Rigorous back analysis of shear strength parameters of landslide slip

A rigorous back analysis of shear strength parameters of landslide slip was presented. Kinematical element method was adopted to determine factor of safety and critical failure surface, which overcomes the disadvantage of limit equilibrium method. The theoretical relationship between the combination of shear strength parameters and stability state was studied. The results show that the location of critical slip surface, F/tan f and F/c depend only on the value of c/tan f. The failure surface moves towards the inside of slope as c/tan f increases. According to the information involving factor of safety and critical failure surface in a specific cross-section, strength parameters can be back calculated based on the above findings. Three examples were given for demonstrating the validity of the present method. The shear strength parameters obtained by back analysis are almost consistent with their correct solutions or test results.

Determination Method for Shear Strength Parameters of Rock-Soil Mixtures Using Close-Range Photogrammetry and 3-D Limit Equilibrium Theory

Using a combination of close-range photogrammetry and three-dimensional(3-D) limit equilibrium theory, a determination method for the shear strength parameters of rock-soil mixture is presented. A close-range photogrammetry method is used for measurement of the 3-D terrain of the experimental target. Auto CAD Lisp and EXCEL VBA are used to perform 3-D limit equilibrium analysis of the stability of sliding mass and perform backanalysis of shear strength parameters. The presented method was used to determine the shear strength parameters of rock-soil mixtures at the Liyuan Hydropower Station. The 3-D terrain of sliding surface could be measured notably well using of closerange photogrammetry. The computed results reveal that the cohesion and friction angle of rock-soil mixtures were 3.15 k Pa and 29.88o for test A, respectively, and 4.43 k Pa and 28.30o for test B, respectively, within the range of shear strength parameters, as determined by field and laboratory tests. The computation of shear strength parameters is influenced by the mesh grid number, especially the cohesion of the rock-soil mixture. The application of close-range photogrammetry can reduce the siteworks and improve the computational efficiency and accuracy.

Shear creep parameters of simulative soil for deep-sea sediment

Based on mineral component and in-situ vane shear strength of deep-sea sediment, four kinds of simulative soils were prepared by mixing different bentonites with water in order to find the best simulative soil for the deep-sea sediment collected from the Pacific C-C area. Shear creep characteristics of the simulative soil were studied by shear creep test and shear creep parameters were determined by Burgers creep model. Research results show that the shear creep curves of the simulative soil can be divided into transient creep, unstable creep and stable creep, where the unstable creep stage is very short due to its high water content. The shear creep parameters increase with compressive stress and change slightly or fluctuate to approach a constant value with shear stress, and thus average creep parameters under the same compressive stress are used as the creep parameters of the simulative soil. Traction of the deep-sea mining machine walking at a constant velocity can be calculated by the shear creep constitutive equation of the deep-sea simulative soil, which provides a theoretical basis for safe operation and optimal design of the deep-sea mining machine.

Shear Failure Criterion and Constant Volume Ring Shear Testing Method for Clayey Soil

This paper discusses the shortcomings of the traditional Coulomb shear criterion and the direct shear-box testing method used for clayey soil and presents a modified shear criterion that considers the elasto-plastic behavior of cohesive soil. This modified approach involves direct shear testing under constant volume, a method that has been developed by the author. A modified ring shear apparatus and the theory behind the shear criterion and its implication for slope stability analysis are then discussed and the results of investigated tuffitic clayey sediments are presented. The results show that the presented new shear criterion does not consider the cohesion as material constant, but rather it depends on the void ratio. In this case, the stress state and the consolidation status and thus the elasto-plastic behavior of the clayey soil are considered.

Experimental study on the shear behavior of grout-infilled specimens and micromechanical properties of grout-rock interface

The grout-rock interfacial property is one of the key factors associated with the strength of grouted rock masses.In this study,direct shear tests and nanoindentation tests were adopted to investigate the mechanical properties of the grout-rock interface at both the macroscale and microscale.The cohesion of the cement specimens was higher than that of the grout-infilled joint specimens,while their internal friction angle was lower than that of the grout-infilled joint specimens.A“separation method”for identifying the different phases according to the qualitative and quantitative estimations was introduced,and the irregular interfacial transition zone(ITZ)thickness and elastic modulus were estimated.The ITZ thickness of the grout-infilled sandstone specimen ranged from 0 to 30μm,whereas it was within the range of 10-40μm for the grout-infilled mudstone specimen.The average elastic modulus of the ITZ in grout-infilled sandstone and mudstone specimens was approximately 58.2%and 54.1%lower than that of the bulk grout,respectively.Regarding the incidence of the rock type,the interlacing between the grout and sandstone was better developed.The ITZ with a higher porosity and lower modulus had a significant effect on the mechanical properties of the grout-infilled specimens.

Rock borehole shear tests in dam foundation of Xiangjiaba hydropower station

Xiangjiaba hydropowcr station is one of the complicated geological conditions of its dam foundation, parameters of rock masses are very important issues. To cascade power stations on the Jinsha River, China. Due to the evaluating the rock mass quality and determining the mechanical address these issues, several groups of rock borehole shear tests （RBSTs） were conducted on the black mudstone in the dam foundation of Xiangjiaba hydropower station in the second construction phase. Forty three groups of shear strengths of black mudstone samples were obtained from RBSTs, and the shear strength parameters （c and f） were calculated using the least squares method. In addition, the limitations and merits of RBST employed in the Xiangjiaba hydropower station were discussed. Test results indicate that the shear strength parameters obtained from RBST have a good correlation with the results from sotmd wave test in borehole. It is believed that RBST has a good adaptability and applicability in geotechnical engineering.

New criterion for rock joints based on three-dimensional roughness parameters

The shear behavior of rock joints is important in solving practical problems of rock mechanics. Three group rock joints with different morphologies are made by cement mortar material and a series of CNL(constant normal loading) shear tests are performed. The influences of the applied normal stress and joint morphology to its shear strength are analyzed. According to the experimental results, the peak dilatancy angle of rock joint decreases with increasing normal stress, but increases with increasing roughness. The shear strength increases with the increasing normal stress and the roughness of rock joint. It is observed that the modes of failure of asperities are tensile, pure shear, or a combination of both. It is suggested that the three-dimensional roughness parameters and the tensile strength are the appropriate parameter for describing the shear strength criterion. A new peak shear criterion is proposed which can be used to predict peak shear strength of rock joints. All the used parameters can be easily obtained by performing tests.

Study on Shear Strength Characteristics of Basalt-Concrete Bonding Interface Based on in-situ Direct Shear Test

In rock engineering,the shear strength of the basalt-concrete bonding interface is a key factor affecting the shear performance of hydroelectric dam foundations,embedded rock piles and rock bolts.In this study,30 sets of in-situ direct shear tests were conducted on the basalt-concrete bond interface in the Baihetan dam area to investigate the shear strength characteristics of the basalt-concrete bonding interface.The bonding interface contains two states,i.e.,the bonding interface is not sheared,termed as se(symbolic meaning see Table 1);the bonding interface is sheared with rupture surface,termed as si.The effects of lithology,Joints structure,rock type grade and concrete compressive strength on the shear strength of the concrete-basalt contact surface were investigated.The test results show that the shear strength of the bonding interface(s_(e)&s_(i))of columnar jointed basalt with concrete is greater than that of the bonding interface(s_(e)&s_(i))of non-columnar jointed one with the same rock type grade.When the rock type grade isⅢ_(2),fcol is 1.22 times higher than fncol and ccol is 1.13 times greater than cncol.The shear strength parameters of the basalt-concrete bonding interface differ significantly for different lithologies.The cohesion of the bonding interface(s_(i))of cryptocrystalline basalt with concrete is 2.05 times higher than that of the bonding interface(s_(i))of breccia lava with concrete under the same rock type grade condition.Rock type grade has a large influence on the shear strength of the non-columnar jointed basalt-concrete bonding interface(s_(e)&s_(i)).cnol increases by 33%when the grade of rock type rises fromⅢ_(1)toⅡ_(1).the rock type grade has a greater effect on bonding interface(s_(i))cohesion than the coefficient of friction.When the rock type grade is reduced fromⅢ_(2)toⅢ_(1),f_(ncol)′increases by 2%and c_(ncol)′improves by 44%.The shear strength of the non-columnar jointed basalt-concrete bonding interface(s_(e)&s_(i))increases with the increase of the compressive strength of concrete.When concrete compressive strength rises from 22.2 to 27.6 MPa,the cohesion increases by 94%.

Shear failure behaviors and degradation mechanical model of rockmass under true triaxial multi-level loading and unloading shear tests OA

The redistribution of three-dimensional(3D)geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane,potentially resulting in engineering disasters.However,the current understanding of rockmass shear behavior is mainly based on shear tests under2D stress without lateral stress,the shear fracture under 3D stress is unclear,and the relevant 3D shear fracture theory research is deficient.Therefore,this study conducted true triaxial cyclic loading and unloading shear tests on intact and bedded limestone under different normal stressσnand lateral stressσpto investigate the shear strength,deformation,and failure characteristics.The results indicate that under differentσnandσp,the stress–strain hysteresis loop area gradually increases from nearly zero in the pre-peak stage,becomes most significant in the post-peak stage,and then becomes very small in the residual stage as the number of shear test cycles increases.The shear peak strength and failure surface roughness almost linearly increase with the increase inσn,while they first increase and then gradually decrease asσpincreases,with the maximum increases of 12.9%for strength and 15.1%for roughness.The shear residual strength almost linearly increases withσn,but shows no significant change withσp.Based on the acoustic emission characteristic parameters during the test process,the shear fracture process and microscopic failure mechanism were analyzed.As the shear stressτincreases,the acoustic emission activity,main frequency,and amplitude gradually increase,showing a significant rise during the cycle near the peak strength,while remaining almost unchanged in the residual stage.The true triaxial shear fracture process presents tensile-shear mixture failure characteristics dominated by microscopic tensile failure.Based on the test results,a 3D shear strength criterion considering the lateral stress effect was proposed,and the determination methods and evolution of the shear modulus G,cohesion cjp,friction angleφjp,and dilation angleψjpduring rockmass shear fracture process were studied.Under differentσnandσp,G first rapidly decreases and then tends to stabilize;cjp,φjp,andψjpfirst increase rapidly to the maximum value,then decrease slowly,and finally remain basically unchanged.A 3D shear mechanics model considering the effects of lateral stress and shear parameter degradation was further established,and a corresponding numerical calculation program was developed based on3D discrete element software.The proposed model effectively simulates the shear failure evolution process of rockmass under true triaxial shear test,and is further applied to successfully reveal the failure characteristics of surrounding rocks with structural planes under different combinations of tunnel axis and geostress direction.

基于Grasshopper及Rhino-inside插件的纵肋叠合剪力墙参数化快速建模

结构工程师在装配式的项目中,需要绘制竖向构件的详图,在目前能够绘制构件详图的软件中,并没有针对纵肋叠合剪力墙新体系的模块,此项工作耗费了很多精力,故考虑将参数化建模与装配式相结合。在BIM参数化研究中,多为幕墙和网壳结构的建模应用,在构件层面的应用较少。本文利用Grasshopper,调整少量参数,实现快速建模,通过Rhino-inside插件,建立Rhino和REVIT软件之间的联系,将犀牛软件中的模型转换为REVIT模型。实现快速绘制纵肋叠合剪力墙的构件详图,并将构件的信息参数化,可视化,传递给构件厂,便于预制构件的深化和生产,全过程节省了很多人力,大大提升了效率,为装配式新体系的构件生产提供参考。

边界层参数化和湿过程对切变线低涡发展影响的中尺度模拟

1981年8月14至22日,在青藏高原东侧陕、甘、川毗邻区,出现了一次持续暴雨过程.对其主过程的涡度诊断表明,切变线低涡初生於青藏高原东侧低空,其后,不仅出现了高、低空涡度中心的叠加和耦合过程,而且在行星边界层(PBL)内发生了迅速加强过程.这种过程与切变低涡的持续发展相伴. 一系列48和72小时中尺度数值模拟结果揭示:只有高分辨PBL参数化的湿物理过程,才能较好地模拟出切变低涡在PBL内的突然加强及其涡度演变和垂直结构;而总体PBL参数化,虽然其涡度演变和垂直结构也能基本模拟出来,但不能模拟出切变线低涡在PBL内的迅速加强;总体PBL参数化干过程的模拟结果指出,该方案较前两种湿过程方案均差,特别是被模拟系统的强度明显减弱,位置偏离. 模拟与诊断和观测之间的比较揭示,尽可能仔细地改进PBL参数化和湿物理过程,才有可能改进对这类中尺度系统发生和发展的模拟.

基于BIM技术的剪力墙边缘构件参数化设计研究

分析了剪力墙结构边缘构件的设计特点及Revit模型中结构构件的对象类型和描述方式,提出了一种基于BIM技术的剪力墙边缘构件参数化设计模型。通过CAD及Revit二次开发,并以Excel作为数据中间储存及补充输入工具,实现了二维图形中Satwe计算结果的信息提取、结构构件的信息提取、边缘构件的优化设计及Revit三维自动建模与交互式设计,在Revit上进行了程序实现,并将其应到实际工程中。

“91.7”江淮暴雨低涡发展结构和演变的中尺度数值模拟

本文对1991年7月4—7日发生在江淮流域的一次低涡切变线特大暴雨过程进行了高分辨行星边界层参数化的中尺度数值模拟。所用模式是通过系列检验和改进的MM4。控制模拟结果揭示:"91.7"江淮暴雨过程与中尺度暴雨低涡的生成和发展以及特有的动力和热力结构密切相关;垂直气旋性涡柱的形成和发展是这类暴雨低涡持续发展的一种重要而特有的中尺度结构;伴随暴雨低涡涡柱耦合发展的强上升运动是维持其低涡持续发展以及完成高、低空诸通量交换和输送所必须的次级垂直环流条件;深厚湿舌、强上升运动与涡柱三位一体的共存结构是暴雨低涡持续发展并产生对流云系和持续暴雨的典型结构;西南低空急流的发展和维持,不仅是暴雨低涡形成和持续发展的重要动力学条件,也是暴雨过程所需水汽的主要载体;对流层下部深厚不稳定层结的形成和维持是暴雨低涡能够产生持续对流活动以及对流性降水所必须的热力层结条件;与西南低空急流相伴的强暖湿带在850 hPaθ_e场上显示得最清楚,其暖湿带中轴北侧及其强湿斜压区与低涡切变线雨带基本一致;在暴雨低涡行星边界层内,感热通量有夜负昼正的日变化;而潜热通量却昼夜均为正值,且远大于相应时间的感热通量。这表明在低涡暴雨过程中,行星边界层内垂直向上输送的水汽通量和潜热通量远较感热通量重要。

改进参数化方法及在低空风切变中的应用

研究对参数化方法进行必要的改进,从而使该方法更好地用于求解最优控制问题。改进的基本思路是设法降低利用该方法转换而得的非线性规划子问题的维数。通常在利用参数化方法求解最优控制问题时,由于对控制变量和状态变量同时参数化,从而导致所转化而得的非线性规划子问题维数高,求解难。通过分析认为,只需对控制变量参数化,而对状态变量在时间节点处的值,则可通过对最优控制问题的微分约束进行分段积分求得,从而降低了转换而得的非线性规划子问题的维数,有利于该算法进一步推广应用。利用改进算法求解了飞机在低空风切变中的最优着陆轨迹问题,求解结果表明,改进算法可以顺利求解一类最优控制问题。

台风“云娜”在近海强度变化及结构特征的数值研究Ⅱ:云微物理参数化对强度和路径的影响

在分析云微物理参数化对云结构和降水特征的影响的基础上,研究云微物理参数化过程对台风"云娜"强度与路径的影响。结果表明:云微物理过程对台风强度和路径有一定影响,其中不考虑雨水蒸发冷却效应后,比其他试验最终地面最大风速强7 m/s以上,但此时登陆地点误差最大,与对照试验偏离150 km左右。我们还从螺旋雨带结构变化及环境风切变影响角度分析台风临近登陆时强度模拟减弱的原因,发现过强的外围螺旋雨带以及环境风场垂直切变对于台风的加深、维持是不利的,他们可能会造成"云娜"临近登陆时强度的下降。不难看出,云微物理过程可以加强甚至产生外螺旋雨带,当外围雨带发展加强之后,可以引起局地辐合强度增强,从而限制了大量水汽和能量向台风内核输送,从而会导致台风强度下降。此外,外围螺旋雨带的发展,还可以从对流层中层带来干冷空气入侵行星边界层;而当入流边界层中雨水下落时,其自身的蒸发也会使周围气块温度下降;这些干冷气团在入流气流的输送下进入台风内核,从而对云墙产生了"冷侵蚀",最终引起台风强度下降。因此,减小上述两方面的模拟误差,应能改进台风"云娜"登陆过程中强度的模拟效果。

白天混合层顶部夹卷层厚度的特征研究

本文首先对Deardorff的一阶模型给予解释 ,在此基础上根据对流边界层湍流动能方程 ,分析机械湍流和对流湍流对边界层发展的贡献 ,提出一个新的速度尺度———混合层顶速度尺度 ,定义了全理查森数 ,给出夹卷层厚度的参数化方案 ,并用Boers和Elotanta的雷达观测数据进行验证 .参数化方案与实验数据符合得很好 .当夹卷层厚度表示为夹卷速度或夹卷理查森数的函数时 ,该函数曲线随边界层发展表现为磁滞回线形状现象 ,文中对此进行了解释 .

Geotechnical Characterization of Silty Clay Reinforcedwith Jute Cloth as Waster Product

Soil reinforcement is a recent and special field of soil improvement.It covers a range of techniques,which consists of placing inclusions in soil.The most conferences devoted partly or totally the behavior of foundation on reinforced subgrade without regarding the basic characteristics of the reinforced soil.So,the paper presents an experimental investigation into the mechanical and compressibility properties of the reinforced silty clay samples by jute cloth at intermediate depth.The effects of the reinforcement on shear stress and shear failure were studied;also,the presence of the reinforcement on behavior of consolidation process was distinctly described.The laboratory tests were supported by the finite element analysis to identify only the consolidation process and explained the effect of the reinforcement on the effective vertical stress and pore water pressure.The results indicated that the presence of such reinforcement has a considerable effect in increasing the shear strength of the reinforced samples and decreasing the compressibility especially decreasing the soil movement also,relieving both the effective and pore water pressure.

Effects of Material Composition and Water Content on the Mechanical Properties of Landslide Deposits Triggered by the Wenchuan Earthquake

Abundant landslide deposits were triggered by the Wenchuan earthquake, providing a rich source of material for subsequent debris flows or slope failures under rainfall conditions. A good understanding of the physical and mechanical properties of the landslide deposits is very important to the research on slope failure mechanisms and the initiation of debris flow. Laboratory biaxial compression tests are used to study the material compositions and water content impacts on the mechanical properties of landslide deposits, and a discrete element method （a bond-contact model） is used to study the particle stiffness, bond force, friction coefficient and confining stress impact on the mechanical behaviors and the relationships between the numerical and experimental parameters. The experimental results show that the failure stress of landslide deposits is decreased with increasing content of fine particles and also with increased water content, especially at the initial increasing stage. Cohesion of the saturated landslide deposits is increased, but the friction angle is decreased with the increase in the fine particle content. Shear strength parameters （the cohesion and friction angle） are decreased with the increasing water content at the initial increasing stage, and then, they slowly decrease. There is a critical value of the water content at 5%-7% （in weight） for the failure stress and shear strength parameters of the landslide deposits. Quadratic equations are presented to describe the relation between the bond force and cohesion, and the numerical friction coefficient and the experimental friction angle.

Diagnosis of dynamic process over rainband of landfall typhoon

This paper introduces a new physical parameter -- thermodynamic shear advection parameter combining the perturbation vertical component of convective vorticity vector with the coupling of horizontal divergence perturbation and vertical gradient of general potential temperature perturbation. For a heavy-rainfall event resulting from the landfall typhoon ＇Wipha＇, the parameter is calculated by using National Centres for Enviromental Prediction/National Centre for Atmospheric Research global final analysis data. The results showed that the parameter corresponds to the observed 6 h accumulative rainband since it is capable of catching hold of the dynamic and thermodynamic disturbance in the lower troposphere over the observed rainband. Before the typhoon landed, the advection of the parameter by basic-state flow and the coupling of general potential temperature perturbation with curl of Coriolis force perturbation are the primary dynamic processes which are responsible for the local change of the parameter. After the typhoon landed, the disturbance is mainly driven by the combination of five primary dynamic processes. The advection of the parameter by basic-state flow was weakened after the typhoon landed.

Study on Shear Strength Characteristics of Columnar Jointed Basalt Based on in-situ Direct Shear Test at Baihetan Hydropower Station

Columnar jointed basalt(CJB) widely distributes in the dam site of the Baihetan Hydropower Station.The columnar joint structure and fracture development of CJB have significant influence on the mechanical properties of rock mass,and the mechanical properties of CJB are of great significance to the Baihetan Hydropower Project.Therefore,in-situ direct shear tests were carried out on ten test adit at different locations in the dam site area to study the shear behavior of CJB.In this study,21 sets of in-situ direct shear tests were conducted for rock types of type Ⅱ_(2),type Ⅲ_(1)and type Ⅲ_(2),with horizontal and vertical shear planes and two different specimen sizes of CJB.Shear strength parameters of CJB were obtained by linear fitting of in-situ direct shear test results based on the Mohr-Coulomb strength criterion.The results indicate that the shear strength parameters of CJB with horizontal shear plane increase as the increase of rock type grade.The shear strength parameters of CJB show obvious anisotropy and the friction coefficient of the horizontal shear plane is greater than the vertical shear plane.The friction coefficient in the horizontal direction of the shear plane is 1.27 times that in the vertical direction of the shear plane.With the increase of rock type grade,the difference of friction coefficient becomes larger.However,the cohesion changes little whether the shear plane is horizontal or vertical.In addition,the size effect of CJB in this area is significant.The shear strength parameters of large size(100 cm × 100 cm) specimens are lower than those of regular size(50 cm × 50 cm) specimens.The reduction of cohesion is greater than that of the friction coefficient.For rock type Ⅲ_(2),the cohesion of large-size specimens is 0.637 of the regular-size specimens.The reduction percentage of the friction coefficient for type Ⅲ_(2)is 1.66 times that of type Ⅲ_(1).The reduction percentage of the cohesion for type Ⅲ_(2)is 1.27 times that of type Ⅲ_(1).The size effect decreases with the increase of rock type grade.The research results of this study can provide an important basis for the selection of rock mechanics parameters in the dam site area of Baihetan Hydropower Station and the stability analysis of the dam foundation and rocky slopes.