Response of Underground Pipes to Blast Loads

Abstract

Underground structures are divided into two major categories, fully buried structures and partially buried structures regardless of the shape of the structure. Underground cylindrical structures like pipes, shafts, tunnels, tanks, etc. are used for services such as water supply, sewage, drainage, etc. Most structures have now become targets of terrorist attack in recent years. Examples are 1995 Paris subway in France, 2004 Moscow subway is Russia (Dix, 2004; Huabei, 2009), 1995 Alfred Murrah Federal Building in Oklahoma City. The main sources of blast are: terrorist attacks, war, accidental explosion from military formations, etc. The constituents of blast comprises of: 1) rock media, 2) soils, 3) structure, 4) thin-layer elements surrounding the structure; blast loads, and 5) procedure for the analysis of interaction and responses of these constituents. In order to synchronize the interaction and responses of these variables, relevant data is required which could be obtained from field tests, laboratory tests, theoretical studies, work done in related fields and extension of work done in related fields (Ngo et al., 2007; Greg, 2008; Bibiana & Ricardo, 2008; Olarewaju at al. 2010a). There are lots of methods available to determine the responses of underground structures to blast loads. These are: i) the analytical methods, and ii) the numerical methods using numerical tools (Ngo et al., 2007; Peter & Andrew, 2009). The problem of analytical method is that the solution allows only a small elastic response or limited plastic response and does not allow for large deflection and may lead to unstable responses. To overcome these problems, the finite element analysis paves the way towards a more rational blast resistance design. Though the drawback is the time and expertise required in preand post-processing for a given structural system. In structural design, the methods of structural analysis and design are broadly divided into three categories, namely, theoretical methods which can be used to carry out analysis and the use of design codes, by testing the full size structure or a scaled model using experimental methods, and by making use of model studies (Ganesan, 2000). There are different types of static and dynamic loads acting on underground pipes. In the case of static loads, there surcharge load on the ground surface due various engineering activities. In the case of dynamic loads, these are cyclic load, earthquake, blast, etc. Blast being one of the dynamic load acting on underground pipes either from surface blast, underground blast, open trench blast or internal explosion is a short discontinuous event.