Application of nonlinear optimization technique to back analyses of deep excavation     

Yu-Geng Tang  Gordon Tung-Chin Kung 《Computers and Geotechnics》2009,36(1-2):276-290

This study presents a nonlinear optimization technique (NOT) for conducting the back analyses of geotechnical engineering problems based on the field observations. Additional auxiliary techniques are incorporated to enhance the convergence and stability of the NOT. The developed NOT and additional auxiliary techniques are incorporated into a finite element code and then applied to the back analysis of excavation-induced wall deflection. A number of hypothetical excavation cases with various scenarios of stratigraphy and two quality excavation case histories are used to validate the developed NOT, in which the dominant soil parameters are treated as target parameters. Results show that the wall deflections of all hypothetical and actual excavation cases at each stage can be accurately and efficiently back-figured. The developed NOT has a potential to be an useful tool for preventing the building damage through accurately and efficiently predicting the excavation-induced deformations at subsequent stages.  相似文献   

The accumulation rate of meteorite falls at the Earth's surface: The view from Roosevelt County,New Mexico     

Michael E. Zolensky  Gordon L. Wells  Helen M. Rendell 《Meteoritics & planetary science》1990,25(1):11-17

Abstract— The discovery of 154 meteorite fragments within an 11 km² area of wind-excavated basins in Roosevelt County, New Mexico, permits a new calculation of the accumulation rate of meteorite falls at the Earth's surface. Thermoluminescence dating of the coversand unit comprising the prime recovery surface suggests the maximum terrestrial age of the meteorites to be about 16.0 ka. The 68 meteorite fragments subjected to petrological analyses represent a minimum of 49 individual falls. Collection bias has largely excluded carbonaceous chondrites and achondrites, requiring the accumulation rate derived from the recovered samples to be increased by a factor of 1.25. Terrestrial weathering destroying ordinary chondrites can be modelled as a first-order decay process with an estimated half-life of 3.5 ± 1.9 ka on the semiarid American High Plains. Having accounted for the age of the recovery surface, area of field searches, pairing of finds, collection bias and weathering half-life, we calculate an accumulation rate of 9.4 × 10² falls/a per 10⁶ km² for falls > 10 g total mass. This figure exceeds the best-constrained previous estimate by more than an order of magnitude. One possible reason for this disparity may be the extraordinary length of the fall record preserved in the surficial geology of Roosevelt County. The high accumulation rate determined for the past 16 ka may point to the existence of periods when the meteorite fall rate was significantly greater than at present.  相似文献   

Hyperspectral mapping of alteration assemblages within a hydrothermal vug at the Haughton impact structure,Canada          下载免费PDF全文

Rebecca N. Greenberger  John F. Mustard  Gordon R. Osinski  Livio L. Tornabene  Alexandra J. Pontefract  Cassandra L. Marion  Roberta L. Flemming  Janette H. Wilson  Edward A. Cloutis 《Meteoritics & planetary science》2016,51(12):2274-2292

Meteorite impacts on Earth and Mars can generate hydrothermal systems that alter the primary mineralogies of rocks and provide suitable environments for microbial colonization. We investigate a calcite–marcasite‐bearing vug at the ~23 km diameter Haughton impact structure, Devon Island, Nunavut, Canada, using imaging spectroscopy of the outcrop in the field (0.65–1.1 μm) and samples in the laboratory (0.4–2.5 μm), point spectroscopy (0.35–2.5 μm), major element chemistry, and X‐ray diffraction analyses. The mineral assemblages mapped at the outcrop include marcasite; marcasite with minor gypsum and jarosite; fibroferrite and copiapite with minor gypsum and melanterite; gypsum, Fe³⁺ oxides, and jarosite; and calcite, gypsum, clay, microcline, and quartz. Hyperspectral mapping of alteration phases shows spatial patterns that illuminate changes in alteration conditions and formation of specific mineral phases. Marcasite formed from the postimpact hydrothermal system under reducing conditions, while subsequent weathering oxidized the marcasite at low temperatures and water/rock ratios. The acidic fluids resulting from the oxidation collected on flat‐lying portions of the outcrop, precipitating fibroferrite + copiapite. That assemblage then likely dissolved, and the changing chemistry and pH resulting from interaction with the calcite‐rich host rock formed gypsum‐bearing red coatings. These results have implications for understanding water–rock interactions and habitabilities at this site and on Mars.  相似文献   

Shock‐induced changes in density and porosity in shock‐metamorphosed crystalline rocks,Haughton impact structure,Canada     

Alaura C. SINGLETON  Gordon R. OSINSKI  Phil J. A. McCAUSLAND  Desmond E. MOSER 《Meteoritics & planetary science》2011,46(11):1774-1786

Abstract– Shock metamorphism can occur at transient pressures that reach tens of GPa and well over 1000 °C, altering the target material on both megascopic and microscopic scales. This study explores the effects of shock metamorphism on crystalline, quartzofeldspathic basement material from the Haughton impact structure on Devon Island, Arctic Canada. Shock levels were assigned to samples based on petrographic examination of main mineral phases. Conventional shock classification schemes proved to incompletely describe the Haughton samples so a modified shock classification system is presented. Fifty‐two crystalline bedrock samples from the clast‐rich impact melt rocks in the crater, and one reference site outside of the crater, were classified using this system. The shock levels range from 0 to 7 (according to the new shock stage classification proposed here, i.e., stages 0–IV after the Stöffler classification), indicating shock pressures ranging from 0 to approximately 80 GPa. The second aspect of this study involved measuring bulk physical characteristics of the shocked samples. The bulk density, grain density, and porosity were determined using a water displacement method, a bead displacement method, and a Hepycnometer. Results suggest a nonlinear, negative correlation between density and shock level such that densities of crystalline rocks with original densities of approximately 3 g cm^?3 are reduced to <1.0 g cm^?3 at high shock levels. The results also show a positive nonlinear correlation between porosity and shock level. These data illustrate the effect of shock on the bulk physical characteristics of crystalline rocks, and has implications for assessing the habitability of shocked rocks.  相似文献   

Analysis of Cassini/CIRS limb spectra of Titan acquired during the nominal mission II: Aerosol extinction profiles in the 600–1420 cm spectral range     

Sandrine Vinatier  Bruno Bézard  Remco de Kok  Carrie M. Anderson  Robert E. Samuelson  Conor A. Nixon  Andrei Mamoutkine  Ronald C. Carlson  Donald E. Jennings  Ever A. Guandique  Gordon L. Bjoraker  F. Michael Flasar  Virgil G. Kunde 《Icarus》2010,210(2):852-866

We have analyzed the continuum emission of limb spectra acquired by the Cassini/CIRS infrared spectrometer in order to derive information on haze extinction in the 3–0.02 mbar range (∼150–350 km). We focused on the 600–1420 cm⁻¹ spectral range and studied nine different limb observations acquired during the Cassini nominal mission at 55°S, 20°S, 5°N, 30°N, 40°N, 45°N, 55°N, 70°N and 80°N. By means of an inversion algorithm solving the radiative transfer equation, we derived the vertical profiles of haze extinction coefficients from 17 spectral ranges of 20-cm⁻¹ wide at each of the nine latitudes. At a given latitude, all extinction vertical profiles retrieved from various spectral intervals between 600 and 1120 cm⁻¹ display similar vertical slopes implying similar spectral characteristics of the material at all altitudes. We calculated a mean vertical extinction profile for each latitude and derived the ratio of the haze scale height (H_haze) to the pressure scale height (H_gas) as a function of altitude. We inferred H_haze/H_gas values varying from 0.8 to 2.4. The aerosol scale height varies with altitude and also with latitude. Overall, the haze extinction does not show strong latitudinal variations but, at 1 mbar, an increase by a factor of 1.5 is observed at the north pole compared to high southern latitudes. The vertical optical depths at 0.5 and 1.7 mbar increase from 55°S to 5°N, remain constant between 5°N and 30°N and display little variation at higher latitudes, except the presence of a slight local maximum at 45°N. The spectral dependence of the haze vertical optical depth is uniform with latitude and displays three main spectral features centered at 630 cm⁻¹, 745 cm⁻¹ and 1390 cm⁻¹, the latter showing a wide tail extending down to ∼1000 cm⁻¹. From 600 to 750 cm⁻¹, the optical depth increases by a factor of 3 in contrast with the absorbance of laboratory tholins, which is generally constant. We derived the mass mixing ratio profiles of haze at the nine latitudes. Below the 0.4-mbar level all mass mixing ratio profiles increase with height. Above this pressure level, the profiles at 40°N, 45°N, 55°N, at the edge of the polar vortex, display a decrease-with-height whereas the other profiles increase. The global increase with height of the haze mass mixing ratio suggest a source at high altitudes and a sink at low altitudes. An enrichment of haze is observed at 0.1 mbar around the equator, which could be due to a more efficient photochemistry because of the strongest insolation there or an accumulation of haze due to a balance between sedimentation and upward vertical drag.  相似文献   

Hydrodynamical simulations of viscous overstability in Saturn’s rings     

Henrik N. Latter  Gordon I. Ogilvie 《Icarus》2010,210(1):318-329

We perform axisymmetric hydrodynamical simulations that describe the nonlinear outcome of the viscous overstability in dense planetary rings. These simulations are particularly relevant for Cassini observations of fine-scale structure in Saturn’s A and B-ring, which take the form of periodic microstructure on the 0.1 km scale, and irregular larger-scale variations on 1-10 km. Nonlinear wavetrains dominate all the simulations, and we associate them with the observed periodic microstructure. The waves can undergo small chaotic fluctuations in their phase and amplitude, and may be punctuated by more formidable ‘wave defects’ distributed on longer scales. It is unclear, however, whether the defects are connected to the irregular larger-scale variations observed by Cassini. The long-term behaviour of the simulations is dominated by the imposed boundary conditions, and more generally by the limitations of the local model we use: the shearing box. When periodic boundary conditions are imposed, the system eventually settles on a uniform travelling wave of a predictable wavelength, while reflecting boundaries, and boundaries with buffer zones, maintain a disordered saturated state. The simulations omit self-gravity, though we examine its influence in future work.  相似文献   

Investigating the effect of soil models on deformations caused by braced excavations through an inverse-analysis technique   总被引：1，自引：0，他引：1  

Yu-Geng Tang  Gordon Tung-Chin Kung 《Computers and Geotechnics》2010

In this study, a series of inverse-analysis numerical experiments was performed to investigate the effect of soil models on the deformations caused by excavation by using the finite element method. The nonlinear optimization technique that was incorporated into the finite element code was used for the inverse-analysis numerical experiments. Three soil models (the hyperbolic model, pseudo-plasticity model, and modified pseudo-plasticity model) were employed in the intended numerical experiments on a well-documented excavation case history. The results indicate that wall deflection due to excavation can be accurately back-figured by each of the three soil models, while the ground surface settlement can be reasonably optimized only by the pseudo-plasticity model and the modified pseudo-plasticity model. Importantly, the modified pseudo-plasticity model can yield more reasonable simulations when the wall deflection and the ground surface settlement are simultaneously back-figured. The results show that selection of an adequate soil model that is capable of adequately describing the stress–strain-strength characteristics of the soils is essentially crucial when predicting the excavation-induced ground response.  相似文献   

Human capital requirements in Singapore's international financial centre     

Gordon Kuo Siong Tan 《Singapore journal of tropical geography》2023,44(3):539-554

International financial centres (IFCs) are regarded as important nodes in governing global flows of money and capital. With increased globalization and rapid technological changes, the rivalry among IFCs has further intensified competition for financial labour—as a concentrated pool of highly skilled finance workers in an open and flexible labour market is crucial to sustaining the competitive dynamics of these urban financial hotspots. This study investigates the importance of different skills and tasks in financial work. Based on surveys and interviews conducted among Singapore's IFC workers, the findings show that cognitive, interpersonal communication and managerial-leadership skills and tasks are more important in financial work, whereas programming, mathematics and systems-based skills are perceived to be less important. Additionally, a network visualization of finance occupational skills obtained from Singapore's national skills database reinforces the importance of cognitive and relational skills in that sector. Higher-order cognitive and relational skills are expected to become even more critical as the financial sector undergoes rapid digital transformation, reinforcing the importance of IFCs as agglomerations of skilled finance talent.  相似文献   

A new theoretical method for analyzing confined dry granular flows     

Gordon G. D. Zhou  Charles W. W. Ng  Q. C. Sun 《Landslides》2014,11(3):369-384

A granular body may deform in a continuous fashion such that the solid particles remain in close contact. Previous research works have always used the frictional Coulomb-like continuum treatment for analyzing granular bodies. However, this approach is only applicable for quasi-static conditions and cannot capture the complicated granular contact behavior of solid particles inside a failing granular body. This paper applies a revised Savage–Hutter equation to model granular flows moving down a confined, sloping channel. The Coulomb contact friction law is modified to consider the effect of the shear rate inside a granular body. This new method also considers the confinement effect of a sloping channel on granular flow mobility. The derived depth-averaged equations of motion bear a resemblance to nonlinear shallow-water wave equations. Results computed using the derived equations are compared with measurements from flume model tests, and consistency is found between the two.  相似文献   

Analysis and Simulation of Propagule Dispersal and Salinity Intrusion from Storm Surge on the Movement of a Marsh–Mangrove Ecotone in South Florida     

Jiang Jiang  Donald L. DeAngelis  Gordon H. Anderson  Thomas J. Smith III 《Estuaries and Coasts》2014,37(1):24-35

Coastal mangrove–freshwater marsh ecotones of the Everglades represent transitions between marine salt-tolerant halophytic and freshwater salt-intolerant glycophytic communities. It is hypothesized here that a self-reinforcing feedback, termed a “vegetation switch,” between vegetation and soil salinity, helps maintain the sharp mangrove–marsh ecotone. A general theoretical implication of the switch mechanism is that the ecotone will be stable to small disturbances but vulnerable to rapid regime shifts from large disturbances, such as storm surges, which could cause large spatial displacements of the ecotone. We develop a simulation model to describe the vegetation switch mechanism. The model couples vegetation dynamics and hydrologic processes. The key factors in the model are the amount of salt-water intrusion into the freshwater wetland and the passive transport of mangrove (e.g., Rhizophora mangle) viviparous seeds or propagules. Results from the model simulations indicate that a regime shift from freshwater marsh to mangroves is sensitive to the duration of soil salinization through storm surge overwash and to the density of mangrove propagules or seedlings transported into the marsh. We parameterized our model with empirical hydrologic data collected from the period 2000–2010 at one mangrove–marsh ecotone location in southwestern Florida to forecast possible long-term effects of Hurricane Wilma (24 October 2005). The model indicated that the effects of that storm surge were too weak to trigger a regime shift at the sites we studied, 50 km south of the Hurricane Wilma eyewall, but simulations with more severe artificial disturbances were capable of causing substantial regime shifts.  相似文献