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The only link we, the Structural engineers, had with The Geotechnical engineers was to receive their Geotechnical report, and use it; often without even meeting its author.
That changed as we faced greater challenges in deep underground structures where Soil-Structure integrated design becomes inevitable, especially with the new computing capabilities.
The first such a challenge happened in 1996 when an existing LRT tunnel, built of slurry walls was to be verified for capacity under imbalanced lateral loads due to new construction. The structure had very little bending moment continuity between slabs and slurry walls (virtually pins). There was only continuity with the CIP middle wall that was too flimsy to offer sufficient continuity. There was no way lateral resistance to imbalanced loads can be achieved without calling on the lateral capacity of soil. That was heresy at the time. But under the pressure of necessity, the Geotechnical provided us with lateral Subgrade Reaction spring modulus. They were so reluctant to provide it to us, that they gave us the softest springs possible (as conservative as they could). Even with that, it made the design possible; yet with a lot of struggle:
Hallelujah, it worked; that existing structure was finally justified.
A precedent was set.
It came handy in 2012 when we were initiating 10 underground LRT stations to a country oversees. Those stations were deeper than usual, and the lateral imbalance was the governing factor. At the same time, their soil was exceptionally firm; offering great help if Soil-Structure integration was used. But there National Transit Authority of that country has never seen it before, and was reluctant to use it. However, with the help of our Geotechnical partner, a reputable European firm, we demonstrated that there will be major savings, running in hundreds of millions of dollars, if we tapped into the hidden capacity of soil. Our proposed method was approved, and it was incorporated in the design criteria of the transit authority of that country.
In 2014, we used the above two precedents to introduce it to Canada's largest transit project of 15 underground stations. This time, with the help of more advanced computer programs that perform the above-mentioned iterations automatically. For that reason, the Geotechnical Engineer was a member of our Structural Focus Group. Perfect Geotechnical-Structural integration resulted in the greatest Value Engineering contribution to Canada's largest project. An added advantage, of thinning the external walls, was reducing the footprint of underground stations; therefore reducing interference with existing utility lines, a winning proposal.
It has been a long journey, from no communication (pre 1996), to bare communication (1996), to cooperation (2012) to integration (2014-…). It's the way of the future. Don't be left behind in the dust.