<![CDATA[AbstractResearch Location, Workshop of PT MHB is located on JL. Soekarno Hatta Km. 13. Research is aimed to investigate root causes of retaining wall failure, and intended to find fact in order could be designed new precised and safe retaining wall. Field activity was conducted at area of PT. MHB workshop, and Laboratory test was conducted at PT. Geosindo Samarinda. This research involved field observation, topographic mapping, cone penetration test, standard penetration test, undisturb sampling, measurement of soil unit weight, atterberg limit, sieve and hydrometer test, unconfine compression est and direct shear. And virtual simulation was conducted using Geostudio student version and Xstable. Although in normal condition unsaturated soil has g = 1.75 g/ cm3 , f = 16o, c = 0.296 kg/cm2 showing safe slope with safety factor 1.63 to 1.64 but in increasing water content gsat = 2,02 g/cm3 internal friction angle reaches 0 o and cohesionless where water content reach 56% safety factor will decreases to 0.452. Retaining wall failure phase I occured when water content reached 56% (saturated condition), so that liquid limit was passed and soil turn to liquid (liquifaction) that caused soil creep and flow and push retaining wall in to failure. Later on in other rainy season while soil naturally more compacted slope become unstabil because increasing water content and unit weight of soil that caused circular landslide with cohession of soil more than zero.Keywords: Factor of Safety, Shearing Resistance, LiquifactionAbstrakLokasi penelitian adalah Workshop PT. MHB berada di Jl. Soekarno Hatta Km.13. Maksud penelitian menyelidiki penyebab kegagalan retaining wall dengan tujuan agar dapat dilakukan kembali upaya desain ulang retaining wall yang tepat dan aman. Kegiatan penyelidikan lapangan dilakukan di komplek workshop PT. MHB, dan pengujian laboratorium di lakukan di PT. Geosindo Samarinda. Metodologi penelitian yang dipakai adalah: observasi lapangan, pemetaan topografi, cone penetration test, standard penetration test, undisturb sampling, pengukuran berat volume, atterberg limit, sieve and hydrometer test, unconfine compression test dan direct shear. Dan virtual simulation menggunakan Geostudio student version dan Xstable. Walaupun pada kondisi normal tanah tidak jenuh air mempunyai g = 1.75 g/ cm3 , f = 16o, c = 0.296 kg/cm2 menujukan kondisi slope aman FK lokal 1,63 dan FK global 1,64 namun dalam kondisi jenuh air gsat = 2,02 g/cm3 gudut geser dalam f mendekati 0 o dan kohesi c mencapai 0 dimana kandungan air mencapai w = 56 % akan terjadi pergeseran nilai FK sampai 0.452 . Keruntuhan retaining wall phase I terjadi ketika kandungan air mencapai 56 %, sehingga batas cair tanah terlampaui dan terjadi liquifaction yang mengakibatkan aliran dan rayapan tanah yang mendorong retaining wall runtuh. Kemudian terjadi longsoran lagi (phase II) disebabkan oleh g tanah yang meningkat akibat air hujan dengan kohesi lebih besar dari 0, sehingga terjadi longsoran guling yang dicirikan bidang longsor yang berbentuk circular.Kata Kunci: Faktor Keamanan, Kuat Geser, Liquifaction]]>
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