Journal of Geotechnical and Geoenvironmental Engineering

The overburden correction factor ($K_{\sigma }$) is used to account for the curvature of the cyclic strength envelope with increasing consolidation stress, and it provides part of the basis for extrapolation of liquefaction-triggering correlations based on standard penetration test (SPT) and cone penetration test (CPT) to larger depths than covered by current databases of liquefaction case histories. This paper presents an updated database of laboratory test results defining $K_{\sigma }$ effects. Laboratory test results included in previous databases are reexamined in light of current understanding of factors that can affect laboratory measurements of cyclic strengths, including the effects of increasing density with increasing consolidation stress, variable overconsolidation ratios, and other factors. The updated database is used to examine potential biases in the $K_{\sigma }$ relationships used in two SPT-based liquefaction triggering procedures. The first relationship was found to be conservative with respect to the data for clean sands and less conservative for sands with fines contents between 7 and 35%. The second relationship was found to provide a reasonably good fit to the data for clean sands and to be slightly unconservative for sands with fines contents between 7 and 35%. Implications for practice are discussed.

Full-scale tests were performed on embankments with a beam foundation supported by floating and end-bearing piles. An analytical model based on the soil arching mechanism appeared to be able to predict accurately the vertical load transferred to a group of beams at a small center-to-center distance. However, when the distance between the beams was too wide or the embankment was too low to mobilize soil arching, the vertical load transferred to a beam could be predicted accurately with a model based on the punching shear mechanism. Greater embankment loads could be transferred to a piled beam through soil arching than could be transferred through punching shear. Beams in a piled embankment should be placed sufficiently close to each other to allow application of the soil arching model for design. Embankment loads could be transferred to both floating and end-bearing piles. Although load-transfer behavior was similar, the settlement of floating piles was significantly larger than the settlement of end-bearing piles. Settlement in a piled embankment could be reduced considerably by the application of end-bearing piles with a group of beams at a small center-to-center distance.

Thickened tailings, defined as mineral wastes that behave as a non-Newtonian fluid, show a small yield stress and release a small amount of water following deposition. Thickening has become an increasingly used option in tailings management. This paper presents a detailed examination of gold mine thickened tailings undergoing self-weight consolidation, which is an important mechanism affecting soft soils immediately after deposition. Self-weight consolidation was evaluated using a column equipped with water pressure transmitters whereas a slurry consolidometer was employed to obtain the compressibility relationship under low vertical effective stresses. The piecewise-linear model CS2 was used to model the experimental self-weight consolidation test. This model proved very accurate in reproducing the observed behavior. Both the test results and the model results also confirmed the absence of sedimentation in the thickened tailings, which is in agreement with values reported in the literature related to similar materials.

The current practices for determining the peak (yield) and postliquefaction (critical) undrained shear strength of liquefiable cohesionless soils for grounds subject to static shear stress (e.g., sloping grounds or grounds beneath foundations) require either a suite of costly laboratory shear tests on undisturbed field samples or empirical correlations with in situ penetration tests, which do not account for the effect of the shearing mode on soil behavior. Improved correlations are developed in this study for estimating the undrained triggering and postliquefaction shear strengths of cohesionless soils, which are based on the most reliable field-liquefaction data from past cases of liquefaction flow failures and soil shearing behavior observed in a large database of 600 laboratory shear tests for different modes of shear. The proposed method accounts for the variations in the mode of shear when providing estimates of the undrained triggering and postliquefaction strengths mobilized in static liquefaction flow failures.

A series of large-scale triaxial compression tests were conducted to investigate the strength and deformation behaviors of Tacheng rockfill material (TRM) in relation to the initial void ratio and initial confining pressure. The critical state friction angle of TRM was expressed as a linear function of the logarithm of the initial confining pressure. The excess peak state friction angle and excess characteristic state friction angle of TRM were formulated as linear equations of a revised relative dilatancy index to capture the influences of density and pressure on the peak state and characteristic state friction angles. The initial elastic modulus, tangent modulus, and secant modulus of TRM were dependent on the initial void ratio and initial confining pressure. In addition, a formulation incorporating density and pressure was proposed to simulate the initial elastic modulus of TRM. The volumetric and deviatoric strains of TRM at the critical state were also dependent on density and pressure. The critical state line of TRM in the $e-\lg p^{\prime }$ space descended with a decrease in the initial void ratio.

The amount of particle breakage of Tacheng rockfill material (TRM) in the process of shearing was quantitatively measured by a relative breakage index. The fractal dimension of TRM at the final state of the tests was found to be linearly related to the void ratio and logarithm of the confining pressure. The influences of the relative breakage index on the friction angle, modulus, and deformation were investigated based on a series of large-scale triaxial compression tests on TRM. An increase in the relative breakage index leads to an increase in the volumetric strain and to decreases in the peak state friction angle, critical state friction angle, deviatoric strain, and critical state void ratio. The test results were used to propose simple formulations pertaining to the relative breakage index for the strength and deformation indexes (e.g., peak state friction angle, critical state friction angle, initial elastic modulus, secant modulus at 50% of the peak strength, volumetric strain, deviatoric strain, and critical state void ratio).

Internal instability is a form of internal erosion in broadly graded cohesionless soils in which fine particles can be eroded at lower hydraulic gradients than predicted by classical theory for piping or heave. A key mechanism enabling internal instability is the formation of a stress-transmitting matrix dominated by the coarse particles, which leaves the finer particles under lower effective stress. In this study, discrete element modeling is used to analyze the fabric and effective stress distribution within idealized gap-graded samples with varying potential for internal stability. The reduction in stress within the finer fraction of the materials is directly quantified from grain-scale data. The particle-size distribution, percentage finer fraction, and relative density are found to influence the stress distribution. In particular, effective stress transfer within a critical finer fraction between 24 and 35% is shown to be highly sensitive to relative density.

Compensation grouting is often employed as a mitigation technique to reduce the settlements induced by tunneling. The efficiency of compensation grouting, defined as the ratio of the volume of heave induced at the ground surface to the volume of injected grout, is strongly dependent on grout properties, injection characteristics, and soil properties. In clayey soils, site observations and laboratory tests show high values of compensation efficiency immediately after injection. However, the efficiency can decrease with time if positive excess pore-water pressures develop in the soil during the injection process. Conversely, in sandy soils, a loss of volume occurs because of pressure filtration of the grout during and soon after the injection process, which reduces the compensation efficiency. This paper describes an analytical model that can be used to evaluate the volume loss produced by pressure filtration of cement-bentonite grouts as a function of soil, grout, and injection parameters. The magnitude of pressure filtration is evaluated as the grout efficiency, which is given by the ratio of the volumes of the final grout body to the injected grout. Results show that the grout efficiency increases with decreasing soil permeability and with increasing grout bentonite content. The result of a grout injection test on a silty soil is back-analyzed using this approach in which the grout efficiency is first evaluated through the proposed filtration model and then used to calibrate a numerical simulation of the test. The good agreement between experimental data and computed results shows that prediction of the efficiency of compensation grouting can be improved using the proposed approach.

New semiempirical design procedures for the determination of ultimate shaft friction and load-displacement response of axially loaded piles in clay are proposed. A main basis for developing the new procedures was detailed review and reassessment of results from a series of pile load-test programs published over the past 30 years on piles well instrumented to monitor soil and pore pressures as well as load distribution along the pile shafts. Two new alternative procedures are proposed for predicting the ultimate shaft friction: an $\alpha$ approach, which uses the normalized undrained strength based on direct simple shear tests as a main correlation parameter, and a $\beta$ approach, which uses the overconsolidation ratio (OCR). Both approaches include the effects of the plasticity index of the clay, $I_p$, which is shown to have an especially large impact on the correlations when $I_p<25\%$. In practical design, it is recommended that both methods be used and design values be selected for the ultimate shaft friction that represents an average for the two methods. Pile diameter, length, or stiffness or whether the pile is open- or closed-ended seem to have little impact on the shaft friction. However, a moderate effect of pile length or flexibility on the total ultimate pile capacity comes out of the proposed $t\text{-}z$ curves, which include some postpeak reduction.

A discrete-element method (DEM) assembly of virtual particles is calibrated to approximate the behavior of a natural sand in undrained loading. The particles are octahedral, bumpy clusters of spheres that are compacted into assemblies of different densities. The contact model is a Jäger generalization of the Hertz contact, which yields a small-strain shear modulus that is proportional to the square root of confining stress. Simulations made of triaxial extension and compression loading conditions and of simple shear produce behaviors that are similar to sand. Undrained cyclic shearing simulations are performed with nonuniform amplitudes of shearing pulses and with 24 irregular seismic shearing sequences. A methodology is proposed for quantifying the severities of such irregular shearing records, allowing the 24 sequences to be ranked in severity. The relative severities of the 24 seismic sequences show an anomalous dependence on sampling density. Four scalar measures are proposed for predicting the severity of a particular loading sequence. A stress-based scalar measure shows superior efficiency in predicting initial liquefaction and pore pressure rise.

Water-retention data for a suite of predominantly sandy soils were analyzed to quantify the effects of two constraints commonly applied to the three-parameter model for the soil-water characteristic curve (SWCC). Systematic effects were observed. Constraining either the symmetry parameter ($m$) to $m=1-1/n$ or residual saturation ($S_r$) to zero resulted in values for the air-entry parameter $\alpha$ that were approximately 25–30% different than if no constraints were applied. The $m=1-1/n$ constraint forced the pore-size distribution parameter $n$ to fall within a narrow range ($\sim 1.5<n<\sim 4.0$), whereas $n$ values using independent $m$ and $n$ were more variable and could be as large as 35. The $m=1-1/n$ constraint produced best-fit residual saturation values that were approximately 0.02 higher than without the constraint. These differences are significant and should be considered when adopting existing or new pedotransfer functions for estimating water-retention behavior of unsaturated soils from more easily measured properties.