SOLUTION: Hydraulic Engineering | My Assignment Tutor

Instructions to Candidates This paper contains EIGHT questions in TWO sections: Section A and Section B Answer FIVE questions only; Section A: Answer TWO questions Section B: Answer TWO questions AND Answer ONE further question from Either Section A or Section B All questions carry equal marks. All stages of calculation must be shown. Marks are awarded for the calculation procedure used and for clearly showing the steps in the calculations process. Number of Pages: 1 – 6 + Figure Q7 (1 page) SECTION A – Hydraulic Engineering 1. A 400 m long pipeline connects an upper reservoir to a lower reservoir where the water level is 25.0 m lower. The pipe is 250 mm diameter with a friction factor,  = 0.024. A valve with head loss = 4.0 v2/2g is located 150 m from the lower reservoir. Including all minor losses, calculate the velocity and discharge through the pipeline. (8 marks) (b) The discharge is to be increased by replacing the top 220 m of pipe with a larger pipe of 325 mm diameter. Ignoring minor losses and valve losses, calculate the velocity in each pipe section and the increased discharge. (7 marks) (c) Plot the energy grade line for cases (a) and (b) above and comment on the effectiveness of increasing the diameter of only part of the pipeline’s length. (5 marks) 2. For a rectangular channel of width of 5 m with discharge of 14.0 m3 s–1 determine the following: Draw the specific energy diagram with the flow depth y (y axis) plotted against specific energy E (x axis). Use the following y values in your plot: 0.2 m; 0.3 m; 0.5 m; 0.9 m; 2.0 m; 3.0 m; 4.0 m; 5.0 m. (8 marks) Find the critical depth, yc and minimum specific energy, Emin. (2 marks) For a flow depth of 3.0 m, calculate its alternate depth using an iteration (trial and error) procedure. Confirm this depth using your graph plotted earlier. (10 marks) All symbols have their usual meaning Continued… 3. (a) A flood relief channel for the River Thames has a rectangular cross-section with a bed width of 78.0 m; the longitudinal bed slope is 1:1250 and Manning’s ‘n’ may be taken as 0.032. Determine the velocity and discharge for a normal depth of 3.5 m. (6 marks) (b) It is proposed to increase the capacity of the channel by retaining the same base width of 78.0 m and replacing the vertical sides with sides sloping at 360 to the horizontal. Determine the percentage increase in channel capacity for the same normal depth of 3.5 m (9 marks) (c) Determine the Froude Number for the discharge in the trapezoidal channel (part b) and state whether flow conditions are supercritical or subcritical. (5 marks) Where Manning Equation is 4. (a). A pump is used to lift water from a storage reservoir to a water treatment works; the static lift is 29 m. The connecting pipeline is 2.8 km long, has a 500 mm diameter and has a Darcy friction factor () of 0.032. The characteristics of 2 available pumps are given below. Discharge (l/s)0.050.0100.0150.0200.0250.0Pump 1 Head (m)353330262114Pump 2 Head (m)4442403233.529 (i). Calculate the system characteristics. From a characteristics graph, determine the discharge and the head across pump 1 and pump 2. (12 marks) (ii). Determine the power input to the 2 pumps respectively if the efficiency is 68%. (4 marks) (b) Explain briefly how dimensional analysis can be used to calculate how a geometrically similar pump will perform under varying speeds, diameter of impellor and heads. (4 marks) Continued… SECTION B – Geotechnical Engineering 5. A ground investigation carried out at the site of a proposed housing development revealed the following soil strata: Depth (m) below ground level 0.0 m –1.5 m : GRAVEL (unit weight  = 17 kN/m3) 1.5 m – 3.5 m : SAND (unit weight  = 19 kN/m3) 3.5 m – 7.5 m : CLAY (unit weight  = 20 kN/m3) Below 7.5 m : BEDROCK As the site was known to be prone to flooding, the ground investigation report recommended placing a 1.5 m FILL over the site and compacting rapidly to a unit weight equal to that of the GRAVEL layer. Assuming the long-term water level to be located at the original ground surface, calculate and plot the distribution of total stress, pore pressure and effective stress with depth: Prior to placing the FILL. (7 marks) Immediately after placing the FILL. (7 marks) A long time after completion of the FILL (long-term conditions). (6 marks) Continued… 6. The following compresssion readings were recorded during an oedometer test on a saturated specimen of clay when the applied pressure was increased from 214 kPa to 429 kPa. After 1440 minutes the thickness of the specimen was 13.60 mm and the excess pore water pressure due to loading had dissipated completely: Time (min)Gauge reading (mm)0 0.25 0.5 1 2.25 4 9 16 25 36 49 64 81 100 200 400 14405.00 4.67 4.62 4.53 4.41 4.28 4.01 3.75 3.49 3.28 3.15 3.06 3.00 2.96 2.84 2.76 2.61 Plot a graph of settlement against square root of time and hence calculate the coefficient of consolidation cv using Taylor’s method. Take the time factor Tv for 90% consolidation as 0.848. Use the familiar equation: (16 marks) If the modulus of volume change mv=0.7 m2/MN, determine the coefficient of permeability k of the specimen. Use the familiar equation: (4 marks) Continued…. 7. (a) Identify THREE factors that can affect the location of the water table and/or distribution of groundwater within the near-surface rocks of the Earth’s crust and briefly explain how each factor affects the groundwater. (6 marks) (b) A dam is constructed on a permeable stratum underlain by an impermeable rock. The dashed line in Figure Q7 indicates the submerged ground surface. A row of sheet piling is installed at the upstream face. Sketch the flow net for seepage under the dam as shown in Figure Q7. Draw on the printed Figure, and attach it to your examination script. (8 marks) (c) Assume that the surface of the impermeable bedrock is the elevation datum (i.e. elevation = 0 m). Using your flow net from part (b), determine the pore water pressure (in kPa) at point A? (6 marks) Continued…. 8. (a) A ‘shearbox’ apparatus provides a simple and cost effective method for measuring the shear strength of soils. However, it has some significant limitations that prevent its widespread routine use (the triaxial method is preferred by industry). Identify and briefly explain FIVE limitations of the direct shear test. (2 marks each = 10 marks total) (b) (i) A quick undrained triaxial test is carried out at a cell pressure of 160 kN m–2, the sample fails at a deviator stress of 142 kN m–2, what is the undrained shear strength? (3 marks) (ii) In part (i), above, if the pore pressure at failure is 128 kPa, what is the angle of friction of the soil if c’ = 0? (7 marks) END OF EXAMINATION PAPER Student ID Number: FIGURE Q7 Please attach to your answer paper.