What is the meaning of R88/70D in this METAR from Ashgabat International airport?
I assume it was a typo, as R88/70D is not a correct METAR format. According to this website with historical METARs the METAR of today at 1300Z at UTAA was:


  METAR UTAA 071300Z 13006KT 9999 FEW050CB BKN050 BKN100 15/06
             Q1013 R88/CLRD70 NOSIG=


All other METARs from UTAA today contain "R88/CLRD70 " as well. 

R88/CLRD70 means: all runways are cleared (no more deposits), and a friction coefficient of 0.70.