Influences of Dynamic Loads of Earthquake on Pore Water Pressure (Tabriz Metro First Line)

Summary : Tabriz metro twin tunnels in some stations are under ground water level. In addition to the loads from the weight of overburden, the load caused by pore water pressure is applied to them. To enter the current load into model certain boundary conditions must be considered that in this study, the probability of liquefaction and the impact of the earthquake on pore pressure loading structure have been investigated.
Geo-technical design of structures is encountered with a variety of different natural conditions (earthquake, liquefaction, etc.). This will be due to the complexity of behaviors and conditions. These structures during his lifetime, because dealing with different situations such as earthquake will not have fixed characteristics and behavior. Complex Mechanical behavior of the soil under statistical loads can be different and more complicated under dynamic loads. In this respect, the modeling of alternative behavior of saturated soil, especially in the interaction zone of soil – structure, has gained increasing research interest over past decades. Because the estimation of structure response in the soil liquefaction depends on pore water pressure, softening strain and decreasing of soil resistance. For correct investigating, linear dynamic analyze in effective stress is necessary. For this type of analyze couple or semi couple methods could be applied. In this regard Finn & Martin and Byrne could be regarded as semi couple models.
Methodology and Approaches : From aforementioned semi couple models, Byrne model was chosen in this research. After calculation of related indexes, the model implemented in Flac2D software. The possibility of liquefaction take place in structure foundation was investigated by local tests results in effective stress method. For numerical modeling, the Bam earthquake acceleration was selected in DBE level among the existing acceleration and impact of earthquake dynamic load of on project structure pore pressure was investigated.
Results and Using available data at the project structure the probability of liquefaction in the project region was investigated by cyclic stress method. It was estimated that with safety factor of 1.28 for Bam earthquake magnitude earthquake 6.5M, liquefaction will not occur. Nevertheless, due to exist of pore pressure at structure needed parameters was calculated in Byrne model to study simultaneous impact of dynamic loads and pore pressure to be used in numerical modeling. The results showed an increase in pore pressure due to dynamic loads caused by earthquakes so higher load values to the desired location (subway tunnel) is inserted and finally more effective maintenance system for the tunnel is estimated.