lj.71. The bendinp- moment if ould be ^ 



> Hd sii\2(X P d P H „ 



¥ = -^^-3 + -V- ^ -IT— ^^ § ^ ^^^^^ 



193 X 6h 193 X 6 X 9 



= 1070 d + 



= B,600 + 6,200 + 2,000 = 17,iiOO foot-pounds oer 



foot of wall, 



U72. As the bending moments resulting from vjave action are less than 

 those resulting from, earth pressure, the sections computed in paragraphs 

 1)62 and I163 would be used, 



U73. Concrete and Stone Block Groins . - This type of groin is not 

 as adaotable to building beaches as sheet i^ile structures or rubble-stone 

 mounds. It is used principally to stabilize a beach in its existing 

 position with only slight accretion exoected on the updrift side. With 

 articulated block groins or single stone block groins, the differential 

 height of the undrift and dwrndrift beach lines is limited to about 5 feet. 

 Accordingly the groin would be so placed with reference to the beach 

 surface that sand would s pill over the top of the structure before erosion 

 had undermined it on the do■^^^ndrift side. 



I17U. Maximum Forces . - Again the forces acting on the structure 

 would be either earth r^ressures or wave forces or combination thereof. 

 jMo combination of these forces would exceed the maximxm that would occur 

 by application of either singly. The maximiim earth pressure would occur 

 with the groin full on one side and unsupported on the other. The maximum 

 wave pressure would occur at the seaward end of the groin where there 

 would be no supnorting fill on either side, aid -Aere the groin would be 

 subject to attack by the largest wave. The end block would be subject to 

 the full impact of the waves. Landward blocks would be subject to reduced 

 wave forces by reason of the angle of wave approach. 



U75>. Earth Pressures . - Maximum earth pressures would occur with 

 one side full and the other side of the groin empty. See Figure lU7. 

 For = 25°, 6=111°, 0^ = 22°, and p = 0°. 



P = 1/2 I ,f"Q -<^ ^ , 



^ (1 + n) sm e ) 



x-rh 



/sin (0 + 



sin (P-^ 



7) sin (0 - p) 

 ~~) sin (9 - p) 



(160) 



226 



