ko for culvert wing wall and bridge winged abutment

[ozziz]

Retaining structures like culvert wing walls and bridge winged abutments are restrained at the base and side which reduce the movement of soil. Therefore should the coefficient of soil presure used be Ko instead of Ka?

Also is there any publication or research paper which relates the coefficient of soil pressure to compaction?

Thanks for any input.

 

[DRC1]

Structure that will not tolerate some movement or are restrained should be designed to Ko conditions.
Compaction can induce stress over Ko. For granular materials, Ko is on the order of 0.5. Comapction stresses can raise K to .6 or better. Typically most specifications will require compaction by hand equipment ( walk behind)with in 5 feet of the back of the wall to prevent high stresses.

 

[jdonville]

ozziz,

NAVFAC DM7-2 Figure 13 shows induced pressures due to compaction near the wall.

Jeff

 

[ozziz]

Apologise for being late.

My point of contention is the development of "ko" for retaining structures. If one consider any bridge abutments, if "ko" does developes, then relieving slab or transition slab is not required as soil settlement will not take place. The soil has achieved "ko".

In normal circumstances, compaction close to retaining wall is some distance away - 1 to 2 ft. At this distance away, the compaction can be at any density. Therefore, it would be very interesting to know the Ko-ka values and this is what I am interested in.

Thanks for any contribution

 

[miecz]

On our wingwalls, there is an isolation/expansion joint between the wingwall and the abutment, although the footings are usually connected. The wingwall is not restrained at the side, so we use Ka.

 

[ozziz]

Even if there is a vertical isolation joint along the wingwall, the coeff of lateral presure depends on the rotation of the wall and it might be ko instead of ka if there is hardly any rotation or is always greater than ka if it is rigid. Therefore could structural engineers err in using ka or ko should be adopted in all cases? However if the backfill is not well compacted, then ka can be used? This is the point I am driving and appreciate if there is any further information on relationship between compaction and coefficient of lateral pressure.

 

[casimmons]

Compaction should have little affect on whether ko or ka is applicable. Compaction results in increased density of the backfill, along with increased shear strength. You can have some direct shear or triaxial tests run on samples remolded to varying degrees of compaction to see this relationship. Also the compaction equipment could put additional stresses on the wall. You just need to understand that a certain amount of lateral movement is required at the top of the wall for active pressures to develop. If your wall is restrained at the top or is so rigid that the required movement will not happen then at rest pressures will develop.