Evaluation of the internal stability of well-graded silty sand through the long-term seepage test

AbstractSuffusion is the phenomenon responsible for internal erosion, and is the process by which finer soil particles are moved through the constrictions between the larger soil particles by seepage forces. Generally, gap-graded soil is known to be susceptible to suffusion. Meanwhile, suffusion of well-graded silty sand and the resulting soil behavior are not well understood. Moreover, the previous researches on laboratory suffusion tests focused on the study of the critical hydraulic gradient, which triggers the internal instability of the soils within a short period of time. Therefore, in this study, long-term suffusion tests were conducted on well-graded silty sand under a hydraulic gradient lower than the critical value. As a result, abrupt increases in permeability and amount of soil discharged were observed due to the progressive migration of the soil particles, resulting in suffusion even at a relatively low hydraulic gradient.

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A hydromechanical relation governing internal stability of cohesionless soil

Canadian Geotechnical Journal ◽

10.1139/t10-070 ◽

2011 ◽

Vol 48 (3) ◽

pp. 413-424 ◽

Cited By ~ 68

Author(s):

Ricardo Moffat ◽

R. Jonathan Fannin

Keyword(s):

Seepage Flow ◽

Hydraulic Gradient ◽

Cohesionless Soil ◽

Cohesionless Soils ◽

Critical Hydraulic Gradient ◽

Internal Instability ◽

Short Period ◽

Flow Through ◽

Permeameter Tests ◽

Novel Concept

Results are presented from permeameter tests involving unidirectional seepage flow through reconstituted specimens of four widely graded cohesionless soils. The onset of instability is defined by a significant decrease in local hydraulic gradient over a relatively short period of time. The novel concept of a hydromechanical path in stress ([Formula: see text]) – gradient (ijk) space is proposed, which describes the response to seepage flow during testing and terminates at the value of critical hydraulic gradient. The path terminus establishes a hydromechanical boundary governing the onset of seepage-induced internal instability in one-dimensional flow. The boundary represents a failure envelope, which is different for each of the four soils tested. A ranking of seepage-induced instability for each soil, from most unstable to least unstable, is found similar, but not identical to, the susceptibility to internal instability determined from empirical analysis of the gradation shape.

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Effect of Clay on Internal Erosion of Clay-Sand-Gravel Mixture

Advances in Civil Engineering ◽

10.1155/2020/8869289 ◽

2020 ◽

Vol 2020 ◽

pp. 1-18

Author(s):

Chen Liang ◽

Cai Guo-dong ◽

Gu Jia-hui ◽

Tan Ye-fei ◽

Chen Cheng ◽

...

Keyword(s):

Hydraulic Conductivity ◽

Fine Particle ◽

Fine Particles ◽

Fine Sand ◽

Hydraulic Gradient ◽

Internal Erosion ◽

Engineering Project ◽

Critical Flow Velocity ◽

Critical Hydraulic Gradient ◽

Mixture Samples

In this study, a one-dimensional seepage test apparatus was used to investigate the effect of clay on the critical hydraulic gradient, hydraulic conductivity, migration of fine particles in soil, and percentage of fine particle loss during the internal erosion of clay-sand-gravel mixture, compared with clean gravel. The critical hydraulic gradient and fine sand loss percentage of the clay-sand-gravel mixture decreased, and critical flow velocity and the hydraulic conductivity increased. Six clay-sand-gravel mixture samples with different clay contents were used to evaluate the effect of different clay contents on internal erosion. As the percentage of clay mass to fine particle mass increases from 0% to 25%, the critical hydraulic gradient of soil samples decreases by nearly half and the fine sand loss percentage decreases from 13.73% to 3.48%. Overall, clay has a significant effect on the development of internal erosion of clay-sand-gravel mixture. And attention should be paid in engineering project; clay-sand-gravel mixture with a small amount of clay is more likely to be damaged than clean gravel.

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Critical Hydraulic Gradient of Internal Erosion at the Soil–Structure Interface

Processes ◽

10.3390/pr6070092 ◽

2018 ◽

Vol 6 (7) ◽

pp. 92 ◽

Cited By ~ 8

Author(s):

Quanyi Xie ◽

Jian Liu ◽

Bo Han ◽

Hongtao Li ◽

Yuying Li ◽

...

Keyword(s):

Soil Compaction ◽

Soil Structure ◽

Clay Content ◽

Hydraulic Gradient ◽

Interface Roughness ◽

Internal Erosion ◽

Single Factor ◽

Critical Hydraulic Gradient ◽

Earth Fill ◽

The Impact

Internal erosion at soil–structure interfaces is a dangerous failure pattern in earth-fill water-retaining structures. However, existing studies concentrate on the investigations of internal erosion by assuming homogeneous materials, while ignoring the vulnerable soil–structure-interface internal erosion in realistic cases. Therefore, orthogonal and single-factor tests are carried out with a newly designed apparatus to investigate the critical hydraulic gradient of internal erosion on soil–structure interfaces. The main conclusions can be draw as follows: (1) the impact order of the three factors is: degree of compaction > roughness > clay content; (2) the critical hydraulic gradient increases as the degree of compaction and clay content increases. This effect is found to be more obvious in the higher range of the degree of soil compaction and clay content. However, there exists an optimum interface roughness making the antiseepage strength at the interface reach a maximum; (3) the evolution of the interface internal erosion develops from inside to outside along the interface, and the soil particles at the interface flow as a whole; and (4) the critical hydraulic gradient of interface internal erosion is related to the shear strength at the interface and the severity and porosity of the soil.

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Critical gradients and pressures in dense swelling clays

Canadian Geotechnical Journal ◽

10.1139/t92-129 ◽

1992 ◽

Vol 29 (6) ◽

pp. 1113-1119 ◽

Cited By ~ 22

Author(s):

D. A. Dixon ◽

M. N. Gray ◽

D. Hnatiw

Keyword(s):

Nuclear Fuel ◽

Effective Stress ◽

Darcy’S Law ◽

Bentonite Clay ◽

Critical Value ◽

Darcy's Law ◽

Hydraulic Gradient ◽

Compacted Clay ◽

Critical Hydraulic Gradient ◽

Swelling Clays

Uncertainties exist with regard to the applicability of Darcy's law to dense swelling clays. These clays may not allow water to pass through them when the hydraulic gradient is below a critical value. Preliminary results are presented from a series of constant-head permeability tests on dry, confined, densely compacted bentonite clays. The tests are intended to clarify the applicability of Darcy's law to dense bentonites: these materials may be used for isolation of nuclear fuel wastes in deep geologic disposal vaults. On wetting and with increasing hydraulic gradient, the clays develop swelling pressures, and some specimens appear to exhibit a critical hydraulic gradient or pressure. Below these gradients and pressures, water does not appear to flow through the materials. Once the apparent critical gradient is exceeded, water flux through the materials increases linearly and directly with gradient. Water continues to flow if the gradient is subsequently decreased to values below the original critical value. The possible importance of this finding to effective stress testing of dense bentonite materials is briefly discussed. The hydraulic performance of dense bentonite clay barriers over the range of conditions anticipated in a nuclear-fuel-waste disposal vault remains uncertain. Studies of material behaviour within the anticipated constraints of emplacement state and hydraulic boundary conditions are required. Key words : clay, bentonite, Darcy's law, effective stress, compacted clay, swelling pressure.

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Spatial and temporal progression of internal erosion in cohesionless soil

Canadian Geotechnical Journal ◽

10.1139/t10-071 ◽

2011 ◽

Vol 48 (3) ◽

pp. 399-412 ◽

Cited By ~ 101

Author(s):

Ricardo Moffat ◽

R. Jonathan Fannin ◽

Stephen J. Garner

Keyword(s):

Seepage Flow ◽

Hydraulic Gradient ◽

Internal Erosion ◽

Cohesionless Soil ◽

Cohesionless Soils ◽

Multi Stage ◽

Internal Instability ◽

Post Test ◽

Erosion Test ◽

Permeameter Tests

Permeameter tests were performed on four widely graded cohesionless soils, to study their susceptibility to internal erosion. Test specimens were reconstituted as a saturated slurry, consolidated, and then subjected to multi-stage seepage flow under increasing hydraulic gradient. The occurrence of internal instability is described qualitatively, from visual observations through the wall of the permeameter during a test and from post-test observations; it is also described quantitatively, from change of hydraulic gradient within the specimen and from axial displacement during a test. The results provide a novel insight into the spatial and temporal progression of seepage-induced internal instability. This insight yields an improved characterization of suffusion and suffosion in cohesionless soils, the progression of which appears governed by a critical combination of hydraulic gradient and effective stress.

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Impacts of Consolidation Time on the Critical Hydraulic Gradient of Newly Deposited Silty Seabed in the Yellow River Delta

Journal of Marine Science and Engineering ◽

10.3390/jmse9030270 ◽

2021 ◽

Vol 9 (3) ◽

pp. 270

Author(s):

Meiyun Tang ◽

Yonggang Jia ◽

Shaotong Zhang ◽

Chenxi Wang ◽

Hanlu Liu

Keyword(s):

Yellow River ◽

Yellow River Delta ◽

Hydraulic Gradient ◽

River Delta ◽

Theoretical Formula ◽

The Yellow River ◽

The Yellow River Delta ◽

Critical Hydraulic Gradient ◽

Seepage Flows ◽

The Yrd

The silty seabed in the Yellow River Delta (YRD) is exposed to deposition, liquefaction, and reconsolidation repeatedly, during which seepage flows are crucial to the seabed strength. In extreme cases, seepage flows could cause seepage failure (SF) in the seabed, endangering the offshore structures. A critical condition exists for the occurrence of SF, i.e., the critical hydraulic gradient (icr). Compared with cohesionless sands, the icr of cohesive sediments is more complex, and no universal evaluation theory is available yet. The present work first improved a self-designed annular flume to avoid SF along the sidewall, then simulated the SF process of the seabed with different consolidation times in order to explore the icr of newly deposited silty seabed in the YRD. It is found that the theoretical formula for icr of cohesionless soil grossly underestimated the icr of cohesive soil. The icr range of silty seabed in the YRD was 8–16, which was significantly affected by the cohesion and was inversely proportional to the seabed fluidization degree. SF could “pump” the sediments vertically from the interior of the seabed with a contribution to sediment resuspension of up to 93.2–96.8%. The higher the consolidation degree, the smaller the contribution will be.

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Management of a Mycotic Aneurysm in a Patient with COVID-19: A Case Report

Medicina ◽

10.3390/medicina57060620 ◽

2021 ◽

Vol 57 (6) ◽

pp. 620

Author(s):

Muzammil H. Syed ◽

Mark Wheatcroft ◽

Danny Marcuzzi ◽

Hooman Hennessey ◽

Mohammad Qadura

Keyword(s):

Abdominal Aortic Aneurysm ◽

Aortic Aneurysm ◽

Stent Graft ◽

Mycotic Aneurysm ◽

Neurological Deficits ◽

Endovascular Stent ◽

Endovascular Stents ◽

Abdominal Aortic ◽

Short Period

The aim of this paper is to share our experience in managing a patient with Klebsiella pneumoniae mycotic abdominal aortic aneurysm who was also infected with COVID-19. A 69-year-old male was transferred to our hospital for the management of an infra-renal mycotic abdominal aortic aneurysm. During his hospital course, the patient contracted severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). He was intubated due to respiratory distress. Over a short period, his mycotic aneurysm increased in size from 2.5 cm to 3.9 cm. An emergency repair of his expanding aneurysm was achieved using our previously described protocol of coating endovascular stents with rifampin. The patient was managed with a rifampin-coated endovascular stent graft without any major complications. Postoperatively, the patient did not demonstrate any neurological deficits nor any vascular compromise. He remained afebrile during his postoperative course and was extubated sometime thereafter. He was then transferred to the ward for additional monitoring prior to his discharge to a rehab hospital while being on long-term antibiotics. During his hospital stay, he was monitored with serial ultrasounds to ensure the absence of abscess formation, aortic aneurysm growth or graft endoleak. At 6 weeks after stent graft placement, he underwent a CT scan, which showed a patent stent graft, with a residual sac size of 2.5 cm without any evidence of abscess or endoleak. Over a follow-up period of 180 days, the patient remained asymptomatic while remaining on long-term antibiotics. Thus, in patients whose surgical risk is prohibitive, endovascular stent grafts can be used as a bridge to definitive surgical management.

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An unusually low density ultra-short period super-Earth and three mini-Neptunes around the old star TOI-561

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3728 ◽

2020 ◽

Author(s):

G Lacedelli ◽

L Malavolta ◽

L Borsato ◽

G Piotto ◽

D Nardiello ◽

...

Keyword(s):

Transit Time ◽

Time Variation ◽

Planetary System ◽

Radial Velocities ◽

Low Density ◽

Outer Planets ◽

Short Period ◽

The Stability

Abstract Based on HARPS-N radial velocities (RVs) and TESS photometry, we present a full characterisation of the planetary system orbiting the late G dwarf After the identification of three transiting candidates by TESS, we discovered two additional external planets from RV analysis. RVs cannot confirm the outer TESS transiting candidate, which would also make the system dynamically unstable. We demonstrate that the two transits initially associated with this candidate are instead due to single transits of the two planets discovered using RVs. The four planets orbiting TOI-561 include an ultra-short period (USP) super-Earth (TOI-561 b) with period Pb = 0.45 d, mass Mb = 1.59 ± 0.36 M⊕ and radius Rb = 1.42 ± 0.07 R⊕, and three mini-Neptunes: TOI-561 c, with Pc = 10.78 d, Mc = 5.40 ± 0.98 M⊕, Rc = 2.88 ± 0.09 R⊕; TOI-561 d, with Pd = 25.6 d, Md = 11.9 ± 1.3 M⊕, Rd = 2.53 ± 0.13 R⊕; and TOI-561 e, with Pe = 77.2 d, Me = 16.0 ± 2.3 M⊕, Re = 2.67 ± 0.11 R⊕. Having a density of 3.0 ± 0.8 g cm−3, TOI-561 b is the lowest density USP planet known to date. Our N-body simulations confirm the stability of the system and predict a strong, anti-correlated, long-term transit time variation signal between planets d and e. The unusual density of the inner super-Earth and the dynamical interactions between the outer planets make TOI-561 an interesting follow-up target.

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Heatwaves in Kenya 1987–2016: Facts from CHIRTS High Resolution Satellite Remotely Sensed and Station Blended Temperature Dataset

Atmosphere ◽

10.3390/atmos12010037 ◽

2020 ◽

Vol 12 (1) ◽

pp. 37

Author(s):

Martial Amou ◽

Amatus Gyilbag ◽

Tsedale Demelash ◽

Yinlong Xu

Keyword(s):

High Resolution ◽

Adaptation Strategies ◽

Reference Period ◽

The West ◽

Tana River ◽

Short Period ◽

The World ◽

Northern Side ◽

Data Source

As global temperatures continue to rise unabated, episodes of heat-related catastrophes across the world have intensified. In Kenya, heatwave phenomena and their associated impacts are ignored and neglected due to several reasons, including unreliable and inconsistent weather datasets and heatwave detection metrics. Based on CHIRTS satellite infrared estimates and station blended temperature, this study investigated the spatiotemporal distribution of the heatwave events over Kenya during 1987–2016 using the Heatwave Magnitude Index daily (HWMId). The results showed that contrary to the absence of heatwave records in official national and international disaster database about Kenya, the country experienced heatwaves ranging from less severe (normal) to deadly (super-extreme) between 1987 and 2016. The most affected areas were located in the eastern parts of the country, especially in Garissa and Tana River, and in the west-northern side around the upper side of Turkana county. It was also found that the recent years’ heatwaves were more severe in magnitude, duration, and spatial extent. The highest magnitude of the heatwaves was recorded in 2015 (HWMId = 22.64) while the average over the reference period is around 6. CHIRTS and HWMId were able to reveal and capture most critical heatwave events over the study period. Therefore, they could be used respectively as data source and detection metrics, for heatwaves disaster emergency warning over short period as well as for long-term projection to provide insight for adaptation strategies.

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