In this paper, we present recent experiments conducted with two 87Sr optical lattice clocks operated at LNE-SYRTE. We report on the first calibrations of TAI with optical clocks, a necessary step towards the redefinition of the SI second. Additionally, we report on the experimental realization of a cavity-assisted non-destructive detection whose improved signal-to-noise ratio can improve the stability of optical clocks by reducing the Dick effect instability contribution, possibly beyond the quantum projection noise. Finally, we discuss the possibility to operate lattice clocks with semi-conductor sources as a lattice trap laser, by evaluating the frequency shift induced by their incoherent background light.