降雨条件下路基土体湿度场迁移预测模型OA

Objective The increasing incidence of rainfall-induced embankment landslides corresponds with the recent rise in extreme rainfall events.During precipitation,moisture field migration occurs within unsaturated embankment soils,which modifies matric suction distribution and soil strength characteristics,threatening embankment stability.Accurately characterizing the spatiotemporal distribution pattern of the water content field and predicting its moisture field migration mechanism is a key prerequisite for advancing slope stability evaluation methods and optimizing geologi-cal disaster prevention strategies.Although current research extensively documents macroscopic principles governing moisture field movement,the prediction equation of the moisture field in soil remains scarce and inadequately validated.Prevailing analytical models predominantly as-sume complete soil saturation behind wetting fronts,but actual field conditions contradict this premise,which influences model accuracy.There-fore,the moisture field migration prediction model is proposed to reveal the migration pattern of the soil moisture field and provide a theoretical basis for improving slope instability warning methods. Methods Firstly,using a self-developed one-dimensional soil column test system,typical embankment filling sand was selected as the research material,and an unsaturated soil column structure was constructed through layered compaction.The test adopted the rainfall intensity control method,with 35 mm/h as the benchmark rainfall intensity,and simulated rainfall conditions using an axial uniform spraying system.Moisture sensors were installed along the depth of the soil column to monitor the dynamic response characteristics of the volumetric moisture content of different soil layers in real time to accurately and continuously capture the moisture migration process.Secondly,using COMSOL finite element soft-ware,the modified Cambridge model,unsaturated empirical formulas,and the VG model were introduced to establish one-dimensional soil column models,and the numerical model was validated using the test results.The variation law of the moisture field was preliminarily revealed through both the model test and numerical simulation.Thirdly,based on the indoor test and simulation results,the main influencing factors of the soil dynamic equilib-rium saturation degree were analyzed,and a prediction formula for the soil dynamic equilibrium saturation degree was proposed and validated through the numerical simulation model.Then,based on the assumption of a homogeneous soil model,the quantitative relationship between the rainfall volume and rainwater retention in soil was analyzed,the soil dynamic equilibrium saturation prediction formula was introduced,and the prediction formula for the dynamic equilibrium saturation of unsaturated soil was established and verified through indoor tests and numerical simulations.In addition,the quan-titative relationship between rainfall volume and the amount of rainwater required to achieve full soil saturation,as well as the prediction formula for groundwater level rise,was established,and the feasibility of these prediction formulas was verified through experiments and numerical models.Finally,based on the above formulas,the effects of wet front migration and groundwater level rise under different compaction degrees(0.75,0.80,0.85,and 0.90)and rainfall intensities(5,10,15,20,25,30,and 35 mm/s)were discussed,and the migration pattern of the unsaturated soil moisture field under different rainfall intensities was revealed,providing an important theoretical basis for embankment landslide warning. Results and Discussions 1)The results of the model tests and numerical simulations showed that the changes in soil volumetric water content un-der rainfall exhibit five distinct stages,namely the initial stage,the first growth stage,the dynamic equilibrium stage,the second growth stage,and the complete saturation stage.Among them,the first growth stage occurs due to the influence of rainfall on the soil,during which the wetting front migrates from the soil surface to the bottom and causes a gradual increase in soil volumetric moisture content from top to bottom.After the wetting front passes through the soil,the volumetric water content enters the dynamic equilibrium stage.As the groundwater level rises from be-low,the volumetric water content enters the second growth stage,and eventually,all soil reaches the fully saturated stage.2)The feasibility of the dynamic equilibrium saturation prediction formula,the wetting front migration prediction formula,and the groundwater level fluctuation predic-tion formula for unsaturated soil under rainfall conditions was double verified through indoor tests and numerical simulations.The results showed that the maximum error between the dynamic equilibrium saturation prediction formula and the simulation was 4%,the maximum error between the wetting front migration prediction formula and both the simulation and test was 8.5%,and the maximum error between the groundwater level fluctuation prediction formula and both the simulation and test was 8.5%.The trend of the humidity field change curve calculated by these formu-las was consistent with the experimental and numerical simulation results.Therefore,these formulas better predicted the migration behavior of the soil moisture field and were suitable for studying unsaturated soil moisture field migration.3)The unit pore volume,soil permeability,and soil compaction degree of unsaturated soil showed a clear inverse relationship.The reduction in unit pore volume accelerates the migration of the unsaturated soil moisture field,whereas the decrease in soil permeability slows the migration speed of the moisture field.When the soil compac-tion degree is less than or equal to 0.80,the migration of the humidity field is mainly controlled by the unit pore volume,and the migration speed increases with increasing compaction degree.When the soil compaction degree exceeds 0.80,the migration of the moisture field is mainly con-trolled by soil permeability,and the migration speed decreases with a higher compaction degree.4)The migration speed of the unsaturated soil moisture field showed a positive correlation with rainfall intensity,indicating that the migration speed increases as rainfall intensity increases.However,as rainfall intensity continues to increase,its rising effect on the migration speed of the humidity field gradually weakens.5)At any given moment,the influence of soil compaction and rainfall intensity on the migration of the humidity field remains consistent and does not change with longer rainfall duration. Conclusions The study demonstrates that the dynamic equilibrium saturation prediction formula,wetting front migration prediction formula,and groundwater level fluctuation prediction formula effectively predict soil moisture field migration.In addition,the effects of soil compaction degree and rainfall intensity on moisture field migration are clarified.The findings are expected to provide a theoretical basis for improving slope instability warn-ing methods and enhancing the capacity for slope stability assessment and disaster prevention.