bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Gravel Stiffness by Pulse Wave Transmission Tests
Authors: Modoni G , Flora A , Mancuso C , Viggiani C , Tatsuoka F
Published: February 2009

Laboratory techniques for the measurements of very small strain stiffness parameters of coarse-grained materials include: (a) static tests using local strain transducers like LDTs and (b) wave propagation measurements performed using bender elements, shear plates, and so on. The former method has been employed for most kinds of soil, while the use of wave propagation methods has been restricted to small specimens of sand and clay. At the University of Naples Federico II (DIG), a simple device to generate and monitor compressional and shear waves has been designed to be used in large-scale triaxial apparatuses. The testing device was first used on densely compacted gravel specimens in a large triaxial apparatus in Naples and, after some further improvements, also in another large triaxial cell in Tokyo. In the tests carried out in Tokyo, dynamic and static measurements were performed simultaneously on the single gravel specimens. In this paper, the details of the new system are presented and the results are discussed. The comparison between stiffness moduli evaluated by dynamic and static measurements shows that density, stress state, and strain history effects are similar, but that the dynamically measured stiffness values are consistently larger, about two times, than the statistically determined ones. Since the stiffness of gravels has proven to be strain rate independent, possible reasons for this difference are addressed.
Variations in Membrane Contact Patterns of Reconstituted Sand Specimens
Authors: Saussus DR , Frost D , Ashmawy AK
Published: February 2009

The penetration of the latex membrane into the peripheral voids of a sand specimen during application of confining stress can cause significant errors in subsequent triaxial test results. Analytical solutions are commonly used to account for this source of error by predicting the shape of the deflected membrane based on a sand particle-membrane contact pattern assumed to be represented by four spheres of diameter D50 whose centers form a square of length D50 on a plane parallel to the undeflected membrane. This paper presents the findings of a study that used image analysis to study actual contact patterns and compare these with the generally assumed configuration. The results show that the generally assumed constant configuration does not reflect the variability of actual patterns, which are a function of the specimen relative density and preparation method and may therefore grossly underestimate the amount of membrane penetration. The study shows that an increase in relative density results in a decrease in inter-contact distance, regardless of the specimen preparation method, and that the inter-contact distance at the sand-membrane interface is larger and more variable for moist tamped than air-pluviated specimens at any given density. These observations suggest that the sand-membrane contact patterns assumed by future analytical solutions, as a minimum, will need to take specimen relative density and preparation method into account if the amount of membrane penetration is to be more accurately predicted.
A Triaxial and Oedometer Apparatus for Testing Unsaturated Soils
Authors: Aversa S , Nicotera MV
Published: February 2009

The paper describes a new system for testing unsaturated soils designed at the University of Naples Federico II. The system is modular and can be configured either as an oedometer or a triaxial cell. Triaxial specimens are 68 mm in diameter and 140 mm in height, and oedometer specimens have a diameter of 56 mm and a height of 20 mm. The suction control is based on the axis translation technique. Radial strains are determined by an accurate measurement of the difference in pressures between the water filling an inner cell coaxial to the sample and that filling a reference double-walled burette, submitted to the same pressure. The water content variations are determined by measuring the difference in pressure in two double-walled burettes, one of which being connected to the drainage circuit, the other one operating as a reference. The calibration of all the devices, as well as their precision and accuracy, is widely discussed in the paper. Finally, the results of tests performed on an unsaturated pyroclastic soil are presented in order to highlight the features of both apparatuses.
A Miniature Soil Inclusion for Measuring Axial Force and Radial Stress
Authors: Standing JR , Burland JB
Published: February 2009

This paper describes the design, development, and manufacture of a miniature soil inclusion 175 mm long and 8 mm in diameter for measuring axial force and radial stress at three points along its length. The individual devices rely on strain gages for their operation and were found to be stable in a laboratory environment. The axial force and radial stress measurements can be resolved to less than 1 N and 1 kPa, respectively. The model inclusion has been used in a study to investigate the development of shear stress along a soil nail. The instrumentation allowed the influence of arching to be positively identified. The paper includes discussion of factors such as calibrating for cross-effects, converting the electrical outputs to engineering units, and cell-action effects. These factors along with the soil stiffness govern the accuracy of measurement.
Mechanical Properties of Shredded Tires
Authors: Yang S , Lohnes RA , Kjartanson BH
Published: February 2009

The use of scrap tires as construction materials in civil engineering applications is one of the most promising ways of recycling this troublesome waste material. Design of scrap tire structures, however, requires data on engineering characteristics of tire-derived materials. Confined compression, direct shear, and triaxial tests were carried out to evaluate the mechanical characteristics of tire chips approximately 2 to 10 mm in size. These test results were synthesized with data from previous shredded tire studies to generate empirical relationships between normal stress and direct shear strength and between confining pressure and initial tangent modulus from triaxial testing. It was found that the shear strength of shredded tires is independent of the particle size of the material, and the strength envelope is a power function for normal stresses from 0 to 90 kPa. The initial tangent modulus relates to confining pressure through a quadratic equation, and the lateral strain ratio is independent of confining stress.
Effects of Small Cement Content on Consolidation Behavior of a Lacustrine Clay
Authors: Feng T-W
Published: February 2009

Natural soft clays are frequently encountered in civil engineering projects. Such soils possess large compression potential that needs to be alleviated by means of effective ground improvement techniques. Current knowledge on mixing soft clay with small cement content to improve its consolidation properties is limited. This study looks into the consolidation behavior of undisturbed lacustrine soft clay treated with small cement contents. Based on the pH values of soft clay and cement mixtures, small cement contents of 3 and 6% were chosen to prepare soft clay-cement oedometer specimens. The oedometer test results show that the preconsolidation pressure may be decreased or increased, depending on the cement content added. The secondary compression index is reduced and the ratio of secondary compression index to compression index is also reduced, indicating a change in grain size characteristics. The coefficient of consolidation is reduced for consolidation pressures near the effective overburden pressure and is about equal or slightly increased for consolidation pressures higher than the preconsolidation pressure. These data indicate that treating natural soft clay with cement at small cement contents can be effective in reducing both primary and secondary settlements.
An Improved Statistically Based Technique for Evaluating the CPT Friction Ratio
Authors: Jaksa MB , Kaggwa WS , Brooker PI
Published: February 2009

This paper examines a statistical technique known as the cross-correlation function (CCF) for determining the shift distance associated with the cone penetration test (CPT). When evaluating the friction ratio, FR ( = fr/qc), for soil classification purposes, it is essential that the measured values of ), for soil classification purposes, it is essential that the measured values of qc and fs are shifted relative to one another because of the physical offset between the cone and the friction sleeve. Generally, the shift distance is estimated by means of empirical and subjective methods, a value of 75 to 100 mm is adopted, or it is ignored all together. Using a series of case studies, this paper demonstrates that the CCF is a useful and objective technique for estimating the shift distance. In addition, a phenomenon associated with sleeve friction measurements related to elastic rebound of clay soils is discussed.
Determination of Water Saturation Using Miniature Resistivity Probes During Intermediate Scale and Centrifuge Multiphase Flow Laboratory Experiments
Authors: Kechavarzi C , Soga K
Published: February 2009

Physical modeling is essential to the conceptual understanding of the mechanisms governing multiphase flow in porous media. However, the need for accurate data is hampered by the limited amount of appropriate instrumentation designed to measure fluid saturation in three-fluid phase flow experiments. In centrifuge testing, this is accentuated by the fact that the instruments must be small and resistant to the effects of increased gravity. Miniature resistivity probes, developed at Cambridge University Engineering Department (CUED), were used to determine water saturation variations during a centrifuge test and a 1 g two-dimensional multiphase flow experiment. These experiments were conducted to study the migration of light non-aqueous phase liquids (LNAPL) in unsaturated sands. Prior to the tests, the resistivity probes were calibrated against the water saturation of unsaturated sand samples. The calibration relationship was compared to Archie's law. The miniature probes proved to be a valuable tool for monitoring water saturation variations during three-fluid phase flow under 1 g conditions, as well as under the accelerated gravity field of 20 g.
Development of a Multiple-Purpose Borehole Testing Device for Soft Rock
Authors: Huang A-B , Fang C-K , Liao J-J , Pan Y-W
Published: February 2009

The authors developed a versatile in situ testing device specifically for soft rock. The main purpose of this device was to provide design parameters for shallow or deep foundations in soft rock. The new device, referred to as the Borehole Testing Device (BTD) consisted of four radial curved platens at the top and a circular steel plate at the bottom. The BTD was designed to be used in a 200-mm-diameter borehole. Driven by a high stress pressuremeter and a hydraulic piston, the BTD can be used to perform a borehole jacking test, plate-loading test, and borehole shear test in the same borehole. A multistage testing procedure was proposed to perform the BTD test. This paper describes the design and operation of the BTD and presents a set of test data to demonstrate the capabilities of the BTD.
Interpretation of Seismic Piezocone Results for the Estimation of Hydraulic Conductivity in Clays
Authors: Burns SE , Mayne PW
Published: February 2009

Seismic piezocone penetration tests with dissipation phases provide sufficient data for outlining the geostratigraphy, soil strength, stiffness, and flow characteristics in fine-grained soils. The dissipation of excess pore water pressures with time can be monitored at regular intervals (e.g., at 1-m rod breaks) and provides information on the coefficient of consolidation (ch). Monotonic and/or dilatory responses of Δu decay can be accommodated. The shear wave velocity (Vs) provides a measure of the small-strain stiffness (G0), or surrogate evaluation of the constrained modulus (D′). A sampling of data from ten clay sites was used to assess the derived magnitude of hydraulic conductivity, as determined from k = chγw/D′.
The Danish Rigid Boundary True Triaxial Apparatus for Soil Testing
Authors: Bo Ibsen L , Prasstrup U
Published: February 2009

The intermediate principal stress plays an important role for the stress-strain behavior of soils. The effect of the intermediate stress cannot be examined in the conventional triaxial apparatus since axisymmetric stress states are prescribed in it. Thus, other testing devices capable of producing asymmetric stress states are necessary for more accurate determination of the stress-strain behavior. This paper describes the Danish rigid boundary true triaxial apparatus developed at Aalborg University and the techniques employed to prepare and test specimens of clay and sand for effects of the intermediate stress. Three series of true triaxial tests are presented together with various conventional triaxial tests to illustrate the capabilities of the apparatus. The first series of tests was carried out on cross-anisotropic specimens from a natural clay deposit. The other two series were carried out on air-pluviated (frozen and unfrozen) specimens of sand that also showed cross-anisotropic behavior.
A Cyclic Gradient Ratio Test Device
Authors: Hameiri A , Fannin RJ
Published: February 2009

Gradient ratio test results are reported from the commissioning of a device that was modified to impose dynamic cyclic flow. The flow conditions, using head control, are similar to those in marine protection works. Each test included a stage of unidirectional flow, followed by stages of cyclic flow at a frequency of 0.2 Hz and 0.02 Hz. Flow reversal invokes an initial transient state of water head distribution in the sample, attributed to changes in hydraulic gradient to accommodate the new values of constant head at the inflow and outflow. Consequently, tests at the higher frequency yielded unsteady flow in the sample, while tests at the lower frequency resulted in steady flow during each half cycle. In unsteady flow, the transient state of water head distribution (and hence gradient ratio) cannot serve as an index of soil-geotextile compatibility. Therefore, a recommendation is made that testing of filtration compatibility in dynamic cyclic flow include a stage of slow flow reversal (or alternatively unidirectional flow) to permit a quantification of water head distribution under steady flow.
One-Dimensional Shock-Induced Pore Pressure Response in Saturated Carbonate Sand
Authors: Veyera GE , Charlie WA , Hubert ME
Published: February 2009

Experiments were performed to investigate the transient undrained pore water pressure response of a shock-loaded saturated carbonate sand (Enewetak coral sand). Specimens were dynamically loaded using an experimental laboratory facility capable of generating compressive shock pulses with millisecond rise times to peak stress. Boundary conditions were for one-dimensional confined compressive loadings without drainage. Pore water pressure increases of 50% or more were observed at compressive strains above about 0.01%. For most tests, liquefaction was observed at peak compressive strains in excess of about 0.10%. An empirical equation for estimating pore water pressure increases from transient compressional shock loadings was developed from a statistical analysis of the data. A silica sand, Monterey No. 0/30, has also been previously tested in this apparatus and a comparison is made. The residual excess pore water pressure equations for Enewetak coral and Monterey No. 0/30 sands are presented. Test results indicate that the response of these two sands is markedly different. Residual excess pore water pressures are proportional to approximately the square root of peak compressive strain for Enewetak coral sand and approximately the cube root of peak compressive strain for Monterey No. 0/30 silica sand. Measured static C parameter values were consistently less than unity for all saturated specimens of Enewetak coral sand tested. The C parameter decreased with increasing specimen density and effective stress.
Polymer Capacitance Sensors for Measuring Soil Gas Humidity in Drier Soils
Authors: Albrecht BA , Benson CH , Beuermann S
Published: February 2009

Polymer capacitance sensors were assessed in this study for measuring soil gas relative humidity and total suction in soils that are too dry for thermocouple psychrometers. Capacitance of the sensors varies as the relative humidity of the gas surrounding the sensor is varied. Soil gas relative humidity is inferred through a calibration curve relating soil gas relative humidity and capacitance. Tests conducted with six finer textured soils and three sands showed that the capacitance sensors can be used to obtain unbiased estimates of relative humidity for a broad variety of soils with a precision of approximately ±3%. Tests also showed that the sensors are non-hysteretic and relatively insensitive to temperature, except when the temperature approaches the freezing point of water. An example is provided illustrating how capacitance sensors can be used to monitor soil gas relative humidities in alternative earthen final covers that employ passive flow of atmospheric air to remove water.
New Wave Equation Technique for High Strain Impact Testing of Driven Piles
Authors: Liang RY
Published: February 2009

The real time records of force and velocity measured at the pile head during each hammer impact constitute the so-called high strain test (HST) data in the modern wave equation technology in connection with pile-driving activities. Currently, the Case method and the CAPWAP match procedure represent the state-of-art in interpreting HST data to obtain useful information, such as bearing capacity of a pile, soil-pile interaction model parameters, and the hammer performance, etc. A new HST data interpretation procedure based on wave equation theories is developed in this paper. For the case where only toe resistance exists, the new method utilizes both force and velocity records to analytically compute the corresponding dynamic soil resistance at the toe of an impact-driven pile. An inverse optimization scheme is developed to use these analytically computed quantities to determine the pertinent soil-pile interaction model parameters. Examples are given to illustrate the use of the new method to determine the pertinent Smith model constants commonly used in modeling the dynamic soil-pile interactions. The developed algorithm is also successfully extended to the case in which both shaft and toe resistances are involved during pile driving.
Shear and Interface Strength of Clay at Very Low Effective Stress
Authors: Pedersen RC , Olson RE , Rauch AF
Published: February 2009

Thin-specimen direct shear (TSDS) tests were conducted to measure the shearing strength of kaolinite, and interface strengths between kaolinite and acrylic plastic and anodized aluminum, at normal effective stresses from 1 to 2400 Pa (0.02 to 50 lb/ft2). At the lowest effective normal stresses, curved strength envelopes fitted through the data exhibited no cohesion and high secant friction angles. Accurate information on the behavior of soil in this low-pressure range is needed to properly interpret the behavior of prototype foundations in laboratory-scale model tests.
Method for Determining the Coefficient of Permeability of Clays
Authors: Moriwaki T , Umehara K
Published: February 2009

A new method for directly determining the coefficient of permeability of clays from the constant rate of strain consolidation tests was proposed by Yoshikuni et al. (1995). In order to confirm the reliability of this method, the constant rate of strain consolidation tests under three kinds of strain rates were carried out on four kinds of clays in this study. The permeability tests using a flow pump and the conventional consolidation tests were also carried out on the same clays for comparing the coefficient of permeability obtained from each test. As the results, it was found that the coefficient of permeability obtained by the proposed method from the constant rate of strain consolidation tests agreed with the coefficient of permeability obtained from the permeability tests.
A Substitute Pore Fluid for Seismic Centrifuge Modeling
Authors: Dewoolkar MM , Ko H-Y , Stadler AT , Astaneh SMF
Published: February 2009

In seismic centrifuge modeling, a time-scaling conflict exists between dynamic and dissipative phenomena. To help alleviate this fundamental problem, a substitute pore fluid consisting of powdered methylcellulose (known commercially as Metolose) dissolved in water was studied. The methylcellulose-water mixtures are referred to as “metolose” in general from here on. To examine the suitability of this substitute pore fluid, an experimental program was conducted using water- and metolose-saturated sand specimens. The program included triaxial compression tests, permeability tests, and a seismic centrifuge experiment on level ground models. In addition, modeling of models type experiments were conducted on metolose-saturated embankment and retaining wall models. Results from the triaxial tests indicated that the constitutive behavior of the saturated sand specimens was not significantly altered with metolose as the pore fluid. Results from the permeability tests showed that the scaling requirements of the centrifuge environment were satisfied. The centrifuge experiments demonstrated clearly that the conflict between the dynamic and consolidation time scales exists and reinforced the need for a substitute pore fluid in tests designed to model prototype behavior. Based on this experimental program, metolose was found to be an acceptable substitute pore fluid.
The Use of Miniature Pore Pressure Transducers in Measuring Matric Suction in Unsaturated Soils
Authors: Muraleetharan KK , Granger KK
Published: February 2009

Matric suction (pore air pressure minus pore water pressure) is an important stress state variable in unsaturated soil mechanics. Currently available devices to measure matric suction suffer from one or more of the following: bulky construction, long time to reach equilibrium, high sensitivity to temperature, and inability to produce continuous output. Tests were conducted using a miniature pore pressure transducer (PDCR81), traditionally used to measure positive pore water pressures in saturated soils, to measure matric suction in unsaturated soils. The results were compared with measurements from a conventional Bourdon-type tensiometer. Due to the small volume of fluid in the measuring chamber, the PDCR81 reached equilibrium much faster than the tensiometer and is more responsive to changes in pore water pressure. However, incomplete saturation produced greater errors in PDCR81 measurements. An increase in the saturation fluid viscosity of the PDCR81 increased the time to reach and maintain equilibrium.
The Effects of Varying Centerline Tube Sampling Disturbance on the Behavior of Reconstituted Clay
Authors: Siddique A , Clayton CRI , Hopper RJ
Published: February 2009

In order to simulate varying degrees of disturbance of soil at the centerline of a tube sampler, triaxial stress and strain path tests have been carried out on normally consolidated and overconsolidated reconstituted London clay specimens. The tests were carried out using an automated system capable of controlling both stresses and deformations imposed on specimens. The specimens were instrumented with local axial and radial strain and mid-plane pore pressure measuring devices.

Test results indicate that the most pronounced effects due to imposed tube sampling strains in reconstituted normally consolidated London clay are significant reductions of mean effective stress and undrained small-strain stiffness, which are accompanied by reductions in the excess pore pressure generated during shearing. The higher the magnitudes of tube sampling strains, the greater the change in behavior. In over-consolidated reconstituted London clay, however, laboratory simulation of tube sampling strains together with deviatoric stress relief (i.e., “ideal” sampling) causes little change in effective stress, stiffness, and strength.
Shrinkage Limit of Soil Mixtures
Authors: Sridharan A , Prakash K
Published: February 2009

Shrinkage limit, one of the Atterberg limits, is widely linked with many plasticity-based soil behaviors. However, in a great majority of these cases, such correlations have been found to exhibit poor performance. Recently, it has been brought out that the shrinkage limit of a natural soil does not depend upon plasticity characteristics, and it is primarily governed by the relative grain size distribution of the soil. The present study confirms this mechanism with the results obtained using clay-clay, clay-non-cohesive soil, and non-cohesive soil mix systems. The present study gains importance from the point of view of criteria with respect to the design of back fill materials to be used in various applications, such as nuclear waste disposal projects.
Cyclic Response of Axially Loaded Tapered Piles
Authors: El Naggar MH , Wei JQ
Published: February 2009

Tapered piles have a substantial advantage over straight-sided wall piles with regard to their load-carrying capacity in the downward frictional mode; however, their behavior under cyclic axial loading has not been investigated. In this study, the characteristics of the cyclic response of tapered piles were established from experimental investigation. A large laboratory facility for testing model piles was developed. In this facility, the soil was contained in a steel chamber and pressurized using an air bladder to model the confining pressure. Three instrumented steel model piles with different degrees of taper were installed in loose sand and subjected to two-way cyclic axial load tests. The results of this study indicated that the pile stiffness under cyclic loading increased with an increase in the confining pressure for all piles examined in this study. Moreover, the pile stiffness increased through cyclic loading due to the densification of the sand surrounding the pile. The amplitude of the cyclic load had a significant effect on the performance of the piles. As a result, it is recommended that the amplitude of the cyclic load be limited to 25% of the static axial capacity and 75% of the static uplift capacity to ensure satisfactory performance of tapered piles. This requirement is readily satisfied in the design of most piles. In this case, the performance of tapered piles under cyclic axial load was found to be superior to that of straight-sided wall piles.
Particle Motion Tracking Utilizing a High-Resolution Digital CCD Camera
Authors: Paikowsky SG , Xi F
Published: February 2009

Digital imaging acquisition and processing is applied for the tracking of a two-dimensional assembly of disks. The disks are used to assemble models for studying granular material behavior for which the kinematics of the individual particles, and hence the disks' trajectory during motion, are of cardinal importance. Large particle size is dictated by photoelastic interparticle interaction analysis. Therefore, a sufficiently large representative number of particles results in a large physical model.

The system requirements of a sizable physical model comprised of a large number of particles, and simultaneous precise tracking of all particles, are achieved through the use of high-resolution digital CCD camera and semi-automatic image processing and analysis algorithms.

The physical system setup, image acquisition procedure, calibration, accuracy, and algorithms of analysis are described. The system's performance is demonstrated through test results describing the displacement field along with the motion and interaction of individual particles.

The system's advantages in providing detailed tracking of a large number of particles with minimal labor are unmatched by any other technique. The data obtained by such systems allow a better understanding of particulate media behavior with the ability to examine and calibrate numerical models on an individual grain basis.
Modified Triaxial Apparatus for Shearing-Infiltration Test
Authors: Wong J-C , Rahardjo H , Toll DG , Leong E-C
Published: February 2009

A triaxial apparatus was modified and developed for performing shearing-infiltration tests under saturated and unsaturated conditions. Miniature pore-water pressure transducers were installed at different heights of the soil specimen for pore-water pressure measurement. Two different types of miniature pressure transducers were used, and problems associated with the transducers are discussed. Ancillary works and equipment to install the miniature transducers onto the soil specimen are also discussed. The measurement of air entry value of the small disk in the transducer was found to be very difficult. The results show that the soil specimen failed during infiltration due to increase in pore-water pressure or decrease in matric suction.
Retaining Wall Model Test with Waste Foundry Sand Mixture Backfill
Authors: Lee K , Cho J , Salgado R , Lee I
Published: February 2009

This paper presents experimental data concerning the lateral earth pressures acting against a small-scale retaining wall, with a backfill consisting of waste foundry sand (WFS) mixtures. The instrumented retaining-wall facility at Dongeui College in Korea was used in the testing. Two different testing methods were employed in this study: the controlled-strain method and the natural-strain method. The lateral earth pressures on the wall depend on the backfilling sequence, the type and drainage characteristic of the WFS mixture, and the shear strength of the mixtures. The mixtures of Green WFS performed best, showing a decrease in the lateral earth pressures and an increase in cohesion with curing time. The measured thrust lateral earth pressure of WFS mixtures was less than that observed for common residual soils in Korea. The stability of the retaining wall with respect to overturning and sliding, calculated using the measured lateral earth pressures, increased substantially with curing time. Judging from the retaining wall model test, the backfilling of a 6-m high retaining wall can be completed in two days with two backfilling stages.
Investigation of Resonant Frequency and Amplitude of Vibrating Footing Resting on a Layered Soil System
Authors: Baidya DK , Krishna GM
Published: February 2009

Influence of layering and presence of rigid boundary in the soil mass on natural frequency and resonant amplitude are studied experimentally by conducting model block vibration tests in vertical mode. Tests are conducted on different layered beds prepared in a tank using a model footing. A Lazan type mechanical oscillator is used for inducing vibration and two different materials (sand and sawdust) are used to form a layered system. In total, 180 tests are conducted in different layering combinations and different static and dynamic loading combinations, and several important observations are reported. Damping factors are found to be within 6.5% for the entire test series, which indicates that radiation damping is insignificant in the test system. It is also found that layering including layer position and thickness has significant effect on natural frequency. Observed natural frequencies are also compared with the predicted one based on static equivalent stiffness; encouraging agreement between observed and predicted values are found.
Effect of Compaction Duration on the Induced Stress Levels in a Laboratory Prepared Sand Bed
Authors: Hanna AM , Soliman-Saad N
Published: February 2009

In foundation engineering, due to the complexity of the problems investigated, the need for laboratory testing of prototype models arises. The results of these tests are usually utilized to validate theories, or to develop empirical formulae for design purposes. The success in obtaining good predictions from these theories and empirical formulae lies heavily on the reliability of the experimental test results, and accordingly, on the test setup used and the procedure followed.

In literature, a wide range of discrepancies can be found among various design theories for shallow and deep foundations in cohesionless soils. These discrepancies can be explained by the fact that the in situ stress levels in the prototype model have not been evaluated but rather ignored, in developing design theories. Accordingly, different theories may generate different results, depending on the techniques and procedures followed in developing the experimental results used to validate the theory.

This paper presents the results of an experimental investigation on the effect of compaction duration in a prototype model on the mechanical properties, and the induced stress levels in the sand mass. The results of this investigation should develop some awareness of the validity of using the results of model testing as a guide in developing design theories. Furthermore, attempts should be made to measure and incorporate the in situ stress level as a governing parameter in design theories.
Shear Strength Characterization of Geosynthetic Interfaces on Inclined Planes
Authors: Lalarakotoson S , Villard P , Gourc JP
Published: February 2009

Tests to characterize the shear strength of geosynthetic interfaces under low confinement pressure were carried out on an instrumented inclined plane apparatus designed at Lirigm. The apparatus was validated through repeatability and reproducibility tests carried out as part of the European project to standardize geosynthetic interface tests. Typical results obtained for geosynthetics of different textures are presented and discussed. Finally, interface test results obtained using the direct shear box under normal confinement pressure and on an inclined plane under low confinement pressure were compared and assessed.
Fast and Accurate Techniques for Determination of Water Content in Soils
Authors: Mendoza MJ , Orozco M
Published: February 2009

This paper describes expeditious and reliable procedures for determining the water content of soils that are alternative to the traditional convection oven technique. There exist linear relationships between the results of the conventional procedure and those obtained by the use of the microwave oven, direct heating of soils on a stove, distilling toluene, or burning alcohol to induce the evaporation of water; proportionality coefficients linking these results vary between 0.96 and 1.02. Microwave ovens are a much faster and cheaper means than convection ovens and are as reliable; for this technique, the mass of water that must be removed and the output power of the oven play the most important roles in defining the drying time for a soil.
Mechanical Durability of Expanded Shale Lightweight Aggregate
Authors: Valsangkar AJ , Holm TA
Published: February 2009

The paper presents results of a laboratory study that investigated mechanical durability of expanded shale lightweight aggregate. Large-size, one-dimensional cyclic compression and direct shear tests were performed to investigate particle breakage under these loading conditions. The results obtained are compared with the data reported by other researchers. The results indicate that the expanded shale lightweight aggregate experiences only a minor amount of particle breakage under one-dimensional compression and direct shear type of loadings.
Relative Moisture and Moisture Deficiency of Desiccated Expansive Cohesive Soil Deposits
Authors: Hanafy EADE
Published: February 2009

The concept of relative moisture in soil mechanics is introduced for assessing the in-situ moisture deficiency and moisture change potential of desiccated expansive clay layers. This paper introduces the terms moisture change potential (MCP), relative moisture (RM), and moisture deficiency (MD) in order to relate the in-situ moisture content to the corresponding equilibrium moisture content at saturation under the same applied pressure. This concept has been developed for sites having variations in moisture content to identify the desiccated zones and to correlate the moisture deficiency to the swelling potential. The paper also defines the saturation coefficient, Sv, as a new term that is numerically equal to the product of void ratio and percent saturation to correlate the initial and final moisture values. Furthermore, it emphasizes that the “relative moisture” term is different from the well-known terms of “degree of saturation” and “relative humidity.”

The suggested terms are found relevant for assessment of field monitoring records of heave-related movements when evaluating long-term stability of foundations, slabs-on-grade, and pavement as a result of moisture increase and when making recommendations of necessary precautionary measures. In addition, the relative moisture term, defined here, is found to be the more appropriate term to be adopted for soil deposits instead of the relative humidity term commonly borrowed and used.

Numerical examples and typical applications are included to illustrate the versatility and validity of the concept introduced. Selected laboratory data of a highly expansive clay are also included. For the application considered, zones of the clay layer showed relative moisture (RM) values of less than 50%, and moisture deficiency (MD) values of more than 100% were classified as highly desiccated. The concept of the relative moisture adopted in this study is concluded to offer a practical means of identifying and evaluating the degree of desiccation of expansive soils for nonuniform sites with varying layer depths and moisture conditions.
Constant Rate of Strain Consolidation with Radial Drainage
Authors: Seah TH , Juirnarongrit T
Published: February 2009

This paper describes a method of determining the consolidation characteristics of soft Bangkok clay under the radial drainage condition by using a newly developed constant rate of strain (CRS) consolidometer. A new formulation for this type of test was proposed. A series of constant rate-of-strain consolidation tests were compared to the results of oedometer tests. The pore water pressure distribution across the specimen in the CRS tests was estimated from measurements made at two locations. The results agreed well with the theoretical solution. A simple method of estimating the preconsolidation pressure by means of the pore water pressure ratio is also proposed. Because the tests conducted at different strain rates indicate that apparent preconsolidation pressure increases with strain rate, it is believed that secondary compression occurred during primary consolidation for this clay. The consolidation characteristics, including coefficient of consolidation and coefficient of permeability, in the vertical and horizontal directions were also compared.
Instrumentation of Anchored Segmental Retaining Wall
Authors: Yoo C , Lee KM
Published: February 2009

This paper presents the measured behavior of an anchored segmental retaining wall. In an attempt to understand the overall mechanical behavior of the anchored segmental retaining wall and to confirm the applicability of the design assumptions, an extensive monitoring program was implemented for a 7-m-high anchored segmental retaining wall. The measured horizontal earth pressures and the inferred tensile loads in the reinforcements indicated that the state of stress within the reinforced soil mass is higher than the Rankine active state of stress and that by Coulomb wedge analysis, approaching to that based on the FHWA design approach for inextensible reinforcements. The measured performance satisfied the minimum performance requirements for the internal stability with a maximum wall movement comparable to that reported for walls with inextensible reinforcements. The wall survived severe rainfalls during and after the wall construction, exhibiting an excellent performance in terms of drainage. Implications and findings from this study are discussed.
Performance Evaluation of Automated Machines for Measuring Gradation of Aggregates
Authors: Browne C , Rauch AF , Haas CT , Kim H
Published: February 2009

Several automated devices are commercially available for measuring the gradation of stone aggregates. These computerized machines, which provide a rapid alternative to manual sieving, capture and process two-dimensional digital images of aggregate particles to determine grain size distribution. Five of these automated gradation devices were evaluated for accuracy using fifteen aggregate test samples. To quantify how well the machine results compare with data from standard sieve analyses, the CANWE (Cumulative And Normalized Weighted Error) statistic was developed and used. While the machine data did not match the sieve data exactly, the evaluated devices were found to provide good measures of particle gradation for most samples. These tests also indicate that some machines will give more repeatable results in multiple tests of a given material, while others yield better results when testing different materials. The methodology used in this study is suitable for objectively evaluating the accuracy of other rapid gradation machines for various applications.
Design and Performance of a 1m Diameter Ring Shear Apparatus
Authors: Kelly R , Airey DW , Tabucanon JT
Published: February 2009

Constant Normal Stiffness (CNS) testing has evolved over the last 15 years in order to study the effects of soil deformations on the capacity of axially loaded piles. The majority of CNS testing in the laboratory has been carried out using modified shear box apparatus. However, results obtained from these apparatus may not accurately represent real behavior due to effects associated with the modifications to the shear box apparatus. The use of ring shear apparatus for CNS testing avoids many of the difficulties associated with modifying shear box apparatus. A large ring shear was constructed at the University of Sydney. This paper provides a description of the ring shear apparatus and some shakedown results to assess its performance.
Alternative Encasement Materials for Clod Test
Authors: Krosley L , Likos WJ , Lu N
Published: February 2009

The Clod test has been often used in the United States for obtaining the relationship between soil volume or volumetric strain and water content for expansive soils. Alternative encasement materials non-toxic to humans and non-hazardous to the environment were examined for the Clod test. It is shown that Elmer's craft glue is superior to the commonly used solution of Dow saran resin and methyl ethyl ketone (MEK) for its non-hazardous nature, low cost, and fast testing time. For several different expansive soils, nearly identical volumetric strain-water content curves were obtained using the traditional solution of Dow saran resin and MEK and Elmer's craft glue. 3M adhesive spray was shown to be not suitable for encasement material. It is concluded that Elmer's craft glue can be reliably used as an excellent alternative encasement material for the clod test.
Measurement of Quasi-Elastic Stiffness Parameters of Dense Toyoura Sand in Hollow Cylinder Apparatus and Triaxial Apparatus with Bender Elements
Authors: Chaudhary SK , Kuwano J , Hayano Y
Published: February 2009

Quasi-elastic stiffness parameters of dense Toyoura sand were measured at various stress states during similar consolidation and p′-constant shear tests in a hollow cylinder apparatus and a triaxial apparatus equipped with local deformation transducers and bender elements. Test results from these two test setups were compared. Although the Young's moduli from the triaxial apparatus were slightly lower than those from the hollow cylinder apparatus, they followed approximately the same power laws with the effective normal stresses. The shear modulus Gvh from the hollow cylinder apparatus was almost the same as that from the shear wave velocity measurement in the triaxial apparatus. The Poisson's ratios were also similar from both test setups. The vertical Young's modulus was found to be smaller than the horizontal Young's modulus. The anisotropy in Young's moduli followed a power law with the effective stress ratio. However, the Poisson's ratios were not dependent on the mean effective pressure or the shear stress level. The symmetry of the stiffness matrix was also examined.
Mechanical Behavior of an Unsaturated Soil Under Multi-Axial Stress States
Authors: Macari EJ , Hoyos LR
Published: February 2009

A series of drained (constant suction) true triaxial tests has been conducted on several identically prepared, 10-cm side, cubical specimens of recompacted silty sand to study the stress-strain-strength behavior of an unsaturated soil under multiaxial stress states and suction-controlled conditions. The experiments were conducted in a stress/suction-controlled true triaxial (cubical) setup following a multi-stage testing scheme. Matric suction states in the specimens were induced and maintained constant during testing by using the axis-translation technique. Imposed stress paths included an initial hydrostatic compression followed by conventional traxial compression, triaxial compression, or simple shear in the first octant of the octahedral stress plane. Test results are used to evaluate the nature of principal strain response of an unsaturated soil along multi-axial stress paths, and to observe the influence of matric suction on the shape, size, and position of the failure envelopes in the octahedral stress plane.
Design and Performance of an Electro-Pneumatic Pile Hammer for Laboratory Applications
Authors: Iskander MG , Olson RE , Bay JA
Published: February 2009

Small piles used in research programs have generally been installed by pushing or driving using slow mechanical drop hammers, because of the expense and technical difficulties associated with manufacture of realistic small-scale pile driving hammers. However, pushing does not model inertial effects and slow driving does not model diffusive effects in the soil. It remains to be demonstrated whether these effects are important or not. To help clarify this issue, an electronically controlled, single-acting air hammer, with a rated energy of 211 J (156 ft · lb), and an operating frequency of up to 1.2 Hz, was designed and built. The hammer was used successfully to drive 90 mm (3.5 in.) diameter piles into dense sand under a confining pressure of 138 kPa (20 psi). The behavior of the hammer was documented using detailed measurements of time-dependent ram movements, accelerations, and chamber pressures. This paper is concerned with the design and performance of the hammer.
Consolidation and Permeability Behavior of Segregated and Homogeneous Sediments
Authors: Sridharan A , Prakash K
Published: February 2009

The ever-increasing demand for the use of marginal lands for various human activities necessitates the need to understand the behavior of soft sediments under the action of external forces. As the segregated sediments are of common occurrence in a freshwater depositional environment, it is essential to understand the compressibility and permeability characteristics of segregated sediments, in addition to those of homogeneous sediments. The present paper discusses the compressibility and permeability behaviors of soft segregated and homogeneous sediments, making use of a simplified seepage consolidation testing procedure developed by the authors. The other variables included in the study are the clay mineralogy of the soil and the stress history of the sediments. The study clearly brings out the significant effect of clay mineralogy on the compressibility characteristics of segregated, normally consolidated sediments. The compressibility behavior of homogeneous soil sediments formed under a given depositional environment, having different clay mineralogy, appears to be similar. It is shown that the coefficient of permeability of any soil is a function of stress history in addition to void ratio and soil type.