Q.: Is there any research data about the levels of chlorides (salts) in soil that will cause damage to concrete and rebar?
A.: Chloride does not, in itself, damage concrete or metals embedded in concrete. It does make damage from cyclic freezing worse if the concrete is so exposed. The presence of any chloride in concrete has the potential to promote corrosion of embedded metal. The effect of chloride on concrete in soil will depend not only on the amount of chloride in the soil, but also on the permeability of the concrete. The extreme would be concrete exposed to seawater. If the soil in question is a former marine environment, then the presence of chloride is probably your least concern.
Corrosion of embedded rebar is of major concern with reinforced concrete exposed to soils containing chlorides. The permeability of the concrete will have an effect but this will only be a “time” effect. If chlorides are present in any but the smallest amounts and there is even a little moisture in the soil, then corrosion of embedded steel will eventually take place. With relatively impermeable concrete, the onset of corrosion will be delayed, but that is all.