Journal of Geotechnical and Geoenvironmental Engineering

Specific surface area (SSA) of soil is an intrinsic property governing many geotechnical and geoenvironmental engineering properties. SSA can be physically divided into two categories: external or particle surface area, and internal or intracrystalline surface area. Although both of them are well known to play different roles in physical, chemical, and biological processes, few methods have been developed to quantitatively distinguish between them. Using a recent theoretical advancement of an augmented Brunauer–Emmett–Teller (BET) adsorption equation for soil, the writers develop a procedure based on measured water adsorption isotherms to quantify the external and internal SSAs. Extensive adsorption isotherms of water, ethylene glycol monomethyl ether, and nitrogen of a variety of silty and clayey soils are used to validate the procedure. Practical implications of SSA are also provided by linking the importance of the internal SSA to swelling behavior, and the importance of the external SSA to adsorption of nonpolar materials. The demonstrated procedure to quantify external and internal SSAs should provide a pressing and powerful method to understand physical, chemical, and biological processes in soils.

Systematic linear-elastic finite-element analyses were performed on a series of unpiled rafts (rafts without piles), pile groups, and piled rafts with different geometries and pile configurations to determine the stiffness of these rafts, pile groups, and piled rafts. Parametric studies were performed in conjunction with regression analysis based on which equations were proposed for quick estimation of piled raft stiffness by combining the stiffnesses of unpiled rafts and pile groups. The average and maximum settlements of piled rafts were calculated using the piled raft stiffness equations. The accuracy of the proposed stiffness and settlement equations was verified and validated against other numerical and experimental results of piled rafts. The study shows that the developed equations can be used to obtain a quick initial estimate of piled raft settlement that can be used in design. The developed settlement calculation method is applicable for piled rafts of shapes and sizes similar to those considered in this study.

The cyclic-stress approach is widely used to evaluate level-ground liquefaction triggering. Although easy to use, several limitations introduce significant uncertainty in the analysis, including: (1) several correction factors are required, including the depth reduction, magnitude scaling, and overburden correction factors; (2) seismic demand is quantified using a total-stress framework to capture an effective stress phenomenon [pore-water pressure (PWP) generation and liquefaction]; and (3) because it is based on surface manifestations, its applicability outside of database parameters (e.g., $\mathrm{depths}>10\mathrm{m}$) is unknown. In this study, the authors performed a broad parametric study to assess the viability of using nonlinear site response analysis with validated constitutive and PWP generation models to evaluate level-ground liquefaction. For a wide range of conditions, the parametric results agreed with published empirical liquefaction-triggering relations. The nonlinear site response analysis with PWP generation also correctly predicted liquefaction for dynamic centrifuge tests and field cases, demonstrating that this approach can assess level-ground liquefaction while avoiding highly uncertain correction factors required in the cyclic stress method.

Presence of skew-angled abutments complicates the seismic behavior of ordinary bridges, primary effect of which is the passive lateral resistance of the engineered backfill behind the abutment. The eccentricity of the soil reaction relative to the bridge’s center of stiffness or mass causes a skew bridge to rotate under seismic excitations, and a nonuniform soil pressure distribution develops behind the abutment backwall. A distributed nonlinear spring model is devised to represent the lateral passive reaction of the backfill soil. The behavior of these springs is based on a model that was previously developed and experimentally validated for straight abutments, dubbed the log-spiral hyperbolic (LSH) model, which is modified herein by a scaling factor that is based on the skew angle. This new modeling approach is verified against three-dimensional finite element model simulations and is validated with data from five prior large-scale experiments that produced direct measurements of load-deformation backbone curves for several skew angles. In the final step, the validated modified [i.e., skew-LSH (SLSH)] model is used in parametric studies to devise a simple bilinear load-deformation relationship that is parameterized with respect to backwall height, abutment skew angle, and backfill soil properties. This simple relationship is intended for routine use in the capacity-based seismic design and analysis of skew bridges.