Reference Specifications for Civil Engineering Work 2001

4.trenchless technologies

General

Refer Annexure. There are numerous methods available for the installation of underground services without the need to excavate a trench. There is no single trenchless technology method that is best for all types of crossings. Site conditions and constraints as well as the purpose of the crossing must be considered when a method is selected. Trenchless technology methods that may be approved by Council include the following:

Auger Boring;

Slurry Boring;

Micro-tunnelling;

Horizontal Directional Drilling;

Pipe Ramming;

Pipe Jacking; and

Thrust Boring.

Execution

Undertake boring or jacking by specialist operators with experience in similar works (diameter, length, ground conditions), using purpose-made equipment capable of maintaining correct lines and levels of completed conduits. Ensure a tight fit to the service pipe or casing.

Protective conduits, concrete encasement, ducts or enveloping pipes

Extend protective casing a minimum of one (1) metre beyond batters and table drains and a minimum of 300mm beyond the rear of existing or proposed kerb. Provide protective casing to all pressurised services (such as high pressure gas, combustible fluids, water mains and rising sewer mains); any service that conveys potentially hazardous substances which may be damaged during construction or maintenance operations; and in any one of the following instances:

Where the cover provided is less than minimum requirement.

Near the footings of a bridge or other structure.

Near other locations where there may be a hazard.

The protective casing shall be either class 4 reinforced concrete pipe or steel pipe designed to withstand the pressure in the carrier pipe should it fail.

Cased bore hole: The diameter of the bored hole must not exceed the diameter of the pipe or service by more than 50 mm.

Uncased bore hole: The diameter of the uncased hole under pavements must not exceed 100 mm unless the void surrounding the pipe or service is filled.

Cavities and voids: Fill cavities and voids by pressure grouting. Fill voids between the bored hole and the pipe or service where the diameter of the bored hole exceeds 200mm with non-compressible material. Where required by the service authority, fill voids between the service and the enveloping casing.