Chris
I have had the same problem with such a tool - the soil was heavy. So
fork and brush in a high grit sand mix to improve drainage. Normally 2
parts grit sand to 1 part peat or loam - if the soil is heavy could
increase to a 5:2 mix,
This task is best done in the autumn to improve drainage over winter,
rather than now, However - can do it now and repeat in the autumn.
There are powered types you can hire that produce satisfactory results
Good luck
Clifford
Bawtry, Doncaster, South Yorkshire