Abstract
To design of countermeasures for the heaving road surface in mountain tunnel in service, it is necessary to estimate the cause and to understand the progression of the damage. Especially, it is necessary to qualify its loosing and deformation zone and to investigate mechanical properties around the tunnel. To investigate the deformation zone, the extensometer is often used. However, it takes a long time to understand the deforming zone. So, we thought that in order to qualify the deforming zone in a short time, it was necessary to investigate the depth distribution of rock strength. Here, it predicted that the strength of the area around the tunnel would have been weaker as the road surface is approached. And test sample of several depths by using core sample picked by boring was made. The strength characteristics according to depth by depth of the rock was investigated by typical laboratory test, which were uniaxial compression test, triaxial compression test, and measuring of unit weight.
Consequently, from the laboratory test described above the following characteristics was found. a) Uniaxial strength, triaxial strength, Young's modulus, and unit weight are decreased depth by depth. b) Poisson's ratio is increased depth by depth. c) At a certain depth or more, all values are almost constant.
As a result of measurement for about one year by using the extensometer installed at the time of the boring survey mentioned above, the slightly displacement in the loosen zone measured. From this measurement, it is considered that there is a correlation between the displacement generation depth due to swelling and the mechanical properties of the rock.
A numerical analysis model was created from the above survey results, and the design of the countermeasure was implemented.
In road tunnels in service in recent years, the number of cases in which vehicle traffic is affected is increasing for heaving. It is necessary to carry out a field survey to estimate the cause and grasp the progress of deformation in order to examine appropriate countermeasures when swelling is confirmed in tunnel in service. In particular, it is important to grasp the loosen zone of natural ground for studying countermeasures. For this purpose, survey boring is carried out, sampled by a boring core, and subjected to laboratory tests for grasping mechanical and physical characteristics, or an extensometer is installed in the borehole to understanding progress.
