横向荷载作用下桩侧极限土抗力的上、下限分析
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摘要
比较和分析了几种典型的P-Y曲线后发现,桩侧土体在横向荷载达到或接近极限土抗力后会发生塑性流动或软化。因此,极限土抗力的合理取值将影响桩侧土体的稳定性分析。将横向荷载下桩土相互作用的三维解问题简化为二维解处理,并运用土体塑性极限分析理论,采用摩尔-库仑屈服准则和相关联的流动法则,构造机动许可的应变率场和静力许可的应力场,推导出横向荷载作用下适用于粘性土的桩侧极限土抗力的上、下限解。利用南海某平台场址的工程地质钻探资料,计算了横向荷载作用下桩侧极限土抗力的真正极限荷载(Pu),并与由典型的P-Y曲线计算的Pu值作了比较。计算结果表明:在不排水抗剪强度较大的土层,由极限分析上、下限解计算的Pu值与由Reese硬粘土P-Y曲线、Matlock软粘土P-Y曲线和Sullivan统一法P-Y曲线计算的Pu值相差较大;在不排水抗剪强度较小土层,由极限分析的上、下限解计算的Pu值和由其它几种典型的P-Y曲线计算的Pu值吻合较好。极限分析上、下限解受深度影响,深度对桩侧极限土抗力的影响是随其增加而逐渐增大的。验证结果表明,计算的极限土抗力上、下限解的合理性较好,这对高层建筑、核电站、近海采油平台、海岸码头等建筑工程的桩基础设计具有重要的工程意义。
Comparison and analysis of several typical P-Y curve methods shows that the pile-side soil will be softened or make plastic flow when the transverse load is close to or reaches the ultimate soil resistance.Therefore,a reasonable ultimate soil resistance value can play a decisive role in the stability analysis of the pile-side soil.Simplifying the three-dimensional solution of the pile-soil interaction under transverse load into a two-dimensional solution,introducing Mohr-Coulomb yield criteria and associated flow rule into the soil plasticity limit theory and constructing kinematically-admissible strain rate field and statically-admissible stress field,the upper and lower limits of the ultimate pile-side soil resistance suitable for cohesive soil under transverse load are obtained.Based on the geological survey data from a drilling platform site in the South China Sea,true ultimate load(P u) of the ultimate pile-side soil resistance under the action of transverse load are calculated and compared with that calculated with existing typical P-Y curves.The results indicate that:(1) In soil with lager undrained shearing strength,the P u value resulted from the calculation with the solution of upper and lower limits of the limit analysis has significant differences compared with that resulted from the calculation of ultimate soil resistance of the existing typical P-Y curves,while they have rather good agreement in soil with smaller undrained shearing strength.(2) The ultimate pile-side soil resistance inceases with the increase of the depth.In conclusion,reasonability of the calculated upper and lower solutions of the ultimate soil resistance are good,which is of great significance for the design of the pile foundation of high-rise building,nuclear power station,offshore platform and costal wharf.
Comparison and analysis of several typical P-Y curve methods shows that the pile-side soil will be softened or make plastic flow when the transverse load is close to or reaches the ultimate soil resistance.Therefore,a reasonable ultimate soil resistance value can play a decisive role in the stability analysis of the pile-side soil.Simplifying the three-dimensional solution of the pile-soil interaction under transverse load into a two-dimensional solution,introducing Mohr-Coulomb yield criteria and associated flow rule into the soil plasticity limit theory and constructing kinematically-admissible strain rate field and statically-admissible stress field,the upper and lower limits of the ultimate pile-side soil resistance suitable for cohesive soil under transverse load are obtained.Based on the geological survey data from a drilling platform site in the South China Sea,true ultimate load(P u) of the ultimate pile-side soil resistance under the action of transverse load are calculated and compared with that calculated with existing typical P-Y curves.The results indicate that:(1) In soil with lager undrained shearing strength,the P u value resulted from the calculation with the solution of upper and lower limits of the limit analysis has significant differences compared with that resulted from the calculation of ultimate soil resistance of the existing typical P-Y curves,while they have rather good agreement in soil with smaller undrained shearing strength.(2) The ultimate pile-side soil resistance inceases with the increase of the depth.In conclusion,reasonability of the calculated upper and lower solutions of the ultimate soil resistance are good,which is of great significance for the design of the pile foundation of high-rise building,nuclear power station,offshore platform and costal wharf.
引文
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[2]陆培炎.横向荷载下土、桩共同作用的简化法[J].广东水电科技,1991(1):1-10.
[3]韩英才,NOVAK M.水平荷载作用下单桩的动力分析[J].地震工程与工程振动,1989,9(2):97-106.
[4]金伟良,朱玉明,李林普.P-Y曲线法在海洋工程地基中的应用探讨[J].中国海上油气:工程,1992,4(4):29-40.
[5]胡安峰,谢康和,肖志荣.水平荷载下单桩动力反应分析[J].浙江大学学报:工学版,2003,37(4):420-425.
[6]王腾,董胜,李华军.考虑桩土作用独桩海洋平台横向振动特性研究[J].中国海洋大学学报,2003,34(2):318-324.
[7]栾茂田,张其一,杨庆,等.均质地基上浅埋矩形基础极限承载力上线分析[J].海洋工程,2008,26(2):69-77.
[8]王惠初,武冬平,田青.粘土中横向静载桩P-Y曲线的一种新的统一法[J].河海大学学报,1991,19(1):9-17.
[9]王成华,孙冬梅.横向荷载桩的P-Y曲线研究与应用述评[J].中国港湾建设,2005,135(2):1-4.
[10]章连洋,陈竹昌.粘性土中P-Y曲线的计算新方法[J].港口工程,1991(2):29-35.
[11]龚晓南.土塑性力学:第二版[M].杭州:浙江大学出版社,1999.
[12]张学言,闫澍旺.岩土塑性力学基础:第二版[M].天津:天津大学出版社,2004.
[13]李广信.高等土力学[M].北京:清华大学出版社,2004.
[14]屈智炯.土的塑性力学[M].成都:成都科技大学出版社,1987.
[15]李作勤.影响粘土静止侧压力的一些问题[J].岩土力学,1995,16(1):9-16.
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