基于颗粒离散元的碳纤维混凝土盾构管片变形及裂纹扩展特性研究

Deformation and Crack Propagation Characteristics of Carbon Fiber Reinforced Concrete Shield Segments Based on Particle Discrete Element

[目的]南京地铁7号线晓庄站—万寿站区间盾构隧道处于岩层破碎、地下水发育处,该区间地质条件极其复杂,对预制管片抗裂和抗压强度要求较高,而普通混凝土管片无法满足结构抗裂要求,因此提出在混凝土中掺入碳纤维,并对碳纤维混凝土盾构管片变形及裂纹扩展特性进行深入研究。[方法]基于颗粒离散元理论,通过单轴DEM(离散元方法)试验的应力-应变曲线确定混凝土材料平行黏结接触模型的细观强度参数,建立碳纤维混凝土管片抗弯强度试验数值模型,对碳纤维混凝土管片的强度、破坏特征、裂纹扩展模式及变形等进行了分析。[结果及结论]抗弯强度试验数值模拟结果表明:在不同加载工况下,碳纤维对混凝土管片强度的提高作用有限,但碳纤维结构具有较大抗拉强度,显著提高了管片的抗变形和抗断裂能力;掺入碳纤维的混凝土管片在加载过程中,其底部先产生1条竖向张拉裂纹,随着加载的继续,底部产生3条竖向张拉裂纹且未出现压溃现象。当加载达到混凝土极限压应力时,管片出现了压缩裂纹;随着压缩裂纹与张拉裂纹贯穿,此时管片将会达到极限强度破坏状态。在加载过程中,碳纤维混凝土管片中存在变形最小区域,随着加载的持续,其变形最小区域从管片接头端部逐渐向压头位置转移。由此可见,碳纤维混凝土管片能够满足岩层破碎和地下水发育区间隧道的安全性和稳定性要求。

[Objective]The Xiaozhuang Station-Wanshou Station interval shield tunnel is located in a highly fractured rock layer with developed groundwater,facing extremely complex geological conditions and requiring relatively high crack resistance and compressive strength for prefabricated segments.However,ordinary concrete segments cannot meet structural crack resistance requirements.It is suggested to incorporate carbon fibers into the concrete and carry out in-depth study on the deformation and crack propagation characteristics of carbon fiber reinforced concrete shield segments.[Method]Based on particle discrete element theory,the microscopic strength parameters of the concrete material parallel bond contact model are determined through the stress-strain curve of a uniaxial DEM(discrete element method)test.A numerical model for the bending strength test of carbon fiber reinforced concrete segments is established to analyze the strength,failure characteristics,crack propagation mode,and deformation of the above segments.[Result&Conclusion]Numerical simulation results of the bending strength test show that under different loading conditions,the improvement effect of carbon fibers to concrete segment strength is limited.However,the carbon fiber structure has significant tensile strength,which notably enhances the deformation and fracture resistance of the segments.During the loading process,the carbon fiber reinforced concrete segments initially develop a vertical tensile crack at the bottom.As the loading continues,three vertical tensile cracks are generated at the bottom without crushing collapse phenomenon occurring yet,but when the loading reaches the ultimate compressive stress of the concrete,compressive cracks appear in segments.As the compressive cracks penetrate the tensile cracks,the segments will reach the ultimate strength failure state.Throughout the loading process,there exists a region with minimal deformation within the carbon fiber reinforced concrete segment.As the loading continues,this region gradually shifts from segment joint end to loading head position.It is observed that carbon fiber reinforced concrete segments can meet the safety and stability requirements of interval tunnels in fractured rock layer with developed groundwater.