Expert Q&A: Damian Siebert on civil & geotechnical engineering
Damian Siebert joined Haley & Aldrich in 2001 and is the Geotechnical Discipline Leader. Here he discusses an innovative approach using ground improvement that saved Haley & Aldrich’s client millions of dollars versus a more conventional foundation approach.
How is geotechnical engineering different from civil engineering?
Civil engineering is the broad category, the science of buildings and structures. Geotechnical engineering is a branch of civil engineering focused on the behavior of soil and rock for providing a stable foundation for a structure. Where it gets interesting is optimizing the infinite combinations of placing a particular foundation onto particular soil stratum (i.e., developing the most cost-effective foundation system for a required structure performance). It could be vertical foundations for a structure like a skyscraper, or horizontal, such as a road or utility project.
Give us an example of a challenging subsurface and the solution.
A very recent project is the Assembly Row development, a mixed-use residential-retail-commercial project on the Mystic River just outside Boston. The property is underlain by urban fill, compressible organic deposits and clay soil – residuals from its waterfront heritage – which meant new ideas were needed to help reduce premium building construction costs resulting from the adverse underground conditions. These conditions usually involve using long piles driven into the ground to reach dependable bearing soils or bedrock, bypassing the weak, compressible layers above. However, we were convinced that if properly designed ground improvement – that is, making the near subsurface layer more solid – could save the client millions of dollars versus deep pile driving.
What kind of ground improvement did you perform at Assembly Row?
The ground improvement technique employed consisted of columns of crushed stone installed through the fill and organic deposits to stiffen these otherwise unsuitable soils, enabled “floating” of the buildings (up to six stories) directly above thick, soft organic soils using shallow spread footings and soil-supported ground floor slabs. We believe that by using creative design, special details and testing allowed ground improvement and shallow foundations to be used in ways that were previously considered unthinkable.
Is saving the client money the most important issue?
We look at it from a slightly different perspective. Given the client’s goals (building performance), how can we deliver a system that provides the maximum value? If we can spend less money and accomplish similar results, great! By spending a little more time and budget on upfront design and testing we were able to reduce downstream expense and provide the best value to the client.
What kind of value do you provide beyond geotechnical engineering?
We work with our clients as their partner to help anticipate and solve problems before they occur. Large construction projects often have a lot of bumps in the road and one of the many things we’ve learned to do really well is to understand who the stakeholders are and what each one values so we can create appropriate, viable solutions that work for everybody. Sometimes that’s the difference between a successful project, and one that never gets off the drawing board.
For more information on Civil & Geotechnical Engineering, contact Damian Siebert.