深切河谷区地应力场分布规律研究

STUDY OF DISTRIBUTION REGULARITIES OF IN-SITU STRESS FIELD IN STEEP AND NARROW RIVER VALLEYS

基于对南水北调西线工程7个坝址区水压致裂法地应力测试结果的统计分析,初步得出深切河谷区最大水平主应力量值随深度呈分段线性关系的结论。分析结果还表明在河谷埋深较浅部位(即应力释放区),最大水平主应力值随深度的增加幅度较小,而在较深部位(即应力集中区),最大水平主应力值随深度的增加幅度较大。此外,利用有限差分程序FLAC3D,对阿达坝址区的地应力场进行反演。研究结果表明:(1)河谷卸荷作用对浅部谷坡的地应力场影响较大,在该区域采用水压致裂法确定地应力场误差可能会比较大;而对河床区域应力场方向的影响较小,采用水压致裂法来确定河床区域的应力场是可行、可靠的;(2)不仅河谷区地应力场存在3个分区即应力释放区、应力集中区和应力平稳区,岸坡地应力场也存在上述3个分区;(3)阿达坝址区河谷底应力集中范围在河床下60～140 m范围内;(4)深切河谷区应力集中区的深度受岩体卸荷强弱程度和地形地貌的差异影响较大。

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（FLAC3~）. 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.