huangyhg

mud jacking specification
hi.
i posted this on the concrete engineering forum, but haven't received a response yet. i was hoping someone here would be able to assist me.
i have a project where a homeowner had some cracking and settlement in his basement floor slab.
after coring through the slab we found voids ranging from 1/16" to 1/2". the slab is underlain by a pea stone below-slab drainage system.
we would like to grout the voids and raise the slab slightly in a couple of areas where it settled.
my fear is that if the grout is too thin it will infiltrate the voids in the pea stone and render his below-slab drainage system useless or at least reduce its capabilities.
has anyone had experience with this type of problem? if so, how do we test the grout to ensure it is thick enough? is there a maximum slump or a flow cone value that would be appropriate?
thanks is advance!
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first you need to address why there are voids in first place. hate to see you go through expense of filling voids and other repairs only to find that additional weight causes more settlement, and thus more voids.
i believe there is a combination of poor compaction of the underlying sand and curling of the slab that have created the voids. i believe most of the settlement is complete. we augered the soil under the slab and compared that to the geotechnical report. we did not encounter organic soils.
i believe that after grouting the slab should be supported. i just don't want to hinder the below-slab drainage system by clogging the pea stone.
hi eric1037
please note that the slab serves as a bond break between wet soil and a dry concrete floor. the gravel prevents water from wicking throgh to the concrete floor. the voids in the gravel prohibit capiliary action (wicking) from continuing into the concrete slab. the point is, if you fill the pores in the gravel with grout or if you reduce the pore size in the gravel you may end up with a damp concrete floor becaus ethe water will wick through the gravel and into the concrete.
maybe the slab is still settling? in which case the grout won't help because in 3 years the slab will settle again.
if the house is new, there may be a poor soil condition below the slab. possibly the contractor backfilled and never compacted and now the soil is settling.
if the house is 20 years old, the settlement has propbably tapered off in which case you may proceed with remedial work.
be careful about filling voids in gravel or you'll end up with a damp floor and maybe a mould problem.
how about setting up your own test? obtain some of the pea gravel, place in a trench, cover with concrete and try injecting grout with different mixes. then inspect for fouling of the gravel.
if you have a drainage system under the slab. it will almost certainly clog with any type of grout .the only way to do this work is to abandon the below slab drainage
and create an alternative ring drain system to intercept any water before it gets under the slab.
instead of grouting and possibly ruining the gravel and draingage system, how about removing the old slab, placing a vapor barrier, and pouring a new slab?
fortunately, after further exploration, we discovered that the voids were not pervasive across the entire slab.
therefore, i believe localized grouting shouldn't significantly compromise the below-slab drainage system since it is a relatively small area. this assums the grout does not enter that actual drains themselves.
thanks for all of your responses!

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