Emerging geosynthetic products have changed the geotechnical engineering perspective concerning soft and compressible soil conditions. The conventional approach of excavate, remove, and replace with quality engineered backfill can be very labourious, time consuming, and uneconomical. An alternate approach involves the use of high-strength geosynthetic material for reinforcement and improvement of subgrade soils. We utilized this technique to support a 40 m-diameter fuel storage tank on a geosynthetic reinforced earth foundation (GREF) that was constructed on soft and compressible soils.
In 2015 Nichols Environmental completed a geotechnical investigation, which revealed that the in situ soil conditions on site comprised compressible, soft, and high plastic black lacustrine clay mixed with organics. It was determined this upper layer of clay soil was not suitable for the foundation of the tank, and a deep pile foundation was not desired by the client due to cost and other site development constraints.
A 3.0 m-thick GREF pad was designed using eight layers of high-strength geotextile sandwiched between imported 6-80 granular (Alberta Transportation) fill material. The settlement calculations were conducted manually and using a computer model. The total maximum uniform settlement of 150 mm was predicted. During hydrostatic load testing of the tank, conducted over a period of 12-days, the measured total uniform settlement ranged between 54 mm and 122 mm, so the uniform settlement was within the predicted values during the design of the GREF.
The GREF performed satisfactorily and resulted in significant cost and time savings to the client, in comparison to a deep pile foundation strategy. A case study paper on this project will be accepted for publication and be presented at the Geosynthetics Conference, Houston, 2019.