Phreatic Level Research Articles

Testing the Causes of a Levee Failure Using Bayesian Networks

Context: Forensic geotechnical engineering aims to determine the most likely causes leading to geotechnical failures. Standard practice tests a set of credible hypotheses against the collected evidence using backward analysis and complex but deterministic geotechnical models. Geotechnical models involving uncertainty are not usually employed to analyze the causes of failure, even though soil parameters are uncertain, and evidence is often incomplete. Method: This paper introduces a probabilistic model approach based on Bayesian Networks to test hypotheses in light of collected evidence. Bayesian networks simulate patterns of human reasoning under uncertainty through a bidirectional inference process known as “explaining away.” In this study, Bayesian Networks are used to test several credible hypotheses about the causes of levee failures. Probability queries and the K-Most Probable Explanation algorithm (K-MPE) are used to assess the hypotheses. Results: This approach was applied to the analysis of a well-known levee failure in Breitenhagen, Germany, where previous forensic studies found a multiplicity of competing explanations for the causes of failure. The approach allows concluding that the failure was most likely caused by a combination of high phreatic levels, a conductive layer, and weak soils, thus allowing to discard a significant number of competing explanations. Conclusions: The proposed approach is expected to improve the accuracy and transparency of conclusions about the causes of failure in levee structures.

Flood Mitigation in Urban Areas through Deep Aquifer Recharge: The Case of the Metropolitan Area of Guadalajara.

The Metropolitan Area of Guadalajara (MAG) experiences water shortage and overexploitation of aquifers. In addition, it suffers from seasonal flooding that is channeled towards inadequate sanitary drainage, creating a strong negative environmental impact. These problems are rooted in the waterproofing of the urban surface. Many cities around the world have used deep injection wells to recover aquifers and remove surface waters. Certain geohydrological conditions are required for the implementation of these deep injection wells, deeper than 30 m, such as significant surface runoff, acceptable water quality for infiltration, considerable depth in the phreatic levels, and good subsoil permeability. All of these conditions exist in the MAG or could be achieved without significant investment. An assessment is presented exploring the viability for a solution based on this technology, as a strategy to recover aquifers and reduce flooding. The first step was to identify, through map algebra, a micro-basin suitable for this technology. Then, mean runoff volumes were obtained and a stratigraphic profile was carried out based on 19 standard penetration tests (SPT). With these data, a numerical simulation of deep injection wells of different dimensions was performed, providing recommendations for a solution based on these calculations. The results show that both problems can be solved with this relatively simple and cheap technology supporting public health.

3D numerical simulation of slope-flexible system interaction using a mixed FEM-SPH model

Flexible membranes are light structures anchored to the ground that protect infrastructures or dwellings from rock or soil sliding. One alternative to design these structures is by using numerical simulations. However, very few models were found until date and most of them are in 2D and do not include all their components. This paper presents the development of a numerical model combining Finite Element Modelling (FEM) with Smooth Particle Hydrodynamics (SPH) formulation. Both cylindrical and spherical failure of the slope were simulated. One reference geometry of the slope was designed and a total of 21 slip circles were calculated considering different soil parameters, phreatic level position and drainage solutions. Four case studies were extracted from these scenarios and simulated using different dimensions of the components of the system. As a validation model, an experimental test that imitates the soil detachment and its retention by the steel membrane was successfully reproduced.

Mixing Controlled Adsorption at the Liquid-Solid Interfaces in Unsaturated Porous Media

The unsaturated zone, located between the soil surface and the phreatic level, plays an important role in defining the fate of any substance entering the subsoil. In addition to the processes of flow and transport taking place in the liquid phase, surface reactions such as adsorption to the solid phase may occur and increase the residence time of the substance entering the system. In this study, we aim to understand the pore-scale mechanisms that control adsorption in unsaturated systems. We combine 2D pore-scale experimental images with numerical simulations to analyze flow, transport, and adsorption under different liquid saturation degrees. We demonstrate the role of mixing on adsorption at the liquid-solid interfaces by analyzing the deformation in time of a pulse-injected surfactant. We also analyze the impact of the isotherm functional shape and the inclusion of the liquid-gas interfaces as adsorption sites on this surface reaction. The enhancement of mixing as saturation decreases is accompanied by a reduction in the amount of adsorbed mass, located mainly along preferential flow paths, where the solute is primarily transported. For the same isotherm, a nonlinear behavior of adsorption as a function of liquid saturation has been observed. This is explained by the nonlinear variation of the volume fraction of liquid behaving as preferential path or stagnation zone as liquid saturation decreases, despite the linear decrease in the surface area of solids accessible for adsorption.

Qualitative assessment in river and phreatic aquifer water in a rural watershed in the Atlantic Forest biome

Watersheds have different water compartments (surface, subsurface, and underground) connected by the soil-water interface. In order to be able to relate these compartments, monitoring data are necessary, such as the case of the Ribeirão Concórdia watershed, in Lontras, Santa Catarina (SC). This study aimed to evaluate the behavior and the correlation between rainfall-runoff and phreatic surface levels with chemical species concentrations in surface and groundwaters in a rural watershed. Data of 3 piezometers installed in the hydrographic basin were used: PZ2127, PZ3, and PZMC. The piezometers are equipped with hydrostatic level sensors. A fluviometric station is located adjacent to PZ2127 (near the catchment outlet). Concentrations of anions and carbon forms were analyzed in water samples (river and piezometers) taken every 2-3 weeks, from January 14, 2012, to December 23, 2016, totaling 103 samples. Correlations between daily data were verified using Pearson’s correlation coefficient (ρ). The river presented a dilution effect, while the adjacent piezometer had the highest average concentrations of chemical species. Precipitation and chemical species concentration showed no seasonal pattern, with events/peaks throughout the year. Higher concentrations of carbon forms were found in the summer, while lower concentrations were observed in the winter. Positive correlations between concentrations of anions and carbon forms in surface and groundwaters were obtained.

COMPARE INFLUENCES OF HORIZONTAL AND VERTICAL MSE WALL DIMENSIONS WITH GEOCOMPOSITE BACK DRAINAGE SYSTEM TO MAXIMUM STEADY STATE PHREATIC LEVEL

Nowadays, with serious risks to the mechanically stabilized earth (MSE) instability especially for soil mass behind the wall face caused by heavy rainfall. Come from high drainage ability, geocomposite is regarded as an appropriate material for drainage purposes in many geotechnical structures, including MSE walls. However, there are insufficient researches investigated MSE wall geometry design especially with wall dimension oriented follow 2D dimension as horizontal and vertical. This paper presents a series of PLAXIS numerical simulations to investigate the influences of MSE wall dimensions and drainage capacity on seepage responses inside the protected zone of the wall. The research results indicated that the distance from the upstream water source to the drainage face (L) influences most to the maximum steady state phreatic level (ho) variation inside the protected zone. In total comparison that shown the horizontal wall dimensions have more affects on ho drops than vertical wall dimensions.

You Can Bend Me but Can’t Break Me: Vegetation Regeneration After Hurricane María Passed Over an Urban Coastal Wetland in Northeastern Puerto Rico

Tropical urban coastal wetland regeneration is complex. Wetland plant biodiversity varies due to past and present land use, nutrient inputs, hydrological conditions, and terrestrial/marine connectivity. The intensity of atmospheric disturbances, such as hurricanes, will determine these systems’ level of disturbance and regeneration capacity. On September 20, 2017, category 4 hurricane María passed over Puerto Rico, leaving behind a path of destruction across the entire island, especially in coastal ecosystems, from the combined effects of winds, severe storm surges, and urban runoff. Our question was: to what extent do human-influenced coastal urban wetlands regenerate after such a massive event. This study determines the spatio-temporal regeneration dynamics of plant cover and composition during the first 2 years after hurricane María in a coastal urban wetland, ciénaga Las Cucharillas, located in San Juan Bay. We assessed the distribution of plant functional types using small unmanned aerial vehicles (s-UAV) and monitored climate and environmental data (salinity, phreatic water levels, and precipitation). Wetland vegetation cover had a high recovery rate – 16 months after the hurricane, vegetation cover occupied 87% of the study area. We found a successional pattern of plant regeneration that seemed to be partly explained by the fast-slow continuum. Plants with high specific leaf area (SLA) colonized bare soil spaces first. Plant regeneration also varied according to changes in phreatic water conductivity and waterlogging. Isotopic analyses of plant species signaled high nutrient availability, increasing the system’s regeneration speed. After 2 years, the wetland’s plant cover and composition of functional plant types proved resilient to the initial hurricane effect and subsequent changes in conductivity and freshwater conditions. Further studies will expand how spatio-temporal conditions will affect long-term plant community dynamics.

Perfomance of a borehole heat exchanger: The influence of thermal properties estimation under tidal fluctuation

This research assesses how groundwater flow induced by tide influences the performance of a borehole heat exchanger (BHE) using a case study in Guayaquil, Ecuador. The Thermal Response Test (TRT) was applied to determine the thermal properties of the ground. The experimental results of TRT showed periodic fluctuations in the response, presumably induced by the tide. An explanation of the effects of the tide on thermal performance was carried out systematically. Later, an analytical solution was proposed to estimate the phreatic level near the shore. A geometric mean model then predicted the thermal properties of the ground, given the groundwater level fluctuations.Consequently, a relationship between the effective thermal capacity of the soil and the phreatic level was found. Results show that thermal diffusivity is overpredicted by 50% and thermal conductivity by 8.8%. Finally, we evaluated the heat dissipation of a borehole heat exchanger using a TRNSYS simulation, revealing an overestimation of 12% in the heat rate capacity of the BHE when ignoring tidal effects. This overestimation shows how using standard thermal properties measurement methodologies may affect the design process resulting in substantial inaccuracies in performance and implementation costs.

Unmanned aerial vehicle (UAV) remote sensing estimation of wheat chlorophyll in subsidence area of coal mine with high phreatic level

Unmanned aerial vehicle (UAV) remote sensing estimation of wheat chlorophyll in subsidence area of coal mine with high phreatic level

Agricultural pesticide residues in water from a karstic aquifer in Yucatan, Mexico, pose a risk to children’s health

ABSTRACT Yucatan is a region with a high impact of water contamination since it has a karst type soil favoring contaminants entry into the phreatic level, the only source of freshwater in the area. However, no studies report pesticides in water for human consumption or the risk it represents. The objective of this study was to detect and measure pesticide concentrations in domestic tap water to estimate the risk (carcinogenic and non-carcinogenic) to health. A non-probabilistic sampling was applied of 48 tap water sources, and then pesticide detection with solid-phase extraction gas chromatography coupled to the electron capture and flame photometric detectors allowed the estimation of risk through hazard ratios. The present results suggest that aldrin, heptachlor, and β-BHC residues in domestic tap water from Ticul, Yucatan, pose a risk to children’s health, particularly for potential carcinogenic risks.

Susceptibilidad a la licuación de suelos y sedimentos en el valle Ullum-Zonda (31º30’ S-68º25’ O), Precordillera, Andes Centrales, Argentina

. The earthquakes of 1894, 1944, 1952 and 1977 occurred in the province of San Juan in central-wesern Argentina caused numerous processes of soils and sediment liquefaction, including those in the Ullum-Zonda valley. Historical records showed cracks, sand volcanoes, craters and differential settlements, which caused significant damage to housing and the agro-industrial sector of the region. In this work, we carried out a study of the susceptibility to liquefaction of soils and sedimentary deposits in the Ullum-Zonda valley. This was conducted using a methodology in which conditioning factors such as depth of the water table, historical records of liquefaction, potential seismogenic sources, origin, age and grain size of the soils and sedimentary deposits, among others, were evaluated and weighted. An iterative process of overlapping maps weighted the influence of the different factors in the assessment of susceptibility. Once the optimal combination was achieved, a final map with the zoning of soils and sediment susceptibility to liquefaction was obtained for the Ulum-Zonda Valley. The achieved zoning was related to a susceptibility index (SI), qualitatively classified as very high, high, moderate and low. The zone of very high susceptibility to liquefaction is located in the distal portion of the alluvial fan formed by the San Juan River in the Ullum-Zonda Valley, the areas of high to moderate susceptibility in the middle sector of the fan, and those of moderate to low susceptibility correspond to the proximal-middle sector of the fan. The main villages of the Ullum-Zonda valley, Ibáñez (head of the Ullum department) to the north of the San Juan River, Basilio Nievas (head of the Zonda department), to the south of the river, Tacú residential sector (located south of the Ullum dam) and the yacht clubs (located on the northeast periphery of the dam) are located in the areas of high to very high susceptibility, where the main conditioning factors are soil and sediments granulometry and the depth of the phreatic level.

Seismic stability analysis of slopes with cracks in unsaturated soils using pseudo-dynamic approach

In practice, soil slopes are commonly unsaturated and may suffer from the adverse effects of earthquakes. Stability assessment of slopes subjected to earthquakes tends to consider whether the soils are dry or saturated while neglecting the time and spatial effects of seismic waves; in such assessments, the actual features cannot be reflected sufficiently. In the present study, a framework considering unsaturated soils was developed to investigate the seismic stability of slopes accounting for tension cracks using the pseudo-dynamic approach. Several expressions for apparent cohesion were applied to analyze the influence of matric suction, and seepage under different phreatic levels was also included. The pseudo-dynamic approach was applied to characterize the time and spatial effects of earthquakes. Two types of cracks, open cracks (cracks existing prior to slope failure) and formation cracks (cracks forming as part of a slope failure mechanism), were considered. A closed-form solution for the critical height of the slopes was derived from the energy balance equation of the Limit Analysis upper bound method, and the safety factor was obtained. The validity of this approach was verified by comparison with published solutions. Through the parametric analysis, it was found that higher amplification factors and seismic coefficients led to a smaller discrepancy in the safety factor between the slopes with open cracks and formation cracks, yet a reverse trend was observed at a higher value of matric suction. The effect of matric suction on slope stability was more apparent with a lower water level. Different shear strength models of unsaturated soils led to different safety factors.

Finite element analysis for identifying locations of cracking and hydraulic fracturing in homogeneous earthen dams

This paper reports a finite element study to identify the locations of crack initiation in a homogeneous earthen dam at its post-construction and reservoir operation stages. The steady state and transient analyses, including reservoir rise-up and drawdown conditions, are simulated to identify the favorable conditions and locations of crack generation. The behavioral response of the dam is represented in terms of the developed total stress, horizontal deformations of the faces, strain accumulation in the dam, and the differential settlement of the dam base. The locations of post-construction cracks are identified based on the negative minor principal stresses developed on the dam faces. For both single-lift and multiple-lift modeling techniques, the upstream face of the dam is found to be the most favorable location for the crack generation. For transient reservoir operations (rise-up and drawdown scenarios), it is identified that hydraulic fracturing may occur on either faces of the dam at specific heights, governed by the minor principal stresses becoming lesser than the developed pore-water pressure. Depending on whether the reservoir drawdown occurs before or after the attainment of steady-state phreatic level within the body of the dam, the pore-water pressure distribution within the dam are found notably different. This results in hydraulic fracturing occurring at different faces of the dam and at different heights. It is important to have a thorough understanding of the tentative location of the cracks developed in homogeneous earthen dams so that proper mitigation measure can be adopted as per requirement.

Determination risk of liquifaction disaster based on spatial distribution unconfined aquifer at the Tindaki Groundwater Basin, Parigi Moutong District

Natural disasters such as earthquake, tsunami and liquefaction in Central Sulawesi Province in 2018 had a significant impact on economic growth. This demands disaster risk reduction, especially liquefaction disasters. This research was conducted in Tindaki Groundwater Basin, Parigi Moutong Regency, especially in Parigi sub-district, which includes: Lebo, Bambalemo, Kampal, Maesa, Bantaya, and Olaya. The purpose of this study was to determine the level of risk of liquefaction based on the spatial distribution of the unconfined aquifer in Tindaki Groundwater Basin. The number of samples is 100 points taken randomly, consisting of community dug wells to obtain phreatic depth. The technique of collecting data is random and proportional sampling.The method used in this study is geological and hydrogeological approaches with rock formation as a determining parameter for groundwater density. The results showed that the average depth of the phreatic level was <10 meters from the ground and was in the alluvium formation. Based on the results of the study, it can be concluded that the potential for liquefaction in the research area is in the medium to high potency.

Los bañados de desborde fluvial: una mirada desde la geohidrología

Los bañados de desborde fluvial (BDF) abarcan tramos (cientos de metros a kilómetros) de los sistemas fluviales pampeanos, con características y funciones particulares. Estos humedales se originan por un afloramiento del nivel freático y una disminución local del gradiente hidráulico, lo que da lugar a un ensanchamiento del curso de agua principal y la aparición de una red de microdrenaje que acompaña a este último. Estas condiciones favorecen el desarrollo de humedales asociados al curso principal, con un importante desarrollo de la vegetación característica de suelos muy húmedos. El objetivo de este trabajo fue el de analizar las características hidrológicas y la calidad del agua de los BDF en zonas urbanizadas con actividad agrícola (localizados en losarroyos Carnaval y Del Gato) y en zonas rurales con ganadería extensiva (ubicados en los arroyos Cajaravillas y Chubichaminí), del NE de la provincia de Buenos Aires, con el fin de reconocer cómo los diferentes usos del suelo modifican las condiciones de conservación de los humedales. Los análisis geohidrológicos se realizaron a escala regional (cuenca), semi-detalle (subcuenca) y detallada (BDF). Los resultados mostraron que la sobreexplotación de las aguas subterráneas afecta a la permanencia del agua en los humedales, debido a la desconexión entre el nivel freático y el nivel basal de los BDF situados en las zonas urbanizadas con actividad agrícola. En estos últimos se ha observado también que el aporte de nutrientes contribuye significativamente al deterioro de la calidad del agua. La conclusión es que un diagnóstico ambiental de estos BDF requiere un enfoque regional de los procesos hidrológicos para adoptar acciones adecuadas para su conservación.

Determination of critical phreatic level for landslide assessment using a scaled down laboratory model

ABSTRACT Catastrophic hazards like landslides are generally associated with extreme hydraulic conditions. Western Ghats, India is characterized as one of the most landslide-prone areas in India, other than the Himalayas, with extreme hydrological conditions acting as the trigger. Although excessive rainfalls usually serve as the trigger, the presence of excess pore-pressure due to past rainfalls has been further identified amongst the factors leading to slope failures. Considering this, the current study is performed to identify the associated Critical Phreatic Level (CPL) triggering slope failure. To study the effect of hydraulic factors on slopes, laboratory-scale models of soil slopes are created. The simulated slopes are instrumented and the effect of change in hydrological condition is monitored in real-time until failure to identify the CPL. The obtained CPL for considered ground parameters are further validated for slope stability analyses using numerical methods, and a correlation is established for assessment of CPL using regression analysis.

Numerical analysis of phreatic levels in river embankments due to flood events

A 2D saturated–unsaturated unsteady-flow numerical study has been carried out to analyze the behavior of levees stressed by flood events. The investigation has involved: i) simulation of the seepage process in a simplified levee over a long period of river flows; ii) the use of a synthetic design hydrograph to be utilized as an alternative to a long-term history of river stages and iii) the influence of the unsaturated parameters on the maximum saturation depth in the levee soil. The results of the analysis show that the statistical properties of the maximum annual phreatic levels are different from those of the corresponding river levels, and that the tested synthetic design-hydrograph is able to guarantee a well-balanced, conservative margin. The analysis shows that the role of the unsaturated zone is also very important. Furthermore, a comparison of the piezometric levels, computed by means of the numerical model, with those computed through simplified solutions, shows that the latter ones may not be conservative.

Late Cretaceous plateau deserts in the South China Block, and Quaternary analogues; sedimentology, dune reconstruction and wind-water interactions

Plateau deserts are among those continental systems with the most significant examples of clastic deposits associated with the complex combination of the action of ice, wind and water. The Late Cretaceous rocks of China contain the record of desert systems migration and partial destruction in a palaeoplateau desert. The evolution of the South China Block during Late Cretaceous was characterized by widespread destructive plate margin activity, this favoured orogenic uplift and high-altitude mountain ranges of which a direct consequence was a widespread rain shadow effect, triggering desertification and erg expansion similar to that of Quaternary counterparts in the Tibetan Plateau. This work presents a detailed analysis of the sedimentology, stratigraphic architecture, palaeogeography and palaeocurrent reconstruction of aeolian and associated alluvial depositional systems. The reconstruction of aeolian bedforms based on field-data analysis indicates that, during Late Cretaceous, draas and crescentic dunes accumulated and migrated in extensive intermontane desert systems. Heavy rains led to partial destruction of aeolian dunes and the reworking of aeolian sands in interdraa corridors. The fault-controlled subsidence and an increasing input of windblown sediments favoured the long-lasting accumulation of the erg system. Possible monsoonal rains recharged the groundwater system causing the rise of the regional phreatic level that favoured the ulterior long-lasting preservation of the aeolian system in the Xinjiang Basin. The dimensions and processes inferred from this Cretaceous desert system are similar to those observed today in the linking zone of the Taklamakan-Gobi Deserts, where meltwater flows from alpine glaciers in surrounding mountain ranges recharge the alluvial and fluvial network of the erg margin. The occurrence of striated cobbles in the alluvial facies suggests glacial activity in the catchment areas of the Cretaceous plateau.

Modeling phreatic levels in a rural watershed in Lontras, High Itajaí Valley, SC-Brazil

This study analyzed the behavior of phreatic levels in a rural watershed located the municipality of Lontras, High Itajaí Valley, Santa Catarina, Southern Brazil. Phreatic levels are monitored by 3 wells (PZMC located in riparian forests and PZ2127 and PZ3 in pasture areas). Rainfall and fluviometric level are also monitored. Fluviometric station is located near PZ2127. Daily evapotranspiration was calculated using the Samani method. Monitoring was performed from January 1, 2012 to July 15, 2019, combining 7.5 years of data. An exploratory data analysis and a trend analysis of groundwater levels was performed. Simulation was performed with the PIRFICT model (from December 31, 2014 to January 19, 2016). Trend analysis identified significant decay trends for PZMC and PZ3, and elevation trends for PZ2127. The PIRFICT model presented acceptable adjustments. The errors were low and it was possible to characterize the dynamic impulse response relationship between the explanatory variables and the observed levels. The information obtained from the phreatic levels monitoring and modeling proved to be necessary for the local groundwater resources management, providing support for planning and decision making.

Subsoil classification and geotechnical zonation for Guadalajara City, México: Vs30, soil fundamental periods, 3D structure and profiles

ABSTRACTGuadalajara, Jalisco, is the second largest city in Mexico with around 4.5 million inhabitants. A high seismic hazard exists in the city due to forces produced by the interaction between the Rivera, Cocos and North American plates and the smaller Jalisco Block. Guadalajara is one of the largest cities built over pumice soil deposits. Furthermore, the near‐surface phreatic level causes a high susceptibility to liquefaction. All these features can cause extreme earthquake site effects. Due to the fragile inner structure of pumice sands, traditional geotechnical tests are inappropriate to characterize the seismic response. Therefore, we propose the use of surface wave analysis methods (multichannel analysis of surface waves and refraction microtremor), which we applied in 33 sites to define the soil classification in terms of VS30 (the average shear wave velocity between the surface and 30 m depth), the bedrock depth and the fundamental period. From the soil classification, we construct a microzonation map consisting of four geotechnical zones, which we superimpose on the known construction systems within the city. The comparison between the construction period of the buildings and the fundamental frequencies of the soil indicates a high vulnerability to resonance in 1‐ to 4‐storied old buildings constructed of adobe and unreinforced masonry within zones II and III, followed by a medium vulnerability to seismic resonance in compact buildings of 1–4 stories within zone I and 1–12 stories within zones II and IV.