考虑蠕变时预压期的近似确定方法

Approximately determining preloading duration considering creep

针对经典预压理论无法考虑次固结沉降以及考虑次固结沉降的Johnson法有时会出现临界固结度超过100%的错误,提出预压荷载一次骤然施加完毕后预压持续时间的近似计算公式.在推导该近似公式过程中,利用Bjerrum等时蠕变图和Yin-Graham等效时间线流变模型,采用曾国熙近似固结度计算公式,因此该近似公式能够克服Johnson法的缺陷,分析软基固结系数、蠕变系数、回弹指数、超固结比、工后允许沉降和预固结时间对预压工期的影响.研究表明:当预压超载较小时,预压持续时间随着超载比的增加呈幂函数趋势减少,增大超载比能够有效地缩短预压工期;当预压超载较大时,预压持续时间随着超载比的增加缓慢减少,增大超载比对缩短工期意义不大.

As the secondary consolidation settlement was not taken into account in classical preloading theory and the flaw sometimes happened that the critical consolidation degree was bigger than 100% considering secondary consolidation settlement in Johnson＇s method,an approximate formula of preloading duration under a single-stage sudden loading was proposed.During the derivation of this approximate formula,Bjerrum＇s equal-time creep diagram and Yin-Graham equivalent-time rheological model are used and Zeng Guo-xi＇s approximate formula of consolidation degree is employed.So the approximate formula can be able to avoid the flaw of Johnson＇s method,and analyze the effects of soft subsoil＇s consolidation coefficient,creep coefficient,swelling index,surcharge pressure ratio,allowable post-construction settlement and preconsolidation time on preloading duration.Research results show that when surcharge pressure ratio is relatively smaller,preloading duration decays with the power growth of surcharge pressure ratio.An increase in surcharge pressure ratio can obviously make preloading duration short.When surcharge pressure ratio become bigger,preloading duration slowly decays with the growth of surcharge pressure ratio.An increase in surcharge pressure ratio can only make preloading duration a little decrease.