A normally consolidated silty clay deposit, varying in depth from 0 to 15 m, was pretreated by surcharging combined with P.V.C. vertical drains. Representative field values of the vertical coefficients of primary (0.0015 m2/kN) and secondary consolidation (0.01) were calculated from the settlements caused by a preliminary fill placed some six years prior to the detailed geotechnical studies. A conservative representative field value of the horizontal coefficient of primary consolidation was established to be 8 m2/year. Asaoka\u27s method was used to predict future settlements due to both primary and secondary consolidation. The vertical drains were installed at a spacing of 1.8 musing a modified crawler crane. The average daily output was 158 drains over 128 working days with an average cycle time per pair of drains of eight minutes. The total cost was (A)0.40percubicmetre,or(A) 3.23 per square metre of the area treated. Surcharging decreased the settlements due to primary and secondary consolidation. Calculated values of settlement over a 10 year period were 80 mm for a 15 m deposit with 50 mm being contributed by secondary consolidation
