Come and explore inside Round Hill Tunnel, on the old Roxburgh Branch Railway. You will need a TORCH to find this cache! The tunnel is 740 feet (226 m) long and it curves, so it is completely dark inside.
This section of the old Roxburgh Branch railway is part of the Clutha Gold Extension trail – a 62 km trail between Lawrence and Waihola which opened on 25 August 2023. A bike ride from Mt Stuart reserve through the Mt Stuart tunnel and Round Hill tunnel, as far as Waitahuna for a picnic lunch if you wish, and back, is a fun day out. (Waitahuna has the closest toilets and drinking water, and the Waitahuna station coffee cart is the closest café.)
If you’re not biking, you can explore this Victorian tunnel by parking at the given waypoint and walking 650 m (take care crossing the main road).
1959 map showing the Milton to Roxburgh railway, Round Hill tunnel and (red dot) Round Hill station
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Work on the Tokomairiro (Milton) to Lawrence railway started in September 1873. The Round Hill tunnel was the last part completed on Saturday 25 November 1876.
The railway line opened to Waitahuna on 22 January 1877, followed by Lawrence on 2 April 1877. In 1907, the junction with the main trunk line was changed from Clarksville to Milton. The passenger service on the Roxburgh branch ceased on 4 September 1936 and the line closed 29 May 1961.
Round Hill station in 1968, looking towards Lawrence.
Photo Cecil Bachop.
This station was about 600 m on the Lawrence side of the tunnel. There was no room for a siding. This was an "unattended flag station" i.e. the train would only stop on request.
Passenger trains ran until 4 September 1936; from that date until the line's closure on 1 June 1968, the line was freight-only.
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Building the Round Hill tunnel was difficult and extremely dangerous because the ground around the cuttings and tunnel was like "soapy water" or "quicksand". There were constant slips and cave-ins; the initial triple brick lining collapsed under the weight of the moving hillside and had to be held up with a "forest" of props.
The government engineer eventually altered the lining design to five bricks thick on the unstable side, four bricks on the stable side, and changed the shape so that the weight was taken by the foundations instead of the side of the tunnel lining. It was sheer luck that no-one got killed...
About a quarter of the way in from the Lawrence end of Round Hill tunnel, you can see where the extra strengthening starts
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The rock at Round Hill is Caples Terrane textural zone IIB semischist. This is usually a hard rock (in fact at the Mt Stuart tunnel, through the same semischist, the rock was so hard that the contractor gave up the job and a gang of experienced Italian miners were called in). So why was the rock at the Round Hill saddle loose and pulverised?
A faultline, part of the Tuapeka Fault Zone, runs through the saddle where the Round Hill tunnel goes. The fault isn't active now but, when it moved in the past, the rock along the faultline got broken down to soft, friable "fault gouge".
Geology map showing an inactive fault (part of the Tuapeka Fault Zone) cutting through the saddle where Round Hill tunnel was built.
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Despite everything, the Round Hill tunnel has lasted almost 150 years now - a tribute to the skill of the people who created it all those years ago. They even built us the perfect place for a smiley... Enjoy!
Safety alcove in middle of Round Hill tunnel - you'll be safe from any passing trains!
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Cyclists inside the Round Hill tunnel
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At the Eastern portal (Milton end) of Round Hill tunnel. The 10 m at this end of the tunnel, and the cutting, were especially difficult ground, with continual slips and cave-ins. This cutting had to be widened to 100 feet across to minimise slipping.
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At the Western portal (Lawrence side) of Round Hill tunnel. When you visit, you'll see some new retaining walls put in by the trail builders to prevent this cutting slipping again.
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Round Hill tunnel timeline:
1872: The Tokomairiro (Milton) to Lawrence branch line was approved by Parliament.
Tender advertised April 1873
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July 1873: Dunedin contractors W D Morrison (a successful Blue Spur goldminer) and C D Irvine (a Dunedin civil engineer) gained the contract for the Round Hill section, at a cost of £19,178. This section was 3 ½ miles, running from Manuka Flat (just west of the Glenore tunnel) through the Round Hill tunnel to Murrays Flat. They immediately subcontracted the entire work to experienced local contractors D and J McKenzie, for £15,274 19s.
Contracts July 1873
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September 1873: The MacKenzie brothers started work on the section of line, but weren’t going to begin on the Round Hill tunnel until the rest of the track was formed.
April 1874: A massive 40,000 ton slip came down at the east side of the Round Hill saddle, blocking the planned line. The McKenzies paid off their entire workforce and no work was done for the rest of the year.
200 workers wanted December 1874
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December 1874: Men were hired again, including a large number of Chinamen, and work resumed in 1875.
Engineer wanted Feb 1875
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March 1875: Much of the line on the Round Hill section had been completed and work on the tunnel was about to start. An engineer took cross sections at the mouth of the Round Hill tunnel, as slips were anticipated. A brickworks was set up close by to provide bricks for lining the tunnel. The track was re-routed around the slumped hillside (which I think changed the tunnel’s eastern entry point, leading to the curved tunnel?).
April 1875: Several contractors, including the McKenzies, ran out of money and stopped work.
The McKenzie brothers reneged on their sub-contract at this point, before the Round Hill tunnel had been started, leaving the original contractors Morrison and Co to take charge again. The McKenzies took Morrison & Co to arbitration, but lost.
June 1875: Morrison & Co were proceeding vigorously, with some heavy work to be done at the approaches to the Round Hill tunnel. At the end of August they were still working on the eastern side cutting, with the sides continually slipping away so the cutting was now 57 feet deep and 100 feet wide at the top. On the western side, a seam of harder rock soon ran out. A gang of men experienced in tunnel work had been engaged.
The railway from Dunedin to Tokomairiro (Milton) was opened on 1 September 1875. Now everyone in Lawrence was frustrated - the branch line contracts were originally to 1 January 1875, extended to July 1875, but the railway still wasn’t completed!
September 1875: Driving the Round Hill tunnel from the eastern (Milton) end finally started. Instructions had been given to build up the face with masonry, with hopes this would prevent further slips from the broken ground. The services of Mr Adamson, who had been manager at the Chain Hills tunnel, had been secured.
The Round Hill tunnel was turning out a difficult piece of workmanship. The nature of the ground is well known… “It requires men to drive who can pierce ‘soapy water’ or sink shafts in quicksand”.
The treacherous ground and constant cave-ins alarmed the workers, who fled out of the workings. The site manager Francis Nicoll (a Blue Spur miner, and one of the contractors) persuaded the workers back each time, but after the fourth major collapse the workers refused to re-enter the tunnel. Nicoll could see this might end the contract, with serious financial loss. Eventually Nicoll agreed to go in first and started shoring-up, and the workers joined him. After an anxious time they managed to prop up the tunnel and continue work.
Early October 1875: The Milton (eastern) face of the tunnel was secured with masonry and 50 feet of the tunnel was lined with three rings of brickwork, 14 inches thick. The heading drive was in 165 feet, lined with a “forest” of timber props, but the extreme pressure from the ground running in was snapping logs a foot in diameter. On the Lawrence (western) side the ground was firmer and the heading drive was in 200 feet. Brick of excellent quality manufactured on site.
Mid-October 1875: The brickwork in the first 30 feet of the tunnel gave way. The workers propped it up to prevent an entire collapse, and kept driving the tunnel at 30 feet per week. “The whole weight of the subsiding hill appears to be bearing upon one of the walls, which is bulged out and full of cracks just ready to give way, and but for the heavy timber beams it would doubtless collapse in a moment.” One man hit on the head by a brick had the bleeding stanched with tobacco leaves. Engineers ordered the tunnel lining to be increased to four bricks thick.
Early November 1875: Twelve men having their “crib” break narrowly escaped death when they noticed the tunnel overhead cracking in an alarming manner. They started running for the tunnel mouth when a large quantity of earth fell on the spot where they had been seated. A few days later, four men were trapped for two hours behind a very serious fall that took three days to clear away. Lawrence citizens were worried about men working in such dangerous conditions, and the lack of progress.
26 November 1875: A delegation to Dunedin MP William Reynolds (on holiday in Lawrence) noted that the line should have been completed on 1 January 1875, contracts were extended to July, but work was still not completed.
26 November 1875: A message was received by the Round Hill tunnel contractors instructing them to cease work.
Early December 1875: A second message arrived from the government engineering department, ordering them to alter the construction of the tunnel interior. The wall on the unstable side was increased to five bricks thick, and the wall brought down to the ground so that the pressure was taken by the foundations rather than the side of the tunnel.
January 1876: Work on the tunnel was at a complete standstill. The contractors wanted the tunnel opened through before the temporary lining or props were moved, to provide a second exit for workers if there were a cave-in. But the main dispute was that the Government was refusing to recognise their claims for extra work, such as the additional brickwork. Negotiations with the government’s District Engineer took a month.
February 1876: A meeting in the Lawrence Town Hall formed the Tuapeka Railway Committee. A deputation met the Minister of Public Works. Mr Richardson said the Government was quite alive to the necessity of getting the work finished as quickly as possible.
26 April 1876: Round Hill tunnel was finally pierced through. But, the challenging job of replacing the lining took some months.
30 September 1876: The Milton end of tunnel was now finished, with 1876 on the cope-stone of the masonry facing. There had been heavy slips at the Lawrence (western) face, kept in place by timber props, which made work difficult and dangerous. Contractors expected the brickwork to be finished in a month.
13 November 1876: Last brick laid at the Round Hill tunnel. Morrison & Co put their railway plant at Round Hill up for auction. Tracks laid inside tunnel.
Saturday 25 November 1876: Invited officials from Dunedin arrived at Round Hill tunnel by train. The final brick was laid by Mr James Brown, the MP for Tuapeka, followed by a substantial luncheon inside the tunnel, toasts, and speeches.
Auction 15 November 1876
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New Zealand Railways Timetable on and after 1 February 1877: Otago Daily Times 23 February 1877
Round Hill tunnel was the highest point of the Roxburgh line at 668 feet (203 m).
The completed line to Lawrence had a steepest grade of 1 in 41 (from Mt Stuart to Round Hill) and no less than 142 curves, the sharpest 5 chains (100 m) in radius.
These curves severely restricted the speed and load capacity of trains, and caused heavy wear and tear on the rolling stock and tracks.
The 22 mile trip to Lawrence usually took 1 ¾ hours; a special non-stop passenger train would take slightly over an hour.
Information:
"Rails to Roxburgh" W J Cowan (2010)
Newspaper articles about the Round Hill tunnel are summarised in log notes (dated 2020).