箱式隧道现浇大体积混凝土温度应力场及裂缝控制研究

Study on Thermal Stress Field and Cracking Control of Cast-in-situ Mass Concrete in a Box Tunnel

大体积混凝土开裂问题一直以来都是工程界亟需解决的研究课题。基于此,文章以江苏省徐州市山体修复项目中的箱式多跨连拱隧道现浇大体积混凝土为研究背景,通过在隧道大体积混凝土浇筑过程中设置温度监测点实测其温度,并利用ABAQUS有限元软件的二次开发功能建立隧道单跨有限元模型进行混凝土温度应力场的模拟分析,考虑改变混凝土入模温度、养护温度、拆模时间及分层浇筑层数等因素,对隧道大体积混凝土的中心点温度峰值、最大里表温差及表面拉应力进行分析,总结出隧道大体积混凝土浇筑温度应力场的变化规律。结果表明:模拟得到的温度值与现场实测温度值的变化规律基本一致;混凝土入模温度和养护温度上升20℃,中心点温度峰值分别增大8.47℃和10.48℃,最大里表温差分别增大6.35℃和下降6.79℃,表面拉应力分别增大0.61 MPa和减小0.52 MPa;浇筑后约3 d(混凝土开始降温时)进行拆模养护,能使中心点温度峰值、最大里表温差及表面拉应力最小;采用合适的分层浇筑层数也有利于大体积混凝土裂缝控制。根据模拟结果制定的现场控制裂缝措施,有效控制了混凝土结构的裂缝产生,取得了良好的实际效果。

Cracking in mass concrete has always been an urgent research topic in the engineering field.So,in this paper,taking the cast-in-situ mass concrete of a multi-span multi-arch box tunnel in the Mountain Restoration Project in Xuzhou City,Jiangsu Province as the research background,temperature monitoring points are installed and the temperature at each monitoring point is measured during the pouring process of mass concrete,and then the secondary development function of ABAQUS finite element software is adopted to establish a finite element model of the single span tunnel,so as to simulate the thermal stress field of the mass concrete.Meanwhile,taking into consideration of the variations of concrete molding temperature,curing temperature,formwork removal time,pouring layer and so on,it analyzes the peak temperature at the center point,the maximum temperature difference between the core and surface as well as the surface tensile stress of the mass concrete in the tunnel.Finally,the variation law is concluded for thermal stress field of cast-in-situ mass concrete in the tunnel.The results show that:the variation law of the simulated temperature is basically consistent with the one measured on the site;when the concrete molding temperature and curing temperature increase by 20℃,the peak temperature at the central point increases by 8.47℃and 10.48℃,respectively,the maximum temperature difference between the core and surface increases by 6.35℃or decreases by 6.79℃,respectively,and the tensile stress on the surface increases by 0.61 MPa or decreases by 0.52 MPa,respectively;Formwork removal and curing should be carried out about 3 days after pouring(when the concrete began to cool down)to minimize the peak temperature at the central point,the maximum temperature difference on inner surface and the tensile stress on the surface;the appropriate number of pouring layers is also conducive to the cracking control of the mass concrete.The on-site cracking control measures formulated according to the simulation results could effectively control the cracks of concrete structure and achieve good practical results.