Influence of Passively Loaded Piles on Excavation-Induced Diaphragm Wall Displacements and Ground Settlements

Abstract

Deep excavations in congested urbanized areas may have a significant impact on existing structures. Therefore, protective measures must be taken to control wall deformations and related soil movements. However, little is known about the use of a pile row as a measure to protect the environment and structures surrounding an excavation. In the present study, a pile row was modeled at the active side behind a diaphragm wall to investigate whether the pile row can serve as a protective measure. A numerical model, based on a well-documented deep excavation, was used to study the impact of placing a pile row behind a diaphragm wall on wall deformations, ground movements, and stresses. Results reveal that a pile row can reduce wall deformation, earth pressure, and soil movement. These effects were the result of the compression of the lateral soil between the piles combined with the vertical frictional resistance forces working along the pile shafts in a direction opposite to the soil movement. Furthermore, a parametric study was carried out to investigate the influence of different pile row parameters on wall deformation and ground settlement. The results of the parametric study indicate that the use of different parameters can cause a significant difference in the effectiveness of a pile row as a protective measure. According to the results, a pile row can be used as an effective controlling measure for deep excavations with diaphragm walls. Also, specific practical design recommendations can be formulated to maximize the reduction of wall deflections and ground settlements by pile rows. It is recommended that piles with great stiffness and roughness are used, such as screw piles. A pile length to excavation depth ratio of 2 and a wall-pile row distance to excavation depth ratio of .4–.5 should be adopted. If possible, a small pile spacing–pile diameter ratio, of 2.5, and two pile rows, should be used.