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Liquefaction resistance of sand can be either increased or reduced due to an undrained cyclic pre-shearing depending on the degree of pre-shearing, which hinders a better prediction of liquefaction potential to be established. The mechanism of such changes in liquefaction resistance has been poorly understood. This contribution aims to gain micromechanical insights into pre-shearing effects on liquefaction resistance of sand using discrete element method (DEM) simulations. In particular, effects of particle shape and initial anisotropy on liquefaction resistance are investigated. The simulation results from samples consisting of non-spherical particles with an initial anisotropy can qualitatively capture the mechanical responses observed in equivalent laboratory experiments. The samples which yielded a qualitative agreement with the laboratory results are further analyzed micromechanically, and the relationships between liquefaction resistance and some microscopic parameters before cyclic loading are discussed. Microscopic analyses reveal that mean mechanical coordination number is well correlated with liquefaction resistance, whereas liquefaction resistance is less sensitive to anisotropy in particle orientation induced by pre-shearing. [ABSTRACT FROM AUTHOR]

The 'press-in' method is a piling technique by which a pile is installed with a static jacking force while a reaction force is obtained from previously installed piles. The applicable ground conditions for this method have been significantly expanded by the 'Rotary Cutting Press-in (RCP)' method, whereby a vertical jacking force and a torque are applied simultaneously onto a pile with cutting teeth on its base while water is injected around the pile base. In this paper, a method to estimate the base capacity of RCP piles is proposed based on the UWA-05 framework. The proposed method utilizes CPT (cone penetration test) or SPT (standard penetration test) results as the input parameters and estimates the plugging condition (Incremental Filling Ratio, IFR) from these results. Four static load tests on open-ended RCP piles are shown to have been predicted well by the proposed method in terms of the base capacity, regardless of the embedment depth into the bearing stratum. [ABSTRACT FROM AUTHOR]

Since the mechanical failure of granular soils is the macro-manifestation of complex internal particle interactions, studying this relevant issue from micro-scale perspective is of fundamental importance. Acoustic Emission (AE) has become a promising approach for this purpose; however, its synthetic and validating study on granular soils with various ground conditions is far from substantive. In an attempt to verify and correlate the relationship between AE behaviors and mechanical behaviors of granular soils with various conditions, results of drained triaxial compression tests along with AE measurements recorded during testing are discussed. These results revealed intrinsically different propagation properties of acoustic waves between saturated and unsaturated/dry sands. The water in saturated sands facilitates acoustic waves to propagate with less attenuation, whereas discontinuities (i.e. particle-particle contacts and particle interfaces with water) in dry/unsaturated sands lead acoustic waves to propagate with larger attenuation. The AE manifestation showed its high sensitivity to different saturation degrees, package densities and confining stress levels, which allows the evaluation of ground conditions to be made by AE. The congruous AE evolution in saturated sands was considered closely related to particle interactions during drained triaxial compression; whereas the changeable AE evolutions in accordance with different failure patterns in dry sands were considered relating to soil structure behaviors. [ABSTRACT FROM AUTHOR]

An image-based measurement system was developed to evaluate the induced local deformations of saturated sand specimens in undrained torsional shear tests. The images of specimens taken by a camera in front of a pressure chamber were noticeably distorted. To correct the errors caused by the curvature of the specimens and by the refraction of rays traveling through water, acrylic resin, and the atmosphere, a coordinate correction method was proposed to convert the apparent coordinates obtained from the distorted specimen image into the real coordinates under planar conditions. This method was verified using a rigid dummy specimen and was illustrated using a sand specimen as an example. The results obtained indicate that the resolution of displacement measurements is approximately 0.01 mm, representing approximately 3.3e-5 of the specimen height. Moreover, high measurement accuracy is obtained even if the dummy specimen has undergone a rotation of up to 26.4°. This measurement system was further extended to directly evaluate the local deformation of sand specimens through a transparent membrane. The direct and indirect evaluations indicate that the direct evaluation is more effective for quantitatively representing specimen deformation than indirect evaluation since membrane wrinkles and vertical slippage between the specimen and membrane occurred during liquefaction. [ABSTRACT FROM AUTHOR]

It has been reported that soils belonging to slope grounds show different types of liquefaction behavior than those belonging to horizontal grounds. Some research has also revealed that liquefaction histories can significantly affect the shear behavior of sandy soils. However, the combined effects of the slope angle and the magnitude of past shear histories on the liquefaction properties of soils have not been studied comprehensively. Based on this background, several multiple liquefaction tests with initial static shear were conducted on Toyoura sand. In each of these tests, a single specimen was sheared several times up to small or large double amplitude shear strain under a constant volume condition using a specially designed stacked-ring shear apparatus. The behavior of the Toyoura sand observed in these tests was discussed considering various perspectives, such as the increase in relative density, the induced anisotropy, the change in liquefaction resistance, and the shear strain accumulation. The findings of this study established that shear histories of smaller magnitude had relatively less influence on densification and induced anisotropy than those of larger magnitude. Moreover, shear histories of smaller magnitude also resulted in the relatively higher liquefaction resistance of sand specimens against the next cyclic shear, while the opposite trend was observed in the case of specimens subjected to shear histories of larger magnitude. Finally, shear strain accumulated less easily in tests with small shear histories than in those with large shear histories. [ABSTRACT FROM AUTHOR]

The multiple liquefaction phenomenon has been attracting the attention of more and more researchers and engineers since the 2010–2011 Christchurch Earthquakes and the 2011 Great East Japan Earthquake. However, little has been known about the multiple liquefaction properties of sloped grounds. In this study, therefore, multiple liquefaction tests that consider the initial static shear stress, which have never been conducted before, were carried out with a special designed apparatus, the stacked-ring shear apparatus. A series of multiple liquefaction tests revealed that induced anisotropy, which is weak against the loading opposite to the direction of the initial static shear stress, was produced by the liquefaction of a sloped ground. As a result, a significant decrease in the liquefaction resistance during the next cyclic of shearing occurred. The indicators which influenced the magnitude of anisotropy were also discussed from the perspective of the reconsolidation procedures, the magnitude of initial static shear stress, and the type of ending of the previous liquefaction stage. In addition, it turned out that in the multiple liquefaction test with a larger initial static shear stress, the re-liquefaction resistance was higher because the shear stress opposite to the direction of the initial static shear stress, causing large negative dilatancy due to anisotropy, was smaller in that test. [ABSTRACT FROM AUTHOR]

Abstract To evaluate the local deformation properties of sand specimen directly in the undrained triaxial test, a procedure based on Particle Image Velocimetry was developed through using a transparent membrane. Cylindrical specimens using a mixture of silica sand particles in black and white colors were prepared by the moist tamping method with five sand layers and the air pluviation method. Comparisons of local deformations between the direct evaluation by sand particles patterns and indirect evaluation by dots pasted on the membrane were made for a single specimen. The results obtained in the undrained cyclic triaxial tests revealed that the local deformation properties of medium dense and dense silica sand specimens evaluated by the indirect observation were consistent with those evaluated by the direct observation before the onset of initial liquefaction, except for some regions near the bottom ends of the specimen. Unlike the air pluviation method, the moist tamping method induced undesirable stratification within the specimen, and this resulted in the occurrence of specimen necking. Meanwhile, a non-uniform local strain distribution was observed along the specimen prepared by moist tamping method even under an axial strain less than 2%. The relative movement between the membrane and sand specimen, or slippage, occurred at the liquefied status. The extent of vertical slippage was also impacted by the relative density of the specimen. [ABSTRACT FROM AUTHOR]

In this paper, a general solution for evaluating the Coulomb-type seismic active earth pressure that acts on a rigid retaining wall from the cohesive backfill soil is shown together with its derivation process. In the proposed solution, the mobilization of the cohesion on the failure plane in the backfill soil of the retaining wall and the associated increase in shear strength are considered in the pseudo-static limit equilibrium approach under the assumption that the cohesion is uniformly distributed in the backfill soil. The angle of the failure plane and the seismic active earth pressure calculated by the proposed equation completely agree with the calculation results by the trial wedge method, which shows the validity of the proposed solution. In addition, by combining the concept of the Modified Mononobe-Okabe method and the proposed equation, a calculation method for the seismic active earth pressure is proposed. It can consider the effect of backfill cohesion and can be applied even under a large seismic load. Furthermore, a series of trial analyses on the effect of backfill cohesion on the seismic performance of the retaining wall is also conducted using the proposed equation. A series of analyses using the case of a retaining wall damaged during the 1995 Hyogo-ken Nanbu earthquake shows that the effect of backfill cohesion is significant in the seismic performance evaluation and the design of aseismic reinforcements. [ABSTRACT FROM AUTHOR]

Over the past several years, the International Maritime Organization (IMO) has become increasingly concerned about the liquefaction of unsaturated solid bulk cargo (e.g. iron ore fines) during maritime transportation. This concern has arisen due to several accidents including the capsizing of vessels. In addition, although the resistance against liquefaction of ordinary unsaturated soils is higher than for saturated soils, possible key parameters governing the liquefaction resistance of unsaturated soils ( R L , unsat ) have not yet been clearly identified. Therefore, in this study, undrained cyclic loading tests of saturated and unsaturated iron ore fines and two sandy soils were conducted using a triaxial apparatus to reveal the liquefaction behavior of iron ore fines and to find the key parameters governing R L , unsat . Through comparisons, it was found that the liquefaction behavior of iron ore fines is similar to that of sandy soils. The degree of saturation and potential volumetric strain, which have been proposed as the governing parameters of R L , unsat , were examined based on experimental data obtained in this study and by other researchers. It was shown that neither of the two parameters correlate with the liquefaction resistance ratio (LRR), a ratio of R L , unsat to the liquefaction resistance of the saturated soils ( R L , sat ) with a unique relationship, especially when considering soils with considerable fines content. Following the concept of potential volumetric strain, which considers the compressibility of pore air in the unsaturated soils, volumetric expansion due to the reduction in confining pressure during cyclic loading is further considered, and a new index, the volumetric strain ratio ( R v ) is proposed in this study. According to the experimental data obtained in this study, R v exhibits a much better correlation with LRR than the two former parameters. [ABSTRACT FROM AUTHOR]

The liquefaction of sandy soil during earthquakes causes the uplift of relatively light structures such as open-cut railway tunnels. The potential for the uplift of underground structures is usually evaluated by the factor of safety against uplift ( F s ), which only considers the force equilibrium of the structures in the vertical direction. However, design procedures which employ the factor of safety to evaluate uplift may be too conservative for assessing the uplift behavior of underground structures. It is necessary to establish a new method to directly predict the residual displacement or to predict whether or not the uplift behavior will have a negative influence on the serviceability of underground structures. In this study, therefore, a series of shaking table tests was performed using the open-cut tunnel model, and the relationship among the uplift behavior of the tunnel, the degree of liquefaction, the external forces acting on the tunnel and the deformation of the liquefied ground was investigated through precise measurements. The experiment revealed that critical uplift behavior does not occur when the level and the area of liquefaction are limited to a restricted range even if the factor of safety against uplift falls to less than 1.0. After the wide area around the tunnel reached complete liquefaction, the uplift behavior of the tunnel increased rapidly. Based on these test results, the detailed mechanism of the uplift behavior and the applicability of the factor of safety were examined. In addition, a new method was suggested to evaluate the stability level of open-cut tunnels against uplift. [ABSTRACT FROM AUTHOR]

A series of drained triaxial compression tests was performed to evaluate the rate-dependent stress–strain behaviour of large- and medium-size undisturbed gravelly soil samples (UGSSs). A newly developed sampling method, using thick water-soluble polymer solutions, was employed for retrieving the samples from three tunnel excavation sites in Toyama Prefecture, Japan. To evaluate the rate-dependent stress–strain behaviour, the loading rate was changed stepwise many times and drained sustained loading was performed at prescribed stress states during otherwise monotonic loading at a constant vertical strain rate in the tests. The UGSSs from natural deposits at two of the sites exhibited Isotach-type viscous properties. For the UGSS retrieved from the site improved by chemical injection prior to the start of the excavation, the type of viscous property changed from Isotach to P&N with strain. A comparison between the values of the viscous parameters of reconstituted granular materials evaluated in previous studies and those of these UGSSs was discussed. Test results from drained unconfined compression tests were also presented to investigate the cementation of UGSSs. [ABSTRACT FROM AUTHOR]

A rammed earth technique is a traditional architectural technique to build soil structures by compacting geo-materials in a form. In this study, tensile strength properties of rammed earth materials and effects of test conditions are evaluated by conducting direct tension tests and splitting tests on several specimens. It is inferred from the result of these test that the direct tension test should be used to evaluate tensile strength of a layer interface, while the splitting test might evaluate the strength related to the tensile strength inside a compaction layer. When rammed earth structures are constructed, the results from the experiments indicate that it is important to scarify interfaces during compaction in order to prevent reduction and variation of the tensile strength of the layer interfaces. The tensile strength of the rammed earth specimens made of compacted soils without lime increased with the decrease in their water contents. The tensile strengths of the specimens represent 5.0–12.5% of corresponding values of unconfined compression strength at the same water content range. The tensile strength of rammed earth specimens made of lime-mixed soil was in the range of 15–20% of the corresponding unconfined compression strength at 28 days curing. In the series of cyclic tensile loading test, no significant reduction of tensile strengths was observed even after undergoing the cyclic loading history. [ABSTRACT FROM AUTHOR]

The creep failure behaviour of three reconstituted sands exhibiting various viscous property types was evaluated by large-, medium- and small-scale drained triaxial, and medium-scale drained unconfined compression tests. The creep characteristics were evaluated by performing sustained loading during otherwise monotonic loading at a constant loading rate. Creep failure and Isotach viscous stress–strain behaviour were observed with well-graded Miho sand compacted heavily under the optimum water content condition. Creep failure of saturated and air-dried Toyoura sand exhibiting TESRA viscosity was observed at the nearly peak stress state. Degradation of the shear modulus of Toyoura sand during creep failure process was measured by the dynamic method. Creep failure did not occur with air-dried Albany silica sand exhibiting P&N viscosity. It was experimentally shown that the stability against creep failure was higher in order of P&N, TESRA and Isotach viscosities. The creep behaviour of various viscous property types was well simulated by the non-linear three-component model taking into account the effects of particle characteristics on the viscous property parameters. [ABSTRACT FROM AUTHOR]

The liquefaction phenomena of sands have been studied by many researchers to date. Laboratory element tests have revealed key factors that govern liquefaction phenomena, such as relative density, particle size distribution, and grain shape. However, challenges remain in quantifying inherent anisotropy and in evaluating its impact on liquefaction phenomena. This contribution explores the effect of inherent anisotropy on the mechanical response of granular materials using the discrete element method. Samples composed of spherical particles are prepared which have approximately the same void ratio and mean coordination number (CN), but varying degrees of inherent anisotropy in terms of contact normals. Their mechanical responses are compared under drained and undrained triaxial monotonic loading as well as under undrained cyclic loading. The simulation results reveal that cyclic instability followed by liquefaction can be observed for loose samples having a large degree of inherent anisotropy. Since a sample having initial anisotropy tends to deform more in its weaker direction, leading to lower liquefaction resistance, a sample having an isotropic fabric potentially exhibits the greatest liquefaction resistance. Moreover, the effective stress path during undrained cyclic loading is found to follow the instability and failure lines observed for static liquefaction under undrained monotonic loading. From a micromechanical perspective, the recovery of effective stress during liquefaction can be observed when a threshold CN develops along with the evolving induced anisotropy. Realising that the conventional index of the anisotropic degree (a) is not effective when the CN drops to almost zero during cyclic liquefaction, this contribution proposes an alternative index, effective anisotropy (a×CN), with which the evolution of induced anisotropy can be tracked effectively, and common upper and lower bounds can be defined for both undrained monotonic and cyclic loading tests. [ABSTRACT FROM AUTHOR]

A constitutive model to describe the cyclic undrained behavior of saturated sand is presented. The increments in volumetric strain during undrained loading, which are equal to zero, are assumed to consist of increments due to dilatancy and increments due to consolidation/swelling. This assumption enables the proposed model to evaluate increments in volumetric strain due to dilatancy as mirror images of increments in volumetric strain due to consolidation/swelling, thus simulating the generation of excess pore water pressure (i.e., reduction in mean effective principal stress) during undrained cyclic shear loading. Based on the results of drained tests, the increments in volumetric strain due to consolidation/swelling are evaluated by assuming that the quasi-elastic bulk modulus can be expressed as a unique function of the mean effective principal stress. On the other hand, in evaluating the increments in volumetric strain due to dilatancy, a normalized stress–plastic shear strain relationship is employed in combination with a novel empirical stress–dilatancy relationship derived for torsional shear loading. The proposed stress–dilatancy relationship accounts for the effects of over-consolidation during cyclic loading. Numerical simulations show that the proposed model can satisfactorily simulate the generation of excess pore water pressure and the stress–strain relationship of saturated Toyoura sand specimens subjected to undrained cyclic torsional shear loading. It is found that the liquefaction resistance of loose Toyoura sand specimens can be accurately predicted by the model, while the liquefaction resistance of dense Toyoura sand specimens may be slightly underestimated. (i.e., the liquefaction potential is higher). Yet, the model predictions are conservative. [ABSTRACT FROM AUTHOR]

In order to describe the volumetric behavior of soil subjected to shearing, a relationship that deals with the ratio of plastic strain increments to stress ratio (i.e. a stress–dilatancy relationship) is required in addition to the stress–shear strain relationship. In view of the above, stress–dilatancy relationships during cyclic torsional shear loadings were experimentally investigated in the current study. Based on the experimental results, a bilinear non-unique stress–dilatancy model was proposed for stress controlled drained cyclic torsional shear loading. The stress–dilatancy relationships during virgin loading and subsequent cyclic loading were modeled separately by considering the effects of stress history (over-consolidation or normal consolidation). Then the volume change of Toyoura sand specimens subjected to cyclic torsional shear loading was simulated by combining the simulation of stress–shear strain relationship with the proposed stress–dilatancy relationships. It was observed from the comparison of the experiment results with the simulation of volumetric strain that, after combining with accurate modeling of stress–shear strain relationship, the proposed stress–dilatancy relationship can reasonably simulate the volumetric behavior of sand subjected to various drained cyclic torsional shear loadings. [ABSTRACT FROM AUTHOR]

The present text is a summary of liquefaction events that occurred in the Kanto Region during the 2011 off the Pacific coast of Tohoku Earthquake, excluding those events in the Tokyo Bay area that are discussed elsewhere. Most liquefaction occurred in the abandoned river channels and former lakes that had been recently filled with liquefiable soils. Noteworthy was the damage to private housing lands and river dikes that had not been well treated against liquefaction risk. Many sites experienced repeated liquefaction after former earthquakes in 1923 or 1987, if they existed in those times. In contrast to the recent liquefaction-prone soils, more-aged sands scarcely liquefied because of what is called the “ageing” effect. The present study analyzed cases in Tokyo area to quantitatively assess the temporal development of ageing so that liquefaction risk in more aged soils might be reasonably assessed. In the appendix, remarks are made of the reliability of air-photo survey in quick detection of liquefaction sites. [ABSTRACT FROM AUTHOR]

Abstract: The results of a series of large-scale triaxial tests performed on dense, prismatic gravel specimens, with a height of 50cm and a cross-section of 23cm×23cm, are described. The specimens were prepared at a density equal to approximately 95% of the maximum density at the optimum moisture content. Deformations were measured locally using vertical and horizontal local deformation transducers. Stress conditions with selected levels of very low confining pressure were used to simulate specific conditions in the case of road and railway embankments. Particular attention was paid to the bedding error at the top and the bottom ends of the specimens, and to fixing transducers onto the membrane to be used under low confining pressure. The confining pressure was applied by vacuum and varied from 10kPa to 75kPa. Unsaturated specimens were tested under drained triaxial compression using monotonic and cyclic loading with frequencies in the range of 0.5–5Hz. The effects of a large number of load cycles and of specimen preloading were investigated. [Copyright &y& Elsevier]

Abstract: A series of medium-scale and large-scale triaxial and unconfined compression tests was conducted in order to evaluate the strength and deformation characteristics and small strain properties of undisturbed well-graded gravelly soils retrieved from three tunnel excavation sites in Toyama prefecture, Japan. Undisturbed gravelly soils were taken by means of a new sampling method using thick water-soluble polymer solutions. The strength and deformation characteristics were evaluated mainly by performing sustained loading and large amplitude unloading and reloading cycles during otherwise monotonic loading at a constant strain rate in drained triaxial compression tests. During isotropic consolidation and shearing, at several stress states, eleven very small vertical cycles were applied to evaluate the quasi-elastic deformation property at small strain levels around 0.001% by static measurement. Dynamic measurements using a pair of accelerometers attached to the side surface of the specimen and wave sources attached to the top cap were also conducted at the same stress levels as static measurements in a single test. Several effects including grading characteristics and pressure level on the difference between the moduli measured statically and dynamically were discussed. The relationship between the small strain and strength properties of undisturbed gravelly soils was evaluated. The small strain properties of air-dried dense Toyoura sand in large-scale triaxial compression tests were also investigated in this study to compare the results of undisturbed gravelly soils. [Copyright &y& Elsevier]

Abstract: Strain localization, or the formation of shear bands, is a key aspect in understanding soil failure mechanisms. While efforts have been made in terms of measuring the shear band properties and the stress–strain behavior within shear bands, there are still uncertainties regarding when shear bands initiate and their influence on the development of large ground deformation. In this paper, the limiting value of shear strain, at which strain localization appears during undrained cyclic torsional shear tests with initial static shear, performed on loose Toyoura sand specimens (Dr=44–48%) up to a single amplitude of shear strain exceeding 50%, was evaluated. Non-uniform specimen deformation was observed at strain levels larger than 20%. However, the onset of strain localization could not be defined on the basis of visual observations. Therefore, the limiting values for half of the double amplitude (γ DA/2) and single amplitude (γ SA) shear strain, to initiate strain localization, were determined from test results based on changes in the deviator stress response and strain accumulation properties as well as changes in the strain-softening behavior during cyclic shear. It was found that γ SA is a more appropriate parameter than γ DA/2. Irrespective of the static shear stress level, the limiting strain value for γ SA was evaluated to be in the range of 23–28% for liquefied loose Toyoura sand specimens (i.e., stress reversal and intermediate tests). Alternatively, the limiting strain value could not be properly defined when liquefaction did not occur (i.e., non-reversal stress tests), although various methods were employed. [Copyright &y& Elsevier]

Abstract: Statistics are compiled on the damage to railway earth structures, soil retaining walls and bridge foundations caused by the 2011 off the Pacific Coast of Tohoku Earthquake in Japan and the subsequent tsunami. Several case histories are reported on the damage they created and the rehabilitation works implemented, including the collapse of a high cut slope, the excessive settlement of embankments in lowland areas, the significant scoring of the backfill soil of bridge abutments, the restoration works of tilted bridge foundations and the tsunami-induced collapse of soil-retaining walls and bridge foundations. The good performance of well-designed foundations, which were able to survive the impact of the earthquake, particularly the effects of the earthquake-induced liquefaction of the subsoil layers, is also described. [Copyright &y& Elsevier]

Abstract: This study focused on the role which static shear plays on the large deformation behavior of loose saturated sand during undrained cyclic loading. A series of undrained cyclic torsional shear tests was performed on saturated Toyoura sand specimens up to single amplitude shear strain exceeding 50%. Three types of cyclic loading patterns, i.e., stress reversal, intermediate and non-reversal, were employed by varying the initial static shear level and the cyclic shear stress amplitude. The observed types of failure could be distinguished into liquefaction (cyclic and rapid flow) and residual deformation by comparing both monotonic and cyclic undrained behavior. It was found that the presence of initial static shear does not always lead to an increase in the resistance to liquefaction or strain accumulation; they could either increase or decrease with an increasing initial static shear level depending on the type of loading pattern and failure behavior. In addition, according to the failure behavior which the specimens exhibited, three modes of development of large residual deformation were observed. [Copyright &y& Elsevier]