A single numerically efficient equation for approximating the Mohr–Coulomb and the Matsuoka–Nakai failure criteria with rounded edges and apex     

Andrea Panteghini  Rocco Lagioia 《国际地质力学数值与分析法杂志》2014,38(4):349-369

This paper presents a novel formulation for defining soil failure. It plots in the principal stress space as a surface with the shape ranging between an approximation of the Matsuoka–Nakai and of the Mohr–Coulomb criteria depending on the value of a single parameter. The new function can be used as a replacement of the original equations of these well‐established criteria for implementing in a program for numerical analyses, and it is particularly effective for approximating the Matsuoka–Nakai criterion. Both the Mohr–Coulomb and the Matsuoka–Nakai failure criteria present numerical difficulties during implementation and also at run‐time. In the case of the Matsuoka–Nakai, the new formulation plots in the first octant only, whereas the original criterion plots in all octants, which causes severe convergence problems particularly for those Gauss points with low stress state, such as those on the side of a shallow footing. When the shape parameter is set to reproduce the Mohr–Coulomb failure criterion, on the other hand, the new formulation plots as a pyramid with rounded edges. Moreover, as the new function is at least of class C², the second derivatives are continuous, thus ensuring quadratic convergence of the Newton's method used within the integration scheme of the constitutive law. The proposed formulation can also provide both sharp and rounded apex of the surface at the origin of the stress space by setting accordingly one additional parameter. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Identifying run‐off contributions during melt‐induced run‐off events in a glacierized alpine catchment          下载免费PDF全文

Michael Engel  Daniele Penna  Giacomo Bertoldi  Andrea Dell'Agnese  Chris Soulsby  Francesco Comiti 《水文研究》2016,30(3):343-364

We analysed contributions to run‐off using hourly stream water samples from seven individual melt‐induced run‐off events (plus one rainfall event) during 2011, 2012 and 2013 in two nested glacierized catchments in the Eastern Italian Alps. Electrical conductivity and stable isotopes of water were used for mixing analysis and two‐component and three‐component hydrograph separation. High‐elevation snowmelt, glacier melt and autumn groundwater were identified as major end‐members. Discharge and tracers in the stream followed the diurnal variations of air temperature but markedly reacted to rainfall inputs. Hysteresis patterns between discharge and electrical conductivity during the melt‐induced run‐off events revealed contrasting loop directions at the two monitored stream sections. Snowmelt contribution to run‐off was highest in June and July (up to 33%), whereas the maximum contribution of glacier melt was reached in August (up to 65%). The maximum groundwater and rainfall contributions were 62% and 11%, respectively. Run‐off events were generally characterized by decreasing snowmelt and increasing glacier melt fractions from the beginning to the end of the summer 2012, while run‐off events in 2013 showed less variable snowmelt and lower glacier melt contributions than in 2012. The results provided essential insights into the complex dynamics of melt‐induced run‐off events and may be of further use in the context of water resource management in alpine catchments. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Pathways for sediment transport and retention in a vegetated,mid-channel island: Connecting sediment dynamics to morphology in Meinmahla Island,Ayeyarwady Delta,Myanmar     

Hannah E. Glover  Andrea S. Ogston  Aaron T. Fricke  Chuck A. Nittrouer  Cherry Aung  Thet Naing  Evan J. Lahr 《Sedimentology》2023,70(1):214-234

Vegetated mid-channel islands play an important though poorly understood role in the sediment dynamics and morphology of tide-dominated deltas. Meinmahla Island is a mangrove-forest preserve at the mouth of the Bogale distributary channel, in the Ayeyarwady Delta, Myanmar. In this relatively unaltered mid-channel island, sediment dynamics can be directly connected to morphology. Field measurements from 2017 to 2019 provide insight into the pathways for sediment transport and resulting morphological evolution. Water depth, salinity and turbidity were monitored semi-continuously, and velocity profilers with turbidity and salinity sensors were deployed seasonally in single-entrance (dead-end/blind) and multi-entrance tidal channels of the island. The morphological evolution was evaluated using grain size, ²¹⁰Pb geochronology, remote sensing and channel surveys. The data show that ebb-dominant, single-entrance channels along the island exterior import sediment year-round to the land surface. However, these exterior channels do not deliver enough sediment to maintain the observed ca 0.8 cm/yr accretion rate, and most of the sediment import occurs via interior, multi-entrance channels. Interior channels retain water masses that are physically distinct from the water in the Bogale distributary, and estuarine processes at the tidal-channel mouths import sediment into the island. Sediment is sourced to the island from upriver in the wet season and from the Gulf of Mottoma in the dry season, as the location of the estuary shifts seasonally within the Bogale distributary. The salinity and biogeochemistry of the distributary water are affected by interactions with sediment and groundwater in the island interior. The largest interior channels have remained remarkably stable while the island has aggraded and prograded over decadal timescales. However, the studied multi-entrance channel is responding to a drainage-network change by narrowing and shoaling. Overall, mid-channel islands trap sediment and associated nutrients at the river–ocean interface, and these resilient landscape features evolve in response to changes in drainage-network connectivity.  相似文献   

Influence of regional background stress fields on the spontaneous rupture of the major faults around Xiluodu dam,China          下载免费PDF全文

Li Liao  Ping′en Li  Jiansi Yang  Jianzhou Feng 《地震科学（英文版）》2022,35(5):398-409

Simulations of the spontaneous rupture of potential earthquakes in the vicinity of reservoir dams can provide accurate parameters for seismic resilience assessment, which is essential for improving the seismic performance of reservoir dams. In simulations of potential spontaneous ruptures, fault geometry, regional stress fields, constitutive parameters of the fault friction law, and many other factors control the slip rate, morphology, and dislocation of the rupture, thereby affecting the simulated ground motion parameters. The focus of this study was to elucidate the effects of the background stress field on the nucleation and propagation of spontaneous ruptures based on the factors influencing potential M > 7 earthquake events on the Leibo Middle Fault (LBMF) and the Mabian-Yanjing Fault (MB-YJF) in the Xiluodu dam (XLD) region. Our simulation results show that the magnitude of the regional background stress field plays a decisive role in whether a destructive earthquake exceeding the critical magnitude will occur. We found that the direction and magnitude of the regional stress significantly affect the range of rupture propagation on the fault plane, and fault geometry affects the spatial distribution of the rupture range. Under the same regional stress field magnitude and orientation, a more destructive, high-magnitude earthquake is more likely to occur on the LBMF than on the MB-YJF.  相似文献   

Magnetite in the unequilibrated CK chondrites: Implications for metamorphism and new insights into the relationship between the CV and CK chondrites          下载免费PDF全文

Tasha L. Dunn  Juliane Gross  Marina A. Ivanova  Simone E. Runyon  Andrea M. Bruck 《Meteoritics & planetary science》2016,51(9):1701-1720

Bulk isotopic and elemental compositions of CV and CK chondrites have led to the suggestion that both originate from the same asteroid. It has been argued that magnetite compositions also support this model; however, magnetite has been studied almost exclusively in the equilibrated (type 4‐6) CKs. Magnetite in seven unequilibrated CKs analyzed here is enriched in MgO, TiO₂, and Al₂O₃ relative to the equilibrated CKs, suggesting that magnetite compositions are affected by metamorphism. Magnetite in CKs is compositionally distinct from CVs, particularly in abundances of Cr₂O₃, NiO, and TiO₂. Although there are minor similarities between CV and equilibrated CK chondrite magnetite, this is contrary to what we would expect if the CVs and CKs represent a single metamorphic sequence. CV magnetite should resemble CK3 magnetite, as both were metamorphosed to type 3 conditions. Oxygen fugacities and temperatures of CV_ox and CK chondrites are also difficult to reconcile using existing CV‐CK parent body models. Mineral chemistries, which eliminate issues of bulk sample heterogeneity, provide a reliable alternative to techniques that involve a small amount of sample material. CV and CK chondrite magnetite has distinct compositional differences that cannot be explained by metamorphism.  相似文献   

Special Issue on the JEM-EUSO Mission     

Andreas Haungs  Gustavo Medina-Tanco  Andrea Santangelo 《Experimental Astronomy》2015,39(1):1-10

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An analysis of intersystem biases for multi-GNSS positioning   总被引：4，自引：3，他引：1  

Andrea Dalla Torre  Alessandro Caporali 《GPS Solutions》2015,19(2):297-307

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Environmental change in subtropical South America for the last two millennia as shown by lacustrine pigments     

Lisa Coianiz  Daniel Ariztegui  Eduardo L. Piovano  Andrea Lami  Piero Guilizzoni  Stefano Gerli  Nicolas Waldmann 《Journal of Paleolimnology》2015,53(2):233-250

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Use of Remote Imagery to Analyse Changes in Morphology and Longitudinal Large Wood Distribution in the Blanco River After the 2008 Chaitén Volcanic Eruption,Southern Chile          下载免费PDF全文

Héctor Ulloa  Andrés Iroumé  Luca Mao  Andrea Andreoli  Silvia Diez  Luis E. Lara 《Geografiska Annaler: Series A, Physical Geography》2015,97(3):523-541

The 2008 Chaitén volcanic eruption generated significant changes in the channel morphology and large wood (LW) abundance along the fluvial corridor of the Blanco River, southern Chile. Comparisons of remote sensing images from the pre‐eruption (year 2005) and post‐eruption (years 2009 and 2012) conditions showed that in a 10.2 km long study segment the Blanco River widened 3.5 times from 2005 to 2009, and that the maximum enlargement was nine times the original width. Changes in channel width were lower between the years 2012 and 2009. The sinuosity and braiding indexes also changed between 2005 and 2009. After the eruption the channel sinuosity was higher and specific river reaches developed a braided pattern, but by 2012 the channel was recovering pre‐eruption characteristics. Huge quantities of LW were introduced to the study segment; individual LW per km of channel length were 1.6 and 74.3 in 2005 and 2009, respectively, and more than 30 log jams km^?1 were observed in the year 2009. Between 2009 and 2012 the quantity of LW was very similar. Statistically significant relationships were found between the number of log jams and channel sinuosity and between the number of pieces of large wood with sinuosity and channel width. Wood was highly dynamic between 2009 and 2012: 78% of individual pieces and 48% of log jams identified in the 2009 image had moved by 2012. Finally the supervised classification of imagery associated with ArcMap tools was tested to identify large wood.  相似文献   

A Modeling Study of the Potential Water Quality Impacts from In-Stream Tidal Energy Extraction     

Taiping Wang  Zhaoqing Yang  Andrea Copping 《Estuaries and Coasts》2015,38(1):173-186

To assess the effects of tidal energy extraction on water quality in a simplified estuarine system, which consists of a tidal bay connected to the coastal ocean through a narrow channel where energy is extracted using in-stream tidal turbines, a three-dimensional coastal ocean model with built-in tidal turbine and water quality modules was applied. The effects of tidal energy extraction on water quality were examined for two energy extraction scenarios as compared with the baseline condition. It was found, in general, that the environmental impacts associated with energy extraction depend highly on the amount of power extracted from the system. Model results indicate that, as a result of energy extraction from the channel, the competition between decreased flushing rates in the bay and increased vertical mixing in the channel directly affects water quality responses in the bay. The decreased flushing rates tend to cause a stronger but negative impact on water quality. On the other hand, the increased vertical mixing could lead to higher bottom dissolved oxygen at times. As the first modeling effort directly aimed at examining the impacts of tidal energy extraction on estuarine water quality, this study demonstrates that numerical models can serve as a very useful tool for this purpose. However, more careful efforts are warranted to address system-specific environmental issues in real-world, complex estuarine systems.  相似文献