## 1 Introduction  
In China, a total area of circa 640,000 km\({}^{2}\) is covered by loess, which is about 6.6% of the territory of the country. With the rapid development of traffic construction in loess area, a large number of loess tunnels have been constructed across the country. Loess is characterized by randomly open and loose particles with high porosity [1; 2]. The construction of the large-section tunnels in loess ground inevitably disturbs the in-situ stress field and causes large ground displacements [3; 4; 5]. The current literature suggests that a considerable proportion of ground displacement caused by excavation occurs before the installation of the primary support system which could cause tunnel instability or even collapse [6; 7; 8; 9]. This explains the necessity of using the pre-supports to minimize the pre-displacement of the tunnel.  
Umbrella arches are identified as the most commonly used pre-supports in various engineering situations [10; 11; 12]. Pipe roofs and leading ductules are the two widely used types of the umbrella arches, applied in the construction of underground space under harsh geological conditions [13; 14; 15]. During the recent years, many studies have aimed to identify the mechanism behind these two types of pre-supports. [PERSON] et al. [16] investigated the effects of the pipe roofing on the surface settlements. In their research, the settlements associated with the twin tunnels in the Istanbul Metro was evaluated by using numerical, semi empirical, and measured values. [PERSON] et al. [17] provided the optimal construction parameters of the combined pre-support technique of the pipe roof and grouting reinforcement for the shallow buried loess tunnels by using Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) software. [PERSON] et al. [18] analyzed the impacts of the pipe roofs on the deformation mechanism of the dry sand soil; the whole process of deformation development was studied in their research. Other authors [19; 20; 21] have studied the influence of design parameters on the performance of pipe roofs research. In their study, different aspects such as the installation angle, diameter and transverse spacing of pipe roofs were considered. There is no doubt that valuable insight could be gained from both experimental investigations and numerical simulations. However, due to the uncertain nature inherent in tunnel engineering, the performance of pipe roofs and leading ductules obtained by such studies can hardly reproduce the actual magnitudes found in a real project. Indeed, the experimental investigations are mainly influenced by the scale effects, and the numerical simulations excessively depend on the establishment of the model and selected parameters.  
In this study, a typical large-section loess tunnel for high-speed railway in China is investigated. We focus on the effect of the three-bench seven-step excavation method (TSEM) and two types of pre-supports (i.e., pipe roof and leading ductule) used in the tunnel construction. Twelve cross-sections were systematically monitored. The monitoring items include the ground surface settlements (GSS), the tunnel arch settlements, and the tunnel horizontal convergences during the excavation process. The characteristics of ground response during tunnel excavation are analyzed using TSEM, based on the monitoring results. Subsequently, through analyzing the GSS, the tunnel arch settlement and horizontal convergence, the performances of two kinds of pre-supports for the ground reinforcement are compared. The research may shed a light on the behaviour of pipe roofs and leading ductules and serve as a practical reference for similar projects.