I have been taking geodynamics as a part of master course in winter session (2013). Geodynamics is the one that suits my interest because I am really curious about dynamic behavior of soil and its impact on earth structures during earthquake. Consequently, soil liquefaction is one of the most important and interesting phenomena usually occurs during earthquake which becomes devastating, and eventually claims several human lives as shown in figure 1. This report has been prepared as a part of home assignment given by Yokohama sensei based on his lecture delivered. This assignment includes the following issues:
Mechanism of soil liquefaction
Testing method of liquefaction strength
Factors affecting soil liquefaction
Figure1: Liquefaction in Nigata, Japan (1964) and in Adapazari, Turkey (1999)
MECHANISM OF SOIL LIQUEFACTION
Liquefaction is one of the most important, interesting, complex, and controversial phenomenon whereby a saturated soil significantly loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid. It can cause spectacular damage including slope failure, bridge and building foundation failures, and floatation of buried structures. Nowadays, many researchers around the world have paid their attention extensively to such a devastating phenomenon to reconcile a smooth path.
The figure 2 indicates the liquefaction mechanism schematically. It shows that when the loosely packed sand is disturbed very slowly, the natural arrangement of particles will be disordered, reducing the volume. As shown in figure, if this sand layer is located below the groundwater level and pore water flows between sand grains, then ...
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...verburden pressure increases.
Cyclic Loading
The level of pore-pressure excess required to initiate liquefaction is related to the amplitude and duration of earthquake-induced cyclic loading. The amount of damage to structures on soils undergoing liquefaction depends on how long the sand remains in a liquefied state. Seed (1976) concluded that the multidirectional shaking is more severe than one-directional loading in terms of pore pressure. Pore water pressure build up faster under multidirectional stress conditions than under unidirectional stress conditions. Densification of soil is expected as a result of cyclic loading since the soil particles are rearranged during the back-and-forth straining. As cycling continues, the pore-pressure increases progressively until finally it reaches, during part of each subsequent cycle, the total stress acting upon the sand.
Earthquakes are a natural part of the Earth’s evolution. Scientific evidence leads many geologists to believe that all of the land on Earth was at one point in time connected. Because of plate tectonic movements or earthquakes, continental drift occurred separating the one massive piece of land in to the seven major continents today. Further evidence supports this theory, starting with the Mid-Atlantic ridge, a large mass of plate tectonics, which are increasing the size of the Atlantic Ocean while shrinking the Pacific. Some scientists believe that the major plate moveme...
such as clay, shale, or blast-furnace slag. Either a dry or a wet process is
Desert pavements are common landforms in arid regions. They consist of flat or sloping surfaces where stones are closely packed angular or rounded, and generally exhibit low relief (Mabbutt, 1977). Pavements tend to form on both alluvial fan toposequences and on weathering volcanic flow fields in arid regions. Soils are often found under desert pavements and they play an important role in the evolution of pavements (McFadden et. al., 1987). In the past there have been several theories as to the formation pavements and soil development beneath them. Deflation, or the erosion of finer grained particles from a surface, stone concentration by wash erosion and upward displacement of stone due to shrink and swell clay characteristics were at one time believed to be the main factors in the formation of desert pavements (Mabbutt, 1977). However, more recent research has shown that desert pavements are born and maintained at the surface, and that the soil below them is mainly eolian in origin. Slow accretion of eolian dust below the pavement is a process that eventually develops cumulate horizons. Eolian dust in environments where pavements often develop is rich in carbonate salts and clays due to the fact it often originates from nearby playa lake evaporate basins (McFadden et. al., 1987). Soils that form below the pavements over time develop calcic horizons and clay rich structure due to the influx of these eolian fines through the pavement surface. In turn the development of mature or plugged calcic horizons effects the form of the pavement surface because it alters the water drainage infiltration rate and causes pavements to decline.
Before examining the Northridge event, understanding the naturally occurring hazard that is an earthquake will help to better understand exactly what happened and why it was such an important geological event. With four distinct layers, two layers, the crust and upper portion of the mantle, compose the skin that is the surface layer of the Earth. The crust is not a single, continuous piece. It is actually several different pieces, or plates, that come together to form the puzzle that comprises the surface of the Earth. These plates are in constant motion rubbing against one another. These areas, known as fault lines, where the plates rub up against one another have spots where one plate ”gets stuck while the rest of the plate keeps moving. When the plate has moved far enough, the edges unstick and is how most of the earthquakes around the world occur” (Wald, 2012). The energy stored from the friction of the two plate...
The hypothesis that was formed in this experiment was that decantation and distillation were the techniques that would be successful in separating the three layered substances. The oil on top of the mixture was to be decanted solely, and the salt and sand layers would be distilled and separated together on filter paper on top of boiling hot water. The reason that the oil is decanted is because it doesn’t mingle with the salt and sand layers, and in addition it was the top layer, which was thought to have been easy to separate first. And as for the sand and salt, sand doesn’t mix and dissolve in water compared to salt, which does in fact dissolve, so distillation was thought to be the proper solution to separating the two
Earthquakes commonly have consequences that are unexpected by an environment they occur in. The consequences may be tsunamis, buildings collapsing, structures distorting, landslides, and liquefaction.
It happens when particles make effective collisions with sufficient energy. The sand is Apparatus = == == =
I have discovered that this is not the case. The sand is Interpretation and Evaluation: a.k.a In this experiment I found out that many different factors including. Concentration, Temperature and Surface Area affect the rate of reaction.
...nt. Due to this observation we can conclude that there were no catalysts or enzymes present in the sand.
Living in Bangladesh, we have seen quite disastrous mudslides from the past few years. Mudslide is also called a landslide or a land slip. It is a downward mass movement of earth or rock on unstable slopes, including many forms resulting from differences in rock structure, coherence of material involved, degree of slope, amount of included water, extent of natural or artificial undercutting at the base of the slope, relative rate of movement, and relative quantity of material involved. There are numerous facts that can cause a mudslide and there are also numerous effects that it can cause us.
Surface Creep occurs when landing sand particles remove the larger and heavier particles, pushing them forward.
Hydrometer test is needed as more than 10 % of soil sample passes the 63 µ m sieve (BS 1377-2:1990). It covers the quantitative determination of the particle size distribution in a soil from coarse sand size to clay size. Particles settle under gravity during testing (Head, 1984). The results of hydrometer analysis can be referred to Appendix C1. The calibrations which used in the hydrometer analysis and water viscosity are shown in Appendix C2 and Appendix C3.
The sand is The variables in this experiment were Volume and Temperature. So as to make this a fair experiment, care was taken to ensure that the beaker. was rinsed every time, and that the thermometer was in the room. temperature, so as not to yield any anomalous results. All the results will be taken on the same day, so that the room temperature does not differ, as this could affect the results also. My Hypothesis: My hypothesis is that the temperature of the water will decrease as the volume increases.
Earthquakes belong to the class of most disastrous natural hazards. They result in unexpected and tremendous earth movements. These movements results from dissemination of an enormous amount of intense energy in form of seismic waves which are detected by use of seismograms. The impact of earthquakes leaves behind several landmarks including: destruction of property, extensive disruption of services like sewer and water lines, loss of life, and causes instability in both economic and social components of the affected nation (Webcache 2).