Internal Erosion Research Articles

What type of gully is that? The need for a classification of gullies

AbstractDespite over a century of investigations into gullies and gully erosion, the characterization and categorization of gullies and the varied definitions, nomenclatures and terminology used has caused some confusion in understanding and communicating the relationships of gully forms and processes around the world. We firstly review the gully literature and highlight how a lack of consistency in gully definition and characterization prevents unifying theory from being developed within this important field of research, since it is often unclear whether different landscape features being discussed are comparable. We propose that conventionally employed qualitative planform and cross‐sectional characteristics of gullies alone are inadequate to define gully types, yet both these features remain central to most modern gully descriptions. We discuss the need to revise and augment these basic characteristics with clearly defined morphogenetic attributes such as landscape context, soil material characteristics, erosion processes, hydrological integrity, modes of development, and head/side‐wall morphology for an effective, practicable, generic gully classification scheme. Central to a gully classification scheme is the need for a clear definition of what a gully is – and is not – for which geomorphological criteria are proposed to differentiate a ‘gully’ from other ‘incisional land surface forms’. This gully definition hinges largely on the identification of a retreating head scarp and the internal erosion by mass‐movement and other sidewall slope erosion processes, coupled with the transport of the soil materials from the gully void. By defining a gully and synthesizing descriptions of gully ‘types’ from the literature and our own experience, we propose key morphogenetic attributes of gullies necessary to form a framework for a systematic gully classification scheme. An initial, eclectic classification framework is presented as both a summation and a synthesis of the literature review, and as a progenitor to a dynamic generic classification scheme that is proposed in a follow‐up article.

Internal erosion vulnerability of core soil due to drought: Case study of three zoned dams

Internal erosion vulnerability of core soil due to drought: Case study of three zoned dams

Conglomerate to mudstone lacustrine cycles revealed in Junggar Basin, Northwest China: Middle Permian Lucaogou and Jingjingzigou formations

The Junggar Basin is one of the very large, long-lived, Late Paleozoic lacustrine basins of China, developed by the closure of the early Paleozoic Junggar Ocean. The novelty of the reported research is outcrop measurements through the mid-Permian Jingzingzigou and Lucaogou formations, allowing reconstruction of interacting very coarse and very fine-grained alluvial-to-lacustrine depositional cycles within a km-thick succession of organic-rich mudstones. The deposits are interpreted as coarse grained fan deltas that extend subaqueously into Junggar lacustrine basin, depositing fine-grained muddy, sediment gravity flow deposits. The coarseness and frequency of both alluvial and subaqueous sediment gravity flows that thin and pinch out over short distances suggests that the margin of the basin was likely steep and fringed by relatively deep lake waters, but was not the main margin of sediment supply. The proposed depositional model highlights the process response to climate-driven lake-level changes around the steep lake margin. However, the coarse-grained alluvial to fan-delta cycles and the muddy lacustrine cycles occur at different thickness scales. The former (5–13 m thick) contain internal erosion surfaces and are dominated by river sheet flood and debris flow deposits and are likely incomplete due to frequent shifting, erosion and reworking of the sediments. The lacustrine cycles (few meters thick) are dominated by current-driven, very fine sandstone, siltstone and organic-rich mudstone beds with ripple lamination and graded beds, as well as dolomites during times or places where subaqueous currents were lacking. The age dating control is not detailed but we propose that depositional cycles were likely a response to Milankovitch orbital cyclicity, also suggested by previous Permian climate modeling, that cause alternating wet and dry periods and trigger tens of meters lake level changes with abrupt grainsize changes in the shallow proximal areas and more subtle changes in sediments of distal/deep lacustrine regions. The climate changes therefore cause both sediment supply changes subaerially and lake accommodation changes subaqueously, though these would also be modulated to a lesser extent in the resultant stratigraphy by autogenic responses and tectonic forcing of sediment yield.

Internal erosion monitoring with a rowe cell type compression–breakthrough–bender element column

Internal erosion monitoring with a rowe cell type compression–breakthrough–bender element column

Study on reducing elbow erosion with swirling flow

Pipe erosion caused by solid particles is an important cause of pipeline damage, for example, parts such as elbows are particularly prone to erosion problems. In this work, the insertion of a twisted tape on different working conditions upstream of an elbow is investigated numerically in order to study the mechanism of the swirling flow reducing the erosion of the elbow. In order to ensure the reliability of numerical calculations, experimental data are used to verify the CFD simulation model of the standard elbow. The influence of the twist ratio of the twisted tape, the insertion position of the twisted tape and the gas velocity on the erosion of the elbow was studied. It was found that the swirling flow induced by the twisted tape make the solid particles suspended and more evenly distributed in the pipeline, which reduces the focusing effect and the impact frequency of particles on the same position of the elbow wall. The insertion of the twisted tape results in a reduction in the area of the maximum erosion zone of the elbow and a significant decrease in the erosion rate along the elbow curvature angle, indicating that the swirling flow can significantly reduce the erosion of the elbow. The smaller the twist ratio of the twisted tape, the closer to the elbow, the more obvious the erosion mitigation effect is. In addition, swirling flow can interfere and inhibits the Dean Vortex on the cross section of the elbow. Under the condition of swirling flow, as the gas velocity increases, the influence range of the Dean vortex increases, the kinetic energy of particle impact increases, and the type of collision changes from sliding collision to direct collision. The erosion rate of the elbow with a twisted tape insert also increases with the increase of the gas velocity, but the swirling flow reduces the velocity index of the erosion rate to a certain extent. • The swirling flow makes the particles distribute more evenly, reducing the focusing effect. • The swirling flow can interfere and inhibits the Dean Vortex. • The swirling flow reduces the velocity index of the erosion rate. • Erosion reduction efficiency of swirling flow depends on twist ratio and insertion position.

The Influence of Internal Erosion in Earthen Dams on the Potential Difference Response to Applied Voltage

Internal erosion is widely perceived as contributing to the failure of earthen dams. To reduce the failure risk, timely monitoring of internal erosion is an effective method in observing their internal structure evolution. A set of earthen dam model experiments were conducted. Under an applied voltage, the response potential differences (PD) at the slope of the dam models were collected before and after the impoundment of the upstream reservoir. The discrepancy among the four dam models, the influence of soil moisture content on PD, and the impact of internal erosion on PD were studied. The results show that it is acceptable to employ different dam models to simulate the development of internal erosion, although the discrepancy among the models is inevitable. The moisture content of the soil significantly affects the PD response to applied voltage. The PD increases with an increase in soil moisture content until the soil is saturated. The change in PD is correlated with the development of internal erosion. With the progression of internal erosion, the starting position for the steep increase in PD distribution continues to move toward the dam toe. In addition, the electrode stability is noted to have an effect on measured PD, which requires further studies to be clarified. This study sets the stage for the PD-based monitoring method in observing the evolution of internal erosion in earthen dams.

Net buffer method for suppressing internal erosion and collapse behind seawalls and quaywalls through caisson joint wave reduction

This paper presents a new wave reduction method, called the Net Buffer Method, to reduce caisson joint waves for suppressing internal erosion and collapse behind seawalls and quaywalls. Caisson joints may fail or widen due to the repeated action of waves that pass though the joints. The new method, in which a net fiber material is installed within the joints, is capable of reducing such caisson joint waves by more than 80% in terms of the maximum and average wave pressures. Unlike previous countermeasures, it is applicable to joints of variable width and can autonomically adjust to changes in the configuration and surrounding environment due to continued wave impacts and other dynamic forcing such as earthquakes. Based on a three-year follow-up survey of its application, the proposed method has proven itself effective in suppressing the occurrence of re-collapse behind seawalls that repeatedly collapsed under severer wave loading.

Design Methodology for Grout Curtains Under Dams Founded on Rock

AbstractGrout curtains are commonly constructed under dams to reduce the seepage through the rock foundation. In the design of grout curtains, empirical methods have mainly been used since the introduction of dam foundation grouting. Although empirical methods have been used with success in several projects, they have their limitations, such as poor control of the grout spread, only an indirect consideration of the threat of internal erosion of fracture infillings in the grouted zones, and the risk of hydraulic jacking. This paper presents a theory-based design methodology for grout curtains under dams founded on rock. In the design methodology, the grout curtain is designed as a structural component of the dam. The risk of erosion of fracture infilling material is explicitly accounted for along with the reduction of the hydraulic conductivity of the rock mass, and an optimization of the total uplift force. By applying the proposed design methodology, engineers can create a design better adapted to the prevailing geological and hydrogeological conditions in the rock mass, resulting in more durable grout curtains. The proposed methodology also enables cost and time estimates to be calculated for the grout curtain’s construction. Applying the principles of the observational method during the grouting execution also allows the design to be modified via predefined measures if the initial design is found to be unsuitable.

Internal Instability in Soils: A Critical Review of the Fundamentals and Ramifications

Seepage-induced fine-particle migration that leads to a change in the conductivity of a soil matrix is referred to as internal instability. This could jeopardize the structural integrity of the soil matrix by initiating suffusion (or suffosion), a form of internal erosion. Susceptibility to suffusion has been studied mostly under extreme laboratory conditions to develop empirical design criteria, which are typically based on the particle size distribution. The physics governing the process have not been comprehensively uncovered in the classical studies because of experimental limitations. Mainstream evaluation methods often over-idealize the suffusion process, holding a probabilistic perspective for estimating constriction sizes and fines migration. Prospective studies on constitutive modeling techniques and modern computational techniques have allowed a more representative evaluation and deeper insight into the problem. Recent advances in sensing technologies, visualization, and tracking techniques have equally enriched the quality of the data on suffusion. This paper sets out to present the long-standing knowledge on the internal instability phenomenon in soils. An attempt is made to pinpoint ambiguities and underscore research gaps. The classical empirical studies and modern visualizing techniques are integrated with particle-based numerical simulations to strengthen the theoretical understanding of the phenomenon.

Experimental study on suffusion under multiple seepages and its impact on undrained mechanical responses of gap-graded soil

An experimental investigation of multiple seepage-induced suffusion and its impact on the mechanical responses of internally unstable gap-graded soil, with a fines content of 25%, is presented in this paper. Using a modified triaxial erosion apparatus, with a redesigned seepage control system, erosion tests under multiple seepage conditions, as well as undrained monotonic and cyclic compression tests, are performed. It is found that multiple seepages cause an eroded mass without a marked change in volume and with a change in hydraulic conductivity as the number of seepage cycles increases. The monotonic compression tests show that eroded soil presents a smaller peak strength, residual strength, and a greater contractive response than non-eroded soil. The peak strength and stiffness of eroded soil are seen to decrease considerably as the number of seepage cycles increases. Multiple seepage-induced suffusion may create a collapsible soil structure in eroded soil, as shown by sudden decreases in deviator stress and stiffness, coupled by sharp increases in pore water pressure at small strain levels. As eroded soil might already be unstable, cyclic loading causes it to collapse, revealing a sudden increase in the generation of cyclic pore water pressure and a decrease in liquefaction resistance. The results highlight the importance of conducting laboratory tests to determine the impact of internal erosion on the strength and liquefaction resistance.

Investigation on Erosion of Continuous Bending Pipes in Different Directions

With the increasing demand for natural gas in the world, ensuring the safety and stability of pipeline transportation of natural gas has become an important subject. Compared with the studies focused on the erosion of single bend, T-pipe, and U-pipe, the studies on the continuous bend in different directions are scarce. In this paper, the model is characterized by three straight pipes with the same length and directions along the Z, Y, and X axes of the Cartesian coordinate system. The numerical simulation of gas-solid two-phase flow under different gas to solid mass ratios in the continuous bent pipeline is carried out by selecting the Oka erosion model. The results indicate that the velocity distribution of the second bend is different from that of the first bend. With the change of flow deflection angle and the accumulation of the centrifugal force, the shape of the velocity contours in the second bend turns from “basin” into a comma and the velocity experiences a process including rapid increase, slow decrease, gradual increase, and steep decrease. When the flow rate is 12.5 m/s, the maximum speed of the second bend is about 5 % greater than that of the first bend. Instead of a “straight-line” shape in the erosion area of the first bend, the second presents a feather shape. As the flow rate increases gradually, the shape characteristics of the feather erosion zone change from short and dense to long and loose. Besides, the maximum erosion rate of the second bend is greater than that of the first even about 1.52 times. Finally, according to the simulation results, the protection suggestion of the continuous elbow is given.

Internal erosion of gravelly mudstone due to drying–wetting and hydraulic pressure cycles in oedometer test

Disintegrated mudstone due to slaking, subjected to hydraulic pressure, could lead to internal erosion. To examine the combined effects of slaking and internal erosion on gravelly mudstone in one dimensional deformation under a constant vertical load, a series of modified oedometer tests and laboratory penetration tests were conducted with drying–wetting and hydraulic pressure cycles. Some loading conditions showed severe erosion along the drying–wetting cycle. Susceptibility to internal erosion was evaluated in terms of nonfilter and filter factor coefficients.

Centrifuge Modeling Study of Backward Erosion Piping with Variable Exit Size

This study presents the results from a series of centrifuge modeling tests conducted to investigate the backward erosion piping across a sandy foundation underlying an impervious cohesive layer with a defined exit hole. Different levels of centrifuge gravitational acceleration and various exit hole sizes were tested. The behavior at different phases of erosion was analyzed based on in-flight video recordings and posttest observations, along with local and global pressure loss measurements. Results showed that the overall mechanism that was modeled was similar to the mechanism described in previous small-scale experimental studies. The results showed that the exit hole size had minimal impact on the critical hydraulic gradient but affected the characteristics of the piping path and the amount of eroded material. The critical hydraulic gradient that initiated the erosion decreased slightly as the centrifuge gravitational acceleration increased. The values of the critical hydraulic gradient, which was studied locally and globally, ranged between 0.15 and 0.40, and fell within a range of estimates from typical analytical methods. This study provides a means to improve the testing protocol and analysis of centrifuge modeling of internal erosion mechanisms, which currently is limited in the literature.

Analysis of volumetric internal erosion in cohesionless soils: Model, experiments and simulations

AbstractA hydro‐mechanical continuous model that accounts for volumetric internal erosion (otherwise called suffusion) is developed based on experimental observations and data to fill the gap between laboratory testing and field applications. The model is proposed based on the mixture theory applied to a two‐phase four‐species porous medium. The erodible soil is partitioned in two phases: one solid phase and one fluid phase. The solid phase is composed of non‐erodible grains and erodible particles. The fluid phase is composed of water and fluidized particles. The modelling of internal erosion is contributed directly by mass transfer from the solid phase towards the fluid phase. Two mass transfer relationships are considered, the power‐based relationship and the energy‐based relationship, and a calibration procedure for all material parameters is proposed. Both relationships assume that the power dissipated by the flow controls the kinetics of suffusion and that detachment prevails upon self‐filtration. Both relationships predict reasonably experimental data for several experimental tests on a gap‐graded cohesionless soil tested under various hydraulic loading paths. The model has been numerically solved with the finite element method and its predictions are next compared with the experimental results of a physical model of dike. The model along with the energy‐based relationship reproduces well the final amount of eroded mass. The spatial distributions of the total water head and the final percentage of fines are also smoothly reproduced.

Prediction model for maximum shear displacement of pipe joints with preexisting defects based on finite element–multiple nonlinear regression method

AbstractUnder the coupling effect of the defects inside and around pipes, the shear displacement of the joints of old concrete pipes fallen into disrepair usually shows an accelerated deterioration trend, and its excessive value can lead to structural damage or fluid leakage. Therefore, developing a prediction model for the maximum shear displacement of concrete drainage pipe joints with preexisting defects is of crucial significance. To this end, this work selects internal corrosion and erosion voids as the typical defects inside and around old pipes, establishes 300 sets of three‐dimensional fine finite element (FE) models of the concrete drainage pipes with corrosion and void, and verifies the reliability of the developed FE model by the full‐scale tests. Based on the verified FE data, a prediction model is successfully proposed for the assessment of the maximum shear displacement of the concrete drainage pipe joints with corrosion and void defects. Moreover, parameter sensitivity analysis is carried out to reveal their relative contribution to the maximum shear displacement of pipe joints. The results show that the model proposed herein has the ability to accurately predict the maximum shear displacement of the pipe joints. The maximum and minimum relative error between the value predicted by the proposed model and the one computed by the FE model is also 12.4% and 4.8% respectively. Moreover, the traffic load with a contribution of 28.7% has the greatest impact on the maximum shear displacement of pipe joints.

Piping of silty sand tailings through a circular geomembrane hole

Experiments are conducted to study leakage and piping through circular geomembrane holes from the overlying silty sand tailings. Three subgrades, a poorly graded gravel, a well-graded gravel, and a poorly graded sand are studied. Test results show that leakage through the geomembrane hole is not proportional to the surface area of the hole. A 5-fold increase in hole diameter from 10 to 50 mm results in an approximately 6-fold increase in leakage. With the filter incompatible subgrade, piping is prone to occur at small consolidation stress and/or with a larger hole. Open voids within soil skeleton induced by piping result in a 2- to 4.5-fold higher leakage than in the no-piping cases. The extent of silty sand piping and internal erosion depends on the filter compatibility and surface regularity of the subgrade, which could be significantly improved by increasing its fine particle component or placing a layer of nonwoven needle-punched geotextile beneath the geomembrane.

An Investigation into the Volumetric Flow Rate Requirement of Hydrogen Transportation in Existing Natural Gas Pipelines and Its Safety Implications

As an alternative to the construction of new infrastructure, repurposing existing natural gas pipelines for hydrogen transportation has been identified as a low-cost strategy for substituting natural gas with hydrogen in the wake of the energy transition. In line with that, a 342 km, 36″ natural gas pipeline was used in this study to simulate some technical implications of delivering the same amount of energy with different blends of natural gas and hydrogen, and with 100% hydrogen. Preliminary findings from the study confirmed that a three-fold increase in volumetric flow rate would be required of hydrogen to deliver an equivalent amount of energy as natural gas. The effects of flowing hydrogen at this rate in an existing natural gas pipeline on two flow parameters (the compressibility factor and the velocity gradient) which are crucial to the safety of the pipeline were investigated. The compressibility factor behaviour revealed the presence of a wide range of values as the proportions of hydrogen and natural gas in the blends changed, signifying disparate flow behaviours and consequent varying flow challenges. The velocity profiles showed that hydrogen can be transported in natural gas pipelines via blending with natural gas by up to 40% of hydrogen in the blend without exceeding the erosional velocity limits of the pipeline. However, when the proportion of hydrogen reached 60%, the erosional velocity limit was reached at 290 km, so that beyond this distance, the pipeline would be subject to internal erosion. The use of compressor stations was shown to be effective in remedying this challenge. This study provides more insights into the volumetric and safety considerations of adopting existing natural gas pipelines for the transportation of hydrogen and blends of hydrogen and natural gas.

Internal erosion behaviour of compacted loess against different hydraulic conditions indicated by enhanced pinhole tests

Internal erosion behaviour of compacted loess against different hydraulic conditions indicated by enhanced pinhole tests

Temporal filtering and time-lapse inversion of geoelectrical data for long-term monitoring with application to a chlorinated hydrocarbon contaminated site

SUMMARYWe present a solution for long-term direct current resistivity and time-domain induced polarization (DCIP) monitoring, which consists of a monitoring system and the associated software that automates the data collection and processing. This paper describes the acquisition system that is used for remote data collection and then introduces the routines that have been developed for pre-processing of the monitoring data set. The collected data set is pre-processed using digital signal processing algorithms for outlier detection and removal; the resulting data set is then used for the inversion procedure. The suggested processing workflow is tested against a simulated time-lapse experiment and then applied to field data. The results from the simulation show that the suggested approach is very efficient for detecting changes in the subsurface; however, there are some limitations when no a priori information is used. Furthermore, the mean weekly data sets that are generated from the daily collected data can resolve low-frequency changes, making the approach a good option for monitoring experiments where slow changes occur (i.e. leachates in landfills, internal erosion in dams, bioremediation). The workflow is then used to process a large data set containing 20 months of daily monitoring data from a field site where a pilot test of in situ bioremediation is taking place. Based on the time-series analysis of the inverted data sets, we can detect two portions of the ground that show different geophysical properties and that coincide with the locations where the different fluids were injected. The approach that we used in this paper provides consistency in the data processing and has the possibility to be applied to further real-time geophysical monitoring in the future.

The Effects of Internal Erosion on the Physical and Mechanical Properties of Tailings under Heavy Rainfall Infiltration

The stability of tailings dam will be affected by the internal erosion under unsteady seepage caused by heavy rainfall infiltration which changes the physical and mechanical properties of tailings. In this paper, the hydraulic sedimentary model was established to investigate the effects of dry beach slope on the sedimentary characteristics of tailings in upstream tailings dam, and the results indicated that the dry beach with a larger slope has a more obvious stratification of tailings. Additionally, the sand column model was built to investigate the effects of internal erosion on the physical and mechanical properties of sedimentary tailings under unsteady seepage, and the results indicated that the migration of fine-grained tailings was caused by internal erosion increases the permeability and reduces the shear strength of the tailings. After internal erosion of tailings under heavy rainfall in 50 years return period for 24 h, the average particle size of downstream tailings (sample DT), midstream tailings (sample MT), and upstream tailings (sample UT) increased by 6.4%, 12.0%, and 2.4%, respectively, the hydraulic conductivity of the samples DT, MT, and UT increased by 27.2%, 17.9%, and 15.3%, respectively, and the shear strength of each samples decreased by 20.9%, 15.1%, and 12.4%, respectively.