Study and Practice on Performance-Based Seismic Design of Loess Engineering in China

Loess is a kind of special soil with porous structure and weak cohesion, which widely deposits in China with an area of 640,000 km2. Especially, it is continuously distributed in the Loess Plateau of China with an area of 440,000 km2 and a thickness ranging from tens meters to more than 500 m, where is a region with the biggest thickness and the most complicated topography of loess deposit in the globe. On the other hand, the Loess Plateau is a strong earthquake-prone region, where 120 earthquakes with Ms ≥ 6.0 and 7 events of Ms ≥ 8.0 occurred in history. These earthquakes killed more than 1.4 million people in the region. The investigation shown that so large casualties should be attributed to a large scale of landslides, liquefaction, subsidence and amplification of ground motion. In this paper, the characteristics of engineering geology and seismic hazards with different probabilities of exceedance in the Loess Plateau of China is introduced. Based on the field investigation and exploration, observation data, in-situ tests, laboratory tests, and numerical analysis, the method of evaluating amplification of ground motion on topography and deposit of loess sites is proposed. The method of risk assessments of seismic landslides is developed. Seismic design for engineering loess slopes with single-step and multi-steps is provided. The methods of evaluating liquefaction and seismic subsidence of loess ground and its treatment measurements are respectively presented. Moreover, the seismic design methods of pile foundation in loess ground are proposed for considering the negative friction on piles due to seismic subsidence and horizontal pushing force on piles under liquefaction. The above-mentioned methods and techniques have been adopted by a national code and a provincial code, which have been proved to be practical, efficient and rational through a large number of major engineering projects and buildings’ construction.