. Bulletin - United States National Museum. Science. subaqueous tunneling, surmised in later years thai Brunei had chosen a rectangular configuration for actual use, as one better adapted to the sectional type of shield. The English civil engineer, Peter W. Barlow, in 1864 and 1868 patented .1 circular shield, of one piece, which was the basis ol one used b) him in constructing a small subwa) ol 1 >50 feel beneath the Thames in 1869, the firs! work to follow the li Brunei, ( acting as Barlow's contractor, was the designer ol the shield actuall) used in the work, but it was obvio
. Bulletin - United States National Museum. Science. subaqueous tunneling, surmised in later years thai Brunei had chosen a rectangular configuration for actual use, as one better adapted to the sectional type of shield. The English civil engineer, Peter W. Barlow, in 1864 and 1868 patented .1 circular shield, of one piece, which was the basis ol one used b) him in constructing a small subwa) ol 1 >50 feel beneath the Thames in 1869, the firs! work to follow the li Brunei, ( acting as Barlow's contractor, was the designer ol the shield actuall) used in the work, but it was obvioush inspired In Harlow's patents. The reduction ol the multiplicity of parts in the Brunei shield to a single rigid unit was of immense advantage and an advance perhaps equal to the shield concept of tunneling itself. The Barlow- 1 Iri tthead shield was like the cap ol .1 telescope with a sharpened circular ring mi the front to assist in penetrating the ground. The diaphragm functioned, .is did Brunei's breasting boards, to resist the longi- tudinal earth pressure ol the face, and the cylindrical portion behind the diaphragm bore the radial pressui e ul roof and walls. I lere also for the lirst time, a permanent lining formed of east-iron segments was used, a second major advancement in soft-ground tunneling practice. Not only could the segments be placed and bolted together far nunc rapidly than masonry lining could be laid up, but unlike the green masonry, they could immediately bear the full tunc ul the shield-propelling screws. Barlow, capitalizing on Brunei's error in burrowing so close to the riverbed, maintained an average cover of 30 feet over the tunnel, driving through a solid stratum of linn London clay which was virtually impervious to water. As the result screws, and a ring of lining segments IS inches in length bolted to the previous ring under cover of the over-. Figure 21, Eni vrc \n ol Brunei's tunneling shield, vciiiial sniion. I lie lnsi two and pan ol the th
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