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Geomechanics and Engineering
  Volume 11, Number 4, October 2016, pages 531-552
DOI: https://doi.org/10.12989/gae.2016.11.4.531
 


Experimental investigation of long-term characteristics of greenschist
Qing-Zhao Zhang, Ming-Rong Shen, Wen-Qi Ding, Hyun-Sic Jang and Bo-An Jang

 
Abstract
    The greenschist in the Jinping II Hydropower Station in southwest China exhibits continuous creep behaviour because of the geological conditions in the region. This phenomenon illustrates the time-dependent deformation and progressive damage that occurs after excavation. In this study, the responses of greenschist to stress over time were determined in a series of laboratory tests on samples collected from the access tunnel walls at the construction site. The results showed that the greenschist presented time-dependent behaviour under long-term loading. The samples generally experienced two stages: transient creep and steady creep, but no accelerating creep. The periods of transient creep and steady creep increased with increasing stress levels. The long-term strength of the greenschist was identified based on the variation of creep strain and creep rate. The ratio of long-term strength to conventional strength was around 80% and did not vary much with confining pressures. A quantitative method for predicting the failure period of greenschist, based on analysis of the stress.strain curve, is presented and implemented. At a confining pressure of 40 MPa, greenschist was predicted to fail in 5000 days under a stress of 290 MPa and to fail in 85 days under the stress of 320 MPa, indicating that the long-term strength identified by the creep rate and creep strain is a reliable estimate.
 
Key Words
    greenschist; hard rock; creep behaviour; creep stage; creep rate; long-term strength
 
Address
(1) Qing-Zhao Zhang, Ming-Rong Shen, Wen-Qi Ding:
Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai, SH 200092, China;
(2) Qing-Zhao Zhang, Hyun-Sic Jang, Bo-An Jang:
Department of Geophysics, Kangwon National University, 1 Kangwondaehak-gil, Chuncheon, Gangwon-do 24341, Republic of Korea;
(3) Ming-Rong Shen, Wen-Qi Ding:
Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai, SH 200092, China.
 

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