EN
EN
**Behro Comprehensive Consulting Engineers**
**Davood Parsapour, Dariush Mohammadi**
geotech geol eng. Journal
**August 11, 2023**
This study investigates the effects of constructing adjacent structures, such as galleries, shafts, and connecting tunnels, on the structural behavior of existing **large-span underground spaces**, such as metro stations. The study focuses on the **connecting tunnel between Tehran Metro Lines 6 and 7** and its impact on the existing **F6G7 interchange station**.Since any deformation of structural elements results in the development of internal forces, **deformation of the ground mass surrounding the existing underground structure due to adjacent excavation** is a key controlling factor in ensuring its structural adequacy. This can only be achieved through the selection of an appropriate **staged construction sequence** and effective control of ground and structural deformations.
To characterize the structural response, the study employs a combination of **three-dimensional numerical modeling, analytical analyses, and observational data**. Eight different construction schemes for excavating the connecting tunnel adjacent to **F6 Station** were evaluated, with particular focus on the **stress field surrounding the non-circular tunnel**, the induced internal forces, and their implications for the structural design of the station. This approach enables the comparison of different construction scenarios under identical **geotechnical conditions**, based on both **structural and operational criteria**.
The results show that the selection of the **excavation sequence and primary support details** for the adjacent tunnel plays a decisive role in reducing **ground-mass deformation** and, consequently, mitigating the **structural response of the station**. In particular, **“sequential/partial excavation,” “the use of an invert (base) as part of the primary support system,”** and **“the use of pre-support systems”** during the staged construction of the connecting tunnel significantly reduce ground deformation and the resulting structural effects on **F6 Station**.
Based on these findings, it is recommended that, in similar urban projects, the selection of the construction method should prioritize **proper excavation sequencing and adequate reinforcement of the primary support system**, including the use of an **invert and pre-support systems**. Such a strategy not only helps maintain the stability of existing structures and reduce operational risks, but also enables the construction of adjacent auxiliary structures with **minimal adverse effects on large-span underground spaces**.
