Engineering geological evaluation of the spillway of dam (II-B) of Bunakha Hydroelectric Project, Chukha Dzong, Bhutan

The 200m long and 106.2m wide spillway of Bunakha Hydroelectric Project is proposed at the centre of the dam to pass the flood discharge. The spillway area was investigated through detailed engineering geological mapping, geophysical survey, exploratory drilling and laboratory testing. The rock mass properties, i.e. joint sets, weathering grade, RQD, RMR, permeability, P-wave velocity etc. of the rock masses to be encountered during the excavation of spillway have been analyzed in detail. Core samples from the exploratory drill hole drilled at the spillway alignment were tested for physico-mechanical properties of rocks in the laboratory. The mapping details indicated that the major rock types which are exposed to the surface and cover the entire spillway area are foliated gneisses with bands of banded gneisses. On the basis of detailed investigations and laboratory testing, inferences and recommendations have been made which will be helpful during the construction of the project.     

Anisotropic Deformation of a Circular Tunnel Excavated in a Rock Mass Containing Sets of Ubiquitous Joints: Theory Analysis and Numerical Modeling

Determining anisotropic deformation surrounding underground excavations for tunnels is an intuitional task that involves many difficulties due to the inherent anisotropies in the strength and deformability of natural rocks. This study investigates joint-induced anisotropic deformation surrounding a tunnel via a numerical simulation that accounts for the mechanical behavior of intact rock, the orientations of joint sets, and the mechanical behavior of joint planes; this numerical simulation can model the complete stress–strain relationship with anisotropic rock mass characteristics. Simulation results demonstrate that the well-known excavation-induced stress variation–decrease in the radial component and increase in the tangential component–decrease shear strength and increase shear stress for the joint plane tangential to the tunnel wall, resulting in joint sliding failure and considerable shear deformation. This joint sliding failure and significant shear deformation account for the joint-induced anisotropic deformation surrounding a tunnel. When a rock mass has two joint sets with unfavorable joint orientations, the area with joint sliding failure can deteriorate mutually, resulting in large anisotropic deformation. Additionally, for a rock mass containing three joint sets with well-distributed orientations, joint sliding in various joint sets and associated stress variations can counter balance each other, resulting in less anisotropic deformation than those of rock masses containing one or two joint sets.     

Engineering geological and geotechnical responses of schistose rocks from dam project areas in India

For a rational and safer design of civil and mining engineering structures in or on rocks, a proper understanding of the quality of rock mass is required. To assess the rock mass quality, evaluation of physical and mechanical characteristics of the intact rocks is essential. Especially if the rock is anisotropic in nature, the genetic complexity associated with its petrofabric makes it more difficult to predict its behaviour. In this paper, a comprehensive study of the compositional, physical and geotechnical responses of four varieties of schists, i.e., quartzitic, chlorite, quartz mica and biotite schists obtained from two hydroelectrical project sites in the foot hills of Himalayas, India, has been presented.

Anisotropic strength behaviour of the schists has been brought out through the testing of specimens with varying orientation of schistosity with respect to the major principal stress under uniaxial and triaxial conditions. The significance of anisotropic response for consideration in the design is emphasized.     

多尺度节理岩体力学特性的颗粒流分析

以白云鄂博露天铁矿东矿岩质高边坡为工程背景,结合现场地质调查、室内岩石和节理力学试验等数据,采用等效岩体技术,构建能充分反映节理分布特征的实验室、现场原位试验和工程尺度等多尺度等效岩体模型。通过对各类等效岩体模型进行单轴压缩试验,研究岩体单轴抗压强度、弹性模量等力学特性的尺寸效应和各向异性。研究表明：节理的存在使岩体表现出尺寸效应和各向异性,且随着尺寸的增大,这种特性基本呈逐渐减弱的趋势;研究区域岩体的表征单元体积、单轴抗压强度和弹性模量分别为20 m×10 m×10 m、1.46 MPa和3.91 GPa;岩体单轴抗压强度、弹性模量与轴向尺寸的关系,近似符合渐进式指数函数关系,且该函数能直观地给出工程尺度岩体的力学特性。     

Construction of underground caverns for petroleum storage in orogenic areas: Geological stability

Japan is located at the boundary between three continental and oceanic plates, and there is a great variety and complexity of geological features as a result of tectonic activities. The possibility of excavating large underground tunnels in the seemingly “fragile” rocks in orogenic areas was considered as a national project for the underground storage of petroleum. One hundred and seventy sites in 57 areas were selected based on a comprehensive survey over the whole country. After a successful experiment with a test tunnel, 112 m long and 250 m² in cross-section area, excavated in Cretaceous granite, three sites in granites and pyroclastic rocks were selected for construction. The largest of these storage tunnels is 550 m in length and20 × 30 m in cross-section.

Before construction, a detailed survey of the subsurface geology was carried out, taking into consideration the structural geology, the mechanical properties of the rocks and the hydrogeology. It was concluded that even in active orogenic areas, there are many suitable sites for large underground excavations and that these can be detected by detailed, planned surveys.     

Geological and geotechnical investigations of Loharinag-Pala Hydroelectric Project,Garhwal Himalaya,Uttarakhand

The project area, forming a part of Bhagirathi valley, exposed rocks classed as central Himalayan crystallines and are medium to high grade metamorphics. The rock types exposed are feldspathic gneisses, quartz-biotite schists, garnet-biotite schist, biotite gneisses, migmatites and amphibolites. To design the rock support for the underground structures of desilting chambers, HRT, surge shaft, pressure shafts, power house, TRT and for the foundations of barrage and intake of desilting chambers, rock mass classifications was attempted following the methods of Bieniawski Rock Mass Rating (RMR) Classification and Tunnelling Quality Index (Q) of Barton et al. RMR technique involves collection of data on rock strength, RQD (%), spacing of discontinuities, condition of discontinuities and groundwater condition, while the ‘Q’ involves collection of data on RQD (%), joint set numbers (Jn), joint roughness number (Jr), joint alternation number (Ja), joint water reduction factor (Jw) and stress reduction factors (SRF). The permeability test in the overburden was done by the constant head method, while in the bed rock portion conducted by packer test. The result indicates that the rock masses of the area fall under the good, fair and poor rock quality. Augen gneiss of power house area is coming under the category of moderately strong rock as proved by deformability characteristics and strength parameter. On the basis of above study recommendations have been made for the proper and safe construction of the project components.     

Palynofacies,Organic Thermal Maturation and Source Rock Evaluation of Nanka and Ogwashi Formations in Updip Niger Delta Basin,Southeastern Nigeria

For the deep underground pump house complex engineering geological and geotechnical investigations were carried out. The area was investigated through detailed engineering geological mapping, exploratory drilling, in-situ stress measurements and laboratory testing. Surface mapping was done on 1:500 scales with 0.5 m contour interval and drill holes logging was done on 1:100 scale. The rock mass properties, i.e. joint sets, weathering grade, RQD etc. of the rock masses to be encountered during the excavation of cavities have been analyzed in detail. Core samples from the exploratory drill holes drilled at the surge pool and pump house area were tested for physico-mechanical properties of rocks in the laboratory. To evaluate the stress regime at the proposed underground pump house complex area, stress measurements were carried out by hydrofracturing method inside the borehole. The mapping details indicated that cavities will be excavated through fresh, coarse to very coarse grained, hard and jointed granites. The average depth recorded of fresh rock from the surface was 15.7 m. The uniaxial compressive strength of the rock mass range from 221 to 246 MPa. The orientation of the long axis of the cavities recommended is N150°. Classification of rock mass using Tunnelling Quality Index Q is attempted and the values are range from 3.58 to 16.40.     

川藏交通廊道黏土化蚀变岩发育特征及其对大型滑坡的促滑作用

黏土化蚀变岩是在岩浆期后热液作用或后期水热作用下形成的具有不良工程地质性质的特殊地质体.在野外调查、黏土矿物测试和物理力学试验分析的基础上,阐述了川藏交通廊道黏土化蚀变岩的形成条件、区域分布特征、地质特征及蚀变程度的判据,以白格滑坡为例揭示了黏土化蚀变岩对大型滑坡的促滑作用.结果表明,黏土化蚀变岩的区域分布受活动断裂、热液作用和地层岩性控制,常沿侵入岩脉、断裂带、岩浆岩节理密集带、侵入岩体与其他岩层的接触带等部位发育,其蚀变程度按蚀变系数可划分为微蚀变、弱蚀变、中等蚀变和强蚀变4个等级,在干湿交替和松弛条件下极易发生崩解、软化,中等-强蚀变的岩体抗剪强度低.黏土化蚀变岩对滑坡的促滑作用主要体现在强度弱化效应、岩体结构劣化效应及失稳滞后效应3个方面,是促进构造混杂岩带深切河谷斜坡失稳、形成大型滑坡不可忽视的重要因素.      

The influence of rock anisotropy on stress measurements by overcoring techniques

SummaryThe Influence of Rock Anisotropy on Stress Measurements by Overcoring Techniques A medium is anisotropic if its properties vary with direction. This is the general characteristic of many rocks, for example, schists, slates, gneisses, phyllites and other metamorphic rocks. Bedded and regularly jointed rocks also display anisotropic behavior.This paper is concerned with the influence of rock anisotropy on in-situ stress measurements. It is limited, to stress measurements by overcoring techniques for which strains and displacements are recorded either on the walls of a pilot hole at the end of one or several boreholes or within instrumented solid or hollow inclusions perfectly bonded to the surface of the pilot hole. The rock is described as homogeneous, continuous, anisotropic and linearly elastic.The following questions are answered with special emphasis on rocks that can be classed as transversely isotropic or orthotropic: the number of independent measurements obtainable in a single borehole; the number of boreholes required to determine the in-situ stress field; the influence of rock anisotropy on these numbers; the influence of the anisotropy type and the error involved by neglecting rock anisotropy.With 5 Figures     

A particle mechanics approach for the dynamic strength model of the jointed rock mass considering the joint orientation

In nature, there exist several forms of anisotropy in rock masses due to the presence of bedding planes, joints, and weak layers. It is well understood that the anisotropic properties of jointed rock masses significantly affect the stability of surface and underground excavations. However, these critical anisotropic characteristics are often ignored in existing uniaxial dynamic failure criteria. This study investigates the effect of a pre-existing persistent joint on the rate-dependent mechanical behaviours of a rock mass using a particle mechanics approach, namely, bonded particle model (BPM), to realistically replicate the mechanical response of the rock mass. Firstly, in order to capture the rate-dependent response of the jointed rock mass, the BPM model is validated using published experimental data. Then, a dynamic strength model is proposed based on the Jaeger criterion and simulation results. To further investigate the dynamic behaviours, the dynamic uniaxial compressive strength (UCS) for anisotropic rock masses with various joint orientations is investigated by subjecting the BPM models to uniaxial compression numerical tests with various strain rate. The proposed dynamic strength model is validated based on numerical simulation results. Finally, the fragmentation characteristics of the jointed rock masses are analysed, which demonstrate that the failure mode affects the dynamic UCS. This is further confirmed by the analysis of the orientations of microscopic cracks generated by the compression loading.     

岩块与岩体的强度

本文以试验资料为依据,论述了岩块和岩体的单轴强度与极低应力区剪切强度参数之间的相互关系,并在简要介绍霍克—布朗强度准则的基础上,提出了确定岩体常数s与m的新方法,进而分别讨论了各向同性和各向异性岩体三轴强度的近似确定问题。     

甘肃北山地质处置库围岩节理抗剪强度经验估算

节理抗剪强度参数是地质处置库预选地段工程地质对比和围岩稳定性分析的重要指标。本文在旧井地段英云闪长岩节理分组的基础上,运用定向统计测量方法估测节理粗糙度系数,通过评价节理粗糙度系数的尺寸效应,确定节理抗剪强度经验估算有效长度,由JRC-JCS模型求得各组节理4个方向的抗剪强度参数,并评价了地质处置库围岩节理抗剪强度的各向异性特征。     

基于改进GSI体系确定三峡地下厂房围岩等效变形模量及强度

基于地质强度指标GSI体系和Hoek-Brown强度准则, 研究岩体强度及变形模量时没有考虑到结构面产状对工程岩体参数的影响.结合三峡工程地下厂房, 根据围岩开挖面与结构面分布的空间位置关系, 确定了结构面分布对围岩结构等级SR的影响系数, 改进了GSI体系中围岩SR的统计方法, 确定了围岩的等效变形模量和强度参数.研究表明, 改进后的GSI体系求解的围岩弹性区等效弹性模量、扰动区等效变形模量和粘聚力分别减小了约15%、8%和28%的误差.      

Isotopic signatures of strontium,neodymium, and lead in metamorphic rocks of the Khavyven highland in eastern Kamchatka

Metamorphic units of the Khavyven Highland that crop out in the northern portion of the Khavyven Uplift of the basement structures of the Central Kamchatka Trough are formed by rocks of the Khavyven Formation, which are metamorphosed in the green-schist facies. The formation comprises two strata: the lower part that consists of amphibole-micaceous ± garnet, epidote-micaceous ± garnet crystalline schists, and micaceous ± garnet quartzite schists has a total thickness of some 500 m, and the upper part, which is formed by epidote-amphibole and phengite-amphibole green schists and overlying epidote-amphibole-micaceous quartzites, with a visible thickness of some 750 m. The isotopic ratios of Sr, Nd, and Pb were determined in the examined rocks of the Khavyven Formation for the first time. The high ⁸⁷Sr/⁸⁶Sr and low ¹⁴³Nd/¹⁴⁴Nd ratios and the high K/La, Ba/Th, Th/Ta, and La/Nb ratios in combination with a deep Ta-Nb minimum indicate that the original volcanites of the crystalline schists of the lower rock mass had a subduction nature. The green schist of the upper rock mass, whose composition corresponds to that of spilitic basalts, have elevated ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios, thus combining indications of depleted melts of the N-MORB and E-MORB types and those of subduction melts, which explains the deep Ta-Nb minimum and the low (La/Yb) _N ratios. The isotopic signatures of lead in rocks of the lower and the upper strata are similar. The composition points of the crystalline schists and the green schists are located near the trend of isotopic evolution of lead in the depleted mantle, which indicates that the rocks are closely related to this mantle source.     

基于GIS的地层剖面图形生成技术

为了清楚地展现地下岩体结构,如裂隙、节理、层理、断层等不连续的结构面,在Visual Basic 6.0平台下对建立在OCX技术基础上的GIS(地理信息系统)功能组件MapObjects进行了集成二次开发,把三维数据结构边界表示法和三维栅格结构有机的结合,以三维栅格结构为主体,力求以最小的数据量表示更为真实的地下结构。改进后的三维栅格结构法实现了对区域平面地质图图层的放大、缩小、漫游以及地下剖面生成,并可以把生成剖面以多种格式输出以进行稳定性分析,成功应用该系统对四川省紫坪铺水利枢纽工程水库两岸重点库段进行了地质建模,有效地指导了该地区的滑坡治理和213国道的改线工程。     

Discrete element method modeling of inherently anisotropic rocks under uniaxial compression loading

A new numerical approach is proposed in this study to model the mechanical behaviors of inherently anisotropic rocks in which the rock matrix is represented as bonded particle model, and the intrinsic anisotropy is imposed by replacing any parallel bonds dipping within a certain angle range with smooth‐joint contacts. A series of numerical models with β = 0°, 15°, 30°, 45°, 60°, 75°, and 90° are constructed and tested (β is defined as the angle between the normal of weak layers and the maximum principal stress direction). The effect of smooth‐joint parameters on the uniaxial compression strength and Young's modulus is investigated systematically. The simulation results reveal that the normal strength of smooth‐joint mainly affects the behaviors at high anisotropy angles (β > 45°), while the shear strength plays an important role at medium anisotropy angles (30°–75°). The normal stiffness controls the mechanical behaviors at low anisotropy angles. The angle range of parallel bonds being replaced plays an important role on defining the degree of anisotropy. Step‐by‐step procedures for the calibration of micro parameters are recommended. The numerical model is calibrated to reproduce the behaviors of different anisotropic rocks. Detailed analyses are conducted to investigate the brittle failure process by looking at stress‐strain behaviors, increment of micro cracks, initiation and propagation of fractures. Most of these responses agree well with previous experimental findings and can provide new insights into the micro mechanisms related to the anisotropic deformation and failure behaviors. The numerical approach is then applied to simulate the stress‐induced borehole breakouts in anisotropic rock formations at reduced scale. The effect of rock anisotropy and stress anisotropy can be captured. Copyright © 2015 John Wiley & Sons, Ltd.     

三峡工程大型浅埋地下厂房围岩变形特征及机理研究

以三峡工程右岸浅埋地下厂房为例,基于施工期变形监测资料及数值模拟分析,结合地质和施工资料,对地下厂房围岩变形特征及其机制进行分析。围岩变形受结构面分布、自然应力场及地形条件等因素影响。由于地下电站区最大水平主应力近垂直于厂房轴线,大跨度高边墙厂房顶拱易产生向上抬起变形,而边墙以近水平向卸荷变形为主,且边墙变形明显较顶拱变形大;与边墙小角度相交的断层主要表现为卸荷张开变形,断层与开挖面之间的岩体变形集中;偏压地形的山峰一侧围岩变形普遍较大。围岩的上述变形特征表明围岩稳定性数值分析中应充分考虑其相关的地质条件,建立如实反映工程实际的地质力学模型是成功的工程实例数值分析的前提。     

A new approach to time-load-deformation-stress hypersurface of rocks to stability analysis of underground openings

The most important developments in rock engineering are about time-dependent deformation behavior of rocks under different loads. Many studies have been done for the purpose of identifying mathematically time-load-deformation (TLD) characteristics of the rocks. These studies have made an important contribution to the research on the stability of constructions built in rock masses, and rock material is the main part of the rock mass in which the engineering constructions. When considered from this point of view, the time-dependent deformation behavior of the rocks under different loads is important to determine unstable conditions of the rock constructions in the long term. Researches in rock masses use surfaces based on TLD data. On the other hand, the strength of the rock is also part of these analyzes. The new model developed in this study has four variables such as time, load, deformation, and strength. Therefore, TLD surfaces developed for time-load-deformation has been associated with another variable and three-component (TLD) surfaces eventually transformed into four-component (time-load-deformation-strength; TLDS) hypersurfaces. Hypersurfaces, which illustrate new TLDS behaviors of the rocks, developed in underground openings in different rock constructions in different areas. It is thought that the TLDS hypersurfaces will especially be contributed to the numerical modeling studies of rock construction analysis.     

甘肃小西弓金矿地质地球化学特征及成因探讨

小西弓金矿产于敦煌岩群的低绿片岩相变质岩层中，受NWW向脆韧性剪切带控制。二云母征岩不仅是矿源层，而且还是赋矿围岩。成矿流体主要是印支期岩浆期后含金热液，还包括少量变质水和大气降水，淋滤韧性剪切带内岩石中的Au元素并在有利的部位成矿。