共查询到20条相似文献，搜索用时 562 毫秒
1.
热-水-力(THM)耦合作用是岩石力学与环境地质中的重要基础理论问题,核废料地质处置库周围的缓冲材料和围岩中的热-水-力耦合现象将影响其力学稳定性、热传导性和渗透性,进而影响放射性核素在裂隙岩体中的迁移规律。核废料或放射性废料的地下深埋处置是国际上正在研究的永久性隔离的有效方法之一。因此,对核废料地质处置法安全性评估的一个重要内容就是对裂隙岩体中力学稳定性与构造应力、地下水渗流及热载荷等的耦合作用之数值模拟和评估。这已成为当前刻不容缓的重要的环境影响评价课题。笔者研究了温度场-渗流场-应力场中热传导系数和渗透率以及岩体力学参数的空间变异性,用实验方法研究三场耦合效应及裂隙岩体的场性能等效处理,试图建立热-水-力耦合作用的随机性数学模型及可视化数值模拟方法,为核废料地质处置安全性评估提供直观的新方法。 相似文献
2.
介绍了高放射性废物深地质处置库热－湿－力耦合作用，着重给出了国际高压实缓冲层热－湿－力耦合作用的研究进展，指出与高放射性废物处置库有关的热－湿－力耦合过程研究是核废物地质处置提出的新课题，涉及多学科，需广大有识之士共同合作研究。 相似文献
3.
膨润土颗粒混合物是高放废物深地质处置库中的一种缓冲/回填材料,掌握其堆积性质与水-力特性是开展处置库安全性能评估的关键基础。本文全面回顾和总结了近年来国内外学者对膨润土颗粒混合物的堆积性质、持水特性、结构特征、渗透特性、胀缩特性及本构模型等方面的研究进展与取得的成果,展望了几个值得进一步研究的问题。结果表明,颗粒混合物的堆积性质与粒径级配密切相关;湿化过程中,颗粒混合物由初始松散结构逐渐转变为胶结融合结构,孔隙结构逐渐趋于均一化,并伴随着颗粒破碎和错动,进而影响其水-力特性。考虑到处置库实际运营环境的复杂性,颗粒混合物的原位填充技术以及多场(热-水-力-化)耦合条件下颗粒混合物的水-力特性是今后值得深入研究的方向。 相似文献
4.
The mid-term safety of deep geological nuclear waste repositories is based in part on the presence of a buffer, the main role of which is to isolate the environment from radionuclides. A design evaluation of such a repository is necessary to assess the potential vertical canister movement inside the drift that could reduce the buffer efficiency. A thermo-hydro-mechanical (THM) simulation is performed in a vertical cross-section of the drift. The THM couplings are described, and their influences on the mid-term (300 years) response of the engineered barrier system (EBS) are revealed. This study uses an advanced constitutive model to simulate the THM processes that occur in a specific EBS design case. The near-field simulations of the nuclear waste canister are performed in a two-dimensional finite element configuration that considers the effect of gravity. The focus of this study is on the mechanical behaviour of the buffer, which consists of two different forms of bentonite. Such an approach allows realistic consideration of the effect of the wetting and drying of the buffer material in non-isothermal conditions. Due to a specific design that includes bentonite blocks and pellets, the canister is observed to heave slightly during the re-saturation period, which extends up to 100 years. 相似文献
5.
Buffer/backfill material is an important engineering barrier in a deep geological repository of high-level radioactive waste (HLW). Its thermo-hydro-mechanical (THM) performance is very important for the safe and stable operation of the HLW repository system. Natural graphite powder mixed with sodium bentonite forms a buffer/backfill material that can dissipate heat quickly and provide strong isolation. In this paper, the THM characteristics of bentonite–sand–graphite–polypropylene fiber (BSGF) mixtures, used as a buffer/backfill material, were studied through a series of laboratory tests. The influence of graphite and polypropylene fiber contents on thermal conductivity, swelling pressure, hydraulic conductivity, and strength properties of BSGF mixtures with different sand contents was analyzed. Experimental results indicated that the graphite content, the maximum graphite mesh number, and the initial dry density of bentonite–graphite mixtures influenced the thermal conductivity of bentonite–graphite mixtures. The addition of polypropylene fiber was found to enhance the shear strength and inhibit cracking without significantly affecting the expansivity, permeability, and thermal conductivity of the BSGF mixtures. This study provides a new buffer/backfill material that can improve the stability, functionality, and thermal efficiency of the HLW repository. 相似文献
6.
The understanding of the thermo-hydro-mechanical behaviour of a clay barrier is needed for the prediction of its final in situ properties after the hydration and thermal transient in a radioactive waste repository. As part of the CEC 1990–1994 R&D programme on radioactive waste management and storage, the CEA (Fr), CIEMAT (Sp), ENRESA (Sp), SCK · CEN (B), UPC (Sp) and UWCC (UK) have carried out a joint project on unsaturated clay behaviour (Volckaert et al., 1996). The aim of the study is to analyse and model the behaviour of a clay-based engineered barrier during its hydration phase under real repository conditions. The hydro-mechanical and thermo-hydraulic models developed in this project have been coupled to describe stress/strain behaviour, moisture migration and heat transfer. A thermo-hydraulic model has also been coupled to a geochemical code to describe the migration and formation of chemical species. In this project, suction-controlled experiments have been performed on Boom clay (B), FoCa clay (Fr) and Almeria bentonite (Sp). The aim of these experiments is to test the validity of the interpretive model developed by Alonso and Gens (Alonso et al., 1990), and to build a database of unsaturated clay thermo-hydro-mechanical parameters. Such a database can then be used for validation exercises in which in situ experiments are simulated. The Boom clay is a moderately swelling clay of Rupellian age. It is studied at the SCK · CEN in Belgium as a potential host rock for a radioactive waste repository. In this paper, suction-controlled experiments carried out on Boom clay by SCK · CEN are described. SCK · CEN has performed experiments to measure the relation between suction, water content and temperature and the relation between suction, stress and deformation. The applied suction-control techniques and experimental setups are detailed. The results of these experiments are discussed in the perspective of the model of Alonso and Gens. The influence of temperature on water uptake was rather small. The measured swelling-collapse behaviour can be explained by the Alonso and Gens model. 相似文献
7.
The hydro-mechanical behaviour of a clay-based buffer material for nuclear waste disposal has been investigated in a laboratory program. In this program, the main focus was on the influence of confinement on water uptake and swelling pressure during suction decrease. The laboratory program and some of the results are presented by Dueck [Dueck, A., 2006. Laboratory results from hydro-mechanical tests on a water unsaturated bentonite. submitted for publication.]. The results from the laboratory tests were used to find a relationship between water content, void ratio, swelling pressure and suction. Two equations for swelling pressure represent the outline of the model. In the first equation, the swelling pressure developed during water uptake is normalised by a pressure corresponding to the swelling pressure at saturation. This is done in order to be independent of void ratio. A relationship between the normalised swelling pressure and the degree of saturation is suggested. The second equation describes a relationship between the swelling pressure, the water content and the actual suction (or relative humidity). The equation is based on a thermodynamic relationship and includes the retention curve (i.e. water content vs. suction under free swelling conditions). The model can be used for a state where two of the four variables; water content, void ratio, swelling pressure and suction are known and can thus be useful to evaluate field measurements and model late stages of the wetting process. An example of an application is given. The equations are mainly based on results from tests with increasing degrees of saturation under constant void ratio but are also suggested for use with increasing void ratio. 相似文献
8.
This paper presents simulation results related to coupled thermal–hydraulic–mechanical (THM) processes in engineered barrier systems (EBS) and clay host rock, in one case considering a possible link to geochemistry. This study is part of the US DOE Office of Nuclear Energy’s used fuel disposition campaign, to investigate current modeling capabilities and to identify issues and knowledge gaps associated with coupled THMC processes and EBS–rock interactions associated with repositories hosted in clay rock. In this study, we simulated a generic repository case assuming an EBS design with waste emplacement in horizontal tunnels that are back-filled with bentonite-based swelling clay as a protective buffer and heat load, derived for one type of US reactor spent fuel. We adopted the Barcelona basic model (BBM) for modeling of the geomechanical behavior of the bentonite, using properties corresponding to the FEBEX bentonite, and we used clay host rock properties derived from the Opalinus clay at Mont Terri, Switzerland. We present results related to EBS host–rock interactions and geomechanical performance in general, as well as studies related to peak temperature, buffer resaturation and thermally induced pressurization of host rock pore water, and swelling pressure change owing to variation of chemical composition in the EBS. Our initial THM modeling results show strong THM-driven interactions between the bentonite buffer and the low-permeability host rock. The resaturation of the buffer is delayed as a result of the low rock permeability, and the fluid pressure in the host rock is strongly coupled with the temperature changes, which under certain circumstances could result in a significant increase in pore pressure. Moreover, using the BBM, the bentonite buffer was found to have a rather complex geomechanical behavior that eventually leads to a slightly nonuniform density distribution. Nevertheless, the simulation shows that the swelling of the buffer is functioning to provide an adequate increase in confining stress on the tunnel wall, leading to a stabilization of any failure that may occur during the tunnel excavation. Finally, we describe the application of a possible approach for linking THM processes with chemistry, focusing on the evolution of primary and secondary swelling, in which the secondary swelling is caused by changes in ionic concentration, which in turn is evaluated using a transport simulation model. 相似文献
9.
An approach for predicting swelling pressure of bentonites based on thermodynamic relationships between swelling pressure and suction is presented in this paper. The proposed method requires sorption isotherm data of the bentonites. A series of swelling pressure tests were performed on compacted specimens of bentonite-sand mixtures with different bentonite contents, water contents, and dry densities. The sorption isotherm of the pure bentonite was measured using a chilled-mirror hygrometer. It is found that the method works well for the bentonite-sand mixtures tested. Several published data on bentonites that have been proposed to be used as buffer and sealing material for nuclear waste repository were collected and used to verify the method. The proposed method is found to be also applicable for other bentonites of different types and therefore, can be used to predict swelling pressure of bentonites. 相似文献
10.
缓冲材料作为高放废物深地质处置库中一道重要的人工屏障,与高放废物容器和处置库围岩直接接触,在高放废物衰变热、辐射作用和地下水等影响下产生复杂的热-水-力-化学耦合作用,为了验证缓冲材料是否能长期有效地发挥其屏障材料的作用,核工业北京地质研究院利用高庙子钠基膨润土组装并运行了模拟中国高放废物地质处置室 尺寸的大型缓冲材料膨润土试验台架（China-Mock-Up）。建立了缓冲材料试验台架的安装和试验方法,依据实测数据和理论分析,揭示了热-水-力-化学耦合作用条件下膨润土中的相对湿度是在加热器的热效应和外部供水的湿效应共同作用下发生变化的,压实膨润土中应力的变化主要是由于膨润土遇水膨胀和加热器的热效应引起的,试验验证了模拟高放废物地质处置室内加热器（废物罐）运行初期的位移过程,为缓冲材料和高放废物地质处置库的设计提供了重要的工程参数和理论依据。 相似文献
11.
In the international DECOVALEX-THMC project, five research teams study the influence of thermal-hydro-mechanical (THM) coupling
on the safety of a hypothetical geological repository for spent fuel. In order to improve the analyses, the teams calibrated
their bentonite models with results from laboratory experiments, including swelling pressure tests, water uptake tests, thermally
gradient tests, and the CEA mock-up THM experiment. This paper describes the mathematical models used by the teams, and compares
the results of their calibrations with the experimental data. 相似文献
12.
Bentonite pellets are recognized as good buffer/backfill materials for sealing technological voids in high-level radioactive waste (HLW) repository. Compared to that of a traditional compacted bentonite block, one of the most important particularities of this material is the initially discrete pellets and the inevitable heterogeneous porosity formed, leading to a distinctive water retention behaviour. In this paper, water retention and mercury intrusion porosimetry (MIP) tests were conducted on pellet mixture (constant volume), single pellet (free swelling) and compacted block (constant volume) of GMZ bentonite, water retention properties and pore structure evolutions of the specimens were comparatively investigated. Results show that the water retention properties of the three specimens are almost similar to each other in the high suction range (>?10 MPa), while the water retention capacity of pellet mixture is lower than those of the compacted block and single pellet in the low suction range (<?10 MPa). Based on the capillary water retention theory (the Young–Laplace equation), a new concept ‘saturated void ratio’ that was positively related to water content and dependent on pore size distribution of the specimen was defined. Then, according to the product of saturated void ratio and water density in saturated void, differences of water retention properties for the three specimens at low suctions were explained. Meanwhile, MIP tests indicate that as suction decreases, the micro- and macrovoid ratios of pellet mixture and compacted block decrease as the mesovoid ratio increases, while all the void ratios of single pellets increase. This could be explained that upon wetting, water is successively adsorbed into the inter-layer, inter-particle and inter-pellet voids, leading to the subdivision of particles and swelling of aggregates and pellets. Under constant volume condition, aggregates and pellets tend to swell and fill into the inter-aggregates or inter-pellets voids. While under free swelling condition, the particles and aggregates in a single pellet tend to swell outward rather than squeezing into the inter-aggregate voids, leading to the expansion of the pores and even formation of cracks. Results including the effects of initial conditions (initial dry density and fabric) and constraint conditions (constant volume or free swelling) on the water retention capacity and pore structure evolution reached in this work are of great importance in designing of engineering barrier systems for the HLW repository. 相似文献
13.
在核废料安全处置分析中,非饱和膨润土常被作为缓冲材料,缓冲层膨润土中的吸力和位移变化是影响处置库性状的两个重要的物理参数。吸力直接影响膨润土的渗透性和力学性质;而位移变化则直接影响处置库设计的成败。本文以FEBEX原位试验数据为依据,应用有限元软件CODE-BRIGHT,分析缓冲层膨润土在热-水-力不同耦合形式下吸力和位移的变化规律,通过对不同耦合模式下吸力和位移的对比,分析影响吸力与位移变化的主要因素。结果可使我们进一步了解核废料处置库中缓冲层的性状,也可为核废料处置库设计计算时选用简单而有效的耦合模型提供参考。 相似文献
14.
Opalinus clay (OPA) is currently being investigated as a potential host rock for radioactive waste repository. The construction of this repository will lead to an excavation-damaged zone (EDZ) in the surrounding. Its sealing ability is crucial for the safety assessment of the geological repository. The sealing ability of OPA has a close relationship with its water retention and gas permeability behaviours. For this purpose, the water retention and gas permeability of OPA and its comparison with the artificial barrier (i.e. bentonite) were investigated in this study. The results show that OPA absorbed less water than granular bentonite material with equal suction. Compared with the other two similar materials (Boom clay and COx argillite), which were selected as natural engineering barriers for nuclear waste storage in Belgium and France, the suction behaviours of OPA are similar to those of COx argillite but notably different from those of Boom clay. The gas permeability tests show that OPA sample is quite sensitive to the changes in confining pressures but is less sensitive to applied gas pressures. Further, it is found that the OPA is more permeable than bentonite barrier after 10.5 years of hydration. Then, the OPA samples were artificially water-saturated. We find that the sealing ability can be recovered after long-time water saturation. However, when comparing with bentonite barrier, it is still a weak zone. This indicates that the EDZ should be paid more attention for the assessment the performance of the nuclear repository. 相似文献
15.
A simple thermohydromechanical (THM) constitutive model for unsaturated soils is described. The effective stress concept is extended to unsaturated soils with the introduction of a capillary stress. This capillary stress is based on a microstructural model and calculated from attraction forces due to water menisci. The effect of desaturation and the thermal softening phenomenon are modelled with a minimal number of material parameters and based on existing models. THM process is qualitatively and quantitatively modelled by using experimental data and previous work to show the application of the model, including a drying path under mechanical stress with transition between saturated and unsaturated states, a heating path under constant suction and a deviatoric path with imposed suction and temperature. The results show that the present model can simulate the THM behaviour in unsaturated soils in a satisfactory way. 相似文献
16.
Bentonite pellet mixtures are considered as one of the candidate sealing materials for deep geological disposals of radioactive waste. One of the particularities of this material is the initial heterogeneous distribution of pellets and porosity within the mixture, leading to complex hydro-mechanical behaviour. In this paper, the hydro-mechanical properties of GMZ bentonite pellet mixtures were investigated in the laboratory by carrying out water retention tests on pellet mixtures under constant-volume condition and single pellets under free swelling condition, as well as a infiltration test on a column specimen of pellet mixture. In the infiltration test, the relative humidity and radial swelling pressure were monitored at five heights, the axial swelling pressure was also recorded. The instantaneous profile method was applied to determine the unsaturated hydraulic conductivities. Results show that, in high suction range (>?10 MPa) the water retention curve of pellet mixture under constant-volume condition was comparable to that of a single pellet under free swelling condition, while in low suction range (<?10 MPa) the latter exhibits a much higher water retention capacity. Due to clogging of large pores, the unsaturated hydraulic conductivity decreases as suction decreases to around 25 MPa. However, with further suction decrease, the hydraulic conductivity increases continuously until the value at saturated state, as in the case of most unsaturated soils. The radial swelling pressure at different heights develops with local sudden increase and decrease, which was attributed to local rearrangement of pellets upon wetting. By contrast, as the axial swelling pressure was measured on the global surface of the specimen, it develops in a more regular fashion. 相似文献
17.
高放废物地质处置库处于温度?渗流?应力（THM）多场耦合环境中,对高放废物处置库进行安全评估时,需进行多场耦合分析。然而,高放废物处置库开挖引起硐壁附近围岩应力重分布,产生损伤,导致围岩热学参数（T）、渗流参数（H）和力学参数（M）发生变化,且在空间上分布不均匀,这将会对运营期处置库THM耦合演化过程产生显著影响。通过分析高放废物处置库温度?渗流?应力三场的耦合原理和处置库围岩损伤的分布和演化规律,定义了损伤变量和损伤演化准则,并将损伤变量与热学参数、渗流参数、力学参数以及多场耦合参数（Biot系数、Biot模量和温度排水系数）建立联系,将围岩损伤与温度?渗流?应力建立联系,形成了一个弹塑性损伤温度?渗流?应力多场耦合数值模型,然后利用建立的模型对瑞士Mont Terri高放废物地质处置库围岩加热试验进行模拟,对比了模拟值和试验值,比较了考虑开挖损伤和不考虑开挖损伤对高放废物地质处置库温度?渗流?应力的影响,并分析了在多场耦合作用下开挖损伤的演化规律。 相似文献
18.
A simple thermo‐hydro‐mechanical (THM) constitutive model for unsaturated soils is described. The effective stress concept is extended to unsaturated soils with the introduction of a capillary stress. This capillary stress is based on a microstructural model and calculated from attraction forces due to water menisci. The effect of desaturation and the thermal softening phenomenon are modelled with a minimal number of material parameters and based on existing models. THM process is qualitatively and quantitatively modelled by using experimental data and previous work to show the application of the model, including a drying path under mechanical stress with transition between saturated and unsaturated states, a heating path under constant suction and a deviatoric path with imposed suction and temperature. The results show that the present model can simulate the THM behaviour in unsaturated soils in a satisfactory way. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
19.
Compacted soil –bentonite mixtures are finding wide application as buffer material for waste repositories for their favorable self-sealing qualities. The swelling properties of such materials which serve as a measure of their self-sealing capabilities and, thus, the efficiency of the repository in sealing off their contents from the environment are closely related to the chemistry of the leachate that emanate from the wastes. For this reason, the swelling parameters (namely swelling potential and pressure) of compacted lateritic soil–bentonite mixtures under consideration for use as barrier in municipal waste landfill were evaluated. Series of swelling potential and pressure tests were performed using variable content (0–10 %) of bentonite at predetermined optimum moisture content. Soil mixtures were compacted with British Standard Heavy compactive effort and saturated with processed tap water as well as three leachate solutions of varying ionic strength that were generated in active open dump landfills. Experimental results showed that swelling potential based on the free swell together with the maximum swell pressures of compacted soil mixtures measured at equilibrium increased approximately linearly with increase in the amount of bentonite when inundated with processed tap water and the three leachate solutions. On the other hand, these swelling parameters decreased as the ionic strength of the leachate solutions measured by their electrical conductivity increased for the various soil mixtures. These results provide an insight into the swelling behavior and the possible degradation in the efficiency of the proposed lateritic soil–bentonite mixtures in relation to their use as buffer material in waste landfills. 相似文献
20.
One of the most suitable ways under study for the disposal of high-level radioactive waste (HLW) is isolation in deep geological repositories. It is very important to research the thermo-hydromechanical (THM) coupled processes associated with an HLW disposal repository. Non-linear coupled equations, which are used to describe the THM coupled process and are suited to saturated-unsaturated porous media, are presented in this paper. A numerical method to solve these equations is put forward, and a finite element code is developed. This code is suited to the plane strain or axis-symmetry problem. Then this code is used to simulate the THM coupled process in the near field of an ideal disposal repository. The temperature vs. time, hydraulic head vs. time and stress vs. time results show that, in this assumed condition, the impact of temperature is very long (over 10 000 a) and the impact of the water head is short (about 90 d). Since the stress is induced by temperature and hydraulic head in this condition, the impact time of stress is the same as that of temperature. The results show that THM coupled processes are very important in the safety analysis of an HLW deep geological disposal repository. 相似文献
|
