Dynamic characteristics of machine foundation under harmonic loading on gypseous soil with various degrees of saturation

Most existing studies on collapsible soils report considerable scatter in their results, primarily due to variations in testing procedures and sampling methods. These studies have also often relied on static testing as the primary method of validation. However, as development continues, a gap remains in our understanding of how collapsible soil reacts to various dynamic stresses, including mechanical equipment, power stations, trains, roadways, and other dynamic loads. Conventional studies often fail to adequately represent real dynamic loading conditions. Accordingly, it is essential to investigate the response of gypseous soils to vibration and varying moisture content. This research aims to characterize the dynamic behavior of gypseous soil under different saturation states (unsaturated and saturated), subjected to harmonic loading at a relative density of 35 %, with additional consideration of foundation depth and eccentric mass. The experimental program aims to establish a database that enables reliable correlations between wave attenuation and soil damping in gypseous soils. Results showed that the dynamic characteristics of gypseous soil increased with frequency by approximately 50–52 % (settlement), 3–6 % (suction stress), 47–68 % (total stress), 42–46 % (acceleration), and 44–48 % (vertical displacement). With rising saturation up to 60 %, these properties decreased by 6–7 % (settlement and total stress), 2–5 % (acceleration), and 6–9 % (vertical displacement). Between 60 % and 100 % saturation, the values rose sharply, reaching 149–150 % (settlement), 139–173 % (total stress), 50–51 % (acceleration), and 52–54 % (vertical displacement). Foundation embedment from 0.0 B to 1.0 B reduced the peak dynamic responses by approximately 10 % to 15 %, whereas increasing the eccentric mass from 28 g to 44.8 g (a factor of about 1.6) amplified them by approximately 17 % to 68 %, with vertical stress and displacement showing the largest increases. Meanwhile, suction stress rose markedly (approximately 453–457 %) as saturation increased to 60 %, then fell by nearly 100 %, approaching zero, as saturation rose toward full saturation, consistent with the loss of matric suction.