Influence of rock mass properties on TBM penetration rate in Karaj-Tehran water conveyance tunnel

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1 Journal of Geology and Mining Research Vol. (), pp. -, October Available online ISSN 97 Academic Journals Full Length Research Paper Influence of rock mass properties on TBM penetration rate in Karaj-Tehran water conveyance tunnel M. Mansouri and H. Moomivand * Tarbiat Modares University, Tehran, Iran. Faculty of Engineering, Urmia University, Iran. Accepted September, Predicting penetration rate (PR) of tunnel boring machine (TBM) due to the properties of rock mass surrounding tunnel has been an important subject in the mechanized method of excavating tunnel. Influence of uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), peak slope index (punch penetration), spacing of discontinuities (of weakness planes), orientation of discontinuities with respect to the tunnel axis ( angle) on penetration rate of TBM was investigated while excavating Karaj- Tehran water conveyance tunnel by a double shield Herencnesht TBM. Statistic analysis was carried out on the relationship between measured test results of the five different parameters of rock mass properties and the penetration rate of TBM. The results showed that each of the five different parameters of rock mass properties individually has affected the penetration rate of TBM. The relationship between peak slope index (PSI) and penetration rate of TBM has the best correlation coefficient (r) of.7 in comparison with the four others relationship between rock mass properties and the penetration rate of TBM. The relationship between BTS of rock and PR of TBM has a very poor correlation coefficient (r) of.. Multilinear regression analysis was applied to indicate the combined influence of the five different rock mass properties on the penetration rate of TBM using a database of measured test results. A new empirical formula was achieved to predict PR of TBM as a function of different rock mass properties (r =.7). Key words: TBM, penetration rate, rock mass properties. INTRODUCTION The performance analysis of the tunnel boring machine (TBM) for finding an accurate predicting model has been an important subject since the first TBM machine was built. Graham (97) estimated the penetration rate of TBM using unixial compressive strength rock (UCS). Farmer and Glossop (98) suggested a relationship between Brazilian tensile strength and penetration rate (PR) in alluvial rocks. Sapigni et al. () used the rock mass classification for prediction of TBM performance. Gong and Zhao (7) studied the influence of rock *Corresponding author. h.moomivand@urmia.ac.ir. brittleness on TBM penetration rate in Singapore Granite. Yagiz (7) incorporated effect of some more rock mass properties on TBM performance in hard rock. Balci (9) in Turkey has studied the correlation of cutting test with field performance of a TBM in a high fractured rock formation. Jafar et al. () has prepared a formula for performance prediction of hard rock TBM by using rock mass rating (RMR) system. Effects of uniaxial compressive strength, tensile strength, peak slope index (punch penetration), spacing of discontinuities and orientation of discontinuities with respect to the tunnel axis (β angle) on penetration rate of TBM were investigated while excavating Karaj-Tehran water conveyance tunnel by double shield Herencnesht

2 Mansouri and Moomivand a U geological map, composed of shale and siltstone Tunnel direction Figure. (a) Geological map of U - (b) Cross section of U (Sahel Consulting Engineers ). b TBM, both in the field and in the laboratory. Karaj-Tehran conveyance tunnel located between Karaj and Tehran transfers water from Amir Kabir dam to Tehran. This tunnel with. m diameter and km length was excavated in sedimentary rock such as shale and siltstone. METHODOLOGY OF SAMPLING AND TESTING The sampling method was regular and each set of samples ( rock properties and TBM penetration rate) is gathered from an advancing period of TBM (each advancing period was. m). In each advancing period, for each intact rock properties, one sample was selected and properties of discontinues was measured. Access to the wall rock and face rock was restricted as double shield TBM was employed. Consequently, sampling was carried out by collecting rock from excavated material in the cars transferring broken rock outside. Therefore, unconfined compressive strength (UCS) could not be determined directly. UCS of intact rock was estimated by point load strength index test using prepared irregular small blocks of excavated rock. The laboratory equipment of point load index testing machine, Brazilian tensile strength testing machine and punch penetration testing machine were performed to determine point load strength index, Brazilian tensile strength (BTS) and peak slope index (PSI) of various rock samples prepared during excavation of Karaj-Tehran water conveyance tunnel by TBM. The study is focused on a geological section of tunnel direction that is named U. Figure shows the geological map of tunnel direction in the field of study, U. DETERMINATION OF ROCK MASS PROPERTIES AFFECTING THE PENETRATION RATE OF TBM Intact rock properties Determination of uniaxial compressive strength using point load strength index Point load strength index was carried out on 9 numbers of prepared irregular small blocks of rock during excavation of Karaj- Tehran water conveyance tunnel by TBM according to ISRM standard (Brown, 98). Point load strength index was determined as follow (Brown, 98): P I s = () D D e = e WD π () Where D e is the equivalent diameter of an irregular block in mm; W is the average width of an irregular block in mm; D is the height (thickness) of an irregular block in mm; P is peak load in N, and I s is the point load strength index of an irregular sample in MPa.

3 J. Geol. Min. Res. The sizes of the samples were not the same and the following factor of size effect on the point load strength index was applied to correct the point load index to be equal to the point load strength index of a sample having mm diameter.. D F e () = I = s( ) FI s () Where F is a correction factor, and I s () is the point load strength index of a sample having mm diameter. The uniaxial compressive strength (UCS) can be estimated using the point load strength index test results as follow (Bieniawski, 98): UCS=I s() () The uniaxial compressive strength (UCS) of 9 rock samples with the other measured parameters of rock mass surrounding tunnel are according to Table. The histogram of uniaxial compressive strength of the results is shown in Figure displacement in KN/mm known as peak slope index (PSI) is determined. This index is an indicator of the brittleness of the sample which represents the resistance against penetration. Peak slope index (PSI) test results is according to Table and the histogram of test results is also shown in Figure 7. In-situ properties of rock mass discontinuities affecting the TBM penetration rate Orientation of discontinuities Discontinuities have critical influences on TBM penetration rate. The discontinuities (weakness planes) orientation respect to the direction of tunnel axis and discontinuities spacing were measured in the field. Discontinuities (weakness planes) orientation with respect to the direction of tunnel axis is named β angle as follow: β = Arcsin[sin(dip) sin (T direction strike)] (7) Where dip is the dip angle of discontinuities in degree; Strike is the strike angle of discontinuities in degree, and T direction is the direction angle of the tunnel axis in degrees. The amount of measured β angle is as shown in Table and the histogram of β angle results is shown in Figure 8. Brazilian tensile strength (BTS) Brazilian test was used to determine the tensile strength of the samples (Figure, ). Number of 9 core samples having mm diameter were prepared according to the standard (Brown, 98). The thickness to - diameter ratio of samples was equal to. Tensile strength of samples was calculated by the following equation: BTS P πtd = () Where P is the peak load in N; t is the thickness of sample in mm; d is the diameter of cylindrical samples in mm, and BTS is the tensile strength in MPa. The Brazilian tensile strength (BTS) test results of 9 samples are according to Table and histogram of test results is shown in Figure. Peak slope index (punch penetration) The punch penetration test apparatus incorporates a compression testing machine which thrusts a tungsten carbide conical tip against a saw cut surface of the sample according to Figure. The cone angle is and its spherical tip diameter is.7 mm (Dollinger, 998). This test was also developed in the laboratory for first time in Iran to carry out this research based on Robbins company method (Dollinger, 998). The amount of increasing load on the indenter con and its displacement are recorded using a data acquisition system. As an example, the load versus penetration is shown in Figure. The ratio of the maximum load to the corresponding Spacing of discontinuities The regional jointing pattern was not separated from the shear zones and faults in rock mass surrounding Karaj-Tehran tunnel; thus, combined effect of faults, shear zone, fissures and joints on TBM penetration rate were evaluated. The distance between weakness planes (Jd) recorded in Table and histogram distribution of the Jd, results are shown in Figure 9. PENETRATION RATE OF TBM The double shield Herencnesht TBM had disc cutters and. m diameter cutter head. The penetration rate of TBM was monitored corresponding to the sampling location for properties of rock mass surrounding Karaj-Tehran water conveyance tunnel. The monitored penetration rate of TBM with all other rock mass properties is shown in Table. Analysis of test results of rock mass properties affecting penetration rate of TBM In order to perform the statistical analyses for predicting the PR, a database composed of UCS, BTS, PSI, β angle, J d and also actual monitored penetration rates in field was established (Table ). To analyse correlations between rock properties (UCS, PSI, PSI, β angle and J d) and actual measured PR, stepwise statistical analysis were carried out and the influence of each rock mass properties on the PR was determined individually. The relationship between BTS of rock and PR of TBM has a very poor correlation coefficient (r) of. as shown in Figure. The relationship between UCS of intact rock and PR of TBM has a correlation coefficient. as shown in Figure. The relationship between PSI of rock and PR of TBM is

4 Mansouri and Moomivand 7 Table. The uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), peak slope index (PSI) of various rock samples, orientation of weakness planes respect to tunnel axis (β angle), distance between weakness planes (J d) and TBM penetration rate (PR) during excavation of Karaj-Tehran water conveyance tunnel. Number of samples UCS (MPa) Number of samples BTS (MPa) PSI (kn/mm) angle (degree) J d (m) TBM penetration rate PR (m/h)

5 Count Count 8 J. Geol. Min. Res. Table. Cont UCS Figure. Histogram of uniaxial compressive strength (UCS) test results of 9 samples BTS Figure. The histogram of Brazilian tensile strength (BTS) test results of 9 samples. Figure. Determination of tensile strength of the samples using Brazilian test. Figure. Punch penetration test. shown Figure with a correlation coefficient (r) of.7. The influence of β angle of rock mass surrounding tunnel on PR of TBM is shown in Figure with a correlation coefficient (r) of.. The influence of J d of rock mass surrounding tunnel on PR of TBM is also shown in Figure with a correlation coefficient (r) of.. The PR of TBM increases with increase of β angle from to and it

6 Count Count Count Mansouri and Moomivand 9 Load (KN) displacment (mm) Figure. The load versus penetration for one of 9 tested samples jd Figure 9. The histogram distribution of the distance between planes of weakness (J d) PSI Figure 7. The histogram peak slope index (PSI) test results of 9 samples. 8 8 BTS, MPa Figure. The relationship between Brazilian tensile strength (BTS) of intact rock and PR of TBM. 8 9 UCS. MPa Beta Figure. The relationship between uniaxial compressive strength (UCS) of intact rock and PR. Figure 8. The histogram values of measured β angle. has highest value at the β angle around, then it decreases with an increase of β angle. Relationship between rock mass properties (UCS, PSI, PSI, β angle and J d) and actual measured PR of TBM individually with the correlation coefficient (r) is shown in Table. Forward stepwise regression analysis was applied to carry out the Influence of combined engineering rock mass properties on PR of TBM. In this statistical approach, the rock mass properties (UCS, BTS, PSI, β angle and J d) were input as dependent variables and the measured PR was chosen as an independent variable.

7 J. Geol. Min. Res. 7 8 PSI, kn/mm Figure. The relationship between peak slope index (PSI) of intact rock and PR of TBM J d, kn/mm Figure. Relationship between spacing of discontinuities (Jd) of rock mass and PR of TBM Table. Relationship between rock properties (UCS, PSI, PSI, β angle and J d) and actual measured PR of TBM individually with the correlation coefficient (r). Correlation coefficient (r) Equation. PR =.8 +.BTS.7 PR =.9 +.PSI. PR = UCS. PR = -.7β +.β +.. PR =.7 -.Jd β angle, degree Figure. Relationship between discontinuities (weakness planes) orientation respect to the direction of tunnel axis (β angle) and PR of TBM. Influence of each variable on the PR of TBM was evaluated using forward stepwise regression analyses. Four different models were generated for different types of input variables (Table ). The maximum correlation coefficient (r) of.7 was achieved when UCS, PSI, J d and β angle were selected as input variables [Model in Table ). It means that each rock mass property has effect on the PR in a certain percentage except BTS that was excluded. The influence of rock mass properties on the PR of TBM as a new empirical formula in the model (Table ) was obtained as follow: PR =.+.7PSI-.J d+. -7 exp (UCS-.β-7) (8) Where PSI is in kn/mm; UCS is in MPa; β angle is in degree; J D is in m, and PR is in m/h. PR of TBM can be predicted by the empirical formula. The relationship between the predicted and the measured PR of TBM with a correlation coefficient (r) of.7 is shown in Figure. Conclusions Influence of various intact and in-situ properties of rock mass while excavating Karaj-Tehran water conveyance tunnel by a double shield Herencnesht TBM was investigated. The results showed that the relationship between β angle and PR of TBM is nonlinear and the relationship between the others rock mass properties and PR of TBM is linear. PR of TBM increases with an increase of BTS, PSI, and UCS and it decreases with an increase of Jd. The PR of TBM increases with increase of β angle from to and it has highest value at the β angle around then it decreases with an increase of β angle. The relationship between BTS and PR of TBM has a poor correlation coefficient (r) of. as BTS of rock does not have a significant effect on the PR of TBM, so it was excluded. Multilinear regression was applied to analyse the effect of rock mass properties on the PR of TBM and different models were generated for different types of input variables (Table ). The maximum correlation coefficient (r) of.7 was achieved when UCS, PSI, J d and β angle were selected as input variables (Model in Table ). It means that each rock mass property has effect on the PR

8 Mansouri and Moomivand Table. Summery of regression analysis of different models. Model variables Method Correlation coefficient (r) R square Adjusted R square Standard deviation (Constant), PSI Forward (Constant), PSI, J d Forward (Constant), PSI, J d, expucs Forward (Constant), PSI, J d, expucs, β Forward Meseaured PR, m/h Predicted PR, m/h Figure. Relationship between predicted PR and measured PR (r =.7). in a certain percentage except BTS that was excluded. Influence of rock mass properties on the PR is summarized to an empirical formula as PR of TBM can be predicted by the obtained empirical formula. REFERENCES Balci C (9). Correlation of rock cutting tests with field performance of a TBM in a highly fractured rock formation: A case study in Kozyatagi-Kadikoy metro tunnel, Turkey. Tunnell and Underground Space Technol., : -. Bieniawski ZT (98). Rock mechanics design in mining and tunnelling. AA Balkema, p. 7. Brown ET (98). Rock Characterization testing and monitoring ISRM Suggested Methods. Pergamon press. Dollinger GL, Handewith HJ, Breeds CD (998).Use of the punch test for estimating TBM performance. Tunneling and Underground Space Technol., (): -8. Farmer IW, Glossop NH (98).Mechanics of disc cutter penetration. Tunnels Tunnell, (): -. Gong QM, Zhao J (7). Influence of rock brittleness on TBM penetration rate in Singapore granite.tunnelling and Underground Space Technol., : 7. Graham PC (97). Rock exploration for machine manufactures. Symposium on Exploration for Rock Engineering, Johannesburg, Balkema. : 8-7. Jafar KH, Kourosh S, Bahram R, Jamal R (). Performance prediction of hard rock TBM using Rock Mass Rating (RMR) system. Tunnell. Underground Space Technol., :. Sahel Consulting Engineers (). Geological report of Karaj-Teharn water conveyance tunnel, Teharn. Sapigni M, Bertib M, Bethazcm E, Busillod A, Cardonee G (). TBM performance estimation using rock mass classifications. Int. J. Rock Mech. Min. Sci., 9: Yagiz S (7). Utilizing rock mass properties for predicting TBM performance in hard rock condition. Pamukkale University, Turkey, Tunnelling and Underground Space Technology.