K0 Condition Research Articles

A comparison of shear modulus of unsaturated sand in triaxial and simple shear tests under different strains and suctions

The shear modulus (G) in sands changes when subjected to variations in the degree of saturation. The matric suction in unsaturated sands increase the effective stress and consequently the shear modulus. The trend of G/Gsat variations is complicated as it is dependent on a number of parameters including stress state and therefore, requires more in-depth evaluations. Several isotropic cyclic triaxial as well as simple shear tests (K0 condition) are carried out under various degrees of saturation and strain amplitudes on a fine angular to sub-angular silica sand. The results show greater values of G from triaxial tests as compared to simple shear tests under similar vertical stress and void ratio, mainly due to a higher mean effective stress at isotropic triaxial condition. Besides, the two different stress states of isotropic and K0 conditions resulted in different curves of G/Gsat at the examined range of suction. Based on the measured values, G/Gsat variations versus matric suction cannot be well predicted solely by contribution of suction in the effective stress, but the variations of the degree of saturation with suction should be taken into account.

Anisotropy of elastic wave velocity influenced by particle shape and fabric anisotropy under K0 condition

Non-cohesive granular materials exhibit fabric-induced anisotropy of small-strain stiffness. The stiffness anisotropy is often measured using dynamic wave measurements in the laboratory. It is widely accepted that elastic wave velocities are influenced by stress state, while the role of particle shape in the wave velocity anisotropy, and thus the stiffness anisotropy, has not been fully understood. The difficulty arises partially from the incomplete understanding of particle-scale responses of granular materials. Considering 1D vertical compressoin with zero lateral strains (K0 condition) analogue to in-situ ground, this contribution performs wave propagation simulations using discrete element method and explores how particle shape and packing characteristics influence the anisotropy of elastic wave velocity. Sphere clumps with various aspect ratios are used. The orientation of the particle major axis is varied systematically by inhibiting particle rotation during dry-pluviation process. The simulation results reveal that the wave velocity anisotropy is largely affected by the combined effect of the particle aspect ratio and the orientation of particle major axis. Micromechanical analyses on assemblies of sphere clumps and ellipsoids shed light on the importance of the inter-particle contact stiffness, in addition to the particle aspect ratio and fabric, to determine the wave velocity anisotropy when non-spherical particles are used.

The effect of confinement in liquefaction tests carried out in a cyclic simple shear apparatus

The cyclic simple shear tests can be used to reproduce in laboratory the complex behaviour of the soil during an earthquake, simulating the continuous rotation of the principal stress axes. In this research a comparison of results between cyclic simple shear tests carried out with confining pressure or confining rings is reported. A cyclic simple shear apparatus is used to carry out tests with confining rings (the conventional way to carry out cyclic simple shear tests) and with a confining pressure applied to the specimen through pressurized water, where the K0 condition during consolidation is guaranteed by a sophisticated control system. The apparatus, in both the configurations, is described in detail. All tests were carried out on reconstituted specimens of an Italian sand with similar initial conditions, such as low relative density and confining pressure. All experimental results are reported in the plane cyclic stress ratio (CSR) and number of cycles where liquefaction occurs (Nliq) in order to evaluate the effect of confinement on the liquefaction resistance of the studied sand.

Flexural fatigue strength of demolition aggregates stabilized with alkali-activated calcium carbide residue

Replacing the base and subbase layers in flexible pavements and sub-ballast layer in railway tracks with recycled materials has attracted significant attention from industry and researchers alike. The semi-rigid stabilized layers in the flexible pavement structure and railway tracks sustain high flexural and tension stresses which reduces the serviceability life of the superstructure. The flexural and compressional modulus of the stabilized materials under repeated loads and at at-rest k0 condition is highly dependent on the specifications of the binder. Industrial by-products including calcium carbide residue (CCR), Fly Ash (FA) and Slag (S) were utilized to improve the compressional resilient modulus, flexural strength, durability and fatigue life of recycled aggregates. The variation of ductility in the blend with different precursors indicated that the service life of the stabilized layers not only depended on the strength but was also controlled by the deterioration rate of the flexural modulus and stiffness of the sample. The ductility of binder with aluminosilicate gels fabric can potentially absorb the stresses of the cyclic loading and postpones development of tension cracks.

Laboratory observation of engineering properties and deformation mechanisms of cemented rubber-sand mixtures

This paper presents details of a study that deals with investigation of compression behaviors, stiffness properties, and microstructural characteristics of lightly cemented and uncemented rubber-sand mixtures. The rubber-sand mixtures specimens were prepared with various sand volume fractions to evaluate its effects on the engineering properties. The specimens were subjected to different levels of vertical stress under K0 condition and the shear wave velocity (Vs) was measured simultaneously by bender elements during the compression process. Investigations were carried out with respect to the effect of sand fraction and the level of vertical stress on the overall rubber-sand mixtures properties including stress-strain characteristics, Vs, and small strain shear modulus (G0). In addition, scanning electron microscopy analysis was conducted to understand the variations in microstructure and the deformation mechanisms controlling the changes in engineering properties of the cemented rubber-sand mixtures. The study reveals that sand fraction has a considerable influence on the mass density (ρ), stress-strain characteristics, and stiffness properties of cemented and uncemented mixtures. These changes are attributed to the remarkable difference of engineering properties between shredded rubber and sand particles. The vertical strain presents three behavior regions as a function of stress in semi-log scale for lightly cemented rubber-sand mixtures: bonding control, bonding degradation, and stress control. Residual strain of the specimen decreases with an increase in sand fraction, and its value of cemented specimen is much lower than that of uncemented specimen. The Vs and G0 dramatically increase with an increase in sand fraction and vertical stress. A good linear relationship is proposed between Vs and vertical stress for uncemented rubber-sand mixtures. Additional loading of the vertical stress decreases the increment of Vs as a result of bonding degradation. The response of stress-strain and Vs can be employed as indicators of cementation degradation. Two different deformation mechanisms: rubber particles deformation and the force chains generated by sand particles were proposed for rubber-sand mixtures with different sand fractions. Rubber particles sustain loads and suffer a dramatical shape change when mixtures with a small amount of sand, whereas they play an important role in preventing the buckling of sand particle chains with high sand fraction.

Strain-Controlled Cyclic Simple Shear Tests on Sand with Radial Strain Measurements

AbstractStrain-controlled cyclic simple-shear tests were performed on silica sand with radial strain measurements. The specimens were tested under a constant K0 condition and subjected to cyclic loading and postcyclic monotonic loading. Threshold cyclic shear strain, volumetric strain, secant shear modulus, and damping ratio are investigated. Generally, the volumetric strain behavior in this study agreed well with literature findings that were investigated using the conventional cyclic direct simple shear test (without radial constraints). Radial strain during monotonic simple shear (postcyclic loading) was found to be a good parameter in monitoring the onset of flow slide in cohesionless soil. The concept of threshold cyclic shear strain, γt, was adequately applied in assessing the specimen volume change. Dynamic engineering properties, including equivalent shear modulus and damping ratio, were also studied. The damping ratio was found to decrease when the cyclic shear strain amplitude was greater than 2...

Structural performance of final lining according to the rock load shape

The purpose of this study is to analyze the structural performance of the lining according to the magnitude as well as shape of rock load. Four cases of rock load shape were applied on the final lining (concrete lining) to perform structural analysis using beam spring model. This study includes two contents; firstly, the stability of the lining was analyzed using capacity diagrams. Secondly, the serviceability of the lining was analyzed using the cracked hinge model. While assessing the stability of the lining, FS = 2.45 was used according to LRFD specifications. The stress-crack opening relationship, represented by g(w) function, was used to assess the serviceability of the lining. The critical parameters used in this study are the K0 condition, load direction and application of the wedge load. Based on the results obtained after analysis, it was concluded that the K0 condition could change the thrust force-bending moment relationship which affects the stability and serviceability of the lining. Rock load in vertical direction affected the lining more than that in horizontal direction. Lastly, the development of wedge load proved to be more adverse than the application of larger uniform rock load on the lining.

Effects of fabric anisotropy on elastic shear modulus of granular soils

The fabric anisotropy of a granular soil deposit can strongly influence its engineering properties and behavior. This paper presents the results of a novel experimental study designed to examine the effects of fabric anisotropy on smallstrain stiffness and its evolution with loading on the elastic shear modulus of granular materials under a K0 condition. Two primary categories of fabric anisotropy, i.e., deposition-induced and particle shape-induced, are investigated. Toyoura sand deposits with relative densities of 40% and 80% were prepared using deposition angles oriented at 0° and 90°. Piezoelectric transducers were used to obtain the elastic shear modulus in the vertical and horizontal directions (Gvh and Ghh). The measurements indicate distinct differences in the values of G with respect to the different deposition angles. Particle shapeinduced fabric anisotropy was examined using four selected sands. It was concluded that sphericity is a controlling factor dominating the small-strain stiffness of granular materials. The degree of fabric anisotropy proves to be a good indicatorin the characterization of stress-induced fabric evolution during loading and unloading stress cycles. The experimental data were used to calibrate an existing micromechanical model, which was able to represent the behavior of the granular material and the degree of fabric anisotropy reasonably well.

Liquefaction characteristics of gap-graded gravelly soils in K0 condition

A series of undrained cyclic direct simple shear tests, which used a soil container with a membrane reinforced with stack rings to maintain the K0 condition and integrated bender elements for shear wave velocity measurement, were performed to study the liquefaction characteristics of gap-graded gravelly soils with no fines content. The intergrain state concept was employed to categorize gap-graded sand–gravel mixtures as sand-like, gravel-like, and in-transition soils, which show different liquefaction characteristics. The testing results reveal that a linear relationship exists between the shear wave velocity and the minor fraction content for sand–gravel mixtures at a given skeleton void ratio of the major fraction particles. For gap-graded gravelly sand, the gravel content has a small effect on the liquefaction resistance, and the cyclic resistance ratio (CRR) of gap-graded gravelly sands can be evaluated using current techniques for sands with gravel content corrections. In addition, the results indicate that the current shear wave velocity (Vs) based correlation underestimates the liquefaction resistance for Vs values less than 160m/s, and different correlations should be proposed for sand-like and gravel-like gravelly soils. Preliminary modifications to the correlations used in current evaluations of liquefaction resistance have thus been proposed.

Impact of multidirectional shaking on liquefaction potential of level sand deposits

Multidirectional shearing, as induced by multidirectional shaking, involves variations not only in shear magnitude but also in shear direction, and in general involves deformations non-coaxial with the stress. Experimental results on saturated sand specimens using a biaxial simple shear device suggest that loading involving changes of direction may introduce significant reduction in the liquefaction resistance of cohesionless soil. However, centrifuge test results indicate that biaxial shaking has only limited impact on the liquefaction potential of level sand deposits. From numerical analysis, using a fully coupled ground response procedure (SUMDES) incorporating a comprehensive constitutive model for sand, and a theoretical study on the basis of the theory of plasticity, it was found that the in situ k0 condition, and the fact that the mobilised shear stress under earthquake tends to decrease as the excess pore pressure builds up, abate the effect of multidirectional shearing on level ground response.

Effect of Microfabric on Shear Behavior of Kaolin Clay

The influence of geometric arrangement of platelets (microfabric) on the mechanical behavior of kaolin clay is investigated using lubricated end triaxial testing on solid cylindrical specimens. A series of compression and extension tests under drained and undrained conditions were performed on clay specimens with different microfabric for overconsolidated ratio values of 1 and 10. The solid cylindrical specimens with dispersed and flocculated microfabric were produced in the laboratory using slurry consolidation technique under K0 condition. Based on the experimental observations, it is evident that microfabric strongly affects the mechanical behavior of kaolin clay, such as its stress–strain relationship, effective stress ratio, shear strength, excess pore-pressure evolution, and volumetric response. The influence of confining pressure on clay specimens with dispersed and flocculated microfabric is also studied in this research. This study shows that the microfabric can change the basic nature of clay. For example the normally consolidated kaolin clay shows its dilative nature during shearing for dispersed microfabric and contractive nature for flocculated microfabric.

K0 estimation in level granular soil from anisotropic wave velocities on the basis of micromechanics

AbstractThis study aims to explore the possibility for estimating K0 in a level ground of granular soil by seismic methods on the basis of micromechanics theory. The idea was to simulate in situ cross‐hole seismic method for the measurement of wave velocities along various directions of wave‐propagation. This work made use of a field simulator to control a K0 condition (zero lateral strain condition) in specimens. A series of vertical loading containing subsequent loading and unloading were applied to the specimen prepared by pluviation. In general, the K0 values determined experimentally in this work agreed with the exiting empirical relations. K0 value was also calibrated from measured anisotropic wave velocities using an optimization procedure. From the comparison of the back‐calculated and measured results of K0, it revealed the feasibility for the determination of the in situ lateral stress in granular soil by seismic methods and on the basis of micromechanics theory as long as enough wave‐velocity measurements along various directions of wave‐propagation were available. The potential for the usage of the presented methodology for the determination of the in situ lateral stress in level‐ground of granular soil by seismic methods seems encouraging. Copyright © 2004 John Wiley & Sons, Ltd.

Fabric evolution of granular assembly under K0 loading/unloading

AbstractThis study attempted to investigate the fabric evolution in K0 loading/unloading. The work made use of a field simulator to control K0 loading/unloading in large specimens prepared by air‐pluviation. In each loading stage, wave velocities along various propagation directions were measured. On the basis of the theories of micro‐mechanics and wave propagation, the microscopic parameters of the granular assembly were back calculated to investigate the fabric evolution of granular soil during K0 loading/unloading.In this study, the Geometric fabric was modelled by fabric tensors of ranks 2 and 4. The comparison of calibrated results using ranks 2 and 4 revealed the advantage of the usage of rank‐4 fabric tensor in modelling fabric evolution in spite of its complexity.By comparing relative magnitudes of vertical and horizontal components of geometric fabric, it was demonstrated that relative constraint in lateral directions increased during K0‐unloading in order to maintain a K0 condition. It revealed that fabric evolution was responsible for a higher K0 in unloading than K0 in loading. Copyright © 2003 John Wiley & Sons, Ltd.

Stress-Induced Anisotropic G m a x of Sands and Its Measurement

Anisotropy in elastic shear modulus Gma x exists in most soils as the result of either anisotropic soil fabric or anisotropic stress conditions. This paper presents a theoretical and experimental study on the anisotropy in a Gma x of sand due to a K0 stress condition. Elastic shear moduli of two types of sand in multiple stress planes under a K0 condition were measured using bender elements. Stress-induced anisotropy in Gma x of the sands during loading and unloading processes and the important influential factors were investigated. An empirical relationship for the estimation of K0 was proposed based on the experimental data. Shear moduli in nonprincipal stress planes were measured and compared with the results from the theory. The influence of stress cycles on Gma x in multiple stress planes was studied.

Application of Bender Elements in Measuring Gmax of Sand Under K Condition

Abstract A new application of bender elements to measure the small strain shear modulus of sand in multiple shear planes under anisotropic loading is developed. The tests were conducted in a specially designed oedometer with the side of the ring smoothed by a Teflon sheet. The soil used in the tests is clean angular pool filter sand. The effects of size of bender elements on the results of shear wave velocity measurement are discussed. Shear modulus in four different shear planes during a loading-unloading cycle is presented. The results of experiments are compared with the Hardin-Blanford equation on Gmax, which shows good agreement. The influence of side friction of the oedometer is investigated.

K0 Consolidation of Undisturbed Clays by Means of Triaxial Cell

ABSTRACT It is well realized that the in-situ K0 stress condition of undisturbed soil samples should be reproduced in the laboratory test in order to inspect the mechanical properties of soil properly. In this study, an automatic triaxial testing system was newly developed, in which triaxial tests on undisturbed clay samples after reproducing the in-situ K0 stress condition can be carried out in a practical manner. According to the results of the tests with this system, it was made clear that the measured K0-value was largely affected by the compressibility of side drain paper and that the correction was necessary in order to reproduce the in-situ stress condition with the proper K0-value. The initial isotropic consolidation pressure at which the control of K0 condition started also had an important effect on the final K0-value. It is recommended that one sixth or one eighth of the preconsolidation pressure should be used as the initial isotropic consolidation pressure.

COMPRESSION AND STRENGTH CHARACTERISTICS OF UPPER PLEISTOCENE CLAY (Ma 12) IN OSAKA BAY

This paper deals with the mechanical properties of the Upper Pleistocene Clay which is deposited typically at the depth of 70 to 90m below sea level in the north areas of the Osaka Bay. The compression characteristics of the clay was investigated by carrying out a series of strain controlled drained triaxial tests including tests with K0 condition. The test results indicate that the variation of pre-consolidation pressure increases almost linearly with depth as compared with a large scatter of the data obtained from standard oedometer tests. Also the effect of aging on the mechanical properties of the clay was studied by comparing the behaviour of undisturbed and re-sedimented samples during oedometer and undrained triaxial tests. The results indicate that there is a significant effect of aging on the clay behaviour.

Integrated Study of Reinforced Earth–II: Behavior and Design

An analytical study using the finite element method of an instrumented reinforced earth wall constructed in Southern California is described. The analytical results are compared with the field performance data to illustrate the overall behavior of the structure. It is concluded that a reinforced earth wall is a relatively rigid self-supporting unit for which under normal conditions, the stress state within the wall is approximately the K0 condition, and the backfill just behind the wall approaches the Ka condition. The boundary geometry of the backfill, the foundation, and the compressibility of the foundation material intimately affect the magnitude and distribution of the reinforcing strip forces; compression forces may develop under particular combination of these physical parameters. Design procedures based on possible failure modes for the determination of size, spacing, and length of reinforcing strips are considered. /ASCE/