Abstract：Due to the complicated structure and the influence of multiple disturbance of surrounding rock in period of construction，the mechanical behaviors of portal section of half-buried tunnel differ greatly in different construction stages，which brings great difficulties to construction and monitoring. According to the proportion of horizontal and vertical loads borne by the structure，the portal of the half-buried tunnels is divided into three types，i.e. thrust portal，compression portal and combined thrust-compression portal. Numerical simulation is carried out to research the distribution and the developing law of displacement and stress under different conditions. By analyzing the mechanical characters，the weakest positions are detected and the essential monitoring items are also listed in different stages of construction for different types of structures. Based on these results，in-situ monitoring is carried out in four actual highway tunnel engineering. In-situ monitoring results indicate that：(1) the distribution and the developing law of displacement and stress agree with the theoretical results perfectly；(2) the positions and failure modes of structures accord with the theoretical results；and (3) abnormal deformation of structures can be effectively controlled by adopting reasonable measures according to the deformation mechanism of corresponding structure under load. The presented conclusions can provide references for design，construction and in-situ monitoring of similar tunnels.
