6 
BULLETIN 1486, U. S. DEPARTMENT OF AGRICULTURE 
abutments will need to be longer on two of the four corners. If the 
wing walls designated as A and D in Figure 3 are not sufficiently long 
to keep the toe of the slope out of the stream, the toe will be eroded. 
The use of right angle piers on a skewed crossing necessitates the 
adoption of a longer clear span length, besides introducing an unduly 
EFFECTIVE CHANNEL OBSTRUCTION 
Fig. 4.— A right angle pier on a skewed crossing requires 
longer span lengths and introduces excessive channel 
obstruction 
large obstruction in the channel. (Fig. 4.) For comparatively still 
or sluggish streams, right angle piers on skewed crossings have been 
successfully used in many instances. For current water, however, 
this practice leads to excessive maintenance for bank protection, and 
to the accumulation of drift with danger of local erosion. Figure 5 
illustrates some of the tendencies where right-angle piers are used on 
skewed crossings. 
INCREASED CURRENTS THROUGH 
CONSTRICTED CHANNEL 
EROSION OF SLOPE 
CAVING OF SHOULDERS 
^7* / 
BREAKING DOWN OR CAVING 
OF ROAD SHOULDER 
v//K .,-y.y 
Km a 
Fig. 5. — Diagram illustrating some of the current tendencies where right-angle piers are used on 
a skewed crossing 
FOUNDATION CONDITIONS 
Many times the range of choice in the location of a bridge may 
involve several kinds of foundation conditions. In order to properly 
balance the various merits of each location, it becomes necessary to 
know the relative advantages of these various types of foundation 
conditions. It is impossible to formulate any definite or fixed rules 
