PENGARUH KERAPATAN TANAH PASIR KALI OPAK PLERET YOGYAKARTA TERHADAP POTENSI LIKUIFAKSI BERDASARKAN UJI SHAKING TABLE

Bimawijaya  Laia

Bimawijaya Laia STKIP Nias Selatan

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Keywords: likuifaksi, uji shaking table, kerapatan relatif, rasio peningkatan tegangan air pori

Abstract

Likuifaksi adalah suatu peristiwa berubahnya sifat tanah dari keadaan padat menjadi keadaan cair, yang disebabkan oleh beban siklik pada saat gempa terjadi sehingga tekanan air pori meningkat melebihi tegangan efektif tanah. Likuifaksi umumnya terjadi di lapisan sedimen granular dengan tingkat kerapatan rendah. Pengaruh kerapatan relatif tanah terhadap mekanisme likuifaksi dapat diketahui dengan melakukan uji eksperimental menggunakan shaking table. Parameter yang digunakan untuk menentukan tanah yang mengalami likuifaksi adalah rasio peningkatan tegangan air pori (r_u). Jika r_u ≥ 1 maka likuifaksi dapat terjadi, sedangkan jika r_u < 1 maka likuifaksi tidak dapat terjadi. Tanah pasir Kali Opak Pleret yang digunakan sebagai objek dalam penelitian memiliki kerapatan sebesar 24,35%. Hasil evaluasi uji shaking table menunjukkan bahwa potensi likuifaksi terbesar terjadi pada kerapatan relatif tanah 25% untuk percepatan gempa 0,4g dan terendah tercatat pada kerapatan relatif tanah 55% untuk percepatan gempa 0,3g. Penurunan muka tanah terbesar terjadi pada kerapatan relatif 25% yakni 4 cm dan terendah pada kerapatan 55% sebesar 0,53 cm. Pengujian ini menunjukkan bahwa pada tanah pasir Kali Opak Pleret dengan kerapatan relatif tanah 25% dan 35% berpotensi likuifaksi, dan pada kerapatan relatif tanah 45% dan 55% tidak berpotensi likuifaksi.

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