KARAKTERISTIK ENDAPAN SEDIMEN PANTAI TERHADAP PENGARUH LIQUIFAKSI DI KAWASAN PESISIR PANGANDARAN DAN SEKITARNYA, KABUPATEN CIAMIS, JAWA BARAT
Abstract
Liquifaksi adalah salah satu bencana geologi yang berhubungan dengan kegempaan, dimana tekanan pori dalam tanah atau sedimen mengalami peningkatan akibat getaran, sehingga mengakibatkan aliran air ke arah permukaan tanah. Liquifaksi umumnya terjadi pada dataran rendah termasuk kawasan pesisir.
Daerah penelitian yang terletak di sekitar pantai Pangandaran dan Parigi terdiri dari endapan lempung, lanau, pasir dan kerikil yang bersifat lepas dan jenuh air, secara regional sering dipengaruhi oleh kekuatan gempa antara 5,5 – 6 skala Richter dengan percepatan tanah antara 150 – 200 mgal. Kondisi seperti ini apabila terjadi gempa sangat memungkinkan untuk terjadi liquifaksi.
Berdasarkan hasil perhitungan secara kuantitatif nisbah pori kritis, tidak semua lokasi penelitian akan mengalami liquifaksi pada percepatan permukaan 150 – 200 mgal. Berdasarkan nilai tumbukan SPT yang dipakai untuk analisis “simplified procedureâ€, daerah penelitian secara umum relatif kecil terhadap bahaya liquifaksi.
Namun demikian berdasarkan korelasi antara sifat mekanik tanah dengan nilai SPT, pada kedalaman 0 – 8 m terdapat lapisan sedimen yang cukup rentan terhadap liquifaksi.
Kata kunci: Liquifaksi,sedimen pantai,Pangandaran
Liquefaction is one of many geological hazards related to an earthquake, where the void ratio pressure in soil or sediment will increase due to the vibration, that causing water flow up to the ground surface. Generally liquefaction is occurred in the low lying areas including coastal zone.
The survey area located in the Pangandaran and Parigi coasts, is consisted of clay, silt, sand and gravel, of loose and saturated properties, generally is frequently influenced by 5,5 – 6 Richter scale of earthquake strength with the ground acceleration between 150 – 200 mgal. The liquefaction will be occurred in this condition if there is an earthquake.
Based on the quantitatively calculation of critical void ratio, the liquefaction at ground acceleration of 150 – 200 mgal will not be occurred at all of the survey area. Based on the number of blows of SPT which is used for simplified procedure analysis, it shows that the study area is less influenced by the liquefaction.
Nevertheless , based on the correlation between soil mechanic properties and SPT value, there is potential liquefiable sediments layer between the depth of 0 – 8 meters.
Key words: liquefaction, coastal sediment, Pangandaran
Daerah penelitian yang terletak di sekitar pantai Pangandaran dan Parigi terdiri dari endapan lempung, lanau, pasir dan kerikil yang bersifat lepas dan jenuh air, secara regional sering dipengaruhi oleh kekuatan gempa antara 5,5 – 6 skala Richter dengan percepatan tanah antara 150 – 200 mgal. Kondisi seperti ini apabila terjadi gempa sangat memungkinkan untuk terjadi liquifaksi.
Berdasarkan hasil perhitungan secara kuantitatif nisbah pori kritis, tidak semua lokasi penelitian akan mengalami liquifaksi pada percepatan permukaan 150 – 200 mgal. Berdasarkan nilai tumbukan SPT yang dipakai untuk analisis “simplified procedureâ€, daerah penelitian secara umum relatif kecil terhadap bahaya liquifaksi.
Namun demikian berdasarkan korelasi antara sifat mekanik tanah dengan nilai SPT, pada kedalaman 0 – 8 m terdapat lapisan sedimen yang cukup rentan terhadap liquifaksi.
Kata kunci: Liquifaksi,sedimen pantai,Pangandaran
Liquefaction is one of many geological hazards related to an earthquake, where the void ratio pressure in soil or sediment will increase due to the vibration, that causing water flow up to the ground surface. Generally liquefaction is occurred in the low lying areas including coastal zone.
The survey area located in the Pangandaran and Parigi coasts, is consisted of clay, silt, sand and gravel, of loose and saturated properties, generally is frequently influenced by 5,5 – 6 Richter scale of earthquake strength with the ground acceleration between 150 – 200 mgal. The liquefaction will be occurred in this condition if there is an earthquake.
Based on the quantitatively calculation of critical void ratio, the liquefaction at ground acceleration of 150 – 200 mgal will not be occurred at all of the survey area. Based on the number of blows of SPT which is used for simplified procedure analysis, it shows that the study area is less influenced by the liquefaction.
Nevertheless , based on the correlation between soil mechanic properties and SPT value, there is potential liquefiable sediments layer between the depth of 0 – 8 meters.
Key words: liquefaction, coastal sediment, Pangandaran
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PDF (Bahasa Indonesia)DOI: http://dx.doi.org/10.32693/jgk.6.3.2008.163