Site Characterization and Modeling

Landslides can cause extensive damage to infrastructure systems including transportation corridors, housing developments, and reservoir systems. Landslides in soil and rock manifest themselves as a surface expression in the earth. An often first step in the delineation and characterization of a landslide is the mapping of the surface of the landslide coupled with the determination of the location of the slip surface. Recent advances in laser scanning technologies provide the ability to delineate surface expressions in intricate detail. Airborne laser swath mapping (ALSM) was used to survey a landslide area along the Missouri River in South Dakota in August 2000. This paper presents the results of a study to assess accuracy of ALSM for application to geotechnical engineering, in particular landslide features. Vertical accuracy of approximately 5 to 20 mm was achieved on the surface of a landslide on the Powerhouse slope near Oahe Dam.

The increase in urbanization, population density and traffic congestion in major metropolitan centers around the world has led to greater demand for underground space. Development of underground space in a timely and cost effective manner while maintaining a safe environment onsite and in the surrounding areas poses tremendous challenges. Open cuts and tunnels have long been used to create underground space, but with the increasing usage of underground space, new constraints on the design and construction of such projects are added. One of the major concerns when constructing underground space is the impact of ground movements related to construction activities. These ground movements can be critical to adjacent sensitive buildings and utilities. Hence, it is very important to predict and control the magnitude and distribution of ground movements, which result from building underground space. Significant progress has been made in the development of automated systems to monitor ground deformations due to excavation activities. However, often enough there is a lack of similar records for the construction activities and excavation geometry. Without information about the corresponding excavation configuration, data on ground deformations will be of very limited use. The engineer will be unable to correlate the movements to the corresponding excavation stage. This paper introduces the use of a promising technology, 3D laser scanning, to significantly enhance collection of as-built data to monitor construction progress for deep supported urban excavations. The paper presents experiences on a recent project currently underway in the Chicago area. It summarizes the processes of conducting 3D laser scanning in the field, along with the lessons learned from the field trials.

The Highways Agency (HA) in the United Kingdom is responsible for managing 9380 km of the motorway and trunk road network in England. This includes around 7000 km of embankment and cutting slopes. Year on year costs for repairing slope failures have been increasing almost exponentially and it has been recognised that significant whole life cost savings could be achieved through implementation of an appropriate pro-active regime through preventative maintenance of marginally stable earthworks. This together with the requirement to increase capacity and reliability of the existing network have led the Highways Agency to implement specific research into the implementation of a pro-active maintenance regime for earthworks. As part of this programme, research into the use of remote sensing techniques for inspecting the network earthworks has been undertaken by the Highways Agency with the aim of improving the speed, safety, quality and repeatability of slope condition data collection and reducing disruption to road users caused by inspections. This is to allow the regular identification of at-risk earthworks slopes and facilitate the improved management of the geotechnical asset. The Remote Rapid Assessment research project comprised a series of trials to evaluate selected remote sensing techniques for highway earthworks inspections. The techniques included satellite and aerial photography, airborne laser scanning and thermal scanning and videography. This paper describes the trials and outlines the extent to which remote sensing techniques can currently identify slope instability features and assist in the asset management process. Costs and benefits associated with remote assessment are also discussed. The HA research into pro-active earthworks asset assessment is ongoing but indications are that the techniques will allow significant improvements to the current regime.

Landslides, lateral spreading and other similar forms of ground failure due to natural disasters impact communities around the world. These ground failures continue to result in human suffering, billions of dollars in property losses, and environmental degradation. As our society becomes ever more complex and urban areas continue to spread, the economic and societal costs of landslides and other ground failures will continue to rise. Although our understanding of the mechanisms of failure and large ground deformation due to rains, floods and earthquakes have improved considerably over the last two decades; the goal of significantly reducing losses from ground failure due to natural hazards remains elusive. This state of affairs stems from the limitations of existing real-time sensing and monitoring tools as well as inadequate predictive capabilities of current computational models. Real-time monitoring programs are essential to develop warning systems of impending danger from active landslides in any site specific or regional hazard program. The current state-of-the-art in real-time monitoring of active slopes is either based on very expensive monitoring systems or on measurement of ground surface displacements. The work presented in this paper constitutes a major step in the direction of establishing a low cost real-time monitoring system for active ground. A ShapeAccelArray sensor is being developed, taking advantage of promising new advances in the fiber optic and micro-machined electromechanical sensor (MEMS) technologies (Danisch et al., 2004). This sensor array is capable of simultaneously measuring acceleration and permanent ground deformation down to tens of meters of depth. The sensor array would be capable of measuring in situ (field) 3D ground deformation as well as 2D soil acceleration at 0.5 m to 1 m intervals. The paper presents the preliminary design of the new sensor array as well as preliminary results from tests aimed at validating and calibrating the accelerations and displacements measured using the newly developed sensor array. The accelerations and displacements measured using the ShapeAccelArray sensor are compared to those measured using traditional accelerometers and displacement sensors. Finally, conclusions are drawn on the effectiveness and accuracy of the new sensor array.

The coastal bluffs located south of San Francisco form one of the more active geologic terrains along the California coast and are typically found to be in some state of failure during each years winter storm season. In certain areas, residences are located less than 10 meters from the edge of these bluffs which highlights the need to constantly monitor the stability, and likewise the detailed geometry, of specific sections of bluffs. Characterization of the geometry of these bluffs for analysis purposes can be difficult due to the steep and constantly evolving profiles of the bluffs from ongoing failures. Ground-based 3D laser scanning technology represents a new method of surface modeling for characterizing bluff failures and is an extremely useful technique for working with steep, evolving landscapes. In this paper, we present a brief overview of the laser scanning process and describe its application in monitoring the slope behavior of three coastal bluffs composed of weakly lithified sand. We then present geomorphological analyses performed using the data gathered from the 3D laser scanning program to show how the predominant triggering mechanisms can be correlated directly to the observed bluff response and linked to the degree of cementation of the coastal bluff units. Finally, we use the data to extract quantitative indicators of failure and make predictions regarding their stability and response to future storm events. In addition to making several qualitative geomorphological conclusions concerning slope behavior and failure mechanisms, we find from the laser data that bluff sections composed of weakly cemented materials typically fail when their overall slope inclination reaches the mid to high 50° range and are stable below 50°. For slopes composed of strongly cemented materials, no correlation between geometry and failure can be deduced.

The application of airborne geophysics to provide solutions for environmental and engineering problems has increased in recent years. This paper will present data collected via helicopter-borne magnetic and electromagnetic surveys (HEM). Airborne geophysics measures the electrical properties of the earth and its constituents as well as man made objects buried in it. Surveying the ground with a helicopter has always offered the ability to overcome physical barriers such as inaccessibility or hazardous environments. Compared with ground surveys, helicopter surveys can offer significant cost reductions for surveys over large areas with typical hourly production rates of approximately 500 acres/hour). Advances in the last 5 years in instrumentation, software, GPS and map products have brought about growing acceptance of HEM by the engineering community. This is due primarily to the ability of today's systems to make accurate, high resolution, precisely positioned measurements. HEM is proven as a technology to: Locate contaminant plumes, characterize industrial sites, measure the extent of salt water invasion, detect buried metal structures and UXO, locate brine leaks from abandoned oil wells, assess groundwater resources and recharge areas, characterize rock and soil along Rights of Way, locate illegally abandoned or lost radioactive sources, map sand and gravel deposits for aggregate resource exploration, measure soil conductivity near oil pipelines to assess corrosion risk, delineate burnt and un-burnt coal and locate igneous dikes in coal mines. A range of data presentations and final products are available to satisfy the various mapping needs of the scientific community such as 2D and 3D presentations of geophysical data and vertical conductivity sections. Integration of information from the complementary datasets is a powerful part of interpretation that leads to a comprehensive understanding of the structural history and geological evolution of an area - a vital part of any exploration or land care management program. Through the recognition of the many advantages provided by HEM, engineers and scientists with a need to map the earth's subsurface are gaining a better understanding of geology, hydrology, natural hazards and the impacts of mankind. This paper will present HEM data acquired for a variety of environmental and engineering projects. This data has contributed significantly to an understanding of the subsurface while providing cost and time efficiencies.

A well conceived and executed geophysical program can lead to overall project cost savings by providing information about local geologic / hydrogeologic conditions, buried utilities and structures, groundwater conditions and other subsurface conditions which allows for more efficient planning of engineering activities and more cost effective deployment of construction equipment. This information ultimately leads to more complete bid packages with less uncertainty in cost estimation and, subsequently, fewer change orders, and surprises in the field. Geophysical programs combine multiple technical and scientific disciplines required to accurately, efficiently and non-destructively detect, locate, and characterize subsurface conditions. Knowledge of these conditions reduces cost and risk. Typical geophysical investigations require extensive experience and expertise in multiple disciplines. There are three keys to a successful geophysical assessment, including: (1) A comprehensive understanding of the site activities, geologic / hydrogeologic conditions, topography and weather; (2) Experience in the review of archive search reports and historic site information, as well as local political and regulatory issues; (3) An in depth understanding of geophysical sensors, navigation technologies, surveying deployment methodologies, and advanced data analysis methods. In order to meet specific project objectives to map the subsurface accurately and efficiently, the following "expedited geophysical approach" has been developed: Fully understand the challenge; Define a suite of geophysical instruments required to efficiently map the target objects; Decide on survey control; Design an appropriate and efficient instrument deployment system; Develop an efficient data processing approach. This paper uses case histories to demonstrate the cost effectiveness and technical approaches typical of geophysical characterization projects related to solving common geotechnical problems.

This paper addresses the development of an electrical resistivity needle probe to be deployed during centrifuge model testing to assess with high-resolution the spatial variability of soil electrical resistivity. The probe is able to detect thin layers and accurately resolve interfaces between soil layers. The prototype probes are made from thin, stainless steel needles, with an insulated wire inserted into the needle, and bonded to it with epoxy resin, to form a coaxial probe. Different tip shapes including single-wedge, double-wedge and cone have been developed to optimize the spatial resolution of porosity, soil interfaces and layering. The calibration and testing of the needle probe has been conducted both at Georgia Tech and UC Davis. This paper presents results of resistance versus depth and porosity versus depth, and compares the porosity based on measurement of mass and volume with the calculated porosity based on the needle probe measurements. Consequently, insertion effects are discussed and theoretical explanations are given. For its deployment in the centrifuge, a special needle probe tool has been developed to be operated by the new NEES robot. Instrumentation, data acquisition and data processing issues associated with the needle probe robot tool are discussed. The basis for selection of materials, probe tip geometry, and the optimum frequency of AC electrical measurements is explained.

Assessment of the depth location of stratigraphic interfaces and the depth and thickness of thin layers can be critical to the proper performance of geosystems. For example, stratigraphic interfaces can promote anisotropic soil strength response and potentially provide preferential slip planes that create slope instability. Similarly, the presence of thin, high permeability layers can alter groundwater flow regimes and rates of consolidation, which can hinder or accelerate methods of ground improvement. A miniature piezoprobe (MPP) with an apex filter location and a measurement frequency of 64 Hz was recently developed in an effort to detect and characterize these stratigraphic features. The piezoprobe's functionality is through the measured excess pore pressure profile, which reflects changes in the drainage conditions, and therefore soil conditions. This paper evaluates the piezoprobe's ability relative to the conventional piezocone penetrometer (CPTu) to characterize distinct interfaces and thin layers through the analysis of soundings performed at two highly characterized test sites. One test site consists of a near normally consolidated clay layer with distinct interfaces with the overlying backfill and interbedded layers of sand and silt below. The second site consists of varved clay, which is comprised of a repeating structure of thin pairs of silt and clay layers. Results demonstrate that the piezocone detects distinct interfaces at a higher resolution than the CPTu and that thin layers may go undetected by the CPTu.

By virtue of its ability to take nearly continuous readings with depth, the CPT presumably provides exceptional stratigraphic delineation, and specifically, precise detection of interfaces. However, the tip and sleeve elements respond to resistance of soils from different elevations, and not just because the sleeve is physically located above the tip at a central distance of 10 cm. The tip resistance is influenced by soils ahead of the advancing probe while the sleeve responds to the soil immediately surrounding it. As such, there is a disjoint between the two readings often resulting in a pronounced friction ratio spike near the interface. The present paper confirms the presence of such spikes by: 1) Evaluating the theoretical tip and sleeve resistances as the cone approaches and passes an interface; 2) Performing numerical simulations of the problem using an advanced autoadaptive remeshing FEM program; 3) Comparing to actual field data, including piezocone readings; and 4) Verifying the interface locations by optical observation using the vision cone penetrometer, VisCPT.

In November of 2001, the Minnesota Department of Transportation (Mn/DOT) began using cone penetration testing (CPT) in addition to traditional borehole drilling as standard practice for geotechnical site characterization. Immediate benefits were observed. Use of the CPT system, in conjunction with drilling, sampling, and lab testing, has improved the ability to resolve small changes in soil stratigraphy and associated soil properties. Major transitions can be clearly identified and the location of the transition determined with greater precision and accuracy previously possible. As compared with traditional investigation techniques, CPT provides increased resolution for characterizing stratigraphic interfaces and the ability to develop continuous profiles of soil properties. Other practical advantages of the technique, of particular interest to geo-engineering agencies and companies, are discussed. The application of CPT methods has been useful on a broad range of transportation projects. Thickness and lateral extent of thin seams in soft clays have been identified. Limits of organic materials have been determined with precision and speed. Refined boring programs, based on CPT data have improved the efficiency of site investigations. Mn/DOT has also applied the CPT to a number of non-traditional projects including verification of contractor "remove and replace" operations and studying open-end pipe-pile plugging and pore-water pressure dissipation behavior. Four briefcase studies illustrating the use of CPT investigation techniques to identify thin seams and complicated site stratigraphy on Mn/DOT projects are discussed.

The Phoenix Sky Harbor International Airport Automated People Mover project will require tunneling in coarse riverbed sand gravel and cobble (SGC) deposits. Significant areas of unstable, running ground, primarily in Holocene deposits of SGC, have been encountered on previous tunneling projects in the area. Several investigation techniques, including the use of state-of-the-art seismic refraction microtremor surveys, and the rotosonic drilling method were implemented in order to accurately locate the Holocene-Pleistocene contact, and define the extent and frequency of clean and clayey lenses and boulders within the project geologic profile. The complete geotechnical investigation consisted of seismic surveys, rotosonic drilling, lab testing, and various downhole geophysical tools including dual induction logging, neutron and gamma logging, acoustic televiewing, and boring diameter measurements with a three arm caliper. The combination of seismic survey, laboratory testing, and field logging provided a good estimate of the Holocene/Pleistocene contact and general assessment of the clay content of each geologic unit. Seismic survey results indicated an abrupt increase in shear wave velocity at depth, and laboratory test results indicated increased clay content at depth within the Pleistocene deposits. Field logging of the continuous rotosonic cuttings verified the increased clay content at depth, but also indicated embedded clean cobble and boulder lenses. The downhole geophysical measurements offered an excellent compromise in scale between the relatively small laboratory test points and the very large scale seismic refraction microtremor surveys. The induction resistivity tool provided an excellent correlation with the clay content identified in the formation, and the neutron logging provided confirmation of the clay content increase at depth.

The process of recording rock descriptions on boring logs (rock core logging) is the primary means of communicating rock properties that should be considered in the design and construction of underground works including foundations in and on rock, rock slope and tunnel support, and excavations in rock. The quality of rock descriptions can have far-reaching implications for the success of a project. An appropriate level of detail (as determined by the project-specific end use objective) must be collected and conveyed. In this paper, important considerations for rock core logging are discussed. First, rock descriptions should be developed for each rock material unit, defined herein as a discrete mass exhibiting a different set of geologic and engineering properties than adjacent materials. Material unit-based rock core logging minimizes the risk of overlooking design-critical rock mass conditions. Secondly, material unit descriptions should be constructed using a standard descriptive code consisting of well-defined terminology arranged in a consistent format. Standardization of the rock core logging descriptive code (at least for individual projects) will result in more useful rock descriptions to facilitate geo-engineering interpretation, spatial correlation of material units, and engineering analysis for developing design recommendations and construction considerations.

Multi-channel surface-wave (MASW) seismic control was acquired along a 6400 ft segment of interstate I-70 in downtown St. Louis, Misouri. The acquired MASW data set (consisting of Rayleigh waves) was transformed into a 2-D MASW shear-wave velocity profile with a trace-spacing of 40 ft. Shear-wave velocity control extends from the surface to depths on the order of 100 ft. The interpreted depth to acoustic bedrock along the 2-D MASW profile varies between 20 ft and 44 ft. The interpreted 2-D MASW shear-wave velocity profile was compared to available borehole, cone penetrometer and seismic cone penetrometer control provided by the Missouri Department of Transportation. The 2-D MASW profile correlates very well with availablegeotechnical control, supporting the conclusion that the multi-channel surface-wave seismictechnique can be used to generate reliable and interpretable 2-D shear-wave velocity profiles of the shallow subsurface.

Near-surface fluvial depositional environments at two field sites were characterized using integrated geophysical surveying techniques to determine the location and extent of paleo-fluvial deposits. The integrated surveys consisted of ground conductivity and electrical dipole-dipole resistivity measurements. The two techniques were used in combination to map the geoelectrical structure of the subsurface from which correlations to geologic structures were made. The correlations were subsequently confirmed by exploratory drilling and test trench data. Subsurface zones exhibiting high electrical resistivity values were correlated to coarse-grained fluvial deposits (i.e., sands and gravels) and zones exhibiting low electrical resistivity values were correlated with fine-grained fluvial deposits (i.e., clays and silts). Ground conductivity surveys were conducted to generate a map of the near-surface expression of the fluvial depositional environment. Dipole-dipole resistivity surveys were subsequently performed to generate vertical images of the subsurface structure and to map the vertical and lateral extent of the paleo-fluvial depositional environments. The integrated geophysical survey method successfully discriminated between fine-grained and coarse-grained fluvial deposits due to the significant electrical contrast that exists between these types of sediments and allowed for greater insight of the subsurface geologic structure and the nature of the depositional environments.

We demonstrate, using data from two different sites, that seismic attribute analysis and constrained seismic inversion applied to high-resolution seismic reflection data can increase the resolution of the data to delineate shallow (< 35 m depth) thin (< 1 m) beds and stratigraphic interfaces that might not otherwise be identified. During site characterization, delineating these features is important because contaminants such as DNAPLs tend to accumulate at stratigraphic interfaces (buried channels) and in fine-grained beds. The traditional method for characterizing these features is drilling numerous boreholes and correlating the interfaces between holes. Noninvasive shallow high-resolution seismic reflection surveys can provide a near continuous record of vertical and spatial geologic/lithologic changes between boreholes. Unfortunately the seismic section is a smoothed version of the subsurface representing differences in reflectivity at a resolution far lower than provided by geophysical logs. Seismic attribute analysis and constrained seismic inversion techniques use the properties of borehole data (fine resolution) and seismic data (coarser resolution) in combination to produce a seismic properties model with a vertical resolution close to that found in borehole logs, but with added horizontal dimension. At United States Department of Energy's Hanford Site in Washington seismic impedance stacks were used to map thin silt layers, not evident on the standard amplitude stacks, where carbon tetrachloride was accumulating. Also buried channels and other stratigraphic features that are potential contaminant pathways at this site were better defined. At Marine Corps Air Station Beaufort, South Carolina seismic impedance stacks were used to map the continuity of a clay confining unit.

Characteristics of phase velocity and incoming angle (azimuth) of passive surface waves as they are observed with a multichannel processing scheme are studied through both synthetic modeling and field experiments. They are analyzed specifically in association with the case of multiple sources and multiple modes of dispersion. The features of artifacts and disturbances in phase-velocity estimation and how they can be alleviated in a processing scheme are described. First, a modeling scheme is introduced to simulate multiple sources at different locations as well as multiple modes of dispersion. With such known characteristics as phase velocity, azimuth, strength, and modes of dispersion, these features are illustrated and explained by using a set of modeled data. Then, the scheme to process passive surface waves is briefly described. It transforms wavefields of horizontal plane-wave propgation, measured with receiver spreads along the two orthogonal axes (x and y), into dispersion images. The scheme first transforms the measured wavefields of a particular frequency (ω) into the energy in phase velocity (c)-azimuth (θ) space where multiple sources and modes of surface waves are represented as energy peaks at different azimuths and phase velocities, respectively. The scheme, then, stacks all the energy through the azimuth axis to produce an energy distribution along the phase-velocity (c) axis only. A final image is then created by repeating these steps for different frequencies and displaying the energy in frequency (ω)-phase velocity (c) space. This process greatly alleviates general complications with the passive method such as disturbance of phase velocities due to multiple sources and modes as well as the spatial aliasing.

A small-scale and a large-scale true triaxial apparatuses (where σ₁≠σ₂≠σ₃) are recently developed at Institute of Industrial Science, University of Tokyo, Japan and described in this paper. In these apparatuses, a comprehensive loading system that can control both strain rate and stress rate are used for the vertical (axial) direction. In the small-scale true triaxial apparatus, one horizontal load is applied by using a hydraulic system (stress control) while in the large-scale true triaxial apparatus it is applied by using a motor-driven gear system (strain control). Another horizontal load is applied by air or water pressure in both apparatuses. The stresses in three orthogonal directions are controlled independently by a personal computer. High-resolution local measurement transducers are set up in these apparatuses to evaluate normal strains in the three orthogonal directions. These apparatuses have been used in a number of research topics such as anisotropy, time effect, behavior of geo-materials from small to large strains and cyclic loading behavior, among others. It helps to obtain advanced knowledge and understanding of properties of various types of geomaterials including gravelly soils.

This paper describes a test program that investigated the potential of residual porewater pressure, or suction, to be a quick and nondestructive measure of sample disturbance. A portable 35 mm diameter suction probe, consisting of a high air-entry porous ceramic stone and pressure transducer capable of direct suction measurements on soil samples, was developed for this study. The suction probe was used at a test site located in Newbury, Massachusetts where a layer of low to medium plasticity Boston Blue Clay (BBC) exists. Six Sherbrooke block samples and several 76 mm split spoon samples were collected. Consolidation tests were conducted on all samples to assess sample quality based on volumetric strain methods. The high quality Sherbrooke block samples had much higher suctions than the poor quality split spoon samples. The results suggest that the suction probe could be a practical tool for making assessments of sample quality in the field immediately after sample collection and during selection for laboratory consolidation and strength testing.

To investigate the feasibility of the use of recycled concrete aggregate as the backfill material of geotechnical engineering structures, such as embankments, geo-synthetic reinforced soil retaining walls and bridge abutments, a series of drained triaxial compression tests were performed. Both axial and lateral strains were measured locally. It was found that the compressive strength, q_max, of recycled concrete aggregate highly compacted at water content in the vicinity of optimum moisture content, w_opt, becomes similar to that of well-graded gravel that has been used as the backfill material of highest quality. When compacted at w_opt, post-compaction saturation does not have any detrimental effect on q_max of recycled concrete aggregate. The viscous aspects of the stress-strain characteristics were evaluated. Upon the restart of MLfollowing each creep stage, t he specimen exhibited very stiff and nearly elastic response for some stress range followed by marked yielding. The changes in the stress ratio upon a stepwise change in the axial strain rate were rather proportional to the instantaneous stress ratio and the logarithm of the ratio of the strain rates after and before a step change. These trends are very similar to those of ordinary type backfill materials.

The concept of the axial shear was developed to catch several aspects of the anisotropic behaviour of soils. It was inspired by the end shear forces and moments which develop when specimens are cut at an angle to the material axes of symmetry and subjected to triaxial testing between rough platens. In routine triaxial and uniaxial compressive strength tests, these horizontal forces are unknown. In the laboratory work presented in this paper, they were measured. Tests were performed on specimens of one-dimensionally consolidated kaolinite. The testing program highlighted the difficulty of producing in the laboratory a material exhibiting a strong stiffness anisotropy. Despite this, the horizontal forces which developed along the base of inclined specimens and are at the base of the concept of the axial shear apparatus could be picked up. They were found to be low (less than 10N) but higher than those measured in vertical and horizontal specimens.

Expansive clays exhibit volume changes in accordance with seasonal moisture fluctuations. Shrinkage cracking in expansive soils followed by heaving usually result in distress to pavements and foundations. This paper presents the characterization of shrinkage strain potentials of a fiber reinforced natural expansive soil compacted at optimum and near wet of optimum moisture contents of the soil-fiber matrix. Soil was treated with three types of fibers at dosages of 0.4, 0.6 and 1.0% by total weight of dry soil. Soil specimens were then compacted and oven-dried at 110°C until no further change in moisture content was observed. Three dimensional images of the dried soil specimens were taken to study crack patterns and volumetric shrinkage strains using an image processing, digital imaging technique. Manual measurements were also made and compared with digital measurements to address the reliability of this method. Improvements in expansive soil characterizations using digital imaging measurement techniques are discussed.

The distribution of local void ratios rather than a single average value is more pertinent to soil's behavior, and different techniques have been applied to quantitatively assess this spatial variation. In this paper, a method based on the local permittivity of soils measured at 1 GHz and associated mixing rules, is used for the same purpose. The local permittivity along the soil specimen is gauged using a slim form probe with an outside diameter of 2.2 mm. The experimental results on saturated soil specimens indicate that this technique is a simple and useful tool to evaluate the spatial variability of soils. Yet, the validity and suitability of mixing rules to soil-water mixtures, as well as the measurement limitations, require further study.

Measurement of elastic parameters is a fundamental problem in soil mechanics. In cross-anisotropic soils, five independent elastic parameters are required to fully describe soil behaviour. It is possible to determine all of these parameters in oedometric testing conditions if lateral stresses are measured during vertical loading. The calculation requires that three tests be conducted on samples trimmed at different orientations. This article examines a new lateral stress oedometer and its practical application for the measurement of cross-anisotropic elasticity parameters for a laboratory prepared kaolinite. Results of a series of tests on one-dimensionally consolidated kaolin yielded values of modulus and Poisson's ratio that are consistent with published literature. The lateral stress oedometer is a robust and relatively inexpensive test for determination of elastic parameters over a wide range of loading conditions.

At natural, in-situ water content, collapsible soils have high strength and relatively high void-ratio with low compressibility. These soils could easily collapse when wet. If the differential deformations and slope stability effects have been neglected in the design and construction processes, they could cause damage to constructions. Therefore, the identification of collapsible soils with estimation of the collapse potential and shear strength become major components in appropriate engineering for these moisture-sensitive soil sites. To deal with shear strength of unsaturated soil or collapsible soil, the direct shear box apparatus for measuring in water content with matric suction must be modified. The electrical sensors for water content measurement are installed near the shear plane. Due to low friction material, Teflon sheets are then used as a spacer to control the water content of the specimen during testing.

This paper describes a newly developed apparatus for measuring the tensile strength of compacted and pre-consolidated saturatedsoft to medium clayey soils. This apparatus is simple to use to perform a soil tensile strength. Two types of tensile molds are described and results obtained from them are compared. Repeatability of test results is also verified. Effects of water content, dry density, proportions of particle size and amount of fines present in the soil are also examined. Tensile strength and unconfined compression test results are compared. It was found that the ratio of unconfined compression strength (q_u) to tensile strength (q_t) for statically compacted Kanto loam soil is around 12.5. In case of compacted Kanto loam, maximum value of q_t and q_u is obtained around 50∼60% of water content for all the samples prepared at three different dry densities (ρ_d = 0.66, 0.68 and 0.7 g/cm³). Both types of strength decrease on wet and dry sides of this maximum value. In case of mixtures of NSF clay, silt and sand in different proportions, it is observed that with the increase in the amount of finer particles, both q_t and q_u increase. But with the increase in the size of finer particles, reduction in the strengths is observed. In case of pre-consolidated saturated NSF clay, tensile and unconfined compression tests are performed. Saturated NSF clay samples are prepared under the pre-consolidation stresses of 100, 200 and 300 kPa. The ratio of strength (q_u/q_t) obtained for this saturated NSF clay is around 6.

The dependence of liquefaction susceptibility and shear behavior of sands and gravels on particle shape and angularity has been well documented in the literature. However, quantification of particle morphology and its direct influence on liquefaction susceptibility and shear behavior has been hindered by the absence of quantitative models for particle shape, as well as the difficulty in modeling angular particle assemblies. In this paper, a method for quantitative identification of particle morphology is described using three-dimensional numerical shape descriptors. Representative particles from six different types of sands and glass beads are scanned using a digital image analyzer. The sands vary in angularity, from subrounded to highly angular, and consist of both natural and industrial sands as well as glass beads. This paper describes the design and development of automated image processing algorithms that can estimate 3-D shape-descriptors for particle aggregates using a statistical combination of 2-D shape-descriptors from multiple 2-D projections. In particular, Fourier descriptors and invariant moments are employed for representing the shapes of the 2-D projections. The consistency, separability and uniqueness of the newly developed 3-D shape-descriptor algorithm are demonstrated by exercising the method on the different particle mixes. This method will eventually be used in a Discrete Element Method (DEM) program to simulate the shear behavior and liquefaction performance of angular soils.

Ageing and viscous effects on the stress-strain behaviour of kaolin and their interactions were evaluated by performing special constant-rate-of-strain 1D compression tests on air-dried and saturated kaolin without and with cement-mixing. The yield stress that was higher than the stress at which curing was made developed by ageing effects associated with cement hydration, which became larger with an increase in the curing period. The stress-strain behaviour of saturated cement-mixed kaolin after monotonic loading continues for some strain range following the start of yielding was rather independent of the stress at which cementation developed. The viscous properties of kaolin was evaluated by measuring the stress jump Δσ_v^' taking place upon a sudden change in the strain rate from (ε˙_v)_before to (ε˙_v)_after at the instantaneous stress σ_v^'. The Δσ_v^'/σ_v^' – log{(ε˙_v)_after/(ε˙_v)_before} relation was linear in all the cases. The slope β, called the rate-sensitivity coefficient, represents the viscous property of clay. The β value of kaolin when dried was about a half of the value when saturated. The effects of cementation on the β value and other aspects of viscous property were evaluated. It is shown that the β value of kaolin when dried was very similar to the values of sand and gravel.

Drained and undrained creep characteristics of saturated loose fine sand were compared and interpreted based on the yielding and viscous properties under general stress conditions. The viscous properties were evaluated by performing specially designed triaxial compression (TC) and extension (TE) tests. To quantify the yield loci for shear and compression yielding mechanisms on the p'-q plane, various loading histories consisting of pre-shearing and pre-isotropic compression were applied. Different developing rates of creep strain during drained and undrained sustained loading were interpreted based on the double yielding concept, by which the yielding soil is explained by two types of yielding (shear and compression), while referring to the viscous properties formulated in a non-linear three-component rheology model.

A series of consolidated drained (CD) triaxial compression (TC) tests were performed on unsaturated specimens of cement-mixed gravel compacted at different values of water content (W_i) and cement/gravel ratio by weight (c/g). It is shown that, even for a fixed dry density, ρ_d, the compressive strength, q_max exhibits a clear peak when compacted at W_i = "W_opt for a given compaction energy". The value of q_max and pre-peak stiffness increases significantly with and increase in ρ_d associated with an increase in the compaction energy not only for a fixed c/g but also for a fixed ratio of cement weight to specimen volume (c/V_t). Moreover, the effect of c/g on q_max becomes more important for higher densities. It is suggested, to attain a high strength of cement-mixed soil, high compaction is one of the most important key factors while the water content (W_i) at compaction should be controlled to be close to the respective W_opt for given compaction energy.

The yield behavior of Leighton Buzzard sand was investigated for different magnitudes of the three principal stresses and rotation of the major principal stress axis using a hollow cylinder apparatus. The magnitude of the deviator stress at yield was found to vary continuously, although in a well-defined pattern, under generalized stress conditions. The Lade yield criteria and Matsuoka-Nakai yield criteria were both found to adequately predict the onset of yielding under generalized stress conditions. The experimental data for the Mohr-Coulomb yield criteria deviated most from the theoretical values and did not follow a consistent pattern. The experimental data indicated that the magnitude of the deviator stress at yield and the magnitude of all three yield criteria were independent of the magnitude of rotation of the major principal stress axis.

A fully automated flexible boundary true triaxial device with real-time feedback control system has been developed for testing cohesive soil. Using this device, a cubical specimen can be subjected to a wide variety of stress paths in three-dimensional stress space. Principal stresses are applied along each principal axis of the specimen using a Proportional - Integral - Differential (PID) based closed loop control algorithm and using electro-pneumatic transducers. This device has the ability to measure both the internal and external pore pressures for a 102 mm cubical specimen and uses custom developed Butyl rubber membranes. Use of flexible boundary conditions, the associated experimental issues, and flexible membrane compliance in strain computations are discussed. This paper describes the procedures involved in true triaxial testing such as preparing the remolded cubical specimens, assembling the specimen in the system, and saturating the specimen using backpressure. The PID coefficients used in feed-back control system show their significant influence in the measured stress-strain and strength behavior of clay. Therefore, for good quality testing, the values of PID coefficients have to be chosen carefully considering the influence of the variation in specimen stiffness during shear and pre-consolidation history.

Digital imaging and the Vic-3D program were used to measure deformations during a displacement-controlled cyclic triaxial test of a clay specimen confined by vacuum. Seven stages of testing, each of 50 cycles, were completed. Measurements from an LVDT and the Vic-3D image correlation program were compared using two methods: 1) A direct comparison of strains with estimated error bands and 2) A statistical test of coincidence of resilient modulus regression curves using a dummy variable model and an F-test. The Vic-3D program successfully replicated LVDT results. Both total and plastic strains exhibited similar trends and magnitudes. Resilient modulus curves were statistically coincident at the 99% confidence level.

In 1997 the Minnesota Department of Transportation (Mn/DOT) began operating fully automated computer controlled geotechnical testing equipment, replacing many existing systems. Existing systems required active technician oversight particularly for consolidation and triaxial testing. An increase in the number of projects requiring testing, shorter project time-lines, rapid advances in computer technologies, a decrease in the number of skilled technicians, and a desire to reduce project costs, made automated systems especially attractive. As a result of the effectiveness of the automated systems, today, the geotechnical section routinely conducts specialized tests previously available only to academic institutions and research labs. Automated laboratory testing combined with automated in-situ cone penetration testing (CPT) has dramatically improved overall site characterization quality while reducing both cost and time associated with geotechnical investigation. Test reliability, repeatability, accuracy, and confidence in the test results have improved, while decreasing subjectivity and operator error. Measurable cost savings, both in field costs and lab costs, and increases in efficiency have been realized, even after the relatively large investment cost of the new equipment. A comprehensive suite of lab and in-situ CPT tests were performed on clay soils at a bridge site in northern Minnesota; results of this study are presented to illustrate the uses and benefits of automated systems. Lab tests included 1-D consolidation, triaxial stress path, flexible wall constant gradient permeameter tests, direct shear, and direct simple shear tests. Shear strength (S_u) and modulus values (M, G, E) were compared with in-situ CPT tests conducted at the site.

Geocentrifuge experiments require rapid event sampling. Electrical Resistivity Tomography is a method well suited for geocentrifuge experiments, however, commercially available systems can not perform at the speeds required to sample these experiments without temporal aliasing occurring. A novel ERT system was designed, and two of these systems were constructed — one for research at the INEEL, and one for research at UC Davis. System performance is comparable to that of existing commercial system, while the maximum system speed is close to four orders of magnitudes higher than that of commercial systems. This system should thus be able to adequately sample processes occurring on the geocentrifuge.

X-ray computed tomography (x-ray CT) was applied to visualise the local deformation patterns caused by miniature cone penetration tests (CPTs) in a calibration chamber filled in with a fine grained quartzic sand and pressurized with vacuum. A reference test was conducted during which the calibration chamber was scanned at several stages of cone penetration. The measured X-ray attenuations were translated into local sand density maps with a resolution of 0.25 x 0.25 x 1mm by using the calibration established by scanning layered sand samples of different densities. Test results showed that a dilating zone having the shape of a sphere was formed ahead of the cone tip before being penetrated by the cone. Friction along the cone shaft did not generate visible density changes. The final dilating zone consisted of several coaxial cylinders of different density, all having a rounded tip. The absence of contractance at proximity to the cone was attributed to the behaviour of the Baskarp sand. When sheared in its dense state under high confining pressure, this fine sand dilates. Also, its particle shape does not promote crushing and re-arrangement of crushed grains in a denser packing. 3 other scanner tests were performed. Decreasing the confining pressure resulted in, despite a decrease in the tip resistance, no large differences in the size of the area affected by density changes and magnitude of density changes. By lowering the sand density, the size of the dilating area was found to be significantly smaller and the loosening much less. The use of rigid boundaries only resulted in a small decrease in the dilating area despite causing a large increase in cone resistance. Using X-ray CT, it was possible to quantify the local loosening generated by CPT in sands under axisymmetrical stress conditions. Deformation patterns different from those observed in plane strain experiments were observed.

The past decade has seen increased interest in standardizing seismic design criteria for structures. In many states the IBC 2000 Building Code is replacing previous codes such as the UBC, SBC, and BOCA. The IBC 2000 code requires a site-specific seismic classification based on the stiffness of the soil or rock in the upper 100 feet of the subsurface. The site classification will drive the structural design and thus the construction costs. For large commercial structures, the difference in construction costs between one category and the next can be many hundreds of thousands of dollars. Traditionally, methods for determining soil stiffness have relied on pressure methods such as undrained shear strength, standard penetration resistance, and dilatometer tests. Research has shown that the apparent stiffness of the soil tends to be largely under-predicted by pressure methods because the apparent stiffness is related to the strain of the test. Pressure methods tend to induce large strains, resulting in under-prediction of stiffness with a corresponding lower site class. At small strains, such as those induced by seismic methods, the apparent stiffness is at its maximum. By using the spectral analysis of surface waves (SASW) method, more realistic stiffness estimations are obtained. Incorporating SASW measurements with two-dimensional resistivity imaging provides two independent non-invasive methods to verify the subsurface distribution of soil and bedrock materials. The authors have correlated SASW measurements with resistivity imaging data at several sites in which a site class had already been determined with standard penetration tests. In each case a higher site class was obtained with the SASW-resistivity investigation than with the SPT. The resulting savings to the client in construction costs have ranged from $80,000 to $650,000.

Sensing of dense non-aqueous phase liquids (DNAPLs) in soils with cross-well radar (CWR) is a challenging geophysical problem that can have significant benefits in geo-environmental applications. Method development and implementation involve forward modeling of electromagnetic source (antenna) and wave propagation in soils, subsurface sensing and reconstruction of the contrasting DNAPL volume. In particular, modeling the antenna behavior in soil is critical because the soil background greatly affects its radiation characteristics. An analytical model is implemented in the frequency domain in terms of the dyadic Green's function solution to describe the physical nature of an ideal dipole source in infinite soil medium half-space. This Green's function model is then incorporated into a first order Born Approximation to linearize the inverse scattering problem. EM wave propagation behavior is studied over a wide frequency band and various soil moisture contents. The forward modeling simulation is compared with experimental data collected using subsurface cross-well radar using broadband antennas. Soil parameter calibration is performed based on this forward model to approximate the most likely soil property in laboratory environment. The calibrated soil parameters are then applied in simulation to compare with fields generated by monopole antennas in the laboratory.

Cross-Well Radar (CWR) is a a promising method for DNAPL (Dense Non-Aqueous Phase Liquid) detection in soils. An important issue for CWR implementation is to deploy the optimum number of antenna boreholes for best balancing the trade off between image accuracy and minimizing risk of drilling through contaminated zone. This requires knowledge about key positions in the scatterer signature on EM field. Using the appropriate 3D antenna pattern to achieve a 3D image is crucial. Computerized tomography is a powerful subsurface imaging technique used in both medical to environmental applications. Fundamental theoretical and experimental forward modeling knowledge of EM wave propagation and scattering are crucial to accomplish image reconstruction. Therefore, a pilot-scale (1/100) cross-well radar tomography setup was developed. Many challenges were encountered and resolved in achieving measurement reproducibility, validity and symmetry. The knowledge gained from these studies has established a specific methodology for cross-well tomography experimental setup and data collection. The required frequency response data was collected and classified, and used to validate the results of a Born Approximation forward model in the frequency domain. Due to the complexity of simulating actual antennas analytically, simplified parametric antenna models were used in the forward model. The experimental measurements are then used to determine the antenna model parameters with the best matching the radiation characteristics.

There are several techniques that may be used in the tomographic imaging of structural and geotechnical systems. X-ray tomography and ultrasonic imaging are two of the extreme techniques as functions of resolution and costs. On one hand, X-ray tomography allows the collection of high-resolution images in small specimens that may be removed from the structure. The application of X-rays in the field is not recommended due to cost and safety issues. On the other hand, ultrasonic testing may be used in the field to obtain stiffness images with lower resolution due to problems of high attenuation, diffraction and scattering around aggregates and inclusions. However the cost of ultrasonic testing is much lower than X-ray imaging systems. This paper presents experimental results of X-ray and ultrasonic tomographic imaging of concrete cylindrical specimens prepared with low-density and velocity and high-density and velocity inclusions. These specimens present the extremes of contrast for the two techniques. Quantitative and qualitative analysis of the results show that the results from each technique are complementary: X-ray tomography may be efficiently used for the collection of advanced model parameters while ultrasonic imaging may be used for the QC/QA of structural and geotechnical elements in the field.

Microfocus x-ray computed tomography is used to study the effect of grain size distribution and consolidation pressure on the spatial distribution of porosity of synthetic rock cores. CT scans were conducted on 12 synthetic rock cores having different grain size distributions and consolidation pressures. Density calibration as described by ASTM standards was performed to correlate the CT number to the bulk density, then to the porosity. A computer algorithm was developed to calculate the porosity for every five voxels of the rock cores, producing about 15 million porosity values within each core. The porosity distributions for all the cores were compared with each other to determine the effect of changing the grain size distribution and the consolidation pressure. CT data showed a good ability to capture the changes in the porosity distribution, for the different cores. Moreover, it was noted that the degree of homogeneity of the pore sizes within the cores could clearly be indicated by the standard deviation of the porosity distribution (i.e. the width of the porosity distribution histogram). However, some mixed trends were observed especially with the cores prepared at very high consolidation pressures. Crushing of the particles was considered as a possible reason for these trends.

X-ray computed tomography (CT) is becoming a useful tool for nondestructive imaging of many geoenvironmental and geotechnical systems. Conventional X-ray CT systems typically utilize a polychromatic X-ray beam. While providing a high throughput of photons, the use of polychromatic energy can make quantifying material concentrations, densities or composition very difficult or impossible without appropriate standards. Synchrotron X-rays have an extremely small angular divergence, thus permitting spatial resolution that is only limited by the optical components of the system. In addition, the ability to tune to a monochromatic X-ray energy allows better phase contrast by reducing beam hardening and allowing for elemental discrimination. In this work we will show how monochromatic energy can be used to provide high-quality images allowing for phase separation several different porous media systems thus improving our ability to quantify a range of processes and phenomena.

Neural network based constitutive models have recently been used to capture soil constitutive response. The neural networks are trained with large data sets. A novel method of enriching these training data sets is presented and tested, showing a limited data set can be expanded to a wider range of problems. A method of selectively reducing data set size is also presented, so that maximum behavior can be gleaned from a minimum amount of data. By using novel visualization techniques to evaluate the learned neural network model responses, it is shown that a large reduction in data set size does not significantly affect the performance of the neural network model.

In order to evaluate the benefit of using three-dimensional (3D) geostatistical interpolation and visualization methods over two-dimensional (2D) methods to characterize a site, we have assembled a database of densely spaced geotechnical data in downtown Boston. Our study area includes several high-rise buildings as well as a 300 m length segment of the Central Artery/Tunnel (CA/T) project. The stratigraphy of the site includes artificial fill, organic deposits, marine clay, till, and bedrock. The assembled geotechnical data include stratigraphy, N-values, sieve analysis, ground water depth, and sample descriptions. The till is the bearing material for most structures in the area; therefore, in this paper we present results on characterizing the till layer using corrected (N₁)₆₀. By using geostatistical interpolation to characterize the site, we could evaluate the confidence level of predictions. We showed that the confidence in prediction was greater when using 3D characterization than using 2D characterization. The 3D characterization maintained the integrity of the vertical variability of the till without needing to subset the data. Test boring data were grouped into three stages: 1) relevant test borings completed prior to 1988 (including 79 borings), 2) CA/T test borings (including 33 borings), and 3) the combined data set (including 112). The site was characterized separately for each stage providing an opportunity to evaluate the effect of boring density and spacing for site characterization. In 3D, we compared confidence volumes for different stages to show that incorporating prior test borings in the general vicinity of the CA/T alignment increased the confidence in the overall prediction. Using the CA/T test borings alone resulted in a predicted model with high variance and therefore low confidence. The interpolation of corrected (N₁)₆₀ values reflects the inherent variability in the test data and results in a prediction with low confidence levels.