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TBM Excavation in Difficult Ground Conditions

Bilgin, Nuh / Copur, Hanifi / Balci, Cemal

TBM Excavation in Difficult Ground Conditions

Case Studies from Turkey

November 2016
  • 354 pages
  • 308 figures
  • 99 tables
  • Hardcover
  • English
ISBN: 978-3-433-03150-6
available, free shipping

Prices incl. VAT

1. Introduction

This book is written with the intention of sharing the tunneling experiences gained during several years in difficult ground and complex geology. The methane explosion in the EPB chamber, the clogging of a TBM, the need to change disc cutters to chisel cutters, the need of changing (CCS) type discs cutters to (V) type disc cutters, excessive disc cutter consumption, the optimum selection of TBM type in complex geology, magmatic inclusions or ‘dykes’, the effect of blocky ground on TBM performance and the mechanism of rock rupture in front of TBMs, TBM face collapses and blockages, the effect of opening ratio in EPB-TBMs in fractured rock, squeezing of TBM or jamming of the cutterhead, probe drilling and umbrella arch ahead of TBMs are discussed within this book.

2. Geology of Turkey and Istanbul, expected problems, some cuttability characteristics of the rocks

The geology of Turkey is complex and it consists of a mosaic of several terranes, which were amalgamated during the Alpide orogeny. Palaeozoic, Mesozoic and Cenozoic formations are recognized in Istanbul. In this chapter a brief summary of the geology of Turkey, and Istanbul is given, describing the main geological formations with physical, mechanical and cuttability characteristics. The information given in this chapter will help job owners and contractors to make rational decisions in designing and executing tunneling projects in Turkey.

3. Difficult ground conditions dictating selection of TBM type in Istanbul

This chapter shows the optimum selection of TBM type in Istanbul, gradually changed from open type TBM (Baltalimani Tunnel), to double shield TBM (Moda-Tuzla Tunnel), to slurry type TBM (Marmaray Tunnels) and finally to EPB-TBMs over the past 25 years. This gradually progressive selection based on the complex geology of Istanbul is a typical example to the concept of ‘learning costs’.

Case study of an open TBM in Baltalimani Tunnel is briefly given explaining why it failed in Trakya Formation. The performance of a double shield TBM in the Istanbul–Moda collector tunnel and the performance of the same type of TBM working without precast segment in difficult ground in Tuzla tunnel in Istanbul are also covered. Difficulties in using slurry TBMs in complex geology in Marmaray Tunnel projects and difficulties in single-shield TBM working in open mode in difficult ground in Kadikoy–Kartal metro tunnel are also outlined in this chapter.

4. Difficult ground conditions affecting performance of EPB-TBMs

In complex geology, especially where EPB-TBMs are used, a methodology based on past experience is necessary for estimating tunneling performance and daily advance rates in highly fractured rock, in sandy-silt, silty-sand formations and anywhere a frequent change in transition zones shows up. This chapter gives a summary of such methodology and depicts a comparison of the predicted and actual results made for Uskudar–Umraniye–Cekmekoy–Sancaktepe metro tunnels that were excavated in complex geology with dyke inclusions. The methodology is based on predicting field specific energies and comparing cutting power of EPB-TBMs. The predicted daily advance rates are compared with field values. The model developed is also verified using some field results from Mahmutbey–Mecidiyekoy metro tunnels.

5. Selection of cutter type for difficult ground conditions

The range of cutter types used in TBMs in terms of the cutting efficiency in difficult grounds is outlined in this chapter. First, a summary of the comparative study of V- and CCS-type disc cutters is given for a double shield TBM intended to be used in the Dragos sewerage tunnel in Istanbul. It is concluded that V-type disc cutters are more efficient in terms of cutter force than CCS disc cutters, but CCS cutters are preferred in practice since they are more resistant to abrasive characteristics of the rocks and lasted longer than the V-type discs. The methodology for changing disc cutters to chisel cutters in the Beykoz–Istanbul Tunnel and the inefficiency of using the tungsten carbide studded disc cutters in Marmaray–Istanbul project are discussed in this chapter.

6. Effects of North and East Anatolian Faults on TBM performances

Turkey is in a tectonically active region which experiences frequent destructive earthquakes. On the large scale, the tectonics of the region are controlled by the collisions of the Arabian Plate and the Eurasian Plate. The Anatolian block is being squeezed to the west. The block is bounded to the north by the North Anatolian Fault and to the south-east by the East Anatolian Fault. Effects of these two faults on TBM performance, including TBMs in the Kargi energy tunnel, Dogancay energy tunnel, Nurdagi railway tunnel and Uluabat energy tunnels. These are explained in detail as well as the causes, effects and precautions to be taken in order to eliminate the problems created by two large sets of faults. Some information of the most problematic tunnels (Ayas and Bolu) ever excavated by drill and blast method is also given within this chapter.

7. Effect of blocky ground on TBM performance and the mechanism of rock rupture

The effect of blocky ground on TBM performance and the mechanism of rock rupture in Istanbul Kozyatagi and Kadikoy metro tunnels are explained in this chapter. The project is part of metro line starting from Pendik, integrating with Marmaray project and going as far as Halkali, south-east of the city. At the beginning, it was observed that the contact zones between dykes and the main rock formation were highly fractured, and in some area big rock blocks having sizes up to 30 × 40 × 50 cm were ripped off by the disc cutters from the fractured zones, passing through the openings of the cutterhead and causing several problems such as collapses of the tunnel face. The face collapses dramatically decreased daily advance rates around to 2.5 m/day. After several technical discussions between project management staff and TBM manufacturer it was decided to install some grizzly bars to limit the big rock blocks passing through the openings of the cutterhead. Daily advance rates increased up to 6 m/day after the modification of the cutterhead. Thrust force, torque and penetration per revolution of the TBM are carefully examined around the collapsed zone. and it is clearly shown that a close look at the change of behavior of the machine provides a good indicator for forthcoming problems such as face collapses.

8. Effects of transition zones, dykes, fault zones and rock discontinuities on TBM performance

The effects of transition zones, dykes, fault zones and rock discontinuities on TBM performance are explained in this chapter. The geology of Istanbul is complex for tunneling projects. Tectonic activities, faults, diabase, dacite and andesite dykes as well as several joint sets cause many serious problems for tunnel excavation. The experience gained in different projects in Istanbul, especially the Beykoz Sewerage project, showed that these geological features cause big problems during TBM excavation resulting in tunnel face collapses, squeezing of the TBM and decreasing daily advance rates.

Eleven different TBM face collapses and blockages which occurred in the very complex geology within the Kadikoy–Kozyatagi metro tunnels were analyzed. The causes and the effects of TBM blockages were explained considering TBM parameters such as opening ratio, working modes and geological parameters. Ninety-three days were spent in rescuing the blocked TBMs. It has been shown that the TBM excavation parameters fluctuate while approaching the collapse regions, and these parameters show an increasing or decreasing trend inside the ‘during collapse’ region and it is concluded that this trend is a good indicator of potential face collapses, which can serve as a guide to foresee critical areas in front of TBM. There is always a critical peak thrust/penetration, torque/penetration ratios and specific energy values at 26 rings before a TBM blockage. These values may be taken as alert values for TBM blockage.

9. Squeezing grounds and their effects on TBM performance

Squeezing grounds and their effects on TBM performance are the main subjects of this chapter. Four types of squeezing were encountered in tunnels excavated by TBMs in Turkey. The first occurred in weak zones such as graphitic schist with high overburden. A typical example to this is Uluabat energy tunnel, where the TBM stuck 18 times during the excavation and also the Kosekoy–Bilecik high speed railway tunnel. The second different type of squeezing was due to weak contact zones between the main rock and dykes, as occurred in the Beykoz sewerage tunnel. Squeezing of the TBM in the Suruc water tunnel occurred due to clayey zones coming in contact with water. However, in some cases like the Kargi energy tunnel, squeezing of the TBM was the result of either collapsing in blocky ground or squeezing clayey zones. Each case is explained in detail with remedial measures to keep TBM stoppages to a minimum. Due to a careful site observation, analyzing the TBM data and remediation program, it is observed that daily advance rates of TBM may increase considerably.

10. Clogging of the TBM cutterhead

Clogging problems of the TBM cutterhead in Suruc water tunnel, Selimpasa sewerage tunnel in Istanbul and Zeytinburnu Ayvalidere-2 wastewater tunnel project are treated in this chapter. The Suruc tunnel with a length of 17,185 m, is the longest water tunnel ever excavated in Turkey. Observations made during the execution showed that clogging of the cutterhead has major adverse effect on thrust force, torque, depth of cut per revolution, specific energy and net excavation rate. Generally, the ratio of thrust force to torque decreased from 2.3 to 1.3. Specific energy increased from 4 kWh/m3 to 24 kWh/m3. In other words, clogging of the cutterhead caused the energy to excavate a unit volume of ground to be six times higher than with a clean cutterhead. Anti-clogging agents were therefore used to prevent the cutterhead clogging. Although the ground was stable in both Selimpasa and Zeytinburnu Ayvalidere 2 wastewater tunnels, the ground was quite sticky, in both cases reducing excavation rates and causing stoppages due to cleaning up operations and muck transportation problems (sliding on the tail belt conveyor). Experimental studies performed in the soil conditioning laboratory indicated that regular application of foam selected by the contractor was adequate to solve the sticking and clogging problems in Selimpasa, while an anti-clay agent different from the one selected by the contractor was suggested in Zeytinburnu. The representatives in both cases applied the laboratory results in the field. The field measurements validated the experimental studies and the net advance rates of the EPB-TBMs increased at least 1.5 to 2.0 times, and the stoppages due to clogging problems reduced to normal ranges.

11. Effect of high strength rocks on TBM performance

The effect of high strength rocks on TBM performance is explained in this chapter. In Beykoz tunnel in complex geology, a rock formation (quartzite) having unexpectedly high strength characteristics appeared in the tunnel route, limiting the penetration of the cutters, thus decreasing the advance rates in most cases to undesired values, even to practically zero level. In that case (CCS) disc cutters were replaced with V-type disc cutters, because, as explained in earlier chapters, for a limited thrust force the penetration is higher in V-type disc cutters compared with other types of disc cutters. Nurdagi railway tunnel was unique in a sense that very high strength rocks having compressive strength up to 250 MPa were the main rocks to be excavated, full-scale laboratory cutting tests were carried out for this tunnel to predict the behavior of the cutters to obtain the optimum design parameters of a TBM.

12. Effect of high abrasivity on TBM performance

Cutter consumption is one of the important cost items in mechanized tunneling due to replacement costs, cutting efficiency (reduction with worn tools), and also time and workmanship spent on replacement. The case studies mentioned in this chapter indicate that the abrasiveness of the rocks excavated is not the only parameter to consider when projecting cutter consumption rate for a TBM tunneling project. In fact, other parameters affecting cutter consumption are more significant than abrasiveness and strength parameters.

In the case of small diameter TBMs equipped with small diameter double-disc cutters (low thrust capacity) such as in the Tuzla wastewater tunnel, although the strength of the rocks excavated was not usually very high, this excavation case could be considered as a difficult ground condition. Small diameter TBMs require the use of small diameter double-disc cutters. Thrust capacity of the disc cutters is directly proportional to their diameters (small diameter disc means low thrust capacity). On the other hand, thrust force applied on double-disc cutters is divided in to two cutter rings, which is another thrust reducing factor.

It was also seen that lamination and discontinuities existing on the formations affect the cutter consumption, due to void occurrence and thus, sudden hitting of the cutters onto the rock, generating shock loads and increasing cutter consumption, as seen in the Yamanli II HEPP tunnel.

The case in Buyukcekmece wastewater tunnel indicated the importance of replaceable center cutters. The medium strength rock blocks encountered within a soft ground gave the TBM a very hard time by slowing down the excavation rate and losing time for replacement of the center cutter.

Another case, the Uskudar–Umraniye–Cekmekoy–Sancaktepe metro tunnel indicated the importance of the quality of cutter manufacturing (cutter brand). Using higher quality disc cutters increased the life of the 17″ single-disc cutters by two to three times. When using EPB-TBMs with mix ground cutterheads for excavation of rock masses, ripper tool and bucket consumption, in addition to disc cutters, should also be considered in the planning stage.

13. Effect of methane and other gases on TBM performance

Methane explosion in the pressure chamber of an EPB-TBM in Selimpasa wastewater tunnel and gas flaming in the Silvan irrigation tunnel were summarized in this chapter. These accidents indicate that the basic negligence starts during site investigations. Especially Carboniferous age formations are the basic formation types having potential gas hazard during underground operations. Also, the geotechnicians, authorities and contractors are not careful enough about the existence of natural gas and oil-bearing formations in the vicinity of the tunnel alignment, as well as natural gas and oil production, which should be always considered as a gas danger to underground operations. Sometimes authorities do use site investigations at different times, but they do not know each other's activities, as there is no communication among the earth-related institutions.

A recent successful application of EPB-TBMs in the excavation of two inclined drifts in a coal mine in Australia indicated that closed face TBM technology can be successfully used for excavation in gassy underground operations.

14. Probe drilling ahead of TBMs in difficult ground conditions

This chapter summarizes the results of probe drilling carried out ahead of TBMs in Melen and Kargi projects in a very complex geology. In summary it may be concluded that normalized penetration rate of a probe drill is a good indicator for detecting weak zones ahead of a tunnel. Probe drilling rate changed with changing geological formations and showed sharp increases and decreases in transition zones. Probe drilling rate is also very much affected in fault zones. In some cases, probe drilling rate increased within fault zones due to swelling and squeezing characteristics of the gauge materials.

The method of analysis of probe drilling rate data in the Melen project permitted the defining of a critical normalized probe drilling value. Values higher than the predetermined critical value point out critical geological zones susceptible to pressurized water ingress.

TBM thrust and torque values increased with decreasing probe drill penetration rates in competent hard rock formations in the Kargi energy tunnel. However, this study introduced a new concept of TBM thrust/probe drilling penetration rate and TBM torque/probe drilling penetration rate ratios explaining the variation of penetration rates in a statistically more reliable manner. This concept showed that by observing closely the variation of TBM thrust and torque values it is possible to predict the transient and fault zones, dictating the carrying out of umbrella arching, which will strengthen the weak zone in front of the tunnel.

15. Application of umbrella arch in the Kargi project

The aim of this chapter is to introduce one of the most comprehensive and successful umbrella arch (UA) operations used ahead of a TBM in the Kargi tunnel in blocky ground and complex geology in Turkey. The increase of TBM torque and the change in penetration rate of the probe drill were used as criteria for the application of UA. The umbrella arch is a very useful technique to prevent the jamming of the TBM cutterhead in blocky ground, as proved on the Kargi project, but it is important to note that some basic criteria should be established for using this technique. A map showing the contours of changing probe drilling rates and change of torque values were used as the two basic criteria in the Kargi project. The increase of TBM torque up to a certain limit can be used as a critical torque value for using UA. This was established as 42,000 kNm in the Kargi project.

The umbrella arch was applied nine times in the Kargi project. As the crew gained experience, time for drilling and injection was reduced from five days to two. However, it should be said that the UA is a good alternative to excavating bypass tunnels for releasing a blocked cutterhead.

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