Paper II — Q8
(a) (i) What is Lacey's Silt Factor? What is its value for standard silt? Design an earthen canal using Lacey's silt theory with…
What is Lacey's Silt Factor? What is its value for standard silt? Design an earthen canal using Lacey's silt theory with the following data: Full supply discharge, Q = 15 m³/s, Lacey's silt factor, f = 1·0, Canal side-slope = 1/2 H : 1 V (ii) What are spillways? Which type of spillways are provided in the following dams? (i) Bhakra-Nangal Dam (ii) Ramganga (Kalagarh) Dam (iii) Hirakud Dam (iv) Rihand Dam. What forces act on a mass-concrete dam? Explain any two of these forces in detail. 10 marks
Determine the dimensions of a rectangular septic tank serving 100 persons in a hostel. The dimensions of the septic tank must be able to accommodate sedimentation, sludge digestion and sludge storage functionalities. The peak discharge of sewage can be considered as 240 litres per minute. Use the following data: - Surface area required for every 10 litres per minute of peak flow = 0·92 m² - Water depth required in the sedimentation tank = 0·3 m - Freeboard required = 0·3 m - Capacity required for sludge digestion process = 0·032 m³/capita - Capacity required for digested sludge = 0·0002 m³/capita/day - Sludge withdrawal (cleaning) frequency = once in a year - Length to width of tank ratio (L/B) = 2·5 15 marks
Uniform sand is used as a filter medium to treat the water. The sand grains are 0·6 mm in diameter with a shape factor (φ) of 0·85 and specific gravity (G) of 2·67. The bed is 0·65 m deep with a porosity (η) of 0·45. The filter medium is to be expanded to a porosity (ηₑ) of 0·75 by hydraulic backwash. Determine the required backwash velocity, resulting expanded depth and loss through the expanded medium. Assume the following data for use: g = 9·81 m/s², Density of water (ρ) = 998·2 kg/m³, Viscosity of water (μ) = 1·002 × 10⁻³ N.s/m² 15 marks
हिंदी में प्रश्न पढ़ें
लेसी का साद गुणक क्या है? मानक साद के लिए इसका मान क्या है? निम्नलिखित आँकड़ों का उपयोग करते हुए लेसी के साद सिद्धांत द्वारा एक मिट्टी की नहर की अभिकल्पना कीजिए: पूर्ण आपूर्ति निस्सरण, Q = 15 घन मीटर प्रति सेकंड, लेसी का साद गुणक, f = 1·0, नहर की पार्श्व-प्रवणता = 1/2 H : 1 V (ii) उत्प्लव क्या हैं? निम्नलिखित बाँधों में किस प्रकार के उत्प्लव प्रदान किए गए हैं? (i) भाखड़ा-नांगल बाँध (ii) रामगंगा (कालागढ़) बाँध (iii) हीराकुड बाँध (iv) रिहंद बाँध। एक पुंज-कंक्रीट बाँध पर कौन-से बल कार्य करते हैं? इनमें से किन्हीं दो बलों की विस्तृत व्याख्या कीजिए। (10 अंक)
एक छात्रावास में 100 व्यक्तियों के लिए उपयोग किए जाने वाले आयताकार सैप्टिक टैंक की विमाएँ निर्धारित कीजिए। सैप्टिक टैंक की विमाएँ अवसादन, अवपंक पाचन और अवपंक भंडारण की कार्यक्षमताओं को समायोजित करने में सक्षम होनी चाहिए। मलजल का चरम निस्सरण 240 लीटर प्रति मिनट माना जा सकता है। निम्नलिखित आँकड़ों का उपयोग कीजिए: – प्रत्येक 10 लीटर प्रति मिनट अधिकतम प्रवाह के लिए आवश्यक सतह क्षेत्रफल = 0·92 वर्ग मीटर – अवसादन टैंक में पानी की आवश्यक गहराई = 0·3 मीटर – आवश्यक मुक्तांतर (फ्रीबोर्ड) = 0·3 मीटर – अवपंक पाचन प्रक्रिया के लिए आवश्यक क्षमता = 0·032 घन मीटर/व्यक्ति – पचित अवपंक के लिए आवश्यक क्षमता = 0·0002 घन मीटर/व्यक्ति/दिन – अवपंक निकासी (सफाई) की आवृत्ति = वर्ष में एक बार – टैंक की लंबाई और चौड़ाई का अनुपात (L/B) = 2·5 (15 अंक)
जल के प्रशोधन के लिए एकसमान रेत को एक छनक (फिल्टर) माध्यम के रूप में उपयोग किया जाता है। रेत के कण 0·6 मिमी व्यास के हैं जिनका आकृति गुणक (φ) 0·85 है और आपेक्षिक घनत्व (G) 2·67 है। परत (स्तर) 0·65 मीटर गहरी है और इसकी संरंधता (η) 0·45 है। फिल्टर माध्यम को द्रविक प्रतिधावन (हाइड्रॉलिक बैकवाश) द्वारा 0·75 की संरंधता (ηₑ) तक विस्तारित किया जाना है। आवश्यक प्रतिधावन वेग, परिणामी विस्तारित गहराई और विस्तारित माध्यम से होने वाले ह्रास को ज्ञात कीजिए। उपयोग के लिए निम्नलिखित आँकड़े (डेटा) मान लीजिए: g = 9·81 m/s², जल का घनत्व (ρ) = 998·2 kg/m³, जल की श्यानता (μ) = 1·002 × 10⁻³ N.s/m² (15 अंक)
The figure this question refers to, in words
The question paper is a scan and the diagram did not survive as text. This is the figure as read from the original page — every component, value and label — so the question can be worked from the text below.
(c) A cross-sectional diagram of a gravity dam structure. The dam has a vertical upstream face and a sloping downstream face. The total height of the dam is 27 m. The top width of the dam is 6 m. The base width is divided into two sections: 6 m on the upstream side and 15 m on the downstream side. The downstream face slopes at a ratio of 0.75 horizontal to 1.0 vertical. The water level on the upstream side is 3 m below the top of the dam. On the downstream side, the ground level is 10 m below the top of the dam, and the total depth to the base is 20 m. Arrows labeled W1 and W2 indicate the direction of water pressure or weight forces acting on the dam. Below the diagram, the following data is provided: friction coefficient (mu) = 0.70, unit weight of concrete (gamma_c) = 24 kN/m3, unit weight of water (gamma_w) = 10 kN/m3, uplift pressure (q) = 1400 kN/m2.
What "Design" is asking you to do
Produce a specification that meets the given brief and demonstrate that it does. In civil and electrical papers the design is incomplete until it is expressed in buildable numbers — diameter, spacing, section, component value — and checked back against every limit stated.
Structure that answers it
Requirements and permissible values listed → code clause or design basis adopted → proportioning calculations → the specification in final dimensions → check against each requirement → sketch
Where marks are lost
Stopping at a required area or a required value without converting it into the bar size, spacing or component actually provided. The provided-against-required comparison and the serviceability or stability check are separately marked and routinely left out.
How this answer will be evaluated
Approach
(a(i)) calculate: given > formula > substitution > result with units > interpretation | (a(ii)) describe: define > structure or process in order > labelled diagram > significance | (b) calculate: given > formula > substitution > result with units > interpretation | (c) calculate: given > formula > substitution > result with units > interpretation Full marks: Complete method with all steps, units, checks, and neat sketches; all parts fully addressed.
Key points expected
- Define Lacey's silt factor and state value for standard silt
- Calculate silt velocity (Vs) and silt unit weight (w)
- Calculate hydraulic mean depth (R) and wetted perimeter (P)
- Calculate bed width (B) and depth (D) for 1/2H:1V slope
- Define spillways and their function
- Identify spillway type for each of the four named dams
- List forces acting on mass-concrete dam
- Explain any two forces in detail with free body diagram
Evaluation rubric
Each sub-part is marked on its own, against the marks and word limit printed on the paper.
- (a(i)) Define Lacey's silt factor and design an earthen canal using Lacey's theory.
calculate— given → formula → substitution → result with units → interpretation
Must cover
- Define Lacey's silt factor and state value for standard silt
- Calculate silt velocity (Vs) and silt unit weight (w)
- Calculate hydraulic mean depth (R) and wetted perimeter (P)
- Calculate bed width (B) and depth (D) for 1/2H:1V slope
Loses marks
- Final value without design check
- Unstated assumptions or missing units
- Incorrect application of Lacey's formulas
Earns more
- Carry units through every calculation step
- State Lacey's formulas explicitly before substitution
- Check final dimensions for reasonableness
- Neat labelled sketch of canal cross-section
Extra mark
- Mention Lacey's regime conditions
- Compare with Kennedy's theory
- (a(ii)) Define spillways, identify types for four dams, and explain forces on mass-concrete dam. 10 marks
describe— define → structure or process in order → labelled diagram → significance
Must cover
- Define spillways and their function
- Identify spillway type for each of the four named dams
- List forces acting on mass-concrete dam
- Explain any two forces in detail with free body diagram
Loses marks
- Final value without design check
- Unstated assumptions in force calculation
- Missing free body diagram for force explanation
Earns more
- Neat labelled sketch of dam with forces
- State code clause for force calculation
- Carry units through force calculations
- Check result against permissible limits
Extra mark
- Mention IS code number for dam design
- Reference specific committee or standard
- (b) Determine dimensions of rectangular septic tank for 100 persons with all functionalities. 15 marks
calculate— given → formula → substitution → result with units → interpretation
Must cover
- Calculate surface area from peak flow (240 L/min)
- Calculate sludge digestion and storage volumes
- Determine tank depth including freeboard
- Calculate L and B using L/B = 2.5 ratio
Loses marks
- Final value without design check
- Unstated assumptions in volume calculation
- Missing unit conversion or arithmetic error
Earns more
- Carry units through every step
- State all given data clearly
- Check final dimensions against all requirements
- Neat labelled sketch of septic tank
Extra mark
- Mention IS code for septic tank design
- Include safety factor in calculations
- (c) Determine backwash velocity, expanded depth, and head loss for sand filter. 15 marks
calculate— given → formula → substitution → result with units → interpretation
Must cover
- Calculate terminal settling velocity of sand grains
- Determine backwash velocity for expansion to ηe = 0.75
- Calculate expanded bed depth
- Calculate head loss through expanded medium
Loses marks
- Final value without design check
- Unstated assumptions in velocity calculation
- Incorrect application of settling velocity formula
Earns more
- Carry units through every step
- State all given data and assumptions
- Check result against permissible limits
- Neat labelled sketch of filter bed
Extra mark
- Mention IS code for filter design
- Reference specific standard for backwash
Model answer coming soon
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