hydrostatic pressure
hydrostatic pressure
(OP)
This is a real quick question:
I am evaluating a failure to a segmental block retaining wall. The backfill is reinforced with a geogrid. In one location behind the wall, a junction box (extending from ground surface down below the base of the wall) interrupts the geogrid reinforcement. The box is located about 1 foot from the back face of the wall. I am determining the excess hydrostatic pressure on the wall due to an intense rain event. I am assuming a column of water built up between the retaining wall and junction box. As we all know, the pressure is computed as unit weight of water multiplied by the depth (in this case 20'). The assumed column of water is 4'x1'x20' My question is, Does the one foot separation between the wall and junction box have any influence on the hydrostatic pressure, since hydro. pressure is only a function of depth and density? Suppose the j-box is 2 inches from the wall and the column is now 4'x2"x20', will the hydrostatic pressure be "allowed" to develop on the wall since the j-box is so close?
It's been a while since i reviewed my old fluid mechanics books. Just looking for insight. thanks.
I am evaluating a failure to a segmental block retaining wall. The backfill is reinforced with a geogrid. In one location behind the wall, a junction box (extending from ground surface down below the base of the wall) interrupts the geogrid reinforcement. The box is located about 1 foot from the back face of the wall. I am determining the excess hydrostatic pressure on the wall due to an intense rain event. I am assuming a column of water built up between the retaining wall and junction box. As we all know, the pressure is computed as unit weight of water multiplied by the depth (in this case 20'). The assumed column of water is 4'x1'x20' My question is, Does the one foot separation between the wall and junction box have any influence on the hydrostatic pressure, since hydro. pressure is only a function of depth and density? Suppose the j-box is 2 inches from the wall and the column is now 4'x2"x20', will the hydrostatic pressure be "allowed" to develop on the wall since the j-box is so close?
It's been a while since i reviewed my old fluid mechanics books. Just looking for insight. thanks.





RE: hydrostatic pressure
Having said that, I'm having a hard time seeing how this total force could cause the failure of a well designed and constructed SBRW with geogrids. I'm curious; could you give us a thorough description of the problem?
RE: hydrostatic pressure
RE: hydrostatic pressure
RE: hydrostatic pressure
to answer Focht3: I also am having a hard time believing that the failure is due to this force. I'm just trying to rule some things out. I hesitate to go into too much detail, just in case.
to VAD: I'll look for that text, thanks.
and for RWF7437: the lower 2-3 feet of the wall bulged outward.
once again, thanks to all
RE: hydrostatic pressure
Anyway, good luck! Let us know what you find -
RE: hydrostatic pressure
i'll look into it. Thanks
RE: hydrostatic pressure
I was associated with a remediation project where a pole was installed 3 ft behind the face of a proposed 45 foot mse wall. There was bulging of the face and settlement of the level pad as the wall was being built. Construction of the wall was halted when the wall was about 50% up. Soil investigation determined loose material as a result of caving during installation of the drilled shaft for the sign pole. the drilled shaft apparently went through an old foundation that had been backfilled with granular material, resulting in ground loss. The other problem was the method used for load transfer through the straps around the sign pole. The problem was corrected by compaction grouting the foundation and building a steel frame for load
transfer around the pole. The wall was then completed with no further problems.
RE: hydrostatic pressure
(the clapping cook - closest I can find to clapping!)
RE: hydrostatic pressure
Excessive bulging normally occurs as a result of a number of interrelated construction and materials selection practices. First of all, look at the design spacing of the grid and whether or not the facing can withstand the shear under idealised conditions (you also may want to consider locked in compaction stresses.)
Secondly consider the soil - is it granular elastic or is it possibly plastic. Plastic fills generally make poor reinforced soils, particualrly with block walls where soil strains can cause the facings to become separated from the soil reinforcement.
Finally, if neither of the above are the case look at poor construction practice such as insufficient compaction and failure to protect the works from rainfall during construction. The effect of lower compaction, of course, is that the fill tends torwards phi cv rather than the peak phi used in design. Ka therefore goes up and the bond of the geogrid (alpha * tan phi) goes down. When you then consider that if the improperly compacted fill is saturated it reduces the effective overbruden stresses acting on the grid(reducing the pullout resistance of the grid even further) again reducing phi (effective stress conditions), and increasing the horizontal pressures on the block facing due to hydraulic compaction, you can start to see how very bad bulging can occur.
It is very important in these cases to monitor the structure to see if any continuing movement is occurring. If movement is continuing - I'd suggest seriously considering taking it down. However, with granular fills, hydraulic events that don't cause catastrophic failure or render the structure unsightly or unserviceable may actually lead to a more stable end condition. This should be evidenced by a lack of movement in the facing blocks.
RE: hydrostatic pressure
What sayest thou, civilmg? What did you observe at the site, and what was the geogrid layout?
RE: hydrostatic pressure
Focht3: the answer to your questions are difficult to answer as I only have photographs of the site. Remediation has already been completed.