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I have a rather unfortunate problem, rats got into my crawlspace and managed to tunnel directly underneath one of the internal piers(there are quite a few down there, maybe every 8 ft square?

I am in the process of collapsing their tunnels but this will need to be fixed, the pier isn't very deep(maybe 6 inches in ground?).

How would you recommend fixing this issue?

If I could build a form around the pier and inject concrete into the tunnel I suspect this would be sufficient but I don't know. I don't know of any mini concrete pumps though.

Suggestions?

I should also say this is a 1 story house built in the 70s, pretty low load.

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Don’t collapse the hole under the pier fill it with sand use water to flush the sand and pack it, I have found adding lime to the mix keeps them from tunneling.

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  • Right, but I'd actually use concrete if possible. By collapsing the burrows or pushing in sand you leave "disturbed soil" under your footings. Footings are to be poured on "undisturbed soil". By extending the footing with concrete you eliminate that condition. – isherwood Feb 26 '20 at 14:11
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    Getting concrete to flow is the problem, sand will flow with water and fill the void depending on soil conditions it may take a time or two, we used to use this method on large pools that started cracking, we had to drill sump holes to pull the water out but sand is very effective, lime makes the soil unfit for most critters as it burns there skin just like it does ours. – Ed Beal Feb 26 '20 at 14:43
  • hmm, how would I encourage the concrete to flow in? – FourierFlux Feb 27 '20 at 2:06
  • Adding water is the only way but then it is not much better than sand and lime. If you want to use something with Portland cement and sand that will flow but may create voids as the excess water dissipates, possibly vibrating but that may collapse the holes, if it does you can shim the post or install a new 4x4, I have had to shim my 1930 farm home every other year in different places, just setting not critter holes so far. Pier blocks added with perimeter foundation just a few years back. – Ed Beal Feb 27 '20 at 6:34
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You may want to consult a local contractor that specializes in foundation repair or foundation "jacking". They often use the technique of "concrete injection" to lift sagging slabs or footings and would likely have experience with a situation like yours.

If you want a DIY solution, you can probably support the area with some temporary piers, remove the damaged one and re-pour it. Often this requires cutting an access hole in the floor which, of course, will need to be repaired as well.

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  • I do agree with a larger area but pier blocks really do not have enough area to Jack like a slab and there is not enough room for even screw jacks piers are easier to replace if something like sand or a dig out and re pour but that would be my last option. – Ed Beal Feb 27 '20 at 6:40

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