It appears you are using the standard triangular shaped soil pressure on the
walls. I suggest you use the trapezoidal loading recommended by Terzaghi &
Peck for cofferdam type construction. It will give a more uniform type
loading for designing the full height. At a four foot side wall I would
think that shear is what will govern the design.
Any design aid/documentation on sheeting and shoring will illustrate this
I am seeking some comments with regard to the design of a
deep wet well which will contain a submersible pump to
discharge storm water. The structure will be a square box
(4' x 4' interior dimensions) that extends from the ground
surface to a depth of 32 ft. below grade. The structure
will be reinforced concrete and is subject to an equivalent
lateral pressure of 100 lbs/ft^3 (i.e. lateral pressure =
100 * depth). Utilizing PCA's "Rectangular Concrete Tanks
Book", and with ACI 350 in mind, I'm getting a wall
thickness at the bottom of the structure in the neighborhood
of 22" thick (shear design controlling). The client thinks
this is ridiculous and we're over-designing. They also say
they have never seen anything over 18" thick and usually
it's 12" thick.
What typical wall thickness have others arrived at for these
types of buried structures ?
We are not utilizing shear reinforcing in the corner of the
tank to handle shear (only the concrete's ability to take
the shear). We are thinking it will be easier to construct
with minimal rebar and more concrete. Any different
philosophies out there ?
Thanks in advance for any help.
Richard Lewis, P.E.
Missionary TECH Team
The service mission like-minded Christian organizations
may turn to for technical assistance and know-how.