By Troy Schultz (Principal Engineer) & Kelly Saron (Senior Urban Designer)
It is commonly known and discussed within the development industry that the easy sites (greenfield or brownfield) no longer exist. What’s less commonly known, and herein lies the challenge, is how to achieve great outcomes on more difficult sites.
A significant challenge often faced is developing on steep sites, and often they are the only ones left in the right areas. The following describes some key steps in achieving great outcomes on sloping sites.
1. Easy Collaboration – Integration of Urban Design and Engineering
Gone are the days where a layout can be developed, DA approved (with minimal or no engineering input) and passed on to the engineers to make it happen at Operational Works Phase. Whilst this was viable when sites were flat/gently sloping, lots were larger and Council requirements were less complex, it is no longer the case.
We highly recommend early collaboration between the Urban Design and Engineering Teams to ensure a well considered, integrated solution is developed. Like is often the case, a balanced outcome yields great results and there needs to be compromise and thoughtfulness from both parties to achieve this.
This collaboration should happen as early on in the development process as possible, ideally before site acquisition/during due diligence. This will ensure that assumptions made from both a yield and cost perspective during acquisition are realistic and achievable.
Collaborative design achieves value managed and high yield outcome with high quality outcomes for the end purchaser.
2. The Dollars – Major Earthworks vs Retaining Strategy
The biggest impact on internal development civil construction costs is earthworks, which is primarily driven by ground conditions and site slope. Whilst neither of these factors can (unfortunately) be changed, there are certainly varying solutions which can be adopted and a one size fits all approach is never appropriate.
To inform the strategy, understanding ground conditions is key. Undertaking geotechnical investigation upfront is critical to informing the earthworks strategy. The main question that needs to be answered: is rock present and at what depths? Appropriate machinery should be used in the investigation to get a real representation of how the material can be dealt with in construction. But it is also valuable to understand other aspects such as potential contamination, unsuitable material, previous filling and pavement parameters.
Once ground conditions are understood, an options/cost benefit analysis can be undertaken to determine the most appropriate strategy. Some sites might be more suitable to major earthworks and ‘flattening’ of the site to minimise retaining. Others (with tough ground conditions) may be better suited to a retaining strategy which generally follows the natural lay of the land. Or a combination of both might also be appropriate, the key is that the options are assessed and a tailored approach is taken.
Additionally, availability of quality fill material for importing should be considered. In areas of high fill availability it can be more cost effective to fill lower lying areas to provide a better working platform (less rock and less slope) for at least part of the development footprint.
Final development aesthetic should also be considered here. Depending on the site and location it may be beneficial to work with the natural slope and maintain the existing amenity of the area.
3. The Detail – Bring the Strategy to Life
Once the overarching strategy is developed, the detail also needs due consideration to ensure the principles set out early in the project lifecycle are upheld during delivery. Items for consideration during latter stages of development include:
- Lot Orientation: Everyone knows that lots should be oriented perpendicular to the contours, however this isn’t always the case. Opportunities may exist to ‘break the back’ of the slope in key areas (for example adjoining conservation areas) which may lend to different orientations.
- Lot Types and Depths: Large (and potentially tiered) walls may need to be accommodated in rears of lots, lending itself to an offset grid to accommodate larger walls in deeper product. Smaller lot frontages work well with steeper roads allowing for smaller, more regular walls to step up the slope.
- Wall Locations: As mentioned briefly above, it is critical to look for opportunities to ‘break the back’ of the slope. Adjoining open space areas, in the rear of larger lots etc.
It all starts with early collaboration, but the principles need to be carried through to the detailed stage to ensure successful, cost effective delivery. Appropriate consideration of slope early on can really be the difference in a project proceeding or not, and effective delivery will ensure cost effective and consumer friendly product is delivered to market.