pit design question (civil)

[STEVE LIU]

hi~~
U = 1.4（D + F）...............（1）
U = 1.2（D + F + T）+1.6（L + H）+0.5（Lr或S或（2）
U = 1.2D + 1.6（Lr或s或R）+（1.0L或0.8W）...（3）
U = 1.2D + 1.6W + 1.0L + 0.5（Lr或S或R）.........（4）
U = 1.2D + 1.2F + 1.0E + 1.6H + 1.0L + 0.2S ............（5 ）
U = 0.9D + 1.2F + 1.6W + 1.6H ......................（6）
U = 0.9D + 1.2F + 1.0E + 1.6h.......................（7）
I design a pit now, and i dont need to consider wind load and earthquake at this area
if i consider combination 6 &7 and have not water inside pit
U = 0.9D + 1.2F + 1.6W + 1.6H ......................（6）
U = 0.9D + 1.2F + 1.0E + 1.6H.......................（7）
F＝0, w＝0, E=0 0.9D+1.6H H including groudwater, this combination make uplift load too large (1.6 multi)
let my analysis model error (compression only spring have tension)
actually uplift check is ok , consider this combination reasonable ?

 

[racookpe1978]

Sketch your problem geometry and and label the dimension letters (to scale).
Your question is not clear enough to answer properly.

 

[racookpe1978]

Depth, Width, Height (?), Floor (?), Uplift (?), Length (?), E ??,

 

[hawkaz]

I have a similar situation going on right now. I'm using the ASD load case .6D+H
Uplift is large with buoyant forces - displaced water = 62.4 pcf and weight of concrete = 150 pcf X .6 = 90 pcf.
Net gain of only 27.6 pcf.

 

[STEVE LIU]

Hi~~~racookpe1978 & hawkaz
thank for your replied

Sorry my roughly describe and i cant upload sketch right now i will do it later.
my pit almost 60 m x 60 m depth 5.5 m (underground)(bottom of baseplate)
wall thickness (0.6 m) baseplate thickness (1 m)
and water level at -3.6m so pit be submerged in groundwater 1.9 m.

My Situation like hawkaz
when i did buoyancy check without any load factor
only concrete weight / uplift force >1.2 ok ( almost 1.2).
But during finite element analysis ,

i consider the case of backfill with groundwater but without internal liquid
U = 0.9D + 1.2F + 1.6W + 1.6H ......................（6）
U = 0.9D + 1.2F + 1.0E + 1.6H.......................（7）
F=0 , w＝0, E=0
=>
U=0.9D +1.6H
this combination make uplift force too large.
so i think that i dont consider wind load and earthquake
i still need to consider these two combination or i can ignore it