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Original Ground Level (OGL) Survey

posted Jun 16, 2018, 8:08 AM by jeffery jim

It has been an interesting week where some are still not sure why OGL survey is extremely important in civil or infrastructure construction. Apart from that, i just noticed that many (even senior engineers) are not sure when OGL survey should commence.

When we look into the road work specifications which form the contract or covenant, it is not directly spelled in certain clauses; instead it is something associated with pre-emptive act and opportunity which supposedly dictate or executed with the discretion of the superintending officer (SO) in order to disallow contractors from delaying physical works and benefits clauses for LAD in relation to government workmen or tradesmen. That is the tactical part of contract administration.

For engineering perspective, OGL survey is essential as a validation activity which confirms the initial LIDAR or survey conducted during the design stage. From my experience, LIDAR survey is not conclusive or accurate when it comes to area covered by forest canopy. The conventional or topography or terrestrial survey too comes with a lot of issues which leads to accrued inaccuracy with more than 12mm per station.

Among the issues which render the importance of OGL survey prior to actual physical works are to establish the validity of the actual surface and the early design change prior to physical works. I encountered a project which involved land acquisition issues. In order to avoid land acquisition for a water pipeline project involving a big chunk of land which was delineated as pipeline right-of-ways and for 2MLD storage tank; the plantation company decided to flatten the hill in order to avoid their land being acquired. This causes the project to delay when the design need to be revised and tremendously increased the project cost (read clause: 44. Claims for Loss and Expense in PWD Form 203/203A) as a result of approved extension of time (Read Clause 43 and Clause 5, PWD Form 203/203A).

OGL survey have a prominent impact when it comes to Bill of Quantity where it established the payment for items under soil stripping, cut/fill or earthworks and embankment works.

OGL survey cannot be done after soil stripping and grubbing. It doesn't reflect the actual quantity and will lead to pointless argument between the SO and the contractor when the thickness is clearly stated (as 150mm or otherwise stipulated) and the actual quantity of earth work is the total quantity generated by design software minus the fixed top soil stratum.

Secondly, soil stripping works involve earthwork when it commence. You cannot trim or strip 150mm on hills with 4:1 surface or gradient without making terraces which is actually earthwork stage. Therefore, OGL survey will have to commence and take precedence in earthwork stage before other physical activities.

The right or appropriate time to conduct OGL survey is upon site possession, before environment department give a green light to go ahead or despite compensation is yet to be paid in full (and as the basis for ROW to be established, legally possessed and handed over to the contractor). It plays important role as in to validate established TBM properties, traversing and partly to establish beacons for surveying work for future earthwork phase.