conditions (DSC) claims, an incentive provision was included in the contract which allowed the contractor to claim a bonus at the completion of each drive as long as a DSC-related claim was not submitted for that drive. In addition, tunnel mining was paid by the hour, with a specified number of hours and minimum unit cost required on the bid form. This innovative approach proved successful, as the contractor completed both microtunnel drives within the allotted time, collecting both incentive payments, despite challenges. This paper details the unique contracting approach used on this project and discusses some of the lessons learned that are being applied to other microtunnel projects in the Seattle area.

Since urban tunnels constructed in the weak ground at shallow depth are highly sensitive to the stress level, surcharge loads resulting from adjacent buildings can dramatically increase the induced stresses and settlements, and even failure of the buildings can take place. In this study, utilizing three-dimensional finite element models, the efficiency of the umbrella arch method (UAM) on stabilizing the tunnels subjected to the surcharge loading is investigated. The analysis considers the actual field conditions of implementing the UAM and the primary supporting system. For the surcharge loads applied in this study, the analysis results showed that using the UAM can efficiently control the tunnel crown and ground surface settlements by at least 48% and 33%, respectively. Consequently, reinforcing the tunnels using UAM is one of the effective ways to overcome the severe conditions, in terms of safety and stability, in urban tunneling under existing adjacent buildings.

In the design of building rectification with underexcavation method, the deformation and the failure mode of the excavation holes are the key problems. In this regard, an experiment was done in a simulation model box with the hole diameter 200 mm. And three cases of hole distances of 400, 600, and 800 mm were considered. It was found that the excavation holes failed principally in 3 failure modes: vertical irregular oval, horizontal irregular oval, irregular circle. Further, it was found that the soil pressures (stresses in the soil) transfer from the above the holes to the side soil between the holes, which mean that the soil arching effect occurs. Furthermore, it is found that as the hole distance becomes bigger, the soil between the holes will form a steady arching foot, which is unfavorable to the building rectifying. Thus, it can be concluded that a critical hole distance exist between steady arching and unsteady arching. It can be concluded from this experiment that hole distance of 2–3 times of the hole diameter is a desirable hole distance for building rectifying design in this type of soil.

One of the most important requirements in the design of underground openings is prediction of ground behavior. In geotechnical engineering practice, there are a multiplicity of ground behaviors, one of the most important of which is squeezing conditions. Squeezing conditions are most common in tunnels driven through fault zones in rock or through soils containing mixed-face sand and clay or full-face clay. At present, the design approach is to compare the free-field stress with the intact strength of the soil/rock medium. The present research is an extension of present practice and involves study of sand and water contents on the squeezing behavior. The research utilizes kaolin clay-sand mixes in unconfined compression similar to the behavior at the tunnel perimeter as the stress concentration increases during advance of the opening through a clay-sand medium. By varying the sand and water content, the effect of the soil constituents on the squeezing stresses and strains are determined. The results of the study provide indexes for predicting squeezing and/or brittle overstressed ground conditions in tunnels and underground chambers. Moreover, squeezing behavior was observed in the laboratory with sand contents up to 80% by weight, water contents at and up to 11% below the plastic limit, and stiff to hard soil consistencies at the tunnel perimeter.

The Southwest Light Rail Transit (LRT) (METRO Green Line Extension) Project is an extension of the METRO Green Line (Central Corridor LRT), which will operate from downtown Minneapolis through the communities of St. Louis Park, Hopkins, Minnetonka, and Eden Prairie, passing in close proximity to Edina. The proposed alignment includes 16 new stations and approximately 23.3 km (14.5 miles) of double track. The project includes two double-cell cast-in-place concrete LRT tunnels. Both tunnels will be constructed by cut-and-cover methods. The shorter tunnel is approximately 180 m (600 feet) long and passes under State Trunk Highway 62. The longer tunnel is approximately 660 m (2,200 feet) long and runs through a narrow right-of-way adjacent to an active railroad line on one side and residential buildings on the other side and passes under a roadway. This paper discusses tunnel design considerations including an innovative support of excavation design to allow the installation to be completed with minimal noise and vibration and control of groundwater inflow during construction.

The load on tunnel lining is the main factor that is used for lining design in mechanized and NATM tunnels. In mechanized tunnelling, the amount of soil convergence near and behind the machine tail is among the main factors that can reduce the lining load. There are different methods for calculation of the lining load in soft soil such as empirical, numerical, and direct field measurements. This study discusses some common methods for estimation of the load on the circular lining in clayey soil. The numerical model used in this study was initially created before actual field excavation and is considered to be class A prediction. Limited measurement data of a tunnelling case in medium soft clay are used to discuss the amount of an imposed load on lining.

Soil movements due to tunnel face collapse have catastrophic effects on both surface and underground structures and utilities. The aim of this study is to determine the extent of the zone of influence resulting from tunnel face movements, experimentally. Several models made of transparent soils were employed to visualize deformations leading to tunnel-face collapse. A soft transparent synthetic clay made of magnesium lithium phyllosilicate (MLPS), which is commercially known as Laponite RD was employed to simulate a soft marine clay. An embedded plane of seeded particles was used to track soil movements. Digital image correlation (DIC, aka particle image velocimetry, PIV) was employed to obtain deformations perpendicular and parallel to the tunnel face. These deformations were combined to obtain the 3D zone of influence and compute the resulting volumetric and shear strains. The effect of tunnel face displacement on surface and subsurface settlements are presented for two tunneling configurations. Settlements due to a range of face losses resulting from retraction of the tunnel face by 5% to 30% of the tunnel diameter, were determined, and correlated to the observed ground displacements.

Underground voids present a unique geotechnical engineering challenge. This paper will address materials and transportation mediums that are typically used for backfilling underground voids with native material. After reviewing traditional backfill and transportation methods, this paper will explore the advancing technology of foam transportation and the advantages of using this technology for transporting fill materials into underground voids to backfill them. The paper will also review the benefits that a foamed backfill brings to these applications and highlight specific case studies in which foam transportation has proven effective and provided cost-effective, environmental benefits.

Ground falls are one of the significant hazards in underground mining which lead to severe fatalities and injuries. Effective roof support is critical to prevent ground falls and ground fall accidents. Several roof support techniques have been used in mining industry, including rock bolts, cribs, posts, long wall shields, cans, and pumpable roof supports. Among them, pumpable roof supports have advantages over other roof support systems and have been increasingly used in underground mines. The major constituent of a pumpable roof support system is the cementitious material such as calcium-sulfo-aluminate (CSA) cement and Portland cement currently used in practice. However, these conventional cementitious materials cannot achieve the normally conflicting responses such as high stiffness and large residual strength required for an effective roof support system. The present study investigates the feasibility of utilizing Class F fly ash and natural biopolymer to develop a hybrid geopolymer-biopolymer cementitious material having high load stiffness, high peak strength, and large residual strength. A series of laboratory tests, including setting time, viscosity, and unconfined compression tests, have been carried out. The results indicate that the new hybrid material is a promising pumpable cementitious material which can possess the normally conflicting properties of high load stiffness, high peak strength, and large residual strength.

In tunnels excavated in squeezing ground conditions, the excess rock pressure may cause failure of the tunnel lining leading to substantial rock deformation. The increase in rock pressure and deformation may be time-dependent, indicating that creep plays an important role. This paper presents a three-dimensional physical model of a lined tunnel subjected to true-triaxial stress state. The model material is a synthetic mudstone prepared by mixing cement, clay, and water in a specific proportion. The model consists of a cubical mudstone specimen with a pre-existing tunnel and lining element. Strain gauges are installed on the lining element as well as embedded around the tunnel. The cubical sample is loaded in a true-triaxial cell at stresses equivalent to the field stress levels. Five acoustic emission sensors are also installed on the surface of a cubical specimen to record and locate any damage in the rock or the lining element. The stresses, deformations, and damages are continuously monitored for several days to study the effect of creep. Results from this experiment show the potential capability of this physical model in understanding and differentiating damage and deformation due to instant stress release and creep behavior of rock around the tunnel boundary.

Sub-surface stratigraphy is critical to the planning, design, and construction of tunneling projects. The differing site conditions (DSC) claims seen in the tunneling industry is often attributed to an inadequate level of geotechnical site investigations. In current tunneling practice, there is only limited guidance available for the geotechnical engineers to identify locations of investigations. This paper proposes incorporating the knowledge of spatial uncertainty into site investigations for tunneling applications. The paper compares the proposed approach with the conventional site investigation approach in reducing the sub-surface domain uncertainty, thus mitigating tunneling risks. The study applies advanced spatial techniques on actual geotechnical site investigation data from a soft-ground tunneling project. Multiple equiprobable realizations of the sub-surface domain are evaluated on a 3D random field and are post-processed to develop a model of spatial uncertainty. Incorporating the knowledge of spatial uncertainty allows a rational and logical approach in designing optimal site investigation campaigns for tunneling applications.

Given the limited capacity of available railway tracks in Australia, to sustain increasingly faster and heavier trains, the development of innovative and sustainable ballasted tracks is essential for Australian transport infrastructure. Upon repeated train loading, ballast aggregates become degraded and fouled owing to the intrusion of external fines either from the subbase or surface, which decreases track drainage potentially leading to track instability. This paper reviews some advancements in testing methodologies and design implications of ballasted tracks stabilized with artificial inclusions, including geocomposites, energy absorbing rubber mats, and end-of-life tires. Measured test data shows that the use of these waste rubber products and geosynthetics provides an appropriate solution for mitigating unacceptable track degradation and for improving sustainable track alignment, apart from reducing the thickness of the ballast layer. Field monitoring data from fully instrumented tracks constructed at Singleton, Australia, is presented and discussed. The outcomes of this study contribute to a better understanding of the performance of reinforced ballasted tracks, which will be imperative for the development of more efficient and cost-effective track designs with enhanced safety and passenger comfort.

Ballast is the most common foundation material of railways and as such is subjected to deformation and degradation from the large cyclic and impact loads generated by heavy, fast moving trains. These inevitable effects hamper the safety and efficiency of tracks and increase the track maintenance frequency. One of several promising approaches to mitigate these problems is stabilizing ballasted track with rubber mats (under sleeper pads—USP and under ballast mats—UBM), to absorb energy and reduce particle breakage, track stability, longevity, and safety. This paper analyses the current knowledge of using rubber elements in ballasted track acquired through large scale laboratory testing carried out at the University of Wollongong (UOW). This investigation reveals that indicate that the damping characteristics of rubber mats reduce the deformation and degradation of ballast. The results shows that USPs are better at reducing vertical permanent deformation while UBMs are better at reducing lateral deformation.

This paper presents a study on ballasted track behavior, capturing particle breakage under dynamic loading using large-scale laboratory testing, supplemented with computational modeling approaches. Four large-scale triaxial tests are conducted to investigate the ballast breakage responses subjected to cyclic loading subjected to varying frequencies, f=10–40Hz. Measured laboratory observations show that an increase in loading frequency and magnitude results in significantly increased degradation (breakage) and deformation of ballast. Computational modeling using a coupled discrete-continuum approach (coupled DEM-FEM) is introduced to provide insightful understanding of the deformation and breaking of ballast under cyclic loading. Discrete ballast grains are simulated by bonding of many cylinders together at appropriate sizes and locations. Selected elements located at corners, surfaces, and sharp edges of the simulated particles are connected by parallel bonds; and when those bonds are broken, they are considered to represent ballast breakage. The predicted axial strain ε_a, volumetric strain ε_v obtained from the coupled DEM-FEM model agree reasonably well with those observed experimentally. The coupled model is then used to investigate micromechanical aspects of ballast aggregates including the evolution of particle breakage, contact force distributions, and orientation of contacts during cyclic loading.

This paper describes a preliminary investigation of an innovative driven-grouted soil nail (x-Nail), which has been designed by combining the facilities and capabilities of a purely frictional driven nail and a compaction grouted soil-nail. In addition, a special type of cementitious grout with an additive was used to minimize grout bleeding and to increase bond strength. A series of fully instrumented laboratory-scale pullout tests were performed to evaluate the performance of the x-Nail compared to a conventional driven soil nail and a pre-buried compaction-grouted soil nail. It was found that the x-Nail worked as an anchor nail instead of a purely frictional soil nail. The results revealed that, for a given injected grout volume, the pullout capacity of the x-Nail nail increased approximately 1,800% compared to the purely frictional driven soil nail, and by approximately 12% compared with the pre-buried compaction-grouted soil nail. Based on these preliminary investigations, it can be concluded that the innovative x-Nail provides a promising alternate for soil reinforcement.

Hybrid retaining walls comprise a lower soil nail wall (SNW) and a mechanically stabilized earth wall (MSEW) on top are typically needed in combined cut and fill wall sections such as in road widening. However, available literature and design guidelines on SN walls in such hybrid systems are limited. The purpose of this research is to numerically investigate the behavior of SN walls in hybrid retaining wall systems during and after construction. Two-dimensional finite element models of different wall configurations are analyzed using PLAXIS 2D software. The base-line model is verified against a published case history of a monitored SN wall with good agreement. The effect of nail length to total height (L_N/H_T), SNW facing slope (ω), nails inclination (α), and setback distance (d) on the tensile forces of nails in the SNW are studied. The results of tensile force distribution of nails are presented in this paper. The calculated tensile forces from the numerical modeling are compared with calculated values from SNW design methods using the Preliminary design charts, Simplified method, and Modified simplified method. Furthermore, the tensile forces of numerical modeling are equal or higher than the tensile forces of the simplified, modified simplified methods (empirical method), and preliminary design charts (limit equilibrium method).

In recent years, the use of mechanical stabilized earth (MSE) wall systems have been becoming dramatically popular worldwide. When MSE walls are compared with conventional retaining walls, MSE walls have various economic and aesthetic advantages. As MSE walls have a higher tolerance for deformations in comparison to rigid retaining walls, they are much preferred specially in earthquake-prone areas. A better understanding of their behavior under static and seismic loading conditions is required to better predict their field performance. This study presents various methodologies developed for calculating the natural frequency of MSE walls. Upon estimating its natural frequency, an 8 m high prototype MSE wall was modeled using two-dimensional (2D) finite element method (FEM) computer program PLAXIS. Numerical analysis of the MSE wall was performed by applying input ground motions with varying frequency content (i.e., earthquake cases). Seismic response of MSE walls was discussed in the context of the frequency of the harmonic loading and the natural frequency of MSE walls by comparing deformations and tensile stresses in the reinforcement for each seismic loading case. Based on the results, the maximum acceleration amplification was observed at the estimated natural frequency of the MSE wall and the maximum horizontal displacements were greatest at the uppermost reinforcement.

Northwestern University Feinberg School of Medicine Simpson-Querrey Biomedical Research Center (SQBRC) is a new facility in the Streeterville neighborhood of Chicago. The earth retention system (ERS) for the facility supports as much as 18.0 m (59 feet) of excavation and provided support of surrounding areas including active city streets with active public utilities on the north and south, and existing buildings on the west and east. Marginal subsurface conditions including loose sands, soft clays, and a groundwater table with a ready supply of water from Lake Michigan steps away, further challenged the design of the ERS. Designers used an observational method in conjunction with a real-time monitoring system of automated total monitoring stations (ATMS) and shape accel arrays (SAA) to determine if contingency measures were required to stabilize the ERS during excavation. The design required addressing three (3) main factors: (1) maintain active public ways and utilities by controlling deflections below tolerable levels, (2) provide stabilizing lateral support for the existing structures during mass excavation due to unbalanced earth pressures, and (3) accommodate the excavation and substructure construction with minimal impact. Using a system of steel sheet piling along the perimeter along with a combination of internal bracing and grouted soil anchors, designers were able to support the required excavation depths and stay within allowable tolerances for deflection. The observational method allowed designers to eliminate potential additional levels of bracing required in the marginal subsurface conditions, thus saving money and time, as well as to continuously monitor the impacts of the excavation on the surrounding area. This paper discusses the ERS as designed and installed, the contingency measures anticipated, the monitoring system used, the results of the monitoring, and the benefits to the project of using an observational approach.

One of the functional and economical methods used to support and mitigate the deformations in urban excavations is Brick Stair Wall method. Like any other techniques, this method needs to be proved to be effective and rational. In this study, utilizing the finite difference method program, FLAC, efforts have been made to distinguish environmental conditions in which, this method of support is applicable. In addition, the effect of buildings adjacent to excavation on the surrounding ground is considered using equivalent elastic beam method (EEB). It was found that using this method in some specific conditions is extremely reasonable, especially in urban areas. In terms of excavation depth, this method of supporting performs more effectively in excavations deeper than two meters. The results also showed that the deformations derived from numerical modeling were captured well by well-known empirical formulas to predict settlements next to an excavation.

Design guidelines to ensure stability and performance of mechanically stabilized earth (MSE) walls under flooding and rapid drawdown conditions are a priority for the Wisconsin Department of Transportation (WisDOT). Performance of a 4-m high MSE wall reinforced with metal strips was evaluated. Seepage and slope stability analysis were conducted on the model wall. Porewater pressure and free water surface obtained from transient and steady state seepage analyses were used as initial conditions for slope stability analysis. Results indicated that for a poorly graded (SP) sand backfill with a hydraulic conductivity of 7.4×10^-4 cm/s, a 2-m high flooding event in front of the MSE wall saturates the backfill and reaches the steady state condition in 6 hours. The limit-equilibrium factor of safety increased from 2.2 before flooding to 2.8 immediately after flooding and equilibrates back to 2.2 after 6 hours. On the other hand, rapid drawdown of a 2-m face flooding event drops the factor of safety from 2.2 to 1.7. Factor of safety increases back to 2.2 in about 6 hours after rapid drawdown. Flooding and rapid drawdown causes variation in the stability factor of safety of the MSE wall of around 25%. Construction of a 4-m high instrumented MSE wall to conduct complementary full-scale physical testing is ongoing. The wall will be subjected to flooding, precipitation, and rapid drawdown conditions. Porewater pressures, displacements, strains, and stresses within the backfill will be measured. The anticipated outcome of the simulation and testing program is a series of design graphs for use by WisDOT engineers.

New York University’s (NYU) 181 Mercer development is a part of NYU’s master plan to provide university programming in the historic Greenwich Village neighborhood of New York City. To provide the desired amount of programming space, NYU proposed a 9 to 26 story building with two cellar levels to the lot-lines of a 7,430 square-meter (80,000-square-foot) site. General excavation extended about 10.7 meters (35 feet) below the adjacent streets, and localized excavations for proposed mechanical space, a pool, and caisson caps extended up to 4.6 meters (15 feet) deeper. Past developments on the project site, adjacent streets, and adjacent structures had a paramount impact on below-grade construction, coupled with the site being next to an NYC Landmark District and a landmarked 33-story tower. The proposed cellar levels extended below part of the de-mapped Greene Street which presented many unknowns regarding existing utilities and other buried structures. The north and south sides of the excavation were supported by bracing the foundation walls of the former building that occupied the site and jet-grout-underpinning the walls. Double-channel soldier piles braced by tiebacks were designed to support the east and west perimeters of the excavation. External bracing was designed to be anchored below the mat foundation of the neighboring landmarked tower, to avoid cellars of the neighboring historic buildings, below a subway, and to avoid utilities. Soil-mixing was constructed to support localized excavations for the proposed pile caps, mechanical pits, and pool below the general subgrade that were up to 3.6 meters (12-feet) below groundwater. Excavation support for the new building and new utilities were adjusted as excavation exposed utilities and foundations of the former industrial buildings that occupied the site in the early 20^th century. The new 181 Mercer building is supported by drilled caissons socketed into bedrock. The caissons were installed using a down-the-hole hammer with an internal air-flow system. Neighboring structures were monitored throughout excavation and foundation construction to verify activities on the site did not cause adverse effects on the structures.

Geosynthetic-reinforced retaining (GRR) walls have been utilized as bridge abutments to support shallow foundations of bridges instead of traditional deep foundations, such as piles. In this technology, GRR walls support both bridge beams on spread footings constructed directly on the reinforced soil mass and approaching roadway embankments. However, limited studies have been carried out to investigate potential slip surfaces and their corresponding factors of safety when the wall is subjected to footing loads. The focus of this study is to investigate the effect of the footing loading on global stability of GRR walls with modular block facing. The limit equilibrium (i.e., the Bishop simplified method) in the ReSSA program was used to determine the potential slip surfaces and their corresponding factors of safety. Parametric studies were carried out by varying two parameters, i.e., the width and the offset distance of the footing from the wall facing, to investigate their effects on the potential slip surface and the factor of safety. The results show that the slip surfaces began from the far edge of the footing and developed into the reinforced zone towards the wall facing. When the width of the footing was increased, under the same applied load, the factor of safety slightly increased. However, the offset distance of the footing from the wall facing had a minor effect on the factor of safety.

The geosynthetic reinforced soil integrated bridge system (GRS-IBS), which consists of closely-spaced layers of geosynthetic reinforcement and compacted granular fill material, is a fast and cost-effective approach for bridge support that is increasingly being used. The in-service performance of this innovative bridge support system is largely evaluated through the deformations of the GRS abutments. This paper presents a predictive model for estimating the lateral deformation of GRS abutments under service loads. The parameters that are considered in the predictive model include abutment geometry (height, foundation width, facing batter), backfill friction angle, and reinforcement characteristics (stiffness, spacing, length), and applied static loads from 0 to 400 kPa. In order to develop this predictive equation, a comprehensive parametric study was conducted using a validated 3D finite difference numerical model. The results of the parametric study were used to derive the predictive equation using statistical analysis. The developed equation was validated using four case studies. Such a prediction model would be useful to practitioners in preliminary GRS abutment design.

This paper presents a numerical investigation on the long-term performance of a geosynthetic-reinforced soil (GRS) pier and a reinforced soil foundation (RSF) under axial loading. A 3D finite-difference program was used to model the performance of the GRS pier and RSF and evaluate the long-term deformations of these structures. To model the creep behavior of the backfill material, the Burgers creep viscoplastic model combining the Burgers model and the Mohr-Coulomb model was used. The input parameters of this model were calibrated based on experimental test results on granular material. To simulate the long-term behavior of the reinforcement layers, the dependency of the geosynthetics tensile stiffness on the generated strain was captured in the simulation. The numerical model was validated against an available long-term large-scale test on a GRS pier. After model validation, the performance of an RSF during 10 years of the service life was investigated. The results of this study showed that the amount of secondary deformation of RSF can increase more than 50% of the immediate settlement during 10 years of service life and the stress distribution and the location of the maximum stress will change with time.

Permanent secant pile walls between 117 to 122 feet deep were designed to provide vertical and lateral support for a 50 to 70 feet deep basement for an ancillary building for a new subway facility. The secant pile wall consisted of overlapping drilled shafts 34.65 inches in diameter and spaced 23.5 inches apart. The secant piles were installed in very soft soils and sensitive glacial deposits. Due to practical limitations of verticality control during drilling, overlap between piles was unlikely beyond 85 feet. To mitigate this, all primary piles were terminated at 85 feet while secondary piles were constructed to the full depth of the wall. The intermediate gaps below 85 feet had to be sealed using jet grouting. Pre-installation ground improvement using jet grouting was implemented to provide underpinning support to an adjacent building. An additional row of jet grouting was required next to the underpinning jet grout columns to form a stable platform for casing installation. Due to the large depth of the piles, maintaining construction tolerance was a challenge. The core beams tended to sink downwards as there was no competent strata to support the pile at the toe. A number of piles became rotated during withdrawal of the casing. This paper discusses the various approaches that were adopted for mitigating the deficiency in design capacity of settled or rotated core beams.

The Mid-Coast Corridor Transit Project is an 11-mile northerly extension of San Diego’s light rail transit (LRT) system. The project includes construction of numerous structures and doubletrack widening of shared portions with the Los Angeles-San Diego-San Luis Obispo (LOSSAN) commuter/freight/Amtrak rail corridor. Corridor widening civil improvements formed a physical “bottleneck” within a narrow channelized section of Rose Canyon (140 feet wide) located below the heavily traveled Interstate I-5 and State Route SR-52 interchange. Structures in this location include the relining of Rose Creek channel and various types of high retaining walls. Significant design and construction challenges presented themselves due to the geotechnical site condition. This case history addresses relevant considerations for the investigation, analyses, design, and construction of this key component of the project.

A temporary cofferdam system was required for a spillway rehabilitation project to provide a dry work area while maintaining the upstream lake at the normal operating pool level. A hybrid cofferdam system consisting of two circular cells and one arc cell connected to the dam embankment by two cantilever sheet pile walls, was designed and constructed on highly plastic, over-consolidated clays. Each of the circular cells has a diameter of 19.5 m and a height of 15.2 m with all cells filled with free-draining, granular fill material. An instrumentation system was designed and implemented to monitor the cofferdam throughout spillway construction. The instrumentation system consists of eleven inclinometers, five settlement plates, seven observation wells, and 224 strain gauges enclosed in eight channels each, strategically located around the cofferdam system. This paper summarizes the unique characteristics of the hybrid cofferdam, challenges encountered during design and construction, and lessons learned from the monitoring program.

A two-tiered mechanically stabilized earth (MSE) segmental retaining wall (SRW) system with a maximum height of approximately 90 feet along its curving, concaved section was built at a new residential development near Asheville, North Carolina, in 2011. The two-tier section of the wall was approximately 400 feet in length where the upper wall was nested within the lower wall to account for a topographic depression and the site-specific grading. During the last layers of fill placement of the two-tier portion, substantial bulging, vertical deformations, and cracking along the face blocks of the wall were observed. As a result, the owner of the wall decided to demolish a significant portion of the upper wall. A detailed field investigation was performed, before and during the wall removal, to evaluate the as-built conditions of the MSE/SRW wall and to assess the potential factors that contributed to the observed movement and distress. The field investigation included detailed observations of various components of the wall: 1) backfill; 2) foundation; 3) geogrid reinforcement; 4) facing blocks; and 5) drainage system. This was done by means of 13 hand-dug test pits, 13 sand cone tests, and laboratory analyses of multiple bulk samples. The results of observations, testing, and analyses illustrate how standard design calculations for MSE/SRW walls do not incorporate the influence of some of these five components. In particular, concave sections of such walls as well as serviceability conditions are not very well accounted for by standard design practices. Finally, this paper provides insights into the design and construction practices that contributed to the observable deformations and distress in the wall, the importance of appropriate construction to appropriately match the design assumptions, and the relative effect of various site conditions on the performance of an MSE/SRW wall.

This paper presents a study on the reliability-based design of a cantilevered retaining wall under seismic earth loading condition. For the simplicity of discussions, the wall is assumed to embed in a granular material and the pseudo-static Mononobe-Okabe equations are used to determine dynamic earth pressures on the wall. The conventional limit equilibrium stability analyses are used to determine the embedment depths of the retaining wall under static and seismic loading conditions. The factors of safety for each loading condition are selected by a pre-determined reliability acceptance criterion and earth load/resistance variances. The probability distributions of earth load and resistance are obtained from Monte Carlo simulations for the given statistical characteristics of soil properties, and they are used to determine the probability of failure or reliability of the wall design under static and seismic loading conditions. For the seismic loading scenario, the exceedance probability of seismic event is taken into account in determining the reliability of the wall design.

In addition to generating uniform vertical surcharges from dead loads, some structures, such as noise wall barriers, generate significant wind loads that contribute to horizontal surcharges and non-uniform vertical surcharges from moments. These horizontal surcharges and moments create additional induced stress on retaining structures. A plastic limit equilibrium solution is proposed to quantify the lateral earth pressure along the retaining wall from the combined effect of the noise barrier loads and self-weight of the soil, assuming an active failure state. A small-scale experimental model was then constructed to test the validity of the proposed methodology using an instrumented thin aluminum plate to model a flexible retaining wall. An L-shaped, weighted surcharge and auxiliary pulley system is used to model the vertical dead load and horizontal/moment caused by wind load. The variables tested include the distance between the surcharge loading and the retaining wall and the magnitude of the horizontal and vertical loads. The experimental testing confirms the validity of the plastic limit equilibrium and shows the limitation of the semi-empirical solutions currently used in practice.

Arching effect causes reduction in earth pressure in retaining wall with narrow backfill which magnifies the need to study actual characteristics of such walls. In this study, series of load displacement/settlement tests on small scale model of narrow RE wall were conducted under static footing loading condition to investigate the effect of lateral displacement, settlement, distribution of lateral earth pressure, and mobilization of tension at each reinforcement layer. Performance evaluation was based on active earth pressure condition where variable parameters include interface connection between narrow RE wall and existing stable wall, footing offset distance, and relative density of sandy soil. Result demonstrated that coefficient of lateral earth pressure decreases as depth of narrow RE wall increases indicates arching effect takes place because of mobilization of soil-wall friction angle developed along the side walls. Also, provision of interface connection helps decrease in lateral displacement by 0.6–0.8 times in upper layer and generates additional frictional resistance to combined wall systems.

This study describes the influence of various factors on the dynamic response of geocell reinforced beds subjected to machine induced vibration. A series of field vibration tests were conducted on two different foundation beds, namely, unreinforced and geocell reinforced. The studied factors include depth of placement of geocell, the width of geocell, and infill materials. Four different geo-materials were used to quantify the effect of infill material on geocell performance. From the results, the optimum width and depth of placement of the geocells for the maximum improvement in the performance were observed as 5B and 0.1B respectively. At the optimum width and depth of placement, a 49% reduction in peak particle velocity (PPV) of the foundation bed was observed. In addition, the peak displacement amplitude of vibration was decreased with the increase in the angle of shearing resistance (ϕ) of infill material.

Experiments were conducted to evaluate the effect of coal combustion product (CCP) leachates on the hydraulic conductivity of geosynthetic clay liners (GCLs). Three commercially available GCLs were evaluated in this study. One of the GCLs contained sodium bentonite (Na-B) and two contained bentonite-polymer (B-P) composites. The B-P-1.5 contains 1.5% polymer loading and the B-P-5.5 contains 5.5% polymer loading. The GCLs were permeated with two synthetic CCP leachates, named as typical CCP (TCCP) leachate and high ionic strength (HI) leachate. Hydraulic conductivity of Na-B to TCCP leachate increased to 2.3x10^-9 m/s whereas B-P-1.5 and B-P-5.5 maintained low hydraulic conductivity to TCCP leachate (<10^-10 m/s). Hydraulic conductivity of Na-B and B-P-1.5 increased to >10^-10 m/s to HI leachate whereas B-P-5.5 maintained low hydraulic conductivity (e.g., 4.3x10^-11 m/s). These results illustrate that B-P GCL with sufficient polymer loading (>5%) can be used to manage aggressive CCP leachates.

Moisture-induced distress is one of the primary causes of premature failures of roadways. It is well understood that unsaturated conditions are the driving force in pavement performance. Geosynthetics have been used to provide separation, filtration, reinforcement, and confinement in pavement systems for decades. They have also been used to provide drainage. Previously the main function of drainage relied on gravitational water flow, hydraulic head development, and saturated conditions. The development and ongoing research of an enhanced lateral drainage geotextile (ELDG) provides new alternatives to designers, contractors, and owners in the active management of moisture content within roadways. This paper explains the functioning mechanism of the ELDG system and summarizes the years of research which have culminated in providing designers the ability to quantify the benefits to unpaved roads and flexible asphalt pavements.

Mechanically-stabilized layer (MSL) with multi-axial geogrid is an effective ground improvement technique that helps to increase bearing capacity and reduce settlement of soil foundations, and increase strength/stiffness of geo-materials. The MSL with geogrid is frequently used for construction platform and foundation applications subjected to static loading. Load distribution in the MSL under static loading is a basic load transfer mechanism. To further investigate the load transfer mechanism, four large-scale plate loading tests were conducted on 300-mm thick MSLs over weak subgrade under static loading. The subgrade had an undrained shear strength of approximately 48 kPa. Three static plate loading tests were performed on the MSLs with three types of multi-axial geogrids. A non-stabilized but similar section was also tested as a control section. During each test, a load was applied at a constant displacement rate until failure. From the load-displacement curves, the ultimate bearing capacities of the test sections at similar displacements were determined. The test results show that the MSL with the geogrid increased the bearing capacity and stiffness of the test section. The benefit of the geogrid to the increased bearing capacity measured experimentally was compared with the established analytical formulae developed by researchers.

Geosynthetic materials are increasingly used to reinforce the soil from past several years. Mostly cohesionless soil such as sands are used as backfill material in the reinforced-soil structures. However, the availability of natural sand is reducing continuously, and that created certain environmental and economical issues. The use of marginal soils can provide an easy and economical solution to this problem. Hence, the aim of the current study is to evaluate the interface shear behaviour of various marginal soils with different types of geosynthetics. The interface shear tests were carried out in a large-scale direct shear apparatus on five marginal soils with varying plasticity index and four different geosynthetics. The interface shear behaviour was analysed through the response of shear stress-horizontal displacement, vertical displacement-horizontal displacement, failure envelopes, and coefficient of interaction. Significant variation was found on the interface shear strength parameters of the same soil with different geosynthetics due to the contribution of different interfacing mechanism.

The objective of this study was to evaluate the effect of mine process solutions on the internal shear behavior of geosynthetic clay liners (GCLs). Displacement-controlled internal direct shear tests were performed on a needle-punched reinforced GCL hydrated with an acidic and an alkaline solution for hydration periods of 1, 6, and 10 months. A stiffer internal shear behavior was observed for internal shear tests on specimens hydrated with the acidic solution, whereas shear behavior of specimens hydrated in the alkaline solution was comparable to specimens hydrated in de-ionized water. Despite the differences in shear behavior, hydration with the acidic or alkaline solutions did not produce a noticeable impact on the peak or large-displacement shear strength of the GCL.

Geotextiles have been widely used in soil infrastructures for reinforcement, separation, filtration, and drainage purposes. For woven geotextiles, which are often used for reinforcing the base and subgrade in road embankments, will cause excess water accumulation near the geotextile installation location. As a result, the benefits of reinforcement are decreased and the deterioration of a roadway will be accelerated under repetitive traffic loads. Recently, a new wicking geotextile has been developed which has the capability to drain both free and capillary water out of a road embankment and has the potential to overcome the limitation of conventional woven geotextiles. The soil-geotextile system works under unsaturated conditions in most of its service life and limited research have been performed to determine the unsaturated hydraulic properties of the wicking geotextile. This paper aims at determining the geotextile-water characteristic curve of the wicking geotextile. Firstly, laboratory tests were performed to determine the geotextile-water characteristic curve. Then, the geotextile-water characteristic curves of wicking and non-wicking geotextiles were compared to demonstrate the advantages of the wicking geotextile in dehydrating soils.

Seismic safety of large embankment dams in earthquake prone regions is critical if a large population lives on the downstream of the dam or the reservoir provides a great amount of water. The main purpose of this paper is to investigate the effects of main reinforcement design parameters (e.g. stiffness, vertical spacing, etc.) on seismic response of geogrid-reinforced embankment dams. Finite element (FE) constitutive model is developed to capture nonlinear response of soil and reinforcement elements at large strains. A series of analyses are performed and results, in terms of normalized horizontal and vertical displacements alongside the embankment dam height, and mobilized reinforcement stresses along the geogrids are plotted in dimensionless figures. The results show significant decrease in both horizontal and vertical displacements, and increase in geogrids tensile stresses due to the increase in reinforcement stiffness. Furthermore, it will be demonstrated that decrease in the geogrids vertical spacing results in lower values of tensile stresses along the geogrids and improves the seismic performance of reinforced earth dams, considerably.

This paper presents the results of wind tunnel tests of the ClosureTurf landfill final cover system. ClosureTurf is a synthetic turf closure system that services as the hydraulic barrier to separate the waste and protect human health and the environment. It consists of a structured geomembrane, an engineered turf, and a specified infill. Wind tunnel testing was conducted on a scaled landfill model constructed with a 3H:1V slope on one end, a top deck, and a 4H:1V slope on the other end. The pressure distribution along the closure system surface was measured using pressure taps. Wind tunnel tests were also conducted on an exposed geomembrane surface. The measured pressure distribution along the exposed geomembrane surface was compared to that along the closure system, as well as the semi-empirical solution by the widely accepted Giroud method. The results of the wind tunnel tests can be used in engineering practice to evaluate whether the closure system has sufficient ballast to protect it from wind uplift under a design wind speed.

Slope failures such as rockfalls and landslides are one type of geohazard that affects state trunk highways. Previous research efforts that model slope failures are limited to one failure type, limited in geographic coverage, and are often subjective. This study presents a new slope failure risk model that accounts for all failure types while covering more ground than previous efforts. For this project, the Minnesota Department of Transportation (MnDOT) partnered with WSB to determine the risk of slope failure along state highways in three regions. This paper outlines the methods and results of this project including the new geographic information systems (GIS) model that can be implemented anywhere in the state. Vulnerability factors including slope, terrain curvature, and proximity to rivers and bedrock outcrops were statistically tested using multi-varaiate regression analysis. Model results were field validated and ranked into four proposed risk management categories: action recommended, further evaluation, monitoring, and no action recommended. Preliminary ranking results indicate that 826 of the 35,000 proposed management areas are recommended for mitigation. The results of this study are intended as the first step of actions required in minimizing the effects of slope failure including costly repairs and potential threats to public safety.

Natural alluvial deposits exhibit variability in strength and stiffness parameters which results in uncertainty in the response of geotechnical structures such as slopes. Random limit equilibrium method (RLEM) offers a conceptually simple, versatile, and efficient approach for the evaluation of the stability conditions of heterogeneous slopes. Limit equilibrium methods (LEM) using non-circular slip geometries have proven more accurate than circular slip geometries in profiling the failure status of heterogeneous slopes by passing through the weak points more effectively. Findings of the current study support the non-circular RLEM approach over the conventional circular slice-based formulations. It is also shown that adopting a very simple and computationally efficient quasi-stochastic RLEM approach, which is based on the block search method, will render fairly accurate predictions of the stability conditions of nonhomogeneous slopes in comparison to the inaccurate 1D approach. Furthermore, it is shown that considering correlation in the shear strength parameters is very important when evaluating the stability of heterogeneous slopes.

Although energy piles are used worldwide as an environmentally friendly foundation technology, quantifying the uncertainties in their thermomechanical performance is still challenging. To properly address these uncertainties, a probabilistic version of energy pile model is needed in practice. In this study, the load-transfer method-based geotechnical design model for energy piles is probabilistically calibrated under the Bayesian framework. Based on the load-transfer method, a deterministic design model for energy piles is developed to predict the thermomechanical behavior of energy piles. Considering the cross-site variability among different sites, the observation data from several widely reported energy pile case histories are adopted to characterize the model bias factor. The Bayesian calibration is realized by using the hybrid Markov chain Monte Carlo sampling.

This paper presents insights obtained from reliability analysis and reliability-based design (RBD) for three geotechnical engineering examples, namely an underwater slope in San Francisco Bay mud that failed during excavation, a spread footing sustaining both vertical and horizontal loads, and laterally loaded piles in soil modelled with nonlinear and depth-dependent Matlock strain-softening p-y curves. The aim is to show how RBD via the first-order reliability method (FORM) can overcome some limitations of the load and resistance factor design (LRFD) method and the Eurocode 7 (EC7) design method. The differences and similarities between the design point in RBD and those in LRFD and EC7 are discussed. The ability of RBD-via-FORM to provide valuable information at its design point and to automatically reflect parametric uncertainties, correlations, and case-specific sensitivities and to resolve subtle load-resistance duality is demonstrated. It is suggested that RBD-via-FORM can be conducted in tandem with partial factor design methods in order to overcome some limitations which sometimes arise in the latter.

In this paper, a numerical analysis is presented using fast Lagrangian analysis of continua (FLAC) 2D for the evaluation of slope reliability. The Cholesky decomposition technique has been used to develop the 2D non-Gaussian homogeneous random field. The performance function against MSW slope failure is formulated based on the linear regression equation of factor of safety obtained using numerical package, FLAC 2D. A reliability index of MSW slopes is computed using first order reliability method (FORM). The spatially variable design parameters of MSW landfill slopes are treated as random variables. The results of the present study provide an ample understanding of the spatial variability associated with shear parameters of MSW landfill slopes. The shear stress and shear displacements along the geomembranes (GMB) interfaces are presented with and without spatial variability. The effect of correlation distance on the reliability index of MSW landfill slope is presented in the form of design charts for different mean and COV values associated with unit weight, cohesion, and friction angle of the MSW.

Earthen levees protecting coastal regions can be exposed to compound flooding induced by multiple drivers such as coastal water level, river discharge, and precipitation. However, the majority of flood hazard analyses consider only one flood driver at a time. This study numerically investigates the performance of an earthen levee in Sherman Island, Sacramento, CA, under compound flooding induced by fluvial and pluvial flooding. A finite element model is built for fully coupled 3D stress-flow simulations of the levee. The finite element model is then used to simulate the hydro-mechanical response of the levee under different flood scenarios. Fluvial flood hydrographs for different scenarios are obtained using a bivariate extreme analysis of peak river discharge and peak ocean level while accounting for the significance of correlation between these two variables. Pluvial flooding is characterized using intensity-duration-frequency (IDF) curves of extreme precipitations for the study area. The fluvial and pluvial flood patterns for different recurrence intervals are used in the finite element model to simulate the hydro-mechanical response of the levee. Results show that considering compound flooding leads to 8.7% and 18.6% reduction in the factor of safety for 2 and 50-year recurrence intervals, respectively.

Due to the tectonic environment, mud pots and mud volcanoes are common at the southern end of the San Andreas Fault near the Salton Sea. These features are generated from carbon dioxide gas at depth. While their level of activity may fluctuate, they are generally stationary. In 2016, a mud pot (referred to as a mound mud spring) began moving southwest. Critical infrastructure, including the Union Pacific Railroad (UPRR) dual tracks, utility and petroleum pipelines, and a state highway had been previously built in the path of the moving mud spring. The mud spring impacted the UPRR tracks in late 2018, which carries freight from the Ports of Los Angeles/Long Beach to the eastern part of the country. To accommodate the mud spring movement, we utilized sheet piles, shoofly tracks, and rip rap to keep the trains operational. Kinder Morgan evaluated the moving mud spring impact on their critical petroleum pipeline that provided fuel to civilian and military facilities in the desert southwest. Their pipeline is located adjacent to the UPRR tracks. After considering a temporary bridge to support the pipeline, Kinder Morgan elected to reroute their pipeline around the mud spring’s path. As of September 2019, the mud spring has moved over 100 m (300 feet) and is located on the (now disabled) UPRR main line tracks. Shoofly (detour) tracks have been constructed to allow train traffic to go around the mud spring. The spring’s rate of movement is variable, but averages about 3 meters (10 feet) per month. The UPRR is currently waiting for the mud spring to clear the main line tracks before backfilling the erosion area and restoring normal service. Scientific studies to understand the mechanism behind the mud spring movement are continuing.

Site characterization is indispensable in geotechnical engineering practice, and it aims at delineating spatial distribution of underground soils and rocks in a project site and estimating soil properties for geotechnical analysis and design through in situ tests, laboratory tests, or other methods. In geotechnical practice, soil properties are often sparsely measured at a limited number of locations, due to time or budget limit, technical or access constraints, etc. This leads to a question of how to select the number of measurements (i.e., sample size) and their corresponding sampling/measurement locations such that as much as possible information on soil properties can be obtained. A smart sampling strategy is developed in this study that leverages on innovative data analytic methods (e.g., Bayesian compressive sensing, BCS, and information entropy) for determination of sample size and locations. Real laboratory test data are used to illustrate application of the proposed smart sampling strategy.

Rainfall is a major cause of slope failures. As rainstorms become more frequent and intense over time due to climate change, the reliability of a large number of existing engineered slopes under extreme rainstorms is of great concern to the public. This study develops a weighted bilinear correlation between the failure frequency of engineered slopes and the triggering rainfall intensity based on a comprehensive engineered slope database in Hong Kong in the past 30 years and evaluates the performance of engineered slopes under future extreme rainstorms. The correlation indicates that the rock cut slopes and soil cut slopes perform similarly, but the fill slopes and retaining walls have higher reliability than the cut slopes.

Geotechnical engineering is considered one of the financially riskiest engineering professions due to the inherent uncertainty associated with characterizing the subsurface. Subsurface investigations rarely provide a complete picture of the nature of the soils at a particular site and the results of the investigation and laboratory tests typically require interpretation in order to be used in design. When the characterization of the subsurface and/or the engineering properties of the soil differ from those expected during design, damage can occur to the constructed project. In the United States, where lawsuits are prevalent, this damage often translates to claims against and thus financial losses for geotechnical engineers. A database comprised of 1,500 claims levied against geotechnical engineering companies between 1988 and 2013 was examined, and the 897 claims that resulted in significant financial losses were subsequently analyzed. $51 M in losses could be attributed to claims in which the primary service provided was geotechnical investigation. This was the single largest area of claims, accounting for 44% of those studied. Several other sources were identified, including technical errors, errors in communication between parties, and improper documentation during geotechnical analysis. This paper will summarize the study database, highlight the primary sources that led to legal action against geotechnical companies, and make recommendations as to how proper site characterization, project documentation, and peer review can be used to implement best practices and minimize the risk of legal liability.

The aim of this paper was: (1) to establish soil-specific laboratory calibration equations for two types of volumetric water content sensors (5TE and GS3); and (2) to evaluate their measurement accuracy and precision for estimating the soil moisture contents in sand, based on the established laboratory calibration equations and the corresponding default factory calibration equations provided by the manufacturers. The study revealed that the developed laboratory calibration equations (linear and polynomial) improved the sensors’ measurement accuracy compared to that obtained using their corresponding factory calibration equations. Based on the root mean square error (RMSE), the 5TE sensor exhibited higher accuracy (RMSE=1.15%) with the third-order polynomial equation, followed by the second-order equation (RMSE=1.32%) and a linear regression equation (RMSE=1.63%). Thus, the third-polynomial type equation was considered to be the most suitable calibration model for the 5TE sensors in sand. In contrast, the second-order polynomial calibration equation provided highest accuracy for the GS3 sensors with the lowest RMSE of 0.86%.

Terrestrial laser scanning (TLS) is a surveying technique that uses lasers to measure coordinates of objects in the scanner’s 360° view space. This paper is evaluating the applicability of this technology into monitoring movements of mechanically-stabilized earth (MSE) retaining walls of a newly-constructed bridge interchange and comparing the results to finite element modelling (FEM). Settlements determined from TLS during and post-construction were 61 mm and 104 mm in the North and South walls respectively. Total station surveying provided from the contractor agreed with these settlements with measured values of 56 mm and 113 mm respectively. The FEM results compared well to what was observed with the TLS as it determined maximum movements of 55 mm and 109 mm in the same locations of the walls. With these results, the modelling performed portrays the variability of site conditions well and is a suitable method for this application.

Earthmoving activities during construction cause disruption of stabilized land, leaving sites susceptible to soil erosion. To minimize water quality implications downstream of active construction sites, regulations require stormwater pollution prevention plans, which encompass the design, installation, and maintenance plan of erosion and sediment control practices used during construction. One common sediment control practice used on construction sites is a sediment basin. This research evaluated the performance efficiency of temporary sediment control basins through in-field monitoring of two basin systems on the U.S. 30 expansion project in Tama County, Iowa. Monitoring was conducted on a single basin over a period of four weeks in the fall of 2018 and captured seven rain events. Turbidity and total solids concentrations were used to determine performance efficiency of the basins. The basin provided an average turbidity reduction of -92 NTU, indicating higher turbidity at discharge than inflow, and total solids reduction of 15.5 mg/L. A five-week monitoring period of two basins in series captured fifteen rain events. The two basins provided average turbidity reductions of 24 and 107 NTU, respectively, and a collective turbidity reduction of 43 NTU. Design modifications to the standard sediment basin were suggested to enhance performance including: use of an upstream rock check dam, geotextile lining, coir baffles, and surface dewatering system.

A federal major disaster declaration was made on August 2, 2018, for the regions affected by the 1,000-year storm on June 17 that yielded nearly seven inches of rain in under nine hours across the Upper Peninsula of Michigan. This event soon became known as the “Father’s Day Flood”. In the aftermath of the storm, the authors performed site inspections to evaluate the resulting culvert washouts and associated damage along the Copper Range and Calumet-Hecla Trails between M-26 and Normand Rd. just north of Lake Linden, Michigan. This trail is vital to the region as it is a main corridor through Keweenaw Peninsula for recreational vehicles (tourism) and provides access to commercial forestry land. Over 160 culverts exist along the 9.5-mile section of trail inspected, and over half were affected by the storm. The use of cloud-based geographical information systems (GIS) mapping software allowed engineers to define specific parameters for condition assessment, record the condition observed at each culvert site, and geo-locate the data in real time. This paper outlines how the collected data was used to determine risk of future failure at stream crossings, assess immediate threats to the surrounding community, and how this workflow allowed the engineers to rapidly perform a data driven cost comparison for remedial work and immediate trail stabilization.