无黏性土中钻孔径向卸荷收缩理论解  

Analytical solution for borehole contraction caused by radial unloading in cohesiveless soil

作　　者：赵春风[1,2] 费逸 赵程[1,2] 吴悦 王有宝 ZHAO Chunfeng;FEI Yi;ZHAO Cheng;WU Yue;WANG Youbao(Department of Geotechnical Engineering,Tongji University,Shanghai 200092,China;Key Laboratory of Geotechnical and Underground Engineering(Tongji University),Ministry of Education,Shanghai 200092,China)

机构地区：[1]同济大学地下建筑与工程系,上海200092 [2]岩土及地下工程教育部重点实验室(同济大学),上海200092

出　　处：《哈尔滨工业大学学报》2020年第4期135-141,共7页Journal of Harbin Institute of Technology

基　　金：国家自然科学基金(41672265,41272295);上海市启明星计划项目(17QC1400600)。

摘　　要：在钻孔灌注桩成孔过程中会引起钻孔周边土体径向应力卸载和钻孔收缩变形,为此,基于SMP屈服准则和非相关联流动法则,推导在无黏性土中竖向钻孔径向卸荷孔周应力场位移场解析解,并结合Berezantsev和夹心墙两种土压力公式,得出孔周孔壁位移沿钻孔深度方向的变化曲线,并与忽略塑性区弹性变形的结果进行对比.参数分析的结果表明,卸荷因子n和钻孔半径a 0及内摩擦角?对孔壁位移均有明显影响,其中n和?的影响存在着临界点,n和?小于该值,孔壁位移则显著增大;而剪胀角ψ的影响有限,可忽略不计.卸荷因子n是一个只与内摩擦角?有关的函数;而r p/a是一个只与?、n有关的定值,与深度方向无关,故无黏性土中竖向钻孔的自立深度为0.忽略塑性区弹性变形的柱孔收缩位移解相对偏小,而塑性区半径解相对偏大,故忽略塑性区弹性变形的解答在工程应用中不保守.另外,选取不同土压力沿深度方向的孔壁位移值存在较大差别,在竖向钻孔时的土压力选取还需与现场实测相结合.The drilling process of a bored pile can cause radial unloading-induced borehole contraction.In this study,the stress-displacement solution for a borehole under radial unloading in cohesiveless soil was derived based on the SMP yield criterion and the non-associated flow rule.By combining with earth pressure formulas derived from cavity wall formula and Berezantsev’s formula,the variation curves of borehole wall displacement with borehole depth were obtained,which were compared the results of the case with elastic deformation ignored in plastic zone.Parameters study shows that the unloading factor n,borehole radius a 0,and internal friction angle?had obvious influences on borehole wall displacement,and the effects of n and?had a critical value where the borehole wall displacement was significantly increased when n and?were less than the value.However,the influence of dilatancy angleψon borehole wall displacement was limited and could be ignored.In addition,n was a function only related to?,while r p/a was a constant value only related to n and?and had no relation with depth,which suggests that the self-supported depth of vertical drilling in cohesiveless soil was zero.Moreover,it can be found that the wall displacement was smaller and the plastic zone radius was larger when elastic deformation was ignored in plastic zone,which indicates that the solution of ignoring elastic deformation in plastic zone is not conservative in engineering applications.Lastly,the value of borehole wall displacement with different earth pressures along depth was quite different,which shows that the selection of earth pressure in vertical drilling should be combined with real field measurement.

关 键 词：竖向钻孔 SMP屈服准则 无黏性土 径向卸荷 理论解 

分 类 号：TU43[建筑科学—岩土工程]