Choice of grouting method for jointed hard rock based on sealing time predictions

Abstract: This thesis concerns subjects related to the choice of agrouting method in a jointed hard rock mass. By calculating thetotal sealing time to reach the requested sealing level,different grouting methods could be compared and the mostfavourable chosen.A methodology, to calculate the sealing time for differentgrouting methods in different rock masses has been developed.Five main activities are included in the methodology; drilling,grouting, waiting, probing and re-grouting, which to differingdegrees contribute to the total sealing time. In addition, anextra activity, post-grouting, is regarded separately, as thepost-grouting time normally is not included in the totalsealing time. Within the different activities, subjects such asrock mass properties, examination of rock mass, groutingtechnique, grout mix and the different waiting times have beenstudied.In practice, the application of the methodology requiresthat the average time and variance for each activity on a fanlevel is expressed. The times for each activity are then addedtogether to achieve the total time for a fan. After which, thetime for each fan is added over the entire tunnel length tocalculate the total sealing time for a tunnel.E.g. for the grouting activity, joints belonging to agrouting fan are randomly selected from a joint aperturedistribution for the appropriate rock mass. For each joint in afan, distributions are calculated for parameters such asinflow, time and grouting volumes as e.g. sealing time andsealing effect. Then a Monte Carlo simulation based on thesedistributions and for each grouting fan is carried out and theaverage grouting time and variance calculated.To test the methodology, numerical calculations for threegrouting methods and in three rock masses have been carriedout. The most favourable grouting method is defined as themethod which fulfils the requirement in the shortest sealingtime.By analysing the result of the numerical calculations, ithas been shown that other activities besides grouting oftenhave a large impact on the total sealing time. To choosebetween pre-grouting and post-grouting is regarded as adecision problem, which is strongly related to other activitiesof the tunnel production cycle. A strong relationship was shownbetween the possibility to seal and the chosen grouting methodand grout mix. A long grouting time is not always equivalent toa good sealing result and the opposite has shown to bepossible.Further, calculations have shown that a correct combinationof hole spacing, grout penetration length and appropriatepumping time is essential for a good sealing result. Inaddition, this thesis has demonstrated a method as to how thiscorrect combination should be chosen in order to achieve anoptimal grouting solution. However, a decision regarding anappropriate grouting method, always needs to regard otheractivities of the tunnel production cycle.