Probabilistic modelling of the plastic zone of underground exca va tions in rock masses

Tese (doutorado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Civil e Ambiental, 2007.A disseminação das obras subterrâneas é uma notória tendência mundial em virtude de todo o seu potencial na liberação do espaço superficial. A integridade de suas estruturas é fundamentalmente conferida pelo sistema de suporte, cujo papel é diretamente influenciado pelo comportamento da zona plástica. Contudo, a previsão desse comportamento é bastante difícil, visto a dependência das tensões na zona plástica com respeito à resistência do maciço rochoso, das condições de carregamento e da geometria da abertura. Assim, esta pesquisa propõe a metodologia probabilística de previsão, onde sua aplicação visa a previsão do comportamento da zona plástica para certo grau de confiabilidade, durante as várias fases de vida das estruturas de uma obra subterrânea. Para tal, se utilizou dados provenientes do túnel de Yacambú-Quíbor, cujo histórico é rico em extremos eventos decorrentes dos processos de "squeezing", por exemplo, em 1979 uma "tuneladora" ("Tunnel Boring Machine" - TBM) foi completamente destruída por um rápido e intenso processo de "squeezing". The dissemination of underground excavations is a well-known worldwide trend due to its potential to release the superficial space. The integrity of its structures is basically assured by the support system, whose function is directly influenced by the behaviour of the plastic zone. However, the prediction of the plastic zone behaviour is very difficult because of the relation between the stresses in the plastic zone and the strength of the rock mass, the loading conditions and the geometry of the opening. Thus, this research proposes a forecast probabilistic methodology where the application aims to predict the behaviour of the plastic zone within certain significance level, during several phases of underground excavation: design, construction and rehabilitation. Finally, it was used data from the Yacambú-Quíbor tunnel, whose constructive history is rich in extremes events due to squeezing process; for instance, in 1979 a tunnel boring machine was trapped and completely destroyed by a fast process of squeezing. ________________________________________________________________________________________________ ABSTRACTThe dissemination of underground excavations is a well-known worldwide trend due to its potential to release the superficial space. The integrity of its structures is basically assured by the support system, whose function is directly influenced by the behaviour of the plastic zone. However, the prediction of the plastic zone behaviour is very difficult because of the relation between the stresses in the plastic zone and the strength of the rock mass, the loading conditions and the geometry of the opening. Thus, this research proposes a forecast probabilistic methodology where the application aims to predict the behaviour of the plastic zone within certain significance level, during several phases of underground excavation: design, construction and rehabilitation. Finally, it was used data from the Yacambú-Quíbor tunnel, whose constructive history is rich in extremes events due to squeezing process; for instance, in 1979 a tunnel boring machine was trapped and completely destroyed by a fast process of squeezing