UNDERGROUND UTILIITIES/SERVICES GENERAL INFORMATION
Before any work is to proceed with excavations, a service location must be performed. A general look over the work area is needed to provide an insight into the likelihood of things that could go wrong.
High pressure gas, certain optic fibre, high voltage 33KV and above, and other utilities may require consultation and site visits from the asset owners. Service assets owned by some authorities (Councils) and domestic services are some examples of services NOT shown on DBYD plans.
In NSW, DBYD (Dial Before You Dig) is law. The plans that you receive from the Utility/asset owners are classified under AS5488 as Quality Level D. There are 4 types of information relating to sub-surface utilities.
On 1 July 2010 New South Wales became the first Australian jurisdiction to enshrine Dial Before You Dig in law. The formal name for the legislation is the Energy Legislation Amendment (Infrastructure Protection) Act 2009.
AS5488 (Classification of Subsurface Utility Information)
2.4 QUALITY LEVEL D
Quality level D is the lowest of the four quality levels. DBYD is Level D- the lowest quality information.
2.5 QUALITY LEVEL C
Quality level C is described as a surface feature correlation or an interpretation of the approximate location and attributes of a subsurface utility asset using a combination of existing records (and/or anecdotal evidence) and a site survey of visible evidence. The minimum requirement for quality level C is relative spatial position.
2.6 QUALITY LEVEL B
Quality level B provides relative subsurface feature location in three dimensions. The minimum requirement for quality level B is relative spatial position.
2.1 QUALITY LEVEL A
Quality level A is the highest quality level and consists of the positive identification of the attribute and location of a subsurface utility at a point to an absolute spatial position in three dimensions. It is the only quality level that defines a subsurface utility as 'validated'. This is Potholing/strip trenching of a service. Even this can have the potential for error.
COMMUNICATION IS A CRITICAL FACTOR.
Service assets owned by the authorities and domestic services (owned by the consumer) above and below ground are some of the assets at risk with excavations. Machinery may also be at risk of damaging thrust blocks, hooking the bucket onto a collar of a pipe or tube, unknown non-metallic services not on completed plans without continuity of tracer wire(s), buried tanks sometimes under pressure, trenching alongside services that have been directional bored, mine working voids, deep services for road crossings, shallow services under concrete, shallow services due to change of grade or change of ground levels and authorities not subscribing to Dial Before You Dig or not realising that they have assets in your work area.
Likely services that you will encounter can be broken into two groups, pipes and cables. Pipes consist of water mains carrier, local feeders and domestic branch lines usually square off the main. Some areas have their own mains i.e. vineyards. Gas mains are sometimes inserted inside older metallic infrastructure or direct buried nylon tube with no warning tape and/or tracer wire. The smaller nylon gas tubes have a very thin wall and are very easy to damage. Sewer and stormwater can be untraceable and deep. Cables can be direct buried with/without mechanical protection or in conduits. They consist of power cables, sometimes high voltage and/or communication cables. Sometimes cables can be buried in a loop near a pole or kiosk. Not all power cables are on Energy provider plans. Fibre optic cables may be untraceable if not screened or have a metallic core extruded into it during manufacture. Sometimes they have a TR marking on the plan to indicate a transponder has been buried with the Optic Fibre which can sometimes be traced or an M on the plan to indicate a marker. Other communication companies have separate plans of their assets, that’s why it is important to check the Dial Before You Dig cover page listing asset owners.
Plant is required to have these minimum distances from aerial conductors.
3M - For voltages up to and including 132,000 volts (<132KV)
6M - For voltages up to and including 330,000 volts (132KV-330KV)
8M - For voltages above 330,000 volts (>330KV)
If workers are required to be in a trench more than 1.5M deep, the sides of the trench must be battered at 45 degrees, or shored up with a trench support system. A cubic metre of soil weighs at least 1.4 tonnes.
When excavating, the material (spoil) must be kept at a distance, so as not to collapse the trench or hole. It is recommended that the spoil be deposited at least the same distance from the excavation as the intended depth. It shouldn’t be stacked higher than the depth either. Due diligence must be exercised by a competent operator and always have a competent spotter supervising the excavation. The spotter shall be competent and experienced in all facets of supervising machinery excavations relating to underground services. Authority may be required when digging too close to high pressure gas mains, fibre optics and buried cables above 11,000 volts.
Only buckets with blade instead of teeth to be used when potholing services under strict supervision by a competent spotter.
Excavation to take place with blade in vertical position.
Vacuum excavation can bea safer approach to excavating buried utilities than backhoes and excavators, but at an increased cost. Air/water systems SHOULDN'T be used below cover strips, tiles or pre-cast blocks of electrical cables. If this happens the cable bedding must be reinstated with sand or other soft materials. Care must be used on older cables, or when locating cable faults so as not to damage the cable jacket or wrapping as high pressure air/water can penetrate through a damaged sheath. Fibre optic cables are often very small in diameter and hard to see if direct buried (no conduit). They are very delicate and the liabilities if damaged are astronomical. Precautions must be used so as to not undermine any services, roads, thrust blocks etc. The material must be tampered for compaction at intervals to avoid sinkage on reinstatement.