###### Abstract  
Based on the \"axial-output method\", the time histories of radial and axial expansive pressures during the hydration process of static cracking agent (SCA) in a cylinder with various diameters were obtained by experiments. With the load input taken as the product of the normalized axial expansive pressure and the amplitude coefficient, a finite element model was established to simulate the experimental chemical expansion process of SCA. The relationships between elastic modulus, radial and axial expansive pressures were then obtained. The results indicate that the elastic modulus increases with increasing radial and axial expansive pressures, and then tends to be constant. The effect of Poisson's ratio was discussed with the elastic modulus unchanged. It is shown that the Poisson's ratio is inversely proportional to the amplitude coefficient, and has no effect on the ratio between the axial and radial expansive pressures. Finally, a mechanical model for the variation of elastic modulus with stress during the hydration process of static cracking agent was established in terms of the major principal stress. The model was verified by the experimental results, which can be extended for numerical simulation of SCA expansion under other compressive loading conditions, and then provide practical mechanical parameters for engineering application of SCA.  
static cracking agent; axial-output method; expansive pressure; model for variation of elastic modulus +
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Currently, the studies on SCA mainly focus on the expansion mechanism [13; 14; 15], cracking mechanism [16; 17; 18], enhancement of expansive pressure [19; 20; 21], controlling the effects of hydration rate and temperature and local controllable cracking [22; 23]. Some publications explored superplasticizer [24], amount of mixing water [25; 26] and the ambient temperature [26; 27] impacts on hydration heat and expansive pressure development. In order to broaden the application of SCA, [PERSON] et al. [7] presented an innovative SCDA cartridge, which can be applied to fracture rock masses using boreholes in any inclination, dry or wet. Despite many efforts have been made in research and development of SCA, the variation of mechanical parameters with the expansion process of SCA is not clear. Further studies on the evolution law of the mechanical parameters during the hydration process of SCA are necessary to understand characteristics of SCA. However, studies on the evolution law of the mechanical parameters during the hydration process of SCA have been seldom reported.  
In this paper, the model experiments of the SCA hydration process in a cylinder with various diameters were conducted to obtain the time histories of radial and axial expansive pressures. Then, a finite element model was established to simulate the experimental chemical expansion process of SCA. In the simulation, the elastic modulus \(E\) was adjusted so that the radial and axial expansive pressures can be consistent with the experimental results. Based on the numerical experimental results, the relationships between the elastic modulus, the radial expansive pressure and the axial expansive pressure of SCA hydrated with constant volume were investigated. Based on the above relationships, a mathematical model for the variation of elastic modulus with stress during the hydration process of SCA is established that can be extended for numerical simulation of SCA expansion under other compressive loading conditions.