Review and Discussion on Seismic Subsidence of Loess

The research and achievements made on seismic subsidence of loess,obtained over the past30 years,were reviewed.Seismic Subsidence of Loess(SSL)has been verified by microstructure characteristics,dynamic triaxial experiments,and in-situ explosion tests,and has become an important subject in the field of seismic loess engineering research.While,the research is still in the stage of theoretical study of saturated soil,and there are no representative cases of seismic subsidence of loess in historical earthquakes.It is difficult to express structure characteristics using microstructure morphology.While,soil mechanics are available methods for this.Seismic subsidence judgment is absolute in some certain value ranges for several parameters.Therefore,probabilistic judgment should be developed.The seismic subsidence ratio is estimated mostly by empirical formulas or semiempirical and semi-theoretical formulas,which are based on laboratory data.These formulas are not established on the basis of physical process and mechanics of seismic subsidence,and this leads to more variables,complicated computation,and poor practicability.To solve these problems,we need to distinguish the main factors and corresponding variables,to establish a mechanics model for seismic subsidence estimation,and to characterize its physio-mechanical process.The key of anti-seismic subsidence treatment is to reduce the seismic subsidence property of soils,and to lower the interaction between the soil body and underground structures.

Experimental study on the influence of seismic subsidence of loess under bidirectional loading modes

Water content,dry density,void ratio,depth of soil layer,and seismic loading may all exert influence on the seismic subsidence of loess.Many scholars have carried out seismic subsidence tests of loess to simulate the stress on soil using unidirectional(axial)vibration instead of bidirectional vibration.We conduct seismic subsidence tests of loess using two different dynamic stress loading methods,unidirectional and bidirectional dynamic stress.In addition,the effects of different dynamic stress loading modes on the development of seismic subsidence of loess are compared for a case-study in northwestern China.The results show that(1)the increasing ratio of radial stress to axial stress has exerted significant influence on the seismic subsidence coefficient of loess under the loading mode of bidirectional dynamic stress(2)there is a critical ratio of radial stress to axial stress for seismic subsidence of loess,ranging from 0.6 to 0.8;when the ratio of radial load to axial load is greater than the critical value,the effect of bidirectional load on the development of seismic subsidence is more remarkable(3)when the ratio of radial load to axial load is smaller,the seismic subsidence of loess calculated by the existing unidirectional stress loading method is safe for engineering projects.However,if the value exceeds the safety ratio range it is dangerous to conduct safety evaluations using the seismic loess subsidence.The prediction value of seismic subsidence at engineering sites directly affects the later foundation treatment and the safety of the overlying structures.The seismic subsidence calculation and evaluation method in this study may provide a scientific basis for safety evaluations of loess sites in northwestern China.