Assignment 2 ( Geology) Instructions and Rubric 2020 PDF

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GEOM2131 Geology: Assignment 2

2020

LNG Site Assignment In this assignment you will assess the ground conditions of your cross-section based on three drill holes including: foundation and slope stability conditions, excavatability and potential for construction material. In addition to lithology (rock type) there is a log of the strength and RQD in the drill holes. Be aware there are many gaps in the strength and RQD data record. In most cases you can assume the value to be zero if it is not provided. Background: The project data is typical of the site preparation of a major LNG facility. Part 1 – Interpretive Geological Cross-section Using the same methods as given in Assignment 1A (Melbourne Interpretive Geological Cross-section) complete a cross-section for the three drill holes allocated to you from the NWLNG database. The drill holes are 50 m apart and should be presented in order of lowest number on the left side of the crosssection. Use a vertical exaggeration of 10. Present the cross-section in the same format as required for Assignment 1A. The base elevation of your cross-section is indicated on the template. Part 1 submission 1 page. Part 2 – Foundations and Stability You will make an assessment of the geological conditions that would be encountered in the base and cut slopes of a trench excavation. You will not actually design a foundation or undertake design calculations. Scenario: The site requires excavation to a depth of 5 m above sea level. The excavation is centred on your middle drill hole. The base of the trench excavation is 15 m wide. The cut slopes at each side of the trench can be 2:1 or 3:1 (H:V). The steeper slope would be recommended if the slope is mainly in sound rock and the shallower slope would be recommended if the slope is mainly in soil or unsound rock. The slopes can be stabilised temporarily against erosion by placing hard rock fragments against any soft rock or soil exposed on the slope. Mark the location of these stabilisation works on your cross-section graphic. Instructions: On a copy of your cross-section graphic from part 1, illustrate the trench excavation floor and show the recommended slopes for the sides of the trench. Prepare a table(s) that addresses the following questions: Are coarse soil (2biii), fine soil (2biv) or clay/silt (3aiii) which all contain high plasticity clays found in the faces and floor (base) of the trench excavation on your section? Are coarse soil (2biii), fine soil (2biv) or clay/silt (3aiii) which all contain high plasticity clays found in the 10 m below the floor (base) of the trench excavation on your section? What are the strengths and RQD values present in the 10 m below the floor (base) of the trench excavation on your section? Comment on the likelihood of occurrence of the flexure or punching bearing capacity failure modes (Kulhawy and Goodman, Fig. 55.6) occurring in the excavation floor at 5m asl (calculation is not required). Summarise the RQD and strength of material within 10 m of the floor (base) level of the excavation. Use Kulhawy and Goodman, Fig. 55.1 to comment on allowable contact pressure at the excavation floor at 5m asl (calculation is not required). Use Hencher’s summary of the British Standards (Table 6.1) to estimate bearing value of a strip footing taking into account material within 10 m of the floor (base) level of the trench (Rock types 1b and 2a have UCS between 12.5-50 MPa, all other materials are weaker). Use Look 2014 (Table 22.1) to estimate the allowable bearing pressure. Do not include the illustrations or tables in these sources in your report. Part 2 submission 2 pages. Page 1 graphic with excavations marked, page 2 table of answers to questions.

GEOM2131 Geology: Assignment 2

2020

Part 3 - Excavatability Addition data: Pettifer and Fookes 1994 [extract] (pdf) Refer to AS1726 [for converting strength descriptions to PLI numbers] The data spreadsheet contains a record of the lithology (rock type), RQD and strength in each drill hole. The intervals (top and bottom) of these three parameters do not coincide. In order to assess the relationships of these three parameters you will undertake a ‘point-sampling’ of the data. At each metre mark (relative to sea-level) between the ground surface and -5m record each of the three parameters in a table. Pettifer and Fookes’ paper explains in a footnote to the chart how to convert RQD to their discontinuity spacing index and the lecture slides provide a modified (new) formula by Palmstrom (which you must use). Plot the spacing in the conventional RQD classes of excellent (>90), good (75-89), fair (5074), poor (25-49), very poor (...