Analysis Of Right Intake Slope Protection Redesign Of Karangnongko Dam With Geomat Using Simplified Bishop Method And PLAXIS 2D

Abstract

Purpose: This study aims to evaluate slope stability and propose an alternative slope protection method at STA 0+175 of the Karangnongko Dam intake using geomat combined with vetiver grass, following a green construction concept. The research addresses the limitations of the existing geocell design, which, despite meeting SNI 8460:2017, experienced localized slope failures due to high soil shrink-swell potential, intense rainfall, incomplete backfill, and lack of geotechnical data in planning.

Methods: A quantitative approach was employed using primary data from soil investigation at STA 0+175 and secondary data including slope cross-sections, geomat catalogs, vetiver specifications, and existing soil parameters. Slope stability analysis was conducted using the Simplified Bishop Method and PLAXIS 2D software to compare safety factors before and after implementing geomat and vetiver, and to determine the optimal planting spacing of vetiver grass.

Findings: Soil classification indicated high-plasticity inorganic clay (AASHTO A-7, USCS CH). Both analysis methods showed increased slope safety factors meeting SNI 8460:2017 standards. The Simplified Bishop Method yielded a safety factor of 2.134, while PLAXIS 2D gave 2.061. Maximum improvement occurred at a vetiver planting spacing of 40 cm, with safety factors reaching 2.189 (Bishop) and 2.126 (PLAXIS 2D). The difference between the two methods ranged from 2.97% to 4.06%, indicating that both methods can provide a reliable assessment of slope stability.

Practical implication: The results suggest that combining geomat with vetiver grass can effectively enhance slope stability and serve as a practical alternative for slope protection at Karangnongko Dam. Implementing this approach may reduce slope failure risk during construction and provide guidance for future green construction practices in similar environments.