Stress ratio effect on fatigue life of tropically weathered rock

This paper investigates the fatigue life of weathered granite and weathered sandstone using a stress ratio of R = 0.17. A small stress ratio is adopted to control data discrepancy between weathered rocks for which stress amplitude is known to affect the fatigue life. The range of varying static strength between weathered rocks, especially for highly weathered rock (grade IV) which has lower static strength, resulted in adopting this small stress ratio. The details of rocks tested, including microscopic petrographic characterization as well as their physical properties obtained from laboratory work, is also explained in this paper. Weathered rock specimens from slightly weathered to highly weathered (grade II, grade III and grade IV) granite and sandstone were used during the investigation. The specimens were representative of rock collected in Sungai Buloh (granite) and Puncak Perdana (sandstone) in Selangor, Malaysia. In order to eliminate the influence of frequency and waveform, all rock specimens (54 in total) were tested under a cyclic compression load with a frequency of 1 Hz using a constant sinusoidal waveform. Result shows that grade IV specimens are the least affected by the small cyclic stress ratio as compared to grade II and grade III specimens. The number of cycles to failure is not dependent on rock weathering grade; it is greatly related to the petrological and microstructure of the individual rock. However, the weathering degree of a rock does contribute to the weakening of the rock's structure, consequently affecting the life of the rock.     

基于微观矿物含量的灰岩细观参数标定研究

随着对岩体力学研究的深入,宏微观岩体力学的研究方法发展迅速。但岩体微观性质改变对引起岩体宏观力学各向异性行为的影响研究却较为缺乏,而在离散元分析方法中,岩体宏观力学行为的准确表征不仅需要合理的细观强度参数,也需要考虑岩体中微观矿物的成分和含量。以灰岩为研究对象,制作灰岩薄片标本,用偏光显微镜观察灰岩样本以确定矿物成分及含量,并以此为依据生成基于矿物含量的离散元模型,以接触软化接触模型模拟矿物间的细观力学行为。分别建立与室内试验对应的单轴压缩模型和巴西劈裂模型,使用试错法不断调整细观强度参数,最终使细观模型表现出的宏观力学性质与实际情况一致。研究结果表明,数值模拟得到的宏观参数与室内试验结果相吻合,说明基于微观矿物含量的岩体离散元模型参数标定方法能够很好地标定出颗粒的细观强度参数,同时细观强度参数又能够很好地表征岩体宏观力学强度,以该参数作为岩体力学响应分析的输入参数,能够更准确认识岩体的力学行为。     

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。     

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.     

Weathering indices and their applicability for crystalline rocks

In the recent past, several weathering indices have been proposed to characterize the extent of weathering and weatherability depending upon the nature and requirement of the study. The weathering index provides a quantitative measure of the extent of weathering of rock; hence it can provide input to the prediction models to assess the strength and deformational properties of rocks and classifications of weathered rock material. In the present study some of the important weathering indices, broadly categorized as chemical, (micro) petrographical and engineering weathering indices, are reviewed and studied experimentally for three common rocks of India, namely granite of Malanjkhand, basalt of Nagpur and quartzite of Delhi, along with results of other rocks reported by other researchers. The study reveals that none of the existing chemical weathering indices is valid for genetically different common rock types and useful for engineering purposes. However, loss on ignition (LOI) may provide an approximate estimation of altered minerals (clays and hydroxides) in tested rocks. It has also shown good correlation with petrographic indices and engineering index properties. Among the petrographic indices, crack density (ρ_cr) and unsound constituent (an input to the micropetrographic index) indices provide good correlation with engineering index properties. To quantify the extent of weathering in terms of strength degradation due to weathering in rock, an index is suggested – strength ratio (R_s) – which is the percentage of uniaxial compressive strength (σ_c) of weathered rock with respect to σ_c of fresh rock. Its significance is shown statistically through the relationships with other indices for several rock types including sedimentary and metamorphic rocks. Electronic Publication     

泉州地区花岗岩残积土地质特征与岩土工程评价

泉州地区广泛分布的花岗岩残积土,由变质-混合岩、酸性-中酸性火山岩和花岗岩风化而成,是一种成分复杂、物理力学指标变化区间很大的特殊性土体,其工程性质主要受母岩及其风化程度的影响,与风化残积物中的成分、结构,特别是粗颗粒含量关系密切,并具有随深度规律变化的特征。本文所称的花岗岩属花岗岩类岩石,包括变质-混合花岗岩、酸性-...     

Classification of geological and engineering properties in weak rock: a case study of a tunnel in a fault zone in southeastern Korea

Given that the rock mass classifications of weak rocks observed in tunnels are evaluated only as ‘poor rock mass’ or grades IV–V using existing rock mass classification methods, a new scheme is needed that would better distinguish the various geological properties of weak rocks. In this study, geological and engineering properties of weak rocks were classified based on the analysis results of a total of 55 faces in a tunnel that passes through a fault zone in southeastern South Korea. Geological observations, point load tests, and Schmidt hammer tests were conducted to analyze the properties of the weak rocks. Through this analysis, the weak rocks were classified into two weathering types: ‘disintegrated rocks’ and ‘decomposed rocks’. This division is based on the tectonic mechanisms and parameters necessary to determine the engineering geological properties of individual rock-weathering types according to their geological properties. The ‘disintegrated rocks’ have been physically weathered by brittle deformation and are classified into three subtypes using the rock quality designation (RQD) and joint set number (J_n), which can characterize the discontinuity properties of the rocks. Point load tests were conducted on these individual subtypes to calculate the point load index (Is₍₅₀₎). The resultant values are clearly related to the assigned three subtypes. The ‘decomposed rocks’ have been chemically weathered by ductile deformation and are classified into five subtypes based on the results of Schmidt hammer tests conducted on faces and Is₍₅₀₎ values calculated using the average of the Schmidt hammer values. The geological properties of the individual subtypes of the ‘disintegrated rocks’ and ‘decomposed rocks’ are clearly related to their engineering properties. Based on these results, rock mass classification diagrams are proposed that can be simply and easily applied to weak rocks.

     

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。     

Influence of weathering on the engineering properties of Harsit granitic rocks (NE Turkey)

Weathering and hydrothermal alteration of the granitic rocks in the Eastern Black Sea Region (NE Turkey) are important phenomena affecting the engineering projects in the region. The study investigated the probable paths of rock-forming mineral transformations due to weathering in the Harsit granitoid rocks, the changes of the major oxides as a consequence of weathering and the effects of weathering on the engineering properties. To identify the changes in the major oxides, the volume concentrations were considered in relation to the dry density. Chemical leaching during weathering was shown to be significant in changing the minerals. It was concluded that the engineering properties of the weathered granitic rocks can be most reliably predicted by P-wave velocity.      

试验设计法在硬岩PFC~(3D)模型细观参数标定中的应用

利用试验设计法针对硬质岩体颗粒离散元数值研究中的细观参数标定问题进行了研究。首先利用Plackett-Burman试验设计分析了细观参数对宏观响应的敏感性,并建立了宏观力学指标和细观参数之间的线性关系,然后利用响应曲面法考查了显著影响参数之间的相互作用,得到了宏观响应与细观参数之间的非线性关系。最后将问题转化为非线性多目标数学规划问题利用MATLAB软件中FGOALATTAIN函数进行求解。通过和典型硬岩物理试验结果对比发现,利用试验设计法标定参数建立的颗粒离散元模型可以很好地反映单轴和低围压下岩石的破坏过程,但是由于采用了球形颗粒对于高围压下的拟合效果偏弱。利用PB设计、响应曲面法并结合数学规划建立的细观参数标定方法可以反映各细观参数对宏观力学响应的敏感性并给出明确的函数表达式,同时可以通过增加求解过程中的约束条件来体现更多的岩石力学特性。     

Deep weathering of a group of thick argillaceous limestone rocks near Three Gorges Reservoir,Central China

Rock mass characterization is one of the most basic and important tasks in rock mechanics and engineering. Literature review indicates that although there are many publications available on weathered rocks, there are few reports in English on weathered argillaceous limestone rocks and their chemical and mechanical properties. This paper presents a case study of characterizing a group of highly weathered thick argillaceous limestone rocks. Most importantly, they can be easily and quickly decomposed into soils after they are exposed due to excavation. Consequently, they would substantially lose their mechanical strengths. Geohazards such as landslides and sinkholes could occur in uncovered highly weathered argillaceous limestone rocks. The problematic weathered rocks were found during the development of a new town in upper mountains above the Three Gorges Reservoir on Yangtze River in Central China in the past 20 years. The factual data are presented on the changes of chemical compositions and mechanical properties of the weathered argillaceous limestone rocks due to chemical weathering. Some empirical correlations are given to quantify the changes in their uniaxial compressive strength and deformation moduli in terms of their contents of calcium carbonate. The data and findings presented in the paper can be useful to future urban development in geologically poor mountainous environments occupied by highly weathered argillaceous limestone rocks in the world.     

A study of the weathering of the bukit timah granite part a: Review,field observations and geophysical survey

The Bukit Timah granite exhibits a full range of weathering grades. Examination of these exposures shows that the weathering has been rapid. Field observations and geophysical surveys show that the rock has been weathered up to 70 meters depth, and that the main mechanisms of weathering is chemical decomposition. The humid tropical condition in Singapore with high annual precipitation has produced secondary weathering of the residual soil. The weathering profiles suggest that the weathering of the Bukit Timah granite is stratified with weathered layers and a sharp boundary between the residual soil and the slightly to moderately weathered granite. This paper (Part A) is a review of current weathering classification systems for weathered rock. Some results from field observations and geophysical surveys are also presented in the paper. A weathering classification and determination method is proposed for the Bukit Timah granite. Results from field and laboratory investigations of the weathering of the granite and material properties will be presented in Part B.     

基于不规则颗粒离散元的土石混合体大三轴数值模拟

在基于CT扫描的不规则颗粒三维离散元精细建模技术的基础上,提出了一种不规则块石三维离散元模型随机生成技术,并建立了符合宏观统计规律的土石混合体三维离散元模型。进行了含石量为0,10%,30%,50%,70%,90%的土石混合体大三轴试验数值模拟研究,对各种含石量下土石混合体的力学特性和变形破坏机理进行了深入地分析探讨。结果表明:随着含石量的增加,试样峰值强度、残余强度、弹性模量和破坏应变逐渐增大,剪缩性减小,剪胀性增强;加载初期,微裂纹主要在块石颗粒与土颗粒之间形成,发展速度很快,而后则主要在土颗粒间形成和扩展,含石量越大,块石周围微裂纹比例越高,局部剪切带越不规则,分布也越分散;高含石量(70%,90%)的土石混合体在加载初期即有比较明显的相互摩擦,随后块石相互接触、咬合与相对摩擦、滑移交替出现。     

Use of electrodeposition to realise the crack-healing and pore-filling of weathered rock: A small specimen case

Medium- to long-term weathering phenomena is one of the major causes of rock instability. Although many geo-protection technologies have been developed to mitigate the hazards such as slope failures of natural rock weathering, these techniques provide no self-healing function of the rock around the facilities. The status quo in rock instability problems is to provide rock maintenance and to constantly monitor the situation depending on the particular conditions. Improper rock maintenance comes with the risk of critical accidents which may result in human casualties as well as significant environmental destruction. It is therefore necessary to develop novel techniques to realise the continuous healing of weathered rock in the medium- and long-term. In this study, the electrodeposition method was applied for the first time to heal weathered rock mass in a series of fundamental experiments, using volcanic tuff sampled in Japan as the weathered rock model. It was noted that a reduction reaction occurs around the cathode side, and the electrodeposits fill the pores and cracks in the rocks selectively, thereby improving the surface hardness in a small specimen scale. Moreover, the application of a weak current over a lengthy period was shown to facilitate the deposition of stable crystals, such as calcite and magnesian calcite. The results of this study on electrodeposition on unstable rock formations show the potential of crack-healing and pore-filling in a self-organised manner.     

Distinct element analysis for Class II behavior of rocks under uniaxial compression

In this study, the radial strain control method for uniaxial compression tests was introduced in the distinct element method (DEM) codes and the Class II behavior of rocks was simulated. The microscopic parameters used in the DEM models were determined based on laboratory uniaxial compression tests and Brazilian tests carried at Äspö Hard Rock Laboratory, Sweden. The numerical simulation results show good agreement with the complete stress–strain curves for Class II obtained from the laboratory experiments. These results suggest that the DEM can reproduce the Class II behavior of the rock successfully. The mechanism of the Class II behavior was also discussed in detail from the microscopic point of view. The loading condition and microscopic structure of rocks will play an important role for the Class II behavior.     

Comparison of the static and dynamic elastic modulus in carbonate rocks

Young’s modulus is one of the most important mechanical parameters in building materials used to assess both the appropriateness of a material as well as its mechanical stability. The paper reports a study to predict the elastic modulus for ten carbonate rocks using the ultrasonic technique. The rocks varied from homogeneous limestones to rocks with abundant stylolite, veins and fissures and were subjected to both salt crystallization and thermal weathering tests in order to modify the number and features of their discontinuities. The dynamic and static elastic moduli were measured in both weathered and unweathered samples. The results confirmed the poor relationship between the static and dynamic moduli for the studied rocks. A new equation is proposed which uses both dynamic elastic modulus and spatial attenuation of compressive waves to provide an accurate prediction of static Young’s modulus. As spatial attenuation is highly sensitive to the presence of rock defects, the correlation is very useful for rocks with fractures, voids and/or which have suffered weathering.     

岩体尺寸效应及其特征参数计算

 岩体的尺寸效应包括完整岩块的尺寸效应与节理岩体的尺寸效应,但两者之间还缺乏有机联系。基于物理力学试验与细观参数统计分布理论,建立试样尺度的随机概率模型。通过统计宏观节理分布,建立包含随机分布节理的岩体尺度模型。将实验室获得的岩块强度应用于岩体的计算中,提出一种从细观层次、宏观层次的多尺度岩体工程计算方法,建立2种尺度效应的联系。最后,就非均匀性、围压与节理密度对岩石尺寸效应的影响问题展开探讨。随着均值度的增加,试样的特征尺度逐渐减小。随着围压的增大,岩体特征强度逐渐增大,而岩体力学参数的特征尺寸增大不明显。随着节理密度的增大,特征尺寸和相应的特征强度都是减小的。本方法试图建立细观与宏观力学参数之间的桥梁,获得岩体计算的力学参数,为解决工程岩体参数取值与计算提供一条思路。     

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.     

Applicability of the geological strength index (GSI) classification for very weak and sheared rock masses. The case of the Athens Schist Formation

 The Athens Schist Formation includes a wide variety of metasedimentary rocks, varying from strong or medium strong rocks such as sericite metasandstone, limestone, greywacke, sericite schist through to weak rocks such as metasiltstone, clayey and silty shale and phyllite. The overall rock mass is highly heterogeneous and anisotropic owing to the combined effect of advanced weathering and severe tectonic stressing that gave rise to intense folding and shearing followed by extensional faulting, which resulted in highly weathered rock masses and numerous shear and/or mylonite zones with distinct downgraded engineering properties. This paper is focused on the applicability of the GSI classification system to these highly heterogeneous rock masses and proposes an extension of the GSI system to account for the foliated or laminated weak rocks in the lower range of its applicability. Received: 5 March 1998 · Accepted: 13 July 1998