# Investigation on Vibration Influence Law of Double-Shield TBM Tunnel Construction
## 1 Introduction  
With the increase in urban areas and population, subways have become the most convenient and environmentally friendly way to travel [1]. By the end of 2021, 50 cities in China have opened subways, with a total operating mileage of 7305 km. What is more, thousands of kilometers of the subway are under construction every year. The tunnel boring machine (TBM) is more efficient than the shield machine in hard rock strata, especially the double-shield TBM [2; 3]. Double-shield TBM integrates the technical features of an open TBM and shield machine; it can realize the simultaneous construction of tunnel excavation and segment assembly [4]. In 2016, double-shield TBM in China was first applied to urban subway construction, and it achieved great success in tunneling efficiency. Subsequently, double-shield TBM is more and more widely used in urban subway construction, such as in Qingdao and Chongqing [5; 6]. However, TBM inevitably passes through houses, roads, bridges or adjacent tunnels when the tunnel is excavated underground. With the popularization of double-shield TBM in urban subway tunnels, the vibration problems caused by construction are worthy of attention [7; 8]. At present, many scholars have performed lots of on-site vibration monitoring to research the impact of tunnel excavation on existing tunnels [9; 10], buildings [11; 12] and pipelines [13; 14; 15], etc. For example, [PERSON] et al. [16] studied the impact of blasting construction on existing tunnels under different blasting schemes by on-site vibration monitoring and analyzed the characteristics of vibration velocity under different excavation footage. Vibration analysis is a key method for studying the dynamic characteristics of vibrating bodies. Many scholars have also proposed some useful dynamic analysis methods [17; 18]. For example, [PERSON] et al. [19] introduced an efficient numerical procedure to solve the dynamic response of functionally graded porous beams. Subsequently, the dynamic response of functionally graded porous beams was studied for several boundary and loading conditions. Moreover, there is a large amount of research on the aspect of vibration attenuation and propagation [20; 21; 22]. For instance, [PERSON] et al. [23] analyzed the propagation characteristics and attenuation laws of blast-induced vibration in rock tunnels and proposed a formula for calculating the peak particle velocity considering diffraction and reflection amplification effects. Nevertheless, these studies mainly focus on blast-induced vibration, and there are few studies on the vibration caused by double-shield TBM construction. One of the important reasons is that double-shield TBM is generally used in mine and water tunnels, not urban subway tunnels. Compared with blast-induced vibration, the vibration caused by double-shield TBM lasts longer, and the amplitude and frequency of vibration in tunnel construction are also different from those in blast-induced vibration [24]. In terms of TBM tunnel construction vibration, current studies have obtained some useful results. For example, [PERSON], [PERSON] et al. [25] have developed a cutter-head vibration monitoring system for TBM tunneling and analyzed the differences in amplitude and frequency of triaxial vibration on cutter-head vibration characteristics. [PERSON], [PERSON] et al. [26] monitored segment vibration during TBM construction; the main influence distance of segment vibration is 9 m. It can be seen that it is relatively lacking in vibration influence law of double-shield TBM construction. Furthermore, studies, at present, only consider the impact of double-shield TBM construction on the buildings and ignore the impact on human comfort in the buildings. This paper is devoted to studying the vibration characteristics and influence laws of double-shield TBM in tunnel construction, determining the vibration influence range of human comfort. First, relying on the Laozhang section in Qingdao Metro Line 4, the double-shield TBM construction site vibration monitoring scheme was developed.