soil pressure on irregular shape
soil pressure on irregular shape
(OP)
I was just interested in how other engineers might determine the loads on a wingwall retaining wall shaped as shown below. I believe that the way I did it was fairly conservative, but would like to hear ideas from people just looking at it for the first time. The wingwall is parallel to a railroad track and will have active soil pressure as well as boussinesq surcharge. The embankment outside the wall might not be above the bottom of the wall, so I cannot consider any passive resistance. It cantilevers out from a bolted connection to the side of the bridge abutment.
_________________________
/ !
/ !
/ o !
/ !
/ !
! o o _
! _
! o o _
! _
! o o _
!___________
_________________________
/ !
/ !
/ o !
/ !
/ !
! o o _
! _
! o o _
! _
! o o _
!___________
~dison






RE: soil pressure on irregular shape
the wing wall is cantilevered off the abutment so the connection would be fairly substantial
Kieran Coyle
BEng(hons),CEng, M.I.Struct.E, M.I.E.I.
RE: soil pressure on irregular shape
RE: soil pressure on irregular shape
~dison
RE: soil pressure on irregular shape
RE: soil pressure on irregular shape
I don't see the need to work with 3D or finite elements. This is a statics problem to determine the load and strength of materials to size the connection and plate thickness.
And yes, I do enjoy using finite elements quite a bit - when the application is truly warranted.
Good Luck.
RE: soil pressure on irregular shape
I agree with Qshake that this probably doesn't warrant the use of finite elements and elementary soil mechanics can be used to determine the appropriate loads. It seems that I forgot to mention the material being used for this member. Ihe wall isn't a steel plate, it is actually a precast concrete piece. To save some time, I figured the soil pressure diagram and surcharge on a rectangular section that was the full depth of the wingwall, divided the wall into two sections (above and below where the sloping bottom starts), and applied the total load above the divide and 2/3 of the load below the divide. This yielded reasonable values to design with and so I did not recalculate the loads exactly. This should be conservative since the max pressure is at the base of the wall and at that point the wall is actually sloping toward lower pressure.
~dison
RE: soil pressure on irregular shape
I watched a crew of about five guys (who knows if they even belonged to a union) put together a new railroad bridge not too far from my house. The abutments were all precast pieces (they sat a big block down on the old abutment and affixed a precast backwall to it. They drove cylindrical pile down between the track and placed a precast pile cap beam ontop and one day when the train traffic was light they pulled the old superstructure out and placed a new one (actually looked like a dupont overhaul as the newly painted girders were riveted!). All that before the next train coming down the track. Amazing!
RE: soil pressure on irregular shape
RE: soil pressure on irregular shape
And if the dynamic loads of the locomotives are akin in impact to vibrating rollers the pressures may go instantly amazing ... experimental impact factors must be covering this...but if only moderate ones are used in bridges tehmselves to apply bigger in approaches would seem strange.
RE: soil pressure on irregular shape
In my experience, impact has not been applied to railroad surcharge loads for design of retaining walls and abutments. I don't know if the reason is due to the damping effect of soil or factors of safety applied in design. In this case, the wall is 14 feet from centerline of the track and the surcharge load at that distance is minimized. If the wall were much closer, that would be a much more important factor in design.
Would you use at rest pressure with this type of cantilevered system and bolted connection? My instinct would say that under soil pressure, the wall would be flexible enough to go active, but my instinct is certainly not always correct:)
Qshake:
Yes, it is amazing what the railroads will do with precast. Whatever it takes to keep the trains running! It makes for efficient construction (assuming that no problems creep up during track outages). The bridge construction sequence that you mention is very common. Where did the term "dupont overhaul" come from? I have never heard that one before. Are you saying that no one is building riveted girders these days?:)
~dison
RE: soil pressure on irregular shape
Contrarily the at rest pressure is understood to develop against nonyielding walls, such a rigid buried box.
One may argue that once the wingwalls have taken the deformation demanded by the pressure, they become nonyielding, but this could also may be said of the cantilever walls with heels in the backfill and the most common use is that of active pressure, irrespectively of the actual upper tip lateral deformation. Furthermore, as in such case, in wingwalls the confinement is as commonly understood for retaining cantilever walls imperfect, and this will signal the use of merely the active pressure as enough.
Other thing is that one feels the pressures being applied be less than required on engineering judgement (for example, on the namend lack of account of impact factors that care for the dynamic load) and then in compensation choose to -for example- use the at rest pressure.
Technically the check would be if the required displacement to develop active pressure is met.
RE: soil pressure on irregular shape
Perhaps somewhere riveted construction is being carried out. But not here...
Anyway, as a new graduate I worked in the construction field and became very familar with the "dupont overhaul" terminology! Just because it looks and smells brand new that is no reason to expect it to run any different than the 30+ year old hunk of junk it was before the coating! Of course, with respect to the big plate girders I have to commend the railroad for rummaging around and making the find - very economical!!