Grouting vs Underpinning
Compaction Grouting vs Sinkhole Underpinning is the most commonly debated topic in the world of sinkhole repair. As a sinkhole repair method, proponents of both sinkhole repair types believe that one is always better than the other . Those that take up this argument are usually staunch supporters of their own chosen favorite and tend to disregard all the positive points of the opposite sinkhole stabilization method. Let’s take a look at both of these.
Compaction Grouting is the process by which grout material is pumped under pressure via steel casing to depths starting at the limestone layer beneath every house. Once that initial layer is filled then the steel casing is slowly extracted a few feet and pumping recommences until that layer is filled and the same scenario is repeated until anywhere from ten to twenty feet below the house is reached where pumping stops and the steel casing is removed from the ground.
The goal of this repair method is to cap and seal the top of the limestone layer and to fill any and all voids found in the soil structure. Compaction Grouting does not support the structure directly but indirectly by increasing the soils bearing capacity beneath the home. This sinkhole repair method works on the fact that by correcting the sinkhole conditions that caused the sinkhole damage in the first place, the home is now stabilized since all that material has been injected beneath it. Once the voids are filled, there is no where for the surficial soils to sink into.
Sinkhole Underpinning is a method of sinkhole repair where foundation supports called piers are placed all the way around the perimeter of the property (and sometimes inside too!) to support the load bearing components of the house. With these steel piers, houses can be raised back where elevations have dropped and structures can be re leveled. The best way to imagine this process is to think of a beach house, only all the steel piers are under the ground (and much deeper).
Here holes are dug where the steel piers are to go. The brackets are placed in the holes and a hydraulic drive assembly is placed on top of the bracket driving the pier sections down deeper and deeper. Driving stops when the pier stops it’s advance and the house starts to lift which is usually limestone or similar competent load bearing strata.
You notice that the deeper soil conditions have not been improved but on the other hand, the structure is now directly stabilized which means that the load of the structure is transferred off the weaker soils down to refusal.
So which is the best?
Saying that one method over the other is always the best way to do things every single time is senseless. Both methods have their strengths in the right scenarios. Engineer’s have multiple tools in their toolbox, it’s up to them to choose the right repair method for the structure and the soils beneath it. The ultimate goal that the engineer’s want to achieve is the stabilization of your home from further movement. Sinkhole underpinning, compaction grouting, chemical injection, grout injected piers, helical piers, internal slab supports, pressure grouting and other methods are all available to engineer’s to help them reach their goals.