Ground Subsidence Essay Example | Topics and Well Written Essays - 6250 words

Ground Subsidence - Essay causaMost human built structures do rely on the fundament for stability but what if the ground suddenly becomes unstable What if cave in occurs This paper aims to answer these questions by discussing the nature of subsidence and its do on civil works. I will be providing definitions and possible causes of subsidence. For the civil works, I will be enumerating the effects along precautionary and remedial measures that can mitigate its effects.Ground subsidence is legally defined as the means or process that is characterized by the downward displacement of surface material caused by pictorial phenomena such as removal of underground fluids, natural consolidation, or dissolution of underground minerals, or by man-made phenomena such as underground mining. (Colorado Geologic Survey)Subsidence may occur abruptly-virtually instantly-or gradually everywhere many years. It may occur uniformly in a small, confined area as shown in ikon 1a or may occur over a w ide area as local depressions as shown in encounter 1b. Subsidence is commonly associated with the dissolution of soluble rocks, such as limestone, down the stairs the surface while those with crystalline rocks in which most metals are mined have greater competency and are less likely to settle or collapse. The resultant landscape has closed depressions and is known as karst topography. Note that the depressions do not necessarily result to holes in the ground as shown in Figure 2. ... ed subsidence occur as a result of withdrawal of fluids from subsurface reservoirs as shown in Figure 4, from the collapse of soil and rock over subsurface holes, such as those left by underground mining and from the draining of wetlands. (Waltham and Cushaw, 2004) body-build 1a. SMALL SINKHOLE. Not all sinkholes are large subsidence features. Small collapse sinkholes, such as this one in Boyle County, Kentucky, are common. (Kentucky Geological Survey)FIGURE 1.b round COLLAPSE SINKHOLE. This sink hole near Montevallo in central Alabama was dubbed the December Giant after it heedful closeto 120 m (400 ft.) in diameter and 45 m (150 ft.) in depth. (U.S. Geological Survey)FIGURE 2. KARST TOPOGRAPHY. This rolling landscape of the Mitchell Plateau in southern Indiana is typical of karst topography in a wet temperate climate. (Samuel S. Frushour, Indiana Geological Survey)Subsidence can also occur due to expansive soils. in that location are clay-rich soils which shrink significantly during dry periods and expand or swell during wet periods. The swelling is caused by the chemical attraction of water molecules to the surface of very fine particles of clay. Swelling can also be caused by the chemical attraction of water molecules to layers at heart the crystal structure of some clay minerals. Figure 3a shows the mechanism by which expansion of soil can occur while Figure 3b shows water consumption by trees as another cause. FIGURE 3. EXPANSIVE SOILS (a) Smectite clay expands as water molecules are added onto and within the clay particles. (b) Effects of soils shrinking and swelling at a home site. (After Mathewson, C. C., and J. P. Castleberry, II. Expansive soils Their engineering geology. Texas A&M University)FIGURE 4. PROCESS OF SUBSIDENCE DUE TO WATER