# Improved Subsidence Assessment for More Reliable Excavation Activity in Tehran
## 1 Introduction  
Reducing further congestion is part of the evolution of the urban environment. Subterranean buildings are utilized whenever feasible to alleviate traffic jams. In order to encounter as few barriers during implementation as feasible, it is imperative to have a comprehensive understanding of the geological environment prior to beginning construction. To provide the detailed results of the geological exploration, data collection is carried out using constantly evolving methodologies [1]. Because there is already a growing requirement for super-large-section tunnels to fulfil the increased transportation needs, tunnel design is also becoming more and more complex [2]. We have come to the point at which the networks of subterranean tunnels are overcrowded in many places. The construction of new tunnels frequently crosses existing ones, altering the geotechnical conditions, and in order to address the issues that emerge, new technological approaches must be employed [3]. Over the past several decades, subsidence has emerged as a significant issue affecting urban, coastal, and mining areas worldwide [4]. Because of ground deformation, tunnel construction, especially using weak materials, may have unintended repercussions on already-existing structures. Because stability, surface deformation, and efficient supports are necessary for safe tunnel design and construction, the ground settlement assessment and its impact on structures above the tunnel are crucial for tunnel projects [5]. Stratum loss, i.e., the discrepancy between the amount of excavated soil and the volume of the created tunnel, is thought to be the primary cause of land subsidence [6]. When feasible, tunnels should be driven full face; however, this is often not practical, especially on rough terrain, in which heading and bending must be used. It can even berequired in the most challenging situations to drive a top pilot heading before opening it out to the entire sector [7]. It is common knowledge that a pile creates stresses around it by supporting the weight of the superstructure by transferring it to the ground. Conversely, tunneling is a stress-relieving procedure that causes ground movements surrounding the tunnel that spread through the soil to the ground surface [8,9]. To fulfil the requirements of significant projects in hydraulic engineering, transportation engineering, etc., in order to enhance the use of subterranean space and minimize backfilling, large-scale non-circular tunnels are currently becoming increasingly prevalent. To lessen the impact of excavation on the surrounding rock, the cross-section is sequentially excavated, typically using the drill and blast method, in a large-scale tunnel building project. In sequential excavation, the entire cross-section is divided into many portions, with excavation taking place over various periods for each segment [10, 11, 12, 13]. The NATM building approach is highly adaptable to shifting cross-sectional geometries and subsurface circumstances. The shotcreate membrane's main job when it interacts with the subsoil is to create a carrying arch around the tunnel. It is feasible to eliminate or significantly reduce bending moments and shearing forces in the shotcrete membrane by designing the tunnel's cross-section in a way that maximizes its benefits. Thus, shotcrete membranes that are relatively thin can sustain huge subterranean holes. Additionally, surface sinking can be kept to relatively low levels with a suitable design. However, a successful tunnel heading using this method requires stability assessments, in which the subsoil-support interaction is modeled in a realistic manner. The authors firmly believe that only numerical calculation techniques can make this feasible. Therefore, finite element codes should be used for stability studies in general [14]. In his 1964 work, \"The New Austrian Tunneling Method\" (NATM), [PERSON] presented the first cross-section of the NATM (Figure 1) in relation to an Austrian tunneling project.