Geotechnical and Geological Engineering

, Volume 28, Issue 3, pp 241–249 | Cite as

Characterization of a Sedimentary Soft Rock by a Small In-Situ Triaxial Test

  • Abbas Taheri
  • Kazuo Tani
Original Paper


To measure the shear strength and deformability of a sedimentary soft rock, a small down-hole in-situ triaxial testing method is developed. The apparatus consists of a triaxial cell and an axial loading device which enables testing at any depth. In this method, a columnar specimen of diameter 90 mm and 285 mm height can be sheared at the bottom of a drill hole. A series of tests were conducted at a 50 m deep experimental cavern. The test gallery is contained in mudstone with some inter-bedded thin sand layers. The tests were done in three different depths in a borehole by a multiple-step loading method. The new testing method was successful to measure stress–strain relation of rock mass. The test results demonstrated that the multiple-step loading method is acceptable in mudstone formation, if an appropriate criterion for load reversal is selected to recognize the instant of failure by stress–strain relation during loading. In addition, different results for mechanical properties of mudstone rock mass were observed in the specimens contained sand layers. It is also concluded that, the same loading method is not successful if a sand layer is located in the middle of the specimen due to large damage induced in early stages of loading.


In-situ test Triaxial test Shear strength Stiffness Mudstone Multiple-step loading 


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Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  1. 1.Geotechnical Lab, Department of Civil EngineeringYokohama National UniversityYokohamaJapan

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