An attempt of the ground risk evaluation in mountain tunnel survey

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In mountain tunnel construction project, the increase of construction expenses is the construction stage which occurs by unbridgeable gulf between ground evaluation in investigation and design stage and actual ground situation becomes a problem. As the one reason why such unbridgeable gulf occurs, the uncertainty of the investigation is considered. Therefore, it is important to evaluate not only ground evaluation as expectation value but also the uncertainty of ground evaluation, if the increase in the construction cost by unbridgeable gulf is caught as a risk.In this study, for the purpose of objectively evaluating the uncertainty of the ground evaluation, the uncertainty evaluation was tried by carrying out optimistic evaluation and pessimistic evaluation based on the seismic prospecting result.Actual ground situation seems to fall during optimistic evaluation and pessimistic evaluation, as long as the preliminary survey is not improper, if the uncertainty is appropriately evaluated. The technique which evaluates the uncertainty of ground evaluation based on the seismic prospecting result has not been established. Then, in making that actual ground situation fell during optimistic evaluation and pessimistic evaluation to be one judgment index, uncertainty evaluation technique of the ground evaluation was examined. In this paper, uncertainty evaluation of the ground evaluation was tried using 2 techniques of ground evaluation by a classification table and ground evaluation using the bore core evaluation point. As the result, we were obtained that actual ground situation falls during optimistic evaluation and pessimistic evaluation by ground evaluation technique using the bore core evaluation point.