Karakteristik Geologi Teknik Lokasi Konstruksi Terowongan Jalan Tol Cisumdawu (Cileunyi-Sumedang-Dawuan), Provinsi Jawa Barat

WAHYU DWI FEBRIYANTO, I Gde Budi Indrawan, S.T., M.Eng., Ph.D

2018 | Skripsi | S1 TEKNIK GEOLOGI

Terowongan merupakan salah satu bentuk rekayasa konstruksi yang memiliki berbagai fungsi, salah satunya adalah sebagai prasarana transportasi jalan raya. Penelitian dilakukan untuk menentukan karakteristik geologi teknik permukaan daerah sekitar terowongan dan karakteristik geologi teknik bukaan terowongan jalan tol Cisumdawu Jawa Barat. Karakterisasi dilakukan berdasarkan 4 aspek yaitu aspek batuan dan tanah, aspek hidrogeologi, aspek kemiringan lereng, dan aspek geodinamik. Berdasarkan aspek batuan dan tanah, permukaan daerah penelitian terdiri atas 1 satuan litologi berupa breksi vulkanik lapuk sangat tinggi hingga menghasilkan 3 satuan tanah residu yaitu clayey sand, sandy elastic silt, dan sandy lean clay, sedangkan bukaan terowongan tersusun terdiri atas 1 satuan litologi berupa breksi vulkanik lapuk sangat tinggi hingga menghasilkan 3 satuan tanah residu yaitu clayey sand, silty clayey sand, dan sandy silty clay. Swelling potential tanah permukaan tergolong sedang hingga tinggi, sedangkan swelling potential tanah bukaan terowongan tergolong rendah. Terowongan Cisumdawu secara keseluruhan dibangun pada horizon tanah dengan swelling potential rendah. Berdasarkan aspek hidrogeologi, terowongan Cisumdawu dibangun dibawah muka airtanah. Berdasarkan aspek kemiringan lereng, lereng portal terowongan memiliki nilai faktor keamanan lereng sebesar 1,594. Lereng portal terowongan dalam kondisi stabil. Berdasarkan aspek geodinamik, terowongan Cisumdawu memiliki nilai faktor keamanan terhadap cyclic softening sebesar 1,436-2,228 pada bagian tengah terowongan dan 1,926-2,407 pada bagian portal terowongan. Terowongan diinterpretasikan dalam kondisi aman dari potensi cyclic softening oleh gempa tertarget sebesar 6,5 SR dengan probabilitas kejadian sebesar 2% dalam 50 tahun. Nilai Liquidity Index (LI) sebesar 0,105 pada bagian tengah terowongan dan 0,804 pada bagian portal terowongan. Nilai tersebut kurang dari 1 dan diartikan bahwa tanah tersebut relatif lebih stabil dibandingkan tanah dengan nilai LI>1 ketika terjadi gempa. Tanah dengan nilai LI>1 dapat berubah menjadi kondisi likuid ketika terjadi gempa.

Tunnel is a form of construction engineering that has a variety of functions, one of which is a highway transportation infrastructure. The research was conducted to determine characteristics of engineering geology at surface of the area around the tunnel and the geological characteristics of the openings of the Cisumdawu highway tunnel in West Java. Characterization is done based on 4 aspects: rock and soil aspect, hydrogeology aspect, slope aspect, and geodynamic aspect. Based on the rock and soil aspect, surface of the study area consisted of 1 unit of lithology in the form of a very high weathered volcanic breccia which produce 3 units of residual soil: clayey sand, sandy elastic silt, and sandy lean clay, while the tunnel openings composed of 1 unit of lithology in the form of very high weathered volcanic breccia which produce 3 units of residual soil: clayey sand, silty clayey sand, and sandy silty clay. Swelling potential of the surface soil is moderate to high, while the swelling potential of the tunnel aperture is low. The Cisumdawu tunnel as a whole is built on a layer of soil with a low swelling potential. Based on hydrogeological aspect, the Cisumdawu tunnel is built beneath groundwater. Based on the slope aspect, the slope of the tunnel portal has a slope safety factor value of 1,594. The tunnel portal slope is in an unstable condition. Based on the geodynamic aspects, the Cisumdawu tunnel has a safety factor value for cyclic softening of 1,436-2,228 at the center of the tunnel and 1,926-2,407 at the tunnel portal. The tunnel is interpreted in a safe condition from potential cyclic softening by a targeted earthquake of 6,5 Richter Scale with a probability of occurrence of 2% in 50 years. The Liquidity Index (LI) value is 0.105 at the center of the tunnel and 0.804 at the portal of the tunnel. The value is less than 1 and means that the soil is stable compared to the soil with a value of LI> 1 when an earthquake occurs. Soil with a value of LI> 1 may turn into a liquid condition during an earthquake.

Kata Kunci : Terowongan jalan tol, karakteristik geologi teknik, swelling potential, faktor keamanan lereng, faktor keamanan cyclic softening