Tunnel Face Stability - VB Module for Quick Estimation

The stability of the tunnel face is one of the fundamental factors in selecting the method for excavating a tunnel in soft ground and in urban areas. When using TBMs, evaluation of the face-support pressure is a critical component in both the design and the construction phases. However, specific recommendations or technical norms are not available as common guidance for the design. In current practice, different approaches are often employed, both to evaluate the stability condition of the face and to assess the required face-support pressure [6].

This blog post presents a VB module built on Microsoft Excel which is set to calculate the face support pressure in Tunnel. This post is based on Prof. Anagnostous' lecture, ITACET training seminars and related practice exercises. This code is set to calculate the Tunnel face pressure to maintain a stable face when there are no seepage forces and for closed EPB drive (with seepage forces). Although these results can not be used for detailed analysis/design but this could help in a quick check on pressure magnitudes and for rough parametric studies.

Screenshots from the VB program - Input and Output

Click here to download. 
[Update: One of the reader reported that the program seem to show some errors in Mac OS. I will update it soon. However, it is working perfectly fine in Windows 8 & Windows 7]

Details about the program are briefly explained below.

Part 1: Support pressure at Tunnel face (without Seepage Forces)

This part calculates face support pressure based on Horn (1961), wedge failure mechanism. As of now, this program calculates face support pressure for Cohesive Soils or for short term condition in low permeable soils. This could be further developed for all types of soils.

Part 2: Support pressure in case of Closed EPB Drive (with Seepage Forces)

The construction methods used in soft ground tunnelling beneath the water table must ensure control of the ground at the tunnel heading and additionally prevent seepage flow towards the working face. In an EPB drive, the face is stabilized by direct support of the pressurized muck and by the reduction of seepage forces. Hence, higher the head difference, the higher the effective support pressure. Higher effective support pressure will cause excessive cutter wear and will require higher torque to operate. The above program calculates effective support pressure using normalized diagrams. For detailed analysis case specific FEM coupled analysis shall be performed.

In some cases, the program shows "No pressure required". This is possible when the compensation of water pressure (along with cohesion in ground) suffices for face stability.

References:

[1] G. Anagnostou and K. Serafeimidis, “The dimensioning of tunnel face reinforcement,” in World Tunnel Congress 2007,. May 2007.

[2] G. Anagnostou and K. Kovári, “Face stability conditions with earth-pressure-balanced shields,” Tunn. Undergr. Sp. Technol., vol. 11, no. 2, pp. 165–173, Apr. 1996.

[3] G. Anagnostou and K. Kovári, “The face stability of slurry-shield-driven tunnels,” Tunn. Undergr. Sp. Technol., vol. 9, no. 2, pp. 165–174, Apr. 1994.

[4] G. Anagnostou and K. Kovári, “Face stability in slurry and EPB shield tunnelling,” in Geotechnical Aspects of Underground Construction in Soft Ground, 1996, pp. 453–458.

[5] G. Anagnostou, “Some remarks concerning EPB and slurry shields,” in Development of Urban Areas and Geotechnical Engineering, 2008.

PS: Please let me know if I have missed any error handling scenario or any other bugs. Thank you.

Week 11 Tunnelling & TBM Course: EPB Tunnelling Soil Conditioning

Along with general aspects of TBM Types and TBM selection, on 4th April, 2014 we had a guest lecture from Singapore (Mr. Richard Schulkins) to deliver a lecture on the topic of Soil Conditioning for EPB Tunnelling.

EPB Tunnelling has experienced a great increase in the number of applications and it can be considered the most used technology of the mechanised tunneling in urban area [3,7]. In this lecture, Mr. Schulkins discussed the objectives of Soil conditioning in EPB Tunnelling and the procedure for soil conditioning using various additives.

Click here for a basic presentation on Soil Conditioning by Prof. Peila (ITACET lecture presented in Argentina).

Followed by the lecture, we had a chance to see the experimental setup and witness some tests. Tests on characterisation of conditioned soil is limited and only recently some large scale tests using laboratory screw conveyor has been proposed [5] (details of past studies and tests are included in this reference) and Politecnico di Torino has one of such facilities to test the conditioned soil [1,3,7].

Experimental Setup in Politecnico di Torino [3]

There are five established tests for optimizing the conditioned soil (Foam penetration test, Slump test, shearing test, Compressibility test and friction test) however, during this lab demonstration, quality assessment of the conditioned soil were tested using slump cone test and permeability test. More details about the experimental setup and the test to assess the behaviour of conditioned soil is covered in the paper Peila et al (2009) [2]. Following video shows the demonstration in the Department of Structural Engineering, Construction and Geotechnical, Politecnico di Torino, Italy.

Following video shows the permeability test on the conditioned soil with 10m constant water head. The details of the setup and the test results could be studied in the paper Borio et al (2010) [4].

References: 

[1] D. Peila, C. Oggeri, and R. Vinai, “Screw conveyor device for laboratory tests on conditioned soil for EPB tunneling operations,” J. Geotech. Geoenvironmental Eng., vol. 133, no. 12, pp. 1622–1625, 2007.

[2] D. Peila, C. Oggeri, and L. Borio, “Using the slump test to assess the behavior of conditioned soil for EPB tunneling,” Environ. Eng. Geosci., vol. 15, no. 3, pp. 167–174, 2009.

[3] R. Vinai, C. Oggeri, and D. Peila, “Soil conditioning of sand for EPB applications: A laboratory research,” Tunn. Undergr. Sp. Technol., vol. 23, no. 3, pp. 308–317, May 2008.

[4] L. Borio and D. Peila, “Study of the Permeability of Foam Conditioned Soils with Laboratory Tests.,” Am. J. Environ. Sci., vol. 6, no. 4, pp. 365–370, 2010.

[5] L. Borio, D. Peila, C. Oggeri, and S. Pelizza, “Characterization of soil conditioning for mechanized tunnelling .”

[6] Pena. A, “Foam as a soil conditioner in tunnelling : physical and mechanical properties of conditioned sands,” University of Oxford, 2007.

[7] R. Vinai, D. Peila, C. Oggeri, and S. Pelizza, “Laboratory tests for EPB tunnelling soil conditioning,” in Underground Space - the 4th Dimension of Metropolises, 2007, pp. 273–278.

• This lecture was a part of ITACET Training Seminar organised in Politecnico di Torino. 

Prof. Georgios Anagnostou's Lecture on Face Stability

50th Lecture day of the 2nd Level Specializing Masters in Tunnelling course and the Last day of  ITACET Training Seminar (28th March '14)  was presented by Prof. Georgios Anagnostou from ETH Zurich, Switzerland. Prof. Anagnostou's lecture was focused on Tunnel face instability in soil and the potential hazards related to it. Professor explained the idealized failure mechanism (wedge in front of face + prismatic body extending upto the surface based on Horm 1961) of face instability using model tests and the derivation of limit equilibrium equations for calculation of support pressure. 

Prof. Anagnostou's Lecture on Face Stability

Professor also gave examples of face stability calculation using Limit Equilibrium equations and based on monograms.

Examples of Support Face Pressure Calculation using LEM Approach

References:

[1] J. Messerli, E. Pimentel, and G. Anagnostou, “Experimental study into tunnel face collapse in sand,” Phys. Model. Geotech., vol. 1, pp. 575–580, 2010.

[2] G. Anagnostou and K. Serafeimidis, “The dimensioning of tunnel face reinforcement,” in World Tunnel Congress 2007, May.

[3] R. Schuerch and G. Anagnostou, “Analysis of the stand-up time of the tunnel face,” in World Tunnel Conference 2013 Geneva, 2013, pp. 709–714.

[4] G. Anagnostou, “Urban tunnelling in water bearing ground – Common problems and soil-mechanical analysis methods,” in 2nd International Conference on Soil Structure Interacton in Urban Civil Engineering, 2002, pp. 233–240.

[5] K. Serafeimidis, M. Ramoni, and G. Anagnostou, “Analysing the stability of reinforced tunnel faces,” in 14th European Conference on Soil Mechanics and Geotechnical Engineering, 2007, pp. 1079–1084.

[6] G. Anagnostou, “Some remarks concerning EPB and slurry shields,” in Development of Urban Areas and Geotechnical Engineering, 2008.

[7] G. Anagnostou and K. Kovari, “Face stability in slurry and EPB shield tunnelling,” in Geotechnical Aspects of Underground Construction in Soft Ground, 1996, pp. 453–458.

[8] P. Perazzelli and G. Anagnostou, “Comparing the limit equilibrium method and the numerical stress analysis method of tunnel face stability assessment,” 7th Int. Symp. „Geotechnical Asp. Undergr. Constr. Soft Gr. “. Rome, 2011.

[9] G. Anagnostou and K. Kovári, “The face stability of slurry-shield-driven tunnels,” Tunn. Undergr. Sp. Technol., vol. 9, no. 2, pp. 165–174, Apr. 1994.

[10] G. Anagnostou and K. Kovári, “Face stability conditions with earth-pressure-balanced shields,” Tunn. Undergr. Sp. Technol., vol. 11, no. 2, pp. 165–173, Apr. 1996.

[11] L. Cantieni and G. Anagnostou, “The interaction between yielding supports and squeezing ground,” Tunn. Undergr. Sp. Technol., vol. 24, no. 3, pp. 309–322, May 2009.

[12] G. Anagnostou and L. Cantieni, “Design and analysis of yielding support in squeezing ground,” in 11th ISRM Congress, 2007, p. 4.

Prof. Nuh Bilgin's Lecture on Cutting Tools and TBM Performance Assessment

Prof. Nuh Bilgin's Lecture of Cutting Tools and TBM Performance assessment

On 26th and 27th March '14, we had a special lecture by Prof. Nuh Bilgin as a part of Second Module of Tunnelling and TBM course and also as a part of ITACET Training seminar being organized in Politecnico di Torino. Prof. Bilgin explained us the mechanics of Rock cutting and different types of Rock cutters used in Roadheaders and TBM. With the help of example case studies, cutting forces (FC & FN) were calculated for different types of cutters. 

Different methods for assessing the performance of mechanical excavators (Roadheaders & High energy impact hammer) were discussed using numerical examples. A good example for the calculation and comparison between excavation rate of Roadheaders, High energy impact hammers and Drill & Blast method can be studied in his paper on Istanbul Kadikoy–Kartal metro tunnels [1]. Types of tools used in TBM and principles of Disc cutters were discussed in detail with numerical examples for V type disc cutters and CSS disk cutters. Case Study of Tuzla-Dragos Sewerage Tunnel was considered for explanation. Prof. Bilgin’s paper on performance prediction of TBM gives further insights and details of the above exercise [2], [3]. The above paper presents prediction model based on Earth Mechanics Institute (ESM) of Colorado School of Mines (CSM). This method is based on full-scale laboratory cutting tests. Prof. Bilgin also introduced another prediction model developed by University of Torenthiem and Norwegian Institute of Technology, which is an empirical model based on database accumulated over time. 

Another study covering 262 different types of TBM and statistically analyzed data presents relationship between TBM diameter, TBM thrust, cutterhead torque, TBM weight, number of disc cutters and maximum rotational speed of cutterhead [4]. 

Numerical examples were taken from the book: Mechanical Excavation in Mining & Civil Industries (link here).

References:

[1] I. Ocak and N. Bilgin, “Comparative studies on the performance of a roadheader, impact hammer and drilling and blasting method in the excavation of metro station tunnels in Istanbul,” Tunn. Undergr. Sp. Technol., vol. 25, no. 2, pp. 181–187, Mar. 2010. 

[2] N. Bilgin, C. Feridunoglu, D. Tumac, CINAR, M, and L. ÖZYOL, “TBM cutting performance in Istanbul,” T T Int., no. FEV, pp. 17–19, 2006. 

[3] N. Bilgin, C. Balci, H. Tuncdemir, S. Eskikaya, M. Akgul, and M. Algan, “The performance prediction of a TBM in difficult ground condition,” AFTES, Journees d’Etudes Int. Paris, pp. 25–28, 1999. 

[4] U. Ates, N. Bilgin, and H. Copur, “Estimating torque, thrust and other design parameters of different type TBMs with some criticism to TBMs used in Turkish tunneling projects,” Tunn. Undergr. Sp. Technol., vol. 40, pp. 46–63, Feb. 2014. 

Some of the research papers of Prof. Bilgin could be accessed here.

Prof. Kalman Kovári's Lecture on Urban Tunnelling and Case Studies

Yestersay (25th March, 2014), we had a special lecture by Prof. Kalman Kovari, as a part of Second Module of Tunnelling and TBM course and also as a part of  ITACET Training seminar being organized in Politecnico di Torino. During the lecture Prof. Kalman Kovari gave us case studies of Urban Tunnelling with extreme conditions of constraints / exceptionally different geologic conditions. Based on these case studies, Prof. Kovari explained us the thought process during the conception stage and the design stage.

Prof. Kovari also gave us the fundamentals required to understand the upcoming lecture on face stability calculations for Slurry and EPB type TBM drivel.

[Update: Prof. Anagnostou's lecture followed this lecture to cover the details about face stability. I have shared a spreadsheet for face stability estimation based on his lecture at this location (link)]

In particular, Prof. explained us the design and construction of the Ceneri Base Tunnel cavern (24m wide and 17m height) along with the complex problems in executing and monitoring [1].

Prof. Kalman Kovári's Lecture on Urban Tunnelling

We also used this opportunity to clarify some of the concepts explained in his paper on NATM [2]. In my previous blog post (here), there was a discussion about Convergence-Confinement Curve and I had mentioned that the trough-shape response curve (as depicted in all NATM literature) are realistic for shallow tunnels and is due to the material softening. But according to Prof. Kovari, trough-shaped ground response curve is simply not realistic. He emphasized that it does not have any theoretical background and can not be accepted even for shallow tunnels. The trough-shaped response curve could be noticed only in certain special cases (eg. when there is a blocky wedge failure in the tunnel).

References:

[1] Filippini, R., Kovári, K., & Rossi, F. (2013). Ceneri-Basistunnel. In Swiss Tunnel Congress 2013 (pp. 236–249).
Retrieved from: http://www.filippini-ing.ch/documenti/STC_2013-CeneriBasistunnel.pdf

[2] K. Kovári, “Erroneous Concepts behind NATM,” in Rabcewicz-Geomechanical Colloquium, Salzburg, 1993, p. 21. (Available at Swiss Federal Institute of Technology site, here)

Dr. Harald Wagner's Lecture on Urban Tunnelling

Module 2 of Tunnelling and TBM course at Politecnico di Torino (which focuses on Mechanized Tunnelling using TBM in soft ground and Hard Rock condition) started on 24th March with special Lecture by Dr. Harald Wagner. Dr. Wagner gave us an overview of use of TBM for Urban Tunnelling with various examples. He also discussed with us about the design of lining segments and ideal design workflow for any tunnelling project. 

Dr. Harald Wagner's Lecture on Advanced Technologies in Urban Tunnelling

This whole week is power-packed with expert lectures from various countries to kick-start our 2nd Module on Mechanized Tunnelling. Politecnico di Torino is offering this week's of lectures as ITACET Training Seminar, open to all practicing engineers and geologists (details here).