Evaluation of Face Support Pressure Prediction for Earth Pressure Balance (EPB) Tunnelling using Analytical and 3-Dimensional Finite Element Modelling

A shield tunnelling technique is usually selected using earth pressure balance or slurry methods for tunnel construction in urban areas with soft and saturated ground. Although shield tunnelling has many advantages, incorrect determination of face pressure could cause ground surface settlement or lifting during tunnel construction. Numerous approaches for determining face support pressure have been published internationally, but a suitability evaluation based on local ground conditions in Indonesia has not been conducted yet. The completion of Mass Rapid Transit Jakarta (MRTJ) tunnel construction project using the earth pressure balance method, along with its adequate data, has become a sample case of the effectiveness of each method to determine face support pressure. The study discussed in this paper aimed to determine the linear relationship between the calculated value and the actual measurement of face support pressure and to identify which method most closely represents the actual condition according to the MRTJ case study. An analytical approach using the limit equilibrium method and the numerical approach using Plaxis 3D were conducted, followed by statistical evaluation in the terms of coefficient of variation. The result shows that the limit equilibrium method is effective in predicting the mean value face support pressure and the upper and lower perimeters for tunnel construction, while the overall face support pressure result using the shell model of the finite element method are lower than the actual measured values. The result probably indicates the balance state condition at the tunnel face, and the additional 80 kPa after the second phase of excavation could indicate the need for greater pressure for tunnel boring machine movement.

Face support pressure; Finite element method; Mass rapid transit; Tunnels

        In urban areas, tunnel construction through soft and saturated ground requires special caution because unsuitable construction methods can disturb the surrounding infrastructures causing them to collapse. Under such conditions, shield tunnelling is usually selected using the earth pressure balance (EPB) method or slurry method. Both methods reduce the disturbance at the tunnel face and around the excavation area using a tunnel boring machine (TBM). Although shield tunnelling has many advantages, incorrect determination of face pressure could cause ground surface settlement or lifting during tunnel construction. Numerous analytical, empirical, and numerical approaches for determining face pressure have been published in international journals or in technical guidelines, but a suitability evaluation according to local ground conditions in Indonesia has not yet been conducted. The Mass Rapid Transit Jakarta (MRTJ) tunnel construction project was recently completed using the EPB method, and face pressure data according to earth pressure gauges, along with soil profile and the results from in situ and laboratory testing, are available as a sample case demonstrating the effectiveness of the limit equilibrium method and the 3-dimensional (3D) finite element method to determine the face support pressure. The study discussed in this paper aimed to determine the linear relationship between the calculated value and the actual measurement of face support pressure and to identify which method most closely represents the actual condition according to the MRTJ case study.

        The EPB method is based on equilibrium between soil pressure and water pressure with jacking force applied on the cutterhead. A screw conveyor has the ability to adjust or control the face pressure during an excavation. For a tunnel constructed below the ground water level, the length of the screw conveyor must be designed to withstand hydrostatic pressure and transform water pressure into atmospheric pressure. An illustration of the EPB machine used in the MRTJ project is shown in Figure 1a, and the position of the pressure gauge instrumentation is shown in Figure 1b. pressure gauges were installed to measure the soil pressure exerted on the cutterhead and to inform the machine operator as to whether the estimated pressures were still safe.

Figure 1 Illustration of an EPB tunnel machine and the position of the earth pressure gauges (SOWJ, 2015)

        Evaluation of the effectiveness of the limit equilibrium method to predict the mean value face support pressure and the upper and lower perimeters for tunnel construction yielded a good result; however, the initial mean pressure is relatively higher than the face pressure measured when using a TBM pressure gauge. Overall, the face pressure results using the shell model of the finite element method are lower than the actual pressure measurements; yet, at the early stage of tunnel construction, the face pressure results perfectly match the actual measured pressure at the tunnel face. This result probably indicates the balance state condition at the tunnel face, and the addition of 80 kPa after the second phase of excavation could indicate the need for greater face pressure to ensure TBM movement.

The author would like to acknowledge the Institute of Road Engineering, Ministry of Public Works, the Research Group of Geotechnical Engineering, Department of Civil Engineering, Faculty of Civil and Environmental Engineering, and the Institute for Research and Community Services (LPPM) of Bandung Institute of Technology.

Anagnostou, G., Kovari, K., 1994. The Face Stability in Slurry-shield-driven Tunnels. Tunnelling and Underground Space Technology, Volume 9(2), pp. 165–174

Anagnostou, G., 2012. The Contribution of Horizontal Arching to Tunnel Face Stability. Geotechnik, Volume 35(1), pp. 34–44

American Society for Testing and Meterials (ASTM D2487-11), 2011. Standard Practice for Classification of Soils for Engineering Purposes. ASTM International, West Conshohocken, United States of America

Calvello, M., Finno, R.J., 2004. Selecting Parameters to Optimize in Model Calibration by Inverse Analysis. Computer and Geotechnics, Volume 31, pp. 410–424

Deutsches Institut fur Normung (DIN 4126), 2013. Nachweis der Standsicherheit von Schlitzwänden (Stability Analysis of Diaphragm Walls), Beuth Verlag GmbH, Berlin

Girmscheid, G., 2008. Baubetrieb und Bauverfahren im Tunnelbau (Construction Operation and Construction Methods in Tunnel Construction). Ernst und Sohn Verlag, Berlin

International Tunneling Association-Association Internationale Des Tunnels Et De L Espace Souterrain (ITA-AITES), 2016. Recommendations for Face Support Pressure Calculations for Shield Tunneling in Soft Ground. German Tunneling Committee, Koln, Germany

Kirsch, A., Kolymbas, D., 2005. Theoretische Untersuchung zur Ortsbruststabilität (Theoretical Investigation of Face Stability). Bautechnik, Volume 82(7), pp. 449–456

Lim, A., Ou, C-Y., Hsieh, P-G., 2010. Evaluation Clay of Constitutive Models for Analysis of Deep Excavation under Undrained Conditions. Journal of GeoEngineering, Volume 5(1), pp. 9–20

Liu, S., 2012. Confidence Interval Estimation for Coefficient of Variation. Master of Science Thesis, Georgia State University, Atlanta, United States of America

Plaxis, 2017. Part 3: Plaxis Material Models Manual. Delf University of Technology & Plaxis B.V., The Netherlands

Ramchandra, Gehlot, V., 2018. Limit State Design of Concrete Structures. Scientific Publishers, Jodhpur, India

Shimizu-Obayashi-Wijaya Karya-Jaya Konstruksi (SOWJ), 2015. Jakarta MRT CP104/105 construction progress. Technical Meeting Material, Wijaya Karya Persero, Jakarta

Zusätzliche Technische Vertragsbedingungen und Richtlinien für Ingenieurbauten (ZTV-ING) 2012. Teil 5 (Part 5): Tunnelbau (Tunnel Construction). Bundesanstalt für Strassenwesen (Federal Highway Research Institute), Koln, Germany