Showing papers in "Journal of Geotechnical and Geoenvironmental Engineering in 2003"
TL;DR: The Hazen formula is less accurate than the Kozeny-carman formula as discussed by the authors, and it is recommended that the former be retired and the latter be adopted, which is also the case in our work.
Abstract: The century-old Hazen formula for predicting the permeability of sand is based only on the D10 particle size. Whereas, the half-century-old Kozeny-Carman formula is based on the entire particle size distribution, the particle shape, and the void ratio. As a consequence, the Hazen formula is less accurate than the Kozeny-Carman formula. It is recommended that the former be retired and the latter be adopted.
500 citations
TL;DR: In this article, a more convenient approach is adopted in which the domain of large shear strain is directly defined by strain space parameters, and the observed cyclic shear deformation is accounted for by enlargement and/or translation of this domain in deviatoric strain space.
Abstract: In saturated clean medium-to-dense cohesionless soils, liquefaction-induced shear deformation is observed to accumulate in a cycle-by-cycle pattern (cyclic mobility). Much of the shear strain accumulation occurs rapidly during the transition from contraction to dilation (near the phase transformation surface) at a nearly constant low shear stress and effective confining pressure. Such a stress state is difficult to employ as a basis for predicting the associated magnitude of accumulated permanent shear strain. In this study, a more convenient approach is adopted in which the domain of large shear strain is directly defined by strain space parameters. The observed cyclic shear deformation is accounted for by enlargement and/or translation of this domain in deviatoric strain space. In this paper, the model formulation details involved are presented and discussed. A calibration phase is also described based on data from laboratory sample tests and dynamic centrifuge experiments (for Nevada sand at a relative density of about 40%).
373 citations
TL;DR: In this paper, a method for the estimation of the time for progression of internal erosion and piping, and development of a breach leading to failure in embankment dams and their foundations is presented.
Abstract: A method is presented for the approximate estimation of the time for progression of internal erosion and piping, and development of a breach leading to failure in embankment dams and their foundations. The method accounts for the nature of the soils in the dam core, the foundation, and the materials in the downstream zone of the dam. Guidance is also provided on the detectability of internal erosion and piping, taking account of the mechanism of initiation, continuation, and progression to form a breach, for internal erosion and piping in the embankment, the foundation and from the embankment to foundation. It is shown that in many dams which have poor internal erosion and seepage control and are constructed mainly of earthfill, the time for potential development of piping is short, and for these dams continuous monitoring of seepage or surveillance would be needed to detect the piping in time to give warning of possible failure, and to give time to attempt intervention to prevent the failure.
288 citations
TL;DR: In this article, a model for predicting the failure stress in triaxial compression was developed, where the failure envelope has two segments: a linear part associated with fiber slip, and a nonlinear one related to yielding of the fiber material.
Abstract: Results from drained triaxial compression tests on specimens of fiber-reinforced sand are reported. It is evident that the addition of a small amount of synthetic fibers increases the failure stress of the composite. This effect, however, is associated with a drop in initial stiffness and an increase in strain to failure. Steel fibers did not reduce initial stiffness of the composite. The increase in failure stress can be as much as 70% at a fiber concentration of 2% (by volume) and an aspect ratio of 85. The reinforcement benefit increases with an increase in fiber concentration and aspect ratio, but it also depends on the relative size of the grains and fiber length. A larger reinforcement effect in terms of the peak shear stress was found in fine sand, compared to coarse sand, when the fiber concentration was small (0.5%). This trend was reversed for a larger fiber concentration (1.5%). A model for prediction of the failure stress in triaxial compression was developed. The failure envelope has two segments: a linear part associated with fiber slip, and a nonlinear one related to yielding of the fiber material. The analysis indicates that yielding of fibers occurs well beyond the stress range encountered in practice. The concept of a macroscopic internal friction angle was introduced to describe the failure criterion of a fiber-reinforced sand. This concept is a straightforward way to include fiber reinforcement in stability analyses of earth structures.
270 citations
TL;DR: In this article, an elastoplastic constitutive model based on the disturbed state concept is adopted to characterize the behavior of the modeled rockfill materials, consisting of rounded and angular particles obtained from two dam sites are subjected to triaxial tests using large size specimens.
Abstract: Modeled rockfill materials consisting of rounded and angular particles obtained from two dam sites are subjected to drained triaxial tests using large size specimens. An elastoplastic constitutive model based on the disturbed state concept is adopted to characterize the behavior of the modeled rockfill materials. The material parameters for the two rockfill materials are determined from the experimental results. The variation of the material parameters with respect to the size of the particles for the rockfill material with the rounded particle is, in general, opposite to that for the rockfill material with the angular particles. The model is shown to provide satisfactory prediction of the behavior of the rockfill materials tested. Material parameters are predicted for prototype size of rockfill materials.
265 citations
TL;DR: In this article, the authors present results of eight centrifuge models of vertical single piles and pile groups subjected to earthquake-induced liquefaction and lateral spreading in a single pile group.
Abstract: The paper presents results of eight centrifuge models of vertical single piles and pile groups subjected to earthquake-induced liquefaction and lateral spreading. The centrifuge experiments, conduc...
200 citations
TL;DR: In this paper, the effect of the soil plug on the static and dynamic response of an open-ended pile and the load capacity of pipe piles in general was investigated on instrumented open-and closed-ended piles driven into sand.
Abstract: Both the driving response and static bearing capacity of open-ended piles are affected by the soil plug that forms inside the pile during pile driving. In order to investigate the effect of the soil plug on the static and dynamic response of an open-ended pile and the load capacity of pipe piles in general, field pile load tests were performed on instrumented open- and closed-ended piles driven into sand. For the open-ended pile, the soil plug length was continuously measured during pile driving, allowing calculation of the incremental filling ratio for the pile. The cumulative hammer blow count for the open-ended pile was 16% lower than for the closed-ended pile. The limit unit shaft resistance and the limit unit base resistance of the open-ended pile were 51 and 32% lower than the corresponding values for the closed-ended pile. It was also observed, for the open-ended pile, that the unit soil plug resistance was only about 28% of the unit annulus resistance, and that the average unit frictional resistance between the soil plug and the inner surface of the open-ended pile was 36% higher than its unit outside shaft resistance.
183 citations
TL;DR: In this article, Cone penetration test (CPT) soundings at historic liquefaction sites in California were used to evaluate the predictive capability of the LPI, which combines depth, thickness, and factor of safety of liquefiable material inferred from a CPT sounding into a single parameter.
Abstract: Cone penetration test (CPT) soundings at historic liquefaction sites in California were used to evaluate the predictive capability of the liquefaction potential index (LPI), which was defined by Iwasaki et al. in 1978. LPI combines depth, thickness, and factor of safety of liquefiable material inferred from a CPT sounding into a single parameter. LPI data from the Monterey Bay region indicate that the probability of surface manifestations of liquefaction is 58 and 93%, respectively, when LPI equals or exceeds 5 and 15. LPI values also generally correlate with surface effects of liquefaction: Decreasing from a median of 12 for soundings in lateral spreads to 0 for soundings where no surface effects were reported. The index is particularly promising for probabilistic liquefaction hazard mapping where it may be a useful parameter for characterizing the liquefaction potential of geologic units.
181 citations
TL;DR: In this paper, a modified Bartlett statistical test is proposed to provide a more rational basis for rejecting the null hypothesis of stationarity in the correlated case, and the accompanying rejection criteria are determined from simulated correlated sample functions.
Abstract: Stationarity or statistical homogeneity is an important prerequisite for subsequent statistical analysis on a given section of a soil profile to be valid. The estimation of important soil statistics such as the variance is likely to be biased if the profile is not properly demarcated into stationary sections. Existing classical statistical tests are inadequate even for simple identification of stationarity in the variance because the spatial variations of soil properties are generally correlated with each other. In this paper, a modified Bartlett statistical test is proposed to provide a more rational basis for rejecting the null hypothesis of stationarity in the correlated case. The accompanying rejection criteria are determined from simulated correlated sample functions and summarized into a convenient form for practical use. A statistical-based soil boundary identification procedure is then developed using the modified Bartlett test statistic. Based on the analysis of a piezocone sounding record, two a...
177 citations
TL;DR: In this paper, a comprehensive experimental investigation was conducted to investigate the effects of loading condition and confining pressure on strength properties and localization phenomena in sands using F-75 Ottawa sand.
Abstract: A comprehensive experimental investigation was conducted to investigate the effects of loading condition and confining pressure on strength properties and localization phenomena in sands. A uniform subrounded to rounded natural silica sand known as F-75 Ottawa sand was used in the investigation. The results of a series on conventional triaxial compression (CTC) experiments tested under very low-confining pressures (0.05–1.30) kPa tested in a microgravity environment abroad the NASA Space Shuttle are presented in addition to the results of similar specimens tested in terrestrial laboratory to investigate the effect of confining pressure on the constitutive behavior of sands. The behavior of the CTC experiments is compared with the results of plane strain experiments. Computed tomography and other digital imaging techniques were used to study the development and evolution of shear bands.
167 citations
TL;DR: In this article, a new simplified method for assessing the liquefaction resistance of soils based on the cone penetration test (CPT) is presented, and probabilistic analyses of the cases in the database are conducted using the Bayesian mapping function approach.
Abstract: This paper presents a new simplified method for assessing the liquefaction resistance of soils based on the cone penetration test (CPT). A relatively large database consisting of CPT measurements and field liquefaction performance observations of historical earthquakes is analyzed. This database is first used to train an artificial neural network for predicting the occurrence and nonoccurrence of liquefaction based on soil and seismic load parameters. The successfully trained and tested neural network is then used to generate a set of artificial data points that collectively define the liquefaction boundary surface, the limit state function. An empirical equation is further obtained by regression analysis to approximate the unknown limit state function. The empirical equation developed represents a deterministic method for assessing liquefaction resistance using the CPT. Based on this newly developed deterministic method, probabilistic analyses of the cases in the database are conducted using the Bayesian mapping function approach. The results of the probabilistic analyses, expressed as a mapping function, provide a simple means for probability-based evaluation of the liquefaction potential. The newly developed simplified method compares favorably to a widely used existing method.
TL;DR: In this article, the authors developed curves of cyclic resistance ratio (CRR) versus cone penetration test (CPT) stress-normalized cone resistance qc1 from a combination of analysis and laboratory testing.
Abstract: Liquefaction of granular soil deposits is one of the major causes of loss resulting from earthquakes. The accuracy in the assessment of the likelihood of liquefaction at a site affects the safety and economy of the design. In this paper, curves of cyclic resistance ratio (CRR) versus cone penetration test (CPT) stress-normalized cone resistance qc1 are developed from a combination of analysis and laboratory testing. The approach consists of two steps: (1) determination of the CRR as a function of relative density from cyclic triaxial tests performed on samples isotropically consolidated to 100 kPa; and (2) estimation of the stress-normalized cone resistance qc1 for the relative densities at which the soil liquefaction tests were performed. A well-tested penetration resistance analysis based on cavity expansion analysis was used to calculate qc1 for the various soil densities. A set of 64 cyclic triaxial tests were performed on specimens of Ottawa sand with nonplastic silt content in the range of 0–15% by ...
TL;DR: The reliability-based design (RBD) initiative sponsored by the Electric Power Research Institute for transmission line structure foundations is presented in this paper, where the role of RBD is presented within the context of geotechnical limit state design.
Abstract: This paper presents the reliability-based design (RBD) initiative sponsored by the Electric Power Research Institute for transmission line structure foundations. The role of RBD is presented within the context of geotechnical limit state design. Design parameters that are amenable to statistical description can be propagated systematically to a consistent measure of design risk using reliability techniques such as the first-order reliability method (FORM). Less quantifiable factors are incorporated approximately into RBD by judicious selection of the target reliability level. A simplified RBD approach based on the load and resistance factor design (LRFD) and multiple resistance factor design (MRFD) formats is proposed for practical implementation. The resistance factors for the LRFD and MRFD formats are calibrated rigorously using FORM to produce designs that can achieve a known level of reliability consistently.
TL;DR: In this paper, a review of long-term stability of stiff clay and clay shale slopes is presented, and detailed reanalyses of 99 case histories of slope failures in 36 soft clays to stiff clays and clay shales.
Abstract: This paper presents a review of long-term stability of stiff clay and clay shale slopes, and detailed reanalyses of 99 case histories of slope failures in 36 soft clays to stiff clays and clay shales. We analyzed 107 sections using the observed actual slip surface. In a first-time slope failure in clay or shale, part or all of the slip surface is unsheared prior to the occurrence of the landslide. Most stiff clays and clay shales contain stratigraphic discontinuities such as bedding planes and laminations. The fully softened shear strength is shown to be the lower bound for mobilized shear strength in first-time slope failures in homogeneous soft to stiff clays and on the slip surfaces cutting across bedding planes and laminations. For many of the first-time slope failures it appears that part of the slip surface is at the residual condition. For excavated slopes, the residual condition could be present before the final slope is formed, or it may develop in response to excavation by progressive deformation along nearly horizontal surfaces including bedding planes or laminations. In addition to the permeability dependent rise in porewater pressure, and softening, delayed first-time failure of slopes in stiff clays and clay shales is caused by propagation of the residual condition into the slope, on horizontal or subhorizontal surfaces including stratigraphic discontinuities. The residual condition is present on the entire surface of reactivated landslides.
TL;DR: In this paper, the results of an experimental investigation undertaken to evaluate different purging solutions to enhance the removal of multiple heavy metals, particularly chromium, nickel, and cadmium, from a low buffering clay, specifically kaolin, during electrokinetic remediation were presented.
Abstract: This paper presents the results of an experimental investigation undertaken to evaluate different purging solutions to enhance the removal of multiple heavy metals, particularly chromium, nickel, and cadmium, from a low buffering clay, specifically kaolin, during electrokinetic remediation. Experiments were conducted on kaolin spiked with Cr~VI! ,N i~II!, and Cd~II! in concentrations of 1,000, 500, and 250 mg/kg, respectively, which simulate typical electroplating waste contamination. A total of five different tests were performed to investigate the effect of different electrode purging solutions on the electrokinetic remedial efficiency. A constant DC voltage gradient of 1 V/cm was applied for all the tests. The removal of heavy metals from the soil using tap water as the purging solution was very low. When 1 M acetic acid was used as the purging solution in the cathode, the removal of chromium, nickel, and cadmium was increased to 20, 19, and 13%, respectively. Using 0.1 M ethylene diamine tetraacetic acid as the purging solution in the cathode, 83% of the initial Cr was removed; however, the nickel and cadmium removal was very low. A sequentially enhanced electrokinetic remediation approach involving the use of water as a purging solution at both the anode and cathode initially, followed by the use of acetic acid as the cathode purging solution and a NaOH alkaline solution as the anode purging solution was tested. This sequential approach resulted in a maximum removal of chromium, nickel, and cadmium of 68 -71, 71-73, and 87-94%, respectively. This study shows that the sequential use of appropriate electrode purging solutions, rather than a single electrode purging solution, is necessary to remediate multiple heavy metals in soils using electrokinetics.
TL;DR: In this paper, the frequency-dependent transmissibility function amplitude uHu was used to estimate free-field ground motions to estimate base slab motions for response analyses of buildings with surface and shallowly embedded foundations.
Abstract: Earthquake strong motion recordings from 29 sites with instrumented structures and free-field accelerographs are used to evaluate variations between foundation-level and free-field ground motions. The focus of the paper is on buildings with surface and shallowly embedded foundations. The foundation/free-field ground motion variations are quantified in terms of frequency-dependent transmissibility function amplitude uHu. Procedures are developed to fit to uHu analytical models for base slab averaging for the assumed conditions of a rigid base slab and a vertically propagating, incoherent incident wave field characterized by ground motion incoherence parameter k. The limiting assumptions of the model are not strictly satisfied for actual structures, and the results of the identification are apparent k values ~denoted k a) that reflect not only incoherence effects, but also possible foundation flexibility and wave inclination effects. Nonetheless, a good correlation is found between k a values and soil shear wave velocity for sites with stiff foundation systems. Based on these results, recommendations are made for modifying free-field ground motions to estimate base slab motions for use in response analyses of buildings.
TL;DR: The bearing capacity of open-ended piles is affected by the degree of soil plugging, which is quantified by the incremental filling ratio ~IFR!. In as discussed by the authors, the authors investigate the effect of IFR on pile load capacity.
Abstract: The bearing capacity of open-ended piles is affected by the degree of soil plugging, which is quantified by the incremental filling ratio ~IFR!. There is not at present a design criterion for open-ended piles that explicitly considers the effect of IFR on pile load capacity. In order to investigate this effect, model pile load tests were conducted on instrumented open-ended piles using a calibration chamber. The results of these tests show that the IFR increases with increasing relative density and increasing horizontal stress. It can also be seen that the IFR increases linearly with the plug length ratio ~PLR! and can be estimated from the PLR. The unit base and shaft resistances increase with decreasing IFR. Based on the results of the model pile tests, new empirical relations for plug load capacity, annulus load capacity, and shaft load capacity of open-ended piles are proposed. The proposed relations are applied to a full-scale pile load test performed by the authors. In this load test, the pile was fully instrumented, and the IFR was continuously measured during pile driving. A comparison between predicted and measured load capacities shows that the recommended relations produce satisfactory predictions.
TL;DR: In this article, a reevaluation of two factors that can strongly affect the estimation of liquefaction resistance for clean sands under high effective overburden stresses (σv′) is presented.
Abstract: A reevaluation is presented of two factors that can strongly affect the estimation of liquefaction resistance for clean sands under high effective overburden stresses (σv′): the relation used to normalize penetration resistances to a σv′ of 1 atm (i.e., CN), and the adjustment factor for the effects of σv′ on cyclic resistance ratio (i.e., Kσ). These two factors have been investigated in a number of ways and several relations exist for each of them. An improved CN relation is developed based on cone penetration theory and validation against calibration chamber test data for both cone penetration and standard penetration tests. A relative state parameter index (ξR) is shown to provide a consistent theoretical framework for interrelating the penetration and cyclic loading resistances. It is subsequently shown that the CN and Kσ relations are interrelated through the sand properties and relative density (DR) in ways that have compensating effects on the predicted cyclic resistance. The derived relations prov...
TL;DR: In this paper, a 3D numerical limit analysis is applied to evaluate the effect of anchor shape on the pullout capacity of horizontal anchors in undrained clay, where the anchor is idealized as either square, circular, or rectangular in shape.
Abstract: Soil anchors are commonly used as foundation systems for structures that require uplift or lateral resistance. These types of structures include transmission towers, sheet pile walls, and buried pipelines. Although anchors are typically complex in shape (e.g., drag or helical anchors), many previous analyses idealize the anchor as a continuous strip under plane strain conditions. This assumption provides numerical advantages and the problem can be solved in two dimensions. In contrast to recent numerical studies, this paper applies three-dimensional numerical limit analysis to evaluate the effect of anchor shape on the pullout capacity of horizontal anchors in undrained clay. The anchor is idealized as either square, circular, or rectangular in shape. Estimates of the ultimate pullout load are obtained by using a newly developed three-dimensional numerical procedure based on a finite-element formulation of the lower bound theorem of limit analysis. This formulation assumes a perfectly plastic soil model with a Tresca yield criterion. Results are presented in the familiar form of break-out factors based on various anchor shapes and embedment depths, and are also compared with existing numerical and empirical solutions.
TL;DR: In this paper, the authors consider the shaking-induced displacement and dynamic response of a rigid block and deformable columns of soil on an inclined plane and demonstrate that because of the coupled d...
Abstract: This study considers the shaking-induced displacement and dynamic response of a rigid block and deformable columns of soil on an inclined plane. This work demonstrates that because of the coupled d...
TL;DR: In this article, a load-settlement response from three plate load tests was carried out directly on a homogeneous residual soil stratum, as well as on a layered system formed by two different top layers, sandcement and sand-cement fiber, overlaying the residual soil.
Abstract: The load-settlement response from three plate load tests ~300 mm diameter, 25.4 mm thick! carried out directly on a homogeneous residual soil stratum, as well as on a layered system formed by two different top layers ~300 mm thick!—sand-cement and sand-cement fiber—overlaying the residual soil stratum, is discussed in this technical note. The utilization of a cemented top layer increased bearing capacity, reduced displacement at failure, and changed soil behavior to a noticeable brittle behavior. After maximum load, the bearing capacity dropped towards approximately the same value found for the plate test carried out directly on the residual soil. The addition of fiber to the cemented top layer maintained roughly the same bearing capacity but changed the postfailure behavior to a ductile behavior. A punching failure mechanism was observed in the field for the load test bearing on the sand-cement top layer, with tension cracks being formed from the bottom to the top of the layer. A completely distinct mechanism was observed in the case of the sand-cement-fiber top layer, the failure occurring through the formation of a thick shear band around the border of the plate, which allowed the stresses to spread through a larger area over the residual soil stratum.
TL;DR: In this article, the geotechnical and geological systems are compared to characterize lunar soil, and the results show that the lunar soil particle size distribution is sandy silt/silty sand, well-graded.
Abstract: Meteorite impact on the lunar surface produces a consistent, broadly graded soil. In this note, the geotechnical and geological systems are compared to characterize lunar soil. In geotechnical terms, the lunar soil particle size distribution is described as sandy silt/silty sand, well-graded. In geologic terms, it is described as very fine sand, very poorly sorted, nearly symmetrical, and mesokurtic. Because of its broad particle size distribution, lunar soil may be internally erodible.
TL;DR: In this article, a load-settlement response from two steel plate load tests (0.3 m diameter, 25 mm thick) carried out on a thick homogeneous stratum of compacted sandy soil, reinforced with polypropylene fibers, as well as on the same soil without the reinforcement was discussed.
Abstract: This technical note discusses the load–settlement response from two steel plate load tests (0.3 m diameter, 25 mm thick) carried out on a thick homogeneous stratum of compacted sandy soil, reinforced with polypropylene fibers, as well as on the same soil without the reinforcement. In addition to the field test program, laboratory triaxial compression tests were performed to determine the static stress–strain response of the compacted sandy soil reinforced with randomly distributed polypropylene fibers. The laboratory test results showed that the reinforcement changed dramatically the stress–strain behavior at very large strains. The strength was found to increase continuously at a constant rate, regardless of the confining pressure applied, not reaching an asymptotic upper limit, even at axial strains as large as 25%. The plate load test on the soil–fiber stratum was performed to relatively high pressures, and gave a noticeable stiffer response than that carried out on the nonreinforced stratum.
TL;DR: In this paper, the results of the six centrifuge models of instrumented single pile foundations presented in a companion paper, are used to calibrate two limit equilibrium (LE) methods to evaluate bending response and factor of safety against bending failure of piles in the field subjected to lateral spreading.
Abstract: The results of the six centrifuge models of instrumented single pile foundations presented in a companion paper, are used to calibrate two limit equilibrium (LE) methods to evaluate bending response and factor of safety against bending failure of piles in the field subjected to lateral spreading. These six models simulate single reinforced concrete piles in two- and three-layer soil profiles, mostly end bearing but including also one floating pile, with and without a reinforced concrete pile cap, and one model where the liquefiable sand layer was densified locally around the pile to simulate the effect of pile driving. The measured permanent maximum bending moments in the pile, Mmax, invariably occurred at the boundaries between liquefied and nonliquefied soil layers, and in most cases the moments at such boundaries reached their peak Mmax and then decreased during shaking. These values of Mmax before decrease, which were associated with failure of the soil against the deep foundation, are used to calibra...
TL;DR: In this paper, numerical upper and lower bounds for the bearing capacity factor of a surface strip footing on a frictional soil were derived using linear programming and linear programming techniques, respectively.
Abstract: This paper presents numerical upper- and lower-bound solutions for the well-known bearing capacity factor Nγ of a surface strip footing on a frictional soil. The analyses use linear programming and...
TL;DR: In this article, the Swedish fall cone method was used to predict undrained shear strength of a remolded soil at any water content based solely on its liquid limit and plastic limit.
Abstract: The concept that plasticity index of soils can be defined as a range of water contents producing a 100-fold variation in undrained shear strength has been experimentally verified with the help of a large number of tests on soils of diverse nature. This has led to the redefinition of the plastic limit as the water content at which undrained shear strength is around 170 kN/m2. Undrained shear strength of a soil at the liquid limit can be considered to be around 1.7 kN/m2. Accordingly, both the liquid limit and the plastic limit have been determined in the present work by a single consistent method, i.e., the Swedish fall cone method. The undrained shear strength-water content relationship has been found to be log-linear for a wide range of water contents beginning from lower than the plastic limit to higher than the liquid limit. This resulted in the formulation of an expression for predicting undrained shear strength of a remolded soil at any water content based solely on its liquid limit and plastic limit.
TL;DR: In this article, the use of electromagnetic induction measurements was evaluated to predict water content in the upper 1.50 m of a prototype engineered barrier soil profile designed for waste containment, and a simple linear regression model accurately predicted average volumetric water content of the profile at any location at any time.
Abstract: The use of electromagnetic (EM) induction measurements was evaluated to predict water content in the upper 1.50 m of a prototype engineered barrier soil profile designed for waste containment. Water content was monitored with a neutron probe, and bulk soil electrical conductivity was monitored with a Geonics EM38 ground conductivity meter at ten locations at approximately monthly intervals over a three-year period. A simple linear regression model accurately predicted average volumetric water content of the profile at any location at any time (R2=0.80,σ=0.009) and spatially averaged volumetric water content over the entire area at any time (R2=0.99,σ=0.003). Although some temporal drift was present in the model residual values, the impact on predicted water content was negligible. Therefore, once the model is calibrated with the neutron probe over a sufficient range of water contents, further neutron probe measurements may not be necessary. EM induction has several advantages over traditional water conten...
TL;DR: In this article, a general reliability calibration procedure is used to derive robust resistance/deformation factors for load and resistance factor design (LRFD) and multiple resistance factor (MRFD) formats, and two target reliability indices of 3.2 and 2.6 are proposed based on an extensive study of existing designs for ultimate and serviceability limit state.
Abstract: This paper presents the development of simplified reliability-based design (RBD) equations that are suitable for spread foundations subjected to uplift. Emphasis is placed on the loading and foundation characteristics relevant to the electric utility industry. A general reliability calibration procedure is used to derive robust resistance/deformation factors for load and resistance factor design (LRFD) and multiple resistance factor design (MRFD) formats. Two target reliability indices of 3.2 and 2.6 are proposed based on an extensive study of existing designs for ultimate and serviceability limit state, respectively. The main advantage of using these RBD factors is that a known level of reliability can be consistently achieved over a wide range of design conditions. Simple design calculations using the MRFD format are shown to demonstrate their ability to account for parametric uncertainties in a rational manner.
TL;DR: In this paper, changes in waste compressibility as a function of the state of decomposition are reported, and the magnitude of compressibility was shown to increase as refuse decomposed and compressibility parameters were correlated with the decomposition.
Abstract: Recently, there has been substantial interest in the enhancement of refuse decomposition in landfills, which results in increased settlement. In this paper, changes in waste compressibility as a function of the state of decomposition are reported. Samples representative of residential refuse were decomposed under conditions designed to simulate decomposition in both control and bioreactor landfills. Twenty four one-dimensional oedometer tests (63.5 mm cell) were performed on refuse prepared in laboratory-scale reactors for measurement of primary (Cc) and secondary (Ci, representing creep, and Ci, representing biological) compression indices. The state of decomposition was quantified by the methane yield and the cellulose (C) plus hemicellulose (H) to lignin (L) ratio. The magnitude of compressibility was shown to increase as refuse decomposed and compressibility parameters were correlated with the state of decomposition. Initial settlement increased with decreasing (C + H)/L ratio while the creep index was fairly independent of the state of decomposition. The coefficients of primary compression (Cc) for bioreactor samples showed an increasing trend with decreasing (C + H)/L ratios. Cc increased from 0.16 to 0.36 as (C + H)/L decreased from 1.29 to 0.25, and similar values of Cc were obtained with control samples at similar (C + H)/L ratios. The creep index range was estimated at 0.020.03 for control and bioreactor samples in various states of decomposition. The magnitude of the biological degradation index (Ci) depended on the degradation phase with the highest value of 0.19 obtained during the phase of accelerated methane production. Proposing a single Cc for landfill settlement calculations may lead to inaccurate predictions. Properties of each waste sublayer will change as a function of the decomposition stage, and dominating processes with appropriate compressibility parameters should be applied to individual sublayers.
TL;DR: In this paper, a procedure is proposed to evaluate the triggering of liquefaction in ground subjected to a static shear stress, i.e., sloping ground, using the yield strength ratio, su(yield)/σv0′.
Abstract: A procedure is proposed to evaluate the triggering of liquefaction in ground subjected to a static shear stress, i.e., sloping ground, using the yield strength ratio, su(yield)/σv0′. Thirty liquefaction flow failures were back analyzed to evaluate shear strengths and strength ratios mobilized at the triggering of liquefaction. Strength ratios mobilized during the static liquefaction flow failures ranged from approximately 0.24 to 0.30 and are correlated to corrected cone and standard penetration resistances. These yield strength ratios and previously published liquefied strength ratios are used to develop a comprehensive liquefaction analysis for ground subjected to a static shear stress. This analysis addresses: (1) liquefaction susceptibility; (2) liquefaction triggering; and (3) post-triggering/flow failure stability. In particular, step (2) uses the yield strength ratio back-calculated from flow failure case histories and the cyclic stress method to incorporate seismic loading.