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。     

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.     

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     

Experimental relation between shear strength under low pressure and S-wave velocity of rock subjected to mechanical weathering

The reduction in the shear strength of rock exposed on slope surfaces due to mechanical weathering is a ubiquitous phenomenon in regions where extreme environmental conditions prevail, i.e., repeated changes in temperature and moisture. In dealing with the slope instability problems in such regions, the long-term effects of weathering on the strength, deformation and durability characteristics of exposed rock are envisaged in this study. Therefore, in addition to conducting multiple-cycle standard slake durability tests on rock samples taken from the lithologies of Pakistan and Japan, and on artificial soft rock, the decrease in strength and stiffness is also studied by reproducing mechanical weathering in the laboratory. The reproduced laboratory weathering (RLW) is conducted with a new device that enables vacuumed saturation, freezing, thawing, drying and cooling under a maintained level of confining pressure. The decrease in strength, stiffness and durability is elucidated from the test results, which indicate that rock having a very low level of reference strain (shear strength/modulus at small strain) is resistant to RLW and slaking. Intact rock exhibits very low reference strain and this reference strain increases with an increase in the degree of weathering, which is the case of weathered rock. The decrease in the strength of rock is an important property for judging the safety of rock slopes undergoing weathering. Thus, the relation between the strength and the S-wave velocity of rock undergoing weathering is established. The authors recommend the use of this relation for a quick assessment of the strength of rock by briefly measuring the S-wave velocity of the weathered surface layer. The relationship will assist practitioners in quickly screening potentially unstable slopes.     

Anisotropy effect on strengths of metamorphic rocks

This paper aims to study the effect of anisotropy on strengths of several metamorphic rocks of southern(Cine) submassif of Menderes metamorphic massif in southwest Turkey. Four different metamorphic rocks including foliated phyllite, schist, gneiss and marble(calcschist) were selected and examined.Discontinuity surveys were made along lines for each rock and evaluated with DIPS program. L-type Schmidt hammer was applied in the directions parallel and perpendicular to foliation during the field study. Several hand samples and rock blocks were collected during the field study for measurements of dry and saturated densities, dry and saturated unit weights and porosity, and for petrographic analysis and strength determination in laboratory. L-and N-type Schmidt hammers were applied in the directions perpendicular(anisotropy angle of 0°) and parallel(anisotropy angle of 90) to the foliation on selected blocks of phyllite, schist, gneiss and marble(calcschist). The phyllite and schist have higher porosity and lower density values than the other rocks. However, coarse crystalline gneiss and marble(calcschist) have higher rebound values and strengths, and they are classified as strong-very strong rocks. Generally, the rebound values in the direction perpendicular to the foliation are slightly higher than that in the direction parallel to foliation. Rebound values of N-type Schmidt hammer are higher than the L-type values except for phyllite. Sometimes, the rebound values of laboratory and field applications gave different results. This may result from variable local conditions such as minerals differentiation,discontinuities, water content, weathering degree and thickness of foliated structure.     

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.     

The geological strength index: applications and limitations

The geological strength index (GSI) is a system of rock-mass characterization that has been developed in engineering rock mechanics to meet the need for reliable input data, particularly those related to rock-mass properties required as inputs into numerical analysis or closed form solutions for designing tunnels, slopes or foundations in rocks. The geological character of rock material, together with the visual assessment of the mass it forms, is used as a direct input to the selection of parameters relevant for the prediction of rock-mass strength and deformability. This approach enables a rock mass to be considered as a mechanical continuum without losing the influence geology has on its mechanical properties. It also provides a field method for characterizing difficult-to-describe rock masses. After a decade of application of the GSI and its variations in quantitative characterization of rock mass, this paper attempts to answer questions that have been raised by the users about the appropriate selection of the index for a range of rock masses under various conditions. Recommendations on the use of GSI are given and, in addition, cases where the GSI is not applicable are discussed. More particularly, a discussion and suggestions are presented on issues such as the size of the rock mass to be considered, its anisotropy, the influence of great depth, the presence of ground water, the aperture and the infilling of discontinuities and the properties of weathered rock masses and soft rocks.     

A study of the weathering of the Bukit Timah granite Part B: Field and laboratory investigations

Field investigations consisting of surface seismic refraction and electrical resistivity surveys, drilling and downhole geophysical logging of the rock mass and of the residual soil indicate that the weathering of the Bukit Timah granite has been rapid and is primarily caused by chemical decomposition due to the tropical climate in Singapore. The granite is usually overlain by a thick layer of residual soil. Laboratory tests indicated a large reductions of the material strength, the modulus of elasticity, the rock mass quality and other mechanical properties of the weathered granite. Apart from the mechanical properties of the residual material and/or of the weathered granite rock, physical properties including density, water content, Atterberg's limits, grain size distribution, permeability, sonic velocity and electrical resistivity were also studied in order to assess the weathering grade and the weathering processes.     

峨眉山玄武岩岸坡深部差异风化岩体特征及成因

西南地区某水电工程的峨眉山玄武岩,其岩体风化具有特殊性,存在岸坡内部（或深部）岩体风化局部加强的特殊现象（称为差异风化）。该差异风化岩体在表观特征、分布特征、化学特征及形成环境上具有与岸坡表部一般风化岩体不同的显著特征。以该处差异风化岩体发育分布规律为基础,结合其化学特征、河谷演化过程及浅生改造理论分析其成因机制。研究表明：差异风化不具随水平深度增大风化逐渐减弱特征,分布受长大张性结构面控制,表现为局部的裂隙式风化加剧,张性结构面两侧 5 ～ 15 cm 范围内岩体红度增加;差异风化岩体发生了化学风化,但并未发生明显的脱硅富铝与盐类淋失迁移,仅表现为二价铁减少、三价铁富集;控制性结构面具浅生改造特征,差异风化岩体赋存于浅生结构所形成的相对封闭空间;浅生改造正是导致差异风化岩体形成的根本原因。     

A field index to determine the strength characteristics of crushed aggregate

The suitability of a simple technique to determine the strength characteristics of aggregates is reviewed. The results indicate that the strength characteristics of aggregates – in terms of crushing, impact and abrasion values – can be estimated and predicted from simple and quick tests for rock strength such as the Schmidt hammer and point load. The rocks and aggregates used in this work were of igneous, sedimentary and metamorphic origin and of different types, ages and degrees of weathering. More than 110 rocks and aggregate samples were tested according to British Standard and ASTM. The laboratory tests included the Schmidt hammer and point load for rock material while the crushing impact and Los Angeles abrasion test were undertaken on the aggregates. Regression analyses were performed and empirical relationships between the strength of rocks (in terms of their compressive strength and point load indices) and aggregates (in terms of their crushing, impact and abrasion values) were developed. Relatively strong relationships were obtained between the compressive strength of the rock and the crushing and impact value of the aggregate, while moderately strong relationships were obtained for the Los Angeles abrasion values. Electronic Publication     

基于纵波波速的块状岩体GSI系统

 为减少目前GSI系统对现场地质观察的依赖程度,降低其应用难度,且使其能更加准确地反映一定深度范围内的岩体特性,根据现有研究成果与GSI系统输入参数的定性、定量对应关系,建立基于纵波波速的GSI系统,据此获得大岗山坝区岩体的GSI,通过对比分析此结果与经验公式的结果及基于GSI的岩体变形模量的预测值与实测值的分布规律及其相关性,探讨了将岩体完整系数和岩石风化程度系数作为GSI系统输入参数的可行性。结果表明：基于岩体完整系数和岩石风化程度系数的GSI系统基本可行;风化程度输入参数采用风化岩石与未风化岩石的波速比平方较为合理;岩体完整系数和岩石风化程度系数丰富了GSI系统的输入参数。     

工程中岩体分级方法及应用研究

在进行涉及岩体的地下空间的开发与利用时,需要对岩石的强度和岩体在开挖时的稳定性等进行研究。目前城市地下空间开发利用中,涉及岩石的工程一般以岩体浅表层的风化带为主,对岩石风化带的认识和研究具有重要意义。本文分析研究了影响岩石强度的风化程度的判断方法,提出了判断岩体完整性标准的野外判别方法,并由此深化认识了工程岩体的分级标准;分析了岩体基本质量等级与隧道围岩基本分级的关系,并最终得出了二者在I～V级基本一致的结论,可以指导工程技术人员对岩体基本质量等级进行正确划分和应用。     

岩石横观各向同性参数试验研究

从横观各向同性理论出发,对现场采集的岩样进行室内单轴压缩试验和巴西劈裂试验,对岩石的各向异性参数进行了研究,探讨了弹性模量、抗压强度和抗拉强度随岩层倾角变化的规律,以及压力和拉力作用下各个不同倾角的岩样的破坏情况,并得出了横观各向同性岩体的弹性特征参数,为岩石各向异性的研究提供了一些有价值的参考信息。     

Evaluation of the block punch index test with particular reference to the size effect, failure mechanism and its effectiveness in predicting rock strength

Measurement of rock strength requires testing which must be carried out on test specimens of particular sizes in order to fulfill testing standards. Often, the coring process breaks up the weaker core pieces, and they are too small to be used in either conventional strength tests or index tests such as point load test. The block punch index (BPI) test, which requires flat disc specimens without special treatment has been developed during the last decade. This paper presents the results of a study of BPI test device to provide new contributions to previous works on size effect in BPI test using a wide range of rock types, in addition, to assess the effectiveness of the test in predicting rock strength by an experimental way. About 2600 disc specimens were tested, and the results were combined with those from previous works and analyzed using statistical and graphical methods. Finite element modeling was also conducted to evaluate the stress distribution created within the rock specimen by punching action of the test device. The test results suggested that size correction in the BPI test was indispensable. Using a very large test database, the size-correction factors suggested by previous workers were modified in the present study. The finite element modeling indicated that the failure surface initiated at the top of the specimen and propagated into the specimen. This demonstrated that failure was not produced by a true shearing. It was also noted that cohesion values predicted from BPI tests were greater than those obtained from conventional tests. Both of these results suggested that the BPI test was not an accurate device for directly determining shear strength of the rock specimen and should only be used as a strength index. The experimental results showed that the corrected BPI values led to lower errors in determining uniaxial compressive and tensile strength when compared to those from point load testing. Possible uses of the BPI in rock mass classification were also briefly reviewed and a strength classification based on BPI was suggested.     

丹巴水电站石英云母片岩力学特性及岩体质量分类

按水电行业HC法将丹巴水电站片理状岩体质量分类定为IV类,围岩稳定性差。通过对丹巴石英云母片岩的宏细观力学特性试验,提出石英云母片岩的“似块状”岩体结构,对岩体质量分类进行合理修正。通过单轴压缩试验、不同围压下真三轴试验表明,高应力作用下片岩的各向异性不明显,并通过薄片的细观试验提出丹巴石英云母片岩并非“层状结构”岩体结构,而是“似块状”结构。在此基础上,对丹巴水电站引水隧洞岩体质量分类进行了修正,隧洞围岩以III类为主。最后,通过现场回弹测试、声波检测和变形分析表明,围岩自稳能力强,修正后的分类标准具有良好的适用性。因此,研究不同应力环境下特殊岩石的力学特征对于岩体质量分类具有重要意义,可为同类水电工程围岩分类提供借鉴。     

风化岩石的破碎分形及其工程地质意义

利用分形统计的方法,对风化花岗岩矿物成分的粒度分布特征进行了分析和统计,并根据分析的结果指出,岩石的风化破碎过程具有分形特征。其粒度分布的双对数曲线为多段折线,不同斜率的折线段对应不同的分形维。因此,分形维至少有2个数值,一为结晶颗粒粒度分形维,一为碎裂颗粒粒度分形维。同时,根据试验结果和理论分析得到,碎裂粒子的累积频率分布也符合指数分布,并给出了用指数分布系数求解碎块的碎裂概率的理论计算公式。随后,讨论了碎裂分形维和岩石强度与颗粒结构的关系,并以岩石的降维碎裂演化,得到以分形维描述的岩石风化速率。     

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.     

Experimental assessment of long-term durability of some weak rocks

Slake durability tests, point load strength tests and X-ray diffraction analyses were carried out on thirteen rock types in an attempt to correlate the durability of the rocks with their strengths and mineral compositions. A concept is proposed to describe the rock degradation characteristics from the results of slake durability test cycles. A new classification system is introduced for rock durability, which allows the prediction of the strength of a rock when it has been affected by the weathering process. The aim of the study was to predict the influence of the weathering process (simulated by wetting and drying and heating and cooling) on the durability and strength of the volcanic, metamorphic and sedimentary rocks outcropping in eastern Thailand. Field studies were carried out in an attempt to relate the heat absorption of the rocks in situ to that measured on the laboratory specimens.     

中风化花岗岩层与基桩侧摩阻性能现场试验研究

 结合港珠澳大桥桥梁试桩工程,采用自平衡法进行2组共4根桩(每组2根桩)的中风化花岗岩与基桩的侧摩阻性能现场试验。试验时,将荷载箱埋设于中风化岩层内的桩身进行测试,并同步观测不同试验荷载下桩顶、中风化花岗岩层顶面对应的桩身截面、荷载箱和桩底的位移和桩身轴力。2组试桩桩位处岩石强度有一定差异,且岩石完整程度不一,但各试桩荷载箱上方桩身的荷载–位移曲线均具有明显的突变特征。处于岩石强度小、破碎岩层内的试桩组,其荷载箱上方岩层与基桩侧摩阻力小于荷载箱下方岩层与基桩侧摩阻力;处于岩石强度高、较破碎岩层内的试桩组,其荷载箱上方、下方岩层与基桩侧摩阻力基本一致。荷载箱以上桩段岩石侧阻发挥系数实测值表现为岩石强度愈高,岩石侧阻发挥系数实测值也愈高;而荷载箱以下桩段,在本项目的试验条件下则表现为岩石强度愈高,侧阻发挥系数实测值愈低。