bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-Gradient Permeability Testing of Fine-Grained Marine Sediments
Authors: Silva AJ , Hetherman JR , Calnan DI
Published: March 2009

A back-pressured consolidation system has been modified to allow direct permeability measurements of fine-grained, low-permeability soils and marine sediments. The system allows for high back pressures (3100 kPa), axial flow in either direction with fresh or saltwater permeants, constant head tests at low gradients, and falling head tests. Low-gradient tests are conducted with a static head or with falling head methods, and high gradients are maintained with a sensitive air-pressure control system. The unit can also be used to study temperature effects in the range of 2 to 200°C.

The apparatus and procedures are described, and a summary of test results is presented. Results of low-gradient constant head tests have agreed very well with falling head tests. Coefficient of permeability values in the range of 10−6 to 10−9 cm/s have been measured. No evidence of a threshold gradient has been indicated at higher void ratios approximating in situ conditions, but small threshold gradients were observed at relatively low void ratios.
Impermeabilization of a 300-Hectare Cooling Pond
Authors: Auvinet G , Espinosa J
Published: March 2009

The project of the 1200 MW Rio Escondido Thermoelectric Plant, now under construction in northern Mexico, includes a 300-hectare (750-acre) cooling pond. The entire reservoir will be created by building a circumferential embankment and developing the total storage requirement above the natural ground level. The makeup water will be obtained at a high cost from the Rio Grande by means of a 30-km-long aqueduct with a maximum capacity of 2.5 m3/s. Severe restrictions were put on the allowable seepage.

This paper describes the geotechnical investigations performed for evaluation of the subsoil permeability and the final solution adopted: a clay liner compacted according to a nonstandard procedure. The results obtained in the laboratory and in a full-scale test pond (50 by 50 m) are also presented. During this study the limitations of some accepted tests were put in evidence, and some new techniques were developed.
Evaluating the Saturated and Unsaturated Hydraulic Conductivity of Soils
Authors: Elzeftawy A , Cartwright K
Published: March 2009

A method of calculating the saturated and unsaturated hydraulic conductivities of soils and similar porous materials based on the pore size distribution was shown to predict the experimentally measured values adequately. For coarse-textured soil materials or materials with a relatively narrow range of pore size, only one matching factor is required to calculate the hydraulic conductivity-water content relation accurately enough for many purposes; however, for fine-textured soil materials with a wide range of pore size distribution, two or more matching factors at a water content in the 0.3 to 0.4 bar range may be needed to obtain a useful evaluation for the unsaturated hydraulic conductivity.
Measurement of Hydraulic Conductivity of Partially Saturated Soils
Authors: Hamilton JM , Daniel DE , Olson RE
Published: March 2009

Increased interest in protection of the environment has led to a need to be able to predict long-term movement of moisture, and contaminants, in the vicinity of shallow land disposal sites for various toxic and radioactive wastes. The advantages of locating potential sites in arid regions has led to a need to develop means for predicting moisture movements in fairly dry, partially saturated soils and for measurements of the hydraulic conductivities of such soils.

A technique was developed in which thermocouple psychrometers and the instantaneous profile method were used to measure conductivities of soils with suctions as high as 80 atm. For one clay of low plasticity, the conductivity dropped from about 10−7 cm/s when saturated to almost 10−12 cm/s for degrees of saturation of the order of 30 percent. Measured conductivities were used in a finite element solution to Darcy's equation to predict final water content profiles. The predicted and measured profiles compared well, which suggests that the measured conductivities were tolerably accurate. Based on data presented, the proposed technique seems promising for conductivity measurements in clays with degrees of saturation between about 30 and 90 percent and in sands with 5 to 50 percent saturation.
Applications of Acoustic Emission Techniques to Rock and Rock Structures: A State-of-the-Art Review
Authors: Hardy HR
Published: March 2009

This paper presents a state-of-the-art review of the subject of acoustic emission as it pertains to the area of rock mechanics, and includes references to some 150 recent papers. Although a limited discussion of laboratory oriented studies are included, the major thrust of the paper is to field applications in geotechnical engineering.

The paper first discusses the general concepts involved in the acoustic emission technique and briefly reviews the early history of the subject. This is followed by a general discussion of techniques currently in use for monitoring and analysis of acoustic emission data, and a description of a number of recent and on-going field studies where acoustic emission techniques are being employed in the general area of geotechnical engineering. Finally, the paper considers the various limitations of the technique as well as areas where further research and development are considered necessary.
Acoustic Emission Behavior and Monitoring of Soils
Authors: Koerner RM , McCabe WM , Lord AE
Published: March 2009

As far as nondestructive testing methods are concerned, acoustic emission techniques are relatively recent additions to the rock monitoring area (dating from the late 1930's) and to the metal testing area (dating from the 1950's). Its application to soils is an even more recent event with little activity prior to the 1970's. However, over the past five to ten years, interest has been generated in the soils area to the point where at least five equipment manufacturers are currently marketing acoustic emission systems specifically for geotechnical engineering applications. This activity is seemingly well founded, for acoustic emissions are indeed generated by deforming soil masses and technical feasibility is now firmly established.

This state-of-the-art paper on acoustic emission activity in soils presents these findings on the basis of fundamentals, small-scale laboratory tests, and large-scale laboratory tests. Furthermore, the technique has been applied to field situations in a number of cases. These include slope stability monitoring of dams and embankments, soil movements arising from horizontal and vertical deformations, seepage monitoring, and grout/hydrofracture monitoring. Specific case histories in each group are presented.

Collectively taken, the information available seems encouraging enough for many investigators to use the technique for a wide variety of applications. With a multi-faceted attack, the current qualitative status of the technique (that is, no acoustic emission indicates stability; low acoustic emission indicates small movement; moderate acoustic emission indicates larger movement; high acoustic emission indicates instability) should move into a better defined quantitative status. In this latter case, acoustic emission signatures of different soils could lead to instant assessment of actual stress levels in any given situation.
Studies of Acoustic Emission in Soils
Authors: Tanimoto K , Nakamura J
Published: March 2009

This paper describes a study on acoustic emission in soils, continued from previous research, by the method of triaxial compression test, to explore a possibility of establishing correlation between the characteristics of acoustic emission in soils subjected to shear stress and deformation properties of the soils. From the results of tests conducted under strain-controlled and stress-controlled conditions, it has been made obvious that the characteristics of acoustic emission are closely connected with the rate of axial strain, the sign of dilatancy, and work done by external stresses during shear process.
Acoustic Emissions Generated During the Quasi-Static Cone Penetration of Soils
Authors: Villet WCB , Mitchell JK , Tringale PT
Published: March 2009

As a rigid object is pushed into a soil, acoustic emissions are generated by soil grains sliding over one another, sliding over the penetrating object, and being crushed.

In 1977, a research project was initiated to develop a system for recording such emissions generated during the quasi-static cone penetration of soils, and to evaluate their potential usefulness as a means for the in situ characterization of soils and soil deposits.

In order to ensure knowledge of and control over all factors governing the engineering behavior of tested soils, all initial tests were performed in the laboratory. A field testing program has recently been initiated.

Laboratory tests to date have been performed on a single graded sand. Variables included relative density, confining stress, and state of saturation. Analyses of the obtained acoustic records include the determination of peak-to-peak voltage, root-mean-square voltage, and frequency distribution analysis.

Initial results indicate that:

1. The resultant frequency distribution curves can be divided into two categories, one associated with lower confining stresses and penetration rates, the other with higher confining stresses and penetration rates, the other with higher confining stresses and penetration rates. These categories may well be signatures uniquely associated with the specific soil.

2. The amplitude of the signal increases with penetration rate.

3. The amplitude of the generated signal is larger in a dry, than in a saturated sample.

The limited field tests performed to data indicate that amplitude of the generated signal may be used as an indicator of layering.

The goal of the ongoing project is the development of a new method for the in situ identification and characterization of soils and soil deposits.
Accelerated Stability Test Techniques for Middle Distillate Fuels
Authors: Stavinoha LL , Westbrook SR
Published: March 2009

Improved test techniques are needed for evaluating the inherent stability of middle distillate fuels both in surveillance and in procurement activities. A project was initiated to define and evaluate the contributing conditions leading to the formation of deleterious products in accelerated aging tests of middle distillate fuels and to relate these results to an experimental definition of more repeatable/reliable middle distillate fuel stability test technique(s).

A literature search was conducted to provide a list of stability test techniques and their interpretations which could be used in a correlative middle distillate fuel stability test program. For this program, seven accelerated stability tests were chosen and evaluated using a set of six test fuels. The test techniques were selected to represent a wide variety of test conditions, including temperature, aging time, and oxygen availability. These six test fuels were purposely chosen to represent a wider range of stabilities than would necessarily be commonly available for procurement. The fuel properties generally measured included both adherent and suspended particulates, steam jet gum, color, and light absorbance at 540 nm. Accelerated stability test results were then related to test results obtained at a storage temperature of 43.3°C, which has generally been regarded as showing good correlation with long-term ambient storage.
Navy Needs and Experience with Distillate Fuel Stability and Cleanliness
Authors: Boyle JF , Layne RP , McGee T , White EW
Published: March 2009

Navy shipboard fuels are subjected to an environment, combat reliability requirements, and occasionally long-term storage that impose stability and cleanliness needs not normally required for fuels for shore use. The Navy satisfies those needs through specifications imposing more constraints than similar American Society for Testing and Materials (ASTM) specifications, through a strict inspection system, and through quality testing at various steps in the acquisition and distribution system. This Navy quality-control system is described. Statistical data based upon inspection data from a random sampling of fuel acquired between February 1977 and January 1980 are presented. Results of an extensive survey of fuel received and used by one class of ships which bunkered at ports around the world are given. Data include the amount, nature, and size of particulate matter, as well as the contents of water, sodium, and copper.
Genetic Response of Mallards to Toxic Effects of Methyl Mercuric Chloride
Authors: Prince HH
Published: March 2009

The reproductive resistance of mallards (Anas platyrhynchos) to the toxic effects of methyl mercuric chloride was studied over four generations. A control group and a highline group of 30 breeding pairs each of “game farm”-type mallards were developed from a parental generation, P1, of 29 pairs of birds. The test was divided into a 4-week pretreatment and a 4-week posttreatment period. The progeny for subsequent generations were obtained during the pretreatment period and based on individual female performance during the posttreatment period. The highline breeders were selected on the basis of the highest percentage survival of ducklings from fertile eggs after a treatment of two doses of 8 mg methyl mercuric chloride in a 2-week interval. A range of 350 to 600 eggs per test period was processed for each line. Survival of the ducklings in the P1 generation was 57 and 12 percent for the pretreatment and posttreatment periods, respectively. Survival of the ducklings from the control birds ranged between 38 and 56 percent and from 53 to 72 percent for the highline birds. Posttreatment survival ranged from 14 to 25 percent for the control and 22 to 38 percent for the highline females. Separation of the percentage of ducklings that survived between the control and highline birds occurred in the F1 generation and tended to increase slightly. Earlier hatch times were noted in the later generations of the highline compared with the control ducklings.
The Laughing Gull (Larus atricilla) as a Model for Assessment of Secondary Poisoning
Authors: Fink RJ , Jaber MJ
Published: March 2009

The assessment of secondary poisoning is an important consideration in the hazard evaluation of predator control agents and rodenticide baits. The selection of an appropriate test animal model is difficult because classic laboratory species are frequently inappropriate, and the availability and reliability of wild species for testing is limited. The laughing gull (Larus atricilla) has demonstrated its usefulness as a secondary poisoning model in the laboratory and shown species sensitivity through case history documentation of secondary poisoning mortality in the field.

A number of new candidate rodenticides are being developed throughout the world for control of rodent pests in domestic, industrial, and agricultural marketplaces. Because one or more of these rodenticides could have a wide variety of outdoor uses, the effects of these substances on the environment must be evaluated in terms of both their toxicity and their exposure. The portion of that evaluation which is to be considered in this paper concerns the assessment of secondary poisoning of birds, utilizing the laughing gull as a model for an avian predator.
Surface Texture Classification: A Guide to Pavement Skid Resistance
Authors: Holt FB , Musgrove GR
Published: March 2009

The ability of a driver to stop on a wet pavement surface has been shown as a relationship between a tire and the pavement surface texture. For a number of years, the Ontario Ministry of Transportation and Communications has been classifying pavement surface textures and correlating these textures with the skid number of the surface, as measured by a brake-force trailer. The skid trailer number can be explained now in terms of the pavement surface texture. This paper contains a summary of the test procedure, a discussion of the texture classification system, and the relationship of the six texture parameters is discussed in terms of the equation used to generate a skid number at 100 km/h (62 mph). The advantages of using this system as a complement to present skid testing procedures are outlined, with particular attention to its use in those areas which cannot be tested by the brake-force trailer and in the area of mix design studies. The paper concludes with a discussion of some potential uses for the test method in future research work in Ontario, including the semiautomation of the interpretation procedure.
Hydroplaning, Hydrodynamic Drag, and Vehicle Stability
Authors: Hayes GG , Ivey DL , Gallaway BM
Published: March 2009

A comprehensive series of experiments is reported involving a variety of full-scale highway pavements and various automobile tires. Test condition variables include vehicle speed, tread depth, water depth, and pavement inundated length.

Extensive test data are shown which define the tire forces encountered during partial and full dynamic hydroplaning as a function of the ASTM E 274 skid number. This enables an engineer to better interpret the actual friction available under specified conditions and shows vividly one reason it is so difficult to relate wet weather accident frequency to ASTM skid numbers.

In the final section of this paper 27 tests in selected water “puddles” are reported. These tests show that loss of tire/pavement contact can occur during puddle traversal and asymmetrical drag forces can develop which have the potential for precipitating a vehicle loss of control. These puddle depths range from zero on the outer edges to 28.5 mm (1 ⅛in.) in the deepest part. Drag forces up to 135 kg (300 lb) were measured.

It is illustrated that hydroplaning drag forces, in some cases coupled with loss of pavement contact due to hydroplaning, may pose a hazard to drivers who exceed a reasonable speed during wet weather.
A Method for Rating the Skid Resistance and Micro/Macrotexture Characteristics of Wet Pavements
Authors: Horne WB , Buhlmann F
Published: March 2009

A method is developed from combined viscous-dynamic hydroplaning theory to rate the skid resistance of wet pavements in terms of pavement microtexture and macrotexture drainage coefficients derived from full-scale tire-pavement friction tests. The friction tests can be conducted using any of the conventional tire test operating modes such as braked rolling, yawed rolling, or locked-wheel sliding. Once the drainage coefficients have been established for a wet pavement surface by friction test in a particular tire operating mode, the method can be used to predict friction coefficients on the wet pavement surface for the other tire operating modes, as well as friction coefficients for different-size tires and inflation pressure conditions. The procedure for using the method is described and examples are given. The method is used to evaluate the skid resistance, microtexture, and macrotexture characteristics of 83 highway pavements in Switzerland which were tested by The Institute of Technology (ISETH) using a skiddometer (locked-wheel test mode) over a 40 to 100-km/h speed range. The results obtained are compared with British pendulum, sand patch, and outflow meter tests of pavement surface texture also performed by ISETH on the same 83 highway pavements. Comparison with experimental data shows that the method gives reasonable estimates of friction coefficient for both aircraft and automobile tires for the examples cited.
Quality Assurance of Graphite/Epoxy by High-Performance Liquid Chromatography
Authors: Sewell TA
Published: March 2009

Factors contributing to the reliability and reproducibility of high-performance composites include advanced resin matrixes with consistent purity and concentration of chemical constituents, as well as mix homogeneity and processing uniformity. Variation of these matrix parameters can affect manufacturing processibility and finished laminate quality. For these reasons, a wide variety of analytical tools have been evaluated for their capability of ensuring matrix reproducibility. In most cases, test development has been required to optimize and tailor the methodology for each new matrix system. In this way analytical information more precisely characterizes the matrix and monitors batch-to-batch consistency.

This paper covers work under U.S. Air Force Contract F33615-78-C-5177, “Chemical Composition and Processing Specifications for Air Force/Navy Advanced Composite Matrix Material.” It discusses the development of high-performance liquid chromatography (HPLC) as a quality-assurance method of certifying resin matrix composition of Air Force/Navy graphite/epoxy AS/3501-6 advanced composite matrix material. A gradient-elution/binary-solvent separation technique was developed by using a Spectra Physics 8000 liquid chromatograph in reverse-phase mode.

Resin and derived prepreg from full-scale production lots having predefined concentration variations were investigated. Lot variations were verified quantitatively by using a standard production batch for baseline comparisons. Resin matrix ingredients were used as concentration standards for test calibrations. Test data are reported in weight percent for two types of epoxies and one curing agent (diaminodiphenyl sulfone).

Details concerning the evolution of method development are discussed. Data are included to demonstrate test capabilities for quantitative measurements of unreacted epoxies and diaminodiphenyl sulfone. Data are presented for test verification of intentional ingredient alterations and tracking capability for compositional changes due to ambient aging and short thermal advancements due to hot-melt fiber impregnation.
The Development of a Material Specification for 177°C (350°F) Curing Graphite/Epoxy Composites
Authors: Rogers AK , Tajima YA , Young RC
Published: March 2009

With the increasing use of graphite/epoxy materials in primary and secondary structures, it has become apparent that specifications which can assure material consistency are required. While numerous analytical methods have been developed for graphite/epoxy materials, their relation to processing behavior has not been established. The development of the new material specification involved the use of new analytical methods as well as the design of a batch acceptance processability laminate to determine the suitability of the batch for constructing a large laminate with a specified process cycle. Material acceptance or rejection is based on chemical composition and mechanical and physical properties, including viscosity profiles and performance of the processability laminate.
Control of Composite Cure Processes
Authors: Hinrichs RJ
Published: March 2009

The control of a composite cure process is an attempt to minimize thermal and pressure gradients within a laminate. The sources of these gradients (fabrication support materials, tooling, part geometry) were investigated for process significance. In addition, the concept of using engineering cure behavior transformation diagrams (heat rate and cure temperature effects on the reaction dynamics of a material) was used to evaluate the effects of gradients on the consistency of laminate processability. Control of these gradients was achieved by the use of an automated composite control system (known as CAPS) developed by Applied Polymer Technology.
Nondestructive Evaluation of Composite Materials: A Philosophy, An Approach, and An Example
Authors: Duke JC
Published: March 2009

Composite materials are being used more and more in critical structural members. It is extremely important to be able to nondestructively evaluate their quality. This paper discusses a philosophy regarding nondestructive evaluation (NDE) which suggests that such an evaluation must include inspection and an assessment, in light of specifications, of existing imperfections in the materials. Advancement in the general area of nondestructive evaluation of composite materials requires an approach that seeks to improve both the inspection and assessment aspects in an integrated fashion. An approach of this type is described.

An example of the approach applied to the characterization of the materials response of boron carbide-coated, boron fiber-reinforced titanium is presented.
Calculation of Cure Process Variables During Cure of Graphite/Epoxy Composites
Authors: Loos AC , Springer GS
Published: March 2009

A model is presented that relates the cure cycle (cure temperature, cure pressure, cure time) to the local temperature, viscosity, degree of cure of the resin, and resin flow perpendicular to the fibers. The results of the model are applicable to the curing process for epoxy matrix composites.
Laboratory Accreditation: More Than Rules
Authors: Harris R , Castino TG
Published: March 2009

Effective accreditation of third-party laboratories offering product evaluation and follow-up inspection services requires a prescription of laboratory performance and measures to assure compliance with the prescription. While documenting the established criteria can be considered the major hurdle for effective laboratory accreditation, the most difficult step may well be assuring that the accredited laboratories meet and maintain desired levels of performance. An effective accreditation program is more than rules: it is evaluation, audit, and follow-up.

This paper reviews key elements of laboratory accreditation programs that must be considered to achieve the targets that the rules have established. Consideration is also given to the critical elements required by agencies implementing laboratory accreditation programs.

An analysis of hypothetical programs that lack these critical elements is presented with the purpose of demonstrating that accreditation programs lacking one or more of the critical elements are ineffective and allow laboratory performance to be lowered to a marginally acceptable level.
The Laboratory Evaluation Process of the National Voluntary Laboratory Accreditation Program
Authors: Federline MV
Published: March 2009

At least 70 laboratory accreditation systems exist in the United States today, and many of them are directed at a single discipline or narrow spectrum of products. The increase in the number of these systems in response to a growing need for laboratory testing services indicates the viability of the laboratory accreditation concept. The National Voluntary Laboratory Acceditation Program (NVLAP) was established by the Department of Commerce to provide a national, multidisciplinary laboratory evaluation scheme.

NVLAP evaluation is based upon compliance with criteria that reflect the latest technology in laboratory operation and management. These criteria are sufficiently flexible to accommodate such diverse testing areas as thermal insulation, carpet, and concrete. The evaluation of laboratories, conducted by the National Bureau of Standards, utilizes a peer review. It combines elements of questionnaire, laboratory on-site survey, and testing of proficiency samples in a comprehensive examination to determine a laboratory’s capability to perform specific tests. NVLAP, an interactive system between laboratory and accreditor, provides a mechanism for overall laboratory improvement.
Inspections, Tests, and Accreditation Activities Associated with Qualification of Safety-Related Equipment for Nuclear Generating Stations
Authors: Rutherford WR
Published: March 2009

In recent years, the Nuclear Regulatory Commission (NRC) has uncovered a generic problem of gross inadequacies in safety-related equipment environmental qualifications conducted by the nuclear industry. This paper describes the NRC’s response to the problem through the development of an accreditation system for laboratories conducting such environmental qualifications.
Reliable Laboratory Data: A Look at a Successful Certification Program
Authors: Schwager GE
Published: March 2009

A laboratory accreditation program administered by the Illinois Environmental Protection Agency (IEPA) is described. The evolution of the program, proposed changes in the rules, procedures for certification, and cooperation between IEPA and the Illinois Department of Public Health in laboratory accreditation are covered.
Proficiency Testing: An Essential Element of Laboratory Performance Evaluation and Accreditation
Authors: Kirkpatrick D , Horlick J
Published: March 2009

The National Voluntary Laboratory Accreditation Program (NVLAP) is administered by the Department of Commerce to accredit testing laboratories upon request. Accreditation is currently available for laboratories that test carpet, thermal insulation materials, and freshly mixed field concrete. Decisions to accredit laboratories are based on evaluations conducted by the National Bureau of Standards which include questionnaires, on-site examination, and proficiency testing.

It was recognized early that while questionnaires and site visits could provide valuable insight into a laboratory’s ability, a true measure of its capability could only be determined through proficiency testing.

This paper discusses the design and operation of the proficiency testing portion of the evaluation of laboratories that test thermal insulation materials and carpets.
Performance Evaluation in the U.S. Department of Agriculture’s Food Safety Inspection Service Science Laboratories
Authors: Barth HJ
Published: March 2009

Laboratory performance evaluation of the U.S. Department of Agriculture (USDA) Food Safety Inspection Service (FSIS) Science chemistry sections is administered by the quality assurance coordinator, who operates interlaboratory check sample programs (known and blind), uses the accredited laboratory program and contract laboratory generated check samples as an outside data source, and conducts onsite laboratory audits. USDA-FSIS-Science laboratory chemistry sections have improved their ongoing analytical capability by the adoption of a formal Quality Control and Quality Assurance Program. Each chemistry section has appointed a Laboratory Quality Control Officer; keeps a Laboratory Standards Book, laboratory performance charts, analyst performance charts, and critical control points evaluation for each analytical procedure; maintains sample tracking control; and operates an intralaboratory check sample program with the associated feedback and corrective actions being taken and recorded.
State of the Art: Laboratory Strength Testing of Soils
Authors: Saada AS , Townsend FC
Published: March 2009

A review and evaluation of the advantages and limitations of laboratory equipment for measuring the shear strength of soils are presented. Equipment evaluated include direct shear, torsional shear, simple shear, triaxial, multiaxial (true triaxial), plane strain, hollow cylinder triaxial, and directional shear devices. The evaluation indicates that the impetus to obtain parameters for constitutive equations and modeling has resulted in the development of improved equipment and testing techniques; specifically, the development of multiaxial (true triaxial) and hollow cylinder triaxial test equipment. Although these devices are more versatile, the conventional solid cylinder triaxial test is still the most popular. The evaluation suggests that direct shear and simple shear devices are best utilized by designers who have gained experience applying the results from such tests to structures that have behaved satisfactorily.

Proper consideration must be given to the effects of membrane penetration, end restrain saturation and consolidation procedures, and rates of loading in any testing program.
Mechanical Behavior and Testing Methods of Unsaturated Soils
Authors: Edil TB , Motan SE , Toha FX
Published: March 2009

The mechanical behavior of unsaturated cohesive soils under different common stress conditions, that is, static compression, dynamic shear, and repetitive compression, is considered as a function of induced initial matrix suction by desorption from the initially saturated state. The hysteresis of moisture retention is considered outside the scope of this work. The test results suggest that the moisture regime can be expressed most suitably in terms of matrix suction. The data suggest that a rather definite change in stress-strain response takes place at a critical value of the matrix suction with modulus values, in general, dropping beyond the critical suction. The direct measurement of the total soil suction in the laboratory in connection with the triaxial compression test is sought by use of thermocouple psychrometers. The total suction of the soil decreases as the applied stresses increase; the quantitative relationship is complicated by a number of factors. The matrix suction appears to be the fundamental suction component controlling the mechanical behavior during a desorption schedule. This implies certain limitations for the use of psychrometers alone in indexing the mechanical behavior of soils, especially if they have a significant osmotic suction component.
A Servo System for Controlled Stress Path Tests
Authors: Law KT
Published: March 2009

This paper describes a servo system capable of imposing a prescribed stress path for the study of soil behavior in the laboratory. Various conditions were examined: (1) stress paths resembling those in the field, (2) both axisymmetric and plane strain shearing, and (3) large strain or post failure (or yield) state.

The servo system is composed of two main parts: A minicomputer and an electric-pneumatic (E/P) transducer. The minicomputer collects and processes data while the experiment is in progress. The appropriate electrical signals are transmitted to the E/P transducer, which regulates the pressure connected to the back-pressure line of the triaxial or plane strain apparatus. With the axial load applied at a constant strain rate, it is possible to measure the complete stress-strain behavior, including that at large strains, along a prescribed stress path.

A series of tests was carried out to illustrate the capability of the servo system. For the particular case of slope stability analysis, another series of tests was conducted from which peak and post-peak strength envelopes were obtained.
A New Control System for Soils Testing
Authors: Mitchell RJ
Published: March 2009

In load-deformation testing of soils it is generally necessary to supply both fluid pressures and direct loads (forces) on the sample boundaries. In addition, soils are tested under both controlled load and controlled deformation. Often three separate systems exist in a standard soils laboratory: gear driven presses, dead load hangers, and a regulated fluid pressure system. This paper describes a control system that employs commercially available rolling diaphragm cylinders and micro-flow needle control valves to supply simple and economical control for soils testing.
Effect of Shearing Strain-Rate on the Undrained Strength of Clay
Authors: Cheng RYK
Published: March 2009

Dynamic testing method is required to determine the strength of soils for problems of dynamic loading. This paper presents an experimental technique for measuring the relationship of undrained shear strength and strain-rate of a clay. Torsion tests were performed on remolded hollow cylinder specimens. The test results show that the undrained shear strength increases initially with strain-rate from the static undrained strength, but subsequently the undrained strength reaches an ultimate value as the strain-rate increases.
State of the Art: Data Reduction and Application for Analytical Modeling
Authors: Ko H-Y , Sture S
Published: March 2009

Due to the availability of large digital computers and advances in computational analysis techniques, it has become feasible to perform stress analyses of geotechnical structures involving complex geometries and material behavior. A key element in such analyses is the proper modeling of the constitutive behavior of soils.

Intensive research in recent years has led to a proliferation of constitutive models which have been postulated to represent soil behavior under general loading conditions. In this paper some of these models are reviewed regarding their basic assumptions and the requirement of input data for their characterization. A classification of constitutive models is given on the basis of basic approaches to relating stress and strain. Representative models from each class are selected for detailed examination, with the hyperbolic model, the elastic—perfectly plastic model, the Cam-Clay model, the cap model, Lade's model, Prevost's model, and the endochronic model being selected. Finally, a comparison is made of these models regarding their range of applicability.
Comparison of Shear Strength Values Derived from Laboratory Triaxial, Borehole Shear, and Cone Penetration Tests
Authors: Lambrechts JR , Rixner JJ
Published: March 2009

To determine the shear strength of two different soils, in situ and laboratory tests were performed and the results compared. The soil shear strength parameters were required to evaluate the cause of movements of a steel sheet pile cofferdam in which piles were being driven for a bridge pier. Two in situ techniques, the Quasi-Static Cone Penetration Test and the Borehole Shear Test, and laboratory CIU triaxial compression tests were used to determine the drained shear strength parameters (¯c and ¯φ) of silt and varved silt soils. Shear strength parameters derived from all three procedures were in close agreement. The angle of internal friction of the varved silt ranged from 28 to 33 deg, and the range for the silt was 32 to 36 deg. Soil densification during sampling and sample transportation is thought to have slightly increased ¯φ-values from the CIU tests. Based on field observations, slope inclinometer measurements, and tension crack occurrence around the land-side of the cofferdam, it was concluded that a “classical” active earth pressure wedge acted against the land-side of the cofferdam. An overall equivalent ¯φ, ranging from 26 to 34 deg, was derived from the location of this wedge.
Behavior of an Overconsolidated Sensitive Clay in Drained K0-Triaxial Tests
Authors: Silvestri V
Published: March 2009

In order to understand the mechanisms that govern the development of lateral stresses in overconsolidated clay deposits, specimens of an undisturbed sensitive clay from Lachute (P.Q.) were tested in a triaxial chamber under K0-conditions. The results of these tests show that the response of the clay can be divided into three distinct phases of deformation. At low stress levels, the clay behaves as an elastic material. At intermediate stress levels, the clay behaves as a plastic material. At high stress levels, the clay becomes normally consolidated.

The experimental data are used to establish a model describing the mobilization of lateral stresses, and it is shown that the in situ coefficient of earth pressure at rest cannot be determined by laboratory testing. The theory of anisotropic elasticity is used to predict the development of lateral stresses and pore water pressures at low stress levels. Predicted values are compared with those measured underneath the St. Alban (P.Q.) test fills.
Discussion of Soil Testing Practices
Authors: Poulos SJ
Published: March 2009

Six questions concerning the advantages and limitations of equipment for measuring shear strength of soils, and related test errors, were posed to the author. The responses are given in this paper. Emphasis is placed on the need to understand the shape of the stress-strain curve when selecting the apparatus. This need arises in soil testing because the soil type, soil structure, state, and stress path all have a strong influence on the stress-strain curves. Details of testing that are discussed are: (1) used of undisturbed or compacted specimens, (2) when to test partially saturated soils, (3) backpressure saturation, and (4) membrane penetration effects. Some suggestions for needed research are given.
Development, Testing Requirements, and Fitting Procedure of Elastic-Plastic Models
Authors: Baladi GY
Published: March 2009

During the past few decades the dramatic growth of computer technology has been paralleled by an increasing degree of complexity in material constitutive modeling. This paper discusses the development, testing requirements, and fitting procedure of elastic-plastic models.

A brief overview of the general characteristics of soil behavior which should be displayed by an elastic-plastic model is presented. The basic requirements and conditions of constitutive models are stated.

To construct an elastic-plastic type model the following (minimum) tests are required: (1) loading and unloading in isotropic consolidation and (2) loading and unloading in triaxial shear. Additional tests, such as uniaxial strain tests, proportional loading tests, direct shear tests, etc., are useful for verification of the model fits.
Fatigue Growth of Initially Physically Short Cracks in Notched Aluminum and Steel Plates
Authors: Leis BN , Forte TP
Published: March 2009

Much of the fatigue life of engineering structures is spent initiating cracks at a notch and propagating one (or more) of these cracks into and through the notch stress field. Experimental results and empirical analysis suggest that early in this process the physically small crack sometimes propagates in a manner inconsistent with analysis based on linear elastic fracture mechanics (LEFM). Available empirical adjustments for this apparent aberration postulate that the data can be made consistent with LEFM by the addition of a constant, with length dimensions, to the current crack length, resulting in a pseudo-crack.

The present paper introduces and analyzes an extensive data set pertinent to this so-called short-crack problem. Included are results for notched plates made from two aluminum alloys and a steel. These plates, which contain either circular or one of two different elliptical notches, have been tested under load or displacement control and encompass both confined flow and gross-section yield. Results for crack lengths as small as 20 μm (0.0008 in.) are reported.

Data presented and analyzed do indeed show trends which differ from those of LEFM analysis of so-called long cracks. More significantly, they show that the so-called short-crack behavior does not occur only for physically short cracks. Results presented indicate that cracks as large as 2.5 mm (0.1 in.) in the aluminum alloys and 1.25 cm (0.5 in.) in the steel also exhibit aberrations in their behavior as compared with longer-crack trends. Also, the results presented suggest that the data cannot be made consistent with the LEFM trend through the addition of a constant pseudo-crack length to the current crack size as has been suggested in one of the currently popular empirical models. It is postulated that the aberrations observed are a consequence of the failure of the LEFM-based analyses to recognize that crack growth in the plastic field of the notch is dominantly displacement-controlled local to the crack tip. Other relevant aspects of the problem are also discussed.
Final Stretch Model of Ductile Fracture
Authors: Wnuk MP , Sedmak S
Published: March 2009

The differential equations defining the material resistance developed during the early stages of a ductile fracture process are derived from the concept of “final stretch.” The model suggests a certain near-tip distribution of displacements associated with a quasi-static Mode I crack such that the resulting strains are logarithmically singular at the crack tip.

The final results, which are illustrated by the diagrams of J-resistance curves, are equivalent to analogous data obtained by other researchers on the basis of the incremental plasticity theory. Similarities between the present results and the solutions due to Paris and co-workers as well as the most recent data obtained by Shih and co-workers are pointed out.
Effect of Higher-Order Stress Terms on Mode-I Caustics in Birefringent Materials
Authors: Phillips JW , Sanford RJ
Published: March 2009

A general theory is developed for determining the sizes, shapes, and locations of the double caustics produced in statically loaded birefringent plates containing Mode-I cracks. Particular attention is paid to the effect of the first few higher-order, non-singular stress terms on the determination of the stress-intensity factor KI associated with the singular stress field.

It is found that the transverse diameters of the inner and outer parts of the double caustic have an average value essentially equal to the transverse diameter of the single caustic produced by an optically isotropic material having the same optical constant. Furthermore, with the superposition of a constant (tensile or compressive) stress parallel to the crack, each part of the double caustic deforms independently but in such a way as to maintain this average transverse diameter.

Other higher-order effects are also investigated and it is concluded that birefringent materials offer the potential of “feature extraction” concerning crack-tip stress fields, in addition to being suitable for the accurate determination of KI-values experimentally.
Influence Functions for Stress-Intensity Factors at a Nozzle Corner
Authors: Heliot J , Labbens R , Robisson F
Published: March 2009

Influence functions are computed for the calculation of stress-intensity factors along partly circular cracks in nozzle corners subjected to pressure hoop stress linearly represented in the plane of the crack. The boundary integral equations method is used. The results are compared with those of previous studies.
Stress-Intensity Distributions for Natural Flaw Shapes Apprximating ‘Benchmark’ Geometries
Authors: Smith CW , Peters WH , Kirby GC , Andonian A
Published: March 2009

Because of its importance and frequency of occurrence, considerable effort has been devoted to the modeling of subcritical surface crack growth in recent years. Due to the geometrical complexities involved, available solutions are generally constrained to elastic numerical models implying self-similar crack growth. By selecting specific geometries (known as ‘benchmark’ geometries) and solving for stress-intensity factor distributions, several of these numerical models have recently exhibited reasonable agreement by assuming semi-elliptic crack shapes (see Ref 6). Over the past decade, the first author and his colleagues have evolved an experimental technique which couples the field equations of linear elastic fracture mechanics with the frozen stress photoelastic method for generating natural crack shapes and their corresponding stress-intensity distributions where neither are known a priori. The present paper focuses upon the application of this technique to two surface crack geometries approximating benchmark geometries and comparing with results from the recent literature in order to assess the validity of the semi-elliptic crack shape assumption for the surface crack in numerical models and to quantify any observed deviations. Results show that shallow crack shapes (a/2c ≈ 0.30 a/T ≈ 0.30) are accurately described by the semiellipse assumption, and the experimental stress-intensity distributions seem to be predicted with reasonable accuracy in regions of highest values. The deeper cracks, however (a/2c ≈ 0.30 a/T ≈ 0.75), exhibit a deviation in shape from a quarter-ellipse in the form of bulging near the points of intersection of the flaw border with the plate front surface, and the accompanying maximum stress intensities are some 25 percent higher than the values predicted in Ref 6 using semi-elliptic crack models with the same aspect ratio and a/T.