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In this study, rubber-sand particle mixtures are investigated to understand their stress-deformation and elastic modulus characteristics. Specimens are prepared with various size ratios, sr (=[D.sub.rubber]/[D.sub.sand]), between sand and robber particles, and different volumetric sand fractions, sf (=[V.sub.sand]/[V.sub.total]). Small strain shear waves are measured under a [K.sub.0],- loading condition incorporated with the stress-deformation test by using an oedometer cell with bender elements. The stress-deformation and small strain shear- wave characteristics of rigid-soft particle mixtures show the transition from a rigid particle behavior regime to a soft particle behavior regime under a fixed size ratio. A sudden rise of the A factor and the maximum value of the [zeta] exponent in [G.sub.max]= [LAMBDA][([[sigma]'.sub.0],/kPa).sup.[zeta]] is observed at sf [approximately equal to] 0.4-0.6 regardless of the size ratio (sr). The transition mixture shows a high sensitivity to the confining stress. The volume fraction for the minimum porosity may depend on the applied stress level in the rigid-soft particle mixtures because the soft rubber particles easily distort under load. In this experimental study, the size ratio and volumetric sand fraction are the important factors which determine the behavior of rigid and soft particle mixtures. DOI: 10.1061/(ASCE)MT.1943-5533.0000027 CE Database subject headings: Mixtures; Shear waves; Velocity; Stiffness; Rubber; Sand, material; Size effect. Author keywords: Ko-loading; Mixtures; Shear-wave velocity; Size ratio; Stiffness; Volume fraction.

This paper explores the standard penetration test (SPT) hammer-anvil behavior and investigates the effect of secondary impact on SPT energy and sampler penetration. It is observed that the hammer-anvil behavior after the impact depends on the characteristics of the wave reflected from the sampler. The type-I secondary impact, which is dominant for N < 25, is induced due to the rapid downward movement of the anvil and the recontact of the following hammer on the rebounding anvil. The maximum energy calculated by integrating force and velocity (EFV) is achieved immediately after the occurrence of the type-I secondary impact and an additional sampler penetration is triggered by the type-I secondary impact. The type-II secondary impact, which is dominant for N > 50, is produced by the restrike of the pushed-up hammer on the resting anvil. The type-II secondary impact causes only recoverable anvil deformation and does not contribute to the maximum EFV energy. For N-values of 25-50, both or either types of secondary impacts happen. As N-value increases, the type-I secondary impact fade away progressively and the type-II secondary impact becomes more distinctive. DOI: 10.1061/(ASCE)GT.1943-5606.0000236 CE Database subject headings: Impact; Penetration tests; Energy. Author keywords: Secondary impact; Standard penetration test (SPT); Energy transfer ratio.

The assessment of the shear stiffness of dredged soft ground and soft clay is extremely difficult due to soil disturbances caused during sampling and field access. Several in situ methods such as spectral analysis of surface waves, multichannel analysis of surface wave, cross hole, and downhole methods have been developed to measure the shear-wave velocity, but a few disadvantages hinder the adoption of existing methods to soft ground. This study presents a new apparatus, the penetration type field velocity probe (FVP), which overcomes several of the limitations of commonly used shear-wave measurement methods in the field. Design concerns of the FVP include the tip shape, soil disturbance, transducers, self acoustic insulation, protectors, and the electromagnetic coupling from transducer-to-transducer and cable-to-cable. The crosstalk between cables is eliminated by grouping and extra grounding of the cables. The shear-wave velocity of the FVP is directly calculated, without any inversion process, by using the travel distance and the travel time. After calibration tests are carded out in the laboratory, application tests in the field are conducted up to 29 m in depth. Calibration results show the velocity profiles obtained by the FVP and by the rods fitted with transducers are similar to each other. The experimental results obtained in the field show that the FVP can produce reasonable and detailed shear-wave velocity profiles in soft clay. This study suggests that the FVP may be an effective technique for measuring the shear-wave velocity in soft ground. DOI: 10.1061/(ASCE)1090-0241(2010)136:1(199) CE Database subject headings: Calibration; In situ tests; Shear modulus; Shear waves; Soft soils; Velocity. Author keywords: Calibration chamber; In situ test; Shear modulus; Shear waves; Soft soils.

The presence of mica changes the mechanical behavior of sandy soils. In this study, micro- and macroscale tests are used to explore the unique packing characteristics that develop in mixtures made of round and platy particles, and the effects that mica exerts on small, medium, and large strain parameters. Mixtures are prepared with different mica contents and various mica-to-sand size ratios, [L.sub.mica]/[D.sub.sand]. Results provide a comprehensive characterization of mixtures made of spherical and platy particles. Mica plates change sand packing through pore filling, bridging, ordering, and mica-mica interaction; bridging prevails and leads to open fabrics when [L.sub.mica]/[D.sub.sand] [greater than or equal to] l. As the mica content increases in mixtures with [L.sub.mica]/[D.sub.sand] [greater than or equal to] 1, the shear-wave velocity decreases and it becomes more sensitive to the state of stress; the constraint modulus decreases; and the peak and residual friction angles decrease. Remixing during disordered granular flow prevents mica alignment and diminishes the otherwise weakening effect of mica on large-strain strength. CE Database subject headings: Compression; Density; Fabrics; Localization; Residual soils; Sand; Shear modulus; Stiffness.

Mixtures of rigid sand particles and soft fine-grained rubber particles are tested to investigate their small and large-strain responses. Mixtures are prepared with different volumetric sand fraction sf to identify the transition from a rigid to a soft granular skeleton using wave propagation, [k.sub.]0 loading, and triaxial testing. Deformation moduli at small, middle, and large strains do not change linearly with the volume fraction of rigid particles; instead, deformation moduli increase dramatically when the sand fraction exceeds a threshold value between sf=0.6-0.8 that marks the formation of a percolating network of stiff particles. The friction angle increases with the volume fraction of rigid particles. Conversely, the axial strain at peak strength increases with the content of soft particles, and no apparent peak strength is observed in specimens with low sand fraction (sf [less than or equal to] 0.6). The presence of soft particles alters the formation of force chains. Although soft particles are not part of high-load carrying chains, they play the important role of preventing the buckling of stiff particle chains. DOI: 10.1061/(ASCE)0899-1561(2007)19:2(179) CE Database subject headings: Elasticity; Mixtures; Porosity; Shear waves; Velocity.

Bender elements are convenient shear wave transducers for instrumenting soil cells due to optimal soil-transducer coupling and compatible operating frequency. Experimental and analytical methods are implemented in this study to explore various aspects of bender element installations including: electromagnetic coupling prevention, directivity, resonant frequency, detection of first arrival, and near field effects. It is shown that electromagnetic coupling effects are critical in soils with high electrical conductivity and can be minimized by shielding and grounding, or by using parallel-type bender elements. Bender elements generate both P- and S-waves. The in-plane S-wave directivity is quasicircular. The resonant frequency of bender element installations depends on the geometry of the bender element, the anchor efficiency, and the soil stiffness. The cross correlation of subsequent reflections is a self-healing measurement procedure which resolves uncertainties in both travel time and travel distance. Near field effects can be effectively taken into consideration by matching the measured signal with the analytical solution, directly rendering shear wave velocity. DOI: 10.1061/(ASCE) 1090-0241 (2005)131:9(1063) CE Database subject headings: Analytical techniques; Coupling; Resonance; Signal processing; Shear waves; Wave reflection.

The global response of a soil is affected by spatial as well as temporal scales. An electrical needle-size probe is developed to effectively assess one-dimensional spatial variability. The probe is designed for laboratory specimens (needle diameter 1.2-2.2 mm), and it can be scaled for field applications. Design considerations include the tip shape, insertion disturbance, electrochemical effects, corrosion, operating frequency, and electrical resonance. Two calibration methods are presented to determine local soil permittivity and resistivity from the measured complex impedance; the simplified calibration procedure is based on resistance measurements only. The local electrical parameters permit one to infer the soil porosity and the electrolyte conductivity. The attainable spatial resolution depends on the needle diameter; submillimetric resolution is typically achieved in laboratory applications. Reconstituted sand specimens and undisturbed clayey specimens are tested to explore the resolution potential of this probe. The electrical needle probe clearly detects the spatial variability that results from different specimen preparation methods in sands and soil layering from natural formation histories such as those in varved clays. CE Database subject headings: Corrosion; Electrical resistivity; Interfaces; Layered soils; Porosity; Penetration; Penetrometers.

Sediments experience shear and volumetric strains during freeze–thaw cycles. Measurements during globally drained and undrained cycles under constant deviatoric stresses show that the asymptotic shear and volumetric response vary with sediment type and drainage conditions. In particular, the sediment response is intimately related to the ice pore habit that results from effective stress and the ice capillary pressure σz′/Δuiw. Pore-invasive ice formation in coarse-grained soils may trigger some contraction during the first freeze–thaw cycle, even in sands denser than the critical state. Grain-displacive ice growth in fine-grained soils causes cryogenic consolidation of the surrounding sediment; subsequent melting of the segregated ice lenses yields a high increase in pore water pressure during undrained thawing, a pronounced volume contraction under drained conditions, and preferential shear deformation along melting ice lenses in either case. Both dilative sand and normally consolidated (NC) clay specimens subjected to deviatoric loading exhibit unceasing vertical strain accumulation (i.e., ratcheting) during freeze–thaw cycles; the void ratio evolves toward asymptotic values in all cases. The freezing rate relative to the pressure diffusion rate Π=DT/Cv regulates drainage conditions during freeze–thaw cycles; globally drained freezing and thawing are anticipated in coarse-grained sediments. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the effects of an inclined base plate on the end bearing capacity of embedded piles and soil behavior below a pile base according to the vertical stress and inclination angle of the base plate. Two types of model piles were prepared: a conventional pile with a flat base plate with a diameter of 50 mm and piles with an inclined base plate with a diameter of 56 mm. Load tests were conducted using model piles with a diameter of 50 mm incorporated with load cells and bender elements in a calibration chamber. The end bearing capacity, unit end bearing capacity, and shear wave velocity increase for all model piles with an increase in the vertical stress and in the inclination angle. The increment in the end bearing capacity may result from the increased projected area, the increased contact area between the inclined base plate and soil, and increased horizontal effective stress. The unit end bearing capacity also demonstrates a good relationship with the shear wave velocity, which is a function of the horizontal effective stress below the pile base. This study suggests that piles with inclined base plates may be effectively used in the embedded pile method to improve the end bearing capacity. [ABSTRACT FROM AUTHOR]

The objective of this study is to develop and apply reflection methods for guided ultrasonic waves used in evaluating the grout condition of rock bolts installed in a rock mass. Three types of rock bolts with different grouting ratios are prepared. First, piezoelectric disk elements are used as the source of guided ultrasonic waves to investigate grouted nonembedded rock bolts. Second, reflection methods with piezo disk elements and hammer impacts are used with rock bolts embedded in concrete columns. Third, a hammer impact with a center punch is applied for investigating rock bolts embedded in a rock mass in the field. The measured guided waves were analyzed using wavelet transforms. The peak magnitudes of the wavelet transform are used for group velocity calculations. Although piezo disk elements are sufficient as sources for nonembedded rock bolts and rock bolts installed in concrete columns, they do not provide sufficient energy in the field. However, a hammer impact with a center punch can generate guided ultrasonic waves with enough energy to evaluate the nongrouted ratio in rock bolts embedded in a rock mass. The group velocities of the guided ultrasonic waves increase with increasing nongrouted ratio. This study demonstrates that the suggested hammer impact method is effective for evaluating the nongrouted ratio of rock bolts in the field. [ABSTRACT FROM AUTHOR]

A weak railway subgrade may lead to instability of the railway track system. The condition of a railway subgrade is typically evaluated using trial pit excavation and a portable ballast sampler, which may severely disturb the ballast layer. Also, nondestructive geophysical techniques, such as ground penetrating radar (GPR), are used to investigate the condition of the ballast and subgrade along the track. The objective of this study is the development and application of a cone penetrometer with a helical-type outer screw rod (CPH) that minimizes the disturbance of the ballast layer for the evaluation of the subgrade condition by measuring the resistance of the cone tip. The CPH consists of a helical-type outer screw rod (helical rod) and a mini cone penetrometer inside the rod. The design concerns include easy installation of the helical rod into the ballast layer, the reaction force of the mini cone penetrometer, installation of the strain gauge, and calculation of the cone tip resistance. The helical rod, which penetrates into the ballast layer with a rotation force, provides the reaction force for the mini cone penetration test. The mini cone penetrometer with a diameter of 15 mm is pushed into the subgrade (sand layer) at the penetration rate of . In addition, dynamic cone penetrometer (DCP) tests are carried out to compare the cone tip resistance with the DCP index (DCPI). Field application tests reveal that the cone tip resistance increases with an increase in the depth and is inversely proportional to the DCPI. On the basis of the cone tip resistance, the soil types of subgrade at three sites are classified as sandy silt to silty sand. This study suggests that the CPH may be a useful device for providing a reliable geotechnical parameter and estimating the subgrade condition with minimal disturbance of the ballast layer. [ABSTRACT FROM AUTHOR]

Electrical properties of soils have commonly been used to estimate geotechnical properties. This paper introduces a new device, an electrical resistivity cone probe (ERCP), to determine the electrical resistivity of seashore soft soils and estimate void ratio in the field. The probe consists of inner and outer electrodes with a coaxial structure. The probe tip is conical to minimize disturbance during penetration. A four-terminal pair configuration is used to prevent electrical interference. The electrical resistance is measured during a consolidation test, penetration tests in a large-scale calibration chamber, and at two field sites. With the resistivity of soils and electrical resistivity of pore water extracted from undisturbed soils, the void ratio is estimated using Archie's law. The void ratio estimated by the ERCP in an oedometer cell is almost the same as the volumetric void ratio of sand determined from consolidation tests. In addition, the void ratio profile obtained by the ERCP agrees well with the volume-based void ratio in a sand-clay mixture prepared in the calibration chamber. The void ratio profile estimated in the field is inversely proportional to the standard penetration testing N-value and the cone-tip resistance of the cone penetration test. This paper demonstrates that the ERCP may be an effective device for the estimation of the void ratio of seashore soft soils. [ABSTRACT FROM AUTHOR]