三轴法测定基床系数探析

基床系数是岩土工程中一个重要参数,文章利用全自动三轴仪模拟土的原始应力状态,得到应力应变关系曲线,计算出土的基床系数,同时介绍了三轴试验法的原理、结果的影响因素以及其合理性、便捷性和经济可行性。

一个试样多级加荷三轴压缩试验方法适用性的探讨

该文运用不同的三轴试验方法 ,对石家庄地区地基土进行了数百次实验 ,并对用其得出的c、φ值推导出的地基承载力fa 值进行了对比分析 。

研究黄土湿陷性的新方法

为了研究吸力对黄土湿陷变形的影响,研制了一套可以控制吸力的非饱和土湿陷三轴仪。该三轴仪底座为二元结构,既能控制吸力又能浸水。将该三轴仪和GDS压力/体积控制器相结合,实现了浸水过程中量测浸水体积的功能,并可施加浸水压力。该设备能精确量测试样体变;控制偏应力;精确量测浸水量。利用该仪器探讨了原状湿陷性黄土控制吸力三轴湿陷试验的方法,并进行了净围压相同吸力不同和吸力相同净围压不同的双线法三轴湿陷试验。结果表明:吸力越大湿陷变形越大,净围压对湿陷变形有显著影响。非饱和土湿陷三轴仪为研究黄土的湿陷特性提供了有力的工具。

True triaxial behavior of sandy soils under both drained and undrained conditions:A discrete element perspective

An advanced discrete element servomechanism that can simultaneously and independently control the evolution equations of six stress and strain components without introducing severe stress concentration is implemented.Such a comprehensive series of discrete element method simulations of both drained and undrained behavior of transversely isotropic sandy soils are successfully conducted in the true triaxial setting.During the simulation process,the evolution patterns of the load-bearing structure of the granular specimen are tracked using a contact-normal-based fabric tensor.The simulation results show that sandy soils exhibit more significant non-coaxiality between the loading direction and the major principal direction of the fabric tensor under extension than under compression.Therefore,the fabric of the sandy soils under extension has a stronger tendency to evolve toward the loading direction than that under compression,causing a more significant disturbance to the load-bearing structure.Consequently,compared with the extension loading condition,the transversely isotropic specimen under compression exhibits a higher shear strength and stronger dilatancy under drained conditions and a stronger liquefaction resistance under undrained conditions.

Numerical and theoretical verification of modified cam-clay model and discussion on its problems

Isotropic consolidation test and consolidated-undrained triaxial test were first undertaken to obtain the parameters of the modified cam-clay(MCC)model and the behavior of natural clayey soil.Then,for the first time,numerical simulation of the two tests was performed by three-dimensional finite element method(FEM)using ABAQUS program.The consolidated-drained triaxial test was also simulated by FEM and compared with theoretical results of MCC model.Especially,the behaviors of MCC model during unloading and reloading were analyzed in detail by FEM.The analysis and comparison indicate that the MCC model is able to accurately describe many features of the mechanical behavior of the soil in isotropic consolidation test and consolidated-drained triaxial test.And the MCC model can well describe the variation of excess pore water pressure with the development of axial strain in consolidated-undrained triaxial test,but its ability to predict the relationship between axial strain and shear stress is relatively poor.The comparison also shows that FEM solutions of the MCC model are basically identical to the theoretical ones.In addition,Mandel-Cryer effect unable to be discovered by the conventional triaxial test in laboratories was disclosed by FEM.The analysis of unloading-reloading by FEM demonstrates that the MCC model disobeys the law of energy conservation under the cyclic loading condition if the elastic shear modulus is linearly pressure-dependent.

Local Data Analysis for Eliminating End Restraint of Triaxial Specimen

A data processing method was proposed for eliminating the end restraint in triaxial tests of soil. A digital image processing method was used to calculate the local deformations and local stresses for any region on the surface of triaxial soil specimens. The principle and implementation of this digital image processing method were introduced as well as the calculation method for local mechanical properties of soil specimens. Comparisons were made between the test results calculated by the data from both the entire specimen and local regions, and it was found that the deformations were more uniform in the middle region compared with the entire specimen. In order to quantify the nonuniform characteristic of deformation, the non-uniformity coefficients of strain were defined and calculated. Traditional and end-lubricated triaxial tests were conducted under the same condition to investigate the effects of using local region data for deformation calculation on eliminating the end restraint of specimens. After the statistical analysis of all test results, it was concluded that for the tested soil specimen with the size of 39.1 mm × 80 ram, the utilization of the middle 35 mm region of traditional specimens in data processing had a better effect on eliminating end restraint compared with end lubrication. Furthermore, the local data analysis in this paper was validated through the comparisons with the test results from other researchers.

A 3D bounding surface model for rockfill materials

A 3D bounding surface model is established for rockfill materials,which can be applied to appropriately predict the deformation and the stabilization of rockfill dams.Firstly,an associated plastic flow rule for rockfill materials is investigated based on the elaborate data from the large-style triaxial compression tests and the true triaxial tests.Secondly,the constitutive equations of the 3D bounding surface model are established by several steps.These steps include the bounding surface incorporating the general nonlinear strength criterion,stress-dilatancy equations,the evolution of the bounding surface and the bounding surface plasticity.Finally,the 3D bounding surface model is used to predict the mechanical behaviors of rockfill materials from the large-style triaxial compression tests and the true triaxial tests.Consequently,the proposed 3D bounding surface model can well capture such behaviors of rockfill materials as the strain hardening,the post-peak strain softening,and the volumetric strain contraction and expansion in both two-and three-dimensional stress spaces.