###### Abstract  
This paper presents a new testing method for the problems encountered in field testing. To this end, single-tunnel and twin-tunnel small-scale rock models are prepared in the laboratory. A new methodology is proposed to encounter problems that are faced during field testing. The test results show that rock strength characteristics, overburden pressure, and tunnel spacing have important effects on the stability of underground structures. For rocks with poor strength properties, the damage degree is greater. When the strength property of rock changes, the deformation value of unlined tunnels changes from 21.05% to 27.58%, while that of lined tunnels changes from 11% to 21.42%. Also, in the twin tunnel, the deformation value reduces from 20% to 15.78% when the spacing between the tunnels is increased. For the measurement of stress and deformation in tunnels, the results obtained from experiments are analyzed. The method adopted in this study helps determine the tunnel's design parameters to make it safe under overlying static loads. Finally, the key factors affecting the stability of underground structures are determined by simulating the field conditions through experimental research. underground structures; static loading; geo-material; lined tunnels; twin-tunnel; physical modelling +
Footnote †: journal: Applied Sciences  
11 September 2021  
12 November 2021  
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**Published: 4 December 2021**  
different loading conditions.In the case of twin tunnels, there is a significant effect of the construction method and position of tunnels on their settlement behaviour [1; 2]. The stability behaviour of brick-lined tunnels under extreme loading was investigated, and results showed that brick-lined tunnels show more brittle behaviour when subjected to concentrated loading conditions [3]. The deformation obtained in the tunnel lining in the clayey medium in the vertical direction is greater than the horizontal displacement [4]. The effect of deconfinement methods on the behaviour of the tunnel is explained [5]. In the case of a twin tunnel, the lagging distance affects the surface settlement behaviour of the tunnel [6]. The construction of a new tunnel significantly affects the settlement behaviour of the existing tunnel [7; 8; 9; 10]. The behaviour of different types of sections of the twin tunnel was investigated and it was found that circular tunnels are the best among all types of tunnel sections [11]. In the case of two crossing tunnels, the surface settlement caused due to excavation is greater when the second tunnel is excavated above the first tunnel [12]. The settlement induced in shield tunnelling is influenced by various factors such as the geological state of the region which is to be excavated, the load acting on the ground surface, methods of construction, and reinforced and unreinforced tunnel faces [13; 14; 15]. The effect of stiffness ratio, the soil layer thickness lying above the tunnel, and the cohesion properties of soil has a significant effect on the stresses acting on tunnels [16; 17]. The effect on the deformation behaviour of a tunnel excavated in soil medium when subjected to internal blast loading wasstudied, and it was found that the failure in the tunnel lining mainly depends upon the different quantities of explosive [18]. The dip angle of the joint in the case of a tunnel having jointed rock mass plays an important role in the stability analysis of the tunnel [19; 20; 21; 22]. The most critical section of the tunnel which experienced the maximum deformation is the top surface of the tunnel, i.e., the crown of the tunnel. The circular tunnel section experienced the maximum deformation compared to the horseshoe section [23]. A numerical study was conducted to determine the deformation effect in the case of cut and cover tunnel structures under the effect of dynamic loading [24].