Reference no: EM132663795

GEOM2131 Site Investigation Geology and Surveying - RMIT University

Assignment

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 cross- section. 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 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 Page 1 graphic with excavations marked, page 2 table of answers to questions.

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 (50- 74), poor (25-49), very poor (<25).

Plot your data for rock type 2a and 2bi on the Pettifer and Fookes chart. Summarise the excavatability conditions for those rock types.
Make a copy of your interpretive cross-section from Part 1 (keep the stratigraphic key but not the table of your data). Show on this version of your cross-section the excavatability conditions for any 2a and 2bi material on your cross section.

Part 3 Page 1 your point sampling data table. Page 2 excavatability chart for rock type 2a (if present) and page 3 excavatability chart for rock type 2bi (if present). Page 4 your cross section with excavatability conditions of 2a and 2bi noted.

Part 4 - Construction Materials
Your three drill holes with interpreted geological cross section (and related data) will form the basis of this part of the 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: Three of the construction materials required for construction of part of the LNG facility are armourstone for marine works protection, aggregate for concrete and sand for pipeline bedding. You are required to assess your section as a source for these material. Use the following specification assumptions in your work.

Armourstone:
The materials which have the potential to yield armourstone are calcrete [a type of limestone] (1b) and crystalline limestone (2a). Calcrete is estimated to yield 20% armourstone regardless of the RQD value. Crystalline limestone (2a) is estimated to yield 20% armourstone only if the RQD is 75% or above (otherwise no armourstone is expected from 2a). If Crystalline limestone (2a) has RQD less than 75%, it can be considered for use as aggregate (see below).

Aggregate:
The units identified as crystalline limestone (2a) and limestone hard (2bi) can be used as aggregate if the strength is medium or above. Note, preference is given to use of crystalline limestone (2a) as armourstone over its use as aggregate where it meets the armourstone RQD specification.
Bedding sand:
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.

Coarse soil (2biii), 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, illustrate rectangular areas of potential armourstone, aggregate 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.

Attachment:- Geology Assignment.rar