1845-1848 AD., Great Britain, white metal Thames Tunnel Construction and Brunel Portrait Medal.

Great Britain, Thames Tunnel Construction and Brunel Portrait Medal, by medallist James Taylor for William Griffin, ca. 1845-1848 AD.,
white metal medal (38mm / 16,80 g),
Obv.: SIR ISAMBART MARC - BRUNEL, F. R. S. & c. / J. TAYLOR , head facing left.
Rev.: THE WONDERFUL IRON SHIELD / 200 Tns Wt. / USED IN CONSTRUCTING / THE THAMES TUNNEL // DIMENSIONS OF EXCAVATION / 38Ft. Wd. 22Ft6In Hgh / 76Ft / BELOW HIGH WATER MARK / J TAYLOR BIRM: - W. GRIFFIN LONDON. , view of section of two tunnels, men working in compartments.
BHM #2086 (1842) RRR ; another one on http://www.limerickcorp.ie/WebApps/Museum/museum_Details.aspx?PF=yes&RowID=645 .

James Taylor (fl 1841-56), medallist, seal-engraver & die-sinker. His place of business was at 71, Summer Lane, Birmingham. In 1856 the business was taken over by his employee, Joseph Moore. (thanks to "constanius" for the reference and this info).

Isambard Brunel (1769-1849) was a French-born engineer who fled to the United States in 1793, and became chief engineer of New York. He moved to England in 1799, and after his business making nautical equipment failed, he spent the years 1825 to 1843 constructing the tunnel under the Thames river in London from Wapping to Rotherhithe.

In 1805 the Thames Archway Company was formed with the intention of driving a tunnel beneath the Thames between Rotherhithe and Limehouse. Richard Trevithick, the celebrated engineer, was engaged by the company to construct the tunnel. He used Cornish miners to work on the tunnel. In 1807 the tunnel encountered quicksand and conditions became very difficult and dangerous. Eventually the tunnel was abandoned after more than 1,000 feet had been completed, and expert opinion, led by William Jessop, was that such a tunnel was impracticable.
Brunel had already drawn up plans for a tunnel under the River Neva in Russia, but this scheme had never come to fruition. In 1818 Brunel had patented a tunnelling shield. This was a reinforced shield of cast-iron in which miners would work in separate compartments, digging at the tunnel-face. Periodically the shield would be driven forward by large jacks, and the tunnel surface behind it would be covered with cast-iron lining rings. It is claimed that Brunel found the inspiration for his tunnelling shield from the shipworm, Teredo navalis, which has its head protected by a hard shell whilst it bores through ships’ timbers. Brunel’s invention provided the basis for subsequent tunnelling shields used to build the London Underground system and many other tunnels. Brunel was so convinced that he could use such a tunnelling shield to dig a tunnel under the Thames, that he wrote to every person of influence who might be interested. At last in February 1824 a meeting was held and 2,128 shares at £50 each were subscribed for. In June 1824 the Thames Tunnel Company was incorporated by royal assent. The tunnel was intended for horse-drawn traffic. Work began in February 1825, and consisted of sinking a fifty feet diameter vertical shaft on the Rotherhithe bank. This was done by constructing a fifty feet diameter metal ring, upon which a circular brick tower was built. As the tower rose in height, its weight forced the ring into the ground, and at the same time workmen excavated the earth in the centre of the ring. This vertical shaft was completed in November 1825, and the tunnelling shield, which had been manufactured at Lambeth by Henry Maudslay’s company, was then assembled at the bottom. Maudslay also supplied the steam-powered pumps for the project. The shield was rectangular in cross-section, and consisted of twelve frames, side by side, each of which could be moved forward independently of the others. Each frame contained three compartments, one above the other, each big enough for one man to excavate the tunnel face, so that the whole frame could accommodate 36 miners. When enough material had been removed from the tunnel face, the frame could be moved forward by large jacks. As the whole shield moved forward, bricklayers followed it, lining the walls of the tunnel. The tunnel required over seven and a half million bricks.
Brunel was assisted in his work by his son, Isambard, who was now 18 years old. Brunel had planned the tunnel to pass no more than fourteen feet below the riverbed at its lowest point. This was to cause problems, later on. Another problem that hindered Brunel was that William Smith, the chairman of the company, thought that the tunnelling shield was an unnecessary luxury, and that the tunnel could be made more cheaply by traditional methods. He wanted Brunel replaced as Chief Engineer and constantly tried to undermine his position. Fortunately the shield quickly proved itself to be an obvious success. During the tunnelling both Brunel and his assistant engineer suffered ill health and for a while Isambard had to bear the whole burden of the work.
There were several instances of flooding at the tunnel face due to its nearness to the bed of the river, and in May 1827 it was necessary to plug an enormous hole that appeared on the riverbed. Finally the resources of the Thames Tunnel Company dried up and despite efforts to raise more money, the tunnel was sealed up in August 1828. Brunel resigned from his position with the Company, frustrated by the continued opposition from the chairman. He undertook various civil engineering projects, including helping his son, Isambard, with his design of the Clifton Suspension Bridge.
In March 1832 William Smith was deposed as chairman of the Thames Tunnel Company. He had been a thorn in Brunel’s side throughout the project. In 1834 the government agreed a loan of £246,000 to the Thames Tunnel Company. The old 80-ton tunnelling shield was removed and replaced by a new improved 140-ton shield consisting of 9,000 parts that had to be fitted together underground. Tunnelling was recommenced but there were still instances of flooding in which the pumps were overwhelmed. Many of the miners were adversely affected by the constant influx of polluted water and there was a high rate of sickness. As the tunnel approached the Wapping shore, work began on sinking a vertical shaft similar to the Rotherhithe one. This began in 1840 and took thirteen months to complete.
On 24 March 1841 Brunel was knighted by the young Queen Victoria. This was at the suggestion of Prince Albert who had shown keen interest in the progress of the tunnel. The tunnel opened on the Wapping side of the river on 1 August 1842. On 7 November 1842 Brunel suffered a stroke that paralysed his right side for a time. The Thames Tunnel finally officially opened on 25 March 1843 and Brunel, despite ill health, took part in the opening ceremony. Within 15 weeks of opening one million people visited the tunnel. On 26 July 1843 Queen Victoria and Prince Albert visited the tunnel. Although it had been intended for horse-drawn traffic the tunnel remained as pedestrian only.
In 1865 the East London Railway Company purchased the Thames Tunnel for £200,000 and four years later the first trains passed through it. Subsequently the tunnel became part of the London Underground system, and is still in use today.