Narrow Results

Conventional methods of quantifying liquefaction hazards involve in-situ drilling techniques however, they are invasive and destructive on the sites and costly in terms of labor, time, and money. In this study, the Horizontal-to-Vertical Spectral Ratio (HVSR) of microtremors was used. It is a passive seismic geophysical technique, and we aim to evaluate its effectiveness in assessing liquefaction hazards. An array of single-station measurements was performed within the confines of selected experimental school sites in the coastal lowlands of the Greater Metro Manila Area (GMMA), Philippines. Measured predominant periods and their relative amplitudes were obtained to calculate the seismic shear strain, γ, of Nakamura and correlated with calculated liquefaction potential indices (LPI) from available downhole data. This study suggests that the employed methodology can be a quick, non-invasive, and cost-effective complement to existing downhole measurements in the assessment of liquefaction. Such a method can be adapted between borehole data gaps to extrapolate information where downhole data is limited or not always available.

HF:BF₃: H₂ catalysed depolymerization and hydroliquefaction of coal was studied. This superacidic system was found to be extremely effective for low temperature liquefaction of coal. Illinois No. 6 coal could be solubilized in pyridine to the extent of >90 % by treating it at ≈105°C for 4 h. Under somewhat more elevated temperature (150–170°C) cyclohexane extractabilities of up to 22 % and distillability of up to 28% is achieved. A hydrogen donor solvent such as isopentane is shown to improve the efficiency of the superacidic catalyst for the conversion of coal to cyclohexane soluble products.

A two-dimensional porous-elastoplastic model, in which the influence of the reduction of the effective stress on the soil strength has been considered, is proposed to investigate the accumulation of pore water pressure under standing wave. The simulation results show that the liquefaction is likely to occur around the node due to the accumulation of pore water pressure. The liquefaction leads to the decrease of soil resistance, which has great effect on the development of the residual pore pressure. The simulation demonstrates that if the decrease of soil resistance is not considered, the soil liquefaction depth will be overestimated.

For ensuring the earth dam's stability of Wangqingtuo reservoir when silt liquefaction happens during Tangshan earthquake, a large amount of laboratory soil tests and field measurements have been performed to obtain the mechanic properties of the soil and silt dynamic parameters. On the basis of the soil tests, the equivalent linear constitutive model is employed in the dynamic numerical simulation of the typical dam and the results indicate that the shear deformation is induced by the foundation liquefaction with the help of the geo-slope software. Moreover, the stability analysis is performed using the finite element elasto-plastic model that is considered the Mohr-Coulomb failure criteria to calculate the stability factor. The factors indicate the local instability would take place because of the shear action. At last, the measures are introduced to the designers for preventing the dam from the instability.

During their propagation tsunamis often traverse continental slopes that are relatively steep compared to deeper oceans. Further due to the change of bed slope from offshore to near shore, there is every likely possibility that a tsunami might steepen and eventually break, thereby generating large pressure gradients that could enhance the likelihood of liquefaction of the seabed. In the drawdown, high shear stresses could trigger debris flow in submarine canyons and on steep ridges. Therefore estimation of the bed stress is important in estimation of the forces induced during tsunami wave propagation, both on the seabed as well as on the subsurface installations. Bed and shear stresses generated by wave forms that represent tsunami (a solitary wave and broken solitary wave in the form of a bore) are measured using a shear cell. This paper deals with the measurements and modeling of the bed stress under the solitary waves.

In September 2010 and February 2011 two large shallow earthquakes occurred in the Canterbury region of New Zealand. The magnitude of the first earthquake was M 7.1 and of the second M 6.3, and the epicentres were, respectively, 44 km and 6 km from the CBD of Christchurch; which, with a population of 390,300, is the second largest city in New Zealand. This paper presents some details of the ground shock resulting from each earthquake. This explains why the lower magnitude earthquake had a more destructive effect on structures and lifelines; with a resulting greater number of casualties. Geotechnical observations and implications of these earthquakes, such as surface fault rupture, rockfalls, liquefaction and lateral spreading are presented and discussed briefly.

A number of theoretical issues related to liquefaction are reviewed. Some findings of recent experimental studies at UNSW at ADFA are presented. These studies aim at capturing the influence of fines by an equivalent state parameter, establishing the linkage between static and cyclic liquefaction of sand with fines, and predicting the form of cyclic liquefaction that may be triggered.

This paper presents the selected case studies of seismic microzonation and the lessons learned from the microzonation studies in India. India has experienced major damages and loss of life due to earthquakes. Macrozonation map in Indian seismic code BIS-1893 is frequently revised soon after a major earthquake in the country. The latest revision, which was published in 2002 after Bhuj earthquake in 2001, contains four macro zones. These zones are delineated based on geology and past seismic activity and without considering geotechnical aspects such as site effects and liquefaction. The government of India has initiated microzonation work of 63 cities in India to evaluate the earthquake vulnerability of major urban centers and prepare new zonation map. Most of these microzonation studies are under progress and a few of them have been completed. This paper presents a brief overview of some of these studies. Most of the microzonation studies done in India have not given due consideration to the geotechnical aspects in microzonation studies. The geotechnical aspects were fully incorporated in the recently completed Microzonation work of Bangalore and the ongoing microzonation study of Chennai. A detailed of description of the microzonation study of Bangalore urban centre is included in this paper.

The liquefaction potential in Padang based on the observation and examination is described in this paper. The last 7.6 RS earthquake of 30 September 2009 has caused damage to houses, water facilities and road ways. Several damages of those are worsened by the soil liquefaction. The liquefaction in Padang was identified by numerous sand boils. The liquefaction was observed at a number of sites including roadway, river bank and play grounds. The samples of sand boils are then tested in the laboratory in the terms of soil grain size distributions. It is found that the fine-sand grains of the soil samples are more than 65%. These types of soils satisfy the criteria of liquefaction susceptibility. Based on the field soil test data, the liquefaction potential is also examined. For the future development of Padang city, it is suggested to make liquefaction resistant constructions on liquefaction susceptible soils that have the same criteria to the observed soils. By characterizing the soil distributions and doing the in situ shear test on a particular site, one can assess the liquefaction susceptibility and decide to make the structures to resist the effects of liquefaction.

The significance of liquefaction related damage to pile foundations has been clearly demonstrated by the major earthquakes that have occurred during past years. Current project investigates seismic behaviour of a single pile in three-layered soil of Babol Citycenter site (located in Babol city, Mazandaran Province, Iran). The site soil consists of sandy and clayey soils modelled based on data collected from drilled boreholes. Numerical analysis performed using Flac2D finite difference program. Three different natural ground motion records are considered and influence of each earthquake on bending moment and horizontal displacement of the simulated pile is investigated. In addition, the effect of vertical surcharge on settlement of the pile during the earthquakes is investigated. Results illustrate that the maximum bending moments has been occurred on the interface of liquefiable and non-liquefiable soil layers.

In performance-based design of geotechnical works, accurate evaluation of deformation is often required. FEM is an effective method in this design process. However, not only the numerical models but also the detail of parameter setting is not unique, and it depends on the engineer. In this research, the difference of simulation results depending on the difference of the parameter set determined by several engineers is investigated. As a result, in liquefaction analysis, residual deformation of structure significantly depends on the parameter set for the liquefaction. And the coefficient of variation for the residual deformation is far larger than that of parameter set. Therefore, even a slight difference of parameter determination can cause a large difference on the estimated residual deformation.