ABSTRACT

Collapses are serious or even disastrous accidents during tunnel construction, which of frequent occurrence. This paper describes a method for assessing the risk associated with collapses in tunnels. The focus is put on collapses which occur in the tunnel constructed by drill and blast method. And the preference is attached to studying their causes and mechanisms and assessing their risk during tunnel construction.

On the basis of an extensive literature search, causes and mechanisms analysis of collapse is carried out. All the potential risk factors related to tunnel collapse are identified. The statistical analysis and the accident tree analysis are carried out to analyze the contribution of each risk factor to tunnel collapse. The importance ranking of risk factors is given. It can be confirmed that precise geological investigation and appropriate construction process are the most effective controllable factors for preventing the occurrence of tunnel collapse. Accident tree analysis is also employed to estimate the probability of collapse occurrence. And the analytic hierarchy process is employed to evaluate the potential loss of collapse. At last a whole approach for tunnel collapse risk assessment is presented.

1 INTRODUCTION

Collapses are a major hazard in tunnels for highways and railways in mountainous terrain, especially in tunnels constructed by drill and blast method. Apart from the damage such as high cost and downtime, the most vital feature of collapse is bringing about fatalities and serious injuries. According to the statistics, there are over 60 collapses during the construction of Guanjiao tunnel in Qingzang railway (Yang et al. 2003); 19 large-scale collapses in the construction of Dayaoshan tunnel (Sun et al. 2006). one collapse occurred every 86m on average in a zone of Dafengyakou tunnel. The statistic data of Japan shows that collapses account for 33% in tunnel accidents (Xian 1998). In brief the impacts of collapses should be taken into account very carefully. Therefore, causes of collapses have to be recognized, and procedure for collapses assessment must be established.

The collapse of tunnel has been discussed in many papers and textbooks. The Health and Safety Executive (HSE) carried out an investigation after the collapse of Heathrow Express Rail Link Station tunnels, and reported the causes of the collapses as unpredicted geological causes, planning and specification mistakes, calculation or numerical mistakes, construction mistakes and management and control mistakes (Dimitrios K. 2008); Seidenfuß (2006)provides a comprehensive categories for tunnel collapses and analyzes the different causes of collapses as well as their mechanisms on the basis of an extensive literature search; Feng w.x. et al.(2001) presents the causes, the treatment and the treatment effect of collapses through a lot of cases analysis. All the researches show that the uncertainty factors, such as inadequacy of geotechnical information, wrong choice of construction methodology, as well as improper organization of the works, initiate collapses.

How can we lower down these uncertainties to avoid or at least reduce collapses in tunnels in future? One effective way to do so is to understand and control these uncertainties.

This content is only available via PDF.
You can access this article if you purchase or spend a download.