Steep incline pipelaying
Laying of ductile iron mains on steep inclines can be performed in two ways:
– using concrete blocks for each pipe,
– using a concrete block at the head of an anchored length.
Beyond a certain angle, the friction between a main and the ground is insufficient to hold the main. The longitudinal gravitational movement then has to be counteracted by the use of anchor blocks or anchored joints, or a combination of both techniques.
In simple terms, it is found that a main needs to be anchored when the incline exceeds:
– 20 % for a surface main,
– 25 % for a buried main.
Anchoring every pipe
This technique is quite suitable for surface mains.
An anchor block behind every pipe socket.
Sockets point uphill to take purchase on the blocks.
A clearance of 10 mm is left between the spigot end and the back of the socket chamber to accommodate expansion (usual EXPRESS and STANDARD joint laying conditions).
Anchoring with anchored joints
This technique is quite suitable for pipes laid below ground. It consists of anchoring a section of anchored pipes:
– either by an anchor block situated behind the socket of the leading pipe,
– or by an additional anchored length installed in the flat section behind the uppermost bend.
The maximum axial force is supported by the first anchored joint below the block. This force is a function of the gradient, and also of the length of the anchored section. The maximum permissible length therefore is defined by the strength limit of the anchored joint.
Note : If the length of the incline exceeds the permissible anchored length, the descent can be made in several independent sections, each being anchored at its head with a concrete block. The end joints of the sections are not anchored in this case.
Note : The main must be laid downhill starting from the highest point, so that the self-anchoring system is fully engaged and tensioned.