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.

Coronary artery calcium data and reporting system: Strengths and limitations

Coronary artery calcium data and reporting system(CAC-DRS)is a recently introduced standardized reporting system for calcium scoring on computed tomography.CAC-DRS provides four risk categories(0,1,2 and 3)along with treatment recommendations for each category.As with any other new reporting platform,CAC-DRS has both advantages and disadvantages.Improved communication,better clarity of details,organized management recommendations and utility in future research and education are the major strengths of CAC-DRS.It has many limitations such as questionable need for a new system,few missing components,use of a less accurate visual method and treatment suggestions based on expert opinion instead of clinical trials.In this contemporary review,we discuss the new reporting system CAC-DRS,its application,strengths and limitations and conclude with some remarks for the future.

Limitations and potential design risks when applying empirically derived coal pillar strength equations to real-life mine stability problems

The method of determining coal pillar strength equations from databases of stable and failed case histories is more than 50 years old and has been applied in different countries by different researchers in a range of mining situations. While common wisdom sensibly limits the use of the resultant pillar strength equations and methods to design scenarios that are consistent with the founding database, there are a number of examples where failures have occurred as a direct result of applying empirical design methods to coal pillar design problems that are inconsistent with the founding database. This paper explores the reasons why empirically derived coal pillar strength equations tend to be problem-specific and should be considered as providing no more than a pillar strength ‘‘index." These include the non-consideration of overburden horizontal stress within the mine stability problem, an inadequate definition of supercritical overburden behavior as it applies to standing coal pillars, and the non-consideration of overburden displacement and coal pillar strain limits. All of which combine to potentially complicate and confuse the back-analysis of coal pillar strength from failed cases. A modified coal pillar design representation and model are presented based on coal pillars acting to reinforce a horizontally stressed overburden, rather than suspend an otherwise unstable self-loaded overburden or section, the latter having been at the core of historical empirical studies into coal pillar strength and stability.

SURFACE YIELD STRENGTH AND FATIGUE LIMIT FOR STEELS

The surface yield strength(σ_(ms))for various carbon steels was studied by means of X-ray diffraction method.The results showed that it is.far below the bulk yield strength,and is the resistance against plastic deformation in the surface layer.The smooth fatigue limit is associ- ated with crack initiation which is a result of accumulation of plastic deformation.Experimen- tal results showed the relation of smooth fatigue limit for 50% survival with σ_(ms)is σ_(ms)=0.81 tO 1.02 σ_(-1)for different steels.The smooth fatigue limit of a medium carbon steel for 99.9% survival with σ_(ms)is σ_(ms)=0.98 tO 1.10 σ_(-1).It is less expensive and time consuming to measure σ_(ms)than σ_(-1).

A novel limiting strain energy strength theory

With applied dislocation theory,the effects of shear and normal stresses on the slide and climb motions at the same section of a crystal were analyzed.And,based on the synergetic effect of both normal and shear strain specific energies,the concept of the total equivalent strain specific energy(TESSE)at an oblique section and a new strength theory named as limiting strain energy strength theory(LSEST)were proposed.As for isotropic materials,the plastic yielding or brittle fracture of under uniaxial stress state would occur when the maximum TESSE reached the strain specific energy,also the expressions on the equivalent stresses and a function of failure of the LSEST under different principal stress states were obtained.Relationship formulas among the tensile, compressive and shear yield strengths for plastic metals were derived.These theoretical predictions,according to the LSEST,were consistent very well with experiment results of tensile,compressive and torsion tests of three plastic metals and other experiment results from open literatures.This novel LSEST might also help for strength calculation of other materials.

Overhanging rock slope by design:An integrated approach using rock mass strength characterisation,large-scale numerical modelling and limit equilibrium methods

Overhanging rock slopes(steeper than 90°) are typically avoided in rock engineering design, particularly where the scale of the slope exceeds the scale of fracturing present in the rock mass. This paper highlights an integrated approach of designing overhanging rock slopes where the relative dimensions of the slope exceed the scale of fracturing and the rock mass failure needs to be considered rather than kinematic release of individual blocks. The key to the method is a simplified limit equilibrium(LE) tool that was used for the support design and analysis of a multi-faceted overhanging rock slope. The overhanging slopes required complex geometries with constantly changing orientations. The overhanging rock varied in height from 30 m to 66 m. Geomechanical modelling combined with discrete fracture network(DFN)representation of the rock mass was used to validate the rock mass strength assumptions and the failure mechanism assumed in the LE model. The advantage of the simplified LE method is that buttress and support design iterations(along with sensitivity analysis of design parameters) can be completed for various cross-sections along the proposed overhanging rock sections in an efficient manner, compared to the more time-intensive, sophisticated methods that were used for the initial validation. The method described presents the development of this design tool and assumptions made for a specific overhanging rock slope design. Other locations will have different geological conditions that can control the potential behaviour of rock slopes, however, the approach presented can be applied as a general guiding design principle for overhanging rock cut slope.

Limit equilibrium analysis for rock slope stability using basic Hoek–Brown strength criterion

Hoek–Brown(HB)strength criterion can reflect rock’s inherent failure nature,so it is more suitable for analyzing the stability of rock slopes.However,the traditional limit equilibrium methods are at present only suitable for analyzing the rock slope stability using the linear equivalent Mohr–Coulomb(EMC)strength parameters instead of the nonlinear HB strength criterion.Therefore,a new method derived to analyze directly the rock slope stability using the nonlinear HB strength criterion for arbitrary curve slip surface was described in the limit equilibrium framework.The current method was established based on certain assumptions concerning the stresses on the slip surface through amending the initial normal stressσ0 obtained without considering the effect of inter-slice forces,and it can satisfy all static equilibrium conditions of the sliding body,so the current method can obtain the reasonable and strict factor of safety(FOS)solutions.Compared with the results of other methods in some examples,the feasibility of the current method was verified.Meanwhile,the parametric analysis shows that the slope angleβhas an important influence on the difference of the results obtained using the nonlinear HB strength criterion and its linear EMC strength parameters.Forβ≤45°,both of the results are similar,showing the traditional limit equilibrium methods using the linear EMC strength parameters and the current method are all suitable to analyze rock slope stability,but forβ>60°,the differences of both the results are obvious,showing the actual slope stability state can not be reflected in the traditional limit equilibrium methods,and then the current method should be used.

基于均匀化理论与上限分析的膨胀土滑坡稳定性分析

在膨胀土和滑坡共同作用下,隧道洞口段施工更容易引发地表开裂甚至滑坡等工程灾害,在隧道内采用微型桩群防治滑坡比抗滑桩具有优势。本文基于均匀化理论与上限分析对某高速公路隧道洞口段膨胀土滑坡的稳定性进行计算,并评价微型桩群和削方卸载不同组合方式的处置效果,计算时将微型桩群及桩周土通过均匀化理论等效为符合摩尔库仑强度准则的等效加固体来,以此提高计算效率,最后通过对现场削方+微型桩群加固处置后的滑坡变形监测来验证计算的合理性,得出如下结论:相较于土的强度参数,等效加固体内摩擦角保持不变,黏聚力从26kPa提高到85.36kPa。处置前后的滑坡稳定性评价结果表明,不做处理时,滑坡滑动面从滑坡上方岩土交界面延续到隧道洞口前;仅采用微型桩群加固时,滑坡安全系数在1.17左右,滑动面从岩土交界面延续到隧道洞口后;同时采用微型桩群加固和削方卸载时,滑坡安全系数提高到1.26~1.28,滑动面上缘由土石交界面前移。现场变形监测表明地表变形与深层土体变形均不超过3mm,该措施能保障滑坡的稳定性,同时也验证了计算方法的合理性,可为同类工程提供参考。

Cu-4Ag合金微细丝拉拔极限预测模型

采用三室真空冷型竖引连铸设备制备了Cu-4Ag合金铸态杆坯,并利用连续冷拉拔变形得到了不同线径的Cu-4Ag合金微细丝,通过拉拔实验获取了不同线径下材料的屈服强度和抗拉强度;基于线径与强度的关系,构建了微细丝拉拔极限预测模型。结果表明,在拉拔过程中,Cu-4Ag合金微细丝的线径与抗拉强度密切相关,具有明显的尺寸效应;修正后的拉拔极限模型能够较为准确地预测不同线径的Cu-4Ag合金微细丝能够达到的拉拔极限。将拉拔极限模型产出的数据导入MATLAB中,构建了三维曲面模型,可以更为直观地分析材料的拉拔极限。

论理智谦逊的内涵与价值

理智谦逊是当代德性知识论领域的前沿话题,其内涵和价值是学界研究的主要内容。学界已有的三种理智谦逊观共同面临理智屈从的问题,本文主张理智谦逊应该理解为准确的自我认知评价,并且把认知者的认知表现放在社会的、自然的环境中。就价值层面来看,理智谦逊有助于在个人认知层面拓宽知识渠道和加深理解深度,在社会层面有助于构建良好有效的信息交流方式,促成群体性的认知协同任务。培养这一美德有两个突出的困难:认知主体不仅要克服机体在进化过程中自带的节能机制,还要对新媒介环境下信息传播方式的影响具有反思和批判意识。

土性对工程泥浆固化强度影响规律及微观机理

本文开展了一系列不同液限高分子吸水树脂固化工程泥浆无侧限抗压强度试验,探讨了泥浆土液限对固化效率的影响规律,对比研究了掺入高岭土对泥浆固化强度的改进程度,最后基于XRD和SEM试验揭示了液限和高岭土对固化泥浆强度影响的微观机理。结果表明:随着泥浆土液限的增大,固化泥浆土强度逐渐降低,固化效率随着泥浆土液限增大显著衰减,当液限增加10%,固化泥浆土强度qu平均减少48.2%。然而高岭土的掺入则显著提升了固化泥浆土的强度,并且强度增长率随着龄期逐渐增大,对于龄期为90天时,增加40%高岭土能够提升固化泥浆土强度qu 1.17倍。微观结构试验表明泥浆土液限变化对水化产物产量的影响较小,固化泥浆土强度随泥浆土液限减小主要是由于固化泥浆土孔隙随着泥浆土液限增大而增多,使得微观结构松散从而导致强度降低。高岭土的掺入则显著提升了固化泥浆土的水化产物产量,增强了固化泥浆土胶结强度,从而提升了固化泥浆土强度。因此,在实际工程中,一方面可以通过调配泥浆土液限来提高固化效率;另一方面可以通过掺入高岭土或者一些高岭土基废弃物(如高岭土尾矿)来提高固化强度,实现“以废制废”绿色环保的理念。

黄原胶-粉煤灰联合处理酸污染土试验研究

绿色环保型生物聚合物黄原胶应用于岩土工程,可提高土体强度及抗风蚀、水蚀能力。鉴于黄原胶分子中的丙酮酸基团和糖苷键在酸性土壤条件下易水解,导致凝胶黏性减小、固土效果减弱,拟采用碱性材料粉煤灰协同黄原胶固化酸污染土,并开展液塑限、击实及无侧限抗压强度试验。结果表明:粉煤灰有助于提高固化土的塑限、最优含水率及最大干密度。酸性土壤条件下,粉煤灰能明显改善黄原胶固土效果,联合法固化酸污染土强度甚至超过联合法固化未污染土。另外,粉煤灰可提高土壤的pH值,缓解黄原胶水解,使其发挥增黏及胶结土颗粒的作用。基于试验结果,建议采用联合法固化酸污染土(FA=9%,XG=3%),可比酸污染上海黏土强度提高310%;在未污染土中采用黄原胶即可(XG=4%),可比未污染天然上海黏土强度提高90%。研究成果有助于绿色环保型生物聚合物的推广与应用。

基于上限定理确定隧道式锚碇极限抗拔承载力

隧道式锚碇作为一种新型的悬索桥锚碇结构,因具有因地制宜、经济环保的优点在多山的西南地区得到了广泛应用。已有研究表明,锚塞体围岩性质较差、埋深较浅,锚塞体与围岩接触界面结合程度较好的隧道式锚碇极易发生倒楔形冲切破坏。将破坏体视为以锚塞体中心线为轴线的旋转楔形体,假定破坏面为最小旋转曲面,利用变分法经典欧拉方程求解破坏体最小旋转曲面问题,确定旋转曲面母线方程;基于改进的Mohr-Coulomb强度准则,由主缆拉拔荷载和楔形体自重所做的外功率与楔形体沿滑移面所消耗的内功率相等的条件建立虚功方程,推导隧道式锚碇极限抗拔承载力上限解。开展隧道式锚碇室内模型试验,研究了拉拔承载过程中的坡面位移的变化规律及隧道式锚碇的破坏模式。研究结果表明,拉拔作用点的荷载-位移曲线可分为4个阶段:克服重力阶段、弹性阶段、弹塑性阶段以及破坏阶段;隧道式锚碇破坏模式为围岩倒楔形冲切破坏,破坏体可近似视为以锚塞体中心线为轴线的旋转楔形体;由推导公式得到的隧道式锚碇极限抗拔承载力计算值与实测值一致性较好,具有一定的可靠性,可为隧道式锚碇的设计提供参考。

考虑水力效应的裂缝边坡稳定性非线性能耗分析

现有考虑水力效应的裂缝边坡稳定性分析大多基于线性破坏准则,而岩土体破坏往往呈现非线性特征,因此开展水力效应影响下的裂缝边坡稳定性非线性极限上限分析具有重要意义。基于极限分析上限定理及强度折减技术,结合“外切线法”非线性破坏准则,构建坡顶含竖直裂缝的边坡对数螺旋线破坏模式,根据虚功原理推导出裂缝边坡安全系数解析式,通过MATLAB优化计算,结合边坡工程实例探讨了典型因素对裂缝边坡稳定性、临界裂缝及滑动面位置的影响规律。研究结果表明:随着地下水位h的持续上升,边坡安全系数不断降低,临界裂缝深度逐渐增大且临界裂缝位置逐渐向坡顶缘偏移;非线性系数m明显影响边坡的稳定性,边坡安全系数随着非线性系数的增大显著减小,采用线性破坏准则会高估地下水位变化对边坡稳定性的影响;随着非线性系数的增大,临界裂缝深度随之增大,临界裂缝位置距离坡顶缘越来越远,滑坡体体积逐渐增大;裂缝与坡顶缘距离l m随着非线性系数m的增大而增大(当m增大0.2时,l m增大约1 m),且随着裂缝与坡顶缘距离的增大,边坡安全系数无明显变化,临界裂缝深度先逐渐减小后趋于稳定。

破碎岩体隧道洞口开挖诱导滑坡与古滑坡耦合分析

以大栗树高速公路隧道洞口施工为工程背景,研究了在考虑古滑坡因素下洞口工作面边坡失稳及其加固技术。利用钻孔测斜数据(BCD)和Midas GTS折减强度有限元分析模型,分别推测了最危险滑动面,得知两者滑动面位置相似。并采用不平衡推力传递法,基于BCD推断滑动面计算安全系数。以BCD和有限元法的滑动面为基础,将滑动面近似假设为对数螺旋线,考虑地形因素,建立考虑多台阶边坡上限分析模型,研究了不同加固措施对边坡稳定的影响。结果表明,3种方法计算出的边坡安全系数结果相近。

非线性M-C强度准则下预应力锚索加固边坡时效稳定性分析M-P法

拓展传统极限平衡方法在复杂条件下边坡稳定性分析中的适用性一直是岩土工程界的研究热点。众所周知,边坡岩土体剪切失效一般服从于非线性强度准则,而传统极限平衡方法仅适用于线性强度准则下边坡稳定性分析。此外,预应力锚索作为一种主动防护措施,可极大地即时提高边坡稳定性而被广泛应用于中、大型边坡工程加固。然而,在应力松弛、蠕变效应以及腐蚀环境影响下预应力锚索加固边坡稳定性时效特征往往被忽视。由此,基于Morgenstern-Price(M-P)法,嵌入非线性Mohr-Coulomb(M-C)强度准则,并融入应力松弛与蠕变效应下锚索预应力损失模型以及腐蚀环境下锚索性能劣化模型,从而,建立非线性强度准则下预应力锚索加固边坡安全系数时程表达式。进一步,为了解决非线性强度准则下隐式嵌套公式难以求解的问题,归零化条间法向力初始值,并应用迭代循环求解策略,在引入循环终止允许误差判别条件后,可实现边坡稳定性理论真实结果的逼近求解。经过后续算例对比分析,验证了所提方法的可行性和合理性,与此同时,还研究了不同预应力损失速率和不同锈蚀环境下预应力锚索加固边坡稳定性的时效变化规律。

瓜尔胶处理铝土矿矿泥强度特性及微观机制

生物聚合物作为一种新型环境友好的土壤处理及改良材料,即使使用量很小,也能对土体具有显著的强化作用,因此近年来得到了广泛的运用。本文对不同胶土比(0%、1%、1.5%和2%)瓜尔胶处理的铝土矿矿泥试样进行了界限含水率测试、快剪试验、核磁共振试验(NMR)和扫描电镜(SEM)等室内试验。试验结果表明,随着生物聚合物的增加,铝土矿矿泥的液塑限及抗剪强度均有所提高,其中2%瓜尔胶含量的铝土矿泥液限提升了26%,黏聚力提升了182%。NMR试验表明了瓜尔胶能够使铝土矿矿泥试样的含水量增大,且其内部会出现大孔隙。而SEM图证实了瓜尔胶和铝土矿矿泥颗粒形成瓜尔胶—铝土矿矿泥基质,从而提高了液塑限及抗剪强度。

带切向接管内压圆筒的极限承载能力计算

针对压力容器切向接管开孔结构存在较大结构不连续性、易产生较高局部应力、目前没有适用的圆柱壳切向接管结构常规设计方法的问题,采用极限载荷分析方法,探讨不同切向接管无量纲结构参数(直径比do/Di≤0.3、径厚比Di/T≤125、厚度比t/T≤1.75)对承压圆柱壳体极限承载能力的影响,并定义了基于无接管壳体的强度削弱系数。结果表明,这3个因素都对圆柱壳切向接管结构的强度具有显著影响,当do/Di和Di/T增大、t/T减小时,强度削弱系数增大,意味着切向接管对圆柱壳的强度削弱程度增大。在大量计算结果基础上,对强度削弱系数进行回归分析,得到了回归方程,为带切向接管内压圆筒结构的强度设计提供参考。

水泥增强固化海相粘土的含水率影响及强度测试研究

针对粘性土初始含水率较低时水泥固化土的拌合质量,通过室内试验研究了水泥固化海相粘土中初始含水率与混合质量之间的关系。结果表明,在初始含水率(w 0)小于粘土的液限(w L)的情况下测试其强度,发现强度在w 0为0.925w L时达到峰值,在w 0为0.85w L时下降;在w 0为0.775w L时相比于w 0为0.925w L时强度有增有减,变得不稳定。使用初始含水率为1.0 w L和1.2w L的强度得到的强度估算公式,随着w 0变得小于w L,固化土的强度降低超过估算强度,认为是粘土初始含水率降低后,水泥掺入引起的强度增加,流动性下降,降低了混合料的质量,以致强度没有充分发挥。

基于极限平衡法和强度折减法的危岩稳定性分析

为了分析评价陡倾结构面相互组合切割形成的危岩体的稳定性,本文以龙寺CIV-1边坡危岩体为例,根据地质调查数据,建立了危岩体的简化地质模型、失稳概化理论模型以及在冻胀、地震、水力等因素影响下的力学分析模型,利用极限平衡理论推导出了危岩体的滑移稳定性系数和倾覆稳定性系数的无量纲表达式,重点分析了不同工况下危岩体的稳定性,并借助UDEC强度折减法对危岩体的形成、破坏机理进行分析研究。结果表明:不同工况下的危岩稳定性为天然工况>地震工况>暴雨工况>组合工况;层面与陡倾结构面的组合关系以及陡倾结构面的贯通程度直接控制着危岩体的稳定性和破坏模式。通过极限平衡法和UDEC强度折减法相结合的危岩体稳定性评价方法,不仅可以通过简单的数学公式高效地获取危岩体的稳定性,还可以通过力与变形的信息,直观的辨别出危岩体易失稳的部位,为陡倾结构面切割形成的危岩提供防治参考。