STUDI MEKANISME LONGSORNYA KEMBALI (RE-SLIDING) BREKSI VOLKANIK DI ATAS BATULEMPUNG ; STUDI KASUS LONGSORAN DI DAERAH GOMBEL, KOTA SEMARANG, JAWA TENGAH

• Main Author: Iskandar, Anan
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69666
• Institution: Institut Teknologi Bandung

The studied area is located at Gombel, southern part of Semarang area of Central Java. This area has been often suffering landslide problems, and it was noted that in the year of 2002 and 2006 a large landslide happened which caused a big damage. The studied area consist of claystone of Kerek Formation (Tmk) and marls of Kalibeng Formation (Tmpk). These two formations are uncorformable overlain by volcanic breccia of Kaligetas Formation (Qtkg) and Conglomerates of Damar Formation (Qtd). Fault developed in the studied area has east-west orientation which continues to the southeast. Based on field observation, it was clear that landslides frequently occurred within the claystones or at the contact between claystones and volcanic breccia. These landslides can be classified as single slide and multiple slides type. Meanwhile, the types of movement of the landslides are sliding and toppling. The landslides have northwest-southeast distribution with the landslide direction to the southwest. It was identified that these landslides are re-sliding of the old ones and retrogressively developed. Based on engineering properties analysis showed that the rocks are consisting of silty clay with high plasticity or classified as CH (clay high plasticity). Meanwhile, result of X-Ray Diffraction analysis, it was found that some of claystone have clay mineral of montmorillonite. This mineral is known as swell prone mineral. The landslide in the studied area are usually caused by the increase of groundwater level or saturation in volcanic breccia which are lower boundary of the impermeable claystones. As consequences, the rocks suffered high pore pressure which could reduce their shear strength. Another factor that influences the landslides