1 / 41

PAT203 SOIL MECHANICS

PAT203 SOIL MECHANICS. PERMEABILITY & SEEPAGE PREPARED BY: LIYANA BINTI AHMAD SOFRI. Permeability. water. Dense soil - difficult to flow - low permeability. Loose soil - easy to flow - high permeability. Permeability And Drainage Characteristics Of Soils. Total Head at B.

mwarden
Télécharger la présentation

PAT203 SOIL MECHANICS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. PAT203 SOIL MECHANICS PERMEABILITY & SEEPAGE PREPARED BY: LIYANA BINTI AHMAD SOFRI

  2. Permeability water Dense soil - difficult to flow - low permeability Loose soil - easy to flow - high permeability

  3. Permeability And Drainage Characteristics Of Soils

  4. Total Head at B Total Head at A The loss of head between A and B The head loss may be expressed as :

  5. where, v: discharge velocity, which is the quantity of water flowing in unit time through a unit gross cross-sectional area of soil (cm/s). k: coefficient of permeability or hydraulic conductivity (cm/s). q: flow rate (cm3/s). Q: volume of collected water (cm3). A: cross-sectional area (cm3). i: hydraulic gradient.

  6. A = Av + As

  7. Example 1 • Water flows through the sand filter as shown in fig. • The cross-sectional area & length of the soil mass are 0.250m2 & 2.00m, respectively. • The hydraulic head difference is 0.160 m • The coefficient of permeability is 6.90x10-4 m/s • Question: Determine the flow rate of water through the soil

  8. Typical values of Hydraulic Conductivity of Saturated Soils

  9. The total volume of water collected may be expressed as: Q: volume of water collected A: area of cross section of the soil sample t: duration of collection of water

  10. where: h1 = initial head difference at time = 0 h2 = final head difference at time T a = x-sectional area of standpipe A = x-sectional area of soil specimen L = length of soil specimen

  11. Example 2 • For a falling-head permeability test, the following values are given. • length of specimen = 200 mm • area of soil specimen = 1000 mm2 • area of standpipe = 40 mm2 • head difference at time 0 seconds = 500 mm • head difference at time 180 seconds = 300 mm. Calculate the hydraulic conductivity of the soil.

  12. Laplace equation of Continuity Flow in: Flow out: Flow in = Flow out (Continuity equation) By simplification, we get

  13. Laplace equation of Continuity From Darcy’s Law: Replace in the continuity equation If soil is isotropic (i.e. kx = kz = k) Laplace equation This equation governs the steady flow condition for a given point in the soil mass

  14. One-dimensional flow Discharge = Q = v. A = k . i . A= k (h/L). A

  15. Water In One-dimensional flow Head Loss or Head Difference or Energy Loss h =hA - hB i = Hydraulic Gradient hA Pressure Head (q) Water out Total Head Pressure Head hB A Soil Total Head B Elevation Head L = Drainage Path ZA Elevation Head ZB Datum

  16. Two-dimensional flow

  17. Two-dimensional flow

  18. Flow nets • Flow netsare the combination of flow lines and equipotential lines. • To complete the graphic construction of a flow net, one must draw the flow and equipotential lines in such away that: 1. The equipotential lines intersect the flow lines at right angles. 2. The flow elements formed are approximate squares. Flow channel Flow line Equipotential line

  19. Flow Net Drawing Technique • Draw to a convenient scale the geometry of the problem. • Establish constant head and no flow boundary conditions and draw flow and equipotential lines near boundaries. • Constant head boundaries (water levels) represent initial or final equipotentials • Impermeable (no-flow) boundaries are flow lines • Sketch flow lines by smooth curves (3 to 5 flow lines). • Flow lines should not intersect each other or impervious boundary • Draw equipotential lines by smooth curves adhering to right angle intersections and square grids conditions (aspect ratio =1). • Continue sketching and re-adjusting until you get squares almost everywhere. Successive trials will result in a reasonably consistent flow net.

  20. Boundary Conditions

  21. H 0 H H-Dh H-5Dh H-2Dh H-4Dh H-3Dh

  22. h1 = h1 - h2 h2

  23. Seepage Flow channel” L

  24. Flow element • In a flow net, the strip between any two adjacent flow lines is called a flow channel. • The drop in the total head between any two adjacent equipotential lines is called the potential drop. Seepage Calculation from Flow Net • If the ratio of the sides of the flow element are the same along the flow channel, then: • 1. Rate of flow through the flow channel per unit width perpendicular to the flow direction is the same. • Dq1 = Dq2 = Dq3 = Dq • 2. The potential drop is the same and equal to: Where H: head difference between the upstream and downstream sides. Nd: number of potential drops.

  25. From Darcy’s Equation, the rate of flow is equal to: Seepage Calculation from Flow Net • If the number of flow channels in a flow net is equal to Nf, the total rate of flow through all the channels per unit length can be given by:

More Related