For surcharge preloading method used in land reclamation

the effect of ground treatment is usually evaluated by subsequent deformation

which depends largely upon the overload ratio and unload controlling time. This research focuses on the double-layer soft clay foundation with the upper soft layer and lower hard layer in coastal area in Tianjin. The appropriate overload ratio and the best time of overload are determined by consolidation experiment used a modified oedometer under various overload ratios and unload controlling times. The results show that when overload ratio is larger than 0.375 and overload time is longer than the primary consolidation time

the foundation deformation is mainly resilient deformation after overload removed. At the same time

the post-construction settlement decreases significantly by up to 70 percent. Secondary consolidation coefficient significantly reduces after removing the overload

and the longer the overload time and the overload ratio are

the smaller secondary consolidation coefficient is. Unlike the homogeneous foundation and the upper hard and lower soft double-layer foundation

the post-construction settlement of upper soft and lower hard double-layer foundation mainly comes from the upper soft soil layer

accounting for more than 73% of the total settlement. According to deformation curves under different overload ratios and overload times

it is suggested that the suitable surcharge ratio is 0.5 or less and the best overload time is controlled within 1 to 3 times the primary consolidation time for the layer soft clay foundation by land reclamation in coastal area in Tianjin