法向卸荷条件下非贯通节理岩体剪切力学特性试验研究  

Shear mechanical properties of rock mass with discontinuous joints under unloading normal stress

作　　者：杨超[1,2] 蒋淏南 岳六一 王乐华[1,2] 骆祚森 王瑞红[1,2] YANG Chao;JIANG Hao-nan;YUE Liu-yi;WANG Le-hua;LUO Zuo-sen;WANG Rui-hong(Key Laboratory of Geological Hazards in Three Gorges Reservoir Area,Ministry of Education(China Three Gorges University),Yichang 443002,China;College of Civil Engineering&Architecture,Yichang 443002,China)

机构地区：[1]三峡库区地质灾害教育部重点实验室(三峡大学),湖北宜昌443002 [2]三峡大学土木与建筑学院,湖北宜昌443002

出　　处：《岩土工程学报》2022年第9期1741-1750,F0003,共11页Chinese Journal of Geotechnical Engineering

基　　金：国家自然科学基金项目(42177132);湖北省自然科学基金重点类项目(2020CFA049,2021CFA090)。

摘　　要：实际中较多处于压剪应力状态的岩体在开挖后的受力路径为法向应力卸荷。鉴于此,通过相似材料制备不同粗糙度JRC的非贯通节理试样,开展了法向应力σ逐渐减小的卸荷直剪试验,并与常规直剪试验进行了对比。试验结果显示,两种应力路径下试样在破坏和强度特征等方面的变化规律均有所不同:随着JRC的逐渐增加,法向卸荷下试样破坏表现出更强的张拉特性,常规直剪下试样则表现出更强的剪切破坏特性;无论是法向卸荷还是常规直剪,试样的强度均随JRC的增大而增大,但法向卸荷主要体现在φ值的增加上,而常规直剪则主要表现为c值的增加。其主要原因在于,法向卸荷下是σ逐渐减小,因此试样的爬坡效应更加明显。常规直剪则是剪应力τ逐渐增大,从而啃断效应更加明显。实际工程中应结合岩体受力路径获取强度参数,若按常规直剪试验强度参数推导法向卸荷下试样的强度,其值将远大于试样的实际强度,从而偏于不安全。最后基于Jennings强度准则提出了考虑岩桥弱化与JRC影响的修正模型,模型预测结果与试验值误差在10%以内,表明建立的模型可较好地用于法向卸荷下非贯通节理岩体强度的预测。In practice, the rock masses in a state of compression-shear stress are subjected to the normal stress unloading path after excavation. In view of this, the specimens of discontinuous joints with different roughnesses JRC are prepared by using the similar materials, and then the unloading shear tests with gradually decreasing normal stress σ are carried out, and compared with the conventional direct shear tests. The test results show that the change laws of failure and strength characteristics of the specimens under two stress paths are different: with the increase of JRC, the specimens under unloading normal stress exhibit stronger tensile failure characteristics, while those under conventional direct shear show stronger shear failure characteristics.The strength of the specimens increases with the increase of JRC under both the normal stress unloading and the conventional direct shear, but the normal stress unloading condition is mainly reflected in the increase of φ, while the conventional direct shear condition is mainly expressed in the increase of c. The main reason is that the normal stress unloading condition exhibits a gradual decrease in σ, resulting in a more obvious climbing effect. The conventional direct shear condition shows a gradual increase in shear stress τ, resulting in a more obvious gnawing effect. If the strength of the specimens under normal stress unloading is deduced according to the strength parameters of the conventional direct shear tests, it will be much greater than the actual strength, which may lead to unsafe results. Finally, a modified model considering the weakening of rock bridge and the influences of JRC is proposed based on the Jennings criterion. The errors between the theoretical prediction and the experimental results are less than 10%, which shows that the proposed model can be better used to predict the strength of discontinuous jointed rockmass under unloading normal stress.

关 键 词：岩石力学 非贯通节理 法向卸荷 粗糙度 强度准则 

分 类 号：TU435[建筑科学—岩土工程]