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Effective Stress, Capillarity & Permeability of Soils | Soil Mechanics - Civil Engineering (CE) PDF Download

Well Hydraulics

  1. Specific yield (Sy)
    The specific yield of an unconfined aquifer is the ratio of volume of water which will flow under saturated condition due to gravity effect to the total volume of aquifer (v).
    Sy = Vwy/V where, Vwy = Volume of water yielded under gravity effect and V = total volume of water.
  2. Specific retention: The specific retention of an unconfined aquifer is the ratio of volume of water retained against gravity effect to the total volume of aquifer (v).
    SR = VWR/V where, VWR = Volume of water retained under gravity effect.

Coefficient of transmissibility
T = kH where, H = Thickness
k = Coefficient of permeability

Unconfined Aquifer

Effective Stress, Capillarity & Permeability of Soils | Soil Mechanics - Civil Engineering (CE)

  1. Theims Theory
    Effective Stress, Capillarity & Permeability of Soils | Soil Mechanics - Civil Engineering (CE)  h1 + s1 = h2 + s2
    where, q = Rate of flow in m3/s
    h= Height of water table of 1st observation well
    h2 = Height of water table of 2nd observation well
    s1 = Drawdown of 1st test well
    s2 = Drawdown of 2nd test well.
    r1 = and r2 are radius of 1st and 2nd observation wells respectively.
  2. Dupits Theory
    Effective Stress, Capillarity & Permeability of Soils | Soil Mechanics - Civil Engineering (CE) 
    R = 3000.S√K and S = H - h
    Where, S = Drawdown in the well
    k = Permeability coefficient in m/s.
    R = Radius of influence in 'm'
    150m ≤ R ≤ 300m
    r = Radius of tes well in 'm'.
    Results of dupits theory are not accurate because 'R' is based on empirical relation.

Confined Aquifer

Effective Stress, Capillarity & Permeability of Soils | Soil Mechanics - Civil Engineering (CE) 

  1. Theims theoryEffective Stress, Capillarity & Permeability of Soils | Soil Mechanics - Civil Engineering (CE) where, b = width
  2. Dupits theory Effective Stress, Capillarity & Permeability of Soils | Soil Mechanics - Civil Engineering (CE) 

Spherical flow through well
qs = K.2πr.s where, r = Radius of well
S = Drawdown
qs = Rate of flow through spherical well in m3/s q= 1/30.qradial flow

Effective Stress, Capillarity & Permeability of Soils | Soil Mechanics - Civil Engineering (CE)

Pumping-In-Test

  1. Open end test
    K = q/5.5rh where, r = Radius of pipe
    h = Head of water above the base of pipe, it may include gravity head and pressure head.
  2. Tacker test
    K = q/(2πLh)log10(L/r) ... when L > 10r
    where, L = Length of perforated section of pipe
    k = q/(2πLh)sin - 1(L/2r) ... when L < 10 r
    r = Radius of pipe
    h = Head of which water is added.

Open well (Recuperation test)
q = (C/A).Volume
Where, C/A = (2.303/T)log10(h1/h2)
C/A = Specific yield or specific capacity of an open well.
T = Time in 'sec'
h1 = Position of water table of t = 0
h2 = Position of water table of t = T

Effective Stress, Capillarity & Permeability of Soils | Soil Mechanics - Civil Engineering (CE)

Value of Permeability
Effective Stress, Capillarity & Permeability of Soils | Soil Mechanics - Civil Engineering (CE) 

The document Effective Stress, Capillarity & Permeability of Soils | Soil Mechanics - Civil Engineering (CE) is a part of the Civil Engineering (CE) Course Soil Mechanics.
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FAQs on Effective Stress, Capillarity & Permeability of Soils - Soil Mechanics - Civil Engineering (CE)

1. What is effective stress in soils?
Ans. Effective stress in soils refers to the stress that is transmitted through the soil skeleton, excluding the pore water pressure. It is the difference between the total stress and the pore water pressure. Effective stress determines the shear strength and deformation behavior of soils.
2. How does capillarity affect soil permeability?
Ans. Capillarity is the ability of a liquid to flow in narrow spaces against the force of gravity. In soils, capillarity plays a significant role in determining the soil permeability. Smaller soil particles and narrower pore spaces increase capillary forces, reducing permeability. Conversely, larger particles and wider pore spaces reduce capillary forces, resulting in higher permeability.
3. What is soil permeability and why is it important in civil engineering?
Ans. Soil permeability refers to the ability of soil to transmit fluids, such as water or air. It is an essential property in civil engineering as it affects the stability and performance of structures built on or with soil. Understanding soil permeability is crucial for designing drainage systems, evaluating groundwater flow, and determining the suitability of soil for construction projects.
4. How can soil permeability be measured?
Ans. Soil permeability can be measured through various laboratory tests, such as the constant head permeability test or the falling head permeability test. In these tests, a soil sample is subjected to a hydraulic gradient, and the rate of fluid flow through the sample is measured. Field tests, such as the pumping test or the slug test, can also be conducted to determine soil permeability in situ.
5. How does effective stress influence soil strength and stability?
Ans. Effective stress directly affects the shear strength and stability of soils. As the effective stress increases, the interparticle forces between soil grains strengthen, leading to greater resistance to deformation and shear failure. It is particularly crucial in slope stability analysis, foundation design, and retaining wall design, where the ability of the soil to withstand external loads and maintain stability is of utmost importance.
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