Surcharging of Soft Ground to Reduce Secondary Settlement

Soft ground, including soft clay and silt deposits and peats, can be improved by precompression. Preloading without surcharge is used to increase undrained shear strength and to limit consolidation under the structure to the recompression range, thus reducing primary settlement. However, preloading with a surcharge is required to produce sufficient preconsolidation with respect to the final permanent structure load in order to also reduce secondary settlement. Secondary settlement without surcharging is especially significant when duration of primary consolidation t_p is small and secondary compression index C_α is large. For any surcharging effort values of C″_α/C_α are larger and values of t_ℓ/t_pr are smaller for peats than for soft clay and silt deposits. In other words, although surcharging can reduce post-construction secondary settlement for both clay and peat deposits, surcharging is less effective for peats. Secondary settlement of soft clay, silt and peat deposits, with or without surcharging, is completely consistent with the C_α/C_c law of compressibility.