WEAK ZONE DETERMINATION IN A TUNNEL USING HVSR METHOD

• Main Author: Hartsa Naufal, Haris
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/51727
• Institution: Institut Teknologi Bandung

Tunnel is an infrastructure that connects two places via underground. Because of the nature of it being underground, some problems might occur, such as tunnel collapse. Such disaster might cause lots of casualties. In order to prevent such event happens, a monitoring to check the reliability of a tunnel is a necessity. Therefore, geophysical method could help solve that problem. One of many geophysical methods that may work is microtremor method. This method utilize seismic ambient to figure what is below the ground. To test the reliability of this method, a test was conducted in a tunnel in ITB. This tunnel connects ITB main campus and Campus sports ground. This tunnel also lays under a main road which many traffic travels on that road. The raw data was acquired by placing measuring station on the wall side of the tunnel and put 6 meters space between stations. Measuring station was also placed on the surface ground right at station’s coordinate inside the tunnel. After that, the raw data was processed with program called Geopsy to reduce the noise of the data and also to acquire HVSR curve, which is essential in this research. After acquire that HVSR curve and make sure every curve considered reliable, the peak frequency and peak amplitude was extracted and then, K index was gathered. The peak frequency and peak amplitude also K index of every station then was plotted to make a contour map which. Then, a 3D model of peak frequency, peak amplitude, and K index was build from that contour map. Also, from the HVSR curve, inversion was done to get 1D Vp and Vs velocity model. As the result, there were some anomalies found. Some positive anomalies were found in station number 9 to 12, while negative anomalies were found in station number 4 and 5. Those anomalies were confirmed from all models. The positive anomalies were caused by reinforced part of the tunnel which the function is to take most of the stress produced by the main road and traffics that travel on it. Mean while, the negative anomalies were caused by part of the tunnel that was not reinforced and closer to source of the stress than any other part that was not reinforced which also make those parts more vulnerable.