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
The oedometer tests are performed on artificially frozen sand, silt and clay. The tests also include ice as a reference material. The results are given by parameters describing the tangent deformation modulus and the time resistance against creep.
The triaxial creep tests are carried out on the artificially frozen clay, and on a permafrost clay from Spitsbergen. The data are interpreted in accordance with Hult's theory. The artificially frozen clay shows much higher creep resistance than the permafrost clay.
In addition to deformation moduli and creep parameters the routine data of the materials tested are also included. 相似文献
For extending the microscopic characteristics of constituent materials to a macroscopic seepage behavior of the micro-inhomogeneous material we apply a homogenization analysis (HA). That is, starting with the Navier–Stokes equation with distributed viscosity that is calculated by the former MD procedure we determine macroscopic permeability characteristics of bentonite for both cases of pure- and salt-water. Then, by using the permeability property we calculate long-term consolidation behavior of buffering clay, which is planed to be used for high-level radioactive waste (HLRW) management. Here the deformation is treated under the well-defined Cam clay model. 相似文献
In the long term, at room temperatures, it is predicted that the material will behave like a normally consolidated clay and strain harden plastically with increasing mean effective stress. In shear, its undrained strength will decrease slightly after failure. Working relationships, based on critical state soil mechanics, have been established for the normal consolidation and failure conditions of the material. The behaviour of the material in drained conditions can be predicted from these relationships. 相似文献
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
The results indicate parallel hardening lines at systematically lower values of specific volume at elevated temperatures. In shear, increased temperatures produced lower values of maximum deviator stressqf, and higher pore water pressure changesΔuf. The net result is curved peak strength envelops in plots ofqf versuspf′ that are higher at elevated temperatures, even though the strengths,qf of individual specimens are lower. The critical state strength envelope is curved inq, p′-planes.
The effect of drained heating on buffer to 100°C is not marked. Compressibilities, stiffnesses, strengths, and pore water pressure generation are all affected, but none of the changes are great. 相似文献
The new approach is very illustrative and conserves the volume of the clay section under consideration. Conservation of the volume gives the right time dependency in the case of a well mixed volume. The nonstationary phase of transport can thus be modelled using in principle the presented simplifying concept as a starting point.
Comparisons of stationary mass transport calculations with previous and present simplifying expressions to more accurate calculations are presented. 相似文献
Herein are presented the results of laboratory and field tests which were carried out on loess in Yugoslavia.
Experience gained during recent decades show that the loess soil in some cases undergoes structural collapse and subsidence due to inundation. In order to find the explanation of such behaviour, numerous laboratory and field load tests on loess soil have been performed. Using the obtained results, several correlations have been established.
On the basis of the unconfined test results, a correlation between the initial dry density, initial water content and unconfined compression strength has been established.
A relatively large number of the consolidation subsidence tests (about 550), carried out on undisturbed loess samples, made possible the determination of the degree of subsidence and the corresponding values of the dimensionless coefficients of subsidence. These coefficients have been determined for several values of the initial dry density, for various degrees of saturation and for several stress levels upon wetting. Using these coefficients, the values of the additional settlement caused by flooding of loess under the foundation can easily be calculated. It is of particular interest to note that, in general, water penetrates under one part of the building, producing differential settlements, which are in most cases very dangerous.
By the comparative laboratory investigation of the undisturbed loess samples obtained by thin walled sampler and samples obtained from pits, it has been shown that the mechanical disturbance is an extremely important factor which governs the shear and deformation parameters of loess soils.
The laboratory test results obtained on undisturbed loess samples, cut from blocks in the vertical and horizontal direction, have shown that this soil exhibits anisotropic properties. For this reason a stress deformation problem in an anisotropic medium has been treated by the finite element method.
Static penetration tests and field load tests in loess soils with natural water content and also after saturation have been performed and are described.
The results of the observed settlements for two statically identical multi-storey buildings are also presented. Using the coefficients of subsidence for the undisturbed samples cut from blocks, very good agreement between the calculated and the observed settlements has been obtained. 相似文献
The objective of the CNFWMP is to develop a disposal concept that will protect human health and the natural environment far into the future. Assessments of the conceptual vault designs are based on system theory in which an attempt is made to correlate experiences with theoretical concepts of planned systems in such a way that the resulting coordination is sound and convincing. By necessity, since experiments with a total disposal system can never be performed, both the design and the performance assessment rely on experiments performed on physical models of vault elements over relatively short times and on information inferred from calculations (mathematical models) that simulate the probable behaviour of the system in the space-time domainof interest. For a simulation model to be successful, that is applied within a real world situation, the model must provide information regarding the behaviour of the system of interest that is clearly better, in some way, than the mental image or other abstract model that would be used instead. The results of a series of tests performed within the activity known as validation serve as tangible evidence regarding the success of a model in representing the system of interest.
This paper focusses on the validation of the models that describe the hygro-thermo-mechanical behaviour of the engineered clay-barriers proposed for application in the Canadian disposal system concept. The strategy being used to address the key issues in modelling to minimize the model error and to maximize the usefulness of the simulation model, based on testing procedures, is reviewed. Finally, a concept of the validation of codes/models that describe the unsaturated behaviour of engineered clay barriers, is described. 相似文献
The computed results using this method were found to be in good agreement with the measured values of some field tests and laboratory model tests. 相似文献
Resulting from the inhomogeneity of salt structures the demanded safety of a permanent repository for radioactive wastes can be demonstrated only by a specific site analysis in which the entire system, “the geological situation, the repository, and the form and amount of the wastes” and their interrelationships are taken into consideration.
The site analysis has three essential tasks: (1) Assessment of the thermomechanical load capacity of the host rock, so that deposition strategies can be determined for the site; (2) Determination of the safe dimensions of the mine (e.g. stability of the caverns and safety of the operations); and (3) Evaluation of the barriers and the long-term safety analysis for the authorization procedure.
The geotechnical stability analysis is a critical part of the safety assessment. Engineering–geological study of the site, laboratory and in situ-experiments, geomechanical modelling, and numerical static calculations comprise such an analysis.
Within a scenario analysis — according to the multi-barrier principle, the geological setting is checked to be able to contribute significantly to the waste isolation over long periods. The assessment of the integrity of the geological barrier can only be performed by making calculations with geomechanical and hydrogeological models. The proper idealization of the host rock in a computational model is the basis of a realistic calculation of stress distribution and excavation damage effects. The determination of water permeability along discontinuities is necessary in order to evaluate the barrier efficiency of each host rock.
In this paper some important processes for the performance assessment are described, namely creep and fracturing, permeability and infiltration, and halokinesis and subrosion.
For the future, the role and contributions of geoscientific and rock mechanics work within the safety assessment issues (e.g. geomechanical safety indicators) must be identified in greater detail, e.g. considerations of geomechanical natural analogy for calibration of constitutive laws. 相似文献
The materials studied in this work had been used in the construction of the impermeable core of the San Clemente Dam, belonging to the hydrographic basin of the Guadalquivir River (southern Spain). These marls present, as their prime characteristic, a carbonate content of the fine fraction consistently exceeding 50%, giving them special importance in the study of this phenomenon.
In this study, a direct relationship was found between the geotechnical properties of the soils studied and their degree of compaction, with the carbonate content and the type of minerals in the clay being the main factors determining the behaviour of these soils. Finally, we conclude that the percentage of carbonates should be used as a classification criterion for the soils used to construct the cores of earth-filled dams. 相似文献
The study of a high-level or long-lived nuclear waste disposal concept is necessarily a step-by-step procedure, with two main objectives: on one hand, ensuring a good disposal design, including feasibility of the vaults and their stability during the operating phase with the eventual continuation of the phase of waste retrievability, i.e. on a long period of time not shorter than one hundred years. On the other hand, the objective is to preserve the long-term clay properties with regard to radionuclide behavior, in particular those properties which influence their containment capacity.
Swelling clays as an engineered barrier material have been considered by ANDRA for a long time. Buffer material as an interface between the nuclear waste packages and the geological barrier and tight core of dams in drifts and shafts are the two types of constructions for which the clay conditioning and performance have been investigated. In both of these applications, the understanding of the THM behavior of the swelling clay is required. In the first case the THM load parameters are much more severe and the geochemical imbalances are of greater consequences.
R & D programmes are necessarily integrated into the design process of the disposal concept. The results will allow selection between technical solutions estimated as valuable candidates for validation within the project duration, i.e. 13 years, and those solutions which cannot be. In return the design process indicates what are the more profitable axis for the future R & D efforts. 相似文献