超大截面沉井着床行为判别分析

Judgment Analysis of Behavior of Landing Super Large Section Caisson onto Riverbed

沪通长江大桥29号墩采用矩形沉井基础，沉井平面尺寸为86．9m×58．7m，高115m。为了准确控制沉井着床精度、把握沉井稳定着床的时机，现场采用刃脚处应力监测和GPS沉井姿态监测2种措施进行监测。通过在刃脚踏面和隔墙底面安装一定数量的土压力盒采集刃脚和隔墙下部与土体的接触应力，并将应力监测数据和GPS姿态监测数据相对比分析，二者相互校核，对钢沉井着床稳定给出准确判断。结果表明，有效接触应力为O．1～O．15MPa可作为沉井开始着床的判据，有效接触应力达到或超过O．4～O．5MPa可作为着床稳定的判据。经现场施工验证，土压力盒保护措施效果良好。

The foundation for the pier No.29 of the Hutong Changjiang River Bridge is the rectangular caisson that has the plan dimensions of 86.9m×58.7mand the height of 115 m.To well control the accuracy of landing the caisson(the part of the steel caisson)onto the riverbed and to seize the right time of stably landing the caisson onto the riverbed,two measures of monitoring the stress at the cutting edge of the caisson and monitoring the posture of the caisson,using the GPS were taken in the field.By installing certain numbers of the soil pressure cells at the undersides of the cutting edge and partition walls,the contact stress between the lower parts of the cutting edge and partition walls and the soil was collected and monitored.The data of the monitored stress and the monitored posture of the caisson of the GPS were compared and analyzed,the stress and posture were mutually checked and the correct judgment of the stability of landing the caisson onto the riverbed could be made.The results show that as the effective contact stress is 0.1~0.15 MPa,the stress can be considered as the basis for judging that the landing of the caisson onto the riverbed starts and as the effective contact stress reaches or exceeds 0.4~0.5 MPa,the stress can be considered as the basis for judging that the landing of the caisson onto the riverbed is stable.The field construction verifies the protective measure of the soil pressure cells works well.