基坑混凝土支撑轴力监测值修正方法

为研究宁句城际轨道句容站基坑工程混凝土支撑轴力监测值异常报警现象,考虑混凝土收缩、徐变、弹性模量和温度等非荷载因素,采用理论分析和现场实测相结合的方法,探讨了基于理论的轴力修正公式法和基于现场实测的轴力修正系数法。结果表明:混凝土支撑轴力修正公式可对徐变应变、收缩应变和温度应变进行修正并考虑混凝土弹性模量的非线性变化,由修正公式算得的支撑轴力修正值为原始监测值的55%～64%,修正值更能反映混凝土支撑的真实受力状态; 对混凝土支撑轴力影响程度由大到小依次为混凝土徐变、混凝土收缩和混凝土弹性模量,徐变对支撑监测值的影响最显著; 结合现场实测数据,根据句容站基坑混凝土支撑轴力理论修正系数随时间变化的公式可直接计算偏保守的轴力修正值; 工程中可采用支撑残余轴力测试、钢箱测试等方法对混凝土支撑轴力监测值进行修正,综合理论分析、现场实测和文献中实测数据,实际基坑工程中混凝土支撑轴力修正系数可取0.5～0.65来估算支撑的真实轴力值。

Correction Method of Axial Force Monitoring Value of Concrete Strut in Excavation

To investigate the abnormal alarm of axial force monitoring value of concrete strut in excavation project of Jurong station of Nanjing-Jurong rail, the theoretical axial force correction formula and the axial force correction coefficient based on field measurements were discussed by combining theoretical analysis and field measurements for non-load factors such as concrete shrinkage, creep, modulus of elasticity and temperature. The results show that the correction formula can correct the creep strain, shrinkage strain and temperature strain considering the non-linear changes in concrete modulus. The axial force correction value calculated by the formula is 55%-64% of the original monitoring value, and the corrected value can better reflect the real state of the concrete strut. The descending orders of the influence on the axial force are concrete creep, concrete shrinkage and concrete modulus, with creep having the most significant influence. Combined with the field measured data of this project, the empirical formula of the axial force correction coefficient of concrete strut in excavation of Jurong station with time is obtained, according to which a conservative correction value can be calculate directly. In engineering practice, the measured concrete axial force can be corrected by means of residual axial force measurement and steel box test. Based on the theoretical analysis, field measurement and measured data in the literatures, a correction coefficient of axial force of concrete strut can be taken as 0.5-0.65 when the non-load factors are considered.