What the role of each phase medium plays and how their interactions do work should be essential problems to understand dynamic behaviours of soils. In order to disclose interactions between solid, water, and air phases of soils, we applied loess samples to analyse controlling effects of residual deformation on pore pressure based on three kinds of laboratory tests. We obtained the similarity and difference of mechanical behaviors of soil samples under different water contents and loading. Both process and cause of pore air/water pressures are independent of initial stress conditions or loadings. However, absolute values of pore water pressure depend on the confining pressure, whereas the pore air pressure is contrary. The uniformity of responding process and cause of pore pressure depend upon the interaction mechanism between solid particles and air/water media, but the different absolute values depend upon the permeability and compressibility of air/water.

The horizontal-to-vertical spectral ratio (HVSR) has been extensively used in site characterization utilizing recordings from microtremor and earthquake in recent years. This method is proposed based on ground pulsation, and then it has been applied to both S-wave and ambient noise, accordingly, in practical application also different. The main applications of HVSR are site classification, site effect study, mineral exploration, and acquisition of underground average shear-wave velocity structure. In site response estimates, the use of microtremors has been introduced long ago in Japan, while it has long been very controversial in this research area, as there are several studies reporting difficulties in recognizing the source effects from the pure site effects in noise recordings, as well as discrepancies between noise and earthquake recordings. In practice, the most reliable way is the borehole data, and the theoretical site response results were compared with the HVSR using shear wave to describe site response. This paper summarizes the applications of the HVSR method and draws conclusions that HVSR has been well applied in many fields at present, and it is expected to have a wider application in more fields according to its advantages.

An Mw6.6 earthquake occurred at 3a.m. on September 6, 2018, in the eastern part of Iburi, Hokkaido. This earthquake killed 41 people, caused a series of service interruptions in Sapporo city. Soil liquefaction and approximately 6000 landslides were triggered. A field investigation was conducted on liquefaction and typical landslides during September 18 to 24, 2018. The liquefaction disaster exhibited soil flow, subgrade collapse, uneven settlement, earthquake subsidence, and deformation of buildings. After investigation of typical landslides, it was found that owing to the continuous heavy rainfall and typhoon, the surface soil had a high-water content. A layered loam of approximately 2 m below ground surface developed into a weak surface. Based on the analysis of sliding morphology, the landslides were classified into translational earth slides and earth flow. To clarify the mechanism of regional landslides, the stability and permanent displacement of slopes considering effect of continuous heavy rainfall and seismic motion was analyzed. Limit equilibrium analysis was applied based on the pseudo-static method. Then Newmark displacement calculation was conducted based on the seismic acceleration record. The distribution range of analysis results showed agreement with actual landslides disasters. The results verified the contribution of continuous rainfall and strong motion to the failure of regional slopes.

A large-scale shaking table test was conducted with simulated earthquakes and groundwater to study the dynamic response and instability mechanism of a loess slope with a saturated bottom. By examining the acceleration, dynamic pore water pressure, corresponding soil pressure and observed macroscopic failure behaviour of the slope under different shaking intensities, the dynamic responses of acceleration and pore water pressure of the loess slope were analysed. By comparing the time history curve of acceleration with the time history curves of pore water pressure and surrounding soil pressure, we found that the instability failure of the slope was first due to the continuous vibration that caused the local structure of the slope soil to be damaged, forming locally saturated soil and the rise in the groundwater table during shaking. Then, the saturated soil liquefied under the action of strong vibration, and the liquefied soil mass slid under the action of a high-intensity earthquake force. Finally, the acceleration and spectral characteristics of the pore water pressure changed sharply with a shift in the predominant frequency at the liquefied locations under a high shaking intensity. The significant changes in dynamic pore water pressure mainly occurred when the shaking components in the low-frequency bands below 1 Hz. This implied that the shift in the frequency mainly resulted from the damage in the structure of the loess slope after high-intensity shaking. These results help us better understand the triggering mechanism and failure mechanism of saturated loess slopes during the Minxian-Zhangxian earthquake.

Shaking table tests were performed to investigate whether the coupling effect of rainfall and earthquake induces the loess slope instability. The loess slope model was made by using the similarity ratio based on a real slope. Artificial rainfall was carried out, and then seismic waves were loaded step by step to adopt a large shaking table of 4∗6 m. The displacement in x, y, and z directions and absolute displacement of loess slope (u_x, u_y, u_z, and u_a) were measured to use the XTDIC displacement test system in 50 s when the seismic waves at peak acceleration were loaded to 600 gal, 700 gal, 800 gal, 976 gal, and 1300 gal, respectively. The results showed that the acceleration of one point was much larger than the other. u_a occurred when seismic waves were loaded to 700 gal, and u_amax was obtained when seismic waves were loaded to 1300 gal finally. The u_max would reach in 20∼25 s, which was the period of amplitude peak. The theoretical value was larger than the test value for the critical seismic acceleration coefficient. Loess liquefaction appeared along the slope top under 976 gal loading condition. The change of displacement in y direction is the main reason for the curve trajectory of the sliding block, and the displacement differences of adjacent measuring points are the main reason for the formation of the sliding block. This study can provide a theoretical basis for loess slope design and risk management.