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Probabilistic analyses of soil consolidation by prefabricated vertical drains for single‐drain and multi‐drain systems 
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下载免费PDF全文 Natural soils are one of the most inherently variables in the ground. Although the significance of inherent soil variability in relation to reliable predictions of consolidation rates of soil deposits has long been realized, there have been few studies that addressed the issue of soil variability for the problem of ground improvement by prefabricated vertical drains. Despite showing valuable insights into the impact of soil spatial variability on soil consolidation by prefabricated vertical drains, available stochastic works on this subject are based on a single‐drain (or unit cell) analyses. However, how the idealized unit cell solution can be a supplement to the complex multi‐drain systems for spatially variable soils has never been addressed in the literature. In this study, a rigorous stochastic finite elements modeling approach that allows the true nature of soil spatial variability to be considered in a reliable and quantifiable manner, both for the single‐drain and multi‐drain systems, is presented. The feasibility of performing an analysis based on the unit cell concept as compared with the multi‐drain analysis is assessed in a probabilistic context. It is shown that with proper input statistics representative of a particular domain of interest, both the single‐drain and multi‐drain analyses yield almost identical results. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Yahia E.-A. Mohamedzein Amer A. Al-Rawas Mohammed Y. Al-Aghbari Ahmed Qatan Abdul-Hamid Al-Rawas 《Engineering Geology》2005,80(3-4):271-281
The possibility of using crushed shales as landfill liners is investigated in this study. Two types of shales were studied by performing the following laboratory tests: hydraulic conductivity, compaction, swelling, consolidation, X-ray diffraction (XRD), scanning electron microscope (SEM) and chemical analysis. For both compacted shales, the hydraulic conductivity was in order of 10− 7 cm/s or less which satisfies the specifications for landfill liners. The results of XRD and SEM support the low values of the hydraulic conductivity. Because of the dominant presence of low-activity kaolinite, there was no significant change in the hydraulic conductivity when the compacted shales are exposed to calcium chloride solution. The compressibility of the compacted clay was low and no serious post-construction settlement is expected. The shear strength of the compacted shales was within the usual expected range for earthen liners and, therefore, should pose no challenges with respect to shear strength. The crushed shales also satisfy the other criteria related to Atterberg limits and grain size. 相似文献
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This paper aims at determining the failure probability and the corresponding most predominant failure mode at both ultimate (ULS) and serviceability (SLS) limit states of a circular foundation resting on a (c, φ) soil and subjected to an inclined loading. The failure modes at ULS are the footing sliding and the soil punching while those at SLS are the exceedance of tolerable horizontal and vertical footing displacements. The probabilistic results based on the response surface methodology have shown that at both ULS and SLS, there is a load inclination where neither mode of failure is predominant. This inclination corresponds to the loading configurations situated on the line joining the origin and the maximal point of the interaction diagram. In a second stage, the results of a sensitivity analysis showing the effect of the different statistical parameters of the uncertain variables on the value of the failure probability were presented and discussed. 相似文献
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Tamara Al-Bittar Abdul-Hamid Soubra 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2017,11(2):215-229
This paper presents a probabilistic analysis to compute the probability density function of the bearing capacity of a strip footing resting on a spatially varying rock mass. The rock is assumed to follow the generalised Hoek–Brown failure criterion. The uniaxial compressive strength of the intact rock (σc) was considered as a random field and the geological strength index was modelled as a random variable. The uncertainty propagation methodology employed in the analysis is the sparse polynomial chaos expansion. A global sensitivity analysis based on Sobol indices was performed. Some numerical results were presented and discussed. 相似文献
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Rotational failure mechanisms for the face stability analysis of tunnels driven by a pressurized shield 总被引：1，自引：0，他引：1
The aim of this paper is to determine the collapse and blow‐out face pressures of a circular tunnel driven by a pressurized shield. The analysis is performed in the framework of the kinematical approach of the limit analysis theory. Two rotational failure mechanisms are proposed for the active and passive cases. These mechanisms have two significant advantages with respect to the available ones: (i) they take into account the entire circular tunnel face instead of an inscribed ellipse to this circular area, and (ii) they are more consistent with the rotational rigid‐block movement observed in the experimental tests. For both the active and passive cases, the three‐dimensional failure surface was generated ‘point by point’ instead of simple use of the existing standard geometric shapes such as cones or cylinders. This was achieved by employing a spatial discretization technique. The numerical results have shown that the present rotational mechanisms provide, in the case of frictional soils (with or without cohesion), a significant improvement with respect to the translational mechanisms. Finally, an extension of the proposed collapse mechanism to include a tension cut‐off in the classical Mohr–Coulomb failure criterion is presented and discussed. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Two advanced Kriging metamodeling techniques were used to compute the failure probability of geotechnical structures involving spatially varying soil properties. These methods are based on a Kriging metamodel combined with a global sensitivity analysis that is called in literature Global Sensitivity Analysis-enhanced Surrogate (GSAS) modeling for reliability analysis. The GSAS methodology may be used in combination with either the Monte Carlo simulation (MCS) or importance sampling (IS) method. The resulting Kriging metamodeling techniques are called GSAS-MCS or GSAS-IS. The objective of these techniques is to reduce the number of calls of the mechanical model as compared with the classical Kriging-based metamodeling techniques (called AK-MCS and AK-IS) combining Kriging with MCS or IS. The soil uncertain parameters were assumed as non-Gaussian random fields. EOLE methodology was used to discretize these random fields. The mechanical models were based on numerical simulations. Some probabilistic numerical results are presented and discussed. 相似文献
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Bearing capacity of strip footings on spatially random soils using sparse polynomial chaos expansion
A probabilistic model is presented to compute the probability density function (PDF) of the ultimate bearing capacity of a strip footing resting on a spatially varying soil. The soil cohesion and friction angle were considered as two anisotropic cross‐correlated non‐Gaussian random fields. The deterministic model was based on numerical simulations. An efficient uncertainty propagation methodology that makes use of a non‐intrusive approach to build up a sparse polynomial chaos expansion for the system response was employed. The probabilistic numerical results were presented in the case of a weightless soil. Sobol indices have shown that the variability of the ultimate bearing capacity is mainly due to the soil cohesion. An increase in the coefficient of variation of a soil parameter (c or φ) increases its Sobol index, this increase being more significant for the friction angle. The negative correlation between the soil shear strength parameters decreases the response variability. The variability of the ultimate bearing capacity increases with the increase in the coefficients of variation of the random fields, the increase being more significant for the cohesion parameter. The decrease in the autocorrelation distances may lead to a smaller variability of the ultimate bearing capacity. Finally, the probabilistic mean value of the ultimate bearing capacity presents a minimum. This minimum is obtained in the isotropic case when the autocorrelation distance is nearly equal to the footing breadth. However, for the anisotropic case, this minimum is obtained at a given value of the ratio between the horizontal and vertical autocorrelation distances. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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The sparse polynomial chaos expansion (SPCE) methodology is an efficient approach that deals with uncertainties propagation in case of high‐dimensional problems (i.e., when a large number of random variables is involved). This methodology significantly reduces the computational cost with respect to the classical full PCE methodology. Notice however that when dealing with computationally‐expensive deterministic models, the time cost remains important even with the use of the SPCE. In this paper, an efficient combined use of the SPCE methodology and the Global Sensitivity Analysis is proposed to solve such problem. The proposed methodology is firstly validated using a relatively non‐expensive deterministic model that involves the computation of the PDF of the ultimate bearing capacity of a strip footing resting on a weightless spatially varying soil where the soil cohesion and angle of internal friction are modeled by two anisotropic non‐Gaussian cross‐correlated random fields. This methodology is then applied to an expensive model that considers the case of a ponderable soil. A brief parametric study is presented in this case to show the efficiency of the proposed methodology. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Probabilistic analyses of tunneling-induced ground movements 总被引：1，自引：0，他引：1
Tunneling-induced ground movements are investigated in this paper using both deterministic and probabilistic analyses. The deterministic model is based on three-dimensional (3D) numerical simulations using the commercial code FLAC3D. This model attempts to reproduce some major phenomena during a typical slurry-shield tunnel excavation (ground movements due to the applied face pressure, the overcutting, the shield conicity, the annular void behind the shield, and the grout injection in this void). Moreover, the model provides useful information about the nature and magnitude of the soil movements at the ground surface. A probabilistic study is then undertaken in order to evaluate the impact of the variability of several input variables on the ground movements. An efficient probabilistic method called CSRSM is used to assess this uncertainty propagation. In a last section, the output variables of the model are linked to failure criteria. This allows one to determine probabilities of failure, depending on the probabilistic properties of the input variables and on the admissible threshold of each criterion. 相似文献
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Continuous velocity fields for collapse and blowout of a pressurized tunnel face in purely cohesive soil 总被引：1，自引：0，他引：1
Face stability analysis of tunnels excavated under pressurized shields is a major issue in real tunnelling projects. Most of the failure mechanisms used for the stability analysis of tunnels in purely cohesive soils were derived from rigid block failure mechanisms that were developed for frictional soils, by imposing a null friction angle. For a purely cohesive soil, this kind of mechanism is quite far from the actual velocity field. This paper aims at proposing two new continuous velocity fields for both collapse and blowout of an air‐pressurized tunnel face. These velocity fields are much more consistent with the actual failures observed in undrained clays. They are based on the normality condition, which states that any plastic deformation in a purely cohesive soil develops without any volume change. The numerical results have shown that the proposed velocity fields significantly improve the best existing bounds for collapse pressures and that their results compare reasonably well with the collapse and blowout pressures provided by a commercial finite difference software, for a much smaller computational cost. A design chart is provided for practical use in geotechnical engineering. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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