## 1 Introduction
The results of the model were close to those of finite element analysis, which proved that the model could be used in engineering practice. Based on the Winkler elastic foundation beam model, [PERSON] et al. [24] established a calculation model for ultra-shallow-buried pipe roof and steel bracing and proposed a new method of ultra-shallow-buried excavation under interactive effects. The accuracy of the calculation method of the interaction effect was verified by the measured data of the example. [PERSON] et al. [25] proposed the steel support cutting pipe method and studied its failure mode and mechanical behavior through laboratory experiments. [PERSON] et al. [26] used MIDAS/GTS to explore pipe cutting and support in the PPM. The measured data were consistent with the numerical simulation results, which verified the reliability of the numerical simulation results. [PERSON] et al. [27] proposed a theoretical analysis of the effectiveness of pipe roofs in shallow tunnels. Through a comparative analysis with the measured results, it was proven that the calculation model for surrounding rock pressure and the calculation model for the stress and deformation of the pipe roof were reasonable. [PERSON] et al. [28] proposed a unified mechanical model of the elastic foundation beam for pipe-roof. The calculation formulas for deflection and internal force in the model were derived. In addition, combined with actual engineering cases, the model was compared and analyzed. [PERSON] et al. [29] presented a case study of ShifuRoad station in Shenyang by the construction of a subway station using the small pipe roof-beam method. [PERSON] et al. [30] proposed a mathematical model of the temperature field and its analytical solution for the freeze-sealing pipe-roof method induced by the radial offset of adjacent jacking pipes. [PERSON] et al. [31] proposed a study on the whole-process application of advanced grouting pipe shed support under urban complex stratum conditions. [PERSON] et al. [32] evaluated the influence of pipe characteristics in the umbrella arch method on controlling tunneling-induced settlements in soft ground. [PERSON] and [PERSON] [33] present a global approach to back-analysis in a probabilistic context to evaluate tunnel static behavior. The use of PPM as an auxiliary construction method has been widely accepted by the engineering community, and there are many successful examples in public works. However, there are few studies on shallow-buried rectangular excavations reinforced by a pipe roof [34; 35]. The formations in the Taipei Basin are mostly composed of weak clay layers, which are highly sensitive, causing the formations to be easily disturbed and the undrained shear strength to be greatly reduced. Soil deformation and ground surface settlement are key issues for the success of the project, especially when applying the PPM to a shallow-buried underground passage project with weak geology in the Taipei Basin. For this reason, this paper uses the new construction of a pedestrian underpass on Zhongxiao East Road in Taipei City as a case study. In other words, the novelty of this paper is the application of the PPM to underground passage projects that were shallowly buried and located in a weak formation. The structure of this paper is divided into the following major sections: project overview of the case study, numerical simulation modeling, numerical simulation results analysis, and conclusions. This study was conducted by using the finite element software PLAXIS 3D CE to simulate and analyze the entire construction process and to consider various overburden depths (i.e., 0.7, 1.7, 2.7, and 3.7 m) and aspect ratios (i.e., 0.30, 0.36, 0.40, and 0.45), defined as the height per the width of the cross-section of the pipe diaphragm structure, and then to investigate the trend of surface subsidence above the pipe diaphragm.