Abstract: 【Objective】 In view of the common technical bottlenecks in the construction of salt cavern gas storage in thin salt layers - the traditional cavity - building process results in a dissolution rate of less than 5% of the salt rock at the bottom of the horizontal section due to the gravity - differentiation effect of brine, and the lack of a quantitative evaluation method for the stability of the interlayer interface under long - term injection - production cycles. This study proposes an "vertical - horizontal - deflecting" three - stage solution mining cavity - building process with engineering innovation significance. This process effectively solves the problem of dissolution inhibition at the bottom of the cavity through the unique lateral scouring dynamic mechanism of the deflecting section. At the same time, a geomechanical evaluation system covering a 30 - year operation cycle is established. 【Method】 At the methodological level, relying on strict engineering similarity criteria (geometric ratio of 1:500, Reynolds number Re = 3200 in the turbulent zone), physical simulation tests are carried out using super - large - sized salt rock specimens (30×30×100 cm). A high - precision pipe - withdrawing system realizes step - by - step shape - controlled cavity - building in the vertical section (3 mL/min), horizontal section (5 mL/min), and deflecting section (20° dip angle). Combined with non - contact 3D laser scanning technology, the details of the cavity shape evolution are captured, and the mapping law of the wavy roof characteristics at the engineering scale is revealed (wave - crest spacing of 60 - 75 m, wave - trough depth of 15 - 25 m). This characteristic is formed by the coupling effect of the low - speed eddy - current zone at the top of the cavity and the mass - transfer efficiency of the dissolved matter. Furthermore, a three - dimensional rheological model (size 2000×1000×760 m) based on the geological characteristics of the Jintan salt layer is constructed. The Burgers model is used to describe the visco - elasto - plastic behavior of salt rock, and the Mohr - Coulomb criterion is used to characterize the mechanical response of the interlayer. Multi - field coupling simulation is realized through a fine grid of 1.78 million tetrahedral elements. 【Results】 Physical tests confirm that the dissolution efficiency of the deflecting section is 18% higher than that of the horizontal section. The dissolution proportion of the salt rock at the bottom of the cavity jumps from a negligible level to 35%, forming a cavity structure with a high - width ratio optimized to 1.32, which is "big at both ends and narrow in the middle". Numerical simulation quantitatively shows that the volume shrinkage rate of the cavity during the 30 - year operation period is stable at 16.52% (significantly lower than the 30% safety threshold), the maximum deformation of the surrounding rock is 3.12 m (deformation/diameter ratio of 4.1%), and the shear - dilation safety factor is maintained at 3 - 5. However, there are high - risk areas where the safety factor of the interlayer interface is less than 1.0 locally, and the stress path needs to be reconstructed by optimizing the cavity height (high - width ratio > 1.5). 【Conclusion】 This achievement breaks through the limitations of the scale - effect of physical simulation, constructs a "test - model" cross - scale closed - loop verification framework, provides technical support for a 26% single - cavity capacity expansion of the Jintan Gas Storage Project of the National Pipeline Network, and promotes the development of gas storage technology in thin salt layers towards high - efficiency and intelligence.