Journal of Geotechnical and Geoenvironmental Engineering

This paper presents 17 separate applications within the current technology of geosynthetics. They were selected as being illustrative of the wide range of applications that can utilize geosynthetics in geotechnical, transportation, hydraulics, and geoenvironmental engineering. All are permanent and/or critical applications wherein design by function is required, thereby necessitating the calculation of a product-specific test result versus a site-specific design requirement. This calculation results in a factor of safety, which must be assessed accordingly. In this regard, geosynthetics are no different from any other engineering material. This paper, however, does not go into calculation details, which are available in the literature. References are provided in this regard. The various applications presented were selected to illustrate that both emerging developments and future possibilities are ongoing. This approach illustrates the dynamic nature of the field of geosynthetics, which is both exciting and stimulating, and speaks well for future endeavors.

Simple reliability analyses, involving neither complex theory nor unfamiliar terms, can be used in routine geotechnical engineering practice. These simple reliability analyses require little effort beyond that involved in conventional geotechnical analyses. They provide a means of evaluating the combined effects of uncertainties in the parameters involved in the calculations, and they offer a useful supplement to conventional analyses. The additional parameters needed for the reliability analyses—standard deviations of the parameters—can be evaluated using the same amount of data and types of correlations that are widely used in geotechnical engineering practice. Example applications to stability and settlement problems illustrate the simplicity and practical usefulness of the method.

Railway track ballast requires regular attention to maintain line and level. A recently developed maintenance method, known as pneumatic ballast injection (PBI) or stoneblowing, re-levels and realigns the track by lifting the sleepers and track and blowing smaller size gravel between the ballast and the base of the sleeper. This creates a two-layer ballast bed. Series of large-scale model tests have been carried out to gain a better understanding of the behavior of such a bed under repeated loading. The results confirm that stoneblowing is a better form of track maintenance than the commonly used ballast tamping method, but the size and type of stone and the thickness of the injected layer are of critical importance in determining the postmaintenance behavior.

The vertical flow of water in cover soils is simulated using published analytical and finite-element methods. The two methods gave virtually identical pressure head and water content profiles during steady infiltration of water in a multilayer soil cover and transient infiltration in a single-layer cover. The finite-element model was then used to simulate flow in two laboratory columns packed with multilayer soils and subjected to downward drainage and conditions of evaporation and no evaporation. The model adequately predicted transient pressure heads and water contents for the first 7.5 h of drainage in a till-sand layer without evaporation. Predictions at times equal to and greater than 3 days were not as good, probably due to the formation of discontinuous water pockets in the draining sand around the residual water content, which apparently produced “locked-in” or “static” nonequilibrium pressures. These pressures are not captured by existing methods used for estimating the unsaturated hydraulic conductivity–pressure function of soils. Further modeling showed that at times greater than 8 days, the flux from the column with evaporation was all in the vapor phase.

A finite-element (FE) model of localized deformation in soft rock taking a strong discontinuity approach is presented. The model is formulated within the context of rate-independent, nonassociated Drucker-Prager plasticity with nonlinear cohesion hardening/softening. Strain localization is modeled as a jump in the displacement field and simulated within the framework of the FE method using the standard Galerkin approximation. The model is used to simulate the load-displacement behavior of Gosford sandstone deforming in plane strain, focusing on the prediction of the stress levels necessary to initiate strain localization, based on the strong and weak discontinuity criteria (jumps in displacement and strain, respectively), and on the demonstration of mesh-independence of the FE solutions in the bifurcated state. For the sandstone, the onset of weak discontinuity is detected first, before the onset of strong discontinuity, suggesting a possible coupling of the two types of discontinuities in the strain-softening regime.

Construction of the MUNI Metro Turnback project involved deep excavations in soft soils along the Embarcadero waterfront in downtown San Francisco, California. The excavations and shoring system were designed by the Engineer of Record to control ground deformations within specified limits in order to minimize the impacts of the deformations on a block of adjacent, settlement-sensitive buildings. The design included estimates of deformations caused by the excavations and other construction activities, evaluation of potential settlements of adjacent buildings, and structural evaluation of the response of the buildings to the estimated settlements. A comprehensive monitoring program combined with an instrumented test section, appropriate contingency measures, and construction controls were planned so as to allow early warning for appropriate response in the event that the deformations exceeded tolerable limits. This paper reviews the subsurface conditions, base stability analyses, and estimated deformations, describes the instrumentation program, and presents a comprehensive summary of the instrumentation measurements. It interprets the instrumentation measurements and draws conclusions regarding the general nature and magnitude of deformations and their impacts on adjacent structures.

A new empirical method, called the EPOLLS model, is developed for predicting ground surface displacements due to liquefaction-induced lateral spreading. Lateral spreading is defined as the mostly horizontal deformation of gently sloping ground as a result of soil liquefaction. In strong earthquakes, lateral spreads often cause considerable damage. The EPOLLS (Empirical Prediction Of Liquefaction-induced Lateral Spreading) model can be used to predict the average horizontal surface displacement that can occur on a potential lateral spread. The model is presented in three parts (designated as the Regional-EPOLLS, Site-EPOLLS, and Geotechnical-EPOLLS components) that allow for progressively better predictions with the addition of more site parameters. The model consists of simple algebraic equations with four to nine parameters that represent the seismic input, site topography, and subsurface conditions. The EPOLLS model was developed from a multiple linear regression analysis of data from 71 lateral spread case studies. The EPOLLS database, regression modeling, quality of the fit, and limitations on the use of the EPOLLS model are discussed.

In situ tests were performed and samples were taken from a uniform layer of clay used as a material for the production of bricks. The shear resistance was measured, using Geonor Inspection Vane Tester H-60, in a quadratic mesh of 961 test points in the horizontal plane, spaced at 15 cm. Vane resistance tests were also performed in the laboratory on 76 undisturbed samples, on which the constrained modulus in consolidometers was determined. The aim of the research was to find the parameters of the 2D random field of shear strength and the correlation of this field with that of constrained modulus. The strong correlation obtained eventually enabled estimating the autocorrelation function of the constrained modulus describing the elastic behavior of the soil. A simple estimation procedure is proposed, enabling curve fitting of different isotropic and anisotropic correlation functions. Additionally, some statistical analyses of data were performed, including regression and time series analysis. The problem of the local and global variabilities of soil properties and their ramifications is also considered.

A comprehensive geotechnical in situ and laboratory investigation into the soils forming the Upper Quaternary basin of the Venetian Lagoon has been carried out. In addition to standard tests, measurements of shear wave velocity were performed using crosshole, seismic piezocone, bender element system, and resonant column tests. Despite the incompatible strain levels of the seismic and piezocone tests, it is shown that piezocone tip resistance and excess pore pressure can be used for a preliminary estimate of the small-strain shear modulus G_max for the Venetian soils.