| Portion of cross-section. | Maximum. | Minimum. | Average. |
|---|---|---|---|
| Invert | 40 | 20 | 26 |
| Duct bench | 36 | 21 | 27 |
| Arch (excluding key) | 37 | 19 | 25 |
| Key of arch | 27 | 15 | 20 |
| Face of bench | 31 | 22 | 27 |
The maximum quantities were used when the stone was dry and contained more than the usual proportion of fine material, the minimum quantity when the sand was wet after rain.
The resulting volumes of one batch, for various kinds of stone, are given in [Table 32].
TABLE 32.— Volume of Concrete per Batch, with Various Kinds of Stone.
| Mixture. | Description of Stone. | Resulting volume per barrel of cement, in cubic yards. | Remarks. | |
|---|---|---|---|---|
| Passed screen. | Retained on screen. | |||
| 1 : 2½ : 5 | 1½-in. | ⅜-in. | 0.815 | Measured in air |
| 1 : 2½ : 5 | 2½-in. | Run of crusher. | 0.827 | Measured in air. |
| 1 : 2½ : 5 | General average. | 0.808[D] | Measured from plan. | |
| 1 : 2½ : 5 | 2-in. | 1½-in. | 0.768[E] | Measured from plan. |
[D] Average for whole of River Tunnel section.
[E] Average from 7,400 cu. yd. in Land Tunnel section.
The sand used was practically the same for the whole of the river tunnel section, and was supposed to be equal to "Cow Bay" sand. The result of the mechanical analysis of the sand is shown on[ Plate XLVI]. The stone was all trap rock. For the early part of the work it consisted of stone which would pass a 2-in. ring and be retained on a 1½-in. ring, in fact, the same as used for the land tunnels. This was found to be too coarse, and for a time it was mixed with an equal quantity of fine gravel or fine crushed stone. As soon as it could be arranged, run-of-crusher stone was used, everything larger than 2½ in. being excluded. About three-quarters of the river tunnel concrete was put in with run-of-crusher stone. The force was:
At Manhattan.