bluuebunny/crossref_metadata_2025 huggingface dataset:
Tensiometers—Theory, Construction, and Use
Authors: Stannard DI
Published: February 2009

Standard tensiometers are used to measure matric potential as low as −870 cm of water in the unsaturated zone by creating a saturated hydraulic link between the soil water and a pressure sensor. The direction and, in some cases, quantity of water flux can be determined using multiple installations.

A variety of commercial and fabricated tensiometers are commonly used. Saturated porous ceramic materials, which form an interface between the soil water and the bulk water inside the instrument, are available in many shapes, sizes, and pore diameters. A gage, manometer, or electronic pressure transducer is connected to the porous material with small- or large-diameter tubing. Selection of these components allows the user to optimize one or more characteristics, such as accuracy, versatility, response time, durability, maintenance, extent of data collection, and cost.

Special designs have extended the normal capabilities of tensiometers, allowing measurement in cold or remote areas, measurement of matric potential as low as −153 m of water (−15 bars), measurement at depths as deep as 6 m (recorded at land surface), and automatic measurement using as many as 22 tensiometers connected to a single pressure transducer.

Continuous hydraulic connection between the porous material and soil, and minimal disturbance of the natural infiltration pattern are necessary for successful installation. Avoidance of errors caused by air invasion, nonequilibrium of the instrument, or pressure-sensor inaccuracy will produce reliable values of matric potential, a first step in characterizing unsaturated flow.
The Bending of a Screw Plate
Authors: Brown PT
Published: February 2009

The bending of a screw plate may have a considerable influence on the value of soil modulus derived from test results. This paper presents the dimensionless results of a study in which the plate is analyzed by finite elements and the soil is analyzed by integrated Boussinesq theory corrected for embedment in the medium. These results enable correction for the effect of plate bending for a range of screw plates. Such corrections may increase the derived value of modulus by 40% or more above the value obtained when a rigid plate is assumed. A correction based on the assumption that the plate is a disc is shown to be somewhat unsatisfactory.
Development of a True Triaxial Testing Apparatus
Authors: Reddy KR , Saxena SK , Budiman JS
Published: February 2009

A stress-controlled, flexible boundary, true (or cubical) triaxial apparatus has been developed to investigate the behavior of cemented sand under various stress paths which are not achievable using conventional axisymmetric triaxial apparatus. The apparatus components, specimen preparation, and test procedure are described. Tests were performed on cemented sand along different stress paths which included hydrostatic compression, conventional triaxial compression, and along different directions on octahedral planes. The test results indicate that stress-strain and volumetric response of cemented sand depends on stress path.
Leach Tests on Lime-Treated Clays
Authors: McCallister LD , Petry TM
Published: February 2009

This paper describes the design, use, and results of a multiple leach-cell operation to test the changes in permeability and calcium removal of a lime-treated expansive clay under continuous water leaching. Seventy laboratory-prepared lime-treated clay specimens were subjected to continuous accelerated leaching for periods of 45 and 90 days with varying lime contents and compactive moisture contents. Permeability, leachate pH, and leachate cation changes were continuously recorded during the leach process.

Results indicate that lime dramatically increased the soil's permeability, with maximum permeability occurring at the lime modification optimum (LMO). Leachate pH increased as the lime content of the soil increased but decreased linearly during the leach cycle. Calcium concentration in the leachate was lowest in specimens prepared at their LMO but increased as the lime content increased. There is strong evidence to suggest that calcium removal and permeability are in direct correlation to the complex ion interaction within the soil-lime mixture, and therefore the LMO is central in determining leaching effects on lime-treated soils.
Static and Cyclic Direct Shear Tests on Carbonate Sands
Authors: Al-Douri RH , Poulos HG
Published: February 2009

This paper examines the static and cyclic behavior of different types of carbonate sediments and one type of silica sand under direct shear test conditions. For both static and cyclic loading, the effects of interface surface roughness, overburden pressure, void ratio, size and shape of grains, and saturation are studied. It is found that the static shear resistance is influenced by most of these factors and that the cyclic behavior depends significantly on the number of cycles and the cyclic displacement amplitude. The amount of crushing caused by cyclic loading is found to depend strongly on particle shape and grading characteristics.

The results of the static tests can supply useful information about the strength parameters (δ and ϕ), which are important in assessing skin friction for the design of pile foundations. The cyclic test results provide useful indications of the likelihood of degradation of pile skin friction under cyclic loading. The larger the volume change under cyclic loading, the greater is the likely amount of degradation.
Hollow Glass Microspheres Inhibit Blast-Induced Liquefaction
Authors: Charlie WA , Johnson CF , Doehring DO
Published: February 2009

This paper summarizes the results of a controlled series of undrained shock tests conducted on mixtures of Monterey No. 0/30 sand, water, and hollow glass microspheres. Hollow glass microspheres, utilized to entrap gas in the sand, have a collapse strength of about 1700 kPa, are stable over time, and remain passive until a pressure sufficient to collapse them is applied. When subjected to a sub-millisecond compressive stress pulse of about 2300 kPa, peak stress transmission ratio decreased about 50% as the saturation decreased from 100 to 99.5%. Positive residual excess pore pressures (decreases in effective stress) were measured at saturations of 100, 99.9, and 99.8%. Negative residual excess pore pressures (increases in effective stress) were measured at saturations of 99.7, 99.6, and 99.5%. Analysis indicates that no change in residual pore pressure should occur at a saturation of 99.77%. The results indicated that microspheres may be used as a passive measure to inhibit blast-induced liquefaction and for reducing peak blast-induced stress in saturated soils.
Estimation of Pile Friction Degradation from Shearbox Tests
Authors: Airey DW , Al-Douri RH , Poulos HG
Published: February 2009

An uncemented carbonate sand has been subjected to cyclic loading in a modified shearbox apparatus under constant normal load and constant normal stiffness conditions. The behaviour in the tests using a constant normal stiffness shows many similarities with the variation of skin friction on piles under cyclic loading. It is demonstrated that the response in the shearbox tests with a constant normal stiffness may be predicted from the response observed in conventional shearbox tests, and that conventional shearbox tests can thus provide valuable information on the degradation of skin friction of piles under cyclic loading.
A Hollow Cylinder Torsional Simple Shear Apparatus Capable of a Wide Range of Shear Strain Measurement
Authors: Ampadu SK , Tatsuoka F
Published: February 2009

The lack of high-quality data at small strains under monotonic loads has led to the assumption of linear elasticity in small strain analysis and the use of low values of stiffness for analysis of geotechnical structures under working loads. In addition, since most simple shear apparatuses cannot measure lateral stresses, various assumptions have to be made in order to define the failure strength in terms of principal stresses. In this paper a hollow cylinder torsional simple shear system that is capable of measuring shear strains accurately from a strain level as small as 10−6 to failure in addition to measuring all stress components is described. This system is also capable of consolidating specimens along both normal and overconsolidated stress paths and during shearing is able to apply extremely small load reversals with little or no backlash effect. Using the special features of this system, the behavior of kaolin specimens under various stress histories from very small strains to failure was studied. The results show that irrespective of the consolidation stress history, the major part of the principal stress rotation occurs at the early stages of undrained simple shear, and the final direction near the peak strength is always a few degrees below 45°. The small strain behavior indicates that there exists a very small elastic zone of the order of 2 × 10−5 shear strain, and that the behavior beyond this region is highly nonlinear. The trend in the variation of the peak strength with OCR obtained in this system is similar to that obtained in the conventional simple shear apparatus as reported in the literature.
G
max-qc Relationships for Clays
Authors: Mayne PW , Rix GJ
Published: February 2009

Data are compiled from 31 clay sites where in-situ measurements of initial tangent shear modulus (Gmax) and cone tip resistance (qc) were available. Values of Gmax were obtained from either seismic cone penetration (SCPT), crosshole (CHT), downhole (DHT), or spectral analysis of surface wave (SASW) tests, and readings of qc were taken either by regular cone penetration (CPT) or piezocone (CPTU) tests. Multiple regression analyses indicate that in-situ values of Gmax depend on void ratio (eo), overburden stress (σ′vo), and stress history (OCR), as previously established from laboratory resonant column tests. Since qc also depends on σ′vo and OCR, a moderate association between Gmax and qc is possible, despite their incompatible strain levels. For preliminary correlative purposes, a power function relates in-situ Gmax, qc, and eo in clay deposits having a wide range in plasticity, sensitivity, stress history, and consistency.
Modified Bromhead Ring Shear Apparatus
Authors: Stark TD , Eid HT
Published: February 2009

The main factor affecting the drained residual strength measured in the Bromhead ring shear apparatus is the magnitude of wall friction developed along the inner and outer circumferences of the confined specimen. The magnitude of wall friction increases with the depth of the remolded specimen, and thus the plane of least wall friction occurs at or near the soil/top porous stone interface. As the top porous stone settles into the specimen container, the wall friction influencing the shear plane increases, causing an increase in the measured residual strength.

A new specimen container is proposed for the Bromhead ring shear apparatus that allows a remolded specimen to be overconsolidated and precut prior to drained shearing. This minimizes settlement of the top platen and the horizontal displacement required to reach a residual strength condition. As a result, a multistage test can be conducted without excessive settlement and thus wall friction occurring in the new specimen container. The use of a multistage test significantly reduces the time required to establish a drained residual failure envelope. The use of an overconsolidated and precut specimen also provides a better simulation of the field conditions that lead to a large post-peak decrease in drained strength in clayshales, claystones, and mudstones, and residual strengths that are in excellent agreement with field case histories.
Use of CPTu to Estimate Equivalent SPT N60
Authors: Jefferies MG , Davies MP
Published: February 2009

Although the CPTu offers many advantages over the SPT, it may be desirable in some instances to use SPT-based experience of soil behavior. An algorithm is presented here for estimation of equivalent N60 values directly from the CPTu without resort to soil sampling. The proposed algorithm is based on data and trends reported in the literature; the algorithm is tested against new data obtained for cross-calibration of the CPTu/SPT in a wide variety of soil types, penetration resistances, and depths. As part of the evaluation of the algorithm, replicate trials of both SPT and CPTu were carried out. The data show the CPTu is five times more precise than the SPT. Further, the equivalent N60 derived from the CPTu using the proposed algorithm is shown to be at least as reliable as values directly determined by the SPT; the much improved precision of the CPTu outweighs the uncertainty in the CPTu/SPT calibration, and the calibration in itself averages the testing error of the SPT. The proposed algorithm is tested for bias against depth, soil type, penetration resistance, and friction ratio; the algorithm is unbiased. Cumulative probability density functions are given for repeatability of the SPT, the CPTu, and an estimation of equivalent SPT values from the CPTu.
Consolidation, Pre- and Post-Peak Shearing Responses from Internally Instrumented Biaxial Compression Device
Authors: Finno RJ , Rhee Y
Published: February 2009

An internally instrumented, servo-controlled biaxial compression device is described for evaluating shear band formation in soils. Internally measured vertical and lateral soil displacements as well as lateral deformations of a very low friction bottom sled allow one to observe the progressive development of shear bands in a specimen. Anisotropically consolidated specimens of relatively insensitive, soft Chicago glacial clay were sheared under undrained conditions. Differences in responses based on the internal and globally derived stress and strain quantities illustrate the uniformities which are attained during both consolidation and shear. Small, outward lateral displacements were observed during K0 consolidation, which was based on globally observed axial and volumetric strains; yet, observed Ko values were similar to those measured by other means. Observed lateral deformations during undrained shear and bottom sled movements showed the progressive development of a shear band in all tests. Nonuniformity of the deformations arose after attaining a peak shear stress. The globally observed strain-softening response was both constitutive and geometric in nature.
Evaluation of Static Capacity of Deep Foundations from Statnamic Testing
Authors: Brown DA
Published: February 2009

A new method of load testing, called statnamic, is evaluated with respect to conventional methods of static load testing. Case histories are examined that provide a basis for comparison of static capacity as estimated from statnamic measurements with that of conventional load-deflection measurements. When evaluated using the simple procedure proposed by Middendorp, the statnamic method is shown to predict load-deflection response that is relatively close to that measured with conventional static load tests in most cases. Comparisons with conventional static load tests outlined in this paper suggest that excellent agreement can be obtained in sandy soils, but that the current evaluation procedure may tend to overpredict capacity by as much as 30% in stiff, overconsolidated clays.
Engineering Properties of Tire Chips and Soil Mixtures
Authors: Edil TB , Bosscher PJ
Published: February 2009

The primary objective of the research described herein is to assess the pertinent engineering properties for reusing shredded scrap tires as a construction material for light-weight fill material in highway construction, for drainage material in highway and landfill construction, and for other similar applications. Reuse of scrap tires would not only provide a means of disposing of them but would also help solve difficult economical and technical problems. This paper presents the characteristics of shredded scrap tires and their engineering properties and behavior alone or when mixed with soils. The properties considered include compaction, compressibility, strength and deformability, and hydraulic conductivity. Described are new test procedures or modification of existing methods developed to characterize this unusual material.
The Effects of Centerline Tube Sampling Strains on the Undrained Behavior of Two Stiff Overconsolidated Clays
Authors: Georgiannou VN , Hight DW
Published: February 2009

Some of the effects of tube sampling of stiff clays are examined. A strain path that simulates strains at the centerline of a tube sample as it is captured by a penetrating sampling tube was applied in the triaxial apparatus. Undrained triaxial strain path tests were performed on two stiff overconsolidated clays that had not previously been subjected to tube sampling. The response of the clays after simulated sampling and reconsolidation is compared with shear behavior established from tests on specimens taken from block or rotary-cored samples. The mean effective stress is reduced by about 10% as a result of the centerline tube sampling strain path. Stiffness is significantly reduced after simulated sampling and isotropic reconsolidation for both clays, whereas peak strength is only slightly affected.
Analysis and Estimation of the Coefficient of Consolidation
Authors: Narasimha Raju PSR , Pandian NS , Nagaraj TS
Published: February 2009

Consolidation is one of the most important behaviors of saturated fine-grained soils that needs to be understood for settlement analysis of these soils. The two most important aspects of laboratory consolidation tests are: (1) estimation of the compression index (Cc), used to predict total settlement of normally consolidated soils provided the void ratio versus log (effective stress) is linear; and (2) the coefficient of consolidation (Cv), used to predict the rate of settlement in the range of primary consolidation. Several researchers have proposed various graphical methods for obtaining estimates of Cv from laboratory oedometer tests. Olson (1985) concluded that since different graphical methods estimate different values for Cv for the same data, the only rational way to estimate the Cv value is to base it on the coefficient of volume compressibility (mv) and the coefficient of permeability (k). Guided by these considerations, an attempt has been made to establish the feasibility of estimating Cv using stress state-permeability relationships (Nagaraj et al. 1993). The input parameters are the liquid-limit void ratio (eL) and the overburden pressure (p).
Screw Plate Insertion in Sand
Authors: Brown PT
Published: February 2009

Laboratory measurements of the depth of penetration at the end of each revolution of a 30-mm-diameter screw plate were made when the insertion was carried out with no vertical thrust applied to the screw plate. The tests were carried out to a depth of 150 mm in a dry, uniformly graded sand with a wide range of densities and two values of surcharge pressure. The results showed that, except for sand with a relative density less than about 30%, the penetration per revolution decreases significantly with increasing depth and decreases more rapidly as the density increases. After insertion, loading tests were carried out using the screw plate; the results show a large increase in apparent modulus at the higher values of density. Measurements of elastic modulus were also made when the screw plate was inserted under the control of a threaded rod having the same pitch as the screw plate and with a flat disk buried in the sand.
A Pluvial Deposition Method to Reconstitute Well-Graded Sand Specimens
Authors: Fretti C , Lo Presti DCF , Pedroni S
Published: February 2009

Stationary pluviators generally use one or more sieves to spread the sand flow exiting from the hopper through one or more holes over the desired area. On the other hand, traveling pluviators do not need a sieve or mesh because in this case it is possible to move an opening or a nozzle over the area of interest. Traveling pluviators are preferable to stationary pluviators, especially in the case of well-graded cohesionless soils, because they provide more uniform specimens. However, traveling pluviators have drawbacks, specimen layering being the most relevant. This technical note illustrates an experimental procedure to reconstitute large specimens of well-graded sands using a traveling pluviator. The effects of specimen layering on mechanical soil properties became negligible with this technique as it was possible to assess performing a series of CPT tests with both a standard cone and a 20-mm cone.
Automated Determination of the Distribution of Local Void Ratio from Digital Images
Authors: Frost JD , Kuo C-Y
Published: February 2009

The frequency distribution of local void ratio is believed to be an important parameter, in addition to the void ratio, for describing the mechanical behavior of granular materials. Oda proposed a method to determine experimentally the distribution of local void ratio from 2-D plane sections. To date, implementations of Oda's method have depended to varying extents on operator judgment to form polygons by joining the centers of gravity of all particles that surround a void. Furthermore, the studies have involved a significant amount of manual work in making the required measurements. This paper describes a fully automated implementation of the method, which uses high-level, image-processing techniques. The proposed method eliminates operator judgment and manual work and makes the determination of the distribution of local void ratio from 2-D plane sections both repeatable and efficient. The method is illustrated with measurements performed on synthetic and real images. The importance of correcting the images to account for factors such as thickness of segmentation lines is demonstrated. Measurements that confirm the stability of the proposed polygon network generation procedure are also presented.
The Relationship Between the Soil-Water Characteristic Curve and the Unsaturated Shear Strength of a Compacted Glacial Till
Authors: Vanapalli SK , Fredlund DG , Pufahl DE
Published: February 2009

Soils compacted at various “initial” water contents and to various densities should be considered as “different” soils from a soil mechanics behavioral standpoint even though their mineralogy, plasticity, and texture are the same. The engineering behavioral change from one specimen to another will vary due to differences in soil structure or aggregation. The shear strength of an unsaturated soil and the soil-water characteristic curve are dependent on soil structure or the aggregation, which in turn is dependent on the “initial” water content and the method of compaction. The laboratory preparation of specimens must, therefore, closely represent the physical conditions and the stress state conditions likely to occur in the field if a proper assessment of the shear strength parameters is to be achieved. This paper is primarily concerned with the study of the relationship between the shear strength of an unsaturated soil and its soil-water characteristic curve.

Consolidated drained direct shear tests were conducted on statically compacted glacial till specimens, both under saturated and unsaturated conditions, representing three “initial” water contents and densities. The “initial” water contents and densities of the specimens were selected to represent the dry, optimum, and wet of optimum water content conditions with reference to the compaction curve. Multistage, unsaturated, direct shear tests were conducted under three different net normal stresses with varying matric suction values for each case. The soil-water characteristic curves were also developed on specimens with “initial” conditions similar to those used for the unsaturated shear strength tests.

The shear strength variation with respect to matric suction was found to be nonlinear for all the tests. The rate of increase in the shear strength contribution due to matric suction, however, was found to be related to the rate of desaturation of the soil. The desaturation characteristics are a function of the “initial” water content of the compacted specimens. For any particular net normal stress and matric suction, specimens compacted wet of optimum water content offered more resistance to desaturation and exhibited a higher shear strength when compared to specimens compacted at dry of optimum or at optimum water content conditions. Under similar “initial” conditions, the soil-water characteristic curve bears a close relationship to the unsaturated shear strength behavior of the soil.
A Device for the Measurement of Sub-Surface Ground Vibrations
Authors: Leong EC , Cheong HK , Pan TC
Published: February 2009

A reliable measurement of free-field stress waves from transient loading has several important applications, for example, in the design of effective wave barriers to protect sensitive equipment and in the design of underground protective structures against explosive loading, to name a few. The characteristics of a stress wave are highly dependent on the energy source and the soil medium through which it propagates. A new device in place of a buried sensor is described in the present paper that can be used to measure the free-field subsurface ground vibrations in the horizontal direction. Laboratory modal analyses showed that the device has a natural frequency of about 600 Hz. For practical applications, the upper frequency limit of the device is taken as 300 Hz, which is well above the range of frequencies normally encountered in practice. Test measurements using both the device and buried sensors in residual soils from an impact load and a blast load are presented. Evaluation of the test results shows that the characteristics of the stress waves generated by these loads can be measured accurately with the device. Compared to a buried sensor, the device has the added advantages of ease of alignment to the source and ease of retrieval.
Dynamic Characteristics of Old Bay Clay
Authors: Guha S , Drnevich VP , Bray JD
Published: February 2009

Unusually strong ground motions at deep stiff clay sites in the East San Francisco Bay area during the 1989 Loma Prieta earthquake called for examination of the dynamic response of this clay deposit and characterization of its dynamic properties. In this paper, correlations of Old Bay clay dynamic properties with various soil parameters (e.g., plasticity, void ratio, magnitude and duration of confinement, consolidation stress history) are presented and compared with the existing database on cohesive soils. A special effort is made to evaluate the effects of sample disturbance on the laboratory measurement of dynamic properties of stiff cohesive soils. The laboratory measurement of low-strain shear modulus and damping ratios is adjusted by considering the aging of the Pleistocene era clay deposit. These adjustments, though effective, are not sufficient to account for the effects of structural disturbance. Shear modulus is reduced significantly by structural disturbance, but, surprisingly, the damping ratio is found to remain largely unaffected.
Suggested Practice for Drilling Boreholes for Pressuremeter Testing
Authors: Briaud J-L , Gambin M
Published: February 2009

A standard practice is suggested for the preparation of the borehole in which the pressuremeter probe is to be inserted. The practice covers the required diameter of the hole, the various drilling tools and methods used to place the probe, the test spacing and testing sequence, and the way to judge the quality of the borehole and of the test. This practice is an adjunct to the suggested practice for pressuremeter testing in soils.
Permeability Testing with Flexible-Wall Permeameters
Authors: Daniel DE , Trautwein SJ , Boynton SS , Foreman DE
Published: February 2009

The equipment and testing procedures used at The University of Texas at Austin for measuring the hydraulic conductivity of fine-grained soil with flexible-wall permeameters are described. The permeability cell is similar to a triaxial cell; it has interchangeable base pedestals to accomodate specimens of various diameters, is equipped with double drainage lines to the top and bottom of the test specimen, and can accomodate a differentially acting pressure transducer to measure head loss across the soil specimen. An air-over-liquid interface is maintained in devices called “accumulators.” Stainless steel accumulators designed with transparent sight tubes offer excellent resistance to corrosion, are convenient to use, and can be used with a wide range in flow rates. The permeability tests are normally performed using back pressure. Care is taken to be certain that flow is steady state and that the soil is permeated long enough for the influent liquid to pass through the soil and to appear in the effluent liquid in full concentration. When clays are permeated with dilute chemicals that are adsorbed by the soil, testing times on the order of months or years may be required to achieve full breakthrough of the permeant liquid. Use of large hydraulic gradient and excessive effective confining pressure are sometimes difficult to avoid but are two of the most important sources of potential error.
A Field Study of an Automatic SPT Hammer System
Authors: Riggs CO , Mathes GM , Rassieur CL
Published: February 2009

A field comparison is made of standard penetration test (SPT) N values obtained using three automatic free fall hammers of the same design with N values obtained by five cathead and rope operators using four different drill rigs. A comparison of mean N values using the t-statistic at the 5% significance level generally indicates no significant difference in means. The tests were performed in a loessial soil in several parallel borings. The field N values were in the range of 5 to 15.
Cyclic Triaxial Behavior of Monterey Number 0 and Number 0/30 Sands
Authors: Charlie WA , Muzzy MW , Tiedemann DA , Doehring DO
Published: February 2009

Results of a testing program to compare the cyclic triaxial behavior of Monterey No. 0 and No. 0/30 sands are presented. Monterey No. 0 sand, the standard sand used by Silver et al in 1976 to establish the performance specification for cyclic triaxial systems, is no longer available and a replacement is needed. The supplier of the test sand, Lone Star Industries, stopped producing No. 0 sand in 1977, and the 4500-kg (10 000-lb) supply stockpiled by the University of California at Berkeley is exhausted. Since 1977, Lone Star Industries has filled requests for Monterey No. 0 by shipping Monterey No. 0/30 sand. The results of a duplicate testing program conducted at two independent laboratories lead to questions regarding the validity of substituting No. 0/30 sand for No. 0 sand. When tested under identical conditions, the Monterey No. 0/30 sand yielded higher cyclic strengths than did Monterey No. 0 sand.
Soil Freezing Response: Influence of Test Conditions
Authors: McCabe EY , Kettle RJ
Published: February 2009

The response of soils to freezing has been assessed in terms of frost heave, and the heaving pressure developed when the specimen is restrained. As both techniques have been suggested for assessing frost susceptibility, it was considered essential to determine the influence of the test conditions on the soil response.

This investigation was concerned with specimen preparation, specimen size, and freezing procedure. The test material consisted of an artificially produced matrix, into which controlled amounts of coarse aggregate could be blended. This reduced the likelihood of variation in the results because of random changes in the test materials. The results clearly demonstrated the sensitivity of both heave and heaving pressure to the test conditions. When modified or new test methods are being formulated, it is essential to consider the influence of such factors, particularly when making comparisons between different testing techniques. Such modifications may also require changes in the particular criteria used to assess frost susceptibility.
Dynamic High Stress Experiments on Soil
Authors: Felice CW , Gaffney ES , Brown JA , Olsen JM
Published: February 2009

The split-Hopkinson pressure bar (SHPB) technique has been adapted to measure the dynamic response of soil to impulse loads. The experimental technique is relatively simple and can investigate soil response in regimes beyond the capabilities of current equipment used for dynamic soil laboratory investigations. Soils have several characteristics that must be considered in designing a SHPB experiment and evaluating the data (for example, low wave speeds, nonlinear hysteretic behavior, and low unconfined compressive strength compared to the applied loads). Insight has been gained as to how these factors affect experimental accuracy and data reliability. It has been shown that the experimental assumptions can be satisfied and that the experimental results can be replicated.
Large-Scale Laboratory Permeability Testing of a Compacted Clay Soil
Authors: Shackelford CD , Javed F
Published: February 2009

Constant-head permeability (hydraulic conductivity) tests were performed on samples of a compacted clay soil using a 0.914 by 0.914 by 0.457-m (3 by 3 by 1.5-ft) large-scale, double-ring, rigid-wall permeameter. A naturally occurring silty clay soil was used for the permeability tests. The soil was separated into five different fractions representing five different ranges in precompaction clod sizes. Soil from each of the soil fractions was used for soil specimens. The soil for the large-scale permeameter was compacted in two 7.62-cm (3-in) lifts. Small-scale, constant-head permeability tests also were performed on soil specimens compacted into standard Proctor molds (9.44 × 10−4 m3). Comparison of the results from the two different scales of permeameters indicated that, in all cases, the permeability for a given soil fraction was higher in the large-scale permeameter than it was in the small-scale permeameter. In addition, the permeability for all soil fractions measured in the large-scale permeameter ranged from 0.6 to 2.4 orders of magnitude higher than the value measured in the small-scale permeameter. As a result of the permeability tests performed in this study, there appears to be a scale effect associated with laboratory permeability testing, especially when a significant proportion of the soil being tested consists of precompaction clod sizes which are large relative to the size of the permeameter. The scale effect in this study is thought to be due to the relationship between the compactive effort and the different degrees of confinement associated with the different scales of permeameters. The implication of the study is that a more realistic evaluation of the fieldmeasured permeability of a compacted clay soil may be possible in the laboratory if the permeameter is sufficiently large to test a representative sample of soil.
Multicylinder Control Units for Prebored Hydraulic Pressuremeters
Authors: Smith TD , Denham M
Published: February 2009

A control unit for hydraulic single-cell pressurementers is described which employs multiple cylinders. The basic control unit can function with a single cylinder for small low-capacity pressuremeter probes and with additional cylinders added to increase the system capacity to serve larger probes. The unit described is portable, rugged, lightweight, and cost effective.

Comparative pressurementer test results are given for the multicylinder control unit (PUP) and the commercial hydraulic unit (TEXAM), with both units serving a 32-mm-diameter EX probe and a 60-mm-diameter BX probe.
Anisotropy of Normally Consolidated San Francisco Bay Mud
Authors: Kirkgard MM , Lade PV
Published: February 2009

Consolidated-undrained tests were performed on intact specimens of San Francisco Bay mud to study the anisotropic behavior of a normally consolidated clay. Large cylindrical block samples were obtained from an excavation in reclaimed tidelands south of the San Francisco International Airport. Evidence of soil fabric and its relation to the stratigraphy of the area were studied in preparation for the investigation of anisotropy. Cubical specimens were trimmed from the block samples and tested in triaxial compression with vertical and horizontal material axes. Consolidation characteristics, as well as stress-strain, pore pressure, and strength relations, were obtained along with lateral strains in two perpendicular directions. The experimental results were carefully evaluated and showed that the clay behaved as an orthotropic material, but for practical purposes could be characterized as being cross-anisotropic. The cross-anisotropic, elastic parameters were determined and related to the initial inclinations of the effective stress paths for vertical and horizontal specimens.
Use of Side Drains in Triaxial Testing at Moderate to High Pressures
Authors: Oswell JM , Graham J , Lingnau BE , King MW
Published: February 2009

Side drains are used in triaxial tests to increase the rate of consolidation and equalize pore water pressures within the specimen. However, the efficiency of the side drains has been shown to be a function of time and effective confining pressure.

This paper presents the results of (1) a mail survey on side drain practice, which indicates that many laboratories use side drains not recommended by standard references, and (2) an experimental program to assess the effects of time and moderate-to-high effective confining pressure on the flow properties of four side drain materials.

The four side drain materials used in the testing program were: (1) a single layer of Whatman No. 1 filter paper; (2) a single layer of Whatman No. 54 filter paper; (3) a double layer of Whatman No. 54 filter paper; and (4) a single layer of geotextile. The lengthwise flow of these materials was examined as a function of effective confining pressure up to 6000 kPa and also of time at a fixed effective confining pressure of 750 kPa.

Tests were also conducted on specimens of natural clay to compare consolidation rates using different drain materials.
Evaluation of Dynamic Properties of Sands by Resonant Column Testing
Authors: Chung RM , Yokel FY , Drnevich VP
Published: February 2009

Torsional resonant column tests were performed on Monterey No. 0 sand of 60% relative density under confining pressures ranging from 10 to 300 kPa to evaluate the dynamic properties of the sand. Both solid and hollow cylindrical specimens were used in testing, and shear moduli and damping ratios were determined for cyclic shear strain amplitudes from 10−4 to 5 × 10−2%. The test results indicated that the type of specimen, that is, solid or hollow cylinder, had no significant effect on the calculated shear moduli and damping ratios, except that at very low strain amplitudes (γ ≤ 10−3%) where the shear moduli of the hollow specimens tended to be slightly lower and the damping ratios slightly higher. Multistage testing had no significant effect on the shear moduli when the values were compared with those from the single-stage testing; however, multistage testing had a significant effect on the damping ratios under a confining pressure 100 kPa. Both shear moduli and damping ratios obtained in this program correlate well with other available data.
A Critical Assessment of Membrane Penetration in the Triaxial Test
Authors: Vaid YP , Negussey D
Published: February 2009

Fundamental assumptions necessary for assessment of volume change because of membrane penetration in triaxial tests on granular soils, by methods that use dummy rod inclusions or assume isotropic behavior of sand in loading, have been critically examined and shown to be invalid. Reliable estimates of membrane effects are essential in the development of constitutive models of soil behavior. Alternative methods, which do not violate any critical assumptions, are proposed for estimating membrane penetration and supported by experimental evidence.
A Calibration Chamber for Cohesive Soils
Authors: Huang A-B , Holtz RD , Chameau J-L
Published: February 2009

The paper describes the design and performance of a calibration chamber system for testing in-situ test devices in cohesive soils. Techniques for preparing “undisturbed” clay specimens from a slurry and consolidating them under zero lateral strain K0 conditions are presented. The chamber was used for strain controlled model pressurementer tests during which pore pressure was monitored. Duplicate model pressuremeter tests performed in normally consolidated (NC) kaolinite (σ′vc = 276 kPa) resulted in essentially identical expansion curves. The specimens had an average water content of 44.9% and a coefficient of variation of 1.5%. Also, the predicted lateral stresses essentially coincide with those applied to the chamber specimen.
Use of Permeability as an Index to Characterize Internal Structural Changes and Fracture Mechanism
Authors: Lee DH , Hsein Juang C
Published: February 2009

This study investigated the possibility of using variation in the permeability as an index to characterize internal structural changes and fracture mechanism of a soft rock under triaxial loadings. Extensive triaxial tests were carried out on soft rock specimens to examine this idea. These tests include (1) triaxial compression tests with low and high confining pressures, (2) triaxial tests with relaxations, and (3) cyclic triaxial tests. The results of the study confirm that observation of change in the permeability provides an excellent way of characterizing the internal structural changes and fracture mechanism of the soft rock under triaxial loadings.
In-Situ Shear Modulus of Sands by a Flat-Plate Penetrometer: A Laboratory Study
Authors: Motan ES , Khan AQ
Published: February 2009

A flat-plate penetrometer, similar to the flat-dilatometer, has been constructed and used in a series of laboratory experiments to estimate the shear modulus of cohesionless soils under repetitive loading conditions. Tests were performed on sand specimens prepared at different relative densities and loaded vertically to simulate the overburden pressure at different depths. Results indicate, despite penetration disturbance, a reasonable agreement between the shear modulus values determined using the flat-plate penetrometer data and the empirical formulations published in the literature.
Sampling of Saturated and Unsaturated Sands by Freezing
Authors: Konrad J-M
Published: February 2009

A 600-mm-long, 100-mm-wide, and 20-mm-thick steel plate containing a wavey groove carrying chilled ethanol at −40°C was used successfully to obtain undisturbed frozen samples of saturated clean sand. The freezing probe was also used in an unsaturated sand dune to obtain samples at a depth of 3.0 m. For sands above the groundwater level, an imbibition test is, however, required prior to freezing in order to increase the in situ water content and bond the sand particles as freezing proceeds. The prismatic freezing probe is very efficient and produced frozen sand masses having an outside diameter of 26 cm after 4 h of freezing. Pushing the probe into the ground resulted in a disturbed zone of about 3 to 5 times its thickness.
Inadequacy in the Classification of Coarse-Grained Soils
Authors: Sivakugan N
Published: February 2009

This note explores the rationale behind the unified soil classification system for coarse-grained soils. A few deficiencies in the system are pointed out. A density function plot of the grain-size distribution is proposed to supplement the grain-size distribution curve, which the author believes will minimize the ambiguities and give a more realistic representation of grain-size distribution.
Microwave Drying of Soils
Authors: Hagerty DJ , Ullrich CR , Denton MM
Published: February 2009

Drying of soil specimens in microwave ovens can permit rapid determination of moisture content; such determination is very important in field quality control of earthwork construction. A laboratory study was performed to investigate differences between soil moisture contents based on microwave oven drying and moisture contents developed from conventional drying procedures. For nine materials ranging from dense graded aggregate to highly plastic clays, differences between moisture contents obtained by the two methods were very small, in many cases not exceeding the variability between values obtained from multiple specimens of the same soil mix dried in a conventional oven.
A Thermally Controlled Test Chamber for Centrifuge and Laboratory Experiments
Authors: Stone KJL , Smith CC , Schofield AN
Published: February 2009

This note describes a novel approach for the provision of a thermally controlled testing chamber. The main principal of the system is to use a layer of cooled air as an active insulation medium to convect away heat transferred through conventional passive insulation. Results from laboratory floor and centrifuge tests are reported. Observed and predicted performance capabilities of the chamber are also discussed.
Particle Size Analysis of Lime-Treated Marine Clays
Authors: Rajasekaran G , Rao SM
Published: February 2009

Lime is commonly used to improve the engineering behavior of marine clay. But there is a need to investigate the lime-attributed changes in a particulate system in a marine environment. Lime columns 50 mm in diameter and 500 mm in length were installed in test tanks 600 mm in diameter at a depth of 550 mm, while lime injection was attempted in a test tank, 1000 by 1000 by 750 mm. The present investigation deals with experimental work carried out in the laboratory using lime column and lime injection techniques to stabilize an Indian marine clay in a salt water environment. Different inorganic additives were used with lime as column filler material to study the effect of lime-attributed changes occurring in the particle growth of soil systems. Grain-size distribution tests and SEM technique were carried out to study the lime-induced changes on the constituent particles. The test results indicate that there is an increase in the size of clay particles towards silt or fine sand fraction due to lime treatment. The formation of aggregates due to lime-soil reactions can be seen in the micrographs of different lime-treated soil systems, and the same has been confirmed using the SEM technique.
Analysis of Bender Element Tests
Authors: Arulnathan R , Boulanger RW , Riemer MF
Published: February 2009

A study is presented of potential errors in, and methods of interpreting, the results of cantilever-type, piezoceramic bender element tests for measuring the shear wave velocity of laboratory soil specimens. Interpretations based on the first direct arrival in the output signal are often masked by near-field effects and may be difficult to define reliably. Interpretations based on characteristic points or cross-correlation between the input and output signals are shown to be theoretically incorrect in most cases because of: (1) the effects of wave interference at the boundaries; (2) the phase lag between the physical wave forms and the measured electrical signals; and (3) non-one-dimensional wave travel and near-field effects. Interpretations based on the second arrival in the output signal are theoretically subject to errors from non-one-dimensional wave travel and near-field effects. Differences in Vs values obtained by the different interpretation methods are illustrated analytically and experimentally.
The Need for a Schema for the Classification of Transitional (Shale) Materials
Authors: Deen RC
Published: February 2009

The need for comprehensive information on the characteristics and behavior of earth materials has been recognized for many years. With the increase in size and importance of structures and facilities designed by engineers in recent years, there has been an increased interest in rock materials underlying the surficial soil layers. Many earth materials, however, are not readily classified as either soil or rock. These transitional materials comprise 50 to 75% of the sedimentary rock of the earth's crust and have been involved in a number of geotechnical engineering problems (slope stability, settlement, and bearing capacity failure) around the world. Various classification approaches are summarized and the continuing need to develop simple field and laboratory procedures for identifying, classifying, and evaluating transitional materials is discussed.