Abstract
The meso-structure of the soil has an important restriction on its engineering properties. Based on dynamic triaxial tests and SEM meso-structure test experiments, this study investigated the meso-scale structural deformation characteristics of Q3 loess samples treated by physical, chemical, and compound improvement methods, before and after strong earthquakes of typical seismic subsidence loess. On this basis, the seismic subsidence performance of the improved method is given under the conditions of frequent earthquakes, fortifying earthquakes, and rare earthquakes. The results show that 1) the physical improvement method has the most obvious effect on the elimination of macropores and overhead pore structures; 2) the chemical method can generate unique glass beads or flocculated fine structures, which can greatly enhance the strength of the soil and play the role of filling, cementing, or buffering, respectively, in the event of a strong earthquake; 3) for several improved treatment methods, the amount of seismic subsidence increases non-linearly with the increase in peak acceleration; and 4) in the event of frequent earthquakes, the earthquake subsidence can be eliminated by the method of adding fly ash, and when the fortification earthquake comes, the dynamic composite method can completely eliminate the seismic subsidence of the site. The related results can give reasonable suggestions for the treatment of seismic subsidence of different foundations in the “resilient urban and rural” and key engineering construction and seismic design of China’s loess area.
Highlights
China’s Loess Plateau and adjacent areas have recorded 395 earthquakes with a magnitude MS ≥ 5 (Xu et al, 2018)
2) At the 20 kPa–60 kPa stage, both methods can increase the seismic performance of loess by more than 5 times, but the fly ash method begins to show the difference from the cement-soil method
The sample body hardly produces fracture damage, can be supported until the dynamic stress is loaded above 120 kPa, and its deformation reaches 7% and above; the seismic subsidence curve of the cement-soil improvement method basically no longer increases with the continuous increase in the dynamic stress
Summary
China’s Loess Plateau and adjacent areas have recorded 395 earthquakes with a magnitude MS ≥ 5 (Xu et al, 2018). For major construction projects in areas that have been judged as seismic subsidence, site selection needs to meet the seismic fortification standards and should fully consider what kind of foundation anti-seismic treatment method is most effective under fortified earthquakes and rare earthquakes. This is the actual problem of the transformation of infrastructure construction to prevention oriented in the new concept of earthquake prevention and disaster reduction.
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