UPSC Civil Services (Main) Examination 2026 — Civil Engineering Optional Paper II: Question Paper

09 Sep UPSC Civil Services (Main) Examination 2026 — Civil Engineering Optional Paper II: Question Paper | Plutus IAS

Posted at 09 Sep 2026 in UPSC by Tushar 0 Comments

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The questions below are from Civil Engineering Optional Paper II of UPSC Civil Services (Main) Examination 2026 (held 2026-08-30) — the actual paper, which is public government content. This page carries the questions for reference and revision; model answers for this paper are not published here.

Official paper (PDF): upsc.gov.in.

A vertical curve is formed when a descending gradient of 0.5% meets another descending gradient of 3.0%. Find the length of the vertical curve to provide the required (i) stopping sight distance, and (ii) overtaking sight distance, for a design speed of 65 km/hr. Assume the coefficient of longitudinal friction as 0.35 and the acceleration as 3.6 km/hr/sec. Assume other necessary data suitably. (b) | — | — | — | — | — | In running fly levels from a benchmark of RL 381.605, the following readings were obtained : | Backsight | 2.215, | 1.030, | 1.595, | 1.655 | | — | — | — | — | — | | Foresight | 1.025, | 3.290, | 2.385 | | From the last position of the instrument, four pegs at 50-metre intervals are to be set out on a uniformly falling gradient of 1 in 100; the first peg is to have an RL of 380.500. Work out the staff readings required for setting the tops of the pegs on the given gradient. (c) | — | — | | 1 – 2 | 10 | | 1 – 3 | 12 | | 2 – 5 | 8 | | 2 – 7 | 12 | | 3 – 4 | 6 | | 3 – 6 | 5 | | 4 – 5 | 8 | | 5 – 6 | 8 | | 5 – 7 | 10 | | 6 – 7 | 6 | | 7 – 8 | 12 | A project plan consisting of the following activities, their interconnectivity and their durations are listed in the following table : | Activity (i – j) | Duration (t) (Days) | | — | — | | 1 – 2 | 10 | | 1 – 3 | 12 | | 2 – 5 | 8 | | 2 – 7 | 12 | | 3 – 4 | 6 | | 3 – 6 | 5 | | 4 – 5 | 8 | | 5 – 6 | 8 | | 5 – 7 | 10 | | 6 – 7 | 6 | | 7 – 8 | 12 | Draw the network diagram and determine the critical path for the above project. Also, determine the activity times and the total float for each activity.
What do you understand by a Gantt or Bar chart with respect to construction project management ? Explain it with a neat sketch and discuss the limitations of Bar chart with suitable examples. (b) Explain with a neat sketch how vibration during the placement of concrete affects the compressive strength development of concrete, which is inversely dependent on the water-cement ratio. Also, state the advantages of inducing vibration to fresh concrete. (c) A BG track comes across a curve of radius 1000 m. The equilibrium cant is provided considering a speed of 90 km/hr. Calculate the maximum and minimum permissible speeds on the track if the limiting values of cant deficiency and cant excess are 75 mm each. Define remote sensing. State how it differs from photogrammetry.
What do you understand by the effective CBR value ? Discuss its significance. How is it calculated as per the latest IRC guidelines ? (b) List the various applications of Origin and Destination (O&D) Studies. Explain the process of orientation in Plane Table Surveying. Discuss the various methods of orientation highlighting suitability, advantages and disadvantages of each. (c) With respect to the chemical admixtures that are added to concrete, briefly differentiate 'Accelerators' from 'Retarders', and also explain how they modify the properties of concrete. What is the creep for hardened concrete ? With a neat sketch, draw the time-versus-deformation diagram of hardened concrete.
(a) | — | — | What is the difference between a flood hydrograph and a mass curve ? Using the following data of a river at a dam site, construct and plot a flood hydrograph and find the values of minimum and maximum discharge in the river. | Month | Flow (m^{3}/s) | | — | — | | January | 110 | | February | 120 | | March | 130 | | April | 140 | | May | 150 | | June | 160 | | July | 180 | | August | 210 | | September | 170 | | October | 140 | | November | 110 | | December | 100 | (b) | — | — | — | — | — | — | — | A catchment has six rain gauge stations. The annual rainfall recorded by the gauges in a year is as follows : | Station | A | B | C | D | E | F | | — | — | — | — | — | — | — | | Rainfall (cm) | 82.7 | 102.9 | 180.3 | 110.3 | 95.8 | 136.70 | (i) Determine the standard error in the estimation of mean rainfall in the existing set of rain gauges. (ii) For a 10% error in the estimation of mean rainfall, calculate the optimum number of rain gauge stations in the catchment. (c) A 30 cm diameter well penetrates 25 m below the static water table. After 24 hrs of pumping @ 5400 l/min, the water table in a test well 90 m away is lowered by 0.53 m and in another well 30 m away, the drawdown is 1.11 m. What is the transmissivity of the aquifer ? (d) A water supply system has several units, and the design of each unit should match with variations in the water demand. How will you take into account the effect of these variations in consumption while designing the following units for water treatment ? – (i) Filter units – (ii) Pumping units – (iii) Distribution mains – (iv) Sedimentation tank – (v) Clear water reservoirs Demonstrate your design values for a town with a design population of 15000 and average per capita demand of 270 litres per capita per day for these units. (e) Determine the theoretical oxygen demand (ThOD) for glycine [CH$_{2}$(NH$_{2}$)COOH] using the following assumptions : – (i) In the first step, the organic carbon and nitrogen are converted to carbon dioxide and ammonia respectively. – (ii) In the second and third steps, ammonia is oxidized sequentially to nitrite and nitrate. The ThOD is the sum of the oxygen required for all three steps.
| — | — | | 0.1 | 87 | | 0.2 | 93 | | 0.3 | 95 | | 0.4 | 95.5 | | 0.5 | 96 | | 0.6 | 96.5 | | 0.7 | 97 | | 0.8 | 97.2 | | 0.9 | 97.3 | | 1.0 | 97.5 | The following information is available regarding the relationship between trap efficiency and capacity-inflow ratio for a reservoir : | Capacity-Inflow Ratio | Trap Efficiency | | — | — | | 0.1 | 87 | | 0.2 | 93 | | 0.3 | 95 | | 0.4 | 95.5 | | 0.5 | 96 | | 0.6 | 96.5 | | 0.7 | 97 | | 0.8 | 97.2 | | 0.9 | 97.3 | | 1.0 | 97.5 | Find the probable life of the reservoir with an initial reservoir capacity of 30 million cubic metres, if the annual flood flow is 60 million cubic metres and average annual sediment inflow is 360000 tonnes. Assume a specific weight of sediment equal to 1200 kg/m$^{3}$. The useful life of the reservoir will terminate when 80% of initial capacity is filled with sediment. (b) A bed of uniform sand, having a particle size of 0.55 mm diameter, a specific gravity of 2.67, a porosity of 0.40 and a depth of 75 cm is to be washed hydraulically. Compute : (i) Backwash rate so that expansion will be 50 percent. (ii) Head loss at this backwash rate. [Take the kinematic viscosity as $1.3 \times 10^{-2}$ cm$^{2}$/s and the coefficient of drag as $C_D = \frac{24}{R}$ for water.] (c) How does the variation of sewage flow affect its velocity in a circular sewer ? If 20 mL of an odorous water sample is diluted with 180 mL of odour-free water to make a 200 mL mixture where the odour is just detectable, determine the threshold odour number of this water sample. Give your comments on acceptability of this sample from the consumer point of view. The odour sensitivity of an individual varies, so what may be the correct procedure and method to carry out an odour test ?
A sedimentation tank is treating 5 million litres of sewage per day containing 250 ppm of suspended solids. The tank removes 60 percent of the suspended solids. Calculate the quantity of sludge produced per day in bulk (volume) and weight, if the : – (i) moisture content of the sludge is 97 percent, – (ii) moisture content of the sludge is 96 percent, and – (iii) specific gravity of the wet sludge is 1.02. Calculate the volume of sludge produced for both moisture contents and the percentage reduction in volume of sludge produced for 1.0 percent reduction in moisture content (wet sludge). (b) Draw a neat sketch of a diversion work (headwork). Briefly explain the functions of the following : – (i) Silt excluder – (ii) Cross regulator – (iii) Canal fall – (iv) Aqueduct – (v) Escape (c) A mass concrete dam is constructed across a river. The bed width of the river is 100.0 m. The depth of water upstream of the dam in the river is 10.0 m. The deepest foundation is at R.L. of 100.0 m. If the R.L. of the crest of spillway is 160.0 m, find : – (I) Hydraulic height of the dam – (II) Total height of the dam – (III) Total hydrostatic force on the upstream face of the dam Classify the following hydraulic devices based upon their mode of operation : – (I) Aqueduct – (II) Super passage – (III) Falls – (IV) Barrage/weir – (V) Dams
Explain Lacey's silt factor. If the value of this factor is 1.0, what does it indicate ? The longitudinal slope of a canal running in an alluvial soil is 1/5000. Design the canal section and also find discharge (Q). Take Lacey's silt factor, $f = 0.90$ and the canal side slope as $\frac{1}{2}H : 1V$ . 15 What are the effects of waterlogging ? (b) | — | — | — | — | — | — | | 8% | 7% | 78% | 2% | 2% | 1% | | — | — | — | Consider a thermoelectric power plant of 1000 Mega Watt capacity with a load factor of 70 percent and an efficiency of 42 percent. Determine pollutants emitted on an annual basis such as particulates, carbon dioxide, and sulphur dioxide, if coal is used as fuel. The ultimate analysis and calorific value of the coal used are as follows : | Moisture | Ash | Carbon | Hydrogen | Nitrogen | Sulphur | | — | — | — | — | — | — | | 8% | 7% | 78% | 2% | 2% | 1% | | Oxygen | Calorific Value | Fly ash | | — | — | — | | 2% | 30 Mega Joules/kg | 77% of ash | Assume complete combustion as per the stoichiometric equation and no air pollution control device. If an electrostatic precipitator is installed which removes 99% of particulates, compute the amount of particulate emissions. (c) Enumerate the key additions in the Solid Waste Management Rules, 2026 in comparison with the Solid Waste Management Rules, 2016 in India, to emphasize that it is a paradigm shift.

Questions reproduced from the official paper for study purposes; verify on the exam-conducting body’s official website.