Abstract
Land and rockslides are natural disasters that threaten people living in the Sultanate of Oman. In this paper, the fundamentals of disaster management are identified from their causes. First, the aspect of slope stability is covered. The involvement of this information follows the need to appreciate the vulnerability of mountainous regions to mass movement. The causes of mass movement are also explained. Further, the risks of rock and landslides are expanded with the intention of directing the focus of the paper. To be objective, the paper progresses to a review of the measures employed by the government of Oman to curb the occurrence of such threats.
Introduction
The location of the Sultanate of Oman is on the Arabian Peninsula. This nation constitutes an arid climate characterized by occasional rainfall (Kwarteng, 2009). About this, the Sultanate of Oman depends on ground features for the supply of water for industrial and domestic use. Most of the nation’s water is obtained from springs and wells that were formed thousands of years ago. The aquifers that hold groundwater are supplied by the rare occurrence of rainfall in the region. Further, such water exhibits variations in quality and quantity distributed throughout the region. The geographic characteristics and human economic activities in Oman expose it to the hazards of various natural disasters. The region’s natural heritage is characterized by the occurrence of topographical features that possess extensive fractures. Specifically, the mountains in Muscat have fractures that affect their slope stability. Without proper slope protection, the people of Oman are in constant danger of rock and landslides.
Factors affecting slope stability
Slope stability is the geological ability of a slope to maintain its form without undergoing movement. Many structural factors determine this aspect. However, the most important determinants of slope stability are shear stress and strength. Stable slopes may change over time. Previously sturdy slopes may be exposed to elements that would condition their instability. Slope instability may be triggered by climatic events that would prompt the movement of such landforms. The occurrence of mass movement can be attributed to the increase in shear stress such as lateral pressure. Correspondingly, shear strength can be affected by weathering.
The factors that influence land stability lead to the development of slope failure. Geological discontinuity is a major factor that affects slope stability (Sonmez, 1999). Slope stability is achieved due to particular structural properties of rock formations. A discontinuity can be defined as a surface that earmarks a shift in the physicochemical attributes of the soil mass. This also includes rock masses that form the surfaces of various geographical features. Such a plane can exist in many forms. It can be a fracture, cleavage of the fault plane. Discontinuities are important in regulating the movement of soil and land masses constituting a slope. Additionally, they affect the type of failure that may occur if the balance of shear stress and strength is shaken. The particular characteristics of discontinuities change the nature of a slope's stability.
Water activities affect slope stability. However, this aspect can be viewed from two dimensions. First, groundwater plays a role in the determination of a slope's stability. Such ground water may be in the form of an aquifer that creates pore water pressure, which occurs below the ground surface. Rainwater is also an important determinant to consider. Concerning this, the infiltration of rainwater through ground surface generates water pressure as the resource flows along a slope. The activities of water are augmented by the physical characteristics that typify a slope’s surroundings. This environment can be described regarding its proximity to water masses and precipitation factors associated with the area. Concerning hard rock surfaces, water embedded in fractures have a significant influence on the stability of a slope. When water pressure is exerted in a discontinuity, the stress on a plane is reduced, and this causes a reduction in the rock or land mass' shear strength. The application of a load at the beginning of a slope leads to a considerable increase in pore pressure. If such a load surpasses the sheer strength of a slope, slope failure becomes inevitable.
Another factor affecting slope stability is vegetation cover. The presence of growing plants along a slope is important in reducing the likelihood of mass movement. This is attributed to the fact that plant roots create a network of interlocking materials that hold unconsolidated soil particles. Additionally, the physiological activities of plants may go a long way in fostering the stability of a slope. The ability to absorb water from soil is a significant factor that increases the shear strength of a slope. Nevertheless, it is crucial to consider the aspect of increased load regarding plants. The occurrence of vegetation may slightly destabilize a slope. However, this is dependent on the plant characteristics and soil attributes. Vegetative material that possesses extensive root networks does hold soil particles efficiently. To understand the effects of vegetation on slope stability, plants can be categorized into grasses, shrubs and trees. The application of grasses in slope stabilization requires regular maintenance because of the nature of their rooting. Shrubs have better rooting than grasses while trees from extensive root networks that may be effective in slope stabilization. Critically speaking, the natural loss of intended removal of vegetative cover can increase the risks and frequency of slope failure.
The causes of rock and landslides
The causes of rock and landslides may be natural or artificial in design. The natural causes of landslides are mainly attributed to seismic activity and erosion. Seismic waves that operate within slope layers may affect the stability of the land mass. If such waves pass through underlying rock, they increase stress on the structural components of the slope. This leads to the development of fractures within a rock mass. After this, the friction that existed within the surface element is reduced significantly. This is particularly the case when a land mass is chiefly composed of unconsolidated material. When earthquakes occur, landslides happen indeed (Dai, 2002). The effects of seismic waves on the stability of rock slopes can be understood in two ways. First, the immediate seismic detachment of rock material from a sloped surface begets a landslide. This happens in a short span of time when a strong earthquake hits a particular location. In a second instance, landslides may occur over prolonged periods. This occurs when seismic waves exert pressure on rock and land masses that constitute a slope. Concerning this, rocks may become fractured thus affecting the consolidation of the materials that make up a slope surface. Seismic waves are also responsible for expanding rock fissures and creating events that accelerate the process of rock dislodgement. Critically, the effects of seismic activity depend on the nature of the slope. This concerns the aspect of rock characteristics that are exposed to these waves. The topographic and geological nature of a slope is an essential factor that determines a slope’s susceptibility to the power generated by seismic waves.
Another natural cause of landslides is erosion. Concerning slope stability, the erosive activity may happen in two ways. First, large-scale erosion may be instrumental in creating pressure that would influence the occurrence of mass movement. Widespread erosion may involve the effects of water masses occurring at the base of a slope. Such masses may include rivers and streams. The second instance may be attributable to the erosive activity of groundwater and surface runoff. Large-scale erosion has a significant influence on the stability of a slope. It changes the physical characteristics of a rock mass. This surrounds the aspect of geometry that contributes to the overall instability of a slope. The movement of material at the base of a potential slide affects the stress that may be sustaining a slope’s stability. Localized erosion of rock material leads to the obtainment of weak weathered material. The interlocking ability of these elements may then be affected, resulting in the vulnerability of a slope to mass movement. The loss of interlocking ability leads to a corresponding decrease in a land mass' shear strength. This event may allow the flow of a stable rock mass causing a landslide. Nevertheless, the reduction in rock stability by localized erosion may lead to the occurrence of a landslide.
Artificially, many human activities cause land and rock slides (Alexander, 1992). Among the common human events include the establishment of construction projects that do not meet sustainable engineering standards. Farming activities that are coupled with the clearing of vegetative matter lead to the occurrence of landslides. Deforestation is usually done to create space for the establishment of agricultural projects. Further, some farming technologies, such as terracing, affect the nature of slopes. Farmers may burn vegetation as a simple method of preparing land for cultivation. These activities affect the physical attributes of slopes leading to the occurrence of slope failure. Notably, farming activities influence the consistency of slope gradients, a factor that affects slope stability.
Additionally, human activities may cause significant changes in water regimes leading to slope failure. The clearing of vegetation paves the way for the rapid movement of surface runoff along a slope. This exposes the landmass to soil erosion, a factor that causes landslides. Concerning underground water, human activities may affect the location of water tables. This may include the raising or lowering of groundwater levels due to events that alter the nature of surface drainage. When people employ irrigation in agriculture, they affect the integrity of natural water drainage. Soils become saturated: they would promote the occurrence of significant surface runoff along a slope. This runoff would then cause significant soil erosion that predisposes to landslides. In a different light, the use of irrigation involves the application of large volumes of water on the ground surface. This water seeps into the underlying surface layers and exerts an additional load on a slope. This aspect affects slope stability and leads to a landslide.
Risks of rock and landslides
Landslides occur when slopes lose their ability to support their weight. When this happens, mass movement takes place and leads to the massive destruction of property. Additionally, lives are lost through this natural phenomenon. Although rock and landslides are common in steep topographies, they may happen in areas characterized by fair gradients.
Some risk factors increase the likelihood of rock and landslides. First, the geometric attributes of a slope may contribute to its instability. Mountainous regions that are exposed to erosive weather elements have a high tendency for mass movement. Concerning slope geometry, some parameters determine its overall vulnerability to slope failure. The height and angle of a slope play a critical role in balancing the forces that hold a slope in place. The critical slope height is associated with the shear strength of a landmass and the slope foundation’s ability to bear the weight of the physical feature. A significant increase in the height of a slope has a corresponding negative influence on its stability. With an increase in the slope angle, shear stress is increased thus leading to a significant reduction in a slope’s stability. Therefore, steep slopes are considered high-risk areas that are prone to mass movement.
Additionally, the geological characteristics of a slope’s material composition determine the risk of its susceptibility to mass movement. The shear strength of the constituting materials contributes to a slope's stability. Additionally, the permeability and moisture content of surface materials gives an idea of the likelihood of mass movement. Areas that are made up of strong rock masses are less prone to mass movement compared to regions comprised of loose unconsolidated surface matter.
Remedies and precautions practiced in Oman
The government of Oman has established many measures to counter the risks of land and rock slides. First, scientific research has been used to investigate the seismic causes of mass movements in Oman (Browning, 2016). Through this, authorities can predict the likelihood of this natural disaster before it occurs. Additionally, experiments are done to evaluate the stability of slopes around the region. Secondly, Oman has signed various international agreements that regard to human safety. Strict legislations are used to ensure the integrity of engineering practice in the area. Mainly, the aspect of workers' safety is handled critically. The rights of employees cover the obligation to ensure worksite safety and the efficiency of operations. In the event of disasters, thorough investigations are done to unravel the underlying facts that lead to the occurrence of particular land and rock slides.
Engineering concepts are used in slope protection projects. Landslide mitigation is important in preventing the occurrence of this disaster. This involves the application of artificial means to promote the stability of slopes. Artificial landslide mitigation is achieved by creating balances between shear strengths and stresses. In most cases, slope characteristics are altered to achieve desirable attributes that foster slope stability.
Figure 1: The design of a slope protection project in Muttrah, Sultanate of Oman.
Many reinforcement measures are used to promote slope stability. This is achieved through the application of metallic materials to reinforce the shear strength of rock surfaces. During construction, this technology is critical in mitigating the occurrence of stress release when topographies are manipulated artificially. Metal elements may include solid anchors and nails.
Figure 2: The stabilization of a hill slope using metallic anchors.
Conclusion
In the Sultanate of Oman, many people have died in mountain mass movements. This includes workers operating in steep mountainous regions. For a long time, land and rock slides have destroyed roads and properties that exist in these areas. The application of modern engineering concepts will go a long way in mitigating the occurrence of this disaster.
Bibliography
Alexander, D., 1992. On the causes of landslides: Human activities, perception, and natural processes. Environmental geology and water sciences, 20(3), pp.165-179.
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Dai, F.C., Lee, C.F. and Ngai, Y.Y., 2002. Landslide risk assessment and management: an overview. Engineering geology, 64(1), pp.65-87.
Kwarteng, A.Y., Dorvlo, A.S. and Vijaya Kumar, G.T., 2009. Analysis of a 27‐year rainfall data (1977–2003) in the Sultanate of Oman. International Journal of Climatology, 29(c 4), pp.605-617.
Sonmez, H. and Ulusay, R., 1999. Modifications to the geological strength index (GSI) and their applicability to stability of slopes. International Journal of Rock Mechanics and Mining Sciences, 36(6), pp.743-760.
