Two high-salinity soils with different types of salts were tested to assess the effects of freeze-thaw (F-T) cycles on their volumetric and low-temperature shear behavior. The testing program, including freeze-thaw cycling and triaxial testing, is described in detail. Experimental results, including volumetric change and low-temperature stress-strain behavior and shear strength parameters are presented, and the causes of changes in shear strength parameters are analyzed. The research results show that soils with a high chloride salt content ($\ge 15\%$ ) and a low sulfate salt content ($\le 0.5\%$ ) exhibited very small volumetric contractions, whereas soils with a low chloride-salt content ($\le 5\%$ ) and a high sulfate-salt content ($\ge 1.5\%$ ) demonstrated very large volumetric expansion after freeze-thaw cycling. There appears to be a residual state for saline soils, at which the void ratio and the stress-strain behavior remains unchanged with an increasing number of F-T cycles. The residual void ratio and the stress-strain behavior at the residual state are much different from those at the initial state for soils with low chloride-salt content and high sulfate-salt content. The large salt expansion and the drop in the apparent cohesion of the soil with a low chloride-salt content and a high sulfate-salt content after F-T cycling is of concern for engineering purposes. These volumetric change and shear strength parameters have a direct or indirect impact on geotechnical analyses, such as assessments of slope stability and bearing capacity and/or load capacity of shallow and deep foundations in similar saline soils.

Flooding can have an effect on each thing of our lives, including road transportation. This study investigated the causes and the effects of flooding on road transportation in Rwanda, Kigali city and contributed to the mitigation measures. The data were collected by administering 150 questionnaires on the respondents within the study area and by physical survey. The hypotheses were formulated and tested using the statistical method of student’s t- test and the data displayed a significant difference (P<0.05). The results of this study revealed that heavy rains, poor drainage systems, illegal disposal of waste in drains, and poor construction and maintenance of roads are the main causes of road flooding in the city of Kigali. The effects of floods on road transportation include traffic jam and increased travel time, damage to road structures, blockage of drains and traffic accidents in the study area. The study recommends green storm water infrastructure practices, good road construction works, controlled dumping sites, the construction and maintenance of drainage systems and an immediate government response to the threat of flooding to address the challenges of flooding on road transportation in the city of Kigali.

Secondary salinization is a common problem in saline soil projects. In order to grasp the mechanism of water and salt migration of high-chlorine saline soil during the cooling process, the saline soils along the Qarhan-Golmud Highway in the Qinghai-Tibet Plateau were selected as test samples. Firstly, the basic physical parameter test and the soluble salt chemical experiment were carried out and obtained liquid and plastic limits, dry density, etc. Secondly, freezing temperature experiments and water-salt migration experiments under one-way cooling conditions were conducted according to the actual environmental conditions, and after the temperature gradient line of the soil sample was stable, water content and labile salt chemistry experiments were conducted to obtain the distribution of water and salt contents of soil samples. Finally, the effect of crystallization-water phase transition on water and salt migration and the effect of chloride salt on the temperature of crystallization-water phase transition were considered, and a mathematical model applicable to the water and salt migration of highly chlorinated saline soils under the effect of unidirectional cooling was established and solved with COMSOL Multiphysics software, and the correctness of the model was verified by comparing the simulation results with the experimental results. The study found that (1) during the one-way cooling process, both water and salt showed a tendency to migrate to the cold end. The MC (saline soil with medium chlorine content) with an initial water content of 16.9 and Cl⁻ content of 3.373 was measured to reach a 17.6 water content and 3.76 Cl⁻ content at the cold (top) end after the experiment. The HC (saline soil with high chlorine content) with an initial water content of 6.6 and Cl⁻ content of 17.928 was measured to reach a 6.83 water content and 18.8 Cl⁻ content after the experiment and (2) after the one-way cooling experiment of the MC, the water content at a distance of 12cm from the cold end has abrupt changes, which may be caused by a small amount of crystallizationwater phase transition at this location. At the same time, according to the temperature change graph during the cooling process, the phase change temperature was set to 9C in the numerical simulation process to match the experimental results.

Groundwater is abundant in soft soil areas, which has a significant impact on the excavation deformation of foundation pits. In this paper, based on the monitoring of deep foundation pits with waterproof curtains in Shanghai deep foundation pits, COMSOL Multiphysics is used to model the layers of the foundation pits and establish a two-dimensional seepage-consolidation coupled model for hierarchical dewatering excavation. The feasibility of numerical simulation of regional foundation pits, the modeling method of the foundation pit seepage model is explored, and the presence or absence of waterproof curtains, and the influence of aquitards on the horizontal displacement of foundation pits and surface settlement outside the pits is analyzed. The research shows that the simulated foundation pit deformation values are in good agreement with the actual monitoring values and that the effect of dewatering and seepage has a great influence on the foundation pit deformation. The waterproof curtain has a significant effect on reducing the drop in the water level outside the pit and controlling the surface settlement. After installing a waterproof curtain, the amount of ground settlement is reduced, but the disadvantage is that the deformation of the enclosure structure increases. Finally, the influence of aquitard on the deformation of foundation pit excavation is simulated, and the distribution characteristics of the flow network diagram under different permeability coefficients are analyzed. According to the analysis of the foundation pit deformation law and flow network diagram, it is considered that the waterproof curtain can effectively reduce the influence of aquitard on foundation pit deformation.