Specifying the real value of volume loss (V _L) and its effect on ground settlement due to excavation of Abuzar tunnel, Tehran

Volume loss (V _L) is one of the most important geological and geotechnical features of ground settlement due to tunneling. This parameter is mostly influenced by engineering geological properties of the tunnel route. Preceding studies about this parameter have led to suggesting approximate ranges of values that are specified based on engineering geological characteristics of the tunnel route and assigned for V _L in semi-empirical methods. According to those studies, a wide range of quantities are assigned for volume loss, and considering other related factors, the evaluated corresponding ground settlements also have a wide range; then it is necessary to specify a definite quantity for V _L. In the present study, this parameter has been evaluated using several methods including the semi-empirical method, numerical method, and real values obtained via performing back analysis on real settlements. The real values of V _L were determined based on the field-measured settlements, obtained using instrumentation and monitoring methods, and performing back analysis according to other required parameters. In the next stage, the obtained results have been compared, and finally the real value of V _L has been specified. According to the numerical modeling performed using FLAC 3D code, the resulting values for V _L were 0.55–0.64 %. Measured maximum settlements of ground (S_max), induced by Abuzar tunnel excavation, were on average 8–12 mm, thus the corresponding volume loss was calculated as about 0.34–0.62 %. Finally, considering the other factors affecting the volume loss, the value of V _L = 0.5 ± 1 % was specified as the real value of volume loss, which occurred during Abuzar tunnel excavation.