Journal of Engg. Research Vol. 11 No.(1B) pp.169-185 DOI:10.36909/jer.17317 Optimization of tunnels excavation sequences in Egyptian soil conditions Ahmed T. Abd Ellaah*, Mohamed A. Eid**, Mostafa Z. Abd Elrehim** and Waleed Abdullah*** * Kuwait Building House Company, Civil Engineering Department, Kuwait. ** Minia University, Civil Engineering Department, Minia, Egypt. *** Kuwait University. Civil Engineering Department, Kuwait. * Corresponding author: ATA20050@yahoo.com Submitted: 30-01-2022 Revised: 28-04-2022 Accepted: 07-05-2022 ABSTRACT Construction of huge metro projects in congested areas in Cairo City, Egypt, calls for optimization of the underground excavation process. The soil profile in Cairo city, Egypt, is generally characterized as soft soil containing layers of clay and sand. To control the ground movements and shotcrete stresses, it is necessary to optimize the ground surface settlements and excavation step. In this paper, several tunnel sections were compared to illustrate how the tunnel shape affects the soil deformations and straining actions results. Results of numerical modeling using plane-strain finite elements are presented; different types of sequences for the tunneling excavation of each section are compared. Analysis results from different models show that using different tunnel section excavation sequences affects the soil behavior differently, and that suitability of the sequence is determined by the soil properties and the dimensions of the tunneling section. Keywords: Underground excavation; Sequences; Tunnels; Soft soil. INTRODUCTION Nowadays, there are many construction methods for underground structures (tunnels & stations) such as machine methods, New Austrian Tunneling Method (NATM) and Cut-Cover method. Cairo metro Line 1 was constructed using Cut and Cover Method. For Lines 2 and 3, the tunnels were constructed using Tunneling Boring Machine (TBM) (NAT, 2009). Since underground structures are usually built in congested areas, major problems generally occur at construction stages. For cases that include large underground openings, successful measures that include pre-supporting systems are employed to enhance ground stability and reduce ground surface settlement (Mostafa Z., Ahmed T., 2016). Section excavation causes stress redistribution, which induces movements in soil media and ground surface (Sauer, 1990). Therefore, it is crucial to assure ground stability during excavation sequences and maintain control over the expected deformations and its effects on nearby structures. In congested urban zones, the effect of underground construction on nearby structures is an important factor since it causes volume losses which are reflected on the surface creating ground movements that can affect the existing nearby structures. Soil movements are estimated in the early stages of designing and planning tunnel excavations using empirical, analytical or numerical methods. However, the interaction between underground works, substructures linings and super structures during the construction of underground structures is a highly complex phenomenon, which may cause the surrounding ground to behave unexpectedly. There are no other studies that particularly focus on the ground surface settlements and excavation steps for optimization. Therefore, this study is aimed at using numerical modeling to better understand the behavior of the soil during the construction of underground structures and to predict the expected effects on nearby structures. NEW AUSTRIAN TUNNELING METHOD (NATM) 169