The project site would house 4 constructed commercial industrial buildings ranging from 89,100 ± ft2 to 789,084 ± ft2 in size. The buildings had to be single-story structures of tilt-up concrete construction. The buildings, with the exception of the building located in the southeast section, would have truck dock areas. All the buildings were to be surrounded by asphaltic concrete and Portland cement concrete pavement. Fills would range from 2 feet to approximately 30 feet. This was required in order to create the planned subgrade elevations for the new development.
Design
It was recommended that remedial grading would be used within the proposed building areas to remove any current compressible native soils. It was also recommended that over-excavation in the former detention pond areas would be replaced by required fills. Based on conditions detected at the boring locations, the current soils in the proposed building areas were to be over excavated to a depth of at least 3-feet below the building pad subgrade elevation and at least 4-feet below the current grade, whichever was greater.
In the areas where the former detention basins were located, it was expected that moist to wet soils would be found at the base of the over-excavation. SCG offered preliminary recommendations in the soil report for subgrade stabilization. It is highly recommended that stabilization through the placement of an absorbent, high ratio geotextile fabric, TenCate Mirafi® RS380i*, at a minimum 18-inch thick layer of crushed stone within 2 to 4-inch particle sizes.
Construction
As expected, the over-saturated soils were met at the base of the over-excavation. The SCG soils tech described the instability of the existing subgrade as moderate to severe. The concrete debris generated by the demolition of the previous site was crushed into 2 to 8-inch particle sizes. The crushed particles were used instead of importing crushed rock for stabilization. They used on-site concrete demo material which was more economical than using imported crushed rock from a gravel pit. In areas of uncompromising instability, SCG suggested the placement of TenCate Mirafi® RS380i before putting down the crushed concrete material.
Mirafi® RS380i was used on the surface of the unstable over-saturated soils. Then 18 to 24-inches of crushed concrete was placed over the geosynthetic. Crushed concrete was pushed onto the Mirafi® RS380i with a truck-mounted dozer. After installing Mirafi® RS380i and the crushed concrete was done, fill soils were deposited on the crushed concrete using Cat 837 scrapers. The stabilization layer was reported to be firm and unyielding underneath the weight of the grading equipment. Fill soils were compacted to approximately 90% of the ASTM D1557 maximum dry density.
Performance
Mirafi® RS380i geosynthetic provided strength to the poor subgrade conditions, allowing for a stable foundation.
Mirafi® RS380i High Strength Geotextile Provided:
• Exceptional tensile strength to support subgrade.
• Excellent separation of poor native soils from the aggregate base.
• Filtering waters from the pumping soils.
• Lateral restriction of the stone section.
The best news, - there was no damage during the placement compaction of highly angular 2 to 8-inch crushed concrete. The final result, a finished, firm, and stabilized platform for the construction of the 4 commercial buildings, the surrounding parking lots, and the loading docks.
