Journal of Geotechnical and Geoenvironmental Engineering

The objective of this study was to evaluate the effects of waste composition and decomposition on the shear strength of municipal solid waste. Waste was collected from two sources (an operating landfill and a transfer station) and degraded in laboratory anaerobic reactors to prepare wastes with different degrees of decomposition. Shear strength was measured in a 280-mm-diameter direct shear ring on nine wastes with normal stress ranging between 12 and 90 kPa. The Mohr-Coulomb failure criterion was used to determine shear strength parameters ($\varphi$ = friction angle and $c$ = cohesion intercept) of the wastes, and shear strength was selected at a horizontal displacement of 56 mm (i.e., 20% of the specimen diameter). A composite failure envelope regressed through shear strength versus normal stress data from all wastes was statistically significant, with $\varphi =37°$ and $c=20 \text{kPa}$. A comparison between tests conducted in this study and in the literature indicates that larger $\varphi$ are obtained for waste with a greater fraction of soil-like, gravel, and inert constituents, whereas lower $\varphi$ are coincident with higher fractions of paper and cardboard or plastic. This effect of waste composition on $\varphi$ is applicable when fibrous particles are primarily parallel with the shear plane, which is the common particle orientation in direct shear. Tests conducted in this study also indicate $\varphi$ increases with decreasing volatile solids or the ratio of cellulose + hemicellulose to lignin (i.e., increasing decomposition). Contrasting correlations have been reported in the literature, attributed to the initial waste composition, which influences the effect of decomposition on $\varphi$. No correspondence was found between $c$ and waste composition or the degree of waste decomposition.

The stability of subgrade soils is a major concern during roadway construction with inappropriately soft layers often undercut and replaced by competent or stabilized materials. Systematic undercut criteria are established using numerical modeling with varying the strength and stiffness parameters of the subgrade and representing the mechanistic behavior as an elastic-perfectly plastic medium. Two modes of domain configurations were considered: the plane strain and axisymmetric conditions. The plane strain mode is assumed to simulate proof roller loading with four parallel tires and mainly provides information about excessive pumping response as materials at deeper layers are affected. The axisymmetric mode provides information related to excessive rutting and is used to simulate the effect of single or dual tires representing construction traffic, rather than a series of closely spaced axle loads. Undercut criteria are proposed for meeting a deformation limit state of 25 mm for both pumping and rutting, with the additional requirement of a performance capacity ratio (PCR) of 1.5. The proposed criteria are applied to data from four field cases in which decisions were made regarding the need for undercutting, and the applicability of the criteria is discussed.

A probabilistic version of the Idriss and Boulanger standard penetration test (SPT)–based liquefaction triggering correlation is derived using a maximum likelihood approach and an updated case history database. Measurement and estimation uncertainties in the cyclic stress ratio (CSR) and SPT ${\left(N_1\right)}_{\text{60cs}}$ values and the effects of the choice-based sampling bias in the case history database are taken into account. The results of sensitivity analyses show that the position of the most likely triggering curve is well constrained by the case history data and that the magnitude of the total error term is also reasonably constrained. The most likely value for the SD of the error term in the triggering correlation is, however, found to be dependent on the uncertainties assigned to the CSR and ${\left(N_1\right)}_{\text{60cs}}$. The results of the sensitivity study appear to provide reasonable bounds on the effects of different interpretations on the positions of the triggering curves for various probabilities of liquefaction. Methods for including model and parameter uncertainties in probabilistic liquefaction analyses are briefly discussed. The derived triggering correlation is compared with relationships developed from cyclic laboratory test results for specimens obtained using frozen sampling techniques.

Liquefaction potential of four Pleistocene beach sand deposits in the Greater Charleston area, South Carolina, is assessed. The assessment is based on a review of 51 sites of conspicuous craterlets and horizontal ground displacement that occurred in beach sand deposits during the 1886 Charleston earthquake and an analysis of 82 seismic cone penetration tests with pore-pressure measurements. Of the 51 ground failure sites, 23 are associated with the Ten Mile Hill beds; 13 with the Wando Formation; 13 with the Silver Bluff terrace and younger deposits that lie adjacent to the harbor, rivers, and creeks; and two with the Ladson Formation. Liquefaction potential is analyzed using the seismic cone data with and without correction for age-related processes (diagenesis) and then expressed in terms of the liquefaction potential index (LPI). Probability curves are developed from the LPI calculations for different earthquake ground-shaking parameters. The probability curves for the Wando Formation overpredict liquefaction potential when no corrections for diagenesis are made. When corrections for diagenesis are made, the probability curves for all four sands generally agree with the observed field behavior.

This paper presents an integrated analytical method for calculating the resultant unfactored geosynthetic force in reinforced earth structures under seismic loading conditions. The method utilizes a pseudostatic limit equilibrium approach for assessing the internal stability of a reinforced earth structure, assuming a potential rotational failure along a log spiral trace. A closed-form solution is presented for determining the sum of all horizontal forces mobilized in the geosynthetic reinforcement along their intersection with the critical log spiral surface. This mobilized sum is then redistributed among the individual layers to determine the unfactored reinforcement forces that are needed to resist the applied seismic acceleration. Parametric studies were utilized, and the results are presented in a series of design charts for different conditions. Such charts can be used to determine the required tensile strength of the reinforcement for a given seismic coefficient. Alternatively, for a given reinforcement strength, the formulation can also be used to determine the yield acceleration that is required for calculating seismic displacements. An advantage of the proposed methodology is that it determines the yield acceleration caused by rotation of the reinforced mass (internal stability), which allows for a rational, yet simple, assessment of the displacement related to the internal movement of the reinforced mass. The design charts illustrate the effect of earth structure backslope and the vertical seismic coefficient. The results also show the impact of the assumed location of the resultant reinforcement force under seismic loading conditions. Variations in the location of this force over a reasonable range have little impact on the results. The inclination of the backslope has a significant effect for earth structures with smaller batters and/or larger horizontal seismic coefficients. Additionally, vertical seismic coefficients with a downward direction increase the mobilized force in the geosynthetic reinforcement.

Large lateral movements of a pile during impact driving can cause yielding of the surrounding soil. When this happens, the effective stresses between the soil and the pile wall diminish, and the pile shaft resistance decreases. A piling project was carried out in a marble area in Hong Kong, where highly variable rockhead contours and deep depressions filled with weak soil deposits were found. Many steel H-piles were driven to depths of more than 100 m, and the verticality of such long piles was a concern. A pile test program consisting of four driven steel H-piles with pile lengths up to 164.5 m was conducted. Verticality monitoring and dynamic pile tests at several penetration depths were performed. This paper aims at interpreting the verticality of the four long piles, studying the relevance of pile verticality to the encountered geological features, and studying the effect of pile verticality on the pile capacity. The maximum lateral pile movement during driving was up to 8.7 m at a depth of 100 m, and the maximum local pile inclination reached 0.139. The lateral movements of the piles during driving well matched the rockhead inclination and soil conditions. Both one-way sway and two-way cyclic sway of the test piles were observed. Cyclic sway was shown to cause more severe reduction of the pile shaft resistance than one-way sway.

Evaluation of the impact of tunnel construction on existing buried structures is an important problem. This paper presents an analytical method for estimating the effect of tunnel construction on end-bearing piles located above the tunnel. The method can be used to estimate the safe relative distance between existing piles and newly constructed tunnels. Spherical and cylindrical cavity expansion/contraction analyses are used to evaluate pile end-bearing capacity and the reduction of confining pressure at the pile tip that results from tunnel volume loss. Pile end-bearing capacity is then reevaluated based on the reduced confining pressure at the pile tip. A modified shear modulus is used to account for the effect of pile installation on soil stiffness. The method is used to analyze centrifuge experiments conducted to study this problem. For the experimental data, where the service load applied to the piles during tunnel volume loss ranged between 50 and 60% of the maximum jacking force, the analytical method showed that pile failure occurred when the load-carrying capacity was reduced below 80% of its original value. A parametric analysis is included that highlights the effect of key soil properties on results.

Several recent studies have investigated failure mechanisms for cast iron water pipes. These studies have primarily focused on the adverse effects of corrosion, frost, reactive backfill, and earthquakes. It appears that leaking pressure pipes can produce erosion voids under the buried structure. In this paper, a parametric study employing three-dimensional finite-element analyses is used to examine buried, continuous, cast iron water pipes. The objective is to understand the effect of such erosion voids on the stability of buried cast iron pipes and the longitudinal soil-pipe interaction. The results of the finite-element analyses demonstrate that the radial (${\sigma }_R$) and the axial stresses (${\sigma }_A$) are low compared with the hoop stresses (${\sigma }_{\theta }$), and the peak tension is always in the hoop direction. As a result of the high hoop stresses induced by the nonuniform bedding support, longitudinal fractures are likely to occur in the pipe, which may consequently cause pipe failure.

The influence of nonplastic silt content on the stress-strain, volume change, and strength characteristics of anisotropic silt-clay transition soils is investigated. A series of one-dimensional compression tests, isotropic compression tests, and undrained and drained triaxial tests on three soils of similar base clay but different nonplastic silt contents are performed on cross-anisotropic specimens prepared from consolidation of slurries. Tests with major loading directions both parallel and perpendicular to the specimens’ axis of deposition are performed. It is observed that the tested silt-clay soils are less compressible with increasing silt content during one-dimensional and isotropic compression tests. During drained and undrained triaxial tests, the normally consolidated soils at the same consolidation stress show larger values of stiffness and drained and undrained shear strengths with increasing silt content. The silt-clay soils also show larger pore pressure changes during undrained triaxial tests but essentially similar volumetric strains during drained tests as the silt content increases. In addition, it is observed that silt content significantly influences the anisotropy of the stress-strain and strength characteristics of the transition silt-clay soils.

A laboratory test program was conducted to evaluate the one-dimensional (1D) compression and creep properties of intact sand (and silty-sand) samples from a deep borehole at the Malamocco Inlet to the Venice Lagoon. The tests were performed with a constant rate of strain consolidometer and included special procedures for trimming the frozen samples and measuring strains during thawing and backpressure saturation. The specimens had variable fine fractions ranging from 6 to 21% and mica contents ranging from 1 to 10%. The results confirmed that there is a strong correlation between the creep rate coefficient and the compressibility index and between the swelling index and mica content. The compression behavior in all tests is well described by a nonlinear compression model with a unique limiting compression curve and a variable transition parameter that reflects the fines and mica content. Creep tests performed at different confining pressures are also well represented by a simple two-parameter model.

A published case history on the performance of a 29-m-deep excavation that occurred in stiff Oxford clay provides direct field evidence that lateral stress relief can produce shear planes. A finite-element model was developed to investigate the impact of lateral stress relief on this slope. The finite-element model utilized published site characterization data and incorporated shear-strength reductions along closed failure planes. Lateral stress relief resulted in an outward slope face movement that produced sufficient differential shear strain to develop and propagate a horizontal crack at the base of the slope. Analyses indicate excellent agreement with observed lateral and vertical slope face movements. The finite-element model suggests that the slope essentially behaved as a shear model. Recognizing the behavior of this slope, the principles of linear elastic fracture mechanics are expanded to consider closed crack propagation under shear loading conditions. Analyses indicate that a closed crack under shear loading will propagate along the preexisting crack plane, as observed in the Oxford Slope.

This paper introduces a new approach that considers the effect of softening to more accurately calculate floor-bearing capacities where difficult mine conditions are present. Because of softening and changes in confining pressures, the geotechnical properties of immediate fine-grained rock vary in the mine floor. Therefore, when floor softening is present, the conventional equations used to determine the floor-bearing capacity are not very accurate. In this study, a methodology is presented that considers the floor softening and existence of a durable layer in the mine floor. The proposed method is based on analysis of a case study located in central Illinois utilizing finite-element method (FEM) and rock mechanics laboratory data. For this case study, extensive geological mapping and laboratory tests, including rock classification, rock swell properties, and triaxial compression tests, were conducted on samples of fine-grained rocks that predominantly consisted of mudstone. The results of laboratory tests are presented and discussed in detail. Aerial and cross-sectional analyses of the floor lithology and stratigraphy were performed to evaluate the important bearing conditions across the project site. From the analyses, the immediate floor thickness and type of the nondurable and the underlying durable rock across the site were determined. DuroIndex is presented and used to determine and rate the durability of mine floor material. Considering certain pillar-to-room width ratios, two-dimensional FEM analyses were performed to evaluate mine floor capacity with both softened and unsoftened floor conditions. Consequently, the softening correction factor, or the correction for the softening effect, was determined. Finally, a procedure that takes into account the effect of softening and the existence of a durable layer was developed to determine allowable floor-bearing capacity.