Simplified Hydraulic Jacking Test to Assess Fracture Normal Stress for Unlined Pressure Tunnels: A Field Experiment Using the Rapid Step-Rate Test

Abstract This paper describes an experimental campaign where a simplified test method. The Rapid Step-Rate Test (RSRT) has been investigated in full-scale field setting. test, originally developed to assess rock stresses for pressure tunnel considerations, had earlier laboratory study demonstrated promising ability the magnitude of fracture normal stress. presented herein was therefore aimed at assessing applicability this test. experiments were conducted inside Løkjelsvatn Hydroelectric Power Plant Norway, under conditions identical those which developed. A total 29 individual tests 7 boreholes, providing 20 cycles with interpretable results. stress estimates made from not affected by near-field showed good correlation minimum principal found preceding hydraulic fracturing and over-coring measurement campaign. experience suggests that RSRT can represent efficient reliable method stress, particularly useful final design unlined tunnels.