ABSTRACT
Hundreds of houses in the Greater Edmonton area sustain damage due to foundation settlements caused by soil subsidence. This problem is remedied by foundation underpinning with torqued-in helical steel anchors (screw piles). Monitoring installation torque of the helical anchors reveals multiple soft layers and lenses scattered throughout the deposit of surficial high plastic glacio-lacustrine clay, silt and sand. It was suspected that the variation of the soil compressibility causes the observed uneven settlements.
In the paper, soil parameters governing both immediate and long-term settlement (its modulus of elasticity and compression index) have been statistically correlated to the installation torque of the helical anchors. Summarizing data from 71 pile installations on 7 underpinning projects in different parts of Edmonton ( > 1000 torque readings) and using Monte Carlo simulation, probability of large differential settlements ( > 13 mm) of the residential foundations was evaluated. The noted statistical variability of soil properties can explain the observed frequency of calls for remedial underpinning.
Keywords: Helical anchor, Histogram, Monte Carlo simulation, Probability, Screw pile, Settlement, Shallow foundation, Soil variability, Statistical distribution, Torque.
