Volume loss assessment for twin tunneling of Klang valley mass rapid transit line 1

Abstract

Ground settlement during tunneling works often affect the above ground structure. This problem may lead to safety risk impact and most worried its possible impact to the surrounding. In this case, the magnitude of ground settlement can be reduced by knowing the sufficient amount of volume loss (VL) to be adopted during the design stage. However, the prediction of optimum VL to be used in the design process relies on the data from previous actual case study area that shares similar ground condition. Although generally it is unusual to obtain homogeneous conditions for every tunneling work, it is preferable to study VL references based on geometrical properties of the same geological area. Realizing unavailability of VL data based on Klang Valley geological conditions, this study aims to provide actual VL magnitude in relation with geometrical properties, within the Klang Valley vicinity. In this research, the actual ground settlements during the twin tunneling works of Klang Valley Mass Rapid Transit Sungai Buloh Kajang Line ( KVMRT SBK ) are monitored. This study focuses on 1.38 km Earth Pressure Balance (EPB) tunnel machine tunneling works from Semantan North Portal to Museum Station. From the actual maximum settlement occurred during tunneling, VL was then evaluated by using back analysis formula proposed by Mair to get the VL percentage. It was found that the average maximum percentage of VL induced both tunneling is less than 1.0%. Comparison on both ground settlement results shows that the second tunnel induced large magnitude of ground movement than that of the first tunnel. This difference can be related to the effect of superposition theory. When twin tunneling works occur in equivalent condition (workmanship, geology, tunnel speed and tunnel type), the superposition effect will take place, and this has resulted in higher VL readings in the second tunnel. Overall, results of VL found in this research are in line with previous research findings where the range of VL for tunneling works falls in the range of 0.2% to 2.0%.