OTC-30547-MS

Innovative as-Built 3D Model and BIM of Subsea Objects Using BasicSensors – Application to Seawall Concrete Armour Units

Yoann Bugnet, COLAS SA – International; Steven Le Bars, Vincent Macaigne, and Timothée Launay, ID OCEAN;Thomas Vessiot, VINCI CONSTRUCTION; Rémi Cartier, HYDROCONSULT

Copyright 2020, Offshore Technology Conference

This paper was prepared for presentation at the Offshore Technology Conference originally scheduled to be held in Houston, TX, USA, 4-7 May 2020. Due to COVID-19the physical event was not held. The official proceedings were published online on 4 May 2020.

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AbstractObjectives/scope: The control of monolayer concrete armour units on coastal protection breakwaters can betime and cost consuming, especially underwater. It is even more the case when - for maintenance and controlpurpose - they are conducted long after the completion of the construction (positioning issues, number ofunits to control, etc).

However, this occurs frequently on construction projects which last for several years, or during theoperation and maintenance of such structures. On top of that, the complexity of this type of projects - usuallycoastal constructions such a dike easily exceeds 6000 units/km - requires precision and productivity for thecontrol inspections.

As a result, specific control solutions have been developed on the NRL project to inspect and monitorthe breakwater after its construction.

Objectives/scopeThe control of monolayer concrete armour units on coastal protection breakwaters can be time and costconsuming, especially underwater. It is even more the case when - for maintenance and control purpose- they are conducted long after the completion of the construction (positioning issues, number of units tocontrol, etc).

However, this occurs frequently on construction projects which last for several years, or during theoperation and maintenance of such structures. On top of that, the complexity of this type of projects - usuallycoastal constructions such a dike easily exceeds 6000 units/km - requires precision and productivity for thecontrol inspections.

As a result, specific control solutions have been developed on the NRL project to inspect and monitorthe breakwater after its construction.

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Figure 1—Typical concrete armour units used on the project NRL

The NRL project takes place at La Réunion island (Indian Ocean). It is due to replace the current coastalroad, which was built at the toe of a 100m high cliff. Indeed, after heavy rainfalls, rocks are falling fromthe cliff. The road is also usually closed during storms as the road is submerged by the sea on one side,and by rainfalls on the cliff side.

The objective of the project is to build a new road at sea to secure this vital economical axis between thecities of Saint-Denis - the island capital - and La Possession.

The road is erected on several breakwaters built by GTOI (Bouygues), SBTPC and VCT (Vinci) with atotal length of 6.7 km (Phase 1 + Phase 2). They are coupled with a 5.4km bridge at sea.

Monolayer precast concrete armour units, composing the protective revetment of seawalls, must be placedaccording to a specific pattern and interlocked according to the patentee specifications.

Figure 2—Example of the New Coastal shoreline road Seawall on the left, Armour unit on the right

For example, to be correctly set up, each precast armour unit must have at least 3 contact points with itssurrounding neighbours – except for the bottom and the top lines.

There are also some forbidden laying configurations. If these rules are not applied properly, the risk tohave structural damages during storms may be significantly increased.

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Figure 3—Breakwater partly damaged

As the swell induces efforts throughout the structures, the assembly pattern evolves and needs to beadaptatively monitored during its operational lifetime by subsea inspections.

The classic way of monitoring these is to deploy both divers and ship/drone for survey. Depending onvisibility and weather conditions, surveys and inspections by divers may be time-consuming, e.g. aroundtwo weeks for a 500-meters dike.

In the end, the subsea inspection deliverables are:

• subsea video (not georeferenced - but divers record approximately where there are supposed to beconsidering the laying drawing on a slate)

• High resolution multibeam bathymetry point-cloud:

Figure 4—Bathymetry point cloud on the left, diver subsea video on the right

Interpreting this kind of data represents a lot of time for quality control engineers and sometimes datado not allow objective conclusions to be drawn. To shift these limitations, an automated as-built 3D modelof a concrete armour units seawall has been developed by ID OCEAN for the New Coastal Road (NRL)project in Reunion Island.

It is fed by existing georeferenced point-cloud provided by bathymetric and UAV photogrammetrysurvey. This survey data is accurate and rapidly acquired. The developed numerical tool, named SEABIM,enables to create a digital twin of the breakwater in order to give a global view of the infrastructure, toidentify and highlight structural issues, and ultimately to enable quality department to schedule localizedsubsea complementary inspections. Quality control engineers process all the identified cases through a fullyintegrated BIM (Building Information Modelling) approach.

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Methods, Procedures, ProcessInput data which is used by the SEABIM algorithm is common point cloud from multibeam bathymetricsurvey/UAV/laser boat survey. A patented shape-matching algorithm was developed to create an as-built3D model based on the automatized recognition of concrete armour units deducted from their visible partsin the point-cloud.

The algorithm can be used with any type of concrete armour unit with a regular known 3D shape.SEABIM also enables to carry-out automatic numbering of armour units on the seawall based on layingdrawings numbering. It can also characterize the laying pattern quality and automatically apply colour codesfollowing determined criteria such as the number of contact points with its neighbours for every singlearmour unit.

For accuracy evaluation, the distance between vectorized 3D models and point-cloud is calculated on eachblock for match quality control and eventually applying a warning filter wherever poor position matchingquality is computed.

Figure 5—Step 1 – Input data: a survey point cloud

Figure 6—Step 2 – Concrete block positioning and numbering

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Figure 7—Step 3 – Virtual 3D building quality check – distance between model and point cloud (blue: inf 2 cm)

Figure 8—Step 4 – Characterisation of laying pattern quality (contact between concrete blocks)

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Figure 9—Interlocking / Contact points identification and characterisation

Whenever required, the critical areas are then inspected by complementary georeferenced visual survey(divers’ control, echo-acoustic ROV inspection, georeferenced optical camera). These surveys producefurther 3D data which can be inserted as an additional as-built control layer into the software (3Dreconstruction from photogrammetry of waterline or broken block for example).

A specific ROV inspection methodology (Georeferenced by Short Base Line system) has been engineeredto minimize costs and to reduce safety and environmental risks. By comparing 3D models generated bypoints clouds acquired through time, SEABIM can be used to follow-up armour units displacement overa certain period and give a colour code to each block in function of its displacement value compared withthe last model:

Figure 10—Through time displacement analysis – red colour: displacement of COG is over a user-defined threshold

Results can be visualised and manipulated by many compatible 3D software. The one which has beenchosen here is ‘Cloud Compare’ developed by EDF R&D. It is an open source software and it can be used to

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overlay and display many populated layers conveniently (3D objects, point cloud, construction plan, etc.),and to perform regular computations such ad calculations easily (distance between points, distance betweenmodel and points, etc.).

One of the main advantages of the SEABIM tool is that it can be applied on any breakwater werehistorical bathymetric data is available even though no block positioning or orientation data is registeredfrom construction by aiding laying device.

Results, Observations, ConclusionsUsing basic sensors and existing data, SEABIM has generated as-built data of high-fidelity at reasonably lowcost. The armour units fit in the point-cloud with an accuracy below range of a centimetre and require a lowdata-processing duration time: less than a day per hundred meters of regular dike with a small workstation.

A time analysis has also been done from installation (2016) to nowadays, which enable quality engineersto spot new kind of points of interest, such as trends and time-related phenomena. Results obtained fromthis tool to characterize the structural condition of seawalls are clearly less subject to subjectivity and canbe an excellent analysis tool during discussions with a customer, insurance, etc.

SEABIM is extremely versatile, initially optimized for post-construction inspections and surveys, it couldbe used conveniently daily following construction to control the position of each precast armour units. Ifone unit has been found wrongly laid in the course of the placement, the site engineer gets instantly theinformation and can replace it properly ‘on the go’ avoiding any non-conformance.

The SEABIM model can then become the standalone database of the structures construction andmaintenance history, converting project into as-built at the pace of the blocks installation. The SEABIMmodel can also feed structural calculation software with an as-built 3D model to check the integrity of thebreakwater after construction against design wave pattern, assembly configuration, density, etc.

The next phase under development by ID OCEAN is to create a cloud based-web mapping platformwhere all data about the structure can be accessed by every stakeholder with administrated access and rightsfor each user. That way, the survey subcontractor can drop its point-clouds with a registration date as anyquality control record. This point-cloud can be archived, and ultimately retrieved and post-processed bySEABIM software for the generation of the 3D model that is dropped on the platform and seen by qualitycontrol engineers. The history of each infrastructure can be accessed online from the website and anomaliesgeoreferenced by engineers.

Once an anomaly is controlled by a subsea inspection, the video can be dropped on the cloud and assignedto the anomaly by the diving company. Work interventions can then be conveniently planned, and repairsnotifications assigned to each anomaly for a complete infrastructure follow-up. This platform is called aBIM management system.

Linkshttps://www.youtube.com/watch?v=QlPv_CexND0 – SEABIM – breakwater 3D reconstruction using subsea video as

raw input data