SSC-JUNIOR ENGINEER (Civil & Structural) Online Exam 2019 (Part-III)

Total Questions: 50

41. Which of the following is an example of stratified rocks?

Correct Answer: C. Sedimentary rock
Solution:Stratified rocks are of aqueous origin. They are so called because they appear in sheet-like masses called strata, each stratum having a uniform thickness. Stratified rocks may usually be split into thin sheets or layers.

Sedimentary Rocks, which have been precipitated and deposited on the earth's surface from a fluid, in which the most minute particles were dissolved or held in suspension. Examples-sandstone, chalk, beds of clay, and some kinds of limestone. When the parts composing them are larger, they are called conglomerates, as the conglomerate of the old red sandstone.

42. Which of the following is true?

Correct Answer: B. A slender section shall not be used as a compression member.
Solution:Slender section is usually associated with a compression member in a structural design. A compression member is one whose primary function is to bear compression loads such as a column. A compression member may not all always fail by crushing, sometimes excessive compression loads can cause the buckling of the member.

Such a member that fails due to buckling instead of crushing is called a slender member. Slenderness is usually defined a classify a section as a slender member. It is the ratio of the length of a column and the least radius of gyration of its cross section, often denoted by lambda.

43. In a consolidation test, when the load is changed from 50 kN/m² to 100 kN/m², then the void ratio changes from 0.80 to 0.60. The coefficient of compressibility will be:

Correct Answer: A. 0.004 m²/kN
Solution:

44. Which of the following statements are true about quicksand?

(i) It is only a condition but not a type of sand.

(ii) It is condition and a type of sand too.

(iii) Quicksand condition reaches when critical hydraulic gradient is approximately equal to unity.

(iv) Quicksand condition occurs more commonly in coarse grained sand or gravels than fine sand.

Correct Answer: B. Both statements (i) and (iii) are true
Solution:Quicksand is a condition and not a soil type. This condition is created in saturated thick layers of loose fine sandy soils when disturbed either due to vibration, such as, from pile driving in the neighbourhood, or due to pressure of flowing water. Thus the effective stress becomes zero for the soil with above values of G and e, when the hydraulic gradient 'i' is unity, i.e., head causing the flow is equal to the length of the specimen. Quick sand can not support the weight of man or animal and it behaves like a liquid with a unit weight about twice that of water.

45. Boiling of water or adding lime in water will remove the hardness of water when it is due to:

Correct Answer: D. Carbonate of calcium
Solution:The presence of magnesium and calcium carbonates in water makes it temporarily hard. In this case, the hardness in water can be removed by boiling the water.

When we boil water the soluble salts of Mg(HCO₃)₂ is converted to Mg(OH)₂ which is insoluble and hence gets precipitated and is removed. After filtration, the water we get is soft water.

46. Which of the following is NOT a dechlorinating agent?

Correct Answer: D. Carbon dioxide
Solution:Dechlorination is the process of removing residual chlorine from disinfected wastewater prior to discharge into the environment. Sulphur dioxide is most commonly used for dechlorination and is the major focus of this fact sheet. Some dechlorination alternatives include carbon adsorption, sodium metabisulphite, sodium bisulphite, and hydrogen peroxide. Sodium metabisulphite and sodium bisulphite are mainly used in small facilities because these materials are more difficult to control compared to sulphur dioxide.

47. Which of the following is NOT a coagulant?

Correct Answer: D. Sodium sulphate
Solution:Coagulation and flocculation are an essential part of drinking water treatment as well as waste water treatment. The commonly used metal coagulants fall into two general categories: those based on aluminium and those based on iron. The aluminium coagulants include aluminium sulphate, aluminium chloride and sodium aluminate. The iron coagulants include ferric sulphate, ferrous sulphate, ferric chloride and ferric chloride sulphate. Other chemicals used as coagulants include hydrated lime and magnesium carbonate.

48. For concrete to be used for making airport runway, the aggregate impact value should not be more than:

Correct Answer: A. 30% by weight
Solution:Aggregate impact value gives a relative measure of the resistance of an aggregate to sudden shock or impact. As an alternative to crushing value, the aggregate impact value should not exceed 45% by weight for aggregates used for concrete other than for wearing surfaces and 30% by weight for concrete for wearing surfaces, such as runways, roads for pavements.

49. For safety of a concrete dam against overturning. what must be the width of the dam of rectangular cross section of height 10 m. If the height of water storage on one side of it 9 m? (Take unit weight of water as 10 kN/m³ and unit weight of concrete as 25 kN/m³).

(Ignore effect of uplift, friction and any other force).

Correct Answer: B.
Solution:

50. Which of the following decreases the workability of concrete?

Correct Answer: B. Angular aggregates
Solution:More the amount of aggregate less will be workability.
  • Using smooth and round aggregate increases the workability. Workability reduces if angular and rough aggregate is used.
  • Greater size of Aggregate-less water is required to lubricate it, the extra water is available for workability.
  • Angular aggregates increases flakiness or elongation thus reduces workability. Round smooth aggregates require less water and less lubrication and greater workability in a given w/c ratio.
  • Porous aggregates require more water compared to non absorbent aggregates for achieving same degree of workability.