Cement grouting pressure
Cement grouting pressure
(OP)
hey everyone this is my first participation in here so hope u all be helpful
I'm owrking on a project where the soil is weathered rock.. so no problem with bearing capacity or settlement.. but the problem is the existence of cavities.. one of the boreholes already identified a 1.2m thick cavity.
we assigned a subcontractor to do cement grouting on a 5mx5m grid and to a depth of 6m (because its a raft foundation)
now the problem is: What grouting pressure to use?
the consultant suggested a 1-2 bar pressure.. whereas the contractor says its insufficient at all because it wont be enough to infill the grout in between the nodes of the grid.. the contractor also says that a 1 bar (atmospheric) pressure is only sufficient to fill the drilled holes and to infiltrate into the ground and improve the soil.
the consultant says: we don't need to grout all the site because it's expensive.. only local grouting of the boreholes is enough since the soil is rocky and strong..
we just can't find a consensus.. any suggestions?? I can't find any pressure limit for grouting in the codes ( only a rule of thumb that results in a 1.2 bar pressure), however i found a pressure limit for anchoring in the BS code that states a limit of 20bar ( not sure but close to 20bar )..
plz help!
I'm owrking on a project where the soil is weathered rock.. so no problem with bearing capacity or settlement.. but the problem is the existence of cavities.. one of the boreholes already identified a 1.2m thick cavity.
we assigned a subcontractor to do cement grouting on a 5mx5m grid and to a depth of 6m (because its a raft foundation)
now the problem is: What grouting pressure to use?
the consultant suggested a 1-2 bar pressure.. whereas the contractor says its insufficient at all because it wont be enough to infill the grout in between the nodes of the grid.. the contractor also says that a 1 bar (atmospheric) pressure is only sufficient to fill the drilled holes and to infiltrate into the ground and improve the soil.
the consultant says: we don't need to grout all the site because it's expensive.. only local grouting of the boreholes is enough since the soil is rocky and strong..
we just can't find a consensus.. any suggestions?? I can't find any pressure limit for grouting in the codes ( only a rule of thumb that results in a 1.2 bar pressure), however i found a pressure limit for anchoring in the BS code that states a limit of 20bar ( not sure but close to 20bar )..
plz help!





RE: Cement grouting pressure
RE: Cement grouting pressure
Given that all fluids take the path of least resistance, unless you have some extremely detailed knowledge of the local geology, grout from an injection point 6 metres below surface is far more likely to flow laterally 3-4 metres than it is to flow vertically 6 metres. If you manage to get grout to come to the surface, you have probably achieved as much lateral grout flow as you can get.
Obviously if you managed to seal the leaks at surface, you could apply increasing ;pressure to PERHAPS improve lateral flow, but now the danger is hydrofracturing / hydrofraccing. You call your geology weathered soil. I call it rotten rock. All rock close to surface is weathered to some extent and has major planes of weakness. Ill guranteee that well befor 20 bar , at a depth of only 6 metres you'd be achieving break up of your rock mass and tghe surface elevation will be increasing adequately that your surveyors could measure it and the volume of grout being pumped would start to rise astronomically.
You need to focus as much on the type of cement you will be using. Search for Microsill products. Altho Ive used regular type 10 , Microsill has some major advantages.
RE: Cement grouting pressure
RE: Cement grouting pressure
can you please refer me to an article/code/paper that mentions the required pressure to be used? or is it as you said an art that isn't yet well scientifically researched?
RE: Cement grouting pressure
RE: Cement grouting pressure
For this specific hole, doesn't he absolutely have to drill though it, fill fro below with the top of the both located and vented, then fill at least that hole until the grout is coming up for the vent hole at a 2x air pressure?
RE: Cement grouting pressure
RE: Cement grouting pressure
And no , sorry I cant give articles or codes. There are a number of relevant articles Ive seen over the years. Google the tailings dam failure in the Phillipines about 15 years ago..... thuis was caused by a lack of appreciation of the potential for hydrofraccing due to over pressurization, at relatively shallow depths.
RE: Cement grouting pressure
The dam concrete was fine. It was just found to be "not" as attached to the canyon walls quite as firmly as they expected.
RE: Cement grouting pressure
http://www.haywardbaker.com/WhatWeDo/Applications/...
RE: Cement grouting pressure
Schmertmann (I forget what year, sometime in the 80's) published 'A Design Theory for Compaction Grouting' which accounts (I recall) for grouting pressure, pier size/spacing, and soil arching effects; however, I've not heard of this being used extensively in practice. I would like to hear if anyone has used this with success; especially in clayey soil sites.
I think with all of the variables, grouting pressure is just a very difficult thing to specify beforehand. In my opinion, it should be recognized that karst areas are generally 'good areas' intermixed with 'poor areas'...; and after an initial grouting pass, these areas can be more fully understood and the grouting pressures refined based on this knowledge. I also like to use the initial pass to identify the lower rock areas, which from my experience tend to be more problematic in terms of grout takes.
If anyone knows of a solid research report on grouting pressures in karst...please let me know.
RE: Cement grouting pressure
Intrusion Prepakt /marineconcrete.com