Journal of Geotechnical and Geoenvironmental Engineering

Recent studies have shown that detection of the onset and evolution of micro shear bands (MSBs) in granular materials can be improved using measurements of the kinematic behavior of particles. Different methods such as the discrete-element method (DEM) or three-dimensional (3D) imaging techniques have been used to measure the kinematics of individual particles within triaxial specimens. However, conventional kinematic techniques that use particle translation and/or rotation cannot detect the onset and growth of MSBs during the hardening phase of axisymmetric triaxial experiments. In order to expose the localized shearing and particle-scale behavior of triaxial specimens, a relative particle translation gradient (RPTG) concept is used to detect and expose the onset of strain localization before the peak principal stress ratio (PSR). RPTG measurements for four different granular materials are reported in this paper. The RPTG concept is used to expose the onset of MSBs during the hardening phase of the experiments. In addition, the contact number of individual particles is quantified and discussed in relation to particle rotation to investigate a particle-scale relationship between particle contacts and rotation. The effects of density, confining pressure, and particle shape on contact number are examined.

The effect of particle shape on the strength, dilatancy, and stress-dilatancy relationship was systematically investigated through a series of drained triaxial compression tests on sands mixed with angular and rounded glass beads of different proportions (0%, 25%, 50%, 75%, and 100%). A distinct overall regularity parameter was used to define the particle shape of these mixtures, which ranged from 0.844 to 0.971. The test results showed that all of the samples at an initial relative density of 0.6 exhibited strain-softening and volume-expansion behavior. It was found that the peak-state deviatoric stress, peak-state axial strain, and peak-state friction angle at a given confining pressure decreased with increasing overall regularity. The maximum differences in the peak-state deviator stress, peak-state axial strain, peak-state friction angle, excess friction angle, and maximum dilation angle due to changes in particle shape could be as much as 0.61 MPa, 5.4%, 8.6, 1.5, and 3° at a given confining pressure of 0.4 MPa. In addition, it was found that the slope of the relationship between the peak-state friction angle and maximum dilation angle was independent of the particle shape, whereas the intercept (i.e., the critical-state friction angle) was significantly influenced by the particle shape. A stress-dilatancy equation incorporating the effect of overall regularity was proposed and provided a good estimate of the observed response accounting for the different particle shapes investigated.

Polymers have gained gradual attention in soil stabilization as a sustainable alternative to inorganic counterparts such as cement. However, the effects of polymers on the strength of soils and soil-waste mixtures are still unclear. Meanwhile, waste recycling has been important in fostering a sustainable environment in recent decades. To solve the deficiency in knowledge, large-strain strength of polymer-modified kaolinite (KA) and Class-F fly ash–kaolinite mixtures (FAKAs) was investigated with isotropically consolidated undrained triaxial compression tests. Both synthetic polymer (polyethylene oxide, PEO) and naturally occurring biopolymers (chitosan and xanthan gum) were used. An interface model was also proposed to account for interfaces of KA, FAKA, and fly ash. Experimental results suggested that (1) polymers induce preexisting fabrics to render dilative behavior to KA and FAKA; (2) normal consolidation lines (NCLs) and critical state lines (CSLs) for polymer-modified KA were nearly parallel to each other, while the CSLs were steeper than NCLs for polymer-modified FAKA, possibly due to kaolinite filling the voids of crushed fly ash cenospheres; (3) the critical state friction angle (${\varphi }_{cs}^{\prime }$) of kaolinite increased from 19.7° to 24.1° and 22.3° with the addition of PEO and chitosan via mechanisms of polymer bridging and charge neutralization, respectively; xanthan gum decreased the ${\varphi }_{cs}^{\prime }$ of kaolinite to 19.1° via Coulombic repulsion; and (4) the just mentioned mechanisms held for polymer-modified FAKA to a lesser extent due to other complicated interactions, such as polymer crosslinking or entanglement and ion-dipole interactions.

Suction caissons have recently been considered as potential anchoring solutions for floating renewable devices (wind turbines and wave energy converters) in shallow waters, where—unlike for floating oil and gas applications in deep water—sandy seabeds are to be expected. This paper presents a simple framework to calculate the maximum drained capacity of a caisson under inclined loading in sand and the associated position of the padeye, as a function of the load inclination. The framework assumes critical-state conditions and is based on the establishment of yield envelopes in the horizontal and vertical loading space at the location of the padeye. The yield envelopes were established through numerical modeling and validated by centrifuge tests; they are described by a closed-form solution that enables the prediction of caisson capacity.

This paper presents probabilistic models for predicting the residual and peak transient tilt of mat-founded structures on liquefiable ground. First, the study presents a completely empirical model based on correlating residual tilt to settlement in case histories. Second, a semiempirical model for residual tilt is developed based on an extensive numerical parametric study of soil–foundation–structure systems in 3D with more than 63,000 simulations, centrifuge tests performed by several researchers, and case history observations from several earthquakes. The model of peak transient tilt is based on centrifuge tests. The uncertainty around the estimates of each model is described using log-normal distributions, and all necessary correlation coefficients are calculated. The proposed procedure is the first methodology for estimating the seismically induced residual tilt of such structures that is not derived solely from settlement models on two sides of the foundation with different soil profiles. It therefore accounts for the influence of complex phenomena (e.g., soil–structure interaction, asymmetric loading, interlayering, and ejecta) that mechanistically affect tilt and settlement differently. The models consider various properties of the soil profile, foundation, and structure, and also characterize total uncertainty. These models constitute a fundamental component of a performance-based approach that could be combined with vulnerability functions in the future to evaluate liquefaction risks in terms of losses associated with tilt of structures.

Currently available perimeter-security systems use ground-buried fiber-optic sensors to detect objects on the ground surface, and some of them compare the observed signal patterns with those in a predefined library to identify specific types of objects. However, such qualitative approaches neglect a wealth of information contained in the measured signal. In this paper a more rational approach is presented that uses ground-buried distributed fiber-optic strain sensors with very high spatial and strain resolution to quantify the strain field induced by an object in contact with the ground surface. The contact interactions on the ground surface are calculated from the strain measurements using a mechanical soil model and inverse analysis algorithms similar to those used in image deblurring. The approach should enable a variety of applications where the knowledge of contact interactions on the ground surface is beneficial, from biodiversity survey, perimeter security, and weigh-in-motion systems to biomechanical applications and sports medicine.

This case report presents two pedestrian passages underneath an urban expressway with a spacing of 0.5 m, which were constructed using rectangular pipe jacking technology in Nanjing, China. To better understand the field performance and the geoenvironmental impacts of rectangular pipe jacking technology, real-time monitoring was conducted with the installation of measurement devices at 43 measurement points. These points were set up to measure lateral earth pressure, excess pore water pressure, soil lateral displacement, and ground surface settlement. By analyzing field measurement data and operational parameters, this study documents operational parameters throughout the jacking process of two successively constructed tunnels and presents geoenvironmental impacts of the rectangular pipe jacking technology. In this process, the study finds that large ground settlements around the jacking shaft were due to the strong soil-carrying effect of the rectangular pipe jacking technology.

Ground surface settlements and lateral wall movements measured during construction of a 13.1–18.0 m deep mixed-support excavation in Chicago are presented. The excavation was supported with sheetpile walls, two or three tieback levels, and one level of internal diagonal bracing. This paper describes the measured ground and wall responses, correlates the responses with construction activities, and evaluates the responses in light of the subsurface conditions, support system stiffness, and other nearby excavations. Expected performance based on semiempirical correlations is compared with the measured response. Lateral wall movements at this and an adjacent excavation are used to indicate the accuracy with which one may be expected, at best, to predict lateral wall deformations in similar conditions.

This paper investigates the effect of jacking two groups of open-ended prestressed high-strength concrete (PHC) piles on an existing highway embankment based on field measurements of excess pore pressure and lateral soil displacement. Excess pore pressure due to pile jacking increased with depth and decreased with increasing distance from the pile; the influence reached a distance of 43 pile diameters from the pile axis. For pile groups, the amount of excess pore pressure dissipated decreased with increasing depth and varied from 54% to 100% in 20 days. Lateral soil displacement and excess pore pressure continued to increase for a period of time after the end of pile jacking, and this could have resulted in significant inclination of piles if pile installation was too quick and pile spacing was too small. Lateral soil displacement due to pile group decreased with decreasing distance to the existing embankment as a result of higher soil stiffness and strength produced by the embankment loading. The effect of pile group installation on the existing embankment was negligible.

This paper investigates the effectiveness of the effective area method (EAM) for assessing the undrained load-carrying capacity of rectangular foundations under combined vertical ($V$), horizontal ($H$), and moment loading ($M$) by comparing with finite-element method (FEM) results. Predicted ultimate limit states under combined loading from the two methods are compared, and the equivalent rectangle derived from the EAM is compared with the contact region obtained from the FEM. For one-way eccentricity, good agreement in the $V\text{-}M$ capacity is achieved with the two methods despite differences between the effective area and actual contact area. However, $V\text{-}M$ capacity for two-way eccentricity obtained from the EAM is significantly smaller than that derived from the FEM, with the discrepancy becoming more pronounced with increasing mobilization of the vertical capacity. $V\text{-}H\text{-}M$ failure envelopes established by the EAM also fall significantly inside those determined using FEM. The contributing factors for the discrepancies are explored systematically in the paper.

A finite-element study is presented for the linear-elastic behavior of rigid suction caisson (bucket) foundations installed in either a homogeneous or nonhomogeneous Gibson soil stratum. Closed-form expressions are developed for the stiffnesses of the suction caisson in vertical (axisymmetric) and lateral (antisymmetric) loading, with emphasis on nonhomogeneous soil. The contribution of the cylindrical sidewall (shell) acting alone to the overall response of the system is also explored. It is then shown that for a shell length (depth of embedment) exceeding half of the caisson’s radius, in particular, the shell can offer essentially the same stiffness as the whole caisson.