Influenced Zone of Deep Excavation on Adjacent Tunnel Displacement and Control Effect of Ground Improvement in Soft Soil

Abstract

The aim of this study is to predict the influenced zone of deep excavation on adjacent tunnel displacement, evaluate the control effect of ground improvement, and give the optimal parameters for ground improvement. Based on the current research, a series of finite element method (FEM) numerical simulations were conducted to study the deep excavation-induced tunnel displacement behaviors, considering different tunnel positions outside the pit. On this basis, the influenced zone of deep excavation on an adjacent tunnel was divided corresponding to 3-level tunnel displacement control standards. Then, the commonly used control measure of ground improvement was chosen to study the effects of strength, depth, and width of the improved soil outside the pit on the displacement behaviors of the tunnel. An index of tunnel displacement control effectiveness (η) was proposed to quantitively characterize the control effect on tunnel displacement. Considering the control effect and engineering economy, the suggested values of strength, depth, and width of the improved soil were provided. Finally, the control effect of ground improvement outside the pit on the influenced zone of deep excavation was studied using the suggested parameters. The research indicates that the range outside the pit can be divided into: I—primary influenced zone, II—secondary influenced zone, III—general influenced zone, and IV—weak influenced zone. Considering the control effect and engineering economy, it is suggested that the ground improvement strength should be kept within 1.5~2 MPa, the ground improvement depth should be 2 times the excavation depth, and the ground improvement width should be increased as much as possible if the site condition allows. After the ground improvement using the suggested parameters, the scope of the influenced zone of deep excavation is reduced and the I—primary influenced zone no longer exists.

Assessment of Safety of Masonry Buildings near Deep Excavations: Ultimate Limit States

“…Pillars be tween windows are the most vulnerable elements in the building structure, Figure 16. The height and thickness of the wall at the highest level are h k , t (1) , respectively. The bearing length of the timber floor at the highest level is a (1) .…”

“…The height and thickness of the wall at the highest level are h k , t (1) , respectively. The bearing length of the timber floor at the highest level is a (1) . The wall at the analysed level has a height and a thickness equal to h k , t. Vertical loads transferred to walls from the roof and the floor at the highest level are resolved into components that are parallel and perpendicular to the longitudinal axis of the wall with the general relationships:…”

“…As the hinge support was taken for wall ends on the supports, there are only horizontal components that provide equilibrium. The resultant at the bottom edge should be within the wall section, which means that the condition e (1) d ≤ 0, 45t (1) should be satisfied otherwise the structural instability of the wall can be observed. For various values of wall thickness, the eccentricity should be transformed against the axis of the analysed wall based on the following relationship:…”

“…However, construction activities affect not only the soil in the construction zone and its immediate vicinity, but also the neighboring buildings located there. Tests on the relationships between the structure, geometry and size of a building, ground deformation, shear deformation of a wall, and the degree of damage were conducted and presented in the paper [1].…”

Response Monitoring and Analysis in Deep Foundation Pit Excavation: A Case Study in Soft Soil at Subway Tunnel Intersections

“…There are established codes and standards in place to limit the impact of soft soil permeability on the excavation process. Now, one of the most significant risks associated with excavation under soft soil conditions is the potential impact on adjacent structures and infrastructure, especially when excavating in close proximity to an existing subway system [5][6][7][8]. In particular, the construction of a deep foundation pit can pose significant risks to the integrity of the subway infrastructure.…”