Geology Of The Area. Sources Of Natural Materials and Construction Problems - Essay Example

?Geology GEOLOGY OF THE AREA According to Amelin et al., (2002), geology is the science comprising of the study of solid earth, the rocks of which it is composed of, and the processes by which they change. The area given on the map consists of three different rock layers including sandstone, mudstone and limestone. Sandstone- This majorly lies on the eastern side of the maps covering both low and high altitude area. Sandstone is a classic sedimentary rock composed of sand sized minerals or rock grains. It may be of many colors though the most pronounced colors are red, grey, pink, white or black. It is composed of quartz or feldspar since they are the most common minerals in the earth crust. The colors of sandstone have been identified with several regions because their beds often form very highly visible cliffs. It usually allows water and other fluids to percolate; additionally sandstone is porous enough to store large quantities of fluids, therefore, are valuable aquifers and reservoirs of petroleum. It finds application in house wares and domestic construction. Structurally, they can be fragments of pre existing rock or mono-mineralic crystals. These rocks are very strong especially when mature therefore suitable for construction purposes. Mudstone-according to the map it is elbow-shaped and uniformly distributed in the map. This is a fine grained sedimentary rock. Its original constituents were clays or mud their individual size can only be identified with the help of a microscope. It has no layers due to original texture or disruption of layering by burrowing organisms prior to lithification. It may show crack or fissures depending on how it is formed. According to Dunham (1962), the classification of limestone, a mudstone is a carbonate rock with less than 10% allochens in carbonate mud matrix. Mudstone is a soft rock material therefore is not appropriate for construction purposes. Limestone- This rock layer appears mainly between northwest and southwest side of the map. It is a sedimentary rock mainly composed of calcite and aragonite minerals that are different forms of calcium carbonate. It’s composed from skeletal fragment of organisms and makes up to 10% of the total volume of any sedimentary rock; it is solubility in water leads to erosion of the landscape over years. It is the hardest rock layer among the three appearing in the map and is used for construction purposes, an aggregate for base of roads, mineral filler passing 0.075mm – 0.425mm of mineral size. It can be used in the manufacture of glass, toothpaste and cement. POSSIBLE PROBLEMS THAT MAY ARISE DURING CONSTRUCTION The following are the possible problems that may arise during the highway construction process between points A and B. As stated by Amelin et al. (2002), ‘It is important to consider that if we choose to ignore the surrounding geology in the construction of engineered works, then the surrounding geology will most certainly assert its influence on our engineered structures.’ First the material cut may be less than the required fill. Cut and fill, is a process of constructing a railway, road canal or high way whereby the total material extracted more or less is the same as the quantity of material for fill. Since the cut is less than fill, it would warrant acquiring materials from other sources for example borrow areas, importing from other areas. The material cut may be more than the required fill any excess cut above the fill would warrant an additional transportation cost. Secondly, there may be mobility problems due to the rugged and steep topography of the land which may not favor human and machine movement during the highway construction. This triggers use of special machinery in cutting, filling and compaction processes to achieve the desired objective or shape. The land’s landscape may be too rugged such that it may incur more cost especially when it as to get the materials from other areas. There is difficulty in cutting due to topography of land, stability of slopes and since any cutting below 5m may require a specific study which may include borehole or test points down to the formation level. Thirdly, the climatic factors are a major setback if not considered during the highway construction. In wet areas with mean annual rainfall greater than 500mm, the use of plastic materials should be limited as they are not economically feasible. Bituminous surface should be as impervious as possible and greater attention should be paid on the internal and external drainage. The above factors may pose a challenge during the construction process. In dry areas with mean annual rainfall of less than 500mm, higher plastics can be accepted and open textured base materials can be used. Difficulties may arise in dry areas with current treated materials due to rapid evaporation of water hindering hydration of cement. Therefore, a tendency of treated material to crack, extension due to shrinkage and volumetric changes may be brought about due to daily temperature variations. In dry areas, drainage is a challenge and may be neglected though protection against erosion is of importance as short but heavy storms are likely to occur. Fourth, the financial constraints could be a major problem especially if some unbudgeted costs are incurred due to surprises as a result of the natural occurrence at the construction site. Some machines that are used may not be able to do the expected duty thus they may need hire more or special machinery that may be applicable this may mean incurring more costs that were not filled in additionally the excess cut above fill or less cut below the fill as result of under or over estimation may make it necessary to transport the excess or import to obtain the right fill. Due to the rugged shape of the land the transportation of materials like bitumen from external sources may prove to be a challenge thus incurring more cost. Fifth, the prevention of failure of the bridge abutment and retaining walls especially when building the support of the highway about 15m above the river surface. This problem may be experienced especially if the river volume increases beyond the expected limit thus may cause more problems trying to retain the water in an enclosure. Sixth, there is shallow ground water which makes the terrain quite unstable. This is evident due to the presence of the river and the surrounding river bank the presence of the river would pose more risk since there is a possibility of underground dissolved limestone, creating an area of weakness along the construction site which would trigger landslide. Due to the large area occupied by mudstone, especially on the southwest part of the map, the land is susceptible to landslides. In the softer and weaker rocks such as mudstone can be the cause of slope failure but in the limestone area, there is absolute firmness and strength. As stated by Reese (2007), ‘moist and saturated shale and mudstones sequences may form landslides’. Soils beneath the loading and unloading zones may be deformed and thus cause a long term threat to the highway. There is slope instability; this includes rock falls, mud flows and landslides amongst others. According to the area, rock falls may pose a great danger to human and machinery since they may cause death or damage to machinery. The area may receive periodic rainfall which may increase the susceptibility of the area to landslides. The slope instability of the area may make it difficult to use certain machinery due to the possible risks involved. Unfavorable weather conditions; this may lead to a stop of the construction process. A non predicted storm or rainfall may cause great damages warranting repair or a repeat of the whole process. For the last stage of the construction a dry weather is of basic need so as to enable the bitumen to dry therefore any unstable weather would lead to a halt in the process. The geological section of the map SOURCES OF NATURAL MATERIALS The sources of materials around the area could be natural materials according to the map. The natural sources include sandstone, mudstone, limestone and water from the borehole. Natural materials should be used as much as possible to minimize construction costs as much as possible. For that reason, it is important to make an inventory of all the available road making materials for example sandstone, limestone and water at the investigation stage. Limestone can be broken down to small rocks thus is put as the first layer on the tarmac. From the map, the borrow areas for limestone can be gotten at the bedrock. The limestone can be refined to produce quick lime mortar and cement which is of importance to construction purposes as cement is required in the making of concrete amongst the various uses in the road construction. Limestone contains calcite that cements the existing rock grains together and can also be used in the construction of the bridge after cutting. Limestone may trigger landslides especially when dissolved in water after several years. It is relatively easy to cut into blocks or elaborate curving. Sandstone is a popular building material from ancient time and is relatively soft, making it easier to curve the limestone extracted can be crushed into aggregate sizes to form the base during road construction. According to the map, sandstone may be obtained from the cut and borrow areas used as fill or crushed and mixed with concrete and used in the highway construction process. Because of the hardness of individual grains of sandstone, some type of sandstone may be excellent materials from which grindstones can be made. The grindstone may be used to shape blades and sharpen them. Cutting this contributes greatly towards the fill material required. The factors that will affect design and cost of cutting include volume and the position of different materials, level of water table, the stability of slope, type of materials to be excavated among others. The boreholes and the river may be used as the water sources during the construction this is due to the availability and the great demand for water that requires a permanent source. The water may be used for various purposes including cooling of the car and tractor engines, domestic purposes and mixing of concrete together with other miscellaneous duties. The borrow areas; this is revoked when the cutting is not enough for the fill. The borrow areas can be adjacent or far from the area of construction. According to the map, sandstone and mudstone can be borrowed from adjacent areas where road is not constructed. The sandstone is used to mix with the concrete to make the bridge structure. The compaction must be completed in two hours after mixing and the protection against evaporation be placed not four hours later upon the construction. The compaction process is done by pouring the soil (concrete or rocks depending on the construction stage) to about 150mm and then compressing it to 100mm this is done repeatedly until the required level of the road is obtained. Natural gravel can be obtained from the borrow areas (Tan 2005). The size of the gravel should be 2/3rd of the layers thickness or 80mmdepending on whichever is lesser. From experience, according to material pavement design, the material which comply with the following requirements, are generally deemed suitable for improvement. Grading natural maximum size is between 10-15mm passing 0.075mm sieve plasticity index of 30% maximum, plasticity modulus of 2500 maximum and an organic matter of 2%. REFERENCES Amelin, Y., Krot, A., Hutcheon, I. & Ulyanov, A., 2002. “Lead isotopic ages of chondrules and calcium aluminum rich inclusions” Science 297 (5587): 1678-1683. Dunham R. J. 1962, “Classification of Carbonate rocks according to depositional texture in Ham W. E classification of carbonate rocks” American Association of Petroleum Geologist Memoir 1: 108-121. Reese O., 2007. Mapping Potential Geologic hazards for proposed highway construction projects in Pennsylvania [pdf] Available at: http://ngmdb.usgs.gov/Info/dmt/docs/DMT07_Draft_Reese.pdf [Accessed 28.10.2013] Tan B. K. 2005, Engineering Geology of Rock slopes in Highway Construction, [pdf] Available at: http://www.mbam.org.my/mbam/images/MBJ2Q05pdf/CsROCKGEOLOGY(22-24).pdf [Accessed 28.10.2013] Read More