Tyre pressures on stony roads

Hi All, we are about to travel into Karijini National Park. Normally we have been reducing our tyre pressures on the van and the cruiser to around 28psi and this has served us well down the Strezlecki and Gibb River Roads except that very unexpectedly we had a blowout on the road into Bell Gorge off the GRR. The road was pretty solid and stone free in the centre but a bit of loose stuff had gathered at the edges. Close inspection and tracking back after the blowout caused us to suspect that the van tyres cut into the loose stones on the edge and the very sharp pointed stones cut the wall which let go approximately 100 metres further down the road. This leads us to suspect that the "bagging"of the walls made them vulnerable to this type of damage with sharp rocks. From memory of 6 years ago, the roads in Karijini have very similar sharp triangular stones and we are concerned if we follow our usual practice of dropping pressures we may have more tyre problems.
I was wondering if anyone else with experience would share their opinions on whether to drop pressures in this area or not?