In this paper, a new method named two points method is proposed to determine the three dimensional stress state over the thickness of the tunnel lining and also the external forces acting at its back surface. It is found that every stress component distributes linearly on the direction perpendicular to the surface of the lining when the ratio R/H larger then 8, where H is the thickness and R the average radius of the lining. Utilizing this characteristics, stress distribution along an arbitrary line perpendicular to the lining can be known by measuring the stress states at two points along its line. It can be recommended that one of the two points should be positioned on the inside surface and the other in the middle section of the lining.
To measure the stresses at these two points the stress relief method is applied. For the second measuring point, a modified Leeman's method is applied and the corresponding observation equations as shown in Eq.2 are derived based on a numerical stress analysis.
In order to verify the reliability of this newly proposed method and to find out every possible factors affecting the results, some laboratory tests were conducted and satisfactory results were successfully obtained.
