A unified mechanical and retention model for saturated and unsaturated soil behaviour   总被引：1，自引：1，他引：0  

Martí Lloret-Cabot  Simon J. Wheeler  Marcelo Sánchez 《Acta Geotechnica》2017,12(1):1-21

The coupled mechanical and water retention elasto-plastic constitutive model of Wheeler, Sharma and Buisson (the Glasgow coupled model, GCM) predicts unique unsaturated isotropic normal compression and unsaturated critical state planar surfaces for specific volume and degree of saturation when soil states are at the intersection of mechanical (M) and wetting retention (WR) yield surfaces. Experimental results from tests performed by Sivakumar on unsaturated samples of compacted speswhite kaolin confirm the existence and form of these unique surfaces. The GCM provides consistent representation of transitions between saturated and unsaturated conditions, including the influence of retention hysteresis and the effect of plastic volumetric strains on retention behaviour, and it gives unique expressions to predict saturation and de-saturation conditions (air-exclusion and air-entry points, respectively). Mechanical behaviour is modelled consistently across these transitions, including appropriate variation of mechanical yield stress under both saturated and unsaturated conditions. The expressions defining the unsaturated isotropic normal compression planar surfaces for specific volume and degree of saturation are central to the development of a relatively straightforward methodology for determining values of all GCM parameters (soil constants and initial state) from a limited number of laboratory tests. This methodology is demonstrated by application to the experimental data of Sivakumar. Comparison of model simulations with experimental results for the full set of Sivakumar’s isotropic loading stages demonstrates that the model is able to predict accurately the variation of both specific volume and degree of saturation during isotropic stress paths under saturated and unsaturated conditions.  相似文献   

On the Machian origin of inertia     

Marcelo Samuel Berman 《Astrophysics and Space Science》2008,318(3-4):269-272

We examine Sciama’s inertia theory: we generalise it, by combining rotation and expansion in one unique model, we find the angular speed of the Universe, and we stress that the theory is zero-total-energy valued. We compare with other theories of the same null energy background. We determine the numerical value of a constant which appears in the Machian inertial force expression devised by Graneau and Graneau (In the Grip of the Distant Universe—the Science of Inertia, World Scientific, Singapore, 2006), by introducing the above angular speed. We point out that this last theory is not restricted to Newtonian physics as those authors stated but is, in fact, compatible with other cosmological and gravitational theories. An argument by Berry (Principles of Cosmology and Gravitation, Adam Hilger, Bristol, 1989) is shown in order to “derive” Brans-Dicke relation in the present context.  相似文献   

An elastoplastic mechanical constitutive model for microbially mediated cemented soils     

Gai  Xuerui  Sánchez  Marcelo 《Acta Geotechnica》2019,14(3):709-726

Microbially induced calcite precipitation (MICP) is an innovative bio-mediated soil improvement technique that develops cementation within originally loose and potentially collapsible soils. This method utilizes biogeochemical processes with microbes. It has the advantage of being friendly to the environment and sustainable. In spite of the current interest in the MICP technique, the mechanical modeling of MICP-treated soils is still limited. In this paper, a constitutive model for MICP-treated sands is presented. The core components of the proposed approach include: a critical state yield surface, sub-loading concepts, a mechanism to account for the MICP-induced cementation enhancement, and an evolution law to consider bonding degradation effects during shearing. The mathematical framework is presented in detail. The model is then applied to analyze recently published experiments involving MICP-treated samples, with different calcite contents, and tested under different conditions (i.e., various confining pressure and loading paths). The model was able to properly capture the main features of MICP-treated sands behavior observed in the tests. It also assisted to interpret the response of this type of soil under different loading conditions.

  相似文献   

Multimodal reliability analysis of 3D slopes with a genetic algorithm     

Tun  Ye W.  Llano-Serna  Marcelo A.  Pedroso  Dorival M.  Scheuermann  Alexander 《Acta Geotechnica》2019,14(1):207-223

Acta Geotechnica - This paper presents a genetic algorithm (GA) to solve the multimodal optimisation problem resulting from 3D slopes prone to multiple regions of failure. A probabilistic approach...  相似文献   

Determination of Moho dip using PS reflections     

Marcelo Assumpção 《Geophysical Journal International》1980,60(1):77-84

Summary. A clear PS reflection was recorded in the northern section of the LISPB line (shot-point N1, profile ALPHA). Travel times of PS and PP phases reflected at the same part of the Moho were used to model the lower crustal structure. The observed high apparent velocity of the PS phase (8.4 km/s) is interpreted as due to a localized Moho dip of 7 per cent (4°) towards the north. This is supported by observations of Pn refractions from other shots. It is shown that PS reflections could be very useful for determination of Moho dips.  相似文献   

Mixing at the front of gravity currents     

Marcelo H. García  Jeffrey D. Parsons 《Dynamics of Atmospheres and Oceans》1996,24(1-4)

Observations made with the help of a movable-bed tank designed and operated to freeze the motion of gravity current fronts indicate that both the scale of the apparatus and the magnitude of the current Reynolds number have a strong influence on mixing rates. Low mixing rates are associated with fronts in relatively shallow fresh water depths and low Reynolds numbers. Mixing rates increase more rapidly as the ratio of current thickness to fresh water depth increases. For the deepest fresh water flow conditions, when scale effects can be expected to be negligible, the dimensionless mixing rate is approximately equal to three times the relative current thickness and has an upper limit of about 0.3. Lower mixing rates are observed as the current Reynolds number decreases, suggesting that viscous effects can still exist even for deep fresh water conditions. Application of the experimental results to estimate some parameters of a hypothetical gravity current on the continental shelf yield reasonable values. However, it is clear that, owing to the scale and Reynolds number effects that might be present in laboratory experiments, particular care should be exercised when trying to extrapolate results to gravity currents in nature.  相似文献   

Waveshapes of continuing currents and properties of M-components in natural negative cloud-to-ground lightning from high-speed video observations   总被引：2，自引：1，他引：2  

Leandro Z.S. Campos  Marcelo M.F. Saba  Osmar Pinto  Jr.  Maurício G. Ballarotti   《Atmospheric Research》2007,84(4):302-310

Continuing current is a continuous mode of charge transfer to ground in a lightning flash. The extent to which the continuing current contributes to the total negative charge lowered to earth is large. In order to study the waveshape of the continuing currents of natural flashes, we developed a computational algorithm that analyzes the pixels of the images obtained by a high-speed camera and plots luminosity-versus-time. Tower measurements have shown that during the continuing current phase of the flash the luminosity of the channel is directly proportional to the current that flows through it. Using this information it was possible to infer the continuing current waveshape for 63 natural discharges and classify them into six different types. Statistics on some characteristics of 345 M-components (that occurred during the same 63 events) are also presented. As far as we know, this is the first study on waveshapes of continuing currents for natural lightning.  相似文献   

Wien effect of Cd/Zn on soil clay fraction and their interaction     

Tingting Fan  Chengbao Li  Juan Gao  Dongmei Zhou  Marcelo Eduardo Alves  Yujun Wang 《Geochemical transactions》2018,19(1):5

  相似文献   

Arsenic in Porewaters of the Unsaturated Zone of an Argentinean Watershed: Adsorption and Competition with Carbonate as Important Processes that Regulate its Concentration     

Virginia Puccia  Fabiana Limbozzi  Marcelo Avena 《Aquatic Geochemistry》2015,21(6):513-534

  相似文献   

BRAMS model performance for significant event involving Brazilian platform ship     

Rodrigues  Karine dos Santos  do Carmo  Luiz Felipe Rodrigues  Palmeira  Ana Cristina Pinto de Almeida  Andrioni  Marcelo 《Natural Hazards》2022,110(3):2277-2302

Natural Hazards - After a storm displaced the P-70 platform ship located in Guanabara Bay to the coast on January 30, 2020, a numerical investigation was carried out with the BRAMS (Brazilian...  相似文献