Posted: November 15th, 2022

Slope stability analysis report

Introduction
Generally, this slope stability analysis report gives a detailed analysis of the characteristics of a slope. In this type of analysis, a wide range of data is required including data on the soil characteristics, groundwater depth as well as the technical data on any surrounding developments (Fellenius, 2006). The groundwater levels are dependent on a number of geotechnical factors including: hydrogeological factors, soil permeability, soil geology as well as rainfall data. A combination of this data gives a detailed outline of the likely scenario on the slope and the possibility of the slope undergoing deformation in case of a failure (Ireland, 2004). There are several techniques that are available for the analysis of the stability of a slope whereby each one of them has its own unique strengths and weaknesses. In this analysis, focus shall precisely be on the Bishop simplified method (Chowdhury, 2008).
Report objectives
The main objectives of this analysis are:
To determine the factor of safety of the slope
To determine the possibility of deformation as a result of failure
To investigate possible solutions to the current state of stability for technical engineering operations
Technical description of the slope
Based on the information provided about the slope conditions, the current slope is inclined at an angle of 60 on the horizontal. It extends for a distance of about 150 m to the left of the site boundary. From the geotechnical data provided, the soil is mainly made up of clay which extends to a depth of 20 m. However, this soil is unconsolidated and is prone to seepage and can easily undergo failure. The stratum dips towards the southeast of the region but there are no distinct features that can be used to identify the nature of the bedding. The water table that marks the level of the groundwater is located between 2 and 3 meters below the ground level and it has been seen to vary depending on the seasons during different times of the year. Laboratory tests from soil samples obtained from boreholes in this area indicate that the bulk weight of the soil is approximately 19 kN/m3 while the shear strength of the soil ranges between 100 and 160 kpa for the under drained soil.
Analytical procedure
In the current situation, the Bishop simplified method is very appropriate. This method requires that the slope is divided into vertical slices which can then be computed independently of each other. The factor of safety of the slope is determined through the examination of the contribution of the slope to moving and resistance forces that are provided by each slice. The forces that act on the slope can be said to be the weight of the slice while the side forces denoted by E and X act on the sides of the slices. In order to provide solutions using this method, a number of assumptions are made. First, the effect of the side forces is ignored and the normal force acting on the slope is determined by calculating the weight of the slice in a direction normal to the arc at the midpoint of the arc. The factor of safety is determined through the division of the sum of the moments of maximum resisting forces by the sum of the moving forces. The procedure is repeated for a number of trials until the lowest value of factor of safety has been determined.
Data analysis
N=Wcosα=522.642cos84=54.63097 N
Effective normal force=N-U=Wcosα-u∆Xsecα
=522.642cos84-2X150X1/(Tan 84)=23.0997
Total maximum resisting force T_max=∑▒〖(c^’+σtan∅)∆Xsecα〗
T_max=(0.7856)150/tan84=-12.386 N
Factor of safety=(Sum of moments of maximum resisting forces )/(sum of moments of moving forces)
F=(∑▒〖(c^’+σtan∅)∆Xsecα〗)/(∑▒Wsinα)
F=T_max/(∑▒Wsinα)=-12.386/2390.05=-0.05182
To compute the value of ʌGEO=A/Mʌ=76448.46559/4619.06=0.0604205
Discussion
Based on the results obtained from the analysis of the stability of the slope, the value of F is greater than 1 and this implies that the slope is practically stable along the first slice. The shearing potential of the slope is approximately 40 kpa in this region. Failure in sloppy grounds has the tendency to occur along some preformed lines of weakness and the end result of this is deformation of the slope. The fact that the value of the factor of safety of the slope was -0.05182 means that the slope has a low level of stability. Based on the data obtained from the tests for the soil, the main soil composition is clayey and goes to a depth of 20 m below the surface of the earth. The water table is located between 2 and 3 meters below the surface meaning that below the 3 meter depth, the slope is practically unstable.
Conclusion
Based on the results of the analytical work, there is minimal evidence of the instability of the slope. The values obtained for the factor of safety is -0.05182 and 0.604205 for ʌGEO meaning that the slope is practically stable. The fact that the subsoil is mainly composed of clay and the water table is is located between 2 and 2 meters implies that the region below the 3 meters mark in depth is prone to high levels of seepage and this ground is prone to deformation unlike the region close to the ground which is stable and can be used for construction. As it was indicated in the data from the ground site, there are a quite a number of structures present in this area and most appropriate region for such structures would be the top of the slope.
Recommendations
From the analysis above, there is needed to carry out a number of design changes to improve the stability of the slope. Some of the recommended design changes include:
The structural and geotechnical experts should consider adding fills to the areas that exhibit lines of weakness. This will aid in the improvement of the stability of the foundations of buildings hence minimizing chances of collapsing or sinking.
During construction timber piles or special concrete can be used to stabilize the foundations of the buildings.

References
Fellenius W., (2006), “Calculation of the Stability of Earth Dams”, Trans. 2nd Cong. on Large Dams, Vol 4, p 445.
Ireland, H.O., (2004), “Stability Analysis of the Congress Street Open Cut”, Geotechnique, Vol. 4, p 163.
Chowdhury, R.N., (2008), “Slope Analysis”, Elsevier Scientific Pub. Co., Amsterdam, 423 p.

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