A novel method, Critical Mechanism Pathway Analysis (CMPA), for analysing rock engineering hazards is presented, together with a pressure tunnel case example. Identification of critical mechanism pathways and stable or instable mechanism feedback loops in the mechanism structure can indicate the potential hazards for the purpose of engineering design control.
Une nouvelle methode - Critical Mechanism Pathway Analysis (CMPA) - d'analyser les hasards d'ingenierie des roches, avec un exemple d'un tunnel hydroelectrique. Identification de routes de mecanisme critique et de feed-back stable ou instable dans Ie structure du mecanisme peuvent indiquer les hasards potentiels dans Ie contrôle de I'ingenierie des roches.
Eine neue Methode - Critical Mechanism Pathway Analysis (CMPA) - die Gefahren des Felsingenicurwesens wird hier prasentiert, zusammen mit der Geschichte eines hydroelektrischen Tunnels. Identifikation der kritischen Mechanismuswege und der stabilen und instabilen Feedbacks in der Struktur des Mechanismus kann die potenticllcn Gefahren der Kontrolle des Felsingenieurwesens bezeichnen.
In rock engineering design, predicting potential hazards that may occur during project construction and performance is one of the major tasks. These potential hazards can be considered as an extreme state in the performance of an engineered project in which energy is released in an unexpected and uncontrolled way. Examples of hazards in rock engineering can be reviewed from historical cases of slope and dam failures, and rock collapse in underground excavations. Earlier failures to predict such hazards have claimed a huge human cost. It is becoming widely recognised that engineering disasters are rarely caused by inadequate precision of numerical modelling but more frequently by neglecting some critical elements in engineering design. This fateful negligence is mainly due to the complexity of rock engineering projects, which is a challenge for engineers in the sense of including all the relevant information necessary for design. To solve the problem, the subject of information audits naturally emerges, as presented in a companion paper ("Information Audits For Improving Rock Engineering Prediction, Design And Performance", Hudson & Jiao) in this Symposium. This paper is a complementary paper to the first one, and is aimed at presenting the analysis on potential hazards using Critical Mechanism Pathway Analysis (CMPA). The causes leading to hazards in rock engineering are divergent. In general, they may be categorised into two groups: external disturbances and the operation of internal mechanisms. External disturbances reflect the man-made and natural perturbations imposed on the engineered rock masses. The internal mechanism operations comprise all the mechanisms simultaneously operating in a project and which generate the systematic response of the combined rock mass-engineering project system to the perturbations. These mechanisms perform as system components that together transform the external perturbations to a system response with an amplifying or attenuating function, as illustrated in Fig 1. When the external perturbations are determined, the system response will depend only on the internal mechanism operations: a stabilising mechanism operation will lead to a stabilised response; otherwise; it will lead to instability - which may be an engineering hazard. Thus prediction of hazards relies on the understanding of the internal mechanisms. The internal mechanism operation in engineered projects has been characterized by Hudson (1992), Jiao (1995), Jiao & Hudson (1995) as mechanism pathways and feedback loops The concept of mechanism pathways and feedback loops can be illustrated by Fig. 2 which presents a network of some mechanisms involved in slope failure. In this figure, mechanisms are represented by arrowed arcs and mechanism pathways by the chains of arrowed arcs.