Determination of critical shear stress of non-cohesive soils using submerged jet test and turbulent kinetic energy

2015 ◽  
Vol 40 (9) ◽  
pp. 1182-1190 ◽  
Author(s):  
Joseph Sang ◽  
Peter Allen ◽  
John Dunbar
Keyword(s):  
Shear Stress ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Critical Shear Stress ◽  
Cohesive Soils ◽  
Submerged Jet

Practical Determination of Critical Shear Stress in Cohesive Soils

2017 ◽  
Vol 143 (10) ◽  
pp. 04017045 ◽  
Author(s):  
Hicham (Sam) Salem ◽  
Colin D. Rennie
Keyword(s):  
Shear Stress ◽  
Critical Shear Stress ◽  
Cohesive Soils

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.

Methods for Analyzing Submerged Jet Erosion Test Data to Model Scour of Cohesive Soils

2021 ◽  
Vol 64 (3) ◽  
pp. 785-799
Author(s):  
Tony L. Wahl
Keyword(s):  
Shear Stress ◽  
Erosion Rate ◽  
Rate Coefficient ◽  
Critical Shear Stress ◽  
Cohesive Soils ◽  
Simple Linear Regression ◽  
Submerged Jet ◽  
Rate Versus ◽  
Erosion Test ◽  
Stress Parameters

HighlightsFifty-two jet erosion tests performed on four cohesive soils were analyzed by nine different methods.Nonlinear methods performed well on some individual tests but fit inconsistently overall.Several alternate linear solution methods outperformed the widely used Blaisdell method.Simple linear regression of erosion rate versus applied shear stress provided the most consistent relationship between erosion rate and critical shear stress parameters.Abstract. The submerged jet erosion test (JET) is widely used in lab and field settings to quantify erodibility of cohesive soils and determine erosion rate coefficients and critical shear stress values. Test devices with different scales and configurations have been developed in recent years, along with several alternative methods for processing the collected data to determine parameters of linear and nonlinear soil erosion equations. To facilitate standardization, 52 JET experiments were conducted on four different cohesive soils compacted at optimum water content and 2% dry and wet of optimum. Each test was analyzed using nine different methods, four based on the linear excess stress equation (including the commonly used Blaisdell method) and five based on nonlinear erosion equations, including two using the recently popular Wilson model. Results were analyzed to determine the erosion equations and parameter-fitting methods that most effectively represent the observed erosion rates and are of greatest utility for soil erosion modeling and the ranking and classification of soils according to erodibility. Methods based on nonlinear erosion equations fit some data sets well, but they exhibited poor correlation between the erosion rate coefficient and the threshold shear stress parameter for initiating erosion, which is problematic for soil erodibility classification work. Linear methods that simultaneously optimized erosion equation parameters to best fit the total depth of scour or the elapsed time needed to reach specific depths of scour performed better than the Blaisdell method, which has been the informally accepted standard of practice since the late 1990s. However, they also exhibited weak correlation of the erosion rate and critical shear stress parameters. Simple linear regression of average scour rate versus average applied stress provided an effective method for representing the erosion rate versus applied stress curve and exhibited the strongest correlation of the erosion rate coefficient and critical shear stress parameters. Keywords: Cohesive soil, Critical shear stress, Erodibility, Erosion, Erosion laws, Erosion models, Jet erosion test, Shear strss, Soil moisture.

Experimental Study on Critical Shear Stress of Cohesive Soils and Soil Mixtures

2021 ◽  
Vol 64 (2) ◽  
pp. 587-600
Author(s):  
Xiaojing Gao ◽  
Qiusheng Wang ◽  
Chongbang Xu ◽  
Ruilin Su
Keyword(s):  
Experimental Data ◽  
Shear Stress ◽  
Critical Shear Stress ◽  
Cohesive Soil ◽  
Future Research ◽  
Cohesive Soils ◽  
List Type ◽  
Soil Mixture ◽  
Linear Relationships ◽  
Soil Mixtures

HighlightsErosion tests were performed to study the critical shear stress of cohesive soils and soil mixtures.Linear relationships were observed between critical shear stress and cohesion of cohesive soils.Mixture critical shear stress relates to noncohesive particle size and cohesive soil erodibility.A formula for calculating the critical shear stress of soil mixtures is proposed and verified.Abstract. The incipient motion of soil is an important engineering property that impacts reservoir sedimentation, stable channel design, river bed degradation, and dam breach. Due to numerous factors influencing the erodibility parameters, the study of critical shear stress (tc) of cohesive soils and soil mixtures is still far from mature. In this study, erosion experiments were conducted to investigate the influence of soil properties on the tc of remolded cohesive soils and cohesive and noncohesive soil mixtures with mud contents varying from 0% to 100% using an erosion function apparatus (EFA). For cohesive soils, direct linear relationships were observed between tc and cohesion (c). The critical shear stress for soil mixture (tcm) erosion increased monotonically with an increase in mud content (pm). The median diameter of noncohesive soil (Ds), the void ratio (e), and the organic content of cohesive soil also influenced tcm. A formula for calculating tcm considering the effect of pm and the tc of noncohesive soil and pure mud was developed. The proposed formula was validated using experimental data from the present and previous research, and it can reproduce the variation of tcm for reconstituted soil mixtures. To use the proposed formula to predict the tcm for artificial engineering problems, experimental erosion tests should be performed. Future research should further test the proposed formula based on additional experimental data. Keywords: Cohesive and noncohesive soil mixture, Critical shear stress, Erodibility, Mud content, Soil property.

Large-scale modes of turbulent channel flow: transport and structure

2001 ◽  
Vol 448 ◽  
pp. 53-80 ◽  
Author(s):  
Z. LIU ◽  
R. J. ADRIAN ◽  
T. J. HANRATTY
Keyword(s):  
Shear Stress ◽  
Kinetic Energy ◽  
Shear Layer ◽  
Turbulent Kinetic Energy ◽  
Large Scale ◽  
Reynolds Shear Stress ◽  
Reynolds Numbers ◽  
Upstream Region ◽  
Two Dimensional ◽  
Normal Plane

Turbulent flow in a rectangular channel is investigated to determine the scale and pattern of the eddies that contribute most to the total turbulent kinetic energy and the Reynolds shear stress. Instantaneous, two-dimensional particle image velocimeter measurements in the streamwise-wall-normal plane at Reynolds numbers Reh = 5378 and 29 935 are used to form two-point spatial correlation functions, from which the proper orthogonal modes are determined. Large-scale motions – having length scales of the order of the channel width and represented by a small set of low-order eigenmodes – contain a large fraction of the kinetic energy of the streamwise velocity component and a small fraction of the kinetic energy of the wall-normal velocities. Surprisingly, the set of large-scale modes that contains half of the total turbulent kinetic energy in the channel, also contains two-thirds to three-quarters of the total Reynolds shear stress in the outer region. Thus, it is the large-scale motions, rather than the main turbulent motions, that dominate turbulent transport in all parts of the channel except the buffer layer. Samples of the large-scale structures associated with the dominant eigenfunctions are found by projecting individual realizations onto the dominant modes. In the streamwise wall-normal plane their patterns often consist of an inclined region of second quadrant vectors separated from an upstream region of fourth quadrant vectors by a stagnation point/shear layer. The inclined Q4/shear layer/Q2 region of the largest motions extends beyond the centreline of the channel and lies under a region of fluid that rotates about the spanwise direction. This pattern is very similar to the signature of a hairpin vortex. Reynolds number similarity of the large structures is demonstrated, approximately, by comparing the two-dimensional correlation coefficients and the eigenvalues of the different modes at the two Reynolds numbers.

On the structure of shear stress and turbulent kinetic energy flux across the roughness layer of a gravel-bed channel flow

2009 ◽  
Vol 638 ◽  
pp. 423-452 ◽  
Author(s):  
EMMANUEL MIGNOT ◽  
D. HURTHER ◽  
E. BARTHELEMY
Keyword(s):  
Shear Stress ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Channel Flow ◽  
Mean Flow ◽  
Local Flow ◽  
Gravel Bed ◽  
Wall Flows ◽  
The Mean ◽  
Conditional Statistics

This study examines the structure of shear stress and turbulent kinetic energy (TKE) flux across the roughness layer of a uniform, fully rough gravel-bed channel flow (ks+ ≫ 100, δ/k = 20) using high-resolution acoustic Doppler velocity profiler measurements. The studied gravel-bed roughness layer exhibits a complex random multi-scale roughness structure in strong contrast with conceptualized k- or d-type roughness in standard rough-wall flows. Within the roughness layer, strong spatial variability of all time-averaged flow quantities are observed affecting up to 40% of the boundary layer height. This variability is attributed to the presence of bed zones with emanating bed protuberances (or gravel clusters) acting as local flow obstacles and bed zones of more homogenous roughness of densely packed gravel elements. Considering the strong spatial mean flow variability across the roughness layer, a spatio-temporal averaging procedure, called double averaging (DA), has been applied to the analysed flow quantities. Three aspects have been addressed: (a) the DA shear stress and DA TKE flux in specific bed zones associated with three classes of velocity profiles as previously proposed in Mignot, Barthélemy & Hurther (J. Fluid Mech., vol. 618, 2009, p. 279), (b) the global and per class DA conditional statistics of shear stress and associated TKE flux and (c) the contribution of large-scale coherent shear stress structures (LC3S) to the TKE flux across the roughness layer. The mean Reynolds and dispersive shear structure show good agreement between the protuberance bed zones associated with the S-shape/accelerated classes and recent results obtained in standard k-type rough-wall flows (Djenidi et al., Exp. Fluids, vol. 44, 2008, p. 37; Pokrajac, McEwan & Nikora, Exp. Fluids, vol. 45, 2008, p. 73). These gravel-bed protuberances act as local flow obstacles inducing a strong turbulent activity in their wake regions. The conditional statistics show that the Reynolds stress contribution is fairly well distributed between sweep and ejection events, with threshold values ranging from H = 0 to H = 8. However, the TKE flux across the roughness layer primarily results from the residual shear stress between ejection and sweep of very high magnitude (H = 10–20) and of small turbulent scale. Although LC3S are seen to penetrated the interfacial roughness layer, their TKE flux contribution is found to be negligible compared to the very energetic small-scale sweep events. These sweeps are dominantly produced in the bed zones of local gravel protuberances where the velocity profiles are inflexional of S-shape type and the mean flow properties are of mixing-layer flow type as previously shown in Mignot et al. (2009).

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