15 questions. Tap an option to check it instantly, then read the solution.
Practice SSC JE and other civil engineering exam questions on consolidation of soils: Terzaghi's theory and its assumptions, initial, primary and secondary consolidation, compression index, coefficient of compressibility, coefficient of consolidation, time factor, isochrones and settlement calculations. Tap an option to check it, then open the full explanation for each question.
Question 1Medium
In saturated soils, the initial consolidation is mainly due to ______.
A saturated soil has no air. The small volume change that occurs the instant the load is applied (initial consolidation) comes mainly from compression of the solid particles.
Question 2Easy
Which of the following statements is correct with respect to compaction and consolidation?
Answer: A. Both compaction and consolidation improve the engineering properties of soil.
Both processes reduce voids and make the soil denser, so both improve strength and reduce compressibility. Compaction expels air; consolidation expels water.
Question 3Easy
A coarse grained soil has a void ratio of 0.7 and specific gravity 2.7. Calculate the critical gradient at which quick condition will occur.
Select the correct option for the given statements. Statement 1: Consolidation is due to a reduction in the volume of air voids at a given water content. Statement 2: In compaction, volume reduction is due to expulsion of pore water from voids.
Answer: A. Both statement 1 and statement 2 are false
Both statements swap the definitions. Compaction reduces air voids at a given water content; consolidation is volume reduction by expulsion of pore water. So both statements are false. (The official answer key marked option (c).)
Question 5Easy
A technician reports the liquid limit of an undisturbed clay as 50%. According to Ralph Peck, what will be the estimated compression index of this clay?
Terzaghi's theory assumes the clay is fully saturated. ‘Not saturated’ is therefore not one of its assumptions.
Question 7Medium
Select the correct option with regard to the following statements (S1, S2) pertaining to consolidation in soils. S1: A soil is termed as normally consolidated if the present effective overburden pressure is less than the maximum to which the soil was ever subjected in the past. S2: The larger the value of the coefficient of consolidation, the shorter it takes for full consolidation to occur.
S1 describes an overconsolidated soil, so it is false. From \(t = T_v d^2/c_v\), a larger \(c_v\) means a shorter time, so S2 is true.
Question 8Medium
A normally consolidated clay layer settled by 20 mm when the effective stress was increased from 25 to 50 kN/m². What will be the settlement when the effective stress is increased from 50 to 100 kN/m²?
\(\Delta H \propto \log(\sigma'_f/\sigma'_0)\). Both stages double the stress (ratio 2), so the settlement is the same: 20 mm.
Question 9Medium
Which of the following statements is/are correct? 1. Isochrones are curves of equal pore water pressure. 2. Isochrones depict the variation of the pore water pressure along the depth of the soil sample. 3. Isochrones vary with time.
An isochrone is a curve of excess pore pressure against depth at one instant (‘iso’ = equal, ‘chrone’ = time). So 2 and 3 are correct; 1 is wrong.
Question 10Easy
In a consolidation test, when the load is changed from 50 kN/m² to 100 kN/m², the void ratio changes from 0.80 to 0.60. The coefficient of compressibility will be:
Terzaghi used a piston, a spring and water in a cylinder to explain how load passes from pore water to the soil skeleton during consolidation.
Question 12Medium
A saturated soil has compression index of 0.28, the void ratio at a stress of 12 kN/m² is 2.05 and its permeability is 35×10³ mm/s. What is the change in void ratio if stress is increased to 21.6 kN/m²? (Take log₁₀(1.8) as 0.255)
A clay deposit of thickness 10 cm and void ratio 0.5 undergoes settlement and its final void ratio is now 0.2. The thickness (cm) of the settlement layer is ______.