In the 1970s Teixeira Duarte started a partnership with the French company Soletange Bachy, who brought know-how and experience in the area of Geotechnics and Foundations, which Teixeira Duarte did not renounce to keep specialised in. Its teams included several French colleagues and directors who contributed to the development of the activity, particularly in this area, known internally as "The Speciality" - following the intention of its founder 50 years earlier.