L. T. W. SEAVER. 



sections and the shearing forces along the base. The lines 

 were photographed before and after the weights were 

 applied, and the distortion of the angles in the latter case 

 showed the amounts of the stresses. The total shear resist- 

 ing weights were equal to the total water resisting weights, 

 but the former could be adjusted so as to give a maximum 

 shear either at the front or at the toe of the dam, and it 

 was found that if the front of the dam was kept down and 

 the maximum shear resisting force applied there, there was 

 a maximum lifting tendency and also a shearing force near 

 the toe. — (Pigs. 1 to 5.) The shear along each horizontal 

 section increased gradually towards the toe, but as a ver- 

 tical section would cut several of these maximum shears, 

 the failure would be more likely to occur in such a section 

 than in a horizontal one. A full account of these experi- 

 ments is given in Engineering for August 4th, 1905. 



In this connection it is interesting to note that the length 

 of the vertical section referred to is in Weigmann's Prac- 

 tical profile equal to ■§■ of the height; in the Furens dam in 

 France, which has its water face curved, \ of the height; 

 and in the great Perrier dam in India, one of the few in 

 which the curve of the toe is upward, also \ of the height. 

 So that these two forms of profiles would seem to be the 

 best for the resistance of vertical strains. 



A great source of danger in a dam may arise from the 

 porosity of the masonry or concrete, which under a head 

 of say 150 feet, will give rise to an upward hydrostatic 

 pressure of about 65ft>s. on the square inch. In some of 

 the more recent German dams provision is made for the 

 free escape of any such water by means of agricultural 

 drain pipes embedded in the concrete which carry it to the 

 back of the dam. It is however along the foundations 

 that such percolation is most likely to take place, as either 

 the joint between the concrete and the rock may be bad, 



