View Full Version : Pipe Bursting tips UPDATED

07-04-2012, 12:17 AM
In a previous thread I had written about removing a belly or sag by pre soaking the sewer path to soften the ground on top of the pipe to help reduce or remove the belly or sag when pipe bursting. And while it can work it also can have the opposite effect and make the belly worse after the bursting operation has been done. I post this as information so others might not have to learn it the hard way. The reason it could make the sag worse is because the ground below the pipe may already be so soft that adding more water to that area just makes it even softer and when the burst head passes by instead of a even displacement of the old pipe outward in a uniform pattern it takes the path of least resistance and displaces the soil more downward than upward toward the surface making the sag even worse than before the bursting operation began. I can only guess that on other times where I was successful I either used just the right amount of water to soak the top portion of the pipe to achieve good results and that this last time I over wetted the soil and caused it to happen. Another thing may be that usually where a sag is located that there are pipe seperations and the leaking as caused the pipe to sink in the first place act like a french drain (perferated pipe) and take the extra induced water away. the pipe sag I just tried to remove that failed did not have and bad joints in the area so the water had no where to go. I did not run the camera while doing the complete job to document anything ( I may in the future on critical jobs) So use water on top of bellies at your own risk it could go either way. Another thing is soil conditions and sewer pipe depth play a big role in the outcome of pipe bursting. A pipe that is closer to grade (shallow) is more likely to raise up as there is less weight resistance on it and that also plays a role in any sag removal. On critical jobs ( which to me means very deep or under concrete which will cost me money in labor or profit loss) I may be more inclined to remove soil over the sewer pipe to reduce the weight and force to help remove the belly. Or at the very least realize that I need to mark out the sags location (ie under dirt or concrete) so that I have the option to raise my price in an effort to remove a sag if needed. And if I had a really critical job I might even want core samples of the soil around the pipe before even doing a pipe burst. Why? Clays are expansive soils when wet like from a leaking sewer joint they can rise and create the belly and when the new sealed pipe is in place the clay will retract and there might not be a belly. Or the water table may have risen since the original sewer was put in and it will always be a belly unless regraded by hand. I have an experiment coming up where we have a sewer with a belly that is not too deep and I plan to inject polyurethane foam that is used to raise concrete under the pipe (very slowly) to see if I can remove or reduce the belly. I just want to see if I can do it, it would be faster since it is so shallow to just dig it up but since it is so shallow if I mess up it's easy to fix, if it works I can plan to use it on deep sewers. I already have the equipment because we do polyurethane and epoxy injection. I would also consider pumping grout around a sewer pipe to fix a sag. Back to pipe bursting tips! If the sewer is located close to the foundation the soil will not expand evenly and may change the pipe path or grade something to remember when bidding the job. I have even had 1 sewer that had a bump in the bottom of the pipe when we where done because a large rock was there (I think) and didn't move when the burster head went by. I am thinking about getting a special bursting head that is longer to use on straight runs to help reduce sags. It would be bad to use it on any bends as it may exit the host pipe. Soil conditions and some of this other stuff might not be crucial on regular residential jobs but some residential jobs it may be as important as commercial.

07-04-2012, 11:55 AM
Also the camera inspection before bursting is very important to a successful burst job. If the line is full of roots or dirt etc. It really should be jetted. That seems like a waste when the line is going to be replaced anyway but if there are things you can't see they could come back and bite you. For instance prior repairs with ferncos must be located or the stainless bands may stop the burst. Also on very old sewers sometimes they would just make a hole in a pipe and push in another line then slap cement around it. Sometimes the cement is thin oother times it can be very thick and that can stop the burst head. So you really need to take the condition of the line into account before doing a burst and if you can't see something it might be shovel and jackhammer time.