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1.
Eduardo E. Alonso Sarah M. Springman Charles W. W. Ng 《Geotechnical and Geological Engineering》2008,26(6):817-826
Two large-scale “in situ” demonstration experiments and their instrumentation are described. The first test (FEBEX Experiment)
involves the hydration of a compacted bentonite barrier under the combined effect of an inner source of heat and an outer
water flow from the confining saturated granite rock. In the second case, the progressive de-saturation of Opalinus clay induced
by maintained ventilation of an unlined tunnel is analyzed. The paper shows the performance of different sensors (capacitive
cells, psychrometers, TDR’s) and a comparison of fill behaviour with modelling results. The long term performance of some
instruments could also be evaluated specially in the case of FEBEX test. Capacitive sensors provide relative humidity data
during long transient periods characterised by very large variations of suction within the bentonite. 相似文献
2.
Marcelo Snchez Antonio Gens Leonardo do Nascimento Guimares Sebastin Olivella 《国际地质力学数值与分析法杂志》2005,29(8):751-787
The constitutive model presented in this work is built on a conceptual approach for unsaturated expansive soils in which the fundamental characteristic is the explicit consideration of two pore levels. The distinction between the macro‐ and microstructure provides the opportunity to take into account the dominant phenomena that affect the behaviour of each structural level and the main interactions between them. The microstructure is associated with the active clay minerals, while the macrostructure accounts for the larger‐scale structure of the material. The model has been formulated considering concepts of classical and generalized plasticity theories. The generalized stress–strain rate equations are derived within a framework of multidissipative materials, which provides a consistent and formal approach when there are several sources of energy dissipation. The model is formulated in the space of stresses, suction and temperature; and has been implemented in a finite element code. The approach has been applied to explaining and reproducing the behaviour of expansive soils in a variety of problems for which experimental data are available. Three application cases are presented in this paper. Of particular interest is the modelling of an accidental overheating, that took place in a large‐scale heating test. This test allows the capabilities of the model to be checked when a complex thermo‐hydro‐mechanical (THM) path is followed. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
3.
FEBEX is a demonstration and research project, which is being carried out by an international consortium led by the Spanish agency ENRESA and simulates components of the engineering barrier system in accordance with the ENRESA's AGP (Deep Geological Disposal) Granite reference disposal concept. The project includes tests on three scales: an “in situ” test at full scale in natural conditions; a “mock-up” test at almost full scale in controlled conditions; and a series of laboratory test to complement the information from the two large-scale test.The components of the mock-up test are similar to those of the “in situ” test: two electric heaters, a clay barrier consisting of highly compacted bentonite blocks, instrumentation, automatic control of heaters, and a data acquisition system for the data generated. The heterogeneities of the natural system (granite formation) are avoided, the hydration process is controlled with unlimited amount of water at constant pressure, and the boundary conditions are better defined than in the “in situ” test.The operational phase -hydration and heating- started in February 1997. It was initially planned to last for three years, but it has been decided to extend the operational phase to get as close as possible complete saturation of the buffer.Fifty-five months after the start of the operational phase, it can be concluded that the synergy achieved from the simultaneous, integrated performance of tests at different scales, is a valuable approach to establishing the viability of the reference concept, and making progress in the understanding and evaluation of the behaviour in the near field, especially the clay barrier. 相似文献
4.
J. Vaunat 《Engineering Geology》2005,81(3):317-328
A deep geological repository for nuclear waste requires the backfilling and sealing of shafts and galleries to block any preferential path for radioactive contaminants. The paper presents the coupled hydromechanical analyses of an in situ test carried out in the HADES underground laboratory in Mol, Belgium. The test examines the effectiveness of an expansive clay seal in a horizontal borehole specifically drilled for this purpose. The analysis covers the phase of seal hydration up to saturation and subsequent pore pressure equilibration. Hydraulic and mechanical constitutive laws suited to expansive clay materials have been chosen for the analyses with all the parameters determined independently of the in situ test. A quite good agreement has been found between test observations and computed results suggesting that the numerical formulation employed is able to reproduce the main features of a real sealing system. 相似文献
5.
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
6.
E. E. Alonso A. Lloret C. H. Delahaye J. Vaunat A. Gens G. Volckaert 《国际地质力学数值与分析法杂志》1998,22(1):1-27
BACCHUS2 in situ isothermal wetting experiment has been analysed by means of a coupled flow-deformation approach. Backfill material, a mixture of Boom clay powder and high density pellets, has been extensively tested in the laboratory in order to determine its hydraulic and mechanical properties. Parameters of constitutive equations were derived from this experimental data base. Two mechanical constitutive models have been used in the simulation of the ‘in situ’ experiment: a state surface approach and an elastoplastic model. Calculations have shown several features of the hydration process which help to understand the behaviour of expansive clay barriers. Predictions using both models have been compared with each other and with actual measurement records. This has allowed a discussion of the comparative mertis of both approaches and the identification of some critical parameters of backfill behaviour. Overall agreement between calculations and field measurements is encouraging and shows the potential of the methods developed to model the behaviour of engineered clay barriers in the context of nuclear waste disposal. © 1998 by John Wiley & Sons, Ltd. 相似文献
7.
《Geomechanics and Geoengineering》2013,8(2):121-127
To minimise potential structural damage to the overlying structures, foundation sites that contain expansive soils need treatment. One of the numerous improvement techniques currently available is thermal stabilisation. In an attempt to enhance the knowledge base on this subject matter, this paper presents the results of a study on the swelling behaviour of two heated expansive soils. The test specimens were heated in a programmable furnace at desired heating rates to desired temperatures. Swelling tests were performed to determine both the amount and rate of swelling. Based on the test results, the effect of heating on swelling behaviour was evaluated and the mechanism of swelling are discussed using the principles of physical chemistry and clay mineralogy. Meanwhile, the engineering significance of the research findings in terms of practical applications of thermal stabilisation are discussed. The findings of this study would provide a database useful for the design of structures that involve cohesive foundation soils using a holistic system approach. 相似文献
8.
Granular pile-anchor (GPA) technique has been found to be an innovative foundation technique for expansive clays posing the dual problem of swelling and shrinkage. Swelling occurs during absorption of water and shrinkage during evaporation of water. Generally, in field expansive clay beds, swelling takes place during rainy seasons and shrinkage during summers. GPA is a recent innovative foundation technique devised to ameliorate the dual swell-shrink problem of structures founded on expansive clay beds. The other innovative techniques are drilled piers, belled piers and under-reamed piles. Laboratory scale model studies and field scale experiments on GPAs yielded useful results and revealed that swelling of expansive clay beds was effectively controlled by GPA technique. Studies on swell-shrink behaviour of GPA-reinforced clay beds have not been performed so far. This paper presents results obtained from laboratory scale model studies on GPA-reinforced expansive clay beds subjected to alternate cycles of swelling and shrinkage. The data presented in this paper pertain to the swelling of test clay beds under the influence of three swell-shrink cycles (N) spanning a time period of 300 days. The test clay beds were reinforced with varying number of GPAs (n = 0, 1, 2 and 3). Heave (mm) in a given swell-shrink cycle decreased with increasing number of GPAs. Further, for a given number of GPAs (n), heave (mm) also decreased with increase in depth from the top of the clay bed. It was found that the resultant thickness of the clay bed (Hr) for swelling increased with increasing number of cycles. However, the percentage heave (ΔH/Hr) decreased as the number of swell-shrink cycles (N) increased. 相似文献
9.
Matthieu Dumont Said Taibi Jean‐Marie Fleureau Nabil Abou‐Bekr Abdelghani Saouab 《国际地质力学数值与分析法杂志》2011,35(12):1299-1317
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
10.
Jonny Rutqvist Liange Zheng Fei Chen Hui-Hai Liu Jens Birkholzer 《Rock Mechanics and Rock Engineering》2014,47(1):167-186
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
11.
The conditions of the bentonite in an engineered barrier for high-level radioactive waste disposal have been simulated in a series of tests. Cylindrical cells with an inner length of 60 cm and a diameter of 7 cm have been constructed. Inside the cells, six blocks of FEBEX bentonite have been piled-up, giving rise to a total length similar to the thickness of the clay barrier in a repository according to the Spanish concept. To obtain the blocks, the clay with its hygroscopic water content has been uniaxially compacted at a dry density of 1.65 g/cm3. The bottom surface of the material was heated at 100 °C and the top surface was injected with granitic water. The duration of the tests was 6, 12 and 24 months. The temperatures inside the clay and the water intake were measured during the tests and, at the end, the cells were dismounted and the dry density, water content and some hydro-mechanical properties of the clay (permeability, swelling pressure and swelling under load) were measured at different positions. The values obtained are compared to those of the untreated FEBEX bentonite. The injection of water provokes in the vicinity of the hydration surface an increase of the water content and a decrease of the dry density due to the swelling of the clay, while heating gives rise to an increase of the dry density and a reduction of the water content in the 18 cm closest to the heater, even after 2 years of thermo-hydraulic (TH) treatment. The swelling capacity and the hydraulic conductivity after TH treatment are mainly related to the dry density and water content attained during it. No major irreversible modifications of these properties with respect to those of the untreated clay have been detected. 相似文献
12.
The Barcelona basic model cannot predict the mechanical behaviour of unsaturated expansive soils, whereas the Barcelona expansive model (BExM) can only predict the stress–strain behaviour of unsaturated expansive soils without the water‐retention behaviour being incorporated. Moreover, the micro‐parameters and the coupling function between micro‐structural and macro‐structural strains in the BExM are difficult to determine. Experimental data show that the compression curves for non‐expansive soils under constant suctions are shifted towards higher void ratios with increasing suction, whereas the opposite is true for expansive soils. According to the observed water‐retention behaviour of unsaturated expansive soils, the air‐entry value increases with density, and the relationship between the degree of saturation and void ratio is linear at constant suction. According to the above observation, an elastoplastic constitutive model is developed for predicting the hydraulic and mechanical behaviour of unsaturated expansive soils, based on the existing hydro‐mechanical model for non‐expansive unsaturated soil. The model takes into consideration the effect of degree of saturation on the mechanical behaviour and that of void ratio on the water‐retention behaviour. The concept of equivalent void ratio curve is introduced to distinguish the plastic potential curve from the yield curve. The model predictions are compared with the test results of an unsaturated expansive soil, including swelling tests under constant net stress, isotropic compression tests and triaxial shear tests under constant suction. The comparison indicates that the model offers great potential for quantitatively predicting the hydraulic and mechanical behaviour of unsaturated expansive soils. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
13.
黏土颗粒水化膜厚度问题是泥质膨胀性岩土膨胀机制研究的理论基础。关于黏土颗粒水化膜厚度测试资料较为丰富,但通过原子力显微镜测试黏土颗粒水化膜厚度的研究成果还较为少见,且在测试方法方面尚不完善。基于3层水化膜结构模型和原子力显微镜测试技术,通过对蒙脱石粉末、泥岩粉末、泥岩岩片3种样品的测试研究,提出了水化膜厚度刺入式测试方法、粉末样和岩石样的制样方法、试验数据的统计处理方法。总结了水化膜厚度测试曲线自由水段、弱结合水段、强结合水段、黏土颗粒段的变化规律。通过和既有研究成果的对比分析,论证了原子力显微镜刺入测试黏土颗粒水化膜厚度的合理性与可行性。结合工程实践,探讨了定量化获取水化膜厚度在理解泥质膨胀性岩土膨胀机制方面的工程意义和理论价值。 相似文献
14.
15.
De la Morena Gema Navarro Vicente Asensio Laura Gallipoli Domenico 《Acta Geotechnica》2021,16(9):2775-2790
This paper presents a constitutive model that predicts the water retention behaviour of compacted clays with evolving bimodal pore size distributions. In line with previous research, the model differentiates between the water present inside the saturated pores of the clay aggregates (the microstructure) and the water present inside the pores between clay aggregates (the macrostructure). A new formulation is then introduced to account for the effect of the macrostructural porosity changes on the retention behaviour of the soil, which results in a consistent evolution of the air-entry value of suction with volumetric deformations. Data from wetting tests on three different active clays (i.e. MX-80 bentonite, FEBEX bentonite, and Boom clay), subjected to distinct mechanical restraints, were used to formulate, calibrate, and validate the proposed model. Results from free swelling tests were also modelled by using both the proposed double porosity model and a published single porosity model, which confirmed the improvement in the predictions of degree of saturation by the present approach. The proposed retention model might be applied, for example, to the simulation of the hydromechanical behaviour of engineered bentonite barriers in underground nuclear waste repositories, where compacted active clays are subjected to changes of both suction and porosity structure under restrained volume conditions.
相似文献16.
南宁膨胀土非线性流变模型研究 总被引：1，自引：0，他引：1
对南宁非饱和膨胀土进行一系列的加载-卸载固结蠕变试验,得到了不同含水率的膨胀土在不同应力水平下应变-时间曲线和不同时刻的应力-应变等时曲线簇。通过对膨胀土各阶段蠕变变形的分析,得到了膨胀土的固结蠕变是包含有黏弹性变形和黏塑性变形成分的非线性蠕变。采用模型流变与经验流变理论相结合的方法,将膨胀土的蠕变变形分成线性和非线性两部分进行分析,蠕变柔量和线性黏弹性模量随时间减小,而线性黏塑性模量随时间增大。结合膨胀土的线性黏塑性模型和非线性黏塑性经验模型,建立能够描述膨胀土非线性流变的黏塑性本构方程。根据试验所得数据,通过非线性拟合方法得到各模型参数,用该模型进行数值分析得到的理论与蠕变试验结果对比非常吻合。研究成果为实际工程提供了流变变形计算分析的可靠依据。 相似文献
17.
Geological and engineering characteristics of expansive soils and rocks in northern Oman 总被引：3，自引：0，他引：3
The geology and former climate of northern Oman favoured the formation of smectite clay minerals in certain materials which are implicated in ground heave problems. Investigations have shown that the smectite content of these expansive materials was developed in Oligocene, Miocene and Pliocene times. No evidence of a significant content of smectite was found in pre Eocene strata or in Quaternary strata, except for Desert Fill. It is shown that the main types of expansive materials in northern Oman are bentonitic mudstones, marls and silty mudstones, argillaceous dolomitic limestone, altered conglomerates and the desert fill derived from these. These swelling materials exist as impersistent bands within the bedrock Tertiary conglomerates and limestones. A geotechnical testing program was carried out on undisturbed samples from Sultan Qaboos University staff housing areas where building damage had occurred, to evaluate mineralogical composition, cation content and swelling characteristics. The test results characterized these soils/rocks as highly expansive type with Na-smectite as the dominant clay mineral. 相似文献
18.
An unconventional numerical scheme is developed to simulate coupled thermo-hydro-mechanical (THM) processes in partially saturated medium. The non-isothermal, unsaturated fluid flow and mechanical processes are sequentially coupled by updating all the state variables using cellular automaton technique and finite difference method on spatial and temporal scale, respectively. A new cellular automaton updating scheme is proposed by introducing a fast successive relaxation index, which greatly improves the computational efficiency in the simulation of THM coupling process. This is implemented in a self-developed numerical system, i.e., an elasto-plastic cellular automaton (EPCA3D), which was used to numerically reproduce the coupled THM behavior of bentonite pellets in a column experiment that was heated up to 140 °C firstly and then was hydrated simulating the resaturation of the backfilling. By using the cellular automaton technique in EPCA3D, the challenging courses of the changing boundary conditions over time and space during the experiment are conveniently implemented. The EPCA3D was able to reproduce the main physical processes of the in laboratory column bentonite experiment within the heating and hydration phase. The modeling results for the evolution of temperature, relative humidity, water uptake and axial pressure are consistent with the experimental data in terms of trends and magnitudes, which verifies the realistic simulation with the developed model and contributes to a deeper understanding of the observed phenomena. 相似文献
19.
In this paper, a numerical solution for the electro-osmosis consolidation of clay in multi-dimensional domains at large strains is presented, with the coupling of the soil mechanical behaviour, pore water transport and electrical fields being considered. In particular, the Modified Cam Clay model is employed to describe the elasto-plastic behaviour of clay, and some empirical expressions are used to consider the nonlinear variation of the hydraulic and electrical conductivities of the soil mass during the consolidation processes. The implementation of the theoretical model in a finite element code allows for analysis of the evolution of the transient response of the clay subjected to electro-osmosis treatment. The proposed model is verified via comparison with data from a large strain electro-osmosis laboratory test, to demonstrate its accuracy and effectiveness. Various numerical examples are also investigated to study the deformation characteristics and time-dependent evolution of the excess pore pressure. Finally, a well-documented field application of electro-osmosis is simulated to provide further verification. The results show that the numerical solution is effective in predicting the nonlinear behaviour of clay during electro-osmosis consolidation. 相似文献
20.
超大断面炭质千枚岩隧道新型支护结构长期稳定性研究 总被引：1，自引：0，他引：1
针对兰渝铁路两水隧道岩质软、跨度大的特点,采用加厚初喷、二衬和双层型钢拱架的新型支护方式。通过对现场岩样的室内三轴蠕变试验,研究炭质千枚岩蠕变特性。试验结果表明,伯格斯蠕变模型能比较准确地描述其长期流变行为。运用大型岩土工程分析软件FLAC3D,结合现场新型支护方式,模拟隧道建成后DK357+976处围岩的流变力学行为,分析隧道在运营过程中围岩的变形和支护结构的受力情况。结果表明：在隧道100 a的使用期限内,二次衬砌能有效地减小围岩蠕变变形,支护结构中仅拱顶初喷在后期产生破坏,现场支护方式可以保证隧道的长期稳定性。 相似文献