In situ stress is important parameter in rock engineering. Lining type of water way system in power plants is depended to minimum in situ stresswhich determined with several methods such as hydrojacking. Siah Bisheh power plant was the first pumped storage project in Iran which experienced hydrojacking tests. In order to precise steel lining limit at water way system some hydrojacking and hydrofracturing tests have done by Solexpert Company. This paper explains preliminary work sequence in the hydrojacking and hydrofracturing tests and presents the results of and conclusion of hydrojacking tests in Siah Bisheh project.


One of the important point in water way system lining is minimum in-situ rock stress which depend to overburden and geotechnical stress. When minimum in-situ rock stress is less than inner water way pressure, steel lining is proposal for prevent water injection to surrounding rock mass. One of the convenience borehole methods for in-situ stress measurement is hydrofracturing. Hydrojacking is the simplified approach for minimum in situ stress which is important method for precise steel and concrete lining boundary. Hydraulic testing of preexisting fracture (HTPF) has similarity with hydrofracturing test but they are different. The hydrofracturing test (HF) is done in rock mass without discontinuity but HTPF is done in more discontinuity rock mass. In HF test direction of minimum stress can be measured by impression packer. HTPF and HFwere done in Siah Bisheh Hydro electrical power plant at the north of Iran.


Several HF and HTPF test were done in water way system. Minimum in-situ stress at test zone of right headrace tunnel with 66m length and surge chamber with 55m shown that permeability are very high. The minimum in-situ is perpendicular of opened crack which impression packer can show the direction of stress tensor.

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