Vertical vibrations of a rigid circular body on a non-homogeneous half-space interrupted by a frictionless plane

An exact formulation is presented for the problem of a rigid circular body performing harmonic vibrations on an elastic half-space whose shear modulus increases linearly with depth and is interrupted at some finite depth by a frictionless horizontal plane. The static case is derived in the limit of zero frequency vibrations while the known result for the uninterrupted half-space is recovered in either extreme limit of the horizontal frictionless plane coinciding with the surface or when it is pushed down to an infinite depth. It is shown that the maximum effect of the interruption occurs when the frictionless plane is at a depth where the shear modulus is about 1·6 times the surface shear modulus. Furthermore, this maximum effect is equivalent to a reduction of about 5 per cent of the surface shear modulus or a reduction of about 2½ per cent in the natural frequency of the rigid body on an uninterrupted half-space. The important conclusion, therefore, is that irrespective of the depth at which a half-space isso interrupted, the surface shear modulus is still the dominant parameter and that both the increase in shear modulus with depth and the interruption are not only secondary but also opposing effects.     

Propagation of a shear band in sandstone

Closed‐loop, servo‐controlled experiments were conducted to investigate the development of a shear band in Berea sandstone at various confining pressures. The tests were performed with the University of Minnesota Plane‐Strain Apparatus, which was designed to allow the shear band to develop in an unrestricted manner. Measured load and displacements provided estimates of the stress and deformation states whereby dilatancy and friction were evaluated prior to localization. Experiments were stopped at various stages of shear‐band development within the strain‐softening regime. The specimens displayed a progression of deformation from inception, where the shear band was characterized by a high density of intragranular microcracks and crushed grains, to the tip where the intragranular microcracks were significantly less dense and separated by intact grains. Decreased slip deformation towards the tip of the shear band indicated that localization developed and propagated in plane. Thin‐section microscopy showed porosity increase within the shear band was 3–4 grain diameters wide. Increased porosity did not extend beyond the tip of the shear band. A cohesive zone model of shear fracture, used to examine the stress field near the tip, showed similarities to principal compressive stress orientations interpreted from intragranular microcracks. Thus, propagation of the shear band could be associated with in‐plane mode II fracture. Copyright © 2006 John Wiley & Sons, Ltd.     

Anisotropic shear strength characteristics of a tailings sand

The deposition process of tailings in a tailings dam may lead to the anisotropy of mechanical properties of tailings. To investigate the anisotropic shear strength characteristics of a tailings sand, samples deposited under gravity were sheared in a modified direct shear apparatus along different orientations of the shear planes relative to the bedding plane. The experimental results reveal that the anisotropy has a substantial effect on the peak shear strength of the tailings sand, leading to a variation in peak friction angle of 10°. It is found that the effect of anisotropy on the peak shear strength of the tailings sand is mainly attributed to the effect of anisotropy on soil dilatancy. On the other hand, the effect of anisotropy on the residual friction angle of the tailing sand is relatively smaller, likely due to the partial erasure of anisotropy at large shear deformation. The degree of anisotropy is reduced by an increase in normal stress. To achieve more accurate stability analysis of tailings dams, it is suggested to take into account the shear strength anisotropy of tailings soils.     

Assessment of dispersive pressure as a beach placer mechanism

The concept of sediment sorting extending from the Bagnold constitutive relationship for sediment under shear is examined in the context of beach placer formation. The traditional interpretation of shear sorting is found to be inconsistent with data from new granular flow experiments. A binary mixture satisfying the shear equivalence relationship displayed pronounced segregation during shear. This observation is contrary to shear sorting as applied in the literature where no such segregation for this pairing of mineral species is expected. Further experiments minimizing the potential of grain percolation of smaller grains or kinetic sieving also demonstrated sorting patterns inconsistent with the existing shear sorting interpretation. Consequently, the shear sorting process, as currently formulated, may not be an appropriate means to describe beach placer formation. Kinetic sieving appears to be a more likely mechanism in this context, enhanced by the shearing and dilation of the granular‐fluid flow.     

剪切带运动学：重点评述三斜模式和区分韧性滑动擦痕与拉伸线理的重要性

详细评述了剪切带运动学和内部几何学研究的新进展。剪切带内的递进变形一般为三斜对称,单斜剪切带(包括简单剪切带)是特例情形。理论模拟表明,如同许多天然剪切带中所见到的,在三斜剪切带中,拉伸线理的方位可从近水平到平行于倾向连续变化。过去一般将拉伸线理的方向当作剪切运动方向的做法是以简单剪切模式为基础的,不适合于一般剪切带。在三斜剪切带中,拉伸线理和剪切方向之间不存在简单关系。然而,C面上的韧性滑动擦痕平行于剪切方向发育,是剪切方向的可靠标志。因此,在剪切带运动学解释中区分韧性滑动擦痕与拉伸线理非常重要。     

一种黄土滑坡渐进破坏过程分析

在中国西北,建设了许多灌溉水渠,由于水渠的灌溉引起了许多滑坡破坏,并带来了人员伤亡和财产损失。以高楼村水渠灌溉引起的黄土滑坡破坏为例,提出了滑坡破环渐进过程为：水的入渗在滑体中产生一定深度的水压力,引起黄土黏聚力和摩擦角下降,使滑坡体在一定深度产生剪破坏,紧接着滑体后缘产生拉剪破坏,致使后缘黄土处于破坏后区状态,并产生不平衡剪应力。该不平衡剪应力驱动滑体向前移动,直至滑面只有一点处于临界状态,随即整个滑坡发生破坏,并伴随着滑体解体,产生泥流。这种破坏过程可以概括为：滑坡先产生剪破坏,紧接着后缘产生拉剪破坏,当破坏后区产生的驱动剪应力大于滑体的摩阻力,会推动滑坡向前移动,直至滑坡发生完全破坏。以理论和试验论证了这种破坏机制的正确性,并验证了一种新剪应力本构模型的合理性。     

Effects of Scale and Normal Stress on Shear Behavior of a Soft Fracture Replica

The effects of the fracture scale (size) and normal stress on the shear behavior of a fracture were investigated in direct shear rig using mortar fracture replicas of different sizes (100–200 mm), which were reproduced from a tensile fracture created in granite. Monotonic shear loading was applied at normal stresses of 0.3 and 1 MPa for shear displacements of 2 and 20 mm. The change in surface topography was measured by using a profile measurement system with a laser profilometer to determine the changes in surface damage and the aperture during shear. Additionally, the effect of gouge material on the non-linearity of the closure curve during shear was investigated. The results show that the standard deviation of the initial aperture during shear increases not only with scale but also with the normal stress, since the matedness decreases due to the fact that asperities are more damaged with normal stress, and accordingly, the non-linearity in the closure curve during shear increases with normal stress. The results also show that the non-linearity of the closure curve during shear increases with the presence of gouge material/debris that is produced in the shearing process. This is mainly because gouge is soft and easily deforms under the application of normal stress. Moreover, gouge material is distributed non-uniformly around the contact areas. Thus, the normal stiffness during shear decreases not only with a decrease in the matedness between the surfaces, but also with the presence of gouge material.     

Fracture geometry of pseudotachylyte generation zones: a study of shear fractures formed during seismic events

The orientation and movement sense of shear fractures in pseudotachylyte generation zones developed in the Ikertôq shear belt, West Greenland are described, and the fracturing sequence is inferred. The generation zones occur in strongly foliated gneisses, and consist of concordant, usually paired, principal displacement shear fractures (paired shears), on which most melt was generated, and a system of minor shear fractures. Minor shear fracturing was most intense between principal displacement shear fractures, and most melt intruded from these paired shears inwards with respect to the zone. Intrusion of injection veins of pseudotachylyte off the principal displacement shear fractures, is believed to be contemporaneous with minor shear fracturing in the generation zones.Generation zones affect intact rocks, and individual principal displacement shear fractures have a maximum displacement of 4.6 m. Paired principal displacement shear fractures are up to 3 m apart, and have a maximum observed length of 1 km. In all the zones described, the fracturing appears to be the result of a single episode of slip. Both dextral and sinistral generation zones occur within the study area, and have different geometries. In each case the displacement is strike-slip.     

Shear behaviour of fractured rock as a function of size and shear displacement

This paper presents laboratory results regarding the shear behaviour of an artificial tensile fracture generated in granite. We used a direct shear rig to test fractures of different sizes (from 100 mm to 200 mm) under various shear displacements up to 20 mm and cyclic shear stresses with constant normal stress of 10 MPa. To determine the evolution of surface damage and aperture during shear, cyclic loading was performed at designated shear displacements. These changes in the surfaces topography were measured with a laser profilometer ‘non-contact surface profile measurement system’. In addition, changes were also measured directly by using pressure-sensitive film.

The results showed that the standard deviation (SD) of the initial aperture of the sheared fracture significantly increases with both shear displacement and size, which result in an increase in the non-linearity of the closure curve (since the matedness of the fracture surfaces decreases with shear displacement). Therefore, we concluded that shear dilation is not only governed by the surfaces sliding over each other, but is also strongly influenced by the non-linearity of closure with shear displacement. Furthermore, while the shear stiffness of the fracture during the initial stage decreases with fracture size, it increases with fracture size in the residual stage. This can be attributed to the fact that only small asperities with short wavelengths were mainly damaged by shearing. Moreover the result showed that the damaged zones enlarge and localise with shear displacement, and eventually tend to form perpendicular to the shear displacement.     

Study of preexisting shear surfaces of reactivated landslides from a strength recovery perspective

Residual shear strength is generally considered in the design of preventive measures for slopes consisting of preexisting shear surfaces of large-scale landslides. Recent research suggests that the preexisting shear surface of a reactivated landslide can regain strength with the passage of time, which might also be considered in designing the slope stability measures. In this study, three reactivated landslide soils were tested in a ring shear apparatus for the discontinued shear periods of 1, 3, 7, 15, and 30 days with the following main objectives: (i) to understand the strength recovery behavior of landslide soils in a residual state of shear after as long as 30 days of discontinued shear, (ii) to understand the comparative pattern of strength recovery in highly plastic and less plastic soils, and (iii) to understand the mechanism involved in strength recovery at a residual state of shear. The results indicate that recovered strength measured in the laboratory is hardly noticeable after a rest period of 3 days, but recovered strength is lost after a small shear displacement. This paper primarily focuses on the effect of strength recovery from residual strength on preexisting shear surface soils and the mechanisms behind it.     

Formation of shear bands in sand bodies as a bifurcation problem

The paper reports on the results of theoretical and experimental investigations on the spontaneous formation of shear bands in sand bodies. The phenomenon is considered as a bifurcation problem. Consequently, material response and configuration-dependent loading determine the bifurcation mode. Both Coulomb's and Roscoe's solutions of inclination of the shear band can be correct theoretically and experimentally. The first one holds for non-rotating stress axes, the second one for co-rotating stress and strain increment axes during failure. Values in between can occur if the rotation of principal stress axes is not equal to one of these limits. If Coulomb's inclination of shear band occurs, there is a thin deforming material layer separating rigid bodies. Inside the shear band non-coaxiality of strain increment and stress holds from the beginning. If Roscoe's inclination of shear band occurs, it is separating two deforming bodies. Inside the shear band strain increment and stress are coaxial at peak.     

岩石多功能剪切试验测试系统研制

详细介绍了所研制的岩石多功能剪切试验测试系统的主要功能、技术指标和仪器组成,并开展了一系列相关力学试验。该试验测试系统主要包括试验装置、测量系统和控制系统3部分,最大法向拉伸应力为40 MPa,最大法向压缩应力为120 MPa,最大水平剪切应力为120 MPa,试样尺寸为50 mm?50 mm?50 mm;可开展多种力学试验,包括直接拉伸试验、直接剪切试验、拉伸-剪切试验和压缩–剪切试验。利用该试验测试系统对花岗岩进行试验研究,研究结果表明：直接拉伸试验中,试样发生脆性破坏,声发射信号瞬间达到峰值,破坏断面表现出拉伸破坏特征;直接剪切试验中,试样发生多次破坏,破坏瞬间声发射信号均发生突增,破坏断面表现出剪切破坏特征;拉伸-剪切试验中,试样在拉应力作用下剪切强度显著降低,声发射信号在破坏阶段表现强烈,破坏断面既有拉伸破坏特征也有一定的剪切破坏特征。上述力学试验结果,表明了所研制的岩石多功能剪切试验测试系统能够开展多种力学试验,为进一步研究岩石的剪切力学特性提供新的测试手段。     

A semi-empirical approach for estimation of bed shear stress in a tailings pond

Wind-driven waves and currents exert shear stress on the bed of a tailings pond. A semi-empirical approach for estimating this bed shear stress is presented in this paper. For the first time in a mine tailings storage facility, the current-induced component of the bed shear stress was obtained using 1,200-kHz acoustic Doppler current profiler measurements of in situ currents and a log-law fit to the mean velocity profiles, while the wave-induced portion was calculated using empirical wave hindcasting equations. The total bed shear stress was obtained by non-linear addition of wave and current components using a wave–current interaction approach. The study was conducted in the middle cell of the Shebandowan tailings storage facility, northern Ontario, Canada. The measured currents facilitated the visualization of the complex near-bed circulatory flow pattern in the pond. The estimated combined wave–current bed shear stress varied from 0.0006 to 0.16 Pa with an average value of 0.028 Pa. The results also showed that linear addition of bed shear stresses due to waves and currents could underestimate the total bed shear stress. A comparison of the results of the present work to those of previous studies suggests that it is more reliable to obtain current-induced bed shear stress from field measurements than to estimate it from empirical equations.     

Evidence of a hidden landslide slip surface beneath a mountain hamlet

Earthquake-triggered landslides are some of the most destructive natural disasters. Although remote detection of landslides is economic and efficient, it may miss the more subtle signs of hidden landslides. The Kizawa Tunnel and facilities in its vicinity were severely damaged in the 2004 mid-Niigata Prefecture earthquake. After investigation of the most prominent cracks, the damage was attributed to the slip along a hidden weakness plane. Evidence supporting this argument is summarized in this paper. However, the extent of the shear plane is not limited to the interior of the northern part of the tunnel. The dislocation observed in the two wells to the south of the Kizawa Tunnel together with other findings from previous studies indicates that Kizawa hamlet lies on the southern extension of the same shear plane. Taking account of the presence of flat sedimentary structures, the shear plane may extend in all directions. The authors also surveyed other signs of damage along the perimeter where the shear plane intersects the ground surface. The geological and geomorphological features of the hidden landslide are discussed. Reactivation of interlayer sliding is a threat to the local residents, and thus more attention should be paid to monitoring the movement of the slope to avoid devastating damages.     

法向刚度对土与结构接触面三维特性影响的试验研究

运用80 t大型三维接触面试验机,对不同法向刚度下粗粒土与结构接触面三维静动力学特性进行了试验研究,重点分析了法向刚度对接触面力学特性的影响规律。法向常刚度条件下,接触面在单调剪切时均先剪缩再剪胀、法向应力先减小后增大;循环剪切时接触面不可逆性剪切体变呈单调增长、可逆性剪切体变峰值逐渐减小后趋于稳定,切向应力峰值不断减小,抗剪强度逐渐减小,主应力比峰值则基本保持不变。法向刚度主要影响剪切体变、可逆性剪切体变、切向应力、主剪应力等接触面力学性能参数的大小;法向刚度越大,单调剪切时法向应力变化越大、切向应力峰值越大、剪缩和剪胀量越小;循环剪切时不可逆性剪切体变增长越慢、最终值越小,抗剪强度减小越快、达到0时对应的循环周次越少。法向刚度对剪切体变、可逆性剪切体变、主剪应力、主应力比等性能参数与切向位移的关系形式及接触面摩擦角基本没有影响。     

Design and application of a kind of direct shear model test apparatus

A kind of direct shear model test apparatus is introduced, which can be used for laboratory model tests of anti-sliding structures for slopes (landslides). The model test apparatus consists of shearing system, loading system and data collecting system. The shearing system is composed of an upper direct shear box, a lower direct shear box and two straight steel rails. The upper and the lower direct shear boxes are connected by the straight steel rails. The loading system is composed of load transducer, hydraulic jack and reaction rack. The shearing system and the loading system are connected by steel base. The apparatus has been successfully used in anti-sliding model test of single row grouting micro-piles based on detailed analysis of its structure design and characteristics. Application results of the apparatus indicate that this kind of direct shear model test apparatus possesses great practicability; and it can be used further in other similar model tests.     

一种直剪式模型试验设备的设计及应用

介绍了一种直剪式模型试验设备,该设备可用于边坡（滑坡）抗滑结构的室内模型试验研究。该模型试验设备包括剪切系统、加载系统和量测系统。其中剪切系统包括上剪切盒、下剪切盒及钢质直线导轨,上下剪切盒通过钢质直线导轨连接在一起;加载系统包括荷载传感器、液压千斤顶及反力架,剪切系统和加载系统通过钢板底座连接为一个有机整体。在详细分析该模型试验设备的设计制作及其优缺点的基础上,将其用于单排注浆微型桩抗滑结构的模型试验研究中。试验结果分析表明,该直剪式模型试验设备具有较好的实用性,可进一步应用于类似的模型试验研究中。     

Measurement of Shearing Characteristics of Granular Materials at Low Stress Levels in a Shear Box

A range of geotechnical applications require measurement of shear strength at effective stresses below those commonly employed in conventional shear testing devices. Of these devices, the shear box testing apparatus is the oldest and remains the most popular for determining the shear strength characteristics of granular materials. The apparatus is, however, generally considered inadequate when testing at low normal stresses because second order frictional effects become significant at these stresses and lead to large errors in the inferred shear and normal loads on the plane of shearing. A number of new, more elaborate, devices have been employed to measure the frictional characteristics of clays at low stress levels (e.g. the Cam-shear and tilt table tests), but these require a high level of expertise to use correctly, and are not readily available in laboratories around the world. In this paper, statics principles are employed to develop a simple means of correcting for the mechanical friction in a shear box. The applicability of the corrections proposed is examined using data obtained in two different shear boxes for three separate sands over a large range of normal stresses. It is demonstrated that these corrections can be used to determine the peak and critical friction angles of granular materials at low stress levels in a shear box apparatus.     

土工膜-土工布界面动力剪切特性试验研究

糙面土工膜（GMX）和无纺土工布（GT）是垃圾填埋场中周边衬垫系统的重要组成部分,其界面特性对于整体填埋场的稳定性尤为重要。但是,目前对GMX-GT界面的动力剪切特性研究较少。为此,利用大型直剪仪,开展了一系列全饱和条件及干燥条件下GMX-GT界面的循环剪切试验,主要研究了竖向应力、位移幅值和循环次数等对GMX-GT界面动力剪切特性的影响,并对比分析了全饱和及干燥两种条件下GMX-GT界面动力剪切特性的差异。研究结果表明,随着位移幅值的增加,GMX-GT界面呈现出由剪切硬化向剪切软化转变的特性。循环剪切作用使得界面的内摩擦角随着位移幅值的增加而增大。GMX-GT界面主要表现为剪缩特性,且总剪缩量随竖向应力、位移幅值和循环次数的增加而增加。剪切刚度随竖向应力和循环次数的增大而增大,随位移幅值的增大而减小。阻尼比随位移幅值的增大而增大,随循环次数的增加而减小,说明位移幅值会增加GMX-GT界面的能量的耗散。GMX-GT界面在干燥条件下的破坏模式与饱和条件下的存在明显差异,干燥条件下GT内部的破坏更加显著,全饱和条件下GMX表面的破坏更加明显。     

Strain analysis of a Northern Apennine shear zone using deformed marble breccias

The Alpi Apuane region of the Northern Apennines appears to have been deformed within a large-scale, low-angle shear zone with an overthrust sense of movement. The presence of mineral stretching lineations, folds progressively rotated into the X strain direction, and schistosities which intersect the nappe boundaries at small angles suggest that a component of shear strain occurred during the deformation. The strain ratios and orientations on two-dimensional sections have been determined from deformed marble breccias, reduction spots, and oncalites. Data from three or more non-perpendicular, non-principal sections have been combined to determine the finite strain ellipsoids at 33 sites within the shear zone.The finite strains have been separated into components of simple shear (γ), longitudinal strain (λ), and volume change (Δ). Algebraic expressions have been derived and graphs constructed which enable components of γ, γ and Δ, and γ and λ to be determined directly from a knowledge of strain ratio (R) within the shear zone and the angle (θ) between the principal strain direction and the shear zone boundary. The Alpi Apuane data indicate that neither simple shear alone, nor simple shear with volume change can satisfactorily explain the observed strains. Consideration of simple shear plus longitudinal strain leads to a general relationship in which the value of shear increases, and the values of longitudinal strain change along a SW-NE profile across the zone. Integration of the resulting shear strain-distance curves gives a minimum displacement of 4 km within the shear zone. Combination of the finite strains with the total time of deformation known from K/Ar studies leads to average strain rates from 1.4 to 9.6 × 10⁻¹⁵ sec⁻¹.A characteristic flat-ramp-flat geometry initially formed the boundaries of what was later to develop into the overthrust shear zone, and deformation of the underlying crystalline basement is believed to have occurred by ductile shearing. Estimates of 21% crustal shortening for the region suggest that the crustal thickness prior to deformation was approximately 20 km in this part of the Northern Apennines.