I have 100sqm of lawn on land that does not drain ..... I installed performance pipes and suds crates .. but once it starts raining all that does is delay things .. then they fill up and after that ground is saturated.
I came across a project one guy did where he drilled vertical holes with a powered auger .. filled with chippings all to improve drainage.
https://www.youtube.com/watch?v=5R8StYZQi_8&t=13s
My ground was built up by around 8-10m to create a railway siding in the 50's ... they used a lot of stone & slag from steelwork to provide infill.
I don't think the small handheld unit will work - as soon as it hits a stone it will go off at a tangent.
Anybody know if you can hire a small tracked machine with a hydraulic auger ..... indeally only want to drill 150mm holes.