Tunnelling and Underground Space Technology 24 (2009) 356–362

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Tunnelling and Underground Space Technology

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Discussion

Swelling rock behaviour in a tunnel: NATM-support vs. Q-support – A comparison

Rudolf Schwingenschloegl *, Christoph LehmannDepartment of Structural Engineering and Natural Hazards, University of Natural Resources and Applied Life Sciences, Peter Jordan Strasse 70, 1190 Vienna, Austria

a r t i c l e i n f o a b s t r a c t

Article history:Received 10 October 2007Received in revised form 12 August 2008Accepted 22 August 2008Available online 7 November 2008

Keywords:Classification systemsSwelling rocksRock supportTunnelling

0886-7798/$ - see front matter � 2008 Elsevier Ltd. Adoi:10.1016/j.tust.2008.08.007

* Corresponding author. Tel./fax: +43 1 47654 5400E-mail address: rudolf.schwingenschloegl@boku.ac

The Q-system is one of the most applied classification tool in modern tunnelling. After an exact evalua-tion of the parameters the rock support can be determined via the ‘‘Q-support chart”. In an alreadyfinished tunnel, mainly driven through limestone, the Q-system was tested under difficult geological con-ditions (shale–marl). Scope of the appraisal was a comparison of the support suggested by the ‘‘Q-supportchart” with the real performed support after the NATM, regarding partly massive damages. This article isa contribution referring to the last publication on the topic ‘‘fitness of various engineering design tools”from [Palmstrom, A., Stille, H., 2007. Ground behaviour and rock engineering tools for undergroundexcavations. Tunnelling and Underground Space Technology 22, 363–376].

� 2008 Elsevier Ltd. All rights reserved.

1. Introduction

In the Northern Calcareous Alps (Lower Austria, Wopfing) a tun-nel (length 700 m), housing a conveyer belt, was driven in theyears 2000–2001. By two shafts (depth 140 m) pre-broken lime-stone reaches the main crusher situated in a small cavern at thesouth-east end of the tunnel. Through the tunnel the material istransported to a loading station (see Fig. 1).

The described tunnel can be reached by an access tunnel of140 m length. At its end (intersection = chainage 0.0 m) the inclin-ing advance of the tunnel started 130 m in the southern directionwhile 570 m were driven in declining advance (12%) reaching tothe breakthrough to an already existing tunnel (see Fig. 3). Bothwere driven by conventional heading and full face excavation(16 m2).

1.1. Project setting

The axis of the tunnel is crossing in a right angle a thrust zone oftwo tectonic units. The northern fourth is located in the ‘‘Oetschernappe”. The southern three fourths are part of the ‘‘Hohe Wandnappe”. Up to tunnel chainage 292 m the declining advance passesthrough the well bedded ‘‘Dachstein-limestone” The 130 m longinclining tunnel section (‘‘E”) to the main crusher cavern cut acrossthe same rock mass (see Fig. 2).

From chainage 292 m to the end of the tunnel at chainage570 m (=breakthrough to an already existing tunnel) the tunnel

ll rights reserved.

/5449..at (R. Schwingenschloegl).

passes through limestone, marl, clayey marl and shale in variousthickness.

In the limestone sections ‘‘A”, ‘‘B”, ‘‘C” and ‘‘E” tripping waterwas seldom observed. In the remaining range we could find heavytrickling water and bottom water in different discharge. Waterconductivity in the limestone appears only in the discontinuitysets. In the fine coarse clastic sediments water inflow is locatedon shear zones, crushing zones and the loosening zone.

In the limestone section we can locate the greatest overburdenwith a height of 150 m. The lowest overlapping of only 70 m issituated at the thrust zone ‘‘Hohe Wand nappe” overriding the‘‘Oetscher nappe”.

The tunnel has an excavating span of 5.4 m and a height of3.95 m in the axis. Both abutments have the shape of a basket arch(see Fig. 4).

1.2. Choice of support according to apply New Austrian TunnellingMethod (NATM)

Referring to the forecasted rock mass four support classes weredefined by the contractor. The actual support was then slightlymodified during excavation according to the geological face map-ping as well as to the feedback of the miners: if necessary the roofwas supported by temporary rock bolts as well as by shotcrete(thickness 5 cm). Due to the geological prognosis reinforced shot-crete, steel arches and if needed permanent anchors were plannedin the clayey-marly rock mass. The actual support is shown inTable 1.

These specifications were given in accordance with the NATM.The basic principles of this method are summarized as (after Singhand Goel, 1999):

Fig. 2. Extract of the geological map ‘‘Hohe Wand”.

Fig. 1. Location of the tunnel.

R. Schwingenschloegl, C. Lehmann / Tunnelling and Underground Space Technology 24 (2009) 356–362 357

� Mobilisation rock mass strength.� Shotcrete protection to preserve the load-carrying capacity

of the rock mass.� Extensive monitoring the deformation of the excavated rock

mass.� Providing flexible but active supports.� Closing the invert to form a load-bearing support ring to

control deformation of the rock mass.

The bottom of the tunnel was constructed as 15 cm thick rein-forced concrete using a specially cement firm to sulphate. Accord-ing to the rock mass the length of the advance steps were variedfrom 1 m to 3 m.

2. Geology of the tunnel

Depending on temporal and economic reasons the geologicalengineering investigation only enfolded – where possible – a sur-face exploration. The outcome of this exploration was the assump-tion that the tunnel will mainly pass through well beddedlimestone. Except for a thrust zone (shale–marl) uniform beddingand uniform rock mass conditions were expected (see Fig. 3).

2.1. Limestone sections ‘‘A”, ‘‘B”, ‘‘C” and ‘‘E” (see Fig. 3)

Rock mass characteristics in the excavated limestone heading(exposition due to a representative working face at chainage169 m) (see Fig. 5).

Rock

Well bedded ‘‘Dachstein-limestone” withhigh intact rock strength, containing rockfragments in greenish to reddish

Bedding

Distinct, 310�/75�, with a thickness from 1 to7 dm

Spacing

10–100 cm, persistence about 1 m Joint properties Rough, uneven Rock mass bonding

strength

Excellent to good

Loosening of therock mass

Minor

Water inflow

Dry to low wet Karst phenomena Minor

2.2. Shale–marl section ‘‘D” (292–542 m) (see Fig. 3)

Rock mass properties in the excavated shale–marl heading(exposition due to a representative working face at chainage388 m) (see Fig. 6).

Intact rock

Shale (80%) and limestone marl (20%), bothin swelling rock zone

Bedding

None, tectonically alignment (about 190�/55�)

Spacing

1–10 cm Joint properties Uneven, smooth, matt to glossy, slaty rock

fragments

Rock mass bonding

strength

Fair

Rock mass behaviour

Friable Rock mass loosening Fair Water inflow None to minor Influence of the

mountain water

Locally; planar failure of some marl rockblocs

3. Observed damages in the period from 2002 to 2006

In 2002 the section 0–292 m (mainly limestone rock mass) isdistinguished of minor to sizeable caving from the tunnel walls.At the shotcrete lining on both tunnel walls many fissures werefound, notably at the position of the steel arches, mostly withinchainage 292–542 m.

3.1. Limestone sections ‘‘A” and ‘‘B” (0–190 m)

In this section some places at the tunnel walls have open joints.This is the reason for the caving of rock bodies from centimetre todecimetre size. In order to prevent drastic loosening and deforma-tion in the tunnel walls as well as at the roof, sealing with shotcreteor reinforced shotcrete would be appropriate.

3.2. Limestone section ‘‘C” (190–292 m)

In this zone the bedding planes and joints are mostly filled withsilty-clayey material. As a consequence in further addition withmountain water the friction decreases considerably, which causesplanar failures of rock bodies (size up to 30 cm).

Table 1Comparison of the required support; geological facts adjusted by the NATM and the Q-system, after Palmstrom and Broch (2006)

Section Typ of support Actual support Support required by the Q-system

After NATM Q-system Reinforcementcategories

Rock classes

(After Palmstrom and Broch (2006))

(A) 0–70 m, limestone Shotcrete – No support required 1 A, very goodReinforced Shotcrete –Steel arches –Anchors Swellex, local

(B) 70–190 m, 542–570 m,limestone

Shotcrete 5 cm, local No support required 1 C (fair)Reinforced shotcrete –Steel arches –Anchors Swellex, local

(C) 190–292 m, limestone Shotcrete 5–10 cm, head area 4–5 cm 4 D (poor)Reinforced shotcrete Local –Steel arches – –Anchors Swellex, local Systematic bolting, spacing 1.4 m

(Within ‘‘D”) 370– 390 m,‘‘swelling rock zone”

Shotcrete – – 5 E (very poor)Reinforced shotcrete Walls: 10 cm, head area: max. 15 cm 5–9 cmSteel arches Spacing 1.30 m –Anchors – Systematic bolting, spacing 2.4 m

(D) 292– 542 m, shaleand marl

Shotcrete – – 5 E (very poor)Reinforced shotcrete Walls: 10 cm, head area: max. 15 cm 5–9 cmSteel arches Spacing 1.3 m –Anchors SN, local Systematic bolting, spacing 2.4 m

358 R. Schwingenschloegl, C. Lehmann / Tunnelling and Underground Space Technology 24 (2009) 356–362

3.3. Shale–marl section ‘‘D” (292–542 m)

Because of a too quick, inappropriate removal of the temporarybases of the steel arches, their settlements induced cracks whichcould be observed over the whole section shortly after finishingexcavation works. This damages concern the shotcrete at and nearby the steel arches.

In this platy breaking zone of tectonically damaged shales,slight inflow of mountain water – mainly from the tunnel floor– induces permanent water saturation in the clayey rock mass.Starting by chainage 420 m calc-sinter scums show mountainwater percolation through the tunnel walls causing the moisteningof the shotcrete.

3.4. Swelling rock zone, chainage 370–390 m

The first indication for a bottom uplift, flaking of the concretefloor along the drainage gully at chainage 378 m, occurred twoyears after finishing tunnel excavation.

At the edge of the drainage groove, which reduces the thicknessof the bottom concrete, the initial point of an array of cracks issituated. At the beginning of the deformation measurements in2003 the fracture width varied from 0.2 to 2 mm.

The floor heave are supposed to be caused by a low amount ofanhydrite (0.8 vol.%) and also by a minor deposit of smectite(4 vol.%). For the chemical detection simultaneous thermal analysisand X-ray diffraction were used.

Hydration of anhydrite leads to a volume increase up to 60%(alteration pressure), while water absorption of smectite causes aswelling pressure. Because of the mountain water inflow and theunmeant leakage under the tunnel floor the alteration of anhydriteand the swelling of the clay minerals have been occurringpermanently.

Due to the distinct damages a restoration by using a floorpressure arch (maximum depth 2 m) was suggested. The spacebetween the tunnel floor and the floor pressure arch should befilled with compressible detrital material in addition. Fig. 7shows the actual, temporary restoration realized in winter2005.

4. Geotechnical measurements to describe the current state ofthe tunnel section 370–390 m (swelling rock zone)

Already one year after completion of the tunnel (in 2001)noticeable damages (countless fissures in the shotcrete of bothwalls) occur in a section of 20 m length from chainage 370 to390 m. The thin-shaly flaking of the concrete floor along the baseof the right tunnel wall was particularly demonstrative. To detectthe rock mass deformations, an extensive measurement was donesince June 2005 by monthly monitoring 42 measurement points onthe tunnel floor as well as convergences and roof settlements intwo profiles. During the survey the above-mentioned damagesincreased in number and shape.

The actual knowledge shows, that the concrete tunnel floor isgaping upward several centimetres. Therefore there is no longerforce fitting contact with the ground. The authors think that thereason for this upward movement is a high horizontal bucklingload resulting from the rock mass behaviour.

This compression load is caused on the one hand byalteration of clay minerals and anhydrite, on the other handby disintegration of the wall bases and stress rearrangement(see Fig. 8).

The maximum of the elevation movement was fixed at ameasurement point, which is correlating with the main crackfound in 2003. This elevation proceeds with 58.20 mm per year,together with a yearly convergence rate of 10.82 mm (chainage377 m) (see Fig. 9).

The geological strength index was used to carry out an assess-ment for the basic rock and rock mass parameters (see Marinoset al., 2005) (see Fig. 10).

5. Analysis of the serviceability of the Q-system concerning thechoice of support by Austrian Standard ‘‘ON B 2203 to satisfy theNATM

After a geotechnical controlling in spring 2005 and 2006– in contrast to the prognosis in the year 2000 – 5 sections(‘‘A”, ‘‘B”, ‘‘C”, ‘‘D” and ‘‘E”) as well as a ‘‘swelling rock zone”

Fig. 3. (a) Longitudinal section and geological facts. (b) Detail of the stratification in the floor swelling area.

R. Schwingenschloegl, C. Lehmann / Tunnelling and Underground Space Technology 24 (2009) 356–362 359

(see Fig. 3) of different rock mass behaviour could be confined.For these selected scopes the RMR-value and Q-value as wellas the deformation modul (Ed) were calculated. The rock massparameters /, c, Erm and UCS were computed with ‘‘Rock Lab1.0”.

Remarks to Table 2:

� The significant difference of the Q-values between section Aand B, although the geological conditions are roughly thesame.

� The difference between the Q-values of section B and C can beprofessed by the occurrence of silty-clayey joint filling as wellas a considerably plenty of mountain water.

� Although the Q-system provides a separate evaluation for swell-ing rocks the discrepancy between section D and the ‘‘rockswelling zone” is not reflected by the Q-values, because of com-pensation of several parameters.

A comparison of the actual support with the support deter-mined by the Q-system is shown in Table 1.

Fig. 4. Cross section with the suggested bottom arch (Lehmann, 2007).

Fig. 5. Typical face of the tunnel at chainage 169 m (limestone section)(Schwingenschloegl, 2001).

Fig. 6. Typical face of the tunnel at chainage 388 m

360 R. Schwingenschloegl, C. Lehmann / Tunnelling and Underground Space Technology 24 (2009) 356–362

6. Discussion and conclusion

Due to significant damages the following annotations relate to arock mass classification which was already done five years afterthe finishing of the tunnel.

On the one hand the limestone units appeared in a strong alter-nation of the rock mass behaviour, here the support fixing due tothe Q-system was not as flexible as the NATM (see Fig. 1). On theother hand it was not possible to assume a geotechnical limitationof the described ‘‘rock swelling zone”. This zone could not berecognised by the documentation during the excavation, sincethe tunnel consists of a shale–marl rock mass over the whole sec-tion ‘‘D”.

In the section ‘‘C” the Ja-value was defined by rare occurrenceof bedding planes filled with clay and silt. The predominantintercept of the tunnel however is free from those fine-grained

(shale–marl section) (Schwingenschloegl, 2001).

Fig. 7. Cross section provisional restoration (Lehmann, 2007).

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0.070

0.080

0.090

uplif

t in

[m]

Fig. 8. Time-uplift diagram, measurement point ‘‘5a”, uplift rate: 4.85 mm permonth (exemplarily) (Lehmann, 2007).

4590

4592

4594

4596

4598

4600

4602

4604

4606

4608

17.02.2005

28.05.2005

05.09.2005

14.12.2005

24.03.2006

02.07.2006

10.10.2006

18.01.2007

28.04.2007

06.08.2007

Dis

tanc

e be

twee

n bo

th w

alls

in [m

m]

Fig. 9. Convergence measurement, time–distance diagram, convergence rate:10.82 mm per year (exemplarily).

00.10.20.30.40.50.60.70.80.91

-0.25 0.25 0.75 1.25 1.75 2.25Normal stress (MPa)

Shea

r str

ess

(MPa

)

Hoek-Brown

Mohr-Coulomb

Fig. 10. Normal stress–shear stress diagram, after Roc Lab 1.0 (Hoek, 2007).

R. Schwingenschloegl, C. Lehmann / Tunnelling and Underground Space Technology 24 (2009) 356–362 361

components. Furthermore the value band Ja = 8 to Ja = 20 (afterPalmstrom and Broch, 2006) is too large for a seriousdetermination.

During the geological documentation uniformly fins of gyp-sum were located. Mineral analyses confirm a minor contentof clay with a sizeable ability of swelling potential. Due tothe actual cognitions from the geological tunnel documenta-tion regarding the swelling rock phenomenon we could notsee an influence of squeezing rocks. After empiricalapproaches (Singh et al., 1992 and Goel et al., 1995a,b) therewere no squeezing conditions. In this context it is noticeablethat SRF-values are existing for swelling as well as for squeez-ing conditions. Though in both cases the values are largelythe same. The high bandwidth of the Ja-value and the SRF-val-ues (SFR = 5 to SFR = 20) do not lead to a distinctdetermination!

In the section ‘‘A” (0–70 m) there is almost no difference be-tween support after the ‘‘Q-support chart” – reinforcement category1, rock class A (Palmstrom and Broch, 2006) and support onto‘‘NATM” (see Table 1).

In the section ‘‘B” (70–190 m, 542–570 m) there are negligibledifferences in the thickness of the shotcrete (roof area), reinforce-ment category 1, rock class C.

At ‘‘C” (190–292 m) there are varieties in the arrangement ofthe anchors, reinforcement category 4, rock class D.

In the ‘‘swelling rock zone” (370–390 m) significant discrepan-cies are recorded in the array of the steel arches and the anchorsupport, reinforcement category 5, rock class E.

Also from chainage 292 to 542 m section ‘‘D” an obvious differ-ence in the configuration of the steel arches and anchors was seen;reinforcement category 5, rock class E.

From this follows that the support after NATM and the supportafter the Q-system differ only a little in good rock mass. Swellingrock mass conditions cause major differences in the choice of sup-port between NATM and Q-system. In our opinion the NATM al-lows a more adaptable support in poor rock mass classes. Usingthe NATM it is possible to give a quick and a certain reaction onthe several rock mass behaviour types at each advance step(Austrian Standard, 2001).

According to our comparison we could see that the engineeringgeological evaluation of swelling rock zones in tunnelling differsonly little using NATM or Q-system.

The same aspect can be find in the current publication of Palm-strom and Stille (2007), Table 5. Regarding this rock mass behav-iour they demonstrate that the fitness of the Q-system andNATM is equivalent.

However, there is a difference in the choice of the required sup-port (see Table 1). Using the Q-system there are only two types ofsupport available.

This paper is an appropriate contribution to the permanent dis-cussion about the applicability of NATM and Q-system (NMT, Bar-ton and Grimstad, 1994, pp. 431–432).

Tabl

e2

Arr

ange

men

tof

geot

echn

ical

data

Sect

ion

Posi

tion

ing

desc

ript

ion

RQ

DU

CS

(MPa

)rc

RM

RR

MR

basi

cQ

-sys

tem

GSI

GSI

valu

eM

ohr–

Cou

lom

bfi

tR

ock

mas

spa

ram

eter

s

JnJr

JaJw

SRF

ESR

De

QD

escr

ipti

onC

ohes

ion

(MPa

)Fr

icti

onan

gle

(deg

)

Ten

sile

stre

ngt

h(M

Pa)

Un

iaxi

alco

mpr

essi

vest

ren

gth

(MPa

)

Glo

bal

stre

ngt

h(M

Pa)

Mod

ulu

sof

defo

rmat

ion

(MPa

)

A0–

70m

,li

mes

ton

e93

.51

100

573

31

11

1.5

3.66

93.5

1A

,ver

ygo

od,1

753.

0150

.52

�1.

4517

.91

24.5

627

410.

27

B70

–190

m,5

42–

570

m,

lim

esto

ne

89.4

310

039

32

81

11.

53.

667.

45C

,fai

r,1

651.

5348

.32

�0.

598.

6216

.90

1541

3.93

C19

0–29

2m

,li

mes

ton

e90

.22

100

333

113

0.66

11.

53.

661.

53D

,poo

r,4

550.

9044

.85

�0.

244.

1112

.18

8667

.89

Wit

hin

‘‘D”

370–

390

m,

‘‘sw

elli

ng

rock

zon

e”

10a

3516

152

11

51.

53.

660.

27E,

very

poor

,5(6

)20

0.14

23.9

20.

010.

111.

2820

9.03

D29

2–54

2m

,sh

ale

and

mar

l10

a35

1615

2.5

2.5

12.

51.

53.

660.

27E,

very

poor

,5(6

)

aR

QD

lim

itva

lue.

362 R. Schwingenschloegl, C. Lehmann / Tunnelling and Underground Space Technology 24 (2009) 356–362

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