Journal of Geotechnical and Geoenvironmental Engineering

Sand deposits are often stratified with thin layers of low-permeability silt. Previous studies have shown that the presence of sharp variations in permeability could slow down the dissipation of earthquake-induced excess pore pressures and cause void redistribution and shear strain localization. However, the relative importance and influence of these phenomena on seismic site response, soil–structure interaction, response of foundation and superstructure, and effectiveness of liquefaction countermeasures is not well understood. In this study, we present the results of dynamic centrifuge tests that evaluate the response of 3- and 9-story inelastic steel structures (A and B) founded on layered liquefiable deposits with and without a silt cap. The thin silt layer is also evaluated in terms of its influence on the effectiveness of prefabricated vertical drains (PVDs) as mitigation. The results indicate that a thin silt cap may have beneficial or detrimental effects on a structure’s performance, particularly when evaluated in terms of foundation’s permanent rotation (or tilt). Under the lighter, stronger, and stiffer Structure A, concentration of shear strains in the relatively thin loose zone below the silt layer reduced permanent rotation by 60%–100% compared with the same structure on the soil profile without silt. However, the greater inertial moment and shear demand on the foundation and loose zone below silt from the heavier, weaker, and more flexible Structure B initiated larger shear deformations and rotations, leading to larger dilation tendencies and a momentary reduction in excess pore pressures in the soil below. This amplified accelerations on the foundation, flexural deformations in the superstructure, and $P\text{-}\mathrm{\Delta }$ effects that further exacerbated rotation and damage to the superstructure. The effect of PVDs was similar on both profiles, reducing the foundation’s permanent settlement (by up to 57%) and tilt (by up to 49%), but the influence of silt on performance was similar to that of unmitigated structures. These results point to the importance of identifying and characterizing thin interlayers in the soil profile, together with the key properties of structure, foundation, and ground motion, when assessing and mitigating the consequences of liquefaction.

Rocking foundations have emerged as an attractive design to reduce the seismic loads of structures during strong earthquakes. However, they cannot be applied in the field directly because of the permanent deformation caused by their rocking behavior. To reduce the permanent deformation induced by a rocking foundation, installation of an unconnected pile below the foundation has been suggested as an improved design. The region of significant plastic strains beneath the foundation caused by the rocking behavior is located at a shallow depth; thus, the length of the unconnected pile is reduced relative to the case of connected piles. In this study, to determine the optimized design for a rocking foundation, horizontal slow cyclic tests and dynamic centrifuge shake-table tests were performed for various types of foundation models incorporating short piles. The foundation–structure system was designed to exhibit rocking-dominant behavior. Based on the results of the horizontal slow cyclic tests and dynamic centrifuge tests, the rocking behaviors of the tested models were compared. A setup featuring unconnected short piles with a soil layer is proposed as an optimized rocking foundation design, focusing on the reduction of the permanent deformation of soil.

The integrity of a levee is an important issue that needs to be checked frequently. This can be done by monitoring the subsidence of the levee for a long time to identify the weak sections and prioritize maintenance efforts. This paper presents the application of a remote sensing technique to monitor the displacement of the London Avenue Canal levee in New Orleans, Louisiana, from 2009 to 2014. The input data were radar images taken by the German Space Agency’s X-band satellite, TerraSAR-X, over those 6 years. The displacement of a levee section at London Avenue was determined by analyzing the displacement of selected points using the interferometric synthetic aperture radar (InSAR) method. The required steps to calculate the displacement at selected points were presented. In situ instrumentation was also installed to measure the displacement at several locations in the London Avenue section. The comparisons of the different monitoring methods revealed similar displacement trends. The favorable comparison increases confidence in the suitability of remote sensing techniques to monitor the displacement of entire levee systems.

Biocementation processes rely on microbial-induced calcite precipitation (MICP), which is a naturally occurring biochemical process. Biocement materials are a form of environmental cementitious agents used to improve the mechanical properties of granular soils by physically binding soil particles together. Efficient improvement of the macromechanical behavior of coarse sand treated by various amounts of biocement materials requires an in-depth understanding of its microstructure. This paper examined the effect of a number of bacterial suspension and cementation solution flushes on the macromechanical behavior of coarse sand. Also, X-ray computed tomography (XCT), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to investigate changes occurring at microlevels. The results show that compressive strength increased with an increase of biocement materials, and the maximum compressive strength achieved was around 14 MPa. The microscopic investigations were linked to the macromechanical changes, providing unique insight into the causation of the changes. Furthermore, several common soil properties (calcium carbonate content, dry density, void ratio, and porosity) were successfully identified using the XCT technique.

Florida carbonate rocks are typically weak, with a median unconfined compressive strength value of approximately 3 MPa. Due to the infeasibility of attaching strain gauges to their vuggy and shelly surfaces, an innovative volume change device was added to a Hoek cell triaxial system, enabling the measurement of volumetric responses during triaxial tests. In this study, 223 triaxial tests on five different Florida rock formations were performed, with confining pressures ranging from 0.35 to 20.7 MPa. The tests indicate that (1) only a small percentage of Florida carbonate rocks exhibit brittle rupture; and (2) most Florida carbonate rocks exhibit ductile stress-strain behavior, even at the lowest confining pressure. A ductile response is typically associated with contractive volumetric behavior due to the rock’s porous structure. The study established a ductile threshold ${\sigma }_d/{\sigma }_3$ ratio, which was found to not be a constant, but to vary with confining pressure. It was confirmed through the triaxial test results that (1) the Hoek-Brown criterion works well for the dense specimens, which are not commonly encountered in Florida; and (2) for the typical porous Florida rocks, the stress-strain response is ductile and the strength envelopes in Lambe’s $p\text{-}q$ diagram have a linear increasing (constant slope) zone followed by a decreasing slope zone, which is a function of the Florida formations as well as the specimens’ bulk dry unit weights.

The influence of the variability of the soil profile on the translational and rotational kinematic interaction factors of pile foundations is analyzed. Variable-with-depth profiles representative of different soil types are considered, and their results are compared to those of equivalent homogeneous soils presenting the same average shear wave velocity. The seismic response of the foundation is computed through an efficient numerical model based on the integral reciprocity theorem in elastodynamics and specific Green’s functions for layered half-spaces. The assumption of the variable soil profile generally leads to a higher filtering effect of soil lateral displacements and increases the rotation of the foundation. The importance of the soil variability on the response of the supported structure is also analyzed in terms of its pseudo-spectral accelerations. The homogeneous assumption is found to be conservative for structures with low periods, while for other systems, especially those with an important contribution of the foundation rotation to the structural response, significantly higher maximum accelerations are obtained when considering the variable profile.

This paper describes the geological–geotechnical study of the occurrence of a mass movement on a hillside in the municipality of Camaragibe, Pernambuco state, Brazil. Comprehensive onsite geotechnical investigation was performed involving borings, collection of deformed and undisturbed samples, moisture profiles, hydraulic conductivity tests (Guelph permeameter), and study of wastewater disposal. Laboratory tests were performed, including chemical, mineralogical and physical characterization, permeability (triflex), suction studies, oedometer, direct, suction-controlled, multiple reversal, and ring shear tests; instrumentation also involved the use of Casagrande and maximum piezometers, water level gauges, slope indicators, and a pluviometer. The data obtained in the laboratory and on site enabled characterization of the materials involved in the landslide (Barreiras Formation and granite residual soil) and understanding of the mechanism, its stability analysis at the failure stages, and reactivation. It is cited as having predisposing factors to instability, namely geology, anthropic action, and relief. Rainfall was indicated as the primary triggering factor. At the failure stage, the movement was classified as multiple rotational landslide. At the reactivation stage, the displacement occurs in blocks.

Piled rafts are increasingly used for various structures due to the enhanced load-carrying capabilities of raft and piles combined as a single structural unit. In this study, an experimental testing program using a full-scale, fully instrumented piled raft was established and field monitoring was carried out. Test results from the field monitoring were presented and analyzed. It was found that various factors affected the measured load-carrying behavior of the piled raft, including those that were not identified and considered in the design. The measured load-transfer curves of the piles showed an increase in axial load with depth within the upper soil zone, which was different from those assumed in the design and commonly observed from axially loaded piles. Factors that contributed to such unusual load-carrying behavior were the subsoil-layer condition, design modification, and the adequacy of the construction procedure. Results from the finite-element analysis confirmed that inclined soil-layer and loading conditions could cause loads that became unevenly and asymmetrically distributed on piles of an axially loaded piled raft with variations in the load-transfer relationship.