This paper compares classic (continuous) fatigue tests and fatigue tests carried out with time intervals of no stress in rock salt using a multifunctional testing machine and acoustic emission equipment. The results show that time intervals of no stress have a strong impact on the fatigue activity of rock salt. In fatigue tests with intervals, the residual strain in circles following an interval (α circles) is generally larger than that in circles before the intervals (β circles). The insertion of a time interval with no stress in the fatigue process accelerates the accumulation of residual strain: the longer the interval, the faster the residual strain accumulates during the fatigue process and the shorter the fatigue life of the rock salt. α circles produce a greater number of acoustic emission counts than β circles, which demonstrates that residual stress leads to internal structural adjustment of rock salt on a mesoscopic scale. During intervals of no stress, acoustic emission activity becomes more active in α circles because of reverse softening caused by the Bauschinger effect, which accelerates the accumulation of plastic deformation. A qualitative relationship between the accumulated damage variable and the time interval is established. A threshold in the duration of the time interval exists (around 900 s).

Flash floods are ferocious and destructive, making their forecasting and early warning difficult and easily causing casualties. In order to improve the accuracy of early warning, a dynamic early warning index system was established based on the distributed spatio-temporally mixed model through a case study of riverside villages in Hubei Province. Fully taking into account previous rainfall and assuming different rainfall conditions, this work developed a dynamic early warning threshold chart by determining critical rainfall thresholds at different soil moisture levels (dry, normal, wet, and saturated) through pilot calculations, to support a quick query of the critical rainfall at any soil moisture level. The research results show that of the 74 counties and districts in Hubei Province, more than 50% witnessed higher mean critical rainfall than empirical thresholds when the soil was saturated, and about 90% did so when the soil was dry. In 881 towns, a total of 456 early warnings were generated based on dynamic thresholds from 2020 to 2022, 15.2% more than those based on empirical thresholds. From the perspective of total rainfall, dynamic early warnings were generated more frequently in wet years, while empirical early warnings were more frequent in dry years, and the frequency of two warnings were roughly the same in normal years. There were more early warnings based on empirical thresholds in May each year, but more based on dynamic thresholds in June and July, and early warnings generated based on the two methods were almost equal in August and September. Spatially, after dynamic early warning thresholds were adopted, Shiyan and Xiangyang, both northwestern cities in Hubei Province, witnessed significant increases in early warnings. In terms of the early warning mechanism, dynamic early warning took into account the impact of soil moisture and analyzed the flood discharge capacity of river channels according to the flood stage of the riverside villages. On this basis, the rainfall early warning thresholds under different conditions were determined. This is a refined early warning method that could improve the accuracy of flash flood warnings in Hubei Province.