Journal of Geotechnical and Geoenvironmental Engineering

Soil particle roundness ($R$) and sphericity ($S$) are two important intrinsic properties that govern a soil’s mechanical behavior. Although $R$ and $S$ have well-established mathematical definitions dating back to the 1930s, the values are much more typically estimated using charts developed in the 1940s and 1950s. The charts, are based on the earlier mathematical definitions. Using these charts, a class of undergraduate civil engineering students at the University of Michigan were asked to estimate ($R^c$ and $S^c$) from images of twenty geologically and geographically diverse sands spanning a range of actual $R$ and $S$ values. The images were of three-dimensional (3D) assemblies of the sands as they would be found in images taken remotely or in situ. The students’ estimates were statistically analyzed and compared with rigorously determined $R$ and $S$ using a recently developed computational geometry algorithm. Overall, the students’ estimates were scattered, particularly for natural sands exhibiting intermediate values of $R$ and low values of $S$. On average, the students underestimated $R^c$ and $S^c$. Reasons for the diverse responses and underestimates of the actual $R$ and $S$ are proposed.

The small-strain shear modulus $G_0$ is a property fundamental to the deformation response of soils to dynamic loading. It depends on soil mineralogy, particle characteristics, void ratio, effective stress, and the degree of saturation. Some theories have been established to predict $G_0$ of soils under variably saturated conditions. Accordingly, a new unified model was developed for $G_0$ of different soils under variably saturated conditions. The model is based on two conceptual mechanisms: material hardening/softening, which is considered using the degree of saturation as a variable, and interparticle contact forces carried by the soil skeleton, which is considered using the effective stress as a variable. By utilizing suction stress theory, it is demonstrated that $G_0$ can be correlated to the parameters of the soil-water retention curve. Results from the literature for 22 soils along with new results for 7 soils were used to validate the model under variably saturated conditions and a range of total stresses.

A study of the clogging of two soils, a sand with grains ranging from 0.4 to 4 mm, and a gravel with grains ranging from 1 to 10 mm, was carried out by feeding the bacteria initially present in the soils. The focus of this research is to study the durability of bioclogging. The results showed that clogging occurred quickly after the injection of nutrients. The soils were subjected to gradient increases and a critical hydraulic gradient $i_{\mathrm{crit}}$ (corresponding to the gradient for which unclogging occurred and an increase in the flow of water was observed) was determined. It is equal to 0.8 for the sand and to 0.06 for the gravel. The durability of bioclogged soils was also studied by performing 10 to 30 hydraulic gradient cycles between the initial value and $i_{\mathrm{crit}}/2$. For the sand, the permeability increase after the cycles was very low. In contrast, in the gravel, unclogging occurred very quickly, highlighting the influence of grain size and materials grading.

The earthquakes of 2010 and 2011 in New Zealand and Japan caused significant liquefaction-induced damage in both countries. Unlike previous experiences in which damage to infrastructures was the main concern of people and engineers, vast distortion of private houses caused serious problems for society. The objective of researchers and engineers after these two events was to propose technically-reliable and economically-affordable mitigation measures to people. This paper examines the efficiency and performance of installing various configurations of drains, and their combination with sheet-pile walls in different groundwater levels. The results revealed that unless there is perfect nonliquefied ground under a building’s foundation, settlement of the structure cannot be reduced significantly. In this regard, preventing liquefaction in shallower depths has crucial importance. It also was found that using sheet-pile walls equipped with drains enhanced individual performance of both drains and sheet-piles.

Commonly used simplified one-dimensional nonlinear seismic site response analyses employ constitutive models based on a variation of the hyperbolic model to represent the initial stress-strain backbone curve. Desirable features of the backbone curve include provision of (1) an initial shear modulus at zero shear strain, (2) a limiting shear stress at large shear strains, and (3) flexible control of the nonlinear behavior between those boundary conditions. Available hyperbolic models have combinations of two of these features. A new general quadratic/hyperbolic (GQ/H) model is developed from the bivariate quadratic equation to provide all desired features. Nonlinear behavior is controlled by a shear-strain-dependent curve-fitting function. The model’s unload-reload rules and coupling with pore-water pressure generation are also presented. Several total-stress site response analyses are presented to demonstrate the performance of the GQ/H model relative to a commonly used hyperbolic model in which the maximum shear stress cannot be defined. The analyses show the importance of properly representing the maximum shear stress in the constitutive model because it may lead to underestimation or overestimation of the computed site response.

This paper reports a series of experiments aimed at studying the effect of grain crushing on the water retention capacity of granular soils. Specimens of granular materials have been subjected to oedometric compression at high pressures, revealing that crushing causes significant alterations of both grain-size distribution (GSD) and soil water retention curve (SWRC). In particular, the experiments have shown that the suction air-entry value ($s_{\text{AEV}}$) changes considerably during crushing, thus controlling the shape of the SWRC in proximity of saturated conditions. Such evidence has been interpreted through a number of GSD-dependent retention models available in the literature. In particular, the results have been used to verify the hypotheses of a recently proposed hydromechanical model based on the breakage mechanics framework, which enables the prediction of simultaneous variations in void ratio, GSD, and SWRC through constitutive relations linking the $s_{\text{AEV}}$ to the predicted degree of particle breakage. Although all models suggest an upward shift of the SWRC with the accumulation of crushing, the change of its shape and location are captured by each model with different levels of accuracy. Most notably, the analytical relations predicted by the breakage mechanics theory are able to capture satisfactorily the observed changes of the suction air-entry point, therefore representing a convenient tool for the analysis of geotechnical systems made of unsaturated soils susceptible to breakage, such as transportation infrastructures and rockfill dams.

Large leakage occurred in several concrete-face rockfill dams (CFRDs) around the world recently, resulting in economic losses and safety problems. To rehabilitate these dams, it is necessary to identify leakage locations on the concrete face slabs and understand the severity of leakage at each location. This technical note presents a method for localizing and quantifying leakage through CFRDs. Analysis models are developed to estimate the leakage rate from horizontal and vertical leakage sources. The relationship between water level and leakage is described for these two leakage sources. Based on a monitored water level-leakage relation, the elevations of leakage are determined, and the leakage rate at each elevation is estimated using these models. A case study on the Buxi CFRD is presented to illustrate the method. The calculated water level-leakage relation is in good agreement with the measured one before rehabilitation, and the leakage has decreased over 80% after rehabilitation.

This paper presents an experimental investigation of the effect of load duration on particle breakage and dilative behavior of a residual soil. To deepen the understanding of particle breakage subjected to load duration, the large-scale monotonic triaxial (TX) tests and creep TX tests were conducted on residual soil in saturated conditions. Values of particle breakage for the monotonic loading condition are compared with corresponding values for the creep loading condition calculated using a relative breakage index. For the creep TX tests, the load duration results in $>1.5$ times greater breakage index than the values of the monotonic TX test did. The obtained results suggest that load duration and stress level beneficially influence the particle breakage in the form of dilation suppression. The linearity is observed between the shear stress ratio and the dilation rate. A cycle with three phases is provided to help understand the creep behavior of coarse-grained residual soil: the concentration of contact stress, particle breakage, and rearrangement of crushed grains. The findings are expected to improve the understanding of the dilative behaviors of residual fills at subgrade sites.