Any geotechnical engineering textbook includes an introductory chapter on soil properties such as grain size distribution and Atterberg limits, and on soil classification. Typically, there is a dedicated sub-section on soil mineralogy with special emphasis on the influence of clay minerals on soil behavior. However, geotechnical engineering practice largely relies on the USCS classification and parameters such as % finer than the #200 sieve (0.075 mm) to assess soil behavior for problems such as swell, chemical stabilization, compressibility etc. This approach is quite limited, since USCS classification does not capture differences in soil behavior between a single class (e.g. CH) that are attributed to soil mineralogy. X-ray Diffraction has been used widely to qualitative identify the type of soil minerals present in a soil, but the lack of quantitative information precludes the translation of this information in quantitative guidelines for soil behavior. This paper presents a new approach to clay characterization, which combines quantitative mineralogical analysis using the Rietveld method, with physicochemical characteristics including specific surface area, cation exchange capacity and potassium content. The combination of several techniques enables the quantification of soil minerals and of the amorphous content of a soil with high accuracy and precision, so that the engineering behavior of different soils can be interpreted quantitatively as a result of chemical/mineralogical and mechanical properties. Such an approach can lead to an improved paradigm for various design problems of clay soils.

Previous laboratory studies and Distinct Element Method (DEM) simulations have shown that the preparation method used to create samples for testing can affect the sample fabric and hence the mechanical response observed. The specimen preparation methods traditionally used in the laboratory were developed to recreate a given depositional pattern or in-situ soil fabric. Differences in soil response have been attributed to variations in the initial fabric of the sample even when the samples are created at the same densities. If DEM simulations are to provide meaningful insight into soil response observed in element tests, it is important for the initial state (packing density and stress level) and fabric anisotropy of the computer generated sample to closely match the physical reality. This is particularly true where element tests are used to validate DEM models. A key challenge is the lack of quantitative data on the fabric of real physical test specimens. Several approaches have been documented in the literature for generating the initial configuration of specimens for DEM simulations, i.e. artificially creating a percolating (stress transmitting) granular material. Approaches that are commonly used include radius expansion, compression using rigid boundaries, and pluviation under gravity loading. This paper examines the influence of the method chosen on the macro- and micro-scale properties of the material generated. The methods considered involved generating particles as a diffuse cloud at their target size, followed by pluviation under gravity loading with and without a mesh that modeled a sieve. The study fits within a broader research project in which multidirectional simple shear tests on steel spheres will be replicated in DEM simulations. © 2012 American Society of Civil Engineers.

The near surface, highly weathered limestones of the southern shores of the Arab Gulf region have complex lithologies attributable to post depositional changes that have altered hard rocks into soils and some carbonate soils into a rock matrix. The matrix, often clayey, sometimes cemented (with gypsum, anhydrite, and /or calcite grains) is not a rock nor could be considered as a soil per se. These deposits are: difficult to sample in the undisturbed state, extremely variable in composition and properties, and are susceptible to degradation, particularly when wet. The paper presents typical geotechnical information from selected sites where these deposits (diagenetic limestone) have been encountered. Plate load test data, carried out to predict settlements, are shown. Arrival at appropriate foundation geometries and allowable bearing capacity values, consistent with field conditions, are noted. For the present, design of shallow foundations along Region’s coasts and in nearby areas, has remained empirical and dependent upon site-specific information aided by: judgment, local experience, and plate load test results. Moving forward, and thus reducing ambiguity and uncertainty in design of shallow foundations, would invariably require a long-term commitment to: i) proper analysis and scrutiny of appropriate field data, ii) modeling of soil/rock behavior under changes in stress, and iii) the arrival at “well thought out” design guidelines to help practitioners overcome the difficulties usually faced, when designing shallow foundations in these deposits.

This paper presents a case study of the evaluation of seismic soil-pile performance in a sloping river embankment containing soft, saturated low-plasticity fine-grained soil. Topics addressed include: i) liquefaction susceptibility of the site soils according to SPT- and CPT- based analysis procedures; ii) cyclic simple shear tests performed in order to assess the fine-grained soil response under earthquake conditions; iii) conducted non-linear numerical time history analyses of the embankment-foundation response to design ground motions; iv) comparison of 3D and 2D model results of ground-pile response in order to determine useful scaling factors for incorporating 3D effects (e.g., soil arching) in 2D models; and v) evaluation of driven timber and reinforced concrete piles for ground improvement as well as stiffening the drilled shaft foundations as strategies for helping the bridge meet the performance-based design criteria under lateral spreading conditions.

Biogrouting is a new potentially sustainable ground improvement method. The process of biogrouting involves carbonate precipitation induced by microorganisms (MICP) e.g. by hydrolysis of urea. In the summer of 2010, biogrouting was applied for the first time in practice to reduce the risk of borehole collapse during horizontal directional drilling in gravel layers. Within this project several gravel columns were treated in the laboratory in order to evaluate the potential of MICP to strengthen gravel and to determine the minimum required amount of cement to prevent borehole collapse. Although it proved to be difficult to produce homogeneously cemented gravel columns a correlation was established between the amount of calcium carbonate and the direct shear strength for different loading conditions.

Rock falls from cliffs and other steep slopes present numerous challenges for detailed geological characterization. In steep terrain, rock-fall source areas are both dangerous and difficult to access, severely limiting the ability to make detailed structural and volumetric measurements necessary for hazard assessment. Airborne and terrestrial lidar survey methods can provide high-resolution data needed for volumetric, structural, and deformation analyses of rock falls, potentially making these analyses straightforward and routine. However, specific methods to collect, process, and analyze lidar data of steep cliffs are needed to maximize analytical accuracy and efficiency. This paper presents observations showing how lidar data sets should be collected, filtered, registered, and georeferenced to tailor their use in rock fall characterization. Additional observations concerning surface model construction, volumetric calculations, and deformation analysis are also provided.

Compaction of highway embankment is a key factor influencing premature pavement distresseses. The current specifications of the Kansas Department of Transportation (KDOT) control embankment compaction are based on in-situ density and moisture content. In the recent past, KDOT participated in a number of projects that studied feasibility of performance-based specifications, specifically in terms of in-situ soil stiffness measured by non-destructive tests and/or produced by the intelligent compaction (IC) rollers, for quality control/quality assurance of highway embankments. Kansas experience shows that in-situ tests with Lightweight Deflectometer result in stiffness that is highly variable like other available tests. Correlation among different test methods is fair. The intelligent compaction results in very uniform compaction in the spatial direction. However, no existing test results are correlated with the stiffness parameters yielded by such rollers. The IC rollers also can detect soft spots in compacted subgrade. Thus such device can be used in proof rolling of compacted highway embankments.

Properties of fiber-reinforced sands are anisotropic because of the distribution of orientation of fibers that is typically characterized by a preferred bedding plane. The development of an anisotropic yield condition for fiber-reinforced sand will be presented. An interesting implication of anisotropy is a lack of uniqueness in the internal friction angle along shear surfaces (kinematic discontinuities) with given orientation. However, the anisotropic internal friction angle can be represented as a function of the principal strain rate directions. Anisotropy of internal friction angle can be accounted for in routine methods, such as kinematic limit analysis. The orientation of the principal directions can be incurred from the kinematics of the mechanism for a given boundary value problem, but the internal friction angle cannot be determined a priori as a unique function of orientation of failure surfaces in space.

Foundations of subsea infrastructure in deep water subjected to asymmetric environmental loads have underscored the importance of combined torsional and horizontal loading effects on the bearing capacity of rectangular shallow foundations. The purpose of this study is to investigate the undrained sliding and torsional bearing capacity of rectangular and square shallow foundations together with the interaction response under combined loading using three-dimensional finite element (3D-FE) analysis. Upper bound plastic limit analysis is employed to establish a reference value for horizontal and torsional bearing capacity, and an interaction relationship for the combined loading condition. Satisfactory agreement of plastic limit analysis (PLA) and 3D-FE results for ultimate capacity and interaction curves ensures that simple PLA solution could be used to evaluate the bearing capacity problem of foundation under combined sliding and torsion.

Groundwater inflows in rock tunnels typically concentrate in narrow zones where conducting fractures cluster together: these concentrations may hamper tunnel advance and are a major source of claims. However, current predictive methodologies do not allow the designer or the contractor to predict these concentrations. The paper describes a geostatistical methodology for the simulation of clusters and fractures in 1D, 2D and 3D. The resulting discrete network of fractures could be used to simulate groundwater flow and predict groundwater inflow into tunnels. The simulation methodology was demonstrated and validated by using data from Pedernales Falls, Yucca Mountain nuclear waste disposal project, and the TBM-excavated South Cobb tunnel project (GA).