Design rule purpose
The purpose of this design rule is to add installation feasibility analysis to Optioneer. Subsea cables are exposed to various such as vessel movements (anchors), fishing (trawling), and seismic or sediment activity. As a result, cables are usually protected, either via burial in the seabed or by protection with rocks or concrete mattresses. This design rule visualises all of the data and contains logic to determine main risks related to installation along the route and derive quantity inputs for further EIA and costing.
How to configure
This design rule has a lot of moving parts but in essence focuses on configuring:
are suitable installation via trenching (usually preferable)
require protection (usually not preferable)
which are considered to be undetermined or no-data
what installation / protection method is applied to crossings
the default method is concrete mattress
N.B. crossing methods are defined as 'dominant' which means that they will overwrite any other conditions at point. Even if the crossing is located in a location where trenching is allowed, Optioneer will still report it as requiring a mitigation method.
The example below shows a realistic (unrelated to any project, however!) settings and how this design rule works in practice.
N.B. In the two figures below, line thickness isn't indicating anything. It's just there to visualise layer overlaps.
The figure above highlights a situation which happens quite often, especially in the context of seabed geology data. Multiple data sources might have overlapping layers which might be categorised differently. As a result, when users want to apply specific rules on a layer basis, there might be areas where conflicting logic is present. In such situations, Optioneer will highlight multiple installation methods as feasible.
In the figure below, the colour coding is as follows:
blue = trenching possible
dark red = protection required
white = layer considered as undefined / no-data
cyan = concrete mattress (crossing).
The logic is intended to reduce possibilities (where it's clear which method has to be used) and highlight risks (areas where conflicting data / assumptions are present).
Optioneer presents a summary of calculations from this design rule in a few ways:
via Option Metrics and providing total lengths along the route where given installation methods can be used
via Vertical Profile Chart where a per-point breakdown is provided and plotted along the chainage of the route.
No-data areas have refer to explicitly defined layers. Optioneer skips areas where data is missing.
The sum of total lengths (via Option Metrics) of possible installation methods might exceed the total length of the route as often multiple methods can be used.
This design rule only calculates metadata and the output of calculations isn't used in generation of options. If specific geology layers should be avoided, users should use other design rules like 'minimizing path constraints'.
Input / output summary
This design rule requires a dedicated 'geology' dataset.
List of layers where trenching is allowed
[Muddy Sand, Soft Sediment, Gravel]
list of GIS layers
List of layers where protection is required
[Hard Substrate, Rock Outcrop, Shallow Quaternary Deposits]
list of GIS layers
List of layers to treat as no-data or undetermined
[Undefined Sediment, Undefined Deposit Thickness]
list of GIS layers
Total length of the route where trenching is possible
Total length of the route where protection is required
Total length of the route where there data doesn't allow to determine a suitable method (no-data)
Total length of the route where crossing mitigation (concrete mattress) is required
Feasible installation methods at every point along the route
plot along the route
plot on the Vertical Profile Chart
This chart can be accessed via Vertical Profile Chart > Composition > Installation.