1922] Proceedings of Elisha Mitchell Scientific Society 27 



When the writer became connected with the University of Cin- 

 cinnati some nine years ago, he decided to construct an earth pres- 

 sure machine of such a size that it would reduce the effect of cohesive 

 stresses to a minimum. 



The method adopted of obtaining the magnitude of the earth pres- 

 sure was to measure the horizontal and vertical components of the 

 action of the filling material upon a "free body." In order to 

 carry out this method a wooden wall or gate five feet wide and six 

 feet high was constructed which fitted into the open front of a con- 

 crete bin five feet wide and nine feet long, six feet high at the front, 

 and twelve feet high at the rear. The wall is supported by two 

 vertical rods or contact points which rest directly upon Fairbanks' 

 platform scales of two thousand pound capacity. Thus, any vertical 

 force acting on the wall is directly transmitted to the scales and is 

 registered. The horizontal thrust of the earth against the wall is 

 measured by three horizontal struts, one at the top in the center 

 of the width and one at each of the lower corners. These struts 

 by rocker-arm arrangements transmit the pressure directly to plat- 

 form scales of one thousand pound capacity. From the individual 

 scale readings, the amount, direction and point of application of the 

 resultant pressure can be computed. 



Method of Operation. Before any filling material is placed in 

 the bin the riders are run out on the scale beams so that the beams 

 will always be down. The reading on the scales will at all times 

 be in excess of the contemplated active earth pressures; the gate is 

 prevented from moving into the bin by bearing angles. Then after 

 the filling material has been placed in the bin, by moving the riders 

 and by allowing the beam to float, we will get active and not passive 

 pressures. 



Description of Experiments. The results of the experiments made 

 on this machine and tabulated below were made, under the direction 

 and supervision of the writer, by Mr. Jacob Feld, a fellow in the 

 Civil Engineering Department of the University of Cincinnati. The 

 filling material consisted of sand weighing one hundred pounds per 

 cubic foot. The angle of natural repose was found to be forty degrees 

 and the angle of internal friction thirty-four degrees. The angle of 

 friction between the sand and the dry wood of the wall was twenty- 

 six degrees. When the wood was wet this angle increased to thirty- 



