Underground Utilities Survey

Document No:  D12#434742
 
Revision:  3
 
Date amended:  16-Jun-2014

The information below is intended to reflect the preferred practice of Main Roads Western Australia ("Main Roads"). Main Roads reserves the right to update this information at any time without notice. If you have any questions or comments please contact Nathan Miller by e-mail or on (08) 9323-4669.

To the extent permitted by law, Main Roads, its employees, agents, authors and contributors are not liable for any loss resulting from any action taken or reliance made by you on the information herein displayed.

 

Revision Register

Revision Register

Ed/Version Number Clause Number Description of Revision Date
1 All  Guideline Developed  27-Nov-2009
​2 ​All ​Content Cleanup ​5-Feb-2013
​3 ​Header ​Document Number Changed ​16-Jun-2014

Table of Content




1 BACKGROUND

Utility information plays a significant role in road planning and design. When a new road is designed or an existing road is modified, it is critical within the initial stages of the design that the location of utilities is known. Known utility information allows design processes to be established which ensures that the utilities are protected or moved and that unforseen additional costs can be minimised when the road is being constructed. Past problems associated with not locating utilities have resulted in complete roads being redesigned during construction or the cost of a road dramatically increasing due to the unforeseen cost of protecting or relocating an unidentified utility.

The Underground Utility Survey Standard 67-08-121 has been developed to provide Main Roads contract managers with a consistent approach to the acquisition of utilities and to make the collected data compatible with existing Main Roads design systems and practices. 

It is important to highlight that the utilities standard and guideline is a tool for gathering information on utilities and not a final solution for problems created by utilities.

All road projects encounter different issues when dealing with utilities. The Main Roads project manager, designer and consultant collecting information on utilities must work together to determine the best solution for their particular road project.

 

2 GUIDELINE FOR UNDERGROUND UTILITY SURVEYS

Most utilities are located underground. Unfortunately, the only definite way a Main Roads project manager can determine the true position of a utility is to unearth it ("pot-hole") and measure directly to it. As this is unrealistic to do for every utility in the project area due to cost, time and the possibility of damaging the utility, it is generally accepted that a number of utility searches and surveys will be performed with varying degrees of accuracy (and cost) over the design period of a road.  It is also not uncommon for the same utility survey to be performed multiple times if the time span from planning, to design, to construction is spread over a number of years.   

The Main Roads "Underground Utilities Survey Standard 67-08-121" has been structured to provide a number of different utility surveys accuracy classes (A, B, C and D). These classes address the different types of utility surveys available during the design process and are presented as a series of options, not a course of compulsory action. 

The following is a brief description of the accuracy classes within the Underground Utilities Survey Standard 67-08-121.


2.1 Class D utility survey

A Class D utility survey is the most basic utilities search request and is the first step toward collecting utility information on a project. It requires a consultant to identify all the utilities within a defined road project area. The consultant will contact "Dial before you dig" and other unlisted utility providers on Main Roads behalf to collect all known existing drawings, plans and digital utilities data. As utility information comes in many different formats, the information must be converted by the consultant into a format that Main Roads can utilise in its existing planning and design software.

The Underground Utilities Survey Standard ensures that the data is transformed into the local project coordinate system (local project grid), with Main Roads string and point codes and presenting it in MX gen file format. The consultant then provides this data with a report outlining the essential background information on the collected data (Metadata).

It is also important to note that the accuracy of Class D data is unverified. Its actual position underground may differ greatly from what is denoted on a plan or within the originally provided digital data from the utility provider.



2.2 Class C utility survey

A Main Roads Class C utilities survey is a Class D utilities request (as above) but additionally  is performed in conjunction with a standard (above ground) ground survey or (aerial ) mapping request. The below ground utilities data (pipes etc) is then adjusted to match the surveyed above ground services features (man hole, breather pipes etc). A Class C utility survey does not guarantee the location of the underground service even though the data is altered to match above ground surveyed objects (i.e. pipes adjusted to fit survey man holes, breather pipes etc). 

Underground utilities data can be extremely hard to interpret and can sometimes be difficult for the utilities consultant to determine which underground feature matches with above ground surveyed features. Previous utility work has shown that services may not travel the shortest possible distance between known manhole lids and that pipe directions can change underground due to under ground barriers. Additionally, utilities do not always join the centre of man holes or can run past above surface features. Therefore the consultant providing the underground utilities data can not guarantee the location of the utilities. For these reasons the collected Class C utilities data is labelled as "unverified" as the utilities information is only considered as an "assumed" location of a utility given that it has not been measured. 


A Class D or Class C utilities survey should provide enough information to the Main Roads project manager to determine if there are utilities within, near or crossing the Main Roads project area. Where any utility from the Class D or C utility survey is identified as potentially impacting a road design, or crossing a road alignment, then an additional utilities survey of a higher order and cost (Class A or B) will be required.

To assist the project manager to accurately locate these utilities and provide survey options for collecting utilities at a higher accuracy, a description of Class A and Class B utility surveys have been provided. 



2.3 Class B utility survey

A Class B utility survey requires the underground utilities to be surveyed indirectly. An indirect survey can be performed by a number of different survey techniques. These can consist of methods such as ground penetrating radar and frequency resonating survey etc. An indirect survey consists of a method that does not require the utility to be unearthed. It must be noted that from this type of survey, the ground conditions, the depth of the utility and the material the utility is constructed from can affect the final accuracy on the location of the utility. 

Accuracies to be achieved are typically plus and minus sign.GIF0.1 m for distances less than 1.2m under the surface and plus and minus sign.GIF0.3m for underground depths greater than 1.2m. These accuracies are nominal and may vary due to different techniques being employed to locate the utilities.

Importantly, a Class B utility survey does not disturb the underground utility. The integrity of the utility will not be compromised and does not have the same problems related to safety or potential damage when a utility is unearthed.



2.4 Class A utility survey

A Class A utilities survey is requested on pre determined utilities that have been identified in a Class D or Class C utility survey that may be in direct conflict with the road design. A Class A utilities survey requires the utility to be "pot holed" (exposed) and directly measured by a total station, theodolite or RTK GPS instrument.  The accuracy for locating the utility is plus and minus sign.GIF30mm for x, y & z. 

The cost for performing this survey is high as the utility is located underground and requires machinery and authorised officials to unearth it. Additionally, the amount of data produced from this survey is restrictive due to the amount of the utility that can be unearthed. A Class A utilities survey is costly and involves the danger of trying to expose and measure the utility without damaging or affecting the integrity of the utility in any way.

It is important that the Main Roads project manager and the utility consultant work together to economically determine where the utilities are located. Assumptions on pipe directions and joins to manholes and structures must be minimised and all practical efforts must be made to minimise disruption or damage.

Utility data gathered under Main Roads Class A is considered to be "verified" as the utilities have been directly measured and its position has been confirmed underground.



3 Main Roads Project manager minimum requirements on requesting a utilities survey

When requested a digital utilities model the Main Roads contract manager and engaged consultant must work together to successfully and efficiently achieve the best outcome. 

To help achieve this, the Main Roads contract manager must provide to a consultant the minimum information;

  1. A brief description of the Main Roads project. (e.g. Main Roads is widening the road to provide additional lanes.
  2. Provide a clear outline of the utilities search area. This can be by either providing a digital coordinated boundary string or a diagram with an outline of the utilities search area. The diagram is preferably to be constructed from aerial imagery overlayed with cadastral boundaries.   A diagram will define without question the search area to be used by the consultant.
  3. State that a utilities survey is to be performed in accordance with the Underground Utilities Survey Standard 67-08-121
  4. Nominate a utility quality class A, B, C or D. At least one class level must be requested from the consultant when procuring utilities data. This will indicate to the consultant the level of detail and accuracy that the utilities data is required. It also dictates the amount of work the consultant will perform and will provide a better indication of costs that will be incurred. 
  5. Provide details about existing utilities that the Main Roads project manager is aware of. This may assist the consultant in searching for standard and non standard utilities data. 
  6. Provide details of the specific project coordinate zone that covers the area of request. This enables the consultant to provide the data in the correct local project coordinate system and will enable the designers and planner to directly overlayed the utilities data over the design. 
  7. Provide Main Roads road number and SLK's to allow Main Roads data lodgement policy to be followed for data files. 
  8. State if hard copy plots are required to assist with providing an over view of the area.
  9. Provide support to the consultant if required with respect to entry onto land.
  10. Identify any environmental constraints and/or responsibilities.


4 Utilities Consultant minimum requirements on providing a utilities survey

Under the Digital Utilities Standard the consultant must provide the Main Roads project manager the following items:

  1. The digital utilities data. This must be formatted using Main Roads string codes and in MX file format.
  2. A digital boundary string denoting the area the utilities search was performed in.
  3. A utilities report as outlined in the digital utilities standard "9. Utilities Report".
  4. The original raw utilities search data as received from the utility providers.
  5. Any hard copy utilities plot - if requested.

A utilities search can be requested from most survey companies. For questions related to utilities data or survey companies capable of collecting utilities data, the Main Roads Data Manger can be contacted.