A Comparison of the Increase in Capacity with Time for Normally and Overconsolidated Clays

Abstract

Abstract This paper presents new findings not observed from the field blow counts alone for normally and overconsolidated clays. Refined analyses, including the Case Method and signal matching, show subtle differences in the driving behavior. Examples presented for normally consolidated clays are the driving of 30-in.(0.76-m)-diameter open-ended pipe piles, 14-in.(0.35-m)-square precast prestressed concrete piles, and 14HP73 H-piles. Examples are also presented for 48-in.(1.22-m)-diameter open-ended pipe piles driven in heavily overconsolidated clay. The shaft resistance and end bearing decrease with every hammer blow applied to the piles redriven in the normally consolidated clay profiles but were generally constant for the heavily overconsolidated clay profile. Set-up factors observed in the normally consolidated clay were 4.3 after a delay of 3.7 days for the 30-in.(0.76-m)-diameter pipe piles, and 3.3 after a delay of 4.7 days for the 14-in.(0.35-m)-square precast prestressed concrete piles. Set-up factors observed in the overconsolidated clay were 1.7 after a delay of one day, 1.8 after a delay of 5 days, 1.9 after a delay of 13 days, and 2.0 after a delay of about 15 days. The shaft resistance did not increase after a delay of one day but did increase for longer delays.