This assignment is designed (a) to develop your appreciation of principles relating to geological strata or soil sampling / investigation, and (b) to improve your skills in the areas of planning an investigation, locating and using information.
1. Attempt to identify the rock type in each exposed layer (use clues from geology notes, talk to somebody who might know, collect small samples if possible, match against pictures or lab samples, find location on geological map and make relevant deductions, etc)
(NB: I already selected the site and also took some photos of rocks. The site is at Barry Road George, Campbellfield, and the type of rock that we found underlying the whole Merri Catchment is yellow to brown (marine limestone & sad-stone).
2. Based on your preliminary identification of rock types, briefly list any information you can find on likely strength parameters relating to these rock types.(NB: Please research)
3. Describe the rock arrangement / bedding system at the site (e.g., sketch or photo(s) from designated point and direction, estimated layer thicknesses, estimated (or measured) apparent dip angle, any obvious zones of weakness / fault crush zones, strata displacements, porosity, etc.) (NB: Please research)
4. Describe the apparent freshness / state of weathering of the rock (consider whether the rock seems to be breaking down somewhat, how hard or soft / flaky it is, any tree root penetrations, etc.) (NB: Please research)
5. Based on all of the above, briefly discuss issues which you think would be important in determining the suitability of the rock strata to withstand the forces associated with any two of (i) cable anchorage for a suspension bridge (ii) abutments for a pier and beam bridge (iii) abutments for a small concrete weir across a stream (assuming the exposed rock-face lay parallel to the stream) (iv) a multi-storey building on an adjacent site. How would you go about finding more detailed / reliable information on which to base subsequent design decisions? (NB: Please research)
Types of Rocks Found in Merri Creek Catchment Area
The most common type of rocks found in the research area in Merri Creek catchment area marine limestone and sad-stone. These stones were formed from sediments millions of years ago. Erosion has occurred over these sediments in the modern-day Merri Creek. However, the rocks still defy their existence and as a result have led to this research (Arroucau, Rawlinson and Sambridge, 2010).
Figure 1 The Site directions
Figure 2 Study area
Marine limestones are formed n calm and shallow waters of marine. Major components leading to their formation are calcium carbonate containing shells from animals that die they accumulate and form limestones . On the other hand, sandstones are formed from grains cemented by fragments of mono-mineralised rock crystals. The grain sizes are typically in the range of 0.0625 to 2 mm. the binding material is usually clay, silica or calcite . The formation of sandstones clearly amplifiers the strength possessed by these rocks possess. They are very strong and is evident from the processes involved in their formation which include a two-step process as follows (Af?ar, Westphal and Philipp, 2014). The first step is sedimentation where layers of sand accumulate by settling from suspension either in water or air. The second step is compaction of the settled sand by pressure of deposits overlying the sediments; precipitation of minerals later on cements the grains into sand stones (Af?ar, Westphal and Philipp, 2014). Such a process gives sandstones strength enough to be mined as a construction material. The rocks are pretty tough as they have restricted the flow of the river due to the fact that they form the river bed and banks, withstanding the force or abrasion by the river waters. It no wonders that since the ancient times, these rocks have been used for purposes of construction for houses and other ancient structures made by man including curving’s (Amorosi, 2011).
In some areas for example the Melbourne Zone, the rock sediments thickness is up to 10 000 metres (Blöcher et al., 2014). These sedimentary formed rocks were uplifted after the completion of compression and cementation. They were further folded to synclines and anticlines (formation of sedimentary rocks). Adjacent areas of the area of study show that the rocks were intruded by little masses of granites and tabular dykes. Compression with thick beds of sandstones deform by brittle fracture causing them to bend around and in the process deforming the less competent mudstones. Such competent mudstones and sediments are responsible for such huge thickness in some areas as early on pointed out. In some place of visit along the creek there are rocks that are broad with upright synclines and anticlines that have fold axes striking South South West direction with spacing of 1 to 3 kilometres apart. The beds have a dip of about 45’ to 70’. During the process of folding there were extensive forces that led to fractures in form of faults and joints . There exist small faults with slips of about one meter. There are shows of intense jointing in some nearby rocks (Blöcher et al., 2014).
Formation and Strength of Marine Limestone and Sandstone
It is clear from the study area that the rocks under scrutiny that weathering has occurred in this area. The form of the rocks was determined before the subsequent and the later volcanic eruptions that released lava from surrounding hills and mountains (Burroughs, 1913). The lava flow covering parts of the rocks is younger as compared to the rocks which as stated stand as the oldest formation in this part. There has been substantial weathering. The joint planes are the major areas of progression for weathering (Burroughs, 1913). The original rock fracturing is an indicator of the depth of weathering of the rock.is soft on the surface from feeling. Weathering soils cover the impervious rock zones (Zhu et al., 2015).
There is a domination of dark grey to brown clays on the rocks. These result from the weathering of basalt which converts feldspathic minerals to clay. There is no quartz in the rocks. There are also trees and vegetation growing from weak joints in the rocks indicating that even the oldest and most strong forms of nature can still be broken by nature itself. The forces of weathering are evident in the rocks as illustrated by these instances of vegetation propagating along fault lines. All this information is illustrated by site images in the appendix section of this paper (Cartwright, 2010).
It is very possible to set up a concrete weir across the stream. The rocks have a very low permeability of about 1.6 to 8.5 millidarcys. The sandstones are well compacted and cemented due to the sedimentation process that occurred millions of years ago. Clay has cemented the particles as early on stated making it less permeable yet very strong for use as a construction material (Kumara and Hayano, 2016).
To set up a multistorey building on a site requires exhaustive research on the type of rocks and soils in the site. The strength, water holding characteristics and durability of the site needs to be determined (Zheng et al., 2014). In the area of study, sand stones dominate the site. Setting up a multi-storey building would require a strong foundation to provide the strength for holding the weight of the building. Construction materials in form of the sand and limestone rocks will also be readily available for construction. It therefore makes setting up a multistorey building to the area adjacent to the study area very plausible. The rocks have shown resistance to abrasion of the river, they have withstood the different erosion and withering occurs slowly and very little over a long period of time (Lu et al., 2015).
The sandstones have a very low permeability of about 1.6 to 8.5 millidarcys. In designing a weir, considerations should also be given to the height of the weir crest. Critical flow must be obtained in a weir and therefore the height should not be too low as it will cause the water to pass without reaching the critical flow (Ruiz-Agudo, Putnis and Putnis, 2014). Unnecessary backwater effect is inevitable if the design height is too high .The sedimentation process used to make the sandstones involved setting layers of sand then compacting them and further cementing with clay and other mineral material making it less permeable over a long period of time (Monecke, 2006).
The building will have numerous loads in terms of live loads from the users; dead loads for the material used for constructing and other factors for example earthquakes. The area adjacent to the study area is suitable for construction of a multistore building because the soils fulfil the design criteria (Schwartz, 2007). The rocks in the area have the right failure bearing capacity; the soils are capable of supporting structural loads due to the hard strata. It is evident by the rock types found in the area-sedimentary rock types hence will be able to support the building due to the strength of such type of soils (Robinson, 2016).
Af?ar, F., Westphal, H. and Philipp, S. (2014). How facies and diagenesis affect fracturing of limestone beds and reservoir permeability in limestone–marl alternations. Marine and Petroleum Geology, 57(5), pp.418-432.
Amorosi, A. (2011). The problem of glaucony from the Shannon Sandstone (Campanian, Wyoming). Terra Nova, 23(4), pp.23-34.
Arroucau, P., Rawlinson, N. and Sambridge, M. (2010). New insight into Cainozoic sedimentary basins and Palaeozoic suture zones in southeast Australia from ambient noise surface wave tomography. Geophysical Research Letters, 37(7), pp.16-67.
Blöcher, G., Reinsch, T., Hassanzadegan, A., Milsch, H. and Zimmermann, G. (2014). Direct and indirect laboratory measurements of poroelastic properties of two consolidated sandstones. International Journal of Rock Mechanics and Mining Sciences, 67, pp.191-201.
Burroughs, W. (1913). Economic geology of the Berea sand-stone formation of northern Ohio. Economic Geology, 8(5), pp.469-481.
Cartwright, J. (2010). Regionally extensive emplacement of sandstone intrusions: a brief review. Basin Research, 22(4), pp.502-516.
Kumara, J. and Hayano, K. (2016). Importance of particle shape on stress-strain behaviour of crushed stone-sand mixtures. Geomechanics and Engineering, 10(4), pp.455-470.
Lu, P., Konishi, H., Oelkers, E. and Zhu, C. (2015). Coupled alkali feldspar dissolution and secondary mineral precipitation in batch systems: 5. Results of K-feldspar hydrolysis experiments. Chinese Journal of Geochemistry, 34(1), pp.1-12.
Monecke, T. (2006). Geology and Volcanic Facies Architecture of the Lower Ordovician Waterloo Massive Sufide Deposit, Australia. Economic Geology, 101(1), pp.179-197.
Robinson, S. (2016). Coloring Craze Comes to Rocks & Minerals! Rocks & Minerals, 91(6), pp.554-557.
Ruiz-Agudo, E., Putnis, C. and Putnis, A. (2014). Coupled dissolution and precipitation at mineral–fluid interfaces. Chemical Geology, 383(7), pp.132-146.
Schwartz, W. (2007). J. D. Milliman (Editor), Marine Carbonates (Recent Sedimentary Carbonates, Part I). XV, 375 S., 94 Abb., 80 Tab., 39 Taf. Berlin-Heidelberg-New York 1974: Springer-Verlag. DM 66,00. Zeitschrift für allgemeine Mikrobiologie, 16(3), pp.242-242.
Zhu, P., Lin, C., Ren, H., Zhao, Z. and Zhang, H. (2015). Micro-fracture characteristics of tight sandstone reservoirs and its evaluation by capillary pressure curves: A case study of Permian sandstones in Ordos Basin, China. Journal of Natural Gas Science and Engineering, 27, pp.90-97.
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