Assignment 2. Rock mass characterization Due date: 1 st of September (week 9) Learning objectives: This activity will provide students with opportunities to develop critical skills necessary to correctly interpret and analyse results of field and laboratory investigations and demonstrate the skills needed to produce comprehensive and concise reports. Weight: 30%. Group B: You are in this group if the first letter of your family name starts from L to Z. Task description: The Khlong Tha Dan dam is one of the major hydro dams in Thailand. After its completion, some neighbouring slopes began to experience slope stability issues during rainy seasons. An underground spillway tunnel was considered to avoid any risk associated with slope instability. To collect more detailed information about the slope conditions, field investigations including geological mapping, boreholes and joint surveys were performed. In addition, a series of lab tests were conducted to obtain the strength characteristics of the rocks. Your task is to interpret and analyse the obtained results and 1) draw a cross-section of the slope and identify the major geological units; 2 for each geological unit (if possible), determine the strength characteristics of rocks and rock mass including the unconfined compressive strength of rocks/rock mass, shear strength of jointed rocks, and the friction angle of rocks/rock mass; 3) determine the rock mass rating (RMR), and characterize the properties of the rock mass. You need to present and discuss your findings in the form of a report (max 10 pages, excluding references and appendix). Report structure (optional): 1. Introduction (What is the problem? What is the objective? Provide a brief description of the studied area. What field investigation and laboratory tests were performed?). 2. Interpretation and analysis of the field and lab data (Draw a cross-section, analyse and discuss the properties of rocks which are given in the bore logs and Tables 1,2) 3. Rock mass assessment. Perform rock mass assessment using RMR for each geological unit and discuss the outcome in relation to the tunnel location. 4. Summary and conclusions. 5. References (if necessary). 6. Appendix (if necessary). Note: Maximum 10 pages (excluding references and appendix). You need to provide a cross-section in your report. No plagiarism. Late submission will be penalised (1 day = -10 points). Marking criteria (similar to the IAP marking criteria) Mark Description Definition 8 Outstanding Exceptional ability and achievement, well beyond expectation XXXXXXXXXX%) 7 Excellent Highly competent work, with achievement above expectation (80-90%) 6 Very Good Very high standard, with achievement up to expectation (70-80%) 5 Good Of fair standard and contains much actual achievement (60-70%) 4 Acceptable Meets minimum standard required and minimum achievement level XXXXXXXXXX%) 3 Failed Weak and limited in achievement (below 50%) Report Grading Categories Mark 1. Report structure The document is written in a clear and concise manner and includes all of the elements that would be expected in this report. All of the section headings appropriately describe the information provided within the text. The text is written as a clearly structured narrative and is organised in a logical manner. The report provides a clear description of the project and its outcomes within the set page limit. 2. Cross-section of the slope Students need to correctly interpret the data from site investigation, draw a crosssection of the studied area and identify the major geological units. 3. Analysis and discussion of results The student has demonstrated that they have identified and analysed the issues related to the data collection and analysis, including the properties of major geological units/rocks. Students correctly perform rock mass assessment for each geological unit and discuss the related issues. 4. Overall Presentation (including citing and referencing) The document contains no spelling or grammatical errors and the reader is able to clearly understand the material presented in the discussion. The document includes figures and tables where appropriate, these are presented in a clear manner, include appropriate captions that clearly describe the figure or table and are supported by a high level of discussion in the main text of the document. Total mark (out of 24) Figure 1. Map of the studied area, and your line (B) for a cross-section. Borehole logs Borehole BH-1. Elevation is 85 m. Depth, m Rock Type Degree of weathering Rock mass properties RQD % Joint spacing Joint characteristics Ground water Density, g/cm3 Note: Soil with inclusions of small rock pieces 3 Heavily weathered sandstone 30 4 Joint surfaces are slickensided, undulating, and highly weathered; joint are separated by about 3-5 mm and filled with clay XXXXXXXXXXSamples were collected at a depth of 5 m and a series of shear box tests were performed. The test results are given in Table 1. Point load strength index was 0.5 MPa. Andesite 71 3 Joint surfaces are generally stepped and rough, tightly closed and unweathered with occasional stains XXXXXXXXXXSamples were collected at a depth of 14 m. JRC of joints was about 10-12; Schmidt hammer tests on the rock joint surfaces resulted in an average value of Schmidt hammer rebound number of 30; the peak friction angle was 57?, and the residual friction angle was 31?. Tuff 92 2 joint surfaces are slightly rough, slightly weathered with stains; no clay found on surface, apertures generally less than 1 mm, XXXXXXXXXXSamples were collected at a depth of 26 m and triaxial tests were carried out. The test results are given in Table 2. I II IIIIV V VI 1: > 3m 2: 1~3m 3: 0.3~1m 4: 5~30cm 5: < 5cm 1:completely dry 2: dry 3: moist only I : Fresh ~ VI completely weathered XXXXXXXXXXEnd of borehole Borehole BH-5. Depth, m Rock Type Degree of weathering Rock mass properties RQD % Density, g/cm3 Ground water Joint spacing Heavily weathered sandstone XXXXXXXXXXAndesite XXXXXXXXXXTuff XXXXXXXXXXI II IIIIV V VI 1:completely dry 2: dry 3: moist only 1: > 3m 2: 1~3m 3: 0.3~1m 4: 5~30cm 5: < 5cm I : Fresh ~ VI completely weathered XXXXXXXXXXEnd of borehole Borehole BH-6. Depth, m Rock Type Degree of weathering Rock mass properties RQD % Density, g/cm3 Ground water Joint spacing Heavily weathered sandstone XXXXXXXXXXAndesite XXXXXXXXXXTuff XXXXXXXXXXI II IIIIV V VI 1:completely dry 2: dry 3: moist only 1: > 3m 2: 1~3m 3: 0.3~1m 4: 5~30cm 5: < 5cm I : Fresh ~ VI completely weathered XXXXXXXXXXEnd of borehole Borehole BH-7. Depth, m Rock Type Degree of weathering Rock mass properties RQD % Density, g/cm3 Ground water Joint spacing Heavily weathered sandstone XXXXXXXXXXAndesite XXXXXXXXXXTuff XXXXXXXXXXI II IIIIV V VI 1:completely dry 2: dry 3: moist only 1: > 3m 2: 1~3m 3: 0.3~1m 4: 5~30cm 5: < 5cm I : Fresh ~ VI completely weathered Table 1. Results of shear box tests on samples of sandstone. ?, MPa XXXXXXXXXX ?, MPa XXXXXXXXXXTable 2. Results of triaxial tests on samples of tuff. ?3f, MPa XXXXXXXXXX ?1f, MPa XXXXXXXXXX XXXXXXXXXXEnd of borehole