高地应力硬脆性围岩破坏影响因素分析

地应力对硬脆性岩体稳定性具有极为重要作用,已有研究主要集中于脆性破坏方式及其是否发生的预测上,而对地应力、洞形等因素与脆性破坏深度间关系的研究较为少见。基于硬脆性岩体脆性破坏准则,利用Examine2D软件,分析不同地应力环境及洞形时围岩脆性破坏深度d_f变化情况。结果表明:最小主应力量值较低时,破坏深度d_f与主应力比k近似为直线关系,较高时则为非线性增长;随着k值增加,屈服范围逐渐偏离最小主应力方向45°夹角发展;洞室断面长宽相近时,主应力方向较主应力量值对d_f的影响小,相同应力量值不同主应力方向,破坏位置不同,深度变化较小。洞形不同应力集中系数不同,选择长短轴长度之比与应力比k相接近的椭圆形谐洞,可有效降低破坏深度。     

Loads on Sprayed Waterproof Tunnel Linings in Jointed Hard Rock: A Study Based on Norwegian Cases

A composite tunnel lining system based on a sprayed waterproofing membrane combined with sprayed concrete is currently being considered for future Norwegian rail and road tunnels. Possible loading of the tunnel linings caused by water pressure is being investigated. This tunnel lining system consists of a waterproof membrane which, during application on the sprayed concrete lining, bonds mechanically to the sprayed concrete on either side. Hence, a continuous, sealing, and non-draining structure from the rock mass to the interior tunnel surface is formed in the walls and crown. Experiences from some successful recent projects with this lining system in Europe are reviewed. However, these experiences are not directly comparable to the Scandinavian hard rock tunnel lining approach, which utilizes a relatively thin sprayed and irregular concrete layer for permanent lining. When considering the sprayed membrane and sprayed concrete composite lining concept, introducing a partially sealing and undrained element in the lining, the experiences with the traditionally used lining systems in Norway need to be reconsidered and fully understood. A review of several hard rock tunnels with adverse conditions, in which the tunnel lining has been subject to load monitoring, shows that only very small loads in the tunnel linings occur. Recent investigations with in situ water pressure testing, including two sites with the composite sprayed membrane in a partially drained waterproof tunnel lining, are discussed. In a case with a cavern located in a hydraulically saturated rock mass subjected to approximately 8 bar hydrostatic pressure, a negative pressure gradient towards the tunnel lining has been measured. The investigation results from the Norwegian test sites indicate that no significant loading of the tunnel lining takes place in a hydraulically saturated rock when applying this composite waterproof tunnel lining in parts of the tunnel perimeter.     

Stress Analysis for Rock Mass Failure with Offset Joints

Two-dimensional finite element model was created in this work to investigate the stress distribution within rock-like samples with offset open non-persistent joints under uniaxial loading. The results of this study have explained the fracture mechanisms observed in tests on rock-like material with open non-persistent offset joints (Mughieda and Alzo’ubi, Geotech Geol Eng J 22:545–562, 2004). Finite element code SAP2000 was used to study the stresses distribution within the specimens. Four-noded isoperimetric plain strain element with two degrees of freedom per node, and the three-noded constant strain triangular element with two degree of freedom per node were used in the present study. The results of the present study showed that the tensile stress in the bridge area caused coalescence for specimens with overlapped preexisting cracks (joints) while the coalescence of the secondary cracks, due to shear stress, caused the failure of specimens with non-overlapping cracks.     

Manuel Rocha Medal Recipient Simulating the Time-dependent Behaviour of Excavations in Hard Rock

Summary Although hard rock is not usually associated with large creep deformation, data collected from the tunnels and stopes of the deep South African gold mines illustrates significant time-dependent behaviour. Apart from application in mining, a better understanding of the time-dependent behaviour of crystalline rock is required to analyse the long term stability of nuclear waste repositories and to design better support for deep civil engineering tunnels in these rock types. To illustrate the subtle problems associated with using viscoelastic theory to simulate the time-dependent behaviour of hard rock, a viscoelastic convergence solution for the incremental enlargement of a tabular excavation is discussed. Data on the time-dependent deformation of a tunnel developed in hard rock further illustrates the limitations of the theory, as it is unable to simulate the fracture zone around these excavations. To simulate the rheology of the fracture zone, a continuum viscoplastic approach was developed and implemented in a finite difference code. This proved more successful in modelling the time-dependent closure of stopes and squeezing conditions in hard rock tunnels. A continuum approach, however, has limitations in areas where the squeezing behaviour is dominated by the time-dependent behaviour of prominent discontinuities such as bedding planes. To overcome this problem, a viscoplastic displacement discontinuity technique was developed. This, combined with a tessellation approach, leads to more realistic modelling of the time-dependent behaviour of the fracture zone around excavations. Received January 15, 2002; accepted June 3, 2002 Published online September 2, 2002     

An Index for Estimating the Stability of Brittle Surrounding Rock Mass: FAI and its Engineering Application

Based on the geometric analysis of the relationship between the stress state at a point and the yield surface defined in the principal stress space, a coefficient ω is set up as an estimation index to describe the stress-induced yield risk. After yield, the equivalent plastic shear strains is usually used to characterize the failure degree (FD) of the material and adopted here as an index of the damage degree for the surrounding rock masses. Then, a unified variable combining ω and FD, named failure approaching index (FAI), is constructed to estimate the stability of rock mass which may be at different deformation stages. The formulas of FAI are derived for some popular yield criteria in geomechanics. Details for such development are addressed in the paper. Its rationality is verified by numerical simulation and comparative analysis of the conventional triaxial compression tests and typical tunnel projects. In addition, the method for applying FAI to the stability estimation of surrounding rock mass is proposed. As examples, the stability of the underground powerhouse, access tunnels and headrace tunnels at the Jinping II hydropower station are estimated by making use of the method we presented. The results indicate that not only is the index rational in mechanics, but the theory also has good expansibility, and the estimation methods are simple and practical as well. It is easier for field engineers to analyze and understand the numerical results.     

含预制裂纹的脆性岩石单轴压缩下渐进性破坏过程的试验研究

对含预制裂纹的花岗岩进行单轴压缩试验研究预制裂纹倾角α对脆性岩石渐进性破坏过程的影响。首先埘破坏过程的轴向应力-横向应变曲线进行总结和讨论,然后分析预制裂纹与加载方向夹角α埘岩石的应应力门槛值：裂纹起始应力σci、裂纹扩展应力σed、峰值强度矿σf,由应变片记录的应力-应变曲线和试样的表嘶裂纹扩展情况的影响机制。结果表明,含有预制裂纹的岩石试样进行加载试验过程中,顶制裂纹倾角α的变化成了决定脆性岩石破裂办式的主要因素。故在对含节理、裂隙的脆性岩石的工程应用上,通过对岩休的轴向应力-横向应变向应变典线进行分析,可以对地下开挖工程起到指导设计开挖方式及支护形式的作用。     

Application of Rock Mass Characterization for Determining the Mechanical Properties of Rock Mass: a Comparative Study

The results of geotechnical explorations, engineering geological investigation (including laboratory and in situ tests) and field observations have been used, along with borehole logging charts, to obtain the rock mass geotechnical data. Based on the data, the rock mass along the Sabzkuh water conveyance tunnel route was classified by rock mass rating (RMR), Q-system (Q), rock mass index (RMi) and geological strength index (GSI) (3 methods). A new series of correlations were established between the systems based on the data collected from the study area. These relationships were then compared with those reported in the literature, and two new relations were recommended. The classifications were utilized to calculate mechanical properties (rock mass strength and deformation modulus) of the rock mass along the tunnel according to available empirical relations, and to distinguish the upper-bound and lower-bound relations.     

软硬相间岩层底板变形研究

引入损伤变量ω理论,分析水平状软硬相间岩层在竖向应力下的应力-应变关系：再引用弹性模量E和岩层厚度L两个变形参数建立软硬相间岩层底板变形参数方程,得出竖向应力随着底板深度的增加而减小的规律：运用数值模拟软件,建立煤层开采模型,模拟软硬相间岩层底板在采动作用下的变形过程。通过数值分析底板在采动作用下的应力-应变关系和位移特征,发现竖向应力作用下软岩受到的水平应力比硬岩大,竖向应变也比硬岩大,而竖向应力和水平应变变化不大,认为在采动影响下软硬相间岩层底板中的软岩具有吸收更多的应变能来保护软岩下硬岩的变形特点。     

Rock Mass Behavior Under Hydropower Embankment Dams: A Two-Dimensional Numerical Study

Sweden has more than 190 large hydropower dams, of which about 50 are pure embankment dams and over 100 are concrete/embankment dams. This paper presents results from conceptual analyses of the response of typical Swedish rock mass to the construction of a hydropower embankment dam and its first stages of operation. The aim is to identify locations and magnitudes of displacements that are occurring in the rock foundation and grout curtain after construction of the dam, the first filling of its water reservoir, and after one seasonal variation of the water table. Coupled hydro-mechanical analysis was conducted using the two-dimensional distinct element program UDEC. Series of the simulations have been performed and the results show that the first filling of the reservoir and variation of water table induce largest magnitudes of displacement, with the greatest values obtained from the two models with high differential horizontal stresses and smallest spacing of sub-vertical fractures. These results may help identifying the condition of the dam foundation and contribute to the development of proper maintenance measures, which guarantee the safety and functionality of the dam. Additionally, newly developed dams may use these results for the estimation of the possible response of the rock foundation to the construction.     

Fragmentation during Rock Falls: Two Italian Case Studies of Hard and Soft Rocks

In recent years, rock fall phenomena in Italy have received considerable attention for risk mitigation through in situ observations and experimental data. This paper reports the study conducted at Camaldoli Hill, in the urban area of Naples, and at Monte Pellegrino, Palermo, Italy. The rocks involved are volcanic Neapolitan yellow tuff (NYT) in the former area and dolomitic limestone in the latter. Both rocks, even though with different strength characteristics, have shown a significant tendency towards rock fragmentation during run out. This behavior was first investigated by comparing the volumes of removable blocks on the cliff faces (V ₀) and fallen blocks on the slopes (V _f). It was assumed that the ratio V _f/V ₀ decreases with the distance (x _f) from the detachment area by an empirical law, which depends on a coefficient α, correlated with the geotechnical properties of the materials involved in the rock fall. Finally, this law was validated by observation of well-documented natural rock falls (Palermo) and by in situ full-scale tests (Naples). From the engineering perspective, consideration of fragmentation processes in rock fall modeling provides a means for designing low-cost mitigation measures.     

测量岩体应力波的压电应力计

本文介绍一种用于岩体爆炸测量的新型压电应力计--RS 型应力计.它利用压电晶体的压电效应直接测量应力。由于外壳采用爆炸现场测点处的岩芯材料制成,避开了应力测量中难以解决的匹配问题.实践表明:只要保证 RS 型应力计按规定工艺要求制作,并进行系统的标定和回填,对中硬和坚硬岩体中自由场和毛洞周边的爆炸应力测量是可行的。     

A piezometer for Stress Wave Measurement in Rock Mass

A new type of stress piezometer, RS stress gage, is presented in this paper. This new type of stress gage make use of piezoelectricity of piezocrystal to measure dynamic stress and read the magnitude directly. To avoid the bad matching of the gage and rock mass in situ, the shell of the gage is made of rock core from in situ. It has been proved that the new stress gage can work well during the measuring of the stress of blast wave in rock mass as long as it was made fine, calibrated accurately, and inserted carefully.     

Research on Meso-mechanism of Failure Mode of Tunnel in Jointed Rock Mass

Geotechnical and Geological Engineering - The natural rock that contains micro particles, holes, cracks, impurities, etc. has a complex composition. According to whether the crack is closed or not,...     

A Study of Optimal Rock-Cutting Conditions for Hard Rock TBM Using the Discrete Element Method

The efficiency of TBM performance affected by the specific s/p (s: spacing and p: penetration) ratio of the disc cutter is a research issue in demand. This article presents a multi-indentation simulation using discrete element method (DEM) analysis to study the optimal rock-cutting phenomena in terms of the interaction of the s/p ratio with intact rock properties. The multi-indentation simulation attempts to represent a linear cutting machine (LCM) test, which is a full-scale test for evaluating the optimal rock-cutting condition and measuring required reaction forces based on the intact rock condition in general practice. A governing equation relating mechanical rock properties with geometric characteristics for the optimal rock-cutting condition is derived by the numerical simulation, and its performance is evaluated with the result of the laboratory LCM tests. The results of simulations and real LCM tests show that the effective rock-cutting condition corresponding to the minimum specific energy can be estimated by an optimized s/p ratio, which, in turn, is linearly proportional to the square of the material brittleness, B ², and cutter tip width, t (i.e., s/p?=?cB ² t, where c is coefficient). The limitation of the numerical simulation associated with the sample preparation is also discussed.     

岩体应力的现场研究

岩体力学不同于力学的其他分支的主要特点之一,是岩体具有内应力.因而,一切与岩体有关的力学问题的合理解决,脆性破裂理论的实际应用,都离不开对岩体应力状态的了解.     

In Situ Study on Stress in Rock Mass

The Significance of the rock stress measurements for studying state of stress in the crust is elucidated in this paper .A brief introduction on the principles and methods of calculating the rock stress by measuring the deformations of the bore-holes by means of the overcoring technique is given .Generally the error is estimated to be about 10% by the laboratory checking methods .Form the practical examples it is summed up for some laws of the stress distribution within 200 meters of the shallow crust: from the viewpoint of the rock-mass strength and energy accumulation, the relationship between the major principal stress and the elastic modules of the rock is shown in diagrams, and its direction is closed related to the topographical conditions .The practical examples reveal the measurement of rock stress is significant to the ground surface and underground engineering projects .