ALLOWABLE PRESSURES ON FOUNDATIONS. 



wlu-rc P the total pressure on the surface; m a constant; v> weight of a cubic foot of 

 w.itrr; a area of wetted surface normal to the current in square feet; velocity of current 

 in l.vt per second; and g = acceleration due to gravity - 32.2 feet. The value of m varies with 

 the shape and the dimensions of the pier. Weisbach's Mechanics gives the following data: 

 For a prism three times as long as broad, m 1.33. For a pier five or six times as long as broad 

 and with a cutwater having plane faces and an angle of 30 degrees between the cutwater faces, 

 m = 0.48. For a square pier, m = 1.28, and for a circular pier, m 0.64. 



The maximum pressure due to floating ice will be the crushing strength of the ice, which 

 varies from 400 to 800 Ib. per sq. in. The principal danger from floating ice and drift is that 

 the current of the stream will be deflected downward and will gouge out the material around 

 and under the pier and cause failure. To prevent this it is quite common to build piers with a 

 " break- water," "starkwater," "cutwater," or nose that will deflect drift and ice, or to put in a 

 pile protection on the upstream side of the pier. If the water can get under the pier the buoyancy 

 of the water must be considered in calculating the stability of the pier. If there is danger of 

 scouring then it is well to deposit large stones and riprap around the base of the pier. 



Batter. Piers and abutments are seldom battered more than one inch to one foot of vertical 

 height, or less than one-half inch to the foot, although high piers are sometimes battered only 

 one-fourth inch to one foot. 



ALLOWABLE PRESSURES ON FOUNDATIONS. The allowable pressures on founda- 

 tions depend upon the material, the drainage, the amount of lateral support given by the adjacent 

 material, the depth of the foundation, and other conditions, so that it is not possible to give data 

 that will be more than an aid to the judgment. If properly designed a moderate settlement of 

 some particular structure may do no harm, while a less settlement in another structure may be 

 disastrous. Professor I. O. Baker gives the values in Table I in his " Masonry Construction." 



TABLE I. 

 SAFE BEARING POWER OF SOILS.* 



Present practice is more nearly given by the values in Table II. Foundations should never 

 be placed directly on quicksand. 



TABLE II. 

 ALLOWABLE BEARING ON FOUNDATIONS. 



Baker's " Masonry Construction," John Wiley & Sons. 



