#BIMfor Geotechnical Engineers

Finding ways to visualise and map what lies underground can be challenging, but BIM represents a leap forward in what ground engineers can do. **Autodesk's Civil 3D and geotechnical analysis packages such as Plaxis make it possible to create and analyse 3D models of the ground in a more detailed, dynamic, integrated and accessible way. - Steven Hassall, Mott Macdonald

In recent years, BIM has focused on the built aspects of construction, however, the ground conditions are just as important, if not more important. Unexpected ground conditions are the most common cause of site delays and can result in significant financila costs. the consequences of delays due to these unforseen ground conditions are far too common, far too expensive to rectify and primarily lead to over spends in the project. According to the UK National Economic Development Office (NEDO), after a review of 5000 industrial building, 50% overran by at least a month, of which around 37% of the overruns in the projects were due to ground problems.

With these things known, it becomes imperative that a better job has to be done of geotechnical investigation, something made possible with a BIM workflow.

As with all previous installments in this series, here and here amongst others, we will highlight 7 things to be gained by geotechnical engineers using BIM.

1. Faster and real time Ground Investigation

Traditional methods of working involve isntructing the contractor to conduct the site investigation. The work will be conducted and a report submitted to the consultant. This whole process can take weeks, during which time many aspects of the job may have changed. Unfortunately, due to time constraints in obtaining the reportand data from the contractor, it is often not possible to refine the investigation, resulting in a report that may not be ideal for what was found or the changed specifications. Best case scenario is a delay in the project while an extra investigation is made, otherwise, this could lead to unforseen ground problems and increased costs when rectifying them.

With a BIM workflow, new information is used to update the model as soon as it is available. This information all helps to plan more appropriate site investigations, with the model representing the current situation on the site.

Modern-day technology, such as KeyLogBook and Pocket SI among others, allow for near real-time data gathering on site. AGS data is sent directly to the consultant's office to be incorporated in the geotechnical BIM model within the same day.

These techniques speed up the whole process which enables a more appropriate investigation to be done for both the ground conditions and the current project specifications.

The Geotechnical BIM (GeoBIM) process also enables the collaboration between different geotechnical partners

2. Improved Visualisation and Interpretation of ground data

One of the biggest benefits of its adoption will be to give geotechnical teams the opportunity to share their visions and concerns for the ground conditions early in the design, as well as to provide input throughout the project, including the operation and maintenance phases.

Using BIM, Geotechnical team members are better able to communicate their intentions early in the project design, as well as to provide input throughout the project as well as during operations and maintenance of the structure.

Tools such as AutoCAD Civil 3D and HoleBASE SI are used to visualise the information to help understand the data and allow the engineer to interpret. For example, using Keynetix's extension for AutoCAD Civil 3D allows visulaisation of information such as geotechnical surfaces for use in both BIM models and the AutoCAD environment. This can also be combined with the results from lab tests to help refine the geotechnical model. This approach allows the model to be refined further than traditional methods.

3. Better representation of ground conditions in models

As Mott Macdonald's Steven Hassall notes

BIM does not change the complexity of identifying hidden features, but it does make them significantly easier to represent in a model. Previous software connected data points crudely and phantom boreholes were commonly created. BIM software like Civil 3D allows customization of geometry between data, permitting the intersection of geological features such as faults anf pockets.

4. Efficiency from the outset

Usually with geotechnical work, the ground modelling involves continuous improvement of the model, incorporating new data as soon as it becomes available and extrapolation of below-ground surfaces. This allows considered design optioneering and refinement at the outset of a project.

During the desk study, for eample, being able to view the latest site plans, is clearly of huge benefit in highlighting any potential points of concern and can help investigation planning.

Engineers can also use the model to identify the best locations for exploratory holes. With these positioned in the model, it's easy to take off quantities and calculate ground investigation cost. Setting-out data can then be fed directly into surveying equipment or extracted as 2D drawings.

5. Interdisciplinary design benefits

Integrating project design models with an accurate BIM ground model enables outline designs to be positioned on the site, making it easier to analyse what's going on.

The GeoBIM model can also be used to automatically update ground conditions for use by other analytical software connected to it, enabling further insights to be gained about the project.

For example, the HoleBASE SI Extension for AutoCAD Civil 3D allows quick and easy inclusion of all geotechnical and site investigation data in the BIM process and CAD drawings. This integration provides the ability to create dynamic geotechnical profiles and sections in seconds as opposed to hours and create civil point groups and surfaces from any data stored in HoleBASE SI.

6. Minimises Geotechnical Risk in Construction

Having access to field data in real time and incorporating it into BIM almost immediately gives the opportunity to refocus sampling and testing mid-investigation. This should deliver more useful data, hence reducing risk and potentially saving money in the long term.

7. Lifecycle monitoring of ground conditions for Building maintenance

The GeoBIM model enables cost-effective repairs and maintenance of assets throughout the project's lifetime. This model can also be regularly updated if there is change in ground conditions over the life of the building, ensuring the most up-to-date information is available when maintenance is needed.