Direct in-situ evaluation of liquefaction susceptibility

textEarthquake-induced soil liquefaction that occurs within the built environment is responsible for billions of dollars of damage to infrastructure and loss of economic productivity. There is an acute need to accurately predict the risk of soil liquefaction as well as to quantify the effectiveness of soil improvement techniques that are meant to decrease the risk of soil liquefaction. Current methods indirectly measure the risk of soil liquefaction by empirically correlating certain soil characteristics to known instances of surficial evidence of soil liquefaction, but these methods tend to overpredict the risk in sands with silts, to poorly predict instances of soil liquefaction without surface manifestations, and fail to adequately quantify the effectiveness of soil improvement techniques. Direct in-situ evaluation of liquefaction susceptibility was performed at a single site at the Wildlife Liquefaction Array (WLA) in Imperial Valley, California, in March 2012. The project included a CPT sounding, crosshole testing, and liquefaction testing. The liquefaction testing involved the measurement of water pressure and ground particle motion under earthquake-simulating cyclic loading conditions. The objective of this testing technique is to observe the relationship between shear strain in the soil and the resulting generation of excess pore water pressure. This fundamental relationship dictates whether or not a soil will liquefy during an earthquake event. The direct in-situ evaluation of liquefaction susceptibility approach provides a more accurate and comprehensive analysis of the risks of soil liquefaction. It also has the ability to test large-scale soil improvements in-situ, providing researchers an accurate representation of how the improved soil will perform during a real earthquake event. The most important results in this thesis include the identification of the cyclic threshold strain around 0.02% for the WLA sand, which is very similar to results achieved by other researchers (Vucetic and Dobry, 1986, and Cox, 2006) and is a characteristic of liquefiable soils. Another key characteristic is the 440 to 480 ft/sec (134 to 146 m/s) shear wave velocity of the soil, which are well below the upper limit 656 ft/sec (200 m/s) and an indication that the soil is loose enough for soil liquefaction to occur. The third significant point is that the compression wave velocity of the sand is greater than 4,500 ft/sec (1,370 m/s), indicating that it is at least 99.9% saturated and capable of generating large pore water pressure due to cyclic loading. These three conditions (cyclic threshold strain, shear wave velocity, and compression wave velocity) are among the most important parameters for characterizing a soil liquefaction risk and must all be met in order for soil liquefaction to occur.Civil, Architectural, and Environmental Engineerin

Mechanism of Soil Liquefaction

A deeper inspection has been made into the physical meaning and mechanism of the soil liquefaction. Emphasis has been laid on the stress condition and stress evolution in saturated cohesionless soils during liquefaction. Typical examples have been described to demonstrate the process of stress evolution in soil liquefaction. Some other related factors such as limit equilibrium condition, strain and pore water pressure evolution in the saturated cohesionless soil mass under cyclic loading or vibration have also been discussed. It has been concluded that the state of stress in saturated cohesionless soils is bounded by limit equilibrium condition and approaches the hydro-static pressure in the course of liquefaction, the pore water pressure evolution during soil liquefaction can be correlated with the fabric characteristics and drainage condition of the soil mass, and the strain does not seem to be a proper reference for the definition of soil liquefaction

Some Geotechnical Aspects of 1999 Chi-Chi, Taiwan Earthquake

The Chi-Chi, Taiwan earthquake with a magnitude of 7.3 occurred on September 21, 1999. It was the largest and most damaging earthquake in Taiwan in a century. It induced extensive geotechnical hazards including landslides, soil liquefaction, foundation failures, and ground movements in central Taiwan, and caused substantial damages to buildings, roadways, bridges, and waterfront structures. Field investigations and studies in geotechnical aspects, including landslides, soil liquefaction, foundations, retaining structures, dams and tunnels, in the affected areas were performed. The results of field explorations and laboratory tests for the study of soil liquefaction and evaluation of the secondary hazard of debris flow are also discussed

The Study of Risk Assessment of Soil Liquefaction on Land Development and Utilization by GIS in Taiwan

The issue of soil liquefaction has been investigated widely in the past 50 years. However, there is no an integrated method have been considered for the factors between regions’ vulnerability of soil liquefaction and resilience capacity to perform the risk assessment of soil liquefaction hazard. This study selects Yunlin and Chiayi County as a demonstration area, and uses Model Builder of geo-processing models to connect multiple analysis processes, the liquefaction risk distribution in Yun-Chia Plain’s area is carried out in 100 × 100 m grid map scale by GIS. The study results could provide the reference of land development and management in Taiwan

Numerical Modelling of Multi-directional Earthquake Loading and Its Effect on Sand Liquefaction

Earthquakes generate multi-directional ground motions, two components in the horizontal direction and one in the vertical. Nevertheless, the effect of vertical motion on site response analysis has not been the object of extensive research. The 2010/2011 Canterbury sequence of seismic events in New Zealand is a prime example among other earlier field observations strongly corroborating that the vertical acceleration may have a detrimental effect on soil liquefaction. Consequently, this study aims to provide insight into the influence of the input vertical motion on sand liquefaction. For this reason, two ground motions, with very different frequency contents, are used as the input excitations. Non-linear elasto-plastic plane strain fully coupled effective stress-based finite element analyses are conducted to investigate the occurrence of liquefaction in a hypothetical fully saturated Fraser River Sand deposit. The results indicate that the frequency content of the input motion is of utmost importance for the response of sands to liquefaction when the vertical loading is considered

Soil Liquefaction Seismic Risk Analysis Based on Post 1979 Earthquake Observations in Montenegro

The scale and consequences of soil liquefaction during April 15, 1979 Montenegro earthquake rose a problem of explanation of this phenomena and assessment of the ground behaviour during future earthquakes. The analysis, the details and results presented in this paper is divided into two parts: The first part comprises soil liquefaction during Aprill5 1979 earthquake including the analysis of both geotechnical conditions and excitation potential inducing them. In order to realise the scale and the properties of the phenomenon, distribution of the locations with manifestations likely to have been induced by soil liquefaction, as observed on the ground surface and on civil engineering structures, has been given and described. To identify the presence of conditions inducing soil liquefaction the geotechnical soil properties for several typical locations have been analysed. Analysis of the characteristic ground surface horizontal acceleration records obtained by the earthquake from the aspect of their potential to cause liquefaction have been also carried out. To determine the liquefaction potential of the considered earthquake detailed analysis of typical geotechnical model of a site have been performed. In the second part is presented the seismic risk analysis background for soil liquefaction aimed at explanation of the essential problems concerning the evaluation of geotechnical media comprising of loose sand under the effect of future earthquakes. At the same time, the complexity of the problems which have to be dealt with during the seismic risk investigations has been pointed out concerning the necessity of investigation in this sense. It is necessary to make some assumptions and simplifications for solving sane of these problems. Applying the results of the analysis from the first part as well as the assumptions and simplifications, an assesment of the seismic risk for soil liquefaction analysed in details in the first part applying one of the possible methodologies, has been carried out

A simulation of earthquake induced undrained pore pressure changes with bearing on some soil liquefaction observations following the 2001 Bhuj earthquake

The Bhuj earthquake of January 26th, 2001, induced wide spread liquefaction within the Kachch peninsula. It has been pointed out that inundation due to soil liquefaction was short lived in some parts than in others in the affected region. Several geological, seismological and hydrological factors would have cumulatively contributed to these observed changes. We simulate in this article, undrained or short-term change in pore pressure in a poroelastic half space, in response to a simplified model of the Bhuj earthquake source. We find that the regions of relatively shorter lived inundation due to soil liquefaction may fall in the region where pore pressure responsible for soil liquefaction attributable to strong ground shaking was counteracted by pore pressure changes due to undrained poroelastic effect and vice versa