SOLOMON'S KNOB DAM

Dominion, Volume 2, Issue 335, 23 October 1908, Page 8

SOLOMON'S KNOB DAM

THE FERRO-CONCRETE METHOD. FULL DESCRIPTION OF THE WORK. Tlio whole of tho engineering faculty of Australasia will be interested in Wellington's decision to have tho now dam at Solomon's Knob, constructed on tho ferro-concreto system, which has become known in Amcrica as the strongest and therefore the safest description of dam. The old stylo of dam —a solid wall, wide at the baso and diminishing in thickness towards tho top, with the head of tho curve up-stream—may bo seen in its modern perfection at Karori, where tho City Council recently erected a second reservoir. From ail engineering point of view tho new structure at Solomon's Knob will not even be a distant relativo to tho new dam at Karori, In Tuesday's issue, when wo announced that tho tender had been secured by Messrs. Martin, Hurrell and Snaddon, of this, city, a description of the new reservoir was given, with some idea of what tho new work meant. The accompanying illustrations will give a better idea of what the form of construction is to be than tho pen can convey to the lay mind. The "beaver" principle—a curved wall, with the fullness of the curve up-stream—is entirely dispensed with, and in its stead is substituted a slab of concrete (3ft. in thickness at the toe, diminishing to 2ft. at the top), fitted slantwise into the gully at an angle of 45 degrees, with the toe up-stream. This. piece of concrete cardboard could not remain in such a position unsupported, so underneath it are a number of vertical walls erected at right angles, 12ft. apart, which are calculated (on a careful computation of" stresses) to carry the wall or deck slab and all the water nature can spill behind it. Such a superstructure must, of course, have an adequate foundation. This is provided in a cut-off concrete wall 6ft. in thickness sunk 'to a depth varying from lift, to 2oft., the full breadth of tho dam under tho toe of tho deck. Having obtained a good grip- on tho ground in that manner a concrete flooring 2ift. thick and extending downstream (on tho flat) for 63ft. 6in. is laid as a solid support for the deck-sup-porting walls. To show what a comparatively light fabric tho whole structure is, these walls are only 2ft. in. thickness, and