IOCL Refinery Surveys — Bongaigaon & Vadodara

Project Overview

BTPL carried out topographic survey at two refineries — Bongaigaon in Assam and Vadodara in Gujarat — for IOCL, through Geomaps, Faridabad / Tractable. The work covered topographic detail, as-built measurement of existing built fabric, and mapping of services traceable at the surface. Each refinery was surveyed on its own control framework and issued as a coordinated CAD dataset covering ground levels, existing structures and visible services.

What did the client require?

Survey work at an existing plant is brownfield work. New units, revamps, tankage, pipe routing, road and drainage alterations all have to be fitted into an estate that is already built. Records held for a facility that has been extended over its life do not necessarily describe it as it now stands, so design cannot rest on them alone. A measured topographic and as-built record puts ground and paved levels, structure and foundation positions, road geometry and the position of visible services on one coordinate framework, so that tie-in points, foundation locations, grading and drainage can be worked out against measured dimensions and clashes found on the drawing rather than on site.

What made this project challenging?

• Access to a refinery estate is permit-controlled, so the control framework had to be capable of extension into whichever area was released next.
• Plant structures break line of sight, ruling out continuous instrument setups across the estate.
• Obstruction and multipath around plant structures, where GNSS observation cannot be relied on and control has to be carried in by traverse instead.
• As-built detail that is reachable only in part, so what could be measured directly had to be distinguished in the record from what could not.
• Buried services that could be mapped only from surface evidence — chambers, covers, markers and the points at which above-ground runs enter the ground.
• Two plants far apart that had to produce one drawing set: separate site permissions and separate control at each, matching content, coding and format in the output.

How did BTPL carry out the survey?

Control came first at each refinery, and it was built to be extended. GNSS was observed where the sky was open enough to trust it; where it was not, traverse carried control into the parts of the estate that satellite observation could not reach. Heights were taken through the same observations, so that one framework served both plan and level at each plant. Detail was then captured by total station and RTK — ground and paved levels, roads, drainage, plinths, foundations, structures, walls and above-ground service routes — with feature coding applied in the field so that civil, structural and services detail could be separated later. As-built measurement worked from the same control, reflectorless where a face could not be approached, and a dimension that could not be taken directly was recorded as such. Services were traced between points visible at the surface and were not carried across a gap where nothing could be seen.

How was the data processed?

Three products had to be built at each refinery, and they were built separately before being brought onto one sheet. The ground surface came from the coded level observations, edited with breaklines along roads, drains, plinths and paved edges so that hard surfaces hold their built shape instead of being smoothed across. The as-built content was drawn from the same control as the topography but kept on its own layers, so that a measured structure position is never confused with general ground detail. The services content was compiled last, and compiled in two grades: features seen on site, and runs inferred between two seen points, each identified as such on the layer. Control reduction and adjustment preceded all three at each location. Layering, coding and sheet composition then followed the conventions agreed for the deliverable, so that the two refineries read as one drawing set.

How was accuracy verified?

Traverses carried into the plant were closed onto independent control at each refinery, and those closures were judged before any detail observation was taken up. Check points were then observed from a second, unrelated setup and compared against the detail already recorded. As-built dimensions that bear on a tie-in were re-measured directly wherever the surface could be reached; the ones that could not be reached are identified in the drawing as measured indirectly. The modelled surface was tested against the observed spot levels and against the breakline structure before issue. The services layer was read back against the field record, so that every run on the drawing traces to something that was seen. The two refinery drawing sets were then compared with each other for layering and coding, so that both plants are delivered in one convention.

What was delivered?

The dataset was issued for IOCL through Geomaps, Faridabad / Tractable: for each refinery, a topographic, as-built and services record in CAD, held on that plant's own control framework. Holding surface levels, existing structures and visible services together lets brownfield modification be planned against the plant as measured, with tie-ins, foundations, grading and drainage worked out on real dimensions. The services content is indicative wherever a run was inferred between surface points, and is issued to be proved by trial pit or other safe exposure before anything is dug.