The Reynolds shear stress is also higher downstream of the well compared to upstream of it. The ratio between the length and width of the pit plays an important role in the calculation of the speed of the mining pit.
Bed surface plot for V12 speed Form-II after start, 4 hours and 8 hours flow (Set-I). Cross-sectional profiles at the center of the pit (7.9 m) for Form-III of the V12 speed (Set-I).
List of Tables
List of Abbreviations
List of Symbols
1 Introduction 1.1 Overview
Impact on River Morphology, Hydraulic Structures, Hydrology and Hydrodynamics of the River
So the duration of the mine pit must be small compared to the time of river bed changes. A schematic diagram of the lowering of the water table due to degradation and widening of the river is present in Figure 1.
Environmental, Water Quality and Ecological Impact
Mining in this lake started in 2001 after sand mining in the Yangtze River was banned. Mining in Poyang Lake was also banned after 2008 due to its impact on biodiversity until proper planning was developed.
Need for Research
Objectives
- Geomorphic characteristics in a mining affected alluvial channel
- Turbulent flow structure and bed load transport characteristics in a mining affected alluvial channel
- Migration of mining pit and multi-scale characterization of migration speed
Comparison of flow characteristics in the area of the mining pit and downstream from it with the upstream section. Explore mining speed from statistical analysis. 1.5.4 Scope of use of the numerical model for the simulation of migration from the cave.
Organization of Thesis
Finally, the literature review identified the need for research and outlined the objectives of the current study.
Chapter 2 describes the experimental program which includes design of experimental flume, description of various instrument used for data collection, shape of various mining pit and bed
2 Methodologies 2.1 Overview
Apparatus and Methods
- The flume
- Bed material
- Main flow discharge
- Flow depth
- Flow velocity
- Ultrasonic ranging system (URS)
From Figure 2.10 it is observed that velocity power spectra of filtered data show good agreement with Kolmogorov's -5/3 hypothesis. In order to interpret the effect of the mine shaft on bed morphology, bed profiles were captured by a Seatak instrument with seven transducers (Figure 2.11).
Bed Preparation
Experimental Program
Form-I: Rectangular pit with vertical side is constructed along the entire width of the channel. Form-III: Trapezoidal well with bench value 10 cm on each side is constructed with side slope 32ᵒ. For the irregularly shaped pit, length to width ratio was calculated by taking the extreme point of length and width of the pit, thus taking into account the maximum disturbance of the channel.
The hydraulic conditions for all experiments are shown in Table 2.1. Table 2.1 Hydraulic conditions of different experiments Discharge.
3 Geomorphic Characteristics in a Mining Affected Alluvial Channel 3.1 Introductions
Morphological Characteristics of Rectangular Mining Pit (Shape-I)
Bed height profile along the center line of the channel is as shown in Figure 3.1 for average velocity V8 and V10 of Set-III. Bed elevation profiles in Figure 3.1 clearly represent channel bed erosion downstream of the pit, which was postulated by many researchers in previous study. This may occur due to the higher values of shear stress downstream of the well than upstream.
The shear stress increases from upstream to downstream, and the highest value is observed at the downstream edge of the well.
Morphological Characteristics of Trapezoidal Mining Pit (Shape-II)
The deposition occurs along the upstream edge of the pit and the edge moves forward towards the downstream. Erosion occurs downstream of the well and it is also observed that the downstream edge of the well begins to flatten out over time. We have also observed more downstream erosion with time, which is represented by the cross-sectional profiles downstream of the well.
-section profile downstream of the well (7 m) shows the degradation of channel bed with time.
Morphological Characteristics of Shape-III, Shape-IV and Shape-V
Fredsoe (1978) also observed the flattening of the cross-sectional slope of a river navigation channel with time. Here, the bank of the pit disappears completely and the upper edge of the pit moves forward from the water along the channel. The width of the pit varied in this case, but the erosion extended across the width of the channel.
The surface graph of Shape-IV for initial and after 8 hours of flow is presented in Figure 3.13 and destruction of the bank of the pit is observed.
Conclusions
Deformation of the cross-sectional shape of the well and its influence on downstream can negatively affect the waterway in the mining area, as well as downstream from it. Experimental observations are discussed on the longitudinal and cross-sectional variation of the channel bed deformation from upstream of the mine pit to downstream of it. The morphological profile shows the propagation of erosion downstream of the pit for all pentaform mine pits.
For the Form-III, Form-IV and Form-V, the erosion is not limited within the excavation area of the pit but is extended to the entire width of the channel downstream.
4 Turbulent Flow Structure and Bed Load Transport Characteristics in a Mining Affected Alluvial Channel
Introductions
Turbulent Characteristics
- Reynolds shear stress distribution (RSS)
- Time-averaged flow velocity
- Reynolds normal stress distribution (RNS)
- Conditional statistics of Reynolds shear stress distribution
The total shear stress is the sum of the Reynolds shear stress and the viscous shear stress. We assumed that the RSS follows the linear law that has zero total shear stress at the free surface. In the center of the pit (section B), the flow velocity is observed to be negative, indicating the presence of reverse flow at the bottom of the pit (Alfrink and van Rijn, 1983).
Vertical distribution of Si H, considering all events at H=0, is shown in Figure 4.8 for four different sections.
Quadrant 2
- Empirical Prediction of Bed Load Transport Rate in a Mined Alluvial Channel
- Comparison of the Non-Dimensional Sediment Transport Parameter between Channel having Mining Pit and Plain Bed Channel
- Conclusions
Downstream of the pit (section D), the dominance of the sweep event over the ejecta can be observed throughout the flow depth. An increase in the dominance of the sweep event in the near-bottom region is observed in sections B, C and D as upstream of the pit. This high-velocity fluid package is sufficient to increase sediment transport in the downstream part of the pit.
An in-stream mining pit also causes a change in the sediment transport characteristics of the channel.
5 Migration of Mining Pit and Multi-Scale Characterization of Migration Speed
Introduction
The dynamic nature of the cleaning process implies flexibility dependent on the scale of the mining pit. 2011) did a thorough investigation of celeriac bed dynamics using multiscale statistical analysis. In this research, the migration speed characteristic of the upstream edge of the pit until it reaches the initial downstream edge is investigated in terms of the scale-dependent flexibility of the mine pit. Based on the experimental data, we have also formulated an empirical function to find the migration speed of the mining pit.
In the later part of the chapter, an analysis has been made for a rectangular mine pit (Shape-I).
Theoretical Backgrounds
- Spectral analysis
- Wavelet transformation
- Length scale dependent celerity
The characteristics of x over time t can be visualized from the PSD of signalx t . The PSD can be defined as the square of the average of the Fourier transform magnitude, over a large time interval: Polynomial trends of a signal can be removed using wavelets with higher order vanishing moments. The scale-dependent velocity can be quantified by decomposing the original signal into wavelet coefficients.
Subsequently, the length scale dependent celerity can be obtained by dividing the delay by the time interval between the two consecutive data series.
Analysis for Shape-II, Shape-III and Shape-IV
- Physical characteristics of mining pit migration
- Multi-scale statistical analysis of mining pit migration
Longitudinal displacement from upstream boundary until the filling of the pit with respect to time is plotted for each form of mine pit for V1 and V5 as shown in Figure 5.1. The empirical formulation developed by Neyshabouri et al. 2002) for mine pit migration was based on only the length and width of the pit as they B). An empirical formulation was developed to determine the migration speed from the upstream edge to the downstream.
The speed of the mining pit increases as the ratio of the length to the width of the pit increases.
Analysis for Rectangular Mining Pit (Shape-I)
For V8 and V10, the mining pit rate is higher in the time duration of (1-4) hours compared to (4-7) hours, which shows the results obtained in previous literature (Singh et al., 2011). It is also observed that the migration/velocity of the mining pit in the sand mining channel increases with the extent and reaches a maximum value and then decreases with the increase in the extent length. This can happen that in the initial time range (1-4 hours) the transport of the upstream layer material increases with the increase of the flow velocity, which causes the mining pit velocity to increase with the increase of the flow velocity.
Over time, sediment transport decreases in both V8 and V10 and the reduced rate of sediment transport is higher in V10 compared to V8 due to which channel becomes stable faster in V10 and the velocity of mine pit is reduced in later time interval (4-7 hour) for V10.
Conclusions
6 Scope of Applying Numerical Model for Simulating Pit Migration 6.1 Introduction
Theoretical Backgrounds
- Governing equations for shallow water hydrodynamics One dimensional shallow water equation can be expressed as
- Governing equation for bed elevation changes
- Sediment transport formula
- Numerical formulation of the governing equation
6 Scope of the application of numerical model for the simulation of well migration 6.1 Introduction. 6.1) Where t is time and x is the longitudinal distance; U represents the flow variable, F and S are the fluxes in x direction and source term respectively. 0c is the critical shear stress, , s is specific gravity of water and sediment respectively, and d50 is median diameter of sediment particle. Where and s are the density of water and sediment, h is the depth of water, D* is the dimensionless particle diameter, from which can be obtained.
Eigenvector associated with a specific eigenvalue of the Jacobian flux matrix can be determined using Eq.
Results and Discussions
- Initial and boundary conditions
- Simulation of pit migration by using proposed numerical model
- Applicability of Equation 4.11 for simulating pit migration
In the present experiment, bedload discharge was collected on the downstream side of the embankment. The erosion at the downstream of the well was observed higher than the upstream and was already discussed in the previous chapters (Chapter 3 and Chapter 4). The migration from upstream edge of the well is not dependent on the sediment transport rate from the downstream of the well.
Thus, using this equation will certainly yield a higher migration rate for the upstream edge of the well.
Conclusions
The mining pit divides the entire system into two parts, one upstream from the pit and one downstream from it. The bedload discharge data used to develop Equation 4.11 were collected at the downstream end of the shaft, which is affected by severe erosion downstream of the pit and results in a higher rate of sediment flow. In this regard, a rigorous study on the comparison of the sediment transport rate between upstream and downstream of the pit can be recommended as future work.
7 Conclusions and Future Recommendations
- Geomorphic Characteristics in a Mining Affected Alluvial Channel
- Turbulent Flow Structure and Bed Load Transport Characteristics in a Mining Affected Alluvial Channel
- Migration of Mining Pit and Multi-Scale Characterization of Migration
- Scope of Applying Numerical Model for Simulating Pit Migration
- Recommendations for the Future Work
Linear projection of Reynolds shear stress shows maximum shear velocity in the center of the well. We also observed higher shear velocity downstream of the well compared to upstream of it. Numerical bed profile shows mine pit migration and erosion downstream of the pit.
The study can also be performed to compare the rate of sediment transport upstream and downstream of the pit.
