The deformation behaviors of soft clay under cyclic loading were investigated with constant loading frequency; however, the response frequency of the subgrade soil varied when the train passed by. Moreover, both deviator stress and confining pressure varied cyclically. Hence, two types of cyclic triaxial tests were conducted on saturated soft clay, in which the differences in deformation behaviors between constant and composite loading frequencies were analyzed, and the impacts of cyclic confining pressure and drained conditions were considered. The strain increment continuously decreased with the progress of the test under cyclic loading with constant loading frequency, while that first decreased, achieving the minimum value at the third loading stage, and then increased under cyclic loading with composite loading frequencies. Nevertheless, compared with the test results of cyclic triaxial tests with composite loading frequencies, the strain with constant loading frequency increased by 65.4% and 117.9% under undrained and partially drained conditions, respectively. The cyclic triaxial tests with constant loading frequency overestimated the strains under cyclic loading. The strain increments were greater in the first loading stage under undrained and partially drained conditions; however, the differences in strain increments between undrained and partially drained conditions in other loading stages can be ignored. Moreover, the effect of cyclic confining pressures was clarified under cyclic loading with composite loading frequencies: the strain ratio of cyclic confining pressures to constant confining pressures decreased from 0.870 to 0.723 as eta increased from 1.00 to 2.00 under undrained conditions, while it increased from 1.227 to 1.837 under partially drained conditions. Nevertheless, the ratios increased linearly with increasing eta under partially drained conditions, and decreased linearly under undrained conditions.

Cyclic triaxial tests with intermittent cyclic loading are usually used to investigate the deformation behaviors of soil; however, both deviator stress and confining pressure vary cyclically under traffic loading. Moreover, the pore water in soil can be dissipated throughout the test, affecting the mechanical behaviors of soils. Therefore, in this study, three test modes were applied to saturated soft clay to analyze the deformation behaviors, in which different cyclic confining pressures were used during cyclic loading periods, and different drained conditions during cyclic loading and intermittent periods were considered. The variations in strain increment were similar in all cases: as the loading stages progressed, the strain increment gradually diminished. The distinct variation in strain increment became evident in the initial loading stage, but it became negligible in subsequent loading stages. Furthermore, the change in strain increment with respect to cyclic confining pressure was influenced by drained conditions during the cyclic loading period: it increases as the cyclic confining pressure increased under partially drained conditions and decreases under undrained conditions. Moreover, the strain increased under partially drained conditions during intermittent periods, companying with the discharge of pore water, while it decreased for the recovery of specimen deformation under undrained conditions. The greater strain increment was caused under partially drained conditions during cyclic loading periods compared with the corresponding strain increment under undrained conditions. Besides, an empirical model was developed to forecast accumulated axial strain of soil subjected to intermittent cyclic loading, and the variations of parameters under different drained conditions were studied.

Investigations on the liquefaction resistance of an open-cast lignite mine soil under loading by earthquake-typical signals For the embankments of the planned opencast mining lakes in the Rhenish mining area, the proof of the stability under earthquake action must be provided. According to the guideline for the investigation of the stability of slopes in lignite opencast mines (RfS - Richtlinie f & uuml;r Standsicherheitsuntersuchungen [1]), the permanent slopes must be designed and constructed in such a way that a soil liquefaction is not to be expected. For the proof, in which actions and soil resistances are locally compared with each other, the irregular earthquake signal is converted into a regular signal with an equivalent number of cycles and constant amplitude. In this paper, this conversion is investigated for a typical earthquake signal of the Rhenish area, which was obtained from a dynamic finite element calculation. Triaxial tests with vertical cyclic loading and hollow cylinder triaxial tests with cyclic torsional loading are performed to investigate the liquefaction behaviour of an opencast mine soil under the influence of this earthquake signal. The results of these tests are compared with data from further tests with constant amplitude. It can be shown that the factor beta for converting irregular to regular signals depends on the type of loading and the magnitude of the static shear or deviatoric stress. On the basis of the experiments, recommendations for the choice of beta for the Rhenish mining area are given.

The dynamic behaviors of subgrade soil are usually investigated by use of continuous loading mode in most studies; however, the dynamic loading induced by traffic loading is composed of cyclic loading and intermittent periods. Moreover, the existence of cyclic deviator stress, cyclic confining pressure, and shear stress has been already observed in the stress field induced by traffic loading. Recognizing this, intermittent cyclic loading was applied to saturated soft clay for this study. The impacts of cyclic deviator stress, cyclic confining pressure, and drained condition during intermittent periods on the deformation behaviors of soft soil were analyzed. The variations in strain increment were similar in all cases: as the number of loading stages increased, the strain increment decreased, and the difference in strain increment was more significant in the first loading stage although it could be ignored in subsequent loading stages. Furthermore, the strain increment increased with increasing cyclic stress ratio (CSR) and decreased with increasing cyclic confining pressure. Moreover, the dissipation of excess pore-water pressure induced during the cyclic loading period resulted in the increase of accumulated axial strain under intermittent partially drained conditions, while the recovery of specimen deformation during intermittent period led to the decreasing of accumulated axial strain under undrained conditions. In addition, an empirical formula of accumulated axial strain under intermittent cyclic loading was established, and the calculated results were consistent with the measured data.

Soil liquefaction would cause significant damage to the safety of cargo transportation. The aim of this article is to conduct a quantitative study of the influence of the main physical characteristic parameters of saturated sand and external loads on its liquefaction. On the basis of the physical cyclic triaxial test (CTT), the finite element simulation model and PSO-BP neural network prediction model and importance analysis model were optimised in this study. Based on this, an innovative intelligent numerical CTT system for saturated sand was constructed. The research results indicate the influence of external load, effective internal friction Angle and plasticity index on the liquefaction of saturated sand is significant, and the average weight is 40.15%, 29.15% and 25.05%, respectively. In this paper, the relevant research provides a theoretical basis for effective control of sand liquefaction and provides new ideas and feasible solutions for subsequent research on sand liquefaction.