受压状态下盾构隧道接缝密封垫老化性能研究

Aging performance under assembly pressure of joint gasket in shield tunnel

随着盾构隧道技术的发展,对接缝密封垫长期防水能力的可靠性要求不断提高。为探索温度作用对盾构隧道管片接缝三元乙丙橡胶(EPDM)密封垫力学性能的影响规律,研究盾构隧道管片接缝EPDM密封垫的长期力学性能,开展受压状态EPDM密封垫100℃以上高温老化试验,对高温老化后的密封垫进行力学性能试验与微观试验。研究发现:受压状态下高温老化后的密封垫,其接触应力显著降低,截面孔洞变小,最大的不可恢复变形量超过了压缩量的50%。而无压缩状态下老化的密封垫接触应力损失不大,在部分情况下甚至有所增强,其截面高度与孔洞没有明显变化。说明压缩力会促使高温老化后密封垫产生更大的永久变形,加快其接触应力的衰减。为更真实地表征温度对接缝密封垫的劣化机制,试验应采用受压状态下密封垫,并将温度控制在100℃以内。受压状态下老化的密封垫,其接触应力随着老化时长、老化温度的增长而减小。错台对接触应力的影响随着老化时长、老化温度的增大而减小。老化后EPDM的热氧稳定性、分子结构变化不大,微观表面产生了坑洞与裂缝,说明密封垫老化后橡胶表面劣化是接触应力衰减的诱因。与橡胶化学性能的老化相比,橡胶永久变形引起的密封垫截面变化对防水性能影响更显著。研究成果可为接缝密封垫密封性能评定提供参考。

With the development of shield tunneling technology,the reliability of joint gaskets’long-term waterproof capacity is required to be improved.In order to investigate the influence pattern of temperature on the mechanical properties of ethylene propylene diene monomer(EPDM)gaskets,and its long-term mechanical properties,an aging test of pressured EPDM gaskets was conducted under the temperature of over 100℃.Besides,the aging gasket was undertaken with mechanical property test and microscopic test.The results are as follows.The contact stress of the aged gasket under pressure and high temperature is significantly reduced.The cross-section holes become smaller,and the maximum irreversible deformation has exceeded 50%of the compression.The generation of permanent deformation of high temperature aged gasket is catalyzed and accelerate the attenuation of its contact stress.In order to expose the deterioration mechanism of the temperature butt joint gasket with greater authenticity,the test shall use pressured gasket while controlling temperature within 100℃.The thermal oxidative stability and molecular structure of EPDM have changed minorly after aging,and holes and cracks are found on the micro surface,indicating that the rubber surface deterioration after aging of the gasket is the incentive for contact stress attenuation.Compared with the aging of rubber chemical properties,the change of gasket section caused by rubber permanent deformation has more significant influence on the waterproof performance.The research results provide reference for sealing performance evaluation of joint gaskets.