Slab Reconstruction Over Landfill
Slab Reconstruction Over Landfill
(OP)
General Information
Existing PEMB built over landfill (1980)
Previous repairs made to perimeter walls (compaction grouted) show negligible settlement.
Slab replaced 1995 (non-structural) has settled 6"+ in several locations.
Contractor has proposed pressure grouting to raise slab (with no guarantees) or 10'X10' grid of micropiles (80+ @ 30';15'refuse +15' embedment; 20k working load) and structural slab.
We would be concerned with the feasibility of the micropiles through the refuse, eccentricity, unbraced length
etc., along with the potential environmental hazards (methane release, groundwater contamination etc.)
We are considering a series of RC beams (no piles) with a structural slab, (Similar to a waffle slab) vs. using a mat slab.
We know there will be additional settlement and these RC beams will have to span the voids below. We will survey the existing slab and design the spans with respect to anticipated settlement.
We are proposing to install ports that will allow such settlement to be monitored and allow future pressure grouting as warranted.
Looking for a discussion (pros and cons).
Thanks in advance
Existing PEMB built over landfill (1980)
Previous repairs made to perimeter walls (compaction grouted) show negligible settlement.
Slab replaced 1995 (non-structural) has settled 6"+ in several locations.
Contractor has proposed pressure grouting to raise slab (with no guarantees) or 10'X10' grid of micropiles (80+ @ 30';15'refuse +15' embedment; 20k working load) and structural slab.
We would be concerned with the feasibility of the micropiles through the refuse, eccentricity, unbraced length
etc., along with the potential environmental hazards (methane release, groundwater contamination etc.)
We are considering a series of RC beams (no piles) with a structural slab, (Similar to a waffle slab) vs. using a mat slab.
We know there will be additional settlement and these RC beams will have to span the voids below. We will survey the existing slab and design the spans with respect to anticipated settlement.
We are proposing to install ports that will allow such settlement to be monitored and allow future pressure grouting as warranted.
Looking for a discussion (pros and cons).
Thanks in advance





RE: Slab Reconstruction Over Landfill
Is there a venting layer under the slabs for methane removal, or don't you have concerns? If there is one, will it be compromised by grouting?
Can the grouting contractor come back later and get through his former work for adding more grout?
RE: Slab Reconstruction Over Landfill
The landfill was closed in the mid 70's. There is no known methane venting system at this or any other developed site.
The owners do not want to pressure grout the existing slab. When it was replaced in 1995 they put no steel in the slab; used fibers. Needless to say the slab has performed poorly.
The intent is to provide a structural slab that will be able to withstand areas of localized settlement.
The slab footprint is 60'X100'.
We are proposing to provide monitoring ports that will also allow the new structural ribbed mat slab to be "mud jacked" in the future as necessary. This is a means to mitigate future issues.
RE: Slab Reconstruction Over Landfill
RE: Slab Reconstruction Over Landfill
RE: Slab Reconstruction Over Landfill
Regards
Eire
RE: Slab Reconstruction Over Landfill
Yes, that is good advice.
Eire,
I took a look at the system you referenced. Very interesting.
We would be attempting to achieve the same goal by a different means.
Thanks for the information.