246 



ENGINEERING. 



62 acres. They include a graving dock 710 

 feet long and 96 feet wide, in obtaining the 

 foundations for which some of the deepest ex- 

 cavation ever accomplished under tidal water 

 has been done. In the construction of the sill, 

 which is 34 feet below high water in ordinary 

 spring tides, a large iron caisson was used in 

 excavating for the foundation. The sill or en- 

 trance is in the form of a groove, the object 

 being to enable the dock to be used as a wet 

 dock for very large vessels when desired. The 

 sill-stones are blocks of granite placed directly 

 on the solid rock, which was excavated to the 

 average depth of eight feet. The gate to the 

 entrance is a floating caisson, the largest ever 

 made of its kind. A large caisson-chamber for 

 receiving the caisson when opening the dry 

 dock, with heavy walls of limestone and con- 

 crete, is 100 feet long, 45 deep, and 15^ wide. 

 This chamber was excavated in the rock to the 

 depth of 12 feet. Some of the deep founda- 

 tions were obtained by sinking a kind of coffer- 

 dam formed by a huge monolith of concrete. 

 This was built up on the surface of the ground 

 to be excavated, and the inclosed earth dug 

 out, the weight of the mass causing it to sink, 

 the sides being built up above the water- 

 level in the beginning or progressively while 

 it was sinking. The largest of these monoliths, 

 used in digging for the foundation of a break- 

 water at the lock-entrance to the graving dock, 

 is 36 feet by 24 feet, with side-walls averaging 

 six feet in thickness. This had to be sunk 57 

 feet below the surface of the ground before 

 reaching the solid rock. This mode of tidal 

 excavation has not before been tried in Eng- 

 land. It promises to be a valuable method for 

 sinking the foundations of piers, breakwaters, 

 or lighthouses. A channel, 100 yards wide, 

 giving 34 feet of water at high spring tide, has 

 been cut from the graving dock to deep water 

 in the haven. The dry dock has an entrance 

 at both ends, communicating with the wet 

 dock and with the haven, allowing it to be 

 used as a tidal basin or as a lock. A small 

 graving dock, 300 feet long, and capable of ac- 

 commodating ships of 20 feet draught, is within 

 the area of the wet dock. In this new graving 

 dock the Great Eastern steamship was recently 

 docked for repairs. Of the 62 acres of dock 

 area in the haven, one half will soon be opened 

 for use, affording 5,000 feet of wharfage, with 

 quays of an average depth of 200 feet. When 

 the whole of the wet docks are completed the 

 wharfage-room will be about 7,000 lineal feet, 

 with 26 feet of water in the basin. The en- 

 trance-lock will be 500 feet long and 70 wide, 

 with 34 feet of water on the sills at spring tide. 

 A low breakwater will protect the entrances 

 to the tidal lock of the basin and to the graving 

 dock. Close to the docks is a deep-water iron 

 pier, with three lines of railroad-track leading 

 to the coal-fields. There are several hydraulic 

 cranes and a powerful hydraulic elevator at- 

 tached to the pier, which are capable of dis- 

 charging 1,000 tons of coal in twenty-four 



hours. The pier can also be used for landing 

 passengers, as it is approachable at all states of 

 the tide. This pier is of a novel design. It 

 is nearly 1,000 feet long and 40 feet wide, and 

 is built of solid wrought-iron bars, or screw- 

 piles. 



Extensive dock accommodations have been 

 added at Hartlepool, which is the only harbor of 

 refuge along an extensive stretch of dangerous 

 coast, and has now been made one of the most 

 accessible and commodious ports on the eastern 

 coast of England. The docks have been ex- 

 tended by successive additions since the first 

 one was commenced in East Hartlepool in 1840, 

 until they now embrace an area of 176$ acres. 

 The east harbor is connected with the harbor 

 of West Hartlepool, which has too shallow an 

 entrance for large craft, by a deep channel. A 

 large flat which was covered at high tide has 

 been excavated to form the new dock. A tidal 

 basin connects this with the deep-water chan- 

 nel, letting into East Hartlepool Harbor, which 

 is open to the sea. The tidal lock or basin, 

 which is 450 feet long and 26 to 27 feet deep, 

 is provided with a double set of gates, the outer 

 pair of which are constructed of wrought-iron, 

 with air-tight compartments large enough to 

 enable them to float on water. They are op- 

 erated by hydraulic machinery. The bridges 

 for railroads over the entrance passage are of 

 remarkably easy action ; though containing 500 

 tons of wrought-iron and 200 tons of cast-iron 

 each, they revolve upon a system of wheels of 

 pure steel as though they were of the lightest 

 construction. 



The boring of the St. Gothard Tunnel has 

 been completed, the latter part of the work 

 having proceeded with increased rapidity. The 

 Belgian system of tunneling by top-headings, 

 adopted by the late engineer, Louis Favre, and 

 ihe use of compressed-air drills of the latest 

 types, compressed-air locomotives, and im- 

 proved methods of ventilation, have enabled 

 the work to be done at quicker rates than 

 would have been possible if the engineers had 

 not so readily availed themselves of new in- 

 ventions. (See ENGINEERING, in "Annual Cy- 

 clopaedia" for 1879.) Before the two sections 

 of the tunnel met, the temperature had become 

 almost insupportable in the headings. Two 

 serious hindrances were encountered in the 

 latter portion of the work : a large influx of 

 water occurred at one point, and at another 

 the tunnel passed through a mass of disinte- 

 grated feldspar with alumina and gypsum, 

 which swelled very rapidly upon contact with 

 air, and was pressed out by the weight of the 

 superincumbent rocks with a force sufficient to 

 crush every kind of arched lining which could 

 at first be devised. Granite arches capable 

 of withstanding the enormous pressure were 

 finally made, though the heavy lining of five 

 feet thickness was sometimes broken down, and 

 had to be reenforced with side-walls, also of 

 granite, about 6| feet thick. The two head- 

 ings met on the 30th of April ; the calculations 



;! 



