Journal of Geotechnical and Geoenvironmental Engineering

This paper presents a kinematic analysis of a single pile embedded in a laterally spreading layered soil profile and discusses the relevancy of conventional analysis models to this load case. The research encompasses the creation of three-dimensional (3D) finite-element (FE) models using the OpenSees FE analysis platform. These models consider a single pile embedded in a layered soil continuum. Three reinforced concrete pile designs are considered. The piles are modeled using beam-column elements and fiber-section models. The soil continuum is modeled using brick elements and a Drucker-Prager constitutive model. The soil-pile interface is modeled using beam-solid contact elements. The FE models are used to evaluate the response of the soil-pile system to lateral spreading and two alternative lateral load cases. Through the computation of force density-displacement (p-y) curves representative of the soil response, the FE analysis (FEA) results are used to evaluate the adequacy of conventional p-y curve relationships in modeling lateral spreading. It is determined that traditional p-y curves are unsuitable for use in analyses where large pile deformations occur at depth.

A modified procedure is presented in this study to evaluate the equivalent top-down load-displacement curve in a bottom-up pile load test considering elastic shortening. On the basis of the results of a parametric study on a bored pile in normally consolidated cohesive soils under undrained conditions, varying shear strength distribution and pile slenderness ratio, it was concluded that the pile shortening caused by the skin-friction component of the load in a top-down test can be related to the measured elastic shortening in a bottom-up test. A $\lambda$-factor is used to define this relationship, that is, the ratio of the top-down to bottom-up pile shortening. The factor $\lambda =1.0$ is used for the case of a pile in soil with uniform shear strength profile, $\lambda =2.0$ for linear profiles, $1.0<\lambda <2.0$ for nonlinear profiles varying above linear, and $\lambda >2.0$ for nonlinear profiles varying below linear. In addition, the method suggests taking the corresponding readings of the skin-friction load component from the upward displacement curve of the top of the pile, which is a closer approximation to rigid pile displacement than the bottom when corrections for elastic pile shortening are to be applied. Assuming a fully mobilized skin-friction, a logarithmic relation for the factor $\lambda$ to the normalized area under the shear strength profile was generally formulated and is limited to the assumptions on which they were derived. The suggested procedure in this study has produced the equivalent top-down load-displacement curves that are in close agreement with the measured top-down curve, as validated in the case studies.

The reliability of surface-wave tests for the evaluation of $V_{S,30}$ in seismic site characterization is assessed with respect to both uncertainty and accuracy. The discussion of uncertainty is mainly focused on the implications of solution nonuniqueness in inverse problems; only the inversion uncertainty is considered within this work, omitting other possible issues such as nontrivial geological settings (e.g., lateral variations) or the influence of different processing procedures. A Monte Carlo approach has been used to select, through a statistical test, a set of shear-wave velocity models that can be considered equivalent with respect to fitting the experimental dispersion curve according to the information content (dispersion velocities and frequency range) and the experimental uncertainties. This set of equivalent solutions is then used to evaluate the uncertainty in the determination of $V_{S,30}$. Moreover, comparisons between the results obtained by surface-wave tests and invasive seismic methods are reported to assess the accuracy of $V_{S,30}$ evaluation by using surface-wave methods. It is shown that, given an adequate investigation depth, the solution nonuniqueness is not a major concern and that the results are comparable in most situations with the results of invasive tests providing an accurate estimate of $V_{S,30}$, even with simplified approaches.

Estimation of spudcan penetration resistance is an important design step to guarantee the stability and functionality of offshore mobile jack-up units. Dependence on in situ penetrometer test data to evaluate the stratigraphy and resulting spudcan capacity profile has been increased. However, this becomes difficult in intermediate soil types in which the degree of consolidation during penetration falls between the extremes of fully drained or fully undrained. In this study, a penetrometer-based methodology utilizing results from cone and $T$-bar penetration tests is developed. Three main steps are involved, comprising estimation of the relative penetration resistance of spudcan and cone or $T$-bar penetrometer under fully drained and fully undrained conditions, and then quantifying the effect of the different normalized penetration rates for spudcan and penetrometer. Values of the various correlation parameters for the proposed model are evaluated. The validity and accuracy of the proposed methodology are evaluated through case studies from centrifuge tests in clay and a field example of spudcan installation in interbedded carbonate silts and sands. The comparisons confirm the potential of the proposed methodology for interpretation of penetrometer tests and application to the prediction of foundation performance.

Deeply weathered lava flows of oceanic basalt reflect the mode and sequence of volcanic deposition, parent mineralogy, and postdepositional erosional and weathering processes. In turn, these are controlled by geology, geography, and climate. One particular site on the Island of Hawaii has been the focus of study to gain a better understanding of complex residual soil deposits, particularly in connection with a need to characterize seismic strong-motion propagation through decomposed surface soil and rock sequences. Materials at the site range from fully weathered volcanic soils, sometimes with unusual mineralogy and plasticity properties, to saprolite, weathered rock, vesicular basalt, and hard rock. Seismic surveys were conducted to investigate the distribution of these materials at the study site. Laboratory tests focused on saprolite and vesicular rock as two materials that are seldom reported on and that remain poorly characterized, at least with regard to conditions found in Hawaii.

A conceptual, analytical model has been developed to describe the fracture grouting process in sand. The objective of the model is to improve understanding about this process in sand and to model propagation of the fractures. The results can be used to assess the parameters that control the fracture process. It is assumed that the complicated shape of a fracture in sand can be simplified to a geometrical shape (such as a tube or a plane) as a first approximation. Filtration of the grout appears to have a significant influence on the fracture shape when grout is injected into permeable subsoil such as sand. By assuming a pressure at which a fracture starts and a minimum pressure for propagation, it appeared possible to calculate the width-to-length ratio of the fracture independent of other soil properties. Quantification of the flow inside a fracture and the filtration processes resulted in a model that has been used to study differences in fracturing behavior in model tests and field tests on fracture grouting in sand. It was concluded that the width-to-length ratio of the fractures in a permeable soil decreases if the injection pressure of the grout or the permeability of the grout cake is decreased.

Portland cement is widely used for the improvement of soft clay in many applications and construction methods. Because of the high initial water content of in situ soft clay, the additional water in the cement slurry to be mixed, and the added air in some applications, the mixtures have a high water content and void ratio in either almost-saturated or unsaturated conditions. The mechanical properties of cement-clay admixtures—including cement-treated clay and air-cement-treated clay—are affected by several parameters, e.g., mixing proportions, curing time, and the initial state of the mixture. To facilitate engineering decisions regarding mixing design and the development of a constitutive model, a single parameter that can characterize the mechanical properties of such mixed materials is advantageous. This paper recommends a parameter defined as the effective void ratio that could appropriately quantify the dependency of the mechanical properties of cement-clay admixtures on the influencing parameters on the basis of the results of unconfined compression, oedometer, and triaxial tests. The proposed parameter tends to capture the mechanical characteristics of cement-clay admixtures under different test conditions.

Lime treatment is an attractive technique for soil improvement in the construction of rail tracks and pavement layers, in slope protection of earth dams, and as a support layer for shallow foundations. However, there are no dosage methodologies based on rational criteria as in the case of soil-cement technology, where the voids/cement ratio is shown to be a key parameter for the estimation of both strength and stiffness. The present study, therefore, was aimed at quantifying the influence of the amount of lime, porosity, and voids/lime ratio on the initial shear modulus ($G_0$) and unconfined compressive strength ($q_u$) of a lime-treated clayey sandy soil. From the results of unconfined compression tests and bender elements measurements, it was shown, for the soil-lime mixtures investigated, that the voids/lime ratio is an appropriate parameter to assess both initial stiffness and unconfined compressive strength. Also, a unique $G_0/q_u$ versus voids/lime ratio relationship was established linking the soil-lime mixture initial stiffness and compressive strength.