Abstract：The thermal diseases generally occur in the exposed rock at the tunnel portal section in the southern region，which is the main high temperature area in China. Solar radiation transmitted to the interior of rock through near-surface fractures，and thus the thermal stress field of rock is determined by the shape and distribution of fractures. The shallow fracture surface is triangle，which is the typical shape to study the stability of fractured rock. For the multi-fractured rock at tunnel portal in high-temperature，a heat source model is established based on the triangle fracture shape，and the distribution form and variation rule of the thermal stress field are obtained by using green's function method and mirror image method. In addition，the influence of fracture shape parameters and multi-fracture interaction are analyzed. The results show that the trend of thermal stress in exposed rock is consistent with that of solar radiation. Because of the fractures，the thermal stress field in shallow rock redistributes and the stresses at the tip of fractures increase. For triangular fractures with the same depth，the greater the apex angle，the worse the thermal stability of rock. The interaction of multiple fractures leads to the superposition of the thermal stress field around the fractures. The smaller the spacing between parallel fractures and coplanar fractures，the stronger the superposition effect of the stress field. The larger the spacing，the more the stress value tends to the stress of a single fracture. For the cross fracture，the superposition effect of the stress field is strongest when the included angle is 45°. The thermal stress isolines of multi-fractured rock appear around the fractures. The thermal stress around the fractures increases significantly，and the thermal stress field presents non-uniformity.
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2021, Vol. 40 
