Influence of groundnut shell ash on strength and durability properties of clay

Groundnut shell ash, cement and their combinations are used as soil stabilizers in various percentages to improve the strength of locally available highly compressible clay soil. The effect of stabilizer in improving the strength of the soil is evaluated through change in consistency limits, compaction characteristics, undrained cohesion and modulus of elasticity. The durability characteristics of stabilised soil were studied based on the improvement of undrained shear strength for various days of curing by increasing the percentage of cement. Stabilised soil showed satisfactory improvement in strength and consistent durability characters. Groundnut shell ash and cement increased the optimum moisture content. There was a slight decrease in the dry density and modulus of elasticity of soil. These can be used as a viable economic alternative in construction of roads and for stabilising soil acting as bearing medium. The use of groundnut shell ash, an agricultural waste, helps in waste management and promotes sustainable development of local construction industry.     

塔克拉玛干沙漠腹地风沙土的力学性质

风沙土是形成于干旱、半干旱区的一种特殊性质的土,其力学性质不同于一般土体,结构松散性为其最主要的特点。通过对塔克拉玛干沙漠腹地14个风沙土样进行压缩试验和抗剪试验,获得了风沙土的基本力学参数:风沙土压缩模量值在50.00~142.86MPa之间,是一种低压缩性土;风沙土的内摩擦角值在31°55'~36°19'之间,低于河流冲积砂的内摩擦角值;风沙土存在结构力,其力学效应相当于粘聚力,可以在剪切试验中测出,其值在0.6~9.3kPa之间。并分析了影响这些力学参数的主要因素。     

荷载对钻孔应变测值影响的实验及力学解析

介绍了弦频钻孔应变仪和体积式应变仪二次地表荷载试验的结果。根据弹性力学的理论和方法,对钻孔地壳应变测量及荷载试验的力学模型、边界条件等予以简化,使得经典的集中力作用于半无限弹性体表面的布辛奈斯克(Boussinesq)解,可有条件地运用于钻孔应变测量中地表荷载变化问题的定量分析研究。所给出的实验方法、研究思路及计算方法等,对定量研究钻孔应变测量中的荷载干扰、研究岩石力学性质、制定台站钻孔应变观测技术标准及观测规范等具有一定意义。     

水泥土-粉土复合试样动弹模量的试验研究

通过水泥土-粉土复合试样的动三轴试验,研究了动荷载作用下围压、置换率及初始干密度对复合试样动弹模量 的影响。结果表明：经过置换后,复合试样的动弹模量得到提高;动应力-应变关系曲线符合双曲线模型;动弹模量和应变相关曲线与纯粉土的有关曲线形状相似;水泥土-粉土复合试样的动弹模量随应变水平的增长而降低;在相同的动应变水平下,随围压、置换率及初始干密度的增大而增大;在围压较小时,置换率、围压和干密度对动弹模量的影响更显著;复合试样的最大动弹模也随围压、置换率、初始干密度的增大而增大;归一化后的 曲线分布在一个相对狭窄的范围内。     

Jaumann率型一维大变形本构关系的双曲线模型

鉴于Jaumann率型本构关系难以得到应力应变全量之间的严格解析形式,采用有限元法研究了一维大变形过程中Kirchhoff应力和Green应变之间的变化规律。首先,基于虚功原理推导了完全拉格朗日描述的大变形有限元方程,然后提出了模拟大变形本构关系的双曲线模型和割线模量处理方法。算例分析结果表明,双曲线模型能够较好地拟合大变形本构关 系。大变形计算本构关系应当考虑初始孔隙比的影响。     

Response of shear wave from a corrugated interface between elastic solid/viscoelastic half‐spaces

The propagation of plane shear wave at a corrugation interface between elastic solid and viscoelastic liquid half‐spaces has been investigated. Adopting Rayleigh's method of approximation, the reflection and refraction coefficients corresponding to reflected and refracted SH‐waves have been derived for the first order of approximation of the corrugated interface. These coefficients are derived in the closed form for a periodic interface. Numerical computation has been performed for a particular model and the results are depicted graphically. The results of Asano (Bull. Earthquake Res. Inst. 1960; 38 (2):177–197) and Kielczynski and Pajewski (J. Acoust. Soc. Am. 1987; 81 (3):599–605) are recovered from this study. Copyright © 2010 John Wiley & Sons, Ltd.     

地基沉降计算中关键参数的选用

为提高地基沉降变形计算的精度,在分析土体变形参数的基础上,分析沉降计算参数的误用情况,提出孔隙比和压缩模量关键参数的正确选用方法,并以工程实例予以说明.     

Modelling of shear stiffness of unsaturated fine grained soils at very small strains

The shear modulus at very small strains (less than 0.001%) is an important parameter in the design of geotechnical structures subjected to static and cyclic loadings. Although numerous soil models are available for predicting shear modulus of saturated and dry soils, only a few ones can predict shear stiffness at very small strains of unsaturated soils correctly. In this study, a few unsaturated soil models are evaluated critically and compared with a newly developed model. This newly proposed model is verified by using measured shear modulus at very small strains for three different low plasticity fine grained soils available in the literature. It is found that this new model can predict shear modulus at very small strain resulting from an increase and a decrease in mean net stress at constant matric suction for low plasticity fine grained soils. Moreover, this model is able to give a reasonably good prediction on shear stiffness at very small strain during wetting of a collapsible unsaturated soil. In addition, the newly proposed model is illustrated to capture a consistent trend with experimental data of shear stiffness at very small strain for non-collapsible soils obtained during drying–wetting cycles. This evaluation revealed that the newly proposed model has better predictive capabilities than some earlier formulations of the same simplicity. In addition, the proposed model with fewer parameters has similar predictive capability as compared with a more complex model.     

A physical and numerical investigation of the failure mechanism of weak rocks surrounding tunnels

The large-scale construction of railway tunnels in China is hindered by several challenges, including large depths, large tunnel cross-sections, and fragile geological conditions. In this paper, we explored a new physical and numerical simulation method that improves upon the currently used methods to investigate the deformation and failure modes of weak rocks surrounding a tunnel. We also compared the results from physical tests and numerical simulations with the field measurements to demonstrate the effectiveness of the proposed numerical simulation method. In the physical model test, an artificial speckle field was developed by staining quartz sand particles and mixing the particles with barite powder and petroleum jelly in preset proportions. The artificial speckle field was employed in the digital speckle correlation method (DSCM) to monitor the evolution of the strain field on the surface of the plain strain model for tunneling during loading. A secondary strain-softening constitutive model using the numerical modeling code FLAC^3D was developed (degradation constitutive model) by considering the deformation modulus degradation in the numerical simulation. The failure mode of weak rocks surrounding a tunnel in the physical model test was examined using the developed degradation constitutive model. Both the physical and numerical results revealed that the least stable area was the shear wedge along the minimum principal stress, which was confirmed in the damage zone of the surrounding rocks. The results were consistent with previous research findings. The results of the DSCM in the physical model test indicated that the shear wedge in the middle part of the tunnel and the cracks around the arch of the tunnel were induced by shear strain, whereas the collapse of the arch was attributed to a combination of tensile strain and shear strain. A comparison of the physical and numerical simulation results demonstrated that the degradation constitutive model can be used to describe the extent and depth of the excavation damage zone of tunneling. A comparison of the displacements from the numerical simulation and field measurements indicated that the degradation model can be used to capture the displacement of weak rocks surrounding tunnels.     

水库拦沙对长江水沙态势变化的影响

为探讨水库建设对水沙变化态势的影响,通过引入来沙系数、输沙模数和流域水库调控系数,深入分析了长江水库拦沙对水沙态势变异的作用。长江干支流水沙参数与流域水库库容参数之间有重要关系,主要水文站年输沙量随流域累积库容增加而逐渐减少,来沙系数和输沙模数随流域水库调控系数成指数关系衰减,表明水库蓄水拦沙是长江水沙态势变异的主要因素。长江干支流输沙量衰减规律有一定差异,支流来沙系数和输沙模数衰减规律相对独立,而干流上游站衰减幅度大于下游水文站,且干流各站输沙模数的衰减规律比较接近。