Acombination of labour and energy costs plus relatively slower advance rates has led to a shift in excavation method from traditional hand-held drills to jumbos on part of the Chang Hong Lin tunnel, a key element of the Chongqing to Lichuan, or ‘Yu Li’ link in China’s expanding highspeed rail network.

The 13.3km long, twin-track rail tunnel is being excavated through slate and clastics, and the contractor for the portal and adit one is Department One of the Tunnelling Bureau. The tubes are being constructed with 110m2 cross sections (10m high by 13m wide) and the depth of cover reaches up to 420m along the tunnel alignment through the mountain foothills. The adit is 2km long and was completed early last year.

By the end of 2010 the contractor had advanced more than 4km into the rail tunnel using two Sandvik, 3-boom Axera T11 jumbos for full-face excavation.

Tunnelling challenge
Local hand-held drills were used to commence excavation of adit one, which is located approximately 2km along the tunnel alignment. The excavation method for the 80m2 tunnel was based on traditionally low labour costs, and the contractor employed up to 22 drills supported by six stationary air compressors.

However, the cost advantage began to erode as labour costs were rising and also from the increase in energy costs for the works; as the face advanced, extra compressors were needed to deliver sufficient air supply. Then there was also the concern of penetration rates being less than the using jumbos – 0.7m per minute versus almost three times that rate for jumbos.

Based on evaluations, the total excavation time using the hand-held drills was also established to be longer than using jumbos. Sandvik says higher availability rates were also noted for the jumbos. It was decided to switch. The hand-held drills were taken off the job early last year.

For the main running tunnel, the jumbos have been working shoulder-to-shoulder to drill a total of 140 x 48mm diameter holes to a standard depth of 3.7m, and taking on average two hours to do so. About an hour is then spent to set charges and undertake the blasting, then approximately three hours spent in spoil removal.

The works then proceed to scaling, and then up to four hours is allocated for bolting. The bolts are placed about 1m apart, and shotcrete is also applied. To take the total cycle time up to the 14.5 hours allowed the final tasks are screening and surveying.

The contractor is working around the clock and the average blast rate is approximately 1.85 per day. The contractor has excavated more than 4km.

Growing network
By the end of 2012 the Chinese highspeed rail network is expected to have expanded to cover a total distance of 13,000km – the world’s largest. The strategic plan for the country’s network, being developed by the Ministry of Railways, will have four high-speed lines running east-west and the same number north-south.

China has more than 40 high-speed rail projects under construction.

The 224km long Chongqing to Lichuan or ‘Yu Li’ link will tie-in to the yet-to-be constructed Huhanrang line, which will extend from Wuhan, Nanjing and Shanghai. The travel time between Chongqing and Shanghai will, then, be reduced dramatically – by approximately 80 per cent – from up to 42 hours to only about eight hours.

While capital investment in the highspeed network to save time and money at the larger, regional and national, scales in future, there is also a focus on economics in the nearer term and at the smaller scale for construction needs. The heating economy and comparative costs of excavation methods are also bringing fresh focus on construction economics, and changes to how things can – and possibly will – be done.


A pair of Sandvik Axera jumbos are working side-by-side to excavate part of Chang Hong Lin tunnel The Chang Hong Lin rail tunnel passes through sedimentary rock, and hand-held drills lost out to jumbos as works progressed Location map of the Chang Hong Lin tunnel on the Chongqing – Lichuan ‘Yu Li’ rail line in China