Effect Of Rainfall Infiltration Research Articles

Failure Mechanism of a Rainfall-Triggered Landslide in Clay Slopes

In December 2013, a portion of a large and deep ancient landslide on the southern slope of the Montescaglioso town (Basilicata, Southern Italy) was abruptly reactivated, as a consequence of exceptional rainfall events, causing relevant damages to structures and infrastructures. The sliding surface is supposed to be located within a thick deposit of Pleistocene stiff clays overlain by dislocated blocks of calcarenites and cemented conglomerates. This paper discusses the research carried out to investigate the failure mechanism that occurred during the landslide event and the factors that controlled the reactivation. To this purpose, geological and geomorphological analyses were first proposed, followed by a back-analysis of the landslide process, performed via limit equilibrium calculations implementing time-dependent pore water pressure distributions derived from transient seepage finite element analyses. Furthermore, the overall landslide mechanism was investigated through a three-dimensional finite element analysis, built using the monitoring campaign carried out in the post-failure stage and calibrated according to the in situ failure mechanism evidence. Both the limit equilibrium and finite element analyses provide results in good agreement with the geomorphological evidence, further allowing us to recognize the effects of rainfall infiltration in the increase of pore water pressure along the sliding surface and the variation of the stress–strain state leading to failure occurrence.

A mechanistic approach to include climate change and unplanned urban sprawl in landslide susceptibility maps

Empirical evidence shows that climate, deforestation and informal housing (i.e. unregulated construction practices typical of fast-growing developing countries) can increase landslide occurrence. However, these environmental changes have not been considered jointly and in a dynamic way in regional or national landslide susceptibility assessments. This gap might be due to a lack of models that can represent large areas (>100km2) in a computationally efficient way, while simultaneously considering the effect of rainfall infiltration, vegetation and housing. We therefore suggest a new method that uses a hillslope-scale mechanistic model to generate regional susceptibility maps under changing climate and informal urbanisation, which also accounts for existing uncertainties. An application in the Caribbean shows that the landslide susceptibility estimated with the new method and associated with a past rainfall-intensive hurricane identifies ~67.5 % of the landslides observed after that event. We subsequently demonstrate that the hypothetical expansion of informal housing (including deforestation) increases landslide susceptibility more (+20 %) than intensified rainstorms due to climate change (+6 %). However, their combined effect leads to a much greater landslide occurrence (up to +40 %) than if the two drivers were considered independently. Results demonstrate the importance of including both land cover and climate change in landslide susceptibility assessments. Furthermore, by modelling mechanistically the overlooked dynamics between urban growth and climate change, our methodology can provide quantitative information of the main landslide drivers (e.g. quantifying the relative impact of deforestation vs informal urbanisation) and locations where these drivers are or might become most detrimental for slope stability. Such information is often missing in data-scarce developing countries but is key for supporting national long-term environmental planning, for targeting financial efforts, as well as for fostering national or international investments for landslide mitigation.

Finite-hillslope analysis of landslides triggered by excess pore water pressure: the roles of atmospheric pressure and rainfall infiltration during typhoons

Abstract. Landslides are often triggered by catastrophic events, among which earthquakes and rainfall are the most depicted. However, very few studies have focused on the effect of atmospheric pressure on slope stability, even though weather events such as typhoons are associated with significant atmospheric pressure changes. Indeed, both atmospheric pressure changes and rainfall-induced groundwater level changes can generate large pore pressure changes. In this paper, we assess the respective impacts of atmospheric effects and rainfall over the stability of a hillslope. An analytical model of transient groundwater dynamics is developed to compute slope stability for finite hillslopes. Slope stability is evaluated through a safety factor based on the Mohr–Coulomb failure criterion. Both rainfall infiltration and atmospheric pressure variations, which impact slope stability by modifying the pore pressure of the media, are described by diffusion equations. The models were then forced by weather data from different typhoons that were recorded over Taiwan. While rainfall infiltration can induce pore pressure change up to hundreds of kilopascal, its effects are delayed in time due to flow and diffusion. To the contrary, atmospheric pressure change induces pore pressure changes not exceeding a few kilopascal, which propagates instantaneously through the skeleton before diffusion leads to an effective decay of pore pressure. Moreover, the effect of rainfall infiltration on slope stability decreases towards the toe of the hillslope and is cancelled where the water table reaches the surface, leaving atmospheric pressure change as the main driver of slope instability. This study allows for a better insight of slope stability through pore pressure analysis, and shows that atmospheric effects should not always be neglected.

Effect of Rainfall Infiltration on the Stability of Compacted Embankments

Effect of Rainfall Infiltration on the Stability of Compacted Embankments

Effect of internal drainage on deformation behavior of GRS wall during rainfall

Global warming-induced changes in the pattern and amount of precipitation are important from the viewpoint of long-term stability of geo-structures. In this paper, the effectiveness of in-plane drainage provided by permeable geosynthetic reinforcement was evaluated as a means to relieve the rainfall infiltration effect on GRS walls backfilled with marginal soil. A series of laboratory tests were performed using a reduced-scale model geosynthetic reinforced soil (GRS) wall (constructed with due consideration of the similitude law) with different rainfall characteristics and backfill soils. Layers of nonwoven geotextiles were used as reinforcement as well as in-plane drainage media. The results showed that the inclusion of internal drainage facilitated the dissipation of pore water pressure, thereby reducing the wall facing displacement. The discharge water volume and volumetric water content data measured in the reinforced soil zone supported the observation. The degree to which the internal drainage improves the deformation behavior of the GRS wall during rainfall was found to depend on the rainfall characteristics and the backfill soil type. Practical implications of the findings are discussed in detail.

From Climate Conditions to the Numerical Slope Stability Analysis of Surface Coal Mines

A new perspective is presented for evaluating the slope stability of coal and lignite mines due to rainfall. The case of Greek lignite mining areas is employed to illustrate the methodology. Initially, past climatic records of rainfall are documented and analyzed; rainfall intensity varies from light (0.8 mm/h) to heavy (up to 9 mm/h). Few extreme phenomena are documented, with the maximum intensity being 17 mm/h. Furthermore, climatic projections of future trends are performed with open-access tools to anticipate possible deviations from the baseline conditions. Although the mean temperature is expected to increase, projections show that the past rainfall range is not expected to change. Finally, the effect of rainfall infiltration on the stability of a typical open-pit lignite mining slope is investigated by finite element analysis. The precipitation range defined by the environmental analysis is used. The SF is practically constant for the lower rainfall intensities (0.8–2.2 mm/h). For the higher intensities of 6.4 mm/h, 9 mm/h, and 17 mm/h, the SF decrease is almost the same (from 2.08 to 1.9), with reduction rates of 8.3%, 8.9%, and 9.3%, respectively. The effect of the critical geotechnical properties—groundwater table depth, unsaturated zone properties, and soil permeability—is also examined for a complete evaluation.

A rainfall event may produce a biased estimation of the indoor vapor intrusion risk through exterior soil-gas sampling

Exterior (i.e., outside the building) soil-gas sampling has been often used to estimate the sub-slab soil-gas concentration and to assess the risk of indoor vapor intrusion. However, the effectiveness of this method can be influenced by rainfall events. In this study, a two-dimensional, water-air two-phase flow numerical model is developed to investigate the effect of rainfall infiltration on the temporal variation of the soil-gas concentration at different depths outside and beneath the building footprint. It is found that rainfall infiltration generally exerts the capping effect and the dilution effect, resulting the increase and decrease in the soil-gas concentration, respectively. Given the soil type of sandy loam, the variation of the shallow and mid-depth soil-gas concentration depends respectively on the rainfall intensity and the total amount of rainwater, while the deep soil-gas concentration is found insensitive to a rainfall event. Moreover, the response timescale of the soil-gas concentration to a rainfall event is larger for a soil type with lower permeability. Considering a rainfall event with the intensity of 4 mm/h and the duration of 24 h, the response timescales of the soil-gas concentration at a depth of 2 m below the ground surface are larger than 1 year for silt loam, sandy clay loam, and sandy loam, and about 5 and 2 months for loamy sand and sand, respectively, where evapotranspiration is not considered. For the soil type of sand, rainfall infiltration can yield a maximum underestimation error of 12%, when using exterior soil-gas sampling to estimate the sub-slab soil-gas concentration. For the relatively less permeable soil type, such as sandy loam, silt loam and sandy clay loam, by contrast, a maximum overestimation error of 8% is found. The results obtained in this study can offer important implications for practitioners to assess the indoor vapor intrusion risk through exterior soil-gas sampling under the rainfall effect.

Seepage and Dynamic Characteristics of Carbonaceous Mudstone Coarse-Grained Soil Embankment with Different Gradations

This study investigates the seepage and deformation characteristics of carbonaceous mudstone coarse-grained soil embankment with different gradations under the action of dynamic load and rainfall. An indoor geotechnical test is conducted, and the mechanical parameters of carbonaceous mudstone coarse-grained soil with different gradations are analyzed. A numerical calculation model of seepage and dynamic characteristics of carbonaceous mudstone coarse-grained soil embankment is established on the basis of the test data. The different effects of rainfall infiltration and vehicle load are evaluated. The seepage, settlement, and slope stability evolution characteristics of graded carbonaceous mudstone coarse-grained soil embankment slope are studied. Results show that under the condition of the same rainfall time, the greater the nonuniformity coefficient, the faster the decrease in pore water pressure of the coarse-grained soil embankment at the same monitoring point. The seepage velocity vector in the embankment is concentrated below the soil shoulder. The smaller the saturated permeability coefficient and saturated water content, the larger the seepage velocity vector. The greater the nonuniformity coefficient, the larger the coarse-grained soil embankment under vehicle load. The smaller the embankment settlement, the lower the safety factor of embankment. The safety factor decreases slowly at first and then decreases rapidly in the whole study period under the effect of dynamic wetting. The research results provide a theoretical reference for the practical engineering application of carbonaceous mudstone coarse-grained soil embankment in rainy areas.

Failure mechanism and stability analysis of bank slope deformation under the synergistic effect of heavy rainfall and blasting vibration

Underwater blasting technique is often adopted to clear away the obstructed reef and dredge-cut in the mountainous waterway dredging engineering. However, the vibration of the underwater blasting and excavation of the riverbed has a certain influence on the stability of bank slopes. Combined with the partial bank collapse phenomenon in the waterway regulation project between two dams in the Three Gorges reservoir area, the change of pore water pressure of unsaturated soil under heavy rainfall and the increase of permanent displacement of soil under blasting vibration in the reservoir area are discussed. This paper explains the weakening effect of rainfall infiltration and blasting vibration on the stability of the bank slope. By studying the law of slope failure deformation under the separate action and coupling action, it is found that rainfall infiltration promotes the increase of slope permanent displacement and the blasting vibration enlarges the infiltration area of the soil, which demonstrated the accelerated failure mechanism of the rainfall-blasting slope.

Coupled hydro-mechanical modelling of soil–vegetation–atmosphere interaction in natural clay slopes

Soil–vegetation–atmosphere interaction has long been known to induce significant pore pressure variations at shallow depths and associated superficial slope movements. Recent findings suggest that the effect of this interaction may also extend to large depths in natural clay slopes. Multiple examples of weather-induced deep landslide mechanisms can be found in the Southern Apennines (Italy), where slopes are often formed of fissured clays. The relationship between the activity of these landslides and the hydro-mechanical processes due to soil–vegetation–atmosphere interaction was investigated herein by means of a two-dimensional coupled hydro-mechanical finite element analysis. A constitutive model capable of simulating the behaviour of highly overconsolidated clays, in both saturated and unsaturated states, was adopted in the analysis, in conjunction with a boundary condition capable of reproducing the combined effects of rainfall infiltration, evapo-transpiration, and run-off. The results of the analysis corroborate the connection between weather conditions, pore pressure variations, and slope movements in natural clay slopes. The importance of adequately reproducing the geological history of a natural slope to define its current state is also demonstrated.

An analysis on the influence of precipitation infiltration on groundwater under different irrigation conditions in the semi-arid area

Abstract The West Liaohe Plain is a typical semi-arid area, where the process of rainfall infiltration to replenish groundwater is a key link in its vertical hydrological cycle. In this paper, we compare and analyze the impact upon soil moisture movement and water infiltration after the shift of irrigation method from flood irrigation to mulched drip irrigation under mulch through setting up in-field in-situ observation points and carrying out groundwater depth dynamic observation. The results show that compared with mulched drip irrigation under mulch, flood irrigation has a stronger response to rainfall infiltration and a quicker response time in the rise of underground depth. With the decrease of groundwater level, the effect of rainfall infiltration to replenish groundwater is significantly weakened. In the flood irrigation area, the groundwater depth at about 8 m already has no obvious response to a small amount of rainfall. However, the groundwater depth at 6 m in the area of mulched drip irrigation under mulch already has no response to rainfall. Therefore, when groundwater extraction is carried out in irrigation areas, reasonable groundwater extraction levels should be designated in light of different irrigation methods to maintain the sustainable utilization of groundwater.

Numerical modelling of coupled seepage-deformation subjected to rainfall infiltration in unsaturated slope

Purpose This study aims to propose another alternative numerical modelling tool, i.e. ABAQUS, to simulate a fully coupled seepage-deformation analysis in unsaturated slope subjected to rainfall infiltration. Design/methodology/approach The effect of rainfall infiltration on the response of pore water pressure and factor of safety has been analysed and discussed. The results of this study have also been validated based on the results of field monitoring and previous numerical modelling. Findings The results from ABAQUS show a better agreement with those from field monitoring compared to other numerical modelling tools. Originality/value The procedures adopted in this study can be adopted and used as a guide to model similar slope problems in ABAQUS.

Research on rainfall infiltration law and slope stability analysis

Rainfall is an important factor leading to slope landslide. Aiming at the problem of slope stability under rainfall, this paper uses the unsaturated seepage theory to dynamically describe the rainfall infiltration effect, and analyzes the distribution characteristics of pore water pressure of slope soil and the change law of slope water level under the action of rainfall, at the same time, deeply analyzes the law of slope stability changes based on strength reduction algorithm. The results show that: with the passage of rainfall time and the increase of rainfall intensity, the slope infiltration depth gradually increased. At the same time, rainfall increased the groundwater level in the slope, and leaded to increased pore water pressure in the slope soil, and the transient saturation zone gradually formed and expanded, and finally leaded to a significant reduction in slope stability coefficient.

Large-Scale Test Model of the Progressive Deformation and Failure of Cracked Soil Slopes

A large-scale test bed (LWH=6 m×3 m×2.8 m) instrumented with various sensors is used to examine the effects of rainfall infiltration and evaporation on the deformation and failure of cracked soil slopes, taking the Anhui area along the Yangtze River as a field example. The results indicate that (1) during rainfall, the soil around the shallow shrinkage fissures attains transient saturation, and the attendant decrease of matric suction is the primary cause of the shallow slope failure; (2) slope deformation continues during post-rainfall evaporation; (3) if a period of evaporation is followed by heavy rainfall, soil creep is concentrated near the deepest cracks, and two zones of steep gradients in pore pressure form at the crest and toe of the slope. Finally, a saturated zone forms near each crack base and gradually enlarges, eventually forming a continuous saturated layer that induces the slope instability or failure.

Analysis of Model Tests of Rainfall-Induced Soil Deposit Landslide

A large number of deposit landslides are induced by rainfall, and those with different weak layers may be subject to catastrophic failure. This research investigates the rainfall infiltration effect on the stability of deposit landslides with a weak layer at different slope angles. Four rainfall physical model tests were conducted with fixed double penetration artificial rainfall technique and dynamic sensor technologies by using the rainfall test methods as modified in the paper. Deformation and mechanics parameters, as well as water content parameters in the key position in the deposit landslide, were monitored by means of various displacement monitoring sensors, dynamic soil pressure sensors, pore water pressure (PWP) monitoring sensors, and water content sensors. The results show that, under the same rainfall conditions, the rule of displacement and mechanical changes of deposit slope with different angles are similar, that the displacement, soil pressure, and PWP are characterized by two stages of rising and falling, and that the displacement of deposit slope with weak layer remains creep after rainfall. In addition, the displacement at the rear edge of the slope with a small angle is larger than that at the front of the steep slope, but the displacement in the front of the slope is opposite. Furthermore, the slope with a smaller angle is prone to form a tensile crack in the back of the slope, and its deformation and failure have the characteristics of a progressive and thrust-type landslide. While the failure in front of a steep slope (slope angle more than 60°) occurred first, the slope failure was characterized by sudden and retrogressive modes. The mathematical analysis of the model is also conducted which shows that deformation and failure can be divided into three stages, i.e., creep inoculation, accumulation uplift, and speed-up sliding. The test results can provide a reference for the investigation, design, and assessment of similar deposit slopes.

Case Study of the Effect of Rainfall Infiltration on a Tunnel Underlying the Roadbed Slope with Weak Inter-Layer

Case Study of the Effect of Rainfall Infiltration on a Tunnel Underlying the Roadbed Slope with Weak Inter-Layer

Analyses and design of steep slope with GeoBarrier system (GBS) under heavy rainfall

A GeoBarrier system (GBS) is a combination system of reinforced soil walls to stabilize near-vertical cut slopes and capillary barrier principles to protect the wall from the effect of rainfall infiltration. Singapore requires construction materials that are cost-effective to support sustainable urban development. Therefore, recycled materials are utilized as GBS materials to avoid the use of high-cost materials, such as steel or concrete. GBS consists of planting geobags with unique geosynthetic pockets for sustainable plant growth as a facing layer of GBS. The negative pore-water pressure (suction) within the reinforced soil behind GBS was assured to be constant during rainfall since GBS is designed specially to minimize the rainfall infiltration into the reinforced soil. This paper presents the practical design and stability analysis of the GBS, considering the presence of suction within the reinforced soil body. The monitoring of GBS performance in the field was carried out via field instrumentation. Finite element analyses of the GBS under extreme rainfalls were also performed for evaluation of the GBS performance. The field instrumentations and numerical analysis results showed that GBS was able to protect the slope from rainfall infiltration; therefore, the stability of the slope retained by GBS was not affected by the rainfall. Results from the analytical calculation showed that the most critical mode of failure is sliding along the base, followed by the global and local slope stability. The GBS is not susceptible to local instability.

The Indoor Model Test on the Characteristic of Expansive Soil Slope under Climatic Conditions

An indoor model of expansive soil filling slope is tested in Pingdingshan city, Henan province, China. Using temperature and humidity detectors, earth pressure cells and so on, the static evaporation - rainfall infiltration cycles are tracked and monitored in the climate condition. The study suggests that atmospheric temperature is the direct cause of soil temperature. Due to the convection heat transfers, the surface temperature of the soil changes rapidly, and the temperature change of the heat transfer to the interior has a hysteresis phenomenon. Under surface evaporation conditions, the greater the depth is, the smaller the change range is in water content. Water loss rate is related to soil, air flow, temperature and humidity, cracks, soil water holding capacity, permeability and other factors. The change of stress in the expansive soil slope is the result of the joint action of soil water content, nature and climatic conditions. Due to the early erosion of rainfall, soil pressure is obviously attenuated. The soil pressure is on the rise due to the effects of rainfall infiltration and expansion force in the late rainfall. In the engineering, the key to prevent and cure engineering disaster of expansive soil is to improve the deformation characteristics and reasonable drainage of expansive soil.

A review on mechanism of rainwater in triggering landslide

Landslide could be evaluated as a very serious issue in tropical countries due to its hazardous impact on lives and properties. One of the factors influencing to the development of landslides is the rainfall infiltration which is considered as a major triggering factor. It decreases the matric suction, increases the pore-water pressure and causes the groundwater table to rise. This paper is reviewing the mechanism of rainfall induced slope failure, the effect of rainfall infiltration, soil suction and the rise of groundwater table on slope stability. The results show high rainfall intensity infiltrates initially in a higher rate than soil permeability and develops a perched water table which induces shallow landslide. While, low rainfall intensity for a longer period is more dangerous than heavy rain for a short period. It increases the saturation of the soil and causes the matric suction to dissipate and this triggers landslide. Moreover, the review reveals that the factor of safety increases when the initial soil suction at the ground surface is high. The rise of groundwater increases the pore-water pressure and soften the slope-forming material and leads to landslide.

Effect of Rainfall Infiltration on Deformation of Geobarrier Wall

GeoBarrier system (GBS) is a system that combines geobag wall with capillary barrier concept as stabilization method against rainfall-induced failure, and vegetation as green cover. This paper presents deformation behaviour of a GBS wall constructed as pilot study when subjected to rainfall infiltration. The GBS wall was 4 m high with 70° slope angle. The wall was subjected to uniform surcharge of 10 kN/m2 and rainfall of 22 mm/h for 8 h. Recycled materials were used as components of the capillary barrier. Coupled deformation-seepage finite element analyses were carried out to evaluate the stress and pore-water pressure variations within and behind the GBS wall during and after rainfall. Limit equilibrium analyses were performed at various stages during and after rainfall to assess the near vertical wall stability. The results of the coupled deformation seepage analysis showed that the reinforced zone in the GBS remained unsaturated during rainfall, indicating that the GBS wall performed well in minimizing the rainwater infiltration. However, the GBS wall face deformation pattern altered during and after rainfall, indicating that the rainfall infiltration increased the lateral stress on the top part of the wall. The variation of lateral stress with depth agrees with field measurements from earth pressure cells.