## 1 Introduction  
During tunnel construction, the challenges of large deformation and intrusion frequently arise due to poor rock mass conditions and insufficient support strength, particularly in complex geological environments characterized by significant buried depth [1, 2]. [PERSON] et al. [3] have highlighted UHPC's high strength and durability as a solution for enhancing tunnel supports in poor geological conditions. [PERSON] et al. [4] have identified insufficient support strength and joint activation as key triggers for intrusive deformation in shallow tunnels under tectonic stress, which requires optimized materials and layouts. Shotcrete is a construction technique where concrete is sprayed onto a surface at high velocity using compressed air [5]. This method is capable of providing early load-bearing capacity for deformed rock strata, thereby offering a rapid solution for the stabilization of the surrounding rock mass [6, 7]. This characteristic makes shotcrete a preferred method for primary or secondary support in underground engineering. However, the high porosity (19.6%) [8] and rebound rate (>15%) [9] of shotcrete hinder its effectiveness in controlling disasters such as collapse and large deformation when applied in unfavorable geological rock formations. Therefore, robust support materials with a specific strength and toughness are required to accommodate variations in rock masses while minimizing internal porosity to prevent water infiltration. UHPC has garnered considerable attention due to its remarkable compressive strength, outstanding toughness, and minimal permeability [10]. These exceptional attributes are a result of its extremely low water-binder ratio (<0.25) and the substantial content of cementitious materials [11], which collectively bestow upon UHPC superior mechanical performance, high-level toughness, and low permeability (the compressive strength is greater than 100 MPa, and the tensile strength is greater than 5 MPa) [12; 13]. These superior properties have led to its extensive applications in underground engineering and structural reinforcement [14]. However, the high content of cementitious materials and sand has increased its cost and reduced its sustainability. To further align with sustainable construction goals, the integration of manufactured sand into UHPC formulations has emerged as a pivotal innovation. Research demonstrates that replacing natural sand with manufactured sand not only mitigates environmental degradation caused by river sand mining but also optimizes particle gradation and interfacial bonding through its controllable particle size distribution and angular surface texture, thereby validating its superior compatibility with UHPC [15; 16]. Sprayed UHPC integrates the advantages of both UHPC and shotcrete. It exhibits the outstanding mechanical properties and durability associated with UHPC, as well as featuring the flexibility of shotcrete, which makes it particularly well suited to intricate working conditions. Currently, only a few studies on sprayed UHPC have been conducted, mainly focusing on its rheological behavior and sprayability. These studies have aimed to improve the stability of wall-hanging and increase the spray's thickness by adding various thickeners and cementitious materials [17; 18]. [PERSON] et al. [19] studied viscosity-enhancing agents in sprayed UHPC, showing improved rheology, enhanced compressive strength, and refined pore structure for durability. [PERSON] et al. [20] linked molecular dynamics to rheology in wet-mix UHPC, proposing a cohesion-shear model for optimizing mix design. [PERSON] et al. [21] highlighted fiber content/alignment in sprayed UHPC, balancing permeability reduction and mechanical gains against workability loss. [PERSON] et al. [22] compared steel/synthetic fibers in wet-mix shotcrete, prioritizing steel for strength/ toughness and synthetics for crack resistance.