Increase In Pore Water Pressure Research Articles

Experimental soft‐sediment deformation caused by fluidization and intrusive ice melt in sand

AbstractIdentifying the driving mechanisms of soft‐sediment deformation in the geological record is the subject of debate. Thawing of ice‐rich clayey silt above permafrost was proved experimentally to be among the processes capable of triggering deformation. However, previous work has failed so far to reproduce similar structures in sand. This study investigates fluidization and intrusive ice formation from soil models in the laboratory. Experimental conditions reproduce the growth of ice‐cored mounds caused by pore water pressure increase during freeze‐back of sand in a permafrost context. Excess pore water pressure causes hydraulic fracturing and the development of water lenses beneath the freezing front. Later freezing of the water lenses generates intrusive ice. The main structures consist of sand dykes and sills formed when the increase in pore water pressure exceeds a critical threshold, and soft‐sediment deformations induced by subsidence during ice melt. The combination of processes has resulted in diapir‐like structures. The experimental structures are similar to those described in Pleistocene sites from France. These processes constitute a credible alternative to the seismic hypothesis evoked to explain soft‐sediment deformation structures in other European regions subjected to Pleistocene cold climates.

A numerical study on Flow Regime Process of Liquefiable Cargo based on Finn Constitutive Model

The safe transportation of liquefiable cargo is an important topic in the research on modern transportation safety of watercraft. The current study on this topic is mainly focused on the research after the liquefiable occurs. A numerical analysis model for the liquefiable of flowing particles is established using the Finn liquefiable constitutive relation, and the kinetic equation analysis module of finite difference method is adopted to analyze the liquefiable problem. The result shows that applying the Finn constitutive model to the analysis of liquefiable of flowable cargo can better predict the increase of pore water pressure and decrease of effective stress under the action of external load.

A force transfer mechanism for triggering landslides during rainfall infiltration

Shallow slope failures induced by rainfall infiltration occur frequently, and the relevant triggering mechanisms have been widely studied. Rainfall-induced landslides are widely recognized to be caused by increases in soil weight, seepage force and pore water pressure or decreases in soil mechanical properties. However, even when all these factors are considered, some landslides still cannot be explained well. The increased pore water pressure in a slope reduces the effective stress of the soil and may trigger slope failure. Similarly, the pore gas pressure in a slope also reduces the effective stress of the soil but has been neglected in previous studies. As the viscosity of air is nearly negligible when compared with that of water, the pore gas pressure spreads faster, and its influence is wider, which is harmful for the stability of the slope. In this paper, the effects of pore gas pressure are considered in a shallow slope stability analysis, and a self-designed experiment is conducted to validate the force transfer mechanism. Numerical simulation results show that the pore gas pressure in the slope increases sharply at different locations under heavy rainfall conditions and that the pore gas pressure causes a rapid decrease in the slope safety factor. Laboratory experimental results show that the pore gas pressure throughout the whole unsaturated zone has the same value, which indicates that the gas pressure could spread quickly to the whole sample.

Effects of principal stress rotation on stress–strain behaviors of saturated clay under traffic–load–induced stress path

A series of cyclic torsional shear tests using hollow cylinder apparatus (HCA) were performed to investigate the effect of principal stress rotation (PSR) on the stress–strain behaviors of saturated soft clay. The traffic–load–induced shear stress path was used in the cyclic test and the investigation mainly concerned the influence of PSR on the shear stiffness and non-coaxiality. It indicated that the effects of PSR substantially depends on the magnitude of deviatoric stress (q = {[(σ1 − σ2)2 + (σ2 − σ3)2 + (σ1 − σ3)2]/2}1/2) as well as the intermediate principal stress ratio (b = (σ2 − σ3)/(σ1 − σ3)). At low deviatoric stress, the trajectory envelope of deviatoric strain path translates with a nearly constant size, showing constant shear stiffness and strong non-coaxiality. However, at high deviatoric stress, the trajectory envelope of deviatoric strain rapidly expands towards instability, showing degenerating shear stiffness and weak non-coaxiality. Moreover, the excess pore water pressure increases and the shear stiffness decreases more rapidly as b value increases. The results can provide an experimental basis for constitutive modelling of clays under traffic–induced loadings.

Variation behavior of pore-water pressure in warm frozen soil under load and its relation to deformation

Containing a considerable amount of unfrozen water, frozen soil may produce excess pore-water pressure under external load, especially at temperatures near the thawing point. The variation of the pressure has a capability in influencing the deformation of frozen soils. In order to investigate the variation behavior of pore-water pressure in frozen soils and its relation to deformation, a series of pore-water pressure tests were conducted at subzero temperatures. A total of 13 frozen specimens were tested at various temperatures, and the pore-water pressures as well as the displacement were recorded. Then, variation behaviors of pore-water pressures and their effect on deformation were discussed. Results indicated that when a frozen soil sample is subjected to load, it responds with a slow increase in pore-water pressure in the early test stage up to a peak value, followed by subsequent extremely slow dissipation. The characteristic of pore-water pressure variations recorded in this study are closely correlated with temperature, soil type, and moisture content. Generally, the variation in pore-water pressure in frozen soils is caused by the coupled action of two opposing processes: an increasing process induced by solid matrix compression and a decreasing process induced by unfrozen water drainage. Thus, consolidation can be shown to occur as a component of compression and plays a significant role in the total deformation of warm frozen soils, although this effect decreases as decreasing soil temperature. However, it is difficult to distinguish the consolidation deformation from the creep deformation when taking into account the continuous variation in pore-water pressure throughout the test period.

Simulation Assessment of Direct Push Injection Logging for High-Resolution Aquifer Characterization.

Direct push injection logging (DPIL) has become one of the most widely used approaches for obtaining vertical profiles of hydraulic conductivity (K) in environmental site investigations. Despite its widespread use, however, there has been no rigorous analysis of the underlying physical processes that take place during DPIL or how the approach would perform under different hydrogeological and operating conditions. We address these issues through a series of numerical simulations. Results show that the ratio of DPIL injection rate over pressure can be used for direct determination of K when K is >10-6 m/s. When K is <10-6 m/s and specific storage (Ss) is >10-3 /m, the ratio becomes increasingly sensitive to Ss; in that case, additional information on Ss is needed for reliable K estimation. For unconsolidated formations of moderate K or higher, the ratio of injection rate over pressure should provide a reasonable K estimate when Ss is <10-3 /m. Although water injection at previous depths during continuous DPIL has only a small impact on the pressure response measured at the current injection depth, probe advancement can have a significant impact when K and Ss are small. Consequently, in fine-grained materials, the advancement-generated pore water pressure increase can comprise a large portion of the measured pressure response. To diminish the impact of probe advancement in such materials, advancement speed should be kept as low as possible (e.g., 0.5cm/s).

Effects of capillary fringe and truncation factor on pore-water pressure and water table variation in dewatering and watering sand column experiments

Abstract Spatiotemporal variations of the pore-water pressure and water table response to small amounts of water exchange were measured in a sand column. In the dewatering experiment, the pressure head variation can be divided into three stages: the initial pressure head declining phase when water table is above the sand surface, a sudden drop in accordance with the capillary fringe when water level passes through the sand surface, and a slow declining phase with respect to the specific yield of the sand. As for the watering experiment of the shallow groundwater with different initial truncation factors (TF), the addition of a minute amount of water results in a rapid rise of the pressure head initially, then a gradually increase to its equilibrium. When the upper extent of the fully saturated capillary fringe coincides with the sand surface (TF ≤ 1), a thin film of water addition produces nearly instantaneous increase in pore-water pressure, corresponding to a rapid rise of groundwater table to the sand surface. Pressure head increment increases linearly with the TF value and reaches its maximum when TF value approaches unity. Considering the vertical distribution of the pressure head, its gradient becomes larger right after the water addition, then decreases to its initial value of hydrostatic condition in the end. In the case of TF > 1, there is an unsaturated layer above the groundwater table, the pressure head increases after the water addition, whose magnitude however decreases as the increase of TF value. Nevertheless, the final position of the groundwater table is still below the sand surface, and the gradient of the pressure head vertical distribution dose not vary significantly throughout the entire process. In consideration of hydrostatic pressure assumption, temporal variation of the water table was also quantitatively obtained based on the measured instantaneous pore-water pressure data, which is consistent with time-varying process of the pressure head during both the dewatering and watering experiments.

Mechanisms leading to the 2016 giant twin glacier collapses, Aru Range, Tibet

Abstract. In north-western Tibet (34.0∘ N, 82.2∘ E) near lake Aru Co, the entire ablation areas of two glaciers (Aru-1 and Aru-2) suddenly collapsed on 17 July and 21 September 2016. The masses transformed into ice avalanches with volumes of 68 and 83×106 m3 and ran out up to 7 km in horizontal distance, killing nine people. The only similar event currently documented is the 130×106 m3 Kolka Glacier rock and ice avalanche of 2002 (Caucasus Mountains). Using climatic reanalysis, remote sensing, and three-dimensional thermo-mechanical modelling, we reconstructed the Aru glaciers' thermal regimes, thicknesses, velocities, basal shear stresses, and ice damage prior to the collapse in detail. Thereby, we highlight the potential of using emergence velocities to constrain basal friction in mountain glacier models. We show that the frictional change leading to the Aru collapses occurred in the temperate areas of the polythermal glaciers and is not related to a rapid thawing of cold-based ice. The two glaciers experienced a similar stress transfer from predominant basal drag towards predominant lateral shearing in the detachment areas and during the 5–6 years before the collapses. A high-friction patch is found under the Aru-2 glacier tongue, but not under the Aru-1 glacier. This difference led to disparate behaviour of both glaciers, making the development of the instability more visible for the Aru-1 glacier through enhanced crevassing and terminus advance over a longer period. In comparison, these signs were observable only over a few days to weeks (crevasses) or were absent (advance) for the Aru-2 glacier. Field investigations reveal that those two glaciers were underlain by soft, highly erodible, and fine-grained sedimentary lithologies. We propose that the specific bedrock lithology played a key role in the two Tibet and the Caucasus Mountains giant glacier collapses documented to date by producing low bed roughness and large amounts of till, rich in clay and silt with a low friction angle. The twin 2016 Aru collapses would thus have been driven by a failing basal substrate linked to increasing pore water pressure in the subglacial drainage system in response to increases in surface melting and rain during the 5–6 years preceding the collapse dates.

An Improved Data-Driven Approach for the Prediction of Rainfall-Triggered Soil Slides Using Downscaled Remotely Sensed Soil Moisture

The infiltration of rainwater into soil slopes leads to an increase of porewater pressure and destruction of matric suction, which causes a reduction in soil shear strength and slope instability. Hence, surface moisture and infiltration properties must be direct inputs in reliable landslide hazard assessment methods. Since the in situ measurement of pore pressure is expensive, the use of remotely sensed soil moisture is practically feasible. Downscaling improves the spatial resolution of soil moisture for a better representation of specific local conditions. Downscaled soil moisture, the relevant geotechnical properties of saturated hydraulic conductivity and soil type, and the conditioning factors of elevation, slope, and distance to roads are used to develop an improved logistic regression model to predict the soil slide hazard of soil slopes using data from two geographically different regions. A soil moisture downscaling model with a better accuracy than the downscaling models that have been used in previous landslide studies is employed in this study. This model provides a good classification accuracy and performs better than the alternative water drainage-based indices that are conventionally used to quantify the effect that elevated soil moisture has upon the soil slide hazard. Furthermore, the downscaling of soil moisture content is shown to improve the prediction accuracy. Finally, a technique that can provide the threshold probability for identifying locations with a high soil slide hazard is proposed.

LIQUEFACTION SIMULATION FOR THE OSAKA GULF COAST USING THE LIQCA PROGRAM

A Nankai megathrust earthquake is expected to occur in the Kansai area within the next 30–40 years. According to the worst-case estimations by The Headquarters for Earthquake Research Promotion [1], the earthquake will cause economic losses of approximately 220 trillion yen, and 134,000 buildings will be damaged by liquefaction. To estimate future damage to the Osaka gulf coast, we conduct liquefaction simulations based on the LIQCA program developed by the research group at Kyoto University. The liquefiable layers are composed of relatively loose sand and the underground water level is high. The input earthquake motion is the L2 spectrum Ⅰ earthquake-resistant standard spectrum, according to the Design Standards for Railway Structures and Commentary [2]. We consider not only the increase of excess pore water pressure, but also its dissipation. The calculated effective stresses in the sand layers approached 0, after which the sand layers liquefied and unevenness occurred at the ground surface. We evaluated the damage due to liquefaction by calculating vertical displacements and unevenness of the ground surface. Countermeasures are proposed for the shallow sand layers to reduce future liquefaction damage.

The response of pore water pressure to snow accumulation on a low-permeability clay landslide

A snowpack is known to affect landslide stability as the snow loading changes. Furthermore, the snowpack can have effects on the hydrological behavior in the landslide mass. To clarify the response of pore water pressure to snow loading, continuous field-based monitoring of hydraulic and meteorological factors in landslides was conducted for a deposit of extremely low-permeability “quick clay” in Mid-Norway. The pore water pressure increased during every snow-covered period. The pressure exhibited little response to meltwater and/or rain, but corresponded closely to changes in snow accumulation. The increase in pore water pressure during the snow-covered period was considered to be excess pore water pressure generated by undrained snow loading on the extremely low-permeability quick clay. The pore water pressure displayed a positive linear relation with the snow load, and the ratio of the increase in the pore water pressure to the snow load (rusnow) was 0.49–0.53. These values show that approximately half of the snow load contributed to the excess pore water pressure. Continuous field-based monitoring was also conducted for another landslide in relatively high-permeability deposits in Japan, where the pore water pressure showed a relatively low rusnow of about 0.15 and a different timing of the pressure peak. This comparative result indicates that the response characteristics of pore water pressure to the snow loading are strongly affected by the permeability of the landslide mass. Although the excess pore water pressure generated by the snow load theoretically had a negative effect on the slope stability, the value of excess pore water pressure at the monitored landslide was relatively too small to affect its stability.

How to avoid permafrost while depositing tailings in cold climate

Managing tailings deposition in cold climate requires specific measures not to create permafrost. The risk of generating permafrost due to tailings deposition exists even in regions where permafrost would naturally not occur. Material being frozen during winter might not fully thaw in the following summer due to added height of the tailings on the surface. Such embedded layers of permafrost should be avoided especially close to tailing dams. Main reasons are to prevent impermeable layers in tailings facilities, and to reduce the risk of having implications if such layers thaw during warmer summers causing increase in pore water pressure, reduced effective stress, and increased water content.This paper presents a numerical study on the effects of tailings deposition in cold regions in relation to the potential formation of permafrost. Various deposition rates, schedules and tailings properties were evaluated. One-dimensional heat conduction analyses were performed with a temperature scenario representing a mine district in northern Sweden. Results show, that the thickness of permafrost layers increase with increased deposition rate and with increased water content. It was also shown that wet and loose tailings must be deposited in short periods during summer to avoid permafrost generation. In the case of dry and dense tailings more time is available for deposition in order not to cause aggradation of permafrost in the deposit.These findings can help mining operation to set up deposition schedules for tailings facilities in cold climate. For known tailings properties, results can be used to identify periods of the year when, and how much, tailings can be deposited in critical areas of a deposit in order to avoid permafrost formation.

Monitoring of a Full-Scale Embankment Experiment Regarding Soil–Vegetation–Atmosphere Interactions

Slope mass-wasting like shallow slides are mostly triggered by climate effects, such as rainfall, and soil–vegetation–atmosphere (SVA) interactions play a key role. SVA interactions are studied by a full-scale embankment with different orientations (North and South) and vegetation covers (bare and vegetated) in the framework of the prediction of climate change effects on slope stability in the Pyrenees. A clayey sand from the Llobregat river delta was used for the construction of the embankment and laboratory tests showed the importance of suction on the strength and hydraulic conductivity. Sixty sensors, which are mostly installed at the upper soil layer of the embankment, registered 122 variables at four vertical profiles and the meteorological station with a 5 min scan rate. Regarding temperature, daily temperature fluctuation at the shallow soil layer disappeared at a depth of about 0.5 m. There was great influence of orientation with much higher values at the South-facing slope (up to 55 °C at −1 cm depth) due to solar radiation. Regarding rainfall infiltration, only long duration rainfalls produced an important increase of soil moisture and pore water pressure, while short duration rainfalls did not trigger significant variations. However, these changes mostly affected the surface soil layer and decreased with depth.

Cyclic threshold shear strain in pore water pressure generation in clay in situ samples

The threshold level of the cyclic shear strain required for pore water pressure generation in clay samples is examined through the results of torsional hollow cylinder cyclic shearing tests according to JGS 0543-2009. The study confirms the previous results, namely, that the threshold cyclic shear strain is dependent on the effective consolidation stress and plasticity index (Ip). The average and standard deviations in the estimated threshold strain levels are 0.038 ± 0.023% (Ip < 30, σ′c ≦ 100 kN/m2), 0.047 ± 0.016% (Ip < 30, σ′c > 100 kN/m2), 0.079 ± 0.028% (30 ≦ Ip < 5 0), and 0.143 ± 0.041% (Ip ≧ 50). As was found in past research, the levels of threshold strain for pore water pressure generation for clay are larger than those for clean sand. An increase in pore water pressure is only observed when the stiffness is reduced to around 80% of its initial value. This delay occurs because there is a difference between the cyclic threshold strain of the pore water pressure generation, γtp, and the cyclic threshold strain of the stiffness degradation, γtd. Since the test procedure of JGS 0543-2009 is a standard scheme in the practical design process, it is expected that more data will become available in the near future which will allow for further discussions on threshold strain.

Slurry Shield Tunneling: New Methodology for Simplified Prediction of Increased Pore Pressures Resulting from Slurry Infiltration at the Tunnel Face Under Cyclic Excavation Processes

Within mechanized tunneling, slurry shields are used for excavations in soils with unstable tunnel face due to the possibility to support the tunnel face with pressurized slurry (bentonite suspension). Two key conditions have to be fulfilled to stabilize a tunnel face. These two conditions are sufficient face support pressure in the excavation chamber and the pressure transfer of slurry excess pressure, exceeding the pore pressure, onto the soil skeleton. In practice, the German standard DIN 4126 [Nachweis der Standsicherheit von Schlitzwanden (Stability analysis of diaphragm walls), Deutsche Institut fur Normung, 2013] is usually used to predict this transfer. However, DIN 4126 (2013) cannot explain increased pore water pressures measured in practice close to the slurry supported tunnel face during excavation. The increased pore water pressures reduce the efficiency of slurry face support. These pressures are explained by on-going disturbance of the pressure transfer mechanism by periodic rotating cutting tools. The characteristics of disturbance are designated as excavation scale. Another factor of influence is the timespan during which the pressure transfer mechanism can achieve a significant decrease in its own permeability, and thereby to decrease considerably the flow through the tunnel face. By scale comparison of these two processes, a prognosis about occurrence of increased pore water pressures in saturated sands can be derived. It turns out that the different combinations of penetration rate and revolutions per minute of the cutting wheel, while keeping the advance rate constant, would result in different chance for causing increased pore pressures. Consequently, an excavation strategy for reducing the chance for increased pore pressures is suggested with respect to three reference slurry shields.

A study on a instability slope in Taiwan subjected to rainfalls

After the long-term monitoring on the Chaishan area in Taiwan from 2005 to 2012 by Kaohsiung City Government, the obtained results showed that annual lateral displacements in the region are about 7-8cm to the Taiwan Strait. The geological surface profiles of Chaishan area are in sequence weathered limestone, clay layer, limestone and mudstone layer, respectively. Thus the frictional resistance between weathered soils and rock layer could decrease after infiltration of rainwater due to impervious to water of the lowest mudstone layer. Typhoon invades often Taiwan each year, resulting in rainfall infiltration and rising groundwater level, as well as increased pore water pressure within the soil mass, causing the earth movements in some parts of Chaishan, especially in the Temple A (Shan Hai Temple) accompanied with cracking phenomenon. In this paper, limit equilibrium (LE) and finite element method (FEM) are used for slope analysis, in which the slope is considered as unsaturated soil. Results showed groundwater amounts are easy to accumulate and increasing pore water pressure give resulting in decreased safety factor. Both of groundwater level and rain durations were also considered in this study.

3D effects of turning corner on stability of geosynthetic-reinforced soil structures

Current design procedures of Geosynthetic-Reinforced Soil Structures (GRSS's) are for walls/slopes with long straight alignments. When two GRSS segments intersect, an abrupt change in the alignment forms a turning corner. Experience indicate potential instability problems occurring at corners. The purpose of this study is to explore the effects of turning corner on the stability of reinforced slopes. Three-dimensional (3D) slope stability analysis, based on limit equilibrium, resulted in the maximum tensile force of reinforcement. Parametric studies required numerous computations considering various geometrical parameters and material properties. The computed results produced efficient practical format of stability charts. For long-term stability of reinforced slopes with turning corner, the influences of pore water pressure and seismic loading are also considered. Turning corner can improve the stability of reinforced slopes by virtue of inclusion of end effects. However, localized increase of pore water pressure or directional seismic amplification may decrease locally thus stability requiring strength of reinforcement larger than in two-dimensional (2D) plane-strain. While using 2D analysis for non-localized conditions may require stronger reinforcement, it also requires shorter reinforcement than in 3D analysis; i.e., 2D analysis may be unconservative in terms of reinforcement length.

The March 25 and 29, 2016 landslide-induced debris flow at Clapar, Banjarnegara, Central Java

The Clapar landslide induced debris flow consisted of the Clapar landslide occurred on 24 March 2017 and the Clapar debris flow occurred on 29 March 2017. The first investigation of the Clapar landslide induced debris flow was carried out two months after the disaster. It was followed by UAV mapping, extensive interviews, newspaper compilation, visual observation and field measurements, and video analysis in order to understand chronology and triggering mechanism of the landslide induced debris flow in Clapar. The 24 March 2016 landslide occurred after 5 hours of consecutive rainfall (11,2 mm) and was affected by combination of fishponds leak and infiltration of antecedent rain. After five days of the Clapar landslide, landslide partially mobilized to form debris flow where the head scarp of debris flow was located at the foot of the 24 March 2016 landslide. The Clapar debris flow occurred when there was no rainfall. It was not generated by rainstorm or the surface erosion of the river bed, but rather by water infiltration through the crack formed on the toe of the 24 March 2016 landslide. Supply of water to the marine clay deposit might have increased pore water pressure and mobilized the soil layer above. The amount of water accumulated in the temporary pond at the main body of the 24 March 2016 landslide might have also triggered the Clapar debris flow. The area of Clapar landslide still shows the possibility of further retrogression of the landslide body which may induce another debris flow. Understanding precursory factors triggering landslides and debris flows in Banjarnegara based on data from monitoring systems and laboratory experiments is essential to minimize the risk of future landslide.

On the reactivation of a large landslide induced by rainfall in highly fissured clays

The paper discusses the field investigations, geotechnical characterization and time evolution of horizontal displacements in a wide landslide. The latter, triggered by an earthquake occurring in September 2002, is located in Sicily and involves a thick body of stiff and highly fissured clays belonging to a Varicoloured Clay formation. In order to characterise the reactivation of landslide mechanisms induced by rainfall, a three-year monitoring programme (2008–2011) was implemented to measure rain, pore water pressures, and deep and superficial displacements. The monitoring data made it possible to recognize three distinct landslides, which evolve at variable rates in different directions, within the overall landslide area. The landslides were reactivated by the increase in pore water pressures in the period autumn 2009–spring 2010. The data clearly show the mechanical role of pore water pressures in the stability of the slope and point out the dependence of the time evolution of the horizontal displacement on the pore water pressure variation induced by rainfall. Back-analysis carried out on the single landslides confirmed that they are reactivated ones since the residual shear strength is mobilised on the pre-existing sliding surfaces. The pore water pressure variation and the landslide body displacement rates can be effectively related to 5-month cumulative rainfall by simple models, characterised by three parameters. These models, calibrated on the period October 2009–September 2010, made it possible to predict the horizontal displacement rates in the ensuing time period. The displacements forecasted by the model in the period September 2010–May 2011 agree very well with the measured ones.

Probabilistic Analysis of Cut-Slope Stability for Tropical Red Clay of Depok, West Java as an Effect of Rainfall Duration and Intensity

Landslide in Indonesia, specifically in Java island, occurs during rainy seasons. In Java island, it is known that the tropical red clay has the ability to stand at steep angles, while in stability analysis due to rainfall, practitioners only consider the rise of groundwater table. Previous studies states that one of the factor affecting factor of safety (FS) for tropical red clay slopes is the formation of saturated zones due to matric suction. This research studies the effect of rainfall intensity and duration to FS of cut-slopes as parametric study with probabilistic analysis for different height of 10m, 20m, and 30m also slope angles of 27°, 45°, 55°, and 70°. Rainfall parameter are taken from FTUI rainfall station for advanced pattern and three-days duration of rain. Analysis of seepage uses SEEP/W and slope stability uses SLOPE/W. It is known that the significant increase of probability of failure due to the three-days rainfall is achieved at the 10m height and 70°-angled slope. Increase of the probability of failure is mainly due to rainfall infiltration which saturates the surface and pore water pressure increase until certain time where infiltration stops and turn into surface run-off.