SSC-JUNIOR ENGINEER (Civil & Structural) Online Exam 2020 (Exam held on 23/03/2021) (Part-IV)

GENERAL ENGINEERING CIVIL AND  STRUCTURAL

Total Questions: 50

31. The valve used for the prevention of reversal of flow in a pipeline is:

Correct Answer: A. a check valve
Solution:Check valves are mechanical devices used in piping and pipeline systems to prevent back-flow. A check valve allows fluid flow only in one direction that's why it is called a one-way valve or non-return valve. Check valve works on the principle of differential pressure. It means the check valve will only open if the upstream pressure is more than the downstream pressure. In situations, if downstream pressure is more, the valve will close preventing back-flow.

32. A continuous beam ABC with span AB = BC = L, is shown in the figure. Support A is fixed type, and supports B and C are roller type. The kinematic indeterminacy of the beam is:

Correct Answer: B. 4
Solution:

33. As per IS 1742-1983, normally a sewer shall be designed for discharging ______ times the dry-weather flow flowing half-full with a minimum self-cleansing velocity of _______.

Correct Answer: B. three; 0.75 m/s
Solution:As per IS 1742, 1983, the minimum dia of sewer recommended is 100 mm, since it is not given in option, so the next higher value of dia recommended is 150 mm is the most appropriate.

Other Provisions:

1. The sewer shall be designed for discharging three times the dry-weather flow flowing half-full with a minimum self-cleansing velocity of 0.75 m/s.

2. The minimum gradient for laying sewer is 1 in 57. (For 100 mm dia pipe).

3. Manning's N to be considered while designing of sewers to be 0.015.

34. The mass of a chunk of moist soil is 20 kg and its dry density is 1500 kg/m³. What is the void ratio of the soil if the specific gravity is 2.50 and density of water is 1000 kg/m³?

Correct Answer: B. 66.67%
Solution:

35. A cantilever of beam of span I is fixed at one end, the other end resting freely on the middle of a simply supported cross-beam of the same span and section. If the cantilever beam is now loaded with a uniform load of w per unit length, find the reaction at the free end offered by the cross beam.

Correct Answer: D. 6/17 wl
Solution:

36. What is the height of a slump cone mould used for testing the workability of the concrete?

Correct Answer: D. 30 cm
Solution:The slump test is carried out to have a rough estimate of the workability of concrete. It does not measure all factors contributing to workability, nor is it always representative of the placeability of the concrete. However, it is conveniently used as a control test and gives an indication of the uniformity of the concrete from batch to batch.

37. What is the approximate composition of silicon dioxide (SiO₂) present in ordinary Portland cement?

Correct Answer: D. 17-25%
Solution:
Sl. No.Common nameChemical nameChemical formula%
1LimeCalcium oxideCaO60–67
2SilicaSilicon dioxideSiO₂17–25
3AluminaAluminium oxideAl₂O₃3.0–8.0
4—Iron oxideFe₂O₃0.5–6.0
5MagnesiaMagnesium oxideMgO0.1–4.0
6—Soda and/or potash (Alkalies)(Alkalies) Na₂O, K₂O0.4–1.3
7—Sulphur trioxideSO₃1.3–3.0
8GypsumCalcium sulphateCaSO₄3–5

38. Identify the test to be conducted for the determination of the modulus of subgrade reaction in pavement design.

Correct Answer: B. Plate bearing test
Solution:Plate bearing test is used to evaluate the support capability of sub-grades, bases and in some cases, complete pavement. Data from the tests are applicable for the design of both flexible and rigid pavements. In plate bearing test, a compressive stress is applied to the soil or pavement layer through rigid plates relatively large size and the deflections are measured for various stress values.

39. A level section has formation width of 10 m, side slope of 1 : 2 (vertical: horizontal) and central height of 2 m. Determine the quantity of earthwork required for a 1 km length of formation (in m³).

Correct Answer: D. 28,000
Solution:Cross section area of formation width

The apparatus for conducting the slump test essentially consists of a metallic mould in the form of a frustum of a cone having internal dimensions as follows:

Bottom diameter - 20 cm

Top diameter - 10 cm

Height - 30 cm

40. The ratio of compressive strength of a material saturated with water to that in dry state is known as:

Correct Answer: C. co-efficient of softening
Solution:Co-efficient of softening: The properties of building materials are influenced by the moisture content. The ratio of compressive strength of material saturated with water to that in dry state is known as co-efficient of softening and describes the water resistance of materials. For materials like clay which soak readily it is zero, whereas for materials like glass and metals it is one. Materials with co-efficient of softening less than 0.8 should not be recommended for those situations where they are permanently exposed to the action of moisture.