Impacts of saturation-dependent anisotropy on the shrinkage behavior of clay rocks     

Ip  Sabrina C. Y.  Choo  Jinhyun  Borja  Ronaldo I. 《Acta Geotechnica》2021,16(11):3381-3400

Geomaterials such as soils and rocks can exhibit inherent anisotropy due to the preferred orientation of mineral grains and/or cracks. They can also be partially saturated with multiple types of fluids occupying the pore space. The anisotropic and unsaturated behaviors of geomaterials can be highly interdependent. Experimental studies have shown that the elastic parameters of rocks evolve with saturation. The effect of saturation has also been shown to differ between directions in transversely isotropic clay rock. This gives rise to saturation-dependent stiffness anisotropy. Similarly, permeability anisotropy can also be saturation-dependent. In this study, constitutive equations accommodating saturation-dependent stiffness and hydraulic anisotropy are presented. A linear function is used to describe the relationship between the elastic parameters and saturation, while the relative permeability–saturation relationship is characterized with a log-linear function. These equations are implemented into a hydromechanical framework to investigate the effects of saturation-dependent properties on the shrinkage behavior of clay rocks. Numerical simulations are presented to demonstrate the role of saturation-dependent stiffness and hydraulic anisotropy in shrinkage behavior. The results highlight that strain anisotropy and time evolution of pore pressures are substantially influenced by saturation-dependent stiffness and hydraulic anisotropy.

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Recreational boat noise level evaluation     

Professor J. M. Vasconcellos  Professor R. G. Latorre   《Ocean Engineering》2001,28(9)

Recreational boats are constantly undergoing modifications and improvements in design, construction materials, and equipment. The boat builder mission is supply customers with a product with better quality, safety and onboard comfort. Onboard comfort should be evaluated along several points. Seakeeping is especially critical on long trips or operations in regions where harsh sea conditions occur. Over the years much attention has been given to boat behavior underway at sea. Recently onboard noise level has become a significant element of comfort and navigation safety. With high onboard noise a boater is unable to detect other boat whistles, horns and calls for help. This becomes a critical problem when sailing in fog and at night. Maintaining the internal noise level within limits is important. In order to address this noise problem, the paper presents a review of existing guidelines and the authors' proposal for Boat Noise Evaluation (BNE) procedure for recreational powerboats. This procedure has been used in a number of boat trials. The use of this procedure is discussed along with representative boat noise level results and a comparison with the acceptable values for passenger comfort and safety.  相似文献   

Reduction of jack-up and crane vessel resistance and bow swamping     

Robert Latorre  Julio Arana 《Ocean Engineering》2006,33(14-15):2000-2011

A large bow wave forms when blunt-shaped vessels like self-propelled jack-up crane vessels (liftboats) operate at high speeds. Above a critical speed, this bow wave spills over the bow causing swamping. To investigate this phenomena, towing tank tests of a 1/25 scale model liftboat hull were done over a speed range of 3–8 kn. The test showed above 4 kn the bow wave formed and the vessel trimmed by the bow. At speeds above 8 kn the bow wave spilled over the bow (swamping). To cancel this critical bow wave a vertical bow plate was fitted ahead of the liftboat bow. This bow plate reduced the bow wave formation and achieved a 10–15% reduction in the towing resistance. The wave cancellation bow plate can reduce the liftboat power or increase its liftboat speed and operating range.  相似文献   

Paleowetlands and regional climate change in the central Atacama Desert, northern Chile     

Jay Quade  Jason A. Rech  Claudio Latorre  Barbra Quade  Timothy Fisher 《Quaternary Research》2008,69(3):343-360

Widespread, organic-rich diatomaceous deposits are evidence for formerly wetter times along the margins of the central Atacama Desert, one of the driest places on Earth today. We mapped and dated these paleowetland deposits at three presently waterless locations near Salar de Punta Negra (24.5°S) on the western slope of the Andes. Elevated groundwater levels supported phreatic discharge into wetlands during two periods: 15,900 to ~ 13,800 and 12,700 to ~ 9700 cal yr BP. Dense concentrations of lithic artifacts testify to the presence of paleoindians around the wetlands late in the second wet phase (11,000?-9700 cal yr BP). Water tables dropped below the surface before 15,900 and since 8100 cal yr BP, and briefly between ~ 13,800 and 12,700 cal yr BP. This temporal pattern is repeated, with some slight differences, in rodent middens from the study area, in both paleowetland and rodent midden deposits north and south of the study area, and in lake level fluctuations on the adjacent Bolivian Altiplano. The regional synchroneity of these changes points to a strengthening of the South American Monsoon — which we term the “Central Andean Pluvial Event” — in two distinct intervals (15,900-13,800 and 12,700-9700 cal yr BP), probably induced by steepened SST gradients across the tropical Pacific (i.e., La Niña-like conditions).  相似文献   

Integrating long-term water and sediment pollution data, in assessing chemical status within the European Water Framework Directive     

Itziar Tueros  ngel Borja  Joana Larreta  J. Germn Rodríguez  Victoriano Valencia  Esmeralda Milln 《Marine pollution bulletin》2009,58(9):1389-1400

The European Water Framework Directive (WFD) establishes a framework for the protection and improvement of estuarine (transitional) and coastal waters, attempting to achieve good water status by 2015; this includes, within the assessment, biological and chemical elements. The European Commission has proposed a list of priority dangerous substances (including metals such as Cd, Hg, Ni and Pb), with the corresponding list of environmental quality standards (EQS), to assess chemical status, but only for waters. In this contribution, a long-term (1995–2007) dataset of transitional and coastal water and sediment trace elements concentrations, from the Basque Country (northern Spain), has been used to investigate the response of these systems to water treatment programmes. Moreover, the approach proposed in the WFD, for assessing water chemical status (the ‘one out, all out’ approach), is compared with the integration of water and sediment data, into a unique assessment. For this exercise, background levels are used as reference conditions, identifying the boundary between high and good chemical status. EQS are used as the boundary between good and moderate chemical status. This contribution reveals that the first approach can lead to misclassification, with the second approach representing the pattern shown by the long-term data trends. Finally, the management implications, using each approach are discussed.  相似文献   

Lattice Boltzmann method with two relaxation times for advection–diffusion equation: Third order analysis and stability analysis     

Borja Servan-Camas  Frank T.-C. Tsai 《Advances in water resources》2008

The objectives of this study are to investigate the third order accuracy and linear stability of the lattice Boltzmann method (LBM) with the two-relaxation-time collision operator (LTRT) for the advection–diffusion equation (ADE) and compare the LTRT model with the single-relaxation-time (LBGK) model. While the LBGK has been used extensively, the LTRT appears to be a more flexible model because it uses two relaxation times. The extra relaxation time can be used to improve solution accuracy and/or stability. This study conducts a third order Chapman–Enskog expansion on the LTRT to recover the macroscopic differential equations up to the third order. The dependency of third order terms on the relaxation times is obtained for different types of equilibrium distribution functions (EDFs) and lattices. By selecting proper relaxation times, the numerical dispersion can be significantly reduced. Furthermore, to improve solution accuracy, this study introduces pseudo-velocities to develop new EDFs to reduce the second order numerical diffusion. This study also derives stability domains based on the lattice Peclet number and Courant number for different types of lattices, EDFs and different values of relaxation times, while conducting linear stability analysis on the LTRT. Numerical examples demonstrate the improvement of the LTRT solution accuracy and stability by selecting proper relaxation times, lattice Peclet number and Courant number.  相似文献   

Thermoplasticity and strain localization in transversely isotropic materials based on anisotropic critical state plasticity          下载免费PDF全文

Shabnam J. Semnani  Joshua A. White  Ronaldo I. Borja 《国际地质力学数值与分析法杂志》2016,40(18):2423-2449

Geomaterials such as soils and rocks are inherently anisotropic and sensitive to temperature changes caused by various internal and external processes. They are also susceptible to strain localization in the form of shear bands when subjected to critical loads. We present a thermoplastic framework for modeling coupled thermomechanical response and for predicting the inception of a shear band in a transversely isotropic material using the general framework of critical state plasticity and the specific framework of an anisotropic modified Cam–Clay model. The formulation incorporates anisotropy in both elastic and plastic responses under the assumption of infinitesimal deformation. The model is first calibrated using experimental data from triaxial tests to demonstrate its capability in capturing anisotropy in the mechanical response. Subsequently, stress‐point simulations of strain localization are carried out under two different conditions, namely, isothermal localization and adiabatic localization. The adiabatic formulation investigates the effect of temperature on localization via thermomechanical coupling. Numerical simulations are presented to demonstrate the important role of anisotropy, hardening, and thermal softening on strain localization inception and orientation. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

An approach to the intercalibration of benthic ecological status assessment in the North Atlantic ecoregion, according to the European Water Framework Directive   总被引：6，自引：0，他引：6  

Borja A  Josefson AB  Miles A  Muxika I  Olsgard F  Phillips G  Rodríguez JG  Rygg B 《Marine pollution bulletin》2007,55(1-6):42-52

The European Water Framework Directive (WFD) establishes a framework for the protection and improvement of transitional and coastal waters; its final objective is to achieve at least 'good water status' for all waters, by 2015. The WFD requires Member States (MSs) to assess the Ecological Status (ES) of water bodies. This assessment will be based upon the status of the biological, hydromorphological and physico-chemical quality elements, by comparing data obtained from monitoring networks to reference (undisturbed) conditions, and then deriving an Ecological Quality Ratio (EQR). One of the biological quality elements to be considered is the benthic invertebrate component and some structural parameters (composition, diversity and disturbance-sensitive taxa) must be included in the ES assessment. Following these criteria, several approaches to benthic invertebrate assessment have been proposed by MSs. The WFD requires that these approaches are intercalibrated. This contribution describes the comparison of the different methodologies proposed by United Kingdom, Spain, Denmark and Norway. Results show a high consistency between the approaches, both with regard to determining the EQR and boundary settings for the ES.  相似文献   

The impacts of hysteresis on variably saturated hydrologic response and slope failure   总被引：1，自引：1，他引：0  

Brian A. Ebel  Keith Loague  Ronaldo I. Borja 《Environmental Earth Sciences》2010,60(6):1215-1225

This investigation employs 3D, variably saturated subsurface flow simulation to examine hysteretic effects upon the hydrologic response used to drive unsaturated slope stability assessments at the Coos Bay 1 (CB1) experimental catchment in the Oregon Coast Range, USA. Slope stability is evaluated using the relatively simple infinite slope model for unsaturated soils driven by simulated pore-water pressures for an intense storm that triggered a slope failure at CB1 on 18 November 1996. Simulations employing both hysteretic and non-hysteretic soil–water retention curves indicate that using either the drying soil–water retention curve or an intermediate soil–water retention curve that attempts to average the wetting and drying retention curves underestimates the near-surface hydrologic response and subsequently the potential for slope failure. If hysteresis cannot be considered in the hydrologic simulation, the wetting soil–water retention curve, which is seldom measured, should be used for more physically based slope stability assessment. Without considering hysteresis or using the wetting soil–water retention curve, the potential for landsliding in unsaturated materials may be underestimated and a slope failure could occur when simulations predict stability.  相似文献   

Millennial/submillennial-scale sea-level fluctuations in western Mediterranean during the second highstand of MIS 5e     

C.J. Dabrio  C. Zazo  A. Cabero  J.L. Goy  T. Bardají  C. Hillaire-Marcel  J.A. González-Delgado  J. Lario  P.G. Silva  F. Borja  A.M. García-Blázquez 《Quaternary Science Reviews》2011,30(3-4):335-346

This paper investigates a series of small-scale, short-lived fluctuations of sea level registered in a prograding barrier spit that grew during the MIS 5e. This interglacial includes three highstands (Zazo et al., 2003) and we focus on the second highstand, of assumed duration ～10 ± 2 ka, given that U–Th ages do not provide more accurate data. Geometry and 3D architecture of beach facies, and thin-section petrography were used to investigate eight exposed offlapping subunits separated by seven conspicuous erosion surfaces, all interpreted as the result of repeated small-scale fluctuations of sea level.Each subunit records a relatively rapid rise of sea level that generated a gravelly shoreface with algal bioherms and a sandy uppermost shoreface and foreshore where most sand accumulated. A second range of still smaller-scaled oscillations of sea level has been deduced in this phase of sea-level fluctuation from lateral and vertical shifts of the foreshore-plunge-step-uppermost shoreface facies.Eventually, progradation with gently falling sea level took place and foreshore deposits underwent successive vadose cementation and subaerial dissolution, owing to relatively prolonged exposure. Later recovery of sea level re-established the highstand with sea level at approximately the same elevation, and there began deposition of a new subunit. The minimum sea-level variation (fall and subsequent rise) required to generate the observed features is 4 m. The time span available for the whole succession of events, and comparison with the Holocene prograding beach ridge complex in the nearby Roquetas (Almería) were used to calculate the periodicity of events. A millennial-suborbital time scale is suggested for fluctuations separating subunits and a decadal scale for the minor oscillations inside each subunit.  相似文献