## 2 Materials and Methods
### Saltstone Stratigraphic Conditions and Cavity Building Plan  
The Pingdingshan Salt Field is rich in mineral deposits, and after nearly 20 years of mining, a large number of abandoned mining cavities have been formed. The salt rocks are distributed in the Cenozoic Paleoproterozoic Loop strata, showing thinly bedded salt rocks and mudstones with alternating lamination, relatively simple tectonics, and horizontal production. The main salt rocks are buried at depths between \(-1400\) and \(-1000\) m [27]. The Pingdingshan salt deposit is a set of Mesozoic and Cenozoic elastic chemical rock series which is contained in the Wuyang Depression. From the Cretaceous to the Quaternary, the Hu Gang Formation (K\({}_{2}\)h), Yuhuangding Formation (E\({}_{2}\)y), Daematgang Formation (E\({}_{2}\)d), Walnut Garden Formation (E\({}_{2}\)h), Liaozhuang Formation (E\({}_{3}\)h), Shangshi Formation (N\({}_{3}\)h), and Plain Formation (Q\({}_{\mathrm{P}}\)) were successively deposited. The salt-bearing strata are the nuclear section (top) of the Paleocene Oligocene Walnut Garden Formation. A set of mudstones with a stable distribution is developed at the top of the nuclear section [28]. The profile of the Mesozoic and Cenozoic strata in the Wuyang Depression is shown in Table 1.  
The sedimentary characteristics and stratigraphic assemblage of the Wulipu salt mine section in Yexian Zhongyan Haolongmazhuang are highly complex. The overall stratig  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Stratigraphic System**} & \multicolumn{1}{c}{**Thickness/m**} & \multicolumn{1}{c}{**Lithologic Association Characteristics**} \\ \hline  
raphy demonstrates a typical lithological sequence comprising alternating salt rocks and mudstones. These are intermixed and distributed, with a large number of intercalated layers, a thin thickness of the single layer, and a deeper burial depth. The geographic location of Ye County is shown in Figure 1.  
Further investigation reveals that the overall thickness of the salt layers in the Pingdingshan Salt Field region ranges from 489.0 to 1070.0 m, which can be categorised into 22 distinct salt group assemblages, with a maximum of 61 layers reachable. The thickness of a single layer of salt is up to 27.7 m, with the thinnest layers measuring less than 1.0 m, and typically within 10.0 m. The thickness of the mudstone interlayer is variable, with an average of approximately 2.8 m and a maximum of 12.3 m. The majority of the interlayers are within 5 m, representing approximately 30% of the overall thickness. From a macroscopic perspective, a stable distribution of interlayers is observed at the base of each salt group. In the 0-20 salt group, for instance, the interlayer thickness ranges from 2 to 13.2 m, with an average of 4.1 m. Notably, the interlayer thickness is minimal, reaching a minimum of 0 m. The interlayer thickness at the bottom of the 7, 10, and 13 salt groups is greater than 10 m, with a maximum of 13.2 m. The interlayer thickness in the 14-20 salt groups is 2-8 m, with an average of 5.1 m, and contains eight interlayers in total. In total, there are eight sandwiches. In order to establish the mechanical model of mudstone entrapment, it is necessary to understand the basic characteristics of the subsurface cavities in detail and obtain relevant data to support the modelling. The consistency of the laboratory simulation studies with the material and joint properties of the field-scale salt cavern conditions helps to improve the relevance and applicability of the studies to real-world engineering, thus providing a reliable guide to real-world engineering applications [29]. [PERSON] and [PERSON] et al. [30; 31]. proposed an acoustic emission positioning technique to effectively reduce the TDOA error by combining the microseismic (MS) source localisation technique and the refraction path study, respectively, which is of good significance for the detection of underground salt cavern gas reservoirs. [PERSON], [PERSON] et al.