مروری بر روشهای توسعه یافته اخیر در مورد کاهش روانگرایی خاک
Abstract
1- Introduction
2- Recently developed methods
3- Applicability
4- Cost
5- Duration time
6- Conclusions and recommendations
References
Abstract
Triggered liquefaction in earthquakes, that soil displays fluid-like characteristics caused by an on-going increase of pore water pressure and reduction of the effective stress, can damage existing building foundations and other structures and result in significant economic losses. Many previous studies have investigated methods, which effectively control sand liquefaction while minimizing cost, environmental impact and other related disturbances. Recently, the rapid development of materials technology and multidisciplinary approaches has made available new materials suitable for improving the liquefaction resistance and enabling other liquefaction mitigation techniques. To raise some important questions and encourage further research and discussions, investigations on the recently developed liquefaction mitigation methods are reviewed in this study. The review first analyzed and discussed the characteristics of the newly developed methods including the mitigating mechanism, effectiveness, and possible executive problems for purpose of building sufficient understanding into the progress of liquefaction resistance. Then, the applicability and uniformity in the soil with different pore size, possible disturbance to nearby structures are discussed. Additionally, the potential cost and duration time of the mitigation measures for site constructions are briefly described. Through this review, some important questions and discussions are raised; the readers will fully understand the research trend of liquefaction mitigation and further explore new methods and techniques that could be effective, easy for on-site construction, low cost, environment-friendly and highly durable. This study recommends long-term in-situ investigation on mitigation effectiveness, duration time and quantitative cost assessment.
Introduction
Liquefaction induced by static or dynamic loading in saturated sandy soil can cause significant damage to building foundations and existing structures, such that the sudden instability may result in the destruction of structures, economic losses and even loss of human life [1–3]. Liquefaction problems have been reported frequently after earthquakes, such as the earthquakes that occurred in 1964 Niigata, Japan, 1976 Tangshan, China, 1999 Kocaeli, Turkey, 2008 Wenchuan, China, and 2011 the Tohoku Region Pacific Coast Earthquake, Japan. This has motivated increasing research into improving liquefaction resistance and other liquefaction mitigation methods. The main cause of liquefaction is the loss of shear strength due to an increase in pore water pressure and a reduction of the effective stress of soil, which eventually leads to the phenomenon where sandy soil displays fluid-like characteristics [4,5]. Soil improvement methods are most commonly employed to reduce or eliminate the effects of liquefaction. Research on the physical properties of liquefiable sand shows that the density of sand [6], content of fines [7,8], coefficient of uniformity [9] and other factors [10–12] has a great influence on liquefaction. However, control of these factors was not the best way to improve liquefaction resistance. Earlier studies have shown that the addition of metal strips and bars, existing plant roots and soil densification can improve liquefaction resistance [13–15]. However, the use of metal strips present problems including reduced ductility and uncertainty of the influence of environmental factors. Additionally, the durability of liquefaction alleviation is poor when utilizing plant roots. Soil densification through dynamic compaction is energy intensive. Moreover, this method has a great impact on the surrounding infrastructures, and the depth of compaction is limited. Therefore, researchers continue to explore new mitigation methods to prevent the occurrence of liquefaction.