The ground movement during the construction of shallow loess tunnels can easily cause deformation damage to surface buildings. Most the current studies focus on the damage soft soil and rock tunnels to independent buildings, and there are few studies on the case of building groups in loess areas. Using the new Xi 'Yan Railway Luochuan Tunnel as a case study, we conducted on -site testing to study building settlement and crack development characteristics. Three-dimensional numerical simulations were carried out to analyze settlement, flexure deformation, and main tensile strain distribution characteristics of the buildings at different buried depths. The study determines the extent of damage resulting from differential settlement and tension cracks. The results show that construction during the upper, middle, and lower bench stages results in significant ground volume loss, leading to a 'wide and steep ' settlement pattern with a maximum settlement value of 567 mm. Building cracks exhibit positive and inverted splayed shapes, with lengths ranging from 0.5 to 6.0 m and widths between 0 to 170 mm. As buried depth increases, maximum settlement, flexure deformation, and main tensile strain of buildings also increase. The severe damage range of buildings initially increases and then stabilizes, with the maximum range caused by differential settlement and tensile cracks being 34 m and 29 m from the tunnel axis, respectively. Based on the analysis of building damage characteristics, it was determined that a combination of surface measures and measures within the tunnel should be used to control building damage caused by tunnel construction. These research findings can serve as valuable references for similar projects.

Loess tunnels are very common in the Loess Plateau, and they pose unique geological threats. Loess tunnels are often difficult to detect and control due to their concealment and sudden appearance. Thus far, research on the genesis and evolution of loess tunnels remains scarce. In this paper, the genesis and evolution mechanism of the loess tunnels in the Loess Plateau is studied in depth, and the location, shape, and size information are obtained via field investigations. The potential correlations between the loess sediment, the basic physical properties (depth, water content, particle size composition, collapsibility coefficient, and self-weight collapsibility coefficient), and the tunnel density are inferred based on the Pearson's correlation coefficients and tests on the physical and mechanical properties of the loess sediments. In addition, spatial statistical modelling is employed to justify and predict the observed spatial distribution of the loess tunnels assuming Gaussian Markov random fields. The formation of loess tunnels is due to a combination of factors, including the formation thickness, soil properties, joints and fissures, topography, hydrogeology, and climatic conditions. The thickness of the loess, loess sediment properties, and their spatial relationship jointly determine the material basis of the formation of the loess tunnels. The loess tunnels at different depths have different main controlling factors that are hierarchical by depth. The evolution process of loess tunnels can be divided into five stages: the incubation stage, formation stage, development stage, failure stage, and withered stage. The characteristics of each stage are discussed in detail. Our work provides novel insights into subsurface erosion from the aspect of soil tunnels. It improves our understanding of hill slope geomorphological evolution and also provides effective techniques for tunnel erosion control.

Humidity diffusion can stimulate soil deformation. However, evidence for triggering water-induced excessive floor deformation in underground structures remains elusive. This study investigated the issue by solving a case of a loess tunnel affected by floor heave. First, the study tracked the development of field damage during tunnel operation and examined the potential influence of base moistening on inverted arch uplift. Subsequently, a largescale field tunnel model test was conducted to analyze the moisture distribution, stress, and deformation development at the tunnel base during the humidification process. Finally, the mechanical properties of the base loess at the humidification stages were tested to assess the degradation caused by moistening. Results showed that the moisture distribution at the tunnel base changes from W- to U-shaped during long-term humidification. Moreover, after base humidification, the soil pressure at the arch foot initially decreases sharply and then increases, while the soil pressure at the inverted arch continues to increase. Furthermore, the lining at the arch foot shows an increase in compressive stress, while the inverted arch shows an increase in tensile stress. The differential settlement between the arch foot and inverted arch widens, transitioning to uplift deformation of the inverted arch and ultimately causing floor heave. Laboratory tests showed that the floor heave is primarily caused by the deterioration of the mechanical properties of the loess resulting from humidity diffusion in the tunnel foundation. A time-dependent floor heave model was established by combining the water content, shear strength, compressive strength, and compressibility of the tunnel-base loess, and its feasibility was verified. The model exhibited a sequential decrease in the influence of the internal friction angle, compressive strength, cohesion, and compression coefficient on the floor heave. The findings of this study are considerably important with respect to uncovering the mechanism of floor heave during the operation of loess tunnels and advancing the prediction of damage.

Pipe roofs are widely used as an effective proactive support measure in the construction of tunnel entrances, shallow-buried and underground excavated tunnels, underground stations, and large- soft and weak soil structures. However, the stress variation characteristics of pipe roofs exceeding 40 m in length are not yet clear. This paper utilizes numerical simulation methods to conduct a comprehensive analysis of the deformation characteristics of three excavation methods: center cross-diaphragm method (CRD), both-side heading method, and the three-bench excavation method with super-long pipe roofs combined with temporary inverted arches. It specifically compares the deformation control effectiveness and stress variation patterns of pipe roofs of different lengths. The results indicate that the deformation control effectiveness of 40 m and 20 m long pipe roofs is inferior to that of super-long pipe roofs. Within a range of 30 m in front of the tunnel face and 20 m behind it, significant stress variations of the pipe roof are observed. The most influential range is within 10 m in front of the tunnel face and 5 m behind it. It is evident that the overall load-bearing capacity of the super-long pipe roof is higher than that of pipe roofs below 40 m. Furthermore, in this study, a novel approach is adopted by utilizing fiber optic grating testing technology to achieve comprehensive monitoring of the axial forces in super-long large pipe roofs. The measured data strongly corroborate the accuracy of the numerical calculations.

A great concern for the construction surface cracks of large cross- tunnels, which are being or to be built in the loess strata of China, is attracted. The mechanism of surface crack formation is analyzed from both internal and external perspectives. Loess is a multi-phase porous medium and develops complex stress and strain variation while executing a tunnel project. The surface is highly susceptible to construction surface cracks in shallow sections. A statistical analysis of the constructed loess tunnels in China shows that the main factors affecting surface cracks are settlement deformation, construction scheme, and the surrounding soil environment. To gain an in-depth knowledge of the mechanism of action of factors influencing surface cracks in loess tunnel construction, we relied on the actual project engineering to conduct numerical simulations, which can reproduce the formation mechanism of surface cracks more intuitively. Through numerical simulation, the influence mechanism of tunnel surface cracks under different tunnel diameters, tunnel depths, excavation methods, and surrounding soil grades was obtained. Through the analysis of the factors affecting surface cracks, specific measures to prevent and deal with construction surface cracks are further optimized to provide new ideas for the selection of surface crack control routes in loess tunnels.