Caso 3 - Control de La Sobrerotura

7/29/2019 Caso 3 - Control de La Sobrerotura

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HONG KONG, CHINA

74 FACE DRILLING

Introduction

The development of Hong Kong as a major

southern gateway for China continues

apace. Integral to the overall plan is the

enlargement of the freight railway system to

handle the huge volumes of goods coming

through the container port, which is now the

largest in the world after Rotterdam. We

describe here two major railway tunnel con-

tracts at which new generation Atlas Copco

Rocket Boomer drillrigs equipped with

CAN-bus control systems worked.

MTRC Pak Shing Kok Tunnels

The Hong Kong MTRC Pak Shing

Kok tunnels comprise a complex of five

interconnected tunnels driven as nine

tunnels totalling 6 km in length. The

tunnels have a cross-section of some

35 sq m and are located in crystalline

pyroclastic rocks, resulting in high bit

wear. For the drill and blast operations, the

contractor Hyundai-Kier Joint Venture

employed three Atlas Copco Rocket Boomer

L2 C drillrigs. These were two-boom rigswith a CAN-bus based control system.

The rigs were equipped with ABC

Regular boom navigation system, with

which the operator guides the booms and

feeds to the correct positions using a preset

drill pattern presented on the display

screen in the cab of the drillrig. The feedscan host up to 14 ft-long rods to provide a

maximum hole depth of 4.2 m.

The rock was hard and abrasive, but not

as brittle as regular hard crystalline

basement rock. As a result, expectations

for penetration would normally be on the

low side, and bit wear would be high.

However, the average penetration achieved

at Pak Shing Kok was in the range of

2.5 m/min, and the service lives of bits,

rods and shanks was around 400 m,

8-9,000 m, and 8-9,000 m respectively.

These results are considered as good,taking into account the high penetration

rate.

A single operator controlled the two

booms on each machine, and the total

drilling time, including positioning, for a

70-hole, 4 m round was 1.5 to 2 h. As the

manual moving of the boom from one hole

position to the next generally took about

40 to 50 seconds, the operator was busy

with the levers for two thirds of the drilling

time. The tunnels are being concrete lined,

so it is very important to keep overbreak ata low level (Fig 1 overleaf).

Controlling Overbreak inHong Kong

ComputerizationImproves EfficiencyThe use of new generation CAN-busdrillrigs in Hong Kong has been moni-tored at two different jobsites. Thefirst is at Pak Shing Kok, where AtlasCopco Rocket Boomer L2C drillrigsequipped with ABC Regular workedfor Hyundai-Kier; and the second is atWest Rail, where larger Rocket

Boomer WL3 C drillrigs worked forNishimatsu and Dragages. Despitehard and abrasive rock in bothsituations, good average penetrationwas achieved, allied to economicconsumption of drillbits and rods.Operator wages were reduced dramat-ically, thanks to computerization ofthe drilling operation, and profilingwas as good as expected, given theother variables involved.

Rocket Boomer WL3 C drillrigs working

for Nishimatsu and Dragages at a

110 sq m face.


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Tunnel No 6 was the first to be excav-ated, and the objective was to keep

overbreak low by demanding smaller

margins than usual, and the consequence

was too much underbreak. Some of the

underbreak is explained by application of

too much shotcrete for primary support.

Certainly, better results with respect to

overbreak have been achieved on other

projects, but it always comes down to the

ambition of the management and the

incentive and skill of the labour.

West Rail Contract DB 350

The West Rail contract DB 350 included

a 5 km-long double-track tunnel located

in the Repulse bay formation, which

comprises mainly crystalline pyroclastic

rocks. The joint venture companies

Nishimatsu and Dragages split the tunnel

half each.

Nishimatsu used the new generation

Atlas Copco Rocket Boomer WL3C CAN-

bus drillrigs for face work. The tunnel

design, which was produced by the jointventure, is a double-track single tube tunnel

with a cross-section of 110 sq m. A concrete

wall along the centre-line separates the two

tracks from each other. The two WL3C

drillrigs had feeds long enough to handle

5.8 m holes. The drilled length of the

rounds varied generally from 5.0 to 5.8 m.

In poor rock, these long rounds were short-

ened. This is important to bear in mind

when overbreak is discussed later. The rigs

were equipped with ABC Total, which

moves the booms and feeds to new positionsautomatically, after each hole is drilled.

The two rigs were positioned side byside at the tunnel face, and each drilled 77

holes of the total 154 holes for the 110 sq m

face, plus three 4 in holes for the parallel

cut. The contour holes were given a spacing

of 35 to 40 cm. Generally, all but the con-

tour and the bottom holes were drilled in

the Total mode. The pull of each round

was about 90%. Two rounds per day, 25

days per month gave a production of 200-

220 m per month. If the perimeter profile

was free of protruding rock, automatic

drilling was also used for the contour holes.The wear on drilling tools was the same

as for the MTRC tunnels described earlier,

with the exception of the bit life, which

was around 500 m. Here again, it can be

concluded that the CAN-bus rig treated the

drilling tools well.

HONG KONG, CHINA

FACE DRILLING 75

Control panel of the new Rocket

Boomer WL3 C.

Fig 1. Profile results at West Railtunnel contract D&B 350 chainage

1556 to 1997.

West rail tunnel contract D & B 350

Hong Kong Overbreak (m)

(after shotcrete support)

Frequency

Frequency

Overbreak (m) Underbreak (m)

West rail tunnel contract D & B 350

Hong Kong Underbreak (m)

(after shotcrete support)


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One man operated the three-boom rig,

and when the Total mode was utilized the

booms had no downtime, even for shorter

rounds. The time for the drilling operation,

including setup, was in the range of

2-2.5 h, and the penetration rate for the

48 mm spherical button bits was

2.5 m/min. In cases where only one drillrig

was used at the face, the drilling of a full

round took 3.5 to 4 h.Considering the length of the round,

with respect to the poorer rock quality,

overbreak could not match the result from

the MTRC tunnels. Without any splitting

on rock-classes, the results from 450 m of

tunnel are shown in Fig 2 below. Here, as

in the MTRC project, the drilling of the

contour holes starts 10 cm outside the

theoretical line, and the bottom holes

30 cm outside the theoretical line. What is

surprisingly encouraging, is that under-

break is found only in half the surveyed

sections and, where found, only small

quantities are registered. As the deviation

is a multiplication of 2x the length of the

hole, a 5.5 m-long hole can be expected to

deviate 50% more than a 4 m-long hole.

Consequently, the underbreak ought to bemore embarrassing than in the MTRC case.

Information on the rock quality provid-

ed by the contractor shows that almost all

excavation is in rock having a value higher

than 10, which can be considered as good.

Overbreak caused by geology should not

have been dominating in this case.

Conclusions

It is very important for machine suppliers

to have good working relationships with

experienced customers, as they, to someextent, become partners in the development

of new equipment. Atlas Copco believes that

its new generation drillrigs are profitable tools

when chasing costs in tunnel construction.

Improvements, such as better drill steel

economy, savings on operator wages, and

higher utilization have resulted in a good

reception of the new series of drillrigs in

Hong Kong. While the results for overbreak

are not conclusive, they are favourable, and

there is no doubt that the higher accuracy

of the CAN-bus drillrigs is a contributingfactor. s

HONG KONG, CHINA

76 FACE DRILLING

Rocket Boomer WL3 Cs used at West

Rail.

Fig 2. Profile results at contract 611,

MTRC.

Over&Underbreak(m)

Tunnel 1-9

Contract 611, MTRC Hong Kong

Over and Underbreak

Overbreak

Underbreak

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Caso 3 - Control de La Sobrerotura