In tunnel construction, shotcrete is sprayed on excavated surfaces to strengthen the walls and prevent rocks from falling off the tunnel face. Soon after, workers enter the face to erect the steel arch support. However, before entering, they must know the maximum rock size supported by the early-age shotcrete. This study aims to reveal the resistance and fracture mechanism of early-age shotcrete when a rock exfoliated from the tunnel face punches through shotcrete. To this end, we developed a novel experimental apparatus in which the strength deformation characteristics of shotcrete were evaluated through a laser scanner by punching a disc rock against the shotcrete on the substrate rock. The punching experiment was simulated, and the fracture mechanism was revealed using the discrete element method. The stress state of shotcrete sequentially reached the tensile failure criterion at the elements adjacent to the edge of the loaded zone. The elements of shotcrete progressively failed at the fracture process zone with punching. Finally, the punching strength of early-age shotcrete was formulated based on its fracture mechanism.

在隧道施工中，喷射混凝土喷在开挖的表面上，以加固墙壁并防止岩石从隧道表面掉落。不久之后，工人进入工作面以竖立钢拱支撑。但是，在进入之前，他们必须知道早期喷浆混凝土所支持的最大岩石尺寸。这项研究的目的是揭示当从隧道面剥落的一块岩石冲过喷射混凝土时，早期喷射混凝土的抗性和断裂机理。为此，我们开发了一种新型的实验设备，其中通过用激光扫描仪通过将圆盘岩石冲向基岩上的喷射混凝土来评估喷射混凝土的强度变形特性。模拟了冲压实验，并采用离散元法揭示了断裂机理。喷浆混凝土的应力状态在邻近加载区边缘的单元处依次达到拉伸破坏准则。喷射混凝土的元素在冲孔过程中逐渐破裂。最后，根据其断裂机理确定了早期喷射混凝土的抗冲强度。