考虑桩周土体流变的静压桩长期沉降理论解析

Theoretical Analysis of a Long-term Settlement of a Driven Pile Considering Rheological Effects of the Surrounding Soil

黏土地基中桩基长期持荷状态下桩周土体流变引起的桩基长期沉降变形显著,从而对上部结构的安全稳定性造成影响。根据静压桩承载过程中桩周土体的实际应力状态,利用剪切流变等效时间线模型和Yin-Graham压缩流变模型分别对桩侧和桩端土体的流变特性进行了探讨。基于静压沉桩效应,加载初始变形理论和流变机理,建立了黏土地基中静压桩考虑加载变形与流变的扩展荷载传递函数。在此基础上,考虑桩侧桩端的初始沉降与流变协调条件,对荷载传递理论进行改进,提出了考虑桩周土体流变的静压桩长期沉降理论计算方法。通过与2根持荷29.4年的静压桩长期沉降现场实测对比,验证了所提方法的可靠性。利用所提方法,进一步分析了剪切蠕变速率、持荷水平、蠕变速率影响因子等因素对静压桩长期沉降的影响。结果表明:桩基持荷初期桩周土体流变效应显著,桩基沉降变形增长速率较大,随后速率逐渐降低;黏土地基中桩周土体流变引起的沉降在静压桩长期沉降中的占比较大,占总沉降的50%左右;桩基长期沉降随剪切蠕变速率和持荷水平的增加而增大。

The effect of the long-term settlement of a driven pile under sustained loading,which depends on the rheological properties of soils and clays,is of critical importance for the safety of a superstructure during its service.Based on the equivalent time-line shear rheology model and Yin-Graham compression rheology model,the mechanisms of soil rheology at pile shaft and base were investigated by considering the actual stress state of soil around the driven pile under a load condition.Furthermore,considering the pile installation effect,initial settlement and the proposed soil rheology mechanisms,as well as the loading response and rheology of clay,the extended load transfer function was established.Based on the proposed extended load transfer function,the load transfer method was further modified by considering the compatible deformation between pile and soil.Thus,a theoretical method considering the rheological effects of surrounding soil was proposed for calculating the long-term displacement of the driven pile.The proposed method was verified by performing a comparison with the field results of the two driven piles remaining under a sustained load for 29.4 years.Then,based on the proposed method,the influence of shear rheology rate,relevant influencing factors,and loading level on the long-term settlement of the driven pile were further analyzed.The results suggest that the rheological effect of the surrounding soil is significant during the initial stage of sustained loading;the pile deformation rate is high at first then gradually decreases with time.The pile settlement caused by rheological properties of the surrounding soil accounts for a significant proportion of the total settlement of clay strata,which is approximately 50%.Additionally,the long-term settlement increases with higher shear rheology rate and higher loading level.