Geology for Initial Planning and
Scoping
Geology for Construction Materials
Geology for Foundation Design
Geohazard Identification
Impacts of Geology on Construction
Initial Planning and Scoping (Part 1)
The geological conditions of a site are a significant
consideration for any development.
The geological conditions of the site were not fully understood
until 2001, when the first serious stabilisation effort was completed. This
was 828 years after construction began!
More details can be found here.
If only they had fully understood the geological conditions during
the planning phase of the project.
Before planning and scoping out a project, it is important that all available geological information is used. This includes, reviewing:
- Published geological maps. What types of soils and rocks are beneath the site? Are there any geological features, like faults, in the area?
- Published topographical maps. Are there changes in slope angles, steep sided valleys, cliffs?
- Hydrogeological and hydrological information. Is there surface water? How high is the ground water? Where might flood waters reach? What direction/s do waters flow in the area?
- Aerial photography and Light Detection and Ranging (LiDAR). To find out additional information about features (geomorphological) and geological boundaries.
Some geological features that are important to identify for civil projects include:
- Soft alluvial (river) or organic soils beneath the site where large structures are proposed. This makes for difficult engineering solutions.
- Highly expansive clay minerals. These are a great risk to roads, rail and other infrastructure as they cause significant movement (through heave and shrinkage).
- Any other geological hazards on the site.
- Construction materials suitable for the project. It is brilliant when some of the things you need are already on site.
Once you have checked for these potential issues (or benefits), solutions can be worked out. These can include:
- Moving the locations of structures and infrastructure (we do NOT want that large building tilting like the Leaning Tower of Pisa!) or where we cannot move them, adjusting their design to suit the geology of the area.
- Finding other sources for construction materials (if they do not already occur on site).
Project Example
The image below is of a published geology map for an area in the north of Western Australia. The area has been proposed for a large civil project. This map displays the surface geology that has been mapped in this area. The area includes:
- Mangrove and marine muds.
- Shelly sands in coastal dunes and beaches.
- Silt and muds in supra and inter-tidal flats and lagoons.
Once we start looking at topography and aerial images, further geological interpretations can be made. The image below highlights the presence of some potentially rocky ledges. These have been identified from changes in slope angles. These could cause problems if we are trying to place structures here or are planning to excavate.
Now we have looked at the data we have an idea of what is present (the geomorphological conditions):
- Marine muds and mangroves (grey hatching)
- Tombolos (red lines)
- Palaeochannels (blue dashed lines)
- Cheniers (black lines)
This information and the additional
data we looked at give us a detailed appreciation of the ground conditions in
the area. This allows adjustment of the design process to account for potential
issues.
In the example above, the proposed
layout of the development was changed to avoid the areas of potential mangrove
muds (remember the problems of clay moving). Instead, they built on more stable
geological areas (terrains). If they had
not gone through this planning phase properly, considering
the geology, their project could have been a disaster.