基于荷载结构法的隧道拱顶欠厚脱空内力修正计算模型

Modified Calculation Model for Internal Force of Tunnel Vault Lining with Voids and Insufficient Thickness Based on Load-Structure Method

拱顶欠厚脱空是隧道衬砌常见的病害,欠厚脱空会导致衬砌应力状态发生改变,造成衬砌开裂、掉块等问题。基于衬砌结构计算的结构力学法,考虑轴线偏移及界面厚度连续变化对内力的影响,提出隧道拱顶存在欠厚脱空时的内力修正计算方法。通过案例分析,分析不同高度的拱顶欠厚脱空衬砌的内力变化规律,对脱空衬砌安全性进行评价,结果表明:拱顶欠厚脱空显著影响衬砌内力,造成衬砌轴力整体减小,脱空边界外侧出现正弯矩,衬砌下表面出现拉应力,且随着脱空高度的增加,弯矩值与拉应力值逐渐增大。当拱顶脱空高度由0.1 m增加至0.5 m时,衬砌拱顶轴力由786.12 kN减小至456.65 kN,减小幅度为41.91%;脱空边界外侧最大正弯矩由79.36 kN·m增大至238.94 kN·m,增大201.08%。当脱空高度达到0.5 m时,最大拉应力达到3.172 MPa,超过衬砌混凝土抗拉强度,造成衬砌开裂。此外,拱顶脱空会造成脱空边界外侧安全系数减小。当脱空高度较大时,脱空边界外侧出现危险截面,对结构安全产生不利影响。

The void and insufficient thickness at the vault is a common disease of tunnel lining,which will change the stress state of the lining,resulting in cracking and block falling of the lining.Based on the structural mechanics method and considering the influence of axis offset and continuous change of interface thickness on the internal force,a modified calculation method of internal force is proposed for the case of tunnel vault lining with voids and insufficient thickness.Through the case analysis,the variation law of the internal force of the vault lining with voids is analyzed in terms of different heights,and the safety of the lining with voids is evaluated.The results show that the voids at the vault caused by the insufficient thickness significantly affect the internal force of the lining,resulting in the overall reduction of the axial force of the lining,the positive bending moment outside the void boundary,and the tensile stress on the lower surface of the lining.With the increase of the void height,the bending moment and the tensile stress value gradually increase.When the void height increases from 0.1 m to 0.5 m,the axial force of the vault decreases from 786.12 kN to 457.65 kN,with a decrease of 41.91%.The maximum positive bending moment outside the void boundary increases from 79.36 kN·m to 238.94 kN·m,with an increase of 201.08%.When the void height increases to 0.5 m,the maximum tensile stress reaches 3.172 MPa,which exceeds the tensile strength of lining concrete,causing lining cracking.Besides,vault voids will cause the decrease of the safety factor outside the void boundary.When the void height is large,dangerous sections appear outside the void boundary,which has an adverse effect on the structural safety.