I Gde Budi Indrawan’s scientific contributions

The purpose of the Jatinegara Dam is to irrigate agricultural land in the villages of Cacaban dan Rambut. Investigations involving engineering geology have been carried out, however a slope stability analysis is still required. The purpose of this study is to evaluate the stability of the slope at the outlet portal of the Jatinegara Dam using the Bishop Simplified and Morgenstern-Price limit equilibrium methods (LEM). These methods analyze the stability of the slope under both static and seismic loading, and the results are used to determine the value of Safety Factor (SF). The primary source of data was rock and soil evaluations taken from the surface and rock cores of the outlet tunnel portal. Rock quality assessment based on Geological Strength Index (GSI) and laboratory testing. The outlet portal slope consists of volcanic breccia, sandstone, and siltstone with quality ranges from very poor to good. The results of LEM show that the outlet portal slope is in stable condition under both static and seismic loads, as per the SNI 8460:2017 standards.

The stability of tunnel portal slopes is crucial to ensure the safety and continuity of tunnel construction projects. This study evaluates the slope stability at the tunnel inlet portal on Jl. Sultan Alimuddin - Jl. Kakap in Samarinda, East Kalimantan, using the Limit Equilibrium Method (LEM). The geotechnical investigation included interpreting borehole data, sampling soil and rock, and conducting laboratory tests to determine parameters such as cohesion, internal friction angle, and unconfined compressive strength. Slope stability analysis was performed using the Bishop Simplified and Morgenstern-Price methods under static and dynamic conditions with Slide 6 software. The results show that the slopes at this location are generally safe, with safety factors of 1.278 and 1.166 for the Bishop method, and 1.336 and 1.225 for the Morgenstern-Price method under static and dynamic conditions, respectively. Although the obtained safety factors indicate stable slopes, additional reinforcement such as soil nailing, rock bolts, or shotcrete is recommended to meet the higher safety standards suggested by SNI 8460:2017. This study demonstrates that the tunnel portal slopes have a good safety factor but require regular monitoring and maintenance to ensure long-term stability, especially considering the complex geological conditions and climate variability in the area.

Slope stability must be analyzed to prevent potential slope collapse by considering the safety factor in the design. In this research, the inlet of the Matenggeng Dam diversion tunnel was analyzed under static load and seismic load using Morgenstern-Price and Spencer’s Limit Equilibrium Method (LEM). The analysis used parameter data obtained from surface geological mapping, evaluation of underground core samples, evaluation of rock quality using the GSI system, and laboratory tests on rock samples such as the Uniaxial Compressive Strength test and Index Properties test. The intake slope consists of andesite, conglomeratic sandstone, and conglomerate rock material with fair to good rock quality. The results of the slope stability analysis are safe as the safety factor value meets the specifications of the Indonesian National Standard SNI 8460: 2017.

Pasir Kopo dam will be built to develop infrastructure facilities in Banten province. This dam is supported by a twin diversion tunnel, which is a horseshoe-shaped tunnel with lengths of 413,11 meters and 433,10 meters. As the stability of the natural slope is disturbed by excavation activity for tunneling, slope stability analysis is required to ensure safety during construction and use. The geological engineering in this research was obtained by identifying the core rock sample from BT 01, BTA 01, and BTA 02 by PT. Mettana in 2017-2018 to get information about lithology, level of weathering, and Geological Strength Index (GSI). The index properties test and the mechanical properties are used as material parameters for slope stability. This paper will focus on the slope stability analysis of the diversion tunnel inlet using the limit equilibrium method, namely Bishop’s method and Morgenstern-Price’s method under static and dynamic loads. The research location geomorphology is a hill formed by volcanic eruptions and can be dePined as a rather steep pyroclastic Plow ridge. The diversion tunnel inlet consists of fair-quality lapilli tuff and tuff with moderate weathering. The safety factor using the Bishop simpliPied method is 3,731 under static load and 2,567 under earthquake load. The safety factor using the Morgenstern-Price method is 3,748 under static load and 2,561 under earthquake load. Both methods indicate that the slope stability of the diversion tunnel can be categorized as stable according to the requirements of the Indonesian National Standard (SNI) 8460:2017

The Public Works and Spatial Planning Office of Samarinda City is currently carrying out road tunnel construction in Selili Village, Samarinda Ilir District, East Kalimantan Province. The rock mass classification, excavation, and support system used is the Rock Mass Rating (RMR). The methods are used to consider uncertain geological conditions. Data was obtained from the results of surface and subsurface geological mapping, assessment of core drill samples located at the tunnel centerline, and laboratory testing. RMR is vital for understanding geological challenges, optimizing tunnel design, and ensuring safety and efficiency throughout the construction process. Surface geological mapping and core drill sample assessment were conducted to Assess the integrity of the rock structure along the road tunnel line. The drill core samples’ mechanical and physical characteristics of the whole rock were obtained through laboratory testing. The tunnel site consists of a sandstone unit and a siltstone unit with rock mass classifications of fair, medium, and poor. Tunnel excavation is designed using a sequential excavation method, including top heading and benching construction methods. The distance between the top-heading excavation face and the bench excavation face is 12 m, and the initial support must be installed immediately after each stage of tunnel excavation is carried out; the tunnel is also divided into 7 zones based on RMR recommendations: 4 areas with The rock structure classification 3, 2 areas with rock mass class 2, and 1 area with rock mass class 4. The tunnel excavation technique used is the top and bench method with parallel buffers 1-1.5 m from the tunnel face for class 4 areas and 1.5-3 m from the tunnel face for class 3 areas, while class 2 areas can be excavated the entire tunnel face at once. The suggested support system, based on the RMR value, consists of rock bolts that are 4-5 m long, spaced 1-1.5 m apart, and have a shotcrete thickness of 10-15 cm throughout the tunnel.