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Faults have large impact on the mechanical behavior of soil in pipeline's construction. These pipelines have been embedded to supply vital resources such as water, oil, and gas for consumers. To prevent damage, it is highly recommended not to construct pipelines around active faults. However, it is generally inevitable to cross the fault due to wide extension of pipelines. In this paper, a numerical analysis and parametric study on an underground water pipeline in Tehran, Iran, under the fault-induced displacement is presented. It is important to note that the main focus of this study is on elbow components which are the most critical sections in pipeline systems. The effects of crossing angle, distance to elbow and various soil properties on the elbow response are investigated. It is aimed at finding a safe regulation to embed pipelines with the lowest level of risk expected in elbow components after fault movement. The results show that the elbow component does not suffer serious damage when the crossing angle is 90°, provided they are not located in the close vicinity of the fault rupture surface. However, when the crossing angle decreases to 60 and 45 degrees, these components are much more vulnerable. [ABSTRACT FROM AUTHOR]

Featured Application: Erosion protection in the Marine piping system of polar ships. Under the erosion of seawater–ice two-phase flow, seawater in pipelines of polar ships can cause the pipeline failures that threaten the safety of navigations. The discrete phase model (DPM) and erosion wear model (EWM) were established by using the computational fluid dynamics (CFD) method for numerical analysis of the 90° elbow with relatively severe erosion. This paper explores the erosion effect of pipelines under different conditions and puts forward optimal measures for pipeline protection. Compared with the existing multiphase flow research, the novelty of this study is that vibration conditions are considered and parameters such as two-phase flow velocity, ice packing factor (IPF), ice particle diameter and ice particle rotation characteristics are combined with vibration conditions. Combined with the comprehensive analysis of erosion effects of static pipelines, a general law of seawater pipeline wear under vibration is obtained. The results show that pipeline wear under vibration is more serious than under static conditions. Under static conditions, the wear of the same section in the pipeline increases with the increases of two-phase flow velocity and IPF. However, under vibration conditions, when the velocity is less than 3 m/s, the wear of the pipeline has no significant change, while when the velocity is over 3 m/s, the wear rate increases significantly. The particle diameter has little effect on the wear of static pipes, but under the vibration condition, the pipe wear rate decreases with the increase of particle diameter, and it starts to stabilize when the diameter exceeds 0.3 mm. If the rotation characteristics of ice particles are taken into account, the wear rate along the pipeline is significantly higher than that without particle rotation. [ABSTRACT FROM AUTHOR]

Erosion under the conveying pipeline affected by river flow at the cross to rivers is one the important reasons for breaking the pipelines that can lead to leakage. While the mechanism of erosion under the conveying pipeline in steady flow has been studied by many researchers, studies have shown the importance of scouring research in flood times under unsteady conditions. So, this study has been concerned with the investigation of bed river erosion under the conveying pipeline at the conflict of river in unsteady condition. To achieve this aim, some effective hydrograph's parameters were changed in different scenarios and the results were compared to the steady condition. The result showed the erosion's ratio of unsteady condition to steady one was 34 to 69 percent. Also, the rise of flood hydrograph's peak led to increasing depth erosion from 7% to 22%. [ABSTRACT FROM AUTHOR]

Soil piping remains a relatively unexplored phenomenon despite its substantial impacts on water and sediment transfer at the watershed scale at numerous locations around the world. One of the main limitations regarding the study of this singular process is the characterization of the pipe networks (in terms of number, position, dimensions, and connectivity of pipes). In this context, noninvasive subsurface imaging using ground-penetrating radar (GPR) has proven to be a promising technique. This study used two three-dimensional (3D), high-resolution GPR surveys performed in loess-derived soils to characterize small pipe networks with little prior information about their location. The adopted methodology relies on high spatial resolution scanning, 3D subsurface imaging, and automated detection of reflection hyperbolas using a 200-MHz center-frequency antenna. Two small watersheds affected by piping were investigated at Sippenaeken and Kluisbergen (Belgium). Over the two scanned zones, results revealed significant subsurface continuous patterns. Even though the most obvious patterns corresponded to recent or past anthropic activities (e.g., artificial drainage pipes), validation tests confirmed that the chosen methodology can be used for pipe network characterization because some important continuity patterns were related to soil piping: for instance, a fairly small pipe (approximately 10-15 cm in diameter) was detected and validated for more than 100 m. Nevertheless, the high variability in size, depth, and orientation of the pipes imply that GPRmay only be truly efficient when using very high spatial resolution scanning, which limits its application to specific conditions not always met in piped areas. [ABSTRACT FROM AUTHOR]

Backward erosion piping is an important failure mechanism for water-retaining structures, a phenomenon that results in the formation of shallow pipes at the interface of a sandy foundation and a cohesive cover layer. This paper studies the effect of two sand types on backward erosion piping; both in case of a homogeneous sand layer, and in a vertically layered sand sample, where the pipe is forced to subsequently grow through the different layers. Two configurations with vertical sand layers are tested; they both result in wider pipes and higher critical hydraulic gradients, thereby making this an interesting topic in research on measures to prevent backward erosion piping failures. Grain size analysis shows that the finer fraction is more likely to be eroded and also indicates that grains usually do not settle once they are eroded. [ABSTRACT FROM AUTHOR]

Erosion caused by sand particles in the pipe system is a major concern in the shale gas industry. In the rectifying plate system, the fluid with high Reynolds number is assumed to be the fully turbulent flow. To investigate particle erosion under the complex flow in the rectifying plate system, various erosion simulations are conducted in this study. Because the gas velocity, sand input, particles size, and particles shape can affect the erosion in rectifying system, the effect of gas velocities (5‐30 m/s), sand inputs (50‐400 kg/d), and particle parameters (various particle sizes and various particle shapes) on erosion is simulated. Moreover, the erosion experiment conducted in Tulsa University is used to verify the accuracy of simulation model. Through the calculation and analysis, it is obtained that different gas velocities will change the position where the max erosion rate appears. Various sand inputs lead to different max erosion rates. In addition, the effect of sand input on the distribution of erosion scars on rectifying plate is more obvious than that of on elbows. Finally, the effect of size and shape of particles on erosion is investigated. It is found that with the increase in particle diameter, the shape of erosion scar on elbow 1 changes gradually from an ellipse to the V‐shape. [ABSTRACT FROM AUTHOR]

Damage induced by erosion-corrosion is the main cause of pipeline failure. In this study, the effect of erosion caused by particles entrained in the conveying fluid was investigated. A new erosion equation that considers the effect of applied load on erosion ratio (ER) was established based on available test data and on the E/CRC erosion equation. A lognormal form for the angle function was found to be more concise and accurate for cases without stress (caused by operating loads), and the stress induced erosion acceleration effect was described by exponential function. A novel numerical simulation method was also proposed that combines the proposed stress-dependent erosion equation with the commercial software COMSOL Multiphysics, providing new ways of understanding erosion behavior and predicting erosion damage in oil and gas pipelines. • A new erosion equation that considers the effect of applied load on erosion was established. • A lognormal form for the angle function is more concise and accurate. • A novel numerical simulation method that considers the effect of applied load on erosion was proposed. [ABSTRACT FROM AUTHOR]

In many industrial applications, sand erosion wear is the main cause of equipment failure, particularly in the transferring pipeline fittings. In order to reduce the adverse consequences of erosion in bends, in this study the potential usage of plugged tees instead of standard elbows under a wide range of flow conditions is examined. A computational fluid dynamics (CFD) model coupled with discrete element method (DEM) was used and the particle-laden flows with different fluid velocities in the corresponding geometries carrying various entrained particle mass loadings were simulated. The reliability of selected turbulence models as well as rebound and erosion models were verified by comparing the model predictions with the available experimental data. The final simulation model included the E/CRC erosion model, and the Grant and Tabakoff rebound model. The DEM used in the computational model includes the effects of particles rotation and collisions between the particles. The study also considered the effect of modifications of the plugged length of the tee geometries. The simulation results indicated that, as the particle mass loading increases, the effectiveness of plugged tee compared to the standard elbow increases. Moreover, although increasing the plugged length will generally reduce the erosion rate due to the cushioning effect, the rate of reduction depends on mass loading. Unlabelled Image • Investigation regarding the optimum use of plugged tees rather than standard elbows. • Discussing erosion rate over a wide range of mass loadings using different interaction regimes. • Examination of modifications on plugged geometry. • Investigation of carrier fluid velocity on erosion rate over a set of conditions. [ABSTRACT FROM AUTHOR]

Backward erosion piping is a prominent failure mechanism in water-retaining structures. It is a phenomenon in which shallow pipes are formed in an upstream direction at the interface of a sandy aquifer and an impermeable top layer. Experiments were conducted at two different scales to investigate the erosion mechanism near the pipe tip that causes the pipe to lengthen at the grain scale. The erosion process of grains at the tip of the pipe was filmed from the top and the side. The observations and video recordings allowed for a better understanding of the features of the pipe tip. A zone of loosened sand grains was formed around the pipe during the pipe development. The extent of the loosened zone was determined by analysing the images captured during the lengthening of the pipe. The motion characteristics of particles at the pipe tip and the erosion mechanism near the pipe tip were obtained by analysing the erosion process observed. The findings can serve as a basis for the establishment of a criterion for pipe progression and the development of a novel piping prediction model. [ABSTRACT FROM AUTHOR]

Backward erosion piping is an important failure mechanism for cohesive water-retaining structures which are founded on a sandy aquifer. This paper studies the effect of the sudden application of critical and supercritical hydraulic loads in small-scale experiments. For supercritical loads, it is clear that a part of the upper sand bed goes in suspension before being eroded, resulting in a relatively dense sand–water mixture being transported through the eroded pipe. A linear relation is found between the average velocity at which the pipe grows from downstream to upstream and the applied supercritical load. The pipe cross section is measured at the end of each test. The variations in pipe width, depth and cross section give more insight into the hydraulic regime within the pipe. The clear correspondence for gradual loading and sudden critical loading, and a smooth transition to higher supercritical loads, indicates that the fundamental erosion mechanism may be the same. Finally, grain size analysis of the eroded sand shows that the finer portion of the sand is eroded in case of subcritical or critical loading, while the coarse grains are eroded in case of supercritical loads. [ABSTRACT FROM AUTHOR]

Highlights • Investigating future hydraulic conditions of coastal flood defences due to climate change; • Modelling asset deterioration from field inspection data using time-dependent state-based stochastic process; • Analysing time-dependent probability of failures related to wave overtopping and soil piping; • Optimising maintenance strategy by minimising both maintenance costs and failure risk. Abstract This paper presents a method for time-dependent reliability analysis, future performance predictions and optimum maintenance strategy of coastal flood defences such as earth sea dykes subjected to changing operation conditions. The reliability analysis takes into account both the changes of hydraulic variables such as water level and wave height due to climate change and the deterioration of structural capacities such as crest freeboard loss and soil seepage length degradation over time. A probabilistic time-dependent semi-Markov process is adopted for estimating the transition probabilities on the basis of available field data through routine inspections and expert judgements. Limit state equations are established for evaluating time-dependent probability of failures associated with wave overtopping through the flood defence crest and piping in the underlying water conductive soils. A multi-objective optimisation method is then employed to find optimum solution space for asset inspection and maintenance by minimising both costs for inspection and annual risk of structural failures. The results for a typical earth sea dyke at Thames Estuary show that the probability of failures associated with wave overtopping and soil piping will increase significantly over time, thus appropriate maintenance strategy is required to reduce the risk caused by changing operating conditions. [ABSTRACT FROM AUTHOR]

This paper presents the erosion results of the AISI H13 steel impinged by resin-bonded silica sand, using a testing rig that closely simulates the real blowing conditions during industrial core-making. Steel specimens were heat treated to obtain hardness of 294, 445 and 595 HV200 (29, 45 and 55 HRC). Erosion tests were carried out at impingement angles from 20° to 90° and air drag pressures of 1.38, 2.07 and 2.76 bar (20, 30 and 40 psi). The main results are summarized as follows: (i) The harder material, the lower erosion; (ii) the maximum erosion rate is at 30°; (iii) Little difference in erosion rate at impact angle of 60° and 90° for a constant pressure tested regardless of the hardness level; (iv) As the pressure increases, so does the erosion rate, being more sensitive for low impact angles. Finally, a differential form of the general erosion equation is applied on a practical core-making case to evaluate the erosion rate of the H13 steel at 30° and 90° impingement angles. [ABSTRACT FROM AUTHOR]

Predicting more accurate sand erosion rate in oil and gas production is important for maintaining safe and reliable operations while maximizing output efficiency. Computational fluid dynamic (CFD) is a powerful tool for erosion prediction and provides detailed erosion pattern in complex geometry. To improve accuracy of erosion prediction, first part of this paper proposes an algorithm to include the effect of dynamically changing pipe geometry in CFD based erosion modelling and second part of this paper provides guidelines for proper treatment of turbulence dispersion in CFD based erosion modelling. Sand erosion is a time-dependent phenomenon where most severe erosion scars are localized and occurs under disturbed flow conditions. These localized high erosion rates cause substantial change in pipe geometry, creating cavities which modify the flow field, the particle trajectories and eventually the erosion pattern. This work has illustrated that the erosion prediction can be influenced by including the effect of dynamically changing pipe geometry in CFD modelling. An algorithm was developed to couple erosion rate calculations with a Moving-Deforming-Mesh, which dynamically deforms the solid wall surface geometry and computational mesh based on the local erosion rate at regular time intervals. This effect will be significant for geometries involving sharp corners and/or regions of recirculation zones. Sand erosion largely depends on particle impact location, impact angle and impact velocity - which is the commutative effect of particle trajectory leading to the bounding surface. The particle trajectory is determined based on mean and the turbulence of the flow field. In steady state CFD simulations with Reynolds Averaged Naiver Stokes (RANS) turbulence models, turbulent dispersion is obtained from mean turbulence quantities using a stochastic random walk model, which estimates the instantaneous characteristics of a turbulent eddy. However, stochastic random walk model parameters will have significant effects on turbulence dispersion of the particles and hence the erosion prediction. Specific guidelines for these model parameters can improve the accuracy and consistency in CFD based erosion prediction. • Localized high erosion creates cavities which modify flow field and erosion rate. • Erosion prediction influenced by continuously adapting geometry to erosion profile. • Turbulence dispersion must be properly accounted in particle tracking algorithm. • Erosion prediction highly dependent on Stochastic particle tracking parameters. [ABSTRACT FROM AUTHOR]

Pipeline erosion in the production of oil and gas often occurs in elbows, tees, valves, pipes, chokes and other pipe geometries that cause a rapid change in flow direction. Liquid-dominated flows are of importance in mining and many oil fields and transportation lines carrying oil and gas including those in deep water subsea flowlines. In this study, experimental data for wall thickness losses were measured with an ultrasonic transducer in a 50.8 mm standard elbow. Experiments were conducted with multiphase flows with water, air and 300 µm average sand particles and with liquid-sand flows. Wall thickness losses were measured on the outer radius of elbows at 63 locations and for several different flow conditions. Computational Fluid Dynamics (CFD) simulation was performed using the Euler-Lagrange approach with the Reynolds Stress Model (RSM) for turbulence and Eulerian Multiphase model for multiphase flow cases. Different flow regimes were investigated in liquid-sand and multiphase flows. It was observed that maximum erosion increases as the mixture velocity increases. In addition, for liquid-sand and dispersed-bubble-sand flows the Euler-Lagrange and Euler-Euler-Lagrange approaches used in the CFD simulations were able to predict the observed maximum erosion rates, erosion locations and erosion patterns. • Erosion in a 90° elbow is predicted by CFD modeling in liquid-solid and dispersed bubble-solid flows. • Experimentally maximum erosion is observed towards the exit of the elbow for all cases. • Predicted erosion rates are in agreement with experimental data. • CFD-based erosion modeling is a powerful tool for predicting erosion with complex flows and geometries. [ABSTRACT FROM AUTHOR]

Particle-laden flows in complex geometries often require a more robust performance from erosion models in order to obtain accurate prediction of wear. Most erosion models developed over the last six decades have not been able to achieve the desired accuracy needed for these complex systems, primarily because they are based on single particle-wear material interactions, experimental correlations, and often do not capture the full physics of the erosion process. Recently, the capability of computational fluid dynamics (CFD) in resolving fluid-particle-wall interactions more realistically has been shown to have great potential in the development of high-performance erosion models, especially when combined with experimental data analysis. This paper adopts this combined CFD-experimental methodology to improve the prediction performance of some selected erosion models. Experimental data for the wear of an elbow in gas-solid flow from a previous study was combined with new CFD predictions of local wear variables such as particle impact angle, particle impact velocity, and particle mass rate. A geometric function is developed which can be combined with some common erosion models to significantly improve their wear prediction accuracy for gas-solid elbows. Also, the effects of target material surface roughness and particle rotation on local wear variables are investigated numerically. The simulation results reveal an increased dispersion of particles and a more even distribution of local wear variables at the elbow. In conclusion, this paper presents a method for improving performance of erosion models, and potentially a method to translate wear data between complex geometries. • Erosion models do not predict wear accurately in complex geometries. • A geometry correction factor can improve the performance of the erosion models. • A combined CFD-experimental data analysis technique is a useful tool. • Knowledge of hydrodynamics is essential in modelling erosion in complex geometries. [ABSTRACT FROM AUTHOR]

In the present study, erosion wear behavior of slurry pipeline due to solid–liquid suspension in the pipeline has been investigated using commercial computational fluid dynamics (CFD) code FLUENT. A multiphase Euler–Lagrange model was adopted to predict the solid particle erosion wear in a 90° pipe bend for the flow of bottom ash–water suspension. A standard k–ε turbulence modeling scheme was used to simulate the flow through the pipeline. Water and bottom ash were taken as liquid and as a dispersed phase of solid–liquid mixture, respectively. A simulation study for erosion wear in a pipe bend was carried out to investigate the influence of various parameters including velocity, solid concentration, and particle size. The velocity of the bottom ash–water suspension varied from 0.5 to 2.5 m/s for solid concentrations with a range of 2.5 to 10.0% (by volume). The particle diameters of the bottom ash were 162 and 300 µm. The simulation results agree with the results of previous studies. [ABSTRACT FROM AUTHOR]

Backward erosion piping is an important failure mechanism for water-retaining structures. It results in the formation of shallow pipes at the interface of a sandy or silty foundation and a cohesive cover layer. This paper analyzes the depth of these erosion pipes through small-scale experiments. The development of the pipe depth reveals a lot of information on the backward erosion process, but it had never been measured systematically during the erosion process. Our analysis shows that the pipes are extremely shallow (in the order of mm) and that the pipe depth increases slightly, as piping progresses. Furthermore, a relation is found between pipe depth, grain size, soil permeability, and pipe length. The experimentally obtained depths are in good agreement with those obtained with theoretically determined pipe depths based on pipe hydraulics. Finally, the experiments are compared to 2D numerical simulations using Sellmeijer's mathematical model and 3D numerical simulations with the correct pipe dimensions. [ABSTRACT FROM AUTHOR]

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Plugging of soil pipes can be detrimental to hillslope stability. A soil pipe commonly becomes plugged through internal erosion when the pipe wall collapses. When a pipe becomes plugged, a pressure buildup occurs upslope from the plug. This pressure may be enough to remove the plug, or the pressure may continue to build in the soil matrix, which may lead to hillslope failures. Based on field observations, it is known that both processes occur, but limited data exist to understand if and when plug removal or pressure buildup occurs or how to model these processes. This study involved wellcontrolled laboratory experiments to determine instantaneous pressure buildup behind soil plugs and conditions for which an idealized plug in a soil pipe will be removed. Laboratory experiments were conducted with a smooth or roughened 100 cm long clear polyvinyl chloride (PVC) pipe. A pipe plug (3 or 6 cm) was established 90 cm along the pipe length. Triplicate experiments were conducted with two pipe diameters, two soil types (sand and sandy loam), two plug lengths, three pipe roughness values, various packing densities, and with both dynamic and constant pressure heads. Digital pressure gauges were installed to monitor pressures in the pipe both before and after the plug. The upslope pressure and the length of time that the plug withstood the pressure before removal were recorded. Regardless of pressurized time, all plugs were initially mobilized as intact plugs and then in many cases quickly disaggregated. Some sandy loam plugs withstood pressures of 100 cm; more cohesive plugs could withstand much higher pressures. In addition, pressurized times exceeded 1000 s for some plug conditions even with short (3 to 6 cm) plugs. Therefore, hillslopes upslope of a plugged soil pipe may experience considerable pressure buildup for extended periods of time. Plug physical characteristics are important; for example, the plug's bulk density had a positive exponential relationship with the pressurized time. Soil water dynamics inside the plug will need to be considered, as well as the hydraulic boundary providing inflow to the soil pipe. These experiments provided insight into the dynamics of plugged soil pipes with the eventual goal of assisting in being able to better predict internal erosion and hillslope failure. Future experiments are needed across a wider range of soil types. [ABSTRACT FROM AUTHOR]

Abstract Soil erosion is not only a geomorphological, but also a land degradation process that may cause environmental damage affecting people's lives. This process is caused both by overland and subsurface flow. Over the last decades, most studies on soil erosion by water have focused on surface processes, such as sheet (interrill), rill and gully erosion, although subsurface erosion by soil piping has been reported to be a significant and widespread process. This paper presents a state of art regarding research on soil piping and addresses the main research gaps. Recent studies indicate that this process (1) occurs in almost all climatic zones and in the majority of soil types, (2) impacts landscape evolution by changing slope hydrology, slope stability and slope-channel coupling, (3) is controlled by various factors including climate and weather, soil properties, topography, land use and land management. These issues are illustrated with various case studies from around the world. However, the majority of the reviewed studies used surface methods for soil pipe detection, although soil piping is a subsurface process. Surface methods, such as geomorphological mapping, may underestimate the piping-affected area by 50%. Moreover, most studies are limited to few case studies without presenting thresholds for soil pipe development in different environments. Subsurface erosion by soil piping is not represented in currently used soil erosion models. Therefore more research is needed to better understand the morphology and connectivity of soil pipes, their subsurface catchments, as well as soil erosion rates by piping in different environments. Knowledge of thresholds that induce erosion in pipes and subsequent initiation of gullies may help to improve models of hillslope hydrology and soil erosion that include pipeflow and piping erosion. The investigation of soil piping also requires improved methods that allow to better predict pipe development and collapses, and thus to detect piping-affected areas. Studies dealing with effective prevention and control measures of soil piping are scarce. Addressing these research gaps will help to improve our insights into subsurface erosion by soil piping, and thus help to better understand landscape evolution and hillslope hydrology, as well as to develop and improve effective piping erosion control techniques and strategies. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: The addition of organic amendments and mulches to degraded soils is a common soil restoration strategy in calcareous quarries that has generated proven benefits in subhumid and semiarid environments. We evaluated their effects in a quarry located in SE Spain in an area of transition from arid to semiarid climate. Amendments consisted of sewage sludges from an urban water treatment plant and compost from urban organic wastes. Mulches consisted of siliceous fine gravels and woodchips. Effects on 3 native species (Macrochloa tenacissima, Anthyllis terniflora, and Anthyllis cytisoides) planted in 9 experimental plots (75 m2) were tested in a two‐way crossed design. Plant monitoring consisted of survival and growth assessment at months 6, 24, 36, and 48, and these results were related to the main soil properties and the hydrological behaviour by means of principal component analysis. The response to soil treatments of each plant species was different due to its own physiology: M. tenacissima had the highest average survival rate, 92%, although both Anthyllis species presented the lowest rates, that is, 15% and 36%, in A. terniflora and A. cytisoides, respectively. Plant growth was favoured by both organic amendments and especially by compost, which improved the hydrological soil behaviour. Conversely, mulches did not show effective results. Run‐off and soil loss were associated with treatments without amendment and without mulch or treatments with gravel mulch. Our results suggest that organic amendments, especially by improving the hydrological response, can create favourable conditions for revegetating with native species in restored mine soils. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Modern filter design procedures for embankment dams respect criteria stemming from no-erosion filter (NEF) tests. The widespread application of NEF testing has provided experimental evidence of some deviations from the established filter criteria. This paper provides a complementary update to similar database studies of NEF test results. A large database of NEF tests, consisting of 258 group I and group II core soils (i.e. having more than 35% fines content) was analysed and the effects of various core soil characteristics (gradation, fines content, clay content, plasticity index and dispersivity) on experimentally defined no-erosion boundary filters were assessed. The database is unique, as it compiles the largest set of NEF test results. Through rigorous statistical and parametrical analysis, this paper critically compares current filter design criteria with experimental results and provides new insights that may assist and improve current procedures of critical filter design. [ABSTRACT FROM AUTHOR]

This paper presents techniques for constructing numerical solutions for some of the problems formulated in Part I. An algorithm to search for periodic solutions is developed and implemented in software. It is shown that there exist a finite number of discrete well defined periodic solutions for the lateral buckling problem of a straight pipeline under constant pressure and temperature. It is also shown that periodic solutions are unstable. A second numerical algorithm is developed for solving lateral buckling problem for an initially straight semi-infinite pipeline terminating at a sliding manifold under constant or varying temperature profiles. The resulting boundary value problem requires special numerical methods due to the stiffness of the governing differential equations. Algorithm is applied to find the solutions of problems for three different size pipelines; an 8.625 inch, a 16 inch, and a 32 inch diameter. Multiple stable chaotic solutions corresponding to distinct but extremely close initial conditions are revealed. The characteristics of these solutions match with the characteristics of the periodic solutions. This suggests that unstable periodic solutions act as separatrix between narrow zones containing stable chaotic solutions. It is seen that chaotic solutions can relieve a significant portion of the thermal and pressure loads without inducing excessive pipeline displacements. The results show that the pipeline end expansion is significantly less than the value given by common engineering methods. It is also shown that pipeline operating conditions and soil-pipe interaction parameters influence the stability and bifurcations of solutions. [ABSTRACT FROM AUTHOR]

A general formulation for the two dimensional lateral buckling problem is developed employing classical rod theory. A nonlinear differential system with seven unknowns is derived. Governing equations include a number of previously unaccounted nonlinear terms expressing interaction of various variables representing pipeline geometry and external loads. A rigorous derivation of the transformation of surface loads due to internal and external pressures to line loads revealed some previously unknown limitations on its applicability. Several boundary value problems are formulated corresponding to common pipeline engineering problems. Nonlinear dynamics methods are employed to draw some preliminary results on the behavior of the solutions. It is shown that the trivial solution corresponding to a perfectly straight pipeline experiencing no initial deformation and initial force is unstable. [ABSTRACT FROM AUTHOR]

Due to the humid climate in Taiwan area, the underground pipes are prone to be damaged by corrosion, which could be more severe for the environment with high salinity near the coast. In addition, the situation could be worse where the underground pipeline planning was not enforced. For example, a water pipe or a sewage pipe may be too close to a pressurized pipe, which could be corroded if the water pipe or the sewage pipe leaked. In this study, the numerical simulation software ABAQUS was used to simulate underground pipelines damaged by corrosion. The stress and displacement behavior was analyzed for scenarios with different internal pressure and surface loading conditions. In addition, the performance of the cured-in-place-pipe (CIPP) method, a trenchless rehabilitation method was also numerically analyzed. The results suggest that it can reinforce the damaged pipe by reducing the stress concentration and reducing the differential displacement. However, the design of the CIPP liner could be further optimized in terms of its design thickness. [ABSTRACT FROM AUTHOR]

Abstract: Subsurface flow can be an important process in gully erosion through its impact on decreasing soil cohesion and erosion resistance as soil water content or pressure increases and more directly by the effects of seepage forces on particle detachment and piping. The development of perched water tables fosters lateral flow that can result in seepage at the surface and/or formation of soil pipes by internal erosion of preferential flow paths. Continued internal erosion of soil pipes can lead to gullies, dam and levee failures. However, the processes involved in particle and aggregate detachment from soil pipe walls and transport processes within soil pipes have not been well studied or documented. This paper reviews the limited research on sediment detachment and transport in macropores and soil pipes and applies the knowledge learned from the much more extensive studies conducted on streams and industrial pipes to hydrogeologic conditions of soil pipes. Knowledge gaps are identified and recommendations are made for future research on sediment detachment and transport in soil pipes. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The present study explored the efficacy of pile shaft surface treatment on the improvement of soil-pile frictional resistance for floating or friction piles. 4 surface conditions of model piles measuring 200 mm long and 20 mm in diameter were examined, namely smooth (control), roughened, fishbone and checked shafts. A pile cap made of plywood was fixed to the top of the pile with 10 mm embedment depth, leaving 190 mm clearance for installation in the sand bed. The test chamber was a see-through glass tank with a footprint of 100 mm x 200 mm and 300 mm height. Coarse sand of D50 = 1.5 mm were loosely placed in the chamber by layers up to 200 mm height before the piles were installed either in single or triple group formations. The incremental load test of conducted via application of dead load ranging between 0.01-0.08 kPa on the pile cap, and the corresponding settlement was recorded. The test results revealed settlement to be reduced by the piles in the order of roughened > fishbone > checked > smooth for the single pile configuration, with maximum reduction of 40% recorded by the roughened pile. As for the pile group, settlement reduction of the piles with surface treatment clearly outperformed the control pile by almost 50%, though differences between the former were marginal with seemingly overlapping stress-strain plots. All in all the surface treatment of pile shaft enhanced the shaft friction for the piles installed in sand, but field implementation would require further examination of the pile-driving efficiency as the improved piles could cause additional resistance during installation. [ABSTRACT FROM AUTHOR]

Soil piping is an important land degradation process that occurs in a wide range of environments. Despite an increasing number of studies on this type of subsurface erosion, the impact of vegetation on piping erosion is still unclear. It can be hypothesized that vegetation, and in particular plant roots, may reduce piping susceptibility of soils because roots of vegetation also control concentrated flow erosion rates or shallow mass movements. Therefore, this paper aims to assess the impact of grass roots on piping erosion susceptibility of a sandy soil. The pinhole test was used as it provides quantitative data on pipeflow discharge, sediment concentration and sediment discharge. Tests were conducted at different hydraulic heads (i.e., 50 mm, 180 mm, 380 mm and 1020 mm). Results showed that the hydraulic head was positively correlated with pipeflow discharge, sediment concentration and sediment discharge, while the presence of grass roots (expressed as root density) was negatively correlated with these pipeflow characteristics. Smaller sediment concentrations and sediment discharges were observed in root-permeated samples compared to root-free samples. When root density exceeds 0.5 kg m − 3 , piping erosion rates decreased by 50% compared to root-free soil samples. Moreover, if grass roots are present, the positive correlation between hydraulic head and both sediment discharge and sediment concentration is less pronounced, demonstrating that grass roots become more effective in reducing piping erosion rates at larger hydraulic heads. Overall, this study demonstrates that grass roots are quite efficient in reducing piping erosion rates in sandy soils, even at high hydraulic head (> 1 m). As such, grass roots may therefore be used to efficiently control piping erosion rates in topsoils. [ABSTRACT FROM AUTHOR]

Many concepts have been proposed to explain hydrologic connectivity of hillslopes with streams. Hydrologic connectivity is most often defined by qualitative assessment of spatial patterns in perched water tables or soil moisture on hillslopes without a direct linkage to water flow from hillslopes to streams. This form of hydrologic connectivity may not explain the hydrologic response of catchments that have network(s) of preferential flow paths, for example, soil pipes, which can provide intrinsic connectivity between hillslopes and streams. Duplex soils are known for developing perched water tables on hillslopes and fostering lateral flows, but the connectivity of localized perched water tables on hillslopes with soil pipes has not been fully established. The objectives of this study were to characterize pipeflow dynamics during storm events, the relationships between perched water tables on hillslopes and pipeflows, and their threshold behaviour. Two well-characterized catchments in loess soil with a fragipan were selected for study because they contain multiple, laterally extensive (over 100 m) soil pipe networks. Hillslopes were instrumented with shallow wells adjacent to the soil pipes, and the wells and pipe collapse features were equipped with pressure transducers. Perched water tables developed on hillslopes during a wetting up period (October-December) and became well connected spatially across hillslope positions throughout the high flow period (January-March). The water table was not spatially connected on hillslopes during the drying out (April-June) and low flow (July-September) periods. Even when perched water tables were not well-connected, water flowing through soil pipes provided hydrologic connectivity between upper hillslopes and catchment outlets. Correlations between soil pipeflow and perched water tables depended on the size and location of soil pipes. The threshold relationship between available soil-moisture index plus storm precipitation and pipeflow was dependent on the season and strongest during dry periods and not high-flow seasons. This study demonstrated that soil pipes serve as a catchment backbone of preferential flow paths that provide intrinsic connectivity between upper hillslopes and streams. [ABSTRACT FROM AUTHOR]

Humans can inhabit other planets in future by advancement in science and technology, starting by closest ones and moving to farther planets. There are some projects underway currently for human settlement on Mars such as Mars-one project or new proposals by NASA. In this paper, possibility of creating and using underground structures in Mars for sheltering humans against harsh environment and dangerous rays goes under investigation. Primary locations such as Arsia Mons for early settlement on Mars was investigated providing its appropriate conditions. Numerical analysis for tunneling to create underground space was conducted considering different spatial orientation of main discontinuities such as fault and joints in Martian gravity. It was inferred that tunneling in near surface Martian rocks is not susceptible to major failures and instabilities. Frozen water in Mars climate, and low gravity result in lower amounts of required cohesion value to keep tunneling structure stable in different scenarios of discontinuities in Martian rocks. It was concluded that underground structures are among the best options for residing humans on Mars and sheltering them against harsh climate by providing insulation and creating enough thickness of burden rock mass against dangerous cosmic and solar rays. [ABSTRACT FROM AUTHOR]

A numerical approach for simulating piping erosion is proposed based on an auto-adaptive moving mesh. This approach adapts a flownet mesh (FM) to discretize the domain. It reduces the simulation of two-dimensional transport of moving particles to one-dimensional problem by taking advantages of flow tube concept. Furthermore, it employs a stepwise procedure to decouple the solid-liquid interaction equations for modeling piping erosion. Specifically, the FM is updated and evolved automatically in accordance to simulated erosion since the flownet is refined in high-velocity regions, where the piping erosion progresses. Therefore, the FM is auto-adaptive to the piping erosion paths. [ABSTRACT FROM AUTHOR]

Piping is a widespread phenomenon in the world and can significantly contribute to the downward movement of water, sediments, and nutrients. This study examines the hydrological functioning of soil pipes in a loess-derived soil under pasture using hydrometric and hydrochemical analyses. It aims to investigate the relation between pipeflow, rainfall, and groundwater table fluctuations and to determine the dominant source of the water flowing through the soil pipes using both hydrometric and hydrochemical approaches. A rapid pipeflow response is observed when a threshold rainfall depth is exceeded. This threshold depth is larger in the summer (9 mm) compared with that in the winter (4 mm) which is related to the prestorm wetness of the soil. Hydrochemical analyses indicate that both groundwater and rainfall contribute to the pipeflow with a dominance of groundwater. This study shows that pipeflow can be an important hydrological pathway in loess-derived soils with a clear seasonal pattern in pipeflow responses to rainfall events. [ABSTRACT FROM AUTHOR]

In this work, the effects of coupled hydromechanical (consolidation) processes associated with shield tunneling excavation in soft clays are investigated with particular attention to the prediction of ground movements at the ground surface. A series of 2d FE analyses have been carried out in parametric form in order to investigate the effects of tunnel excavation velocity relative to the soil consolidation rate and the hydraulic boundary conditions at the tunnel boundary. The shield advancement process has been simulated with a simplified procedure incorporating both volume loss and ovalization of the tunnel section. In order to investigate the relative importance of soil consolidation during the excavation process, different characteristic times for the tunnel face advancement and for the consolidation process around the tunnel have been considered, for the two limiting conditions of fully permeable liner and impervious liner. The potential damage induced by the tunnel excavation on existing structures, based on computed ground surface distortions and horizontal deformations, has been found to vary significantly with time during the consolidation process. The results of the simulations allowed to obtain useful information on the minimum tunnel face advancement speed for which the assumption of fully undrained conditions for the soil during the excavations is acceptable, as well as on the speed range for which solving the fully coupled hydromechanical problem is necessary. [ABSTRACT FROM AUTHOR]

In this review, we explore the significance of rock fragments in studies of soil hydrological processes, because according to research, the effects of rock fragments on soil hydrological processes are inconsistent (positive/negative). Rock fragments play a critical role in the biosphere as the primary filter for water and solutions containing contaminants and heavy metals. Rock fragments have a complex influence on soil hydrological processes (e.g. soil erosion, runoff generation, water infiltration, solute transport and water flow) and are highly relevant in a typical system in the soil–plant–atmosphere continuum. Cracks related to rock fragments provide preferential flow paths through which pollutants are transported into groundwater. In this paper, the published literature is reviewed concentrating on rock fragments and their effects on soil hydrological processes. Systematic studies and examples illustrate the effects of rock fragments architecture (i.e. coverage, content, size, position, spatial heterogeneity, morphology, weathering and topography) on soil hydrological processes. Methods and models applied to evaluate the effects of rock fragments on soil hydrological processes are examined in detail. We conclude that the relationship between rock fragments and soil hydrological processes is complicated and requires more international research efforts. This review concludes with a discussion of perspectives on areas of research that can improve understanding of the effects of rock fragments on soil hydrological processes, with insights and suggestions also being provided regarding potential research trends, requirements and solutions. [ABSTRACT FROM AUTHOR]

Overcut is a critical issue in pipejacking, especially for the cases with difficult geology conditions or with a curved alignment. For those cases, lubricants are frequently applied to fill the gap or to reduce the friction between soil and pipes. However, it is very difficult to quantitatively determine the real contact condition between the soil and pipe. New technology for soil-pipe interaction measurement is still scarce and requires further development. There are only indirect methods practically available for soil-pipe interaction, and engineering judgment is required for those measurements. In this study, the finite element software ABAQUS is used for the numerical analysis of the pipejacking, including the influence of lubricant property and the overcut on the soil-pipe interaction. The results show that lubrication can significantly reduce the stress concentration surrounding the pipe, the disturbing of the pipejacking on the surrounding soil was increased as the overcut increasing, the soil stress was decreased but the disturbance on the excavation face will be increased. [ABSTRACT FROM AUTHOR]

Conventional design guidelines for buried pipelines are based on the assumption that soil is either dry or fully saturated. In unsaturated soils, such an assumption may lead to underestimation of load from externally imposed ground movement. Such loads are generated because the water meniscus between soil particles creates an additional interparticle force due to suction, which in turn makes the soil stiffer and stronger. This paper presents a methodology for predicting lateral loads on pipelines in unsaturated sandy soils by investigating soil-pipe interaction with full-scale tests and characterizing unsaturated soil behavior with properties from triaxial tests. A constitutive model was developed, and finite-element (FE) simulations were performed and compared with the full-scale test results to validate the modeling process. Additional FE simulations were conducted to assess the maximum lateral load on pipelines buried in different Class II unsaturated sands. The full-scale tests and FE simulations show that increased strength and stiffness associated with soil suction increases lateral loads on pipelines and thus need to be considered when designing pipelines for externally imposed ground movement. The modeling procedures and results can be used to predict lateral loads on underground pipelines subjected to construction and earthquakeinduced ground movements, landslides, and subsidence. Because most pipelines are buried in unsaturated soil, the results have widespread relevance in design and construction. [ABSTRACT FROM AUTHOR]

Multiple on-site and off-site effects of gully erosion threaten sustainable development, which is especially evident in dryland environments. To control soil erosion by gullying, various soil and water conservation measures have been developed, of which check dams are the most common. Where soil piping occurs, soil and water conservation measures have a limited effect on gully stabilisation, and check dams easily collapse. Therefore, new integrated approaches are needed to control gully erosion induced by soil piping. Here, a subsurface geomembrane dam is proposed as an innovative measure to reduce subsurface flow in soil pipes near gullies. Application of such a dam in Northern Ethiopia resulted in a decrease of gully erosion rates in vertisols and a rising water table in the intergully areas near the gully channel. The consequence of this effect for agriculture near gully channels is the reduction of soil desiccation and, hence, increased crop yields in the intergully areas near the gully channels. In addition, runoff flow diversions into infiltration sites can increase off-site benefits by strengthening economic activities or fasten environmental rehabilitation. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Nearly all of Europe is affected by soil erosion. A major policy response is required to reverse the impacts of erosion in degraded areas, particularly in light of the current climate change and water crisis. Soil loss occurs not because of any lack of knowledge on how to protect soils, but a lack in policy governance. The average rate of soil loss by sheet and rill erosion in Europe is 2·46 Mg ha−1 yr−1. To mitigate the impacts of soil erosion, the European Union's Common Agricultural Policy has introduced conservation measures which reduce soil loss by water erosion by 20% in arable lands. Further economic and political action should rebrand the value of soil as part of ecosystem services, increase the income of rural land owners, involve young farmers and organize regional services for licensing land use changes. In a changing World of 9 billion people with the challenge of climate change, water scarcity and depletion of soil fertility, the agriculture economy should evolve taking into account environmental and ecological aspects. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper aims at a better understanding of the role of soil characteristics in piping activity in a mountainous area under a temperate climate. The recognition of favourable soil properties is widely described in badlands with dispersive materials, and in loess-covered hilly regions. In other regions – without dispersive materials or without extensive loess deposits – piping conditions draw hardly any attention. The survey was carried out in the Tyskowa catchment, in the Bieszczady Mts. (Eastern Carpathians). We focused on soil characteristics that can impact erodibility, including texture, structure, consistence, porosity, and bulk density. These characteristics, as well as selected chemical properties (pH, exchangeable cations, and sodium absorption ratio — SAR), were studied in detail for 4 soil profiles with a different position in relation to collapsed pipes (CPs): on a slope with abundant CPs and on one lacking CPs. We tested a hypothesis that soil properties control the occurrence of pipes, and we checked if there is any difference in soil properties on slopes with and without CPs. Moreover, we compared soil profiles within the slope with CPs. Additionally, detailed geomorphological mapping of piping forms was carried out in the selected catchment in order to determine the depth of the pipe formation. No clear difference in soil characteristics was observed between the slope with high piping activity and the one without it with Cambisols occupying both sites. The soils exhibit a large content of silt, which potentially enhances piping. The chemical properties do not differ among the analysed soils. However, the profiles at the site above CPs (with potential piping) and in the sinkhole are characterized by intense biological activity, the development of soil structure in deeper horizons (angular and subangular blocky structure down to 90–105 cm), high porosity, and low bulk density. To summarize, it is the combination of biological activity and soil properties (silty texture, well-developed soil structure, low bulk density, and high porosity) that determines the formation of pipes in the study area. Combining all the results from the soil profiles and the depth of pipes indicates that pipes develop on the boundary of B and C soil horizons, and the mean depth of pipe formation is almost 0.80 m with the maximum of 1.55 m. [ABSTRACT FROM AUTHOR]

BACKGROUND Crop residue removal for bioenergy production can alter soil hydrologic properties and the movement of agrochemicals to subsurface drains. The Root Zone Water Quality Model ( RZWQM), previously calibrated using measured flow and atrazine concentrations in drainage from a 0.4 ha chisel-tilled plot, was used to investigate effects of 50 and 100% corn ( Zea mays L.) stover harvest and the accompanying reductions in soil crust hydraulic conductivity and total macroporosity on transport of atrazine, metolachlor and metolachlor oxanilic acid ( OXA). RESULTS The model accurately simulated field-measured metolachlor transport in drainage. A 3 year simulation indicated that 50% residue removal reduced subsurface drainage by 31% and increased atrazine and metolachlor transport in drainage 4-5-fold when surface crust conductivity and macroporosity were reduced by 25%. Based on its measured sorption coefficient, approximately twofold reductions in OXA losses were simulated with residue removal. CONCLUSION The RZWQM indicated that, if corn stover harvest reduces crust conductivity and soil macroporosity, losses of atrazine and metolachlor in subsurface drainage will increase owing to reduced sorption related to more water moving through fewer macropores. Losses of the metolachlor degradation product OXA will decrease as a result of the more rapid movement of the parent compound into the soil. Published 2015. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Soil pipes are important subsurface flow pathways in many soil erosion phenomena. However, limited research has been performed on quantifying and characterizing their flow and transport characteristics. The objectives of this research were to determine the applicability of a streamflow model with transient storage in deriving flow and transport characteristics of soil pipes. Tracer data from pulse inputs were collected in four different soil pipes after a fluorescein dye was injected in the upstream end of each soil pipe network in three branches (west, middle, and east) of a main catchment and a back catchment in Goodwin Creek Experimental Watershed in Mississippi. Multiple sampling stations were positioned along each soil pipe network. The transient storage zone model OTIS-P was executed inversely to estimate transport parameters by soil pipe reach such as the soil pipe cross-sectional area ( A), soil storage zone cross-sectional area ( As), and exchange rate between the soil pipe and the soil storage zone ( αs). Model convergence was achieved, and simulated breakthrough curves of the reaches were in good agreement with actual tracer data for eight of the nine reaches of the three branches of the Main Catchment and five of the seven reaches of the Back Catchment soil pipe. Simulation parameters for the soil pipe networks were similar to the range of values reported for flow and transport characteristics commonly observed in streams. Inversely, estimated soil pipe flow velocities were higher with increased tortuosity, which led to a smaller cross-sectional areas predicted for the soil pipe flowpaths, while other parameters were not sensitive to tortuosity. In general, application of One-Dimensional Transport with Inflow and Storage-P to this unique soil pipe condition suggested larger transient storage ( As and αs) compared with most stream systems. This was hypothesized to be because of relatively higher ratio of the wetted perimeter to flow area in the soil pipe, the hydraulic roughness of the soil pipe, potential retention in collapsed portions of the pipe, and interaction with smaller preferential flow systems. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Much debate has occurred in catchment hydrology regarding the connectivity of flow paths from upslope areas to catchment outlets. This study was conducted in two catchments, one with three upper branches, in a loess soil with a fragipan that fosters lateral flow and exhibits an extensive distribution of soil pipe collapse features. The study aimed to determine the connectivity of multiple soil pipe networks as well as determine pipe flow velocities during storm events. Fluorescein dye was injected directly into soil pipes at the upper most pipe collapse feature of four different hillslopes. Breakthrough curves (BTC) were determined by sampling multiple pipe collapse features downslope. The BTCs were used to determine the 'average' (centre of mass) and 'maximum' (first arrival) flow velocities. This study confirmed that these catchments contain individual continuous soil pipe networks that extend over 190 m and connect the upper most hillslopes areas with the catchment outlet. While the flow paths are continuous, the individual pipe networks consist of alternating reaches of subsurface flow through soil pipes and reaches of surface flow through gullies formed by pipe collapses. In addition, flow can be occurring both through the subsurface soil pipes simultaneous with surface flow generated by artesian flow from the soil pipes. The pipe flow velocities were as high as 0.3 m/s, which was in the range of streamflow velocities. These pipe flow velocities were also in the range of velocities observed in pinhole erosion tests suggesting that these large, mature soil pipes are still actively eroding. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Piping, or backward erosion, resulting in tunneling under an embankment or foundation, is an important phenomenon that can lead to the failure of the embankment or foundation. We have experimentally investigated the erosion mechanism of this piping phenomenon using a laboratory-scale model. We discovered two types of coupled erosion in the evolution of piping through an analysis of the grain size distribution of the eroded mass. Overall, grain sizes in the eroded mass ranged from 0.1 to 0.5 mm. The 0.1-0.25 mm grains were found to dominate when the erosion was induced by stress release, whereas in the case of clogging, the dominant grain sizes were 0.25-0.5 mm. The first form of erosion caused the tunnel to advance upstream, whereas the second increased the depth of the tunnel; otherwise, the two types of erosion were coupled. Furthermore, the eroded mass throughout the evolution of piping was non-uniform and intermittent. [ABSTRACT FROM AUTHOR]

Summary Macropores and soil pipes in stream banks are common geomorphic features. Macropores and soil pipes that are open to the channel (i.e. “bank face-connected” macropores) are inundated when channel stage is elevated (e.g., from precipitation, snowmelt, dam release). However, previous studies have not investigated macropore impact on bi-directional water exchange between the channel and bank/riparian groundwater under variable hydrologic conditions. We monitored two transects of riparian groundwater wells perpendicular to the bank of a 2nd order stream for a year: one with bank face-connected macropores (M transect) and one without bank face-connected macropores (NM transect). Fluctuations in water level and temperature during storms in those wells closest to the channel were on average 139% and 29% higher, respectively, in the presence of macropores. Rising head tests in the same wells indicated that hydraulic conductivity was 61–140 times higher in the presence of macropores. Bank storage, indicated by gradient reversals between channel and riparian zone, occurred on two temporal scales. Bank storage during storms was more frequent in the M transect (occurred all year) than in the NM transect (occurred just in winter and spring). Smaller magnitude gradient reversals at the M transect are consistent with faster head equilibration and greater exchange volume. Bank storage also occurred on an annual basis, with channel water entering storage during summer and fall and returning to the channel during winter and spring. Taken together, these results suggest that macropores act as preferential flow paths that enhance the connectivity between channels and riparian groundwater that influences bank storage. Where bank macropores are present, conceptual models of hyporheic and groundwater flow should account for their effects. [ABSTRACT FROM AUTHOR]

Little is known about the association of soil pipe collapse features with soil properties or land use history. Three loess covered catchments in northern Mississippi, USA were characterized to investigate these relationships. Soil pipe collapses were characterized for their size, type feature and spatial location along with soil properties across the three catchments. Although mapped as the same soil, one of the catchments did not contain pipe collapse features while the other two had 29.4 and 15.4 pipe collapses per hectare. These loess soils contained fragipan layers that are suspected of perching water, thereby initiating the piping processes. Pipe collapses associated with subsurface flow paths were not always consistent with surface topography. The surface layer tended to be non-erodible while layers below, even the upper fragipan layers, were susceptible to erosion by pipeflow. Soil properties of the lowest fragipan layer were highly variable but tended to prevent further downward erosion of soil pipes and thus formed a lower boundary for gullies. Middle to lower landscape positions in one of the piped catchments contained anthropic soils that were highly erodible. These anthropic soils were previously gullies that were filled-in in the 1950s when forested areas, assumed to have been established when land was previously converted from crop to forest land, were converted to pasture. Three decades after this land use change from forest to pasture, pipe collapses became evident. In contrast, the adjacent catchment that does not exhibit pipe collapse features experienced severe sheet and rill erosion prior to the 1930s while in cotton production. The surface horizons above the lower fragipan layer were completely removed during this period, thus the top-soil layer that tends to form a bridge above soil pipes in the more erodible subsoil layers was removed. This study showed that knowledge of soil characteristics or topography alone do not explain the distribution of soil pipe collapses as past land use can play a definitive role. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Mountain Lake, located in Giles County, southwestern Virginia, is one of only two natural lakes in the state of Virginia. The lake exhibits rare self-draining behavior, with recent episodes in 2008, 2011, and 2012 that drained the lake almost completely and revealed the presence of four sinkhole-like depressions, with piping holes at their bottoms and sides, near the northeastern and northwestern margins of the lake. This phenomenon has raised concern over declining tourism to the Mountain Lake Lodge. The purpose of this study was to investigate the piping potential of lake-bottom sediment and its role in seepage and lake-level fluctuations. Sixteen grab samples of lake-bottom sediment were collected from the vicinity of the depressions. Additionally, five Shelby tube samples were obtained to determine the in-situ density of the sediment. Grain size distribution, Atterberg limits, and compaction-mold permeameter tests were used to evaluate lake sediment's susceptibility to piping. Grain size distribution and Atterberg limits test results reveal that the lake-bottom sediment consists predominantly of fine sand and silt, which are well known for their susceptibility to piping. Results of the compaction-mold permeameter test show that the critical hydraulic gradient (i c ), the hydraulic gradient at which the sediment starts to pipe, ranges between 1 and 10, depending on the density, grain size distribution, and plasticity characteristics of the sediment. These results suggest that piping of lake sediment is the primary mechanism responsible for the formation of lake-bed depressions and lake level fluctuations. [ABSTRACT FROM AUTHOR]