338 



RETAINING WALLS 



uncertainties of pile driving are so great that it is useless to 

 attempt to use a more accurate formula. 



EXAMPLE. A pile was driven with an ordinary hammer 

 weighing 2,400 Ib. The sinking under the last five blows was 

 22 in. The fall of the hammer during the last blows averaged 

 28 ft. What was the safe bearing power of the pile? 



SOLUTION. Here the value of 5 may be taken as the average 

 of the total sinking during the last five blows, or 22-7-5 = 4.4 in. 

 Then, w = 2,400 Ib.; h = 28; and s = 4A. Substituting these 

 values in formula 1, 



2X2,400X28 

 R= 4.4 + 1 



RETAINING WALLS 



STABILITY OF RETAINING WALLS 



VERTICAL BACK 



A retaining wall is a wall that sustains the pressure of earth 

 filling or backing deposited behind it after it has been built. 



t Analysis of Forces. 

 In Fig. 1 is shown a 

 retaining wall with a 

 vertical face and a ver- 

 tical back; ib is the 

 natural slope of the back 

 filling, which on an 

 average is 1J horizontal 

 to 1 vertical. The top 

 ci is level with the top 

 of the wall. 



In making calcula- 

 tions, only 1 ft. of 



FIG. 1 the length of wall and 



of the backing is taken ; 

 thus, it is simply necessary to take the area of the section of 

 the wall and backing. The material composing the backing 



