Use of the Observational Method to Verify Design of Earth Retention Structures

Two case histories are presented for earth retention structures where the results of construction monitoring were used to verify key criteria used for the design of the structures. One case history consists of a sheet-pile bulkhead structure for the unloading of bulk aggregate products in Bay City, Michigan. The front wall of the sheet-pile bulkhead was analyzed for heavy surcharge pressures from the adjacent aggregate stockpiles. The sheet-piles are laterally supported by sheet-pile deadman and tierods. Slope indicator tubes were used to monitor lateral movements next to the sheet-piles. The results from the slope indicators were then used to verify the stability of the bulkhead under the heavy surcharge loads from the aggregate stockpiles. A second case history consists of a deep braced excavation for the construction of a processing pit for a new steel rolling mill in Dearborn, Michigan. A very stiff “King Pile” system was used to resist the large lateral pressures below the bottom of the excavation due deep deposits of soft clay soils. Multiple levels of heavy bracing consisting of double rows of heavy steel sections for the walers and large pipe struts were used to support the walls. During construction strain gauges were affixed on selected struts to verify the design strut loads