吹填场区双层软黏土地基超载比与卸载控制试验研究

对于围海造陆工程所开展的超载预压处理方法，地基处理效果通常采用后续变形大小来评价，其大小与超载比和卸载控制时间密切相关。针对天津滨海地区围海造陆工程所形成的典型的上软、下硬的双层软黏土地基，采用改装的固结仪进行了多种超载比和卸载控制时间的试验研究，提出了适宜的超载比和最佳超载作用时间。试验表明：双层软黏土地基超载比大于0.375，超载作用时间超过主固结时间时，超载卸除后地基变形以回弹变形为主，后续的工后沉降将明显减小，减小幅度可高达70%以上；超载卸除后的土体次固结系数明显减小，减小的幅度随超载比的增大、超载作用时间的增加而减小；不同于均质地基和上硬下软的双层地基，上软、下硬双层地基的工后沉降以上部软土层沉降为主，约占总沉降量的73%以上。根据不同超载比和超载作用时间下土体的变形时程曲线，建议适宜天津滨海地区围海造陆工程软黏土地基的超载比控制在0.5以下，超载作用时间控制在1～3倍的主固结时间内。

Experimental study of overload ratio and unloading control of double-layer soft clay foundation in a dredger fill site

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,