Abstract
This paper presents design results of the tunnel portal slopes at the Tanju Dam, Dompu, West Nusa Tenggara. The objective of this research was to analyse the stability of the tunnel portal slopes using circular failure chart (CFC) method, limit equilibrium method (LEM), and finite element method (FEM). Input parameters were obtained from drill core evaluations and laboratory tests. By considering the rock mass rating (RMR) values of rock masses, which are categorized as class II, at the two slopes, adjustments for the cohesion and inner friction angle values are made. The inlet slope (IL) have cohesion values of 350 kPa and 40º inner friction angle and the outlet slope (OL) have cohesion values of 400 kPa and 45º inner friction angle. The CFC method shows that the IL and OL have safety factor (FS) values of 3.5 and 3.44, respectively. The LEM shows that the IL and OL have the FS values of 3.69 and 3.65, respectively. Meanwhile, the FEM shows that the IL and OL have FS values of 4.78 and 4.79, respectively. The stability analysis results indicate that designed slopes are stable.
Highlights
The study location is carried out at the drainage tunnel construction site of tanju dam
By considering the rock mass rating (RMR) conditions of the two slopes that are included in the class 2 category, adjustments for the cohesion value and inner shear angle are made according to (Table 1)
From the calculation of the circular failure chart (CFC) value, the safety factor value is 3.5 on the inlet slope (IL) and 3.44 on the outlet slope (OL), both of which are included in safe conditions
Summary
The study location is carried out at the drainage tunnel construction site of tanju dam. In Administrative, the tunnel is located in the village of Bara, Woja, Dompu District, West Nusa Tenggara Province (Fig. 1). Drainage is built to drain the drain 1.9 m3/sec water to fill Tanju reservoir. This research is purposed to determine the slope stability of the designed slope of the drainage tunnel in Tanju dam. The research area is in morphology with hilly conditions around the tunnel which is a ridge that extends in a relatively northeast-southwest direction, with a ridge length of about 2.2 km and a peak elevation of 320 m [1]. The morphology around the location is quite steep with an angle of 45o – 60o
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