Properties of Soil Formula – Soil Mechanics


1. Water Content

    \begin{equation*} w=\frac{W_w}{W_s}\times 100 \end{equation*}


where ,

Ww = Weight of water

Ws = Weight of solids

Note – There can be no upper limit to water content i.e. w≥0


2. Void Ratio

    \begin{equation*} e=\frac{V_v}{V_s} \end{equation*}

where ,

Vv = Volume of voids

Vs = Volume of solids

Note – though size of individual void of coarse grained soil is more , total volume of voids in fine grained soil is more

in general case there is no upper limit for void ratio . i.e. e>0

3. Porosity

    \begin{equation*} n=\frac{V_v}{V}\times 100 \end{equation*}

where ,

Vv = Volume of voids

V = Total Volume of soil

Note – 1. Porosity cannot exceed 100% i.e. 0<n<100

2. in comparison to porosity , void ratio is more frequently used because volume of solids remains same , whereas total volume changes


4. Degree of Saturation

    \begin{equation*} S=\frac{V_w}{V_v}\times 100 \end{equation*}

where ,

Vw = Volume of water

Vv = Volume of voids

Note – 1. Range of Degree of saturation. 0≤S≤100

2. For perfectly dry soil – S=0

3. For Fully saturated soil – S=100%

4. Air Content

    \begin{equation*} a_c=\frac{V_a}{V_v} = 1-S \end{equation*}

where ,

Va = Volume of air

    \begin{equation*} S_r+a_c=1 \end{equation*}

where S= Degree of saturation

5. Percentage Air Void

    \begin{equation*} n_a=\frac{V_a}{V} \times 100 \end{equation*}

where ,

Va = Volume of air

    \begin{equation*} n_a=n \cdot a_c \end{equation*}


5. Unit Weight

(A) Bulk unit Weight (γ)

Bulk unit weight is total weight per unit volume

    \begin{equation*} \gamma=\frac{W}{V} = \frac{W_s+W_s}{V_s+V_w+V_a} \end{equation*}


(B) Dry Unit Weight (γd)

Dry unit weight is the weight of soil solids per unit volume

    \begin{equation*} \gamma_d=\frac{W_s}{V} \end{equation*}


Note – Dry unit weight is used as a measure of denseness of soil . more dry unit weight means more compacted soil

(C) Saturated Unit weight (γsat)

Saturated unit weight is the ratio of total weight of fully saturated soil sample to its total volume.

    \begin{equation*} \gamma_{sat}=\frac{W_{sat}}{V} \end{equation*}


(C) Submerged Unit weight or Buoyant unit weight (γ)

Submerged  unit weight is the ratio of submerged weight of  soil solid per unit volume

    \begin{equation*} \gamma^,=\gamma_{sat} - \gamma_w \end{equation*}


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