Critical Hydraulic Gradients of Internal Erosion under Complex Stress States

Chang, Dong Chil; Zhang, Li Min

doi:10.1061/(asce)gt.1943-5606.0000871

Cited by 249 publications

(110 citation statements)

References 32 publications

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“…6, the LCHG acquired in TS-3, TS-4, and TS-5 is 0.215, 0.4, and 0.6, respectively, whereas the HCHG is 0.415, 0.6, and 0.78, respectively. Clearly, the CHG, no matter the LCHG or the HCHG, increases gradually as the effective mean stress and deviatoric stress increase, which is consistent with the studies carried out by Chang and Zhang (2012) and Tomlinson and Vaid (2000).…”

Section: Effect Of Stress Statesupporting

confidence: 79%

“…The comprehensive analysis of the erosion curves of TS-7 and TS-8 also reveals that the collapses of the two tests are associated with the same amount of eroded particles, which is about 270.0 g. The total quantity of fine particles in a specimen is solved by combining the dry density and PSD of the specimen, which is about 580.0 g. Hence, the collapse of the specimen can be predicted once 46.5 % of fine particles are eroded. A study carried out by Chang and Zhang (2012) also revealed similar results, and the collapse was regarded as the failure stage of the erosion, and attributed the collapsing to the increasing hydraulic gradient. However, the results in this study reveals that the quantity of the eroded particles is also a vital factor besides the hydraulic gradient.…”

Section: Figsupporting

confidence: 49%

“…Using the Least Square Method, the fitted initial permeability coefficients of TS-1 and TS-2 are 0.1584 and 0.1756 cm/s, respectively. The turning point, which corresponds to the hydraulic gradient equal to 0.4 for both tests between the first and second stages, is usually adopted as the CHG of the piping erosion (Chang and Zhang 2012;Fleshman and Rice 2013). Nevertheless, despite the hydraulic gradient exceeding the CHG, there are few visible particles observed in the outflow of the specimen until the hydraulic gradient reaches 0.60.…”

Section: Typical Results and Repeatabilitymentioning

confidence: 99%

“…Nevertheless, despite the hydraulic gradient exceeding the CHG, there are few visible particles observed in the outflow of the specimen until the hydraulic gradient reaches 0.60. The hydraulic gradient 0.60 is also regarded as a type of CHG (Chang and Zhang 2012). In the study, the CHG corresponding to the turning point of the relation between seepage velocity and hydraulic gradient is named the lower critical hydraulic gradient (LCHG).…”

Section: Typical Results and Repeatabilitymentioning

confidence: 99%

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Constant Gradient Erosion Apparatus for Appraisal of Piping Behavior in Upward Seepage Flow

et al. 2017

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Seepage direction is crucial for understanding the critical state and development of piping erosion. A stress-controlled apparatus was designed to investigate the piping behavior of cohesionless soil under upward flow condition. The components of the new apparatus included a loading chamber, a vertical and confining loading system, an upstream water supply device, a soil-water separating system, and a water collecting system. The loading chamber provides space for a soil specimen setting and loading. The combination of a vertical and a confining loading system was designed to apply complex stresses to a soil specimen. Under the stresses, the specimen was then eroded by the gradually increasing hydraulic head supplied by the water supply system. The eroded particle and spilling water were collected and detected by the soil-water separating system and the water collecting system. A series of experiments were carried out using the new apparatus. Results demonstrated the repeatability experiments and usefulness of the apparatus. The new apparatus allowed us to investigate the piping behavior under different stress states and hydraulic gradients. With this new apparatus and experiments, we found that lower and high critical hydraulic gradients (CHGs) should be included as the criteria of piping development based on the relationship between the hydraulic gradient and the seepage response. In addition, the stress state on the CHG and the particle erosion rate played important roles in the piping development. The outer pressure on the specimen can retard the development of erosion. In contrast, the hydraulic gradient was found to be positively correlated to the erosion rate. Results also indicated that a specimen would collapse once the amount of eroded small particles exceeds the critical value of 46.5 % of the soil.

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Section: Effect Of Stress Statesupporting

confidence: 79%

Section: Figsupporting

confidence: 49%

Section: Typical Results and Repeatabilitymentioning

confidence: 99%

Section: Typical Results and Repeatabilitymentioning

confidence: 99%

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Constant Gradient Erosion Apparatus for Appraisal of Piping Behavior in Upward Seepage Flow

et al. 2017

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“…Creation of suffosion holes is a phenomenon specially typical and onerous for water supply systems of a high intensity rate placed in internally unstable soils. The result of a breakage of a buried water pipe is the water movement in soil, which can cause that fine soil particles are washed out from the solid matrix and transported through pores (suffosion process) [16,17,18,19,20,21]. As a result, depressions or holes can form on the soil surface.…”

mentioning

confidence: 99%

Suffosion Holes as the Results of a Breakage of a Buried Water Pipe

Iwanek

Suchorab

Karpińska-Kiełbasa³

2017

Period. Polytech. Civil Eng.

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The result of a breakage of a buried water pipe is the water movement in soil, which can cause that fine soil particles are washed out from the solid matrix and transported through pores (suffosion process IntroductionDepressions or holes creating on the soil surface as a result of suffosion can be very dangerous, especially in urban areas. It is widely known that the most hazardous phenomena of this kind relate to water-engineering structures [1,2,3]. It stems from the fact that failures and damages of pipes occur in water, sewage and storm water systems all over the world during their operation [4,5,6]. Even the high-tech methods of pipes condition assessment do not enable to prevent leakages occurrence, because of their random character and multiplicity of their reasons [7,8,9]. Still insufficient knowledge about them [10] is caused by many different, both static (pipe and soil parameters) and dynamic (hydraulic working conditions), factors [11,12,13,14,15]. Creation of suffosion holes is a phenomenon specially typical and onerous for water supply systems of a high intensity rate placed in internally unstable soils. The result of a breakage of a buried water pipe is the water movement in soil, which can cause that fine soil particles are washed out from the solid matrix and transported through pores (suffosion process) [16,17,18,19,20,21]. As a result, depressions or holes can form on the soil surface. Holes creating on the soil surface by water outflowing after a failure of a buried pipeline (suffosion holes), are in different shapes and sizes.Recognition of factors influencing holes shapes and sizes would facilitate the prevention of hazardous suffosion effects connected with failures of water distribution systems. In the range of the presented article, the influence of pressure head in a water pipe on dimensions of suffosion holes was analysed. The basis of the analysis was results of laboratory investigations of the controlled leakage from a buried water pipe.

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Numerical simulation of backward erosion piping in heterogeneous fields

Liang

Yeh

Wang

et al. 2017

Water Resources Research

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Backward erosion piping (BEP) is one of the major causes of seepage failures in levees. Seepage fields dictate the BEP behaviors and are influenced by the heterogeneity of soil properties. To investigate the effects of the heterogeneity on the seepage failures, we develop a numerical algorithm and conduct simulations to study BEP progressions in geologic media with spatially stochastic parameters. Specifically, the void ratio e, the hydraulic conductivity k, and the ratio of the particle contents r of the media are represented as the stochastic variables. They are characterized by means and variances, the spatial correlation structures, and the cross correlation between variables. Results of the simulations reveal that the heterogeneity accelerates the development of preferential flow paths, which profoundly increase the likelihood of seepage failures. To account for unknown heterogeneity, we define the probability of the seepage instability (PI) to evaluate the failure potential of a given site. Using Monte‐Carlo simulation (MCS), we demonstrate that the PI value is significantly influenced by the mean and the variance of ln k and its spatial correlation scales. But the other parameters, such as means and variances of e and r, and their cross correlation, have minor impacts. Based on PI analyses, we introduce a risk rating system to classify the field into different regions according to risk levels. This rating system is useful for seepage failures prevention and assists decision making when BEP occurs.

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Critical Hydraulic Gradients of Internal Erosion under Complex Stress States

Cited by 249 publications

References 32 publications

Constant Gradient Erosion Apparatus for Appraisal of Piping Behavior in Upward Seepage Flow

Constant Gradient Erosion Apparatus for Appraisal of Piping Behavior in Upward Seepage Flow

Suffosion Holes as the Results of a Breakage of a Buried Water Pipe

Numerical simulation of backward erosion piping in heterogeneous fields

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