Analyses of driving performance in mechanized tunnelling Determination model and actual examples

Transcription

1 Analyses of driving performance in mechanized tunnelling Determination model and actual examples Rainer Stempkowski Technical University of Vienna, Austria ABSTRACT: This paper presents a determination model for estimating the driving performance in mechanized tunnelling. To come to an average driving performance, the penetration has to be calculated first. With the help of the penetration an the rotational speed of cutter head the net-rate of advance is determined. After calculation the utilization factor, that describes the percentage of drilling time in comparison to the working hours, the action time or commission time, the total rate of advance can be worked out. With the aid of three examples the determination model is tested. Finally sensitivity analyses show the extent of influence of different parameters to the advance rate. 1 INTRODUCTION Since a main basis of costs in tunnelling is the determination of driving performance, all the main influences to the driving performance and their dependence on each other have to be analysed. Beside all the influences of the machine, various influences of the rock, the minerals, the water, and the training effect have to be taken into consideration. With the help of the presented model for determining the driving performance it is possible to estimate the advance rate and the construction time of any tunnel that is driven with TBM. The new driving-rate model is presented on three different examples, one tunnel with a small diameter, that has already been driven, one tunnel in progress and one tunnel with a big diameter, that is being designed at the moment. 2 DETERMINATION OF THE DRIVING PERFORMANCE To come to an average driving performance, the penetration has to be calculated first. In the second step the net-rate of advance depending on diameter of the machine and the penetration is determined. The next step is the calculation of the utilization factor that describes the percentage of drilling time in comparison to the working hours, the action time 1 or commission time. The result is an average total rate of advance per working day or per month. penetration [mm/r] net-rate of advance [theoretical maximum advance rate in m/h] utilization factor [%- drilling time / working hours, action or commission time] total-rate of advance [average driving performance in m per working day or m per month] Figure 1. Four steps to determine the advance rate 1 st step - penetration p The penetration is defined as intrusion depression of the discs into the rock during one revolution of the cutterhead. It depends on the drilling pressure of the TBM, the geology and the rocks. The higher the drilling pressure of the TBM the weaker the rock, and the smaller the strenghts of rock and minerals the higher is the penetration. One possibility to estimate the penetration was shown in my dissertation [Stempkowski 199]. With the help of a Drilling Rate Index (DRI) that is determined by the kind of rock and rock strength,

2 and the rock mass factor (f g ) that is determined by the classification of ground and the angle of tunnel axies and sheeting, the penetration can be found in the following figure. penetration p in mm / r Wienerwald-tunnel penetration p,5 1 1,5 2 2, rock mass factor fg DRI = 9 DRI = 8 DRI = 7 DRI = DRI = 5 DRI = 4 DRI = 3 DRI = 2 The net-rate of advance is the advance during drilling time. It is determined by the penetration [p] and the rotational speed of the cutter head [n]. net-rate of advance I N = p n 1 [m per hour] The rotational speed of the cutter head is in inverse proportion to the diameter of the cutter head and it can be calculated with n = f n / d [rpm]. The average rotation speed factor f n amounts to 5 with a bandwidth of +/- 1 %. More detailed datas for the maximum rotation speed of the cutter head can be received by the machine producers. For calculation it makes sence to reduce the maximum rotation speed to 8%, because a machine can t dive all time with a full speed. Figure 2. Penetration in dependence of rock factor and Drilling rate index (DRI) Dr. Gehring from the Tamrock company found a direct connection between penetration an axial compressive strength, that is shown in the next figure. I in m/h 8, 7,, 5, 4, 3, NET-RATE of ADVANCE I depending on the penetration p and the diameter of the TBM 1,24-2,18 m/h p=1mm/u p=8mm/u p=mm/u p=4mm/u p=2mm/u 2, 1,, 3, 4, 5,, 7, 8, 9, 1, 11, TBM - diameter in m Figure 4. Net-rate of advance 3 rd step - Utilization factor UF Figure 3. penetration in dependence of axial compressive strength [Gehring 1995] In general the penetration is of the order of 4 to 1 mm/r, with a technical maximum of 15 mm/r. As long as no detailed drillings have been made, the average penetration can never be calculated exactly but has to be estimated. 2 nd step - net-rate of advance I N The measure of utilization describes the real advance rate of the TBM. To determine the utilization factor the different components of the service life time of a TBM have to be analysed. The following figure gives an overview over service life time, commission time, action time and the working hours of the TBM. The drilling time is the only time when the TBM advances. In all other cases the machine stands still. (see figure 5) Three different kinds of utilization factors can be defined: 1. The Utilization Factor UF1 corresponds to the relation between the drilling time and the working hours and amounts in general to about 4 to 7%. 2. The Utilization Factor UF2 corresponds to the relation between the drilling time and the action time and is of the order of 3 to 5%. 3. The Utilization Factor UF3 corresponds to the relation between the drilling time and the com- 2

3 mission time - including the time for transport, installation and dismantling - and amounts in general to about 2 to 35%. SERVICE LIFE TIME OF A TBM COMMISSION TIME at site ACTION TIME REST DURATION at storage area UTILIZATION FACTOR 3 2% 2% 14% 1% % 11% 13% drilling time relocation time standstill due to working hours support & small repairs big repairs & down time installation time installation working time repair and down time Figure and 7. Utilization faktor UF1 and UF3 (example Wienerwaldtunnel) transportation drilling time big repairs site breaks 4th step - total advance rate I T installation dismantling measurement standstill due to working hours relocation time time for cutter-change small repairs & support- and lining work difficulties due to water training time Figure 5. Service life time of a TBM general alteration measures mush areas To come to the utilization factor every part of the service life time has to be analysed in detail. It would go beyond the scope to analyse all these parts within this paper, more details therefor can be found in the dissertation [Stempkowski 199]. On the example of the Wienerwald-Tunnel the Utilitation Factors UF1 and UF3 are shown in the following figures. 18% 21% UTILIZATION FACTOR 1 17% 44% drilling time relocation time standstill due to working hours support & small repairs The total advance rate is the real average driving performance of the TBM. Within the total advance rate not only the drilling time ( = base for net-rate of advance) is considered, but also all kinds of standstill, repairs and s, that are all considered for calculation in the utilization factor. In dependence on the three different utilization factors, three different total advance rates can be defined, too. I T 1 = I N x (UF1 / 1) x 24 I T 2 = I N x (UF2 / 1) x 24 I T 3 = I N x (UF3 / 1) x 24 [m per day] [m per day] [m per day] In the following figure 8 the three different total advance rates are shown in a time-advance-diagramm. The more flat the curve, the higher is the advance rate. I T 1 describes the advance rate of the working time, without considering bigger geological problems or bigger repairs. All bigger standstills like standstills due to mush areas or machine breakdowns can be figured out in the diagramm shown above. The second total rate of advance (I T 2) shows the average driving performance from the beginning of the driving work till the end of the driving. This is the most usual comparative figure for the advance rate. The third total rate of advance (I T 3) is the average advance rate of the period the TBM is on the site. In this rate the time for installation and dismandling of the TBM is also taken into account. 3

4 installation TBM time TOTAL-RATE of ADVANCE time - advance total lenght of tunnel training time advance mush area 1 I T 3 I T 1 Figure 8. Total rate of advance total rate of advance in m/month repair TBM dismantling TBM TOTAL RATE OF ADVANCE mush area 2 I T 2 7% % 5% 4% 3% 2% Utilization Factor UF2 5, m/h 4,5 m/h 4, m/h 3,5 m/h 3, m/h 2,5 m/h 2, m/h 1,5 m/h 1, m/h,5 m/h Figure 9. Total rate of advance as a function of the net advance rate (,5 to 5 m/h) and the Utilization factor UF2 (2 to 7%) As the total advance rate depends on the net rate of advance an the Utilization factor, the total rate of advance can be found with the help of the following figure. The curves are calculated on the base of 24 hours per day and 3,4 days per month. All standstills (for example due to working hours or site breaks) were already taken into consideration with the Utilization Faktor. 3 EXAMPLES The determination model was tested on three examples, the Austrian Sondierstollen Zell am See, a tunnel with a small diameter (3,5m), a part of the Vereina tunnel (diameter 7,m) in Switzerland and finally the Wienerwaldtunnel, a tunnel for high speed railway near Vienna with a lenght of 13 km and a diameter of 9,5m that should be build within the next years. For different kinds of rock classes (classification ÖNORM B 223,1994) the total rate of advance was calculated. The following figures show in a simplified way the results. penetration in mm/r net advance rate in m/h , 8, 7,, 5, 4, 3, 2, 1,, PENETRATION NET ADVANCE RATE Figure 1 Results of the calculation of the penetration and net advance rate for three different examples and three different rock classes (A,B,C) The better the geology and the harder the rock, the smaller is the penetration. The diameter of the tunnel leads to the net advance rate. The smaller the tunnel diameter, the higher is the rotational speed and the higher is the net rate of advance. Although a worse geology increases the penetration, a worse rock class also increases the part of standstills, what can be seen in the results of the utilization factor. 4

5 R1 utilization factor (UF2) in % total advance rate in m/month, 5, 4, 3, 2, 1,, 12, 1, 8,, 4, 2,, UTILIZATION FACTOR TOTAL ADVANCE RATE Figure 11 Results of the calculation of the utilization factor and total rate of advance for three different examples Due to the very low utilization factor in the bad rock classes (C) the total rate of advance decreases with worse rock class. The smaller the tunnel, the more difference is between good and bad geology. The results of a study made by P.P. Nelson show the average total rate of advance for a big number of tunnels. Most of the tunnels had an average total rate of advance between 2 and 4 meters per month. 4 SENSITIVITY ANALYSES The base for the calculation of the advance rates are special boundery conditions. To relativate possible changes in these boundery conditions, sensitivity analyses of the calculation of the advance rate have to be made. Therefor the basic influences of the advance rate - the machine, the rock and the rock formation - have to be taken into consideration. On the one hand there is a continous developement in the technology of machines and discs. An increase of the drilling pressure and of the rotational speed leeds to a high increase of the advance rate. (see figure 13) % variation of the advance rate 1% 2% 3% 4% 35% 3% 25% 2% 15% 1% 5% % 5% increase of the drilling pressure and increase of the rotational speed in % increase of the advance rate Figure 13. Variation of the advance rate resulting of an increase of drilling pressure and rotational speed number of tunnels total rate of advance in m per month average total rate of advance in m / month über 1 On the other hand the big question is always the geology of the rock. A variation of the axial compressive strenght of the rock leeds to a slightly less than inverse proportional variation of the advance rate. A reduction of the compressive strenght for example of 45% increases the advance rate to nearly 3%, an increase of the compressive strenght of the rock of 45% reduces the advance rate just a little bit more than 2 %. Figure 12. Average total rate of advance 5

6 5 CONCLUSION The aim of these analyses of possible szenaries which are based on mathematical models and other case studies is to work out the estimation of costs, advance rates and construction time of a tunnel as realistic as possible. The base for every estimation of construction time and in further way of costs is the advance rate. The paper figures out how important the definition of advance rate and utilization factor is. As there are big differences between for example the total rate of advance I T 1 and I T 3 a comparison between different kinds of tunnels would make not much sence without defining the conditions of the frame that is looked at. REFERENCES Amberg, Der Einsatz einer TBM bei hoher Überlagerung und großer Gebirgsfestigkeit, Felsbau 12/1994 Beckmann Uwe, Tunnelbohrmaschinen und ihr Einsatz im Festgestein, Tunnelbau Taschenbuch, 1985 Gehring Karlheinz, Leistungs- und Verschleißprognosen im maschinellen Tunnelbau, Felsbau 13/1995 Hamburger, Weber, Tunnelvortrieb mit Vollschnitt- und Erweiterungsmaschinen für große Durchmesser im Festgestein, Tunnelbau Taschenbuch, 1993 Jodl H.G., Stempkowski R., Operation research aspects of TBM drives - Case study of the Wienerwald Tunnel, in: Wagner, Schulter, Tunnel Boring Machines, Trends in Design and Construction of mechanized Tunnelling, Balkema, Rotterdam, 199 Platz H. Problem der Bauzeitprognose bei konventionellen Vortrieben, ETH Symposium, 1991 Maidl B., Herrenknecht M., Anheuser L. Maschineller Tunnelvortrieb im Schildvortrieb, Ernst&Sohn, Berlin, 1995 Nelson P.P., Tunnel Boring Machine Data Bases and Construction Simulation, Geotechnical Engineering Report, University of Texas, 1994 Stempkowski Rainer, Kosten- und Leistungsanalysen im maschinellen Tunnelbau, Dissertation TU Wien, 199 Uni Trondheim, Hard Rock Tunnel Boring, Projekt Report 1.88, Trondheim, 1988