Today I would like to discuss about site land survey works.

The normal practice is when the Main Contractor takes possession of a work site, they will engaged a license land surveyor to setup the position of the building or structure to be constructed and confirm the setback or clearances of the building to the boundary lines. After doing that the field surveyor team will established their control points using true coordinate’s survey. Having established their control points the can setup up the building grid lines immediately or later. The license surveyor field team will also set up temporary bench marks. The reduce level has to be transferred from the nearest ordinance point given by the government land survey department. After the land survey field work is done, the License Surveyor will prepare a drawing showing the coordinates of the land boundary points, position and coordinate value of their control points and temporary bench mark values and site location. 

The license surveyor has to then endorse and sign on the survey drawing and submit it to the Main Contactor for onward transmittal to the Architect’s, Owner, Site Office etc.

The Main Contractor’s site engineer or in-house surveyor has to verify that the temporary bench marks values are in order. Normally two or three temporary bench marks are given all the  Site engineer or in-house surveyor has to do is take a level instrument and check whether the bench mark values tally with each other before transferring into the site. Often the Main Contractor’s site staff makes the mistake of not checking and verifying the TBM values given by License surveyors.

There are many cases of site being built on a wrong platform level because of this carelessness. There are a few reasons why TBM given by a License Surveyor is wrong are, firstly the License Surveyor does not do the work himself, his field staff does the work but more often he subcontracts the work to third parties.

Properly the field staff has to transfer from a given or approve government ordinance point which can be a few kilometers away, but commonly practice by field surveyors is that they may have historical records of TBM previously done by themselves nearer to the site.

Another situation is third parties field surveyors either share or sell their TBM data and control point coordinates. Many of times these TBMs and control points may get disturbed for many reasons such as earth settlement.  

Another error that may occur is calculation errors. What I mean by this is that sometimes the nearest TBM may not be that near or the area topography may be undulating etc. and sometimes you may not get clear line of sight for your reading. This means you have to transfer your level instrument to a new position a few times. The more transferring of the level instrument station, the more room for errors there will be in staff readings, log entries and calculation.

As far as the Main Contractor is concern it is the responsibility of the License Surveyor’s responsibility and liability. All the Main Contractor has to ensure is that he has an endorse hardcopy of the License’s surveyor drawing. And that his site engineer or in-house site surveyor check whether the TBM values tally.