"- Soil variability. Very different techniques are required for different soils. Sometimes the soil has to be "conditioned", adding something to make it solid e

"- Soil variability. Very different techniques are required for different soils. Sometimes the soil has to be "conditioned", adding something to make it solid enough it can be drilled through.[1] This is the biggest practical problem in tunneling. Too much water is the usual problem." Too much water won't be a problem on Mars... where I think the end-game here is for Musk on why he's learning how to build tunneling machines.