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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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

For a pipe jacking construction, reducing the soil–pipe interface friction and providing enough jacking force are the most common approach to optimize the construction efficiency. In practice, jacking force is generally estimated by various empirical equations. However, the estimations of empirical equations frequently deviate from the reality. In this study, a model coupling finite element method and a displacement control method were applied to estimate the required jacking force in pipe jacking. Two cases were examined from Central Taiwan, where the primary geological foundation composed of gravel formations. Case A pertained to pipe jacking construction during which sewage pipes with a diameter of 2.4 m were utilized. The monitoring data from this case were used to establish the jacking force estimation model. The jacking force history observed in Case B, in which sewage pipes of 1.0 m diameter were used, was compared with those obtained by the developed model to demonstrate the applicability of the model. The results suggested the developed model can estimate the jacking force with a better accuracy towards the middle and the final stage of the pipe jacking process. [ABSTRACT FROM AUTHOR]

Abstract: Characterizing a dilation angle in terms of a single effective vertical stress at a pipe centerline is a simplification that does not account for a variable dilation angle and peak plane strain friction angle with depth. The current research is to evaluate the effects of more comprehensive characterization of soil strength. To accomplish the goal, finite element simulations for soil-pipe interaction were performed for layered soil conditions in which the dilation angle and peak plane strain friction angle were varied with depth and normal stress was estimated with greater accuracy. Finite element simulations using dilation angle and peak plane strain friction angle linked to a single effective vertical stress were performed for comparison. The results of soil-pipe interaction were converted into dimensionless force vs. dimensionless displacement curve for both simulations were compared. Because the comparisons of layered soil conditions and the single soil layer model show little difference in the results, the single soil layer model can be replaced with the layered soil conditions model, which is a simpler and straight forward characterization of dilation angle and peak plane strain friction angle. The predicted force of the effective vertical stress model is slightly higher than that of the normal stress model, and thus tends to produce conservative estimates for the analysis of pipeline deformation in the ground. Because the comparisons show very small difference in the results, the more simple and straightforward characterization of friction angle relative to the effective vertical stress at the pipe centerline can be used in the numerical simulations to predict the soil-pipe behavior. [Copyright &y& Elsevier]

Abstract: After a wildfire the soil is covered by ash. Ash properties depend on vegetation type, amount of fuel and fire intensity. The ash layer controls the post-fire soil hydrologic response, but little is known about the effect of ash thickness and ash type on infiltration, which is relevant for post-fire runoff and soil losses and for ecosystems rehabilitation and restoration. This paper analyses the role of i) ash type (black or white), ii) thickness (5, 15 and 30mm-thick) and iii) temporal variation (0, 15 and 40days) under three simulated rain events (55mm for 1h) on soil surface hydrology. The rainfall was simulated on 0.25m2 plots, and time to ponding, runoff and runoff discharge were measured. The infiltration rates, the initial infiltration rate (f0 ), the steady-state infiltration rate (fc ), and the infiltration decay factor (k), were calculated and the Horton infiltration equation applied. The results show that soils covered with white ash doubled the runoff rates of soils covered with black ash. In general, runoff decreases as the ash thickness increases and the runoff decreases with the number of rainfall events after the fire in plots covered with white ash. Ponding time and k are positively correlated by the ash thickness and f0 and fc are correlated by the rainfall events (in three runs). Ash type and ash depth are key factors on the soil hydrology after a wildfire. [Copyright &y& Elsevier]

Abstract: This study investigates the role of soil characteristics and land use in the development of soil pipes in the loess belt of Belgium. First, we tested the hypothesis that discontinuities in the soil profile enhance lateral flow and piping by impeding vertical infiltration. We focus on discontinuities in soil characteristics that can vary with soil depth, including texture, saturated hydraulic conductivity, penetration resistance, and bulk density. These characteristics as well as soil biological activity were studied in detail on 12 representative soil profiles for different land use types. Twelve sites were selected in the Flemish Ardennes (Belgium): four pastures with collapsed pipes (CP), four pastures without CP, two sites under arable land without CP and two sites under forest without CP. Secondly, this study aimed at evaluating the interaction of groundwater table positions (through soil augerings) and CP in a larger area, with a focus on pastures. Pasture is the land use where almost all CP in the study area are observed. Therefore, the position of the groundwater table was compared for 15 pastures with CP and 14 pastures without CP, having comparable topographical characteristics in terms of slope gradient and contributing area. Finally, the effect of land use history on the occurrence of pipe collapse was evaluated for a database of 84 parcels with CP and 84 parcels without CP, currently under pasture. As to the first hypothesis, no clear discontinuities for abiotic soil characteristics in soil profiles were observed at the depth where pipes occur, but pastures with CP had significantly more earthworm channels and mole burrows at larger depths (>120cm: mean of >200 earthworm channels per m2) than pastures without CP, arable land or forest (>120cm depth, a few or no earthworm channels left). The land use history appeared to be similar for the pastures with and without CP. Combining all results from soil profiles and soil augering indicates that intense biological activity (especially by earthworms and moles), in combination with a sufficiently high groundwater table, favours the development of soil pipes in the study area. [Copyright &y& Elsevier]

Abstract: Thermal performance of Earth Air Tunnel Heat Exchanger (EATHE) under transient operating conditions has been evaluated for predominantly hot and dry climate of Ajmer (India) using experimental and Computational Fluid Dynamics modeling. Effects of time duration of continuous operation, thermal conductivity of soil pipe diameter and flow velocity on thermal performance of EATHE under transient conditions have been analyzed. Results show that the transient thermal performance of EATHE is significantly dependent on thermal conductivity of the soil and duration of its continuous operation. The analyzed cases have shown the range of derating to be as minimal as 0% to as high as 64%, which if ignored while designing may lead to poor performance of EATHE. Study reveals that the effect of pipe diameter due to prolonged use of EATHE system on its thermal performance is least in case of soil with higher value of thermal conductivity. Results show that the increase in flow velocity leads to deterioration in thermal performance of EATHE system. Under steady state condition, drop of 18.8°C in air temperature is obtained, whereas, under transient conditions cooling of air reduces from 18.7°C to 16.6°C for soil thermal conductivity of 0.52Wm−1 K−1, after 24h of continuous operation. [Copyright &y& Elsevier]

Abstract: Due to overgrazing and agricultural intensification, gully erosion severely affects sub-Saharan countries; however, insufficient quantitative studies exist for this part of the world. This paper presents data on gully head retreat rates in Northern Ethiopia and relates these rates to gully and environmental characteristics. The monitoring of headcuts over one rainy season (2010) revealed that present-day retreat rates are low, with average annual linear (R l), areal (R a) and volumetric (V e) retreat rates of 0.34my−1, 1.70m2 y−1 and 5.2m3 y−1, respectively. These results express the positive effects of recent soil and water conservation practices on gully stabilization. Significantly higher values of R l (up to 1.93my−1) occurred in the Vertisol areas affected by soil piping. When considering the medium- to long time scale (1–47years) using archival terrestrial (and aerial) photographs, headcut retreat rates proved to be significantly higher than those in the short term. The averages for R l, R a and V e are 3.8my−1, 31.5m2 y−1 and 47.7m3 y−1, respectively. Retreat rates are up to 10 times higher after road construction. For the medium to long term, headcut retreat rates were positively related to the catchment area (A). A power relationship that best describes the relation between V e and A is V e =0.53 A 0.31 (r 2 =0.27, n =18). Compared to other areas worldwide, regressive erosion has been rapid in Ethiopia as a result of the degraded and steep landscape combined with erosive rains and the occurrence of Vertisols. In Vertisols, headcut retreat is controlled by soil piping. Because no adequate techniques exist to control gully initiation and development in Vertisols, alternative techniques should be developed that deactivate soil pipes. [Copyright &y& Elsevier]

Abstract: We present the development and calibration of a macroelement model that captures the response of piles in cohesionless soils subjected to biaxial lateral loading. The model is founded on actual physical mechanism of soil resistance and provides the framework for extending a uniaxial model to biaxial case by means of a single cross-stiffness parameter. Both upper and lower bounds for the cross-stiffness parameter are also presented. The model is calibrated and verified using three-dimensional finite element (FE) simulations of soil-pile interaction for uniformly prescribed displacement along the pile length. Comparison of predictions from uniaxial and biaxial models with the FE results for transient loading indicates that the response assuming no coupling between the two horizontal directions for biaxial loading can differ significantly from the ‘true’ response for some cases. Accounting for coupling in the lateral direction, the proposed model captures the transverse pile response with very good accuracy while retaining the simplicity and computational efficiency of macroelement formulations compared to 3D FE analyses. [Copyright &y& Elsevier]

Abstract: Biological soil crusts are important microbiotic communities which are considered a key factor in combating desertification in terms of sand dune remobilitation. Because of their greater concentration of clay, silt and hydrophobic organic matter, they create a physical discontinuity in surface profile which potentially contribute to variability in soil hydrology of arid and semiarid land and should be considered in the development of hydrological and erosion models. However, until recently limited inconclusive research has been conducted to determine the functional relationship between soil and microbiotic crusts. We investigated the influence of microbiotic crust on hydrological behaviour of crusted sand dunes in NW China. The infiltration data on a crusted and crust-removed sand dune were obtained with dish permeameter which was not moved during the measurement at a sequence of nominal pressure head values, h, of −1, −4, −7, −10, −18cm. Hydraulic conductivity K(h) was measured by steady-state infiltration experiments and piece-wise application of the exponential relation between K and h, according to Wooding''s analytical solution of a three-dimensional flow field. The transient experimental infiltration data, along with initial and final water contents were used for numerical analysis within sand profiles without and with microbiotic crust. Specifically, we provided evidences that the main physical and hydrological consequences occurring locally, always cause lower unsaturated fluxes in the sand beneath the crusted layer. Nevertheless, due to the effective rainfalls regime, it has insignificant effects on the local soil water regimes with unchanged storage and deep fluxes. [Copyright &y& Elsevier]

Abstract: The pinhole test is an empirical test based on the qualitative evaluation of the dispersivity (colloidal erodibility) of compacted fined-grained soils. This paper evaluates the pinhole test device for the quantitative assessment of the susceptibility of soil horizons to piping, assesses the effects of hydraulic head, water quality, antecedent soil moisture content and soil disturbance on the hydrological and erosion response during pipeflow, and formulates recommendations for the application of the pinhole test to study piping erosion processes. In total, 255 pinhole test experiments were conducted. The results obtained from disturbed soil samples (Ap horizon) indicate: (i) a significant positive linear increase in pipeflow discharge (Q w) and sediment discharge (Q s) with increasing hydraulic head, (ii) no relationship between Q w and antecedent soil moisture content (ASM), but significant and negative relationship between Q s and ASM, and (iii) significantly higher Q s for distilled water than for tap water. The use of disturbed soil samples resulted in significantly more rapid flow responses and lower sediment discharges than for undisturbed soil samples. The pinhole test experiments performed on different loess-derived soil horizons show that the plowed topsoil (Ap) and the underlying clay-enriched horizon (Bt) are at least two times less susceptible to piping than the decalcified (C1) and the calcareous horizons (C2). This confirms field observations indicating that loess-derived soil horizons are very susceptible for piping erosion, especially when the C horizon crops out. This study demonstrates that the pinhole test is suitable for assessing the susceptibility of soil horizons to piping in a quantitative way (i.e. Q w, Q s, the time to outflow and the cross-section of the pipe after the test). We recommend the use of: (i) two different hydraulic heads (i.e. 180 and 1020mm), (ii) distilled water, (iii) contrasting antecedent soil moisture contents of the soil samples to be tested, and (iv) different soil sampling methods to investigate the effect of soil disturbance, and particularly to obtain a better understanding of the sediment response during pipeflow. [Copyright &y& Elsevier]

Abstract: The knowledge of the soil saturated hydraulic conductivity (K s) is essential for irrigation management purposes and for hydrological modelling. Several attempts have been done to estimate K s in base of a number of soil parameters. However, a reliable enough model for qualitative K s estimation based on the expert assessment of field characteristics had not been developed up to date. Five field characteristics, namely macroporosity (M), stoniness (S), texture (T), compaction (C) and sealing (L), in addition to tillage (G) were carefully assessed according to three classes each, in 202 sites in an agricultural irrigated area in Eastern Mediterranean Spain. After the evaluation of field characteristics, a single ring infiltrometer was used to determine the K s value as the solution of the infiltration equation when the steady state was reached. The distribution of the K s was assessed and five classes with 10-fold separations in class limits were defined accordingly. The relationships among site characteristics and K s were analyzed through a correspondence analysis (CA). Next, an ordered logistic regression model (OLRM) for the prediction of the K s class was developed. The CA revealed that, though tightly related, the set of six site characteristics should not be simplified into a smaller set, because each characteristic explains a significantly different aspect of K s. Consequently, the OLRM was based on the six characteristics, which presented the following order of importance: L>M>G>T>C>S. According to the cross-validation of the OLRM the hit probability for the prediction of the K s class attained an average value of 50%, which increased to 63% for the highest class of K s. Moreover, wrong estimation of the K s class exceeded the ±1 range only in 3% of sites. Therefore, a reliable enough assessment of K s can be based on the expert assessment of field characteristics in combination with an OLRM. [Copyright &y& Elsevier]

Abstract: Soil-pipes (porous pipes inside a hillslope) are often detected in collapsed slopes indicating their influence on slope failure processes. Only limited studies can be found regarding the impacts of soil-pipes on landslide mechanisms. Hillslope models prepared in a flume are experimented with different soil-pipe configurations: a) no pipe, b) closed pipe and c) open pipe. Pore-water pressures were measured at six different locations along a slope. Discharges at the outlet of soil-pipe and groundwater seepage were also recorded. For the above mentioned pipe configurations two types of experiments were conducted: a) rainfall-induced failure and b) seepage-induced failure. Experimental results show that a closed pipe accumulates water around its lower end and continuously increases pore-water pressure till a failure. An open pipe works as a means of hillslope drainage and reduces the pore-water pressure of an entire slope. However, if open pipe is blocked, pore-water pressure close to its lower end rises rapidly, leading to immediate soil mass movement. For both seepage and rainfall-induced failure experiments, the maximum pressure before the failure was larger at a slope with an open pipe (once it is closed) than a slope with a pipe closed from the beginning or that without a soil-pipe. This indicates that the blockage of soil-pipes makes a slope more susceptible to failure. Displacement vectors show that soil movement velocity close to the surface was highest at slopes with open pipes after closure and lowest at slopes without pipes because of a higher degree of saturation and pore-water pressure at the time of failure of the former. Before a large failure, small fluctuations in pore-water pressure were also observed which can be an indicator of impending failure. [Copyright &y& Elsevier]

Abstract: Soil piping (tunnel erosion) has been recognised as an important erosion process in collapsible loess-derived soils of temperate humid climates, which can cause collapse of the topsoil and formation of discontinuous gullies. Information about the spatial patterns of collapsed pipes and regional models describing these patterns is still limited. Therefore, this study aims at better understanding the factors controlling the spatial distribution and predicting pipe collapse. A dataset with parcels suffering from collapsed pipes (n =560) and parcels without collapsed pipes was obtained through a regional survey in a 236km² study area in the Flemish Ardennes (Belgium). Logistic regression was applied to find the best model describing the relationship between the presence/absence of a collapsed pipe and a set of independent explanatory variables (i.e. slope gradient, drainage area, distance-to-thalweg, curvature, aspect, soil type and lithology). Special attention was paid to the selection procedure of the grid cells without collapsed pipes. Apart from the first piping susceptibility map created by logistic regression modelling, a second map was made based on topographical thresholds of slope gradient and upslope drainage area. The logistic regression model allowed identification of the most important factors controlling pipe collapse. Pipes are much more likely to occur when a topographical threshold depending on both slope gradient and upslope area is exceeded in zones with a sufficient water supply (due to topographical convergence and/or the presence of a clay-rich lithology). On the other hand, the use of slope-area thresholds only results in reasonable predictions of piping susceptibility, with minimum information. [Copyright &y& Elsevier]

Abstract: Biological soil crusts are receiving increasing attention due to their potentially positive effects on desert ecosystems. Artificial propagation of crusts is one way to restore degraded desert soils. However, little is known about their effectiveness on overland flow or water infiltration. Consequently, a study was done on soils of the Loess Plateau of China that had crusts propagated on different slopes. The results show that: (1) it is feasible to artificially grow moss-dominated biological soil crusts (moss crusts) in laboratory; when inoculated by sprinkling crushed fragments of stems and leaves of natural moss crusts they will cover the soil surface almost completely after about 10 months; (2) the artificially propagated moss crusts significantly increase infiltration consequently decreasing overland flow and this increase in infiltration is positively correlated to the soil coverage extent; (3) overland flow results increased by slope in moss-protected and bare soils, consequently the action of moss crusts is particularly important for protecting steep slopes; (4) the start time of runoff process is delayed by moss crusts, and the soil water redistribution process is also greatly affected. These results may be useful for helping to control desertification on the Loess Plateau of China or similar regions. [Copyright &y& Elsevier]

Abstract: Lubricants are frequently applied in pipe-jacking, especially under difficult geological conditions or in cases of a longer alignment. The main purpose of lubricant application is to reduce the friction between pipe and soil. However, it is very difficult to quantitatively determine the real contact conditions between the two. New technology for soil–pipe interaction measurement is still scarce and requires further development. Only indirect methods are available for practical measurement of soil–pipe interaction, and engineering judgment is required for the application of those measurements. In this study, a simple test method was applied to obtain the frictional properties of the most popular lubricants in the Taiwan area. Those frictional properties were used for jacking force estimation and numerical analysis of soil–pipe interaction for linear and curved pipe-jacking. The analyses of jacking force show that reduction in jacking force is closely related to reduction in friction coefficients, and the effect of lubrication is slightly more significant in the case of curved alignment than the case of linear alignment. In addition, a study of a 400-m linear pipe-jacking case in the Taichung Science Park shows overestimation of the jacking force by an empirical formula. It reveals the reduction in pipe-soil contact area induced by over-cutting is significant for pipe-jacking in gravel formations. [Copyright &y& Elsevier]

Abstract: Collapsible loess-derived soils are prone to soil piping erosion, where enlargement of macropores may lead to a subsurface pipe network and eventually to soil collapse and gully development. This study aims at understanding the main factors controlling spatial patterns of piping in loess-derived soils under a temperate climate. To map the spatial distribution of piping and identify the environmental controls on its distribution, a regional survey was carried out in a 236km2 study area in the Flemish Ardennes (Belgium). Orthophotos taken at optimal field conditions (winter) were analyzed to detect piping in open landscapes and ground thruthing was systematically done through field surveys. In total, 137 parcels having 560 collapsed pipes were mapped. Dimensions of the sinkholes and local slope gradient were measured in the field and topographical variables were derived from LiDAR data. Land use plays an important role as 97% of the sites with piping are found under pasture. The probability of piping increases rapidly on hillslopes with gradients exceeding 8% and with a concave profile and plan curvature, enhancing subsurface flow concentration. The zones with soil profiles on shallow loess over a relatively thin layer of homogeneous blue massive clays (Aalbeke Member) are most prone to piping. Soil characteristics are of less importance to explain piping occurrence. Furthermore, the topographical threshold line indicating the critical slope gradient for a given contributing drainage area was determined. This threshold line (negative power relation) is similar to the threshold line for shallow gully initiation. [Copyright &y& Elsevier]

Abstract: Piping phenomena into the upstream face of an earth dam can be approximated by a finite cylinder model. A formula of the streaming potential (SP) effect of such a model was developed by integrating an equation of an infinite cylinder section. Numerical modelling allows the conclusion that the oblong SP field shape of a model is only for relatively long and shallow piping models. The SP field shape of a model can actually be circular below a certain ratio value between the depth and length of the model. The resulting SP field of a finite cylinder is symmetrical with respect to its middle point, which allows, in some cases, reaching conclusions about piping phenomena outside the measured area. This finite cylinder formula needs smaller values of moments of polarisation to generate SP data almost identical to the SP magnitudes obtained from the expression of an infinite cylinder section. A random component was added to the SP effect of several computed models. Relatively short and deep piping phenomena can pass unnoticed, especially for a low signal-to-noise ratio. However, detection of anomalous patterns can be improved if the measured data are pre-processed according to a “studentized” deviate concept, which is then subjected to a statistical test based on the Chebyshev inequality. A field example of an SP piping process was detected at the upstream face of an earth dam. Its existence was also confirmed by a geoelectrical survey. [Copyright &y& Elsevier]

Abstract: On US military installations, training activities such as vehicle use disturb ground and vegetation cover of landscapes, and increase potential rainfall runoff and soil erosion. In order to sustain training lands, soil erosion is of major concern. Thus there is a need for sampling designs to monitor degradation and recovery of land conditions. Traditionally, permanent plots are used to obtain the change of land conditions. However, the permanent plots often provide less information over time in characterizing the land conditions because of the fixed number and locations of plots. In this paper, we analyzed the sufficiency of a permanent plot sample and developed a method to improve the re-measurements of the permanent plots over time for a monitoring system of soil erosion based on spatial and temporal variability of a random function. We first applied a local variability based sampling method to generate reference samples that have sampling distances varying spatially and temporally to monitor a soil erosion relevant cover factor for an installation, Fort Riley, USA. Then, we compared a permanent sample with the reference samples annually over 13 years to determine additional sampling in the areas with high variability and temporarily suspending measurements of the permanent plots in the areas with low variability. The local variability based sampling provides estimates of local variability of the cover factor and thus is more cost-efficient than random sampling. By comparison with a reference samples, the re-measurements obtained should more accurately characterize the dynamics of the land conditions. [Copyright &y& Elsevier]

Abstract: The combination of the mountainous terrain of Albania and a seasonally wet Mediterranean climate has led to some of the most extreme erosion in Europe. New methodology is used in this work to estimate soil erosion risk and provide a framework for soil conservation that can effectively and economically control soil loss. A onedimensional hydrology, vegetation and erosion model (RDI/CSEP) is used to calculate accumulative soil erosion. This model provides an integrating the climatic, topography and associated vegetation components into soil erosion modeling. The forecast runoff, accumulated across the frequency distribution of storms, is used to give a climatic potential, which is then appropriately combined with measures of topography and soil erodibility to estimate the expected rate of soil erosion at a resolution of 1 km. Annual and monthly soil erosion maps of Albania are also developed in this research. The proposed approach for evolution and mapping soil erosion by water uses existing soil maps, land use maps, a digital elevation model (1km), and interpolated climate data. The erosion maps clearly show that Albania is a country where erosion is potentially severe. The annual erosion rates are estimated at 10 t ha–1y–1 or more, especially in the south and center part of the country. In three areas (two in Gjirokastër, and one in Sarandë) the annual erosion rate is more than 100 t ha–1 y–1. Erosion rates are highest in October, November, February and December and lowest in June and July. [Copyright &y& Elsevier]

Natural pipes are common in many upland blanket peats, yet little is known about pipe network morphology or pipeflow processes. Most information on soil piping comes from the shallow peaty podzols of the Welsh uplands, where monitoring suggests that pipes may be important contributors to streamflow. This paper presents information on piping and pipeflow from a deep upland blanket peat catchment in the Pennine Hills of Northern England. Pipe outlets are found throughout the soil profile ranging from the underlying substrate at ∼3-m depth to pipes which are within a few centimetres of the surface. Mean pipe diameters range from 3 to 70 cm; some pipes are over 150 m long. Slopes in the catchment are less steep than those usually associated with soil piping. Continuous flow records were obtained from 15 gauging sites on 8 separate pipes. The pipeflow response from deep blanket peat was found to be different to that reported in the shallow peaty podzols of the Welsh uplands; the distinction between ‘ephemeral’ and ‘perennial’ pipe types does not appear to be useful within the deep Pennine blanket peat. Response times from all of the pipes are short, even from pipes deep within the peat. At the same time pipes have a prolonged recession limb such that they maintain low flow for longer periods than most other runoff production processes within the catchment. Pipeflow contributes around 10% of the streamflow volume, but can at times contribute up to 30%. Soil pipes may, therefore, be far more important in some upland peat catchments than previous work has hitherto suggested. [Copyright &y& Elsevier]

Field monitoring of natural pipeflow over the last two decades has demonstrated its potential importance both as a hillslope drainage process and as a source of streamflow, yet very few attempts have been made to model the process. The main model designed to simulate pipeflow to date is shown to be unrepresentative of the natural field situation. This paper describes a semi-distributed simulation model with physically based parameters that has been designed around the field situation, as monitored in the longest run field experiment on pipeflow. The results are encouraging, despite the fact that data on a number of relevant parameters can be difficult to obtain at less intensely studied field sites. [Copyright &y& Elsevier]