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1.
This paper presents an international, multiple-code, simulation study of coupled thermal, hydrological, and mechanical (THM) processes and their effect on permeability and fluid flow in fractured rock around heated underground nuclear waste emplacement drifts. Simulations were conducted considering two types of repository settings (1) open emplacement drifts in relatively shallow unsaturated volcanic rock, and (2) backfilled emplacement drifts in deeper saturated crystalline rock. The results showed that for the two assumed repository settings, the dominant mechanism of changes in rock permeability was thermal–mechanically induced closure (reduced aperture) of vertical fractures, caused by thermal stress resulting from repository-wide heating of the rock mass. The magnitude of thermal–mechanically induced changes in permeability was more substantial in the case of an emplacement drift located in a relatively shallow, low-stress environment where the rock is more compliant, allowing more substantial fracture closure during thermal stressing. However, in both of the assumed repository settings in this study, the thermal–mechanically induced changes in permeability caused relatively small changes in the flow field, with most changes occurring in the vicinity of the emplacement drifts.  相似文献   

2.
This paper presents numerical modeling of excavation-induced damage, permeability changes, and fluid-pressure responses during excavation of a test tunnel associated with the tunnel sealing experiment (TSX) at the Underground Research Laboratory (URL) in Canada. Four different numerical models were applied using a wide range of approaches to model damage and permeability changes in the excavation disturbed zone (EDZ) around the tunnel. Using in situ calibration of model parameters, the modeling could reproduce observed spatial distribution of damage and permeability changes around the tunnel as a combination of disturbance induced by stress redistribution around the tunnel and by the drill-and-blast operation. The modeling showed that stress-induced permeability increase above the tunnel is a result of micro and macrofracturing under high deviatoric (shear) stress, whereas permeability increase alongside the tunnel is a result of opening of existing microfractures under decreased mean stress. The remaining observed fracturing and permeability changes around the periphery of the tunnel were attributed to damage from the drill-and-blast operation. Moreover, a reasonably good agreement was achieved between simulated and observed excavation-induced pressure responses around the TSX tunnel for 1 year following its excavation. The simulations showed that these pressure responses are caused by poroelastic effects as a result of increasing or decreasing mean stress, with corresponding contraction or expansion of the pore volume. The simulation results for pressure evolution were consistent with previous studies, indicating that the observed pressure responses could be captured in a Biot model using a relatively low Biot-Willis’ coefficient, α ≈ 0.2, a porosity of n ≈ 0.007, and a relatively low permeability of ≈ 2 × 10−22 m2, which is consistent with the very tight, unfractured granite at the site.  相似文献   

3.
In order to demonstrate the feasibility of geological disposal of spent CANDU fuel in Canada, a safety assessment was performed for a hypothetical repository in the Canadian Shield. The assessment shows that the maximum long term radionuclide release from such repository would meet international criteria for dose rate; however, uncertainties in the assumed evolution of the repository were identified. Such uncertainties could be resolved by the consideration of coupled Thermal-Hydro-Mechanical-Chemical (THMC) processes. In Task A of the DECOVALEX-THMC project, THM models were developed within the framework of the theory of poroelasticity. Such model development was performed in an iterative manner, using experimental data from laboratory and field tests. The models were used to perform near-field simulations of the evolution of the repository in order to address the above-mentioned uncertainties. This paper presents the definition and rationale of task A and the results of the simulations. From a repository safety point of view, the simulations predict that the maximum temperature would be well below the design target of 100°C; however, the stress on the container can marginally exceed the design value of 15 MPa. However, the most important finding from the simulations is that a rock damage zone could form around the emplacement borehole. Such damage zone can extend a few metres from the walls of the emplacement holes, with permeability values that are orders of magnitude higher than the initial values. The damage zone has the potential to increase the radionuclide transport flux from the geosphere; the effect of such an increase should be taken into account in the safety assessment and mitigated if necessary by the provision of sealing systems. Prepared for publication in Environmental Geology. DECOVALEX-THMC Special Issue.  相似文献   

4.
 A site specific evaluation of geological barriers is required for landfills and waste repositories. The waste-repository-rock system has to be taken into consideration for this. Since the geotechnical barrier in conjunction with geological barriers contributes considerably to long-term isolation of the harmful substances from the biosphere, it is absolutely necessary to use engineering geology and hydrogeological methods for a quantitative assessment of the barrier effect of the host rock and the geological environment. For a waste disposal mine, the load-bearing capacity of the rock, the protective properties of the surrounding rock formations and the geological stability of the area are important factors in a safety analysis, of which the geotechnical stability analysis is an important part. Such an analysis comprises an engineering geological study of the site, laboratory and in situ experiments and model calculations, long-term monitoring, and special geological and geochemical investigations. Existing geomechanical modelling techniques provide a useful tool to perform barrier integrity calculations and to design an underground disposal mine. As an example, the barrier performance of the rock salt of the Gorleben salt dome is demonstrated using various safety indicators. Received: 3 January 1997 · Accepted: 29 January 1997  相似文献   

5.
This paper describes current knowledge about the nature of and potential for thermo–hydro–mechanical–chemical modelling of the excavation damaged zone (EDZ) around the excavations for an underground radioactive waste repository. In the first part of the paper, the disturbances associated with excavation are explained, together with reviews of Workshops that have been held on the subject. In the second part of the paper, the results of a DECOVALEX [DEmonstration of COupled models and their VALidation against EXperiment: research funded by an international consortium of radioactive waste regulators and implementers (http://www.decovalex.com)] research programme on modelling the EDZ are presented. Four research teams used four different models to simulate the complete stress–strain curve for Avro granite from the Swedish Äspö Hard Rock Laboratory. Subsequent research extended the work to computer simulation of the evolution of the repository using a ‘wall-block model’ and a ‘near-field model’. This included assessing the evolution of stress, failure and permeability and time-dependent effects during repository evolution. As discussed, all the computer models are well suited to sensitivity studies for evaluating the influence of their respective supporting parameters on the complete stress–strain curve for rock and for modelling the EDZ.  相似文献   

6.
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.  相似文献   

7.
2000-2040年我国高放废物深部地质处置初探   总被引:1,自引:0,他引:1  
徐国庆 《铀矿地质》2002,18(3):160-167
本简要介绍了国内外高放废物地质处置研究概况,探讨了我国高放废物地质处置研究阶段的划分,各阶段的研究目标,任务和研究内容以及各研究阶段的大致时间安排,提出了我国高放废物地质处置研究在2000-2040年的远景规划设想。  相似文献   

8.
谈成龙 《铀矿地质》2003,19(1):58-61
地气与核废地质处置库是自然界独立存在的两个实体,当地气途径核废地质处置库时,会把存放于此的相关物质(以纳米微粒物质形式)携带至地表进入生物圈、大气圈,进而构成危及人类环境的隐患。  相似文献   

9.
10.
Many hazardous waste sites in the south Louisiana Gulf Coast have been emplaced in sediments of Plio-Pleistocene to Recent age. Because of the fining upward nature of these regressive-transgressive fluvial-deltaic sequences and the purported confining capabilities of the shallow clay layers within them, this area would seem to be ideal for the location of surface waste landfills. However, detailed geologic mapping at a site in southeastern Louisiana documents how the three-dimensional distribution of sediment types and early diagenetic features, both of which were ultimately controlled by depositional history, can increase effective vertical permeability of finegrained sequences. Many bodies of sand that appear to be isolated in standard geotechnical cross sections can be shown to be part of spatially complex three-dimensional distributary networks, with fine-grained sediments representing overbank and backswamp deposits. Some clay layers are actually a composite of thinner clay beds, each subjected to subaerial exposure and the development of secondary porosity related to soil formation. There has been documented leakage of wastes down through the clays, and a recent study indicates that the effective vertical hydraulic conductivity of the clay layers exceeds 10–5 cm s–1, or from one to four orders of magnitude higher than values measured on samples from cores of the same sediment. An understanding of the depositional framework, facies architecture, and diagenetic history of geologic materials underlying waste disposal sites in Louisiana is required for rational development of monitoring and remediation plans.  相似文献   

11.
12.
张玉军 《岩土力学》2007,28(12):2489-2494
笔者描述了所建立的饱和-非饱和介质中热-水-应力耦合现象的控制方程。针对国际合作项目DECOVALEX II 中Task-2的核废物地质处置轴对称模型试验及计算参数,使用所研制的有限元程序进行了热-水-应力耦合过程模拟。对缓冲层及岩体中若干部位的温度、含水量及接触应力的分布、变化进行了分析, 并将其与量测值和使用THAMES程序的计算结果作了比较,看到了三者的异、同之处,并指出了可能的影响原因。通过与量测值和THAMES程序的计算结果的对比,显示了笔者所研制的有限元程序在热-水-应力耦合数值分析中是可靠和实用的。  相似文献   

13.
Summary  When modeling the mechanical behavior of underground excavations, it is necessary to include the influence of the rock mass characteristics on the Excavation Damaged/Disturbed Zone (EDZ). In this paper, the Realistic Failure Process Analysis code, RFPA, is used to model the extent of the EDZ. The inhomogeneous characteristics of rock at the mesoscopic level are included by assuming that the material properties of the constituent elements conform to a Weibull distribution; the anisotropy is incorporated as a transversely isotropic medium; the non-elastic characteristic is simulated via an elastic damage-based constitutive law. A finite element program is adopted as the basic stress analysis tool. In this study, a notable feature is that no a priori assumptions need to be made about where and how fracture and failure will occur – cracking can take place spontaneously and can exhibit a variety of mechanisms when certain local stress conditions are met. The deformation and failure process of anisotropic rock around excavations of different geometries is analyzed, and compared to experimental tests, showing similar fracture patterns. Additionally, the effect of confining stress and of different material layers is modeled and discussed. It is found that the model clearly illustrates that fracturing, both initiation and propagation, occurs as a combination of the stress concentrations and weakness planes introduced via the transverse anisotropy – which could represent either foliations or ubiquitous joint sets. Correspondence: Dr. Shuhong Wang, Box 265, School of Resource and Civil Engineering, Northeastern University, Shenyang 110004, P.R. China  相似文献   

14.
张玉军 《岩土力学》2009,30(7):2126-2132
将所建立的热-水-应力-迁移耦合模型及开发的有限元程序,由二维分析拓展到三维分析,并从方法论研究的角度,以一个简单的核废物地质处置模型为算例,进行热-水-应力-迁移耦合过程的三维数值模拟,考察了近场的温度、饱和度、核素浓度、孔隙水压力、位移、正应力、流速等的分布与变化,认为计算结果符合规律,得出了若干结论:为了精确地模拟放射性核素迁移,就必须将温度场、渗流场、应力场和核素浓度场进行耦合分析;核废物埋存若干年后将在处置孔壁附近产生较高的压应力;缓冲层内各点的核素浓度达到相对稳定的时间要比温度和饱和度达到相对稳定的时间长得多。  相似文献   

15.
据1999—2007年资料的不完全统计,甘肃省地勘部门在北山地区一共投入4488.2万元人民币,矿产资源潜在价值估计为13.28亿元。一旦把甘肃省北山列为高放废物处置库的预选区,则潜在的经济损失将会很大,还可能影响西北地区的土地利用程度和经济发展。核试验场有多种围岩可供处置库地质选址选择,而且远离国境线与居民区,有利于高放废物处置库的安全管理。结合中国国情,在地质和社会条件有利的核试验军事禁区开展国家高放废物处置库的预选场址工作有独特的优势。提出了尽快在中国核试验场址开展高放废物地质处置库场址预选工作的建议。  相似文献   

16.
朱立  王秀娟  曾志  程建平  王永江  王晓亮  王青海   《地质通报》2009,28(2-3):354-358
据1999—2007年资料的不完全统计,甘肃省地勘部门在北山地区一共投入4488.2万元人民币,矿产资源潜在价值估计为13.28亿元。一旦把甘肃省北山列为高放废物处置库的预选区,则潜在的经济损失将会很大,还可能影响西北地区的土地利用程度和经济发展。核试验场有多种围岩可供处置库地质选址选择,而且远离国境线与居民区,有利于高放废物处置库的安全管理。结合中国国情,在地质和社会条件有利的核试验军事禁区开展国家高放废物处置库的预选场址工作有独特的优势。提出了尽快在中国核试验场址开展高放废物地质处置库场址预选工作的建议。  相似文献   

17.
Scoping calculations were performed in order to assess the influence of radiogenic heat on the performance of the rock mass around a nuclear fuel waste repository. The full coupling between the thermal, mechanical and hydrological processes involved was considered by using the finite element code, FRACON, developed through an extension of Biot's classical theory of soil consolidation. By considering the full T---H---M coupling, several important safety features, which would otherwise be omitted in uncoupled analyses, were detected in the present study. In particular, it was shown that the heat-induced pore pressure increase around the repository has the potential to significantly increase the rate of groundwater flow, and affect the structural integrity of the rock mass.  相似文献   

18.
A. J. van Loon   《Earth》2000,50(3-4):269-276
Man does not only extract material from the Earth but increasingly uses the underground for storage and disposal purposes. One of the materials that might be disposed of this way is high-level nuclear waste. The development of safe disposal procedures, the choice of suitable host rocks, and the design of underground facilities have taken much time and money, but commissions in several countries have presented reports showing that — and how — safe geological disposal will be possible in such a way that definite isolation from the biosphere is achieved. Political views have changed in the past few years, however, and there is a strong tendency now to require that the high-level waste disposed of will be retrievable. Considering the underlying arguments for isolation from the biosphere, and also considering waste policy in general, this provides an irrational context. The development of new procedures and the design of new disposal facilities that allow retrieval will take much time again. A consequence may be that the high-active, heat-generating nuclear waste will be stored temporarily for a much longer time than objectively desirable. The delay in disposal and the counterproductive requirement of retrievability are partly due to the fact that earth-science organisations have failed to communicate in the way they should, possibly fearing public (and financial) reactions if taking a position that is (was?) considered as politically incorrect. Such an attitude should not be maintained in modern society, which has the right to be informed reliably by the scientific community.  相似文献   

19.
Federal regulations governing the disposal of high-level radioactive waste in deep, geologic repositories require an assessment of performance over thousands of years. Because of the long regulatory period involved and the complex nature of the events and processes of interest, prediction of the performance of the disposal system will inevitably include uncertainties. These uncertainties come from a variety of sources, and some are quantifiable and others are not. This paper discusses these uncertainties and outlines approaches for their treatment. Recommendations for the potential resolution of current limitations in the treatment of uncertainties in performance assessment are made. Some general issues, as well as a suggested approach for incorporating expert judgment into quantitative performance assessment analysis, are discussed also.This paper was presented (by title) at Emerging Concepts, MGUS-87 Conference, Redwood City, California, 13–15 April 1987.  相似文献   

20.
The damage model presented in this article (named ‘THHMD’ model) is dedicated to non‐isothermal unsaturated porous media. It is formulated by means of three independent strain state variables, which are the thermodynamic conjugates of net stress, suction and thermal stress. The damage variable is a second‐order tensor. Stress/strain relationships are derived from Helmholtz free energy, which is assumed to be the sum of damaged elastic potentials and ‘crack‐closure energies’. Damage is assumed to grow with tensile strains due to net stress, with pore shrinkage due to suction and with thermal dilatation. Specific conductivities are introduced to account for the effects of cracking on the intensification and on the orientation of liquid water and vapor flows. These conductivities depend on damage and internal length parameters. The mechanical aspects of the THHMD model are validated by comparing the results of a triaxial compression test with experimental measurements found in the literature. Parametric studies of damage are performed on three different heating problems related to nuclear waste disposals. Several types of loading and boundary conditions are investigated. The thermal damage potential is thoroughly studied. The THHMD model is expected to be a useful tool in the assessment of the Excavation Damaged Zone, especially in the vicinity of nuclear waste repositories. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

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