Interpretive Geological Cross-section,Excavatability,Foundations and Stability,– Construction Materials

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GEOM2131 Geology: Assignment 3 2017
LNG Pipeline Assignment
In this assignment you will assess the ground conditions of your cross-section for a buried pipeline including: excavatability, foundation and slope conditions and potential for construction material.
Background: The project data is from the site preparation of a major LNG facility.
Part 1 – Interpretive Geological Cross-section
Using the same methods as given in Assignment 2 (Melbourne Interpretive Geological Cross-section) complete a cross-section for the three drill holes allocated to you from the NWLNG database. Use a vertical exaggeration of 10. Present the cross-section in the same format as required for Assignment 2.
Part 1 submission 1 page.
Part 2 – Excavatability
Files provided:
Data spreadsheet (Excel)
AS1726 [needed for converting strength descriptions to numbers]
Pettifer and Fookes 1994 [extract] (pdf)
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. Plot your data for rock type 2a on the Pettifer and Fookes chart. Summarise the excavatability conditions for that rock type. Choose another rock type from your data and present it also on the P-F chart. Pettifer and Fookes’ paper explains in a footnote to the chart how to convert RQD to their discontinuity spacing index the lecture slides provide a modified calculation by Palmstrom (which you should use). Also show excavatability using codes on the interpretive cross-section from Part 1.
Part 2 submission 3 pages. Page 1 your point sampling data table. Page 2 excavatability chart for rock type 2a and page 3 excavatability chart for your selected rock type. Your brief statement of the excavatability conditions will be shown on page 2 and 3.
Part 3 – Foundations and Stability
Kulhawy and Goodman – Foundations on Rock (provided with this assignment)
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: A buried pipeline installation requires excavating a trench with a level base 15m across at a depth 5m above sea level. You are required to assess your section for this purpose. The trench would be centred on your middle drill hole. The cut slopes at each side of the trench can be 1:1 or 2:1 (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.
Instructions: On a copy of your cross-section graphic from part 1, illustrate the trench excavation floor and show recommended slopes. Prepare a table(s) that addresses the following questions:
Cut slopes
For each slope what rock/soil types would be exposed on a 1:1 slope?
What rock/soil types would be exposed on a 2:1 slope?
What gradient (1:1 or 2:1) do you recommend for the slope on each side of the excavation?
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-

GEOM2131 Geology: Assignment 3 2017
section graphic.
Floor level foundation
What rock/soil types would be exposed on the floor of the excavation at 5m above sea level?
What rock/soil types are present below the floor of the excavation between 5m above sea level and 5m below sea level?
Are fine soil (2biv) and clay/silt (3aiii) which contain high plasticity clays found in the pipeline foundation (-5m to 5m asl) of 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 and 10m asl (calculation is not required).
Use Kulhawy and Goodman, Fig. 55.1 (applied to material within 10m of the floor level) to comment on allowable contact pressure at the excavation floor at 5m asl (calculation is not required). How does this value compare to the strength estimate of the material in the database.
Do not include the Kulhawy and Goodman figures/illustrations in your report. Refer to geological materials by name with the code following in brackets.
Use Hencher’s summary of the British Standards (presentation slides) to estimate bearing value of a strip footing taking into account material within 10m of the floor level of the trench (Rock types 1b and 2a have UCS between 12.5-50 MPa, all other materials are weaker).
Part 3 submission 2 pages. Page 1 graphic with excavations marked, page 2 table of answers to questions.
Part 4 – Construction Materials
Your three drill hole interpreted geological cross section (and related data) will form the basis of this assignment. You should check that your cross-section conforms to the vertical and horizontal scales in the original template as this will influence the calculation of areas from the cross section. You will make an assessment of selected construction materials available at your part of the site.
Scenario: Two of the construction materials required for construction of part of the LNG facility are armourstone for marine works protection and sand for pipeline bedding. You are required to assess your section as a source for these material. Use the following assumptions in your work. The materials which have the potential to yield armourstone are caprock (1b), crystalline limestone (2a) and limestone hard (2bi). Caprock is estimated to yield 25% armourstone regardless of the RQD value. Crystalline limestone (2a) and limestone hard (2bi) are estimated to yield 25% armour if the RQD is 90% or above (otherwise no armourstone is expected). Sand (with fines) (3ai) has been found to be a suitable pipeline bedding material.
For practical extraction reasons, areas of potential construction materials must be defined as rectangles with horizontal and vertical sides with a minimum dimension of 1m. Areas must not include other materials. Areas must include at least one drill hole section.
Fine soil (2biv) and clay/silt (3aiii) are found to contain high plasticity clays deleterious to use as site fill. If these materials occur on your section outline the materials with rectangles so that material outside these rectangles (with horizontal and vertical sides with a minimum dimension of 1m) would not be contaminated during excavation.
Instructions: On your cross-section graphic (following template from assignment 1), illustrate rectangular areas of potential armourstone and bedding sand. Also show outlines of rectangular areas to be excluded during excavation to avoid contamination with highly plastic clay. Only material above the -5m (5m below sea level) datum is to be considered. Include a table which summarises your defined areas including the width of each area, the elevation of the top and bottom of each area, total area and material type. Also report the data in tonnes assuming 25m distance ahead and behind the plane of the cross section. The main constituent of limestone (calcium carbonate) has a specific gravity of 2.7 times water but with an average 6% porosity of the rock. The sand comprises quartz (specific gravity 2.65 times water) but with an average 20% porosity. Tonnage is not required

GEOM2131 Geology: Assignment 3 2017
for the clay materials.
Part 4 submission 2 pages. Page 1 cross-section graphic, page 2 table of construction materials type and quantity.
Combined Parts 1-4.
Your 8 page report (powerpoint or pdf of the powerpoint, in landscape layout) must be submitted to the Blackboard by week 12. Your file name should include “LNG Pipeline” and your name.
Marking rubric
Criteria
Mark allocation (partial marks can be awarded)
Level 0
Level 1
Level 2
Level 3
Level 4
Level 5
Marks 3 /30
0
1
2
2.5
3
1. Geological interpretation shows a clear, accurate realistic, evidence-based distribution of lithology between and beyond drill holes
Interpretation not realistic or evidence-based
Few aspects of interpretation realistic and evidence-based.
Almost all aspects of interpretation realistic and evidence-based.
Interpretation realistic and evidence-based. But does not show good awareness of geological features
Interpretation realistic and evidence-based. Shows good awareness of geological features
Marks 9 /30
0
1-2
5
7
9
2. Excavatability assessed according to instructions.
Assessment not conducted according to instructions
Few aspects of assessment conducted according to instructions.
Some important aspects of assessment not conducted according to instructions.
Some minor aspects of assessment conducted according to instructions.
All aspects of assessment not conducted according to instructions with excellent clarity.
Marks 9 /30
0
1-2
5
7
9
3. Stability assessed according to instructions.
Assessment not conducted according to instructions
Few aspects of assessment conducted according to instructions.
Some important aspects of assessment not conducted according to instructions.
Some minor aspects of assessment conducted according to instructions.
All aspects of assessment not conducted according to instructions with excellent clarity.
Marks 9 /30
0
1-2
5
7
9
4. Construction materials assessed according to instructions.
Assessment not conducted according to instructions
Few aspects of assessment conducted according to instructions.
Some important aspects of assessment not conducted according to instructions.
Some minor aspects of assessment conducted according to instructions.
All aspects of assessment not conducted according to instructions with excellent clarity.

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