共查询到20条相似文献，搜索用时 93 毫秒
1.
天然土体的初始各向异性通常可对其后继循环特性产生显著影响。现有考虑循环载荷作用的土体弹塑性模型,往往采用类似修正剑桥模型的椭圆形屈服面,已有研究表明,该椭圆形屈服面因其拉伸弹性区域偏大,针对天然K0固结状态的土体,其计算精度较差。基于新近提出的广义各向同性硬化准则,在边界面方程中引入初始各向异性张量,并采用空间滑动面破坏准则（SMP）的变换应力法,建立了能考虑饱和黏土初始各向异性的循环边界面塑性模型。分别针对等压和偏压固结的饱和黏土静、动三轴试验进行模拟,结果表明,该模型能合理反映土体的初始各向异性及其后继循环动力特性。 相似文献
2.
Quantitative Parameters for Rock Joint Surface Roughness 总被引：17，自引：5，他引：12
Summary
The morphologies of two artificial granite joints (sanded and hammered surfaces), one artificial regularly undulated joint
and one natural schist joint, were studied. The sanded and hammered granite joints underwent 5 cycles of direct shear under
3 normal stress levels ranging between 0.3–4 MPa. The regularly undulated joint underwent 10 cycles of shear under 6 normal
stress levels ranging between 0.5–5 MPa and the natural schist replicas underwent a monotonous shear under 5 normal stress
levels ranging between 0.4–2.4 MPa. In order to characterize the morphology of the sheared joints, a laser sensor profilometer
was used to perform surface data measurements prior to and after each shear test. Rather than describing the morphology of
the joints from the single profiles, our characterization is based on a simultaneous analysis of all the surface profiles.
Roughness was viewed as a combination of a primary roughness and a secondary roughness. The surface angularity was quantified
by defining its three-dimensional mean angle, θs, and the parameter Z2s. The surface anisotropy and the secondary roughness were respectively quantified by the degree of apparent anisotropy, k
a, and the surface relative roughness coefficient, R
s. The surface sinuosity was quantified by the surface tortuosity coefficient, T
s.
Comparison between the means of the classical linear parameters and those proposed shows that linear parameters underestimate
the morphological characteristics of the joint surfaces. As a result, the proposed bi-dimensional and tri-dimensional parameters
better describe the evolution of the joints initial roughness during the course of shearing. 相似文献
3.
In this paper, a simple bounding surface plasticity model is used to reproduce the yielding and stress–strain behavior of the structured soft clay found at Shanghai of China. A series of undrained triaxial tests and drained stress probe tests under isotropic and anisotropic consolidation modes were performed on undisturbed samples of Shanghai soft clay to study the yielding characteristics. The degradation of the clay structure is modeled with an internal variable that allows the size of the bounding surface to decay with accumulated plastic strain. An anisotropic tensor and rotational hardening law are introduced to reflect the initial anisotropy and the evolution of anisotropy. Combined with the isotropic hardening rule, the rotational hardening rule and the degradation law are incorporated into the bounding surface formulation with an associated flow rule. Validity of the model is verified by the undrained isotropic and anisotropic triaxial test and drained stress probe test results for Shanghai soft clay. The effects of stress anisotropy and loss of structure are well captured by the model. 相似文献
4.
This paper presents a fabric tensor-based bounding surface model accounting for anisotropic behaviour (e.g. the dependency of peak strength on loading direction and non-coaxial deformation) of granular materials. This model is developed based on a well-calibrated isotropic bounding surface model. The yield surface is modified by incorporating the back stress which is proportional to a contact normal-based fabric tensor for characterising fabric anisotropy. The evolution law of the fabric tensor, which is dependent on both rates of the stress ratio and the plastic strain, rules that the material fabric tends to align with the loading direction and evolves towards a unique critical state fabric tensor under monotonic shearing. The incorporation of the evolution law leads to a rotational hardening of the yield surface. The anisotropic critical state is assumed to be independent of the initial values of void ratio and fabric tensor. The critical state fabric tensor has the same intermediate stress ratio (i.e. b value) and principal directions as the critical state stress tensor. A non-associated flow rule in the deviatoric plane is adopted, which is able to predict the non-coaxial flow naturally. The stress–strain relation and fabric evolution of model predictions show a satisfactory agreement with DEM simulation results under monotonic shearing with different loading directions. The model is also validated by comparing with laboratory test results of Leighton Buzzard sand and Toyoura sand under various loading paths. The comparison results demonstrate encouraging applicability of the model for predicting the anisotropic behaviour of granular materials.
相似文献5.
The main purpose of the paper is to present a relatively simple, yet realistic, constitutive model for simulations of structured sensitive clays. The proposed constitutive model can simulate 1‐D and isotropic consolidation, and drained and undrained shear response of sensitive structured clay. The proposed sensitive bounding surface model is based on concepts from the modified Cam clay model 8 and bounding surface plasticity 27 , with the addition of a simple degradation law. The key material parameters are M, λ, κ, and ν from the modified Cam clay framework, h from the bounding surface framework to model a smoothed elasto‐plastic transition, and ωv, ωq, and Ssr to model softening associated with destructuration. The model has separate parameters to model destructuration caused by volumetric strain and deviatoric strain. The model is capable of modeling unusual behavior of strain softening during 1‐D compression (i.e., a reduction of effective stress as void ratio decreases). A good match between test results and the model simulation is demonstrated. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
6.
Improved rotational hardening rule for cohesive soils and definition of inherent anisotropy 
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下载免费PDF全文 Improved, microfabric‐inspired rotational hardening rules for the plastic potential and bounding surfaces associated with the generalized bounding surface model for cohesive soils are presented. These hardening rules include 2 new functions, fη and , that improve the simulation of anisotropically consolidated cohesive soils. Three model parameters are associated with the improved hardening rules. A detailed procedure for obtaining suitable values for these parameters is presented. The first 2 parameters affect the simulation of constant stress ratio loading where, because of the presence of fη, the third parameter is inactive. The second new function, , accelerates the rotation of the plastic potential and bounding surfaces during shearing, which is particularly important for overconsolidated soils tested in extension. This paper also describes the proper manner in which to define the inherent anisotropy. This seemingly straightforward test has rarely been discussed in sufficient detail. 相似文献
7.
In this paper an experimental study was planned on rock mass model with three joint sets under triaxial and true-triaxial
stress states to assess the influence of joint geometry and stress ratios on deformational behaviour of rock mass. The physical
models were composed of three continuous orthogonal joint sets in which joint set-I was inclined at angle θ=0°, 20°, 40°,
60°, 80° and 90° with x-axis, joint set-II was produced at staggering s=0.5 and joint set-III was kept always vertical. Thus, rock mass models with medium interlocked smooth joints (ϕ
j
=36.8°) were simulated under true triaxial compression (σ1>σ2>σ3). Modulus of rock mass shows anisotropy with joint inclination θ which diminishes with increase in σ2/σ3 ratio. The rock mass at θ=60° shows the highest modulus enhancement (599.9%) whereas it is minimum (32.3%) at θ=90°. Further
two empirical expressions for estimation of deformation modulus were suggested based on experimental results, which were developed
by incorporating two basic concepts, e.g. Janbu’s coefficients and joint factor, J
f. 相似文献
8.
Gu Xiaoqiang Li Youhong Hu Jing Shi Zhenhao Liang Fayun Huang Maosong 《Acta Geotechnica》2022,17(8):3229-3243
Natural clays usually show anisotropic stiffness due to their deposition process and anisotropic in situ stress state. The stiffness anisotropy depends on both of the stress anisotropy and fabric anisotropy, while the latter can be quantified by the stiffness anisotropy at isotropic stress states. This paper measures the K0 value (i.e., stress anisotropy) and elastic shear stiffness anisotropy of natural Shanghai clay in a triaxial apparatus with horizontal and vertical bender elements. The results show that the K0 value of Shanghai clay lies in the range of 0.40–0.66, and an empirical equation is proposed to estimate the K0 value based on the plasticity index and initial void ratio. The fabric anisotropy of natural Shanghai clay lies in the range of 1.2–1.4 with a stronger fabric in the horizontal plane. Moreover, the experimental data of the stiffness anisotropy and fabric anisotropy of different clays in the literature are reviewed and analyzed. It reveals that the stiffness anisotropy generally increases, while the fabric anisotropy remains nearly the same during K0 consolidation. For normally consolidated clay, the fabric anisotropy generally lies in the range of 1.1–1.7. For overconsolidated clays, the fabric anisotropy generally increases as the overconsolidation ratio increases. Empirical equations are proposed to approximately estimate the fabric anisotropy of clays based on its stress normalized elastic shear stiffness.
相似文献9.
Poul V. Lade 《国际地质力学数值与分析法杂志》2006,30(4):307-333
Data from three‐dimensional experiments performed on sand in true triaxial equipment have been reviewed to sort out apparent disarray resulting from their interpretation. This has been done based on analyses made possible by recent developments and understanding of factors influencing sand behaviour: occurrence of shear banding, boundary conditions and/or specimen slenderness ratio, cross‐anisotropy, and stability of experimental technique. These factors are reviewed and test data from the literature are evaluated. Experimental data are divided into three groups in which: (a) homogeneous behaviour controls the sand strength; (b) shear banding affects the shape of the three‐dimensional failure surface in the midrange of values of b=(σ2?σ3)/(σ1?σ3), and (c) the data has been misinterpreted. Appropriate interpretation of three‐dimensional strength data for sand exhibiting isotropic, homogeneous behaviour is represented by a smoothly rounded triangular failure surface expressible in terms of the first and third stress invariants. Shear banding effects will cause the failure surface to be ‘indented’ in the midrange of b‐values in all sectors of the octahedral plane. Effects of cross‐anisotropy will result in lower strengths in sector III than in sector I of the octahedral plane, and the failure surface will appear as rotated around the stress origin in principal stress space. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
10.
We use an analytical model for the post-injection spreading of a plume of CO2 in a saline aquifer under the action of buoyancy and capillary trapping to show that the spreading behavior is at all times
strongly influenced by the shape of the plume at the end of the injection period. We solve the spreading equation numerically
and confirm that, at late times, the volume of mobile CO2 is given by existing asymptotic analytical solutions. The key parameters governing plume spreading are the mobility ratio,
M, and the capillary trapping number, Γ—the former sets the shape of the plume at the end of the injection period, and the latter sets the amount of trapping. As
a quantitative measure of the dependence of the spreading behavior on the initial shape, we use a volume ratio. That is, we
evolve the plume from a true end-of-injection initial shape and also from an idealized “step” initial shape, and we take the
ratio of these mobile plume volumes in the asymptotic regime. We find that this volume ratio is a power-law in M, where the exponent is governed exclusively by Γ. For conditions that are representative of geologic CO2 sequestration, the ratio of mobile volumes between “true” and “step” initial plume shapes can be 50% or higher. 相似文献
11.
适用于砂土循环加载分析的边界面塑性模型 总被引：1，自引：0，他引：1
基于临界状态土力学框架,建立了一个适用于砂土排水循环加载的边界面塑性模型。采用了考虑虚拟峰值应力比的偏应变硬化准则,初始加载阶段应力点位于边界面上,反向加载阶段以历史最大屈服面作为边界面,同时实现了对密砂软化现象的模拟和对历史所受最大应力的记忆。边界面采用修正的椭圆形,引入考虑密度与应力水平的状态相关剪胀函数,采用非相关联流动法则和以应力反向点作为映射中心的径向映射准则。模型仅有10个参数,通过常规三轴试验即可确定,并且使用一套参数可以模拟不同围压、密度的单调和循环加载情况。分别对饱和砂土的单调、循环排水三轴试验进行模拟,结果表明,该模型能够合理地反映饱和砂土排水条件下的应力-应变特性。 相似文献
12.
The cyclic behaviours of embedded offshore structures under different cyclic loading levels are related to the cyclic shakedown and degradation of the surrounding soils. In the present study, a damage-dependent bounding-surface model based on a newly proposed hardening rule was developed to predict the cyclic shakedown and degradation of saturated clay and the effect of the initial anisotropic stress state. By extending the Masing’s rule to the bounding-surface plasticity theory, the stress reversal point is taken as the generalised homological centre of the bounding surface. With movement of the generalised homological centre, at lower stress amplitudes, the cyclic process ends at a steady state, and cyclic shakedown is reached. At higher stress amplitudes, a damage parameter related to the accumulated deviatoric plastic strain is incorporated into the form of the bounding surface, which is hence able to contract to model degradations in stiffness and strength. To take into account the effects of initial anisotropic conditions on the cyclic behaviour of soils, an initial anisotropic tensor is introduced in the bounding surface. The developed model is validated through undrained isotropic and anisotropic cyclic triaxial tests in normally consolidated and overconsolidated saturated clay under both one-way and two-way loadings. Both cyclic shakedown and degradation are well reproduced by the model, as is the anisotropy effect induced by the initial anisotropic consolidation process. 相似文献
13.
Consideration of fabric anisotropy is crucial to gaining an improved understanding of the behavior of granular materials. This paper presents a constitutive model to describe the sand behavior associated with fabric anisotropy within a framework of a strain space multiple mechanism model. In the proposed model, a second-order fabric tensor is extended by incorporating a new function that represents the effect of inherent (or initial fabric) anisotropy, along with three additional parameters: two of them, a1 and a2 , control the degree of anisotropy, and the second mode of inherent anisotropy can be expressed by introducing the parameter a2 as well as the first mode by the parameter a1 . The third parameter, θ0 , expresses the principal direction of inherent anisotropy (eg, the normal vector direction of bedding planes relative to horizontal axis). The formulation of the dilative component of dilatancy (ie, positive dilatancy) is also extended to consider the effect of inherent anisotropy based on the interlocking mechanism. Experimental data on the complex anisotropic responses of Fraser River sand and Toyoura sand under monotonic loading is used to validate this model. The proposed model is shown to successfully capture anisotropic responses, which become contractive or dilative depending on different principal-stress directions, with a single set of anisotropy parameters; thus, the model is considered to possess the capability to simulate the anisotropic behaviors of granular materials. In addition to different loadings on the same fabric, the effects of different fabric anisotropies upon the sand behavior under the same loadings are also investigated. 相似文献
14.
The paper presents an incremental plasticity constitutive Model for Structured Soils (MSS–2) to describe the effects of structure (stress history and bonding) on the mechanical behaviour of cohesive soils. Such effects are high initial stiffness, dilatancy and peak strength, their appreciable reduction upon strain-induced de-structuring and the evolution of material anisotropy. The proposed model advances present practice in incremental elasto-plasticity for structured soils by incorporating: (a) distorted ellipsoids, rotated with respect to the isotropic axis, for the Structure Strength Envelope (bounding surface) and the Plastic Yield Envelope (yield surface) to describe the evolution of structure and anisotropy, (b) an Intrinsic Compressibility Framework and a corresponding Intrinsic Strength Envelope which represents a lower bound of the Structure Strength Envelope and is used as reference locus for the structureless material, (c) an improved damage mechanism to model structure degradation by plastic strains and (d) a non-associated flow rule controlled by structure. The proposed model is modular, its features can be activated simultaneously or selectively, and the 3-D tensorial formulation facilitates direct implementation in finite elements codes. 相似文献
15.
Sensitivity of high-resolution tropical cyclone intensity forecasts to surface flux parameterization
Chi-Sann Liou 《Natural Hazards》2007,41(3):387-399
Surface flux parameterization schemes used in current dynamic models are primarily based upon measurements at low and moderate
wind speeds. Recent studies show that these parameterization schemes may be incorrect at high wind speeds (e.g., tropical
cyclone forecasts). Five high-resolution numerical model experiments are designed to assess the sensitivity of tropical cyclone
intensity forecasts to changes in the surface flux parameterization. The sensitivity experiments are conducted by running
48 h forecasts of the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) for six selected tropical cyclones with
individual modifications to surface flux calculation that include: (1) limiting the surface stress for wind speeds greater
than 33 m s−1, or 64 knots (kt); (2) computing the stress at the top of the model bottom grid layer (MBGL) by averaging results from surface
layer similarity and turbulence mixing parameterization for wind speeds greater than 33 m s−1; (3) increasing the roughness lengths for heat and moisture transfer by a factor of ten; (4) setting the roughness lengths
for heat and moisture transfer to 1/10 of the momentum roughness length; and (5) cooling the sea surface temperature (SST)
by a prescribed rate at high winds. Averaged responses for the six storms to these sensitivity tests show that: (i) the limit
on surface stress at high winds significantly increases the cyclone intensity in 48 h forecasts; (ii) the averaged surface
layer stress at high winds increases the cyclone intensity but to a much lesser degree than limiting the surface stress; (iii)
large increases in the roughness lengths for heat and moisture transfer are needed to significantly impact the intensity forecast;
(iv) the different roughness length formula for surface transfer coefficients notably increases C
h/C
d ratio from 0.59 to 0.79 for 25 m s−1 and 0.41 to 0.75 for 50 m s−1 that significantly increases the predicted cyclone intensity; and (v) cooling of the SST by −5.8°C in 48 h reduces the maximum
surface wind speed by −32 kt, or 16.5 m s−1, at 48 h forecast. These results suggest that a surface flux parameterization scheme suitable for tropical cyclone intensity
forecast must correctly model the leveling-off character of surface stress and C
h/C
d ratio at high winds. All modifications to surface flux calculation have little influence on 48 h track forecasts, even though
they may significantly impact the intensity forecasts.
相似文献
| Chi-Sann LiouEmail: |
16.
Paolo Paronuzzi 《Rock Mechanics and Rock Engineering》2009,42(5):783-813
This paper reports the field evidence and the kinematical study of the motion of two blocks (A and B) mobilised by a rockfall
in Lavone (Valtrompia, northern Italy) on 14th February 1987. The two sequences of impact marks left by the blocks on the
ground surface were measured and the lithostratigraphical features of the debris slope were surveyed. On the basis of the
field-collected input data, several computer simulations were carried out to calculate the coefficients of restitution (E) satisfying the trajectory conditions. The computed output values, obtained by running a specific automatic program for rockfall
modelling, show that rebound trajectories require high coefficients of restitution (0.8 ≤ E ≤ 0.9). Back-calculated impact velocities range from 9.2 to 19.8 m/s. Trajectory heights vary from 0 to 2.4 m above the slope
surface. Block trajectories differ considerably according to the circumstances of initial air projection, i.e. to the initial
rebound angle (α
r). The calculated values of α
r denote a considerable range (36°), emphasising the high variability and the random nature of this parameter. The described
case history shows that rockfall computer analyses can be an effective tool to describe the bouncing propagation of single
blocks, but care must be taken in choosing the restitution coefficient E and the geometrical parameters of initial air projections. 相似文献
17.
Some thermal infrared anomalies on the earth’s surface are omens of stronger earthquakes, and have a close relationship with
the stress fields. Satellite-based remote sensing is an important means of monitoring and researching this phenomenon. The
M
S 7.3 Yutian earthquake in Xinjiang on March 20, 2008 and the M
S 8.0 Wenchuan earthquake in Sichuan on May 12, 2008 both happened in the Qinghai–Tibet Plateau, China, with epicenters more
than 2,000 km apart. The two events, however, were a production of an identical stress field in different developing phases.
Prior to the M
S 7.3 Yutian earthquake, a large-scale abnormal temperature rise not only covered the epicenter of the forthcoming Yutian earthquake,
but also arrived at the epicenter of the farther Wenchuan earthquake. The revolving elliptic stress thermal field reflecting
earthquake gestation moved from the west to the east of the Wenchuan epicenter at the time of the Yutian event occurrence.
The rotation of the calefactive ellipses and belts prior to the two strong events agreed with the stress field, the focal
mechanism, and modality and mechanism property of the ruptures in the crustal surface induced by the events. It should be
a reflection of the partial mantle uprush and rotation. 相似文献
18.
An incremental plasticity theory has been developed to describe the mechanical behaviour of anisotropically consolidated clays. The theory removes some of the shortcomings of the existing critical state models by incorporating the effects of the initial anisotropy due to a known depositional stress history and its subsequent alteration during further plastic deformation under a general stress system. From the extensive comparisons with the reported results in the literature, it is established that the model is satisfactory in predicting the various aspects of drained as well as undrained behaviour of K0-consolidated clays. 相似文献
19.
Circular opening is commonly encountered in wellbore drilling of petroleum engineering, boring for cast-in situ pile installation, and tunneling excavation. This paper presents a rigorous solution for the elastoplastic responses of the anisotropic soft soil mass around a circular opening excavated under undrained and drained conditions. Both the anisotropic elastoplastic behavior and the 3D strength of the soft clay are incorporated in the present solutions. The well-established anisotropic critical state elastoplastic model S-CLAY1, which can represent the initial fabric anisotropy and stress-induced anisotropy of soft soil, is further modified by the Spatially Mobilized Plane criterion to consider the 3D strength of geomaterials. Then, the investigated problems, excavation of a circular opening under both short-term (undrained) and long-term (drained) conditions, are formulated as a system of first-order differential equations and are solved as initial value problems. The distributions of stress components and anisotropy parameters around the opening, the stress trajectory of a soil particle at the opening wall, as well as the stress–displacement curve at the opening wall are presented to investigate the elastoplastic responses of the opening. Extensive parameters show that the overconsolidated ratio and coefficient of earth pressure at rest (K0) have remarkable effects on the elastoplastic responses around a circular opening.
相似文献20.
Quantification of Aperture and Relations Between Aperture,Normal Stress and Fluid Flow for Natural Single Rock Fractures 总被引：1，自引：0，他引：1
Pinnaduwa H. S. W. Kulatilake Jinyong Park Pirahas Balasingam Robert Morgan 《Geotechnical and Geological Engineering》2008,26(3):269-281
Accurate quantification of rock fracture aperture is important in investigating hydro-mechanical properties of rock fractures.
Liquefied wood’s metal was used successfully to determine the spatial distribution of aperture with normal stress for natural
single rock fractures. A modified 3D box counting method is developed and applied to quantify the spatial variation of rock
fracture aperture with normal stress. New functional relations are developed for the following list: (a) Aperture fractal
dimension versus effective normal stress; (b) Aperture fractal dimension versus mean aperture; (c) Fluid flow rate per unit
hydraulic gradient per unit width versus mean aperture; (d) Fluid flow rate per unit hydraulic gradient per unit width versus
aperture fractal dimension. The aperture fractal dimension was found to be a better parameter than mean aperture to correlate
to fluid flow rate of natural single rock fractures. A highly refined variogram technique is used to investigate possible
existence of aperture anisotropy. It was observed that the scale dependent fractal parameter, K
v, plays a more prominent role than the fractal dimension, D
a1d, on determining the anisotropy pattern of aperture data. A combined factor that represents both D
a1d and K
v, D
a1d × K
v, is suggested to capture the aperture anisotropy. 相似文献