Journal of Geotechnical and Geoenvironmental Engineering

In discrete numerical modeling of granular materials, idealization of individual particles is required, as it is not practical to model a large number of particles, each with its actual shape and size. To minimize computation times, researchers often use two-dimensional, circular elements. However, biaxial and direct shear tests on such specimens result in low strengths compared to granular materials, due, in part, to excessive rolling of the perfectly circular particles. In this paper, a new particle type, disk clusters, is presented. A disk cluster is a group of circular disks permanently connected to form an irregularly shaped particle that more closely represents the shape of granular materials and has less tendency to rotate. Development and implementation of disk cluster particles into a discontinuous deformation analysis program is presented. Validations of the mechanics of a single disk cluster, biaxial shear, and anchor pullout simulations illustrate the usefulness of this new particle type.

A soil engineering classification derived from the cone penetration test (CPT) involves the uncertainty of correlation between soil composition and soil mechanical behavior. This uncertainty results in overlaps of different soil types in currently used CPT soil classification systems. Accordingly, two statistical soil classification criteria, region estimation and point estimation, are suggested to address this problem. Further, a new fuzzy subset approach is introduced to develop a truly independent CPT soil engineering classification, and to establish a transition between the new fuzzy approach and conventional soil classifications by utilizing local site- and project-specific calibrations. CPT results conducted at the National Geotechnical Experimentation Site at Texas A&M University are used to demonstrate this new CPT soil engineering classification methodology.

A fully nonlinear finite-element (FE) model is developed to investigate the impact of hysteretic and viscous material behavior on the downhole motion recorded by an array at a large-scale seismic test site in Lotung, Taiwan, during the earthquake of May 20, 1986. A stick model with the same spatial interpolation accuracy as a three-dimensional FE model is used for vertical wave propagation analysis. The constitutive model is based on a three-dimensional bounding surface plasticity theory with a vanishing elastic region, and accounts for shear stiffness degradation right at the onset of loading. The model is cast in a time-domain nonlinear FE code SPECTRA and is used to analyze the 1986 earthquake data. It is shown that the recorded downhole motion of Lotung was dominated by nonlinear response. Results of the fully nonlinear analysis are compared with the predictions of the program SHAKE so that the performance of the nonlinear model may be assessed relative to that of an equivalent linear model.

This paper presents a case study on embankment dam seepage problems encountered at one site over the last 30 years and various remediation efforts. The Hodges Village Dam in Oxford, Mass. is part of an extensive flood control network built and operated by the U.S. Army Corps of Engineers in the Thames River basin of Massachusetts and Connecticut. The dam consists of a relatively homogeneous and pervious sand and gravel embankment on stratified glacial outwash sands, gravels, and cobbles. Because it was designed primarily as a run-of-the-river, flood control facility with no anticipated long-term pool storage, no significant seepage control measures were ever constructed for the dam. This paper describes a series of seepage events that have occurred at the dam starting in 1968 and continuing to 1993. Remediation efforts after each of the events are described as are their effects on dam performance. The paper concludes that the past seepage problems at the dam were caused by assumptions made about foundation soil conditions prior to dam construction, problematic drains and relief wells that resulted in significant head buildups in their respective zones of influence, and insufficient subsurface information prior to design and construction. Investigation and analyses of the dam conducted after the 1993 event are presented, and plans are described for a seepage control remediation project currently under construction.

In this paper, a two-stage approach is used to analyze the lateral and axial responses of piles caused by tunneling. First, free-field soil movements are estimated based on an analytical method, and, second, these estimated soil movements are imposed on the pile in simplified boundary element analyses to compute the pile responses. Through a parametric study, it is shown that the influence of tunneling on pile response depends on a number of factors, including tunnel geometry, ground loss ratio, soil strength, pile diameter, and ratio of pile length to tunnel cover depth. Simple design charts are presented for estimating maximum pile responses and may be used in practice to assess the behavior of existing piles adjacent to tunneling operations. A published case history has been studied in which the measured lateral pile deflections are compared with those computed using the present method and fair agreement is found.

Some influencing factors on vertical drain behavior were investigated by laboratory tests as well as by back-analyses of test embankments on vertical drain improved subsoil at Saga Airport, Saga, Japan. Based on the results from this study, suggestions are made on determining the design parameters for vertical drain improvement. For the discharge capacity test of a prefabricated vertical drain, confining the drain in clay is essential. Also, due to the creep of the filter and the clogging caused by the fine particles entering the drainage channel, the long-term discharge capacity is significantly smaller than the short-term one, and this should be considered in design. For smear effect, a new equation is proposed for determining the ratio of the hydraulic conductivity of the natural subsoil to that of the smear zone, which considers the fact that laboratory tests normally underestimate the hydraulic conductivity of natural deposits. Regarding the effect of the sand mat, the numerical analysis results in this study show that if the hydraulic conductivity of sand is larger than 10⁻⁴ m/s, the assumption of a free drainage condition in the sand mat may not result in significant error. Finally, a methodology of predicting the behavior of vertical drain improved subsoil is proposed.