pile supported wall - foundation engieering by peck hanson

huangyhg

pile supported wall - foundation engieering by peck hanson t
i am using the pile supported retaining wall example on page 436 as a reference for a problem that i am working on.
here are the loads i have about point a:
sum v = 13.16 k
sum h = 9.39 k
sum m about point a = 176.55 k-ft clockwise, (i have water pressures).  with this type of loading my vertical resultant is near the edge of the toe, but still within the footing.
i am following the same pile layout right now, except i am using 5.5 ft spacing instead of 3 feet.
when i calculate the vertical components of pile reaction, i get a positive value for row 1, a positive value for row 2. but i get a negative value for row 3.
do you guys know what this negative value means?  also do you guys have an idea of what i can do to make this value positive?
thanks
the pile is in tension.
do you have any advice on what i can do so that, that pile will not be in tension.  i added another pile in row 2, but i still get a tension on pile 3.  should i make the footing longer?  or do you have any other suggestions?
appreciate your help.
i don't have the book but you are referencing but  make a suggestion: can you move the stem (wall) so that it is closer to piles in row three?
yes, i can do that.  if i do that i will be decreasing my heel lenght and increasing my toe length.  do you still recommend i do that?
tahnks
i also, can also move both my batter piles about 2.5 towards the driving side.  or i can move my middle pile 2.5 away from the driving side.  should oen of these approaches help me out?
thanks
really the best way to figure out what will help you is to do both kxa's suggestion and your own and see what happens to your results in each case.  then you will see how changing something like stem wall location affects the resulant forces and pile forces and so on.  
i typically switch heel and toe dimensions on pile supported walls from standard practice with two rows of piles but still have one in tension.  there is a resultant bearing point on the footing.  if you want them all in compression keep them on the toe side of that point, but a tension pile design is the most economical.
one important thing to re  
bigh, i agree with your posting regarding the uplift capacity of the piles. the uplift load may not even overcome the friction capacity + wt. of pile. the footing attachment to the pile however will have to be designed for uplift.
can you explain the safety factors a bit more. i was under the impression that we use fs=2. if we test a pile to the failing point, the pile capacity becomes the load at failure divided by 2. can you please elaborate on the 2, 3 and the 6 safety factors.
thanks
thanks for the help, just wanted to confirm some calcs. - if someone has this book.
on page 437 the following equation is being used for the vertical components of pile reactionssum v/n) +/- (sum m *d/ sum d^2).  is the second term positive when "d" is to the left of c.g. and negative when "d" is to the right?  i think there is more to it, but i can figuere it out since a vertical load is being calculated.
appreciate your help