Evaluasi Kondisi Geologi Teknik dan Analisis Kestabilan Zona Portal Terowongan Jalan Tol Yogyakarta - Bawen Seksi 5 Jalur Temanggung - Ambarawa
Daniel Tamado, Ir. Gde Budi Indrawan, S.T., M.Eng., Ph.D., IPM.; Dr. Fahmi Aldiamar, S.T., M.T.
2024 | Tesis | S2 Teknik Geologi
Terowongan
Jalan Tol Yogyakarta - Bawen Seksi 5 merupakan infrastruktur yang mendukung
kepentingan nasional untuk meningkatkan konektivitas dan pertumbuhan wisata
nasional seperti Ambarawa, Magelang, Borobudur, dan Yogyakarta. Secara
administrasi, lokasi rencana terowongan terletak di Kecamatan Grabag, Kabupaten
Magelang, Provinsi Jawa Tengah. Berdasarkan perencanaan yang telah
dilaksanakan, kondisi geologi teknik hanya didasarkan oleh kondisi geologi
regional serta masih terbatasnya pengujian sifat properties dan mekanik.
Mengingat konstruksi zona portal merupakan pekerjaan yang sulit serta belum
dilakukannya penyelidikan geologi teknik yang lebih detail, evaluasi kondisi
geologi teknik dan analisis kestabilan zona pertal secara numerik diperlukan.
Pemetaan
geologi dilakukan pada lokasi penelitian dengan skala 1 : 12.500 dengan luas
area penelitian sebesar 4 km2. Berdasarkan hasil analisis kondisi
geologi dan tingkat pelapukan, zona portal terowongan berada pada satuan tuf
dan breksi tuf lapuk sangat tinggi. Namun, berdasarkan evaluasi penampang
geologi, andesit hadir sebagai satuan tambahan yang berada di bawah elevasi
terendah terowongan. Berdasarkan hasil analisis geomorfologi, zona portal
terletak di satuan perbukitan vulkanik berlereng curam. Zona portal Outlet
Terowongan A, yang mempunyai kemiringan 190, merupakan zona portal
yang mempunyai overburden yang paling tipis dan dapat mewakili zona
geologi paling lemah dalam analisis kestabilan zona portal. Selain itu, berdasarkan
kondisi air tanah, zona portal outlet Terowongan A berada pada kedalaman 6 - 18
m dari permukaan.
Yogyakarta -
Bawen Toll Road Tunnel Section 5 is an infrastructure that supports national
interests to improve connectivity and growth of national tourism such as
Ambarawa, Magelang, Borobudur, and Yogyakarta. The road tunnel was planned in
Grabag District, Magelang Regency, Central Java Province. Based on the detailed
engineering design report, geological conditions were designed based on consideration
of regional geological conditions. Moreover, testing of properties and
mechanical properties was not detailed. Since construction of the portal zones
were difficult, this research was needed to give detailed and comprehensive
geological condition resulting more precise stability analysis.
Geological
mapping was carried out at the research location with a scale of 1: 12,500 with
a research area of 4 km2. Based on geological condition, the portal
zone of the tunnel consisted of extremely weathered tuff and tuff breccia. Moreover,
andesite was identified as an additional which placed below the lowest
elevation of the tunnel. Based on geomorphological analysis, the portal zone was
located at steep-sloped volcanic hills. The portal zone of outlet Tunnel A,
which had a slope of 190, had the lowest overburden and can
represent the weakest geological zone in the portal zone stability analysis. In
addition, the outlet portal zone of Tunnel A had the ground water table at a
depth of 6 - 18 m from the surface.
Based
on the results of empirical and numerical analysis, the tunnel required arch
reinforcement with a thickness of 40 cm; side wall with a thickness of 40 cm;
invert with a thickness of 50 cm; steel support H-Beam 200 x 200 with a
distance between steel supports of 1 m; shotcrete with a thickness of 25 cm;
12,5 m-long face bolt; 12,5 m-long forepiling, and dewatering. Secant piles are
needed at the beginning of the construction of the portal zone.
Kata Kunci : Terowongan Jalan, Kestabilan Zona Portal, Analisis Empiris, Analisis Numerik, Sistem Perkuatan