A Treatise On The Principles And Practice Of Dock Engineering

STEAM NAVVIES. 8i will not excavate heavy or strong material ; they are difficu.lt and expen- sive to maintain, and therefore cause delay to the worh; they require a costly and a heavy road, and special précautions on soft ground to prevent them from tilting over into the cutting; and they are expensive to move from one cutting to another.” Steam Navvies represent a dass in which excavation is performed by a single bücket working at the end of an arm or lever. The machines travel along the bottom of the cutting, and the mode of action is an upward curved sweep of the bucket against the face of the ground in front. Steam navvies or excavators, as they are sometimes called, are characterised by great power. They are capable of worhing in the stiffest clay and the hardest marl. They will also tahe soft roch unaided, and hard roch with the assistance of a little blasting. The Huston Steam Navvy, manufactured by Messrs. Ruston, Procter & Co., Ltd., of Lincoln, has a strong spandril-shaped jib, intersected at its centre by a long arm, at the lower end of which is the buchet. The arm is capable of forward motion by means of rach and pinion gearing, and it also rotates about the pinion under the tension of a chain leading from the buchet to the head of the jib. The method of action is clearly indicated in fig. 47. The size usually employed for doch worh is that developing 10 H.P., in which case the capacity of the buchet ranges from 1| cubic yards for stiff ground to 2^ cubic yards for sand. The best results are obtained when the excavation has a depth of from 20 to 25 feet. Under such circum- stances from 1,700 to 2,000 cubic yards of sand, and very dry, friable material, have been obtained in a day of 10 hours, but a fair average in mixed earth, under ordinary conditions, would be 600 to 700 cubic yards per diem. In hard material, such as roch and rochy marl, the output is necessarily less again than this. At Barry Dochs from 450 to 500 cubic yards per day were excavated, the marl being first loosened by powder. Of soft material, 1,000 cubic yards were obtained in a single day, on several occasions, at the same place. The disadvantages attaching to the machine, undoubtedly powerful and useful though it be, are its great weight (about 45 tons), which nécessitâtes a very solid road, and its inability to worh otherwise than directly forward. The waggons to be filled must be ranged alongside, as the pivot only rotates through a semicircle, and a wide base is required to accommodate two waggon roads in addition to the navvy road. The first cost of the machine is about £1,200, and the worhing expenses, including wages, amount to about 30 shillings per day. The Simpson and Porter Excavator (fig. 48), manufactured by Messrs. J. H. Wilson & Co., Ltd., of Liverpool, is a lighter machine, but very effective in suitable soil. The special point in its favour is its ability to revolve through a complété circle, and therefore to deliver the excavated material into waggons at its extreme rear, if necessary; and further, by disconnecting the buchet gear, the machine is readily available for use 6