Week 6 Seepage Flashcards
(20 cards)
How is total vertical stress (σ) at any depth (d) within soil calculated?
σ = γ × d, where γ is the unit weight of the soil and d is the depth of soil.
What does total stress (σ) in soil consist of?
It consists of stress distributed between the soil skeleton and the pore water in the voids.
What is the formula for total stress in soil considering effective stress and pore water pressure?
σ = σ’ + u, where σ’ is effective stress and u is pore water pressure.
When is pore water pressure (u) above zero in soil?
Only in saturated soils.
What happens to total stress (σ) if there are no external loads and soil unit weight and depth remain constant?
The total stress (σ) remains constant.
How does water flow (seepage) affect total stress (σ)?
Seepage changes pore water pressure (u) but not soil depth (d) or unit weight (γ), so total stress remains constant.
How are effective stress (σ’) and pore water pressure (u) related to maintaining total stress (σ)?
Any change in pore water pressure (u) must cause a change in effective stress (σ’) to keep total stress constant.
Why is effective stress (σ’) important for soil stability?
It governs the stress acting along potential failure surfaces and influences soil shear strength.
What is discharge velocity (v) in soil?
v = k × i, where k is the permeability of soil and i is the hydraulic gradient.
What do the Continuity and Laplace equations allow for in seepage analysis?
Mathematical determination of water flow through soils.
Why are flow nets constructed in seepage analysis?
To graphically determine the flow of water through soils.
What do flow nets represent?
Seepage flow in saturated soil only; they do not represent water flow in unsaturated soil or water-only regions.
What does a flow net diagram show?
Direction of water flow and head of water within saturated soil.
What is the head difference (h) between upstream and downstream water levels in the example?
2.50 m.
How many equipotential drops (Nd) are there in the flow net example?
12
How do you calculate the head of water (hP) at a specific point in a flow net?
hP = (nd / Nd) × h, where nd is the equipotential number at the point of interest.
What is the value of hP at point ‘x’ located between equipotentials 8 and 9?
hP = 1.77 m, calculated as (8.5 / 12) × 2.5 m.
How is total head (hT) at point ‘x’ calculated?
hT = hz + hP, where hz = 5.9 m and hP = 1.77 m. Therefore, hT = 7.67 m.
What formula is used to determine pore water pressure (u) at point ‘x’?
u = hw × γw, where hw = 7.67 m and γw = 9.81 kN/m³.
What is the calculated pore water pressure (u) at point ‘x’?
u = 75.24 kN/m².
