The mechanical behaviour of intersection of horizontal adit and main tunnel in Wanxian to Liangping expressway in Southwest China is studied by using 3D finite element numerical simulation method and in-situ test. Due to adit construction

the research demonstrates the disadvantageous distribution of deformation and internal forces in intersection of adit and main tunnel

particularly in its side-wall connected to the adit. Comparing with the case of no adit

because of arch tunnel set being broken; the intersection structure is subjected to combination of complicated stresses including transverse stress

but not the axial stress. Therefore

it is necessary to take some reasonable reinforcement measures to guarantee safety of the intersection of adit and main tunnel. Furthermore

the intersection angle is more small

the stress concentration of intersection is more high. For example

while intersection angle is 60 degree

the maximum coefficient of stress concentration is up to 1.95; but while intersection angle is 90 degree

the maximum coefficient of stress concentration is about 1.5. The results are helpful for designing and construction of intersection of main tunnel and adit in major highway tunnel.