Extended model of shear modulus reduction for cohesive soils

Acta Geotechnica - The shear modulus of a soil, G, shows a hyperbolic degradation curve relationship with increasing shear strain, γ. G is usually normalized against the small-strain modulus...     

Experimental studies of groundwater pipe flow network characteristics in gravelly soil slopes

Piping flow networks have often been identified in hydrogeological field studies of gravelly soil slopes in the southern part of China. The present experimental studies have shown that under long-term groundwater seepage, piping flow networks gradually develop in the slope. Factors affecting the development of flow pipe seepage network included the grain size distribution, the degree of soil compaction, and soil depth. Piping seepage networks favorably form if the content of the gravel was high, the soil cohesion was low, the degree of the soil compaction was low, or the soil depth was shallow. Due to the enhanced permeability associated with the presence of flow pipe seepage network in gravelly soil slopes, groundwater can be effectively drained away. This can beneficially prevent the rise of groundwater level in the slope during raining seasons, hence reducing pore water pressure along the potential failure surface and increasing slope stability. Once the flow pipe seepage network was disturbed or damaged, the water level in the upper portion of the slope experienced a great rise, hence reducing the slope stability. Therefore, slope toe excavation and excessive loading at the slope crest should be avoided for slopes with well-developed flow pipe seepage network in order to preserve it.     

Water effects on rock strength and stiffness degradation

Reduction in strength and stiffness in rocks attributed to an increase in water content has been extensively researched on a large variety of rock types over the past decades. Due to the considerable variations of texture and lithology, the extent of water-weakening effect is highly varied among different rock types, spanning from nearly negligible in quartzite to 90 % of uniaxial compressive strength reduction in shale. Readers, however, often face difficulties in comparing the data published in different sources due to the discrepancy of experimental procedures of obtaining the water saturation state and how the raw laboratory data is interpreted. In view of this, the present paper first reviews the terminologies commonly used to quantify the amount of water stored in rocks. The second part of the paper reviews the water-weakening effects on rock strengths, particularly focusing on uniaxial compressive strength and modulus, as well as tensile strength, under quasi-static loading and dynamic loading. The correlation relationships established among various parameters, including porosity, density and fabric of rocks, and external factors such as strain rate, surface tension and dielectric constant of the saturating liquid, absorption percentage and suction pressure, are reviewed and presented toward the end of the paper.     

Visualization and Analysis of Multi-terabyte Geophysical Datasets in an Interactive Setting with Remote Webcam Capabilities

Visualizing and analyzing datasets in the geosciences is becoming increasingly complicated as their volumes are growing explosively. This poses a challenging problem for researchers who must sift through terabytes of data to discover useful relationships inside the information. There is a great need for geophysicists to interactively explore their data sets. Conventional visualization systems lack adequate bandwidth and rendering capabilities necessary for the largest data sets. CAVE and Powerwall display devices are necessary for researchers to explore their data sets in an immersive setting. We describe a utilitarian system targeted specifically at the cost-effective interactive exploration of data sets tens of terabytes in size and harness this system for visualization and analysis of geophysical simulations. Webcams can be used as a steering device to track a local region of interest, which is useful for remote visualization of large data sets. This system will be employed as a web-service under the auspices of Narada-Brokering, while using webcam technologies to enable remote visualization for collaborating researchers. Webcams can be incorporated in a point-to-point network for rapid exchange of information and quickly announcing natural disasters, such as tsunamis, landslides and earthquakes.     

Quartz Rheology and Short-time-scale Crustal Instabilities

We present numerical results of thermal-mechanical feedback in crustal quartz rheology and contrast this behavior to the vastly different character of an olivine mantle. In the numerical experiments quartz is found to have a very strong tendency for short-time-scale instabilities, while our numerical experiments show that olivine has a decisive tendency for a stable thermally lubricated slip. At the same time, olivine can also go through a transitional period of creep bursts, which are physically caused by multiple interacting ductile faults at various length and time scales which collocate quickly into a major shear zone. Since olivine has this strong propensity to self organize in a large apparently stable fault system, it lacks the dynamics of interacting ductile faults evident in other minerals. Quartz behaves totally different and keeps its jerky slip behavior for prolonged deformation. An example is shown here in which a 30 × 50 km piece of a wet quarzitic crust is extended for about 2 Ma. The associated total displacement field clearly shows the unstable slipping events, which have a characteristic time frame of one to several years, In contrast, olivine is very stable and has a much longer time scale for thermal instability of 100 kyrs.     

Visualization of multi-scale dynamics of hydrous cold plumes at subduction zones

Recent increases in the computational power of high-performance computing systems have led to a large gap between the high-resolution runs of numerical simulations—typically approaching 50–100 million tracers and 1–5 million grid points in two dimensions—and the modest resolution of 1–2 million pixels for conventional display devices. This technical problem is further compounded by the variety of fields produced by numerical simulations and the limited bandwidth available through the Internet in the course of collaborative ventures. We have developed a visualization system using the paradigm of web-based inquiry to address these mounting problems. We have employed, as a case study, a problem involving two-dimensional multi-scale dynamics of hydrous cold plumes at subduction zones. A Lagrangian marker method, in which the number of markers varies dynamically, is used to delineate the many different fields, such as temperature, viscosity, strain, and chemical composition. We found commercially available software to be insufficient for our visualization needs and so we were driven to develop a new set of tools tailored to high-resolution, multi-aspect, multi-scale simulations, and adaptable to many other applications in which large datasets involving tens of millions of tracers with many different fields are prevalent. In order to address this gap in visualization techniques, we have developed solutions for remote visualization and for local visualization. Our remote visualization solution is a web-based, zoomable image service (WEB-IS) that requires minimal bandwidth while allowing the user to explore our data through time, across many thermo–physical properties, and through different spatial scales. For local visualization, we found it optimal to use bandwidth-intensive, high-resolution display walls for performing parallel visualization in order to best comprehend the causal and temporal relationships between the multiple physical and chemical properties in a simulation.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s10069-004-0017-2     

Finite Prandtl number 2-D convection at high Rayleigh numbers

Finite Prandtl number thermal convection is important to the dynamics of planetary bodies in the solar system. For example, the complex geology on the surface of the Jovian moon Europa is caused by a convecting, brine-rich global ocean that deforms the overlying icy “lithosphere”. We have conducted a systematic study on the variations of the convection style, as Prandtl numbers are varied from 7 to 100 at Rayleigh numbers 106 and 108. Numerical simulations show that changes in the Prandtl number could exert significant effects on the shear flow, the number of convection cells, the degree of layering in the convection, and the number and size of the plumes in the convecting fluid. We found that for a given Rayleigh number, the convection style can change from single cell to layered convection, for increasing Prandtl number from 7 to 100. These results are important for determining the surface deformation on the Jovian moon Europa. They also have important implications for surface heat flow on Europa, and for the interior heat transfer of the early Earth during its magma ocean phase. Electronic Supplementary Material is available if you access this article at . On that page (frame on the left side), a link takes you directly to the supplementary material. Electronic Supplementary Material is available if you access this article at . On that page (frame on the left side), a link takes you directly to the supplementary material.