On Dec. 18th, 2023, a magnitude 6.2 earthquake hit Jishishan Town of Linxia City in Gansu Province, and caused an unusual mud sliding disaster in Jintian Village and Caotan Village of Zhongchuan Town in Qinghai Province. The mud flowslide resulted in catastrophic consequences as casualties and demolishing and burying of residential houses. Such large mud sliding phenomenon has not been frequently reported in historical earthquakes. Through field investigation, it is confirmed that the underlain soil liquefied and triggered the disastrous phenomenon which has already been termed liquefaction-induced flowslide. Nevertheless, the massive liquefaction-induced flowslide is the first time been reported and verified by field evidence in recent 70 years. The investigation and analytical results demonstrate that the underlain soil layer in the upstream area liquefied, triggering instability and catastrophic flowslide, and the soil and water conditions in the flowing channel potentially accelerated the sliding. It is deduced that liquefaction possibly occurred in many a place, that is, the sliding channel was suspected of liquefying in various spots. The ground shaking intensity in the sliding area maintained relatively high, and that the peak ground-motion acceleration was estimated around 0.4 (±0.1) g. The findings and investigation results are useful to help understanding the mechanism and process of the uncommon flowslide disaster.

The investigation of earthquake damage shows that the lateral spread of gently inclined soil is a common form of foundation failure. As the concrete pile has a high vertical bearing capacity and shear resistance, and the stone column has a high permeability, which can effectively reduce the degree of liquefaction of the surrounding soil, whether the concrete-stone composite pile can be used as an effective engineering measure to deal with the large lateral deformation of liquefaction in gently inclined soil, its feasibility is worthy of in-depth research. Therefore, the numerical model of liquefiable soil-pile foundation is established based on OpenSees finite element platform, then the reliability of the numerical model is rerified. On this basis, the reinforcement effect of concrete-stone composite pile on inclined liquefaction soil is studied. In addition, the effects of area ratio of core pile and thickness of stone shell on dynamic response of inclined liquefaction soil are discussed. The results show that the concrete-stone composite pile has a significant anti lateral displacement effect, which can effectively reduce the lateral displacement of the surrounding soil and the bending moment of the concrete core pile. When the proportion of concrete core of pile body is about 20% and the proportion of stone shell area is 80%, it is the optimal design scheme.

In order to improve the refinement level of mechanical parameters of layered structures explored by Rayleigh wave, this study constructed the Rayleigh wave dispersion equation in layered elastic semi-infinite stratum based on the spectral element method. For the two stratum structures of semi-infinite and “upper soft and lower hard”, compared and calculated the dispersion curves of multi-modes Rayleigh wave with spectral element method and fast vector-transfer algorithm. The results show that the relative error between the calculation results of spectral element method and the corresponding results of fast vector-transfer algorithm is under 0.05%, which has high calculation accuracy. On this basis, for the three complex layered structures of “upper hard and lower soft”pavement structure, containing “soft interlayer” and containing “hard interlayer”, this study derived the calculation method of surface displacement based on spectral element method, and established an semi-analytical method to determine the superposition coupling mechanism of multi-modes Rayleigh wave in complex stratum structure by analyzing the contribution of each mode phase velocity of Rayleigh wave to surface displacement energy, which are in good agreement with the corresponding simulation results of velocity-stress finite element method, indicating that it is reasonable and feasible to calculate the dispersion curves of Rayleigh wave and reveal the superposition coupling mechanism of multi-modal Rayleigh wave based on spectral element method.

When the lifting platform works at heights in the outside field, river beach and other environments, the dynamic interaction between the soft soil and outriggers of lifting platform will change the dynamic characteristics of the lifting platform system. In this paper, three dynamic models of lifting platform, which are incorporated with three different inerter dynamic vibration absorber (I-DVA) systems defined as SIS, SPIS-1 and SPIS-2, are presented with the consideration of soil-structure interaction. The expression of the amplification factor and the displacement mean square value of the operating platform is derived under harmonic and random force excitation, respectively. The optimal stiffness ratios and damping ratios of the I-DVAs are obtained based on H_∞ and H₂ optimization criteria by genetic algorithm in terms of three different soil foundations. The vibration reduction performance of three I-DVA systems is evaluated under the conditions of their optimal design parameters. The numerical studies show that: SPIS-2 performs the most effective vibration reduction, which not only suppress the resonance amplitude of the lifting platform, but also widen the frequency bandwidth. The soil-structure interaction can reduce the amplification factor under harmonic excitation and the mean square value under random excitation of the operating platform. The soil-structure interaction influences the optimal design parameters of the inerter systems insignificantly under harmonic and random excitation. Therefore, some empirical formulations of the optimal parameters for I-DVAs are fitted in order to provide reference for the vibration reduction design of lifting platform.

This paper aimed to investigate the seismic failure characteristics of the railway gravity piers with pile foundation under the influence of frozen soil layer and the influence of different influencing factors on the seismic performance of railway gravity piers with pile foundation in the seasonal frozen soil region. Firstly, the seismic damage characteristics of the railway gravity bridge pier with pile foundations in frozen soils were investigated by quasi-static model test. Secondly, a finite element model of bridge pier with pile foundation considering frozen soil effect was established. Then, the influence of the seasonal frozen soil layer thickness, shear-span ratio, axial compression ratio and bearing depth of pile cap on seismic performance of the railway gravity bridge pier with pile foundation was discussed by numerical simulation method. The results showed that the increase of seasonal frozen soil layer thickness in a certain range is beneficial to improve the seismic performance of the railway bridge pier with pile foundations, but if the frozen soil layer thickness increased beyond this range, its influence on the lateral bearing capacity of the bridge pier is weakened and the damage of pile-soil-pier system will be accelerated. Increasing the shear-span ratio and decreasing the embedded depth of the pile cap can significantly reduce the seismic performance of the bridge pier with pile foundations in frozen soils. Increasing the axial compression ratio can increase the lateral bearing capacity of the bridge pier with pile foundations, but it will accelerate the appearance of peak load of the bridge pier with pile foundations and accelerate the damage of the pile-soil-pier system.