following article on my dissertation at the University of Tokyo, shortly before Christmas 2009 in Schaffhausen in the series Researchers the Schaffhauser Nachrichten published. The original layout. Pdf by clicking here reach. Below the text is copied.
If the ground melts beneath your feet
craft of civil engineers
The actual craft of civil engineers is the mathematical proof of serviceability (deformation) and loading ratio (tension) of a building. For this proof the action is compared to the structure with its resistance at the critical points. If the calculated exposure is greater than the resistance have to design measures of the structural design may be taken. Possible effects are net of the building material, wind, snow, live loads, fire or earthquake. Since the size of the load - which will arise in future - not exactly known, they are determined statistically by the data from the past.
The resistance on the other hand is determined from physical models and material properties. The latter are determined from material tests in the laboratory and in part on the site. It can even change the material properties under the strain, as the phenomenon of soil liquefaction occurs very pronounced, which is described below.
phenomenon of soil liquefaction
soil (so-called soft ground as opposed to rock as hard rock) is composed of individual grains of different sizes, the gaps are filled with air and water. The overall behavior is determined by the density of storage, shape and size of the Grains and the type of Lasttaufbringung. The load is transmitted only through direct contact between the individual grains, so these contact forces are key to the understanding of soil behavior. If
loosely stored, compacted sand saturated with water is very fast (like in an earthquake), has the water to escape in his intervals not enough time to the surface. This creates a very large water pressure, which can float to the sand soil mixture which behaves like a viscous liquid. This phenomenon is called soil liquefaction and can destroy all the dams, retaining walls move or houses can fall over.
liquefaction occurs in Japan specifically for two reasons often. First, since the earthquake intensity is very high on the tectonic boundary of the Eurasian, North American and Philippine plate. Second, because many landfills are in loose sand near the coast through mounds of artificial islands for lack of space.
exchange after Tokyo
let My special interest in earthquake engineering me of a stay at a host university Japan think about where this art is created by the great earthquake hazard very far. Through an academic mobility program, I received the opportunity, my last Academic year and complete it to my graduate work at the prestigious University of Tokyo (Japanese: Tokyo Daigaku). Thesis was supervised by Professor Puzrin of the ETH and Professor Towhata of Tokyo, which I always had two opinions from two disciplines, two education systems and two cultures.
shaking table tests in the laboratory studies of earthquake phenomena
earthquake phenomena through experiments on the one hand and on the other hand, systematically investigated by computer simulations. As part of my dissertation at the University of Tokyo, I was dealing with the avoidance of large deformation of liquefied ground by ground improvement with cement pillars. The latter are made by mixing cement with the existing soil material into a solid column. The floor must be liquefied to flow as the pillars around, which reduces the movement strong. Question was how stiff the columns are still present and in what kind of screen they are to be arranged.
In model experiments on the shaking table (see pictures below), the influence of column parameters on the extent of soil liquefaction and the extent of deformation. These two factors are, remarkably, not directly related, since the high water pressure can escape better for soft structures. These experiments were conducted on a scale of 1:10, so that the models generally found on the shaker table space. The scale effects are always examined in detail, in this case, the forces of weight are very small because the model is much lower.
In a second step, a computer model calibrated by previous experiments and compared various arrangements of the cement pillars in detail. The computer calculations based on fluid dynamics and not on solid mechanics, which is applied to this problem, a new approach. Since the computer model could be scaled, the scale effect has been checked here again.
From these studies it was concluded that the inherent stiffness of the columns a key parameter for the overall behavior of the soil and that a random, chaotic arrangement is better than in straight rows, as the ground then has no straight flow channels.
This research project is in collaboration continued with the private industry to develop concrete recommendations for improvements in building construction practice.
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