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1.
The behavior of loose sand-structure interface under the high frequency cycle shearing is analyzed by using Particle Discrete Element Method (DEM).The changes of sand box porosities of DEM model and sand volume strains are examined in detail.The results show that sand volumetric shrinkage due to shearing is not obvious in spite of the larger loose sand particle friction coefficients and particle stiffness.The particle stiffness ratio has a little effect on the mechanical properties of sands.In addition,the decrease in volume of sand under shearing is more obvious with the increase of the confining pressures.Moreover,the decrease in volume of loose sand under shearing is greater with the increase of the high frequency cycle shear amplitude and the shear frequency.  相似文献   

2.
The mechanical behaviors of the interface between coarse-grained soil and concrete are investigated by simple shear tests under conditions of cemented soil slurry (clay mixed with cement grout). The results show that the relation curve between shear stress and shear strain appears stress-strain softening and shear dilatation is significant. The point of peak strength and the position when the shear dilatation occurs are related to normal stress. In addition, shear dilatation occurs before the shear stress reaches peak value. In shear failure state, with the same height, the shear displacement increases as the normal stress increases. While with the same normal stress and at the same height, the shear displacement increases as the concrete content increases. A particle flow model of simple shear test between interface between coarse-grained soil and concrete is constructed by PFC (particle flow code). The disturbed height of the sample and the main influence factors are determined by analyzing the laws of particle motion at different heights inside the sample. The PFC results show disturbed height of the sample is related to maximum particle diameter of the soil, normal stress and roughness of the interface (with or without slurry) etc. In terms of the coarse-grained soil, the shear displacement is significant in the area which is close to the interface and about 3-4 times of the maximum particle diameter, and informed the obvious shear band. Further, the thickness of the interface can be regarded as the value.  相似文献   

3.
The mechanical behavior and mechanism of the interface between structure and coarse grained soil are investigated through simple shear tests on the conditions of bentonite slurry, clay slurry and without slurry, respectively. The results indicate that different kinds of slurry have important influence on shear strength. Compared with the interface without slurry, the shear strength with bentonite slurry reduces by 45% approximately, significantly more than clay slurry which reduces by 10%. The value of the friction angle with bentonite slurry is about 60% of that with clay slurry. Shear displacement increases as upright stress increases when reaches its failure states at the same height, and shear displacement with bentonite slurry is smaller than that with clay slurry when with the same upright stress and height. The upright displacement with bentonite slurry is greater than that with clay slurry under the same upright stress. In addition, shear dilatation is apparent under the low normal stress when without slurry. Otherwise, it appears as shear contraction.  相似文献   

4.
Based on concepts of mechanics, a mechanical model of novel type of steel plate composite shear wall is presented. The novel type of structure is formed by steel plate shear wall and T-shaped solid-web composite columns. Flexural stiffness of steel beams, lateral stiffness of the T-shaped solid-web composite columns, shear stiffness of steel plate composite shear wall and shear stiffness of beam-column connection are taken into account in the mechanical model. And the equivalent damping between steel plate and boundary is considered. Based on the deformation features of structures and the calculation hypothesis, the lateral stiffness model and the energy dissipation model of structures are developed. Meanwhile, the calculation equations of elastic ultimate and plastic ultimate of shear strength of structures are set up. The theoretical analysis results inosculate better with the results of experiment. The comparison between the result calculated from the formula and the experimental result shows that the calculation precision is high enough to meet the demand of theoretical analysis. The difference, including equivalent model, stress states, manufacturing defect and installation error, between the formula and the experiment has been further discussed.  相似文献   

5.
Negative shear property of soil-concrete interface is one critical issue in civil engineering. According to negative simple shear tests of soil-concrete interfaces with various water content, quantitative analysis on changes of shear strength, friction angle and cohesion force of negative sheared interface against positive shear experience were conducted. Several empirical formulae were proposed for above changes, and critical positive shear ratio was put forward. Based on improved stress-strain equation, mathematical model for tangent modulus of negative sheared soil-concrete interface was established. This new model consists ten parameters which can be determined by simple shear test. Process for determining these ten parameters was presented, and empirical values of them were obtained. Simulations for stress-strain curves of soil-concrete interface were carried out, and good ability of the model was found.  相似文献   

6.
In order to discuss the influence of stress history on the constitutive relations for soils,a series of drained conventional triaxial compression tests for normally consolidated and overconsolidated clays have been carried out.It is found through comparing the stress-strain relation curves under the different stress histories that the overconsolidated ratio is the determining factor for volumetric strain.The volumetric strain is less sensitive to consolidation pressure,however.For the shear capacity,the consolidation pressure is the determining factor,but the influence of the overconsolidated ratio can not be neglected since it determines whether there will be strain hardening or strain softening as well as the grade of strain softening.Despite that,the soil specimens will finally reach a unified critical state and approximately the same residual strength.According to the principle of interaction between plastic volumetric and shear strains,the mechanism of generating two types of stress-strain relation curves for clays is explained.It is shown that the critical state is a pure process of shearing deformation in which the interaction between plastic volumetric and shear strains completely disappears.The critical state is independent of the previous stress history.  相似文献   

7.
In earlier calculation models,the stiffness centers in frame-shear wall structures have been located by the structural torsion stiffness.However,the results are illogical owing to the difference between the distortion character and the shears distribute mechanism of the frames and shear walls.In this paper,a new formula for calculating story stiffness is introduced,which can consider the stiffness of the frames and shear walls at the same time.The structural stiffness centers,the torsion eccentric distances and torsion effect are calculated,and the stiffness of elements is considered also.It is shown that the concept of the presented stiffness model is clear and the results are reasonable,which can be used to calculate the appreciative torsion effect.  相似文献   

8.
Sandstone is sediment rock composed of many cemented sand particles, and corresponding particle constraint and force bearing capacity are greatly controlled by the cemented property. In order to better reflect the cemented property influencing on the mechanical characteristics of the sandstone, take the oil sandstone reservoir for instance, a numerical model based on 3Dimensional Particle Flow Code (PFC3D) considering the parallel bond model was brought forward to simulate the failure mechanism during shearing process. The sandstone cemented property is modeled based on random mathematics and advanced development of Particle Flow Code (PFC), and the relation of the stress ratio, volume strain, coordination number and bond-broken number and the axial strain is analyzed in detail, especially the contact network evolution indicated the force chain is important to transfer the external force, which verifies the feasibility of the numerical model. Based on the above PFC3D model, a series of researches on changing the cemented radius ratio, parallel bond stiffness and cemented volume of the particles have been done to clearly illuminate the importance of cemented property for the bearing capacity of the sandstone structure, which provides a scientific base for research on the failure mechanism of the sandstone under special conditions. Therefore, the above numerical method is more efficient and applicable for comparatively large scale and complex experiments, and the obtained research results can bring a new thought for the real cemented sandstone to research on its macro-micromechanical response and the structure failure mechanism, and also is significant for the sand production mechanism, sand volume prediction and sand control measures for the sandstone reservoir.  相似文献   

9.
In this paper the static stress distribution of closed valve during diastole under the peak across valve pressure difference is analyzed with nonlinear finite element method. We analyzed the three shapes i. e.,spherical,cylindrical and rotating paraboloid type valves, respectively as a result of computation, it is suggested that the maximum principal normal and shearing stress for rotating paraboloid type valve are smaller than those for the cylindrical and spherical type valves. It shows that there exist some similarities of the stress distribution among these three type valves.  相似文献   

10.
Based on complex variable theory in plane elasticity, the equivalent spring stiffness is derived from the analytical solution by means of simplifying shallow shield tunneling to semi-infinite plane with hole, which is applied to response displacement method. The performances of the analytical solution are evaluated and compared with that of the deep shield tunneling through a series of selected various tunnel depths and soil Poisson's ratios. The relation of compression and shear spring stiffness is discussed. Meanwhile, two factors affected soil spring stiffness, tunnel depth and soil Poisson's ratio, are also analyzed. It is shown that soil spring stiffness of shallow shield tunneling is different from that of deep shield tunneling, and the ratio of compression and shear spring stiffness varies along shallow shield tunneling. It is also found that the value and distribution law of soil spring stiffness of shallow shield tunneling greatly depend on tunnel depth and soil Poisson's ratio.  相似文献   

11.
针对平面应变条件下各向异性砂土剪切带角度的试验规律,采用传统的3种理论和分叉理论进行对比分析。将平面应变条件下剪切带角度的试验结果按照传统3种理论整理发现,尽管传统3种理论可以估算同种砂剪切带角度的极小、中间和极大值,但无法解释其各向异性规律。砂土在平面应变条件下破坏时会产生明显的剪切带,当剪切带方向和砂土沉积面方向接近时,会较早诱发剪切带的产生,使材料强度降低,造成了平面应变条件下各向异性强度规律明显不同于常规三轴条件下的试验规律,采用分叉理论结合各向异性模型则可以有效解释这个规律。随砂土沉积面角度的变化,模型可以从细观角度解释常规三轴条件下剪切带角度的单调变化的试验规律,结合分叉理论可以描述平面应变条件下其先减小然后增大的规律。通过几种理论对比分析表明,模型结合分叉理论不但能够描述多种应力状态下的平面应变和常规三轴应力条件下剪切带角度表现的不同规律,而且能够从细观角度解释其各向异性成因。  相似文献   

12.
A study which focuses on the role of matric suction in the stress strength of roadbed unsaturated soil was presented. Two types of tests were described, namely, the suction controlled shear test and microstructure scanned test. For the former, four sub tests were conducted under different suction and net normal stress conditions. And two unsaturated soil samples that belong to the same type but with different water contents were scanned. In contrast with clay soil, the corresponding results show that the strength of silty sand soil does not always increase as matric suction increases or soil water content decreases; there exists a peak contributed by matric suction that acts on soil stress strength. The main reason for this kind of phenomenon is due to the typical microstructure of this type of soil and the various types of pore water retention. Additionally, the state of stress in which soil sample meets can also exerts important influence on soil strength.  相似文献   

13.
采用3 种模型对光响应曲线进行拟合,比较不同拟合模型的优劣,旨在优选出水分胁迫下最优的光合作用光响应模型,为深入了解扭黄茅光合生理生态特征、合理使用水资源有效地进行植被恢复提供科学依据。利用Li-6400 光合仪测定了元谋干热河谷扭黄茅雨季在不同土壤水分胁迫程度下光合作用的光响应过程,并用直角双曲线模型、非直角双曲线模型和直角双曲线修正模型对光响应曲线进行拟合,通过决定系数(R2)、拟合的初始量子效率(α)、最大净光合速率(Pnmax)、光饱和点(LSP)、光补偿点(LCP)和暗呼吸速率(Rd) 6 个参数的对比,比较3 种模型的差异。研究结果表明：（1）随着土壤水分胁迫的加重,扭黄茅净光合速率、光补偿点、暗呼吸速率降低,强光下扭黄茅的光合作用发生光抑制现象,表现为光合速率随光合有效辐射强度的增加而呈现先升高后降低的趋势;（2）从决定系数比较来看,拟合效果优劣排序为直角双曲线修正模型＞非直角双曲线模型＞直角双曲线模型;（3）直角双曲线修正模型的Pnmax、LSP、LCP 和Rd 4 个光合参数均与实测值较为接近,而其他模型除个别参数较为接近外,多数参数差别较大。直角双曲线修正模型可以直接得出饱和光强和最大净光合速率,能够较好地拟合土壤水分胁迫下扭黄茅的光响应过程及其特征参数,拟合值较符合植物实际的生理情况,更接近实测值,该模型可以更好地拟合土壤水分胁迫下扭黄茅的光响应曲线。  相似文献   

14.
The disruption, yield and water content change of a remolded unsaturated loess is studied during the course of shear tests with controlled net mean stress equaling constant. Two types of density's triaxial drained shear tests with controlled net mean stress and suction equaling constants are conducted. The test results show that the disruption stress increases with suction. A new method to identify the field stress under triaxial drained shear tests with controlled net mean stress equaling constants is suggested, and the shape of loading-collapse yield curve are similar in q-s plane and in p-s plane. The soil-water characteristic curve is dependent on deviatoric stress, and the soil-water characteristic curve including water content, suction, net mean stress and deviatoric stress is proposed.  相似文献   

15.
The lateral structures of frame-shear wall system are simplified into bending beams and shear beams which stiffness can vary in different stages along the building height. The three-dimension stiffness matrix and mass matrix are deduced, and the characteristic equation is established to calculate the tortuous free vibration of the asymmetric system. The method is simple and has satisfactory precision, and it is easily fulfilled in micro-computers.  相似文献   

16.
By using servo control shear loading system, specimens with non-coplanar rock-like intermittent joints were tested by the way of forward and reverse direct shear, rupture mechanism and shearing law for rock bridge with non-coplanar intermittent joints were studied under direct shear. The experimental studies showed that five apparent stages are presented in the process of rock bridge rupture under direct shear, which are linear elastic stage, initiation and extension of crack, fracture and transfixion of rock bridge, climbing and occlusion of shear plane and residual friction. Rock bridge presented profile fracture plane under forward direct shear. While under reverse direct shear, band form fracture plane is showed which penetrated along with the direction of forward shear, and the shear strength of initiation and peak shear strength under reverse direct shear are bigger than that under forward shear. Crack angle, normal stress and lap proportion among adjacent joint are the main factors that influence the initiation strength and peak shear strength. The FLAC 3D simulation for the process of non-coplanar intermittent joints rock bridge rupture and formation of shear rupture surface under forward and reverse direct shear was conducted. The results of numerical simulation agreed well with those of experiment. The simulation results revealed tension crack failure of non-coplanar intermittent joints rock bridge and shear yielding mechanism of fracture plane.  相似文献   

17.
In order to study the influence of stress path on the constitutive relations for reshaped clay,the triaxial compression tests under stress paths with drainage in cases of increased,constant and decreased mean normal stress and undrained conventional triaxial compression test have been carried out,the stress-strain relations under the four stress paths are obtained.Through visualization the three-dimensional surfaces of shear and volume strain in the whole stress field under the four stress paths are given respectively by numerical modeling.In addition,the four families of shear and volume yield loci are plotted respectively.It is found through comparing the deformation results under the four stress paths that there are obvious differences in the stress ranges,the strain peaks,the shapes of strain surfaces and the trends of variation of volume yield loci,however,for the four families the shear yield loci are similar.These results demonstrate that the influence of stress path on the constitutive relations of clay is considerably large and could not be neglected,and it relates to the effective mean normal stress closely.  相似文献   

18.
Lightweight foamed concrete is a new arresting material for arresting overrun aircraft. To reveal its compression properties and mechanism of deformation and destruction, a study on lightweight foamed concrete with different density, 0.21 and 0.31 g/cm 3 respectively, has been carried out. Experiment system include CSS4410 electronic universal testing machine and Dynatup9250 drop-hammer testing machine and VHS8800 high strain rate system. Then, extrusion strength under different indenter area is predicted with a theoretical model, and a crushing flow stress constitutive equation is proposed. The results show that it is characterized by the movement of crushing driving interface during the process of deformation, crush to compaction of the material, and the deformation is notably in local. The compression strength is relevant to density and impact velocity. Moreover, theoretical model can predict the extrusion strength under different indenter area exactly, and the crushing flow stress equation can describe mechanic properties of compression well.  相似文献   

19.
桩-岩（土）接触面力学特性的研究是桩基承载机理研究的基础。通过红层泥岩桩岩接触面大型直剪试验,研究了红层泥岩桩岩接触面的力学特性,结果表明：接触面剪应力先随剪切位移增大而增大,在达到峰值后,剪应力随着剪切位移增大而降低,并最终趋于稳定值,应力应变曲线呈现出应变软化的特征。根据剪切试验结果,推导出桩岩接触面应变软化本构方程。利用fish语言对FLAC3D中自带的理想弹塑性接触单元进行二次开发,并应用开发的模型对桩岩接触面直剪试验进行了数值模拟,分析剪应力与剪切位移之间的关系,证明了该本构能够较好地模拟接触面间的应变软化特性。  相似文献   

20.
The load carrying test for four steel plate shear walls specimens with various ratio of width thickness are carried out so as to test the failure mode and the shear strength of steel plate with trilateral constrained, and the lateral stiffness and the buckling mode are investigated in the test. The result indicates that the ratio of width thickness of steel plate exerts effects on the shear carrying capacity and failure mode; the buckling of steel plate does not have lateral stiffness. Based on the failure mode of steel plate, the computation model of lateral performance is presented by theoretical analysis. The restraining stiffness of double angle and the buckling restrained stiffness of steel plate are the important design conditions. Formulae to determine the elastic lateral stiffness and the angle type is proposed, which can be used in the preliminary design of steel plate with trilateral constrained.  相似文献   

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