Problem of High Embankment on Clay Shale at Semarang-Ungaran Toll Road STA 5 +500 TO 6 +300

Abstract

Most Tol Roads between Semarang and Bawen lies on the Kaligetas formation in which the main rock consist of volcanic breccia, lava flow tuff, tuffaceous sandstone, and claystone. The small part that passes througn the formation of kerek, consist of claystone, marl, conglomerate, volcanic brecciaand limestone. Claystone, young-old gray contain fozzilized forams and molluscs. A large landslide occured in Susukan Village Semarang District Sta. 5 +500-6 +000 in 1974, where more than 80 houses collapsed, and nearly one village relocated to the safe area. it was found that there is transport rock (Material coluvium) as tick as 6.0 to 8.0 m that will be filled about 15.0 to 25.0 m, and under that location there are expansive clay shale. Topography under /on the left side of the embankment foot is quite. To avoid erosion and creep landslide, the installation of bored pile was carried out. In Sta. 5 +625 - 5 +750 there are 2 small hills, a rock breccia with a thickness of more than 12.0 m and be used as a counter-weight, so that bored piles were not installed. based on the inclinometer observations on the embankment with a height of about 7.0 m there are ground motion at a depth of -10.0 to -15.0 m and review design was conducted. Slope stability analysis was conducted by back analysis technique, based on field position sliding inclinometer monitoring result. Asuming that during a crack in the embankment, safety factor value FK = 1, then with a high embankment which is planned, bored pile design can be determined. By using the X-STABLE and Plaxis programs to the depth of field of sliding -10.0 m to -15.0 m of the subgrade, the shear force against bore pile was (Pmax) = 189.3 to 231.3 tons/m and the moment (Mmax) = 946.5 to 1156.5 tm/m. Referring to Chang's method, the area of sliding -10.0 m to -15.0 m, the length of bored pile is about 25 m to 31.0 m. At the end of the accumulation of inclinometer monitoring that has been conducted, due to extreme rain occurs a few days, saturation and increasing pore pressure occured on the embankment and yield crack on the road. Inclinometer monitoring result of sliding occurs at a depth of -16.0 m and ground water level increased from -9.00 m to -3.00 m.