Showing 2 results for Instrumentation
Kambiz Hedayatnasab, Ahmad Adib, , ,
Volume 7, Issue 1 (8-2013)
Abstract
Various types of numerical analyses such as Finite Element Method, Boundary Element Method and Distinct Element Method, are used in rock mechanics and in engineering practices for designing rock structures such as tunnels, underground caverns, slopes, dam foundations and so on. In this paper, the results of back analysis of Koohin tunnel which is located in the first section of Qazvin-Rasht railway have been presented. The main purpose of this paper is to perform the back analysis of the mentioned tunnel with the use of numerical models. For modeling the tunnel, two different sections of 30+150 km and 30+900 km are analyzed with FLAC 2D software. To perform back analysis the suitable interval of geomechanical parameters according to the tests which were performed on the core drillings has been determined. With the use of direct method in back analysis, the errors of models have been corrected in several steps and finally the geomechanical parameters in 30+150 km station (Elastic Modulus = 0.3 GPa, Cohesion = 0.21 MPa and Internal Angle of Friction = 34°) and in 30+900 km station (Elastic Modulus = 0.3 GPa, Cohesion = 0.21 MPa and Internal Angle of Friction = 35°) have been achieved. The geomechanical parameters which obtained from back analysis are completely in the chosen interval and compliance with the results of tests which performed on core drillings. On the basis of geomechanical parameters obtained from back analysis with the parameters which used in the design of the tunnel, the tunnel design and the structure method were confirmed.
Milad Masomi Aghdam, Mehdi Hosseini,
Volume 12, Issue 5 (12-2018)
Abstract
In the mechanized boring method, the factors affecting ground surface settlement can be mainly divided into five categories: geometric, geomechanic, boring machines working, operating and management parameters. In urban tunnels bored mainly in shallow soil bed, face pressure can be one of the factors preventing ground settlement. The Line A tunnel in Qom metro project is bored with an EPB (Earth Balance Pressure) mechanized boring machine. The effect of face pressure on ground surface settlement was analyzed in the present study according to five sections of the tunnel. These five sections were selected in different kilometers of the tunnel where settlement gauges were installed and the results could be validated. To investigate the effect of face pressure on maximum ground surface settlement, four pressure levels of 100 kPa, 150 kPa, 200 kPa, and 400 kPa were taken into consideration. These were 1, 1.5, 2, and 4 times of the initial face pressure level, respectively. The ground surface settlement was assessed at four pressure levels using the finite element software, PLAXIS 3D TUNNEL. The results were validated using ground-level instrumentation (settlement gauges) on all sections. The validation showed that the modeling results are in good agreement with the results obtained from settlement gauges. Comparison of the results indicated that a 4-fold increase in the face pressure led to a maximum decrease of 4.45 mm in the maximum settlement. Therefore, an increase in the face pressure can reduce settlement, although quite minimally. It was also found that an over-increased face pressure (face pressure over 200kPa) not only did not reduce the maximum ground surface settlement but also may lead to passive failure or uplift of ground surface ahead of the shield.
