Rainfall Infiltration Research Articles

Stability Analysis of Rock Slope under Rainfall Infiltration Based on A Zero-Thickness Cohesive Element

There are often a large number of joints, fissures and other water channels in rock slopes. Under the condition of short-term heavy rainfall or continuous rainfall, a large amount of rainwater enters the slope body, which can easily induce landslide disaster on rock slopes. Therefore, it is of great significance to study the stability of rock slope under the infiltration of rainfall. Based on the ABAQUS numerical simulation platform, this paper implements continuous-discontinuous simulation of the deformation and damage of rock slopes under rainfall conditions by embedding zero-thickness cohesive elements and focuses on the effects of rainfall intensity, rainfall duration and rainfall infiltration location on the slope stability using vector method safety factors as indicators. The results show that as the rainfall intensity and rainfall duration increase, the depth of fissures in the slope gradually becomes larger, and the stability of the slope gradually decreases. The farther the initial location of rainfall infiltration is from the shoulder of the slope, the shorter the rain-induced fissure extension length is and the better the stability of the slope is. The research results provide reference for the engineering treatment of rock slope under rainfall conditions.

A Modified SCS Curve Number Method for Temporally Varying Rainfall Excess Simulation

The SCS curve number (SCS-CN) method has gained widespread popularity for simulating rainfall excess in various rainfall events due to its simplicity and practicality. However, it possesses inherent structural issues that limit its performance in accurately simulating rainfall excess and infiltration over time. The objective of this study was to develop a modified CN method with temporally varying rainfall intensity (MCN-TVR) by combining a soil moisture accounting (SMA) based SCS-CN method with the SMA method in the Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS). In the MCN-TVR, the SMA-based SCS-CN method is utilized to simulate the cumulative rainfall excess and infiltration, while the SMA method in the HEC-HMS serves as an infiltration control function. A key advantage of the MCN-TVR is that it eliminates the need for additional input parameters by inherently linking the parameters in the two SMA-based methods. Sixteen hypothetical 24 h SCS Type II rainfall events with different soil types and five real rainfall events for the Rush River Watershed in North Dakota were used to assess the performances of the MCN-TVR method and the SMA-based SCS-CN method. In the hypothetical simulations, the rainfall excess simulated by the SMA-based SCS-CN and MCN-TVR models was compared to that simulated by a Green–Ampt model. Discrepancies were observed between the rainfall excess simulated by the SMA-based SCS-CN and Green–Ampt models, especially for coarse soils under relatively light rainfall. However, the MCN-TVR model, incorporating an infiltration control function, demonstrated its improved performance closer to the Green–Ampt model. For all the hypothetical events, the Nash–Sutcliffe efficiency (NSE) coefficient of the rainfall excess simulated by the MCN-TVR method compared to the Green–Ampt model was greater than 0.99, while the root mean standard deviation ratio (RSR) was less than 0.03. In the real applications, the SMA-based SCS-CN model failed to provide acceptable simulation of the direct runoff for rainfall events with durations of less than the time of concentration. In contrast, the MCN-TVR model successfully simulated the direct runoff for all the events with NSE values ranging from 0.65 to 0.91 and RSR values from 0.31 to 0.56.

Experimental study on moisture and heat migration and deformation properties of unsaturated soil column under a temperature gradient during rainfall infiltration.

Mountainous areas in southwest China are rainy in summer. The rainfall infiltration process involves complex soil thermal-hydraulic-mechanical (THM) coupling problems. The researches on soil THM coupling are mostly focused on numerical simulations, whereas the corresponding model tests are relatively few, and the existing model test studies often ignore the effect of temperature gradients in the soil. However, temperature gradients in the soil can cause water migration and affect the THM behavior of soil, so it cannot be ignored. This paper describes an experimental device that can test the changes of temperature, moisture and displacement in unsaturated soil columns with temperature gradients under rainfall infiltration conditions. By using the apparatus, the model tests of homogeneous soil column (H), homogeneous soil column with infiltration (HI), and preferential flow soil column with infiltration (P) under different temperature gradients are respectively conducted, and the results of moisture and heat migration and deformation properties in soils under different conditions are presented and discussed. A rainfall of low intensity and long duration is applied in the experiments, and the temperature of infiltration rainwater is consistent with that of the soil upper boundary. The results show that: (1) The infiltration of rainfall will increase the temperature of the soil column. The appearance of preferential flow results in faster heat transfer within the soil column, but causes the steady-state temperature to be lower than that of the homogeneous soil (HI); (2) Under infiltration conditions, the preferential flow soil column has an earlier outflow time but a later time for water field to reach steady state, while its water distribution is different from that of the homogeneous soils, with accumulation occurring near the end of preferential flow channel; (3) Under the action of temperature gradient, water migration occurs in homogeneous soil column (H), accompanied by soil settlement, while the infiltrated columns (HI and P) exhibit an increase in both water content and top displacement. In addition, the larger the temperature gradient, the more obvious the thermally induced hydraulic-mechanical response. The research results in this paper can provide experimental evidence for the theoretical study and numerical simulation of the soil THM coupling problems.

Hydraulic behavior of sandy subgrade under extreme rainfall in Alashan, China

Unsaturated aeolian sand is the main railway/highway sandy subgrade filling material in the desert area of Alashan, Inner Mongolia. In recent years, the extreme climate events frequently happen in Inner Mongolia. Under the extreme rainfall conditions in the desert area, the rainfall infiltration process and the unsaturated state evolution of aeolian sand subgrade is significant to the hydraulic behavior distribution and the deformation development under traffic loading.In this study, the SWCC (soil-water characteristic curve) parameters of aeolian sand was firstly calculated and discussed through van Genuchten model and the linear approach. Then a unified framework was proposed to describe the hydraulic behavior evolution of aeolian sand subgrade under extreme rainfall. Considering the effect of soil properties and rainfall conditions on infiltration process of aeolian sand subgrade, a normalized SWCC model was established. An analytical model of maximum infiltration depth for aeolian sand subgrade affected by extreme rainfall was further developed. Lastly, the numerical simulation results of the maximum infiltration depth for aeolian sand subgrade under an extreme rainfall event verified the correctness of the analytical model. This research can lay a foundation for studying the hydro-mechanical coupling behavior of sandy subgrade in desert areas.

Evolution of Seepage and Stability Characteristics of Lateritic Soil Slopes Containing a Tension Crack Zone Under Rainfall Infiltration

Evolution of Seepage and Stability Characteristics of Lateritic Soil Slopes Containing a Tension Crack Zone Under Rainfall Infiltration

Rainfall infiltration and slope stability of alpine colluvial terraces subject to storms (NE Italy)

In the alpine environment, rainfall-induced shallow landslides can involve thin covers of colluvial soil (50–300 cm) on terraced belts that were formed as a result of fill-and-cut sedimentary processes that followed the deglaciation of the alpine valleys. Notably, research on shallow slope failures involving alpine terraces consisting of a near-flat upper ground surface (“tread”) and a moderately steep scarp (“riser”) is lacking in the literature. This paper describes the engineering geological characteristics and failure mechanisms of a large number of shallow landslides (soil slips or slide-debris flows) that were activated on alpine stratified colluvial terraces due to a rainstorm that hit the mountain area of the Friuli Venezia Giulia Region (NE Italy) on 21–22 June 1996. The paper reports data on the geomorphological and engineering geological characteristics of the soil slips acquired through extensive fieldwork and shows the outcomes of some two-dimensional seepage and slope stability analyses that were carried out in order to investigate the critical hydrological conditions and mechanisms that were responsible for the soil slip activation during and after rainfall. The soil slip activation can occur at two different stages during the infiltration process, based on the interacting water flows through the terrace tread and riser. The first critical stability condition is reached during the phases of greater precipitation intensity or at the end of the rainstorm because of the saturation of the top soil layer on the terrace riser and the subsequent formation of an ephemeral water table accompanied by a seepage sub-parallel to the slope face. The second critical condition is achieved some hours after the end of rainfall as a result of a tread-to-riser water outflow that is supplied by the water amount stored within the near-flat terrace tread during the peak rainfall stages (reservoir-like effect). This study also shows that a critical value of rainfall intensity of about 40–45 mm/h can cause the activation of soil slips in mountain basins characterised by a humid continental climate and by the occurrence of colluvial deposits with a high content of fine fraction. This critical value of rainfall intensity should be considered as a rainfall threshold for a basin-scale under geomorphological and geological conditions similar to those investigated in this paper.

Hydrologic-geotechnical modelling of shallow landslide and flood hazards caused by heavy rainfall

Landslides and flooding are two of the most common hazards associated with heavy rainfall. Most studies, however, tackle the occurrence of these hazards separately or independently. Therefore, this study introduces a catchment-scale, multihazard approach that unifies the assessment of both phenomena through a combination of hydrological and geotechnical principles. By incorporating surface flow, infiltration, and slope stability analyses, the spatio-temporal response of both landslides and flooding during intense or heavy rainfall is characterized. To improve computational efficiency, a hybrid approach, consisting of the zero- and local-inertia flow models, is introduced to approximate the surface flow. Additionally, rainfall infiltration is estimated using the one-dimensional Green-Ampt model, and the results are incorporated in a deterministic slope stability analysis whose failure mechanism is generated from the forces arising from the effects of surface flow and the downward propagation of water along the assumed failure surface. The model is applied in the catchment of Marumori Town, Japan which suffered numerous landslide and flooding disasters during Typhoon Hagibis in 2019. The results indicate that the proposed model successfully simulates the hydrologic and geotechnical response of the catchment showing the distribution of both unstable slopes and inundated areas indicative of landslide and flooding hazards. The model’s capability to identify the timing and location of potential landslide and flood-prone areas could provide a practical framework for a unified early warning system, enhancing emergency planning and response efforts during heavy rainfall.

Calibration of the root water uptake spatial distribution of a young Melaleuca styphelioides, an Australian-native plant, by means of a large-scale apparatus experiment

The stability of slopes is greatly influenced by seasonal variations in pore water pressures (pwp) induced by rainfall infiltration and evapotranspiration processes. Despite that, the prediction of the hydrological effects of long-stem planting is often simplified or neglected because it is challenging to address. Its computation requires a proper definition of the plant root water uptake spatial distribution, which depends, in turn, on geometry and spatial root density. A well-suited case study in this field of application has been provided by a soil-filled embankment, close to an important traffic artery in Newcastle (Australia), which experienced shallow instability. The implementation of long-stem planting has been suggested as a remediation intervention. Based on this, an experimental study focusing on the effects of plant roots on the distribution of pwp in the site soil has been performed by means of a large-scale laboratory experiment on a 2-year-old native plant. Suction measurements were recorded within the vegetated soil mass under controlled boundary conditions and used to calibrate two different root spatial distributions in a seepage simulation. One is based on a flexible RWU spatial distribution function, and the other, specific for the plant RWU pattern, is simpler in its formulation and requires the definition of a lower number of parameters. A comparison between their performances in reproducing pwp distribution suggests that the second one is a better alternative. The methodological approach adopted has proven to be suitable for representing the hydraulic behaviour of a vegetated hillslope, to be eventually implemented in a proper stability assessment problem.

Reduction of rainfall infiltration in soil slope using a controllable biocementation method

Reasonable control of rainwater infiltration rate can ensure that soil slope will not fail due to rapid infiltration of rainwater in heavy rainfall, and at the same time, more rainwater can be infiltrated in light rainfall to meet the water demand of animals and plants. In this study, based on microbial-induced calcium carbonate precipitation (MICP) technique, a controllable bio-method for rainfall infiltration of soil slope was proposed. To have a comprehensive understanding the relationship among the rainwater infiltration control capacity, biocement treated soil permeability, slope angle and rainfall intensity, a series of physical modelling experiments of rainfall diversion on slopes with three types of soils and three slope angles were carried out in the presence of various rainfall intensities. Experimental results indicated that the proposed bio-method had the ability of controlling rainwater infiltration in term of varying rounds of biocement spraying treatment. In general, it was found that the rainwater infiltration decreases with the increase in slope angle and rainfall intensity. In the worst case of smallest slope angle (15°) and lightest rainfall intensity (n = 50 mm/h), more than 82.6%, 92.2% and 84.4% of rainwater were prevented from infiltration into the MICP treated natural sand, fine sand and medium sand, respectively, while the untreated soils were not able to prevent the rainwater infiltration at all. The corresponding maximum local uniaxial compressive strength for the MICP treated natural sand, fine sand and medium sand, respectively, were found to be 2.3 MPa, 2.0 MPa, 2.6 MPa, whereas the flexural stresses were 0.46 MPa, 0.33 MPa, 0.67 MPa, which could resist rainfall droplet impact force. Overall, the proposed bio-method showed good rainwater infiltration control capacity and high bearing strength against the impact of heavy rainfalls, suggesting a good potential to mitigate the rainfall-induced landslides.

Numerical analysis of the impacts of rainfall on permafrost-related slope stability on the Qinghai–Tibet Plateau

Study regionThis study interrogates a landslide in ice-rich permafrost region in the Eastern Qinghai–Tibet Plateau, China. Study focusClimate warming has increased the frequency and intensity of rainfall events, changing hydrothermal processes and the soil mechanical properties, thus affecting slope stability in permafrost region. The purpose of this paper is to elucidate the variations in soil volumetric water content (VWC) which may influence the mechanical properties of unstable slopes in ice-rich permafrost region under different rainfall conditions. New hydrological insights for the regionThis paper integrates the rainfall infiltration boundary conditions and Mohr–Coulomb criterion into a thermo–hydro–mechanical (THM) model and analyzes a landslide case in the permafrost regions. The results show that the THM model can effectively account for the impacts of VWC variation under different rainfall conditions. The influence of rainfall on the VWC diminishes as depth increases, with a more pronounced effect observed at depths less than 1 m. At depths exceeding 1 m, the impact is relatively minor. Under the condition of low-intensity, long-duration rainfall, with accumulated precipitation exceeding 60 mm, the cohesion and internal friction angle decrease to 4.2kPa and 8.1°, respectively, with a deep-layer integral slippage. In contrast, under the condition of high-intensity, short-term rainfall, the accumulated rainfall exceeds 75 mm and the internal friction angle decreases from 39° to 26°, with shallow-layer slippage. The results add on to our understanding engineering problems and periglacial geomorphic processes under the influence of climate warming.

Assessing rainfall-induced wetting band depth for stability analysis of unsaturated soil slopes

Because of factors such as plant root action, soil capillary action, and evapotranspiration, the soil near the surface of a slope tends to be drier and in an unsaturated state. However, when rainfall infiltrates the soil, the soil near the surface can become saturated, creating a wetting band that may trigger shallow landslides on the slope. This study performed transient finite element seepage and slope stability analyses on unsaturated soil slopes during rainfall. The analysis considered a representative rainfall pattern observed in Taiwan from 2010 to 2022, accounting for potential impacts of climate change. The objective of this study was to explore the impact of wetting band development on the stability of unsaturated soil slopes under rainfall conditions. Additionally, the investigation aimed to analyze the variations in pore water pressure and volumetric water content throughout the rainfall process. These analyses were conducted to determine the slope safety factor and investigate the relationship between the wetting band and the potential sliding surface. The results showed that the soil pore water pressure and water content near the surface of the slope were highly influenced by rainfall. The wetting band gradually extended downward from the surface with increasing rainfall duration, resulting in an increased wetting band depth (WBD), while the potential sliding surface approached the slope surface. When the safety factor was at its lowest, the potential sliding surface intersected the edge of the wetting band and was included within the range of the wetting band. This observation indicates a significant relationship between the potential sliding surface and the evolution of the wetting band during slope failure at the moment of minimum safety factor. The study also observed that water infiltration near the toe of the slope was more rapid, leading to a deeper wetting band at this particular location.

Analysis of the pore structure characteristics of saline soil in the profile within the frozen depth

Soil pores play a critical role in the complex physical coupling process and are closely associated with the mechanism of soil salinization. This research used mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and laser particle size analysis on a soil profile about 230 cm deep in Qian'an, where soda saline–alkali soil is distributed and the deepest underground freezing depth is 180 cm. The material composition of the soil in active layer was identified, and the soil pores were classified as micropores (<0.04 μm), small pores (0.04–0.4 μm), mesopores (0.4–4 μm), and macropores (>4 μm). The soil deposited at a depth of 0 to 80 cm was affected by freeze–thaw cycles and dry–wet cycles, developing longitudinal cracks. During the rainy season, clay particles and salt were carried downward by rainfall, whereas at a depth of 30 to 80 cm, the exchangeable sodium ions and clay particles in the soil created a thick diffused layer and hindered rainfall infiltration, resulting in salt accumulation. The small pore diameter and low porosity of the soil in this depth range caused pores degradation, further exacerbating the salinization process. The soil deposited at a depth of 80 to 120 cm had low clay content, resulting in limited upward migration of unfrozen water during freezing periods. Upon thawing, the salt and fine clay particles moved upward with capillary water, leading to a lower salt content than the upper soil. Additionally, this depth range had a high content of macropores with a large average pore diameter. The soil deposited at a depth of 120 to 180 cm had high clay content, and during short freezing periods, salt migrated upwards with unfrozen water along poorly connected longitudinal cracks with limited clay particle migration. The macropore content was low, and the average pore diameter was small due to clay particles filling the pores. The salt content in this depth range was lower than in the upper soil. The pore structure characteristics of the saline soil in the active layer provide insights into salt deposition mechanisms, and this research offers data support from a pore-scale perspective for preventing the salinization process.

Correction to “Effect of soil thickness on rainfall infiltration and runoff generation from karst hillslopes during rainstorms”

Correction to “Effect of soil thickness on rainfall infiltration and runoff generation from karst hillslopes during rainstorms”

Numerical Analyses of Slope Stability Considering Grading and Seepage Prevention

The normal operation of the Yulangpei tailings reservoir is affected by landslide stability. In this paper, taking the main and side slopes near the dam bank of the Yulangpei ditch as an example, the water–soil coupling theory is applied to comprehensively evaluate the reliability of the side slopes of the tailings reservoir. Grading and seepage prevention (GSP) measures and the suction of the substrate are considered, as well as the infiltration of different rainfall and reservoir water levels. We numerically simulate the typical three forms of side slopes under the coupling conditions and conduct a reliable and comprehensive evaluation of the tailings reservoir side slopes. This study shows that the analysis of condition 1 indicates that the factor of safety (FS) of the bank slope shows a lag effect and that GSP can improve the FS of the slope, but not significantly for the main slope. The analysis of condition 2 shows that the weakening effect increases with the intensity of rainfall during the rainfall process, while the FS rebounds when the rainfall stops. The initial stability of the bank slope under different conditions improves after the GSP measures, but the main slope is more sensitive to the changes in rainfall and water level. The analysis of condition 3 shows that the overall trend of FS and displacement of the main slope shows a small decrease followed by a sharp increase. The FS of the side slope is negatively correlated with the change in total displacement, with a general trend of a slight increase followed by a sharp increase. After GSP, the overall FS of the main slope increases by about 3% and the total displacement decreases by about 87%, and the overall FS of the side slope increases by about 41%, while the total displacement decreases by about 66%.

Analytical modeling of contaminant transport along sloping coastal beaches in presence of tidal waves and exponential rainfall infiltration

Coastal beaches are the most important part of the marine environment and are highly influenced by the interactions taking place between groundwater and surface water of any form. Generally, the purity index of the groundwater is based on the concentration of Total Dissolved Solids (TDS) in it. Analytical solutions are the best tools for groundwater flow and transport modeling. However, contaminant transport along the sloping coastal beaches with complex boundaries cannot be addressed with available analytical solutions. In the present study, new analytical models are developed for groundwater flow and contaminant transport for sloping coastal beaches with continuity and tidal boundary conditions. To assess the performance of the new analytical solution and to validate the range of aquifer parameters, numerical simulation is performed using Du-Fort Frankel (DFF) Scheme. Numerical experimentation is carried out using the Tchebycheff and L2 norms. It is observed that the new analytical solution for the contaminant transport gives acceptable results over the wide range of the aquifer parameters. To show the effectiveness of the developed models, two case studies from Indian coastal aquifers namely, Kalpakkam, Tamil Nadu, and Bhavnagar, Gujarat are considered. The profiles of the contaminant concentration are obtained to study the TDS behavior along these complex coastal beaches in the spatiotemporal directions. The results are compared with numerical model results and found to be satisfactory. The combined effect of the initial rainfall and rainfall decay constants showed a significant impact on the concentration of TDS. TDS concentrations are observed to be varying highly with the variation in the tidal constituents and bed slope.

도시홍수 통합관리모델 수립연구

Urban areas with high levels of impervious cover and inadequate flood-mitigation policies are becoming increasingly vulnerable to flooding compared to other areas. Despite nationwide efforts to mitigate flood damages, which primarily focus on major rivers, smaller rivers and urban catchments still experience frequent floods. This study utilized a semi-distributed hydrologic model and SWMM to consider the potential backwater effect on inland flooding. Through complementary analysis using observed rainfall and flow data from early October 2016 (Typhoon Chaba), the study was conducted on the Yugok Catchment. The results demonstrate the advantages of the semi-distributed model, which can handle spatial-temporal rainfall distribution and infiltration parameters while maintaining relatively faster calculation speed compared to a fully-distributed model. Furthermore, this study suggests that integrating the model with the SWMM can provide sufficient, accurate, and prompt information to enable effective flood crisis management plan.

Experimental Study on the Influence of Substrate Properties on Rainfall Infiltration and Runoff from Ecological Slopes

Rain is an important factor influencing the instability of ecological slopes. There is little research on the inherent quantitative influence of substrate properties on slope runoff and water infiltration to support accurate ecological slope protection design. In this paper, the influence of substrate characteristics on slope runoff and water infiltration is quantitatively analyzed by constructing large physical models with different substrate characteristics for artificial rainfall simulations. The experimental results showed that the cumulative runoff volume and slope runoff rate were positively correlated with the cement content and substrate thickness in a 4 h, 60 mm/h artificially simulated rainfall. Specifically, the cumulative runoff volume increased by 2.06% for every 1% increase in cement content, and the cumulative runoff volume increased by 3.93% for every 1 cm increase in substrate thickness. The substrate inhibited the advance of the wetting front, and at different slope locations, the transport rate of the wetting front exhibited a mid-slope &gt; upslope. Moreover, the transport rate of the wetting front showed a non-linear relationship with time as a power function V = a·tb, with the cement content showing a linear relationship with parameters a and b, and the substrate thickness showing a non-linear relationship with parameters a and b. The cumulative infiltration and infiltration rate were negatively correlated with cement content and substrate thickness, as shown by a 2.2% decrease in cumulative infiltration for every 1% increase in cement content and a 4.73% decrease in cumulative infiltration for every 1 cm increase in substrate thickness.

Correction to: Slope stability analysis under rainfall infiltration condition using the minimum potential energy method

Correction to: Slope stability analysis under rainfall infiltration condition using the minimum potential energy method

Reliability analysis of compacted embankment with geocomposite under infiltration

Embankment failures can be prevented by introducing geocomposites to act as drains. The effect of the geocomposite layer on the pore pressure distribution and surface displacements of an unsaturated embankment upon infiltration has been studied numerically using deterministic and probabilistic approaches. The inclusion of the geocomposite layer leads to an increase of suction below the interface and a decrease in suction above it by functioning both as a capillary barrier and a drainage layer, thereby reducing the surface displacements upon infiltration. The load in the form of rainfall and the resistance such as suction of the embankment material being variable leads to a variability in the displacements; therefore, reliability analysis has been carried out using hydraulic permeability and soil water characteristic curve (SWCC) parameters as random variables. To assess the probability of failure (Pf), a surrogate model based on augmented radial basis function has been used. Probabilistic analysis revealed that the embankment with geocomposite has less Pf compared to the embankment without geocomposite considering the rainfall infiltration. Moreover, sensitivity analysis predicted that SWCC parameters influence the Pf of embankment containing geosynthetics under infiltration to a larger extent.

A Time-Scale Varying Finite Difference Method for Analyzing the Influence of Rainfall and Water Level on the Stability of a Bank Slope

A time-scale varying finite difference method (TSFDM) was proposed to analyze the influence of rainfall infiltration and water level fluctuation on the stability of a bank slope in the Yunnan Pulang tailings pond. The stability of the slope obtained by the TSFDM and the limit equilibrium method (LEM) were compared. The result indicates that the TSFDM can obtain reliable spatiotemporal variation features of geotechnical parameters of the bank slope under different conditions. The water level fluctuation has a greater impact on the stability than rainfall infiltration. In addition, the safety factor decreases as the shear strain rate increases on the weathering interface. The safety factors under all conditions are smaller than one, so corresponding measures should be taken. The research provides references for preventing disasters caused by bank slope failure.