Based on system for structure and surrounding rockmass of highway tunnel

a three-dimensional model tests about forked tunnel with different altitudes were carried out to study the influence of construction of new forked tunnel with different altitudes on existing tunnel. Existing tunnel’s internal forces of supporting structure

surrouding rockmass internal pressure and internal displacements induced by constructing new tunnel

were measured. Testing data show as follows. Existing tunnel’s crown radial stress and hance tangential stress are keeping increasing

and crown tangential stress and hance radial stress are keeping decreasing. Surrounding rockmass internal displacements are compression deformation at crown and tensile deformation at hance. Existing tunnel’s axial forces and bonding moments of supporting structure keep increasing; and right hance moment of supporting structure increased most obviously. Constructing new tunnel has bad influence on existing tunnel’s section L1 and L4

and has little influence on existing tunnel’s section L8. The area in which adjacent spacing is less than section L8 should be strengthened.