A roughness parameter considering joint material properties and peak shear strength model for rock joints

This study aims at proposing a reasonable roughness parameter that can reflect the peak shear strength(PSS) of rock joints. Firstly, the contribution of the asperities with different apparent dip angles to shear strength is studied. Then the shear strength of the entire joint asperities is derived. The results showed that the PSS of the entire joint asperities is proportional to a key parameter hs, which is related to the geometric character of the joint surface and the joint material properties. The parameter hsis taken as the new roughness parameter, and it is reasonable to associate the PSS with the geometric characteristics of the joint surface. Based on the new roughness parameter and shear test results of 20 sets of joint specimens, a new PSS model for rock joints is proposed. The new model is validated with the artificial joints in this paper and real rock joints in published studies. Results showed that it is suitable for different types of rock joints except for gneiss joints. The new model has the form of the Mohr-Coulomb model, which can directly reflect the relationship between the 3 D roughness parameters and the peak dilation angle.     

剪切速率对岩石节理强度特性的影响

不同剪切速率下岩体结构面的力学特性研究是进行岩质边坡动力反应分析的重要前提。基于Barton峰值抗剪强度理论和均方根一阶导数值法的节理粗糙度系数计算方法,对前人研究中关于定法向应力条件下不同剪切速率的岩石节理峰值抗剪强度的室内直剪试验结果进行整理与计算,探究剪切速率对岩石节理总摩擦角的影响规律,提出与速率相关的岩石节理峰值抗剪强度经验公式。结果表明:当剪切速率在0~0.8 mm·s^-1范围内时,岩石节理试样的总摩擦角随剪切速率的变化呈现负对数变化规律;对于均质性和各向同性较强的岩石节理随剪切速率的增大,总摩擦角呈现减小趋势,对于非均质性和各向异性较强的岩石节理随剪切速率的增大,总摩擦角呈现增大趋势,且后者总摩擦角增大幅度小于前者的减小幅度;岩石节理的物性和微观几何形态对总摩擦角随剪切速率的增加而变化的影响较大,节理面的物性主要影响总摩擦角随剪切速率增加呈现增大或减小的变化趋势,节理面的微观几何形态主要影响总摩擦角随剪切速率的变化幅值。     

岩石结构面直剪试验下力学特性的研究

在对三种岩石结构面进行直接剪切试验的基础上，探讨了结构面的变形特性和表面粗糙度的效应。发现残余抗剪强度与峰值强度之比与结构面粗糙程度之间有较强的相关关系。     

考虑粗糙度影响的不同土与混凝土界面大型直剪试验研究

土与结构接触界面的力学特性对于土体与结构相互作用系统的研究具有重要意义,结构周围土体性质与结构表面粗糙度是影响接触面力学性质的重要因素。为研究结构表面粗糙度对不同土体与结构接触面的剪切力学特性的影响,采用大型直剪试验仪进行了3种土体（红黏土、砂土与碎石土）与混凝土接触面剪切试验。通过在混凝土表面预制不同数量的规则半圆型凹槽来改变表面粗糙度,并采用灌砂法对混凝土表面粗糙度进行定量评价,研究粗糙度对不同类型接触面的剪切应力与剪切位移曲线以及强度参数的影响。结果表明：土体类型对接触面的剪切应力与剪切位移曲线形态具有较大的影响,红黏土与混凝土接触面剪切曲线表现为剪切软化型,砂土与混凝土接触面剪切曲线表现出理想弹塑性特征,碎石土与混凝土接触面剪切曲线主要表现为应变硬化型。粗糙度对接触面的剪切强度有着显著的影响,不同土体与混凝土接触面的剪切强度随粗糙度的增大均有明显提高,但法向应力的增大会弱化粗糙度对接触面剪切强度的影响。不同粗糙度条件下接触面的剪切强度与法向应力之间均存在着良好的线性关系,表明接触面的剪切破坏符合摩尔-库伦准则。粗糙度的增大能显著提高接触面的表观黏聚力,但对接触面内摩擦角的影响较小。     

节理倾角对单节理岩样变形破坏影响的数值模拟

采用FLAC模拟了节理倾角对各向异性岩样峰值强度、力学行为及剪切带图案的影响。节理由实体单元模拟。对于节理之外的岩石,采用莫尔库仑与拉破坏复合的破坏准则,峰后本构关系选择线性应变软化模型;对于节理,采用理想弹塑性的莫尔库仑准则。结果表明,无节理密实岩石的峰值强度最高。节理岩样的剪切应变或集中在节理上,或集中在新剪切带上,峰值强度随节理倾角而改变。新剪切带启动于节理的端部,然后沿其固有方向传播。当节理倾角适中时,节理岩样的峰值强度较低,岩样的行为受控于节理。当节理倾角较高或较低时,可观测到应变软化行为。若节理倾角较低,新剪切带的长度随节理倾角的降低而增加,这导致了陡峭的峰后应力-应变曲线。若节理倾角较高,由于节理倾角对新剪切带的厚度和倾角几乎没有影响,因此,峰后斜率不依赖于节理倾角。     

岩石节理剪切强度研究

利用断裂力学理论分析了纯剪切应力状态和双向压应力状态作用下节理模型的断裂机制。在已有的数值模拟和实验基础上,通过引入分形维数,推导了粗糙节理的摩尔-库仑剪切强度的改进公式。该公式的分析结果显示,节理尺度相对于岩体尺寸越大,节理的抗剪强度就越低,并且节理的抗剪切强度与分形维数的关系是一种非线性增长关系。     

高压力下界面抗剪强度的试验研究

在 DRS- 1型微机高压直残剪试验系统上进行了建筑砂、标准砂、粉砂和粘土与混凝土界面、金属光滑界面、金属粗糙界面的正交直接剪切试验 .研究结果表明 :在高压力作用下 ,由于颗粒破碎的原因 ,界面的剪切应力 -剪切位移曲线呈现出应变硬化特征 ,与低压力作用下土与不同结构界面的软化剪切特性存在明显差别 .试验数据的正交误差分析和直观分析揭示 ,界面的剪切峰值强度、残余强度与法向压力均呈现线性关系 ,峰值强度、残余强度受法向压力的影响最大 ,其次为土体性质 ,剪切速率和基底粗糙度的影响较小     

弃渣混合料与混凝土接触面剪切力学特性

为理清粗糙度、含石量、法向应力对灰质岩弃渣混合料与混凝土接触面剪切力学特性的影响，采用新型大型直剪仪对4种含石量的灰质岩弃渣混合料和5种粗糙度的混凝土面板分别在不同法向应力条件下进行系列接触面剪切试验，探究粗糙度、含石量、法向应力变化对接触面剪切强度的影响，揭示三者与接触面剪切力学特性的内在关联及接触面抗剪强度机制。结果表明：相同法向应力条件下，随粗糙度的增加，接触面抗剪强度呈现先增加后减小的趋势，且粗糙接触面能显著提高接触面的剪胀程度，但随法向应力的增加，粗糙度对接触面抗剪强度和法向变形的影响均减弱；相同法向应力条件下，随含石量的增加，接触面抗剪强度的变化规律与法向应力的大小密切相关。同时，试验数据分析表明接触面抗剪强度与Mohr-Coulomb强度准则高度吻合，且粗糙度和含石量对接触面表观黏聚力的影响相比对接触面内摩擦角的影响更为显著。合理的粗糙度和含石量能较大程度地提高弃渣混合料与混凝土接触面的抗剪强度。     

A modified model of a single rock joint's shear behavior in limestone specimens

The shear behavior of a single rock joint in limestone specimens,under a constant normal load(CNL),was analyzed in this study.Test specimens with different asperity roughness were prepared and tested.Goodman's model of a rock joint's shear behavior,under CNL,was modified to render a better representation of the data obtained.The model's applicability was validated.The proposed model showed better correlation with experimental data.It also,requires fewer variables.The steps to calculate all the necessary variables for the model are discussed.     

Macro and meso characteristics evolution on shear behavior of rock joints

Direct shear tests were conducted on the rock joints under constant normal load(CNL), while the acoustic emission(AE) signals generated during shear tests were monitored with PAC Micro-II system. Before and after shearing, the surfaces of rock joints were measured by the Talysurf CLI 2000. By correlating the AE events with the shear stress-shear displacement curve, one can observe four periods of the whole course of shearing of rock joints. By the contrast of AE location and actual damage zone, it is elucidated that the AE event is related to the morphology of the joint. With the increase of shearing times, the shear behavior of rock joints gradually presents from the response of brittle behavior to that of ductile behavior. By combining the results of topography measurement, four morphological parameters of joint surface, S p(the maximum height of joint surface), N(number of islands), A(projection area) and V(volume of joint) were introduced, which decrease with shearing. Both the joint roughness coefficient(JRC) and joint matching coefficient(JMC) drop with shearing, and the shear strength of rock joints can be predicted by the JRC-JMC model. It establishes the relationship between micro-topography and macroscopic strength, which have the same change rule with shearing.     

铝合金板混凝土界面的粘结滑移性能及其本构关系

铝合金板具有轻质高强、耐腐蚀性和延展性好等优点,是复杂恶劣环境中加固混凝土结构的理想材料。基于双剪试验进行铝合金混凝土界面粘结滑移性能研究,完成了45个构件的双面纯剪试验,得到了其破坏形态、荷载应变关系曲线、粘结界面剪应力分布曲线、荷载滑移关系曲线以及界面极限承载力,分析了不同的混凝土强度等级、铝合金板表面粗糙度、铝合金板粘结长度和粘结宽度条件下界面粘结滑移性能的演化规律。研究表明：加载过程中,界面应力从加载端向自由端逐步传递,且随着混凝土强度等级、铝合金板的粘结长度和宽度的增加,试件的剥离承载力也有所提高。但铝合金的粘结长度存在一个有效粘结长度值,超过该值试件的剥离承载力将不再增加,同时,铝合金表面粗糙度对试件剥离承载力的提高没有实质影响。通过测量铝合金板的应变得到了不同参数条件下铝合金板混凝土粘结滑移本构曲线,结果表明：铝合金板混凝土粘结滑移本构曲线存在明显的界面软化特征和非线性行为。     

岩石节理面剪切流变的试验研究

通过对龙滩水电站岩石节理样本进行快剪和剪切流变试验的比较研究，分析了节理面流变对剪切强度的影响及剪切蠕变机理，确定了节理面的长期抗剪强度，并从岩石理论模型出发，对试验数据进行了回归分析，建立了不同正应力作用下的剪切蠕变经验公式，以便于了解岩石材料在给定条件下的蠕变特性。     

直剪作用下不共面断续节理岩桥 破断试验与数值研究

在伺服控制剪切加载系统下对不共面类岩石断续节理试件进行正向、反向直剪试验,研究直剪下不共面断续节理的岩桥破断机理和剪切规律,试验研究发现,直剪作用下不共面断续节理岩桥破坏过程具有明显的阶段性,经历线弹性阶段、裂纹起裂扩展阶段、岩桥断裂贯通阶段、剪切面爬坡咬合阶段和残余摩擦阶段5个阶段,正向剪切下岩桥呈齿形破断面,反向剪切作用下岩桥产生沿直剪方向贯通的带形破断面,与正向剪切相比,反向剪切下节理的初裂抗剪强度和峰值抗剪强度较大,裂纹倾角、法向应力和相邻节理搭接比例是影响试件初裂抗剪强度和峰值抗剪强度的主要因素。采用FLAC3D对正向、反向直剪作用下不共面断续节理的岩桥破断、剪切破断面的形成过程进行数值试验,数值试验结果和类岩石直剪试件的试验结果基本吻合,数值试验揭示了直剪作用下不共面断续节理岩桥的拉裂破坏和破断面的剪切屈服机理。     

剪切速率对黏性土混凝土界面抗剪强度影响的试验研究

通过自行研制的大型恒刚度桩土界面直剪仪,进行6种剪切速率的黏性土混凝土界面剪切试验,探讨剪切速率对黏性土混凝土界面抗剪强度的影响规律。结果表明：在黏性土混凝土界面,超孔隙水压力随着剪切速率的提高而增大;法向应力和剪切速率通过影响超孔隙水压力大小,决定黏性土混凝土界面剪切峰值强度和剪切破坏位移的大小;剪应力剪切位移关系曲线由基本一致变化到一定范围内产生偏离,且法向应力和剪切速率越大偏离越显著,并出现明显的应变软化现象;剪切速率从0.4 mm/min增加至5.0 mm/min,黏性土混凝土界面抗剪强度减小幅度增大,摩擦系数减小0.1,有效黏着力的变化介于0.81~5.93 kPa之间。     

Preliminary Investigation of Copper Joints Soldered with Sn58Bi

In recent years, intensive studies have been carried out to find an alternative for Tin (Sn)-Lead (Pb) solder alloys with increasing demand over lower temperature solder alloys in current electronic packaging industry. High temperature operational solder alloys seem to produce drawback to other components on the printed circuit board (PCB). Low melting temperature Sn58Bi substrate as a potential replacement was investigated in this paper based on the melting properties, wettability, and shear strength. The Sn58Bi was soldered at a temperature below 200 ℃ on the Cu substrate, and the shear strength and contact angle were calculated. A peak temperature (melting temperature, TM) of 144.83 ℃ was identified. Single lap joint method was performed at a strain rate of 0.1 mm/min and an average shear strength of 23.4 MPa was found from three samples. The contact angle (wettability) was calculated to study the solder joint behaviour at reflow temperature of 170 ℃. The contact angle of the Sn58Bi was found to be 32.4 ° and considered to be desired value since the angle is less than 50 °. The low temperature soldering provides a preliminary result to allow further application on the real PCB.     

页岩烧结保温砌块砌体基本力学性能试验研究

通过对页岩烧结保温砌块砌体轴心抗压、沿通缝抗剪、剪压复合抗剪性能试验研究,分析其破坏特征和破坏机理。试验结果表明:页岩烧结保温砌块砌体受压破坏时,在竖向灰缝附近形成主裂缝,接近极限荷载时砌体出现表皮剥落现象;沿通缝抗剪破坏模式主要为单剪破坏,脆性明显;剪压破坏有剪磨、剪压和斜压3种类型;实测轴心抗压强度平均值高于规范值,沿通缝抗剪强度、复合抗剪强度平均值低于计算值,并分别给出砌体轴心抗压强度平均值、抗剪、剪压复合受力抗剪强度平均值建议公式;剪压复合抗剪强度随着压应力的增大而增大;建立了页岩烧结保温砌块砌体受压应力应变关系表达式;给出该类砌块的弹性模量和泊松比的建议值。     

钢纤维混凝土框架边节点的抗震性能

本文通过12个钢纤维混凝土框架边节点的试验,研究了这种节点的破坏过程、抗裂强度、抗剪强度及剪切延性等问题;给出了节点抗裂强度及抗剪强度的计算公式;并建议以剪切延性作为评价节点抗震性能的指标之一。     

剑麻纤维/砂土复合材料三轴剪切强度特性

为改善砂土的抗剪强度特性,针对剑麻纤维加筋砂土复合材料,通过一系列不固结不排水三轴试验,对不同纤维掺量、纤维长度和砂土干密度条件下剑麻纤维/砂土复合材料的剪切强度特性进行深入研究,并对剑麻纤维加筋机制进行分析。试验结果表明：复合材料中纤维相对含量改变时,初始刚度变化不大;适量的纤维掺量和纤维长度可以在砂体内形成三维网状结构,对比未加筋试样黏聚力显著提高,表明纤维加筋可有效提高砂土的抗剪强度;由于密度增加使得剪切过程中纤维与砂颗粒间的咬合和滑动摩擦力增加使复合材料抗剪强度显著提高;围压增加纤维与砂土界面有效接触面积导致砂土抗剪强度与峰值偏应力明显增强。采用剑麻纤维加筋砂土可增强砂土间界面作用力,明显改善砂土抗剪强度特性。     

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.     

漳州软土直接剪切蠕变特性及蠕变参数的研究

为了研究软土蠕变特性与蠕变参数的变化规律,对漳州软土进行不同固结压力下的直接剪切蠕变试验,并通过陈氏法处理蠕变试验数据。结果表明,漳州软土具有非线性蠕变特性,应力水平越高,非线性特征越显著。相同剪应力下,剪切模量G的最大值与稳定值随固结压力的增大而增大;相同固结压力下,剪切模量G的最大值与稳定值随剪应力的增大而减小。瞬时剪切模量G0与长期剪切模量G∞关系可通过G0=a t-b+G∞来确定。粘滞系数随剪应力的增大达到峰值,固结压力越大峰值体现越明显,峰值对应的剪应力也越大,这主要是微观结构随剪应力增大逐渐破损所引起的。得到漳州软土的C∞=6.71 kPa,φ∞=9.66°。剪切模量系数K=(0.424～0.56),长期强度与瞬时强度比值C∞/C=86.3%,φ∞/φ=72.4%,说明工程中需要考虑蠕变影响时,变形与强度参数应采用长期剪切模量与长期强度。研究结果对掌握软土蠕变参数变化规律,快速预测模型参数具有一定理论意义。