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Theory of structures
Published in Angus J. Macdonald, Structure and Architecture, 2018
It was fortunate that, as Addis has pointed out, ‘One of the advantages of the masonry arch is that it is actually quite difficult to build an arch that will fall down’ (1990, p. 137). This should not be judged as a flippant remark as it encapsulates a fundamental property of masonry: the ability to bridge an opening without the support of a lintel. Such a property is demonstrated when an opening in a wall occurs unintentionally, for example in war zones where shell holes may occur in masonry walls without causing them to collapse. The mechanism that produces the ‘bridge over unintended openings’ is one of natural arch formation. The stones above the hole settle slightly under gravity and lock themselves together to form an arching effect that re-establishes equilibrium without the need for any particular profile along the upper edge of the opening.
Excavations
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
A correctly-supported excavation prevents the new conditions of loading in the ground around it from causing either excessive deformation of the excavated profile or failure of the surrounding ground. The movement of ground into an excavated space encourages an arching effect, as illustrated in Fig. 16.19a. This strengthens the ground in the vicinity of the excavation and in strong rocks the natural arch may have strength enough to support the surrounding ground: a condition described as ‘self-supporting’. This response requires time to occur (Fig. 16.19a) which means that there is no unique value for ‘ground pressure’, and that the response will happen more quickly at some sites than at others, depending upon the strength of the ground, the stresses within it and the size, and shape of the excavation (Brown et al., 1983).
Centrifugal model test on the clay arching
Published in T. Adachi, K. Tateyama, M. Kimura, Modern Tunneling Science and Technology, 2017
W. Binglong, Z. Shunhua, G. Quanmei, Y. Longcai
Enough thickness of superimposed soil and certain deformation are important conditions for arching.The stable natural arch emerges in the layer II. During the excavation of single hole, the height of arch is 5.1m.In the layer II, the excavation of double holes needs the thickness of superimposed layer II to be at least 7.0 m.When there is bracing structure, the earth pressure at the top of the hole is basically equal to the own weight of the superimposed soil. In this case, arching can not emerge.
Stress redistribution and formation of the pressure arch above underground excavation in rock mass
Published in European Journal of Environmental and Civil Engineering, 2021
Xiaoxuan Kong, Quansheng Liu, Yucong Pan, Jianping Liu
The location and features of the pressure arch have also been studied based on the description and analysis of the deformation and the stress state of the surrounding rock mass after the excavation. Jakobson (1958) defined the extent of a pressure arch where the ratio of the horizontal to vertical stress was greater than the lateral pressure coefficient, and Evans (1983) established the relationship between vertical deflection, lateral thrust and stability of a jointed roof. The peak value of the transferred load was considered as the ability of the arching mechanism (Liang & Sanping, 2002). Huang, Broch, and Lu (2002) and Liang, Liu, and Zhao (2005) studied the formation mechanism of the natural arch and defined the boundary of arching area based on the direction and the magnitude of the principle stress. Lee, Wu, Chen, and Chiang (2006) evaluated the arching zone by the arching ratio, the ratio of the change of stresses and the total overburden pressure above the spring line, during tunnelling by centrifuge tests and 2D numerical simulations. The inflection points of vertical stress-depth curves above the tunnel roof were analysed by Chen, Huang, and Tseng (2011) as an index to show the development of ground arch, and the arching coefficient was proposed by Zhang, Zhang, Zhou, Dong, and Ma (2016) to analyse the arching effect by the height of the shearing bands around the underground openings.