Abstract
The objective of this research is to evaluate the stability of the natural slopes at the inlet and outlet portals of the Bolangu Ulu diversion tunnel, Gorontalo. The natural slopes were considered stable, and therefore slope stability analyses were not carried out previously in the tunnel portal design. The slope stability analyses were carried out using the Circular Failure Chart (CFC) and Limit Equilibrium Methods (LEM). Input data for the slope stability analyses were obtained from field mapping and laboratory testing of soil and rock samples. The results show that the portal slopes consist of diorite and residual soil. Both stability analysis methods yield nearly the same results. The slope at the outlet section had the factor of safety (FOS) values of 1.29 and 1.30 based on the CFC method and LEM, respectively, indicating the slope in a stable condition. However, the slope at the inlet section had the FOS values of 1.01 and 1.07 based on the CFC method and LEM, respectively, indicating the slope in a critical condition. The results suggest that stabilization of the portal slopes, particularly the portal slope at the inlet section, is required to prevent slope failures under static and earthquake loads.
Highlights
Slope failures are a serious geo-environmental hazard that endangers human populations, transportation routes such as highways and rail lines, and civil structures such as dams, buildings, and other structures [1]
This paper presents the results of stability analyses of natural slopes at the inlet and outlet portals of the Bolango Ulu Dam's diversion tunnel using the Circular Failure Chart and Limit Equilibrium Method
Surface samples were collected along every section taken up for stability analysis and collected from the subsurface for different sections chosen for analysis
Summary
Slope failures are a serious geo-environmental hazard that endangers human populations, transportation routes such as highways and rail lines, and civil structures such as dams, buildings, and other structures [1]. Predicting and analyzing the slope's stability is a serious challenge for geotechnical engineers [2]. It plays an essential role for a designer to plan engineering structures, namely dams, tunnels, roads, etc. Slope stability analysis is required to ensure the portal is stable during the construction and operation [3]. It helps the designer to estimate the construction cost that will be involved. Many researchers focused on assessing and developed various methodologies for slope stability
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