|Publisher||International Society for Rock Mechanics||Language||English|
|Content Type||Conference Paper|
|Title||Tunnelling Performance Estimation Based On Drillability Testing|
|Authors||A.BRULAND, The University of Trondheim, The Department of Construction Engineering; T.S.DAHLØ, SINTEF Rock and Mineral Engineering; B.NILSEN, The University of Trondheim, The Department of Rock and Mineral Resources Engineering|
|Source||8th ISRM Congress, September 25 - 29, 1995 , Tokyo, Japan|
|Copyright||1995. A.A. Balkema. Permission to Distribute - International Society for Rock Mechanics.|
The Norwegian drillability tests and models for prediction of performance represent a useful tool for estimating time consumption and costs for tunnel excavation. Test results are discussed and an example of application is given.
Les tests de pénétrabilité Norvegiens et les modèles de prevision de fonctionnement offrent un moyen d'évaluation de la consommation de temps et des côuts pour Ie perçage de tunnels. Les résultats du test sont discutés et un example d'application est présenté.
Die norwegischen Versuche und Modelle zur Prognostizierung der Bohrbarkeit sind zusammen ein nützliches Instrument zur Veranschlagung von Zeit und Kosten beim Tunnelbau. Resultate von ausgeführten Versuchen werden vorgelegt, und ein Anwendungsbeispiel wird gegeben.
A variety of test methods and analyses are used to estimate tunnelling performance. One of the laboratories in the world having the widest experience with drillability testing is the rock engineering laboratory at the Norwegian Institute of Technology (NTH/SINTEF). The test procedures were developed in the 1960s for evaluating the drillability of rocks by percussive drilling. The last 15-20 years, the method has been used mainly for TBM performance prediction. Geological field mapping, rock sampling and rock testing form the basis for the performance prediction. Since the 1960s, about 2000 different rock samples have been tested at NTH/SINTEF (roughly 1500 Norwegian and 500 from other countries). By correlating laboratory and in-situ geological data to tunnelling results, performance prediction and cost evaluation models have been developed for drill and blast as well as TBM tunnelling (NTH 1988a, 1988b and 1994). The models are continuously updated and improved as new tunnelling data become available (Movinkel & Johannessen 1986, Lislerud 1987).
2. TEST METHODS
The Drilling Rate Index (DRI) is calculated on the basis of two tests, the Brittleness Test and the Sievers Miniature Drill Test. The Brittleness Test gives a measure of the ability of the rock to resist crushing from repeated impacts, see Figure 1. The volume of test material corresponds to 500 grams of specific gravity 2.65 g/cm³ of the fraction 16-11.2 mm. The Brittleness Value (S²º) equals the percentage of material passing the 11.2 mm mesh after the aggregate has been chrushed in the mortar, taken as the mean value of 3-4 parallel tests. The Sievers' Miniature Drill Test gives a measure of the surface hardness (or the resistance to indention) of the rock. The test is performed on a precut rock sample as shown in Figure 2. The Sievers' J-value (SJ) is the drill hole depth after 200 revolutions, measured in 1/10 mm, taken as the mean value of 4-8 drill holes. The precut surface of the sample must be parallel or perpendicular to the foliation of the rock. The SJ-value measured parallel to the foliation is used to calculate the DRI. Figure 3 is used to calculate the DRI. The DRI may be described as the Brittleness Value adjusted for the SJ-value. Chrushed rock powder finer than 1 mm passes under the loaded tungsten carbide bit. The Abrasion Value is the weight loss in milligrams of the test bit after 100 revolutions of the steel disc. 100 revolutions equals 5 minutes testing time. Figure 5 is used to calculate the BWI from the DRI and the Abrasion Value AV. The BWI is used to estimate the life time of drill bits (BWI expresses life in drilled volume). The Cutter Life Index (CLI) is calculated on the basis of Sievers' J-value and the Abrasion Value Steel, AVS. CLI expresses life time in boring hours of steel cutter rings on tunnel boring machines.
|File Size||1547 KB||4|