scholarly journals How to Prevent Flow Failures in Tailings Dams

2021 ◽  
Author(s):  
Roberto Rodríguez ◽  
Alejandro Muñoz-Moreno ◽  
Ana Vanessa Caparrós ◽  
Cristóbal García-García ◽  
Ángel Brime-Barrios ◽  
...  
Keyword(s):  
Shear Stress ◽  
Pressure Coefficient ◽  
Drainage System ◽  
Stationary Flow ◽  
Influential Factor ◽  
Degree Of Saturation ◽  
Tailings Dams ◽  
Dam Stability ◽  
Approach Zero ◽  
Porous Sediments

AbstractBased on research carried out at 67 tailings dams in Spain: (1) tailings dams contain alternating sedimentary layers with contractive and dilative geomechanical behaviours; (2) tailings saturate quickly but drain more than 10 times slower due to the high-suction capacity of the porous sediments (2–300 MPa); and (3) over the long-term, a stationary flow regime is attained within a tailings basin. Four temporal and spatial conditions must all be present for a tailing dams flow failure to occur: (1) the tailings must experience contractive behaviour; (2) the tailings must be fully saturated; (3) the effective stress due to static or dynamic load must approach zero; and (4) the shear stress must exceed the tailings residual shear stress. Our results also indicate that the degree of saturation (Sr) is the most influential factor controlling dam stability. The pore-pressure coefficient controls geotechnical stability: when it exceeds 0.5 (Sr = 0.7), the safety factor decreases dramatically. Therefore, controlling the degree of tailings saturation is instrumental to preventing dam failures, and can be achieved using a double drainage system, one for the unconsolidated foundation materials and another for the overlying tailings.

Investigation of Parameters Affecting the Limiting Shear Stress-Pressure Coefficient: A New Model Incorporating Temperature

1994 ◽  
Vol 116 (3) ◽  
pp. 612-620 ◽  
Author(s):  
Victoria Wikstro¨m ◽  
Erik Ho¨glund
Keyword(s):  
Shear Stress ◽  
Film Thickness ◽  
Contact Pressure ◽  
Pressure Coefficient ◽  
Oil Viscosity ◽  
New Model ◽  
Lubricated Contacts ◽  
Limiting Shear Stress ◽  
Essential Parameter ◽  
Maximum Contact

When calculating film thickness and friction in elastohydrodynamically lubricated contacts, assuming a non-Newtonian fluid, the lubricant limiting shear stress is an essential parameter. It influences minimum film thickness and determines traction in the contact. The limiting shear stress is pressure dependent according to the Johnson and Tevaarwerk equation: τL=τ0+γp The limiting shear stress-pressure coefficient γ has in a previous screening investigation been shown to depend on several parameters: oil type, oil viscosity at + 40°C, maximum contact pressure and temperature. In the present investigation, the preliminary data is used together with response surface methodology. With these results in mind, further experiments are made and an empirical model is built. This paper presents a new model for γ which is valid for two types of oil (a polyalphaolefine with diester and a naphthenic oil) with different viscosities at +40°C. The model incorporates the influence of maximum contact pressure and oil temperature on γ. The measurements on which the model is based were carried out at temperatures ranging from −20 to + 110°C. The pressure range was 5.8–7 GPa and the shear rate was about 106 s−1.

scholarly journals Analysis of External Water Pressure for a Tunnel in Fractured Rocks

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Ze-jun Liu ◽  
Yong Huang ◽  
Ding Zhou ◽  
Hong Ge
Keyword(s):  
Water Conservation ◽  
Water Pressure ◽  
Scientific Evidence ◽  
Drainage System ◽  
Fracture Network ◽  
Influential Factor ◽  
Normal Operation ◽  
Fracture Development ◽  
External Water Pressure ◽  
External Water

External water pressure around tunnels is a main influential factor in relation to the seepage safety of underground chambers and powerhouses which make managing external water pressure crucial to water conservation and hydropower projects. The equivalent continuous medium model and the discrete fracture network (DFN) model were, respectively, applied to calculate the seepage field of the study domain. Calculations were based on the integrity and permeability of rocks, the extent of fracture development, and the combination of geological and hydrogeological conditions in the Huizhou pump-storage hydropower station. The station generates electricity from the upper reservoir and stores power by pumping water from the lower to the upper reservoir. In this paper, the external water pressure around the cavern and variations in pressure with only one operational and one venting powerhouse were analyzed to build a predictive model. The results showed that the external water pressure was small with the current anti-seepage and drainage system that normal operation of the reservoir can be guaranteed. The results of external water pressure around the tunnels provided sound scientific evidence for the future design of antiseepage systems.

Sliding with Cavity Formation

1987 ◽  
Vol 33 (115) ◽  
pp. 255-267 ◽  
Author(s):  
A. C. Fowler
Keyword(s):  
Exact Solution ◽  
Shear Stress ◽  
Power Law ◽  
Drainage System ◽  
Cavity Formation ◽  
Effective Pressure ◽  
Dynamic Phenomenon ◽  
Basal Shear ◽  
Tunnel System

AbstractWe present a model for the determination of a sliding law in the presence of subglacial cavitation. This law determines the basal stress at a clean ice‒bedrock interface in terms of the velocity and effective pressure. The method is based on an exact solution of the Nye—Kamb (linearly viscous) sliding problem with cavities, and uses ideas of Lliboutry (1979) to construct, via renormalization methods, an approximate law for general bedrock form. We show that, for a bedrock whose spectrum has a power‒law behaviour, one obtains a sliding law which gives the basal shear stress proportional to a power of the velocity, and to a power of the effective pressure.The effect of subglacial cavitation on the drainage system is examined, using recent ideas of Kamb. For sufficiently high velocities, drainage through a Röthlisberger tunnel system is unstable, and drainage takes place through the linked system of cavities. This leads to a reduction of the effective pressure, and by taking account of this, one can rewrite the sliding law in terms of stress and velocity only.This sliding law can be multi‒valued, and it is suggested that this underlies the dynamic phenomenon of surges.

Study on Reliability Analysis of Tailings Dam Stability

2007 ◽  
Vol 353-358 ◽  
pp. 2619-2622
Author(s):  
Chao Zhang ◽  
Chun He Yang ◽  
Feng Chen
Keyword(s):  
Probability Distribution ◽  
Reliability Analysis ◽  
Limit Equilibrium ◽  
Reliability Theory ◽  
Sensitivity Analyses ◽  
Tailings Dam ◽  
Tailings Dams ◽  
Dam Stability ◽  
The Stability ◽  
Distribution Type

Since the construction method of tailings dams determines the uneven distribution of tailings, a reliability theory is introduced to analyze the stability of tailings dams. Based on the limit equilibrium method and reliability theory, the sensitivity and reliability of a typical tailings dam are analyzed. Reliability analyses with different types of the variable probability distribution types show that the effect of the probability distribution type on reliability analysis can almost be ignored. Besides, the sensitivity analyses of different variables show that the strength indexes and density of tailings will affect the analysis results of stability reliability. Therefore the strength indexes c, φ and density ρ must be considered as basic variables to analyze the stability reliability of tailings dams.

Turbulent Flow in the Entry Region of a Rough Pipe

1974 ◽  
Vol 96 (1) ◽  
pp. 62-68 ◽  
Author(s):  
Jeng-Song Wang ◽  
J. P. Tullis
Keyword(s):  
Boundary Layer ◽  
Mathematical Model ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Velocity Profile ◽  
Turbulent Flow ◽  
Boundary Layer Thickness ◽  
Static Pressure ◽  
Pressure Coefficient ◽  
Reynolds Numbers

The general characteristics of mean turbulent flow in the entry region of a rough pipe are discussed. A mathematical model is presented for predicting the development of boundary layer thickness, core velocity, and pressure coefficient. Measurements were made of static pressure and velocity profiles in a 12-in. dia pipe at Reynolds numbers between 7 × 105 and 3.7 × 106. Water was used as the fluid. Data are included on the length required for the wall shear stress to become constant, for the boundary layer to reach the pipe centerline and for the velocity profile to become fully developed.

CFD Numerical Simulation of the Submarine Pipeline With Spoiler

2008 ◽  
Author(s):  
Jianping Zhao ◽  
Xuechao Wang
Keyword(s):  
Shear Stress ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Hangzhou Bay ◽  
Submarine Pipeline ◽  
Long Distance ◽  
Oil Transportation ◽  
Pipeline Failure ◽  
The Stability ◽  
Coating Weight

Submarine pipeline is one of the most important oil transportation components, pipeline failure due to over-span is the most serious failure mechanism. There are four reasons of pipeline span formation, including erosion of seabed, bumpy seabed, submarine pipeline climbing slope, and pipeline ascending to offshore platform. The Hangzhou Bay submarine pipeline is the most important subproject of the Yong-Hu-Ning network, and it is also the biggest long-distance pipeline for crude oil in China. Due to the dynamic nature of Hangzhou Bay, including high tides and high current amplified by the shallow waters, a self-burial method was selected as the best solution. By increasing the velocity of the stream between the pipeline and the seabed, shear stress on the seabed was enhanced. This localized increase in shear stress causes the seabed under the pipe to erode more quickly and facilitates self-burial of the pipe. To facilitate self-burial, a non-metallic vertical fin is fastened to the top of the pipeline. In this paper flow around a pipeline with and without a spoiler near a smooth wall is simulated with FLUENT version 6.1. The influences of the spoiler on pressure coefficient, lift coefficient, shear stress on the wall, as well as velocity profile are investigated. It is indicated that the coefficients for Drag and Inertia are increased with the application of the spoiler. The lift coefficient is reversed with the application of the spoiler increases the stability of the pipeline resulting in the reduction of the required coating weight.

Numerical Analysis of the Impact of the Stope Blasting Vibration on Tailings Dam Stability Based on GeoStudio

2014 ◽  
Vol 501-504 ◽  
pp. 200-206
Author(s):  
Qing Nan Wei ◽  
Shu Ran Lv
Keyword(s):  
Vibration Monitoring ◽  
Vibration Velocity ◽  
Blasting Vibration ◽  
Tailings Dam ◽  
Vibration Acceleration ◽  
Tailings Dams ◽  
Stability Against Sliding ◽  
Dam Stability ◽  
The Stability ◽  
The Impact

In this paper, based on the establishment of the finite element calculating model, the influence of the blasting vibration to tailings dams stability was analyzed in accordance with actual stope blasting vibration monitoring data. The laws of the blasting vibrations impact on tailings dam stability was reached by importing different vibration amplitude of vibration wave intensity. When the blasting vibration acceleration remained under 0.333g and vibration velocity remained under 17.005cm/s, the coefficient of the healthy tailings dam stability against sliding has a increasing trend with the increase of vibration strength. When the vibration acceleration and the vibration velocity reached the maximum value, the coefficient rapidly decline; But the influence of stope blasting vibration on the stability of the risky tailings dams is more significant. The coefficient of stability against sliding had a straight-line decrease to the risky tailings dams. In Engineering, more than 4 times margin is considered to find the control vibration velocity. The value is 4.25 cm/s. An analysis shows that the effect of blasting vibration on healthy tailings dam stability has two sides. When the blasting vibration intensity remains within control vibration velocity, it can be beneficial to the stability of tailings dam. Otherwise it will be harmful.

scholarly journals Pengaruh Silinder Downstream terhadap Karakteristik Aliran Silinder Upstream Menggunakan Square Disturbance Body Tersusun Tandem

2018 ◽  
Vol 11 (2) ◽  
pp. 58
Author(s):  
Rina Rina ◽  
Sanny Ardhy
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Drag Force ◽  
Turbulence Model ◽  
Bluff Body ◽  
Pressure Coefficient ◽  
Model Parameters ◽  
Square Cylinder ◽  
Shear Stress Transport ◽  
Unsteady Rans

Fluida yang mengalir di sekitar bluff body silinder sirkular, akan menimbulkan gaya-gaya aerodinamika salah satunya gaya drag. Drag sangat tidak diinginkan untuk keselamatan struktur body. Reduksi gaya drag dilakukan dengan mengontrol medan aliran seperti meningkatkan kekasaran permukaan, mengiris silinder dengan sudut iris tertentu, dan menempatkan pengganggu di sisi upstream silinder. Penelitian ini bertujuan untuk melihat pengaruh silinder downstream terhadap karakteristik aliran silinder upstream menggunakan square disturbance body yang disusun tandem pada saluran sempit. Geometri yang digunakan adalah dua silinder sirkular yang disusun tandem berdiameter (D) 25 mm dengan variasi jarak antar silinder (L/D) 1,5; 2; 2,5; 3; 3,5; 4. Square Cylinder sebagai body pengganggu ditempatkan pada sisi upstream silinder utama berdiamensi 4 mm. Posisi sudut pengganggu (?) 30°, dan jarak gap (d=0.4mm). Reynolds number berdasarkan diameter silinder, yaitu ReD 2,32x104. Penelitian iini dilakukan secara numerik 2D Unsteady-RANS menggunakan CFD software FLUENT 6.3.26 dengan model viscous Turbulence Model Shear-Stress-Transport (SST) k-?. Parameter yang diamati adalah koefisien pressure (Cp), Koefisien drag pressure (Cdp) dan visualisasi aliran berupa velocity pathline. Hasilnya menunjukkan bahwa Penambahan silinder downstream memberikan kontribusi dalam pengurangan gaya drag pada silinder upstream menggunakan square disturbance body. Pengaruh wake silinder upstream terhadap silinder downstream berkurang dengan meningkatnya rasio L/D. Interaksi wake silinder upstream terhadap silinder downstream terjadi pada konfigurasi L/D 1,5 – 3. Pengurangan gaya drag optimum terjadi pada konfigurasi L/D 3. The fluid flows around the circular cylinder bluff body will produce aerodynamic forces, one of which is the drag force. Drag is very undesirable for the safety of the body structure. Reduction of drag force is carried out by controlling the flow field such as increasing the surface roughness, slicing the cylinder with a certain iris angle, and placing the disturbance on the upstream side of the cylinder. This purpose of the study is to see the effect of downstream cylinders on the flow characteristics of upstream cylinders using a square disturbance body arranged tandem in a narrow channel. The geometry used is two circular cylinders arranged in tandem diameter (D) 25 mm with a variation of distance between cylinders (L / D) 1.5; 2; 2.5; 3; 3.5; 4. Square Cylinder as a disturbing body is placed on the side of the main cylinder upstream with a diameter of 4 mm. The position of the disturbing angle (?) is 30 °, and the gap distance (d = 0.4mm). Reynolds number is based on cylinder diameter, ie ReD 2.32x104. This research was carried out numerical 2D Unsteady-RANS using a FLUENT 6.3.26 CFD software with viscous Turbulence model Shear-Stress-Transport (SST) k-? model. Parameters observed were pressure coefficient (Cp), drag pressure coefficient (Cdp) and flow visualization in the form of velocity pathline. The results show that the addition of a downstream cylinder contributes to the reduction of the drag force on the upstream cylinder using a square disturbance body. The wake influence of upstream cylinder to downstream cylinder decreasing with increasing the ratio of L/D. The interaction of wake cylinder upstream to downstream cylinder occurs at L/D 1.5 - 3. The optimum for the drag force reduction occurs at L/D 3.

scholarly journals Crack Initiation Criteria and Fracture Simulation for Precracked Sandstones

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
R. Q. Huang ◽  
L. Z. Wu ◽  
B. Li
Keyword(s):  
Shear Stress ◽  
Stress Intensity ◽  
Fracture Mode ◽  
Lateral Pressure ◽  
Pressure Coefficient ◽  
Fracture Propagation ◽  
Mode I ◽  
Mode Ii ◽  
Fracture Angle ◽  
Mode Ii Fracture

The friction coefficient, tip curvature, and different-width crack state influence the stress intensity factor (SIF). The maximum circumferential tensile stress (MTS) and minimum strain energy density criterion (S) face challenges in explaining the mode-II fracture propagation of cracks. The maximum radial shear stress (MSS) and modified twin shear stress factor (ITS) criteria are proposed as the brittle mode-II fracture criteria. The experiments and numerical analysis are also performed. The results indicate that the fracture angles of the MSS and ITS were similar and different from the results of MTS and S. The equivalent stress intensity factors (ESIFs) from the mixed mode I-II are proposed to determine the fracture mode. There are different fracture models for different cracks under tensile and compressive stresses. The ratio of the tensile strength to uniaxial compressive strength influenced the fracture angle of ITS. The lateral pressure coefficient (k) had a significant effect on the mode-II fracture angle when the angle between the crack and the vertical direction is less than 40° and the lateral pressure coefficient is more than 0. Because the same fracture mode k (k > 0) can inhibit mode-I fracturing, conversely, it can also promote mode-I fracturing. Experimental results and numerical simulations of fracture propagation under uniaxial compression confirmed that the theoretical results were correct.

Numerical Flow Simulation in a Horizontal-to-Vertical Elbow

2014 ◽  
Vol 541-542 ◽  
pp. 559-563
Author(s):  
Ai Zhao Zhou ◽  
Jian Guang Wu ◽  
Luo Peng Li ◽  
Dong Mei Chen ◽  
Huan Qiang Yang ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Behavior ◽  
Pressure Coefficient ◽  
Petroleum Industry ◽  
Flow Simulation ◽  
Pipe Elbow ◽  
Inner Radius ◽  
Calculation Results ◽  
Wall Shear

The petroleum industry has been faced with the problem of flow-related erosion and corrosion during oil production and transportation for decades. In this paper, to characterize the flow behavior inside a pipe elbow, the RNG k-ε turbulence model with MUSCL discretization scheme is applied to the simulation. The calculation results are analyzed and conclusions can be drawn from these analyses: The simulations predicted value for the diametrical pressure coefficient is in excellent agreement with published correlation obtained from experimental data; The simulations indicate that the maximum wall shear stress occur near the inner corner wall, just downstream of the entrance to the elbow; At the entrance of the elbow, it is clear that the faster moving fluid starts out displaced towards the inner radius and the wall shear stress taking on its maximum value there; just downstream of 45°plane, the flow separates from the inner radius and a large separation vortex is formed that extends downstream.

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