Ground moving like a water bed help"!"

[BIGBOF]

hi ,I have removed a old concrete base (4" thick)from a old garage and aproxx 4" of soil from under that .everything was going ok until i noticed that under the 1.5 ton mini digger the ground appeared to to be spongy moving like a water bed (mostly where the digger had being working the most)
Is this because ive aggravate ground close to the "water table"
there is no water coming to the surface and lifting the nearest manhole cover every thing is flowing fine there

it appears the day after its hardening slightly

what have i done !!!

 

[carryoncamping]

Sounds like liquefaction, possibly due to the vibration of the digger.

 

[Static]

Is it the ground below the removed slab you are worried about, as that soil hasnt seen the light of day for years and a little water will cause local heave.

 

[BIGBOF]

Looked at some web site regards liquefaction and it appears to be that will it fix itself i will be putting a new conc base down as the old garage is changing from a single to a double

thanks for replies