共查询到20条相似文献，搜索用时 578 毫秒
1.
QI Jianfeng LUAN Maotian FENG Xiuli MA Tailei NIE Ying 《中国海洋大学学报(英文版)》2007,6(4):413-420
The apparatus for static and dynamic universal triaxial and torsional shear soil testing is employed to perform stress-controlled cyclic single-direction torsional shear tests and two-direction coupled shear tests under unconsolidated-undrained conditions. Through a series of tests on saturated clay, the effects of initial shear stress and stress reversal on the clay’s strain-stress behavior are examined, and the behavior of pore water pressure is studied. The experimental results indicate that the patterns of stress-strain relations are distinctly influenced by the initial shear stress in the cyclic single-direction shear tests. When the initial shear stress is large and no stress reversal occurs, the predominant deformation behavior is characterized by an accumulative effect. When the initial shear stress is zero and symmetrical cyclic stress occurs, the predominant deformation behavior is characterized by a cyclic effect. The pore water pressure fluctuates around the confining pressure with the increase of cycle number. It seems that the fluctuating amplitude increases with the increase of the cyclic stress. But a buildup of pore water pressure does not occur. The de- formations of clay samples under the complex initial and the cyclic coupled stress conditions include the normal deviatoric deforma- tion and horizontal shear deformation, the average deformation and cyclic deformation. A general strain failure criterion taking into account these deformations is recommended and is proved more stable and suitable compared to the strain failure criteria currently used. 相似文献
2.
在冻结法施工中, 冻土的强度及变形特性对冻结壁的稳定性至关重要。为了研究不同含水率对冻结作用下土的强度和蠕变的影响, 以江西红黏土为研究对象, 通过冻结三轴试验, 在-10℃下研究含水率对冻结红黏土强度及蠕变特征的影响。试验结果表明: 16%~32%含水率范围内, 冻结红黏土的抗压强度随含水率的增加先增大后减小; 16%~28%含水率范围内, 随着含水率增大, 其黏聚力逐渐增大, 内摩擦角逐渐减小; 围压为0.2 MPa与0.5 MPa下的蠕变曲线都显示含水率较低时只会出现衰减蠕变阶段和稳定蠕变阶段, 含水率较高时会出现加速蠕变阶段。含水率对红黏土的力学性质影响较大, 研究成果可为江西地区红黏土地层地铁隧道建设人工冻结法施工提供参考。 相似文献
3.
《中国海洋大学学报(英文版)》2021,20(5)
Marine geological disasters occurred frequently in the deep-water slope area of the northern South China Sea, especially submarine landslides, which caused serious damage to marine facilities. The cyclic elastoplastic model that can describe the cyclic stress-strain response characteristic for soft clay, is embedded into the coupled Eulerian-Lagrangian(CEL) algorithm of ABAQUS by means of subroutine interface technology. On the basis of CEL technique and undrained cyclic elastoplastic model, a method for analyzing the dynamic instability process of marine slopes under the action of earthquake load is developed. The rationality for cyclic elastoplastic constitutive model is validated by comparing its calculated results with those of von Mises model built in Abaqus. The dynamic instability process of slopes under different conditions are analyzed. The results indicate that the deformation accumulation of soft clay have a significant effect on the dynamic instability process of submarine slopes under earthquake loading. The cumulative deformation is taken into our model and this makes the calculated final deformation of the slope under earthquake load larger than the results of conventional numerical method. When different contact conditions are used for analysis, the smaller the friction coefficient is, the larger the deformation of slopes will be. A numerical analysis method that can both reflect the dynamic properties of soft clay and display the dynamic instability process of submarine landslide is proposed, which could visually predict the topographies of the previous and post failure for submarine slope. 相似文献
4.
Undrained behaviour of sand under low cell pressure was studied in static and cyclic triaxial tests. It was found that very loose sand liquefies under static loading with the relative density being a key parameter for the undrained behaviour of sand. In cyclic triaxial tests, pore water pressures built up during the cyclic loading and exceeded the confining cell pressure. This process was accompanied by a large sudden increase in axial deformation. The necessary number of cycles to obtain liquefaction was related to the confining cell pressure, the amplitude of cyclic loading and the relative density of sand. In addition, the patterns of pore water pressure response are different from those of sand samples with different relative densities. The test results are very useful for expounding scour mechanism around coastal structures since they relate to the low stress behaviour of the sand. 相似文献
5.
水库滑坡变形破坏受其岩土体蠕变特性及环境因素的影响。当滑坡进入加速变形阶段后,变形骤然增大,失稳概率增加。为了研究滑坡岩土体蠕变特性及其稳定性,选取锦屏一级水电站呷爬滑坡为研究对象,采用坡表位移监测曲线分析与室内三轴蠕变试验相结合的方法,建立了Burgers蠕变模型结合FLAC3D软件进行了滑坡稳定性研究。分析坡表位移-时间曲线发现,坡体变形特征与一般滑坡土体的蠕变特征具有相似性,滑带土室内三轴蠕变试验结果表明,滑带土变形可划分为瞬时蠕变、减速蠕变与稳定蠕变3个阶段,同时其瞬时变形量、稳定蠕变速率均随围压以及应力水平的增大而增大。基于滑带土蠕变特性的Burgers蠕变模型的计算结果,对比了常规强度折减法与考虑蠕变的强度折减法的滑坡稳定性系数,计算结果表明呷爬滑坡目前处于稳定状态,在一个计算周期内考虑蠕变的强度折减法较常规强度折减法的稳定性系数下降了0.04,因此,揭示滑坡土体蠕变特性并在此基础上研究其稳定性具有实际意义。 相似文献
6.
In this study, the undrained behaviour of silt under low stress level is studied. An effective preparation method for built—in
silt samples in the triaxial test was firstly developed. By triaxial testing of samples at low confining pressures it was
found that silt easily loses stability and liquefies. Loose silt may show temporary liquefaction under static loading, and
develop full liquefaction under cyclic loading. The most important factors influencing the silt behaviour are porosity, confining
pressure, consolidation state, cyclic loading level and number of cycles. The maximum obtainable shear stress is primarily
a function of the confining pressure and the internal frictional angle. The actual structure of the silt material is the key
factor in controlling its behaviour. 相似文献
7.
《山地科学学报》2015,(6)
The cutting slopes in soft rock of redbed appeared in Yichang-Badong highway often suffer from the instability along weak intercalations, so the creep behaviors of weak intercalated soils are crucially important for the stability of cutting slopes. Because the deformation of weak intercalated soils is significantly affected by water content due to the strong water sensitivity, it is necessary to study the influence of matric suction on the creep behaviors of weak intercalated soils. In order to find out the unsaturated creep characters of weak intercalated soils, a GDS unsaturated triaxial apparatus was used. Then the triaxial creep experiments on weak intercalated soil samples under varying matric suction were conducted to obtain the unsaturated creep curves. The results show that the weak intercalated soils have obvious creep behaviors, and the creep strain is in nonlinear relationship with stress and time. When the matric suction is constant, a larger deviator stress will lead to a larger creep strain; When the deviator stress is constant, a smaller matric suction will lead to a larger creep strain. Based on the Mesri creep model, an improved creep model for weak intercalated soils under varying matric suction was established, in which the relationship of stress-strain was expressed with a hyperbolic function, and the relationship of strain-time was expressed with power functions in stages. Then an unsaturated creep model including stress-matric suction-strain-time for weak intercalated soils was established based on the power function relationship between matric suction and Ed(a parameter of the improved creep model). The comparison of the calculated values of creep model and the experimental values shows that the creep behaviors of weak intercalated soils can be predicted by the unsaturated creep model by and large. 相似文献
8.
The foundations of some ocean engineering structures are built to withstand not only the vertical gravity load V, but also the horizontal load H induced by sea waves and current. The horizontal load includes the concentrated force load, the moment load M, and the torque load T termed also as combined loading. It is of academic and engineering significance to study the deformation law of submarine seabed due to combined loading. On the basis of the three-dimensional elastic mechanics solution of circular foundation, numerical methods are used to analyze the deformation law of submarine soil under circular foundation with six degrees of freedom. The finite element analysis results give the elastic deformation law of soil in three dimensional spaces, modify the theoretical elasticity solution, and presents nonlinear soil deformation mechanism under the circular foundation with six degrees of freedom. 相似文献
9.
The aim of this study is to numerically investigate the influence of particle breakage on the mechanical behavior of granular materials using a discrete element method (DEM). To enable particle crushing, non-crushable elementary particles are boned together to represents the granular aggregates which can be crushed when the external force exceeds its strength. The flaw of the aggregate was also modeled by randomly distributed void. Single particle crushing tests were carried out to determine the distribution of particle strength. The results of single particle crushing tests illustrate that the simulated single particle fracture strength and pattern agree well with the Weibull’s distribution equation. Conventional oedometer tests, drained monotonic and cyclic triaxial tests were also carried out to investigate the crushing of the aggregates and the associated mechanical behaviors. The effect of confining pressure on the crushing of aggregates and the mechanical behavior was also analyzed. It was found that the peak stress and dilation decrease significantly when particle crushing was considered. The deformation behavior of the specimen is essentially controlled by two factors: particle rearrangement - induced dilation and particle crushing - induced contraction. The increase of permanent strain and the reduction of dilation were observed during cyclic loading and they tend to reach a stable state after a certain number of cycles. The crushing of aggregate is most significant in the first two cycles. The results also indicated that for the same axial strain the volumetric strain and the bound breakage in the cyclic loading tests are significantly larger than that in the monotonic loading tests, especially at high cyclic stress ratio. 相似文献
10.
岩石蠕变特性对岩体工程的长期稳定有着重要影响, 尤其是在酸雨等水化学作用下, 岩石的细观结构遭到破坏, 蠕变特性及变形更为显著。以重庆二佛寺红层砂岩为研究对象, 通过开展室内三轴压缩分级蠕变试验, 研究了酸腐蚀状态下砂岩的蠕变特性。结果表明: 酸的腐蚀和浸泡会使砂岩内部孔隙增加, 导致砂岩在第一级荷载下会产生较大的瞬时应变和蠕变量, 之后瞬时应变量和蠕变量随着应力增加而增大; 岩样受到腐蚀软化, 蠕变破坏强度为抗压强度的76%, 长期强度仅为抗压强度的54%。为了描述蠕变全过程, 建立了一个损伤蠕变模型来拟合试验数据, 验证了其适用性, 可以为岩土工程建设的稳定性提供参考。 相似文献
11.
水对岩土体的力学参数存在明显的劣化效应。开展了不同含水率条件下滑坡堆积体三轴力学试验, 建立了饱和度和力学参数之间的经验方程; 对建立的经验方程进行了二次开发, 通过饱和度和力学参数的耦合, 实现了库水位实时变动过程中考虑岩土体力学参数变化对滑坡稳定性的影响, 克服了库水位变动过程中岩土体物理力学参数不能随库水入渗变化的局限性。通过云南省兰坪县大华滑坡在库水位变动环境下的模拟结果和现场监测数据的比对, 验证了考虑岩土体力学参数水致劣化效应的合理性, 并对大华滑坡考虑水致劣化效应的变形演化规律进行了工程应用。 相似文献
12.
《山地科学学报》2020,17(1):230-243
This paper describes model tests of single piles subjected to vertical cyclic compressive loading for three kinds of topography: sloping ground, level ground, and inclined bedrock. Comprehensive dynamic responses involving cyclic effects and vibration behaviours are studied under various load combinations of dynamic amplitude, mean load,frequency and number of cycles. Test results show that permanent settlement can generally be predicted with a quadratic function or power function of cycles.Sloping ground topography produces more pronounced settlement than level ground under the same load condition. For vibration behaviour,displacement amplitude is weakly affected by the number of cycles, while load amplitude significantly influences dynamic responses. Test results also reveal that increasing load amplitude intensifies nonlinearity and topography effects. The strain distribution in a pile and soil stress at the pile tip are displayed to investigate the vibration mechanism accounting for sloping ground effects. Furthermore, the dynamic characteristics among three kinds of topography in the elastic stage are studied using a three-dimensional finite method. Numerical results are validated by comparing with experimental results for base inclination topography. An inclined soil profile boundary causes non-axisymmetric resultant deformation, though a small difference in vertical displacement is observed. 相似文献
13.
新疆塔县地区广泛分布的大规模片麻岩崩塌、滑坡主要是由于长期地震力循环作用下岩体劣化所致。为揭示该地区片麻岩在地震力作用下的劣化损伤机理,采用在不同应力水平条件下对片麻岩岩样进行循环荷载试验和三轴压缩试验的方法,分析了片麻岩阻尼参数及循环加、卸载前后三轴抗压强度的变化规律。研究结果表明:片麻岩阻尼比和阻尼系数随着循环荷载次数的增加而逐渐降低,随着应力水平的升高而增大;循环荷载作用后,片麻岩的三轴抗压强度均明显降低,且应力水平越高,降低的幅度越大;此外,片麻岩内部矿物颗粒的相互摩擦,原生微裂隙、孔洞的张开、闭合以及次生裂隙的产生、发展是导致其劣化损伤的主要机制。总的来说,长期地震力作用下,研究区片麻岩由于内部劣化损伤导致的力学性质降低,是该区域广泛发育大规模崩塌、滑坡等地质灾害的主要原因之一。 相似文献
14.
《山地科学学报》2019,(12)
During the constructions of motorways and high-speed railway lines in the Yanji Basin, large amounts of excess mudstones due to the enormous tunnel excavations and slope cuts would be deposited as landfills. Assessing the deformation and permeability of Yanji mudstone became important for the design, construction and operation of the landfills.This paper presents an experimental study on the deformation and permeability of Yanji mudstone by carrying out a series of oedometer tests with loading/unloading cycles. The results show that the sample with a lower initial water content exhibited greater swelling deformation after inundation, a lower yield stress, greater deformation and a higher hydraulic conductivity during the loading/unloading cycles. As the number of loading/unloading cycles increased, the yield stress and accumulated plastic deformation increased, while the compression index,rebound index and hydraulic conductivity decreased.The samples became stiffer and their hydromechanical behaviour tended to be stable after three cycles. The compression curves could be divided into pre-yield and post-yield zones. The post-yield zones of compression curves and the rebound curves could be normalized into a unique line, and the pre-yield zones of the compression curves could be described as lines.Basic equations were developed to predict mudstone deformation under cyclic loading and unloading.Additionally, an empirical relationship between the hydraulic conductivity and void ratio was also proposed. The ability of the proposed methods was verified by the overall good agreement between the experimental results and predicted values. 相似文献
15.
在三轴条件下,对饱和土(砂土和黏土)进行排水与不排水条件下的冲击试验及冲击后再固结试验,对比研究了不同渗透性土在不同排水条件下的冲击动力响应和冲击后再固结性状.结果表明:饱和黏土不排水冲击时的孔隙水压力随冲击击数增加而升高并逐渐稳定,排水冲击时的孔隙水压力则是先达到峰值然后有所下降;砂土不排水冲击时的冲击能量对孔隙水压力影响最明显;饱和砂土不排水冲击时的轴向应变与冲击击数呈近似线性关系,饱和黏土冲击及饱和砂土排水冲击则呈近二次曲线关系;饱和砂土不排水冲击后再固结阶段的孔隙水压力立即消散为0,同时体变迅速增大到一定值;饱和黏土在冲击后再固结阶段的孔隙水压力在一定时间内逐渐消散完毕,同时体变逐渐增大;饱和黏土排水冲击时,冲击阶段产生的体变占冲击引起总体变的39%~49%,冲击后再固结阶段产生的体变占51%~61%;砂土和黏土的总体变均表现为排水冲击明显大于不排水冲击,改善冲击时的排水条件有利于提高加固效果. 相似文献
16.
Soil behavior can reflect the characteristics of principal stress rotation under dynamic wave and traffic loads. Unequal amplitudes of tensile and compressive stresses applied to soils have complex effects on foundation soils in comparison with the pure principal stress rotation path. A series of undrained cyclic hollow torsional shear tests were performed on typical remolded soft clay from the Hexi area of Nanjing, China. The main control parameters were the tensile and compressive stress amplitude ratio(α) and the cyclic dynamic stress ratio(η). It was found that the critical η tended to remain constant at 0.13, when the value of the compressive stress amplitude was higher than the tensile stress amplitude. However, the influence of the tensile stress was limited by the dynamic stress level when α= 1.For obvious structural change in the soil, the corresponding numbers of cyclic vibration cycles were found to be independent of α at low stress levels and were only related to η. Finally, a new method for evaluating the failure of remolded soft clay was presented. It considers the influence of the tensile and compressive stresses which caused by complex stress paths of the principal stress rotation. This criterion can distinguish stable, critical, and destructive states based on the pore-water-pressure-strain coupling curve while also providing a range of failure strain and vibration cycles. These results provide the theoretical support for systematic studies of principal stress rotation using constitutive models. 相似文献
17.
Debris flow is one of the major secondary mountain hazards following the earthquake. This study explores the dynamic initiation mechanism of debris flows based on the strength reduction of soils through static and dynamic triaxial tests. A series of static and dynamic triaxial tests were conducted on samples in the lab. The samples were prepared according to different grain size distribution, degree of saturation and earthquake magnitudes. The relations of dynamic shear strength, degree of saturation, and number of cycles are summarized through analyzing experimental results. The findings show that the gravelly soil with a wide and continuous gradation has a critical degree of saturation of approximately 87%, above which debris flows will be triggered by rainfall, while the debris flow will be triggered at a critical degree of saturation of about 73% under the effect of rainfall and earthquake(M>6.5). Debris flow initiation is developed in the humidification process, and the earthquake provides energy for triggering debris flows. Debris flows are more likely to be triggered at the relatively low saturation under dynamic loading than under static loading. The resistance of debris flow triggering relies more on internal frication angle than soil cohesion under the effect of rainfall and earthquake. The conclusions provide an experimental analysis method for dynamic initiation mechanism of debris flows. 相似文献
18.
根据三轴蠕变试验曲线的特点,建立了云母石英片岩七元件线性黏弹塑性蠕变模型,采用最小二乘法对蠕变柔量时间曲线和应变时间蠕变曲线进行拟合确定蠕变模型参数,讨论了确定蠕变模型参数的影响因素及参数的合理性与可用性。结果表明:由于受到分级加载次数、初次加载应力值和加载时间的影响,两种曲线拟合确定的参数各不相同;云母石英片岩蠕变模型的非线性较明显;蠕变柔量时间曲线拟合确定的参数不予采用,应变时间蠕变曲线拟合确定的参数在各级应力水平下变化规律不明显;采用某种单一方法确定蠕变模型参数不够全面,建议采用综合辨识法,这样才能保证岩土工程中蠕变数值分析结果的正确合理性以及施工设计的安全可靠性。 相似文献
19.
高寒、高海拔地区由于反复冻融导致的岩体变形破坏,对区内工程建设有重大影响。为研究不同裂隙条件下岩体循环冻融特性,在汶马高速沿线选择具有代表性的千枚岩和砂岩,制备了不同裂隙条件（长度、张开度、裂隙组数）试样,在干燥和饱水两种状态下分别进行大温差（-20℃到20℃）循环冻融（50次）试验。试验揭示了饱水裂隙岩样冻融变形过程:冻缩→冻胀→冻缩（冻结阶段）→融胀→融缩→融胀（融化阶段）,干燥裂隙岩样冻融变形过程:冻缩（冻结阶段）→融胀（融化阶段）。进一步,选择冻胀量εd为指标,分析了两类岩样冻融循环次数与εd的关系,揭示了裂隙长度、宽度和组数对εr的影响规律;选择残余变形量εr为指标,揭示了千枚岩和砂岩试样在饱水条件下εr随εd的增加规律,获得了εd与εr间的定量关系;分析了干燥和饱水试样单轴抗压强度随冻融循环次数增加而减小规律,确定了冻融次数与试样劣化间的线性关系。最后,初步讨论了饱水条件、岩性和裂隙条件对岩体冻融循环变形的影响机制。 相似文献
20.
《山地科学学报》2021,(7)
In cold regions, the creep characteristics of warm frozen silty sand have significant effect on the stability of slope and subgrade. To investigate the creep behavior of warm frozen silty sand under thermo-mechanical coupling loads, a series of triaxial creep tests were carried out under different temperatures and stresses. The test results reveal that the creep strains decrease as the consolidation stress increases, and finally tend to be equal under the same loading stress, regardless of whether the stress is isotropic or deviatoric. Additionally, warm frozen silty sand is highly sensitive to temperature, which greatly influences the creep strain both in the consolidation stage and loading stage. Furthermore, based on the creep test phenomena, a new creep model that considers the influence of the stress level, temperature, hardening, and damage effect was established and experimentally validated. Finally, the sensitivity of the model parameters was analyzed, and it was found that the creep curve transitions from the attenuation creep stage to the non-attenuation creep stage as the temperature coefficient and stress coefficient increases. The hardening effect gradually changes to the damage effect as the coupling coefficient of the hardening and damage increases. 相似文献