## 1 Introduction  
Underground structures suffer damage or even collapse not only in the site of soft soil, but within the strata of the rock mass during strong earthquakes. The investigated damage of mountain tunnels after the 1999 Chi-Chi earthquake [1] and the 2008 Wenchuan earthquake [2; 3; 4; 5] have attracted the attention of practitioners and academics. Surveying the underground powerhouses after Wenchuan earthquake revealed a large area of cracking and spalling [6]. These investigations suggested that the damage to underground caverns was owing to the discontinuity of the rock mass [7; 8; 9]. Engineering geology has paid close attention to discontinuity, whether it is the fault, joint, folding, or other types of anisotropy [10]. Fractures, also called joints, are the planes along which stress has caused a partial loss of cohesion in the rock. It is a relatively smooth planar surface representing a plane of weakness (discontinuity) in the rock. Conventionally, a joint is defined as a plane where there is hardly any visible movement parallel to the surface of the joint; otherwise, it is classified as a fault. Although joints are extremely common and widespread in rocks, geologically they are still not well-studied [11]. Joints are created by stresses which may have diverse origins, such as (a) tectonic stresses related to the deformation of rocks; (b) residual stresses; (c) contraction due to shrinkage because of the desiccation of sediments; and (d) weathering. Generally, the deformation and damage of a rock mass are mainly controlled by the rock characteristics and the structure of joints [12]. Rock quality evaluation methods can be categorized into single-factor and multi-factor evaluation methods, including the elastic wave velocity method [13], rock quality designation (RQD) [14], rock mass rating (RMR) [15], Q system [16], and so on. The lower the rock quality, the denser the distribution of joints in the rock, and the higher the degree of heterogeneity of the rock mass. However, there are limited reports on the effect of rock joints on the seismic response of underground caverns. The shaking table test, used to investigate the characteristics of underground caverns under an earthquake, is a powerful tool in revealing the dynamic interaction between rock and a structure. It is important to note that the strata-structure interaction plays a controlling role in the seismic response of underground caverns [17; 18]. [PERSON] et al. [19; 20] conducted a large-scale shaking table test for a tunnel with varying stiffnesses of its linings under strong earthquakes. [PERSON] et al. [21; 22] investigated the aseismic effect of grouting in a fault-crossing tunnel through shaking table tests, and explored the seismic mitigation performance of grouting, which reduced the acceleration response of fault-crossing tunnels. [PERSON] et al. [23; 24] investigated the dynamic characteristics of a tunnel-crossing soil-rock interface using shaking table tests, and the combined effect of the soil-rock interface and the tunnel was due to the differential ground seismic response. The aforementioned studies primarily focused on a single underground cavern and assumed that the strata were a continuous medium. Experimental studies on jointed rock masses under earthquakes are rare, except for with numerical simulations [25; 26; 27; 28]. The tunnel-group metro station is a new type of station structure form, which is characterized by a shallow burial depth, separation of the hall from the platforms, which is connected by horizontal passages and inclining shafts, and large-span column-free structures for the station hall. These structural features distinguish the tunnel-group metro station structures significantly from the frame-box metro stations in soft soil, making them more akin to underground caverns. However, they differ from the underground powerhouses of hydroelectric stations due to the high density of people and the frequent train services within the metro stations.