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Questions and Answers
In two-dimensional flow scenarios, the uplift pressure beneath a hydraulic structure remains unaffected by alterations in the anisotropic properties of the subsurface soil.
In two-dimensional flow scenarios, the uplift pressure beneath a hydraulic structure remains unaffected by alterations in the anisotropic properties of the subsurface soil.
False (B)
The graphical solution of Laplace's equation for two-dimensional flow is uniquely represented by a velocity hodograph, irrespective of the boundary conditions.
The graphical solution of Laplace's equation for two-dimensional flow is uniquely represented by a velocity hodograph, irrespective of the boundary conditions.
False (B)
In a flownet, the intersection of flow lines and equipotential lines at acute angles signifies a mathematically valid solution for isotropic soil conditions, indicative of non-Darcian flow.
In a flownet, the intersection of flow lines and equipotential lines at acute angles signifies a mathematically valid solution for isotropic soil conditions, indicative of non-Darcian flow.
False (B)
For anisotropic soils where $k_h$ significantly exceeds $k_v$, the accurate representation of a flownet necessitates shortening the vertical distance of the problem by a factor of $\sqrt{k_h/k_v}$ to account for directional permeability differences.
For anisotropic soils where $k_h$ significantly exceeds $k_v$, the accurate representation of a flownet necessitates shortening the vertical distance of the problem by a factor of $\sqrt{k_h/k_v}$ to account for directional permeability differences.
In a confined aquifer subjected to two-dimensional flow, the hydraulic gradient is solely a function of the total head loss and the thickness of the aquifer, remaining invariant to the flow path's tortuosity.
In a confined aquifer subjected to two-dimensional flow, the hydraulic gradient is solely a function of the total head loss and the thickness of the aquifer, remaining invariant to the flow path's tortuosity.
In the context of seepage analysis beneath hydraulic structures, the exit gradient is invariably minimized at the downstream toe, ensuring structural stability against piping and soil erosion, regardless of soil heterogeneity.
In the context of seepage analysis beneath hydraulic structures, the exit gradient is invariably minimized at the downstream toe, ensuring structural stability against piping and soil erosion, regardless of soil heterogeneity.
The Laplace equation, when applied to two-dimensional flow through porous media, directly quantifies the advective transport of contaminants, thereby precluding the necessity for separate solute transport modeling.
The Laplace equation, when applied to two-dimensional flow through porous media, directly quantifies the advective transport of contaminants, thereby precluding the necessity for separate solute transport modeling.
In a flownet construction, equipotential lines always converge towards regions of higher hydraulic conductivity, irrespective of the geometric constraints imposed by impermeable boundaries.
In a flownet construction, equipotential lines always converge towards regions of higher hydraulic conductivity, irrespective of the geometric constraints imposed by impermeable boundaries.
A flow line represents the locus of points where the total mechanical energy of a fluid particle is constant, thus remaining invariant to changes in the fluid's velocity or elevation within the flow field.
A flow line represents the locus of points where the total mechanical energy of a fluid particle is constant, thus remaining invariant to changes in the fluid's velocity or elevation within the flow field.
The critical hydraulic gradient for the onset of piping in a soil is exclusively dictated by the soil's void ratio and specific gravity, rendering it independent of the effective stress conditions within the soil matrix.
The critical hydraulic gradient for the onset of piping in a soil is exclusively dictated by the soil's void ratio and specific gravity, rendering it independent of the effective stress conditions within the soil matrix.
In a typical flownet diagram, the total number of flow channels ($N_f$) and equipotential drops ($N_d$) are inversely proportional such that their product always equals a constant value determined by the hydraulic conductivity of the medium.
In a typical flownet diagram, the total number of flow channels ($N_f$) and equipotential drops ($N_d$) are inversely proportional such that their product always equals a constant value determined by the hydraulic conductivity of the medium.
The presence of a low-permeability clay layer at the base of an excavation invariably mitigates the risk of heaving, irrespective of the pore water pressure distribution and the geometry of the excavation.
The presence of a low-permeability clay layer at the base of an excavation invariably mitigates the risk of heaving, irrespective of the pore water pressure distribution and the geometry of the excavation.
In a fully confined aquifer beneath a dam, the uplift pressure at any point is calculated assuming a linear equipotential drawdown between the upstream and downstream boundaries, irrespective of the flownet configuration.
In a fully confined aquifer beneath a dam, the uplift pressure at any point is calculated assuming a linear equipotential drawdown between the upstream and downstream boundaries, irrespective of the flownet configuration.
The average path of a water particle flowing from upstream to downstream in a porous medium, also known as a flow line, is influenced by the largest gradient.
The average path of a water particle flowing from upstream to downstream in a porous medium, also known as a flow line, is influenced by the largest gradient.
The solution of Laplace's equation gives two sets of lines, namely flow lines and equipotential lines, which intersect each other at right angles.
The solution of Laplace's equation gives two sets of lines, namely flow lines and equipotential lines, which intersect each other at right angles.
The space between two adjacent flow lines is called the flow channel.
The space between two adjacent flow lines is called the flow channel.
In isotropic soil, the flow follows the path of largest gradient; therefore, the flow lines intersect the equipotential lines at a right angle.
In isotropic soil, the flow follows the path of largest gradient; therefore, the flow lines intersect the equipotential lines at a right angle.
A flow net is a numerical solution of Laplace's equation in 3-dimensional flow for a given set of boundary conditions.
A flow net is a numerical solution of Laplace's equation in 3-dimensional flow for a given set of boundary conditions.
In seepage analysis, flow nets are constructed to determine seepage losses, water pressure under a dam or structure, and the amount of exit gradients.
In seepage analysis, flow nets are constructed to determine seepage losses, water pressure under a dam or structure, and the amount of exit gradients.
An imperious boundary is a flow line.
An imperious boundary is a flow line.
Flashcards
Seepage Analysis
Seepage Analysis
The analysis of water flow (seepage) under structures like dams to determine seepage losses, water pressure, and exit gradients.
Flow Net
Flow Net
A graphical solution of Laplace's equation for 2D flow, illustrating flow patterns and pressure distribution.
Flow Lines
Flow Lines
Lines representing the average path of a water particle flowing through soil.
Equipotential Line
Equipotential Line
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Hydraulic Gradient
Hydraulic Gradient
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Flow Channel
Flow Channel
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Field (in Flow Net)
Field (in Flow Net)
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Flow Net Orthogonality
Flow Net Orthogonality
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Piping
Piping
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Uplift Pressure
Uplift Pressure
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Exit Gradient Location
Exit Gradient Location
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Critical Gradient
Critical Gradient
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Energy Loss (Seepage)
Energy Loss (Seepage)
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Heaving or Boiling
Heaving or Boiling
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Kh # Ky
Kh # Ky
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Study Notes
- Two dimensional flow involves analyzing:
- Uplift pressure below structures
- Heaving or boiling in cofferdams and piping in earth dams
- Heaving of clay layers at the bottom of excavations
Energy Losses in Flow Under a Dam
- Examines energy losses as water flows through soil under a dam
- Illustrates datum lines and hydraulic head at various points
Flow Lines and Equipotential Lines
- A flow line represents the average path of a water particle from upstream to downstream (tailwater)
- An equipotential line is a contour line connecting points of equal potential or head
- The gradient is the head difference between adjacent equipotential lines divided by the distance between them
- In isotropic soil, flow follows the path of the largest gradient, causing flow lines to intersect equipotential lines at right angles
- The flow condition is 2-dimensional
Flow Nets
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Flow nets are used in seepage analysis to determine seepage losses, water pressure under dams/structures, and exit gradients
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Determined through the construction of flow nets
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A flow net is a graphical solution of Laplace's equation in 2D flow for a given set of boundary conditions
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Laplace's equation represents energy loss through a resistive medium
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The solution of Laplace's equation yields flow lines and equipotential lines
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Flow and equipotential lines intersect at right angles
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The space between two adjacent flow lines is called a flow channel
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The space between two adjacent flow lines and two successive equipotential lines is called a field
Properties of a Flow Net
- Flow lines and equipotential lines intersect at right angles; they are mutually orthogonal
- A circle can be drawn in each field, touching all four sides
- For homogenous soil, transitions in the shapes of curves will be smooth, elliptical, or parabolic
- The same potential drop occurs between successive equipotential lines
- An impervious boundary acts as a flow line
Determination of Seepage
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The gradient (i) is calculated as Δh/Δl, which simplifies to hL/Nd (total head loss divided by number of potential drops)
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Flow rate (Δq) through the channel is k(Δh/Δl)A, which is k(hL /Nd)(a/b)
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Since a ~ b, total seepage (q) is q = k * hL * (Nf/Nd)
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Nf represents the total number of flow channels
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Nd refers to the total number of equipotential drops
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The rules mentioned are applicable to isotropic soils
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In nature soils are anisotropic, accounted for by direction differences
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Directional differences are taken into account by transforming the scale of the flow net:
- If kh >> ky, shorten the horizontal distance of the problem by √(kh/kv)
- q = (Nf/Nd) * √(kh*kv) * hL
Uplift Pressure Below a Structure
- Uplift pressure acts upwards on the base of a concrete weir due to water seeping underneath
Exit Gradient
- ie = dh/le
- dh = H/Nd, le = average length of the smallest exit field adjacent to the structure
- Critical conditions (piping) occur when the gradient reaches unity
- Piping occurs at the corner of a dam since le is the least at this point, resulting in the largest exit gradient
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