Rise In Pore Water Pressure Research Articles

Application of Capillary Barrier Systems for Slope Stabilization Under Extreme Rainfall: A Case Study of National Highway 10, India

Global warming has led to an increase in extreme rainfall events, which often result in landslides, posing significant threats to infrastructure and human life. This study evaluated the effectiveness of the Capillary Barrier System (CBS) in enhancing slope stability along a vulnerable section of India’s National Highway 10 (NH10) during maximum daily rainfall. The GEOtop model was employed to conduct water balance simulations and obtain the pore–water pressure (PWP), which was then used to calculate the Factor of Safety (FoS). Results showed that CBS effectively delayed the rise in PWP, leading to lower peak values and smaller areas of very high and high risk levels. Spatial distribution mapping further confirmed that CBS minimized very high risk zones. At three historical landslide points, CBS slopes generally maintained FoS values above 1, demonstrating enhanced stability and improved resilience to extreme rainfall. These findings highlight the potential of CBS as a viable strategy for slope reinforcement in regions susceptible to heavy rainfall.

Experimental Study on Erosion Process of Expressway Embankment Subjected to Tsunami After Earthquake

On March 11, 2011, the Great East Japan Earthquake triggered tsunamis that reached extensive areas along Japan’s Pacific coast. There have been instances where embankments built on plains for expressways mitigated the impact of tsunami damage. In the vicinity of the Sendai-tobu highway, the presence of an embankment approximately 10 m high altered the course of the advancing tsunami, thereby preventing flooding. Establishing a multiplied defense system using road embankments necessitates understanding the deformation and collapse mechanisms of road embankments impacted by tsunamis following seismic motion. In this study, overtopping experiments were conducted by first applying seismic motion to model embankments, followed by introducing the first wave of breaking bores, and then simulating prolonged overtopping by the tsunami. The experimental findings indicated that within the embankments impacted by the tsunami, there was an immediate increase in what is presumed to be pore air pressure following the arrival of the breaking bores, followed by a rise in pore water pressure during subsequent overtopping. Moreover, embankments subjected to seismic motion exhibited accelerated erosion following the overtopping. These results imply that when embankments settle due to an earthquake, leading to relatively higher anticipated inundation depths and the potential for overtopping, it is crucial to implement measures to prevent the settlement of the crest for embankments expected to serve as part of a multiplied defense system.

Effects of temperature on the time-dependent compression and shear behaviour of a soft marine clayey soil

The thermal effects on geomaterials, especially on clayey soils are getting increasing concerns in many geotechnical applications. To study the effects of temperature on the stress-strain behaviour of Hong Kong marine deposits (HKMD), a series of temperature-controlled experiments were carried out. Oedometer and constant-rate-of-strain consolidation tests under temperatures from 10 °C to 60 °C were conducted on both intact and reconstituted HKMD considering different temperatures and stress paths. The effects of temperature history on the compression curves, thermally induced strain, and the characteristics of creep are revealed and discussed. The concept of virgin heating is proposed for interpreting the thermal plastic deformation. With increasing temperature, the creep coefficient is found to decrease while the creep strain rate increases. Consolidated undrained triaxial tests were performed on intact and reconstituted HKMD under different strain rates and temperature conditions. Under constant temperature, the undrained shear strength of HKMD is not significantly influenced by temperature. In triaxial tests subjected to step-changed temperature, the undrained heating causes a significant reduction of effective stress and rise of porewater pressure in HKMD. Finally, microscopic investigations with mercury intrusion porosimeter and scanning electron microscope are presented and discussed in this paper. It is found that the micropores of HKMD are evolutional with temperature.

Analysis of Liquefaction Potential of Soils in Guntur Region (CRDA)

In earthquake-prone areas that are susceptible, liquefaction is a severe natural hazard. Due to a rise in pore water pressure, soil liquefaction happens Due to the reduction in strength and stiffness of saturated and cohesion-less soil. By being rapidly loaded or shaken during an earthquake, soil can occasionally lose part of its strength. Liquefaction results in soil failures, which severely harm buildings supported on such grounds and incur large economic losses. Regarding the protection of both life and property, study of liquefaction potential is crucial. The aim of the study is to assess the liquefaction potential in the Guntur region. Understanding the liquefaction mechanism is necessary for a methodical approach to the improvement of capacities to evaluate the liquefaction potentiality of soil deposits & earth structures. So, utilizing the information from the (SPT), liquefaction analysis is done utilizing the strategy of the simplified approach described by Seed and Idriss. It is possible to determine a number of parameters, including reduction factor, cyclic stress ratio (CSR), cyclic resistance ratio (CRR), and liquefaction potential index. More detailed studies can be done by using software to acquire more accuracy.

An experimental investigation into the evolving instability of a subaqueous mild silty slope under progressive waves

The silty sediments that are widely distributed in estuaries and deltas are susceptible to slope instability due to ocean storms. Flume experiments were carried out in this study to investigate the characteristics and failure process of a subaqueous mild silty slope subjected to ocean waves. The results show that the wave steepness varies accordingly to wave propagation over the mild silty slope due to shoaling effect. Where the wave steepness is up to the threshold value of 0.04, liquefaction may occur in silty slopes due to the substantial amount of residual pore water pressure development. In this process, the maximum wave pressure appears near the wave breaking point where it may be increased by about 40% compared with that at bottom of the slope; this means that liquefaction may primarily first occur in regions near the wave breaking point and become the predominant trigger for the overall slope instability. The maximum liquefaction and sliding depth of silty seabed may reach 0.1–0.15 times the wavelength for wave steepness of 0.04–0.10. Unlike the failures of a loose sandy slope that are characterized by a slumping stage along with a sudden rise in pore water pressure, wave induced failure of the mild silty slope progresses in three distinct stages, i.e., (i) initial erosion and scouring, (ii) coupled development of liquefaction and scour, and (iii) oscillating and sliding of sediments.

Geotechnical Issues in Decommissioning Surface Lignite Mines—The Case of Amyntaion Mine in Greece

Recent changes in the fossil-fuel energy sector require coal mining industries to plan for the future, including developing procedures for decommissioning and closure associated with mines. In surface coal mining, the geotechnical issues of decommissioning include the long-term stability of the pit slopes, particularly as the pit is gradually filled with water. This paper investigates such slope stability issues, with emphasis on the conditions prevailing in the Amyntaion surface lignite mine, in Western Macedonia, Greece. Analytical and numerical methods have been developed and used to estimate the temporal evolution of the overall safety factor, as the water level in the pit rises, creating a lake. It is shown that until the water level in the lake reaches a critical depth of approximately 15–35% of the final equilibrium condition, the safety factor against the overall slope instability decreases slightly (by about 3% in the case study, and up to 5–10% in other conditions) compared to its value at the end of exploitation. At higher lake levels, the safety factor increases significantly, as the beneficial effect of the lake water pressure acting on the slope overcomes the adverse effect of pore water pressure rise inside the slope. In typical mines, the critical water depth is achieved within a few years, since the surface area of the pit is smaller at deeper levels; thus, more favorable slope stability conditions are usually reinstated a few years after mine closure, while the small reduction in safety during the initial stages after closure is inconsequential. The paper investigates the parameters influencing the magnitude of the small reduction in the short-term safety factor and produces normalized graphs of the evolution of the safety factor as the lake water level rises. The results of the analyses can be used in preliminary closure studies of surface coal mines.

Characteristics of Rainfall-Induced Slope Instability in Cisokan Region, Indonesia

A 25.5 km long access road has been constructed in a hilly area in Cisokan region. Several slope instabilities occurred during the rainy season, particularly at the end of heavy rainfall. A comprehensive study was performed to understand the characteristics of rainfall-induced slope instability. The study consisted of field observation, analyses of field and laboratory test data, and numerical analyses. The study revealed that in general there were two categories of slopes with instability characteristics: (i) slopes with a significant groundwater level increase during rainfall; (ii) slopes with an insignificant groundwater level increase during rainfall. In the first category, the slope instability was caused by a loss of matric suction and eventually the pore-water pressure, uw became positive as indicated by an increase of the groundwater level. In the second category, the slope instability was caused by a loss of matric suction without a rise in pore-water pressure, uw, to a positive magnitude. Two empirical curves of slope stability were developed as a preliminary guidance to assess slope stability during rainfall in the region.

Unsaturated Flow Processes and the Onset of Seasonal Deformation in Slow‐Moving Landslides

AbstractPredicting rainfall‐induced landslide motion is challenging because shallow groundwater flow is extremely sensitive to the preexisting moisture content in the ground. Here, we use groundwater hydrology theory and numerical modeling combined with five years of field monitoring to illustrate how unsaturated groundwater flow processes modulate the seasonal pore water pressure rise and therefore the onset of motion for slow‐moving landslides. The onset of landslide motion at Oak Ridge earthflow in California’s Diablo Range occurs after an abrupt water table rise to near the landslide surface 52–129 days after seasonal rainfall commences. Model results and theory suggest that this abrupt rise occurs from the advection of a nearly saturated wetting front, which marks the leading edge of the integrated downward flux of seasonal rainfall, to the water table. Prior to this abrupt rise, we observe little measured pore water pressure response within the landslide due to rainfall. However, once the wetting front reaches the water table, we observe nearly instantaneous pore water pressure transmission within the landslide body that is accompanied by landslide acceleration. We cast the timescale to reach a critical pore water pressure threshold using a simple mass balance model that considers variable moisture storage with depth and explains the onset of seasonal landslide motion with a rainfall intensity‐duration threshold. Our model shows that the seasonal response time of slow‐moving landslides is controlled by the dry season vadose zone depth rather than the total landslide thickness.

Coupling Mineralogical Analyses, Leaching Tests and Kinetic Modelling to Unravel Groundwater Flow-Paths in a Complex Landslide: An Attempt from the Vedriano Case Study (Northern Italian Apennines)

As the rise in pore water pressure is one of the main factors in triggering landslides, the understanding of groundwater processes taking place at the hillslope scale is a crucial issue in slope stability analysis. However, identifying flow-paths travelled by water molecules from their infiltration is still a complex task. Hydrochemistry is recognized as a powerful tool that can help to gain useful hydrogeological information and has gradually become increasingly used in addition to conventional study methods. This manuscript presents a comprehensive geochemical investigation consisting of leaching tests and quantitative mineralogical analyses on soil samples, chemical analyses on groundwater samples and modelling. Our results highlighted the usefulness of coupling, even in hydrogeological studies focusing on landslides, geochemical surveys on both water and the soil matrix to constrain the interactions between host-rocks and groundwater. Moreover, it demonstrated that kinetic-based geochemical models, if properly calibrated on leaching tests, can provide valuable information on groundwater dynamics, allowing us to elucidate water-mixing processes beneath the soil surface.

Impact of seismicity on Nice slope stability—Ligurian Basin, SE France: a geotechnical revisit

The shallow Nice submarine slope is notorious for the 1979 tsunamigenic landslide that caused eight casualties and severe infrastructural damage. Many previous studies have tackled the question whether earthquake shaking would lead to slope failure and a repetition of the deadly scenario in the region. The answers are controversial. In this study, we assess for the first time the factor of safety using peak ground accelerations (PGAs) from synthetic accelerograms from a simulated offshore Mw 6.3 earthquake at a distance of 25 km from the slope. Based on cone penetration tests (CPTu) and multichannel seismic reflection data, a coarser grained sediment layer was identified. In an innovative geotechnical approach based on uniform cyclic and arbitrary triaxial loading tests, we show that the sandy silt on the Nice submarine slope will fail under certain ground motion conditions. The uniform cyclic triaxial tests indicate that liquefaction failure is likely to occur in Nice slope sediments in the case of a Mw 6.3 earthquake 25 km away. A potential future submarine landslide could have a slide volume (7.7 × 106 m3) similar to the 1979 event. Arbitrary loading tests reveal post-loading pore water pressure rise, which might explain post-earthquake slope failures observed in the field. This study shows that some of the earlier studies offshore Nice may have overestimated the slope stability because they underestimated potential PGAs on the shallow marine slope deposits.

The effect of fines plasticity on monotonic undrained shear strength and liquefaction resistance of sands

The paper presents results of an investigation into the effects of fines plasticity on the undrained monotonic and cyclic response of sands. Monotonic and cyclic triaxial tests on mixtures of sand with 5% and 15% fines content were performed. Non-plastic and plastic fines of varying plasticity were used. At a given fines content, confining effective stress and void ratio, the results show that the undrained shear strength and cyclic resistance decrease with increasing plasticity index of fines up to a threshold value. Above this threshold value, the undrained shear strength and cyclic resistance increase with increasing plasticity index of fines. This pattern of behaviour was also reflected in the excess pore water pressure rise during both monotonic and cyclic loading. The mechanism controlling the behaviour of sands with fines and the implications of the test results to the engineering practice are finally discussed.

Occurrence of landslides in Nepal and their mitigation options

Landslides are very common occurrences in Nepal that have been affected development infrastructures, lives, and properties of the people every year. Many hill villages are situated on or adjacent to unstable slopes and old landslides are reactivated from time to time. The rapidly increasing construction of infrastructure, such as roads, irrigation canals, and dams without due consideration of natural hazards is contributing to triggering of landslides and debris flows. Thus, this paper has explored the cause and characteristics of landslides occurrences and their mitigation practices in Nepal. Topographic, geologic and triggering factors, and human intervention causing landslides are characterised to suggest the suitable mitigation options that can be implemented in the mountain hill-slopes. Among the wide range of slope stabilisation measures which are available to practitioner engineer, the lowering of groundwater level in combination of controlling of surface infiltration (e.g. sealing of tension cracks) of water into landslide are the most cost effective options for mountainous terrain because the rise in pore water pressure is one of the basic cause of landslides during the rainy season. In addition, removing of unstable slope debris, surface drainage, and retaining walls are the useful landslide mitigation measures depending on site conditions, availability of budget, and specific requirements. Various support systems and elements can be crafted for creative solutions of the slope instability problems in Nepal.

Evaluating the capability of a critical state constitutive model to predict the collapse potential of loose sand

Many catastrophic flow failures in granular soil slopes are believed to be caused by a rise in pore water pressure associated with substantial loss of soil shear strength. This failure mechanism is known as prefailure instability or static liquefaction. Constant shear (CS) and consolidated undrained (CU) triaxial tests can reproduce stress paths, in which such instability may occur before reaching the failure. In the present study, a previously proposed critical state constitutive model was first used to simulate the behavior of loose saturated sand in CU tests. It was then employed to predict the instability of loose sand subjected to the CS loading. Under such loading, loose dry sand initially experience small volume increase, and then start to contract substantially. In saturated sand, such contractions can lead to the generation of pore water pressure and sudden decrease of shear strength. The capability of the model to predict the onset of the volume contraction and collapse potential of loose dry sand was examined by comparing the model predictions with experimental results of CS tests. The comparison showed that the effect of initial void ratio, consolidation and deviatoric stresses on behavior of loose dry sand can be well predicted by the model.

The causes and mechanisms of rain-induced highway and pavement collapse in Obolo-eke, Southeast Nigeria

Majority of highway failures in Nigeria occur during or immediately after heavy rainfall. Although rapid rise in pore water pressure is usually adduced as the major factor leading to these failures, the mechanisms that initiate or propagate the failures have not been adequately clarified. To investigate these mechanisms, a series of laboratory experiments, detailed field survey and digital elevation model produced from Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) digital elevation models (DEM) were integrated to investigate the failure processes on the unconsolidated sandy terrains where failures were common. The study area is underlain by loosely consolidated, moderately sorted sandstone sequence and shale intercalations. Results of the ASTER DEM clearly revealed the topographic, geomorphic, and hydrologic features associated with instability and showed that streams played key roles in the failure processes. While many collapsed portions were observed where rivers were close to the highway, there were no failures on the parts far from the streams. Field analysis showed that the failures were restricted to only the portions of the highway with damaged man-made drainage systems. The broken drainages probably facilitated saturation and erosion of the underlying sediments. The liquefaction resistance of the saturated sediments was weakened and transient surface flows arising from prolonged rainfall initiated failure. The rapid post-failure strength reduction and the low steady-state strength suggested the sediments were liquefiable. The results showed that a good drainage system can serve as an effective preventive measure for protecting engineering structures on collapsible sands.

ICL/IPL activities in West Africa: landslide risk assessment and hazard mapping approach

The ICL/IPL Project achieved results in capacity building, investigation of landslides in West Africa and also evaluated some other slope movements in the region. These include the catastrophic rock–debris avalanche at the Cameroon–Nigeria border and the Iva Valley landslides in Enugu. During the avalanche, an estimated 100 M m3 of rock and debris was moved more than 2 km from the source of the slide at 600 m above sea level to the toe in the valley in a few minutes. The materials range from mud and soil debris to blocks of rocks up to 20 m in diameter. The grain size of moved material tended to increase upslope and closer to the head scarp though it tended to decrease again close to and at the source area. Nature and composition of the basement bedrock with foliation planes dipping in the direction of slope, dominant joint sets oriented perpendicularly to the foliation, the nature of weathered material and high relief were strong factors in the avalanche. Field studies identified 43 landslides at the Iva Valley area of Enugu state, which were shallow, short run-out movements with slip-surface depth less than 2 m. The shallow slides and the avalanche are triggered by water infiltration in slopes with high topographic gradient. The soil saturation leads to a reduction of the shear strength of the soil because of a rise in pore water pressure. These landslides are known to occur during or after intense rainfalls at the beginning or at the tail end of rainy season.

Origin and assessment of deep groundwater inflow in the Ca' Lita landslide using hydrochemistry and in situ monitoring

Abstract. Changes in soil water content, groundwater flow and a rise in pore water pressure are well-known causal or triggering factors for hillslope instability. Rainfall and snowmelt are generally assumed as the main sources of groundwater recharge. This assumption neglects the role of deep water inflow in highly tectonized areas, a factor that can influence long-term pore-pressure regimes and play a role on local slope instability. This paper aims to assess the origin of groundwater in the Ca' Lita landslide (northern Italian Apennines) and to qualify and quantify the aliquot attributable to deep water inflow. The research is essentially based on in situ monitoring and hydrochemical analyses. It involved 5 yr of continuous monitoring of groundwater levels, electrical conductivity and temperature and with groundwater sampling followed by determination of major ions (Na+, K+, Mg2+, Ca2+, Cl−, HCO3−, SO42−), tracers (such as Btot and Sr2+), and isotopes (δ18O, δ2H and 3H). Leaching experiments on soil samples, hydrochemical modelling and water recharge estimation were also carried out. Results show that the groundwater balance in the Ca' Lita landslide must take into account an inflow of deep and highly mineralised Na-SO4 water (more than 9500 μS cm−1) with non-negligible amounts of Cl− (up to 800 mg l−1). The chemical and isotopic fingerprint of this water points to oilfield water hosted at large depths in the Apennine chain and that uprises through a regional fault line crossing the landslide area. It recharges the aquifer hosted in the bedrock underlying the sliding surface (at a rate of about 49 000–85 700 m3 yr−1) and it also partly recharges the landslide body. In both the aquifers, the hydrochemical imprint of deep water mixed with rainfall and snowmelt water was observed. This indicates a probable influence of deep water inflow on the mobility of the Ca' Lita landslide, a finding that could be applicable to other large landslides occurring in highly tectonized areas in the northern Apennines or in other mountain chains. The paper demonstrates that hydrochemistry should, therefore, be considered as a valuable investigation method to define hydrogeological limits and the groundwater sources in hillslope and to assess groundwater flow patterns in deep-seated landslides.

Soil nailing for rehabilitation of reinforced earth wall distress

In the present study, an investigation was performed to assess the possible cause of distress to the geogrid reinforced earth walls constructed for a flyover. The investigation methodology included site visits and observations, collection of the material samples (backfill and geogrid) for laboratory testing, and back analyses of original design using a conventional method and numerical analysis. The temporary rise of pore water pressure due to the heavy rains during the construction period and the internal stability of reinforced earth walls have been identified as the possible causes of the observed distresses. Further, installation of the driven soil nails of specified diameter and length at suitable spacings, particularly in the locations of distress, were proposed as the rehabilitation measure. The results of the numerical analyses indicated that introduction of soil nails: (a) caused redistribution of axial forces among the geogrid layers and soils, (b) significantly reduced the lateral displacement and (c) improved the overall stability of the reinforced earth walls.

Volumetric behavior of saturated sands under poor drainage conditions

Permeability variations have been identified as a key factor in controlling slope failure locations in rainfall‐induced landslides. In this research, failure behavior in limited drainage conditions was investigated. Tests were performed on saturated sands by means of a modified triaxial system that could mimic the effect of low‐permeability barriers present in the field. The tests were conducted by increasing the pore water pressure at different rates to study the effects of the speed of pore water pressure rise on soil failure. The results revealed a dependence of soil volume changes on the rate of pore water pressure increase. In general, the results showed that volume change of granular soils, which are under shear and confined laterally by low‐permeability materials, depends on the initial porosity and the pore water pressure rate. These results are particularly valid during the early stages of soil deformation that precede wholesale slope failure.

Instrumented Model Slope Failure due to Water Seepage

Many slope failures have been observed to occur during or immediately after rainfall. Although conditions leading to these failures have been described as caused by a rapid rise in pore-water pressure as a result of rainwa- ter infiltration, the important factors that influence the initiation of slope failures have not been adequately clari- fied. To investigate these factors, a series of laboratory experiments was conducted on model sandy slopes to determine the initiation process of rainfall-induced slope failure. In the tests, failures were induced in small-scale model slopes either by water percolation from the side upslope or by artificial rain falling on top of the slope. Besides monitoring pore-water pressure, changes in soil moisture contents and ground deformation were mea- sured. Test results showed that slope failure was always induced when the soil moisture content within a certain region near the toe of the slope reached nearly full saturation, even though other parts of the sliding mass were still in a partially saturated state. In addition, minute deformations along the slope were shown to precede failure. The findings presented here show that by monitoring the soil moisture content of slopes and performing displace- ment measurements, it is possible to predict the occurrence of rainfall-induced slope failure.

Residual Shear Strength Mobilized in First-Time Slope Failures

This paper presents a review of long-term stability of stiff clay and clay shale slopes, and detailed reanalyses of 99 case histories of slope failures in 36 soft clays to stiff clays and clay shales. We analyzed 107 sections using the observed actual slip surface. In a first-time slope failure in clay or shale, part or all of the slip surface is unsheared prior to the occurrence of the landslide. Most stiff clays and clay shales contain stratigraphic discontinuities such as bedding planes and laminations. The fully softened shear strength is shown to be the lower bound for mobilized shear strength in first-time slope failures in homogeneous soft to stiff clays and on the slip surfaces cutting across bedding planes and laminations. For many of the first-time slope failures it appears that part of the slip surface is at the residual condition. For excavated slopes, the residual condition could be present before the final slope is formed, or it may develop in response to excavation by progressive deformation along nearly horizontal surfaces including bedding planes or laminations. In addition to the permeability dependent rise in porewater pressure, and softening, delayed first-time failure of slopes in stiff clays and clay shales is caused by propagation of the residual condition into the slope, on horizontal or subhorizontal surfaces including stratigraphic discontinuities. The residual condition is present on the entire surface of reactivated landslides.