Determining Important Grade of Environmental Risk Factors at Slopes
Abstract
Both, natural and man-made slopes formed for various purposes may cause numerous permanent problems in engineering applications. Therefore, it is important to know composition and mechanical behavior of soil environment leading to geotechnical problems on slope surfaces. The risk analyzes of natural and artificial slopes, realized detailed, can lead to reliable results. Based on those results, it is possible to produce optimal technical solutions with respect to an acceptable risk level. The researches on these subjects give new opportunities to improve the existing knowledge by reviewing them. The main aim of this study is objectively to evaluate the parameters caused slope stability problems. In this regard, the parameters of slope angle, internal friction angle and cohesion of soil, and groundwater level, which are main risk factors for a slope, and should contribute to raise awareness about this issue, were investigated.
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Introduction
Surfaces that are oriented horizontally at a certain angle are defined as slopes. If angle of earth surface is great enough, soil moves downward due to gravity. Thus, slope loses its stability and this event caused an environmental risk situation. In order to assess the environmental risk of slopes, it is necessary to know the safety factor of natural slopes, on which are frequently encountered in the natural ear surface, excavation slopes and slopes compacted as controlled against landslide. The all factors affecting displacements need to be considered for a slope, which the environmental risk ratio (slope safety) will be determined. The safety of soil structure is often defined by a parameter called the safety factor (the environmental risk factor). This parameter can be described as the ratio of strength of soil to the load applied to it. Since this is a mathematical term, which represents the stability of the structure examined, this ratio varies based on the shear strength and stresses examined in the slope stability. A number of safety factor (environmental risk factor) definitions are available in engineering literature. The safety factor is a ratio of resistive forces along the sea surface to the shear forces; of the existing shear strength of soil along the potential shear surface to the mean shear stresses; and is a factor that the shear strength parameters decrease to maintain slope at limit equilibrium condition along a specific shear surface.
Conclusion
Series of numerical analysis by using finite element method (Plaxis 2D) [14] were performed to investigate the effect of a change of cohesion, internal friction angle, slope angle and groundwater level on the safety factor of slope failures. From the data and assessments presented in this paper the following conclusions can be drawn:
Based on increasing of slope angle, the safety of slope against landslide (failure of slope) decreases. An increasing in the slope angle of range from 30 to 400 leads to an average 28% reduction in the safety factor.
It was determined that the safety of slope against to failure decreases depending on the increment of the internal friction angle. An increase of the internal friction angle ranging from 300 to 430 causes an increment in the safety factor as per 39%.
The enhancement of cohesion value of soil forming a slope causes significantly the safety of slope against to failure. An increase of the cohesion ranging from 0.500 to 1.500 kN/m2 leads to an increment in the safety factor as per 72%.
In case of lowering groundwater level from top of the slope, there is no significant change in safety factors up to a certain depth (0.20 m from the top of slope), and distinct changes in safety factor occur from 0.2 meter by deepening the ground water level. The relationship between the safety factor and the groundwater level has an asymptotic with strong correlation coefficient.