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The property of one-dimensional compression for hydrate-bearing soil is an important means to analyze the deformation of hydrate-bearing strata. Based on the physical properties of sediments from SH3 boreholes in Shenhu sea area of the South China Sea, fine-grained soil was artificially prepared as hydrate occurrence medium, and hydrate-bearing soil samples were formed and one-dimensional compression tests were carried out. The effects of hydrate saturation and ambient temperature on the compression deformation of hydrate-bearing soil were studied. The test results show that as the saturation of hydrates increases and the ambient temperature decreases, the soil containing hydrates becomes more difficult to compress and its compressibility decreases. The influence of hydrate saturation and ambient temperature on pre-yield compression index and swelling index is not obvious, but the increase of hydrate saturation and decrease of ambient temperature will significantly reduce the pre-yield compression index and increase the preconsolidation pressure. The formation of hydrate fills the pore space and solidifies soil particles, but the decrease of environmental temperature makes the cementation more obvious, and it is difficult for the soil particles and hydrate particles to move and rearrange, so the soil is difficult to be compressed and the overall structure becomes stronger and stronger as the pre-consolidation pressure increases. According to the analysis, the empirical relationship between the preconsolidation pressure and the hydrate saturation is proposed, and the mathematical expression which can effectively describe the one-dimensional compression curve is given. [ABSTRACT FROM AUTHOR]

Freeze–thaw (F-T) cycles are one of the most important factors affecting the performance of silty soils with high kaolin content in seasonally freezing regions. This study investigates the improvement of a high-plasticity clayey silt soil (MH) with microencapsulated phase change material (mPCM) to prevent changes in mechanical properties when subjected to freeze–thaw cycles. Unconfined compression, one-dimensional compression, and freeze and thaw tests were performed to evaluate the behavior of treated soil under different freeze/thaw cycles and with different mPCM ratios. It has been observed that the mPCM additive decreased the unconfined compression strength (UCS); however, the strength of the soil held constant during the increasing F-T cycles, and the increase in the mPCM additive content increased the strength of the soil. The inclusion of mPCM affected the compression of the soil and increased settlement (∆H), although the settlement remained constant with increasing freeze–thaw cycles. It has been noted that the compression behavior, which is least affected by the unconfined compressive strength and freeze/thaw cycles, is achieved with the addition of 10% mPCM. As a result of the tests, it was determined that the most suitable additive mPCM ratio is 10% for the compression and strength behaviors. [ABSTRACT FROM AUTHOR]

We proposed a new gasification method to convert unused organic matter in sedimentary rocks to bio methane gas using microorganisms, known as Subsurface Cultivation and Gasification (SCG). Our approach uses hydrogen peroxide (H2O2) to decompose organic matter rapidly into usable substrates for methanogens. We previously reported that H2O2 would be useful for effective SCG at lignite, and conversion of organic matter from lignite into biogenic methane with the help of microorganisms is expected to be highly profitable. However, physical properties of the sedimentary rock are thought to change with the decomposition of sedimentary rock in the SCG method. A series of one-dimensional compression tests were performed for artificial coal seams prepared using the lignite sampled from Tempoku coalfield in the northern Hokkaido to investigate the stability of coal seam during an industrial production of substrates for methanogens in the subsurface environment. H2O2 was used in the one-dimensional compression tests to produce lower-molecular-weight organic components as a substrate of methanogen. Moreover, H2O2 solution was repeatedly injected into the artificial coal seam under compressive pressure. Oxidative decomposition of the artificial coal seam produced a high yield of low-molecular-weight organic acids. However, settlement of the artificial coal seam subjected constant loading was dependent on concentration and injection amount of H2O2. The biomethane deposits might become mechanically unstable during promoting decomposition of organic matter of coal seams, even if lignite has the greater resource potential for biomethane.

Particle breakage and the corresponding change of morphology are two key factors governing the mechanical behavior of calcareous sands in offshore geotechnical engineering constructions. To reveal the characteristics of these two factors, oedometer tests on calcareous sands have been performed in this study. The materials were sampled from the South China Sea with a homogenous composition but different particle size ranges and relative densities. In these tests, the dynamic imaging analysis (DIA) by Microtrac PartAn3D and acoustic emission (AE) techniques were employed to investigate the evolution of particle morphology and characteristics of AE signaling associated with the material deformations, respectively. The compressive deformation of calcareous sands was mainly induced by the particle rearrangement and particle breakage which are effectively irreversible plastic deformations. The irregular particle shape has led to strong interparticle filling and interlocking effects, which affected the particle slippage and rearrangement significantly during the deformation. The intensity and type of AE-triggering micro-mechanical behaviors were characterized by AE ringdown counts (RDC) and peak frequency, respectively. The RDC values concentrated primarily in the compression stage and increased rapidly under the normal stress of 400–3200 kPa. The RDC values increased with the increase of particle size but decreased with the increase of initial relative density. The compressive deformation and breakage characteristics of calcareous sands are consistent with the existing acoustic emission laws. [ABSTRACT FROM AUTHOR]

An elastoplastic numerical model for calculating the consolidation settlement of wide embankment on soft ground is established using PLAXIS finite element software to investigate the settlement behaviour of soft ground under the wide embankment. The distribution rules are analysed and compared to narrow embankments, such as surface settlements of ground and embankment, lateral displacement of soft ground at the foot of embankment slope and excess pore pressure in soft ground. The influence rule of elastic modulus of soft ground on the settlement of soft ground under wide embankment is discussed. The results show that the settlement distributions of wide and narrow embankments on soft ground are “W” and “V” shapes, respectively. The maximum settlement of wide embankment is near the foot of the embankment slope, which is unequal to the settlement at the centreline of the embankment. The lateral displacement distribution rules of soft ground are both “belly” shaped at the foot of two types of embankments slope. However, the lateral displacement of the wide embankment is larger in each corresponding stage. During the construction period, the excess pore pressure in the soft ground under the wide embankment is much higher than that of the narrow embankment, so the post-construction consolidation time of the wide embankment is longer. Moreover, the macroscopic settlement rule of the wide embankment is still the same with the increase of elastic modulus of soft ground.

For islands in marine environments, groundwater levels vary due to the influence of tides. As a result, the external environment of backfilled carbonate sands on islands alternates between dry and wet conditions. In this paper, a series of one-dimensional compression tests and direct shear tests were carried out to examine the compression characteristics, shear strength and particle breakage of carbonate sand from the Xisha Islands subjected to drying and wetting cycles. Drying and wetting cycles dramatically increased the compressibility and reduced the shear strength of the carbonate sand. Based on the test results, a modified compression model was suggested to consider the effect of drying and wetting cycles, and the influence of drying and wetting cycles on shear strength was also presented. Sieving test results showed that the carbonate sand particles were more prone to crushing under the influence of drying and wetting cycles, which could be the main reason for the changes in the mechanical properties of the carbonate sand. In both compression and shear tests, there was a good linear relationship between relative breakage and drying and wetting cycles, as well as between fractal dimension and drying and wetting cycles. However, the relationship between fractal dimension and relative breakage differed between the two tests, suggesting that particle breakage evolves according to different modes under different stress paths. The changes in the mechanical properties and particle breakage of carbonate sand under drying and wetting cycles warrant the attention of engineers. [ABSTRACT FROM AUTHOR]

Despite the significant progresses in the multi-scale studies of sand-rubber mixtures, the load-transfer mechanism within the soft-rigid granulate networks is highly unexplored. In this study, roles of sand and rubber particles in different contact networks subjected to constrained compression were investigated using DEM. The simulations were respectively calibrated using experimental data at element and grain scales, providing an opportunity to look at the role of rubber within whole granulate networks. When the behavior of mixtures is dominated by sand (rubber content <30%), the constitutive responses at sand - sand, sand - rubber and rubber - rubber contacts can be described by the Hertz contact model; within this range, the rubber majorly formulates the weak and intermediate contacts, but sliding fraction in the strong network increases with rubber content. A more homogeneous fabric and a lower deviatoric stress at the strong network were observed after rubber inclusion. [Display omitted] • Conduct a double-scale calibration and present the grain-scale calibration results. • Justify the abilities and limitations of the hertz model at soft contacts. • Divide the contact network based on the absolute contribution to external stress. • Investigate features of divided networks at different rubber contents. [ABSTRACT FROM AUTHOR]

Soil settlement is an essential criterion in the design and performance assessment of geotechnical structures, often evaluated using results from one-dimensional compression test. However, assessment of the results from this test involves graphical methods, which produces inconsistent interpretations on the parameters to be used in design. The nonlinear compressibility curve is also subjected to bilinear idealization with divergence from the actual behavior at high stresses. In order to overcome these problems, a nonlinear mathematical formulation is developed to represent the soil compressibility with high precision over a wide range of stresses. The adequacy of the formulation is validated against a large and diverse dataset comprised of different geological materials, including undisturbed and reconstituted soils as well as stabilized soils. The proposed formulation is dependent on two fitting coefficients, which are defined in terms of commonly used compressibility parameters compression index, recompression index and preconsolidation pressure. A single expression is also derived to calculate soil settlement without numerical discontinuity. Finally, a method for evaluation of swelling pressure of soils is also developed using the parameters of the same mathematical formulation. [ABSTRACT FROM AUTHOR]

To explore the fractal dimension, particle shape, and particle breakage of calcareous sand (CS) under multi-level ending pressure, a series of one-dimensional compression experiments along with microscope image recognition tests were performed. Test results demonstrated that compression behavior of CS was similar to that of silt soil for the reason that considerable particle breakage occurred under high-stress level. In unloading process, rebound index of tested specimens was in the range of 0.0027–0.0052 which suggested that irrecoverable plastic deformation consists of the main part of compression. The shape index sphericity ( S C ), aspect ratio ( A R ), convexity ( C X ), and overall regularity ( O R ) increased as increasing axial stress or decreasing average grain size. Besides, there existed a turning point of axial stress of 3200 kPa; these shape indexes increased rapidly first and then approached to a stable value after that. At present study, the surface and mass fractal dimension of tested specimens were in the range of 1.12–1.93 and 2.14–2.92, respectively. Both fractal dimension and relative breakage ratio increased logarithmically as increasing axial stress from 0 to 6400 kPa. In addition, an increase in the average grain size led to an increase in the relative breakage ratio and a decrease in fractal dimension which indicated that larger particles are more easily broken for the reason that the stress concentration between granular grains. Furthermore, there existed approximate linear relations between surface or mass fractal dimension with relative breakage ratio which might be helpful to quantitate the particle breakage of granular materials. [ABSTRACT FROM AUTHOR]

A series of one-dimensional compression tests up to 60 MPa were conducted to study the compression behavior and particle breakage for carbonate sand and quartz sand in different locations. The results show that at high stress, particle breakage is the main factor of compression, and the carbonate sand from South China Sea is the most compressible and easily crushed for its angular particle shape, smaller single particle strength, and higher calcium carbonate content. A relationship between applied stress and plastic work considering particle breakage was established by taking Hardin's relative breakage index Br as an intermediate variable, and a compression model is developed which could describe the compression deformation caused by crushing. At the same time, the proposed model is also applicable to the whole compression process, and it could well describe the results of test in this paper and in previous studies. [ABSTRACT FROM AUTHOR]

Copyright of Guangdong Architecture Civil Engineering is the property of Guangdong Architecture Civil Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The gas hydrates in the pore space constitutionally affect the mechanical properties of gas hydrate-bearing sediments. The hydrates contribute to the mechanical properties of hydrate-bearing sediments by densifying, bearing and bonding effects. A discrete element model of hydrate-bearing silt was established by randomly filling hydrate particles into a silt-sized granular skeleton reservoir. Three ideal types of hydrate-bearing silt, namely, distributed particulate hydrate-bearing silt (type I), cluster hydrate-bearing silt (type II) and cemented cluster hydrate-bearing silt (type III) are proposed to study the mechanical effects of hydrate. One-dimensional loading (oedometer test) was applied to the numerical sample to investigate its stress evolution, volume change, bond degradation, coordination condition and stress transmission. The main conclusions are as follows. Type III sample exhibits a convex stress path due to bonding and then the stress path gradually returns to the pseudo linear stress path of type I sample due to bond breakage. The compression curve for the type II or type III sample exhibits a structural yield stress, which corresponds to abrupt bond breakage; the compression curves for types I, II and III evolve to be approximately coincident with each other at the end of compression. The average coordination number Z in type II or type III is approximately constant before widespread bond breakage, and then it will evolve to the curve of type I; the inflexion stress of the coordination numbers corresponds to the structural yield stress. The greatest magnitude of the mean stress bearing by hydrates in type II or type III sample is near the structural yield stress; the mean stresses p s - h b and p h - h b (created by bonded silt-hydrate and hydrate-hydrate contacts, respectively) in type III sample first increase under compression and then decrease due to widespread bond breakage, and they are exceeded by p s - h u and p h - h u (created by unbonded silt-hydrate and hydrate-hydrate contacts, respectively) after reaching the structural yield stress. [ABSTRACT FROM AUTHOR]

It is important to assess the permeability characteristics of clays in the prediction of the postconstruction settlement of geotechnical projects on clay grounds. The coefficient of permeability in the vertical direction (kv) and horizontal direction (kh) of clays under different vertical effective stresses were measured using newly developed permeability test equipment to investigate the variations in the permeability and permeability anisotropy of reconstituted clays and their influential factors under one-dimensional (1D) compression. The evolution of the pore sizes and pore orientations was also investigated to clarify the corresponding micromechanisms. The test results showed that the permeability of the reconstituted clays was related to the mineral composition, clay content, void ratio, and clay fabric. The variations in kv and kh with the void ratio could be represented in terms of a linear e–log(k) relationship. Under the same strain, the values of kh were obviously larger than those of kv, and the permeability anisotropy ratio (kh/kv) values increased from 1 to 2 with increasing vertical strain. For all the tested reconstituted clays, both kv and kh generally decreased linearly with decreasing cumulative pore volume. For different clays with the same cumulative pore volume, kv and kh decreased with an increase in the plasticity index. In general, the anisotropy index of the pores increased, and the main orientation angle of the pores decreased with increasing vertical effective stress. For a certain clay, the increase in permeability anisotropy with vertical strain resulted from the gradual development of microstructural anisotropy. The findings of this study may assist in the accurate prediction of the consolidation behavior of reconstituted clays with vertical and horizontal drainage. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A numerical investigation of the effect of particle breakage on the one-dimensional compression behavior of a realistic granular assembly was carried out using the discrete-element method. The morphologies of sands were obtained using X-ray microcomputed tomography. Sand assemblies were generated in terms of the statistical distribution of sphericity from real sands. The results of single-particle compression tests showed that particle shape significantly affects crushing strength. Particle breakage had a significant influence on compressive deformation, as demonstrated by comparing breakable assemblies with unbreakable ones. The strong force distribution became broader, and the proportion of weak force increased with particle breakability. Looser samples underwent much more particle breakage than did denser samples. It was found that breakage dissipation was a small fraction of energy input compared with frictional dissipation. An excellent hyperbolic relationship between relative breakage and energy input was found, which was independent of initial void ratio. [ABSTRACT FROM AUTHOR]

Time-dependent deformation of crushable soils attributable to particle breakage could dominate the postconstruction stability of high rockfill dams and pile foundations. The evolutionary trends of the volumetric strain, particle-size distribution (PSD), and particle breakage of carbonate sands with 10% fines content for various loading durations and vertical stress levels are investigated by performing a series of one-dimensional compression tests. Loading durations ranging from 1 to 10,000 min, vertical stress levels ranging from 200 to 3,200 kPa, and fines content percentages ranging from 0 to 20 are considered. The results indicate that the increased loading duration in the initial stage has a significant effect on the volumetric strain; however, as the loading duration increases, this effect gradually decreases. In addition, the PSD curve shifts upward as the loading duration increases, indicating that the amount of particle breakage increases accordingly. Both the loading duration and the vertical stress can induce PSD changes in carbonate sands. Empirical equations are proposed to describe the relationship between the relative particle breakage index and the loading duration as well as the relationship between the relative particle breakage index and the vertical stress. [ABSTRACT FROM AUTHOR]

The behavior of model granular materials (glass beads) wetted by a small quantity of liquid forming capillary bridges is studied by one-dimensional compression test combined with X-ray computed tomography (XRCT) observation. Special attention is paid to obtain very loose initial states (initial void ratio of about 2.30) stabilized by capillary cohesion. XRCT-based analyses involve spherical particle detection adapted to relatively low-resolution images, which enable heterogeneities to be visualized and microstructural information to be collected. This study on an ideal material provides an insight into the macroscopic compression behavior of wet granular materials based on the microstructural change, such as pore distance distribution, coordination number of contacts, coordination number of neighbors and number of contacts per grain. [ABSTRACT FROM AUTHOR]

Strength and deformation behaviors of rockfill materials, key factors for determining the stability of dams, pertain strongly to the grain crushing characteristics. In this study, single-particle crushing tests were carried out on rockfill materials with nominal particle diameters of 2.5 mm, 5 mm and 10 mm to investigate the particle size effect on the single-particle strength and the relationship between the characteristic stress and probability of non-failure. Test data were found to be described by the Weibull distribution with the Weibull modulus of 3.24. Assemblies with uniform nominal grains were then subjected to one-dimensional compression tests at eight levels of vertical stress with a maximum of 100 MPa. The yield stress in one-dimensional compression tests increased with decreasing the particle size, which could be estimated from the single-particle crushing tests. The void ratio-vertical stress curve could be predicted by an exponential function. The particle size distribution curve increased obviously with applied stresses less than 16 MPa and gradually reached the ultimate fractal grading. The relative breakage index became constant with stress up to 64 MPa and was obtained from the ultimate grading at the fractal dimension (α = 2.7). A hyperbolical function was also found useful for describing the relationship between the relative breakage index and input work during one-dimensional compression tests. Image 1 • A further investigation of the Weibull distribution for rockfill materials. • Particle size has a great influence on the fracture strength of rockfill materials. • The fractal dimension of rockfill materials could be obtained. • The relationship between the relative breakage index and input work could be described. [ABSTRACT FROM AUTHOR]

Due to the presence of organic matters, peaty soils have a highly compressible nature, and the consolidation process is complicated by the occurrence of rheological deformation. This paper presents the behaviors of the peaty soils sampled from the city of Kunming, the capital of Yunnan province in southwestern China. A series of one-dimensional compression tests are carried out on the peaty soil specimens with different organic matter contents. Considering the rheological properties of peaty soils, the three-element viscoelastic rheological model is introduced into the consolidation equation, then the analytical solution is derived for the viscoelastic rheological-consolidation model. Finally, the influences of consolidation pressures and organic matter contents on the model parameters determined by test data fitting are investigated. It has been shown that the model is coinciding fairly well with test results, and the consolidation pressure and organic matter content have a remarkable effect on the model parameters. [ABSTRACT FROM AUTHOR]

Prediction of the evolution of particle size distribution (PSD) is of great importance for studying particle breakage. This paper presents a stochastic approach, namely a Markov chain model, for predicting the evolution of PSD of granular materials during one-dimensional compression tests. The model requires the survival probability of each size group particles in an assembly, named as the survival probability matrix. The Weibull distribution is used to capture the particle size and particle strength effects of single particles. The evolution of the coordination number is investigated via 3D discrete element simulations. The proposed analytical form of survival probability matrix with consideration of the coupling effect of particle-scale factors (i.e., particle size, particle strength) and evolution of the coordination number during one-dimensional compression shows that the largest particles in an assembly do not always have the maximum breakage probability (or the minimum survival probability). This also confirms the dominant role of the coordination number on the balance of evolution of PSD within granular soils. The proposed model is validated against experimental data from one-dimensional compression tests on different granular materials. The limitations as well as possible future developments of the model are discussed. [ABSTRACT FROM AUTHOR]

Particle breakage alters particle size, shape, surface roughness, and co-ordination number, which in turn changes macro-mechanical behaviour including compressibility and shear strength. This study conducted a series of one-dimensional (1D) compression tests on quartz sands with different initial void ratios, ending the tests at various stress levels up to 13.5 MPa. The size and shape of particles were quantified using a dynamic particle shape analyser, while the surface roughness of thirty randomly selected particles for each sample was measured by an optical interferometer and quantified using flattened root-mean-square roughness (RMS f). The results demonstrate that a unique normal compression line is defined due to extensive particle breakage, with denser sample exhibiting a higher yield stress. Prior to yielding (vertical stress < 6 MPa), the changes in the three shape descriptors are limited, as the primary particle damage modes are abrasion and grinding. Conversely, at high stress level, a greater number of particles undergo splitting or explosive damage, leading to the creation of more irregularly shaped particles. The occurrence of plastic deformation at particle asperities under one-dimensional compression is identified, resulting in a decrease in surface roughness. This study highlights the significant role of the initial void ratio in shaping the evolution of surface roughness of particles under 1D compression. [Display omitted] • Change in particle shape is limited prior to yielding. • Breakage creates more irregularly shaped particles at high stress level. • Plastic deformation at particle asperities leads to decrease in surface roughness. • Initial void ratio affects significantly the evolution of surface roughness. [ABSTRACT FROM AUTHOR]

This study presents an investigation of the effects of cement addition to expansive clay on its deformation characteristics and stress responses during swelling. The effects were evaluated by focusing on the unconfined compressive strength, swelling-shrinkage strains under various conditions, and the lateral coefficient of earth pressure during one-dimensional deformation for artificial mixtures of two different clays at three different ratios. The clays used in this study were a Na-montmorillonite bentonite and a non-expansive Bangkok clay, mixed at different proportions to simulate naturally encountered expansive clays with different degrees of swelling potential. The experimental programme involved unconfined compression, areal shrinkage strain by unconfined drying, vertical free swelling strain, and confined swelling pressure tests. The experimental results show that the cement addition led to marked decreases in the areal shrinkage strain and vertical free swelling strain in addition to the obvious improvement of strength and stiffness of soils. The confined swelling pressure test results indicated that the cement had a greater effect in reducing vertical swelling pressure than the lateral swelling pressure of the soils during one-dimensional swelling. The measured lateral coefficient of earth pressure and stress paths of untreated and cement-treated soils and their engineering implications are discussed. [ABSTRACT FROM AUTHOR]

Nansha clay is an interactive marine and terrestrial deposited soft clay that is widely spread in Guangzhou, Pearl River Delta, China. To avoid excessive settlement after construction, there is a need for better quantifying the time-dependent deformation of the soft clay. This paper presents a preliminary study to predict the one-dimensional compression of Nansha clay using fractional derivatives. A fractional Merchant model was introduced to describe the time-dependent settlement, and analytical solutions were obtained in terms of the Mittag-Leffler function. The oedometer test results were presented to validate this model. Compared with classical rheological models, the fractional derivative-based model enabled close estimation of the one-dimensional compression with fewer parameters. The meaning of the order of fractional derivative and its relationship with the clay physical properties were explored. It shows that a smaller value of this order corresponded to a higher coefficient of consolidation and a lower coefficient of secondary consolidation. The amplitude of both the primary and secondary consolidation of clay may be estimated quantitatively by the order of fractional derivative. Taken together, these results may open up new avenues for theoretical and empirical modeling of rheological phenomena in clay using fractional derivatives. [ABSTRACT FROM PUBLISHER]

The paper presents the results of a physical and mechanical characterization of a compressible and crushable volcanic ash collected during a recent eruptive event of Mount Etna. The characterization of this complex natural material required appropriate equipment, to carry out a comprehensive experimental programme, and a rigorous scientific approach to critically analyze the experimental results and put them in the theoretical framework of soil mechanics and of critical state theory. The experimental activities involved X-ray diffractometry, electron scanning microscopy ( SEM ) and one-dimensional compression tests carried out on both wet and dry soil specimens characterized by different initial densities. To examine the effects of loading on the evolution of the micro-structure, both the particle size distribution and the particle shape, before and after the tests, were analyzed through a dynamic image analysis using several size and shape parameters. The experimental results show that grain crushing becomes evident at vertical pressures larger than 1 MPa whereas it seems to be progressively inhibited for pressures larger than 10 MPa. Furthermore, regardless the initial void ratio of the soil specimens, at high stresses the obtained non-linear e −log σ′ v relationship converges toward a unique limiting compression curve. [ABSTRACT FROM AUTHOR]

Crushing is one of the micromechanisms that govern the mechanical behaviour of sands at medium-high stresses. It depends on mineralogy, form and strength of single particle, mean stress level, coordination number, time, etc.. It causes changes of grain-size distribution, porosity, number and type of grain contacts, fabric, structure of the material, etc.. Results of an experimental research on the crushing of pumice sands compressed under 1-D conditions to vertical effective stresses σ′ v up to 100MPa are reported here. They show marked crushing already at σ′ v of about 200kPa. The evolution of the grain-size distribution can be represented by ΔDi= h/(K(1+C exp(–hlgσ′ v ))) in which ΔDi is the decrement of the generic characteristic diameter. C, h, K are positive parameters depending on the sand's nature and initial state. This relation properly accounts for the existence of an upper limit to ΔDi (or the existence of a limit grading). It is able also to describe the evolution of the global relative breakage indexes. [ABSTRACT FROM AUTHOR]

The influence of strain rate and moisture content on the behaviour of a quartz sand was assessed using high-pressure quasi-static (10 s) and high-strain rate (10 s) experiments under uniaxial strain. Quasi-static compression to axial stresses of 800 MPa was carried out alongside split Hopkinson pressure bar (SHPB) experiments to 400 MPa, where in each case lateral deformation of the specimen was prevented using a steel test box or ring, and lateral stresses were recorded. A significant increase in constrained modulus was observed between strain rates of 10s and 10s, however a consistently lower Poisson's ratio in the dynamic tests minimised changes in bulk modulus. The reduction in Poissons ratio suggests that the stiffening of the sand in the SHPB tests is due to additional inertial confinement rather than an inherent strain-rate dependence. In the quasi-static tests the specimens behaved less stiffly with increasing moisture content, while in the dynamic tests the addition of water had little effect on the overall stiffness, causing the quasi-static and dynamic series to diverge with increasing moisture content. [ABSTRACT FROM AUTHOR]

Discrete element modelling of normal compression has been simulated on a sample of breakable two-ball clumps and compared to that of spheres. In both cases the size effect on strength is assumed to be that of real silica sand. The slopes of the normal compression lines are compared and found to be consistent with the proposed equation of the normal compression line. The values of the coefficient of earth pressure at rest $$K_{0{,}\mathrm{nc}}$$ are also compared and related to the critical state fiction angles for the two materials. The breakable samples have then been unloaded to establish the stress ratios on unloading. At low overconsolidation ratios the values of $$K_{0}$$ follow a well-established empirical relationship and realistic Poisson ratios are observed. On progressive unloading both samples head towards passive failure, and the values of the critical state lines in extension in q- $$p'$$ space are found to be consistent with the critical state angles deduced from the values of $$K_{0}$$ during normal compression. The paper highlights the important role of particle shape in governing the stress ratio during both normal compression and subsequent overconsolidation. [ABSTRACT FROM AUTHOR]

Tools are developed to predict damage to archaeological remains caused by the construction of line infrastructure on soft soil. They are based on numerical modelling and laboratory testing supported by X-ray microcomputed tomographic observations, and micromorphological analyses of thin sections. They have been validated for one-dimensional (1D) loading at two sites in the Netherlands where soil has been placed on top of organic layers rich in ecofacts and overlaying Pleistocene sands. Numerical prediction of the deformation of soft layers underneath an embankment remains a challenge for geo-technical engineers. Errors on surface settlement prediction reach ±15% of the measured total settlement. Laboratory observations show that vulnerable artefacts can get crushed when packed loosely in pure assemblies under 1D loading equivalent to less than 5 m of sand. Fragmentation is assimilated to loss of archaeological value as it compromises recovery during sieving. Embedment in a sandy or a very compressible organic matrix has a beneficial effect on the resistance of ecofacts. Embedded ecofacts can resist a load of more than 12 m of sand. Flattening and re-orientation of soft plant remains occur during 1D loading without microscopic damage of tissues. [ABSTRACT FROM AUTHOR]

A Discrete Element Method (DEM) model is developed to study the particle breakage effect on the one-dimensional compression behavior of silica sands. The ‘maximum tensile stress’ breakage criterion considering multiple contacts is adopted to simulate the crushing of circular particles in the DEM. The model is compared with published experimental results. Comparison between the compression curves obtained from the numerical and experimental results shows that the proposed method is very effective in studying the compression behavior of silica sands considering particle breakage. The evolution of compression curves at different stress levels is extensively studied using contact force distribution, variation of contact number and particle size distribution curve with loading. It is found that particle breakage has great impact on compression behavior of sand, particularly after the yield stress is reached and particle breakage starts. The crushing probability of particles is found to be macroscopically affected by stress level and particle size distribution curve, and microscopically related to the evolutions of contact force and coordination number. Once the soil becomes well-graded and the average coordination number is greater than 4 in two-dimension, the crushing probability of parent particles can reduce by up to 5/6. It is found that the average contact force does not always increase with loading, but increases to a peak value then decreases once the soil becomes more well-graded. It is found through the loading rate sensitivity analysis that the compression behavior of sand samples in the DEM is also affected by the loading rate. Higher yield stresses are obtained at higher loading rates. [ABSTRACT FROM AUTHOR]

A series of one-dimensional compression tests have been carried out on three kinds of granular materials in a dense state to investigate their mechanical and crushing behaviours. A new testing apparatus that can simultaneously measure the axial and lateral stresses acted on the cylindrical specimen was also developed. Experimental results show that the break-point stress on e - log p curve is the largest for glass beads ballotini. A rise in compression index with the increasing axial load is observed for all three granular materials. The lateral earth pressure coe fficient at rest Ko for the three granular materials slightly increases with the increasing axial load and attains a steady value between 0.25 and 0.3 at the initial loading stage. The value for Ko markedly increases as the axial load is removed during the unloading process. The axial strain of Masado is the largest at the same axial load level due to its mineral hardness. Experimental results demonstrate that the crushing degree of granular material is greatly influenced by the loading modes and conditions. [ABSTRACT FROM AUTHOR]

Abstract: Natural loess is a kind of under-consolidated and unsaturated loose granulates (silts) with its microstructure characterized with large voids and inter-particle cementation. This paper presents a distinct element method (DEM) to investigate its macro- and micro-mechanical behaviour (compression and collapse behaviour) under one-dimensional (1D) compression condition. A relationship between bond strength in DEM model and initial water content is used to develop a bond contact model for loess. Then, DEM structural loess samples are prepared by the multi-layer under-compaction method, and cemented with the bond contact model. The effect of water content and void ratio on compression and collapse behaviour of loess is numerically investigated by simulating 1D compression and wetting tests on the DEM material. The DEM results agree qualitatively with available experimental observations in literatures. The wetting-induced deformation is independent of the sequence of wetting and loading under 1D compression condition. The macroscopic yielding and collapse behaviours are associated with bond breakage on microscopic scale. Moreover, bonds break in one of the two failure types in the simulations, i.e. tensile failure and shear failure (compression-shear failure and tension-shear failure), with bonds broken firstly mainly due to tension followed by shear when the samples are compressed, while mainly due to shear when the samples are wetted under a certain pressure. In addition, the contact orientations and deviator fabrics of contacts under 1D compression and wetting were also investigated. [Copyright &y& Elsevier]

Breakage-induced evolution of particle size distribution (PSD) will greatly affect the mechanical behavior of granular materials, and has been an important concern in geotechnical engineering. This paper presents a breakage matrix approach to investigate the evolution of PSD with detailed breakage information of each single-sized particles via conducting one-dimensional compression tests on dyed calcareous sands with different initial conditions. The breakage of each single-sized particles of soil samples with multi-sized particles under different initial conditions was analysed by the PCAS image recognition technologies. It has been found that the breakage-induced PSD of each single-sized particles of the soil samples tends to be fractally distributed, regardless of their initial PSDs. Furthermore, the degree of particle breakage of each single-sized particles is linearly related with the input work per unit volume. Finally, the proposed model establishes the breakage matrices of both uniform and gap-graded calcareous sands, which demonstrates its satisfactory performance. [Display omitted] • Detailed particle breakage of dyed calcareous sands are analysed. • The relationship between breakage index and input work is established. • A breakage matrix model is developed to predict the evolution of PSD of calcareous sands. [ABSTRACT FROM AUTHOR]

Tire-derived aggregate (TDA) has been successfully used for highway embankment applications in the past. Previous applications mainly used small and medium tire sizes as TDA sources. There are no published test results in the literature regarding the compression behavior of TDA made solely from off-the-road tires (OTR). In this study, large-scale, one-dimensional compression tests are carried out to study the compression behavior of TDA from OTR as well as from passenger and light-truck tires (PLTT). Samples for the tests are prepared by varying the initial unit weights. The results show that there is a general trend of decreasing compressibility with increasing initial unit weight for both TDA sources. The compression test results are also used to compare compression behavior between the two TDA sources. It is found that the compression behavior of TDA from OTR and PLTT is more or less similar. Moreover, one-dimensional stress-strain regression equations were developed for TDA from OTR. [ABSTRACT FROM AUTHOR]

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• An annular cylinder container was built to hold the crushable Li 4 SiO 4 particles. • One-dimensional compression was performed by moving the upper wall at a constant velocity. • The presence of crushed particles could soften the pebble bed. • The impact of the crushing ratio on the macro response of the pebble bed was shown and discussed. • The effects of the coefficient of friction and restitution under different crushing ratios were investigated. The mechanical behavior in one-dimensional compression of a crushable ceramic pebble bed for the fusion reactor, which is under different crushing ratio assumptions (0% - 2%), was numerically investigated by the discrete element method (DEM) simulation. The crushed particle was modeled by a reduction of the particle radius, therefore, the instantaneous decrease of the local stress could be produced. To guarantee the mass conservation of the particles in the pebble bed, the sub-particle insertion process was conducted. Please note that this paper mainly deals with the post of failure of the particles, hence the pebble failure process was not captured. The results showed that the crushed particles could make the pebble bed softer, and with the same Li 4 SiO 4 pebble bed strain, the bed stress decreased as the crushing ratio grew larger. The impact of the crushing ratio on the radial and axial local packing factor was limited on the oscillating amplitude without affecting the oscillating width. Besides, the effects of the coefficient of friction and restitution under different crushing ratios were investigated. At last, the analysis of changes in the average coordination number with the bed strain under different crushing ratios was performed. [ABSTRACT FROM AUTHOR]

Particle-scale mechanisms that control the static creep behavior of crushable sands are not well understood. In this context, this study examines the problem of creep of crushable sands undergoing one-dimensional (1D) compression by using a three-dimensional (3D) discrete element method (DEM) simulation. The rate process theory (RPT)-based creep contact model considering rolling resistance and a probabilistic particle fracture model satisfying mass conservation were incorporated into a large-scale DEM simulation. The coupled effects of the interparticle sliding and delayed particle fracture and the influences of rolling resistance, initial porosity, and characteristic particle strength on the creep behavior were then investigated. The high capabilities of the model in reproducing many facets of the soil behavior during the 1D compression and creep seen in the laboratory was demonstrated by comparing the simulation results with published experimental data. It was found that the creep deformation was mainly caused by stress redistribution at low vertical stress while particle rearrangement and particle breakage became more prevailing with the increase of vertical stress. [ABSTRACT FROM AUTHOR]