Soil Liquefaction and cyclic mobility for level ground during earthquakes
It is shown that the design engineer has two basic choices if he considers it appropriate to neglect the possible effects of drainage occurring during the period of cyclic stress applications: (1)To calculate the stresses induced in the ground by the design earthquake, and to compare these stresses with those required to cause cyclic mobility or liquefaction of representative samples in the laboratory. The main problem in this approach lies in correctly assessing the characteristics of the in-situ deposit from laboratory tests performed on even good quality undisturbed samples. (2)to be guided by the known field performance of sand deposits correlated with some measure of in-situ characteristics, such as the standard penetration test. In some cases it is desirable to evaluate the possible effects of pore pressure dissipation in different layers of a deposit during and following earthquake shaking. Methods of accomplishing this are reviewed and described.
Available from: Gabriele Chiaro
- "However, an alternative approach to use field data is to use laboratory data. In fact, the cyclic resistance from triaxial tests (CSR tx ) can be converted to field values using the following expression proposed by Seed (1979) "
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ABSTRACT: A site investigation program was undertaken in Chiba (Japan) to evaluate the undrained cyclic strength properties of two sandy soils (Holocene and landfill deposits), which is believed to have experienced liquefaction during the 2011 Off the Pacific Coast of Tohoku Earthquake. In this regards, the application of advanced sampling technology was crucial for obtaining high quality undisturbed samples, as soil fabric and ageing effects would be significant. This paper examines the quality of undisturbed samples which were taken by " Gel-push " (GP) sampling using comparisons between dynamic shear moduli directly evaluated in-situ (downhole) and those measured in the laboratory on undisturbed triaxial samples extracted by both GP and conventional triple-tube sampling (TB) techniques. Preliminary results are presented endorsing the ability of the GP sampler to achieve higher quality samples suitable for liquefaction strength testing compared to the TB sampler.
International Conference on Goetechnical Engineering; 08/2015
Available from: Raul Miranda-Avilés
- "The combination or association of flame structures with sandstone dikes indicates a mixture of driving forces acting together during liquefaction (horizontal shear stress together with a gravitationally unstable density gradient). Liquefaction features are mainly generated by earthquake shaking (Youd, 1978; Allen, 1975; Seed, 1979). Atkinson (1984) mentioned that magnitude 5 earthquakes can produce liquefaction processes when suitable conditions exist. "
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ABSTRACT: Siliciclastic deposits of the Eocene-Oligocene Losero Formation, which crop out in the Sierra de Guanajuato in central Mexico, show several types of soft-sediment deformation structures that are interpreted as seismites. The Sierra de Guanajuato is a complex tectonic pile of thrust sheets composed of Mesozoic lithostratigraphic successions. During the Paleogene, the Sierra de Guanajuato was affected by extensional tectonism that occurred in a short time interval, which was contemporary with clastic sedimentary depositional
processes. Eocene-Oligocene deposits are characterized by a red bed sequence represented by the “Guanajuato Conglomerate” and the Losero Formation, which has many syn-sedimentary faults and microfaults oriented NE 35°– 45°SW, with a dip of 70°–87°SE. These sediments are the result of a braided fluvial system characterized by plane parallel laminae, desiccation cracks, ripples, and cross bed sets, antidunes, groove and flute casts. In the study area, two stratigraphic sections (Caídos y Socavón) were measured in detail (facies distributions, primary structures and stacking patterns). Several types of soft-sediment deformation structures were recorded in Losero deposits and these occur interbedded with undeformed strata throughout the entire stratigraphic interval. The lateral extent of the deformation is of several hundred meters long and the deformed bed involves the mid-upper part of the 30 meter thick succession. Deformation affects about two meters of coarse-grained sandstone, fine-grained sandstones, and mudstones. This deformation is represented by layers with asymmetric and symmetric folds, dish structures, pseudonodules, sandstone dikes, flame structures, syn-sedimentary normal microfaults and convolute laminae. It can be described as a gradient system of unstable density layers. Soft-sedimentary deformation structures observed in the Losero Formation are interpreted as seismites, developed as a result of increased pore pressure and vertical or horizontal stresses induced by seismic activity
Revista Mexicana de Ciencias Geológicas 08/2015; 32(2):203-218. · 0.57 Impact Factor
Available from: Izuru Takewaki
- "The hazard seems to be caused by the sedimentary sand layer of the alluvium plain. This drastic seismic hazard in buildings and bridges were propagated in the world through the photographs and the seismic records, from which the researches were focused on the dynamical cyclic process of the liquefaction phenomenon   . In the fifty years after this seismic event, several seismic hazards due to soil liquefaction occurred and new findings were accumulated by many researchers   . "
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ABSTRACT: Focusing on soil liquefaction, the seismic records during the Niigata-ken earthquake in 1964, the southern Hyogo prefecture earthquake in 1995 and the 2011 off the Pacific coast of Tohoku earthquake are analyzed by the non-stationary Fourier spectra. The shift of dominant frequency in the seismic record of Kawagishi-cho during the Niigata-ken earthquake is evaluated based on the time-variant property of dominant frequencies. The reduction ratio of the soil stiffness is evaluated from the shift ratio of dominant frequency. It is detected that the pulse wave in the transient process during the progressing liquefaction is composed of the primary mode and the secondary modes. Using the seismic records at the underground of Port Island during the southern Hyogo prefecture earthquake in 1995, the amplification of liquefaction is evaluated by comparing the maximum amplitude spectra of seismic records at GL 0 m and GL-83 m. The average shear strain of underground is calculated from the numerically integrated displacement profiles and the deterioration ratio of stiffness is evaluated from the G- relation. The amplification of liquefaction at Chiba bay area is evaluated by using the ratio of the maximum amplitude spectra of CHB024 and CHBH10 (Borehole) from the mainshock and the aftershock of the 2011 off the Pacific coast of Tohoku earthquake.
Soil Dynamics and Earthquake Engineering 04/2015; 71. DOI:10.1016/j.soildyn.2015.01.017 · 1.22 Impact Factor
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