Measuring piping erosion rate in bentonite using spectrophotometry and X-ray computed tomography

HighlightsThis study provides data from internal erosion tests on four intermediate-scale homogeneous embankment dams.Soil properties influence the breach formation process and breach timing.Results showed that observed erosion rates of the internal flow path varied by several orders of magnitude.Quality control of embankment construction can greatly influence breach development.Abstract. Internal erosion and embankment overtopping are the two most common causes of embankment dam and levee failures and incidents. Internal erosion is the removal of soil material by the flow of water through a continuous defect, cavity, or crack within a compacted fill and/or its foundation. Internal erosion initiates from vulnerabilities within the embankment. The embankment soil material plays a key role in both the erosion process and rate of failure, but characterizing soil properties and how they relate to the rate of failure can be challenging. Soil properties such as texture, density, strength, moisture content, and erodibility can vary greatly; thus, it is important to study the effects of these properties on the breach formation process and breach timing. The USDA Agricultural Research Service performed internal erosion breach experiments on four intermediate-scale homogeneous earthen embankments constructed of soils ranging from a silty sand to a lean clay material. The embankments were constructed to a height of 1.3 m, a top width of 1.8 m, and upstream and downstream slopes of 3(H):1(V). The embankment materials were characterized by water content, density, texture, strength, and erodibility. Erodibility was measured using a jet erosion test (JET) apparatus. A 40 mm diameter, continuous steel pipe was placed through each embankment during construction and removed to form an open-ended void through the embankment connected to the upstream reservoir. The removal of the pipe initiated internal erosion. The objectives of the experiments were to observe the development of the internal erosion process over time and to examine the influence of soil properties on the erosion rate, breach timing, geometry of the breach opening, and breach outflow. The rate of erosion and failure observed in these tests varied by several orders of magnitude, with the silty sand embankment eroding most rapidly and the lean clay embankment with a mean moisture content of 18% dry basis at standard compaction eroding the slowest. These observations were indicative of the soil textures. Although the two lean clay embankments were constructed of similar soils, the difference in erosion rates speak to the importance of quality control (e.g., compaction moisture content) during construction. Soil properties including soil texture, erodibility, and compaction moisture content are key predictors of erosion rate and observed failure. Keywords: Breach, Dam failure, Dams, Embankments, Erodibility, Internal erosion, Levees, Overtopping.

High-speed fluid-carried sand particles pose a significant challenge to oil well screen pipes, leading to sand control failure and adversely affecting the well's production and recovery rates. This research targets the commonly used metal mesh screen pipe in oil well sand production and establishes a full-sized three-dimensional structure model. A fluid-solid coupling of discrete particle flow numerical simulation algorithm is incorporated to formulate a novel method for predicting the screen pipe's erosion life. This method provides a solution to the complex task of predicting the pipe's lifespan under oil sand fluid erosion. The analysis elucidates the impact of sand particles on the velocity distribution and erosion rate of the metal mesh at varying velocities, facilitating the prediction of the mesh screen pipe's erosion life. Key findings reveal that the velocity and erosion rate vary across the different layers. The first layer screen experiences velocity and erosion rates that are 3.6-3.76 times and 2.45-2.50 times, respectively, higher than those at the inlet. The second layer screen undergoes velocity and erosion rates 2.32-2.43 times and 1.04-1.06 times, respectively, higher than those at the inlet. Erosion failure primarily occurs in the first layer screen due to velocity expansion instigated by the screen tube's structure. The discrete flow numerical simulation method proves valuable in predicting the mesh screen's erosion life at different flow rates, with a maximum error of 6.38% when compared with field monitoring life values. This method introduces a new technical approach to predicting the life span of metal mesh screens in oil wells. The study concludes by suggesting measures to extend the screen pipe's lifespan, thereby enhancing oil recovery.

SummaryIt has been reported that sand production, which is a simultaneous production of soil particles along with gas and water into a production well, forced to terminate the operation during the world's first offshore methane production test from hydrate‐bearing sediments in the Eastern Nankai Tough. The sand production is induced by internal erosion, which is the detachment and migration of soil particles from soil skeleton due to seepage flow. The inflow of the eroded soil particles into the production well leads to damage of the production devices. In the present study, a numerical model to predict the chemo‐thermo‐mechanically coupled behavior including internal erosion during hydrate dissociation has been formulated based on the multiphase mixture theory. In the proposed model, the internal erosion is expressed as mass transition of soil particles from soil skeleton to the fluidized soil particles. Since the internal erosion is considered to depend on the soil particle size, mass of soil particles are divided into several groups that have different representative particle diameters, and the constitutive equations for the onset condition and the mass transition rate of the internal erosion are formulated for each group. Also, transportation of soil particles in the liquid phase is formulated for each particle size group in the proposed model. Finally, a simulation of the methane gas production from the hydrate‐bearing sediment by depressurization method is presented, and the internal erosion and the dissociation behavior are discussed.

Internal erosion by piping is one of the main causes responsible for the failure of earth structures such as embankments, dams, and foundations. This phenomenon occurs when concentrated leakage develop in pre-existing defects in the soil structures. The erosion characteristics are described by the erosion rate index ranging from 0 to 6 indicating that the rate of erosion of soil can vary up to 106 times. To study this complex behavior, a new experimental device was developed to simulate the conditions of internal erosion. It was designed using CAD and made up of stainless steel. It mainly consisted of a semi-cylindrical mold and rectangular sheet made of perspex. A digital camera was used to capture the propagation of groove in the soil to measure the internal erosion characteristics. The effect of plasticity index and fine fraction on the rate of internal erosion and critical shear stress were studied. A series of erosion tests was performed under constant head loss in order to quantify the critical shear stress (τc) and the coefficient of piping erosion (ker) of five different soils. It was observed that critical shear stress increased while coefficient of soil erosion decreased with increase in fine fraction. An easy, quick, and economical approach which could be applicable in both constructed earth structures and natural river banks for determining their susceptibility to internal erosion was achieved through this study.

In slopes where a mixture of coarse and fine particles is present, the infiltration of rainfall can cause the migration of fine particles. This migration alters the hydraulic properties of the soil and has implications for slope stability. In this study, the slope under investigation is a tailings dam composed of loosely consolidated soil with a wide particle size distribution. Due to rainfall infiltration, fine particles tend to migrate within the voids of the coarse particle framework, leading to changes in hydraulic properties and inducing slope instability. The classical internal erosion constitutive model, known as the Cividini and Gioda erosion criterion, is commonly used to predict the behavior and effects of fine particle erosion in geotechnical engineering. However, certain parameters in this erosion criterion equation, such as long-term density, are challenging to obtain through experiments. To investigate the coupled evolution of seepage and erosion within landfill slopes under the influence of rainfall infiltration and to understand the mechanisms of slope instability, this research assumes the erosion of fine particle suspension and adopts the Worman and Olafsdottir erosion criterion to establish a coupled model of unsaturated seepage and internal erosion. The developed model simulates the coupled response of seepage and erosion in unsaturated landfill slopes under three different rainfall intensities. It is then combined with the infinite slope model to quantitatively analyze the impact of fine particle migration on soil permeability and slope stability. The numerical simulations provide the following findings: The Worman and Olafsdottir erosion criterion, unlike the Cividini and Gioda erosion criterion, only requires the determination of the soil’s gradation curve to estimate the erosion rate. Internal erosion primarily occurs within the leading edge of moisture penetration, accelerating the advancement of the wetting front and reducing slope stability. When the rainfall intensity is lower than the saturated permeability coefficient, the influence of internal erosion can be disregarded. However, under rainfall intensities equal to or greater than the saturated permeability coefficient, considering internal erosion results in a difference in the depth of the wetting front of up to 34.2 cm after 6 h in the R2 scenario. The safety factor without considering internal erosion is 1.12, whereas considering internal erosion yields safety factors between 1.08 and 1.09. In the R3 scenario, the difference in the depth of the wetting front reaches 53.8 cm after 6 h, with a safety factor of 1.12 without considering internal erosion and safety factors between 1.06 and 1.07 when considering internal erosion.

Internal erosion is one of the most common causes of failure in hydraulic engineering structures, such as embankments and levees. It also plays a vital role in the geohazards (such as landslides and sinkhole developments) and more importantly, the earth landscape evolution, which has a broad environmental and ecosystem impacts. The groundwater seepage is multi‐directional, and its multi‐dimensional nature could affect the initiation and the progression of internal erosion. With a newly developed apparatus, we carry out nine internal erosion experiments under five different seepage directions. The results reveal that the critical hydraulic gradient increases as the seepage direction varies from the horizontal to the vertical. After a global erosion is triggered, preferential erosion paths distribute randomly from the bottom to the top of the specimen. If the seepage direction is not vertical, small preferential erosion paths merge into a large erosion corridor, in which the loss of fine particles is significant but negligible outside. Results of experiments manifest that the erosion is heterogeneous and three‐dimensional, even in the unidirectional seepage flow. The particles are rapidly eroded at the early stage of the erosion, indicating a high erosion rate. With the erosion time increasing, the particle loss slows down and even ceases if the time is long enough. The erosion rate increases if the seepage direction approaches a vertical direction. Overall, the erosion rate approximately decreases with erosion time exponentially. We proposed exponential equations to illustrate the variation of the erosion rate in the erosion process.

Assessment of grass root effects on soil piping in sandy soils using the pinhole test

The appearance of breaches in recent hydraulic earthstructures due to internal erosion confirms that improving our physical understanding of the phenomenon is urgent. Under the effect of internal flows, earthstructures can undergo a migration of their particles, which modifies the particle size distribution and affects both hydraulic and mechanical characteristics. This paper initially presents a parametric study conducted on sand/kaolin samples. The experimental device described here consists of three modified triaxial cells used to control sample confinement, prevent any parasitic flow and survey sample large deformations. The tests reveal that internal erosion (suffusion or piping) is initiated by the transport of clay particles. The erosion rate, then, depends on the values of the different parameters considered (hydraulic gradient, clay content and filter pore opening size).

<abstract> <b>Abstract.</b> Cohesive sediment transport is typically modeled for channels, levees, spillways, earthen dams, and internal erosion using a linear excess shear stress approach. However, mechanistic nonlinear detachment models, such as the Wilson Model, have recently been proposed in the literature. Questions exist as to the appropriateness of nonlinear relationships between applied shear stress and the erosion rate. Therefore, the objective of this research was to determine the suitability of linear and nonlinear detachment models for cohesive sediment transport using two applicable data sets: (i) rill erodibility studies across a limited range of applied shear stress (0.9 to 21.4 Pa) and (ii) hole erosion tests across an extended range of applied shear stress (12.6 to 62.0 Pa). Using these two case studies, it was determined that the nonlinear, mechanistic detachment model was more applicable across a wider range of applied shear stress. In situ and laboratory tests sometimes confine the collection of erosion rate data in terms of the applied shear stress, and therefore, users of these measurement techniques should be aware of the nonlinear behavior of cohesive sediment detachment especially at higher shear stress. Nonlinear detachment models should be used in the place of the linear excess shear stress approach in design and predictive models for cohesive sediment detachment.

Piping, as the result of internal erosion of embankments, is a primary cause of embankment breaks. Moreover, hollows or cavities of soil structures have been occasionally reported due to erosion within soils. The inner states of embankments are needed to be estimated to take appropriate measures for the prevention of the accidents of soil structures. In this study, simultaneous modeling of the internal erosion and the deformation of soils is carried out. As for the internal erosion, the equations governing the erosion and the transport of fine particles within a soil mass are derived with the concept of erosion rates of soils. Additionally, the constitutive model which can describe the deformation of soils caused by the internal erosion is proposed in this paper.

CFD–based erosion and corrosion modeling in pipelines using a high–order discontinuous Galerkin multiphase solver

Summary The saltmarshes of south‐east England are eroding rapidly. Field and laboratory experiments were used to test the hypotheses that: (i) at the mudflat–saltmarsh boundary there are two alternative states, one dominated by pioneer zone vegetation that excludes burrowing infauna, and the other dominated by infaunal invertebrates that exclude vegetation; and (ii) the major cause of the loss of saltmarshes in south‐east England is internal creek erosion, which is exacerbated by bioturbation and herbivory by the infaunal polychaete Nereis diversicolor. In laboratory experiments Nereis ate the seeds and seedlings of Salicornia spp., and Salicornia deterred burrowing by Nereis. In field experiments, at Tollesbury in Essex, UK, exclusion of Nereis from the sediment surface increased the density of Salicornia, but only when a source of seeds was close by. In the Tollesbury saltmarsh the plants and Nereis had mutually exclusive distributions within a vertical zone of overlap. The recently vegetated area of the managed realignment site at Tollesbury contained no Nereis, but Nereis colonized areas where Salicornia had been removed. These observations and data support the first hypothesis. Much of the loss of the Tollesbury saltmarsh is by lateral erosion of the internal creeks. Physical factors alone cannot be responsible for this erosion because experimental exclusion of Nereis led to sediment accretion. These results support the second hypothesis. Creek erosion may create a positive feedback where creek enlargement leads to faster tidal currents and further erosion until creeks have widened to their new equilibrium morphology. Synthesis and applications. We conclude that the infauna are a major cause of reduction in area of saltmarsh vegetation and this has implications for the management of saltmarsh restoration. These results call into question the assumption that saltmarsh erosion in south‐east England is due to sea level rise and coastal squeeze, and demands re‐examination of the role of management realignment in the regeneration of saltmarshes. Reducing the rates of saltmarsh creek erosion, by exclusion of the infauna, and/or by reducing current velocities in the saltmarsh creeks, would reduce the need to replace eroded marshes by managed realignment, and would reduce future erosion of existing sea walls by wave action.

Experimental and numerical study of drill pipe erosion wear in gas drilling

Previous studies have indicated that piping erosion greatly threatens the safe operation of various hydraulic structures. However, few mathematical models are available to perfectly describe the erosion process due to the complexity of piping. The focus of the present work is to propose a new fluid-solid coupling model to eliminate the shortcomings of existing work. A “pseudo-liquid” assumption is suggested to simulate the particle movement in the erosion process. Then, based on the mass and momentum conservations of the moving particles and flowing water, a new two-flow model is established by using the continuity equations and motion equations. In the model, the erosion rate of soil is determined with a particle erosion law derived from tests results of STERPI. And ERGUN’s empirical equation is used to determine the interaction forces between the liquid and the solid. A numerical approach is proposed to solve the model with the finite volume method and SIMPLE algorithm. The new model is validated with the tests results of STERPI. And the soil erosion principles in piping are also explored.

Cohesive sediment transport is typically modeled for channels, levees, spillways, earth dams, and internal erosion using a linear excess shear stress approach. However, mechanistic nonlinear detachment models, such as the Wilson Model, have recently been proposed in the literature. The objective of this research was to determine the suitability of linear and nonlinear detachment models for cohesive sediment transport using three applicable data sets: (1) a rill erodibility study across a limited range of shear stress (0 to 10 Pa), (2) a hole erosion test across an extended range of shear stress (10 to 60 Pa), and (3) streambank erodibility as quantified by jet erosion tests for the linear excess shear stress equation and the nonlinear Wilson Model across a small range of shear stress (2.5 to 7.5 Pa). The Wilson Model was incorporated into the Bank Stability and Toe Erosion Model (BSTEM) as an option for simulating fluvial erosion and used to simulate bank retreat in the streambank erodibility study. Using these three case studies, it was determined that the nonlinear, mechanistic detachment model was more applicable across a wider range in applied shear stress. The use of the nonlinear detachment model also alleviates questions about the most appropriate solution technique for jet erosion tests in deriving erodibility parameters. In situ tests may confine the collection of erosion rate data in terms of the applied shear stress, and therefore, users of these techniques should be aware of the nonlinear behavior of cohesive sediment detachment especially at higher shear stress.