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Abstract Based on statistical analysis of the measured in-situ stress results in seven dam areas of the west route of South-to-North Water Transfer Project by using hydrofracturing method，the piecewise linear relationship between magnitude of maximum horizontal principal stress and borehole depth is obtained in steep and narrow river valleys. The analysis results also show that the magnitude of maximum horizontal principal stress increases less in shallower parts(stress relief zone) but increases more in deeper parts(stress concentration zone) with the increment of buried depth of rocks. In addition，back analysis for in-situ stress field in Ada dam area is carried out by using the fast Lagrangian analysis of continua in 3 dimensions(FLAC3D). The results are as follows：(1) The stress field in shallow bank slope areas is obviously affected by unloading effect of river valleys；so the hydrofracturing method might not be used to determine the stress of this local area. The orientation of stress field in the riverbed is practically unaffected by unloading effect；and the hydrofracturing method can be used to determine the state of stress in the river valley. (2) The initial stress field both in the river valley and along the bank slope may be divided into three parts，i.e. stress relief zone，stress concentration zone and smooth stress zone. (3) The depth of stress concentration zone in steep and narrow river valleys is between 60–140 m beneath the riverbed. (4) The depth of stress concentration zone in steep and narrow river valleys is greatly affected by unloading characteristics of rock masses as well as geographical and topographic features.
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Received: 14 February 2011
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2011, Vol. 30 
