Adding more solid to a solid/gas equilibrium
The concentrations of the solids change only negligibly with temperature or other reaction conditions and so are involved in the equilibrium only as constants. The amount of solids present does not change the concentration of each solid in its crystal structure. Therefore the equilibrium of the reaction is written as:  

$\mathrm{K = constant}\times \ce{[CO2]}$ 

If one of the reactants ($\ce{CaCO3, CaO, CO2}$) is not present, there is no equilibrium.