Implications of LEP Results for SO(10) Grandunification with Two   Intermediate Stages
  We consider the breaking of the grand unification group $SO(10)$ to the standard model gauge group through several chains containing two intermediate stages. Using the values of the gauge coupling constants at scale $M_Z$ derived from recent LEP data, we determine the range of their intermediate and unification scales. In particular, we identify those chains that permit new gauge structure at relatively low energy $(\sim 1\, {\rm TeV})$. 
N.G. Deshpande, E. Keith, Palash B. Pal