Perencanaan Groundsill Sebagai Bangunan Pengaman Pilar Jembatan Glonggong Madiun Akibat Gerusan Lokal

Wardana, Dhimas Krisna (2024) Perencanaan Groundsill Sebagai Bangunan Pengaman Pilar Jembatan Glonggong Madiun Akibat Gerusan Lokal. Diploma thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Sungai Jeroan, merupakan anak Sungai Madiun di Kabupaten Madiun, mengalami degradasi dan agradasi, terutama di sekitar Jembatan Glonggong. Pilar jembatan menyebabkan lubang gerusan semakin dalam dapat merusak jembatan secara umum. Penanganan diperlukan untuk mengurangi kedalaman lubang gerusan, dan groundsill diusulkan sebagai solusi. Perencanaan groundsill dapat menyebabkan aliran balik, tetapi normalisasi sungai dapat mengatasi hal tersebut. Pembangunan groundsill dengan debit banjir rencana 25 tahun diharapkan dapat mengendalikan gerusan dasar sungai, melindungi pilar dan abutmen jembatan. Rencana ini sesuai dengan debit banjir historis yang pernah terjadi pada Sungai Jeroan dan rekomendasi dari pihak BBWS Bengawan Solo. Pada analisis debit banjir rencana perlu dilakukan analisis luas Daerah Aliran Sungai (DAS) dan tutupan lahan menggunakan program bantu ArcGIS. Analisis debit banjir rencana Q25 tahun digunakan metode Nakayasu sesuai dengan karakteristik DAS Jeroan. Selanjutnya dilakukan analisis hidraulika sungai untuk melihat kondisi penampang Sungai Jeroan existing apakah mampu menampung debit banjir yang direncanakan. Perencanaan tinggi groundsill berdasarkan analisis gerusan lokal akibat pilar yang terjadi. Selanjutnya dilakukan analisis tata letak effektif groundsill berdasarkan kecepatan aliran yang dicoba beberapa alternatif sehingga dipilih reduksi kecepatan terbesar. Mercu groundsill dianalisis menggunakan tiga tipe mercu yaitu mercu ambang datar, bulat, dan ogee lalu dipilih muka air di atas mercu yang terendah. Selanjutnya dianalisis pengaruh groundsill terhadap backwater. Desain mercu groundsill perlu dilakukan kontrol Factor of Safety (FS) terhadap guling, geser, daya dukung tanah fondasi, dan rembesan. Selanjutnya dilakukan anailisis pola aliran dan kecepatan aliran yang terjadi pada kondisi pasca perencanaan dan kondisi Sungai Jeroan existing. Dari hasil analisis gerusan lokal akibat pilar jembatan, diperoleh kedalaman gerusan yang terjadi sedalam 2,7, 1,8 m dan 2,3 m. Groundsill diletakkan pada lokasi paling effektif yaitu STA 0+560. tinggi groundsill direncanakan setinggi 1,8 m dengan lebar mercu 17,20 menggunakan kolam olak tipe USBR III yang menghasilkan panjang kolam olak 10 m. hasil analisis stabilitas groundsill dengan kontrol stabilitas guling, geser, daya dukung tanah fondasi, dan rembesan berturut – turut FSGuling = 1,946 > 1,5, FSGeser = 4,903 > 1,5, Kontrol daya dukung tanah fondasi Q1 = 9,27 t/m2 < 29,74 t/m2 dan Q2 = 3,56 t/m2 < 29,74 t/m2 dan aman terhadap rembesan 0,000016 m3/det < 4,18 m3/det. Groundsill setinggi 1,8 m mampu mereduksi kecepatan aliran sebesar 44,41% pada kondisi base flow dan 2,09% pada kondisi muka air banjir Q25 tahun.
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The Jeroan River, a tributary of the Madiun River in Madiun Regency, is experiencing degradation and aggradation, especially around the Glonggong Bridge. The bridge pillars cause scour holes to deepen, which can damage the bridge in general. Treatment is needed to reduce the depth of the scour hole, and a groundsill is proposed as a solution. Groundsill planning may cause backflow, but river normalization can overcome this. The construction of a groundsill with a 25-year plan flood discharge is expected to control riverbed scour, protecting the bridge pillars and abutments. This plan is in accordance with the historical flood discharge that has occurred in the Jeroan River and recommendations from the Bengawan Solo BBWS. For analysis of the planned flood discharge, it is necessary to conduct an analysis of the watershed area and land cover using the ArcGIS software. The 25 year planned flood discharge (Q25) is analyzed using the Nakayasu method, according to the characteristics of the Jeroan watershed. Next, a hydraulic analysis of the river is conducted to determine whether the current cross section of the Jeroan River can accommodate the planned flood discharge. The design of the groundsill height is based on the analysis of local scour caused by piers. An effective placement analysis of the groundsill is then conducted based on flow velocity, testing several alternatives to select the one with the greatest velocity reduction. The groundsill crest is analyzed using three types of crests flat, rounded, and oge the one with the lowest water level above the crest is selected. The impact of the groundsill on backwater is then analyzed. The groundsill crest design needs to be checked for Factor of Safety (FS) against overturning, sliding, bearing capacity of the foundation soil, and seepage. Finally, an analysis of the flow pattern and velocity is conducted for both the post-planning condition and the existing condition of the Jeroan River. From the analysis of local scour caused by bridge piers, the scour depths were found to be 2,7 m, 1,8 m, and 2,3 m. The groundsill is to be placed at the most effective location, which is STA 0+560. The planned height of the groundsill is 1,8 m with a crest width of 17,20 m, using a USBR III-type stilling basin, which results in a basin length of 10 m. The results of the groundsill stability analysis, considering the stability against overturning, sliding, bearing capacity of the foundation soil, and seepage, are as follows: Factor of Safety against overturning (FS_overturning) = 1,946 > 1,5, Factor of Safety against sliding (FS_sliding) = 4,903 > 1,5, bearing capacity control of the foundation soil Q1 = 9,27 t/m² < 29,74 t/m² and Q2 = 3,56 t/m² < 29,74 t/m², and safe against seepage 0,000016 m³/s < 4,18 m³/s. A groundsill with a height of 1,8 m can reduce flow velocity by 44,41% under base flow conditions and 2,09% under the Q25 floodwater level condition.

Item Type:	Thesis (Diploma)
Uncontrolled Keywords:	Jeroan Riverd, Bridge Pillar, Local Scour, Groundsill, Sungai Jeroan, Pilar Jembatan, Gerusan Lokal
Subjects:	T Technology > TC Hydraulic engineering. Ocean engineering > TC167 Dams, reservoirs T Technology > TC Hydraulic engineering. Ocean engineering > TC175.2 Sediment transport T Technology > TC Hydraulic engineering. Ocean engineering > TC555 Spillways. Energy dissipation. Hydraulic jump.
Divisions:	Faculty of Vocational > Civil Infrastructure Engineering (D4)
Depositing User:	Dhimas Krisna Wardana
Date Deposited:	15 Aug 2024 08:47
Last Modified:	15 Aug 2024 08:47
URI:	http://repository.its.ac.id/id/eprint/112540

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