This experimental study investigated the characteristics of nonplastic silt subjected to multiple freeze-thaw cycles. The study used a novel, open test system developed to better represent field conditions in seasonal frost areas than can be achieved with conventional laboratory test setups. Various sensors were used to measure changes in temperature, water content, surface displacement, and electrical conductivity in the soil during five cycles of freeze-thaw testing. The test system featured a transparent window for visual observations of the soil (high resolution photographic images) throughout the duration of testing. The experimental results showed that volumetric water contents in the active layer of the soil sample decreased during the freezing period whereas they increased again when thawing started, reaching water content values closer to the initial values at the end of the thawing period. However, the electrical conductivity in the active layer became much greater than the initial value after freeze-thaw cycles, indicating changes in the pore structure of the soil in the active layer. High-resolution images of the soil sample taken during the freeze-thaw cycles and from soil samples exhumed after completing the five cycles of freeze-thaw confirmed that the nonplastic silt in the active layer became more porous after freeze-thaw cycles, whereas no visible changes in pore structure occurred in the soil beneath the active layer. The amount of the thaw settlement was greater than the amount of the total frost heave for each cycle, indicating a decrease in sample height after freeze-thaw cycles. The experimental results further showed that the frost depth increased after multiple freeze-thaw cycles.

Liquefaction, which typically occurs in saturated sandy soil deposits, is one of the destructive phenomena that can occur during an earthquake. When the soil reaches liquefied state, it loses a significant amount of resistance and stiffness, which often results in widespread catastrophic damages. Therefore, accurate evaluating the potential of soil liquefaction occurrence is of great importance in earthquake geotechnical designs in regions prone to this phenomenon. The strain energy-based approach is a novel robustness technique to evaluate liquefaction potential. In the current research, 165 laboratory data sets from cyclic experiments were collected and analyzed. A predictive model using gene expression programming (GEP) was proposed to assess strain energy needed for occurrence of soil liquefaction. Assessing physical behavior of developed GEP-based model was conducted through sensitivity analysis. Performance of GEP-based was validated by comparing with a series of centrifuge experiments and cyclic triaxial tests results. Subsequently, after experimental verification of numerical modeling, the strain energy required for soil liquefaction under cyclic loading at different conditions were numerically evaluated and compared with the strain energy calculated by proposed model. Finally, the developed GEP-based model was compared with established strain energy-based relationships. The results indicated high precision of proposed GEP-based model in determination of strain energy required for soil liquefaction triggering.

Artificial pulling tests are the most practical method of assessing the maximum resistance of trees to lateral forces (e.g., from the wind), particularly in relation to their anchoring capacity in the ground. The traditional method is to pull the tree monotonically until failure. However, there are still many uncertainties regarding the possibility of mimicking wind gusts in such a tree pulling test. More specifically, it is supposed that a succession of wind gusts during a windstorm may cause fatigue to the root system, leading to a propagation of damage at the rootsoil interface which will eventually lead to the collapse of the tree. This work aims to provide initial insights into the biomechanical response of shallow-rooted Norway spruce (Picea abies (L.) Karst.) growing in mineral soils by repeatedly pulling to failure six trees with increasing load magnitude. The mechanical behaviour of the tested trees was first analysed using a classical equilibrium approach by calculating peak applied loads, stem base rotation, equivalent stiffness trend over subsequent cycles and residual rotations. Then, the biomechanics of the trees were analysed using an energetic approach, focusing on the energy absorbed and dissipated during either the single load cycle or the complete cyclic test, by applying consolidated procedures used in the field of mechanical engineering. Results show how small but measurable residual rotations were measured after each load repetition, indicating permanent damage even in seemingly undamaged trees. Additionally, loads producing base rotations about 0.3 - 0.4 times those corresponding to the peak resistance dissipate less than 1 % of the maximum dissipated energy calculated at the same peak point. Additionally, this peak energy is found to be strongly correlated to both the peak moment and a typical stem volume predictor such as diameter at breast height squared times height. All these outcomes are intended to provide a starting point for the development of a different characterisation of tree resistance as an alternative to the current methodologies, especially when it is important to consider the effects of repeated loading on trees.