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在一些大坝工程中,有关岩体应力的现象引起人们的关注。J·Muller(奥地利,1963)曾以瓦依昂坝失事为例,说明残余应力对地面工程的影响,并提出一些相应的处理方法。在第八届国际大坝会议上(1966),N.Hast(瑞典)指出,在修筑大坝前必须充分分析坝基岩体的应力状态,并预测建坝后的应力状态的变化。在第三届国际岩石力学会议上(1974),一些欧州学者如Manuel Rocha陈述过开挖基坑将引起基坑底板岩石斜交地表的剪切断裂和水平分离。关于地表和地下大尺寸开挖及其有关应力问题被列为国际工程地质协会第五层会议的主要议题之一,这表明人们的认识日益深化且受到重视。 全世界地壳应力实测的上万数据表明,水平应力大于垂直应力且大于按自重计算应力的例子大约占75％。我国几个大尺寸开挖的水电工程现场如葛洲坝、三峡和二滩工程等亦属此类。在大的初始水平应力作用下,决定大尺寸开挖或自然侵蚀而引起的应力～应变变化的主要因素是地表几何形态随开挖或侵蚀过程的变化。 本文以葛洲坝工程二江电厂基坑为实例,视发生卸荷效应的地表人工坑槽和自然侵蚀河谷为半无限空间弹性体的边缘缺口,建立其卸荷效应的线弹性断裂力学模型。本模型用于岩质高边坡和坝基稳定分析可能是可取的简便方法。
In some dam projects, the phenomenon of rock mass stress has drawn attention. J. Muller (Austria, 1963) used the case of the Wairang dam as an example to illustrate the effect of residual stress on the ground engineering and proposed some corresponding treatment methods. At the 8th International Dam Conference (1966), N. Hast (Sweden) pointed out that the stress state of the rock mass of the dam foundation must be fully analyzed before the construction of the dam, and the change in the stress state after dam construction must be predicted. At the 3rd International Symposium on Rock Mechanics (1974), some European scholars such as Manuel Rocha stated that excavation of foundation pits would cause shear fracture and horizontal separation of the basement rock of the foundation pit. The issue of large-scale excavation of ground surface and underground and its related stress has been listed as one of the major topics of the fifth session of the International Engineering Geological Association. This shows that people’s understanding has become increasingly deeper and more important. The tens of thousands of data on the measured crust stress in the world show that the horizontal stress is greater than the vertical stress and is greater than about 75% of the calculated stress based on its own weight. Several large-scale excavated hydropower projects in China, such as the Gezhouba, Three Gorges, and Ertan Projects, also belong to this category. Under the influence of large initial horizontal stress, the main factor that determines the stress-strain change caused by large-scale excavation or natural erosion is the change of surface geometry with excavation or erosion process. In this paper, the excavation of the Erjiang Power Plant on the Gezhouba Project is taken as an example. The artificial pits and natural erosion valleys with unloading effect are considered as the edge gaps of the semi-infinite space elastic body, and a linear elastic fracture mechanics model of the unloading effect is established. This model may be a desirable and convenient method for the stability analysis of high rock slopes and dam foundations.