## 1 Introduction  
Rational coal pillar size can not only maintain the roadway's rock stability but also increase coal production. As mining height increases, the roadways experience multiple mining influences: the mining pressure is strong, the rock's deformation is large [1], the narrow coal pillar cannot maintain the stability of the roadway, and the wide coal pillar will cause great waste of coal resources, so how to analyze the coal pillar's size has become an important problem.  
Current research on the mining effects of working face on coal pillars mainly focuses on the following aspects: The first is the cause of the formation of mining-induced mechanics, which often refers to the movement of rock and the redistribution of stress, especially the abutment stress distribution of the coal rock body in front of the working face [2, 3]. Under the constraints of spatial conditions, different structural modes of the overlying rock formation have been formed, such as the cantilever beam theory, the hinged rock theory, and pre-existing fracture theory [4], and the theory of masonry beams and key stratum proposed by [PERSON], which provides a cornerstone theory for the study of mining pressure in the quarry [5; 6; 7; 8]. Secondly, the analysis of coal pillar abutment pressure and destruction under the mining influence. The purpose of shortening the coal pillar is achieved by studying the redistribution of abutment pressure [9; 10], constructing the coal pillar bearing structure, analyzing the distribution of stress and plastic zone in the coal pillar [11; 12; 13; 14], and avoiding the penetration of high-stress zone and plastic zone. Third, the theoretical and technological development of the surrounding rock stability control Support theory, in addition to the traditional theory of suspension, combined beams, and reinforced arches, also includes the surrounding rock loose circle theory and surrounding rock strengthening theory [15; 16; 17; 18]. Supporting techniques include crossed anchor support, constant resistance anchor support, partition combined support [19; 20; 21; 22; 23], etc. Those theories provide technical support for narrow coal pillar stability.  
In summary, although research on the retention of coal pillars in digging along the goal has gradually deepened, basically, it is based on the condition that the coal pillars are affected by mining on one side; research on the optimization of coal pillars in double roadway digging (i.e., the coal pillars are affected by mining on both sides) is still lacking.  
Therefore, based on the key stratum's surrounding rock destruction theory, this article establishes a mechanical model of the mining area structure, analyzes the surrounding rock failure and the coal pillar's abutment pressure distribution, uses the limit equilibrium method and FLAC3D to analyze the reasonable coal pillar size and the distribution of stress zone and plastic zone of the coal pillar during one-side mining and both-sides mining, and verifies the rationality of the calculated coal pillar width. The engineering application and mine pressure monitoring in the 113 working faces of Jinjitan Coal Mine demonstrate the feasibility of the findings and reference value in engineering applications and in academia.