###### Abstract
Furthermore, the high geothermal temperature is known to bear a significant impact on plastic zone extension. The expansion of the rock body caused by high temperature, influenced by geothermal flow and constrained by the surrounding rock, generates thermal stress. [PERSON] et al. [4] proposed an approximate formula for calculating the temperature stress field of the rock body. Additionally, [PERSON], et al. [11] suggested that for each degree Celsius change in temperature, the rock generates thermal stress ranging from 0.4 to 0.5 MPa. [PERSON] et al. [12] investigated the influence of geothermal temperature gradients on predicting rock bursts, highlighting that thermal stress can double under constant pressure and horizontal principal stress conditions. They found that at the Sangzhuling tunnel site, rock thermal stress constitutes approximately 61% of gravitational stress. They emphasized that neglecting this thermal stress in rock burst predictions could lead to significant inaccuracies. [PERSON] et al. [13] performed experimental research focusing on the effects of temperature on tunnel rock bursts under thermal coupling conditions. Their study aimed to understand how thermal factors contribute to the occurrence of rock bursts in tunnels. Furthermore, [PERSON] et al. [14] carried out a comparative analysis of the impact of high geostress and high geothermal temperature on rock bursts in the Sangzhuling and Bayu tunnels. Their research aimed to elucidate how these factors individually and collectively influence the propensity for rock bursts in tunnel environments. Previous studies by experts have primarily focused on the impact of high geopathic stress on plastic zone expansion, along with the impact of temperature on thermal stress and surrounding rock stability. However, not many studies have explored the specific impact of thermal stress on the plastic zone expansion of tunnel surrounding rock, particularly in tunnels subject to both high geothermal temperatures and high geopathic stresses. This gap in research stems from the vertical stress measured by the hydraulic fracturing method in high geothermal environments failing to account for thermal stresses induced by the geothermal temperature gradient [12], thus resulting in potential deviations in the analysis of plastic zone expansion laws. Therefore, it is imperative to investigate the influence of these unaccounted thermal stresses on the expansion patterns of the surrounding rock's plastic zone in tunnels characterized by high geothermal temperatures and high geostresses using hydraulic fracturing methods. This paper emphasizes the high-temperature diversion tunnel of the Bulunkou-Konger hydropower station as the research subject. In particular, it assesses the morphology and expansion patterns of the plastic zone in tunnels with high geothermal temperatures and high geostresses. This study examines the influence of thermal stress on plastic zone morphology and surrounding rock stress characteristics through engineering examples by integrating plastic zone boundary equations that consider thermal stress in rock bodies with measurement data obtained from hydraulic fracturing methods. The endeavor is to provide a theoretical framework for understanding plastic zone expansion laws in tunnels along with the damage mechanisms of surrounding rock, facilitating tunnel excavation and support in practical applications.