scholarly journals STUDY ON EFFECT OF FACTORS ON CRITICAL SHEAR STRESS OF COHESIVE BANK MATERIALS FOR COASTAL EROSION

2011 ◽  
Vol 14 (2) ◽  
pp. 5-15
Author(s):  
Vinh Trong Bui ◽  
Deguchi Ichiro
Keyword(s):  
Shear Stress ◽  
Moisture Content ◽  
Laboratory Experiments ◽  
Critical Shear Stress ◽  
Clay Content ◽  
Experimental Results ◽  
Vegetation Density ◽  
Submerged Jet ◽  
Erosion Processes

The aim of this study is to investigate effect of sand-silt-clay content, moisture content, salinity, consolidation, and vegetation density on critical shear stress (tc) of cohesive bank materials for erosion processes of rivers and coastal regions. The authors used the non-vertical submerged jet test apparatus designed by Hanson et al. (2002) and reproduced by Deguchi et al. (2007) to carry out both laboratory and in situ measurements. The laboratory experimental results showed that the tc increased as the rate of clay content, salinity, consolidation, and vegetation density increased. The t c decreased as the moisture content increased. The in situ experimental results of five severely eroded sites of the Soai Rap river banks, southern Hochiminh City were similar to thoses of laboratory experiments. The erodibility (kd) of cohesive bank material can also be determined when the t c is measured.

Soil Moisture Impacts Linear and Nonlinear Erodibility Parameters from Jet Erosion Tests

2020 ◽  
Vol 63 (4) ◽  
pp. 1123-1131
Author(s):  
Anish Khanal ◽  
Garey A. Fox ◽  
Lucie Guertault
Keyword(s):  
Shear Stress ◽  
Soil Moisture ◽  
Moisture Content ◽  
Soil Moisture Content ◽  
Critical Shear Stress ◽  
Loam Soil ◽  
Initial Resistance ◽  
Erosion Test ◽  
Linear And Nonlinear

HighlightsThe jet erosion test (JET) remains the most commonly used instrument for measuring in situ erodibility.This research investigated the impact of soil moisture content below saturation on erodibility parameters.Erodibility parameters were derived for both linear and nonlinear detachment models.Higher soil moisture increased initial resistance to erosion but also increased erosion rate.Abstract. The jet erosion test (JET) is a commonly employed technique to measure the erodibility of soils in situ by estimating the parameters of linear and nonlinear cohesive sediment detachment models. However, additional research is needed to understand the effect of soil moisture, a critical in situ test condition, on the derived erodibility parameters. This study compared the erodibility parameters, i.e., critical shear stress (tc) and the erodibility coefficient (kd) for the linear excess shear stress equation and two parameters (b0 and b1) for a nonlinear detachment model, from laboratory JETs across two soil types with contrasting texture and moisture contents. The general pattern was that higher soil moisture content increased the soil’s initial resistance to erosion (i.e., higher tc and b1), but once erosion was initiated the rate of erosion was greater (i.e., higher kd and b0). The magnitude of the changes in the erodibility parameters across the three soil moisture profiles investigated in this research were statistically significant, with kd and b0 varying by as much as a factor of 3. This research also confirmed the greater impact of soil moisture content on kd and b0 as compared to tc and b1. For the range of shear stress applied during these JETs, a linear detachment model was more appropriate for the sandy loam soil but less so for the more cohesive clay loam soil, but results were limited to a narrow range in applied shear stress. The results further support existing research conclusions that in situ erodibility measurements obtained under one set of soil moisture conditions may need to be adjusted to better predict soil detachment during storm events. Keywords: Cohesive soil, Critical shear stress, Detachment model, Erodibility, Jet erosion test, Shear stress, Soil moisture.

In situ jet-testing of the erosional resistance of cohesive streambeds

2007 ◽  
Vol 34 (9) ◽  
pp. 1192-1195 ◽  
Author(s):  
Daniel Shugar ◽  
Ray Kostaschuk ◽  
Peter Ashmore ◽  
Joe Desloges ◽  
Leif Burge
Keyword(s):  
Shear Stress ◽  
Critical Shear Stress ◽  
Sediment Surface ◽  
Cohesive Soils ◽  
Flood Events ◽  
Southern Ontario ◽  
Submerged Jet ◽  
Erodibility Coefficient ◽  
Bed Scour

Fletcher’s Creek is located in an urbanizing basin near Toronto and has a bed and banks composed primarily of cohesive Halton Till. Critical shear stress and an erodibility coefficient for the till were determined using an in situ jet-tester that directs a submerged jet of water perpendicular to the sediment surface. The results from 10 jet-tests indicate that the till has a relatively low critical shear stress and relatively high erodibility coefficient and could be susceptible to bed scour during flood events. Many other streams in southern Ontario have urbanizing watersheds with cohesive till beds that may also be susceptible to erosion.Key words: critical stress, submerged jet, erodibility, cohesive soils.

Experimental Investigation on the Erosion Threshold and Rate of Gravel and Silty Clay Mixtures

2019 ◽  
Vol 62 (4) ◽  
pp. 867-875 ◽  
Author(s):  
Xiaojing Gao ◽  
Qiusheng Wang ◽  
Guowei Ma
Keyword(s):  
Experimental Data ◽  
Shear Stress ◽  
Erosion Rate ◽  
Critical Shear Stress ◽  
Clay Content ◽  
Silty Clay ◽  
Stress Model ◽  
Wilson Model ◽  
Excess Shear Stress ◽  
Better Than

Abstract. The field of cohesive and noncohesive mixture erosion is not fully understood because of the numerous factors that influence soil erodibility. In this study, erosion experiments were conducted on mixtures of gravel and silty clay in proportions varying from 0% to 100% by weight. The critical shear stress of erosion and the erosion rate were quantified using an erosion function apparatus (EFA). Experimental data revealed that the mixture critical shear stress first decreased and then increased with an increasing cohesive fraction for mixtures with silty clay contents up to 50%. The critical shear stress of the mixture showed an increasing trend as the silty clay content varied from 60% to 100%. A transition from noncohesive to cohesive erosion behavior occurred at silty clay contents between 30% and 35%. The appropriateness of a dimensionless nonlinear excess shear stress model and the Wilson model was tested based on the EFA experimental data. The dimensionless excess shear stress model was shown to be appropriate for noncohesive mixtures, while the Wilson model performed better than the dimensionless excess shear stress model for cohesive mixtures. Keywords: Critical shear stress, Erosion rate, Dimensionless nonlinear excess shear stress, Soil mixture, Wilson model.

Experimental Device and Study on Interfacial Shear Stress of the Laminar Soil

2013 ◽  
Vol 353-356 ◽  
pp. 2715-2719
Author(s):  
Chun Yan Zhang ◽  
Guo Hui Xu ◽  
Gang Wang
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Moisture Content ◽  
Interfacial Shear Stress ◽  
Clay Content ◽  
Interfacial Shear ◽  
Future Research ◽  
Measuring Device ◽  
Experimental Soil ◽  
Soil Interface

A designed measuring device of soil interfacial shear stress is introduced in this paper. We used the device for measuring the shear stress between the soil interface, of which the moisture content was 30% and the clay content were 5%, 9%, 15%, 21%, 30% respectively. The results show that the shear strength of experimental soil and friction between the layers decreases with the clay content increasing when the moisture content is 30% and clay content is more than 15%, and the results increase with the clay content increasing when the clay content is less than15%. Based on the study of the laminar soil interfacial shear stress, it provides the basis for the future research of the laminar motion of the sediment and the deposition of the liquefied motion soil.

Modelling Erosion and Deposition of Cohesive Sediments from Hay River, Northwest Territories, Canada

2003 ◽  
Vol 34 (1-2) ◽  
pp. 125-138 ◽  
Author(s):  
David Milburn ◽  
B.G. Krishnappan
Keyword(s):  
Shear Stress ◽  
Northwest Territories ◽  
River Sediment ◽  
Critical Shear Stress ◽  
Cohesive Sediment ◽  
Cohesive Sediments ◽  
Bed Shear Stress ◽  
Flume Experiments ◽  
Annular Flume ◽  
Erosion Processes

A large volume sample of river-bed cohesive sediment and water from Hay River, Northwest Territories, Canada was collected during a spring field program in 2000 as part of a study on under-ice movement of sediment just before breakup. Controlled laboratory experiments were subsequently conducted on the Hay River water/sediments in a rotating annular flume at Burlington, Ontario, Canada to better understand the deposition and erosion processes of cohesive sediment transport. The deposition experiments in the rotating flume confirmed that the Hay River sediment is cohesive and the critical shear stress for deposition and the rates of deposition are a function of bed shear stress and the initial concentration of the sediment in suspension. The erosion experiments provided quantitative data on the critical shear stress for erosion and the rates of erosion as a function of bed shear stress and the age of the sediment deposit. The erosion experiments also indicated that the growth of the biofilm had an influence on the erosion characteristics of the Hay River sediment. Based on the data from the rotating circular flume experiments, a modelling strategy is proposed for calculating the under-ice transport of the cohesive sediments in the Hay River.

scholarly journals Flume Experiments to Assess the Effect of Bottom Roughness, Temperature, Water Velocity and Oil Condition on Critical Shear Stress Estimates of Heavy Fuel Oil

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
MELISSA GLOEKLER ◽  
NANCY KINNER ◽  
TOM BALLESTERO ◽  
ESHAN DAVE
Keyword(s):  
Shear Stress ◽  
Critical Shear Stress ◽  
Maximum Velocity ◽  
Water Velocity ◽  
Fuel Oil ◽  
Bed Shear Stress ◽  
Heavy Fuel Oil ◽  
Kaolinite Clay ◽  
Sunken Oil

Non-floating oil is challenging to detect, track, and recover due to limited visibility inhibiting verification of the oil's location and subsurface movement. Oil that sinks to the bottom (i.e., sunken oil) can form large mats or small agglomerates on the bottom, mix into sediments, or remobilize into the water column and move with currents potentially impacting shorelines, benthic and pelagic organisms, intakes for drinking water, and power plants. Trajectory models exist that predict movement of floating and submerged oil; however, many models cannot accurately address sunken oil movement because the bed shear stress (BSS) necessary to mobilize oil (i.e., critical shear stress (CSS)), neglects the effects of bottom roughness and assumes an immobile bed. The goal of this research is to provide responders and modelers with more precise CSS estimates that include the effect of bottom roughness and incorporate results into a response tool to predict sunken oil movement. The transport of oil depends upon in-situ environmental conditions and oil properties. This research used the Coastal Response Research Center's (CRRC) 2180-liter straight flume to test the effects of water velocity, water temperature, oil mass, and bottom friction on fresh and weathered No. 6 Heavy Fuel Oil (HFO) on an immobile boundary. The flume's test section provided a uniform, one-dimensional flow field measured in 3D by an acoustic Doppler velocimeter (ADV), a Nortek AS (Norway) Vectrino II Profiling Velocimeter. The fresh or weathered (%Ev=5) HFO was mixed with kaolinite clay as a sinking agent, and 100 grams of the mixture was injected into static water via subsurface injection. The water velocity was incrementally increased in a stepwise manner by 0.07 m/s intervals and held for 15 minutes at each velocity. This occurred until: (1) oil had stopped eroding or was completely eroded from the substrate, or (2) the maximum velocity of 1.04 m/s was reached. Bottom roughness was evaluated using the velocity profile and bed shear stress (BSS) was calculated using multiple methods applicable to lab and field conditions. The oil's behavior was documented by downward- and side-facing GoPro cameras and reviewed to estimate mass loss per velocity interval, the distance the oil migrated along the bottom, and the corresponding CSS. In the case of an oil spill, responders can compare CSS estimates, determined through this research, with in-situ BSS estimates predicting under what conditions the sunken oil will become mobile.

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