Chemical Grout /Ground Stability

[Prepakt1]

We have been asked to stabilize by chemical grouting .Ground that consists of fairly liquid sand for a building foundation. We have done this a few times before in the past with mixed results. I would like some comments on currently appropriate grouts and any previous experiences and problems with this technique.

 

[Geocontractor]

We have pumped 1,000s of gallons of sodium silicate grout to stabilize running sands for subways, buildings, shafts, etc...Do you have more specific information?

 

[Prepakt1]

The requirement is to stabilize against laterel earthquake movement. Its a 3 storey structure 50 X 45 and we have a 4 ft crust that the geotech states, would with a 1 ft thick gravel and geogrid mat would support the building load.This would not however protect against lateral earthquake movements .The proposal is to grout a layer of fine sand 4-7 ft thick 18 ft below the surface with chemical grout.This fine sand extends to 40 ft deep then another 60 ft or so of sandy riverbed silt . I would like comments and suggestions.

 

[rchanke]

Sodium silicate grout is very good for constructability purposes for shaft and tunnel work but may not be the best soil improvement technique for longterm stability such as you require. For the longterm I would rely on a cementious grout. Sticking to the concept of permeation grouting, this would be the use of microfines. Remembering that microfine is in suspension, unlike the solution of sodium silicate, the permeation distances are not as great, especially since you are in a silty sand (SM). Therefore the use of microfine is less advantageous.

I would VE with the use of compaction grout or possibly look at jet grouting, whichever turns out to be cheaper. In terms of equipment usage and mobilization, compaction grouting is cheaper than both chemical and jet grouting.
In addition, permeation grout can be tricky at times, ie. not going where you intended, always taking the path of least resistance. I guess this is where you have had limited success with chemical grout in the past. Such is not the case with JG and CG. I assume you have borings defining the site stratigraphy, so to verify the effectiveness of the grouting program, pre and post CPTs should suffice.

 

[lallatin]

I think we need some more information before a best grouting program can be suggested, whether a single or combination procedure is used. Where is the water table? Is this an existing building, or is this a ground improvement stage prior to construction? Access has a lot to do with the economics of some procedures. You will get different recommendations from different practitioners, based on their degree of specialization in the field. As has been mentioned, careful charactorization of the sands/silty sands is important if permeation grouting is used. A simple compaction grouting may suffice.

 

[Prepakt1]

Thanks for all the help ,project on hold for present