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Acid mine drainage can be curbed or reduced significantly by covering tailings sites with an oxygen barrier. In this study, the ability of pulp and paper residues, more specifically deinking residues, to function as such a barrier was investigated. Field data from two sites show that O2 diffusion through the barriers can be greatly reduced. To better understand how oxygen migrates through deinking residues and to develop prediction tools for future design with deinking residues, one-dimensional effective diffusion coefficients (De) were determined by fitting laboratory experimental curves (O2 concentration versus time data) to curves obtained from computer simulations. The results obtained confirmed the behaviour observed in soil covers: the effective diffusion coefficients are highly dependent on the degree of saturation (Sr) of the compacted material. The De values obtained in this study compare well with those published in the literature for several materials compacted at similar Sr. The De values varied from 8.3 × 10-9 m2/s (Sr approximately 91%) to 9.7 × 10-7 m2/s (Sr approximately 76%). The O2 consumption by biodegradation appears to be an important factor in the reduction of the O2 flux that can reach the bottom of the barrier.Key words: oxygen diffusion, pulp and paper residues, barrier, acid mine drainage.

The authors have presented an interesting paper on the use of deinking residues to create an oxygen barrier. The paper includes some results from laboratory tests, which can be difficult to perform, and an interpretation based on Fick’s laws solutions. Although the writers, like other researchers active in this field, have expressed some reservations regarding the placement of organic cover materials on reactive (acid producing) tailings (as opposed to inorganic materials such as soils and non-acid generating tailings), it is nevertheless recognized that the proposed approach for controlling the production of acid mine drainage (AMD) is certainly worth investigating. Covers made with deinking residues may eventually be added to the few control methods available for mine operators faced with the prospect of dealing with sulfidic mine and milling wastes. In the following paragraphs, the writers would like to discuss some issues relevant to the problem at hand, including some comments and questions for the authors and interested readers. Air versus equivalent porosity

A waste-derived paste of a mixture of paper sludge and tire derived aggregate (TDA) was investigated for daily cover application in municipal solid waste (MSW) landfills. The use of earth materials as daily covers not only consumes valuable landfill space, but also creates a series of operating issues. In this study, an experimental testing program was undertaken with the goal of evaluating the mechanical behaviors of the paste based on the findings of the index properties, compressibility, hydraulic conductivity, stress-induced deformation, stress–strain response, and shear resistance of the materials. The mechanical behaviors of the individual TDA, the sludge, as well as the mixture of the two, were evaluated. When compared to traditional soil covers, the proposed paste was: (i) 2–3 times lighter in weight; (ii) at least two orders of magnitude more impermeable; and (iii) comparable in shear resistance. It was also found that with the addition of TDA to the sludge, the shear strength of the paste was improved considerably. The reinforcing mechanisms were explored and quantified, suggesting an optimal TDA content of about 55% by weight. The results from this study indicate that the proposed paste has mechanical characteristics that are desirable for a potential landfill daily cover.

Marine geotechnical engineering in Canada is over one hundred years old, having started with overwater drilling and testing for bridges and nearshore structures. Its growth has been sporadic, with not much attention being directed to the geotechnical properties of marine soils until the late 1970's when design of artificial islands made up of large caissons started to develop. For about the last 15 years, marine geotechnical engineering has been driven by the oil and gas industry. Most of the action has been in the Beaufort Sea, where complex site conditions have necessitated detailed geotechnical field drilling, sampling programs, and in situ testing. Very little geotechnical engineering research work or site investigation has been carried out off the east coast except for the Hibernia site on the Grand Banks. In the coming years we can expect to see dramatic changes in site investigation methods. The use of robotics and expert systems coupled with innovative geophysical techniques could dramatically change our methods of site characterization and measurement of geotechnical properties. Key words: marine geotechnical engineering, Beaufort Sea, Grand Banks, Scotian Shelf, in situ testing, geophysical – geotechnical relationship, future trends.

Bulk pours of cemented tailings sands are used as ground control backfill in underground mines. This paper presents laboratory test data relating design factors, such as cement content, pour pulp density, and curing humidity, to backfill strength. Unconfined strengths were found to increase with increased cement content, increased pulp density, decreased porosity, and decreased curing humidity. Numerical relations between these factors are presented. Test data showing the behaviour of cemented tailings under triaxial compression are also presented. These data indicate that there is a relation between the unconfined strength and the strength envelope defined by c, [Formula: see text] parameters and that either strength can be used in design providing the confining stresses do not approach those required to cause cement bond crushing. Some practical considerations with regard to backfilling with cemented tailings are discussed. Keywords: cemented sand, tailings, strength, curing effects, mine backfill.

This paper has been written to achieve two objectives. The first objective is to provide a discussion of the practical limitations of numerical modelling in the field of geomechanical engineering. Too many discussions of numerical methods in geomechanical engineering are centred on the impressive ability of numerical tools to conduct complex and sophisticated analyses with relative ease and efficiency. Practitioners need to have grounded conversations on numerical modelling regarding the reality that geomechanical designs are often data-limited with high degrees of uncertainty. When data limits and uncertainty are overlooked, geomechanical engineers are at risk of introducing unforeseen fatal flaws into engineering design. The second objective is to provide “how to” guidelines for model calibration using a variety of data types to qualify and quantify ground reaction. Model calibration is truly the only means to reduce numerical uncertainties. Formal training in numerical modelling is often focused on software utilization and computational methods; however, there are few opportunities for formal training on how to calibrate a model for practical engineering applications. This paper provides guidelines for calibration methods and procedures.

Successful geotechnical projects occur when the design is based on a thorough understanding of the geologic and environmental systems and the interaction of these systems over time. The ability to examine and track movement through space and time has been an essential part of the geoprofessional’s toolkit since the onset of the practice. Since the early 2000s, high-resolution three-dimensional (3D) topographic data have begun to transform how we map and understand movement through time across spatially extensive regions at unprecedented levels of accuracy and confidence. This paper examines how high-resolution 3D topographical data, four-dimensional (4D) analysis, and visualization of data in 3D environments can improve our ability to better understand changes in the morphology and material behaviour through time, leading to better decisions and better outcomes. Evolution of advancements made over the past 20 years is presented through case studies where positive impacts were realized through the adoption of 3D remote sensing and 4D analysis, and cases where data could be used in the future to improve outcomes. The paper presents current research being done to further improve processing techniques and exploit new data collection and computational processing capabilities, pushing the capability of time-dependant 4D geotechnical monitoring to new limits.

This paper describes an experimental study of the effects of sampling disturbance in an Australian natural soft clay and the consequences of different sample quality on the representativeness of soil parameters used in geotechnical designs. The paper is divided into three sections. Laboratory test results obtained from specimens retrieved using three different tube samplers as well as the Sherbrooke (block) sampler are first described. Then, the sample quality assessment, using available indices proposed for soft soils, is presented. It is shown that sample quality varies with the stress paths and boundary conditions applied in laboratory tests. Finally, mechanical soil properties derived from specimens retrieved using the different samplers are used in the prediction of two classical problems in soil mechanics: the settlement and excess pore pressure response underneath an embankment as well as the settlement and bearing capacity of a shallow footing. These two examples are used here to highlight the consequences of poor sampling in practice.

This paper is the second of two companion papers in relation to a new design method for ballasted railway track foundations. Development of the new design method has been explained in the first paper (i.e., Part I: Development), and the procedures for using the method and its practical application on some field case studies are presented in this paper. A special feature of the proposed design method is that it considers the true impact of train dynamic moving loads and number of repeated applications of the traffic tonnage. The proposed method is applied to four case studies of actual tracks and the results are compared with field measurements and found to be in good agreement. It should be noted that, although the proposed design method is able to overcome most shortcomings of the existing methods and found to provide excellent outcomes, further verification with more field case studies is highly desirable.

In this paper, a new design method is developed for ballasted railway track foundations that must support high-speed trains and heavy axle loads. The proposed method is intended to prevent the two most common track failures; namely, progressive shear failure of the track subgrade and excessive plastic deformation of the track substructure (i.e., ballast plus subgrade). The method is based on improved empirical models and sophisticated three-dimensional (3D) finite element (FE) numerical analysis. The improved empirical models are used for predicting the cumulative plastic deformation of the track, whereas the stress parameters of the ballast and subgrade layers are obtained from the 3D FE numerical analysis. The outcomes are then synthesized into a set of design charts that form the core of the proposed design method so that it can be readily used by railway geotechnical engineers for routine design practice. The design method can be applied to various practical conditions of train–track–ground systems, including the modulus, thickness, and type of ballast and subgrade. In addition, the traffic parameters that have a significant influence on track performance are also considered in the design method, including the wheel spacing, train speed, and traffic tonnage. The new design method has significant advantages over the existing methods and would provide a major contribution to modern railway track design and code of practice. The applications of the new design method are presented and explained in a companion paper (i.e., Part II: Applications).

International audience; This paper describes research done on a new testing device including its laboratory test procedure; namely, a laboratory punching test for cementitious backfill materials that evaluates their excavatability with a pick. Three-dimensional and two-dimensional numerical studies using a finite element method were carried out according to calibrated parameters of the material obtained by triaxial tests. This made it possible to study the behavior of the backfill material under action induced by a tool (a pick) as well as to optimize the geometry of the punching test specimen. This paper provides detailed information and results for the experimental study of this laboratory test. Attention was particularly focused on energy relating to displacement as well as types of ruptures. The behavior of these types of materials was found to be greatly influenced by gravel in the material. Repeatability of the test was also studied. Finally, a method for this punching test of backfill materials is also provided.

This study proposes a reliability-based design procedure to evaluate the allowable load for augered cast-in-place (ACIP) piles installed in predominately granular soils based on a prescribed level of reliability at the serviceability limit state. The ultimate limit state (ULS) ACIP pile–specific design model proposed in the companion paper is incorporated into a bivariate hyperbolic load–displacement model capable of describing the variability in the load–displacement relationship for a wide range of pile displacements. Following the approach outlined in the companion paper, distributions with truncated lower-bound capacities are incorporated into the reliability analyses. A lumped load-and-resistance factor is calibrated using a suitable performance function and Monte Carlo simulations. The average and conservative 95% lower-bound prediction intervals for the calibrated load-and-resistance factor resulting from the simulations are provided. Although unaccounted for in past studies, the slenderness ratio is shown to have significant influence on foundation reliability. Because of the low uncertainty in the proposed ULS pile capacity prediction model, the use of a truncated distribution has moderate influence on foundation reliability.

The breaching of containment of conventionally deposited mine tailings impoundments, and the consequent release of tailings flows with long run-outs, unfortunately remains not uncommon and often has devastating ecological and economic consequences, occasionally including the loss of human life. Rather than the breaching of containment itself, which can result from a number of causes (poor control of the phreatic surface, unrecognized dam foundation issues), the contributing factor to the severe consequences of dam breach is the low density and strength and (or) susceptibility of the tailings to liquefy or soften under loading, combined with the driving weight of the ponded water, which allows for significant run-outs (in some cases tens of kilometres) to occur. Hence the motivation for developing alternative technologies that dewater tailings before deposition to the point where reliance on containment is minimized or eliminated. In this paper, these technologies are referred to as “high-density” tailings, which includes any technology that at least produces nonsegregating tailings that will form a sloped stack when deposited, including thickened, paste, and filtered tailings. The paper explores a number of issues related to high-density tailings, including shear behaviour, dewatering behaviour, acid generation, and surface deposition rheology. The paper concludes with some discussion on what the limitations are on this technology that are holding back its wider adoption, and how these limitations might be overcome.

Canadian hard rock mines continue to reach deeper deposits, which poses greater challenges to mine safety including rock burst control. Destress blasting techniques have been successfully employed in such underground mines with the aim of preconditioning highly stressed rock mass to mitigate the risk for rock burst occurrence in deep mines. In the present study, the efficiency of destress blasting is examined through a comparison between traditional and alternative numerical modelling approaches. The traditional modelling approach assumes a uniformly distributed blast-induced damage zone extending over the entire drift face, whilst the alternative modelling approach, presented herein, simulates the damage zone for each individual blast hole. In the first part of this paper, a three-dimensional numerical model of a single blast hole is constructed, whereby the extent of blast-induced damage zone is delineated. The latter part of this paper uses the single-hole model results to examine the efficiency of destress blasting as practiced in drift development in deep mines. It is demonstrated through comparison of FLAC3D numerical simulation results that the traditional modelling approach may lead to an overly optimistic indication of destress blasting efficiency when compared with the alternative modelling approach, in which a more precise simulation of the damage zones is applied.

The paper describes the anisotropic undrained stiffness behaviour of four medium-plasticity heavily overconsolidated UK stiff marine clays as revealed through hollow cylinder testing. The experiments contributed to two broader studies on stiff-to-hard London, Gault, Kimmeridge, and Oxford clay strata. They involved static and dynamic testing of multiple high-quality natural specimens sampled at similar depths from inland sites. This paper explores the directional dependency of the clays’ highly nonlinear undrained stiffness characteristics. New data-analysis approaches are outlined that allow the stiffnesses associated with one-dimensional vertical, horizontal, or pure horizontal shear modes to be isolated in complex undrained stress paths. In the presented experiments, loading progressed from in situ stresses to reach ultimate failure at a range of final major principal stress orientation angles α (defined in the vertical plane) while keeping fixed values of the intermediate principal stress ratio, b. The tests reveal strong undrained stiffness anisotropy that can impact significantly on the prediction and understanding of ground deformation patterns in numerous geotechnical engineering applications.

The paper presents the numerical modelling details using the finite difference method (FDM) to simulate the performance of a well-instrumented geogrid-reinforced incremental concrete panel soil retaining wall. Two different constitutive models were investigated for the backfill soil (linear elastic–plastic model and nonlinear elastic–plastic model). Both constant stiffness and strain-dependent secant stiffness models were used for the reinforcement elements. The paper provides valuable lessons to modellers to simulate the performance of this type of earth retaining structure. For example, parametric investigation of the effect of a constant Young’s modulus ranging from 40 to 120 MPa for the linear-elastic Mohr–Coulomb model had only minor influence on the wall facing displacements and reinforcement loads. However, the choice of magnitude of transient compaction pressure near the facing can result in large differences in facing displacements. The paper also demonstrates that the method of construction including the location, sequence, and stiffness of the temporary supports used to construct the wall plays an important role on measured and predicted wall performance. The physical measurements reported in this paper provide a benchmark for numerical modellers to verify other numerical models for walls of the type investigated here.

This paper focuses on the effect of tunneling-induced ground deformation on the response of jointed cast iron and ductile iron pipelines that (i) cross the settlement profile perpendicular to the tunnel centerline and (ii) connect through 90° tees with a pipeline parallel to the tunnel centerline. The modeling involves two-dimensional finite element analyses that account for coupled forces both parallel and perpendicular to the pipeline, and incorporates the results of large-scale laboratory tests to characterize the joints. Pipeline response is quantified with respect to joint rotation and pullout at various leakage levels as well as the allowable tensile strain. The paper describes soil displacements induced by a 6.1 m (20 ft.) diameter tunnel in clay and sand. Joint rotations and maximum tensile strains for pipelines in sand exceed those in clay by up to three for the same geometric conditions. Cast iron pipelines crossing the tunnel centerline are most vulnerable to leakage from joint rotation; ductile iron pipelines have sufficient capacity against joint leakage in all cases studied. Cast iron pipelines that connect with 90° tees are highly vulnerable to leakage from pullout due to lateral soil movement. Guidance is provided for risk assessment, design, and utility operations.

Extraction of resources in remote locations can require temporary haul roads to transport extremely large, slow-moving, indivisible loads (e.g., plant, oil–gas production modules, and reactors, weighing in excess of 1000 t) without interruptions. Poor subgrade soils may experience larger cyclic strains and greater cyclic degradation under these conditions than under conventional roads, yet the short engineering life precludes many foundation-strengthening options due to cost. As there is little research into this unique situation, this paper synthesizes research from a broad range of applications to discuss implications on expected soil response. Reference is made to critical state theory and discrete element method (DEM) modelling to develop fundamental concepts considering particle-scale interactions. Cyclic failure is proposed to be a kinematically unstable process, triggered by shear banding on the Hvorslev surface, tensile liquefaction or fabric-governed meta-stable liquefaction; the latter is particularly influenced by stress history and anisotropy. This paper finds pore-water pressure accumulation under load and dissipation between loads are key to cyclic degradation and furthermore to be dependent upon load duration, principal stress rotation, and repetition frequency. For meta-stable, liquefiable soils in particular, inclination of principal stresses is at least as important in assessing failure risk as magnitude of stresses.

Risk management for safety in mountain tunnel construction is of great significance. However, existing research lags behind engineering applications. In this paper, the risk of mountain tunnel collapse is used as an example to illustrate a new assessment method based on case-based reasoning, advanced geological prediction, and rough set theory. First, the risk surroundings and risk factors involved in tunnel collapse are integrated and summarized, and a risk assessment index system is established for tunnel collapse. At the same time, because the dynamic response parameters obtained by the advanced geological prediction usually indicate a typical geological structure, sensitive response parameters are introduced in the assessment index system. Advanced risk assessment can be performed for tunnel sections at a certain distance ahead of the tunnel face. Second, the major risk surroundings and the advanced geological prediction results are analyzed for the tunnel under assessment. Cases with similar attribute characteristics are selected via comparison with previous cases. Attribute reduction and calculation of weights are subsequently performed for the risk surroundings and risk factors of similar cases based on the attribute significance theory of rough sets. Finally, index screening and objective weights are applied in the fuzzy comprehensive assessment model. The results of this paper can be used to improve the theoretical level and reliability of risk assessment in tunnel safety and serve as a reference for tunnel construction.

Rockburst is an unstable rock failure and one of the most hazardous problems in deep hard-rock mines. Before excavation, rocks are loaded under a polyaxial condition. Upon excavation, the rocks at the excavation boundaries are loaded in the tangential direction and unloaded in the radial direction. Understanding rock behaviour under this excavation loading condition is critical for developing measures to control rock failure in underground construction. In this paper, numerical simulation results of unstable rock failure using an explicit finite element tool are presented. Firstly, uniaxial compression tests were simulated to confirm the suitability of the adopted numerical tool for simulating unstable rock failures. Transferred energy ratio (TER) and loading system reaction intensity (LSRI) were proposed as indicators to distinguish between stable and unstable failures. Secondly, unstable rock failures under polyaxial unloading conditions were simulated. The influences of loading system stiffness (LSS), specimen’s height to width ratio (H/W), and intermediate principal stress (σ2) on rock failure were investigated. The simulation results showed that rock failure was more violent when the loading system was softer, the specimen was taller, and the confinement was lower. The modelling approach presented in this paper can be useful for predicting unstable rock failure and estimating released kinetic energy, which is important for designing rock support in deep tunnels to control rockburst damage.

Sampling requirements for the quality control (QC) of cement-based “solidification/stabilization” (S/S) construction cells do not currently specify the sample size considering the accuracy of the estimated effective hydraulic conductivity of the cells from the samples, nor considering the risk associated with drawing the wrong conclusions about the acceptability of the cells. In this paper, probabilistic simulations are performed to examine the influence of a soil–cement material’s mean, variance, and correlation length on sampling requirements for a QC program of cement-based S/S construction cells. The sampling requirements are determined by considering a hypothesis test, having nulled that the constructed material is unacceptable, and targeting acceptable probabilities of making an erroneous decision. Two types of errors can be made: (i) concluding that the material is acceptable when it actually is not, or (ii) failing to conclude that the material is acceptable when it actually is. The paper investigates how many samples are required to keep the probabilities of making these errors acceptably small. Plots are provided, which can be used to estimate the required number of samples. The paper concludes by discussing how the simulation-based results compare with current sampling requirements for the QC of an actual set of cement-based S/S construction cells.

A precise evaluation of shear wave velocity, Vs, is a crucial issue in the design of foundations subjected to dynamic loading, liquefaction evaluation, and soil improvement control. Laboratory techniques such as resonant column (RC) and bender element (BE) have been developed over the years to measure Vs. At low strain (γ < 10−3), techniques based on piezoelectric elements (e.g., BE) can be considered superior to RC, as they can be used in conventional geotechnical devices (e.g., triaxial, oedometer, direct simple shear, etc.). However, it is a difficult task to verify that the obtained Vsvalues are correct and accurate, as there are several difficulties associated with these methods, including the mixed radiation of both primary and shear waves, near-field effects, boundary effects, and uncertain detection of first arrivals. This paper presents the use of a new technique to measure Vsin granular material, called the piezoelectric ring-actuator technique (P-RAT), developed at the Université de Sherbrooke. The paper also provides a detailed description of a unique interpretation method of the signals produced from this technique to minimize the difficulties associated with other techniques. The P-RAT has been incorporated into the well-known oedometer cell to measure the Vsof Péribonka sand through a series of oedometric tests, and the obtained results have been detailed, analyzed, and discussed in light of the basic state of knowledge of Vsand factors affecting it. Particular emphasis is also placed on the validation of the accuracy of the P-RAT by means of reliable experimental measurements available in literature.

This paper presents the results from a series of three-dimensional finite element analyses, which examine the benefits of adopting square pile–tower structures instead of circular monopiles. The advantages of square monopiles are brought out in this paper through a parametric study with a Tresca soil model, where the shear strength and modulus of elasticity varied with depth and the pile–tower structures were modelled as an elastoplastic material. The effects of pile diameter, pile thickness, eccentricity, and pile length for free-head pile–towers embedded in lightly overconsolidated and heavily overconsolidated clays were investigated. From the results of the numerical models, it is clear that the ultimate lateral capacity and stiffness of square pile–tower structures are substantially higher than of circular structures embedded in clay layers. Moreover, the amount of rotation and displacement of square structures are not significantly affected compared to circular monopiles.

Lateral loads often control the design of deep foundations. This paper focuses on improving the understanding of soil–structure interaction (SSI) of laterally loaded piles and developing p–y curves based on simultaneous direct measurements of the soil–pile interaction pressure (p) and lateral pile displacement (y) along the length of the pile. This paper summarizes the methodology, instrumentation, soil–pile interaction measurements, and procedure used to investigate the soil–pile interaction and to develop the directly measured p–y curves. A 102 mm diameter, 1.42 m long precast concrete pile was fully instrumented with advanced sensors and installed in well-graded sand. The digital image correlation (DIC) data indicated that the soil movement in front of the pile extended up to 6.3 pile diameters (6.3D) from the pile center. The normalized measured maximum soil–pile interaction pressures closely matched the normalized pressures provided in the literature for short, stiff laterally loaded piles installed in cohesionless soils. In addition, the direct measurement-based p–y curves at different depths showed nonlinear behavior, in which the initial stiffness and ultimate soil reaction increased as the depth increased. When compared to p–y curves calculated from measured strain along the pile length, the directly measured p–y curves showed differences of ultimate soil reaction ranging from 8% to 33%. When compared to p–y curves calculated using the procedures available in the literature, the measurement-based p–y curve ultimate soil reactions have differences ranging from 5% to 189%. The differences in ultimate soil reaction could be mainly attributed to the installation method.

With the rapid growth of the helical piling industry for oil and gas projects and transmission lines, reliable installation torque estimates and measurements become crucial. This paper presents a theoretical model developed to estimate the torsional resistance of cohesionless soils to helical pile installation. The theoretical torque model was verified using installation records collected from different sites. The paper also highlights factors that affect helical pile installation, including soil properties, fluctuation in groundwater levels, shape of pile shaft, pile geometry, and method of helical pile installation. The proposed torsional resistance model was then used to establish the traditional torque factors to proportionally correlate the axial capacity of helical pile and the installation torque. The results of the study indicated that the torque factor is a function of the load path (i.e., tension or compression). Therefore, torque factors in compression and tension, Kcand Kt, respectively, were formulated and presented in the paper.

This paper thoroughly investigates the bearing capacity of strip footings on sand under combined loading by using a lower-bound limit analysis in conjunction with finite elements and second-order cone programming (SOCP). Two analyses were performed: one using a constant friction angle and the other using a variable friction angle. The analyses with a constant friction angle were used to calibrate the existing results, including the classical solutions commonly used in foundation design practice and other numerical or experimental solutions. The analyses with a variable friction angle allow us to investigate the effect of footing width B on the bearing capacity of strip footings. An iteration computational procedure is employed to account for the dependency of the friction angle on the stress level. According to the numerical results, it is found that the bearing capacity factor Nγ for eccentrically or obliquely loaded strip footings linearly decreases with the increase of B on a log–log scale, where the range 0.3–5 m of footing width was considered in this paper. In addition, it is found that the footing width has a negligible effect on the shape and size of the normalized failure envelopes.

Dynamically embedded plate anchors (DEPLAs) are a type of offshore anchor that combine the capacity advantages of vertically loaded plate anchors with the installation benefits of dynamically installed anchors. DEPLA capacity under monotonic loading conditions in clay has been investigated through centrifuge and field tests. In this paper, the monotonic capacity of DEPLAs in normally consolidated clay was studied using a three-dimensional large deformation finite element approach based on frequent mesh regeneration. Results from the numerical simulations were validated by comparison with centrifuge test data and existing numerical and analytical solutions for circular and rectangular plates. The effect of anchor embedment depth, anchor roughness, fluke (or plate) thickness, plate inclination, and DEPLA geometry were investigated in a parametric study where soil was prescribed to remain attached to the DEPLA base. The findings indicate that for a horizontal anchor subjected to vertical loading, most DEPLA geometries exhibit deep behaviour at an embedment ratio of 2.5, but that this embedment ratio is dependent upon the plate inclination, with vertical plates requiring the highest embedment depth for a deep localized failure mechanism. At a shallow embedment depth equal to one plate diameter, the reduction in capacity factor as the plate inclination changes from horizontal to vertical is 23.4%, compared with 1.3% at an embedment depth equal to four plate diameters. Plate roughness and fluke thickness are shown to have a minimal effect on the anchor capacity factor for vertical loading. Analyses that considered the breakaway (no tension) at the DEPLA base demonstrated that the anchor capacity factor approaches the no breakaway value as the embedment depth increases and as the soil strength (relative to the effective unit weight of the soil) decreases. The paper proposes a simple means of approximating the anchor capacity factor for breakaway conditions, by summing the capacity factor in weightless soil (which is unique for a given DEPLA geometry) and the normalized overburden pressure.

Integral abutment bridges accommodate thermal superstructure movements through flexible foundations rather than expansion joints. While these structures are a common alternative to conventional design, the literature on measured field stresses in piles supporting integral abutments appears to be quite limited. Therefore, field data from strain gauges installed on the abutment foundation piles of a 76 m long; two-span integral abutment bridge are the focus of this paper. Axial load, weak- and strong-axis bending moments of the foundation piles, as well as abutment movement and backfill response, are presented and discussed. Results indicate that the abutment foundation piles are bending in double curvature about the weak axis, as a result of thermal bridge movements, and bending also about the strong axis due to tilting of the abutments. A simple subgrade modulus approach is used to show its applicability in predicting behaviour under lateral loading. In the past, much emphasis has been placed on the lateral displacements of piles and less on variations of axial load. In this paper, a new hypothesis, which offers insight into the mechanisms behind the observed thermal variations in axial load, is proposed and assessed. The data from the field monitoring are also compared with the limited data reported in the literature.

The discusser has recently published a paper in Géotechnique titled “Investigation by limit analysis on the stability of slopes with cracks” (Utili 2013) that includes, for the first time (to the discusser’s knowledge), a systematic investigation of the influence of the presence of cracks in uniform slopes for rotational failure mechanisms via the limit analysis upper bound approach. Looking at the discusser’s paper and the paper under discussion (Michalowski 2013), a reader may note that the aim of the two papers is the same, namely, to assess quantitatively the effect of the presence of cracks on the stability of slopes employing the upper bound approach of limit analysis. The discusser’s paper was sent to Géotechnique when the discusser had no knowledge of either the author’s conference paper (Michalowski 2012) or of the paper under discussion published in July 2013. On the other hand, the discusser’s paper was published after the publication of the author’s conference paper (Michalowski 2012). Hence, it can be concluded that the discusser and the author had independently developed an original formulation for the calculation of upper bounds based on rotational failure mechanisms for cracked uniform slopes at similar times.\ud

A finite element (FE) formulation for electro-osmotic consolidation (EOC) analysis is developed in this paper which was implemented in a FE analysis (FEA) program. This formulation is integrated with the elastoplastic Modified Cam Clay (MCC) model to capture the nonlinear stress–strain behaviour of the soil during EOC using the fully coupled analysis approach. The numerical model is verified against triaxial EOC test data and close form solutions of typical one-dimensional EOC problems. Details of the formulation and the results of the validation analyses are reported in this paper.

Liquefaction often causes damage to infrastructure such as buildings, bridges, and lifelines. Liquefaction-induced ground movements such as settlement and lateral spread are of major concern to engineers who have to evaluate seismic risk. This paper deals with evaluation of liquefaction-induced settlement using a cone penetration test (CPT). Existing CPT-based models often overestimate liquefaction-induced settlement. In this paper, a database of case histories of settlement in recent earthquakes is compiled and used to calibrate the model bias of a CPT-based model, from which a simplified procedure is developed that allows for estimation of the probability of exceeding a specified settlement at a given site. Reasonable results are obtained using the developed simplified CPT-based model, as demonstrated in the examples presented.

Jack-up rigs are commonly employed to perform offshore oil and gas drilling. During the installation of the spudcan foundation, the large volume of soil displaced may induce severe stresses on the piles supporting the adjacent platform. The increasing numbers of jack-up rigs being deployed at close proximity to piled platforms accentuates the need for research into quantifying the effect of spudcan penetration on adjacent piles. The main difficulty with the numerical simulation of spudcan–pile interaction lies in the need to model continuous spudcan penetration in a three-dimensional (3-D) modeling space. In this paper, the three-dimensional Eulerian numerical technique is adopted to perform a coupled interaction analysis whereby the process of continuous spudcan penetration is simulated and the corresponding pile responses are obtained. The salient features of the proposed numerical approach with particular emphasis on the incorporation of a pile in the numerical model are first described. The validation of the numerical model against centrifuge experimental data under different geometric configurations and soil profiles are then presented. The final part of this paper demonstrates the usefulness of the proposed numerical approach through a series of parametric studies. This numerical approach can be readily applied to perform site-specific assessment to mitigate the risks associated with spudcan–pile interaction.

A case study of a double-cell, large-span prefabricated reinforced concrete box culvert with a total length of 52 m, a width of 46.8 m, and a height of 9.3 m, which passes beneath the Beijing – Hong Kong –Macau highway, is presented. The culvert is embedded in silty sand and silty clay at a depth of 1.2 m. To ensure the safety and normal operation of the highway, hydraulic jacking with the protection of a pipe roof was adopted for this project. This paper introduces the construction scheme in detail. A three-dimensional numerical simulation of the responses of the highway under which a wide box culvert jacking passes was conducted. The monitoring results on the highway as well as the actual construction process and problems encountered were analyzed. The different development characteristics or trends for the settlement and horizontal displacement of a highway surface are presented. In addition, this paper discusses the reasons for the large deformation of the highway surface as well as proposes reasonable suggestions.

The consolidation process could be slow in an upstream tailings dam; therefore, the stability can reduce due to an increase in excess pore pressures when the dam is raised. The safety of the dam can be enhanced by constructing rockfill berms on the downstream side. This paper presents a case study on the strengthening of an upstream tailings dam with rockfill berms. The finite element analyses were performed for modelling the staged construction of the dam and for optimizing the volume of the rockfill berms. The dam was raised in 11 stages; each stage consisting of a raising phase and a consolidation phase. The study shows that the slope stability of the dam reduced due to an increase of excess pore pressures during the raising phase. The stability of the dam was successfully improved by utilizing rockfill berms as supports on the downstream side. A technique has been presented to minimize the volume of the rockfill berms so that the required stability can be achieved at minimum cost. This paper shows that the finite element method can be a useful tool for modelling the consolidation behaviour of an upstream tailings dam and minimizing the volume of the rockfill berms that may be needed to maintain the stability of the dam during staged construction.

Based on the excessive deformations and support failure encountered during tunnel construction at the Driskos Twin Tunnel site in Northern Greece, this paper provides insight on how tunnels designed in such weak rock environments can be realistically analyzed with a view of determining better analytical tools to predict deformations and improving current design methods. Specific factors that were assessed include rock strength based on the geological strength index (GSI), tunnel deformation, numerical analysis techniques employed, three-dimensional model type, support considerations, dilation, sequencing of tunnel excavation, influence of single bore construction on twin bore, and homogenization of tunnel faces. This work involves the use of nominally identical two- and three-dimensional numerical models of tunnel sequencing for analytical simulation of weak material behaviour and sequential tunnel deformation response with the goal of investigating the strength and deformation of such weak rock masses. These have been used in combination with monitoring data that were obtained in the field during the Driskos Twin Tunnel construction. A discussion of the geological conditions, material property determination, monitoring data, and model calibration strategy is given. This paper provides insight into these issues and poses many more fundamental questions regarding the analysis of tunnel excavation within weak rock masses requiring further investigation.

Lam and Jefferis (2011) have produced a timely, well written, and worthy paper. I would like to add a few comments to the authors’ presentation of the strain measurements. Moreover, the authors’ recommendations regarding the E-modulus to be used for determining the load distribution in a pile subjected to a static loading test from the strain measurements need both to be emphasized and moderated, which is what the following brief compilation of case records aims to do. The authors’ paper presents the changes of strain of up to 100+ μ3 in the pile occurring as a result of the concreting and during the set-up time between pile construction and the static loading test. I think it is worthwhile to emphasize that the changes are caused by three different processes: temperature change (heating and cooling), swelling of the concrete, and reconsolidation by the soil (Fellenius et al. 2004). First, changes of strain are imposed during the hydration process as a consequence of the differences in thermal response between the concrete and the steel (in the sister bar gages). The hydration process causes an increase of temperature, which takes place over several hours, about 24 h rather than the 3 h the authors report. At first, the concrete is fluid, and there is very little strain or stress transferred between the concrete and the sister bars. Second, when the concrete starts to harden, bonding develops between the rebars and the concrete, and a further temperature increase will result in an apparent elongation — tension — of the rebars. During the subsequent cooling, which can take weeks or months, the concrete (usually) reduces more than the rebars, manifested by a shortening of the rebars — apparent compression — co-occurring with tension in the concrete. During the following period, the concrete absorbs water from the soil, which results in a volume increase — swelling — recorded as a rebar elongation — apparent tension — and, conversely, compression in the concrete. Third, at depth, when the soil recovers from the disturbance imposed by the construction, it usually tends to settle, which causes negative direction shear forces to develop, resulting in an increase of load in the pile — noticeable as residual load, which the authors showed to have taken place for the subject pile. Consequently, when the static loading test commences, a state of stress and strain exists in the pile that to some extent will affect the response to the applied load increments, as registered by the strain gages. The evaluation of the strain-gage records, in particular when the secant stiffness method is applied, needs to consider this, as suggested for a few of the following case histories.

The paper presents a methodology to evaluate flow slide susceptibility in potentially liquefiable sandy slopes. The proposed approach accounts for both contractive and dilative volumetric behaviour during shearing using the MIT-S1 constitutive model. As a result, it is possible to distinguish among different types of undrained response induced by a rapid shear perturbation. The first part of the paper describes the general methodology for infinite slopes, providing an index of stability for incipient static liquefaction in shallow deposits. The methodology accounts for the anisotropy due to the initial stress state and uses simple shear simulations to assess instability conditions as a function of slope angle, stress state, and density of the soil. The resulting stability charts define the margin of safety against static liquefaction and the depths likely to be affected by the propagation of an instability. The second part of the paper applies the methodology to the well-known series of flow failures in a berm at the Nerlerk site. The MIT-S1 model is calibrated using published data on Nerlerk sands and in situ cone penetration test (CPT) data. The analyses show that in situ slope angles α = 10°–13° are less than the critical slope angle needed for incipient instability. Liquefaction and flow failures were therefore promoted by small perturbations in shear stresses that could be generated by rapid deposition of hydraulic fill.

This paper presents an integrated bearing capacity–settlement approach to the design of shallow foundations on heavily overconsolidated clays by alterations of the “modified Cam clay” (MCC) model. The bearing capacity of soils and their settlements from loads imposed on shallow footings have been studied extensively. Yet, there is no consensus on a method that provides both reliable load-bearing capacity and settlement predictions. Current methods treat the soil under shallow footings as different ideal materials for the purpose of calculating the bearing capacity and settlement. The method proposed in this paper treats the soil as a single ideal material for both bearing capacity and settlement. The MCC model is tailored by adding Hvorslev’s findings on overconsolidated clays and delineating stress states that bring the soil to tensile failure from those that cause it to yield or behave elastically or to show discontinuous response. A limiting stress surface is established as defining a limiting bearing capacity. A heavily overconsolidated clay is assumed to behave elastically if its stress state is below the limiting stress surface. Predictions from the method proposed in this paper compare favorably with model tests and field test results. Examples are provided illustrating how to use the proposed method.

The application of electro-osmosis (EO) for stabilizing soft clays is receiving more attention in geotechnical engineering. When the application of traditional ground improvement techniques, such as surcharge, pre-loading, wick drains, and vacuum pre-loading, is not appropriate for a particular situation, innovative techniques such as electro-osmosis need to be considered. Although the effectiveness of electro-osmosis has been widely demonstrated in many field applications, geotechnical engineers are still hesitant to apply electro-osmosis due to unknown effects such as electro-chemical changes, which could not be accounted for in the design. This paper presents a design of an electro-osmotic triaxial testing apparatus suitable for electro-osmotic treatment of soft clays and for measuring electro-osmotic permeability and generated pore-water pressure, as well as a testing procedure that accounts for the contribution of electro-chemical changes in the improvement of soil properties. A series of electro-osmotic triaxial tests with various initial stresses and boundary conditions were conducted and the results are presented in the paper.

Dam safety has drawn increasing attention from the public. To ensure dam safety, it is essential to diagnose any dam distresses and their causes properly. The main objective of this paper is to develop a robust probability-based tool using Bayesian networks for the diagnosis of embankment dam distresses at the global level based on past dam distress data. A database of 993 distressed in-service embankment dams in China has been compiled, including general information on the dams, distresses, and causes. Based on the database, general characteristics of embankment dam distresses are studied using Bayesian networks, which can tackle not only the multiplicity of dam distresses and causes, but also the complex interrelations among them. Common patterns and causes of distresses are identified. The interrelations among the dam distresses and their causes are quantified using conditional probabilities determined based on the historical frequencies from the dam distress database. A sensitivity analysis is also conducted to identify and rank the most important factors that cause the distresses. With the prior information of common characteristics extracted from the database, Bayesian networks are further used to diagnose a specific distressed dam at the local level by combining global-level performance records and project-specific evidence in a systematic structure, which is presented in a companion paper.

Based on prior information on common characteristics of dam distresses extracted from the dam distress database described in a companion paper, this paper attempts to extend the technique of Bayesian networks to the diagnosis of a specific distressed dam. The diagnosis is conducted by combining two sources of information, i.e., global-level knowledge from the database and project-specific evidence. Based on results of the diagnosis, key distress factors for a specific dam can be identified and suitable remedial measures can be suggested. Further, the Bayesian network analysis is conducted to evaluate the effectiveness of the adopted remedial measures. A case study on the diagnosis of a distressed embankment dam, Chenbihe Dam, with seepage problems is presented to illustrate the methodology. In this case study, the observed leakage rates, seepage exit locations, and boundary conditions of the embankment are used as project-specific evidence.

This paper investigates the ultimate limit state load and resistance factor design (LRFD) of deep foundations founded within purely cohesive soils. The geotechnical resistance factors required to produce deep foundation designs having a maximum acceptable failure probability are estimated as a function of site understanding and failure consequence. The probability theory developed in this paper, used to determine the resistance factors, is verified by a two-dimensional random field Monte Carlo simulation of a spatially variable cohesive soil. The agreement between theory and simulation is found to be very good, and the theory is then used to derive the required geotechnical resistance factors. The results presented in this paper can be used to complement current ultimate limit state design code calibration efforts for deep foundations in cohesive soils.

This paper uses finite element upper and lower bound limit analysis to produce chart solutions for three-dimensional (3D) natural slopes for both short- and long-term stability. The presented chart solutions are convenient tools that can be used for preliminary design purposes. The rigorous limit analysis results in this paper were found to bracket the true factor of safety within ±10% or better, which can be used as a benchmark for the solutions from other methods. The depth of the slip surfaces is observed to be generally shallow for most analyzed cases, particularly for the long-term slope stability problem. In addition, it was found that using a two-dimensional (2D) analysis may lead to significant differences in estimating safety factors, which can differ by 2%–60% depending on the slope geometry and soil properties. Therefore, great care and judgement are required when applying 2D analyses to 3D slope problems.

This paper reports a series of geotechnical centrifuge model tests conducted to investigate the mechanical reinforcement of slopes by vegetation. Some of the model slopes contained young willow trees, which were grown in controlled conditions to provide different root distributions and mechanical properties. Slopes were brought to failure in the centrifuge by increasing water pressures. The failure mechanisms were investigated photographically and using post-test excavation. By measuring the soil properties and pore pressures in each test when failure occurred, slope stability calculations could be performed for each slope failure. These back-calculations of stability suggest that only a small amount of reinforcement was provided by the root system even when it was grown for 290 days before testing. In contrast, the use of the measured root properties and a commonly used root reinforcement model suggests that significant reinforcement should have been provided by the roots. This disparity is probably due to either inappropriate assumptions made in the root reinforcement model or soil alteration produced by root growth. Such disparities may exist in the application of root reinforcement models to full-scale slopes and therefore require additional study. The modelling technique outlined in this paper is suitable for further investigation of root mechanical interactions with slopes.

This paper explores factors that contribute to claims of changed soil conditions in infrastructure and building projects through a limited review of Canadian legal cases. Forty-one cases, relating to geotechnical problems covering a period of 25 years (1982–2006), were studied. The information obtained was categorized according to the causes for geotechnical claims. The most frequent causes of geotechnical disputes were found to be different soil conditions and recommendations than expected from those given in the geotechnical report, inaccuracies in the design plans and specifications, and the owner’s failure to disclose important information. The paper also discusses the special requirements for preparing geotechnical information for construction and suggests precautionary measures to reduce the number of disputes or to arrive at an equitable resolution. These measures require more proactive planning and may require additional funds before the bidding stage to perform a more detailed soil investigation, keep communication clear among all participants, and make a greater effort to provide accurate designs and specifications.

Stope backfilling is used in underground mines to provide a safer working space for personnel and machinery. To ensure a secure application of backfill, it is critical to accurately evaluate the pressures exerted on the walls and barricades placed near the base of the stope to retain the fill materials. In this paper, existing solutions for evaluating the stresses on barricades are reviewed. The authors then propose a new three-dimensional analytical solution that takes into account the stress transfer from the backfill to the walls in both the stope and access drift. In particular, the solution considers the influence of the barricade position within the drift on the stress state. Comparisons are made between the proposed solution, physical model test results, and numerical simulations. The good agreement between various results indicates that the proposed formulation provides a good estimate of the pressure on a barricade. The solution presented here is applicable to fully drained backfill (without water-pore pressure); the solution for saturated backfill is given in a companion paper (see Part II, this issue).

This paper summarizes the experimental results of a series of cyclic simple shear tests on liquefiable silty sand with and without sample improvement with colloidal silica grout. The objective of the paper is to evaluate the effectiveness of colloidal silica grouting in reducing the liquefaction potential of natural silty sand. Colloidal silica was selected as a stabilizing material due to its low viscosity, wide range of gel times, nontoxicity, and low cost. The soil tested in this experimental program is a poorly graded sand with 11.5% of nonplastic silt from the Port of Lázaro Cárdenas, México. Colloidal silica treated and untreated sand specimens show different pore pressure response and deformation behavior under cyclic loading in simple shear tests. The results indicate that, for a given initial relative density and initial effective vertical stress, liquefiable silty sand specimens stabilized with colloidal silica grout generally exhibit significant gain in liquefaction resistance compared with untreated specimens. It was also found that the colloidal silica grout reduces considerably the rates of pore pressure generation and shear strain of the silty sand specimens subjected to cyclic loading.