EN
EN
**Behro Comprehensive Consulting Engineers**
Davood Parsapour, Mohammad Heydarizadeh, Mohsen Mohsenpour, Hamzeh Heydari
Road, Housing and Urban Development Research Center
November 18, 2025
This article emphasizes the fundamental role of **geotechnical investigations** in the design and construction of underground structures, such as tunnels and metro stations, highlighting the need to identify the **geological conditions** and **engineering properties of soil layers**. The authors demonstrate that uncertainty in geotechnical parameters can compromise project safety, result in additional costs, and extend the project schedule. Therefore, conducting **comprehensive geotechnical investigations in urban environments** is an integral part of any metro project.
The article further examines **code-based recommendations for determining the number, depth, spacing, and type of boreholes and test pits** required for the accurate collection of subsurface information, and provides a framework for the selection and implementation of **conventional field and laboratory tests**. With reference to the relevant standards, these tests form the basis for determining the **physical, mechanical, and strength parameters of the soil**, as well as evaluating **groundwater conditions and the seismicity of the alignment**.
The **Tehran Metro Line 10 case study**, while introducing the alignment, provides an overview of the **geological conditions** and **geotechnical characteristics of the tunnel**, and reviews the potential and encountered **hazards and challenges associated with mechanized tunnelling**. The findings demonstrate that establishing a systematic link between **field investigations, in-situ and laboratory testing, and engineering analyses** is a prerequisite for sound decision-making in the selection of the **tunnelling method, construction staging plan, and support system design**.
Based on the findings, the **outputs of geotechnical investigations** play a direct role in the design of the **main tunnel and station structures**, the **excavation support and lining systems**, the determination of the **tunnelling method and TBM type**, the assessment of risks to **adjacent structures**, and the identification of **hazards during excavation**. Accordingly, investment in **geotechnical investigations** is regarded as a key tool for **optimizing design, reducing risks, and ensuring the safety and stability of metro projects**, particularly at the urban scale.
