Rehabilitating underground pipes with expanding helically wound liner

A method of rehabilitating underground pipes (1) using a lining consisting of a helically formed liner pipe (5) made of a synthetic resin, which comprises the steps of:

• (a) forming a liner piper (5) by winding a strip (4) made of a synthetic resin into a helical shape around a virtual cylinder, so that the side edges of the convolutions of the wound strip (4) are interengaged with each other;
• inserting a slip restraining member in the form of a wire rod (6) continuously to the interconnected edges of the convolutions of the said strip (4), and then removing the said strip (4) when the diameter of said liner pipe (5) is to be increased at the same rate as said strip 94) for forming said helical liner pipe (5) is conveyed;
• (b) continuously introducing said liner pipe (5) into an underground pipe (1) while said liner pipe (5) is being advanced inside the underground pipe (1);
• (c) fixing the leading end of said liner pipe (5) to the underground pipe when a required length has been advanced;
• (d) further advancing said liner pipe (5) inside the underground pipe (1) with its leading end fixed to the underground pie (1), so that the wound strip (4) is allowed to slide around the virtual cylinder with its side edges still being interengaged with each other, resulting in the gradual increase in the diameter of said helical liner pipe;
• and (e) injecting a backfilling material into the space between the outer surface of said liner pipe (5) and the inner surface of the said underground pipe (1) by moving a nozzle (22) for supplying the backfilling material in the direction of the axis of said liner pie (5) synchronously as said rod is withdrawn and the increasing diameter is shifted in the same direction.