Numerical study of the basic parameters effects on ground subsidence during pipe jacking operations

Pipe jacking is a scientific, economic and environmental solution for the construction of underground facilities that performs a key role in the implementation of projects. In this method, simultaneously with the excavation operation by the shield, the pipes are jacked using hydraulic jacks. Ground deformation during pipe jacking operations is one of the main challenges that its analysis is necessary for safety purposes and project design. Several factors affect the pattern of ground deformation during pipe jacking operations. The effect of each parameter and their sensitivity must be determined so that the ground deformation can be controlled with proper design. The study of displacement patterns in the field of layers based on numerical simulation of finite elements and finally, the analysis of their sensitivity is a subject that has been the subject of limited studies in this field. In this study, modeling details such as a conical excavation shield, increased gradient of grout injection pressure and excavation plate pressure have been considered to be close to the real state. The displacement values at the ground surface and the crown of the pipeline are analyzed. In this study, numerical simulation has been performed using the PLAXIS finite element numerical software and considering a case study. The results of numerical modeling were calibrated with the results obtained from field and theoretical studies, and then the effect of each parameter on the pattern of ground deformation as well as estimating the quantity of uplifts and their exact location were investigated. In the next step, the relationship between each parameter and ground subsidence was estimated and finally, the effect of each of the different factors was measured using sensitivity analysis and the sensitivity index of each was determined. The results show that the most sensitive factor to subsidence is the diameter of the excavated space and the least important factor is the face excavation pressure. Most subsidence occurs at the end of the excavation shield due to the conical nature of the shield and the stress relaxation. Finally, according to the results, it was determined that the relationship between the internal friction angle and the elastic modulus with the ground surface settlement is linear but indirect. The relationships of other parameters were also evaluated nonlinearly.