I’m involved in designing a liquid filled fuel delivery pipe network, buried 3m underground. I am considering NOT to install thermal relief valves, but this is dependent on how big thermal fluctuation temperatures are at that soil depth over a given period, say 4-, 12- and 24-hours.
Anyone know where I can access public domain information or purchase QC’d data for Malaysia?

I am researching on soil temperature vs depth profile in Malaysia too. I wonder if you have found anything useful so far?
Anyway, I have found the paper “Soil temperature regimes under mixed dipterocarp forests of peninsular malaysia,” Pertanika 9(3),277-284, (1986). which has a small study on the temperature vs depth.
If you have more, appreciate sharing…