Kajian Teknis pada Rancangan Model Geoteknik Low Wall Failure Blok 07-12 Pit Elang PT. Manambang Muara Enim Kabupaten Muara Enim Provinsi Sumatera Selatan

Abstract

abstrak. Failure occur in the low wall opening area Block 07-12 Pit Elang PT. Manambang Muara Enim. The effect of water, geological structure, and uncertainty on the interpretation of the value of the safety factor from the previous recommendation were identified to be the cause of the failure. The existence of 590,000 tons of coal in the opening of the low wall based on the mining design in 2019, necessitates a handling effort by redesigning the geotechnical model.

Technical studies on the design of this geotechnical model are focused on simulating slope stability to meet Bowles (1989) criteria with a safety factor value (> 1.25). In achieving the real model, three-point problems are used in determining groundwater conditions, kinematic analysis to determine the orientation of weak fields and types of landslides, as well as the Generalized Hoek & Brown empirical approach in analyzing the mechanical properties of rocks.

The back analysis of the opening model before the landslide has a safety factor value of 1.127 (critical), caused by the inaccurate determination of the slope design under conditions of water infiltration and decreasing rock strength resulting from deformation characterized by fractures on rocks with normal faults that intersect, common heights and bedding field oriented in the direction of the low wall openings.

The recommended technique is single slope geometry 25⁰, 15⁰, and 35⁰ with a height of 5 m for sandstone, coal, and claystone. Overall slope is made by lowering the upper face on the overall bench to the coal roof D seam.

Keyword : Failure, Deformation, Single slope, Overall slope

abstrak Longsoran terjadi pada area bukaan low wall Blok 07-12 Pit Elang PT. Manambang Muara Enim. Pengaruh air, struktur geologi, dan ketidakpastian interpretasi nilai faktor keamanan dari rekomendasi sebelumnya diidentifikasikan menjadi penyebab longsoran. Adanya 590.000 ton batubara pada bukaa low wall berdasarkan desain penambangan tahun 2019, mengharuskan adanya upaya penanganan yaitu dengan melakukan perancangan ulang terhadap model geoteknik.

Kajian teknis pada rancangan model geoteknik ini difokuskan terhadap simulasi stabilitas lereng hingga memenuhi kriteria Bowles (1989) dengan nilai faktor keamanan (>1,25). Dalam mencapai model yang real, digunakan problema tiga titik dalam penentuan kondisi muka air tanah, analisis kinematik guna menentukan orientasi bdang lemah dan jenis longsoran, serta pendekatan empiris Generalized Hoek & Brown dalam menganalisis sifat mekanik batuan.

Analisis balik terhadap model bukaan sebelum terjadinya longsor memiliki nilai faktor keamanan 1,127 (kritis), diakibatkan oleh ketidaktepatan penetapan desain lereng pada kondisi adanya infiltrasi air dan menurunnya kekuatan batuan hasil deformasi yang dicirikan oleh rekahan pada batuan dengan sesar normal yang berpotongan, arah umum kekar serta bidang perlapisan yang berorientasi searah bukaan low wall.

Teknis yang direkomendasikan berupa geometri single slope 25⁰, 15⁰, dan 35⁰ dengan tinggi 5 m untuk batupasir, batubara, dan batulempung. Overall slope dibuat dengan menurunkan upper face pada overall bench hingga roof seam D batubara.

Kata kunci: Failure, Deformation, Single slope, Overall slope