Index properties are indicative of behavior of soil. e.g grain size distribution, relative density, Atterberg limits, etc.

Important sizes of soil particles:
$D_{10}$, $D_{30}$, $D_{60}$ where D is the diameter and 10, 30 and 60 are the % finer.

Attenberg limits:
These are boundary water contents between two different states of soil.

1. Liquid limit
2. Plastic limit
3. Shrinkage limit

1. Shrinkage Ratio SR \[SR = \dfrac{\dfrac{V_1 - V_2}{V_d}}{w_1 - w_2} \times 100\]
2. Volumetric Shrinkage V$_s$ \[\dfrac{V_1 - V_d}{V_d} \times 100\]
3. Plasticity Index I_$P$ \[I_P = w_L - w_p\]
4. Shrinkage Index I$_s$
\[I_s = w_p - w_s\]
5. Toughness Index I$_T$
\[I_T = \dfrac{I_p}{I_f}\]
6. Consistency Index I$_c$
\[I_C = \dfrac{w_L - w}{I_p} \times 100\]
7. Liquidity Index I$_L$ \[I_L = \dfrac{w - w_p}{I_p} \times 100\]
8. Activity Number A \[A = \dfrac{I_p}{C}\] where C = % of clay particles

Solved Example: 9073-01

A soil has a discharge velocity of 6 $\times$ 10$^{-7}$ m/s and a void ratio of 0.5. What is its seepage velocity? (UPPCL JE CE 2015)

A. 3 $\times$ $10^{-7}$ m/s

B. 6 $\times$ $10^{-7}$ m/s

C. 12 $\times$ $10^{-7}$ m/s

D. 18 $\times$ $10^{-7}$ m/s

Correct Answer: D

Solved Example: 9073-02

A tracer takes 100 days to travel from Well-1 to Well-2 which are 100 m apart. The elevation of water surface in Well-2 is 3 m below that in Well-1. Assuming porosity equal to 15%, the coefficient of permeability (expressed in m/day) is: (GATE CE 2016 Shift II)

A. 0.30

B. 0.45

C. 1.00

D. 5.00

Correct Answer: D

Solved Example: 9073-03

A value of toughness index less than unity indicates that the soil is friable at the ______: (DFCCIL Jr. Manager Civil Sep 2021)

A. Plastic limit

B. Liquidity limit

C. Composite limit

D. Elastic limit

Correct Answer: A

Solved Example: 9073-04

The void ratio of a given soil A is twice that of another soil B, while the effective size of Particles of soil A is one-third of that of soil B. The ratio of height of capillary rise of water in soil A to that B will be: (ESE Civil 2014 Paper II)

A. 0.67

B. 1.0

C. 1.5

D. 2.0

Correct Answer: C

Classification of Soils:

• Residual soils (Sedentary soil) : Soil which remains at or near the parent rock.
• Transported soil: Transported away from the parent rock.

• Gravitational force or body force: Proportional to mass, e.g weight. Predominant in gravel and sand.
• Surface force: Proportional to surface area, e.g. cohesion, electrochemical forces, etc. Predominant in clay

• Single grained structure: In gravel and coarse sand
• Honey comb structure: In fine sand and silt
• Flocculant structure: in clays
• Dispersed structure: in remoulded clays
• Combined structure: In soil mixtures

Solved Example: 9074-01

Which one of the following is the correct assumption of Rankine's theory? (ESE Civil 2021)

A. The soil mass is infinite

B. The soil mass is non homogeneous

C. The soil mass is cohesive

D. The ground surface is a plane which may be horizontal or inclined.

Correct Answer: D

Solved Example: 9074-02

The soils which plot above the A line in a plasticity chart are known as: (MP Sub Engg Civil Sep 2018 - Shift II)

A. Clays

B. Sands

C. Silts

D. Organic soils

Correct Answer: A

Solved Example: 9074-03

The graphical method for the determination of earth pressure is: (MP Sub Engg Civil Sep 2018 - Shift I)

A. Rebhann's method

B. Taylor's method

C. Mohr's diagram method

D. New mark's influence chart method

Correct Answer: A