BACK ANALYSIS ON THE SWELLING PHENOMENA IN DIVERSION TUNNEL OF DAM X USING THREE DIMENSIONAL MODELING

• Main Author: Josua Sampetoding, Abraham
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/76807
• Institution: Institut Teknologi Bandung

Dams are important infrastructures in controlling the flow of natural water and fulfilling the community's need for clean water. In the construction of a dam, several supporting buildings are needed. One of them is the diversion tunnel. Diversion tunnels are built to maintain the continuity of the dam construction. However, during the construction, obstacles were found in the construction domain. The diversion tunnel penetrates the lithology in the form of tuffaceous silty claystone. In one of the diversion tunnel’s segments, failure occurred which was preceded by a high convergence at the tunnel sidewall resulting in damage to the initial support system that had previously been installed in the tunnel. This intense deformation is caused by the swelling phenomenon in the clay material that is penetrated by the diversion tunnel construction. The swelling phenomenon causes rock mass decreased strength around the tunnel and creates additional excess pressure on the tunnel walls. In this research, 3-dimensional numerical modeling was made along the segment to determine the condition of the rock mass around the tunnel when failure will occur. The rock mass condition modeling variables are deformation modulus, earth pressure coefficient, and swelling pressure. The result of numerical modeling iterations shows that the strength-reduced zone around the tunnel has a deformation modulus that has decreased to 55 MPa and increased swelling pressure to 0.65 MPa. After that, several models of additional support recommendations will be formulated to overcome the swelling phenomenon that occurs, namely (1) installation of grouted forepoling on the roof with ? 90o accompanied by the addition of an invert beam WF 100 x 100, (2) installation of forepoling on all parts of the roof accompanied by the addition of an invert beam WF 100 x 100, and (3) installation of grouted forepoling on all parts of the roof and tunnel sidewalls accompanied by the addition of an invert beam WF 100 x 100. These handling methods of swelling phenomena sequentially were able to reduce the total convergent values to 2.36 cm, 2.2 cm, and 2 cm. Thus, this study defines that the best treatment for the swelling phenomenon in the diversion tunnel is the installation of grouted forepoling on the roof of tunnel with ? = 90o accompanied by the addition of a 100 x 100 WF invert beam.