tut1a A_Embankment Dam_Borrow Sources

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Apr 3, 2024

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GEOL3003/5010 - Tutorial 1– Borrow Sources for Embankment Dam Construction Question 1) Using the geological map sheet “Lissadell – First Edition 1968” from the Geological Survey of Western Australia, mark areas on the map where you may find the following material types. During the desktop study phase, the engineering geologist reviews available geological and geotechnical information. Published information includes geological maps and accompanying explanatory notes available from the Geological Survey of Western Australia, and aerial photography. Prospective Borrow Pit Locations: Sand for Filter Zone - river and creek beds in the northern parts of Australia are often ephemeral with low flows during the dry season. When flows are low, extensive deposits of sand and gravel can be accessed. The aerial image below shows the Ord River bed before the Ord Dam was built. Borrow areas would have been established where the deposits contain the most sand, and least gravel. Source: https://maps.landgate.wa.gov.au/maps-landgate Clay Zone - clayey soils suitable as impervious clay core can be hard to find. Prospective areas can be low-lying areas where soils are deposited by slow flowing water or sheetwash across a relatively flat landscape. Areas of Alluvial (Qa) along the edges of the Ord River valley are prospective areas, although it’s likely the soils will not be pure clay but will have a sand component. For the Ord Dam, material for the core was sourced from alluvial areas (floodplain areas) upstream of the dam site. The Black Soil (Czb) is a potential source of clayey soils. The explanatory notes mention cracking clays. However, according to the map, this material is quite a long way from the dam site. Rock-Fill - of the locally available rock types, the massive quartz sandstone has the best qualities. It is massive. Quartz is a hard, durable, erosion-resistant mineral. The interbedded siltstone may be problematic and result in some wastage of material that fails to meet the construction specification for rockfill). Shale and micaceous rocks tend to be foliated and have closely-spaced planes of weakness. Slate and schist are also typically foliated. The Bow

River Granite is potentially a suitable source of rock fill but it does not outcrop close to the dam site. The actual quarry site can be seen immediately south of the dam in the image below. The Lissadell Formation (Pcl) outcrops on both the north and south sides of the dam location, both areas are prospective quarry sites. The southern site was chosen because it was the site with sufficient quantity of material and located far enough away from the dam for aesthetic reasons. Source: Google Earth

Actual quarry site is in this area. Another prospective area for a rock fill quarry. Actual area used Prospective a rea for clayey soils. Prospective area for clayey soils. Prospective area for clayey soils. Prospective area for clayey soils. There is clay in this area but it is a long away from the dam site. Prospective area for sand and gravel and river channel.

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