Department of Infrastructure Engineering ENEN20002 Earth Processes for Engineering End of Semester 2 2018 Reading Time: 15 minutes – no writing or annotating allowed anywhere Writing time: 120 minutes This paper has 15 pages including this page and any Appendices. Instructions to Students • No annotating is allowed in reading time or after the end of writing time. • Possible marks total 120 in 120 minutes of examination. • Questions are NOT of equal weight. The numbers in parentheses at the end of each question indicate the marks allocated to that question. Note that these are NOT percentage marks. • ALL 6 questions should be attempted. • Candidates should attempt questions 1 to 2 and questions 3 to 6 in two SEPARATE SCRIPT BOOKS. • Start the answer to each question on a new page in the script book and write the question number in the top right hand corner. • Ensure your student number is written on all script books and answer sheets during writing time. • On the front cover (top left hand corner) of each script book, tick the numbers of questions that have been attempted. • Answer all questions on the right-hand lined pages of the script book. The left-hand unlined pages of script books are for draft working and notes and will not be marked. • Candidates need to ensure that the relevant student enrolment number is provided at the top right hand corner of the graph on pages 13 & 14 when it is submitted as part of your answer for Question 6. • Mobile phones, tablets, laptops, and other electronic devices, wallets and purses must be placed beneath your desk. • All electronic devices (including mobile phones and phone alarms) must be switched off and remain under your desk until you leave the examination venue. No items may be taken to the toilet. Exam Paper to be lodged with Baillieu Library Authorised Materials: Drawing instruments including scale rules, compasses and protractors may be used. Calculators: Casio fx82 or fx100 calculators are permitted Instructions to Invigilators • Two 14 page script books are to be provided to each candidate; each candidate should attempt questions 1 to 2 and questions 3 to 6 in two SEPARATE SCRIPT BOOKS. • Provide extra script books on request ENEN20002 Earth Processes for Engineering Page 2 of 15 ***** ATTEMPT QUESTIONS 1 TO 2 IN A SEPARATE SCRIPT BOOK ***** Question 1 (a) Which one or more of the following four statements provides information about climate (as opposed to weather)? A. Melbourne’s average monthly rainfall in May is 55.7 mm. B. The maximum daily temperature in Melbourne on the 10th of May 2018 was 12.8 ºC C. The rainfall in Melbourne on the 10th of May 2018 was 8.0 mm. D. On average May is the fourth coldest month in Melbourne. (2 marks) (b) Draw a diagram of the vertical global atmospheric circulation cells, name the cells and briefly explain why the circulation forms this way. (7 marks) (c) The following diagram shows the seasonal pattern of extraterrestrial radiation at the top of the atmosphere above four locations (A, B, C and D) on the Earth’s surface. (i) Which of these locations are in the Southern Hemisphere (list between zero and four locations by letter)? Briefly explain your answer. (3 marks) (ii) Which of these locations is closest to one of the Poles (could be either North or South Pole). Briefly explain your answer? (2 marks) (Question 1 continued on the next page) ENEN20002 Earth Processes for Engineering Page 3 of 15 (d) The following diagram shows a weather front. (i) Is this a warm front or a cold front? (1 mark) (ii) Is it more likely to be raining at point A, B or C? Provide a brief explanation for your answer based on how rainfall is generated in this context. (5 marks) (e) A house in Vienna, Austria (latitude 48.22º north, longitude 16.37º east) has an eave over a south facing window as shown in the diagram below. For this house, what would the smallest and largest solar noon zenith angles be over the year (the Tropic of Cancer is located at 23.5º north, the Equator at 0º and the Tropic of Capricorn at 23.5º south)? Would the window be fully shaded by the eave at the height of summer? Would sunlight shine through the window in winter? Justify your answer. (5 marks) (f) In terms of atmospheric processes, describe briefly how the greenhouse effect works? Distinguish between the greenhouse effect and the enhanced greenhouse effect. (5 marks) (Total marks for Question 1 = 30) ENEN20002 Earth Processes for Engineering Page 4 of 15 Question 2 (a) Draw a diagram of the catchment water cycle and label the important fluxes and stores of water. (7 marks) (b) For the last 90 years, the average annual rainfall for the Nimrodel River catchment was 1,500 mm, the average annual potential evapotranspiration was 1,800 mm and the average annual runoff from the catchment was 120,000 ML. The Nimrodel River catchment area is 200 km2. (i) What was the average annual runoff depth in mm? (ii) Estimate the runoff coefficient (also known as the runoff ratio). (iii) Estimate the average annual actual evapotranspiration in mm. (iv) What assumption did you make in answering (iii)? (2 marks) (1 mark) (1 mark) (1 mark) (Question 2 continued on the next page) ENEN20002 Earth Processes for Engineering Page 5 of 15 (c) You have a one store catchment model that represents base flow, evapotranspiration and surface runoff due to saturation excess. The following information is available. • The initial soil water storage, S, (i.e. at the start of the day) is 200 mm. • The soil water storage capacity, Smax, is 300 mm. • The rainfall fo r t he day i s 40 mm. • 20% of the catchment area is saturated. • All rainfall falling on the saturated area can be assumed to runoff as surface runoff and it can be assumed that the saturated area does not change during the day. • The potential evapotranspiration (PET) for the day is 6 mm. • The actual evapotranspiration can be calculated as AET = PET × S / Smax • The base flow for the day is 3 mm. • The catchment area is 400 km2. (i) Estimate the actual evapotranspiration for the day. (ii) Estimate the surface runoff depth for the day. (iii) Estimate the total runoff volume for the day. (iv) Estimate the soil water storage at the end of the day. (1 mark) (2 marks) (2 marks) (3 marks) (Total marks for Question 2 = 20) ENEN20002 Earth Processes for Engineering Page 6 of 15 ***** ATTEMPT QUESTIONS 3 TO 6 IN A SEPARATE SCRIPT BOOK ***** Question 3 (a) Name four different agents of erosion, which move soil, sediment, or rocks from their in situ location. (2 marks) (b) Briefly explain the four factors that influence the degree of ground surface movement in response to a nearby earthquake. (4 marks) (c) Using a diagram, show the typical soil horizons available in a soil profile and briefly describe their characteristics. (4 marks) (Total marks for Question 3 = 10) ENEN20002 Earth Processes for Engineering Page 7 of 15 Question 4 (a) Why are some clay soils more reactive than others? (1 mark) (b) A small warehouse is to be constructed on a clay soil deposit. A representative soil sample was taken from the deposit to check the suitability of the site for the proposed construction and the soil properties found are given below; Total volume 120 cm3 Total mass 240 g Moisture Content (mass basis) 20% Specific Gravity 2.7 i. Calculate the degree of saturation of the ground based on the given properties of the representative soil sample. (7 mark) ii. What can you tell about the saturation condition of the ground (saturated or unsaturated)? Explain your answer. (1 mark) iii. In order to check the effect of seasonal changes on the proposed construction, the above soil sample was then soaked for a day. A 10.07 cm3 total volume increment and 8% total moisture content (mass basis) increment was found. Is the sample saturated now? (6 marks) (c) According to the conducted laboratory tests, the soil sample has a liquid limit of 40% and plastic limit of 21%. i. Classify the soil in the ground according to the Unified Soil Classification (USCS) system (plasticity chart is given in Figure 4.1) (2 marks) ii. What can you tell about the reactivity of this soil? High or low? Explain your answer. (1 mark) iii. How does the clay sample’s physical state (or phase) change with the soaking process? Explain your answer (2 marks) (Question 4 continued on the next page) ENEN20002 Earth Processes for Engineering Page 8 of 15 Figure 4.1 (Total marks for Question 4 = 20) ENEN20002 Earth Processes for Engineering Page 9 of 15 Question 5 A 1 m3 fine-grained soil sample was collected from a building construction site in an extremely wet season. The moisture content (mass basis) and total density of the collected soil sample were 28% and 2000 kg/m3, respectively. According to predictions, moisture content (mass basis) of this site can drop to 10% during the extremely dry season. Such a large reduction in moisture content may create a significant impact on the building stability and therefore the potential of the soil’s volume variation with moisture content was tested. In this regards, the obtained 1 m3 soil sample was oven dried for a period of two weeks with periodically recording the total volume and water content at 24 hour time intervals. Figure 5.1 shows the variation of the soil sample’s total volume with its moisture content. Figure 5.1 (a) What is the shrinkage limit of this soil? Explain your answer (2 marks) (b) According to the laboratory measurements (Figure 5.1), the soil sample’s total volume can be reduced to 0.8 m3 in the extremely dry season (with the reduction of the moisture content to 10%). Check the accuracy of these laboratory volume measurements (the reduction of the soil sample’s total volume to 0.8 m3 in the extremely dry season) by calculating the maximum volume reduction that can happen in the soil sample with the seasonal change from extremely wet to extremely dry (hint: assume the same shrinkage limit (Question 5a) and use relevant phase diagrams for the calculation). (8 marks) (Total marks for Question 5 = 10) ENEN20002 Earth Processes for Engineering Page 10 of 15 Question 6 It is required to construct a 4 m deep underground carpark in the heart of the city of Melbourne without disturbing the surrounding area. The required excavation for the proposed carpark and also the adjacent ground condition are shown in Figure 6.1. As can be seen from the figure, the adjacent ground consists of a 2 m deep clay deposit, resting on a 2 m thick sand deposit, where stable soil could be found below the sand deposit (see Figure 6.1). According to the conducted investigations, the water table is available at 2 m depth below the ground surface (Figure 6.1) and the capillary rise through the available clay in the clay deposit was found to be much greater than 2 m. Representative soil samples were collected from the clay and sand deposits to conduct required laboratory tests and the following results were obtained; For clay; ρsat = 2000 kg/m3 At rest earth pressure coefficient, k0 = 0.6 Drained cohesion, C' = 20 kPa Drained friction angle, φ' = 20o For sand; ρsat = 1800 kg/m3 At rest earth pressure coefficient, k0 = 0.5 Drained cohesion, C' = 10 kPa Drained friction angle, φ' = 32o In order to check the stability of the clay and soil deposits against the excavation, two soil elements, located at the center of each soil deposit, were considered for stability analysis (see Figure 6.1). Assuming the ground surface is horizontal and gravitational acceleration (g) is 10 m/s2; (a) Draw the pore water pressure distribution (prior to the excavation) of the adjacent ground that consists of clay and sand deposits (up to 4 m depth). Show the relevant calculations. (3 marks) (b) Calculate the total horizontal and vertical stresses applying on each soil element (prior to the excavation). (5 marks) (c) Draw the total stress Mohr circles corresponding to the each soil element in Figures 6.2 and 6.3 (prior to the excavation). (2 marks) (d) The horizontal stress relief associated with the excavation will cause a 20 kPa total horizontal stress reduction in each soil element (located in clay and sand deposits). The total vertical stresses applying on each soil element can be assumed to remain unchanged (as no additional vertical load will be applied). Show how the total stress acting on each soil element will change upon the excavation, by drawing the new total Mohr circles corresponding to each soil element (after the excavation). (4 marks) (Question 6 continued on the next page) ENEN20002 Earth Processes for Engineering Page 11 of 15 (e) It can be assumed that no drainage will take place in the saturated clay within a short period of time after excavation due to its very low soil permeability. This will cause a 10 kPa temporary pore water pressure reduction in the soil element located in the clay deposit (there won’t be any pore water pressure reduction in the sandy soil deposit). Draw the effective Mohr circles corresponding to each soil element for the short term after the excavation condition in Figures 6.2 and 6.3. (6 marks) (f) Superimpose the failure envelopes based on the shear strength parameters (cohesions and friction angles) obtained from the laboratory tests onto your Mohr circles drawn in Figures 6.2 and 6.3 and provide assessments of the stability of each soil deposit for the short term after the excavation condition. (4 marks) (g) Which soil deposit will fail with the excavation (consider only the short term after the excavation condition)? Briefly explain your answer (without any additional calculation). (1 mark) (h) Find the orientation of the failure plane (consider only the short term after the excavation condition). (4 marks) (i) Can you come to a final conclusion on the stability of the sandy soil deposit when only considering the short term after the excavation condition? (1 mark) Figure 6.1 (Question 6 to be continued on next page) ENEN20002 Earth Processes for Engineering Page 12 of 15 Note: • Assume g = 10 ms-2 in your calculation. • All graphical parts of your answers should be drawn on Figures 6.2 and 6.3. Figures 6.2 and 6.3 should be detached and submitted with your answer book. Make sure you put your student number at the top right-hand corner of the pages. • Please use Figure 6.2 for the soil element located in the clay layer and Figure 6.3 for the soil element located in the sand layer. • Please use different colours to denote your total and effective Mohr circles in Figures 6.2 and 6.3. (Question 6 to be continued on next page) ENEN20002 Earth Processes for Engineering Page 13 of 15 Student No. Figure 6.2 (Question 6 to be continued on next page) ENEN20002 Earth Processes for Engineering Page 14 of 15 Student No. Figure 6.3 (Total marks for Question 6 = 30) ENEN20002 Earth Processes for Engineering Page 15 of 15 Total marks for examination = 120 END OF EXAMINATION
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