The DSCA (Differential Strain Curve Analysis) which was proposed by Strickland and Ren in 1980 was applied to measure in-situ stress in the Kan-etsu 2nd tunnel. The basic assumption of the DSCA is that microcracks will be generated in a rock specimen by the stress relief when it is taken from borehole and the microcrack density is related to the earth stress. The object of this study is to validate this method. The overburden of the boreholes from which test specimens were taken was about 800m. Fourteen test pieces were carefully formed into a cubic shape with a side length of about 30mm. Total number of 18 foil strain gages were attached to each test piece, and hydro-static pressure up to about 50 MPa was applied on the test piece. The directions of principal strains were calculated using the outputs of 18 strain gages as a function of hydro-static pressure. From the relations between hydro-static pressure and principal strain, the directions of in-situ principal stresses were estimated. As a result, azimuths of principal stresses estimated from fourteen samples had almost the same tendency, although the dips of those were divided into two groups of different tendency. The ratio of the maximum, intermediate and minimum principal stress was estimated using both Strickland and Ren's method and Dey and Brown's method. The ratio estimated by the former method was 1.00: 0.69: 0.42 while the latter gave the ratio of 1.00: 0.64: 0.45. Finally, these results estimated from DSCA were compared with another method such as hydraulic fracturing method or stress relief methods. There were no apparent contradiction between these results.
