EN
EN
**Behro Comprehensive Consulting Engineers**
**Dariush Mohammadi, Kourosh Shahriyar, Parviz Maarefvand, Ebrahim Farrokh**
Journalof Mining and Environment (JME)
**August 9, 2024**
The proper design of **cutterhead openings in full-face Tunnel Boring Machines (TBMs)** is one of the key factors determining excavation performance, particularly in soft and mixed ground conditions. As the primary component in contact with the tunnel face, the cutterhead is subjected to continuous pressure, and the configuration of its openings plays a critical role in excavation efficiency, preventing soil clogging, and ensuring the uniform transfer of excavated material.This article compiles a comprehensive database of cutterhead designs used by various **TBM manufacturers** and classifies **36 different opening patterns** for machines with diameters exceeding **5 meters**. Based on industry experience and data from actual projects, the study establishes the key principles for the **optimal design of cutterhead openings**.
The study then employs the **Discrete Element Method (DEM)** to analyze the performance of the cutterhead under different opening configurations, including openings in the **central and peripheral regions**. The numerical assessment is based on mechanical parameters, soil characteristics—including **cohesive, non-cohesive, and mixed ground**—and particle contact properties.The results show that increasing the **opening ratio in the central region** of the cutterhead for cohesive soils improves soil flowability, reduces the likelihood of clogging, and decreases the required **thrust forces and torque**. In contrast, for non-cohesive soils and mixed ground conditions, increasing the opening ratio in the **peripheral region** ensures more uniform transfer of excavated material and prevents dead zones on the cutterhead. These findings were further validated through an analysis of **three cutterheads used in Tehran Metro projects**.
Overall, the findings of the article emphasize the need to divide the cutterhead into two main zones when designing its openings: **“Zone 1,”** extending from the center to the rotary arms, and **“Zone 2,”** covering the peripheral areas from the rotary arms to the cutterhead edge. The results indicate that in **cohesive ground**, a higher opening ratio should be provided in the central region, whereas in **non-cohesive ground**, larger openings in the peripheral regions provide better performance.Based on a combination of **manufacturer data, numerical simulations, and field studies from actual projects in Iran**, the article proposes an optimal opening ratio for **Tehran alluvial soils** of **30–50% in Zone 1** and **30–40% in Zone 2**. This range can serve as a basis for future cutterhead designs in **urban tunnelling projects**.
