18. Methods of Testing

Probably the easiest method of determining the bearing power of the foundation bed is by means of a platform from 3 to 4 feet square, having four legs, each 6 inches square. The platform should be set on the bottom of the trench, which should be carefully leveled to receive the legs. A level should then be taken from a stake or other bench mark not liable to be disturbed to each of the four corners of the platform, and the platform then loaded with dry sand, brick, stone or pig iron, as may be most convenient. The load should be put on gradually, and frequent levels taken until a sinkage is shown. From one-fifth to one-half of the load required to produce settlement is generally adopted for the safe load, according to circumstances. In testing the ground under the Congressional Library a traveling car was used, having four cast iron pedestals, each measuring 1 square foot at the base and set 4 feet apart each way. The car was made to move along the trenches, and halted at intervals in such a way as to bring the whole weight of the car and its load upon the pedestals which rested on the bottom of the trench. In this case the car was loaded with pig lead.

* Ira O. Baker, C. E. American Architect, November 3, 1888.

The only objection to this method is that if the legs do not settle evenly it is impossible to tell just what the pressure on the lowest corner amounts to, but it would not be safe to consider it as more than one-fourth of the whole load.

19. In testing the soil under the State Capitol at Albany, N. Y., the load was placed on a mast 12 inches square, held vertical by guys, with a cross frame to hold the weights. The bottom of the mast was set in a hole 3 feet deep, 18 inches square at the top and 14 inches at the bottom. Small stakes were driven into the ground in lines radiating from the centre of the hole, the tops being brought exactly to the same level, so that any change in the surface of the ground could readily be detected and measured by means of a straight-edge. In this case no change in the surface of the ground was noticed until the load reached 5.9 tons, when an uplift of the surrounding ground was noticed.