THE RESERVOIR RUIN.

New Zealand Herald, Volume XXIII, Issue 7824, 18 December 1886, Page 3

THE RESERVOIR RUIN.

TO THK KDITOBv Sir,—T will, if you please, give yott my idea of this disaster and its remedy. First, I must say I know nothing of the planners or constructors, nor yet of the way in which the work has been done; in fact, I did not know the thing was in existence, till I saw the account of its failure Iα the HbEald, By appearance, then—for I have been several times to look at it—it is evidunt the cause is the bottom end of the work was not mad* as aelid aa the top. Some may say any fool could tell that. Perhaps so, bat it is neoee! sary to keep this in mind, for if the embank* ment is to be made safe that i* what must yet be done. There is no mystery in the case. Plainly enough, it is the natural settling pf loose earth, which, it appears, moat have been tipped down, so forming a series of slanting strata (or mainly bo done), and the wall has been depended upon to hold it back. But a wall fit for such a purpose ought to have the base nearly equal to the height, and I see, by the plan in the Hebald, the base is only one-quarter of the height. Now a slanting strata causes a much greater lateral pressure than a horizontal one, and that pressure, as against this wall, is, as four times multiplied, being applied, as, it were, at the end of a lever of four to one against the base', and the watertight stone wall, retaining the moisture, adds to this weight, . making the wall of ao use, except where it is held up by a sufficient backing of earth. This is self-evident, for where the backing is too elighb the wall has bulged considerably, bat where the wall is well supported by the earth the outthrust is not perceptible. What, then, is the use of a stone wall for an embankment? just so much (and that only) that stone ie heavier than solid earth; 200 yards of solid earth would (for this purpose) give more support than 200 yards of stone, and'a mortar-built wall In this plaoe is positive waute of money, For repairing they should commence at the bottom, and throw the present bank down in steps, spreading it oat in continual horizontal strata, well ramming each step solid, alwaya keeping the floors horizontal its they go on till it is raised to the proper height. The earth should be spread regularly six or eight inches thick, or lets, and rammed solid before the next layer is spread on. Of course, the wall stones need using up, and they might be built in anywhere convenient to get rid of them. They should be built without mortar, bat the interstices of each course filled in with earth. If some each plan as this is adopted, it will last for ever. There is no necessity to reduce the capaoity of the reservoir, for if properly done it would be aa solid as the top.—l am, &c,, Mechanic.