查看更多>>摘要：? 2022This paper presents a methodology to assess the influence of geological uncertainty (stratigraphic uncertainty) on designing an offshore wind turbine foundation (OWTF). To consider the stratigraphic uncertainty, we create a synthetic stratigraphic model (SSM) and then sample multiple sets of boreholes to develop a series of stratigraphic models, each with a different degree of uncertainty (entropy). Using Markov random field (MRF) theory, these stratigraphic models were simulated, and their entropies were evaluated. The results indicate the entropies of the stratigraphic models decrease as the number of boreholes increases. The OWTF monopile is then designed based on these stratigraphic models with different entropy levels. Next, Monte Carlo simulation (MCS) is used to evaluate the failure probability of the design, considering uncertainties of the stratigraphic model and soil properties. Then, two monopile designs simulating piles located at different stratigraphic configurations are analyzed to assess the effects of stratigraphic uncertainty and strength parameter variability on their failure probabilities. Finally, insights gained regarding the effect of stratigraphic uncertainty on the OWTF monopile design are discussed.
查看更多>>摘要：? 2022 Elsevier B.V.Earthquake-induced landslides can cause enormous damage and numerous casualties in mountainous areas worldwide; consequently, accurate assessment of the potential distribution of earthquake-induced landslides is an important issue. For a national disaster prevention agency, it is desirable to be prepared to rapidly evaluate disasters and risks from information that can be scarce or easily available. The present study examined landslides triggered by reverse and strike-slip fault earthquakes, focusing on recent cases in Japan with relatively complete landslide inventories and detailed active-fault information. The landslide distributions and parameters of active faults were compared, and it was found that the skewness and kurtosis of the landslide distribution for each earthquake event was close to zero, indicating that the distributions followed the normal distribution. The mean distance of the landslide distribution from the active fault is negatively correlated with the inclination of the active fault, while the standard deviation is negatively correlated with the fault-top depth of the active fault and positively correlated with the magnitude of the earthquake. Based on our findings, we conducted a regression analysis of the relationship between the mean distance from the active fault and the inclination of the active fault. The mean distance of the landslide from the active fault increased when the active fault had a lower inclination, and was regarded as zero when the inclination was greater than 60°. In addition, a relationship between the standard deviation, depth of fault top, and earthquake magnitude was established using multiple regression analysis. We thus confirmed the accuracy of the methodology using the actual landslide distributions of recent earthquakes in Japan. The length of the active fault can be used as input for the methodology, to estimate the maximum magnitude of the respective earthquake. Furthermore, the 95% confidence interval appears to cover almost all the large landslides, which enables us to limit the extent of areas that should be considered as the most exposed to co-seismic landslide hazards. The applicability of the proposed methodology was successfully tested using the case of the 1999 Chi-Chi earthquake in Taiwan with a seismic mechanism similar to the Japanese earthquake. Consequently, the proposed methodology can be applied to estimate the potential distribution of landslides caused by reverse and strike-slip fault earthquakes, based on the parameters of the active faults.
查看更多>>摘要：? 2022In order to evaluate the potential for using environmental controls as a preventive conservation strategy for Reigate Stone masonry, this paper tests the hypothesis that powdering and flaking decay patterns are a direct consequence of climatic variables. Samples of masonry affected by each decay pattern are analysed for soluble salt content using ion chromatography. The results are used to build thermodynamic models in ECOS Runsalt. These identify NaCl and NaNO3 crystallisation in both environments, with NaCl dominating in powdering masonry and NaNO3 dominating in flaking masonry. Freshly quarried samples of Reigate Stone with a range of physical characteristics are contaminated with a mixture of these salts. Replicates of each sample are subjected to two distinct accelerated ageing regimes. These regimes are based on environmental monitoring and designed to reproduce the observed decay pathways. One set is subject to partial immersion and relatively stable, high RH, to stimulate a zone of NaCl crystallisation near the surface. The replicate set is subject to occasional wetting and frequent drops in RH, to stimulate NaNO3 crystallisation within the fabric of the stone. The results provide some indication that the intended decay mechanisms were achieved, supporting the hypothesis; however, physical variation in the stone was a far greater control on the rate of decay and the emergence of distinctive decay phenomena. This extended to both the mineralogical composition of the stone and to pre-existing decay features, such as crusts and cracks. The implication of these results is that the emergence of decay patterns in Reigate Stone cannot be explained solely by environmental mechanisms; baseline mineralogy and historical contingency can play a crucial role. Whilst environmental controls may provide a conservation strategy in some cases, it is likely that detailed assessment of the case specifics will be necessary.
查看更多>>摘要：? 2022 Elsevier B.V.Artificial ground freezing methods have been widely used in many engineering applications to change the mechanical and hydraulic properties of soil. Two freezing methods, open and closed systems, have been commonly utilized depending on the target freezing rate and budget of the project. In this study, a novel freezing pipe was designed, which enables the frozen soil to be formed in an elliptical shape to satisfy special construction demands such as tunneling projects. Temperature evolution of silty deposit in open and closed system were assessed respectively by injecting liquid nitrogen and circulating ethanol. In addition, the efficiency of hybrid freezing operation (open+closed system) in a silty deposit was investigated by injecting liquid nitrogen (open system) followed by the circulation of ethanol (closed system). The elapsed time for freezing and the freezing duration is also evaluated from the measured temperature data at distances of 25, 50 and 75 cm from the freezing pipe. The results show that the designed freezing pipe enabled forming a frozen soil in an elliptical shape. In addition, the hybrid freezing operation is an effective method for forming and sustaining a relatively large volume of frozen soil without continuously injecting liquid nitrogen.
查看更多>>摘要：? 2022 Elsevier B.V.In a deep geological repository for disposal of high-level radioactive waste, understanding of gas migration behavior in bentonite materials is one of the most important issues for safety assessment of the repository. This study tries to provide insights into gas transport properties in saturated bentonite tested under a constant-volume condition using the residual capillary pressure (RCP) technique. In this regard, a test setup was developed and gas injection tests were conducted on saturated GaoMiaoZi (GMZ) bentonite specimens using the RCP technique. Among which, some specimens that experienced initial gas breakthrough processes were re-saturated and re-submitted to conduct the subsequent gas injection tests. During the tests, gas permeability and gas breakthrough pressures were measured. Gas migration mechanism at lower gas injection pressures was analyzed and the influence of repetitive breakthroughs on sealing efficiency of saturated GMZ bentonite was discussed. Results show that as dry density increases from 1.3 to 1.7 g/cm3, gas breakthrough pressure increases from 1.37 to 8.56 MPa. Explanations to this conclusion could be that with increasing dry density, the proportion of large pores decreases and the strongly adsorbed water on the surface of minerals increases, leading to harder capillary displacement of pore water and thus a higher gas breakthrough pressure. Meanwhile, both diffusion and advection could play significant roles during the gas migration process at lower injection pressures, while advection could gradually become the dominant transport mechanism as gas injection pressures increase to higher values. Finally, after experienced a gas breakthrough process, the breakthrough pressure of compacted bentonite specimen might not recover to its initial value by re-saturating the specimen, indicating that degradation of sealing capacity of the bentonite materials induced by gas breakthrough process is irreversible.
查看更多>>摘要：? 2022 Elsevier B.V.The mechanical properties of a high plasticity expansive clay from South Africa are reported. The experimental programme considered wetting after loading tests followed by one-dimensional consolidation and unloading of undisturbed and statically compacted samples. The results of this study illustrate that laboratory preparation of expansive clays do little to alter the soil's swell characteristics. This finding is attributed to the fact that, due to numerous swelling and shrinking cycles over a geological time frame, expansive clays tend to have reworked fabric in-situ. The effects of structure are also assessed in both undisturbed and compacted specimens by comparison of the various consolidation tests with that of a reconstituted sample. The results illustrate a gradual yielding process for both undisturbed and compacted specimens, indicating progressive disruption of structure. After consolidation, while the expansion indices were found to be similar for both compacted and undisturbed samples, measured values were lower than that of the reconstituted specimen. Such a result is indicative of some preservation of structure after testing. It is also emphasised that consolidation tests on expansive clays are likely to exist in structure permitted space if swelling strains are restricted during the inundation process. Conversely, for most results presented it is seen that the swell caused by the inundation phase is approximately as disruptive to structure as laboratory preparation and compaction.
查看更多>>摘要：? 2021Soil ground heat flux (G0) is a key parameter in analyzing soil-atmosphere interaction. It is not only an indispensable component in the surface energy balance, but also an essential boundary condition in the coupled hydro-thermal-mechanical (HTM) numerical analysis of soil-atmosphere interaction. In this study, three G0 measurement methods (gradient method, calorimetric method and combination method) are evaluated based on the measurements (temperature, volumetric water content and thermal conductivity) using the actively heated distributed temperature sensing (AH-DTS) technology. In addition, through a series of in-situ tests, the feasibility of these methods is verified, and their applicability and application potential are compared and analyzed. The results indicate that the G0 values measured by the three AH-DTS technology-based methods are in the same order of magnitude, indicating that the three methods are feasible. Among them, the G0 measured by the gradient method is an instantaneous value which is closely related to the soil surface water content, while the G0 measured by the calorimetric method and combination method is an average values over a period of time. The gradient method is applicable for all types of soil, including the frozen soils. The calorimetric method and the combination method are suitable for soils of which water content can be measured by the AH-DTS sensor. It is recommended that an appropriate G0 measurement method based on the AH-DTS technology be selected according to the site situations.
查看更多>>摘要：? 2022 Elsevier B.V.Three-dimensional stability of roofs in deep flat-ceiling cavities is analyzed. The stability number, factor of safety, and required supporting stress are used as measures of roof stability. Despite the simplicity of the flat roof geometry, the three-dimensional stability analysis presents some complexities owed to the shape of the failure surface geometry in the collapse mechanism. The failure mode assumes a rock block moving downward into the cavity, and the study aims to recognize the most critical shape of the failing block. Three specific block shapes are described in some detail, but more have been analyzed. Blocks defined by a special case of a 4th order conical surface (quartic) on a rectangular base, and a 2nd order elliptic surface (quadric) are found to be the most critical in the stability analysis. The kinematic approach of limit analysis was used, with the rock strength governed by the Hoek-Brown failure criterion. The parametric form of the Hoek-Brown function was employed. Interestingly, an absence of diagonal symmetries in the most critical failure mechanisms was observed in roof collapse of square-ceiling cavities. Computational results in terms of dimensionless measures of stability are presented in charts and tables.
查看更多>>摘要：? 2022 Elsevier B.V.This paper presents a numerical investigation about the effect of particle shape on small strain properties (e.g., shear stiffness and Poisson's ratio) of granular soils through 3D discrete element simulations of drained triaxial shearing tests. To this end, different mass proportions of realistic shape clumps and ideal spheres with the same grading are mixed together to prepare five types of granular samples with varying particle shape features. Four independent 3D shape descriptors including aspect ratio, sphericity, convexity and roundness are determined for constituent particles within each samples to describe their shape polydispersity characteristics from different shape scales (e.g., global form and local roundness). A well-defined and practical 3D shape parameter named particle overall regularity is adopted to collectively quantify multiscale shape differences among the five samples. Based on the simulated shape dependent small strain properties results, the applicability of two common empirical expressions to capture the confining pressure and density dependent small strain stiffness are evaluated. Correlations between model parameters of these two equations and different shape descriptors are also built. Moreover, the micromechanical quantities (e.g., mechanical coordination number and contact stiffness) are explored to unravel the underlying micro mechanisms of particle shape dependent small strain properties of granular soils.
查看更多>>摘要：? 2022 Elsevier B.V.The design and optimization of the dewatering scheme for deep foundation pits in a highly permeable heterogeneous layer are critical to protect water resources, control subsidence and mitigate environmental impacts. Numerical simulation is an important and sometimes the only tool in the design of dewatering schemes, especially when the dewatering projects are planned under complex hydrogeological conditions with limited data. The open excavation method was chosen for a project to drain a deep foundation pit (35–44 m) in an upland river valley landscape. Quaternary alluvial deposits (129.0 m thick) are generally distributed in the riverbed and the overburden consists mainly of alluvial-diluvial sandy gravel cobbles, clayey soils, sandy clay, and silty fine sand, making the study area very heterogeneous. There may be water inrush from foundation pit, uneven subsidence and deformation due to the uneven structure of the sand and slope stability. MODFLOW-USG (Unstructured Grid) and Subsidence and Aquifer-System Compaction (SUB) Package were used to create a coupled 3-D groundwater flow-subsidence numerical model for foundation pit dewatering. MODFLOW-USG provides greater flexibility in the design of the grid to achieve a high degree of accuracy in numerical simulation, while effectively reduces computational costs. A combination of waterproof curtain and a partial penetrating well was proposed for lowering the groundwater table. The optimized dewatering scheme with a curtain depth of 60 m and a hydraulic conductivity of 0.00518 m/d, and four rows of dewatering wells with an equal row spacing of 40 m, well depth of 50 m, and well spacing of 12.5 m in each row can meet the dewatering requirements with minimum groundwater discharge in the scenarios. The numerical simulation of this study provides a powerful and useful tool for dewatering and subsidence control of deep foundation pit under complex hydrogeological conditions.
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