Mechanics and Modeling of Cohesive Frictional Granular Materials
18 Jan 2017-pp 493-500
TL;DR: In this paper, the authors used a hollow cylinder torsional testing apparatus which is capable of independently controlling the magnitude and the direction of the three principal stresses in weakly cemented granular materials.
Abstract: In nature, weakly cemented granular materials are encountered in the form of soft rocks such as limestone, sandstone, mudstone, shale, etc. The mechanical behaviour of these materials is quite different from the purely frictional granular materials. The presence of cementation between the grains causes a significant variation in mechanical response under complex boundary conditions. In order to understand the manifestation of this interparticle cohesion at the ensemble level, we have used a hollow cylinder torsional testing apparatus which is capable of independently controlling the magnitude and the direction of the three principal stresses. From this experimental programme, the small strain response, peak strength and post peak behaviour with changing intermediate principle stress ratio (b) and initial mean effective stress (I1) is studied. In addition to the analysis of stress strain behaviour at different b and I1, stress-dilatancy characteristics of these cohesive frictional material are also discussed. This experimental study is followed by calibration and validation of a single hardening constitutive model which considers cementation as additional confinement. Observations from validation exercises suggest that this consideration works well for stress-strain response whereas it fails to predict the volumetric behaviour.
Citations
More filters
TL;DR: In this article, five groups of slate specimens with different bedding angles (β, angle between bedding plane and vertical angle) were used to provide guidance for Muzhailin tunnel design and construction.
Abstract: In order to provide guidance for Muzhailin tunnel design and construction, in this study, five groups of slate specimens with different bedding angles (β, angle between bedding plane and vertical a...
6 citations
TL;DR: In this paper, the proposed stress-dilatancy relations for compressive monotonic loading for cohesionless and cemented sand constitutive models are summarized and the proposed potential function can be calculated by integration of stress-dlatancy relationship.
Abstract: Stress-dilatancy relationship or plastic potential function are crucial components of every elastoplastic constitutive model developed for sand or cemented sand. This is because the associated flow rule usually does not produce acceptable outcomes for sand or cemented sand. Many formulas have been introduced based on the experimental observations in conventional and advanced plasticity models in order to capture ratio of plastic volumetric strain increment to plastic deviatoric strain increment (i.e. dilatancy rate). Lack of an article that gathers these formulas is clear in the literature. Thus, this paper is an attempt to summarize plastic potentials and specially stress-dilatancy relations so far proposed for constitutive modelling of cohesionless and cemented sands. Stress-dilatancy relation is usually not the same under compression and extension conditions. Furthermore, it may also be different under loading and unloading conditions. Therefore, the focus in this paper mainly places on the proposed stress-dilatancy relations for compressive monotonic loading. Moreover because plastic potential function can be calculated by integration of stress-dilatancy relationship, more weight is allocated to stress-dilatancy relationship in this research.
5 citations
TL;DR: In this paper, the residual strata distribution of Carboniferous-Permian in Jiyang Depression, the organic geochemical characteristics of shale and the correlation of hydrocarbon-generating potential of shale by applying geochemistry, petroleum geology and coal geology.
Abstract: This paper studied the residual strata distribution of Carboniferous-Permian in Jiyang Depression, the organic geochemical characteristics of shale and the correlation of hydrocarbon-generating potential of shale by applying geochemistry, petroleum geology and coal geology, for study hydrocarbon generation potential of Permo-Carboniferous coal shale in Jiyang Depression. The results show that the thickness of Carboniferous-Permian residual strata in Jiyang Depression is generally 200-800 m, the thickest can reach 900 m; coal shale has good organic matter abundance and is type III kerogen, which is conducive to gas generation, and organic matter maturity reaches maturity-higher maturity stage; Benxi Formation and Taiyuan Formation have better hydrocarbon generation potential; medium to good hydrocarbon source rocks can be found in every sag of Shanxi Formation hydrocarbon source rocks, but the scope is limited, and the overall evaluation is still medium. Compared with other areas in China, it is found that the hydrocarbon-generating capacity of coal-bearing shale of Carboniferous-Permian in Jiyang Depression is generally at a medium level, which has a certain shale gas exploration potential.
1 citations
References
More filters
TL;DR: In this article, the authors investigated the behavior of artificially cemented carbonate sand at confining pressures of up to 9 MPa and found that an important effect of cementing is a reduction in specific volume resulting from the increase in fines content, which influences both the stress-strain behaviour and the peak strength at strains beyond those required to fracture the cement bonding.
Abstract: The behaviour of artificially cemented carbonate sand was investigated in triaxial tests at confining pressures of up to 9 MPa. The results show that an important effect of cementing is a reduction in specific volume resulting from the increase in fines content This influences both the stress-strain behaviour and the peak strength at strains beyond those required to fracture the cement bonding. Comparisons between the behaviour of cemented and uncemented soils should, therefore, be carried out on samples with the same gradings. For cemented samples it is possible to identify a yield curve outside the state boundary surface of the uncemented soil. A framework for the behaviour has been defined which depends on the relative magnitudes of the confining pressure and cement bond strength. The behaviour of a natural cal-carenite agreed well with this framework which is also likely to be applicable to other cemented soils. Le comportement d'un sable carbonate artificiellement cimente a ete etudie a l'aide d'essa...
358 citations
TL;DR: In this article, an analysis of the stress-strain strength behavior of an artificially cemented sandy soil produced through the addition of portland cement was performed from the interpretation of results from unconfined compression tests, drained triaxial compression tests with local strain measurements, and scanning electron microscopy, in which the influence of both the degree of cementation and the initial mean effective stress was investigated.
Abstract: This work aims at studying the stress-strain-strength behavior of an artificially cemented sandy soil produced through the addition of portland cement. An analysis of the mechanical behavior of the soil is performed from the interpretation of results from unconfined compression tests, drained triaxial compression tests with local strain measurements, and scanning electron microscopy, in which the influence of both the degree of cementation and the initial mean effective stress was investigated. For cemented sandy soils, it was concluded that the unconfined compression resistance is a direct measurement of the degree of cementation. Consequently, the triaxial shear strength can be expressed as a function of only two variables: (1) the internal shear angle of the nonstructured material; and (2) the unconfined compression resistance. In addition, a logarithmic formulation is adopted to express the relationship between static deformation moduli and axial strain amplitude in axisymmetric conditions. Data from other reported investigation programs give to the proposed correlations a broader acceptance to general geotechnical applications.
271 citations
TL;DR: In this paper, a parametric study was carried out to identify the specific effects of each type of cement, namely, Portland cement, gypsum, and calcite, on the engineering behavior of calcareous soil under triaxial loading.
Abstract: There is little information in the geotechnical literature regarding the influence of the type of cement on the engineering behavior of cemented soils. This paper explores the mechanical behavior of a calcareous soil under triaxial loading after treatment with different types of cement, namely Portland cement, gypsum, and calcite. To identify the specific effects of each cement type a parametric study was undertaken, where factors such as density and unconfined compressive strength were maintained constant for each cementing agent. Samples of the cemented soil were examined under optical and electron microscopy to understand the bond mechanism created by each cement. Results from triaxial testing have shown that, despite having the same unconfined compressive strength and density, the effective stress paths and postyield response are significantly different, mainly because of the different volumetric response upon shearing. Samples prepared using Portland cement showed ductile yield and strong dilation afterwards; calcite and gypsum-cemented samples exhibited brittle yield, generally followed by contractive behavior. The paper discusses the results and explains the reasons behind the differences in the mechanical response.
232 citations
TL;DR: In this paper, the influence of this variability on the properties of cemented materials is investigated by producing artificially cemented specimens at dry unit weights ranging from 12 to 19 kN/m3 and gypsum cement contents ranging from 0% to 20%.
Abstract: Naturally cemented materials often have inherent variabilities in density and degree of cementation. The influence of this variability on the properties of cemented materials is investigated by producing artificially cemented specimens at dry unit weights ranging from 12 to 19 kN/m3 and gypsum cement contents ranging from 0% to 20%. Tests have been performed to investigate the index strengths, the behavior in isotropic and K0 compression, and the responses from standard triaxial compression tests over a wide range of confining pressures. The index properties, and the compression and stiffness parameters of the cemented sands are presented, with particular attention given to the influences of density and degree of cementation. For the artificial soil, the effects of the bonding are only significant for stresses below an apparent preconsolidation stress. The strength and stiffness increase with increasing density and cement content, but the influence of the cementation decreases as the density increases.
192 citations
TL;DR: In this paper, a general three-dimensional plastic potential function expressed in terms of stress invariants is proposed based on review and evaluation of a large number of test data, which includes tensile behavior of materials with effective cohesion.
182 citations