TRANSPORT and ROAD RESEARCH LABORATORY Department of … ·

TRANSPORT and ROAD RESEARCH LABORATORY

Department of the Environment Department of Transport

SUPPLEMENTARY REPORT 532

SOME OBSERVATIONS OF MACHINE TUNNELLING AT THE KIELDER AQUEDUCT

by

T D O'Rourke (University of Illinois at Urbana-Champaign),

S D Priest* and B M New (Transport and Road Research Laboratory)

* Now at Imperial College, London

A shortened version of the text of this Report was presented to the 19th US Symposium on Rock Mechanics, Lake Taho,

Nevada, May 1978.

Any views expressed in this Report are not necessarily those of the Department of the Environment

or of the Department of Transport

Tunnels and Underground Pipes Division Structures Department

Transport and Road Research Laboratory Crowthorne, Berkshire

1979

ISSN 0305-1315

CONTENTS

Page

Abstract I

I. Introduction I

2. Geology 3

2.1 Discontinuity characteristics 3

2.2 Intact rock strength 4

2.3 Seismic velocity 5

3. Tunnelling procedure 6

4. Observed conditions and tunnelling performance in sandstone 7

4.1 Tunnel geology 7

4.2 Tunnelling performance 8

4.3 Comparison of seismic velocities with ground conditions 10

5. Observed conditions and tunnelling performance in limestone 10




6. Observed conditions and tunnelling performance in mudstone 12




7. Discussion 14

7.1 Tunnelling delays and geology 14

7.2 Machine construction and tunnelling performance 15

7.3 Seismic velocity measurements 16

8. Conclusions 17

9. Acknowledgements 19

10. References 19

(C) CROWN COPYRIGHT 1979

Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.

Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on 1 st April 1996.

This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.

SOME OBSERVATIONS OF MACHINE TUNNELLING AT THE KIELDER AQUEDUCT

ABSTRACT

The Kielder Water Scheme, currently under construction in north-east England, will consist of 32 km of tunnel to direct water from the Tyne to the Wear and Tees River Valleys. The project, which is promoted by the Northumbrian Water Authority, involves excavation through sedimentary strata using 3.5 m-diameter tunnel boring machines.

The Tunnels Division of the Transport and Road Research Laboratory (now the Tunnels and Underground Pipes Division) planned and implemented an observation programme during tunnel construction for the North Wear Drive, a portion of the Kielder tunnel system linking the River Wear with a companion tunnel drive from the Derwent Valley. The observations were performed with the assistance of Babtie, Shaw and Morton, the general engineering consultants for the Kielder Water Scheme.

Detailed observations and measurements were taken in the first 1600 m of the North Wear Drive, where the tunnel was driven through approximately equal lengths of sandstone, limestone and mudstone. This paper summarises the structure and material properties of the in-situ rock in each of the principal lithologies and compares the observed ground conditions with the machine advance rates and rock support adopted during tunnelling.

Attention is directed to the performance of the tunnel boring machine in light of the geological conditions, and improvements are suggested as an expedient to future machine excavation. In addition, the results of seismic scans, taken along the tunnel, are summarised and compared with detailed observations of the rock conditions.

I. INTRODUCTION

Many authors have recognised the importance of ground conditions in

contributing to rock displacement and overbreak, and in dictating the amount I-5

and types of support required in tunnels An appreciation of how various

ground conditions translate into support and excavation requirements is

especially important in the use of tunnel boring machines, where the nature

of machine construction can restrict the application of support at the tunnel

face, and deteriorating ground conditions can diminish the capacity for

machine thrust and manoeuvreability. To this end, case studies are

particularly useful in that they help to point out important characteristics

of the construction method and provide a basis for estimating machine

performance in various subsurface environments.

An evaluation of ground behaviour must, of course, be preceded by site

investigation so that the structure and engineering properties of the ground

can be determined. Various techniques are currently used for this purpose

that include logging vertical and inclined boreholes, mapping the surface

geology, stereo photography, and geophysical sensing.

Of the geophysical methods, measuring the seismic velocity of

compressional waves through in situ rock has been proposed and studied as

an indication of rock quality 6-9. Borehole measurements of seismic velocity

have been used at several sites10-11; to identify relatively large faults,

and seismic scans along a completed tunnel have been used to estimate the 12

in situ moduli of the rocks Judgements regarding the reliability of

the method will no doubt benefit from additional field studies where seismic

scans can be correlated in detail with rock structure and ground behaviour.

In the light of these considerations, the Tunnels Division of the

Transport and Road Research Laboratory planned and implemented an

observation programme during tunnel construction at the Kielder Water Scheme.

The Kielder Water Scheme 13 is promoted by the Northumbrian Water Authority

and will consist of 32 km of tunnel principally through sedimentary rock.

It was felt that the scale of the project and variety of tunnelling

conditions required close examination, and where appropriate, to report the

ground behaviour and construction performance to the tunnelling industry.

The site chosen for observation was the North Wear Drive, a portion of the

Kielder tunnel system linking the River Wear with a companion tunnel drive

from the Derwent Valley. The observations were performed with the assistance

of Babtie, Shaw and Morton, the general engineering consultants for the

Kielder Water Scheme. The Contractor for tunnel construction was Tyne-Tees

Tunnelling, an international consortium of three contractors. Excavation

was performed with a tunnel boring machine, manufactured by Demag

Verdictertechnik.

Detailed observations and measurements were taken in the first 1600 m

of the North Wear Drive, where the tunnel was driven through approximately

2

equal lengths of sandstone, limestone and mudstone. This report summarises

the structure and material properties of the in situ rock in each of the

principal lithologies and shows how these features influenced tunnel

construction. Attention is directed to the performance of the tunnel boring

machine in light of the geological conditions, and improvements are suggested

as an expedient to future machine excavation. In addition, the results of

seismic scans, taken along the tunnel, are summarised and compared with

detailed observations of rock conditions.

2. GEOLOGY

The general geology of the area along the line of the tunnel was determined

from surface mapping, site investigation boreholes and existing published 14

data The stratigraphy of rocks encountered during the sinking of a

borehole, approximately 600 m from the North Wear portal, and a diagrammatic

section based on the site investigation results are given in Figure I.

The rocks in the first 1600 m of the tunnel drive belong to the Middle

Limestone Group of the Lower Carboniferous Series. The drive takes the

tunnel into progressively younger strata, which dip at approximatly 1.5 °

along the tunnel route. The initial 500 m is in a strong, fine-grained

siliceous sandstone, followed by approximately 600 m in the Four Fathom

Limestone, a very strong, crystalline material. This grades through a

muddy limestone into a micaceous and carbonaceous mudstone which lasts for

another 600 m of the drive and ultimately gives way to the Quarry Hazle

Sandstone (a strong siliceous sandstone) followed by the Iron Post Limestone

(a strong, crystalline muddy sandstone). The predicted and actual geology

correlate remarkably well, considering the amount of site investigation

data available and the depth of the tunnel. Any discrepancies between them

are largely due to minor variations in the dip of the sedimentary strata.

2.1 ~iscontinuity characteristics

The general term 'discontinuity' is used in this report - avoiding any

generic connotations - to describe a mechanical break or interruption of

the properties of a rock 15. In this report the following terms are used to

described specific types of discontinuities:

16 Joint - fracture in rock along which there has been little or no movement

vein - tabular rock or mineral that fills and cements an open joint.

3

Features such as iron staining and calcite or clay infilling were taken

to indicate that the given discontinuity pre-dated tunnel excavation.

Fractures induced by the tunnelling procedure, notably the fractures that

were caused by expansion of the anchor pads, were ignored. Measurement of

veins was carried out, despite the fact that they did not form significant

mechanical breaks in the rock, to supplement orientation data obtained at

other locations in the tunnel.

Representative sections in each rock type were closely examined along

horizontal scanlines to determine discontinuity orientation, spacing,

continuity and width of opening and the nature of infill materials. This 17

method of sampling discontinuities is discussed by Priest and Hudson

Owing to the limited access in the tunnel, vertical scanlines were not

performed. Statistical data snmmarising the results of these measurements

are listed in Table 1.

The frequency of the most conspicuous and continuous (trace lengths

exceeding 1.5 m) was logged over 10 m lengths of tunnel. This was performed

in conjunction with seismic velocity measurements. Although the joints were

recorded along the springline of the tunnel, they were, in the great

majority of cases, continuous into the shoulders and crown. In many

instances, the joints logged at springline could be traced through their

mutual intersections in the roof where rock wedges were apparent.

Throughout all sections of the tunnel, the majority of the discontinuities

were vertically inclined. This was especially evident for the most continuous

joint sets in the sandstone and mudstone, as well as the calcite veins in the

limestone. In view of the vertical nature of the discontinuities it was

considered more appropriate to present orientation data in terms of strike

direction rather than dip direction, the strike of a plane being the azimuth

of a horizontal line in that plane. This strike information is presented

in the form of rose diagrams in Figure 2. The azimuth of the tunnel drive

is shown in each of the diagrams.

2.2 Intact rock strength

A measure of intact rock strength was obtained by using a Schmidt

rebound h~mmer (Type L). The hammer was used at axis level in the

horizontal mode, thus obviating the need to apply the angle corrections

described by Kolek 18. The results obtained from in situ testing of

natural rock should be viewed with caution as (a) the surface of the rock

was often uneven and (b) the presence of an open joint behind the test area

could give an artificially low rebound number.

In order to minimise the effect of these problems, at least five tests

2 were taken within an approximately 0.5 m area at each test location.

Experience has shown that, whilst it is possible to get an artificially low

rebound value due to the influence of open joints and fractures, it is very

rare to obtain an artificially high value. Consequently, the two lowest

values were discounted as a means of screening anomalously low readings, and

the mean of the three highest rebound numbers was taken as a measure of the

intact rock strength. Measurements were made at 10 m intervals along the

tunnel. Mean rebound nNmbers and ranges of compressive strength are

presented in Table 2 for the principal rock types encountered during

tunnelling. The compressive strengths were estimated from the rebound numbers

using a calibration curve in the operating handbook. The influence of

intact rock strength on the performance of the tunnelling machine in this

length of tunnel is discussed in a companion paper by Morgan et a119 using

the above data.

2.3 Seismic velocity

A Bison signal enhancement seismograph was used at 10 m intervals along

the tunnel to make velocity measurements over the intervening baselengths.

Owing primarily to the attenuative nature of the rock, 10 m was the maximum

range possible using the equipment in the manner described. A lesser

separation between hammer impact and geophone may have resulted in

anomalously high sensitivity to individual discontinuities, and the

resolution of the seismograph timing system would have proved inadequate.

A sledge hammer generated the seismic waves and a geophone was used as a

receiving transducer. An impact switch on the hammer triggered the cathode

ray tube sweep where the geophone output was displayed and held. An

electronic cursor was set by the operator at the first wave arrival and the

time elapsed since the impact was numerically displayed in milliseconds. The

system described was successful in the tunnel environment and the complete

survey was carried out during two eight hours shifts.

Certain problems inherent in the technique and others imposed by the

limited time and access to the tunnel must be considered when interpreting

the data. They are as follows:-

(a) The direct hammer impact on the sidewall tended predominantly to

generate shear and surface waves rather than the compressional waves

required. Thus, in highly attenuative rock masses, the first

observed arrivals may be those of the slower, but higher amplitude

shear or surface waves.

(b) The axis of sensitivity of the geophone was pointed towards the hammer

source to provide maximum sensitivity to compressive wave arrivals.

However, the time available in the tunnel did not allow rigid mechanical

coupling of the geophone to the rock. Consequently, the relatively low

signal to noise ratio may have further impaired discrimination of the

first wave arrivals.

Intact specimens of the three main rock types were taken and the

unconfined compressional wave velocities measured in a direction parallel

to the bedding. The results of these laboratory measurements are summarised

in Table 3.

3. TUNNELLING PROCEDURE

The tunnel was driven at an azimuth of 015°NE. The initial 127 m of

tunnelling were undertaken by drill and blast methods to form a D-shaped

opening, 3.85 m high and 3.80 m wide. Steel arches and posts were used

as primary support in the drill and blast section, with shotcrete applied

in a thickness of approximately 80 mm at the crown and side-walls. Starting

at chainage 127, excavation was performed with a full-face tunnel boring

machine of 3.5 m diameter.

A simplified diagram of the tunnel boring machine is presented in

Figure 3. The rotating cutting head was equipped with 17 triple disc

cutters. The rock debris, generated by the cutting process, was collected

behind gathering arms, or scrapers, that were spaced at quarter points

around the periphery of the cutting head. Near the springline of the

cutting head the debris was fed into an intake chute from which the

excavated material was directed on to a conveyor belt in the tunnel invert.

6

The opening of the intake chute was approximately 300 mm by 225 mm in plan

dimensions. Access to the cutting face was available through the access

corridor, which is shown in cross-section A-A. The access corridor was

approximately 0.75 m high and I m wide. Reaction for the forward thrust

to the cutting head was provided by two rear anchor pads that were expanded

laterally to obtain a bearing against the rock. The position of the cutting

head was continuously adjusted with respect to the line of horizontal

reaction at the rear anchor pads, thus providing a control on the gradient

of excavation. The application of pressure across the front anchor pads

helped stabilize the head during cutting and contributed to the control

of alignment. Tunnel support was installed from a working platform located

approximately 12 m from the tunnel face. As the working platform was

positioned less than 2 m below the crown, a rock bolt length of 1.85 m was

the maximum that could be placed from this location. The operator's cabin

was located immediately behind the working platform. This, in turn, was

followed by a section that carried the dust extractor equipment and an

elevated Malhauser conveyor.

4. OBSERVED CONDITIONS AND TUNNELLING PERFORMANCE IN SANDSTONE

4.1 Tunnel geology

From chainage 150 to 220* the tunnel was driven through mixed beds of

mudstone and sandstone, and from chainage 220 to 770 tunnelling was performed

principally in sandstone. A geological cross-section of this portion of

the tunnel is illustrated in Figure 4.

The principal sets of discontinuities in the sandstone included

bedding and two sets of nearly vertical joints (NE and NW joints). The

characteristics of these discontinuities are summarised in Table 4. All the

NW joints and some of the NE joints were filled in soft clay, the properties"

of which are listed in Table 5. In particular, the thick, infilled nature

of the NW joints contributed to instability by allowing rock blocks to slip

and rotate at their clay-filled boundaries. Samples of clay for testing

were taken from depths of 5 to 10 cm in several joints. The particularly

low shear strength reflects the remoulding of the material as well as the

likelihood of increased water content due to exposure near the tunnel wall.

* Chainages are measured in metres.

7

There were three types of wedges that were potentially unstable during

tunnelling:

I. Tetrahedral wedges: These were formed at the shoulders of the tunnel;

they were bounded on top by a bedding plane, and on each side by a NE 3

and NW joint. Most tetrahedral wedges were from 0.25 to 0.50 m in 3

volume, however many wedges of I m were also observed. Plate I shows

a tetrahedral wedge that became unstable in the west tunnel wall.

2. Diamond-shaped wedges: These were formed at the crown by the

intersection of two NE and two NWjoints. Wedges of this type tended to

break at the bedding plane immediately above the crown. In locations

where the joint spacing was low for both principal joint sets, overbreak

occurred as far as the third and fourth bedding plane above the tunnel.

Plate 2 is a photograph of the crown near the intersection of a NE and

NW joint. In the picture, portions of several diamond-shaped wedges

can be seen.

. Wedges bounded by parallel joints: The NW joints frequently occurred

in pairs that were separated by less than 0.5 m. In these instances

the elongated slab of rock between the joints tended to fall from the

crown, thus leaving a void which extended to the first or second

bedding plane above the tunnel. Loosening at the edges of the void

led to slabbing of the intact rock and further deterioration.

4.2 Tunnelling performance

In Figure 4, joint frequency, volume of overbreak, rock bolt support

per metre run, advance rate and seismic velocity are plotted for chainages

150 to 770. The tunnelling advance rate is referenced to the location of

the support platform. Each advance rate is computed from the distances

tunnelled during several 11-hour working shifts divided by the time elapsed

during the shifts. As such, it includes the time required for all cutting,

mucking and support activity, as well as the time needed for repairs or

cutter changes during the working shift. It does not include the time

spent during scheduled maintenance periods.

Rock bolts were common to all methods of ground support except shot-

creting and were in particularly high use during the erection of steel

arches. In the latter case, arches were supported on steel beams that were

bolted to the tunnel wall with as many as six bolts per metre length of

beam.

Between chainages 200 and 250, some joint openings were as thick as

60 mm and the number of joints per 10 m length was approximately 30. The

low advance rates in this section are related to the high density of support

and to delays caused by a rock fall at chainage 235. With distance from the

portal, there was a decrease in joint frequency and, in particular, a

substantial decline in the number of NE joints. From chainage 525 to 575,

the spacing of NE joints was in excess of 10 m. Correspondingly, there was

a notable decrease in the number of tetrahedral and diamond-shaped wedges.

In addition, joint thickness diminished with distance from the portal so

that, from chainage 500 onward, the joints were rarely in excess of 15 to

20 mm thick.

In places, tunnelling progress was retarded by wedges of rock that

obstructed the intake chutes at the cutting head. When blockage occurred,

the machine had to be stopped until the chute was cleared. This problem

was persistent throughout the sandstone, but was especially bad between

chainages 150 and 450 where, in certain locations, the machine advance was

interrupted several times during a shift. For example, between chainages

300 and 400, an average delay of 8 hours per 10 m advance can be attributed

to blockages at the cutting head. In general, the blockages decreased as

both joint frequency and thickness declined. From chainage 480 to 580,

the delay caused by blockages had decreased to an average 2 hours per 10 m

length. The highest rates of advance in the sandstone were recorded along

this section of the tunnel. When seat earth was exposed in the crown,

between chainage 600 and 650, blockages at the cutting head caused an

average delay of 3 hours per 10 m length, whereas the installation of roof

support required from 6 to 20 hours per 10 m length.

Shotcrete was used in two areas. Between chainages 200 and 240 it was

sprayed directly from the machine. Long delays for cleaning, as well as

the potential for mechanical and electrical damage, discouraged further

application of shotcrete near the tunnelling equipment. When used again

between chainages 590 and 770, shotcrete was placed only after the machine

and conveyor system had advanced for their full length of 110 m beyond the

point of application. In this section shotcrete was used as additional

support for seat earth exposed in the crown. The seat earth was extremely

friable and showed substantial deterioration with time. The shotcrete,

applied in thicknesses of 60 to 100 mm, provided both support and insulation

for the seat earth.

In the sandstone the tunnel was advanced mainly under dry conditions,

although locally wet areas were encountered. In the vicinity of the rock

fall at chainage 235 the water inflow was approximately 250 m3/day.

4.3 Comparison of seismic velocities with ground conditions

The seismic velocities that were measured between chainages 250 and

550 show a bimodal structure, with upper and lower bounds of about 4000 m/sec

and 2500 m/sec. It is likely that much of the spread in the measurements

can be accounted for by the difference in velocity of compression (P) and

shear (S) waves. The upper velocities are very close to laboratory P-wave

velocities whilst the lower are similar to S-wave velocities calculated by

assuming a Poisson's ratio of 0.25. The attenuative nature of the rock in

this section made it difficult to interpret the time of first wave arrival

and, consequently to discriminate clearly between P and S wave arrivals. As

many as five or six hammer blows were required to achieve signal enhancement

sufficient to allow the first wave to be distinguished above the noise level

at the geophone.

From chainage 550 to 770 the decreased number of joints and diminished

joint thickness in the sandstone corresponds to a relatively high and

constant seismic velocity. This trend continues until chainage 850, where

seat earth was encountered at the springline. The average of the 22

velocities measured from chainage 550 to 850 was 4096 m/sec, giving a

ratio of in situ to intact seismic velocity of 0.96.

5. OBSERVED CONDITIONS AND TUNNELLING PERFORMANCE IN LIMESTONE

5.1 Tunnel geology

Between chainages 770 and 1130 the limestone was a hard, crystalline

material with relatively few impurities. From chainage 1130 onward an

increasing proportion of clay impurities was apparent as the limestone

graded into a nearly full face of mudstone at chainage 1270. A geological

cross-section of these portions of the tunnel is illustrated in Figure 5.

10

Bedding was apparent as stylolitic bands of impurities throughout the

limestone. Two well-defined sets of vertical veins were observed; one

striking at 335 to 345 ° NW, and the other at 60 to 75 ° NE. Owing to their

cemented nature, the bedding and vertical veins did not cause overbreak or

wedge movement.


In Figure 5, joint frequency, volume of overbreak, rock bolt support

per metre run, advance rate, and seismic velocity are plotted for chainages

770 to 1270 in a manner similar to that for the tunnel section in sandstone.

The relatively low advance rates between chainages 770 and 900 were related

to shotcrete placement at the seat earth exposures between chainages 590

and 770. There, shotcrete operations blocked access to the machine, and

advance was not possible until the tracks had been cleared to allow free

communication for the muck cars between the machine and portal. From

chainage 900 to 1000, there was a gradual increase in advance rate. In this

section tunnelling was slowed by difficulties in changing several of the

cutters. Beyond chainage 1000, the average advance rate of 0.9 m/hr was

relatively close to the average cutting rate of 1.4 m/hr. The rock bolts

between chainages 810 and 1100 were used primarily to support the

ventilation equipment. Tunnelling in the limestone was performed under dry

conditions.

Throughout the limestone and shaly limestone, the intact nature of the

rock contributed to a conspicuously smooth bore, with little or no delay

caused by ground instability or support installation. In fact, the most

significant delays in this portion of the tunnel were associated with

support operations for the seat earth and difficulties in changing individual

cutters. Owing to the uniform ground conditions and lack of open jointing,

advance rates of a consistently higher value were sustained in comparison

to the rate predominant in the sandstone portion of the tunnel.


Between chainages 850 and 1270 the seismic velocities again show a

bimodal structure, with upper and lower bounds of 5600 m/sec and 3600 m/sec.

As was the case for most of the sandstone, this material was highly

attenuative. Correspondingly, there was difficulty in distinguishing whether

the first arrival was that of a P or S wave so that the spread in the

11

measurements was again related to the difference in velocity for the two

different wave types. By way of contrast with the sandstone, the joints in

the limestone were filled and well cemented with calcite. The anomalously

high attenuation in the limestone is most likely the result of multiple

reflection and scattering as the acoustic impedance of the calcite was

significantly different from that of limestone. A similar effect has been

noted in carboniferous limestone by McCann (personal communications).

6. OBSERVED CONDITIONS AND TUNNELLING PERFORMANCE IN MUDSTONE

6.1 Tunnel geology

A geological cross-section of the mudstone between chainages 1270 and

1600 is illustrated in Figure 6. The mudstone was fissile, showing a

marked tendency to split in horizontal planes parallel to the bedding. Its

slake durability index was 74 per cent, which indicates that the mudstone 20

was only moderately resistant to air and water slaking

Surficial slabbing was observed in all portions of the mudstone. The

over-break associated with the slabbing was up to 0.2 m deep. The surface of

the mudstone was subjected to at least two wetting and drying cycles and this

would have contributed to slaking of the rock. During cutting, the rock near

the face was saturated by the dust abatement spray. As the machine advanced,

the rock was dried by heat generated near the transformer. With further

advance, the decline of temperature and humid atmosphere caused condensation

which, in turn, was dissipated with time.

Most of the continuous joints (3.5 m) in the mudstone were calcite-filled.

Generally, the calcite was 2 to 3 mm thick with planar, smooth surfaces.

Bonding along the contact between the mudstone and calcite was weak. The

rock tended to break at this interface, thereby contributing to overbreak

and wedge movement.

Between chainages 1450 and 1480, a set of calcite-filled joints was

observed, striking nearly parallel to the tunnel axis at 15 ° to 30 ° NE.

Figure 7 contains a plan and profile view of the tunnel in the vicinity of

chainage 1472. As shown in the figure the subparallel joints contributed

both to the large overbreak at the east crown and to the displaced rock

at the west wall. Plate 3 shows the east crown and springline areas at

this location. The magnitude of overbreak can be judged relatiVe to the

12

protective cover of the tunnel boring machine, which marks the approximate

outline of intended excavation. These observations corroborate those of

Cording and Mahar 3 and Whittle 5 for similar conditions of subparallel

jointing in schistose gneiss and slate, respectively.


In Figure 6 joint frequency, volume of overbreak, rock bolt support

per metre run, advance rate, and seismic velocity are plotted for sections

of the tunnel in mudstone.

From chainage 1270 to 1390 the mudstone was substantially intact with

a low joint frequency. Correspondingly, a relatively high advance rate is

shown. After chainage 1390, the conspicuous decline in advance rate is

consistent with the worsening ground conditions in the zones of faulting.

These, in turn, are reflected in the increased joint frequency, volume of

overbreak, and quantity of rock bolts.

The faults at chainages 1410 and 1570 were minor, involving down-throws

of approximately 2 and Im, respectively. By way of contrast, the fault at

chainage 1515 was more substantial, with a vertical offset of approximately

8 m and a zone of intensely fractured rock that was 20 m wide (McFeat-Smith,

personal communication). The nature of the rock in the fault zone not only

caused support problems, but interfered with the operation of the tunnel

boring machine. Plate 4 illustrates an important aspect of this interference

by showing the ground condition immediately adjacent to a rear anchor pad at

chainage 1512. The lateral overbreak and fractured quality of rock placed

severe limitations on the reaction force that could be sustained by the

anchor pads. As indicated in the picture, a suitable reaction could be

obtained only by 'packing out', or wedging, timber beams between the pad and

rock surface. Tunnel support at this location was accomplished by means of

steel arches or by steel beams that were bolted directly into the more

competent limestone and mixed beds beyond chainage 1520.

Excavation in the mudstone was mostly under dry conditions with one

notable exception at chainage 1575. At this location, holes drilled for

the rock bolts intercepted an aquifer approximately I m above the tunnel

crown. The ensuing water inflow of 1500 m3/day was eventually controlled by

diverting the water through hoses, which were socketed into the crown.

13


The mudstone was the least attenuative material to seismic waves. Often,

only I or 2 hammer blows were sufficient to produce clear P wave arrivals.

The general trend of the measurements shows fairly gradual changes in seismic

velocity probably due to changes in the in-situ modulus of the material.

At chainages 1420, 1520 and 1570, there is a sudden and distinct drop in

velocity. This is indicative of highly disturbed areas of rock and is

exactly correlated with observed areas of faulting. A reduction in velocity

was also noted between chainages 1455 and 1475. This corresponds to a zone

where frequent subparallel joints resulted in large overbreak (see figure

8 and Plate 3). In general, the measurements of in-situ seismic veloc&ty

were considerably higher than laboratory measurements on unconfined samples

from this section (see Table 3). This discrepancy is apparently related

to the in-situ confining stress and its compressional effect on the highly

laminated mudstone.

7. DISCUSSION

7.1 Tunnelling delays and geology 19

In a companion paper, Morgan et al have shown that, during machine

excavation in the first 1600 m of the North Wear Drive, it took an average

3.25 hours to excavate and support I m of tunnel. As an overall average,

20.3 per cent of the time was devoted to installation of support, 7.4 per

cent was caused by delays due to blockage of the intake chutes, and 6.1 per

cent was caused by delays resulting from problems such as rock falls and

water inflow. These percentages are the proportions of total time in

addition to the time required for rock cutting and, thus, do not reflect

the services performed concurrently with actual rock excavation.

In Table 6 are s,lmmarised the times for unit advance in each of the

main rock types together with the percentage of this time taken up by the

s,lmmed delays from the categories above. The record of tunnel delays shows

that progress was closely dependent on the local geology and in-situ rock

structure. The principal zones of delay correspond to portions of the

tunnel in highly jointed sandstone and mudstone. In particular, the high

percentage of delay time between chainages 1500 and 1600 was associated with

fault zones and an area of high water inflow. The high percentage delay

shown for the limestone, between chainages 770 and 890, did not result from

poor ground conditions near the face, but rather from shotcrete application

14

to the seat earth, which was a full 110 m behind the face of the machine.

Where the rock was self-supporting, the time for unit advance showed a

marked reduction. The low frequency of joints, and stable intact nature of

the clayey limestone, between chainages 1127 and 1270, contributed to an

environment where only 1.6 per cent of the tunnelling time was associated

with delays caused by ground support or mucking difficulty.

7.2 Machine construction and tunnelling performance

Blockages of the intake chute, which caused substantial delay at the 21

North Wear Drive, are not without precedent. Bennion reports that

similar difficulty in highly jointed andesite restricted progress during

construction of the Kaimai Tunnel.

If the exposed area at the periphery of the cutting head is larger than

the dimensions of the intake opening, blockages of the opening may occur.

This is illustrated in Figure 8 which shows a three-dimensional view of the

cutting head of the Demag machine. The gathering arms of the machine are

located at quarter points around the cutting head, and the distance

separating the dust shield and excavated face is approximately 1.25 m. At

the periphery of the cutting head, the spaces between the scraper arms are

open to penetration by relatively large blocks. Consequently, rock exceeding

the dimensions of the intake chute could be swept towards the intake opening

and wedged there.

The vulnerability of the cutting head to obstruction is evidenced by

the many delays caused by the blocked intake chute. The close relation

between blockages and rock structure is substantiated by the recorded

locations of the blockages. For example, obstructions of the intake chute

were negligible when excavating through full-face limestone and intact

mudstone. By way of contrast, the delay associated with blockage was highest

during initial tunnelling in the sandstone where the high frequency of

mud-filled joints contributed to loose rock and overbreak.

At Kielder the Demag machine was equipped with front anchor pads whose

forward movement was controlled independently of the movement of the

central shaft. Thus, as the cutting head was pushed\forward, the front

anchor pads remained stationary, providing stability for the cutting head

15

and alignment for the machine. At the end of the cutting stroke, the front

pads were retracted and moved forward to a new position. If steel arches

had been erected immediately behind the cutting head, it would have first

been necessary to retract the front pads far enough to move them past the

recently erected arches. For Demag machines greater than approximately 4 m

diameter, it is possible to design for this operation. However, the space

restraints imposed by a 3.5 m diameter tunnel preclude this capability.

Consequently, the machine construction was not compatible with installation

of support ~mmediately behind the cutting head. Instead, the support

platform was located behind both the front and rear anchor positions at

12 m from the excavated face. In view of the average 3.25 hours per metre

advance, the location of the support platform represents some one to two

days without rigid support. As it is well established that delay in

supporting the excavated rock will frequently contribute to higher support

loads and overbreak this aspect of the machine construction must be

carefully considered when evaluating the tunnelling performance.

7.3 Seismic velocity measurements

The seismic velocities obtained between chainages 250-550, corresponding

to sandstone with a high frequency of clay-filled, continuous joints, and

chainages 850-1300, corresponding to a limestone with a high frequency of

continuous, calcite veins, were not useful as a measure of rock quality.

However, they have interesting geophysical implications.

Figures 9a and 9b show waveforms typical of those received in areas

of rock with moderate and high attenuative properties, respectively. The

amplitude of the shear and surface wave arrivals was at least three times

that of the P wave arrivals as shown in Figure 9a. This is in accord with 22

estimates made by Miller and Pursey that for a surface source producing

small strains, the energy is divided between wave types as follows:-

(I) Rayleigh surface waves

(2) Shear waves

(3) Compressional waves

67%

26%

7%

It should be noted that the energy in a wave is proportional to the square

of its amplitude. Areas of moderate attenuation required relatively low

16

signal amplification and only one or two hammer blows for good signal

fidelity. However, areas of high attentuation required high electronic

gain (this also amplifies the noise) and as many as six hammer blows to

achieve a suitable signal. As a result, the P wave signal to noise ratio

was severely degraded and settings could only be made on the later wave

arrivals (see Figure 9b). Further signal enhancement did not noticeably

improve this situation. The wave forms shown illustrate the best and worst

case of amplitude profiles. The received wave forms in highly attenuative

rock usually lay somewhere midway between the best and worst case, making

accurate field measurement extremely difficult. At certain locations in the

tunnel this resulted in the tendency toward a bimodal distribution of

velocity measurements related to P and S wave velocities. Had more time

been available, the measurement technique could have been improved by

drilling holes in the tunnel sidewall at each measuring point. This would

have allowed for rigid geophone coupling to the rock, and, by striking a pin

located in such a hole, a greater proportion of the hammer energy would have

transmitted into P waves travelling toward the geophone.

Whereas the measurement of seismic velocity in rock with a high frequency

of continuous, infilled joints or veins was inconclusive with respect to rock

quality, the measurements in other areas of the tunnel have given a much

better indication of the existing ground conditions. From chainages 550 to

850 and from 1270 to 1400, the measurements of consistently high values of

seismic velocity correspond to areas of infrequently jointed sandstone and

mudstone, respectively. Most notable are the measurements associated with

areas of faulting in the mudstone. At the location of each fault, there was

a prominent drop in the seismic velocity. Furthermore, the extent of this

drop was related to the intensity of fracturing associated with each fault.

The minor faults at chainages 1413 and 1570 correlate with seismic velocities

decreased to approximately one-half the velocities in adjoining sections of

the tunnel. The larger fault at chainages 1510-1530 correlates with a seismic

velocity decreased to approximately one-fourth of the velocities in

adjoining sections of the tunnel.

8. CONCLUSIONS

Observations during the first 1600 m of machine tunnelling at the North

Wear Drive indicate the rate of advance was closely dependent on the nature

of the rock jointing and variations in the local geology. These aspects of

17

the tunnel environment affected both the support and mucking operations,

thereby exerting a dominant influence on the tunnelling progress.

The time required for placement of support and delays associated with

blockages of the cutting head, rock falls, and water inflow amounted to

between 55 and 60 per cent the time for unit advance through sections of

highly jointed sandstone and faulted mudstone. In contrast, the time loss

from rock support and difficulties related to local geology was insigni-

ficant through sections of clayey limestone and intact mudstone. In the

former case, the machine progress was relatively insensitive to the time

required to cut, or bore, a unit length of ground. In the latter case,

progress was very sensitive to the cuttability of the rock, as the average

time per unit advance was relatively close the the average time per unit

cutting.

Two specific features, which show the inter-dependence between ground

conditions and machine performance at the North Wear Drive, are worthy of

comment :

I. Blockage of the intake chute was a frequent difficulty. Observations

regarding the in-situ rock structure and locations of frequent blockage

suggest that this problem should be anticipated in ground with two or more

sets of relatively open and closely spaced joints unless the periphery of

the cutting head is designed to prevent the penetration and subsequent

movement of large blocks toward the intake area.

2. The relatively large distance separating the excavated face and working

platform at the North Wear Drive left the rock without rigid support for

long periods of time. Without support, loosening and dislocation of the

rock, especially under conditions of open jointing, led to high overbreak

in some areas and increased support requirements. Consequently, there is

considerable advantage in designing so that support can be placed immediately

behind the cutting head.

In sandstone and limestone with a high frequency of continuous,

infilled joints and veins, respectively, the measurement of seismic

velocity was inconclusive with respect to rock quality. However, seismic

velocity was shown to reliably indicate the presence of faults in mudstone.

18

Moreover, the velocity decrement associated with each fault zone was related

to the degree of rock fracturing in the fault. Whereas seismic scans will

generally have little practical application once the excavation has been

performed, they may be useful for providing information during horizontal

probing in advance of tunnelling. Further research and development will be

needed to improve the technique and to build a body of experience in various

geological environments.

9. ACKNOWLEDGEMENTS

The work described in this report forms part of the programme of research

on tunnels at the Transport and Road Research Laboratory.

The Laboratory wishes to thank the Northumbrian Water Authority, the

consulting engineers Babtie, Shaw and Morton, and the contractors Tyne

Tees Tunnelling for permission to carry out and their co-operation in these

studies.

The authors wish to thank Mr J G W Brown, Mr D Fawcett and

Mr H S Eadie (Babtie, Shaw and Morton), Mr K Milow and Mr S Keis for their

helpfulness and assistance on site and their colleagues Dr J A Hudson,

Mr J M Morgan and Mr D A Barratt for their assistance with the study.

I.

10. REFERENCES

BREKKE, T L and T R HOWARD. Stability problems caused by seams and

faults. Proc. North American Rapid Excavation and Tunnelling Conf.

ed Lane and Garfield. Vol I, 25-64 (AIME, Chicago, 1972).

2. CORDING, E J and D U DEERE. Rock tunnel supports and field measure-

ments. Proc. North American Rapid Excavation and Tunnelling Conf.

ed Lane and Garfield. Vol I, 601-622. (AIME, Chicago, 1972).

. CORDING, E J and J W MAHAR. The effects of natural geologic

discontinuities on behaviour of rock in tunnels. Proc. North

American Rapid Excavation and Tunnelling Conf. ed Pattison and

D'Appolonia. Vol I, 107-138 (AIME, San Francisco, 1974).

19

. WARD, W H, D J COATS and P TEDD. Performance of tunnel support

systems in the Four Fathom Mudstone. Proc. Symp. Tunnelling 76,

London, 1976 (Institution of Mining and Metallurgy).

. WHITTLE, R A. Geotechnical aspects of tunnel construction for the

Dinorwic power station. Ground Engng. 1977, 10, 15-20.

. ONODERA, T F. Dynamic investigation of foundation rocks in situ.

Proc. Symp. Rock Mech., 5th Minnesota, New York, 1963 (Pergamon).

. DEERE, D U, A J HENDRON Jr, F D PATTON and E J CORDING. Design of

surface and near surface construction in rock. Proc 8th Symp on

Rock Mechanics, Minnesota, 1966 (AIME).

8. DEERE, D U. Indexing rock for machine tunnelling. Proc. Conf. on

Rapid Excavation: Problems and Progress, 32-38. (Society of Mining

Engineers of America, Institute of Mining, Metallurgy and Petroleum

Engineers) 1968.

. HUDSON, J A, E J W JONES and B M NEW. P-wave velocity measurements

in a machine-bored chalk tunnel. Quart. J Engng. Geol. (in press).

10. MOSSMAN, R W and G E HEIM. Seismic exploration applied to undergound

explorations. Proc. North American Rapid Excavation and Tunnelling

Conf. ed Lane and Garfield. Vol I, 169-192 (AIME, Chicago, 1972).

11. CRATCHLEY, C R, P GRAINGER and D M McCANN. Some applications of

geophysical techniques in engineering geology with special reference

to the Foyers hydro-electric scheme. Proc. 24th Internation Geological

Congress, Section 13, 1972, 163-175.

12. MURPHY, V J. Seismic velocity measurements for moduli determinations

in tunnels. Proc North American Rapid Excavation and Tunnelling

Conf. ed Lane and Garfield. Vol I, 209-216 (AIME, Chicago, 1972).

13. BURSTON, U T and D J COATS. Water resources in Northllmhria with

particular reference to the Kielder Water Scheme. J. Instn Water

Engrs, 1975, 29 (July), 226-51.

20

14. CARTER, P G and D A C MILLS. Engineering geological investigations

for the Kielder tunnels. Quart. J. Engng Geol., 1976, 9 (2),

125-41.

15. FOOKES, P G and B DENNESS. Observational studies on fissure patterns

in Cretaceous sediments of south-east England. Geotechnique 1969,

19, 4, 493-7.

16. PRICE, N J. Fault and joint development in brittle and semi-brittle

rock. Oxford, 1966 (Pergamon Press).

17. PRIEST, S D and J A HUDSON. Discontinuity spacings in rock. Int J.

Rock Mech. Min. Sci and Geomech Abstr. 1976, Vol 13, 135-148.

18. KOLEK, J. An appreciation of the Schmidt rebound hammer. Mag.

Concrete Research 1958, 10, 28, 27-36.

19. MORGAN, J M, D A BARRATT and J A HUDSON. Tunnel boring machine

performance and ground properties. Report on the initial I% km of

the North Wear Drive, Kielder Aqueduct. Department of the Environment

Department of Transport, TRRL Report SR 469. Crowthorne, 1979

(Transport and Road Research Laboratory).

20. FRANKLIN, J A and R CHANDRA. The Slake-Durability Test. Int. J. Rock

Mech, Min Sci. and Geomech. Abstr, 1972, 9, 325-344.

21. BENNION, J D. The Kaimai tunnel, New Zealand - a case history.

Proc. Symp. Tunnelling 76. London, 1976 (Institution of Mining

and Metallurgy).

22. MILLER, G F and H PURSEY. On the partition of energy between elastic

waves in a semi-infinite solid. Proc. Royal Society, ]955, 233,

55-69.

23. TERZAGHI, K and R B PECK. Soil Mechanics in Engineering Practice.

1967, New York (John Wiley and Sons Inc).

21

TABLE 1

Discontinuity data from scanline surveys

Chainage (m)

339- 369

525- 575

1052-1170

1210-1280

1315-1345

1405-1425

1455-1467

1555-1566

Rock Type

Sandstone

Sandstone

Limestone*

Calcareous Mudstone

Mudstone

Mudstone

Mudstone

Mudstone

Number of

Values

96

39

(177)

18

32

64

39

Mean discontinuity

spacing (m)

0.31

0.79

(0.67)

3.89

0.94

0.31

0.30

57 0.19

Discontinuity spacing, standard deviation

(m)

0.38

1.11

(0.67)

3.64

1.13

0.29

0.23

0 .19

* Calcite veins

22

O~

O N 0

0

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0

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23

TABLE 3

Seismic velocities in intact rock specimens

(Unconfined)

*P-Wave Rock type Seismic velocity

m/sec

Sandstone 4280

Limestone 5550

Mudstone 3580

* Note: All velocity measurements were performed parallel to the bedding

24

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25

TABLE 5

Properties of clay infill

Property Value

Water content 58%

Liquid limit 67%

Plasticity index 41%

Undrained shear strength* 4 kN/m 2

* Determined from laboratory

shear vane tests

26

TABLE 6

Summary of advance rates and delays

caused by ground conditions

Rock

type Chainage (m)

Unit advance time (hrs/m)

% Unit advance time caused by delay

from ground conditions

124- 309 8.24 56.2

Sandstone 309- 599 2.96 18.6

599- 770 3.04 15.8

770- 890 4.11 32.4

Limestone 890-1127 1.86 10.8

1127-1270 1.25 1.6

1270-1397

1397-1500

1500-1600

124-1600

Mudstone

1.28 3.9

2.07 31.9

4.28 59.1

3.25 33.8 TOTALS

27

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200 ~ 1 6 0 200 160 190 180 170 190 180 170

Chainage 250--300m 32 values Chainage 339--369m 97 values

~ \ ~ t i " l / / 320 40

3 ~ ~ / / O ~ 50 ~ l ~ O / J .J~/~j 3103 ~ ' ~ ~ 20%/ ' -~

280 _ ~76°/ 8O 2 8 ( ~ 270 - ' ~ ~ 90 270

2 6 0 ~ 1 0 0 260

. o - . < j / / ~ \ \ ~ , , o .o 210"--~/ / I I I \ \ ~--~50 22°210"'~///I ! II \ "~ / / / 7 - ~ - ~

200 ~ 1 6 0 2 0 0 - " ' ~ _ J _ _ . ~ 190 180 170 190 180 170

Chainage 422- -479m 30 values Chainage 545--575m

100

0

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38 values

3 5 0

3 0 0 ~ _ _ ~

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250 ~ J ~ //~////

190

0 10 ) 3

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, 120 0 -o

50 180 170

Chainage 1025--1200m 61 values

Fig. 2 D I S C O N T I N U I T Y ROSE D IAGRAMS

340

~ o ~

28O 2 7 0 ~ 260 25O

240 230

220

190 180 170

Tunnel drive direction

200

~ . ~ 340 330 40 50 60 310-^:~320~

300 70 2 9 0 ~ , 8O 28O 9O 270 100 260

~ 110 2514 ~ 120 ~ 24O ~ 0 ~ 130

140 220 160 2O0

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130

150 190 180 170

Chainage 1210--1345m 48 values Chainage 1405--1440m 73 values

350 0 10 3~^ 3 ~ s T T ~ -

3 , o z ~ \ ~ \ \ III I / I 300 I I I

2 8 0 ~ 270 260

~ o - . < . / / / ~ \

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Chainage 1455-1467m

350 0 10 I0 3 ~

280 ~"~o

270

~ i O0 260 0 250

1~140 2 2 0 ~

160 190 180 170

39 values Chainage 1555--1566m

0 30

' ° °

0 1~20

130

150

57 values

Fig. 2 (cont.) DISCONTINUITY ROSE DIAGRAMS

0~

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6000

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3000

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I I I I I I I |

150 200 300 400 500 600 700 770

Chainage (m)

Fig. 4 S U M M A R Y OF D A T A F O R T U N N E L L I N G IN S A N D S T O N E

E o

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B e r n o l d sheets

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ABSTRACT

SOME OBSERVATIONS OF MACHINE TUNNELLING AT THE KIELDER AQUEDUCT: T D O'Rourke, S D Priest and

B M New: Department of the Environment Department of Transport, TRRL Supplementary Report 532: Crowthorne, 1979 (Transport and Road Research Laboratory). The Kielder Water Scheme, currently under construction in north-east England, will consist of 32 km of tunnel to direct water from the Tyne to the Wear and Tees River Valleys. The project, which is promoted by the Northumbrian Water Authority, involves excavation through sedimentary strata using 3.5 m-diameter tunnel boring machines.

The Tunnels Division of the Transport and Road Research Laboratory (now the Tunnels and Underground Pipes Division) planned and implemented an observation programme during tunnel construction for the North Wear Drive, a portion of the Kielder tunnel system linking the River Wear with a companion tunnel drive from the Derwent Valley. The observations were performed with the assistance of Babtie, Shaw and Morton, the general engineering consultants for the Kielder Water Scheme.

Detailed observations and measurements were taken in the first 1600 m of the North Wear Drive, where the tunnel was driven through approximately equal lengths of sandstone, limestone and mudstone. This paper summarises the structure and material properties of the in-situ rock in each of the principal lithologies and compares the observed ground conditions with the machine advance rates and rock support adopted during tunnelling.

Attention is directed to the performance of the tunnel boring machine in light of the geological conditions, and improvements are suggested as an expedient to future machine excavation. In addition, the results of seismic scans, taken along the tunnel, are summarised and compared with detailed observations of the rock conditions.

ISSN 0305-1315

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