TGB5110 Engineering Geology and Tunneling Exam 2021 PDF

Examination paper for TGB5110 Engineering Geology and Tunneling Academic contact during examination: Krishna Panthi Phone: 48240695 Examination date: 03.12.2021 Examination time (from-to): 09:00 – 13:00 Permitted examination support material: A - All support material is allowed. Language: Engl...

Examination paper for TGB5110 Engineering Geology and Tunneling Academic contact during examination: Krishna Panthi Phone: 48240695 Examination date: 03.12.2021 Examination time (from-to): 09:00 – 13:00 Permitted examination support material: A - All support material is allowed. Language: English Technical support during examination: Orakel support services Phone: 73 59 16 00. OTHER INFORMATION Make your own assumptions: If a question is unclear, make your own assumptions. In case of errors or insufficiencies in the question you may contact academic contact person. Saving: Answers written in Inspera Assessment are automatically saved every 15 seconds. If you are working in another program remember to save your answer regularly. Cheating/Plagiarism: The exam is an individual, independent work. Examination aids are permitted. All submitted answers will be subject to plagiarism control. Read more about cheating and plagiarism here. Notifications: If there is a need to send a message to the candidates during the exam (e.g. if there is an error in the question set), this will be done by sending a notification in Inspera. A dialogue box will appear. You can re-read the notification by clicking the bell icon in the top right-hand corner of the screen. All candidates will also receive an SMS to ensure that nobody misses out on important information. Please keep your phone available during the exam. Weighting: The weightage to each questions are given at the end of the question. Your answer will be submitted automatically when the examination time expires and the test closes, if you have answered at least one question. This will happen even if you do not click “Submit and return to dashboard” on the last page of the question set. You can reopen and edit your answer as long as the test is open. If no questions are answered by the time the examination time expires, your answer will not be submitted. Withdrawing from the exam: If you become ill or wish to submit a blank test/withdraw from the exam for another reason, go to the menu in the top right-hand corner and click “Submit blank”. This cannot be undone, even if the test is still open. Students will find the examination results in Studentweb. Please contact the department if you have questions about your results. The Examinations Office will not be able to answer this.  Question 1: Geology and Rock mass a) The bedrock in a area is granitic gneiss. The foliation joints have strike angels varying between N1400 - 1500E and dip 750 - 800 NE. The cross joint set has strike degrees varying between N150 - 200E and dip 800 - 850 NW. What is the best orientation of the length axis of an underground cavern? What could be the alternative orientation of this cavern? Plot a joint rosette and indicate both orientations of the cavern. The joint rosette of two joint sets and best cavern alignment is shown in Figure below. As one can observe, the recommended cavern alignment is oriented with N800E and is the best alignment in regards with two prevailing joint sets. The cavern alignment can however be maneuvered between N600E to N1000E, which gives flexibility for the cavern alignment. b) Rock mass are jointed. What joint characteristics should be mapped by an engineering geologist in connection with investigations for a planned tunnel project? Explain why these joint characteristics are of importance? Jointing characteristics that should be mapped are; - Orientation - Intensity (number of joint sets) - Spacing - Persistence (length) - Separation (aperture) - Roughness characteristics - Infilling conditions - Infilling material Joint characteristics are important because the overall quality of the rock mass is controlled by the joint characteristics and has direct influence on the; - Overall rock mass strength - Frictional properties - Deformability properties - Long term stability of the structure  c) For what purposes are rock mass classification methods used for a tunnel project? List three widely used rock mass classification methods. What six different parameters of the Q-system are mapped by an engineering geologist in connection with the field mapping for a tunnel project? Purpose of the use of rock mass classification methods: - Classify quantitatively the quality of rock mass - Estimate rock support based on quality description - Use the quality rating for stability assessment using failure criterion Three widely used rock mass classification methods: - Q-system of rock mass classification - Rock Mass Rating (RMR) - Geological Strength Index (GSI) Six different parameters of Q-system: RQD J r J Q   w Jn J a SRF - Rock Quality Designation (RQD) - Number of Joint Sets (Jn) - Roughness of most Unfavorable Joint (Jr) - Degree of Alteration or Filling in the Joint (Ja) - Water Inflow (Jw) - Stress Reduction Factor (SRF) Question 2: Rock stress, design principles and rock support A road alignment that follows a steep valley side slope is under planning and design phase where the valley side slope is over 35 degrees. The rock type in the area is granitic gneiss, which is homogeneous, massive and brittle in nature. The laboratory investigation indicated an average intact rock strength (𝜎ci) of 150 MPa, Poisson ration of 0.2 and specific weight (γ) of 0.0265 MN/m3. a) What type of joints may be formed at the outer part of the valley side slope and what could be the reason for this? What kind of slope stability problems may most likely be met along this slope while excavating the slope side to open a new road and why? Joint types in the outer part of the valley slope - Ex-foliation joints will be formed at the outer part of the valley side slope. The main reasons for such joints are that the valley side slope is steep (over 35 degrees) and the major principal stress will follow almost parallel to the valley side slope where stress normal (minimum principal stress) to the valley side slope inclination will be too small causing stress an-isotropy. Most likely slope stability problem - In general, the surfaces of ex-foliation joints are smooth and planar (low roughness). Upon excavation on the slope for road, these joints will daylight to the road cut slope. This will increase the chance of plane slope failure. b) A 6 km long road tunnel with 10 m diameter is planned as an alternative solution to slope stability problem along this valley slope. The tunnel is located deep into the rock mass to avoid valley slope impact on the in-situ rock stress. The maximum rock cover along the road tunnel is 600 m and the tectonic horizontal stress (𝜎tec) is 25 MPa and rock mass strength (𝜎cm) is about 35 % of the intact rock strength (𝜎ci). Calculate vertical gravity stress representing minimum principal stress (𝜎3) and horizontal stress representing maximum principal stress (𝜎1), maximum tangential stress (𝜎θ-max), minimum tangential stress (𝜎θ-min) and rock mass strength (𝜎cm). Given Intact rock strength (𝜎ci): 150 MPa Poisson ratio (𝜗): 0.2 Specific weight (γ): 0.0265 MN/m3 Rock cover (h): 600 m Tectonic horizontal stress (𝜎tec): 25 MPa Tunnel length (L): 6 km Tunnel diameter (d): 10 m Solution Rock mass strength (𝜎cm): 0,35 x 150 = 52.5 MPa Vertical minimum principal stress (𝜎3): 0.0265 x 600 = 15,9 MPa Horizontal maximum principal stress (𝜎1) is; 𝜎 = ×𝜎 +𝜎 𝜎 = ×𝜎 +𝜎 , 𝜎 = , × 15,9 + 25 = 28,98 MPa Maximum tangential stress (𝜎θ-max) will be; 𝜎 = 3𝜎 − 𝜎 = 3 × 28,98 − 15,9 = 71,03 MPa Minimum tangential stress (𝜎θ-min) will be; 𝜎 = 3𝜎 − 𝜎 = 3 × 15,9 − 28,98 = 18,73 MPa c) What type of stability problem this road tunnel will face and why? In what area of the tunnel this stability problem will occur and why? What could be the support solution to this? Explain. Type of stability problem and cause - Since the granitic geniss is homogeneous, massive and brittle in nature and the rock mass strength (𝜎cm) is much lower (52.5 MPa) than the Maximum tangential stress (𝜎θ-max), which is of magnitude 71.03 MPa, there is a high chance that the tunnel will face stability problem associated to rock burst. Tunnel area impacted by rock burst - Since the maximum principal stress (𝜎1) is horizontal, the maximum tangential stress (𝜎θ-max) will be concentrated to the roof of the tunnel. Hence, the rock burst activity will be in the tunnel roof where stability problem will be met. Support solution - The best support solution in rock burst condition is the use of combination support consisting of end anchored rock bolts with large triangular plates (dynamic bolts) and the steel reinforced shotcrete. Question 3 a) Discuss factors that may influence the choice of tunnelling excavation method – i.e. Drill and Blast or TBM. b) Discuss how the blast design may influence excavation time and costs of Drill and Blast tunnelling. Discuss at least four factors that may have a positive or negative influence. c) Discuss possible reasons for large overbreak in a drill and blast tunnel. Include the following topics (at least): Geology, blast design and excavation system factors (equipment, crew and organization)