1、英文原文3D Behaviour of bolted rock joints:experimental and numerical study G. GrasselliDepartment of Earth Science and Engineering,Imperial College of Science,Technology and Medicine, London SW7 2BP,UK Accepted 29 June 2004Available online 16 September2004Abstract: Rock bolting is the most effective an
2、d also the most economical means of supporting excavations in rock. Various types of bolts are used today,and an understanding of the way in which these bolts work is essential for an optimal,safe,and economical use.Fully grouted,untensioned bolts have been commonly used in rock mechanics(i.e.,mines
3、,rock fall stabilisation,underground works)for many years.In the 1980s a new type of bolt,called Swellex,was developed,becoming more and more widespread because of their easy and fast installation. However,regardless of the type,the mechanical behaviour of the bolted rock jointis not fully understoo
4、d,and only the experience accumulated on rock bolting gives the know-how for the reinforcement calculation and execution.In this paper the different mechanical responses of full steel bars as opposed to the frictional Swellex are discussed. The study was done through experimental tests coupled with
5、numerical simulations.The analysis of the results obtained both from nite element(FEM) modelling,and from large-scale(1:1) shear tests on rock joints,reinforced with fully grouted rods and Swellex bolts, clearly shows that the two bolt types deform in dissimilar ways,responding very differently to s
6、hear load.Published by Elsevier Ltd.Keywords: Rock bolt; Swellex; Shear tests; Experimental tests 1.Introduction Excavation size is a key parameter in the stability of underground openings in rock, and the larger the excavation, the less stable the roof tends to be. In very poor rock masses, large e
7、xcavations have an unsupported stand-up time less than the minimum time required to support the roof after the excavation. Therefore, the principal objective in the design of a support system is to help the rock mass to support itself. During recent decades the use of rock bolts, which actually form
8、 a part of the rock mass, has become more and more widespread. Indeed, the use of rock bolts is a very exible method that can be combined with wire mesh, shotcrete and concrete lining to cope with almost any situation encountered during mining or tunnelling. According to Kovari, the history of rock
9、bolting began with a patent specication (no. 302909) submitted by Stephan, Frohlich and Klupfel in 1913. However, it was only in the 1940s that the use of rock bolts became common in the American mining industry. Although anchors have been used for few projects in North America and Europe in the ear
10、ly 1950s, it was in Australia with the Snowy Mountains Scheme Project that, for the rst time, a series of studies have been undertaken for a better scientic understanding of the mechanics of rock bolting, establishing anchors as method of permanent rock support in civil engineering. In Europe, rock
11、bolting began to be used extensively only when the rst tunnels were built according to the New Austrian Tunnelling Method (NATM) in the 1960s. During the 1970s and 1980s a number of researchers carried out in-situ tests for monitoring the behaviour of installed rock bolts, and the use of rock boltin
12、g became a standard method for rock mass support. In those years a wide variety of dowels and bolt types were developed to meet different needs which arise in mining and civil engineering. In the 1990s Lunardi showed that, instead of relying on supporting the ground following excavation, the use of
13、rock bolts for systematic pre-reinforcement of the front of the tunnel increases rock strength prior to excavation, increasing the stability and safety of the underground works. Today, especially in tunnelling, the reinforcement of jointed rock masses with anchors is widely used because of its prove
14、d efcacy and its low cost. However, the exact mechanism of resistance of the bolted system is difcult to analyse, and this is due to three aspects: the presence of a discontinuity with its roughness, the presence of several different materials (bolt, rock, grout or resin) with different mecanical be
15、haviours, and the three-dimensional aspect of the system that is hard to simulate (i.e., bolt typology, bolt orientation, and load conditions). It is certain that the bolts increase the rock mass resistance, but the magnitude of this increase is hard to calculate. As a consequence, there is no unani
16、mously approved method for the design of the reinforcement system, and most of the techniques are left to the practical experience of the engineer. 2.Past studies Many experimental tests have been performed in order to study the mechanical behaviour of bolted rock joints. A number of researchers carried out experimental programs on different types of rocks, reinforced by various elements. A wide variety of bolt and dowel types have been developed, indeed, t
