tut1a Q_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 INTRODUCTION The Ord Irrigation Scheme involved the construction of two dams, the Kununurra Diversion Dam and the Ord River Dam. Construction of the Kununurra Diversion Dam across the Ord River was completed in 1963. Kununurra Diversion Dam The Ord River Dam was completed in 1972 with the work carried out over three dry seasons. The Ord River Dam provides a major storage reservoir, called Lake Argyle. Lake Argyle is now one of the world’s largest man-made water bodies. The Ord River Dam is a rockfill dam with an earth core and internal filter zone. The dam is ca. 100 m high and the crest is ca. 340 m long.

SCOPE OF WORK It’s the mid-1960s, your client is looking for suitable borrow pits/ quarries for construction of an embankment dam across the Ord River. They are looking for specific materials for the following construction components (see photograph below): • Road Construction – soil to construct a dirt access road into the dam site from the main highway • Impervious Clay Core – soil to act as the impermeable membrane in the dam embankment • Chimney Filter/Drainage Blanket – soil to act as drainage layers within the dam • Rockfill Information sign at the Ord River Dam lookout showing the internal structure The sequence of activities you as the engineering geologist will undertake to complete this task are: 1. Desktop Study 2. Fieldwork 3. Laboratory Testing 4. Assessment DESKTOP STUDY Your client has shown you the location of three old borrow pits near the proposed dam location. However, these borrow locations will not provide the quantity of material required for construction. You need to identify possible areas which you will investigate with test pits during the fieldwork phase. Ideally, your borrow locations will be as close as possible to the proposed dam site to minimise the distance the materials have to be transported from the borrow area to the dam site. 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: • Clayey soils that could be used for building the impervious clay core; • Sandy soils with little or no clay that could be used to build the filter/drainage blanket zone; and • A hard durable rock type that could be quarried to use as rockfill. An extract of the Lissadell map showing the geology in the area surrounding the map is presented below.

Source: Geological Survey of Western Australia. Lissadell, WA, Sheet SE 52-2, 1:250,000 Geological Series Map. First Edition, 1968 The location of the Ord River Dam (which had not yet been built in 1968) is shown as the red line.

Source: Geological Survey of Western Australia. Lissadell, WA, Sheet SE 52-2, 1:250,000 Geological Series Map. First Edition, 1968

The Explanatory Notes that accompany the map describe the superficial soils present in the area as: Unit Name Description Qa Alluvium Consists of sand and gravel in present day drainage channels. Becomes finer grained in valley and flat plain areas. Czs Sand, soil cover, alluvium Silt, sand, and gravel (Czs) covers valley floors and large plains. Czb Black Soil Covers broad floodplains adjacent to the larger creeks. These plains consist of black and dark grey-brown soils and cracking clays. The main rock types in the area surrounding the proposed dam location are described as follows: Unit Name Description Pcl Lissadell Formation Quartz sandstone with interbedded siltstone. Sandstone units are massive and can be thickly bedded. High to very high strength. Pcd Golden Gate Siltstone Mostly interbedded siltstone and sandstone. Can be thinly interbedded with shale. Sandstone beds often cross-laminated. Pbo Bow River Granite Coarse-grained granite. High Strength. Ah Halls Creek Group Greywacke, slate, schist, conglomerate. Variable rock characteristics. FIELDWORK During your fieldwork you visited three old borrow pits (B1-B3) and carried out test pitting at three other potential borrow sources (TP1-TP3) based on examination of the local geology map. You collected soil and rock samples for testing. LABORATORY TESTING You selected soil samples for laboratory testing, and you have received Particle Size Distribution and Atterberg Limit tests results back from the laboratory. The lab reports are the six Separate Graphs / Lab Reports included as part of the tutorial package. ASSESSMENT The client requires that the soil materials meet previously established properties. These properties are outlined below. Dam Core Material - Liquid Limit Between 40% to 60% - Plasticity Index Maximum = 20% to 40% - % fines > 50% Road Construction - Liquid Limit Maximum = 25%

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