## 1 Introduction  
The underground utility tunnel is one kind of underground structure in which there are more than one utility pipe or cable. For the utility tunnel, it can not only reduce the excavation needs and costs, and consequently reduce traffic congestion caused by excavation, but also provide enough shallow underground space to avoid utility interference and enough space for new utilities, which meets the sustainable development requirements of underground space. Therefore, in light of urban development and the growing need for public facilities in big cities, the utility tunnel has been rapidly developed in the world. The first utility tunnel was built in France in 1850 [1]. However, the development of utility tunnels in China was very late, and the first one was built in Shanghai in 1994 [2]. Actually, the rapid development of the utility tunnel in China is from the 21 st century, and recently, China has made big progress in utility tunnel construction as an essential urban infrastructure development. In China, the eastern coastal area is the economically developed region, and there are many big cities. In this area, the soft soil layers are widely distributed. Therefore, in China, many utility tunnels are constructed in the soft foundation. As a kind of urban underground engineering that is shallowly buried under the road, pavement and green areas, the utility tunnel in a soft foundation will be seriously affected by the ground traffic loads during the operation period. Because the mechanical properties of soft soils are very poor, under the loading disturbance, large deformation will be caused for the soft soils. Therefore, it is very hard work to determine the long-term mechanical status of soft soil after a disturbance, which will cause significant difficulties for the safety operation of the utility tunnels. Thus, it is a very important work to analyze the safety status of utility tunnels constructed in a soft foundation during the operation period. Nowadays, there are many works on the safety analysis of utility tunnels during operation periods affected by external loads similar to ground traffic loads. These studies include two main types, which are experimental studies and numerical studies. For the experimental studies, based on the in-field explosion experiments, the protective performance of utility tunnels under a ground accidental explosion has been studied, which includes two types of utility tunnels (steel bars-reinforced concrete utility tunnel and basalt fiber reinforced polymer bars-reinforced utility tunnel) [3; 4]. By a similar ground surface explosion experiment, the structural dynamic responses of a double-box-reinforced concrete utility tunnel buried in calcareous sand have been analyzed [5]. Moreover, based on a quasi-static experiment, the cross-sectional mechanical behavior of a prefabricated multi-cabin-reinforced concrete utility tunnel under free-field racking deformation by earthquake action has been studied [6]. Also, based on quasi-static load tests on the full-size model, the mechanical behavior of a prefabricated concrete utility tunnel and the seismic behavior of top joints for the hybrid precast utility tunnel consisting of the precast composite top slab and double-skin sidewalls with reserved rebar have been researched [7; 8]. Based on the quasi-static cyclic tests for simulating earthquake action, the seismic performance of the precast concrete composite walls of utility tunnels with a grouting-sleeve connection out-of-plane has been studied [9]. By using the low-cyclic-loading tests conducted on the bottom joints, the seismic behavior of the prefabricated utility tunnel created by transferring reserved rebars from the double-skin concrete sidewalls to the bottom slab has been investigated [10]. Moreover, the shaking table model test is one widely used method for studying the dynamic response of utility tunnels, and there are many works involving this experimental method.