140 Mr. Brunei's Ncxv Plan of Tunnelling 



able to proceed until they were stopped by a second irruption, 

 which in a few minutes filled it. Nothing comes more satis- 

 factorily in support of the system that is adopted here, than 

 the residt of the operations that were carried, under that cir- 

 cumstance, to an extent of 1011 feet, and within 130 feet from 

 the opposite shore. 



It is to be remarked, that at the second irruption, on examining 

 the bed of the river, a hole was discovered 4 feet diameter, 9 

 feet deep, with the sides perpendicular ; — a proof that the body 

 of quicksand was not extensive ; but what is most remarkable 

 is, that this hole could be stopped merely by throisoingfrom 

 above, clay partly in bags and. other materials : and after pump- 

 ing the water out under a head of 25 feet of loose ground and 

 30 feet of water, the miners resumed the work, and proceeded 

 a little further ; but finding the hole at the first irruption in- 

 creased, and the jilling over the second very much simk, the 

 undertaking was abandoned. 



The character of the plan before us consists in the mode of 

 effecting the excavation, by removing no more earth than is to 

 be replaced by the body of the Tunnel, retaining thereby the 

 surrounding ground in its natural state of density and solidity. 



In order so to effect an excavation 34 feet in breadth by 18 

 feet 6 inches in height, the author of this plan proposes to 

 have the body of the Tunnel preceded by a strong framing of 

 corresponding dimensions, as represented in the accompany- 

 ing di-awings, (Plate III.) and in the model proposed to be 

 submitted for inspection. The object of this framing is to 

 support the ground, not only in front of the Tunnel, but at 

 the same time to protect the work of excavation in all di- 

 rections. Tlie body of the Tunnel, which is to be constructed 

 in brick, is intended to be fitted close to the ground ; and in 

 proportion as the framing is moved forward, so the brick work 

 is made to keep pace with it. But as this framing could not 

 be forced forward all in one body, on account of the friction of 

 its external sides against the surrounding earth, it is composed 

 of eleven perpendicular frames which admit of being moved 

 singly and independently of each other, in proportion as the 

 ground is worked away in front. These several frames are 

 provided with such mechanism as may be necessary to move 

 them forward as will as to secure them against the brick-work, 

 when they ai-e stationary. It is to be observed, that six alter- 

 nate frames are stationary, while the five intermediate ones 

 are left free for the purpose of being moved forward, when re- 

 quired; these, in their turn, are made stationary for relieving 

 the six alternate ones, and so on. Thuii die progressive move- 

 ment of the framing can be eflected. 



