冻胀融沉过程中井塔基础稳定与结构应力变化规律研究

Stability and structural stress variation of the shaft tower foundation during frost heaving and thawing settling

在高耸的井塔周围开展冻结法施工将会造成井塔基础的抬升或沉降,对井塔基础稳定及其结构安全造成严重威胁。针对上述问题,采用缓慢冻结、局部冻结和温控孔热水循环等保护措施,成功避免了冻结锋面波及井塔基础。在造孔—冻胀—融沉过程中对井塔基础高程进行持续测量,测量结果表明:造孔—冻胀—融沉期间井塔基础依次经历缓慢下沉、轻微抬升、快速下沉和下沉稳定4个过程;采取的冻结保护措施有效保障了井塔基础的稳定性,井塔基础的最大倾斜值远小于规定的允许值。结合井塔基础沉降监测数据开展井塔结构应力的数值模拟,模拟结果表明:井塔主梁上表面拉应力峰值出现在井塔壁柱与主梁的连接处,随着井塔倾斜值的增加,井塔主梁上表面拉应力峰值不断增大;造孔—冻胀—融沉期间井塔主梁上表面最大拉应力小于C25混凝土强度极限,井塔结构安全性得到有效保障。建立温度-表土-井塔相互作用相似材料模型并开展模拟实验,实验结果表明:冻结时间越长、冻结温度越低,井塔基础的抬升量和融沉后的下沉量越大且井塔基础融沉稳定所需的时间越长,井塔基础的抬升量峰值明显小于井塔基础的融沉量,模拟结果与实测结果、数值模拟结果相吻合。

Freezing method construction around tall tower causes lifting or settlement of tower foundation,which seriously threaten the stability of tower foundation and its structural safety.In order to solve the problem,symmetrical drilling,local freezing protection,and hot water circulation of temperaturecontrolled hole are adopted to avoid freezing front and tower foundation.The elevation of tower foundation is measured continuously during the process of drilling,frost heaving and thawing settling.The measurement results show that during the period of drilling,frost heaving and thawing settlement,the tower foundation successively experiences a process of slow subsidence,slight uplift,fast subsidence,and settlement stability.The maximum inclination value of the tower foundation is far less than the allowable value,and the freezing protection measures adopted effectively guarantee the stability of the tower foundation.the numerical simulation of tower structure stress is carried out with the monitoring data of tower foundation settlement.The simulation results show that the peak value of tensile stress on the upper surface of the main beam of the shaft tower appears between the pilaster and the main beam where the peak value of tensile stress on the upper surface of the main beam of the shaft tower increases with the increase of the inclination value of the shaft tower.When the maximum tensile stress on the upper surface of tower girder is within strength limit of C25 concrete during the period of drilling,frost heaving and thawing settlement,the safety of tower structure can be guaranteed.A similar material model of temperature⁃topsoil⁃well tower interaction is established and simulation experiments are carried out.The experimental results show that the longer the freezing time,the lower the freezing temperature and the greater the lifting amount and settlement amount of well tower foundation after thawing settlement,and more time required for the stability of well tower foundation after thawing settlement,the peak value of the lifting amount of well tower foundation is much smaller than that of the thawing settlement amount of well tower foundation.The simulation results are consistent with the measured results and numerical simulation results.