Geo-Congress 2019: Soil Erosion, Underground Engineering, and Risk Assessment

Wind erosion is a critical factor in coastal engineering regarding its role in, e.g., coastal dune stability, dune morphology, and beach erosion. This phenomenon has been studied for decades from different research fields such as sedimentology, morphology, agriculture, or coastal engineering, resulting in different approaches to determine the wind velocity threshold required for particle mobilization. However, geotechnical parameters such as bulk density, friction angle, or the soil water characteristic curve (SWCC) have not been considered in these expressions, which contributes to uncertainties when predicting the fluid threshold velocity for a given sand using the existing predictive equations. This study proposes a new set of analytical expressions to estimate the initiation of wind erosion that includes the influence of the shear strength and moisture content. An infinite slope stability analysis has been performed in which the wind velocity effect is expressed as a set of normal and tangential stresses on the slope surface, and the shear strength of the sand is defined in terms of moisture content via the SWCC. The equations were calibrated and tested using a compiled dataset from the literature, which is composed of wind tunnel experiments performed on different types of uniform sands and water contents. Preliminary results show good agreement between the predicted and observed threshold velocities, which indicates that the erosion initiation by wind can be predicted using geotechnical parameters.

Bridge scour is the primary cause of bridge failure in the United States. An important aspect of infrastructure management at the state and local level is to prioritize bridges for scour inspection, countermeasure installation, and mitigation. This becomes particularly significant in wake of severe storms. In this paper, a modified version of the HYRISK model for scour risk assessment of bridges is implemented in a geographic information system (GIS) platform. The tool is envisioned to assist post-storm risk assessment of bridges for scour assessment supported by autonomous underwater vehicles (AUV) monitoring missions. The HYRISK model, a risk assessment model used in determining the monetary risk and probability of scour failure, is used for bridge risk assessment in New York State. Data required for the model are obtained from the National Bridge Inventory (NBI), and are implemented in a GIS software. A normalized risk map of bridge scour failure in New York State is presented to demonstrate the efficacy of the method in identifying and prioritizing bridges for scour-related inspection and mitigation works.

This paper uses case studies of scour at bridges in Rhode Island to evaluate the current HEC-18 scour equations used to assess bridge safety and design. The study utilizes data from two major historical storm events—a 500-year flood and a 25-year hurricane (Sandy). Hydraulic analyses were performed using the HEC-RAS program at three bridge study sites, two in riverine environments and one in a tidal environment. Detailed bathymetry and topography of each site was obtained using a variety of methods. Flow boundary conditions were obtained from USGS gages and a numerical storm surge model. Sediment samples indicated that the bed materials were cohesionless ranging from silts to boulders. Scour predictions were compared to sounding data collected before and after the historical events. The results of the analyses indicated that the HEC-18 equations yielded conservative predictions of scour at all bridges analyzed in this study. The level of conservatism depended on the particular equation that was utilized. The results also suggested that the level of conservatism could be reduced by better characterization of the D₅₀ of the bed materials and consideration of the transient nature of storm events.

Internal erosion is one of the leading causes of embankment dam failures, which involves the migration and reconstruction of soil particles within the soil skeleton. The loss of fine particles in an earth structure will induce grain rearrangements and affect the contacts between soil particles, leading to a coarser and more permeable structure, significant displacements, or even failure of the earthen structure. Therefore, to understand soil deformation and mechanical consequences subjected to particle loss is of great importance to prevent internal erosion-induced failures. In this study, a series of upward seepage tests was conducted on a self-developed triaxial erosion apparatus, combined with a digital photographic method. Complex stress conditions were considered to gain insights into the role of stress state on soil deformation and mechanical response after experiencing loss of particles. Significant axial and radial deformations can be observed from both the global and local aspects. The radial strain was non-uniform along the sample, while the axial strain along the vertical direction was uniform. After internal erosion, the soil strength decreased, and the soil behavior changed from a softening behavior to an obviously strain-hardening response.

Stream bank erosion is a naturally occurring process that is known to be affected by the increased runoff volumes and peak flows associated with dense urban development. The observed widened channel and undercut stream banks near the headwaters of the Chrome Run, located in Middletown Township, Pennsylvania, suggest the development within the watershed has accelerated the rate of bank erosion. As part of a robust before-after-control-impact study, the stream geometry of the Chrome Run (at the headwaters and downstream) and two additional streams were monitored to assess rates of erosion and accumulation. Bank pins and channel cross-section surveys were used to document changes to the stream geometry. This paper presents documented changes in stream geometry from four different monitoring sites observed between October 2017 and May 2018. Bank erosion occurred at each of the sites during the monitoring period; however, as expected, the rate of bank erosion within the more densely developed watersheds was greater than the rate of bank erosion within the less developed watershed.

Increased coastal erosion rates have forced communities to rethink how to manage vulnerable coastlines. In many locations there is a trend towards implementing temporary engineering solutions, such as geotextile sand containers (GSCs) and geo-tubes, to stabilize erosion hot spots and assess the impact of these designs while long-term solutions are developed. GSCs and geo-tubes have the potential to increase the resilience of natural systems to protect coastlines from smaller storm events (e.g. 25-year storms) while providing flexibility in design considering the uncertainty regarding future rates of sea level rise and storm frequency. The objective of this paper is to summarize the performance of geotextile stabilized coastal sites and present results of on-going field studies to assess the performance of GSC reinforced dunes in Montauk, NY. The better-than-expected, resilient performance of GSCs and geo-tubes at most locations and recent reinforcement of dunes, bluffs, and shorelines in New York, Massachusetts, and Hawaii emphasizes the need for continued field research and in situ monitoring to collect high-quality performance data to better evaluate laboratory experiments and numerical models developed to predict the hydraulic stability of these systems.

Internal erosion, also known as piping, is one of the major causes of earth dam failures. Piping occurs when flowing water transports soil particles out of the structure of the dam creating a hole within the embankment. According to the U.S. Department of the Interior Bureau of Reclamation almost 30% of dam failures are due to piping. Lebanon, a developing country, also has its share of dam failure. Recently, two earth dams failed in Laqlouq area, Lebanon, due to erosion causing a massive inundation. No systematic studies have been conducted to provide better insight on piping evolution/failure in Lebanon. Plaxis 2D, a commercial finite element software, was used to model one of the sustained earth dams in Laqlouq area. The aim of this study is to show the piping evolution using an iterative approach within the body of the structure. Soil properties (i.e., permeability, strength, density) were determined in the laboratory using ASTM standard methods. Disturbed soil samples were collected from the earth dam. 2D model of the dam was created and the initiation of piping was determined based on the hydraulic gradient $“i”$ versus the critical hydraulic gradient $“i_{cr}”$. Piping was identified at the location where the hydraulic gradient was greater than the critical hydraulic gradient. Findings showed that the current dam is susceptible to internal erosion, triggering the formation of a pipe and failure.

Claypan soils cover approximately 40,469 km² in the United States and are characterized by a highly impermeable layer within 0.5 m from the ground surface. This impermeable layer acts as a barrier for infiltrating water, which may increase erosion rates and sediment transport. Two of the main problems associated with these processes are abutment scour and reservoir sedimentation. This study focuses on the undermining of surficial soils due to an impermeable claypan layer in southeastern Kansas. The potential areas of critical soil loss and hydrologic flow patterns were determined using LiDAR-derived digital elevation maps across two 0.45 km² sites. These sites were located in areas of both high and low elevation. Electrical resistivity tomography (ERT) was used in areas identified with LiDAR to measure the depth to claypan, which was originally believed to be uniform across the region. The results indicated that the claypan layer was located from 0.5 to 0.75 m and dissipated moving across the site from an area of high elevation to an area of low elevation. Undisturbed soil samples were collected based on the ERT analysis, in areas with and without the claypan. An erosion function apparatus (EFA) was used to directly measure erosion due to sheet flow and to identify the controlling mechanism causing surficial soil loss. The knowledge gained on claypan erosion mechanisms will improve the prediction of near surface soil erodibility to support aging infrastructure.

Although several studies have indicated that vegetation on coastal marshes protects the coast from erosion by providing soil reinforcement, wave buffering, sediment trapping, and overall hydrologic regime control, the complex nature of coastal erosion processes makes it too difficult to quantify the net erosion resistance provided by the vegetation. This research uses a novel method of combining different available tools: laboratory tests, in situ tests, and analytical models, to study the soil binding ability provided by smooth cordgrass, Spartina alterniflora. Field vane shear tests and direct shear tests were conducted to investigate the overall effect of roots on the shear strength of dredged soils in Sabine Refuge Marsh Creation Project in Louisiana. Laboratory tensile strength tests of the plant roots were conducted, and two different root reinforcement models were used to estimate the root reinforcement. Root reinforcement calculated from the direct shear tests was compared with that from the analytical models. Analysis using the root reinforcement models showed an overestimation of root-induced cohesion and a new correlation was proposed.

A series of upward flow tests in sandy soil models with similar geometry have been performed to provide new insights into the physical modeling of piping erosion. The tests were performed by increasing the differential head across the models until total heave occurred. To assess the centrifuge scaling effects, several tests were conducted at different gravitational accelerations. Observations of the pressure loss in different sections of the specimens demonstrated that the erosion initiates with progressive loosening of the soil near the surface and then advances downward before total heave occurs. Although the process was similar in all tests, visual observation showed that the thickness of loosened zone before total heave decreased as the gravity increased. The critical hydraulic gradient required to initiate piping erosion was found to increase linearly with the gravitational acceleration. Hence, a linear scaling factor was estimated for models with the same grain size and model size.

Landslide susceptibility assessment is a fundamental part of landslide hazard mitigation. A traditional one-off assessment can hardly respond to new observations of landslide incidents. Hence, this paper presents a novel method to update regional scale landslide susceptibility considering real-time observations of landslides. First, the correlation among the susceptibility of zoning cells is quantified to build connections among adjacent zoning cells using Monte Carlo simulation and random field theory. Then the prior susceptibility of the zoning cells is evaluated using a slope stability analysis model. After that, real-time observations of landslides are used to update the landslide susceptibility utilizing the Bayesian approach. As an example, a research area of 1 km² in size is studied in this paper. This method is able to respond to new inputs of landslide records timely and update the landslide susceptibility while considering correlations. Hence, the accuracy and capacity of landslide susceptibility assessment are effectively improved.

Hampton Lake, a recreational reservoir located in northern Nassau County, Florida, USA, was heavily impacted by the effects of Hurricane Irma. A combination of heavy precipitation and hurricane-induced high water stages in the St. Mary's River caused catastrophic failure of the earthen dam containing the reservoir and complete loss of the stored water. The failure was initially documented by a NSF supported Geotechnical Extreme Event Reconnaissance (GEER) reconnaissance site visit. After this initial effort, the investigation was expanded to evaluate the cause of the dam failure. During the storm event, the spillway was overtopped leading to toe erosion. Based on the analyses conducted to date, the most likely cause of the dam failure was erosion of the downstream embankment areas which were not adequately protected by riprap. Failure case studies are useful to design engineers around the world by providing "lessons learned" to improve future design efforts for similar projects.

Quantitative landslide risk assessment is a key step in creating appropriate land use policies. The forced migration of those displaced by recent events in Syria has highlighted the need for studies to guide humanitarian aid and resettlement policies. In 2011, armed conflict in the region precipitated the largest refugee crisis in a generation. Over 1.5 million displaced Syrians now reside in Lebanon, rapidly changing the population distribution in geomorphically-active areas of the country. We use a multi-step process to quantitatively assess the landslide risk profile of Lebanon throughout the ongoing Syrian conflict. First, mode-specific geotechnical models are utilized to assess the individual hazard contributions of a suite of triggering scenarios and types of landslides appropriate to the varied terrain of Lebanon. Second, vulnerability estimates and population data from the United Nations High Commissioner for Refugees (UNHCR) are combined to produce scenario-specific risk. Finally, risk data is aggregated to create a comprehensive landslide risk profile for Syrian refugees in Lebanon and compared to that of the pre-conflict Lebanese population.

George B. Stevenson (GBS) Dam, located in north-central Pennsylvania, is part of a flood risk reduction system along the West Branch Susquehanna River. A 2002 feasibility study identified potential dam safety concerns, and in 2011, a grant was obtained to rehabilitate the dam. Initial estimates for rehabilitation were nearly $20M. The design team developed and performed an evaluation of the risk-driving PFM that showed confidence in the risk estimate was low due to the lack of data to support quantification of the nodal probabilities in the event tree. To address these uncertainties, an extensive ($1M) exploration program was undertaken to improve confidence in the input parameters controlling the risk estimate which was driving the costly rehabilitation. The additional data gathered was used to perform a more comprehensive evaluation of the risk-driving PFM (as well as others) and evaluate the rehabilitation in a risk-based framework, which showed the risk-driving PFM was not credible. Rehabilitation was still considered prudent, to provide a filtered outlet for foundation seepage, but with a greatly reduced rehabilitation cost of about $3M (completed in 2017).

Reliability of soil slopes has been studied extensively under the assumption of homogeneous properties for soil layers. However, an abundance of field measurements obtained from fall cone tests (FCT), field vane tests (FVT), and cone penetration tests (CPT) have shown spatial variability of strength properties of soil layers. Several recent investigations noticed the importance of spatial variability of soil properties for estimation of failure probabilities, and the potentials for unrealistic results if such variations are not properly modeled. This paper integrates a new error rate-based adaptive Kriging method called REAK and a weakly stationary random field modeling procedure called Karhunen-Loeve (K-L) expansion method to analyze the failure probability of soil slopes. Under the weakly stationary spatial distribution assumption, mean and variance of soil properties are considered constant, and the autocorrelation function is defined using a spatial lag. The reliability method, REAK, employs Kriging surrogate modeling for adaptive and strategic sampling of random variables to generate most effective training points for model refinement. This feature significantly reduces the high computational demand for failure probability analyses of slopes with spatially varying soil properties. A numerical example on real soil slopes from previous studies indicates the high efficiency and accuracy of the proposed procedure for reliability analysis of slopes and potentially for other systems in geotechnical engineering.

The importance of geotechnical risks concerned with predicting ground movements caused by tunnel and open-cut excavations when building in urban environment is by and large recognized. Ground movements associated with tunnel and open-cut excavations share some common characteristics. Both types of excavation cause horizontal and vertical ground movements and most of the movement is in response to ground loss. This paper discusses simple probabilistic and back analysis approaches aiming to integrate the geotechnical site-specific information in the assessment of ground movement risks related to tunnel and open-cut excavations. The first project example, concerning temporary excavations in soft clay, highlights a probabilistic framework for assessment of excavation basal instability and emphasizes that deterministic and probabilistic approaches can often be regarded as complementary. The second project example deals with the prediction of soft ground tunnel-induced settlements in an urban environment where two tunnel projects were driven in the same geologic conditions. While the design of the first tunnel relied on industry accepted values for the design, the second tunnel used back-calculated design parameters from the first project.

Our nation’s transportation system is routinely impacted by geohazards and climate conditions. Recent examples include wildfires followed by rainfall and associated mudslides in California as well as intense rainfall with associated flooding leading to roadway washouts in Texas, Virginia, and Maryland. Guidance is being developed to assist state departments of transportation (DOTs) and federal land management agencies (FLMAs) in developing or improving existing transportation geohazards programs. This includes considerations for climate conditions and extreme weather events. To respond to the threat of geohazards, many state transportation agencies have developed geohazards management programs. A geohazards program helps agencies manage cost-effective methods for characterizing and reducing risk.

In this paper, the effect of soil spatial variability on the soil-structure interaction in braced excavations is investigated. The excavation-induced wall deflection, wall bending moment, wall shear force, and strut force are modeled by finite element method implemented with non-linear soil constitutive relationships. The vertical spatial variability of sands is simulated by random field theory. This random finite element modeling (RFEM) is realized with the use of Monte Carlo simulation. As a result, the statistical distributions of the excavation-induced responses are probabilistically assessed. It is illustrated that the soil spatial variability has significant influence on the mean value and standard deviation of maximum wall bending moment, maximum wall shear force, and strut axial force. Three major failure modes in the probabilistic structural assessment are explicitly explored with the consideration of soil spatial effect. This study points to the importance of addressing soil spatial effect to ensure design safety and robustness.

This paper aims to investigate a reliability-based analysis for the settlement calculation of surface square footing, resting on homogeneous cohesionless soil, using fuzzy sets theory in conjunction with the finite element method (FEM). Spatial variation of the soil parameter (elastic modulus, E_s) is also considered to capture the soil’s inherent variability. Both isotropic and anisotropic scale of fluctuations are considered to examine the effect of the same on the probability of failure (P_f) values. A parameter (s⁰_lim) indicating the required minimum limiting settlement for zero P_f is suggested by acknowledging the severity of the existence of P_f in any geotechnical settlement problem. Results reveal that as the coefficient of variation (COV) of E_s increases, the failure probability for a particular limiting settlement (s_lim) also increases. Further, the correlation length in the horizontal direction is found to be more effective than other two directions. Finally, the effect of the inclusion of the spatial variability into the geotechnical settlement problem is observed, and the importance of considering spatial variability is well established.

Due to the subtropical weather condition and the changing climate, Hong Kong is experiencing extreme rainstorms more and more frequently, which can trigger a large number of natural hazards such as landslides, debris flows, and flooding. These hazards do not occur separately, but often occur simultaneously or consecutively, and interact with each other, creating amplification and cascading effects. For example, landslides can provide loose materials for debris flows, and debris flows can cause surface erosion and blockage of flood-control facilities. Therefore, it is necessary to evaluate possible scenarios of geo-hazards under extreme rainstorms. This paper aims to predict regional multiple hazards under extreme rainstorms and hazard interactions. Previously, landslides, flooding, and debris flows are often considered as separate hazards and simulated individually. In this paper, an integrated full-process model (EDDA 2.0, Erosion-Deposition Debris flow Analysis 2.0) is implemented to predict slope failures, debris flows, and flooding in a single simulation. Slope stability is analyzed first, and then debris flow initiation from landslides and from surface erosion is considered. Dynamic changes of flow materials are also modeled in the program. The model is first validated with the historical records during the June 2008 rainstorm. Then consequences under three extreme storms (i.e. 44%, 65%, 85% of 24-h PMP, probable maximum precipitation) are predicted. The results show that with the increase of rainstorm intensity, the hazard magnitude increases dramatically, which can pose great threat to the society. This study can be helpful for multi-hazard risk assessment and government policy making.

Conventional underground instrumentation systems, embedded in soil, suffer from major limitations imposed by their wired connectivity. Congestion of instruments and vulnerability of connections to defects due to human activities and aggressive underground conditions, cause significant cost increases and robustness limitations. Numerous attempts for developing through-soil wireless communication systems have been made recently, employing electromagnetic waves, magnetic induction techniques, and seismic waves, though none has provided a complete practical and cost-effective communication scheme. In this paper, a biologically-inspired, through-soil wireless communication system that employs acoustic and seismic waves is described. Successful data transmission has been achieved in laboratory experiments over 1 m range at kbps data rates and in the field over tens of meters at tens of bps rates. The deployment of this system in geotechnical applications and the accompanying challenges are also outlined. This technology has the potential of impacting geotechnical, geophysical, earthquake, mining, agricultural, and numerous other applications.

The shield tunneling in deep stratum of the soft soil can produce soil arching effect on a certain degree. The degree and the later development of the arching effect are directly related to the economy and safety of the project. The development of soil arching effect in the whole process can be available through the whole measure section of soil pressure monitoring in the field for a long time, including the construction, consolidation, and creep stage. The boundary range, the attenuation rule of soil arching effect, and the variation amplitude of earth pressure can be obtained by the monitoring data of earth pressure in deep soft soil. Through the monitoring in the field, the passive soil arching effect influence range of tunneling is concentrated in the range of 1.5 times tunnel diameter in the condition of buried depth for 4 times tunnel diameter. In front of shield cutter, soil arching disturbance range is one time tunnel diameter. The value-added rate of earth pressure in the passive arching effect is 40–50% by the soil squeezing effect in front of the cutter. The earth pressure is affected by the friction force produced by the shield shell when the shield passes through the monitoring section, so the change of earth pressure in the soil arching is small. The change of the soil arching effect in the process of the grouting and slurry hardening mainly depends on the filling rate of the grouting amount to the gap between the shield and the tunnel. It can be seen from the monitoring data that the attenuation stage of the soil arching effect is mainly concentrated in the two years after the completion of the construction. The most obvious position of the attenuation effect on soil arching during consolidation and creep stage is the most obvious position of the variation of soil arching effect during tunnel construction. The spatial position of the soil arching effect corresponding to the tunneling stage and creep stage is basically the same. The ratio of soil arching effect is reduced from 45% to 25% in two years. The field test provides a certain reference value for the proportion of arching effect in the deep layer of soft soil and development rule in the whole process.

Despite the well-known stress anisotropy that may be present in rock masses, tunnel design is often done with the assumption that the tunnel is aligned with one of the geostatic principal stress directions. However, this alignment is improbable and so axial shear stresses may be unintentionally neglected. These shear stresses distort the tunnel cross-section in the axial direction, which is not accounted for in 2D analyses. In this paper, the effects of axial shear stresses on shallow tunnels misaligned with the principal in situ stress directions are assessed. 3D FEM models are conducted for that purpose and the results are compared with 2D plane strain models, often used in practice. Two scenarios are studied: competent rock mass, which behaves as a linear-elastic material, and soft ground, which undergoes plastic deformations. For soft ground, the axial stresses increase the size and change the shape of the plastic zone around the tunnel, thus inducing larger ground deformations.

Characterization of rock masses may benefit from photogrammetry, which is the science of turning photographs into 3D models. Two case histories (one for a slope, and one for a cavern) show the data that may be extracted from the models, and how a much clearer understanding of the fracture sets and of the geologic controls in general may be achieved within a permanent, unbiased documentation of a rock mass.

The Bay Park Sewage Treatment Plant improvement project involved the replacement of three detritus-type grit tanks with three vortex grit tanks within an existing treatment building. The proposed tanks extend 20 ft below grade, 12 ft below existing foundations, and 6 ft below groundwater. Complex site issues included: high groundwater table, pervious soils, space constraints, utility constraints, existing foundation concerns, and a construction staging plan which required one tank remain operational during construction. Traditional underpinning was not possible since dewatering would cause excessive foundation settlements. An innovative solution utilizing jet grouting was implemented to provide support of excavation, underpinning, and control groundwater infiltration during construction. The installation and performance of jet grouting operations was verified and monitored by rig instrumentation and column coring. Near real-time displacement monitoring was utilized to monitor the structure. This paper presents details of the jet grouting design, construction, monitoring and verification results, and lessons learned.

The Chesapeake Bay Bridge and Tunnel Authority is expanding their bridge tunnel network by adding a parallel tunnel under the Thimble Shoal navigation channel utilizing a design build contract. As part of the design build contract a supplemental site investigation was planned and performed. The dynamic depositional environment of the Chesapeake Bay between estuarine and marine conditions, in addition to historic construction and dredging activity, resulted in variability in the soil composition over short distances at the project site. This investigation was carried out by the Authority to refine the ground parameters presented in the geotechnical baseline report (GBR) considering planned alignment changes from the base technical concept as well as to gather information to be used in design and permitting. The scope of the supplementary investigation included land-based and water-based investigations. Over one mile of land-based borings and cone penetrometer tests (CPTs) were completed, including seismic cone CPTs, dilatometer tests, and instrumentation installation. For the water-based investigation, nearly a half mile of borings and CPTs were completed in just 24 days. This paper describes the rationale behind the supplemental investigation, its scope, how the resulting data were integrated into the design of the project, and the technical challenges inherent with working on open waters in close proximity to the area’s highly active commercial and Navy ports.

Foundation selection, design, and construction for sites with complex geotechnical profiles require continual involvement of the geotechnical engineer during design and construction. This paper presents the geotechnical aspects of design and construction of foundations for a seven-level parking deck at a site with deposited boulder and blast rock-laden uncontrolled fill and highly variable depth and quality of rock. Many foundation types including auger-cast piles, spread footings, and micropiles are being used, and the foundation elevations and types are being revised during construction as unanticipated conditions are encountered. As the construction work progresses, complications associated with the boulder and blast rock-laden fill and the depth and quality of rock continue to keep the design team fully engaged. The challenges faced and lessons learned from the exploration, design, value engineering, and construction work for this project are chronicled in this paper.

Backfilling underground mine stopes with mine wastes has become a common mining operation. This practice generally serves to stabilise the stope openings, improve the ore recovery, and reduce the surface disposal of mine wastes. Hydraulic fill, mainly consisting of classified mill tailings and/or sands, remains one of the major filling materials in underground mines. It is usually delivered as a slurried mixture at solid contents in the range of about 65 to 75%. Due to its grain size distribution, pipelines transportation requirement, and relatively high permeability, particles of hydraulic backfill segregate during the placement and curing periods. This results in a fill mass having more fine particles in the upper part and more coarse particles in the lower part of the stopes, which have an impervious base. This phenomenon, known as fluidization’s segregation, can induce heterogeneity and anisotropy in the geotechnical properties of the placed backfill. To quantitatively describe the intensity of spatial segregation of settled backfill, a degree of segregation, defined as the gradient of D₅₀, has been proposed. To investigate the effect of fluidization’s segregation on the geotechnical properties of hydraulic fill placed in an opening, sedimentation tests and unconfined compression tests were performed. In this paper, a few experimental results are presented. It will be seen that the unconfined compressive strength (UCS) obtained in laboratory by following the current practice can be not representative of the real strength of cemented backfill placed in mine stopes.

The Alaskan Way Viaduct Replacement (AWV) project in Seattle includes a 1.7 mile bored tunnel, excavated by the world’s largest EPB TBM at the time it was built in 2012. The TBM finished its journey in April 2017, which was highly successful in ground settlement control, supported by a comprehensive geotechnical instrumentation and monitoring program. This case study describes conventional and state-of-the-art monitoring technologies, the data acquisition and transmission system, as well as the integrated data management platform that were implemented in the project. The monitoring baseline and frequency are also discussed, providing guidelines to similar projects. In the end of the case study, new advancements in tunnel instrumentation and monitoring are also introduced.

Construction in urban areas, e.g., excavation, can generate negative impacts on the foundations of surrounding structures. In this study, based on the surface subsidence measurements due to earth pressure balance shield (EPB shield) tunneling in Chengdu Metro, displacement back-analysis was conducted for a typical cross section using the Peck formula and the stochastic medium theory. The engineering properties of a sandy cobble stratum in the Chengdu area, the settlement trough width (i), stratum loss rate (η), settlement trough effecting angle (β), and cross section contract value (ΔR) were analyzed statistically, and the ranges of these parameters under normal working conditions were corrected as: for the stochastic medium theory, tanβ=1, $\mathrm{\Delta }\text{R}$=16mm (lower limit), and tanβ=1, $\mathrm{\Delta }\text{R}$=5mm (upper limit); and for the Peck formula, k=0.3, η=0.9% (lower limit), and k=0.6, η=0.3% (upper limit). Comparison of the Peck formula and the stochastic medium theory formula, although composition and principle differ, show that the two methods can both be applied to the prediction of surface subsidence caused by tunnel excavation of sandy cobble formation through statistical experience, parametric inversion, and example verification.

This paper presents a numerical analysis of soil steel composite bridges (SSCBs). The bridge is a flexible steel corrugated sheet surrounded by carefully compacted backfill soil. The numerical analysis is performed using the finite element program PLAXIS 2D, and the results are then compared to the typically used Swedish design method (SDM). This analysis focuses on the Skivarpsån composite bridge case study in Sweden. The analysis compares the recorded field measurements of straining actions and vertical deflections with the SDM design approach predictions and numerical model results. Then, the paper investigates the use of arching inducement techniques to reduce straining actions on the steel body without compromising the serviceability of the roads above. Embedding layers of a deformable material such as Pneusol causes significant decrease in the straining actions in the steel sheet. Two patterns are suggested herein, which decreases the developed straining actions from 10% to 15%.

Tunnel projects usually hold risks especially in populated and complex urban environment. Onsite monitoring can obtain useful environment information and provides dynamic feedbacks. This paper takes the Shanghai Bund Tunnel project as a case study and describes how onsite monitoring assists shield tunneling. It is the first application of super-large diameter (14.27 m) earth pressure balanced (EPB) shield in China. In order to control tunneling risk, dense onsite monitoring has been taken and both electrical gauges and fiber Bragg grating (FBG) sensors are applied in data acquisition. The working principle and installation of the FBG sensor, as well as the data analysis are specified. The dense monitoring significantly mitigates the risks and contribute to a successful finishing of the project.

Statistical data indicated that more than 65% excavation projects in China encountered different problems during construction and remedial measures had to be taken to mitigate risk of excavation failures. In some cases, catastrophic excavation failures led to massive fatalities and property losses. Lessons learned from failed cases will help designers, contractors, and owners avoid similar problems/mistakes in advance and then failure incidence can be reduced for future projects. In light of this consideration, this paper reviews typical excavation failure cases encountered in practice within the past three decades in China. Generally, these excavation failures can be categorized into 15 different models; for each failure type, its failure mechanism and major triggering factors were explored and discussed and then schematically illustrated by a conceptual model.