Rainwater Infiltration Research Articles

Rain garden hydrological performance – Responses to real rainfall events

Rain gardens, as bioretention facilities belonging to blue-green infrastructure solutions, are becoming increasingly implemented in cities. The main reason for this is to support traditional drainage systems in receiving runoff from impermeable surfaces and managing it through temporary retention and infiltration into the ground. However, as practice shows, investors focusing on the construction of the systems and their commissioning skip their monitoring during the operating period, thus missing the opportunity to obtain reliable data on their hydrological performance under actual field conditions.The purpose of the study was to evaluate the effectiveness of a rain garden, located in an urban area, to capture runoff from the roof of a building. The assessment was based on the results of measurements carried out in 2021 on the variability of the levels of water retained in the rain garden and on measurements of growing medium moisture content at several selected points in the rain garden depression against thermal and rainfall conditions. The results showed that the rain garden demonstrated good hydrological performance. This was proven by the observed direct infiltration of rainwater into the structural layer or the short retention time for rainfall events with a higher rainfall total. The highest growing medium moisture was observed in the area of rainwater inflow to the rain garden. The results of the research may be useful in the planning and realization of future investments with rain gardens, which are to be situated in areas of similar meteorological conditions.

Evaluation of Landslide Disaster Mechanism and Control Scheme in Beixi Village

Taking beixi village landslide as an example, the cause and mechanism of rain-induced landslide are deeply analyzed. The stability of landslide under natural state and rainfall state is analyzed respectively by using finite element strength reduction method, and the influencing factors of landslide are analyzed and the safety and stability of landslide is evaluated. The results show that :(1) The disaster mechanism of beixi village landslide is due to the strong water permeability of clay layer, and the weathering layer is easy to soften when it meets water, and rainwater infiltration is easy to form weak interlayer, which induces local deformation and finally slides.(2) The landslide of Beixi Village is in a stable state under natural conditions; the landslide was in an basically stable state under saturation condition. (3) According to the plastic cloud map of sliding surface, there is stress concentration in the landslide front, which endangers the lower buildings. It is suggested that slope cutting + gravity retaining wall + drainage engineering prevention and control measures. The formation mechanism of the landslide can provide engineering reference for the disposal and prevention of similar landslides.

Simulating the entire rainfall-induced landslide process using the material point method for unsaturated soil with implicit and explicit formulations

Rainfall-induced landslides cause various types of damage, including damage to infrastructure, leading to devastating economic losses and human casualties. Although various numerical methods have been developed to predict landslide occurrence and the extent of sediment flow, three-dimensional analysis of the entire landslide process in a unified manner is still challenging owing to limitations in computational efficiency and the representation of deformation and flow. In this study, we present a numerical method of rainfall-induced landslides using the coupled hydromechanical material point method (MPM) for unsaturated porous media based on implicit and explicit formulations, which enables the efficient analysis of all rainfall-induced landslide processes, including both quasi-static and dynamic processes. The developed method includes an implicit MPM based on a simplified formulation, which is first applied to the quasi-static analysis in the pre-failure stages in which rainwater infiltrates the ground. The explicit MPM is then applied to the dynamic analysis for post-failure stages in which the ground collapses and flows. A constitutive law for soils is improved in the simulation of landslide initiation and sediment flow by incorporating the effect of cohesion in a visco-plastic model for granular materials. The proposed method was applied to a three-dimensional terrain model of Ashikita town, Kumamoto, Japan, where an actual landslide occurred owing to intense rainfall on July 3–4, 2020. Numerical results from the proposed hydromechanical coupling compared with single-phase MPM indicated that pore water plays an important role in understanding all rainfall-induced landslide processes, from landslide initiation to sediment discharge.

Analysis of a landfill cover without geomembrane using varied particle sizes of recycled concrete

Previous studies have demonstrated the effectiveness of a novel three-layer landfill cover system constructed with recycled concrete aggregates (RCAs) without geomembrane in both laboratory and field. However, no systematic investigation has been carried out to optimize the combination of the particle sizes for fine-grained RCAs (FRC) and coarse-grained RCAs (CRC) that can be used for the three-layer landfill cover system. The aim of this paper is to assist engineers in designing the three-layer landfill cover system under a rainfall of 100-year return period in humid climate conditions using an easily controlled soil parameter D 10 of RCAs. The numerical study reveals that when D 10 of FRC increases from 0.05 mm to 0.16 mm, its saturated permeability increases by 10 times. As a result, a larger amount of rainwater infiltrates into the cover system, causing a higher lateral diversion in both the top FRC and middle CRC layers. No further changes in the lateral diversion are observed when the D 10 value of FRC is larger than 0.16 mm. Both the particle sizes of FRC and CRC layers are shown to have a minor influence on the percolation under the extreme rainfall event. This implies that the selection of particle sizes for the FRC and CRC layers can be based on the availability of materials. Although it is well known that the bottom layer of the cover system should be constructed with very fine-grained soils if possible, this study provides an upper limit to the particle size that can be used in the bottom layer ( D 10 not larger than 0.02 mm). With this limit, the three-layer system can still minimize the water percolation to meet the design criterion (30 mm/yr) even under a 100-year return period of rainfall in humid climates.

Rainwater infiltration and nutrient recharge system significantly enhance the growth of degraded artificial forest in semi-arid areas with shallowly buried soft bedrock

The improvement of deep soil water and nutrient pools by maximizing in situ rainwater resource utilization and soil nutrient recharge is an important approach to promote slope vegetation restoration in the Chinese Loess Plateau, especially in areas with shallowly buried soft bedrock (Pisha Sandstone). However, the effects of integrated slope engineering measures (fish scale pits (a semicircle-shaped pit), infiltration holes, organic fertilizer) on runoff utilization, nutrient restoration and vegetation growth are not well known. This study combined rainwater infiltration and nutrient recharge (RINR), and evaluated the effect of RINR on soil water, organic carbon, total nitrogen storage and vegetation growth in a field experiment in slope artificial forestland (David peach, Prunus davidiana Franch) one year later (from 2018 to 2019). Four treatments: (1) rainwater infiltration and nutrient recharge (RINR) system (fish scale pit + infiltration hole + hole filling with 30% organic fertilizer and 70% surface loess, PHF treatment), (2) fish scale pit + infiltration hole + filling surface loess (PH treatment), (3) pure fish scale pit (P treatment) and (4) natural slope land (control, SL treatment, CK). The results showed that, compared with the control (162 mm), PHF, PH and P treatments increased the soil water storage of 0–100 cm soil layer by 37 mm, 76 mm and 30 mm, respectively. The RINR system (PHF treatment) had a significantly higher restoration effect of SOC and STN value than other treatments in all soil profiles (0–100 cm), especially at 40 cm. Compared with the control (2.42 kg/m2, 0.28 kg/m2), the RINR system 0–40 cm soil layer soil organic carbon storage increased by 320%, and total nitrogen storage increased by 129%. Meanwhile, changes in height of tree (David peach), crown width and annual branch length under RINR system increased by 0.18 m, 0.30 m and 0.33 m, respectively. Overall, the RINR system is an effective approach for enhancing the growth of degraded revegetation. This system is conducive to mitigating the water and nutrient scarcity and maintaining the persistence of vegetation restoration in arid and semi-arid areas with shallowly buried soft bedrock.

An Analysis of Landslide Risk Using the Change in the Volumetric Water Content Gradient in the Soil Layer Per Unit Time of Effective Cumulative Rainfall

The topographical characteristics of South Korea are coupled with heavy rain and typhoons concentrated from July to September, which take up two-thirds of the country’s annual precipitation, causing substantial damage from slope failures, landslides, debris flows, and other mountain disasters. This study uses the Land-Atmosphere Modeling Package (LAMP) data to study the area, which has been affected by numerous landslides in the past. Specifically, to analyze the likelihood of slope failure, this study simulates the rainfall events in the area at the time of the landslides as well as changes in the volumetric water content in the soil layer and uses the changes in the volumetric water content per unit time, which are affected by the effective cumulative rainfall within the soil layer. To that end, this study assesses the risk of landslides based on how rainwater infiltration in the saturation depth changes the saturation depth ratio and compares the results with the landslide spots in the past. Moreover, this study analyzes the landslide risk by applying the saturation depth ratio (Ht) to an infinite slope stability analysis model. The landslide threshold proposed in this study was obtained by analyzing the rainfall events that caused the landslides in the study area using the LAMP model. It can then be concluded that, when compared with the spatial information on the previous landslides, if the change in the volumetric water content per unit time during the first and second rainfall events is 0.7, a landslide may occur. These results indicated that the landslide risk increases the volumetric water content in the soil layer, along with the congruence between past landslide risk points and spatial landslide risks.

Characterization and Productivity of Alluvial Aquifers in Sustainability Oasis Areas: A Case Study of the Tata Watershed (Southeast Morocco)

Groundwater from alluvial aquifers is a critical source of water supply for rural agriculture, particularly in semi-arid and arid regions. Effective management of these aquifers requires an understanding of the factors that influence their water resources. In this study, we present a case study of the Tata watershed in southeastern Morocco, where the economy is heavily dependent on agriculture and relies exclusively on groundwater. We demonstrate the importance of integrating geological, hydrogeological, and geophysical methods to characterize the aquifer and evaluate groundwater productivity. Analysis of 64 data wells tapping into the aquifer revealed significant disparities in flow yields, ranging from 0.05 to 15.50 L per second. The highest yields were found between depths of 12 and 43 m, which correspond to the alluvium and the altered and fractured part of its substrate. The maximum alluvial thickness of 57 m was determined using geo-electrical prospecting. A piezometric map was created to define the recharge zones, which correspond to the lateral contributions of the bordering Georgian limestones, and infiltration of both rain and surface water along the Tata wadi. Since 1987, there has been a continuous drop in groundwater level, which can be attributed to the increase in irrigated areas following financial incentives provided by the Moroccan government to the agricultural sector. A proposal has been made for the construction of a recharge dam to enable the recharge of the alluvial aquifer. This development is expected to serve a dual purpose by mitigating the deleterious impacts of flooding and facilitating the gradual water infiltration of the alluvial aquifer. This case study provides insights into the hydrodynamics of the aquifer and establishes a simplified model of its functioning. These findings have important implications for the management of alluvial aquifers in similar regions.

Effect of soluble salts in electrolytic manganese residue on its geotechnical characteristics

Electrolytic Manganese Residue (EMR) is a solid waste containing soluble sulfate, discharged by electrolytic manganese industries. The accumulation of EMR in ponds poses a significant hazard to both safety and the environment. This study utilized innovative geotechnical test techniques to conduct a series of tests, investigating the effect of soluble salts on the geotechnical characteristics of EMR. The results revealed that soluble sulfates had a significant impact on the geotechnical characteristics of the EMR. In particular, the infiltration of water leached away the soluble salts, causing a non-uniform particle size distribution and decreasing the shear strength, stiffness, and liquefaction resistance of the EMR. Nevertheless, an increase in the stacking density of EMR could improve its mechanical characteristics and inhibited the dissolution of soluble salts. Therefore, increasing the density of stacked EMR, ensuring the effectiveness and non-obstruction of the water interception facilities, and reducing rainwater infiltration could be effective measures to enhance the safety and reduce the environmental hazard of EMR ponds.

Relationship of Rainfall Intensity with Slope Stability

The impact of rainfall on landslides is not an uncommon issue worldwide, including in Malaysia. It is a major challenge for geotechnical engineers to ensure the constructed slope is safe and can sustain longer periods of time, including during heavy rainfall. Kota Belud, Sabah, has been selected as the study area to meet the study objectives. Heavy rainfall has been recorded every year within Kota Belud, which has caused a repetition of landslide occurrences within the hilly areas, especially during the monsoon season. Presently, there is no local procedure for determining the rainfall intensity value for slope stability analysis. This study utilized the rainfall intensity value from Hydrology Procedure 26. Seepage analysis conducted shows rainwater infiltration has caused the groundwater level to increase from rainfall starts until 0.5 m below ground level and decrease after rainfall stops, creating fluctuations in the groundwater level during the wet and dry conditions within the wetting front. The factor of safety of the slope shows a decreasing trend, with a reduction of around 27 to 33% after 24 hours of rainfall in conjunction with the changes in groundwater level. However, the factor of safety increased by around 3% from the initial condition after 48 hours. The objective of this study is to identify the factor of safety of a rainfall-induced slope within Kota Belud utilizing the rainfall intensity design limits from Hydrology Procedure 26. Doi: 10.28991/CEJ-SP2023-09-06 Full Text: PDF

Hydrogeochemical Responses of MTMS-Coated Capillary Cover under Heavy Rainfalls

To limit the oxidation of waste rocks that originates from mining operations and the subsequent leaching of acidic solutions with high concentration of metal ions, a tailing–rock–clay triple layer capillary cover system was developed to prevent rainwater infiltration in humid climatic regions. The fine grained soil (FGS) layer consists of mine tailing and a hydrodesulfurization (HDS) clay from waste-water treatment with a 95:5 mass ratio. The coarse grained soil (CGS) layer consists of local waste rock granules with a size of 1–10 mm. Methyltrimethoxysilane (MTMS), an oxidation-inhibiting agent with strong hydrophobicity, was passivated on the rock grains to further reduce water infiltration and leaching of metal ions. Prototype-scale column tests were performed with matric suction and water content measurements under 680 min rainfall of 60 mm/h, the most severe annual precipitation case scenario for the Dexing Copper Mine (Jiangxi Province, China, 28.95° N, 117.57° E, humid climate). Both the uncoated and the coated covers exhibited zero leakage throughout the experiment. The passivation on rock granules in the coated cover increased the water entry value (WEV) of the CGS layer to −0.56 kPa. This led to a 15 mm water storage increment in the overlain FGS layer as compared to that in the uncoated cover, and induced lateral drainage (5% of the precipitation) in the FGS layer, which was not overserved in the uncoated cover. The concentrations of the leached Fe2+, Cu2+, Zn2+, Mn2+ and Mg2+ cations drained from the CGS layers of the uncoated cover were 0, 0.4, 0.8, 73.5, and 590.5 mg/L, which are all within the regulation limits of industrial discharge water standards. The concentrations of Cu2+, Mn2+ and Mg2+ cations drained from the coated CGS layer were reduced by 1–3 orders of magnitude. The abovementioned laboratory studies validated the water retention and leaching prevention abilities of the proposed three-layer capillary covers and the MTMS coating, which hold promises in engineering applications.

Biovalley analysis as a LID control to delay surface runoff in the city of Recife/PE

Urban growth brought with it the formation of large impermeable areas in cities, causing a reduction in the infiltration of rainwater into the soil and an increase in the volume of surface runoff, causing setbacks on days of extreme precipitation events. In this context, the present research aimed to analyze the use of a biotaver as a Low Impact Development (LID) for delaying surface runoff in areas prone to flooding in the city of Recife/PE. As a methodology, the QGIS model was used to extract data from raster images, and the Storm Water Management Model (SWMM) for scenario simulation. Three scenarios were simulated with rainfall of 20.00mm, 39.00mm and 60.00mm. The results showed that the implementation of the bioditches provided a reduction in the total flow of the study area by 0.50% and in the maximum flow of the SB1 sub-basin for scenarios 2 and 3 by 77.96% and 41.23% respectively. In addition, there was a reduction in surface runoff of 11.15% on average and an increase in green area of 4.00%. The bioretention system showed infiltration ranging from 29.83mm to 89.35mm between the three scenarios. Thus, through the SWMM model, it was possible to analyze that the implantation of bioditches as a control for delaying surface runoff and increasing infiltration into the soil is valid, and the literature recommended that various types of sustainable devices be implemented and integrated into the existing drainage network and urban space so that more expressive results are possible.

Quantitative analysis of rainwater redistribution and soil loss at the surface and belowground on karst slopes at the microplot scale

On karst slopes, soil and bedrock form soil-rock structural units (SRSUs), leading to complicated soil erosion for which quantitative attribution can hardly be achieved through whole-slope tests. This study aimed to quantify the role of different SRSUs in the soil erosion process, including rock covering the soil (RCS), bedrock exposed at the surface (RES), and a thin soil layer covering bedrock (SCR). Surface flow (SF), subsurface flow (SBF), infiltrated rainwater entering underground bedrock fissures (UF) and transported sediments were measured in soil boxes representing these SRSUs on karst slopes (5° and 25°) under 50 mm/h rainfall. The results indicated that among the three SRSUs, SF accounted for < 1% (2.5%-4.2%) of the total rainfall on the 5° slope (25° slope); SBF of the SCR, RES and RCS SRSUs accounted for 12.9% (37.9%), 14.9% (46.9%) and 10.8% (35.9%), respectively, of the total rainfall on the 5° slope (25° slope), and UF accounted for 28.6% (6.5%), 25.7% (10.0%) and 32.3% (3.7%), respectively, of the total rainfall. The SBF values of the SCR and RES SRSUs were 23% higher than that of the RCS SRSU on average. The UF values of the SCR and RES SRSUs were 16% lower than that of the RCS SRSU on the 5° slope and were 125% higher than that of the RCS SRSU on the 25° slope on average. Soil loss mainly occurred through SF, and the amount of soil lost through SBF or UF was < 0.01 g/L. These results suggest that both the type of SRSU and slope could greatly influence rainwater redistribution in soil and that the rain-driven soil loss through underground bedrock fissures was low on karst slopes. This occurred because the infiltrated rainwater or rock surface flow reaching the rock-soil interface (RSI) underground became preferential flow (RSI-PF). Thereafter, part of RSI-PF entered bedrock fissures as UF, whereas the remaining RSI-PF likely seeped into the soil and contributed to SBF or SF. Therefore, on the whole slope, which comprises different SRSUs with high heterogeneity, the soil erosion process is very complex because of the interaction between the surface and subsurface.

Vertical Capillary Barriers and Wick Drains to Mitigate the Rain-induced Slope Failures: Numerical Analysis

Slope failures are catastrophic when they suddenly occur in human habitats. The stability of slopes gradually diminishes with heavy rainfall due to the increase in pore water pressure; subsequently, the shear strength of the slope soil decreases. The effect of rainwater on the instability of slopes was studied in this research with respect to factor of safety values. Accordingly, finite element analysis and limit equilibrium analysis were conducted using a 2D model of a soil slope in SEEP/W and SLOPE/W programs to observe the responses of the slope soil profile under heavy rainfall. Movement of the wetting front and the fluctuation of the groundwater table were studied to develop a drainage mechanism, thereby to control the effect of infiltrated rainwater on slope failure. A conceptual method was introduced in this study by developing a numerical model with an effective drainage system which consists of vertical capillary barriers with combination of horizontal wick drains in a cascade manner in the slope. This method exhibited high stability of the slopes even with continuous rainfall for number of days, therefore, applicable as a sustainable prevention method of slope failures.

Evolution process and failure mechanism of a large expressway roadside landslide

Site investigation, deformation monitoring, laboratory test, and theoretical calculations were used to analyze the evolution details of a large expressway roadside landslide during the start-up sliding process. The monitoring results show that the initial deformation and failure occurred on the protective wall at the slope toe, then gradually developed to the upper part of the slope, and finally led to tensile cracks at the slope trailing edge. Accelerated deformation of the slope support structures, such as the protective wall at the slope toe, the anti-slide pile, and the anchor cable, were observed during the continuous extreme rainfall. The infiltrated rainwater can change the weight, the osmotic pressure, the anti-sliding force, the sliding force of the sliding mass, and further soften the fully weathered tuff soil and reduce its strength, resulting in the landslide occurrence. Block the slope surface runoff is an effective measure to reduce the landslide risk. The current analysis will be helpful to the prevention, control, and emergency disposal of similar landslides.

Deformation and failure mechanism of colluvial landslide under sustained rainfall-a case study of Xinzhan landslide in Tongzi County, China

The failure mechanism of Xinzhan landslide were investigated systematically based on multiple-integrated geotechniques, including field investigations, monitoring, and numerical simulations. Xinzhan landslide is a typical colluvial landslide, composed of gravelly soil in upper part and sandstone interbedded with mudstone in underlying part. The sliding surface is closing to the soil-rock interface with average depth about 8 m and the main sliding direction 287°. The occurrence of Xinzhan landslide is attributed to its unique geological environment and sustained rainfall. The hydro-mechanical coupling results indicate that under sustained rainfall, the rainwater infiltrates into gravelly soil, rising the pressure and forming transient saturation zone near the soil-rock interface, where the strength parameter is weakened under effect of water. As a consequence, the plastic deformation is intensified. Additionally, the deformation evolution trend of landslide under different rainfall intensities is also studied. The results show that the greater rainfall intensity, the shorter rainfall duration required for the landslide to produce accelerated deformation. The rainfall intensity-duration curve is used to construct the critical rainfall early warning criterion of Xinzhan landslide. The R2 of the fitting formula is 0.971, which indicates that the formula can effectively serve the early warning and provide convenience for highway safety construction.

Research on the improvement of rainfall infiltration behavior of expansive soil slope by the protection of polymer waterproof coating

The repetitive expansion and contraction cracks, as well as the strength attenuation induced by the precipitation-evaporation cycles, are important factors influencing the instability of expansive soil slopes. In this study, a polymer waterproof coating was proposed to protect the expansive soil slope against slope instability caused by precipitation penetration. The bonding performance of expansive soil blocks (with different soil densities) and polymer waterproof coatings (with different coating thicknesses) were analyzed by performing a laboratory pull-out test. The impacts of different protection methods and protection layer coverage on rainwater infiltration behavior were studied using three groups of slope model tests and numerical simulation approaches. The results showed that the bond strength between the expansive soil test block and the coating increased with the increase in soil compaction density, and the test block strength was an important factor affecting the bond performance. The influence of density of test block on bond strength was greater than that of coating thickness. The calculation formula of bond strength was obtained by fitting the test results. Compared to the unprotected slope, the fluctuation of soil moisture content and rainwater infiltration rate in the slope protected by polymer coating was found to be the least. Protective layer of polymer coating proved to have the most significant role in blocking rainwater infiltration, followed by polymer coating + three-dimensional vegetation net protective layer. When the coverage rate of the protective layer exceeds more than 90%, the effect of blocking rainwater infiltration was remarkable. Simultaneously, the variation range of slope water content, rainwater infiltration depth, and infiltration rate decreased significantly. This research result provides a new solution for expansive soil slope protection and rainwater infiltration control.

Influence of Suction on Capacity of Pile Foundation

In the common practice of geotechnical design, the state of soil is considered fully saturated, while recent examples show the importance of the consideration of unsaturated conditions as well due to the location of the groundwater table at deeper levels. However, it is problematic to design a foundation and calculate bearing capacity as the internal stress in unsaturated conditions needs to be quantified. The mechanics of unsaturated soils are critical in geotechnical engineering, especially when the case of the foundation design is required. This study aims to investigate the influence of suction on the shaft capacity of pile foundations based on the data obtained from in situ and laboratory testing. The three modified methods (i.e., modified α, β, and λ) were implemented in this study in order to calculate the shaft capacity of the pile foundation incorporating unsaturated soil mechanics principles. In addition, the effect of varying matric suction on shaft capacity was discussed. The results of obtained changes show the importance of rain infiltration in the design of piles in unsaturated conditions. It can be concluded that the most conservative method is found to be the modified β method in designing pile foundations incorporating the suction changes due to rainwater infiltration. However, cost optimization shall be considered while choosing the method for the design. As for the increase in GWT, the modified λ method depicted the most conventional behavior. The possible rain infiltration decreases matric suction, mostly in the upper layers.

Impact of leachate and landfill gas on the ecosystem and health: Research trends and the way forward towards sustainability

Globally, a whopping increase in solid waste (SW) generation and the risks posed by climate change are major concerns. A wide spread practice for disposal of municipal solid waste (MSW) is landfill, which swells with population and urbanization. Waste, if treated properly, can be used to produce renewable energy. The recent global event COP 27 mainly stressed on production of renewable energy to achieve the Net Zero target. The MSW landfill is the most significant anthropogenic source of methane (CH4) emission. On one side, CH4 is a greenhouse gas (GHG), and on the other it is a main component of biogas. Wastewater that collects due to rainwater percolation in landfills creates landfill leachate. There is a need to understand global landfill management practices thoroughly for implementation of better practices and policies related to this threat. This study critically reviews recent publications on leachate and landfill gas. The review discusses leachate treatment and landfill gas emissions, focusing on the possible reduction technology of CH4 emission and its impact on the environment. Mixed leachate will benefit from the combinational therapy method because of its intricate combination. Implementation of circular material management, entrepreneurship ideas, blockchain, machine learning, LCA usage in waste management, and economic benefits from CH4 production have been emphasized. Bibliometric analysis of 908 articles from the last 37 years revealed that industrialized nations dominate this research domain, with the United States having the highest number of citations.

Hazard Mitigation of a Landslide-Prone Area through Monitoring, Modeling, and Susceptibility Mapping

Indigenous tribes living in the mountainous areas account for about one-fifth of the extreme poor of the world, and this has made their lives more vulnerable to climate change impacts and natural hazards. After a series of earthquakes and very strong typhoons, the tilting and cracking of dwellings, localized slope failure, and severe subgrade settlements, together with damages of retaining structures and drainage ditches along a section of the Provincial Highway No. 7A on the west wing of the Central Mountain Range in central Taiwan, have raised concerns to the safety of a nearby Indigenous settlement, which is situated at an elevation of about EL. +1800 m. This study investigated and identified the possible causes for a large-scale landslide-prone area on the Central Mountain Range by employing multi-temporal satellite and aerial images, site investigation, field instrumentation, geophysics tests, and uncoupled hydromechanical slope stability analyses. The results were then applied to deduce a sliding susceptibility map and remedial plans to prevent or mitigate the sliding in the vicinity of an Indigenous settlement. The infiltration of rainwater, an upraised river-bed elevation, and the erosion of the river bank at the toe of the large-scale slope were found to be the main triggering factors in inducing sudden and localized failures. Meanwhile, the process of mass rock creep was deduced to have activated the process of large-scale deep-seated gravitational slope deformation (DSGSD) on the study slope; the DSGSD could eventually turn into a huge and catastrophic landslide. The findings of this study would be valuable for formulating detailed countermeasures to protect and maintain the stability and safety of the Indigenous settlement located at the crest of the slope.

The effects of soil properties and sorbent amendments on immobilization of perfluorooctane sulfonate (PFOS) in contrasting soils: Experimental and numerical study

Per- and polyfluoroalkyl substances (PFAS), a class of manmade organo-fluorine chemicals, are a serious challenge to water supplies. In this study, the effects of physicochemical properties of Florida topsoil and Ringold formation Hanford site sediment as well as the influence of immobilizers on the sorption behavior of PFOS were tested. Activated charcoal (AC) and food waste compost amendments were added to the soil and sediment at 0.1 and 3 wt% concentration, respectively. The PFOS adsorption fits best to pseudo second-order kinetic and Freundlich isotherm models. PFOS uptake was greater in Florida topsoil compared to Hanford site sediment, indicating that organic matter played a key role in the retention of PFOS. The food waste compost amendment at 3 wt% had no impact on PFOS uptake. However, AC amendment at 0.1 wt% enhanced PFOS sorption in Florida topsoil by 80% and Hanford site sediment by 99% through increasing the soil/water partitioning coefficients (kd value). A one-dimensional model was used to simulate the influence of AC in Florida topsoil on the leaching of PFOS to the groundwater by the percolation of rainwater over time. The results demonstrated the addition of 0.1 wt% AC, to the soil dramatically inhibits or delays the leaching of PFOS for up to one year under certain conditions to below the guideline for maximum concentration level (0.02 ng/L). The amendment could control PFOS release for more than 10 years by increasing the kd value by 10 times.