Journal of Geotechnical and Geoenvironmental Engineering

The use of load and resistance factor design (LRFD) to design geotechnical components of transportation infrastructure in the United States is now mandated by the Federal Highway Administration (FHWA). The advantages of LRFD over working stress design (WSD) may lead to its gradual adoption in geotechnical design even in the absence of any mandates. If load and resistance factors are based on reliability analysis, a mechanically stabilized earth (MSE) wall may be designed to a target reliability index (or a target probability of failure). Load and resistance factor design of MSE walls must consider multiple ultimate limit states, associated with both external and internal stabilities. This paper develops factors for use for the two ultimate limit states, sliding and overturning, used in design that are related to the external stability of MSE walls. Equations that closely reproduce the ultimate limit states with as little uncertainty as possible are proposed. The uncertainties of the parameters and the transformations for ultimate limit state equations are assessed using data from an extensive literature review. The first-order reliability method (FORM) is then used to produce resistance factor values for each limit state for different levels of target reliability index.

Subtitle D landfills may contain aluminum from residential and commercial solid waste, industrial waste, and aluminum production wastes. Some aluminum-bearing waste materials, particularly aluminum production wastes, may react with liquid in a landfill and cause uncontrolled temperature increases, significant changes in gas composition and pressure, nuisance odors, and changes in leachate composition and quantity. Such reactions may also cause degradation of leachate quality (e.g., increased ammonia, sodium, potassium, chloride, and TDS concentrations), combustion of the surrounding waste, damage to engineered components (gas collection systems, leachate collection systems, and liner system materials), and slope instability. Temperatures exceeding 150°C (300°F), generation and accumulation of undesirable explosive and toxic gases (e.g., hydrogen, acetylene, ammonia, carbon monoxide, and benzene), and gas pressures exceeding 210 kPa (30.5 psi) have been observed. Water from leachate recirculation, precipitation, the waste, or groundwater infiltration can initiate the exothermic reaction if aluminum production wastes are present. This paper uses a case history to illustrate some indicators of an aluminum reaction and problems that can develop from such a reaction in a Subtitle D landfill.

Drainage methods for liquefaction remediation have been in use since the 1970s and have traditionally included stone columns, gravel drains, and more recently prefabricated vertical drains. This paper presents the results from a dynamic centrifuge test designed to evaluate the performance of a liquefiable site treated with prefabricated vertical drains. The centrifuge model consisted of gently sloping, untreated and treated liquefiable soil deposits overlain by a clay crust. The model was subjected to multiple shaking events that included both recorded earthquake acceleration-time histories and sinusoidal input motions. Comparisons of deformations and excess pore water pressures in the untreated and treated areas showed that drains were effective in expediting the dissipation of excess pore water pressures and reducing deformations. However, depending on the characteristics of the input ground motion, the peak excess pore pressures in the treated area were not always substantially smaller than in the untreated area. Nevertheless, the deformations in the treated area were consistently smaller, which illustrates that the peak excess pore pressure ratio may not be a good indicator of overall performance. On the basis of the data from the centrifuge test, a better indicator of overall performance may be the time spent at elevated excess pore water pressures, which related better to the magnitude of the resulting deformations.

Site characterization for the design of geotechnical structures such as deep foundations is crucial, as unanticipated site conditions still represent the most common and most significant cause of problems and disputes that occur during construction. Surface-based refraction methods have been widely used recently to assess spatial variation, but one of the biggest limitations of these methods is that they cannot well characterize reverse profiles (decreasing in velocity with depth), buried low-velocity zones, or deep bedrock. An addition of borehole data to surface data is expected to improve inversion results. In this study, the coupling of so-called downhole and refraction tomography techniques using only one borehole is presented. To both qualitatively and quantitatively appraise the capability of the data, a global inversion scheme based on simulated annealing was investigated. Many synthetic and real test data sets with or without boreholes were inverted using the developed technique to obtain both inverted profiles and associated quantitative uncertainties. A comparison of tomograms utilizing the combined borehole and surface data against tomograms developed using just the surface data suggests that significant additional resolution of inverted profiles at depth are obtained with the addition of a borehole. The uncertainty estimates provide a quantitative assessment of the reliability of the interpreted profiles. It is also found that the quantitative uncertainties associated with the inverted profiles are significantly reduced when adding a borehole. In addition, the inversion results of the combined data provide credible information for the design of deep foundations, particularly useful in implementing the new load and resistance factor design methodology that can explicitly account for spatial variability in design parameters.

Impact loads generated because of wheel and rail defects cause accelerated ballast breakage leading to adverse performance of ballasted rail tracks. In the present study, experimental and numerical investigations have been carried out to develop an understanding of the performance of shock mats in the attenuation of dynamic impact loads and subsequent mitigation of ballast degradation. The investigations include different locations of shock mats considering stiff and weak subgrade conditions. With the provision of shock mats, the magnitude of impact forces decreases, and the time duration of impact ges prolonged. In the case of stiff subgrade, the efficiency of the shock mat in reducing the impact forces is greater when it is located at the bottom of ballast rather than at the top, whereas the reverse is true for weak subgrade. However, the provision of shock mats both at the top and bottom of the ballast bed, irrespective of the subgrade condition, is the best solution for minimising the impact force. The shock mats can bring down the impact-induced strains in the ballast bed by as much as 50%, apart from substantially reducing the ballast breakage.

A series of large-scale laboratory experiments, along with numerical analyses, using the commercial finite-element software package, ABAQUS, were performed to investigate the installation of mandrel-driven prefabricated vertical drains (PVDs). The laboratory tests were conducted using a specially designed large-scale consolidometer and a novel mandrel-driving machine capable of working at installation rates in the range of usual practices. The finite-element simulations include coupled analyses with a large-strain formulation. Coulomb’s law of friction and the penalty method are incorporated into the numerical models. The variations of pore water pressure at different locations during installation of a PVD and withdrawal of the mandrel are presented. Good agreement is found between pore pressures measured in the laboratory and predicted numerically. Moreover, finite-element analyses reveal that when a mandrel is pushed into the soil deposit, the soil surrounding the mandrel moves radially and downwards. Laboratory tests for moisture content and the numerically predicted variations of plastic shear strain, normalized with the rigidity index of the soil, show that for a given type of soft soil subjected to a particular rate of mandrel installation, the size of the smear zone decreases as the in situ effective stresses increase. The finite-element model has been applied to a case history from the Second Bangkok International Airport in Thailand and proves that the model can be applied to field conditions.

Semiempirical probabilistic models are described to assess cyclic large strain and induced excess pore-water pressure responses of fully saturated clean sands. For this purpose, available cyclic simple shear and triaxial tests were compiled and studied. The resulting $r_u$ versus $\gamma$, and $\gamma$ versus $N$ databases are composed of 101 and 84 cyclic test data, respectively. Key parameters of the proposed $r_u$ and $\gamma$ models are defined as critical shear strain, relative density, effective confining stress, and equivalent number of loading cycles. Consistent with the maximum likelihood methodology, model coefficients were estimated by maximizing the likelihood function. For comparison purposes, the compiled database was again used to evaluate the performance of existing $r_u$ models. Both for comparison and calibration purposes, for each framework, two separate sets of limit-state models were used: model implemented with (1) the original and (2) the updated model coefficients. The model performances are assessed by simple statistics (i.e., mean and standard deviation) of residuals. It is concluded that existing models produce inconsistently biased predictions that vary in the range of 2.5 to 70%. The successes of the proposed and existing models are also assessed for the validation database composed of additional 10 cyclic test results. In addition to (1) repeated improved predictions, (2) differentiating contractive or dilative cyclic soil responses, and (3) incorporation of strain-dependent modulus degradation effects, the main advantage of the proposed methodology is the probabilistic nature of model predictions, which enables the incorporation of the model uncertainty into pore pressure generation predictions.

More pronounced at relatively smaller magnitude events, significant variations to an extent of a factor of two in magnitude (duration) scaling factors (MSFs) explain the need to further study this issue, which is also recognized and recommended by the National Center for Earthquake Engineering Research Group. Inspired from this gap, the main motivation of this study is defined as to (1) comparatively assess the validity of existing magnitude scaling models and the accuracy of their predictions; (2) develop robust and practical to use semiempirical magnitude scaling models applied on CRR: separate sets for strain (cyclic mobility) or excess pore pressure (cyclic or flow liquefaction) problems. The writers’ excess pore water pressure and shear strain accumulation models were used for the assessment of magnitude (duration) scaling factors. On the basis of the proposed framework, it is concluded that (1) MSFs are not only a function of number of equivalent loading cycles but increase with increasing $r_u$ or ${\gamma }_{\max }$ thresholds and decreasing dilational response (i.e., decreasing relative density and/or increasing effective stress states) of soil layers, (2) significantly different set of MSFs than the NCEER recommendations can be estimated for different combinations of ${\gamma }_{\max }$ (or $r_u$), $N_{1,60,CS}$, ${\sigma }_{v,0}^{\prime }$, (3) for the assessment of critical structures (e.g.,  nuclear power plants), where significantly smaller shear strain performance targets are needed, use of existing models may produce significantly higher MSFs, leading to unconservative estimates of cyclic mobility potential.

In good soil conditions, spread footings for bridges are less expensive than deep foundations. Furthermore, rocking shallow foundations have some performance advantages over conventional fixed-base foundations; they can absorb some of the ductility demand that would typically be absorbed by the columns, and they have better recentering characteristics than conventional reinforced-concrete (RC) columns. Foundations designed for elastic behavior do not have these benefits of nonlinear soil-structure interaction. One potential disadvantage of rocking systems is that they can produce significant settlement in poor soil conditions. Centrifuge model tests were performed to account for the interaction between soil, footing, column, deck and abutments systems. Bridge systems with rocking foundations on good soil conditions are shown to perform well and settlements are small. An improved method for quantification of settlements is presented. The model tests are described in some detail. One of the important factors limiting the use of rocking foundations is the perception that they might tip over; experiments show that tipping instability is unlikely if the foundations are properly sized. In one experiment, a column for a system with large fixed-base foundation collapsed while the systems with smaller rocking foundations did not collapse.

The grade raising associated with the Third Runway Project at Seattle-Tacoma International Airport included construction of tall mechanically stabilized earth (MSE) walls, including the near-vertical, two-tier, 26-m North MSE wall and the near-vertical, four-tier, 46-m tall west MSE wall. Twenty reinforcement strips at critical wall cross sections were instrumented with over 500 strain gauges to monitor strains during and following construction. The reinforcement loads inferred from observed strains are of interest because of their great height and global reinforcement stiffness, which place these walls outside the range in height and stiffness used to calibrate commonly used design methods. This paper presents the development and distribution of reinforcement strains measured during and following the construction of these walls. The reinforcement stresses calculated using the original reinforcement load design methods and design friction angle agreed with those inferred from the measured strains. The accuracy of two standard-of-practice and two alternate design methods is evaluated by comparing the reinforcement loads inferred from measured strains to those calculated using the actual friction angle of the reinforced fill material. Advantages and limitations in these design methods are identified, and recommendations for the improvement of some of these methods are provided.

Monopiles are used as foundation structures for offshore wind energy towers. To ensure stable behavior of the monopile under cyclic loading conditions, a minimum embedded length is usually required. For this, different design criteria are used, some of which result in very large embedded depths for large-diameter monopiles. The suitability of these criteria is tested by means of numerical simulations. To account for cyclic loading, a new approach called the stiffness degradation method is applied. The results of a parametric study show that the design criteria used can indeed ensure optimum pile performance under static and cyclic loads. It is recommended that the requirement of a critical pile length, which leads to the minimum pile deflection under extreme load, is used as a design criterion. For the cases considered, this requirement results in only slightly greater cyclic deformations compared to the optimum case of very long piles. A further optimization of the required monopile length with respect to cyclic loading is possible, but requires specific consideration of cyclic behavior, as is done in this paper.

Piles are required to withstand large lateral loads compared with the imposed vertical loads in certain applications in the offshore environment, such as for foundations for offshore wind turbines or as anchors for floating facilities. Although typically the soil strength increases with depth, close to the sea bed, the lateral capacity is often low. The requirement to limit pile head deflections necessitates the design of relatively long piles. Increasing the effective pile cross-section through “wings” close to the pile head is shown here with centrifuge model tests to reduce pile head deflections by approximately 50% compared with regular monopiles without “wings” for the same load level. The stiffer initial response of the winged pile also leads to smaller pile head deflections under cyclic loading, although the relative rate of accumulation is similar to that of a monopile. Simple methods for extrapolating from the monotonic pile head deflection to the deflection after thousands of cycles are compared with the results, and are shown to work equally well for piles with and without “wings”.

This paper presents an experimental study of the behavior of an eccentrically loaded model ring footing resting on a compacted replaced layer of sand that overlies an extended layer of loose sand. Particular emphasis is placed on the potential benefits of reinforcing the replaced sand layer with geogrid reinforcement. Load configuration was designed to simulate ring footings under vertical loads and overturning moment caused by lateral loads. Several configurations of geogrid layers, number, and stiffness were used to study ring footings with different inner-to-outer-diameter ratios and load eccentricities. The effect of the depth and the relative density of the replaced sand layer was also investigated. Test results indicate that the behavior of an eccentrically loaded ring footing significantly improves with an increase in the depth and the relative density of the replaced compacted sand layer. However, the inclusion of soil reinforcement not only leads to a significant reduction in the depth of the replaced sand layer but also causes a considerable increase in the bearing capacities of the eccentrically loaded rings, leading to the cost-effective design of the footings. On the basis of the test results, the effects of different parameters are presented and discussed.

Estimation of a footing’s bearing capacity under general loading is a topic of wide interest, especially for the offshore energy industry. Although there have been several studies in the past few decades on shallow footings under general loading, limited work has been done for deeply buried footings. This paper presents results of a numerical investigation into the undrained bearing capacity of deeply buried flat circular footings in clay of both uniform and linearly increasing shear strength profiles. The footings’ uniaxial bearing capacities and failure surfaces under combined vertical, horizontal, and moment loading are reported. The results are analyzed in the context of application by the mobile jack-up industry, for which understanding of the circular spudcan footing’s bearing capacity under general loading is required for site-specific assessments. The paper also presents a parametric study on the effect of a footing’s aspect ratio (thickness/diameter) on its bearing capacity. To conclude, a closed-form expression is proposed to formulate the failure surfaces of the footings under general loading.

This paper presents a simplified approach for the analysis of shallow landslides triggered by heavy rainfalls, which occur after a rainy period. On the basis of some analytical solutions, this approach combines a simple infiltration model to calculate the change in pore water pressure caused by rain infiltration within the slope, with a sliding-block model to assess whether a slope failure occurs owing to a prescribed rainfall. If this is the case, the method also allows the time at which the landslide is triggered and the subsequent slope movements to be readily evaluated.

This paper is the last in a series related to pozzolanically stabilizing dredged material (DM) using up to 20 different combinations of lime, cement kiln dust (CKD), fly ash (FA), Portland cement (PC), and slag cement. The fine-grained nature of the DM and the presence of high sulfate concentrations (0.6–3.25% by weight) in the stabilized dredged material (SDM) blends derived from the raw materials themselves posed concern for potential ettringite formation and swell. The sulfate contents of the SDM blends were well in excess of the National Lime Association’s thresholds for mitigating against swell ( $<0.8\%$ by weight ${\mathrm{SO}}_4$ ). The quantitative mineralogical results showed that the lime and lime/FA SDM blends showed moderate to high ettringite formation (1.6–4.6% by weight) up to 6 months of curing, with all available sulfate bound to ettringite. The lime and lime/FA SDM blends consistently maintained the highest pHs through 6 months, which caused continued release of alumina and increases in strength. The CKD and CKD/FA SDM blends showed the highest ettringite contents through 28 days of curing (up to 5%), but with little additional formation of ettringite through 6 months of curing. The total sulfate content of the SDM blends was not a good predictor of ettringite formation potential, because of decreases in pH below the ettringite stability threshold and, even more importantly, the apparent limited availability of soluble alumina in the SDM blends. Swell tests performed on six SDM blends showed slight consolidation, and no ettringite was detected in the two specimens that swelled.

The design of deep tunnels underneath the water-table in clayey soils should carefully take into account the influence of pore pressures and seepage forces on the stability of the excavation and on the loading conditions of the support systems. This paper focuses on the application of analytical solutions and numerical models to the analysis of stress and deformation around deep tunnels, in the short and long term, considering the idealized situation of axisymmetric conditions. General remarks on the influence of hydro-mechanical coupling, artificial boundary conditions and lining permeability are presented. Theoretical predictions are compared with measurements made in tunnels excavated in the Boom clay formation at Mol (Belgium).

The vertical uplift resistance for a group of two horizontal coaxial rigid strip anchors embedded in clay under undrained condition has been determined by using the upper bound theorem of limit analysis in combination with finite elements. An increase of undrained shear strength of soil mass with depth has been incorporated. The uplift factor $F_{c\gamma }$ has been computed. As compared to a single isolated anchor, a group of two anchors provides greater magnitude of the uplift resistance. For a given embedment ratio, the group of two anchors generates almost the maximum uplift resistance when the upper anchor is located midway between ground surface and the lower anchor. For a given embedment ratio, $F_{c\gamma }$ increases linearly with an increase in the normalized unit weight of soil mass up to a certain value before attaining a certain maximum magnitude; the maximum value of $F_{c\gamma }$ increases with an increase in embedment ratio.