Geostatistical Evaluation of the Mechanical Properties of Rock Mass for TBM Tunnelling by Seismic Reflection Method

Summary. The evaluation of the rock mass mechanical properties by the seismic reflection method and TBM driving is proposed for TBM tunnelling. The relationship between the reflection number derived from the three-dimensional seismic reflection method and the rock strength index (RSI) derived from TBM driving data is examined, and the methodology of conversion from the reflection number to the RSI is proposed. Furthermore a geostatistical prediction methodology to provide a three-dimensional geotechnical profile ahead of the tunnel face is proposed. The performance of this prediction method is verified by actual field data.     

Application of the adaptive neuro-fuzzy inference system for prediction of a rock engineering classification system

The rock engineering classification system is based on six parameters defined by Bieniawski [5], who employed parallel sets of linguistic and numerical criteria that were acknowledged to influence the behaviour of rock masses and the stability of rock structures. Consequently, experts frequently relate rock joints and discontinuities as well as ground water conditions in linguistic terms, with rough calculations. Recently, intelligence system approaches such as artificial neural network (ANN) and neuro-fuzzy methods have been used successfully for time series modelling. Using neuro-fuzzy approaches, which enable the information that is stored in trained networks to be expressed in the form of a fuzzy rule base, would help to overcome this issue. This paper presents the results of a study of the application of neuro-fuzzy methods to predict rock mass rating. We note that the proposed weights technique was applied in this process. We show that neuro-fuzzy methods give better predictions than conventional modelling approaches.     

A rock damage constitutive model and damage energy dissipation rate analysis for characterising the crack closure effect

Due to the insufficiency of the previous damage constitutive model for rock, an improved damage mechanics model for rock is proposed with characterising the crack closure effect. Otherwise, the effective methods of determining the model parameters and crack closure coefficient are proposed. The results represent that the model can reflect the damage evolution of rocks in the deformation process in the crack closure stage and this improved model is more reasonable than the previous model. Crack closure coefficient also has great effect on distribution parameters. The calculation formula of damage energy dissipation rate considered that crack closure effect is derived and the relationships between damage energy dissipation rate and crack closure coefficient are analysed. Crack closure coefficient has great effect on damage dissipation energy rate. Damage energy dissipation rate increases with the decrease of crack closure coefficient and damage energy dissipation rate increases quickly in the post-peak stage.     

A 3D model of a jointed rock mass and its deformation properties

Conclusion A geometric model of a jointed rock mass and some formulae of strain and deformation parametersE, G and were given. They may be useful for evaluating the deformation parameters of rock masses and classifying the rock mass quatitatively.     

A technique for estimating permeability of a randomly fractured rock mass

Extensive field and laboratory testing programs were performed to develop a relationship between the permeability of a fractured limestone and the core recovery values. The studied limestone does not encompass any jointing system but is consistently and randomly fractured. Nineteen in situ falling head permeability tests were carried out to measure permeability of the fractured rock mass at a representative study area. Analysis of test results has led to the formulation of an empirical equation that estimates the permeability of the rock mass in terms of its solid core recovery value and the permeability of the fractures filling material. Unlike the existing equations for estimating the permeability of rock masses, the proposed equation is simple and utilizes parameters that can be easily determined in regular geotechnical field and laboratory investigations. A technique is also presented to estimate the permeability of a rock layer, the quality of which significantly changes with depth, using the proposed equation that utilizes a single value of core recovery. Analysis of well-documented pumping test results supported the validity of the proposed equation and technique.     

基于岩石统一能量屈服准则的硬岩损伤模型

为了更准确、便捷地确定深埋地下工程中硬岩的力学行为,开展了如下研究：根据损伤与塑性演化存在相似机制,假设损伤阈值与初始屈服采用相同的确定方法,将岩石统一能量屈服准则作为损伤阈值的判定准则;基于Rabotnov对损伤变量的定义和Lemaitre应变等效性假设,并考虑未损伤部分的应力-应变关系符合广义虎克定律,提出了简化形式的硬岩损伤本构方程;为了更好地表达硬岩从低围压到高围压条件下的脆-延转化特性,提出了改进的Mazars损伤演化方程;基于锦屏T2b大理岩常规三轴压缩试验结果,对损伤模型参数进行求解,并分别与基于Mazars损伤演化方程和Mohr-Coulomb准则为损伤阈值判定准则的损伤模型进行对比,结果表明：提出的损伤模型可更好地表达硬岩从低围压的脆性到高围压的延性转变过程,特别是对损伤阈值后岩石的损伤演化过程的模拟更为精确,对硬脆性岩石的工程计算有一定的借鉴意义。     

一种基于地质指标的裂隙岩体渗透系数估算模型

裂隙岩体的渗透特性受控于裂隙的发育特征、连通特性和充填情况,并与岩体的地应力水平具有显著的相关性。基于裂隙岩体渗透性的影响因素,并考虑现有渗透系数估算模型的不足,利用钻孔压水试验和钻孔电视图像资料,建立考虑埋深(Z)、岩石质量指标(RQD)以及充填物指标(FSD)等3个指标的渗透系数估算ZRF模型,并应用到牙根二级水电站及其他工程区的渗透系数估算中。结果表明,与已有的渗透系数估算模型相比,ZRF模型较好地反映了岩体渗透性的影响因素,且模型参数物理意义明确,便于获取,对分析裂隙岩体渗透性具有一定的工程参考价值。     

On the importance of choosing a change of support model for global reserves estimation

The practical problem considered here is: how can block distribution in an orebody be forecast from sample data? The task is arduous because information yielded by samples is too often insufficient to allow an accurate evaluation of blocks. In practice, necessary additional information is obtained via a model. Choosing that model is crucial; the value of results reflects the model, i.e., its adequacy to represent reality. In this paper, the importance of choosing the change of support model is illustrated with simulations and practical examples (especially deposits with a skewed sample distribution and a large spike at the origin). An attempt to quantify this importance is made also.This paper was presented at Emerging Concepts, MGUS-87 Conference, Redwood City, California, 13–15 April 1987.     

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.     

A method for assessment of excavation damaged zone (EDZ) of a rock mass and its application to a dam foundation case

Excavation of slope is an unloading process, and also an energy releasing process when the stress in the rock mass is unloaded, leading to the rebounding deformation towards the free face. And then a zone, namely excavation damaged zone (EDZ), will be formed near the excavation boundary, where the rock is damaged or disturbed and its physical, mechanical and hydraulic properties are greatly changed. This paper is to put forward a new method to quantify the extent and damage degree of the EDZ according to the unloading strain energy which is released in the process of excavation. A simple relationship between unloading strain ε and accumulative opening displacement T of cracks, , is proposed to describe the damage degree of rock mass in the EDZ, where h is the depth variable in normal direction of the open cracks.This method is used to assess the EDZ of the dam foundation at Xiaowan hydropower station in southwestern China by the accumulative opening displacement curves of cracks along boreholes based on boreholes camera photos. We find that the EDZ can be naturally divided into two sub-zones, i.e. the excavation heavily disturbed sub-zone (EHDZ) and excavation slightly disturbed sub-zone (ESDZ), according to the variation of unloading strain ε. Two inflexions of the accumulative opening displacement curve indicate the lower limits of EHDZ and ESDZ respectively.     

A methodology to constrain the parameters of a hydrogeological discrete fracture network model for sparsely fractured crystalline rock,exemplified by data from the proposed high-level nuclear waste repository site at Forsmark,Sweden

The large-scale geological structure of the crystalline rock at the proposed high-level nuclear waste repository site at Forsmark, Sweden, has been classified in terms of deformation zones of elevated fracture frequency. The rock between deformation zones was divided into fracture domains according to fracture frequency. A methodology to constrain the geometric and hydraulic parameters that define a discrete fracture network (DFN) model for each fracture domain is presented. The methodology is based on flow logging and down-hole imaging in cored boreholes in combination with DFN realizations, fracture connectivity analysis and pumping test simulations. The simulations suggest that a good match could be obtained for a power law size distribution where the value of the location parameter equals the borehole radius but with different values for the shape parameter, depending on fracture domain and fracture set. Fractures around 10–100 m in size are the ones that typically form the connected network, giving inflows in the simulations. The report also addresses the issue of up-scaling of DFN properties to equivalent continuous porous medium (ECPM) bulk flow properties. Comparisons with double-packer injection tests provide confidence that the derived DFN formulation of detailed flows within individual fractures is also suited to simulating mean bulk flow properties and their spatial variability.     

A Quartz-bearing Orthopyroxene-rich Websterite Xenolith from the Pannonian Basin, Western Hungary: Evidence for Release of Quartz-saturated Melts from a Subducted Slab

An unusual quartz-bearing orthopyroxene-rich websterite xenolithhas been found in an alkali basaltic tuff at Szigliget, Bakony–BalatonHighland Volcanic Field (BBHVF), western Hungary. Ortho- andclinopyroxenes are enriched in light rare earth elements (LREE),middle REE and Ni, and depleted in Nb, Ta, Sr and Ti comparedwith ortho- and clinopyroxenes occurring in either peridotiteor lower crustal granulite xenoliths from the BBHVF. Both ortho-and clinopyroxenes in the xenolith contain primary and secondarysilicate melt inclusions, and needle-shaped or rounded quartzinclusions. The melt inclusions are rich in SiO₂ and alkalisand poor in MgO, FeO and CaO. They are strongly enriched inLREE and large ion lithophile elements, and display negativeNb, Ta and Sr anomalies, and slightly positive Pb anomalies.The xenolith is interpreted to represent a fragment of an orthopyroxene-richbody that crystallized in the upper mantle from a hybrid meltthat formed by interaction of mantle peridotite with a quartz-saturatedsilicate melt that was released from a subducted oceanic slab.Although the exact composition of the slab melt cannot be determined,model calculations on major and trace elements suggest involvementof a metasedimentary component. KEY WORDS: quartz; mantle; silicate melt inclusion; SiO₂-rich melt; subduction; Carpathian-Pannonian Region     

A new kinematic evolutionary model for the growth of a duplex — an example from the Rangit duplex, Sikkim Himalaya, India

The Lesser Himalayan duplex (LHD) is a prominent structure through much of the Lesser Himalayan fold–thrust belt. In the Darjeeling - Sikkim Himalaya a component of the LHD is exposed in the Rangit window as the Rangit duplex (RD). The RD consists of ten horses of the upper Lesser Himalayan Sequence (Gondwana, Buxa, Upper Daling). The duplex varies from hinterland-dipping in the north, through an antiformal stack in the middle to foreland-dipping in the south. The Ramgarh thrust (RT) is the roof thrust and, based on a balanced cross-section, the Main Himalayan Sole thrust is the floor thrust at a depth of ~ 10 km and with a dip of ~ 3.5° N.Retrodeformation suggests that the RD initiated as a foreland-dipping duplex with the Early Ramgarh thrust as the roof thrust and the RT as the floor thrust. The RT became the roof thrust during continued duplexing by a combination of footwall imbrication and concurrent RT reactivation. This kinematic history best explains the large translation of the overlying MCT sheets. The restoration suggests that RD shortening is ~ 125 km, and the original Gondwana basin extended ~ 142 km northward of its present northernmost exposures within the window.     

Organic matter maturation under the influence of a deep intrusive heat source: A natural experiment for quantitation of hydrocarbon generation and expulsion from a petroleum source rock (Toarcian shale, northern Germany)

Four shallow boreholes were drilled in the Hils syncline, northern Germany, in order to determine quantitatively the amount of hydrocarbons generated and expelled during maturation of a typical kerogen-type-II-bearing source rock. The holes penetrated the carbonceous Lias shales (Posidonia shale, Lower Toarcian) and part of the adjacent Dogger α and Lias δ mudstones. The maturity of the organic matter in the cores recovered ranges from immature (0.48% R̄₀) to overmature 1.45% R̄₀) due to location of the Hils syncline in the vicinity of the Vlotho Massif, which is deep-seated intrusive body. Facies variations of the Lias within the short geographical distances in the study area are negligible.Organic matter mass balance calculations were based on detailed organic geochemical analyses of residual material in the Lias shales (kerogen, bitumen etc.) and on the evidence of a uniform initial composition of these sediments in the study area. Dead carbon determinations supported this latter criterion but were not used as a parameter in the calculations.About 50% of the initial kerogen was transformed into oil, gas and inorganic compounds during the vitrinite reflectance increase from 0.48 to 0.88% R̄_o and only marginally more during the maturity increase from 0.88 to 1.45% R̄_o. Only a small portion of the generated material remained in the source rock even at a relatively early stage of generation (0.68% R̄_o). Expulsion efficiency of oil plus gas reached a value of 86% at the end of the main generation stage (0.88% R̄_o).