The effect of weathering on durability and deformability properties of granitoid rocks

In this paper, the effects of weathering on durability and deformability properties for three different types of granitoid rocks were investigated. Five weathering grades ranging from fresh to completely weathered rocks were considered for each rock type. Deformability has been evaluated based on failure strain, tangent and secant modulus. For measuring these parameters, at least five uniaxial compressive strength tests with axial strain recorded were conducted on each weathering grade. To assess the weathering effect on the durability behavior of these rocks, a slake durability test was performed up to 40 cycles. The obtained results indicated that uniaxial compressive strength and elastic modulus dramatically decrease with increasing weathering grade. After moderately weathering grade, remarkable damage was observed in the structure and fabric of considered rocks. The results from slake durability tests showed that the slake durability index for each weathering grade has a certain changes trend which can be used in determination of the weathering grade and the long-term durability assessment. Moreover, the results showed that for evaluation of the long-term durability of the mentioned rock types, at least eight cycles should be considered, while two cycles were sufficient for estimation of weathering grade.     

基于强度折减法的某路堑边坡开挖支护优化分析

以某山区高速公路路堑边坡工程为背景,通过PLAXIS有限元程序构建平面应变数值模型,借助程序内嵌的稳定性分析强度折减法,首先依据该边坡开挖现场揭露地层情况,对开挖稳定性及支护方案的加固效果进行了分析,可知对该边坡一、二级坡进行锚杆(索)框架加固即可满足整体稳定性要求;然后针对现场上覆强风化层厚度变化复杂,研究发现其对边坡稳定性的影响十分显著,可作为优化设计的主要研究对象;最后利用PLAXIS内置的参数敏感性分析功能,分析了强风化层和中风化层的强度参数c、φ值对边坡稳定性的影响,结果可确认,强风化层的c值对边坡稳定性影响最大。     

On the anisotropy of the athenian schist and its relation to weathering

The influence of schistosity on the strength of the “Athenian schist” when considering the anisotropy index as derived from point load testing, is examined. Furthermore, the influence of the degree of weathering upon the anisotropic characteristics of the schist is also investigated. Anisotropy index values are found to range between just below 1 and 3 approximately. Low anisotropy values correspond to rock in its very weathered state, higher values are related to less weathered material and there is also a trend for anisotropy to decrease towards sound rock conditions. Point load testing proved a reasonable means for assessing those rock characteristics associated with strength, anisotropy and weathering state, while slake durability testing showed considerable insensitivity towards the latter.     

Investigation of mechanical properties of soft rock due to laboratory reproduction of physical weathering process

The focus of the present study is on soft rocks (moderately weathered granite and artificial rock) that have suffered physical weathering due to changes in temperature and confining pressure. Unconfined compression tests were conducted on moderately weathered granite, and triaxial compression tests were conducted on artificial rocks. Two test plans were conducted to study the effect of weathering. In the first plan, the specimens suffered weathering process cycles under unconfined conditions, followed by triaxial tests with different confining pressures (0 kPa, 30 kPa, 60 kPa, and 90 kPa). In the second plan, the specimens suffered weathering process cycles under a certain confining pressure (0 kPa, 30 kPa, 60 kPa, and 90 kPa), and the shear strength and initial Young's modulus in each weathering cycle was then studied. Finally, based on the formula of the shear wave velocity and initial Young's modulus, the relationships between normalized shear strength and normalized shear wave velocity were found. These relationships can be used in a further study to understand rock strength on site by detecting the shear wave velocity.The results of this study show that artificial rocks (cement treated sand, CTS) can be used as a homogeneous material to simulate soft rock. In the stress-strain curves, the initial Young's modulus showed no significant change when increasing the confining pressure. The initial Young's modulus showed a nonlinear decrease when the weathering process cycle increased. When soft rocks suffer the weathering process at a certain confining pressure, the relationship between normalized shear strength and normalized shear wave velocity was linear. When soft rocks suffer the weathering process at different confining pressures, the normalized shear strength under a lower confining pressure dropped faster than when the confining pressure was higher.     

云母石英片岩片理面力学特征试验研究

云母石英片岩的矿物成分和微观结构决定了其各向异性特征,通过铸体磨片和电镜扫描试验,获得了云母石英片岩的矿物组成和微观结构特征;通过三轴剪切试验,获得了微风化岩样片理面力学参数;通过强风化和中风化岩块的点荷载试验,结合强风化岩样的片理面剪切试验,得出了强风化和中风化岩样的片理面力学参数;按照材料力学理论,采用片理面力学参数计算得出岩样的最小单轴抗压强度,进而计算得出岩样的各向异性系数;以垂直片理面的抗压强度作为计算依据,计算得出岩样的风化系数,进而总结出岩样的各向异性系数与风化系数的关系,揭示了风化过程中片理面力学特征的变化规律。     

《爆破安全规程》(GB 6722—2014)边坡岩体爆破振动速度安全允许值的理论探讨

开挖爆破诱发的地震波对岩质边坡有显著影响,我国《爆破安全规程》(GB 6722—2014)给出了边坡岩体的爆破振动速度允许值,但未明确说明取值的理论依据。为此,分析露天开挖爆破条件下邻近边坡岩体的附加动应力和质点振动速度场分布特征,推导以坡表质点振动速度表征的岩体附加动应力表达式。以边坡岩体不发生剪切和张拉破坏为控制要求,考虑边坡岩体分级特征和坡体结构特征,提出基于简单边坡模型的浅层岩体的爆破振动速度允许值。分析表明,岩体强度、边坡坡度、滑动面深度和地震波频率等均对边坡岩体的允许振动速度存在显著影响。其次,无剪切破坏条件下计算的爆破振动速度允许值与《爆破安全规程》(GB 6722—2014)的控制标准在量级上较接近,而无张拉破坏时各级岩体的爆破振动速度允许值差别不大,《爆破安全规程》(GB 6722—2014)中岩质边坡爆破振动控制标准应在理论分析和工程实践基础上进一步细化。     

Impact of weathering on slope stability in soft rock mass

Weathering of soft rocks is usually considered as an important factor in various fields such as geology, engineering geology, mineralogy, soil and rock mechanics, and geomorphology. The problem of stability over time should be considered for slopes excavated in soft rocks, in case they are not protected against weathering processes. In addition to disintegration of material on slope surface, the weathering also results in shear strength reduction in the interior of the slope. Principal processes in association with weatherinz are discussed with the examnles of marl hosted on flvsch formations near Solit. Croatia.     

某边坡抗滑桩失效机理研究

采用二维有限元强度折减法,分析了基坑开挖、抗滑桩桩径、桩长和强降雨等因素对某边坡稳定安全系数、最大剪切应变和抗滑桩最大弯矩的影响.通过类比分析表明,该边坡抗滑桩失效原因是由基坑开挖、抗滑桩桩长太短和强降雨等因素共同促成;在此边坡工程岩层情况下,当抗滑桩桩长达到18 m以上时,最大剪切应变可以控制发生在中风化泥岩以下,而且不会对上部坡体产生较大剪切变形;采用有限元强度折减法计算出来的抗滑桩弯矩图和传统的悬臂桩法计算的结果接近,且和工程上采用经验法计算出的抗滑桩弯矩图近似.本文的分析方法和分析结果可以为以后边坡抗滑桩设计提供一定借鉴意义,也为基坑开挖后果的预测提供可行的研究方法.     

润扬大桥风化花岗岩工程特性与影响因素研究

由于风化会对岩石强度、刚度和耐久性产生重大影响，故在岩石工程勘察设计中需对其进行重点研究。风化是润扬大桥花岗岩类基岩岩体质量和桥基选址与设计的控制因素之一。系统的地质分析和多种测试结果表明，桥区风化壳厚度的变化很大，岩性以及地壳升降、断裂切割、卸荷作用、江水下切与入渗等地质作用是控制花岗岩风化作用及其风化岩分布的主要因素；桥区花岗岩易风化、卸荷敏感，处于化学风化的早期阶段：细密的蚀变裂隙对岩石强度起着控制作用。在此基础上讨论了风化带来的主要岩土工程问题以及桥型方案、基础选址与设计、地基参数取值以及风化因素控制等方面的工程对策。     

红层软岩环境下某站场高填方工程设计

红层软岩是一种特殊岩土,具有抗压强度低、易风化、遇水易软化、崩解、膨胀、填筑密实度对含水量很敏感等特点,大量的红层地区填料工程实践表明,红层地区软岩填料在填方工程中引发的边坡病害问题非常严重.论文结合工程实例,对这类填方工程的填筑工艺和边坡防护设计进行分析探讨,总结相应工程经验,以供类似工程参考.     

粘土矿物与斜坡失稳

作为微米级材料，粘土矿物的单晶尺寸及特殊晶体结构使其集合体-粘土呈现低渗透性、分散-凝絮性及粘滞性等重要工程特性。除沉积岩斜坡含粘土矿物外，76％以上的斜坡岩石造岩矿物还可形成次生粘土矿物。粘土矿物广泛分布于原生沉积岩、三大岩类风化带及第四系松散堆积物构成的斜坡中。泥屑岩因含粘土矿物而易于失稳，且水稳定性差。次生粘土矿物的形成将引起源矿物、矿物集合体及岩块的强度与变形特性的显著变化，诱发岩石向松散介质转化。宏观结构面是粘土矿物最主要的形成和聚集场所，结构面及其内侧一定范围内不同成因粘土矿物的淀积将导致结构面及岩体强度的衰减。粘土矿物是滑坡滑带的常见矿物组分；粘土滑带可以在滑体与滑床之间起到润滑作用。滑带中粘土矿物的含量越多，其润滑效应越显著。粘土型滑带还具有隔水边界之功效，可将滑体与周围介质隔离，使之成为独立水文地质单元，提高坡体拦截、吸收渗入水的能力及斜坡稳定对降雨过程的敏感度。粘土矿物可以促进斜坡时效变形，甚至成为斜坡破坏的关键因素，对斜坡演化及失稳的贡献是显著的。     

Engineering geological properties of weathered swelling mudstones and their effects on the landslides occurrence in the Yanji section of the Jilin-Hunchun high-speed railway

To identify the mechanisms that caused landslides during the construction of the Jilin-Hunchun high-speed railway line in Yanji, China, the engineering properties of weathered swelling mudstones extracted from a representative landslide site were investigated. The experimental results indicate that both yellow-brown and magenta mudstones exhibit significant swelling and shrinkage behaviour due to significant amounts of swelling clay minerals. The yellow-brown mudstone has an obvious schistose structure with stacked flaky plates interconnected with a face-to-face pattern, while the magenta mudstone has an aggregated structure cemented by iron oxides. Both mudstones are prone to disintegration when soaked in water. The shear strengths of swollen samples decrease dramatically compared with those of unsaturated samples, and the lower the initial water content is, the smaller the shear strength of a sample after swelling. By repeatedly increasing the repeated drying-wetting-freezing-thawing cycles, the shear strength decreases. According to the experimental findings, the effects of the engineering properties of mudstones on the landslides occurrence in the Yanji section are discussed. Heavy rainfall and the weathering of mudstones induced by fluctuating climatic conditions are regarded as the principal factors that triggered the landslides. Given the high landslide incidence on south-facing slopes, the influence of slope orientation on the stability of mudstone slopes is studied and discussed.     

改扩建公路岩质高边坡爆破开挖稳定性分析

为研究不同爆破开挖方式对岩质高边坡稳定性的影响,依托京沪高速公路改扩建工程,建立岩质高边坡爆破荷载时程曲线,研究了边坡采用同时起爆和微差爆破两种起爆方式的动力响应特征,对比分析了两种起爆方式的安全系数以及质点速度变化规律。结果表明:采用修正的爆破荷载常量B计算等效爆破动载的方法,研究爆破作用下的岩质高边坡的稳定性是合理可靠的; 采用微差爆破边坡稳定性较高,边坡的安全系数随等效爆破动荷载的施加呈现出递减的周期性变化,在等效爆破动荷载F达到最大值F_max和0.6F_max时所对应的安全系数为极小值点; 各质点的速率变化与爆破动荷载的施加有同步变化,随着质点距爆破区的距离增加,规律逐渐减弱,仅在最大值附近出现峰值振动,而同时起爆的各质点的速率要大于微差爆破,不利于边坡开挖,各测点之间的峰值依次出现了递减和滞后的现象; 采用微差爆破在爆破区附近出现了应力集中现象,局部剪应力大于岩体的抗剪强度,产生剪切破坏,爆破前后的位移监测差值较小,取得了良好的松动作用,岩体出现局部裂隙,应注意后期及时支护。     

某核电站强风化花岗岩原位直剪试验研究

强风化花岗岩在某核电站厂址区普遍发育,研究其剪切强度对于核岛边坡及常规岛地基的稳定性评价具有重要意义。由于该岩体风化不均匀,常夹有中等风化及微风化较硬夹层或球状风化体,扰动后即碎裂,现场取样和室内试样的难度较大,而且目前进行岩体强度参数反分析的资料相对匮乏。本文作者通过设计堆载式加荷直剪试验方法,并经野外大量现场试验,获得了强风化花岗岩原位直剪的剪应力—应变关系曲线,对强风化花岗岩的剪切强度性质进行了相应的理论分析,为工程区强风化花岗岩设计输入提供了可参考的c、φ值,保证了工程的可靠性,也避免过于保守,并为类似工程积累了经验。     

含倾斜强风化带及局部边坡复杂场地的动力响应及破坏模式研究

 基于大型振动台模型试验,研究了含倾斜强风化带及局部边坡场地在地震波作用下的动力响应特征,同时结合边际谱理论分析、土层内部应变和边坡位移规律,探究了场地内部的损伤发展过程。试验结果表明：模型加载El Centro地震波时,基岩和基覆内加速度放大系数随高程增加而增大,当加载地震波幅值大于0.33 g时,输入幅值越大,加速度放大越小;强风化带处加速度峰值削弱明显,加载幅值越大,削弱程度越大。模型加载3 Hz正弦波时,边际谱能量识别显示场地损伤从平台与局部边坡拐角下的强风化带开始,此后局部边坡底部强风化和平台中部下的强风化带出现损伤,平台与局部边坡拐角处强风化带的损伤逐渐与顶部损伤贯通;土层应变、坡面位移规律印证了场地损伤的发展过程;由破坏现象、边际谱损伤发展分析、土层应变及边坡位移规律可知,该含倾斜强风化带场地的破坏模式表现为拉裂–剪切–滑移以及拉裂–剪切–破碎2种破坏模式。     

柏叶口水库坝址基岩风化的综合判定

通过勘察研究,阐述了工程场区岩体风化类型及岩体强风化带、弱风化带、微风化带在空间上的分布及其规律,分析了岩体风化波速比Kw、岩体完整性系数KV和RQD值之间的相关性,确定了综合划分工程场区岩体风化带的定性和定量指标。     

典型红层软岩软弱夹层剪切蠕变性质研究

 红层软岩边坡岩体中软弱夹层发育且具有蠕变性,很多边坡岩体的失稳破坏都是沿软弱结构面的滑移失稳,软弱夹层剪切强度参数的选取是边坡工程勘察中的关键问题。通过2个典型红层软岩边坡工点软弱夹层样品室内剪切蠕变试验研究,表明红层软岩软弱夹层具有显著的蠕变特性,在边坡剪切强度参数选取中应考虑软弱夹层蠕变的影响。通过软弱夹层长期强度与短期强度试验资料分析,建议软弱夹层长期剪切强度可取短期剪切强度的75%。     

Stability analysis of stratified rock slopes with spatially variable strength parameters: the case of Qianjiangping landslide

Jurassic strata prone to slope failure are widely distributed in the Three Gorges Reservoir region. The limit equilibrium method is generally used to analyze the stability of rock slopes that have a single failure plane. However, the stability of a stratified rock mass cannot be accurately estimated by this method because different bedding planes have variable shear strength parameters. A modified limit equilibrium method is presented with variable water pressure and shear strength used to estimate the stability coefficient of a sloping mass of stratified rock and to identify the potential sliding surface. Furthermore, an S-curve model is used to define the spatial variations of the shear strength parameters c and ? of the bedding plane and the tensile strength of the rock mass. This model can also describe the variation of strength parameters with distance from the slope surface, which depends on the reservoir water level. Also, it is used to evaluate the stability of the Qianjiangping landslide, located at Shazhenxi Town, Zigui County, Three Gorges Reservoir area, China. The results show the most probable sliding surface is the interface between a slightly weathered layer and subjacent bedrock. When reservoir water rises above the elevation of the slide mass toe, the stability coefficient of the slope declines sharply. When the reservoir water level is static at 135 m, the stability coefficient decreases gradually as the phreatic line changes as a result of heavy rainfall.     

水电岩质边坡的稳定性概率分级方法研究

 引入荷兰学者R. Hack等[1-3]提出的边坡稳定性概率分级(SSPC)方法,针对该方法在水电边坡稳定性评价中存在的两个局限性：一是仅适合于45 m以下边坡的稳定性评价和对完整岩石抗压强度的估计主观性和随意性较强,提出采用Hoek-Brown经验强度准则和边坡最大坡高经验公式,对SSPC方法中边坡岩体的抗剪强度和最大坡高进行修正。典型水电边坡实例的研究结果表明,SSPC修正方法对34个水电边坡稳定性评价的准确率为61.8%,对10个非构造性控制破坏的水电边坡稳定性评价的准确率达80%。SSPC修正方法对于水电岩质边坡的稳定性概率分级具有较好的适用性,可以为水电岩质边坡的稳定性快速评价提供一条新的途径。     

The effects of discontinuity surface roughness on the shear strength of weathered granite joints

Surface roughness is one of the most important parameters governing the shear strength of rock discontinuities. Roughness types may vary based on genesis, physico-mechanical, and mineralogical properties of rocks. In this study, granite samples representing three different weathering degrees were selected to evaluate the effects of surface roughness and weathering degree on shear strength. To this aim, we determined the profile roughness coefficient (PRC), profile roughness angle (PRA), and joint roughness coefficient (JRC) for the selected fresh and weathered granite joint samples. Values of PRC were in the range of about 1.043–1.073, and PRA and JRC varied in the ranges of 16.67–21.45 and 12–18, respectively. Weathering led to the increment of joint surface roughness of the selected granitic joints due to the higher resistance of quartz crystals in the weathered matrix. However, the increment in surface roughness did not result in an increase in the shear strength. On the contrary, the shear strength of discontinuities dramatically decreased.