测定粮食内摩擦角的直剪仪研制

分析了直剪试验原理和部分大型直剪仪的研究现状,详细介绍了用于测定粮食内摩擦角直剪仪的设计原理和结构组成,以全面比较分析剪切速率对粮食物料内摩擦角的影响。     

直剪试验与三轴试验的对比探讨

介绍了直剪试验与三轴试验的仪器设备及方法，通过对两种不同试验方法及结果的对比，指出三轴试验结果更接近土的实际理论值，数据更安全可靠，为岩土工程师使用抗剪强度指标提供了依据。     

Microstructural investigation on mechanical behavior of soil-geosynthetic interface in direct shear test

Interface shear strength between soil and geosynthetics mainly depends on the mechanical and physical properties of soil, geosynthetics and the normal stress acting at the interface. This paper presents results of an extensive experimental investigation carried out on sand-geosynthetic interface using modified large direct shear box. The study focusses on the shearing mechanism at the sand-geosynthetic interface and the effect of different parameters on the shearing mechanism. Smooth HDPE geomembrane, nonwoven needle punched geotextile and two types of sand having different mean particle size, have been used in the present study. Microstructural investigation of deformed specimen through Field Emission Scanning Electron Microscope (FESEM) reveals the shearing mechanism which includes interlocking and fiber stretching for sand-geotextile while sliding, indentation and plowing for sand-geomembrane interface. The shearing mechanism for sand-geomembrane interface highly depends on the normal stress and degree of saturation of sand. The critical normal stress that demarcates the sliding and plowing mechanism for sand-geomembrane interface is different for dry and wet sand. The amount of scouring (or plowing) of the geomembrane surface reduces with increase in the mean particle size of sand. FESEM images revealed that the sand particles get adhered to the geotextile fibers for tests involving wet sands. The present microstructural study aided in understanding the shearing mechanism at sand-geosynthetic interface to a large extent.     

Interface shear characteristics of jute/polypropylene hybrid nonwoven geotextiles and sand using large size direct shear test

In this study, large-size direct shear tests were conducted to determine the interfacial shear characteristics of sand–geotextile under three different normal stresses. The geotextiles used in the present study were hybrid needlepunched nonwovens containing defined weight proportions of jute and polypropylene fibers. Subsequently, the interfacial shear characteristics of hybrid and that of a nonwoven geotextile consisting of solely polypropylene fibers with sand were compared and analyzed under different normal stresses. Initial higher shear stiffness of sand-polypropylene geotextiles was observed corresponding to sand-hybrid geotextiles specifically under higher normal stresses. Nevertheless, the contact efficiency of sand-hybrid nonwovens was similar to that of sand-polypropylene geotextiles. The surface morphology of sand particles has been investigated based on the images obtained from scanning electron microscopy (SEM) and quantitatively analyzed by means of Wadell roundness and degree of angularity methods.     

某边坡勘察工程中直剪试验的应用

通过工程实例说明在边坡勘查工程中室内直剪试验与现场直剪试验不同方法和结果,由于室内试验土样与现场实际的土样情况难达到一致,笔者分析说明了现场直剪试验的必要性,为边坡勘查工程提供较为可靠的抗剪强度指标。     

Role of soil inherent anisotropy in peak friction and maximum dilation angles of four sand-geosynthetic interfaces

Using a modified direct shear apparatus, an extensive experimental investigation is conducted into the influence of the inherent anisotropy of sand on the mobilization of the peak and critical state friction angles as well as the maximum dilation angle of the interfaces between an inherently anisotropic crushed sand and two woven geotextiles, one nonwoven geotextile, and one geomembrane. Experimental findings confirm that both peak and maximum dilation angles of sand-geosynthetic interfaces are affected from soil inherent anisotropy depending on the bedding plane inclination with respect to the shear plane. However, a unique critical state (residual) friction angle is attained for each interface type irrespective of the bedding plane inclination angle. Compiling results of a total of 141 tests, it is shown that a unique rule describes stress-dilation relationship of four different dense crushed sand-geosynthetic interfaces. The experimental data indicate that the ?_p vs. θ and ψ_max vs. θ curves are symmetrical with respect to θ?=?90° for the sand-woven geotextile and sand-geomembrane interfaces. Finally, it is shown that a constitutive equation by Pietruszczak and Mroz (2001) can predict the variation of ?_p with θ for the sand-woven geotextile and sand-geomembrane interfaces.     

土的直剪试验研究

通过对非饱和状态和饱和状态下土的直接剪切试验,分析对比在不同剪切条件下的试验结果,得出了土在不同条件下的剪切试验规律,为土工试验数据处理提供参考依据。     

Soil element assessment of cyclic-load-induced settlement considering combination of vertical,horizontal, and shear stresses in cohesive soil

Grounds subjected to cyclic loading, either continuous or fragmentary, widely exist in natural deposits and at reclaimed sites, e.g., induced by traffic loads, earthquakes, and wave-induced loading environments. Assessing the ground deformation under cyclic loading conditions is necessary for proper design and maintenance planning for traffic services. Accordingly, a testing program, in which vertical, horizontal, and shear stresses are automatically controlled, were newly developed in this study to reproduce the actual cyclic traffic load conditions using a hollow-cylindrical torsional shear apparatus.Estimations based on the results obtained from cyclic triaxial stress conditions were seen to underestimate the ground settlement compared to actual stresses, with combined vertical, horizontal, and shear stresses. Two kinds of vertical strain arose after a certain number of cycles: incremental collapse, in which unstable deformation (failure) is caused, and plastic creep, in which deformation continues to accumulate with the dampened rate (per cycle). The number of cycles of combined vertical, horizontal, and shear stresses necessary to reach a certain vertical strain increased linearly on a logarithmic scale when the magnitude of loading decreased. Moreover, the relationship between vertical strain and excess pore water pressure presented the same trend independent of the magnitude of loading. Practical uses of the obtained results were proposed and discussed.     

Large scale direct shear tests of soil/PET-yarn geogrid interfaces

The interface shear strength of soil against geosynthetic is of great interest among the researchers in geosynthetic properties. This study conducts a series of large scale direct shear tests to investigate the interface shear strength of different soils (sand, gravel, and laterite) against PET-yarn geogrids of various tensile strengths, percent open area, and aperture patterns. First, the appropriateness of different set-ups of a lower shearing box is examined in this study. It reveals that a lower box which is filled with the test soil and is of the same size as the upper box is more suitable for testing the soil/geogrid interface. The test results show that the soil/PET-yarn geotextile interface has significantly lower shear strength than soil strength. The ratio of shear strength soil/PET-yarn geotextile interface to internal shear strength of soil is about 0.7–0.8 for Ottawa sand and for laterite, and it is about 0.85–0.95 for gravel. On the other hand, the soil/geogrid interface has higher shear strength. The ratio of shear strength soil/PET-yarn geogrid interface to internal shear strength of soil is about 0.9–1.05. It is found that the shear strength ratio of soil/PET-yarn geogrid interface is positively correlated to the transverse tensile strength of the PET-yarn geogrid. However, it is negatively correlated with the aperture length and percent open area of the PET-yarn geogrid. The interface shear test results of PET-yarn geogrid against different soils are compared with the test results predicted by a classical model for analyzing the applicability of the classical model. Further, a simple model is proposed herein to estimate the bearing resistance provided by the transverse ribs of geogrid. It shows this component to be about 0–15% when PET-yarn geogrid is against Ottawa sand or laterite, while it is smaller when the PET-yarn geogrid is against gravel.     

Effect of slaking on direct shear behaviour of crushed mudstones

This study investigates the effects of wetting and drying cycles, known as slaking, on the strength-displacement characteristics of crushed mudstone. A series of direct shear tests was conducted by simulating cyclic wetting and drying under different stress conditions using a modified direct shear apparatus. The effects of the stress ratio, the density of specimen, the initial water content before wetting, the slaking index, and the number of wetting and drying cycles on the test results was investigated. Experiments were also performed on less-slakable materials, including crushed sand stone, silica sand and glass beads, to compare the results with the crushed mudstone. Considerable creep displacement on the crushed mudstones was observed during both drying and wetting phases under the constant shear stress conditions. The creep displacement during the drying was more significant than during the wetting phase. The creep displacement accumulated with progressive wetting and drying cycles. The drying-induced displacement was observed when the water content became smaller than the amount of water absorption of the mudstone specimens. Correspondingly, a gradual decrease of the peak stress ratio was observed with the number of wetting and drying cycles. In contrast to the mudstones, the influence of cyclic wetting and drying on the crushed sand stone, silica sand and glass beads is almost negligible. A higher slaking index, a lower water content before wetting, and lower initial density accelerate the slaking of mudstones.     

Concise formula for the critical buckling stresses of an elastic plate under biaxial compression and shear

This study aims to develop a concise formula for the critical buckling stresses of a simply supported plate under biaxial compression and shear. The critical stresses are obtained for different aspect ratios using classical plate theory and the Ritz method. The four-dimensional critical stress formula, which is expressed in terms of the three in-plane stresses and the aspect ratio, is developed empirically according to the two-dimensional relationships between the in-plane stresses. The findings that are of interest are: (1) the critical stress relationship is linear for the aspect ratios within the range 1 to and nonlinear for the aspect ratios within the range to 5; and (2) as shear stress approaches its critical value, the critical stress relationship becomes increasingly linear and less dependent on aspect ratio.     

有转角窗高层住宅短肢剪力墙结构设计

对短肢剪力墙结构设计过程中遇到的问题进行了总结,着重探讨了短肢剪力墙结构的截面形状、平面布置等,通过建立计算模型提出了设计转角窗剪力墙的加强方案,以保证结构安全可靠。     

摩擦角与摩擦自锁的一般性解释

从分析物体接触相互作用出发,讨论了摩擦角的概念,并按照摩擦平衡问题推导出摩擦自锁的条件,使学生更容易对这两个概念建立一般性的理解,达到灵活运用理论力学知识的目的。     

Stress-controlled direct shear testing of geosynthetic clay liners I: Apparatus development

The use of geosynthetic clay liners (GCLs) in waste containment applications can induce long-term normal and shear stresses as well as expose GCLs to elevated temperatures and non-standard hydration solutions. Considering the importance of GCL internal shear strength to the design and integrity of waste containment barrier systems, innovative laboratory testing methods are needed to assess shear behavior of GCLs. There were two main objectives of this study: (i) develop a stress-controlled direct shear apparatus capable of testing GCLs exposed to elevated temperatures and hydrated in non-standard solutions; and (ii) assess internal shear behavior of GCLs under varying experimental conditions (e.g., stress, temperature, solution). These two objectives were partitioned into a two-paper set, whereby Part I (this paper) focuses on the shear box design and Part II focuses on an assessment of shear behavior. The direct shear apparatus includes a reaction frame to mitigate specimen rotation that develops from an internal moment within needle-punched reinforced GCLs. Rapid-loading shear tests were conducted to assess functionality of the apparatus and document baseline shear behavior for a heat-treated and a non-heat treated needle-punched GCL with comparable peel strength. These two GCLs failed at comparable applied shear stress; however, the heat-treated GCL yielded lower shear deformation and failure occurred via rupture of reinforcement fiber anchors, whereas the non-heat treated GCL yielded larger shear deformation and failure via pullout of reinforcement fibers.     

膨胀砂岩的抗剪强度与含水量的关系

针对南京红山窑水利枢纽工程中的红砂岩圆柱体试样,采用RMT-150B多功能刚性岩石伺服试验机,通过常规直接剪切试验的方法对不同含水量状态下的红砂岩圆柱体试样进行室内试验研究。通过对试验结果的线性回归分析得到膨胀岩的凝聚力c和内摩擦角φ与含水量w之间良好的对数关系,lgc和lgφ与含水量w之间呈线性相关,结合摩尔-库仑准则可以分析某些特定地区膨胀岩的抗剪强度与含水量的关系,这对工程设计、工程安全监测都具有非常重要的实际意义,可以为实际工程提供参考。     

十字板剪切试验在某地基处理工程中的应用

十字板剪切试验是在现场直接测定软土抗剪强度的一种方法。此方法比采取原状土样,运至试验室测定抗剪强度的方法优越,可以测定不能取得土样的极软土的抗剪强度。多年实践证明,在软土地基处理效果检测方面是一种实用性强、经济有效的原位测试手段。     

粗粒土与结构接触面三维力学特性的直剪试验研究

运用80t三维多功能土工试验机,对粗粒土与人造粗糙钢板接触面的三维力学特性进行试验研究,包括常法向应力条件下单调剪切试验(法向应力σ=200kPa、400kPa、700kPa、1000kPa)及十字、单向圆形和往返圆形路径下循环剪切试验(σ=400kPa)。结果表明:在单调和循环剪切时接触面均产生了明显的剪切体变,循环剪切时可分为遵循不同规律的可逆和不可逆两部分;不同剪切路径下接触面切向应力-应变关系曲线有很大差别,但主剪应力-主切向位移关系类似;随循环剪切的进行,接触面在逐渐剪切硬化,主剪应力-主切向位移曲线形式均由双曲线形式向理想弹塑性模式转变;接触面抗剪强度具有各向同性,其与法向应力关系符合摩尔-库伦准则;法向应力对接触面单调力学特性影响显著,剪切路径对其循环力学特性(剪切体变、切向应力-应变关系及破坏状态等)有重要影响。     

几种数据整理方法在冻土直剪试验中的应用

通过图解法、斜率公式和斜截式公式法、最小二乘法的应用，对冻土直剪试验数据进行处理，分析了各种方法的优缺点，便于在今后工作中合理选择方法应用。     

常州市浅层粘性土两种抗剪强度试验指标分析

对常州市区浅层Q3al粘性土不固结不排水三轴试验与直剪快剪试验抗剪强度指标粘聚力c、内摩擦角φ值进行了统计分析,建立两者间的相关关系方程,对该地区土工试验人员具有一定指导意义。     

Influence of yield stress and compressive strength on direct shear behaviour of steel fibre-reinforced concrete

This study aims in examining the influence of the paste yield stress and compressive strength on the behaviour of fibre-reinforced concrete (FRC) versus direct shear. The parameters studied are the steel fibre contents, the aspect ratio of fibres and the concrete strength. Prismatic specimens of dimensions 10 × 10 × 35 cm made of concrete of various yield stress reinforced with steel fibres hooked at the ends with three fibre volume fractions (i.e. 0%, 0.5% and 1%) and two aspects ratio (65 and 80) were tested to direct shear. Three types of concretes with various compressive strength and yield stress were tested, an ordinary concrete (OC), a self-compacting concrete (SCC) and a high strength concrete (HSC). The concrete strengths investigated include 30 MPa for OC, 60 MPa for SCC and 80 MPa for HSC.The results show that the shear strength and ductility are affected and have been improved very significantly by the fibre contents, fibre aspect ratio and concrete strength. As the compressive strength and the volume fraction of fibres increase, the shear strength increases. However, yield stress of concrete has an important influence on the orientation and distribution of the fibres in the matrix. The ductility was much higher for ordinary and self-compacting concretes (concrete with good workability). The ductility in direct shear depends on the fibre orientation and is significantly improved when the fibres are perpendicular to the shear plane. On the contrary, for concrete with poor workability, an inadequate distribution and orientation of fibres occurred, leading to a weak contribution of the fibres to the direct shear behaviour.