An excavated opening (10) through a pavement (12) of a highway and through the underlying base material (14) to expose a gas main (16) is filled by (i) mixing on site cement, foaming agent and water to produce a fluid grout (26), (ii) mixing the grout with loose excavated spoil (22) in the opening, (iii) agitating the mixture using a hand-held poker vibrator (30), (iv) and repeating this procedure until the level (40) is reached. The level (40) corresponds to the underside of a protective layer (50) which is subsequently applied. The majority of the excavated loose spoil from the opening is reused.