Explanation:

Statement 1: Incorrect

As residual soils remain in place directly over the parent rock and are relatively shallow in depth.

Statement 2: Incorrect

The soils transported by gravitational force are termed colluvial soils.

Statement 3: Correct

Loess is the wind blown silt or silty clay of little or no stratification.

Statement 4: Incorrect

The accumulation of decaying and chemically deposited vegetable matter under the condition of excessive moisture results in the formation of cumulose soil.

Therefore, option 3 is correct.

The soils formed at a place may be transported to other places by agents of transportation, such as water, wind, ice and gravity.

1) Water transported Soils: Flowing water is one of the most important agents of transportation of soils. Swift running water carries a large quantity of soil either in suspension or by rolling along the bed.

The size of the soil particles carried by water depends upon the velocity.

All type of soils carried and deposited by water are known as alluvial deposits. Deposits made in lakes are called lacustrine deposits. Such deposits are laminated or varved in layers. Marine deposits are formed when the flowing water carries soils to ocean or sea.

2) Wind transported Soils: Soil particles are transported by winds. The particle size of the soil depends upon the velocity of wind. Soils deposited by wind are known as aeolian deposits.

Loess is a silt deposit made by wind. These deposits have low density and high compressibility. The bearing capacity of such soils is very low.

3) Glacier-Deposited Soils: Glaciers are large masses of ice formed by the compaction of snow. As the glaciers grow and move, they carry with them soils varying in size from fine grained to huge boulders.

Drift is a general term used for the deposits made by glaciers directly or indirectly. Deposits directly made by melting of glaciers are called till. The soil carried by thw meling water from the frint of a glacier is termed out-wash.

4) Gravity deposited soil: These are soils transported through short distances under the action of gravity. Colluvial soils such as talus have been deposited by the gravity. Talus consists of irregular, corase particles. It is a good source of broken rock pieces and coarse grained soils for many engineering works. 

Concept:

Dry density: The dry density is the mass of solids per unit area of total volume of the soil mass.

${\rho }_d=\frac{M_d}{V}$

Saturated density: When the soil mass is saturated its bulk density is called saturated density. Thus, saturated density is the ratio of the total mass of the saturated sample to its total volume.

Submerged density: The submerged density is the submerged mass of soil solids per unit of total volume V of the soil mass.

Submerged density (ρ’) = ρ_sat - ρ_w

In saturated soil, since voids are completely filled with water hence mass of soil is very high.

In wet soil, voids are partially filled with water hence mass of wet soil is less than saturated

In dry soil, voids are filled with air only hence mass of dry soil is less than the wet & saturated.

∴ Saturated density (saturated soil mass) > wet density (partially saturated soil mass) > dry density (dry soil mass)

When a soil in water is submerged, buoyant force reduces the weight of soil or mass of soil due to which submerged density becomes very less.

So the order will be

Saturated density > wet density > dry density > submerged density

Tricks to remember:

1) ${\gamma }_t=\left(\frac{G+Se}{1+e}\right){\gamma }_w$

2) ${\gamma }_{sat}=\left(\frac{G+e}{1+e}\right){\gamma }_w$

3) ${\gamma }_d=\frac{G{\gamma }_w}{1+e}=\frac{{\gamma }_t}{1+w}=\frac{\left(1-{\eta }_a\right)G{\gamma }_w}{1+wG}$

4) ${\gamma }^{\prime }=\frac{\left(G-1\right)}{1+e}{\gamma }_w$

Where G = Specific gravity of soil

E = void ratio

S = degree of saturation

From the above four formula the order can be decided mathematically.

For all the densities the Denominator is constant.

From the numerator values the order can be decided for a constant value of G and e.

Concept:

Degree of saturation (S): 

It is the ratio of volume of water to the volume of voids present in soil sample. Its value vary from 0 to 1.

Void ratio (e): 

It is the ratio of volume of voids to the volume of solids present in soil sample. Void ratio of fine grained soid is greater than coarse grained soil.

Water content (w): 

It is the ratio of weight of water to the weight of solids present in soil sample. Water content of fine grained soid is greater than coarse grained soil.

Specific gravity (G): 

It is the ratio of unit weight of any substance to the unit weight of water.

The relationship between S, e, w and G is given by,

∴ Se = wG

Calculation:

Given,

w = 15 % = 0.15, e = 0.55, G = 2.6

Se = wG

S × 0.55 = 0.15 × 2.6

S = 0.709 × 100 = 70.90%

Hence the degree of saturation of soil is 70.90%

Trick: 

We can remember it as Se = wG on sehwag’s name.

Explanation:

Liquid limit:

• Liquid limit is defined as the minimum water content at which soil has a tendency to flow.
• At liquid limit soil posses from the liquid stage of consistency to the plastic stage of consistency and vice versa.
• All soils at liquid limit possess the same negligible shear strength of 2.7 kN/m2, which can be just measured.
• Liquid limit is found out by the following two methods:
  • Cassagrande's apparatus
  • Cone penetration test

With reference to the standard liquid limit device (Casagrande's apparatus), the liquid limit is the water content at which a part of soil cut by a groove of standard dimension, will flow together by a distance of 12 mm under an impact of 25 blows.

In the fall cone method/Cone penetration test, the liquid limit is taken as the moisture content at which a standard 30 degree, 80 g cone will penetrate the soil sample a distance of 20 mm in approximately 30 sec. 

Explanation:

Hydrometer:

• It is an instrument used for carrying out sedimentation analysis based on Stokes's law for particle size less than 75 μ.
• They are typically calibrated and graduated with one or more scales to measure the density or specific gravity of suspension.​

​Note:

The calibration temperature is 27°C.

Assumptions

• It is assumed that particles show discrete settling (i.e. grains of different sizes fall through a liquid at different velocities).
• Particles assumed spherical in shape.
• Medium is assumed infinite.
• Particles size range 0.2 μ to 0.2 mm.

​

Settling velocity,

$V_s={\frac{(G-1){\gamma }_{w}d}{18\mu }}^2$

where,

G = specific gravity, γw = unit weight of water, d = diameter of particle, μ = dynamic viscosity

Density by a hydrometer, 

 $\rho =\frac{R_h}{1000}+1$ ( Rh = Reduced hydrometer reading)

% Finer by a hydrometer, 

$\mathrm{\%}N=\frac{100R_h}{M_D}(\frac{G}{G-1})$ (MD = Mass of solids)

Explanation:

Water content

• It is defined as the ratio of the weight of water (W_w) to the weight of solids (W_s or W_d).
• $w=\frac{W_w}{W_d}$
• $w\ge 0$
• It is significant for theoretical consideration since stable as W_d don't change.

Note:

• The water content of soil can also be expressed in terms of the total weight of soil mass.
• $w^{\prime }=\frac{W_w}{W}$
• At field calculation, it is more significant for practical consideration.
• It is not stable as W is not constant.

The relationship between w and w' is given by

$w^{\prime }=\frac{W_w}{W}=\frac{W_w}{W_w+W_d}$

$\frac{1}{w^{\prime }}=\frac{W_w+W_d}{W_w}=1+\frac{1}{w}$

$\frac{1}{w^{\prime }}=1+\frac{1}{w}$

Explanation:

Consistency index:

• It is defined as a ratio of the difference between the liquid limit and natural water content of the soil to the plasticity index.
• $I_c=\frac{LL-w}{LL-PL}=\frac{LL-w}{PI}$
• It is used to study in situ behavior of saturated fine-grained soil at its natural water content.

Explanation:

Shrinkage ratio, R can be defined in the following ways:

1. It is the ratio of given volume change in soil, expressed as a percentage of the dry volume of soil to a corresponding change in water content above the shrinkage limit.

$R=\frac{\frac{V_1-V_2}{V_d}}{w_1-w_2}$

V₁ is the volume of soil mass at water content w₁.

V₂ is the volume of soil mass at water content w₂.

V_d is dry volume of soil

2. It can also be defined as the mass-specific gravity of the soil in a dry state i.e. ratio of dry unit weight to unit weight of water represents the weight of water.

$R=\frac{{\gamma }_d}{{\gamma }_w}$

∴ Statement ‘4’ is true.

3.  It is also given by:

$\frac{1}{\mathrm{R}}={\mathrm{w}}_{\mathrm{s}}+\frac{1}{\mathrm{G}}$ (w_s is shrinkage limit)

Specific gravity of soil solids, G = unit wt of soil solids (γ_s)/unit wt of water (γ_w)

Specific gravity of soil mass, G_m = unit weight of soil mass (γ)/unit wt of water (γw)

Concept:

1. Group index of a soil is given by

G.I = 0.2 a + 0.005 ac + 0.01 bd

a = It is the portion of % passing through 75 μ (p) sieve greater than 35 but not exceeding 75 expressed as whole number in between [0 - 40].

b = It is the portion of % passing through 75 μ (p) sieve greater than 15 but not exceeding 55 expressed as the whole number in between [0 - 40].

c = It is the portion of the numerical liquid limit greater than 40 but not exceeding 60 expressed as a whole number in between [0 - 20].

d = It is the portion of the numerical plasticity index greater than 10 but not exceeding 30 expressed as a whole number in between [0 - 20].

2. Fine-grained soil is classified on the basis of a plastic chart. Clay is found to exist above A-line whereas silt & organic soil found to exist below A-line.

Calculation:

Given,

Group index, G.I. = 10

Liquid limit, LL = 40

Plastic limit, PL = 20

Plasticity index, I_p = 40 - 20 = 20

a = p - 35

b = p - 15

c = LL - 40 = 40 - 40 = 0

d = I_p - 10 = 20 - 10 = 10

G.I. = 0.2 × (p - 35) + 0.005 × (p - 35) × (LL - 40) + 0.01 × (p - 15) × (I_p - 10) 

10 = 0.2 × (p - 35) + 0.005 × (p - 35) × 0 + 0.01 × (p - 15) × 10 = 0.2p - 7 + 0.1p - 1.5 = 0.3p - 8.5

p = 61.67 %

Since % passing through 75 μ sieve is 61.67 % i.e. greater than 50 %. Hence, soil is fine grained either clay or silt.

According to A line, I_p = 0.73 ( LL - 20) = 0.73 (40 - 20) = 14.6 %

I_p for given soil is 20 > I_p of A-line. Hence, the given soil is Clay.

Explanation:

Liquid limit:

• Liquid limit is defined as the minimum water content at which soil has a tendency to flow.
• At liquid limit soil posses from the liquid stage of consistency to the plastic stage of consistency and vice versa.
• All soils at liquid limit possess the same negligible shear strength of 2.7 kN/m², which can be just measured.
• Liquid limit is found out by the following two methods:
  • Casagrande's apparatus
  • Cone penetration test

•  Soils having a higher value of liquid limit possess high compressibility (volume change in these soils are more).