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CivilSoil Mechanics
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The relation between void ratio (e) and porosity (n) is

A

n=1+een = \frac{1+e}{e}n=e1+eтАЛ

B

n=e1+en = \frac{e}{1+e}n=1+eeтАЛ

C

e=n1+ne = \frac{n}{1+n}e=1+nnтАЛ

D

e=1тИТnne = \frac{1-n}{n}e=n1тИТnтАЛ

Correct Answer

тЪЩя╕П TE тАв Technical Concept & PrincipleCivilSoil Mechanics
Option B

n=e1+en = \frac{e}{1+e}n=1+eeтАЛ

Quick Summary:

Void ratio (e) is defined as the ratio of the volume of voids (VvV_vVvтАЛ) to the volume of solids (VsV_sVsтАЛ), while porosity (n) is the ratio of the volume of voids (VvV_vVvтАЛ) to the total volume (VVV). The relationship n=e1+en = \frac{e}{1+e}n=1+eeтАЛ is derived from these volumetric definitions by observing that the total volume V=Vs+VvV = V_s + V_vV=VsтАЛ+VvтАЛ.

тЪЩя╕ПTETechnical SolutionConcept & Principle
ЁЯТб Explanation

Void ratio (e) is defined as the ratio of the volume of voids (VvV_vVvтАЛ) to the volume of solids (VsV_sVsтАЛ), while porosity (n) is the ratio of the volume of voids (VvV_vVvтАЛ) to the total volume (VVV). The relationship n=e1+en = \frac{e}{1+e}n=1+eeтАЛ is derived from these volumetric definitions by observing that the total volume V=Vs+VvV = V_s + V_vV=VsтАЛ+VvтАЛ.

ЁЯФв Key Formulas

n=e1+en = \frac{e}{1+e}n=1+eeтАЛ тАФ Porosity in terms of void ratio

e=n1тИТne = \frac{n}{1-n}e=1тИТnnтАЛ тАФ Void ratio in terms of porosity

тЪЩя╕П Working Principle

The soil mass is considered a three-phase system comprising solids, water, and air. By setting Vs=1V_s = 1VsтАЛ=1, we get Vv=eV_v = eVvтАЛ=e, which makes the total volume V=1+eV = 1 + eV=1+e. Substituting these into the definition of porosity n=VvVn = \frac{V_v}{V}n=VVvтАЛтАЛ, we obtain n=e1+en = \frac{e}{1+e}n=1+eeтАЛ. Similarly, algebraic rearrangement allows us to express eee in terms of nnn as e=n1тИТne = \frac{n}{1-n}e=1тИТnnтАЛ.

ЁЯУМ Key Points
  • тЦ╕

    Void ratio (e) can range from 0 to infinity, whereas porosity (n) is always less than 1 (0 < n < 1).

  • тЦ╕

    For soil, eee is a more commonly used parameter in calculations involving consolidation, while nnn is used in permeability studies.

  • тЦ╕

    Both eee and nnn are unitless measures of the relative density of the soil packing.

тЬЕ Advantages
  • тЦ╕

    Simplifies conversion between different soil state descriptors.

  • тЦ╕

    Essential for calculating unit weight and degree of saturation.

тЭМ Disadvantages / Limitations
  • тЦ╕

    Mathematical expressions can be easily confused if signs are misplaced.

  • тЦ╕

    Porosity does not have a linear relationship with void ratio, making simple estimation difficult.

ЁЯЫая╕П Applications / Uses
  • тЦ╕

    Geotechnical design for soil settlement analysis.

  • тЦ╕

    Determination of seepage velocity in saturated soils.

ЁЯУД Additional Information
  • тЦ╕

    Option A is mathematically incorrect (n>1n > 1n>1 is impossible for soil).

  • тЦ╕

    Option C represents eee in terms of nnn incorrectly; the correct form is e=n/(1тИТn)e = n/(1-n)e=n/(1тИТn).

  • тЦ╕

    Option D is an algebraic inversion error.

ЁЯУК Diagram / Illustration
Void Ratio vs Porosityn = e1 + e
тЬЕ

B is correct тАФ The relationship between porosity (nnn) and void ratio (eee) is defined by the formula n=e1+en = \frac{e}{1+e}n=1+eeтАЛ.

Core Concepts Used
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Phase relationships of soil Volumetric properties of soil Index properties
ЁЯТб EXAM TIP

Always remember the simple mnemonic: 'n' (porosity) is always smaller than 'e' (void ratio) for the same soil sample, which helps in checking the direction of the fraction (1+e1+e1+e in the denominator ensures n<1n < 1n<1).

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