infiltration at drop inlet connections

[cemorway]

I have a situation that involves grout failure resulting in infiltration at pipe connections to drop inlets in areas with sandy soils and hydrostatic pressure from very high groundwater tables. The connections (supposedly) were made using non-shrink grout on precast drop inlets. The problem does not seem to have occured on built in place drop inlets, which leads me to believe it may be a result of a lack of dewatering with the precast and hence improper installation of the grout. However, I am certainly reluctant to recommend a repair (after the one year warranty) using the same technique that was should have been employed in the first case. The municipality currently requires precast to have booted connections, which seems to be working well thus far. However, several repairs need to be made in fairly new inlets (out of pavement), where I would prefer to find an option to replacement. One suggestion i have heard was the use of bentonite clay, however i have found no evidence of this being utilized elsewhere. Has anyone heard of such use or have any other ideas?

 

[LHA]

It is common to put a bentonite "clay dike" around the pipe outside of the penetration to help seal out water, but you can't just put clay INTO a failing penetration.

Depending on how many feet of water head is on the penetrations, I don't think you are going to permanently fix this without pumping down the water table.

Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve

 

[sam74]

I attended a seminar on trenchless technologies in December and this was one of the widely covered topics. The following is from a list of manhole rehabilitation methods.

Rehabilitation Method/Cost per Vertical Foot(4'Dia.Manhole)

Injected Chemical Grout / based on volume used cannot
predict cost

Cementitious:
Portland / $100-150
Calcium Aluminate / $120-200

Epoxy:
Thin film (20-80mils) / $100-180
Thick film (80-200mils) / $120-300

Cement with Epoxy Topcoat / $200-350

Cement with Composite Liner / $225-400

And there were a few others but most of these were promoted for repair of ancient, extremely corroded brick manholes or concrete manholes that have turned to paste. In fact the ones listed above were promoted for major repairs. I believe If you are having problems only at the connections a lot of these probably wouldn't apply. I thought the coolest method was the injected chemical grout but I'm not sure if you can get it to work effectively if you only inject in a small area (at connections) or if you must inject all around the manhole for proper protection. A company that put on a presentation on this particular subject was De Neef Construction Chemical Company. You might contact them to see if this would be a cost effective remedy. Hope this helps.

 

[dicksewerrat]

De Neef works very well for about 10-20 years. the other chemical grouts also work well. You want to use the grout that DOES react with water. This forms a foam seal. As long as it stays wet it shouldn't shrink. We used the grout to seal new oval RCP in ground water. If there are small less than 1/2 inch gaps, the best way we found was to use open cell foam ropes. Mix the grout in a bucket and put the foam rope in the grout. then squeeze the foam under the surface and releaseit. This will suck the grout into the foam rope. Put the rope in just like you do with oakum and tar. the water will activate the grout and no more leak.