Section at Sta. 76+20.
FIG. 20.–GRAPHICAL EXHIBIT OF STUDIES OF
JEROME PARK RESERVOIR EMBANKMENT.
Wherever bed rock was not considered too deep below the surface the core walls were built upon it. In other places the foundation was placed 8 to 10 ft. below the bottom of the reservoir and rested upon the sand.
It appears that the plans of the Jerome Park embankment were changed from their original design, prior to the report of the board of experts, on account of two alleged defects, namely, “cracks in the core wall” and “foundation of quicksand,” and incidentally on account of the supposed instability of the inner bank.
In describing the materials on which these embankments rest the experts remarked
that all these fine sands are unstable when mechanically agitated in an excess of water, and that they all settle in a firm and compact mass under the water when the agitation ceases. That they are quite unlike the true quicksands whose particles are of impalpable fineness and which are “quick” or unstable under water.
[Fig. 20] is a graphic exhibit of the results of tests made at “Station 76 + 20,” and at “Station 99,” to determine the flow line of water in the sand strata underlying the embankment and bottom of the Jerome Park reservoir.
The experts reported that there was no possible danger of sliding or sloughing of the bank; that the utmost that could be expected would be the percolation of a small amount of water through the embankment and the earth; and that this would be carried off by the sewers in the adjacent avenues; that a large expenditure to prevent such seepage would not be warranted nor advisable.
In concluding their report, however, they recommended changing the inner slope of 2 on 1 to 2½ on 1, and doubling the thickness of the concrete lining at the foot of the slope to preclude all possibility of the sliding or the slipping of the inner bank in case of the water being lowered rapidly in the reservoir.